Patent Application
20070117164
The present invention relates to a method of diagnosing colorectal cancer in human samples using several novel protein markers. Differential expression pattern of these markers are indicative of a person having colorectal cancer and/or predictive of the stage of the disease in a colorectal cancer patient.
Colorectal cancer is one of the world's most common cancers and the second leading cause of death due to cancer in the western world. Investigations of colorectal cancer show that most colorectal cancers develop from adenomatous polyps. The polyps are usually small and pre-neoplastic growths that develop on the lining of the colon and can over time progress into colorectal cancer. Colorectal cancer occurs as a result of a sequence of mutations during a long period of time and these mutations mark the several different pathological stages of the disease. A model put forward by Fearon and Vogelstein describes colorectal cancer progression from normal epithelia to metastasis through the phases of dysplasia, early, intermediate and late adenoma and carcinoma.
A rare, inherited condition called familial polyposis (FAP) causes hundreds of polyps to form in the colon and rectum and unless this condition is treated, FAP is almost certain to lead to colorectal cancer. These individuals are therefore in a special need for an accurate screening test, where biopsies can be taken from a polyp during colonoscopy and analysed for neoplastic changes.
Several mutations in oncogenes and tumour-suppresser genes have been identified in colorectal cancers and some of them have been associated with the phases of the disease mentioned above.
The risk factors for developing colorectal cancer seem to be age, diet, colon polyps, personal medical history, family medical history and inflammatory bowel disease (Ulcerative colitis and Crohn's disease).
Colorectal cancer incidences and mortality rates increase with age and sharply so after the age of 60. It is estimated that more than one-third of colorectal cancer deaths could be avoided if people over the age of 50 had regular screening tests, since over 90% of all cases occur in people 50 and older. This is due to the fact that colorectal cancer is one of the most preventable cancers, if it is detected at its early stages. If screening tests were performed on the risk groups for colorectal cancer, it could help to prevent deaths due to the disease by finding pre-cancerous polyps so they can be removed before they turn into cancer.
Studies have shown that women with a history of cancer of the ovary, uterus, or breast have a somewhat increased chance of developing colorectal cancer. The risk of developing colorectal cancer the second time seems to be evident as well. So these findings suggest that personal medical history seems to be relevant in terms of the assessment of risk for colorectal cancer. The same seems to be true for family medical history. First-degree relatives (parents, siblings, children) of a person who has had colorectal cancer are somewhat more likely to develop this type of cancer themselves. Ulcerative colitis is a chronic condition where the lining of the colon becomes inflamed and persons having this condition are considered at a greater risk of developing colorectal cancer than others
The usual diagnostic methods for colorectal cancer are procedures such as sigmoidoscopy and colonoscopy, that involve looking inside the rectum and the lower colon (sigmoidoscopy) or the entire colon (colonoscopy) and allowing for removal of polyps or other abnormal tissue for examination under a microscope. A polypectomy is the removal of polyp(s) during a sigmoidoscopy or colonoscopy, which is a procedure often performed on individuals suffering from FAP and individuals with sporadic, recurrent colorectal polyps. Another way is to do X-rays of the large intestine, which is a technique that can reveal polyps or other changes in the intestine. A much less cumbersome method, but less indicative, is the faecal occult blood test (FOBT). It is a test used to check for hidden blood in the stool, as it has been observed that cancers or polyps can bleed, and FOBT is able to detect small amounts of bleeding in the stool.
The potential use of mass spectrometry as an aid for diagnosing cancer has been demonstrated in WO 01/25791 A2, disclosing protein markers from prostate cancer patients being differently expressed as compared to samples from healthy subjects or patients with benign prostate hyperplasia (BPH).
Several studies describe useful markers for the diagnosis of colorectal cancer. U.S. Pat. No. 6,455,668 describes a screening method for identifying bioactive agents being capable of binding to a colorectal cancer modulating protein (BCMP). It further describes a method for screening drug candidates, wherein a gene expression profile is used including CJA8, or fragments thereof. The expression profile can further include markers selected from the group consisting of CZA8, BCX2, CBC2, CBC1, CBC3, CJA9, CGA7, BCN5, CQA1, BCN7, CQA2, CGA8, CAA7 and CAA9 (WO 00/55633). Another publication, US 2001/0044113, describes the use of PKC isozyme, in combination with more conventional cancer markers such as bcl-2, bax and c-myc, to detect changes in colonocyte gene expression associated with early stages of colon tumorigenesis by isolation of poly A+ RNA from faeces. It should also be mentioned that the use of an undefined Defensin-polypeptide (Defensin-X) in diagnosing cancer is described in WO 99/11663.
There is, however, still unmet need for a simple diagnostic and/or prognostic test to provide an indication of whether or not an individual has colorectal cancer. It would also be of tremendous help to have a test giving indication of the status during surveillance of the disease.
The present invention relates to a method of diagnosing colorectal cancer in a sample using novel protein markers. The markers have been identified by assaying a number of tissue and serum samples from healthy individuals and persons diagnosed with colorectal cancer by means of protein chip technology using mass spectrometry.
Differential expressions patterns of these markers are indicative of a person having colorectal cancer and/or predictive of the stage of the disease in a colorectal cancer patient. The diagnosis is based on comparing at least one intensity value, obtained using the method, to a reference value.
It is an object of preferred embodiments of the present invention to provide a method for diagnosing colorectal cancer in a sample from a mammal, the method comprising obtaining a sample from said mammal and assaying said sample by a quantitative detection assay, and determining the intensity signal of at least one marker.
In this text the words protein, peptide, polypeptide are used interchangeably, and all describe a chain of amino acids. In some cases the chain of amino acids have so called post translational modifications or bind certain ligands (for example ions). In some cases the chain of amino acid is a full-length (native) protein, in some cases it is a smaller fragment of a full-length protein. The mass values correspond solely to the measured mass.
The present invention relates to a number of markers. The at least one marker, such as two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, twenty-one, twenty-two, twenty-three, twenty-four, twenty-five, twenty-six, twenty-seven, twenty-eight, twenty-nine, thirty, thirty-one, thirty-two, thirty-three, thirty-four, thirty-five, thirty-six, thirty-seven, thirty-eight, thirty-nine, forty, forty-one, forty-two, forty-three, forty-four, forty-five, forty-six, forty-seven, forty-eight, forty-nine, fifty, fifty-one, fifty-two, fifty-three, fifty-four, fifty-five, fifty-six, fifty-seven, fifty-eight, fifty-nine, sixty, sixty-one, sixty-two, sixty-three, sixty-four, sixty-five, sixty-six, sixty-seven, sixty-eight, sixty-nine, seventy, seventy-one, seventy-two, seventy-three, seventy-four, seventy-five, seventy-six, seventy-seven, seventy-eight, seventy-nine, eighty, eighty-one, eighty-two, eighty-three, eighty-four, eighty-five, eighty-six, eighty-seven, eighty-eight, eighty-nine, ninety, ninety-one, ninety-two, ninety-three, ninety-four, ninety-five, ninety-six, ninety-seven, ninety-eight, ninety-nine, hundred, hundred and one, hundred and two, hundred and three, hundred and four, hundred and five, hundred and six, hundred and seven, hundred and eight, hundred and nine, hundred and ten, hundred and eleven, hundred and twelve, hundred and thirteen, hundred and fourteen, hundred and fifteen, hundred and sixteen, hundred and seventeen, hundred and eighteen, hundred and nineteen, hundred and twenty, hundred and twenty-one, hundred and twenty-two, hundred and twenty-three, hundred and twenty-four, hundred and twenty-five, hundred and twenty-six, hundred and twenty-seven, hundred and twenty-eight, hundred and twenty-nine, hundred and thirty, hundred and thirty-one, hundred and thirty-two, hundred and thirty-three, hundred and thirty-four, hundred and thirty-five, hundred and thirty-six, hundred and thirty-seven, hundred and thirty-eight, hundred and thirty-nine, hundred and forty, hundred and forty-one, hundred and forty-two, hundred and forty-three, hundred and forty-four, f hundred and forty-five, hundred and forty-six, hundred and forty-seven, hundred and forty-eight, hundred and forty-nine and hundred and fifty markers, can be selected from the group consisting of the polypeptides having apparent molecular weight of 66800 Da, 66500 Da, 66300 Da, 64860 Da, 60730 Da, 60500 Da, 60475 Da, 46000 Da, 45500 Da, 44300 Da, 33000 Da, 28040 Da, 28025 Da, 28010 Da, 28000 Da, 27700 Da, 19966 Da, 19900 Da, 19865 Da, 16150 Da, 15935 Da, 15580 Da, 15200 Da, 15140 Da, 14470 Da, 14300 Da, 14100 Da, 14030 Da, 13870 Da, 13747 Da, 11723 Da, 13700 Da, 13331 Da, 13265 Da, 12000 Da 11989 Da, 11987 Da, 11900 Da, 11700 Da, 11650 Da, 11550 Da, 11500 Da, 11133 Da, 11080 Da, 10830 Da, 9950 Da, 9700 Da, 9600 Da, 9197 Da, 9140 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8931 Da, 8930 Da, 8652 Da, 8580 Da, 8230 Da, 7469 Da, 7324 Da, 7023 Da, 6880 Da, 6850 Da, 6660 Da, 6650 Da, 6635 Da, 6450 Da, 6436 Da, 6435 Da, 6430 Da, 6125 Da, 6110 Da, 6090 Da, 5920 Da, 5906 Da, 5905 Da, 5900 Da, 5871 Da, 5857 Da, 5540 Da, 5360 Da, 5330 Da, 5266 Da, 5260 Da, 5234 Da, 5075 Da, 4977 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4460 Da, 4330 Da, 4300 Da, 4290 Da, 4281 Da, 4270 Da, 4266 Da, 4264 Da, 4168 Da, 4136 Da, 4039 Da, 4024 Da, 4000 Da, 3984 Da, 3980 Da, 3960 Da, 3895 Da 3882 Da, 3878 Da, 3816 Da, 3777 Da, 3712 Da, 3680 Da, 3651 Da, 3574 Da, 3570 Da (def 2), 3487 Da, 3480 Da (def 3),3450 Da (def 1), 3444 Da, 3408 Da, 3372 Da, 3280, 3275 Da, Da, 3160, Da, 2960 Da, 2955 Da, 2933 Da, 2878 Da, 2850 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, 2450 Da, 2364 Da, 2330 Da, 2275 Da, 2230 Da, 2210 Da, 1945 Da, 1930 Da, 1688 Da, 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da.
Thereafter, the method in a preferred embodiment comprises comparing said intensity signal(s) with reference value(s) and identifying whether the intensity signal of at least one marker from the sample is significantly different from a reference value.
It is an object of the present invention to provide a method of diagnosing colorectal cancer in a sample from a mammal. The method comprises obtaining a sample from said mammal, detecting in the sample from the mammal at least one marker by a quantitative detection assay and determining the intensity signal of the least one marker, wherein the marker is selected from the group consisting of the polypeptides having apparent molecular weight of:
66800 Da, 66500 Da, 66300 Da, 64860 Da, 60730 Da, 60500 Da, 60475 Da, 46000 Da, 45500 Da, 44300 Da, 33000 Da, 28040 Da, 28025 Da, 28010 Da, 28000 Da, 27700 Da, 19966 Da, 19900 Da, 19865 Da, 16150 Da, 15935 Da, 15580 Da, 15200 Da, 15140 Da, 14470 Da, 14300 Da, 14100 Da, 14030 Da, 13870 Da, 13747 Da, 11723 Da, 13700 Da, 13331 Da, 13265 Da, 12000 Da 11989 Da, 11987 Da, 11900 Da, 11700 Da, 11650 Da, 11550 Da, 11500 Da, 11133 Da, 11080 Da, 10830 Da, 9950 Da, 9700 Da, 9600 Da, 9197 Da, 9140 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8931 Da, 8930 Da, 8652 Da, 8580 Da, 8230 Da, 7469 Da, 7324 Da, 7023 Da, 6880 Da, 6850 Da, 6660 Da, 6650 Da, 6635 Da, 6450 Da, 6436 Da, 6435 Da, 6430 Da, 6125 Da, 6110 Da, 6090 Da, 5920 Da, 5906 Da, 5905 Da, 5900 Da, 5871 Da, 5857 Da, 5540 Da, 5360 Da, 5330 Da, 5266 Da, 5260 Da, 5234 Da, 5075 Da, 4977 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4460 Da, 4330 Da, 4300 Da, 4290 Da, 4281 Da, 4270 Da, 4266 Da, 4264 Da, 4168 Da, 4136 Da, 4039 Da, 4024 Da, 4000 Da, 3984 Da, 3980 Da, 3960 Da, 3895 Da 3882 Da, 3878 Da, 3816 Da, 3777 Da, 3712 Da, 3680 Da, 3651 Da, 3574 Da, 3570 Da (def 2), 3487 Da, 3480 Da (def 3),3450 Da (def 1), 3444 Da, 3408 Da, 3372 Da, 3280, 3275 Da, Da, 3160, Da, 2960 Da, 2955 Da, 2933 Da, 2878 Da, 2850 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, 2450 Da, 2364 Da, 2330 Da, 2275 Da, 2230 Da, 2210 Da, 1945 Da,1930 Da, 1688 Da, 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da.
The method further comprises comparing said intensity signal(s) with reference value(s) and identifying whether the intensity signal of at least one marker from the sample is significantly different from the reference value for said marker.
In one aspect of the present Invention a method is provided for diagnosing colorectal cancer by means of a serum sample from a mammal. The method comprises obtaining a serum sample from said mammal, detecting in the serum sample from the mammal at least one marker by a quantitative detection assay and determining the intensity signal of the at least one marker, wherein the marker is selected from the group consisting of the polypeptides having apparent molecular weight of:
66500 Da, 60500 Da, 46000 Da, 45500 Da, 44300 Da, 28040 Da, 27700 Da, 33000 Da, 19900 Da, 16150 Da, 15935 Da, 15580 Da, 15200 Da, 15200 Da, 13700 Da, 11900 Da, 11700 Da, 11650 Da, 11550 Da, 11500 Da, 11080 Da, 10830 Da, 9140 Da, 8940 Da, 8930 Da, 8230 Da, 6880 Da, 6650 Da, 6660 Da, 6450 Da, 6430 Da, 6125 Da, 6110 Da, 6090 Da, 5920 Da, 5900 Da, 5540 Da, 5330 Da, 5260 Da, 4660 Da, 4640 Da, 4460 Da, 4330 Da, 4300 Da, 4290 Da, 4000 Da, 3980 Da, 3960 Da, 3680 Da, 3280 Da, 3275 Da, Da, 3160 Da, 2955 Da, 2450 Da, and 1536 Da.
The method further comprises comparing said intensity signal(s) with reference value(s) and identifying whether the intensity signal of at least one marker from the sample is significantly different from the reference value for said marker.
In another aspect of the present invention a method is provided for diagnosing colorectal cancer in a tissue sample from a mammal. The method comprises obtaining a tissue sample from said mammal, detecting in the tissue sample from the mammal at least one marker by a quantitative detection assay and determining the intensity signal of the at least one marker, wherein the marker is selected from the group consisting of the polypeptides having apparent molecular weight of:
15140 Da, 11989 Da, 11987 Da, 9700 Da, 9600 Da, 9197 Da, 9079 Da, 8971 Da, 8652 Da, 8580 Da, 7324 Da, 7023 Da, 5871 Da, 5857 Da, 5360 Da, 5234 Da, 5075 Da, 4749 Da, 4634 Da, 4281 Da, 4266 Da, 4168 Da, 4039 Da, 4024 Da, 3984 Da, 3878 Da, 3777 Da, 3712 Da, 3651 Da, 3574 Da, 3487 Da, 3444 Da, 3408 Da, 3372 Da, 2933 Da, 2878 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, 2364 Da, 2330 Da, 1930 Da, 1688 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da,
the method further comprises comparing said intensity signal(s) with reference value(s) for said marker(s) and identifying whether the intensity signal of at least one marker from the sample is significantly different from the reference value.
In yet another aspect of the present invention a method is provided for diagnosing colorectal cancer by means of a plasma sample from a mammal. The method comprises obtaining a plasma sample from said mammal, detecting in the plasma sample from the mammal at least one marker by a quantitative detection assay and determining the intensity signal of the at least one marker, wherein the marker is selected from the group consisting of the polypeptides having apparent molecular weight of:
66800 Da, 66500 Da, 66300 Da, 64860 Da, 60730 Da, 60475 Da, 19966 Da, 19865 Da, 14470 Da, 14300 Da, 14100 Da, 14030 Da, 13870 Da, 13747 Da, 11723 Da, 9950 Da, 8931 Da, 7469 Da, 6635 Da, 6435 Da, 5905 Da, 5266 Da, 4977 Da, 4480 Da, 4136 Da, and 3895 Da,
the method further comprises comparing said intensity signal(s) with reference value(s) for said markers and identifying whether the intensity signal of at least one marker from the sample is significantly different from the reference value for said marker.
Another embodiment of the present invention provides a use of at least one marker selected from the group consisting of the polypeptides having apparent molecular weight of
66800 Da, 66500 Da, 66300 Da, 64860 Da, 60730 Da, 60500 Da, 60475 Da, 46000 Da, 45500 Da, 44300 Da, 33000 Da, 28040 Da, 28025 Da, 28010 Da, 28000 Da, 27700 Da, 19966 Da, 19900 Da, 19865 Da, 16150 Da, 15935 Da, 15580 Da, 15200 Da, 15140 Da, 14470 Da, 14300 Da, 14100 Da, 14030 Da, 13870 Da, 13747 Da, 11723 Da, 13700 Da, 13331 Da, 13265 Da, 12000 Da 11989 Da, 11987 Da, 11900 Da, 11700 Da, 11650 Da, 11550 Da, 11500 Da, 11133 Da, 11080 Da, 10830 Da, 9950 Da, 9700 Da, 9600 Da, 9197 Da, 9140 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8931 Da, 8930 Da, 8652 Da, 8580 Da, 8230 Da, 7469 Da, 7324 Da, 7023 Da, 6880 Da, 6850 Da, 6660 Da, 6650 Da, 6635 Da, 6450 Da, 6436 Da, 6435 Da, 6430 Da, 6125 Da, 6110 Da, 6090 Da, 5920 Da, 5906 Da, 5905 Da, 5900 Da, 5871 Da, 5857 Da, 5540 Da, 5360 Da, 5330 Da, 5266 Da, 5260 Da, 5234 Da, 5075 Da, 4977 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4460 Da, 4330 Da, 4300 Da, 4290 Da, 4281 Da, 4270 Da, 4266 Da, 4264 Da, 4168 Da, 4136 Da, 4039 Da, 4024 Da, 4000 Da, 3984 Da, 3980 Da, 3960 Da, 3895 Da 3882 Da, 3878 Da, 3816 Da, 3777 Da, 3712 Da, 3680 Da, 3651 Da, 3574 Da, 3570 Da (def 2), 3487 Da, 3480 Da (def 3),3450 Da (def 1),3444 Da, 3408 Da, 3372 Da, 3280, 3275 Da, Da, 3160, Da, 2960 Da, 2955 Da, 2933 Da, 2878 Da, 2850 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, 2450 Da, 2364 Da, 2330 Da, 2275 Da, 2230 Da, 2210 Da, 1945 Da, 1930 Da, 1688 Da, 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da,
for the prediction of the clinical outcome, complications and mortality of an individual diagnosed with colorectal cancer.
In the present context, the term “diagnosing” includes determining whether a person has colorectal cancer as well as indicating the stage or prognosis of a cancer in a patient.
As will be evident to a person of skill in the art, it is not always possible to diagnose with certainity whether a person has colorectal cancer by use of a method of the invention.
Within the broad term “diagnosing” is thus also included determining a diagnosis by use of at least one of the markers disclosed herein with a certain specificity i.e. 50% or 60% and preferably with a higher specificity, such as 70%, 75%, 80%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or most preferably 100%.
The sensitivity of the method of diagnosing is also of importance. The sensitivity that the diagnosis provided by use of at least one of the markers disclosed herein is correct should be 50% or 60%, preferably higher such as 62%, 70%, 72%, 74%, 77%, 80%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or most preferably 100%.
The experimental part of the application provides a number of examples of preferred markers and combination of markers and the combination of specificity and sensitivity obtained when using said markers. These markers and combinations of markers are presently preferred embodiments of the invention.
In the context of the present invention, the term “prognosis” relates to an opinion (professional or non-professional, preferably a professional) on how an illness or a disease will develop and how the illness or disease will influence on other health conditions and death/survival of the mammal.
It is contemplated that by use of at least one of the markers of the invention or a combination of markers it will be possible to determine the prognosis or clinical outcome for an individual patient.
The present invention provides the means for giving a prognosis of the clinical outcome, complications and mortality of said mammal. In the context of the present invention, the term “clinical outcome” relates to the ‘final result’ or the ‘final situation’ or the condition of the patient after the patient has experienced a disease, e.g. a colorectal cancer or related diseases of the gastrointestinal tract. Thus, the clinical outcome may be death within a year or survival, and survival can be everything from poor health condition (moribund) to a healthy period for a period of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 years.
In the context of the present invention, the term “complications” relates to symptoms of anything arising after the diagnosis of the disease, e.g the cancer spreading to other organs or tissues (metastasis), recurrence of carcinoma within the colon or development of a second primary colorectal cancer.
It should be understood that any feature and/or aspect discussed above in connection with the determination according to the invention apply by analogy to the “diagnosis”, “prognosis” and “clinical outcome” according to the invention.
The term “colorectal cancer” relates to diseases such as colon cancer, familial adenomatous polyposis (FAP), rectal cancer and inflammatory bowel disease (IBD). It also relates to the non-invasive pre-cancerous lesions such as adenomatous polyps.
In the present context, the term “phases of colorectal cancer” relates to the progressive stage of the disease. This diagnosis of the severity of colorectal cancer is most often based on pathological observations after surgery. This currently used diagnostic model describes colorectal cancer progression from normal epithelia to metastasis through the phases of dysplasia, adenoma (early, intermediate and late) and carcinoma.
In the present context, the term mammal refers to a primate, preferably a human.
In order to detect the presence of a gene product in a biological sample, one can measure either DNA/RNA or protein or both using quantitative detection assay(s). Such detection assay can be selected from the group consisting of immunoassay, kinetic/real-time PCR, 2D gel, protein array, gene array and other nano-technology methods.
In the present context, the term “immunoassay” refers to assays such as ELISA (Enzyme-Linked Immunosorbent Assay), RIA (Radioimmunoassay) and FIA (Fluoroimmunoassay), which are based on the ELISA sandwich concept of catching antibody and detection antibody with different specificity to the same molecule. The detection antibody is then labelled with an enzyme, fluorochrome or a radioactive substance or the like, to quantify the desired molecule (protein), and the sensitivity of the assay depends partially on the label of the detection antibody.
The term “2D-Gel” (two-dimensional electrophoresis) relates in the present context to the electrophoresis technique where a protein extract is subjected to an electrophoresis in one dimension and then directly afterwards to a second electrophoresis in a second dimension. The conditions during the separate steps are different, in terms of time of separation, voltage, buffer and agents present during the separation.
In a preferred embodiment of the present invention mass spectrometry is used to detect the protein markers. Furthermore the mass spectrometry method used is preferably a SELDI-TOF (Surface Enhanced Laser Desorption Ionization)-TOF (Time of Flight) technique, where the protein extract is bound to a protein chip. The chips have an active surface chemistry, which can be modified to retain proteins with certain properties. Thereby, proteins with different properties can be retained by different set of conditions and measured by MALDI-TOF or the like.
The SELDI-TOF/MS Technique:
General Description:
SELDI-TOF/MS (Surface Enhanced Laser Desorption/Ionisation-Time Of Flight/Mass Spectrometry) (Ciphergen) is mass spectrometry where the samples are purified on Protein Chips (Ciphergen) prior to analysis. In this purification step the majority of proteins (and salts & lipids) are removed and only a relatively small number of proteins remains on the chip surface. This chip is then analysed by mass spectrometry.
Protein Chips and Buffer Solutions:
Different chips are available, and by varying the buffer solutions used in the binding and washing steps, different protein profiles are observed when analysing the chips in the PBS II instrument (Ciphergen). Thus, a person skilled in the art normally would test different chips and buffer solutions.
The chips are composed of common chromatographic materials, also used in HPLC techniques (anion-, cation, and hydrophobic-/reverse phase-surfaces) and the buffer solutions are also commonly used in other purification techniques. There is basically no difference between purification on a protein chip, as described here, and purification on a chromatographic column or by precipitating proteins by chromatographic pearls.
Analysis on the SELDI Instrument:
The chips are analysed on the PBS II Instrument (Ciphergen), which is an MALDI-TOF/MS (Matrix assisted Laser Desorption/Ionisation-Time Of Flight/Mass Spectrometry) instrument. The PBS II has a special loading device that allows analysis of protein chips, but is otherwise a normal MALDI-TOF/MS instrument. Instead of using specific chips, with specific binding abilities, a gold chip (Au Chip (Ciphergen)) can be used. In this case the protein solution is not purified on the chip but applied directly on to the gold surface and left to dry up together with the crystallisation solution; this is MALDI-TOF/MS.
Some proteins are present at very low concentrations in serum and can therefore only be detected after they have been in-concentrated on the protein chip (which is the initial step in the SELDI technique) and not directly by MALDI.
The only difference between SELDI and MALDI is that in SELDI the samples are treated in a special way before analysis. This allows for homogenous comparison of samples, which allows for sensitive identification of proteins that are differentially expressed. But the way the proteins are detected is exactly the same.
Basically, there is no difference between purifying proteins by standard purification techniques ((nano)-HPLC, gel-filtration, precipitation) and subsequently analysing the samples by MALDI, and by purifying the proteins on protein chips and analysing them by MALDI. The latter combination is called SELDI.
MALDI-TOF/MS is a technique that is highly sensitive in measuring the mass of molecules, especially proteins. The PBS II instrument has an accuracy of below +/−0.20/0, and in most cases around +/−0.1%. Thus the mass value of a protein with m/z: 5000 is in most case m/z 5000 +/−5. Therefore the measured masses are all defined as +/−maximum 0.2% and +/−minimum 0.1%.
Protein chips of the invention can be chips with an immobilized metal affinity capture array with a nitriloacetic acid (NTA) surface. An example of such a chip is the IMAC30 ProteinChip Array, which is activated with transition metals prior to use.
Other protein chips of the invention are arrays comprising a carboxylate chemistry (negatively charged) acting as a weak cation exchanger. The CM10 ProteinChip Array is an example of such an array.
Protein chips of the present invention may further be arrays, which bind proteins through reversed phase or hydrophobic interaction chromatography and have binding characteristics similar to that of a C6 to C12 alkyl chromatographic resin. The H50 ProteinChip array is an example of such an protein chip.
The protein chips of the present invention can also be arrays being strong anion exchange array comprising quaternary amine functionality such as the SAX2 ProteinChip Array.
Furthermore, the protein chips of the present invention can be mimic normal phase chromatography with silicate functionality such as the NP20 ProteinChip.
In the present context, the term “gene microarray” relates to low density nucleotide arrays, where nucleotide probes are attached or synthesised onto a surface and used as probes to retain nucleotides, mostly mRNA. This is usually referred to as transcription profiling, i.e. detection of the mRNA transcripts currently being used in a tissue at a certain time. Examples of such arrays are oligonucleotide arrays, where oligonucleotides are printed on glass slides and cDNA arrays, where cDNA (complementary DNA) is spotted on glass slide.
In a preferred embodiment of the present invention, the intensity signal detected in the quantitative detection assays is selected from the group consisting of fluorescence signal, mass spectrometry images, radioactivity, enzyme activity, and antibody detection.
The reference value can be calculated from a pool of samples from individuals with cancer and by comparison with a pool of samples from healthy individuals, a range for positive and negative calls can be made. Another possibility is to set a reference value based on a pool of samples from various phases or stages of the cancer to determine the progression or a stage of the disease. It may even be desirable to set reference values for prognosis of the disease. The reference value can be calculated as a mean or a median value of each intensity signal value(s) calculated from data from one or many of the markers, wherein the negative values are made positive. The reference value could even be the area under the curve (AUC) of at least one of the protein markers.
In one embodiment of the present invention the reference value is indicative of the stage of colorectal cancer. This may be accomplished by collecting a number of samples from several patients and after the samples have been diagnosed by the stage of the disease, the samples from the same stage are assayed.
In the present context, the reference value can be based on data calculated from intensity signal value(s) of said marker(s) obtained from a sample without colorectal cancer from the same mammal. The reference value can also comprise data calculated from intensity signal value(s) of said marker(s) obtained from samples from normal and colorectal cancer tissue from the same mammal. Samples can furthermore be obtained from both a healthy control population and a population having said cancer which samples are used to determine the reference value. After the reference value is determined with a statistical significance, such as but not limited to p-values of levels below 0.1. By assaying a significant number of patients and healthy individuals, the specificity of the method can be determined, obtaining a specified sensitivity. Thereby, it can be determined whether a person is likely to have colorectal cancer or not with a predetermined specificity and/or a predetermined sensitivity.
In the present context the term “data” relates to any calculation made using the intensity signal(s) as data input. The intensity signal(s) may be fluorescence signal, mass spectrometry images, radioactivity, spectrometry values, etc. The data can be obtained using any kind of mathematical formula or algorithm.
Samples for setting the reference value will vary depending on the purpose of the assay. For diagnosis tissue samples may be taken from a “normal” tissue section and a cancer from the same individual, but reference samples may also be taken from healthy individuals in this context. It is also possible to collect blood samples from healthy individuals together with blood samples from individuals, which are known to be suffering from colorectal cancer.
The prognosis of cancer patients is usually determined by the stage of the disease. The classification or the staging of the disease can be made using more than one model, but the most commonly used classification of colon cancer is based on the tumour morphology. This is the so-called Dukes' classification (referring to the original classification described by Lockhardt-Mummery & Dukes in the 1930'ies) classifying the disease into three stages using the terms Dukes' A-C. Dukes A describes a cancer, where the cancer is limited to the lining (mucosa or sub-mucosa) of the colon and has not penetrated the colon. At the Dukes' B stage, the cancer has penetrated the muscularis propria and invaded nearby organs. Dukes' C is characterised in that a regional metastasis of lymph nodes has occurred. Later, a commonly used stage “Dukes' D”, referring to colorectal cancer with distant metastasis to organs like liver, lungs and brain was added to the classification. The 5-year survival prognosis for colorectal cancer is 80-90% at the Duke's A stage. Patients with Duke's B colorectal cancer have 60-70% 5-year survival rate whereas patients with Duke's C colorectal cancer are down to 20-30%. The 5-year survival rate for patients with Duke's D colorectal cancer is practically zero (Arends J W. et a).).
In a preferred embodiment of the present invention the reference value is indicative of the stage of colorectal cancer, wherein the stage is selected from the group consisting of Duke's A, Duke's B, Duke's C and Duke's D.
In the present context, the sample is a biological sample. The sample can be selected from the group consisting of blood, serum, plasma, faeces, saliva, urine, a cell lysate, a tissue sample, a biopsy, a tissue lysate, a cell culture, semen, seminal plasma, seminal fluid and cerebrospinal fluid.
In a preferred embodiment of the present invention a protein extract is made from the biological sample containing the total protein content including membrane proteins, nuclear proteins, cytosolic proteins and blood/serum proteins. When the protein extract has been established, the protein concentration of the extract is made constant. In the present context the term constant refers to that the protein concentration of the sample to be analysed should be standardised to a value being the same between different samples in order to be able to quantify the signal of the protein markers. Such standardisation could be made using photometry, spectrometry and gel electrophoresis.
In a presently preferred embodiment of the present invention, the intensity signal for markers 2850 Da, 3570 Da (def 2), 3450 Da (def 1), 3480 Da (def 3), 4270 Da, and/or 6850 Da, is preferably increased, whereas the intensity signal for markers 9090 Da and/or 12000 Da is preferably decreased. These markers are preferably selected for evaluation of the presence of the disease from tissue samples or biopsies. Furthermore, for evaluation of the presence of the disease from blood samples, the intensity signal for 5900 Da, 3882 Da, and/or 5906 Da, is preferably raised and the intensity signal for 3816 Da, 6436 Da, 13265 Da, 11133 Da, and/or 13331 is preferably decreased.
In a presently most preferred embodiment of the present invention, the intensity signal for markers 1945 Da and 2210 Da is decreased and the intensity signal for 5906 is increased. These markers are preferably selected for evaluation of the presence of the disease from blood samples.
In another presently preferred embodiment of the present invention, the intensity signal for markers 1945 Da, 2210 Da, 2230 Da, 2250 Da, 2275 Da, 4300 Da, 4480 Da, and/or 4500 Da is decreased. These markers are preferably selected for evaluation of the presence of the disease from blood samples.
In a further presently preferred embodiment of the present invention, the intensity signal for marker 5906 Da is raised. This marker is preferably selected for evaluation of the presence of the disease from blood samples.
Also in a presently preferred embodiment of the present invention, the intensity signal for marker 1945 Da is decreased. This marker is preferably selected for evaluation of the presence of the disease from blood samples.
Also in a presently preferred embodiment of the present invention, the intensity signal for marker 2210 Da is decreased. This marker is preferably selected for evaluation of the presence of the disease from blood samples.
One aspect of the present invention provides the use of degradation products of Human Serum Albumin as marker for cancer. The degradation products are selected from the group consisting of the polypeptides having apparent molecular weights of 60500 Da, 6187 Da, 6090 Da, 5920 Da, 5906 Da, 5901 Da, 5900 Da, and 5333 Da.
In an embodiment of the present invention the use of at least one polypeptide having apparent molecular weight of 6187 Da, 5901 Da, or 5333 Da as a marker for cancer is provided, wherein at least one of the polypeptides is alpha-fibrinogen protein. In the present context the cancer is colorectal cancer.
In a presently preferred embodiment of the invention, the intensity signal for markers 66800 Da, 66500 Da, 66300 Da, 64860 Da, 46000 Da, 45500 Da, 44300 Da, 28040 Da, 28025 Da, 28010 Da, 28000 Da, 27700 Da, 15580 Da, 15140 Da, 13700 Da, 13331 Da 13265 Da, 12000 Da, 11989 Da, 11133 Da, 9700 Da, 9600 Da, 9197 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8931 Da, 8652 Da, 8580 Da, 8230 Da, 7324 Da, 7023 Da, 6880 Da, 6660 Da, 6650 Da, 6635 Da, 6450 Da, 6436 Da, 6435 Da,6430 Da, 5360 Da, 5075 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4330 Da, 4300 Da, 4290 Da, 4168 Da, 4000 Da, 3984 Da, 3980 Da, 3960 Da, 3816 Da, 3777 Da, 3680 Da, 3280 Da, 3160 Da, 2450 Da, 2330 Da, 2275 Da, 2230 Da, 2210, 1945 Da, 1930 Da 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da is increased and the intensity signal for markers 66500 Da, 46000 Da, 45500 Da, 44300 Da, 28040 Da, 27700 Da, 15580 Da, 15140 Da, 13700 Da, 13331 Da 13265 Da, 12000 Da, 11989 Da, 11133 Da, 9700 Da, 9600 Da, 9197 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8652 Da, 8580 Da, 8230 Da, 7324 Da, 7023 Da, 6880 Da, 6660 Da, 6650 Da, 6450 Da, 6436 Da, 6430 Da, 5360 Da, 5075 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4330 Da, 4300 Da, 4290 Da, 4168 Da, 4000 Da, 3984 Da, 3980 Da , 3960 Da, 3816 Da, 3777 Da, 3680 Da, 3280 Da, 3160 Da, 2450 Da, 2330 Da, 2275 Da, 2230 Da, 2210, 1945 Da, 1930 Da 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da is decreased.
In an embodiment of the present invention the intensity signal for markers 60500 Da, 19900 Da, 11080 Da, 10830 Da, 9140 Da, 8930 Da, 6110 Da, 6090 Da, 5920 Da, 5900 Da, 5540 Da, 5330 Da, 5260 Da, 4460 Da, and 2960 Da is increased and the intensity signal for markers 66500 Da, 44300 Da, 28040 Da, 27700 Da, 15580 Da, 13700 Da, 6880 Da, 6660 Da, 6430 Da, 4660 Da, 4640 Da, 4330 Da, 4300 Da, 4290 Da, 4000 Da, 3980 Da, 3960 Da, 3680 Da, 3280 Da, and 3160 Da is decreased when assaying a serum sample on IMAC30 chip (Ciphergen).
In an embodiment of the present invention the intensity signal for markers 11900 Da, 11700 Da, 11650 Da, 11550 Da, and 11500 Da is increased and the intensity signal for markers 46000 Da, 45500 Da, 8940 Da, 8230 Da, 6650 Da, and 6450 Da is decreased when assaying a serum sample on H50 protein chip.
In an embodiment of the present invention the intensity signal for markers 15200 Da, 6125 Da, 5900 Da, 3275 Da, and 2955 Da is increased and the intensity signal for markers 4290 Da, 2450 Da, 1536 Da is decreased when assaying a serum sample on CM10 protein chip.
In an embodiment of the present invention the intensity signal for markers 33000 Da, 16150 Da, 15935 Da, and 15200 Da is increased when assaying a serum sample on Sax2protein chip.
In an embodiment of the present invention the intensity signal for markers 5857 Da, 4264 Da, 3878 Da, 3712 Da, 3651 Da, 3574 Da, 3487 Da, 3444 Da, 3372 Da, and 1688 Da is increased and the intensity signal for markers 9700 Da, 8652 Da, 8652 Da, 8580 Da, 7023 Da, 5360 Da, 4168 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da is decreased when assaying a tissue sample on NP20 protein chip.
In an embodiment of the present invention the intensity signal for markers 11987 Da, 5871 Da, 5234 Da, 4281 Da, 4266 Da, 4039 Da, 4024 Da, 3408 Da, 2933 Da, 2878 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, and 2364 Da is increased and the intensity signal for 15140 Da, 11989 Da, 9600 Da, 9197 Da, 9079 Da, 8971 Da, 7324 Da, 5075 Da, 4749 Da, 4634 Da, 3984 Da, 3777 Da, 2330 Da, and 1930 Da is decreased when assaying a tissue sample on Sax2protein chip.
In a presently preferred embodiment of the invention the intensity signal for markers 5340 Da and 5906 Da is increased and the intensity signal for 3980 Da, 6880 Da, and 28010 is decreased when assaying a serum sample on IMac30 chip.
In the present context, the term “plasma sample” relates to a sample wherein a blood sample is tapped into “EDTA-liquid-glass”, centrifuged and where the supernatant is optionally frozen immediately at −80° C.
In the present context, the term “serum sample” relates to a sample wherein a blood sample is tapped into a dry-glass, left to coagulate at room temperature for one hour, after which they are centrifuged and the supernatant is optionally frozen immediately at −80° C.
In the present context, the term “increased” in relation to the term “intensity signal” for a marker, refers to a comparison of an intensity signal from a sample to a reference value, wherein the samples have been normalized to ion noise or “housekeeping genes”. The intensity signal for a specific marker, having a certain size, weight, number of nucleotides or amino acids, is “increased” if it is higher in the sample as compared to the reference value. If the term “raised” is used this is to be interpreted to also mean “increased”.
In the present context, the term “decreased” in relation to the term “intensity signal” for a marker, refers to a comparison of an intensity signal from a sample to a reference value, wherein the samples have been normalized to ion noise or “housekeeping genes”. The intensity signal for a specific marker, having a certain size, weight, number of nucleotides or amino acids, is “decreased” if it is lower in the sample as compared to the reference value.
In one aspect of the present invention a method is provided for determining the presence of colorectal cancer on the basis of a sample from a mammal. The method comprises selecting a normalized protein expression data set from the sample, wherein the expression data set comprises a plurality of expression intensities of proteins on at least one protein chip. Thereafter, at least one marker is selected from the normalized protein expression data set from the group consisting of the polypeptides having apparent molecular weight of:
66500 Da, 60500 Da, 46000 Da, 45500 Da, 44300 Da, 33000 Da, 28040 Da, 27700 Da, 19900 Da, 16150 Da, 15935 Da, 15580 Da, 15200 Da, 15140 Da, 13700 Da, 13331 Da, 13265 Da, 12000 Da 11989 Da, 11987 Da, 11900 Da, 11700 Da, 11650 Da, 11550 Da, 11500 Da, 11133 Da, 11080 Da, 10830 Da, 9700 Da, 9600 Da, 9197 Da, 9140 Da, 9090 Da, 9079 Da, 8971 Da, 8940 Da, 8930 Da, 8652 Da, 8580 Da, 8230 Da, 7324 Da, 7023 Da, 6880 Da, 6850 Da, 6660 Da, 6650 Da, 6450 Da, 6436 Da, 6430 Da, 6125 Da, 6110 Da, 6090 Da, 5920 Da, 5906 Da, 5900 Da, 5871 Da, 5857 Da, 5540 Da, 5360 Da, 5330 Da, 5260 Da, 5234 Da, 5075 Da, 4749 Da, 4660 Da, 4640 Da, 4634 Da, 4500 Da, 4480 Da, 4460 Da, 4330 Da, 4300 Da, 4290 Da, 4281 Da, 4270 Da, 4266 Da, 4264 Da, 4168 Da, 4039 Da, 4024 Da, 4000 Da, 3984 Da, 3980 Da, 3960 Da, 3882 Da, 3878 Da, 3816 Da, 3777 Da, 3712 Da, 3680 Da, 3651 Da, 3574 Da, 3570 Da (def 2), 3487 Da, 3480 Da (def 3),3450 Da (def 1),3444 Da, 3408 Da, 3372 Da, 3280, 3275 Da, Da, 3160, Da, 2960 Da, 2955 Da, 2933 Da, 2878 Da, 2850 Da, 2840 Da, 2799 Da, 2693 Da, 2462 Da, 2450 Da, 2364 Da, 2330 Da, 2275 Da, 2230 Da, 2210 Da, 1945 Da,1930 Da, 1688 Da, 1536 Da, 1365 Da, 1256 Da, 1042 Da, 1026 Da, and 1005 Da. Thereafter the weight for said at least one marker is set and the intensities of said at least one marker is/are multiplied with the weight of said at least one marker. If the markers are more than one the sum of the multiplication obtained above is calculated and that sum value is compared with a cut off value (as explained in example 7).
In the present context the weight for each marker is set by assigning a number between −0.9 and +0.9 to each marker. The exact number (between −0.9 and +0.9) is selected as the number that results in the highest combination of a sensitivity and specificity value. This can be tested as shown in table 15 in example 7.
In a presently preferred embodiment the determination is based on the following algorithm:
In the present context, the term “cutoff” in relation to the program refers to a value for classification. The predicted grouping of a sample is classified as positive for colon cancer if it is above the cutoff value and negative for colon cancer if it is below the cutoff value.
In mass spectrometry the measured mass is given i Daltons (Da) or m/z. Dalton is a weight unit, wherein m/z relates to mass over charge (mass/charge). In the present context there is no difference between Daltons (Da) or m/z.
In the present context, the term “storage means” relates to hard disk, DVD disk, CD disk or floppy diskettes for storing digital data.
In the present context, the term “processing means” relates to a computer comprising a processor, RAM memory, etc. . . .
In the present context, the term “interface between a user and the computer system” relates to keyboard, computer mouse, and a monitor.
In one aspect of the present invention a kit for diagnosis of colorectal cancer is provided, the kit comprising: a first antibody including a portion bound to a solid phase and a region which specifically binds to alpha-fetoprotein, a second antibody including a region which specifically binds to alpha-fetoprotein and a portion which has a label, and optionally a reference protein.
In another aspect of the present invention a kit for diagnosis of colorectal cancer is provided, the kit comprising: a first antibody including a portion bound to a solid phase and a region which specifically binds to alpha-fibrinogen, a second antibody including a region which specifically binds to alpha-fibrinogen and a portion which has a label, and optionally a reference protein.
In yet another aspect of the present invention a kit for diagnosis of colorectal cancer is provided, the kit comprising: a first antibody including a portion bound to a solid phase and a region which specifically binds to human serum albumin (HSA) or fragments of HSA, a second antibody including a region which specifically binds to human serum albumin (HSA) or fragments of HSA and a portion which has a label, and optionally a reference protein.
In an embodiment of the present invention the kit for diagnosis of colorectal cancer may comprise components to detect one or more of the proteins alpha-fetoprotein, alpha-fibrinogen and human serum albumin (HSA). The antibodies may recognise epitopes which are only exposed when the protein is degraded.
In the present context the term “epitope” relates to a certain area on the surface of the protein comprising a number of amino acids.
Several mutations in oncogenes and tumour-suppresser genes have been identified in colorectal cancer. The majority of these genes are associated with certain phases of the disease. A mutation in the tumour-suppresser gene Adenomatous Polyposis Coli gene (APC), is considered to be a molecular “gatekeeper” for development of adenomas and it has been estimated that over 80% of all colorectal cancers have a somatic mutation in the APC gene. There are actually very few oncogenes, which have been shown to be involved with colorectal cancers apart from k-ras, but a small percentage of colorectal cancers show mutations in the myc, myb and neu oncogenes. A mutation in k-ras is considered to be an intermediate event in colorectal carcinogenesis advancing the disease from early adenoma to intermediate adenoma. Several other products of tumour-suppresser genes have also been associated-with colorectal cancer, many of those genes are located on the long arm of chromosome 18. Allelic loss on 18q has been associated with the DCC gene (deleted in colorectal cancer), MADR2 gene (also known as JV18) and DPC4 gene (deleted in pancreatic cancer), the last two are players in the TGF-beta signalling pathway. It has been proposed that DCC, DPC4 and MADR2 play a role in the progression over to late adenoma (Gryfe R et al.).
One of the best known and studied tumour-suppresser genes, p53, is associated with driving the disease towards carcinoma. The product of the gene, which is located on chromosome 17, is a nuclear protein and has a function in cell cycle regulation, but a loss of heterozygocity on 17p has been demonstrated in over 70% of all colorectal cancers.
In a preferred embodiment of the present invention, the detection method using at least one of the novel protein markers for the detection of colorectal cancer could be supplemented with the detection of one or more protein markers selected from the group consisting of APC, k-ras, myc, myb, neu, DCC, DPC4, MADR2, p53, BCMP, CJA8, CZA8, BCX2, CBC2, CBC1, CBC3, CJA9, CGA7, BCN5, CQA1, BCN7, CQA2, CGA8, CAA7, CAA9, PKC isozyme, bcl-2, bax, TIMP-1 and c-myc.
Average intensity values of markers of colorectal cancer. Tissue samples from 12 cancer patients including a normal tissue sample and cancer tissue sample from the same individual were homogenised and protein extracts were analysed by mass-spectrometry using SAX2 chips and the SELDI-TOF technique. The figure shows the intensity levels of the markers selected based on highest sensitivity and specificity.
Discriminating values calculated for 8 markers. The average intensity value for each marker was calculated for normal and cancer tissue sample sets, after removing the highest and lowest values. The discriminating value for each marker was found by dividing the average intensities from each of the sample sets.
Average intensity values of possible markers in serum. Serum samples from 10 cancer patients and 10 healthy individuals were analysed by mass-spectrometry using IMAC3 chips and the SELDI-TOF technique. The figure shows the intensity levels of the markers selected based on highest intensity.
Threshold value: 8.9 (maximum value for cancer serum)
12 out of 78 normal serum samples fall below threshold, producing a specificity of 85%.
Threshold value: 12.7 (maximum value for cancer serum)
18 out of 78 normal serum samples fall below threshold, producing a specificity of 77%.
Threshold value: 5.6 (maximum value for cancer serum)
18 out of 78 normal serum samples fall below threshold, producing a specificity of 77%.
Threshold value: 3.6 (maximum value for cancer serum)
22 out of 78 normal serum samples fall below threshold, producing a specificity of 72%.
Threshold value: 3.1 (maximum value for cancer serum)
30 out of 78 cancer serum samples fall below threshold, producing a specificity of 62%.
Threshold value: 1.1 (maximum value for cancer serum)
20 out of 78 cancer serum samples fall below threshold, producing a specificity of 74%.
Threshold value: 2.1 (maximum value for cancer serum)
20 out of 78 cancer serum samples are below threshold, producing a specificity of 74%.
Threshold value: 2.1 (maximum value for cancer serum)
20 out of 78 cancer serum samples are below threshold, producing a specificity of 74%.
Threshold value: 5.4 (maximum value for normal serum)
49 out of 78 cancer serum samples fall below threshold, producing a specificity of 37%.
Peptide pattern in the region from 1900 to 2500 Da.
Mass spectra from a same sample analysed by the SELDI TOF technique (A) and the MALDI-TOF technique (B)
A scatter-plot of the sample scores and variable loading of a data set comprising data from healthy individuals and individuals diagnosed with colon cancer.
A and B. Representative SELDI-TOF/MS spectra of normal colon tissue (A) on NP20 chip and normal serum (B) on iMAC30 chip. The two spectra differ significantly and each produce a total of 40 to 60 peaks, the majority of which lie in the specified range from 2 to 10 kDa.
C. Comparison of typical colon tumour spectrum (above) and normal colon spectrum (below) in the range from 3 to 4 kDa. The arrows point to the three differentially expressed peptides, subsequently identified as HNP 1-3. The three peptides are expressed in both the normal colon samples and the colon tumour samples, but the expression is up-regulated in the cancer samples. The same observation was made in the serum screening, but here the average signal intensity was significantly lower.
A. HNP profiles of normal and colon tumour tissue. 40 colon tumour and 40 normal colon tissue samples were analysed on NP20 chips. Differences in mean intensities of HNP1-3 in normal and colon tumour tissue are statistical significant at 5% level (p<0.0005).
B. HNP profiles of normal and colon cancer serum. Serum samples (125 colon cancer and 100 normal) were analysed on iMAC30 chips. The mean intensities are significantly different at 5% level (p<2.2e-16). The box-plot shows the 25th quintile, median, 75th quantile, and whiskers extend to min. and max. values.
Protein extract from tumour tissue was separated on a peptide gel-filtration column. The elution volumes of forty (unidentified) peptides is plotted against their respective mass values and an approximate elution curve is calculated. The arrows point to HNP 1-3, which are eluted in two fractions: in the void volume (8 ml) together with High Mass proteins (above 20 kDa) and after 14 ml together with peptides of similar mass range (2-4 kDa). We interpret this as evidence for binding between HNP 1-3 and High Mass proteins.
Normal microscopy (A&B) and fluorescence microscopy (C&D) of MDCK cells. MDCK cells were exposed to calcein with (A&C) and without HNP 1-3 (B&D). By fluorescence microscopy (C&D) the cells were observed to uptake calcein only when treated with fractions containing HNP 1-3/calcein (C). Fractions containing other peptides (unidentified peptides also purified from colon tumours) were used as negative controls together with calcein and did not stimulate the cells to uptake calcein (D) Also, cell islands treated with HNP 1-3 appeared diffuse and showed enlarged nuclei, indicating apoptosis (A).
A-E shows the average intensity spectra of healthy individuals (solid) and patients diagnosed with colon cancer (dashed). The standard errors of means (SEM) are shown with bars.
The aim of the study was to identify protein markers indicative of colorectal cancer by comparison of normal and cancer tissue from colon and rectum.
Method
Sample Preparation
Samples from 12 cancer patients were collected. Normal tissue samples and cancer tissue samples from the same colon were taken and frozen at −80° C. Prior to analysis the samples were taken out of the freezer and placed into homogenisation/Lysis buffer.
Lysis Buffer:
The samples were homogenised in a Wheaton Overhead Stirrer for 2 minutes at speed step 2.
Analysis
Protein extracts were analysed by mass-spectrometry using the SELDI-TOF technique.
SAX2 chips were pre-treated with 50 μl 100 mM TRIS pH 8.0 buffer.
10 μl homogenised sample+60 μl TRIS pH 8.0 buffer were mixed and incubated on SAX2 Chip in a Bioprocessor for 30 minutes at room temperature. Thereafter spots were washed twice in 250 μl 100 mM TRIS pH 8.0 for 5 minutes.
2 times 0.5 μl Matrix (CHCA) was applied onto spot surface.
Instrument Settings
Proteinchips were analysed at Laser intensities of 190, 210, and 230, and the sensitivity level was set at 8.
Results
Putative markers were identified by visual examination of the mass spectra from cancer and normal samples.
Possible Markers:
In order to the determine the specificity and sensitivity of the possible markers all spectres were normalised based on total ion current.
Possible Multi-Protein Marker:
Based on values of sensitivity and specificity the most promising single protein markers were selected:
Conclusion
Eight promising single protein markers were found using the SELDI-TOF mass-spectrometry technique and applying samples on protein-chips. Three of the markers have been fully identified as Alpha-Defensin 1, 2, and 3. A multi-protein marker based on a combination of one or more of the eight proteins shown above appears to be a very effective way of screening for colorectal cancer.
The aim of the study was to identify protein markers indicative of colorectal cancer by comparison of serum samples from normal and cancer patients.
Method
Sample Preparation
Serum was isolated from blood of 10 patients diagnosed as having colorectal cancer and 10 healthy individuals.
Analysis
An IMAC3 chip was pre-treated with 2 times 5 μl 100 mM NiSO4 followed by wash with 5 μl MQ water and equilibration with 2 times 5 μl binding buffer.
Binding Buffer:
2 μl of each serum sample was diluted in 48 μl binding buffer of which 4 μl was applied to the protein chip surface. The chip was left on shaker at room temperature for 40 minutes. The sample was removed from the chip surface and each spot was washed with 3 times 5 μl washing buffer (PBS, pH 7.4, 700 mM NaCl). Finally the chip was air-dried and 2 times 0.6 μl CHCA (100%) was applied to each spot.
Protein extracts were analysed by mass-spectrometry using the SELDI-TOF technique.
Instrument Settings
Protein-chips were analysed at varying laser intensities and sensitivity levels to obtain optimal spectra.
Results
Sensitivity and specificity of putative serum markers:
Conclusion
Eight possible single protein markers were found using the SELDI-TOF mass-spectrometry technique and applying serum samples on protein-chips. None of the markers have been fully identified and annotated. A multi-protein marker based on a combination of one or more of the eight proteins shown above appears to be a very effective way for diagnosis of colorectal cancer.
Materials and Method
Chip:
Serum samples were analysed on IMAC3 chip (Ciphergen).
Pre Treatment:
Each spot is outlined with hydro pen.
5 μl 100 mM NiSO4 is added, shake (150 rpm) 1 min. Remove. Repeat once.
5 μl MQ water is added shake 1 min. Remove.
5 μl Bind buffer is added shake 1 min. Remove.
Binding Step:
Chip is placed in Bioprocessor.
50 μl binding buffer+5 μl serum is mixed in eppendorf tube, solution is loaded in bioprocessor. Leave on shaker (250 rpm) for 40 min. Remove.
Washing Step:
200 μl washing buffer is added. Shake (250 rpm) Smin. Remove. Repeat once.
Dry Step:
Chips are removed from bioprocessor and left to air dry for 20 minutes.
Crystallation Step:
0.6 μl matrix solution is added to each spot. Air dry chip for 5 min. Repeat once.
Analysis:
Chips are analysed on PBS II instrument (Ciphergen) at laser intensity 210 and detector sensitivity 4.
Results
Biomarker Wizard Analysis
78 colon cancer serum and 78 normal serum samples were analysed as described above.
All spectra were pooled and normalised based on total ion current.
Possible markers were identified by Biomarker Wizard (Ciphergen) analysis with the following parameter settings:
First pass: 5, Min peak threshold: 0%, Cluster mass window: 0.3%, Second pass: 5. Based on the results from the Blomarker Wizard 9 peptides showed promising marker characteristics.
Mass values of possible serum marker peptides:
Down-regulated in colon cancer serum:
1945, 2210, 2230, 2250, 2275, 4300, 4480, 4500 Da.
Up-regulated in colon cancer serum:
5906 Da.
Threshold Values for Possible Serum Markers
Optimal threshold values for the 9 serum markers were selected in order to determine maximum specificity of individual markers:
Principal Component Analysis
Based on principal component analysis of a sample set of 38 cancer serum and 31 normal serum, it was shown that especially three markers were of high importance for discriminating between cancer and normal serum.
Conclusion
Especially important markers: 1945 Da, 2210 Da, and 5906 Da.
The aim of this study was to compare the outcome of markers detected with different expression of proteins in healthy individuals vs. patients diagnosed with colorectal cancer, using either SELDI-TOF/MS or an MALDI-TOF/MS.
Method
The PBS II instrument allows variation of three important parameters when analysing protein chips or MALDI-TOF/MS samples.
Laser intensity, detector sensitivity and optimisation range.
Laser intensity was permanently set at 220. However, since the laser source is constantly becoming weaker as the instrument is being used, and varies significantly from instrument to instrument, this is not a value that has any general meaning. Most often values from 190 to 230 are chosen.
Detector sensitivity was set at values of 3, 4, 5, 6, 7, 8 depending on the signal. The intensity (and only the intensity, not the protein profile) of the sample is highly dependent on the matrix solution which is made immediately prior each screening. The detector sensitivity value is chosen such that none of the protein peaks will ever produce a signal that overrides the maximum limit. Thus the appropriate detector value will depend on the specific matrix solution, and thus has no general meaning.
Optimisation range, this range specifies the mass interval where the instrument will measure the signal with highest accuracy. For each screening we made two measurements. One with low optimisation range (m/z 2000-20000) and one with high (m/z 20000-150000) The identified markers below m/z 20000 were all measured in the low screening and the markers above m/z 20000 were all measured in the high screening
Protein chips were analysed on the PBS II SELDI instrument (Ciphergen). SPA (Sinapinic Acid) matrix was used in the crystallisation step in all screenings:
SPA (Ciphergen) was dissolved in 150 μl MQ+150 μl Acetonitrile+1,5 μl TFA (tri-flouro-acetic-acid) and left on shaker for 10 minutes and centrifuged at 14.000 rpm for 15 minutes.
Analysis
Mass spectra from serum samples of healthy individuals and patients diagnosed with colorectal cancer were analysed for potential markers.
An analysis of a serum sample by SELDI-TOF/MS indicated a protein marker of m/z 5900. The same sample was prepared for MALDI-TOF/MS analysis by removing salt and lipids from serum by gel-filtration. The results shown in
The aim of this study was to analyse the effect of using different protein chips in differential protein expression analysis using SELDI mass spectrometry.
Materials and Methods
Samples
The IMAC study was based on analysis of serum from 12 cancer patients and 35 healthy individuals. The other studies (CM10, H50, and SAX2) were based on studies of analysis of serum from 8 cancer patients and 8 healthy individuals.
Cancer serum samples were obtained from cancer patients prior to surgery. Normal serum was obtained from a group of healthy individuals matched by age and gender to the cancer patients. Serum samples were stored at −80° C. until use. Samples were assayed by the SELDI-TOF/MS technique (Ciphergen).
Sample Preparation
Samples were pre-treated by applying 5 μl of pre-treatment solution to the chip surface and the chip was left on shaker for 5 minutes. The pre-treatment solution varies for different chip types. This process was repeated twice. The chip was washed in MQ-water twice and once in binding buffer.
Serum samples were thawed on ice and 5 μl serum was diluted in 50 μl binding buffer and left on shaker for 40 minutes. Next the samples were removed and chips were washed twice in washing buffer, followed by wash in MQ-water.
Chips were left to dry at room temp for 20 minutes. 0.6 μl crystallisation solution was applied twice.
Analysis
The PBS II instrument (Ciphergen) was calibrated prior to use and chips were analysed with detector sensitivity and laser intensity at suitable values.
Data Mining:
All spectra were pooled into one experiment file and were normalised based on total ion current. Markers were identified by the Biomarker Wizard software (Ciphergen) and markers were compared and combined by principal component analysis
Description of Chips Used for Serum Screening.
As described, the protein chip surfaces are composed of common chromatographic resins commonly used in other purification techniques:
IMAC30 ProteinChip Array
The IMAC30 ProteinChip Array is an immobilised metal affinity capture array with a nitriloacetic acid (NTA) surface. The IMAC30 ProteinChip Array is activated with transition metals prior to use.
CM10 ProteinChip Array
The CM10 ProteinChip Arrays incorporate carboxylate chemistry (negatively charged) that acts as a weak cation exchanger.
H50 ProteinChip Array
H50 ProteinChip Arrays bind proteins through reversed phase or hydrophobic interaction chromatography and have binding characteristics similar to that of a C6 to C12 alkyl chromatographic resin.
SAX2 ProteinChig Array
The SAX2 ProteinChip Array is a strong anion exchange array with quaternary amine functionality.
Description of Buffers used for Binding and Washing Steps in the Serum Screening
The buffer solutions Used, are common buffers used in other purification techniques:
IMAC30 Screening
Pre-treatment: 100 mM NiSO4
Binding buffer: 100 mM TRIS, pH 7.5; 500 mM NaCl; 0.1% Triton X-100
Washing buffer: PBS, pH 7.5; 700 mM NaCl
CM10 Screening
Pre-treatment: None
Binding buffer: 50 mM TRIS, pH 7.5
Washing buffer: 50 mM TRIS, pH 7.5
H50 Screening
Pre-treatment: 100% acetonitrile
Binding buffer: PBS, pH 7.4; 10% ACN; 250 mM NaCl
Washing buffer: PBS, pH 7.4; 10% ACN; 250 mM NaCl
SAX2 Screening
Pre-treatment: None
Binding buffer: 50 mM TRIS, pH 8.0; 0.1% Triton X-100
Washing buffer: 50 mM TRIS, pH 8.0; 0.1% Triton X-100
Results
Only markers with above 70% sensitivity are shown.
Conclusion
We have compared the protein population of serum from colon cancer patients with serum from healthy individuals by different methods (different chips and different binding conditions). By the described procedure, we have identified a number of proteins that are differentially expressed (either up- or down-regulated) in serum from colon cancer patients compared to serum from normal individuals.
We find that the IMAC30 screening gives the prominent results, and the markers obtained from these screenings have been shown to have predictive power in discriminating between samples from healthy individuals and patients diagnosed with colorectal cancer.
The difference of markers detected in serum of this study as compared to the study described in example 1 is based on the state of the samples. The samples of this study were freshly frozen and thawed once prior to analysis, whereas the samples from example 1 have been thawed and refrozen several times.
The study further shows that some markers are detected on more than one type of chip, such as the up-regulation of 5900 as well as the down-regulation of 4290 on both CM10 and IMAC. Moreover, the study shows that by using more than one type of chip, the number of markers detected by using this technology can be increased considerably.
The aim of this study was to separate healthy individuals from colorectal cancer patients using a Principal Component Analysis (PCA) on a normalised data set from mass spectra.
Methods
Samples
Serum samples were obtained from 12 healthy individuals and 35 patients diagnosed with colon cancer and the samples were assayed on IMAC30 chips according to the protocol described above in example 5.
Data Mining
Raw data sets from mass spectra were normalised based on total ion current.
Data sets containing m/z, intensity and area of the peaks identified by “biomarker wizard” were generated as follows:
Computer Programs:
Parameters
Biomarker Wizard Settings:
Principal Component Analysis Settings (MVSP):
Results:
Principal component analysis of data set 1 resulted in two distinct groups, and identified as healthy individuals and patients with colon cancer. The separation was on the first principal component and all peaks irrelevant for the separation was removed from the analysis. Potential markers: 2960, 3170, 3980, 4650, 5340, 5906, 6120, 6840, 6880, 8940, 9140, and 28010 were identified.
Principal component analysis of data set 2 resulted in two distinct groups, and identified as healthy individuals and patients with colon cancer.
Potential markers: 1530, 3980, 4650, 5340, 5545, 5906, 6090, 6120, 6880, 11799, 13745, and 28010 were identified.
The most prominent combination of markers in both data set 1 and 2 were the following markers: 3980, 5340, 5906, 6880, and 28010 with 100% sensitivity and 100% specificity.
Data set 3 was used to verify the power of the selected markers.
The theoretical example shown here below demonstrates the power of the prediction model.
The intensity and m/z of the 5 markers (3980, 5340, 5906, 6880, and 28010) were then used on a data set comprising 2 healthy individuals, 2 patients diagnosed with colon cancer, and 4 unknown by applying PCA.
Conclusion:
Principal Component Analysis can separate healthy individuals from patients with colon cancer using the intensity of the selected markers.
The aim of the study was to develop a method for discriminating between healthy individuals and patients with colon cancer based on data from mass spectra generated using protein chips and the SELDI TOF mass spectrometry technique.
Data Mining
Data Sets:
Data set A: Intensities of the five serum markers from 24 patients diagnosed with colon cancer and 47 healthy individuals.
Data set B: Data set A minus the average of the intensity in healthy individuals.
The intensities were normalised based on total ion current.
Data Format
The input data from each sample contained: Sample ID, intensity of 3980, 5340, 5906, 6880, 28010, and a grouping variable (1=cancer, 0=healthy).
Cut-Off Values
Three different cut-off values were analysed (0.4, 0.5, and 0.6).
Predicted Grouping
If the predicted result is above cut-off, the sample is classified as positive for colon cancer (1).
If the predicted result is below cut-off, the sample is classified as negative for colon cancer (0).
Weights
Calculation
The program reads the data-file line by line, and stores them. For each combination of weights and each sample the predicted grouping is calculated:
Predicted grouping=a*int(3980)+b*int(5340)+c*int(5906)*0.1+d*int(6880)+e*int(28010)
Specificity and sensitivity is calculated, based on the predicted result, cut-off value, and grouping variable.
In order to identify the parameters for predicting cancer from a biological sample using selected markers, the following algorithm was used:
The input-file consists of intensities of the five markers and the desired result (if cancer=1, if healthy=0)
Place all lines from input-file in a list
A weight can take one of the following: −0.9, −0.8, −0.7, −0.6, −0.5, −0.4, −0.3, −0.2, −0.1, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9.
Make all possible weight combinations:
for each cut-off (0.4, 0.5, 0.6)
for each possible combination of weights and each input line:
calculated result=one+two+three+four+five
calculate sensitivity and specificity for this combination of weights
change specificity and sensitivity into integers
if sensitivity>70 and specificity>70
When all combinations of cut-off, weights, and input have been explored sort the array.
Results %
The algorithm used for prediction is as follows:
Conclusions
The program found equations, which had sensitivity and specificity above 90%. The intensity of the marker 5906 is approximately 10 times higher than the other markers. Therefore, in order to prevent the 5906 marker to carry more weight than the other markers it is multiplied by 0.1. The best performing equations were number 1, 4, and 6. This shows that computer algorithms are able to discriminate between healthy individuals and patients with colon cancer. With a larger number of samples it would be possible to use artificial neural network or other computer algorithms to be trained on the data. This might result in increased sensitivity and specificity of the markers.
Samples
Tissue samples were obtained from cancer patients after surgery. Tissue samples were obtained from the removed fragment of the patient's colon following surgical treatment for colon cancer and were stored at −80° C. until use.
Sample Preparation
100 mg tissue sample was thawed on ice and homogenised on a Wheaton Overhead Stirrer for 2 minutes at speed step 2, in 500 μl Lysis buffer (100 mM TRIS-HCl, pH 8.0, 9.5 M UREA, 2% CHAPS). The samples were centrifuged at 14,000 rpm for 10 minutes and the pellet was discarded (repeated twice). The tissue protein extracts were stored at −80° C. until use. Samples were compared by the SELDI-TOF/MS technique (Ciphergen).
Samples were pre-treated by applying 5 μl of pre-treatment solution to the chip surface and the chip was left on shaker for 5 minutes. This process was repeated twice. The solution was removed by washing the chip twice in MQ-water and once in binding buffer.
Tissue samples were thawed on ice and 10 μl tissue sample was diluted in 50 μl binding buffer and left on shaker for 40 minutes. Next the samples were removed and the chips were washed twice in washing buffer, followed by wash in MQ-water. The chips were left to dry at room temp for 20 minutes and 0.6 μl of crystallisation solution was applied twice.
Analysis
The PBS II instrument (Ciphergen) was calibrated prior to use and chips were analysed with detector sensitivity and laser intensity at suitable values.
Data Mining
All spectra were pooled into one experiment file and were normalised based on total ion current. Markers were identified by the Biomarker Wizard software (Ciphergen).
Description of Chips Used in Tissue Screening
As described, the protein chip surfaces are composed of common chromatographic resins commonly used in other purification techniques:
SAX2 ProteinChip Array
The SAX2 ProteinChip Array is a strong anion exchange array with quaternary amine functionality.
NP20 ProteinChip Array
NP20 ProteinChip Arrays, mimic normal phase chromatography with silicate functionality.
Description of Buffers Used for Binding and Washing Steps in the Tissue Screening
The buffer solutions used, are common buffers used in other purification techniques:
SAX2 Screening
Pre-treatment: 100 mM TRIS-HCl, pH 8.0
Binding step: 100 mM TRIS-HCl, pH 8.0
Washing step: 100 mM TRIS-HCl, pH 8.0
NP20 Screening
Pre-treatment: 50 mM TRIS-HCl, pH 8.0
Binding step: 50 mM TRIS-HCl, pH 8.0
Washing step: 50 mM TRIS-HCl, pH 8.0
Table 16 shows a number of putative markers for colon cancer using more than one type of chip. Although some markers may be detected using different chip with various surface characteristics, most of the markers detected by the different chip types do not overlap. This allows for detection of a larger number of markers in the same sample.
The aim of this study was to use bioinformatics to associate the identified markers with annotated genes with a known function.
Many of the possible tumour markers have masses that correspond to specific peptides in the database. The mass values of the individual tumour markers may in some cases correspond to the mass values of specific human proteins in the database. By searching with the mass value of each tumour marker, a number of possible hits occur. These hits are possible identifications of the proteins.
Data Bases and Search Engines
Database: Swiss-Prot (Human)
Search tool: TagIdent (Expasy)
Allowed deviation: Up to 0.5% deviation from noted mass accepted
Results and Conclusion
It should be noted that the hits may not necessarily refer to the full length protein encoded by the specified gene, but in many cases to a specific peptide produced by alternative splicing or post-translational processing, hence one mass value may produce more than one hit within one gene.
The results show that some of the markers identified in the examples listed above can be linked to proteins, which have been associated with tumour initiation, tumour growth or tumour progression, such as Def 1 and 3 as well as Cathepsin B.
Furthermore, it should be noted that some of the markers detected by the mass spectrometry might reflect degradation products of larger proteins.
SELDI-TOF/MS (Surface Enhanced Laser Desorption/Ionisation-Time Of Flight/Mass Spectrometry) protein profiling was used to demonstrate that the expression of human neutrophil peptides-1, -2 and -3 (HNP 1-3), also known as alfa-defensin-1, -2 and -3, is up-regulated in colon tumour tissue relative to normal colon tissue. Further, by comparing serum from colon cancer patients with serum from a group of healthy individuals, we show that this abnormal HNP 1-3 expression is reflected in colon cancer serum.
The tissue screening was performed on NP20 chip, whereas the serum screening was performed on SAX2 chip.
NP20 ProteinChip Array
NP20 ProteinChip Arrays, mimic normal phase chromatography with silicate functionality.
Pre-treatment: 50 mM TRIS-HCl, pH 8.0
Binding step: 50 mM TRIS-HCl, pH 8.0
Washing step: 50 mM TRIS-HCl, pH 8.0
SAX2 ProteinChip Array
The SAX2 ProteinChip Array is a strong anion exchange array with quaternary amine functionality.
Pre-treatment: 100 mM TRIS-HCl, pH 8.0
Binding step 100 mM TRIS-HCl, pH 8.0
Washing step: 100 mM TRIS-HCl, pH 8.0
The Defensin screening was performed by as described for the general serum/tissue screenings. The expression of three peptides with mass/charge ratio (m/z) values of 3372, 3443 and 3486 (+/−0.1%) were found to be up-regulated in the tumour samples compared to the samples and up-regulated in serum from patients with colon cancer when compared with serum from healthy individual. The three peptides were subsequently identified as HNP 2, 1 and 3, respectively. This was done by peptide mapping (trypsin digest) and reduction with DTT.
The aim of this study was to define the relationship of the expression of human neutrophil Peptides-1, -2 and -3 (HNP 1-3) and colon cancer.
Materials and Methods
Tissue Screening
Tissue samples were obtained from the removed fragment of the patient's colon following surgical treatment for colon cancer and were stored at −80° C. until use. 100 mg tissue sample was thawed on ice and homogenised on a Wheaton Overhead Stirrer for 2 minutes at speed step 2, in 500 μl Lysis buffer (100 mM TRIS-HCl, pH 8.0, 9.5 M UREA, 2% CHAPS). The samples were centrifuged at 14,000 rpm for 10 minutes and the pellet was discarded (repeated twice). The tissue protein extracts were stored at 80° C. until use. Minor pilot studies were performed on different chips (data not shown) and the NP20 (Normal Phase) (Ciphergen) chip was chosen for the tissue screening. NP20 chips was placed in bioprocessor and pre-treated with 50 μl tissue binding buffer (50 mM TRIS-HCl, pH 8.0) for 5 minutes on shaker (250 rpm) (repeated twice). 5 μl tissue protein extract was diluted in 50 μl tissue binding buffer and incubated in bioprocessor on NP20 chips for 40 minutes at room temperature on shaker (250 rpm). Spots were washed twice in 250 μl tissue washing buffer (50 mM TRIS-HCl, pH 8.0) for 5 minutes. The chips were air-dried for 20 minutes, followed by treatment with two times 0.6 μl 100% SPA matrix solution.
Serum Screening
Cancer serum samples were obtained from cancer patients prior to surgery. Normal serum was obtained from a group of healthy individuals matched by age and gender to the cancer patients. Serum samples were stored at −80° C. until use. Serum pilot studies were performed on different chips to monitor the presence of HNP 1-3 in serum (data not shown). The immobilised metal affinity capture (iMAC30) chip was chosen for the actual screening and pre-treated with nickel before analysis: 5 μl 100 mM NiSO4 were added to each spot and left on shaker (150 rpm) for 5 minutes (repeated twice). The chips were placed in bloprocessor and incubated with 100 μl MQ for 5 minutes on shaker (250 rpm). Each spot was treated with 50 μl serum binding buffer (100 mM TRIS-HCl, pH 7.5, 500 mM NaCl, 0-1% Triton X-100) and left on shaker for 5 minutes (250 rpm). Serum samples were thawed on ice and 5 μl serum was diluted in 50 μl serum binding buffer and applied to spots and left on shaker (250 rpm) at room temperature for 40 minutes. Samples were removed and spots washed twice in 200 μl serum washing buffer (100 mM PBS, pH 7.4, 700 mM NaCl), followed by one wash in 200 μl MQ-water. The chips were removed from the bioprocessor and left to air dry for 20 minutes followed by treatment with two times 0.6 μl SPA (100%). Only freshly made matrix solutions were used and the instrument was calibrated prior to use. Cancer and normal samples were run side by side. The chips were analysed on a PBSII instrument (Ciphergen). All spectra in each screening were normalised based on total ion current.
Purification and Identification of HNP 1-3
100 μl protein extract from cancer tissue in tissue lysis buffer was loaded unto a RP-HPLC column (uRPC C2/C18 ST 4.6/100, Pharmacia Biotech, Flow rate: 0.5 ml/min, Fraction size: 0.5 ml) in buffer A (0.065% Tri-flouro-aceticacid (TFA) in MQ-water) and proteins were eluted in a gradient of 0-100% buffer B (0.05% TFA in acetonitrile (ACN)). Elution of peptides was monitored by absorption spectrometry (OD280). All protein containing fractions were analysed by MALDI-TOF (Matrix Assisted Laser Desorption/Ionization-Time of flight) on the PBS II Instrument: 1.5 μl fraction was incubated with 0.6 μl SPA (100%) on a Gold array (Ciphergen) and left to crystallise on chip, followed by an additional 0.6 μl SPA (100%) and the Gold array was analysed by MALDI-TOF. The HNP 1-3 containing fraction (32% buffer B) was further purified on a peptide gel-filtration column (Superdex Peptide HR 10/30, Pharmacia Biotech, Flow rate 0.9 ml/min, Fraction size: 0.5 ml, Buffer: 50% ACN, 0.1% TFA). Elution of peptides was monitored by absorption spectrometry (OD280) and protein containing fractions were again analysed by MALDI-TOF on the PBS II instrument as described. Purified HNP 1-3 was subjected to on-chip trypsin digestion. 10 μl HNP 1-3 fraction was applied to NP20-chip and left on shaker (250 rpm) at room temperature for 40 minutes. Sample was removed and spot was washed twice with 10 μl water (on-chip purification step). In order to denature peptides prior to digestion, the chip was left on heating block (80 C) for 5 minutes. The chip was cooled on ice for 2 minutes. 10 μl trypsin digestion solution (0.01 μg/μl trypsin in 50 mM NH4HCO3, pH 8.0) was added, and the chip was left for 10 hours at 40° C. In humidity chamber after which the chip was left to air dry for 20 minutes. 1 μl CHCA (100%) was added and the peptide map was analysed on PBS II instrument. Identification was done by the use of PepIdent on the Expasy server.
Size Exclusion Chromatoaraphy of HNP 1-3
50 um colon cancer serum was loaded unto a peptide gel-filtration column (optimal separation range: 1 to 7 kDa, flow rate: 0.5 m/min, fraction size: 0.5 ml, buffer: 10 mM Ammonium carbonate, pH: 8.0). Elution of peptides was followed by absorption spectrometry (OD280). All protein-containing fractions were analysed by MALDI-TOF on PBSII (Ciphergen) as described above. Maximum signal intensity of 40 individual peaks was plotted as a function of elution volume and an approximate elution curve was calculated.
Functional Study of HNP 1-3 by Microflow
For micro flow experiments, MDCK cells were plated onto poly-d-lysine coated cover slips at a concentration 3000 cells/well, grown in DMEM with 10% FBS for five days with the result of confluent islands. Microflow was performed in an Eppendorf micromanipulator 5171 and transjector 5246 system mounted on a Leica DMIRBE inverted research microscope. Micro capillaries (borosilicate with filament, Sutter Instruments Company, Novato, Calif., USA) were pulled to an outer diameter of 0.85 nm on a Sutter P-97 Micropipette Puller. The dye-loaded cells were visualised by excitation at 470 nm and recorded at 509-nm emission using Haupage version 3.3.18038 software and Kappa CF 15/4 MC-S camera (Leica). The MDCK cells were recorded (in CO2 independent media) on the inverted DMIRBE inverted research microscope. The capillary was placed 20 nm over the confluent cells with a constant flow (1300 hPa) of calcein (20 mM). The MDCK cells were exposed to peptide fractions purified from colon tumours by size-exclusion chromatography.
Results
HNP1-3 Expression in Tissue and Serum
Pilot studies of colon tumour and normal colon tissue was performed on a variety of chips with different chemical properties and under different binding and washing conditions. Based on these preliminary studies, the expression of three peptides with mass/charge ratio (m/z) values of 3372, 3443 and 3486 (+/−0.1%) (subsequently identified as HNP 2, 1 and 3, respectively), were found to be up-regulated in the tumour samples. The three peptides were visible on different chips and under different binding conditions (data not shown). However the strongest signals of HNP 1-3 in tissue extract were obtained on the NP20 (Normal Phase) chip, whereas the strongest signal of HNP 1-3 in serum was observed on the iMAC30 (immobilised metal affinity capture) chip activated with nickel, and these conditions were chosen for the actual screenings. Protein extract from 40 colon tumour and 40 normal colon tissue samples were analysed on NP20 chips and 125 colon cancer serum samples and 100 normal serum samples were analysed on iMAC30 chips. All spectra in each screening were pooled and normalised based on overall ion current. Each spectrum produced approximately 40 to 60 protein peaks in the range from 2 to 80 kDa (
Identification of HNP 1-3
The three possible markers were purified by RP-HPLC, peptide gel-filtration and on-chip purification, after which they were identified by peptide mapping as HNP-2 (3372 Da), HNP-1 (3442 Da) and HNP-3 (3486 Da) (Table 1A.). The measured masses correspond to the peptides in their oxidised states, with three disulphide bridges. After heat denaturation (10 minutes, 80° C.) and treatment with DTT (200 mM DTT, room temperature, 30 minutes), HNP-1 and HNP-2 increased 6 Dalton in mass, due to reduction of the six cysteines (Table 1B). We were not able to reduce HNP-3, due to degradation during the reduction process.
Size Exclusion Chromatography of HNP 1-3
50 μl colon tumour extract in Lysis buffer was applied to a peptide gel-filtration column. Elution of peptides was followed by absorption spectrometry (OD280). All fractions were analysed by MALDI-TOF on PBSII (Ciphergen). Maximum signal intensity of 40 individual peaks was plotted as a function of elution volume and an approximate elution curve was calculated (
Cytoxic Assay
The cytotoxicity of HNP 1-3 purified from colon tumours was tested by exposing MDCK cells to different fractions purified from colon tumours. Calcein were added to the fractions and the solutions were left to overflow the cells for one hour. By fluorescence microscopy calcein was observed to accumulate only in cells exposed to HNP 1-3/calcein fractions, whereas cells treated with fractions containing other (unidentified) tumour peptides did not uptake calcein (
Discussion
Elevated concentrations of HNP 1-3 in colon cancer serum
Abnormal concentration of HNP 1-3 in body fluids has previously been demonstrated. Elevated concentrations of HNP 1-3 following infection (bacterial-/non-bacterial-infection and pulmonary tuberculosis) has been found in plasma, blood and a number of body fluids and plasma HNP 1-3 concentrations have been shown to be elevated in patients with septicaemia or bacterial meningitis. HNP 1-3 have been found in urine from patients with transitional cell carcinoma of the bladder and in salvia of patients with oral carcinomas.
Our study is the first that demonstrate elevated concentrations of HNP 1-3 in serum following tumour growth.
Elevated Concentrations of HNP 1-3 in Colon Tumours
HNP expression has previously been linked to different types of tumours and cell lines. HNP-1 has been detected in lung tumours and in the submandibular glands of patients with oral carcinomas. By RT-PCR, mass spectrometry and flow cytometric analysis, HNP 1-3 have been shown to be expressed by cell lines deriving from renal cell carcinomas and the expression of a specific HNP precursor peptide has been shown to be up-regulated in human leukaemia cells. In a study of squamous cell carcinomas of the human tongue it was suggested that the tumour expressed HNP 1-3 originated from tumour invading neutrophils. Since our tissue screening is based on comparison of whole tissue samples, the up-regulated expression of HNP 1-3 may not necessarily originate from the colon cancer cells, but could originate from tumour infiltrating neutrophils. HNP 1-3 are known to stimulate bronchial epithelial cells to up-regulate lnterleukin-8 production, a potent neutrophil chemotactic factor and HNP 1-3 are also capable of regulating the systemic immune response (discussed below). Thus, the up-regulated expression of HNP 1-3 in colon tumours may primarily originate from invading neutrophils, but could be initiated by HNP 1-3 produced by cancer cells. Even though the signal intensity in mass-spectrometry can not directly be interpreted as a measure of protein concentration, our results suggests that HNP 1-3 are very abundant in colon tumours. This is in agreement with the study of HNP-1 in lung tumours, where the maximum observed level was 26 nano-moles per gram wet tissue. It follows, that in order for these excessive amounts of peptide to be detectable in serum, the peptides must be released from the cells. This is in agreement with studies of HNP 1-3 expression in kidney and brain.
Size Exclusion Chromatography of HNP 1-3
We explain the elevated concentrations of HNP 1-3 in colon cancer serum by unspecific binding between HNP 1-3 and high mass serum proteins. We believe the peptides attach to serum proteins in the tumour area and are carried into the bloodstream. Even though the HNP 1-3 we observe in high mass fractions from size exclusion, could also be explained by multimerisation, we interpret the size exclusion results as evidence for interaction between HNP 1-3 and unidentified high mass proteins through unspecific interactions. In one study, it was demonstrated that Defensins form voltage dependent channels in lipid bi-layer membranes, supported by further conductance investigations, suggested that the channels were formed by multimers containing 2-4 molecules and a crystal structure study of HNP-3 revealed an amphiphilic dimer. We add to the growing realisation that common plasma proteins bind disease specific peptides and therefore should not be ignored in marker research. Our size-exclusion results are in agreement with a number of previous studies that show that HNP's are bound to plasma protein in vitro and that high concentrations of HNP's causes precipitation of plasma proteins, specifically 2-macroglubulin and C1 complement has been shown to bind Defensin. Another study showed that HNP-1 bind to various serum proteins, notably serum albumin, and it was found that serum, or serum albumin, was able to inhibit the anti-viral activity of HNP-1. This ability to bind to serum proteins could also explain why HNP 1-3 lysis of mammalian cells is hindered in the presence of serum.
Common to beta-Defensin 2, another member of the Defensin family, and HNP 1-3 is an uneven distribution of surface charges. Beta-Defensin 2 has been shown to bind to a chemokine receptor and it has been suggested that the positively charged cluster, which is also shared by chemokines, may play a common role in binding to receptors in general, but is not important for determining receptor specificity. The same surface charge could also explain the binding of HNP 1-3 to plasma proteins. The observation that Defensins are localised to lymphocyte nuclei could similarly be explained by unspecific binding to shuttle proteins.
HNP 1-3—Cytotoxic Peptides
The exact concentration of HNP's in the tumour microenvironment may have profound influence on the in vivo function of HNP 1-3. One study shows that HNP 1-3 mediates lysis of tumours in a concentration dependent manner. This is in agreement with another study that show that only relatively high concentrations of HNP-1 (10-4 M) are cytotoxic for human monocytes, whereas lower concentration of HNP-1 (10-8 to 10-9 M) increases TNF-alpha production by monocytes. In a study of renal cell carcinoma lines it was shown that HNP 1-3 were cytotoxic to all tested cell lines when present in high concentrations (above 25 ug/ml), but at lower concentration HNP 1-3 stimulated growth of a subset of tumour cell lines. We add to the established theory that HNP 1-3 are cytotoxic to mammalian cells, by demonstrating that HNP 1-3 purified from colon tumours are capable of lysing MDCK cells. Our study was based on a 30 minutes microflow study and did not allow us to investigate the minimum concentration of HNP 1-3 necessary for lysis.
Conclusion
The high concentration of HNP 1-3 observed in tumours and the observation that HNP 1-3 are capable of lysing mammalian cells leads to the immediate conclusion that the peptides serve to the benefit of the host by primarily killing tumour cells. However, HNP 1-3 bind to HLA-Class II molecules and are capable of reducing the proliferation of a HLA-DR-restricted T-cell line after stimulation and could in this way help the tumour avoid immune recognition. Defensins also regulate the systemic immune response. Through interaction with the chemokine receptor CCR6, beta-Defensins recruit dendritic cells and T cells and HNP 1-3 are capable of recruiting leukocytes to sites of infection in mice. Up-regulated Immune responses are known to stimulate tumour proliferation: immune cells are actively recruited by tumours to exploit their pro-angiogenic and pro-metastatic effects. Whether the high concentrations of HNP 1-3 in the tumour limits the tumour growth or on the contrary stimulate tumour proliferation is not clarified. Recently, it was found that the excess amounts of HNP 1-3 observed in urine from bladder cancer patients was produced by the actual bladder cancer cells, (and not by tumour infiltrating neutrophils), and that highly invasive bladder cancer cells produced more HNP 1-3 than less invasive ones. We suggest that the prominent surface charge on Defensins, their ability to bind to high mass proteins and the observed excess amounts of peptides seen in tumours, could provide the peptides with broad antagonising effects, that may influence numerous receptors in the tumour microenvironment.
The plasma screening was performed on IMAC30 chips according to the protocol used for serum screening described above on IMAC30 chips, with the exception of adding 5 μl plasma instead of 5 μl serum to the binding buffer.
The aim of this study was to separate healthy individuals from colorectal cancer patients using a Principal Component Analysis (PCA) on a normalised data set from mass spectra.
Methods
Samples
Plasma samples were obtained from 16 healthy individuals and 16 patients diagnosed with colon cancer and the samples were analysed on IMAC30 chips according to the protocol described above in Example 12.
Data
Two data sets containing m/z and intensity of the peaks identified by “blomarker wizard” were generated. The first data set contained half of the spectra. The second data set contained all spectra. Spectra were pooled and normalised based on total ion current in the two data sets.
Computer Programs:
Parameters
Biomarker Wizard Settings:
Principal Component Analysis settings (MVSP):
Results:
Potential markers from a principal component analysis of the first data set: 1455, 1500, 1532, 1573, 1704, 1725, 3445, 3545, 3895, 4136, 4480, 4977, 5266, 5910, 6110, 6435, 6635, 6673, 8931, 9015, 9173, 9950, 10838, 11723, 13747, 13870, 19865, 28028, 32490, 33233, 50820, 60638, 65706, 66213, and 79155 Da.
The following combinations of markers yielded 100% sensitivity and 100% specificity:
3895, 6110, 8931, and 6635 Da.
6110, 8931, and 6635 Da.
19865, 13747, 8931, and 9015 Da.
8931, 9015, 33233, and 13747 Da.
19865, 13747, 8931, 9015, and 33233 Da.
Principal component analysis on the second data set yielded the following potential markers: 1573, 1704, 1725, 6435, 6673, 9015, 9173, 10838, 11341, 11723, 13747, 13880, 28028, and 50825 Da.
The most prominent combination of markers was the following: 9173, 11728, and 13880 Da with 100% specificity and 100% sensitivity.
Conclusion:
Principal Component Analysis can separate healthy individuals from patients with colon cancer using the intensity of the selected markers.
As presented in Example 9, a peptide of mass 2364 is up-regulated in tumour tissue when analysed on SAX2 Chip (table 17, line 1). This peptide was purified (by RP-HPLC and peptide-gel-filtration) and subsequently identified by ESI-MS/MS. The peptide was found to consist of the following sequence: FLGMFLYEYARRHPDYSVV (m/z 2363.7) SEQ ID NO 1. This sequence corresponds to a fragment of human serum albumin, demonstrating that human serum albumin is excessively degraded in colon tumour samples compared to normal colon tissue samples and thus supports the results that show that there is an abnormal degradation of serum albumin in serum from cancer patients
Abnormal Protease Activity in Colon Cancer Serum
When serum is analysed on the IMAC30 chip (as described in the procedure for the serum screening) two high mass proteins are found to be differentially expressed (as described in the results of the serum screening): a protein with m/z: 66500 is down-regulated in cancer serum whereas a protein with m/z: 60500 is up-regulated in cancer serum (see table 10).
The protein of 66500 is human serum albumin (HSA) (ALBU_HUMAN (P02768)) The theoretical mass of HSA is 66472 Da, well within 0.1% of the observed mass of 66500 Da. The peak at 66500 is an easily identifiable and prominent peak of high intensity, often observed in mass spectrometry analysis of biological samples and any person familiar with mass spectrometry would immediately identify the prominent peak at 66500 as serum albumin.
Therefore, we show that HSA is present in lower amounts in serum from cancer patients than in serum from normal individuals.
The protein at 60500 appears in a reverse proportional manner to HSA: in the normal serum where there is high amounts of HSA, there is only little amount of 60500, and in the cancer serum where there is relatively low amounts of HSA, there is relatively high amount of 60500.
From this we conclude that 60500 is a degradation product of HSA, that is produced when a fragment of approximately 6000 Da is lost from HSA.
HSA is produced in the liver which is not influenced by tumour growth in the colon, at least not at this stage in the disease, and the observation, that there is relatively more HSA in serum from normal individuals than in serum from cancer patients, can therefore not be explained by an altered expression of HSA by liver cells. The only meaningful explanation for this abnormality is altered proteolytic degradation of HSA in serum from cancer patients. Since the proteolytic product, in this case the HSA fragment at 60500, is also present in serum from normal individuals, albeit at lower amounts than in serum from cancer patients, the exact proteolytic mechanism responsible for the specific degradation of HSA leading to the production of 60500 is not unique to serum from cancer patients.
Therefore, our results show direct evidence for altered proteolytic activity in cancer serum.
Finally, as presented in Example 9, a peptide of mass 2364 is up-regulated in tumor tissue when analysed on SAX2 Chip (table 17, line 1). This peptide was purified (by RP-HPLC and peptide-gelfiltration) and subsequently identified by ESI-MS/MS (as described in example 15). The peptide was found to consist of the following sequence: FLGMFLYEYARRHPDYSVV (m/z 2363.7). This sequence corresponds to a fragment of human serum albumin, demonstrating that human serum albumin is excessively degraded in colon tumor samples compared to normal colon tissue samples. This supports the results that show that there is an abnorm degradation of serum albumin in serum from cancer patients.
Identification of Serum/Plasma Marker 28040/28025/28010
By HPLC, gel purification and trypsin peptide mapping we positively identify 28040/28025/28010 as apolipoprotein (P02647).
Results:
Best match:
Peptide map:
Apolipoprotein information:
Function: Participates in the reverse transport of cholesterol from tissues to the liver for excretion by promoting cholesterol efflux from tissues and by acting as a cofactor for the lecithin cholesterol acyltransferase (LCAT).
Subcellular location: Secreted.
Tissue specificity: Major protein of plasma HDL, also found in chylomicrons. Synthesized in the liver and small intestine.
As discussed above, abnormal concentrations of common plasma/serum proteins produced by the liver will probably not be due to altered transcription/translation of the relevant gene, but instead a consequence of abnormal proteolytic activity.
The purpose of this project is to identify a number of peptides which have been found in blood serum and which are identified as markers for colon cancer.
Analysis
Two samples were purified, wherein one sample contained two peaks. Each sample was initially analysed by MALDI-TOF to establish the molecular weight of the components and to have an estimate on the amount of peptide present in the sample.
The peptides of interest, found during MALDI analysis, were fragmented by both MALDI-TOF/TOF and ESI-MS/MS analysis.
Sample 1 (containing the 5901 Da peptide) was purified by reversed phase HPLC and each fraction was analysed by MALDI-TOF to locate the fractions containing the 5901 Da peptide. The fractions containing the peptide were pooled and analysed both directly by MS/MS analysis and further purified by 1D SDS gel electrophoresis. The band at 6000 Da was cut out, digested with trypsin and analysed by MALDI-TOF and TOF/TOF.
Instruments
Bruker Reflex IV (MALDI-TOF)
Bruker Ultraflex (MALDI-TOF/TOF)
Micromass Ultima (nanoLC-MS/MS)
Applied Biosystems Vision Workstation (HPLC)
Results
Human serum sample (300 μl) was purified by reversed phase HPLC. The three fractions containing the 5900 Da peptide were pooled and analysed by MALDI-TOF. The final fraction contains 4 major peaks; MH+ at 4961.8 Da, 5333.5 Da, 5901.1 Da and 6187.05 Da.
The pooled fractions were dried down and loaded on a SDS PAGE gel. The gel band of interest was cut out of the gel, reduced and alkylated, and digested with trypsin.
The digest sample was micro-purified over a graphite/carbon column. A peptide fingerprint was made. One peptide (MH+ 1190.5) was selected for MALDI-TOF/TOF analysis. Database search of the fragmented peptide gave a Mascot search score of 69 and an ion score of 47. The peptide is part of alpha-fibrinogen.
The sequence from gi|1706799|sp|P02671 was used to search for the masses found in the pooled fraction. The m/z 5901.9 Da peptide can be a part of alpha-fibrinogen, and the tryptic peptide (MH+ 1190.5) can be included in the m/z 5901.9 Da peptide. The sequence is:
Peptide Sequences
5901.9 Peptide
The bold underlined part of the sequence shows the tryptic peptide (MH+ 1190.5 Da).
The tryptic peptide does unfortunately also fit to the masses 5333.5 and 6187.05 Da found in the fraction.
5333.5 Peptide:
Conclusion
One peptide was found after digest of the gel band containing the “5900 Da peptide”. Fragmentation of the peptide (MH+ 1190.5) by MALDI-TOF/TOF gave the sequence (QFTSSTSYNR). This is part of alpha-fibrinogen. Searching the alpha-fibrinogen sequence for the mass m/z 5901.9 gave a hit where the sequence from the tryptic peptide also is included. The sequence does also fit to the masses 5333.5 and 6187.05, respectively.
Sample 2
Results:
From the MALDI-TOF spectra, the peaks m/z 2363.05 and 1686.84 Da were found to corresponds to the masses from the SELDI approach.
It was only possible to make ESI-MS/MS on 2363.05. The peptide was seen a triply charged ion. Attempts were also made to make MALDI-TOF/TOF on these peaks, but without success.
Peptide Sequences
De-Novo sequencing gave the tag: FLGMFLYE (SEQ ID NO 10). This was searched as a sequence tag together with the mass MH3+ 788.3 Da. This matched the peptide
FLGMFLYEYARRHPDYSVV (SEQ ID NO 11).
A similarity search of the sequence shown in table 22, resulted in the following hit:
Conclusion
Direct analysis of the sample with MALDI-TOF showed the peptides of interest. ESI-MS/MS was only possible on mass MH3+788.3 Da. This matched the peptide: FLGMFLYEYARRHPDYSVV. This can be a part of alpha-fetoprotein/human serum albumin.
1) Fragmentation of a larger protein
2) Ligand binding peptides
3) Proteolytic processing of peptides
4) Translational/transcriptional regulation of peptides.
The aim of the study was to determine if visual inspection of mass spectra is a method for discriminating between healthy individuals and patients with colon cancer.
Computer Programs:
Data:
Serum samples from 47 healthy individuals and 24 patients diagnosed with colon cancer were assayed on IMAC30 chips and analysed as described above. Intensities were normalised based on total ion current.
Method:
Raw data was exported from Ciphergen ProteinChip Software to Excel, mean and standard error of means (SEM) was calculated for each m/z value.
Mean and SEM was imported in R. Plots for specific regions of the spectra were designed. The specific regions were chosen to include the 5 markers used for Principal component analysis as described above.
Results:
A: The area from 3900 to 4100 Da, SEM shown for 3960 and 3980 Da. B: The area from 5200 to 5400 Da, SEM shown for 5340 and 5350 Da. C: The area from 5800 to 6000 Da, SEM shown for 5906 and 5920 Da. D: The area from 6800 to 7000 Da, SEM shown for 6880 and 6940 Da. E: The area from 27000 to 29000 Da, SEM shown for 28025 Da.
Conclusion
Visual inspection of specific regions can be used for discriminating healthy individuals from patients with colon cancer.
The aim of this study was to search a database for proteins with known mass corresponding to the measured mass value of the markers identified. This may constitute a possible identification.
Methods
The measured mass value is analysed on the “TagIdent Tool” on the ExPASy server.
With the following parameters:
Mass value range: 0.2%
pI: Complete range
Organism: Human
Database(s) on which the scan should be performed: Swiss-Prot
Results
By searching the database with the mass value of each of the markers a number of possible identifications occur (hits):
This identification of plasma markers was performed as described for the serum markers in Example 17.
In some cases the measured markers correspond to the theoretical mass of a protein in the database (for example the Swiss-Prot database for human proteins) in other cases no significant hit can be obtained (there is no protein with a theoretical mass within for example 0.2% of the identified mass of the marker). There could be a number of reasons for this: the database is not complete (databases are continually being updated), the identified mass is a protein with post-translational modifications (these modifications add to the final mass, and are never accounted for in the database), the identified mass is not a mass of a full length protein, but a fragment of a protein (there is an almost infinite number of fragments for every protein and these are not accounted for in the database). If the identified mass corresponds to a fragment of a marker, a possible identification can be obtained by so called “artificial digest” or “in silico digest” of a protein of interest. In this procedure the sequence of a protein is pasted into a digestion program. This program then cleaves the sequence into specific fragments and calculates the mass values of these fragments. Some of these mass values may correspond to the measured mass values of the markers. This fragment may be an identification of the marker. However, there are more than one hundred thousand protein sequences in the database, which in theory each produces an infinite amount of fragments. Our screening was done on blood samples (serum or plasma), therefore we focused solely on a few common blood proteins.
Methods
The protein sequence was obtained from the NCBI Entrez Protein Bank in fasta format.
The sequence was digested by “PeptideMass” on the ExPASy server.
The following parameters were chosen:
Mass value: [M], average.
Enzyme: Trypsin (higher specificity)
Allowed missed cleavage sites: 5
We have chosen Trypsin (higher specificity) based on the assumption that most proteases in blood are members of the trypsin-familiy of proteases.
The program allows for a maximum of 5 missed cleavage sites. This means that fragments of proteins that contain more than 5 cleavage sites will not be presented. Fragments containing more than 5 cleavage sites are however possible.
Results:
In some cases the measured markers correspond to the theoretical mass of a protein in the database (for example the Swiss-Prot database for human proteins). We have artificially digested the following common blood proteins:
Human Serum Albumin (P02768), Haptoglobin (P00738), Alpha 2 Macroglobulin (P01023), C2 Complement (P06681), C3 complement (P01024)
In some cases the measured markers correspond to the theoretical mass of a protein in the database (for example the Swiss-Prot database for human proteins).
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| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2003 00541 | Apr 2003 | DK | national |
| PA 2003 01085 | Jul 2003 | DK | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DK04/00263 | 4/7/2004 | WO | 12/27/2006 |
