Patent Application
20240385191
The present invention relates to immunoassays, in particular immunoassays for detecting and/or monitoring cancer in a patient, and to monoclonal antibodies and immunoassay kits for use in carrying out said immunoassays.
Cancer is a major global health problem and the burden of cancer incidence and mortality is rising worldwide (1). One part of the problem is the lack of relevant biomarker tools that can, amongst other things, detect cancer earlier and predict response to treatment. Further, traditional biomarkers usually involve invasive procedures such as tissue biopsies (2). A promising alternative to these approaches is liquid biopsies. In recent years, the tumor microenvironment surrounding the cancer cells has been given more attention and is a prime place to look for non-invasive biomarkers.
In particular, the extracellular matrix, defined as the non-cellular part of tissues has been recognized as an important part of cancer development (3). The dominant ECM proteins are the collagens, which are important for tumor stiffness, tumor immunity and cancer metastasis (4). In cancer, the dynamic balance of ECM formation and degradation is knocked askew. Cells in the tumor microenvironment influence the remodelling of collagen and collagen reciprocally influences the behaviour of cells (4,5). Collagens such as type IV have well-described expression patterns, localization and function in the cancer context. It is ubiquitous in basement membranes and serves as a barrier for invading tumor cells, one that can be broken down to facilitate metastasis (6,7). However, most of the cancer research into collagens has focused on the abundant and well-characterized collagens, such as type I, III or IV collagens, whereas many of the more poorly characterized collagens remain unexplored.
Type XX collagen is one such unexplored collagen. Based on its structural features, type XX collagen is part of the family of fibril-associated collagens with interrupted helices (FACITs). This family of collagens is thought to associate with the fibrillar collagens to regulate their organization and interactions (8). Structural features of type XX collagen include several fibronectin type III repeats, a von Willebrand factor A domain, a thrombospondin-like domain as well as collagenous triple-helix domains (G-X-Y) interspersed with non-collagenous domains (8). Within the FACIT family, type XII and XIV are the closest relatives to type XX collagen since they are the only FACITs to also have fibronectin domains (8).
Only a little is known about the expression, localization and function of type XX collagen. It was originally cloned from chick embryos in which expression was mostly limited to corneal epithelium, but detectable in embryonic skin, lung, sternal cartilage, and tendon (8). Several authors have pointed out the parallels between cancer and development (9,10). RNA expression data from the human protein atlas (https://www.proteinatlas.org/ENSG00000101203-COL20A1/tissue) also suggests an enrichment of COL20A1 expression in human brain and comparatively minor upticks in testis and spleen tissues. A role in the brain is also confirmed by data from the cancer genome atlas (TCGA) initiative wherein COL20A1 levels are comparatively elevated in glioma tissues (https://www.proteinatlas.org/ENSG00000101203-COL20A1/pathology). Thus, looking strictly at expression levels, type XX collagen seems to play a role in brain function and in brain cancers. From this perspective, type XX collagen does not seem to be present in appreciable amounts in other tissues.
Despite the apparent scarcity of type XX collagen expression, COL20A1 has been described in the cancer literature. Reports usually describe COL20A1 at the DNA or RNA level and usually in broad and general screenings. In line with the brain association described above and based on cDNA microarrays, COL20A1 was elevated in so-called brain-tumor initiating cells versus regular glioma cell lines and normal brain astrocytes (12). In a separate study, using biopsy-derived glioma cell models, a downregulation of COL20A1 RNA was observed after treatment with histone deacetylase inhibitors (13). In other cancers, reports on type XX collagen are rare, but COL20A1 was included in a 16-gene signature associated with breast cancer recurrence, metastasis and poor survival in a Chinese population (11). And COL20A1 is reportedly also upregulated in early-stage prostate tumorigenesis (14). Notably, these screenings do not follow up with any functional studies on type XX collagen, so insight into its function and distribution is still sorely lacking.
The applicant has now developed an enzyme-linked immunosorbent assay (ELISA) to quantify the presence of a biomarker (referred to herein as “PRO-C20”) of type XX collagen, in blood. The assay was optimized and validated, and used to determine the levels of circulating type XX collagen in the serum of cancer patients and healthy controls. It was found that the assay was robust, with specificity for type XX collagen and with sensitivity to detect levels in both healthy controls and patients with disease (cancer). The data shows that PRO-C20 levels were significantly elevated in the serum of cancer patients compared to healthy controls. The data also shows that, in patients with cancer, high levels of PRO-C20 are associated with poor overall survival rates.
Accordingly, in a first aspect, the present invention provides a method of immunoassay, the method comprising:
The method is preferably a method of immunoassay for detecting and/or monitoring a disease in a patient and/or assessing the severity of a disease in a patient. The method preferably further comprises:
In preferred embodiments, the disease is cancer. The cancer may for example be bladder cancer, breast cancer, colorectal cancer, head and neck cancer, kidney cancer, liver cancer, lung cancer, melanoma, ovarian cancer, pancreatic cancer, prostate cancer, or stomach cancer. The disease may in particular be pancreas ductal adenocarcinoma (PDAC).
As noted above, the method may in certain embodiments be a method for assessing the severity of a disease, such as for example cancer, in a patient. For example, the method may be a method for determining the prognosis of a cancer in a patient, such as for example determining the likely survival time and/or probability of survival of the patient.
In preferred embodiments, the monoclonal antibody does not specifically bind to an elongated version of the target sequence which is QGASTQGLWES (SEQ ID NO: 2) (i.e. a version of the PRO-C20 target sequence extended at its C-terminus by the addition of a serine residue). Preferably, the ratio of the affinity of said antibody for the PRO-C20 target sequence to the affinity of said antibody for the elongated version of the target sequence is at least 10 to 1, and more preferably is at least 20 to 1 or at least 30 to 1.
In preferred embodiments, the monoclonal antibody does not specifically bind to a truncated version of the target sequence which is QGASTQGLW (SEQ ID NO: 3) (i.e. a version of the PRO-C20 target sequence truncated by removal of the final glutamic acid residue). Preferably, the ratio of the affinity of said antibody for the PRO-C20 target sequence to the affinity of said antibody for the truncated version of the target sequence is at least 10 to 1, and more preferably is at least 20 to 1 or at least 30 to 1.
Preferably, the monoclonal antibody is a monoclonal antibody that is raised against a synthetic peptide having the C-terminus amino acid sequence QGASTQGLWE (SEQ ID NO: 1).
The sample is preferably a biofluid. The biofluid may be, but is not limited to, blood, serum, plasma, urine or a supernatant from cell or tissue cultures. Preferably the biofluid is blood, serum or plasma.
The immunoassay may be, but is not limited to, a competition assay or a sandwich assay. The immunoassay may, for example, be a radioimmunoassay or an enzyme-linked immunosorbent assay (ELISA). Such assays are techniques known to the person skilled in the art.
As used herein the term “amount of binding” refers to the quantification of binding between the monoclonal antibody and peptides in the patient sample. Said quantification may for example be determined by comparing the measured values of binding in the patient sample against a calibration curve produced using measured values of binding in standard samples containing known concentrations of a peptide to which the antibody specifically binds, in order to thereby determine the quantity of peptide to which the antibody specifically binds in the patient sample. In the Examples set out below, an ELISA method is used in which spectrophotometric analysis is used to measure the amount of binding both in the patient samples and when producing the calibration curve. However, any suitable analytical method can be used.
As used herein the term “predetermined cut-off value” means an amount of binding that is determined statistically to be indicative of a high likelihood of a disease or a particular severity thereof in a patient, in that a measured value of the target peptide in a patient sample that is at or above the statistical cut-off value corresponds to at least a 70% probability, preferably at least an 75% probability, more preferably at least an 80% probability, more preferably at least an 85% probability, more preferably at least a 90% probability, and most preferably at least a 95% probability of the presence of said disease or said particular severity thereof. For example, in patients with PDAC, a PRO-C20 level of 2.59 nM may in certain embodiments be used as a predetermined cut-off value indicating that the severity of the cancer is such that the patient has about a high (e.g. about 75%) probability of dying within the next 6 months, and/or has a very high (e.g. at least 95%) probability of dying within about the next 2 years.
As used herein, the term “values associated with normal healthy subjects” means standardised quantities of binding determined by the method described supra for samples from subjects considered to be healthy, i.e. without disease; and the term “values associated with known disease severity” means standardised quantities of binding determined by the method described supra for samples from patients known to have disease of a known severity.
As used herein the term “C-terminus” refers to a C-terminal peptide sequence at the extremity of a polypeptide, i.e. at the C-terminal end of the polypeptide, and is not to be construed as meaning in the general direction thereof.
As used herein, the terms “peptide” and “polypeptide” are used synonymously.
As used herein the term “monoclonal antibody” refers to both whole antibodies and to fragments thereof that retain the binding specificity of the whole antibody, such as for example a Fab fragment, F(ab′)2 fragment, single chain Fv fragment, or other such fragments known to those skilled in the art. As is well known, whole antibodies typically have a “Y-shaped” structure of two identical pairs of polypeptide chains, each pair made up of one “light” and one “heavy” chain. The N-terminal regions of each light chain and heavy chain contain the variable region, while the C-terminal portions of each of the heavy and light chains make up the constant region. The variable region comprises three complementarity determining regions (CDRs), which are primarily responsible for antigen recognition. The constant region allows the antibody to recruit cells and molecules of the immune system. Antibody fragments retaining binding specificity comprise at least the CDRs and sufficient parts of the rest of the variable region to retain said binding specificity.
In the methods of the present invention, a monoclonal antibody comprising any constant region known in the art can be used. Human constant light chains are classified as kappa and lambda light chains. Heavy constant chains are classified as mu, delta, gamma, alpha, or epsilon, and define the antibody's isotype as IgM, IgD, IgG, IgA, and IgE, respectively. The IgG isotype has several subclasses, including, but not limited to IgGI, IgG2, IgG3, and IgG4. The monoclonal antibody may preferably be of the IgG isotype, including any one of IgGI, IgG2, IgG3 or IgG4.
The CDR of an antibody can be determined using methods known in the art such as that described by Kabat et al. Antibodies can be generated from B cell clones as described in the examples. The isotype of the antibody can be determined by ELISA specific for human IgM, IgG or IgA isotype, or human IgG1, IgG2, IgG3 or IgG4 subclasses. The amino acid sequence of the antibodies generated can be determined using standard techniques. For example, RNA can be isolated from the cells, and used to generate cDNA by reverse transcription. The cDNA is then subjected to PCR using primers which amplify the heavy and light chains of the antibody. For example primers specific for the leader sequence for all VH (variable heavy chain) sequences can be used together with primers that bind to a sequence located in the constant region of the isotype which has been previously determined. The light chain can be amplified using primers which bind to the 3′ end of the Kappa or Lamda chain together with primers which anneal to the V kappa or V lambda leader sequence. The full length heavy and light chains can be generated and sequenced.
The monoclonal antibody or fragment thereof may preferably comprise one or more complementarity-determining regions (CDRs) selected from:
Preferably the antibody or fragment thereof comprises at least 2, 3, 4, 5 or 6 of the above listed CDR sequences.
Preferably the monoclonal antibody or fragment thereof has a light chain variable region comprising the CDR sequences:
Preferably the monoclonal antibody or fragment thereof has a light chain that comprises framework sequences between the CDRs, wherein said framework sequences are substantially identical or substantially similar to the framework sequences between the CDRs in the light chain sequence below (in which the CDRs are shown in bold and underlined, and the framework sequences are shown in italics):
RSSQSIVHNNGKIYLE
WFLQKPGQSPKALIQ
KVSNRFS
GVPDRFSGSGS
GTDFTLKISRVEAEDLGVYYC
FQGSHVPYT
Preferably the monoclonal antibody or fragment thereof has a heavy chain variable region comprising the CDR sequences:
Preferably the monoclonal antibody or fragment thereof has a heavy chain that comprises framework sequences between the CDRs, wherein said framework sequences are substantially identical or substantially similar to the framework sequences between the CDRs in the heavy chain sequence below (in which the CDRs are shown in bold and underlined, and the framework sequences are shown in italics):
DYSMH
WVKQAPGKGLKWMG
WINTETGEPTYADGFKG
RFAFSLETSASTA
YLKINNLKNDDTATYFCAR
GPY
As used herein, the framework amino acid sequences between the CDRs of an antibody are substantially identical or substantially similar to the framework amino acid sequences between the CDRs of another antibody if they have at least 70%, 80%, 90% or at least 95% similarity or identity. The similar or identical amino acids may be contiguous or non-contiguous.
The framework sequences may contain one or more amino acid substitutions, insertions and/or deletions. Amino acid substitutions may be conservative, by which it is meant the substituted amino acid has similar chemical properties to the original amino acid. A skilled person would understand which amino acids share similar chemical properties. For example, the following groups of amino acids share similar chemical properties such as size, charge and polarity: Group 1 Ala, Ser, Thr, Pro, Gly; Group 2 Asp, Asn, Glu, Gln; Group 3 His, Arg, Lys; Group 4 Met, Leu, Ile, Val, Cys; Group 5 Phe Thy Trp.
A program such as the CLUSTAL program to can be used to compare amino acid sequences. This program compares amino acid sequences and finds the optimal alignment by inserting spaces in either sequence as appropriate. It is possible to calculate amino acid identity or similarity (identity plus conservation of amino acid type) for an optimal alignment. A program like BLASTx will align the longest stretch of similar sequences and assign a value to the fit. It is thus possible to obtain a comparison where several regions of similarity are found, each having a different score. Both types of analysis are contemplated in the present invention. Identity or similarity is preferably calculated over the entire length of the framework sequences.
In certain preferred embodiments, the monoclonal antibody or fragment thereof may comprise the light chain variable region sequence:
DVLLTQTPLSLPVSLGDQASISC
RSSQSIVHNNGKIYLE
WFLQKPGQSP
KALIQ
KVS
NRFSGVPDRFSGSGSGTDFTLKISRVEAEDLGVYYC
FQGSH
VPYT
FGGGTKLEIK
QIQLMQSGPELKKPGETVKISCKASGYPFT
DYSMH
WVKQAPGKGLKWMG
WINTETGEPTYADGFKG
RFAFSLETSASTAYLKINNLKNDDTATYFCAR
GPY
WGQGTLVTVSA
In a second aspect, the present invention provides a monoclonal antibody that specifically binds to a C-terminus amino acid sequence QGASTQGLWE (SEQ ID NO: 1). The monoclonal antibody is suitable for use in an immunoassay according to the first aspect of the invention, and preferred and other optional embodiments of the monoclonal antibody according to the second aspect of the invention will be apparent from the discussion supra of the monoclonal antibodies for use the in the first aspect of the invention and preferred and other optional embodiments thereof.
In a third aspect, the application relates to an immunoassay kit comprising a monoclonal antibody according to the second aspect, and at least one of;
The presently disclosed embodiments are described in the following Examples, which are set forth to aid in the understanding of the disclosure, and should not be construed to limit in any way the scope of the disclosure as defined in the claims which follow thereafter. The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the described embodiments, and are not intended to limit the scope of the present disclosure nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.
A 10 amino-acid target peptide 1275QGASTQGLWE1284 (SEQ ID NO: 1), corresponding to the C-terminus of type XX collagen (UniprotKB: Q9P218) was purchased from Genscript (Piscataway, NJ, USA) and used for immunization.
More specifically, an immunogenic peptide (KLH-CGG-QGASTQGLWE (SEQ ID NO: 7)) was generated by covalently cross-linking the target peptide to Keyhole Limpet Hemocyanin (KLH) carrier protein using sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate, SMCC (Thermo Scientific, Waltham, MA, USA, cat. no. 22322). Glycine and cysteine residues were added at the N-terminal end to ensure right linking of the carrier protein. Monoclonal antibodies were generated by subcutaneous immunization of six-week-old Balb/C mice with 200 μL emulsified antigen containing 100 μg immunogenic peptide mixed with Sigma Adjuvant System (Sigma cat. No. S6322). Consecutive immunizations were performed at 2-week intervals until stable sera titer levels were reached. The mouse with the highest titer was rested for four weeks and was then boosted with 100 μg immunogenic peptide in 100 μL 0.9% NaCl solution intravenously. Hybridoma cells were produced by fusing spleen cells with SP2/0 myeloma cells as previously described (Gefter, Margulies and Scharff, 1977). The resultant hybridoma cells were then cultured in 96-well microtiter plates and standard limited dilution was used to secure monoclonal growth.
The monoclonal antibodies were purified using protein-G-columns according to the manufacturer's instructions (GE Healthcare Life Sciences, Little Chalfont, UK, cat. #17-0404-01).
The best antibody clone for the biomarker was selected based on a preliminary competitive ELISA for the reactivity towards the selection peptide (the target peptide, QGASTQGLWE (SEQ ID NO: 1)), and not an elongated peptide (QGASTQGLWES (SEQ ID NO: 2)), a truncated peptide (QGASTQGLW (SEQ ID NO: 3)), and a non-sense KLH-conjugated peptide (IRQCPDRTYG-GGC-KLH (SEQ ID NO: 10)).
The antibody produced by the best performing clone was sequenced and the CDRs determined. The sequence of the chains are as follows (CDRs underlined and in bold, constant region italic):
WINTETGEPTYADGFKG
RFAFSLETSASTAYLKINNLKNDDTATYFCAR
GPY
WGQGTLVTVSAAKTTAPSVYPLAPVCGDTTGSSVTLGCLVKGYFPE
PVTLTWNSGSLSSGVHTFPAVLQSDLYTLSSSVTVTSSTWPSQSITCNV
AHPASSTKVDKKIEPRGPTIKPCPPCKCPAPNLLGGPSVFIFPPKIKDV
LMISLSPIVTCVVVDVSEDDPDVQISWFVNNVEVHTAQTQTHREDYNST
LRVVSALPIQHQDWMSGKEFKCKVNNKDLPAPIERTISKPKGSVRAPQV
YVLPPPEEEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKNTEPV
LDSDGSYFMYSKLRVEKKNWVERNSYSCSVVHEGLHNHHTTKSFSRTPG
LDLDDVCAEAQDGELDGLWTTITIFISLFLLSVCYSASVTLFKVKWIFS
SVVELKQTISPDYRNMIGQGA
VPYT
FGGGTKLEIKRADAAPTVSIFPPSSEQLTSGGASVVCFLNNFYPK
DINVKWKIDGSERQNGVLNSWTDQDSKDSTYSMSSTLTLTKDEYERHNS
YTCEATHKTSTSPIVKSFNRNEC
Several optimizations were made to the ELISA including the choice of assay buffer, incubation time and temperature as well as concentrations of antibody and peptides. The final PRO-C20 assay protocol was performed as follows: a 96-well streptavidin-coated ELISA plate was coated with 100 μL/well of 1.25 ng/ml biotinylated target peptide (Biotin-QGASTQGLWE (SEQ ID NO: 5)) peptide dissolved in assay buffer (25 mM TBS, 1% BSA (w/v), 0.1% Tween-20 (w/v), 2 g/L NaCl, pH 8.0) and incubated for 30 minutes at 20° C. with shaking at 300 RPM. After washing five times with washing buffer (25 mM Tris, 50 mM NaCl, pH 7.2), 20 μL/well of sample was added in duplicates followed by 100 μL/well of 50 ng/mL HRP-labelled monoclonal antibody in assay buffer and incubated for 1 hour at 20° C. with shaking at 300 RPM. After a second washing cycle, 100 μL/well of TMB was added and incubated for 15 minutes in darkness at 20° C. with shaking at 300 RPM. The reaction was stopped by adding 100 μL/well of 1% H2SO4. Absorbance was measured at 450 nm with 650 nm as reference. To generate a standard curve, 20 μL/well of 50 ng/ml standard peptide (RHLEGRGEPGAVGQMGSPGQQGASTQGLWE (SEQ ID NO: 6)), serially diluted two-fold, was added to appropriate wells and a four-parametric logistic regression model was used to fit a curve. Each plate included 5 quality control samples comprising one human serum, one horse serum, one human plasma and two peptide-in-assay-buffer samples to monitor intra-and inter-assay variation.
Antibody specificity was evaluated by the inhibition of signal by two-fold serial dilutions of the standard peptide (RHLEGRGEPGAVGQMGSPGQQGASTQGLWE (SEQ ID NO: 6)), elongated peptide (QGASTQGLWES (SEQ ID NO: 2)), truncated peptide (QGASTQGLW (SEQ ID NO: 3)) as well as a non-sense standard peptide (SHAHQRTGGN (SEQ ID NO: 8)) and a non-sense coater peptide (Biotin-SHAHQRTGGN (SEQ ID NO: 9)).
Linearity or parallelism was evaluated by two-fold serial dilutions of human serum samples and calculating the percentage recovery relative to the dilution. Accuracy was evaluated by spiking a known quantity of the standard peptide into a human serum sample and calculating the percentage recovery of the measured concentration of the spiked sample relative to the expected concentration of the non-spiked sample plus the known quantity spiked in. Similarly, accuracy was also evaluated by spiking one human serum sample into another human serum sample at different ratios (eg. 50:50 or 25:75) and calculating the percentage recovery relative to the sum of their separately quantified values.
The influence of commonly interfering substances including hemoglobin, lipids and biotin were evaluated by spiking human serum samples with a known quantity of the interfering substances (hemoglobin low=2.5 mg/mL, high=5 mg/mL; lipids low=1.5 mg/mL, high=5 mg/mL; biotin low=5 ng/ml, high=100 ng/mL) and calculating the percentage recovery relative to the non-spiked sample.
Assay variation was tested by running ten independent run of the assay using ten quality control samples in double determinations. Five of the quality control samples were human serum, one horse serum, one human plasma and three were standard peptide in assay-buffer of varying concentrations. Intra-assay variation was calculated as the mean coefficient of variance (CV %) between the double determinations on each of the ten runs. Inter-assay variation was calculated as the overall CV % for all determinations on the ten runs. Lower-and upper-limit of the measurement range (LLMR and ULMR) were determined as the concentrations that denotes the limits of the linear range of the assay. Lower limit of detection was calculated as the mean interpolated concentration of 21 blank samples, only containing assay buffer, plus three standard deviations. Upper limit of detection was calculated as the mean interpolated concentration of standard peptide corresponding to the highest concentration of the standard curve minus three standard deviations.
Analyte stability was evaluated for three human serum samples incubated at either 4 or 20° C. for 2, 4, 24, or 48 hours and calculating the percentage recovery of the incubated samples relative to the corresponding control sample kept at −20° C. Freeze-thaw stability was evaluated by repeatedly freezing and thawing human serum samples for up to 4 cycles and calculating the percentage recovery of the cycled samples relative to the corresponding control samples that underwent a single freeze-thaw cycle.
The cohort included 222 cancer samples and 33 healthy samples. It included 20 patients each of pancreatic-, colorectal-, kidney-, stomach-, breast-, bladder-, lung-, melanoma-, head and neck- and prostate-cancer, 19 ovarian cancer patients, 3 liver cancer patients and 33 age matched healthy controls. All cancer samples were obtained from Proteogenex (Los Angeles, CA, USA) and the healthy controls were obtained from BioIVT (Westbury, NY, USA). A summary of the cohort characteristics can be found in Table 1.
Comparisons of PRO-C20 levels across groups was done using ordinary one-way ANOVA followed by pair-wise comparisons to the control group using the Dunnett test. Diagnostic accuracy was tested by the area under the receiver operating characteristics (AUROC) curve. A p-value below 0.05 was considered significant. Asterisks in the figures indicate the following significance levels: *p<0.05; **p<0.01; ***p<0.001; ****p<0.0001.
Statistical analysis and graphs were done in GraphPad Prism (version 9.1.0 for Windows, GraphPad Software, San Diego, California USA, www.graphpad.com) and R version 4.0.4 (R Core Team (2021), R Foundation for Statistical Computing, Vienna, Austria, https://www.R-project.org).
The cohort included 20 healthy donors and 36 patients with pancreas ductal adenocarcinoma (PDAC). All patients were from the Danish BIOPAC study “BIOmarkers in patients with Pancreatic Cancer” (NCT03311776). Patients were recruited from six Danish hospitals from December 2008 until September 2017. PC patients had histologically confirmed tumors. The PDAC patients were treated with various types of chemotherapy according to national guidelines (www.gicancer.dk). The study was carried out in accordance with the recommendations of the Danish Regional Committee on Health Research Ethics. The BIOPAC protocol was approved by the Danish Regional Committee on Health Research Ethics (VEK ref. KA-20060113) and the Data Protection Agency (j.nr. 2006-41-6848). Blood (serum) samples were obtained at the time of diagnosis or before operation. All subjects gave written informed consent in accordance with the Declaration of Helsinki. Table 2 summarizes the characteristics of the cohort.
The Wilcoxon test was used to compare PRO-C20 levels between healthy and PDAC samples. Diagnostic accuracy of PRO-C20 was tested using the area under the receiver operating characteristic curve (AUC). In addition, sensitivity, specificity, positive predictive value, and negative predictive value were determined at the PRO-C20 cut-off value where the Youden-index was maximized. The 75th percentile of PRO-C20 levels (i.e. a PRO-C20 level of 2.59 nM) in PDAC samples was used as a cut point to define a group with high PRO-C20 levels. The association of high PRO-C20 levels and overall survival was evaluated using a Kaplan Meier curve with a log-rank test. In addition, multivariate Cox regression analysis evaluated the associated of high PRO-C20 levels when corrected for the presence of metastasis as well as age and sex. The following significance levels are indicated by asterisks: ****p<0.0001.
Optimizations to the ELISA protocol included the best time and temperature of incubation, choice of assay buffer and concentrations of kit components. The settings were chosen based on which gave the best sensitivity in human serum whilst upholding the technical requirements outlined below. The chosen format for the ELISA was competitive, so the specificity of the assay was evaluated by the ability of different peptides to compete for binding to the monoclonal antibody. The set of peptides included the standard peptide, corresponding to the C-terminus of type XX collagen (RHLEGRGEPGAVGQMGSPGQQGASTQGLWE (SEQ ID NO: 6)); an elongated peptide, corresponding to the C-terminus epitope with an extra amino acid (QGASTQGLWES (SEQ ID NO: 2)); a truncated peptide, with an amino acid less (QGASTQGLW (SEQ ID NO: 3)); a non-sense standard peptide, corresponding to an unrelated epitope (SHAHQRTGGN (SEQ ID NO: 8)); and lastly, a non-sense coater peptide (Biotin-SHAHQRTGGN (SEQ ID NO: 9)).
Only the standard peptide dose-dependently inhibited the signal in a meaningful way—the elongated and truncated had minimal competition even at high concentrations (
Other aspects of the technical validation are summarized in Table 3.
Linearity of dilution or parallelism was accepted from undiluted down to 1:2 dilution. At 1:4 dilution the recovery of human serum samples dropped below the acceptance limit of 80% analyte recovery. Accuracy testing using spiking recovery tests revealed excellent recovery of the standard peptide in human serum with a recovery of 101%. The same was true with matrix-in-matrix spiking where a spiking of analyte from a human serum sample into another separate human serum sample resulted in a recovery of 95%. Interference from commonly interfering substances was not observed, with recoveries within 15% even for the highest concentrations of biotin. Assay variation was excellent at approximately 6% for both inter-and intra-assay variation. Analyte stability was evaluated for up to 48 hours at either 4 or 20° C. and recoveries were within 15%. Stability following four freeze-thaw cycles was also good with a recovery of 90%.
PRO-C20 levels were significantly elevated in all cancers compared to the healthy controls (
PRO-C20 was particularly good at discriminating between lung cancer and healthy controls with an AUROC of 0.92. Overall, these results suggest that circulating levels of PRO-C20, and hence type XX collagen, are elevated in multiple different cancer types.
Quantification of PRO-C20 in serum of healthy controls (n=20) and patients with PDAC (n=36) revealed elevated levels of PRO-C20 in PDAC compared to healthy controls (
1HR = Hazard Ratio, CI = Confidence Interval
In this study, an ELISA to quantify the presence of type XX collagen in blood was successfully developed, optimized, and validated. The PRO-C20 ELISA was technically robust, accurate and sensitive. The levels of circulating type XX collagen could be assessed in the serum of cancer patients and healthy controls, with levels of PRO-C20 being significantly higher in all cancers tested compared to healthy controls. In the serum from pancreas ductal adenocarcinoma (PDAC) patients, high levels of PRO-C20 were furthermore found to be associated with poor overall survival rates.
In this specification, unless expressly otherwise indicated, the word ‘or’ is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator ‘exclusive or’ which requires that only one of the conditions is met. The word ‘comprising’ is used to mean ‘including or consisting of’. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date hereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2108802.6 | Jun 2021 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/066635 | 6/18/2022 | WO |
