Patent Application
20230165982
The present disclosure relates to the field of visualization of HER2 expression in human patients.
Human epidermal growth factor receptor 2 (HER2) functions as a molecular target for several therapeutics efficient in the treatment of breast and gastroesophageal cancers. The response to such therapeutics depends on the HER2 expression level, and accurate assessment of HER2 status in tumors is therefore required to avoid under- and overtreatments (Wolff 2013; Bartley 2017). The current standard of care includes the collection of biopsy material followed by an assessment of HER2 status using immunohistochemistry (IHC) and in situ hybridization (ISH) analysis. Tumors with 3+IHC score or 2+IHC and ISH positive are considered as HER2-positive and eligible for HER2-targeting treatment. A major issue of this method is the HER2-expression heterogeneity, and breast cancer patients often have both HER2-positive and HER2-negative metastases (Sörensen 2016; Gebhart 2016). In addition, the invasiveness of biopsies prevents sampling of all metastases, which is associated with a risk of non-representative findings.
Radionuclide molecular imaging of HER2 expression could serve as a non-invasive alternative for patient stratification, offering advantages such as repetitive mapping of HER2 expression in multiple metastases (Tolmachev 2008; Gebhart 2016 review; Mankoff 2016). One promising approach used for the detection of HER2 expression is immunoPET. This strategy utilizes specific recognition of HER2 by monoclonal antibodies as well as superior spatial resolution, registration efficiency and quantification accuracy of positron emission tomography (PET). Therapeutic anti-HER2 antibodies trastuzumab (Dijkers 2010; Laforest 2016; Gebhart 2016; Bensch 2018, Ulaner 2017; Mortimer 2014) and pertuzumab (Ulaner 2018) have both been labeled with the long-lived positron emitters 89Zr or 64Cu and evaluated in the clinic. Several clinical studies have demonstrated the potential for radionuclide molecular imaging of HER2. For example, 89Zr-trastuzumab PET imaging resulted in altered therapeutic decisions for 40% of the patients in cases when clinically relevant lesions could not be biopsied (Bensch 2018). However, the use of full-length antibodies is complicated due to their slow penetration into tumors and slow clearance from the blood. These traits entail the demand of a prolonged delay period between injection and imaging, with the best results obtained 4-8 days after injection (Dijkers 2010; Ulaner 2018). Moreover, the bulky antibodies tend to accumulate in tumors in an unspecific manner, thus creating a risk of false-positive diagnostics.
The present inventors have realized that the use of much smaller targeting vectors, such as Engineered Scaffold Proteins (ESPs), is a promising alternative to immunoPET.
ADAPTs are affinity proteins, based on the three-helical scaffold of the albumin-binding domain of streptococcal protein G (Nilvebrant 2013). The small size of ADAPTs and affinities in the low nanomolar range creates promising preconditions for their successful use as imaging agents. A series of ADAPTs has previously been selected for their potential use as HER2-imaging probes (Nilvebrant 2014). To facilitate a rapid clearance of the unbound agent from blood, one particular ADAPT variant, ADAPT6, was developed by eradicating its inherent binding to serum albumin (Nilvebrant 2014).
The objective of the present disclosure is to provide for safe, efficient and accurate visualization of HER2 expression in human patients. After such visualization, the patient can be stratified for HER2-targeting therapies.
Accordingly, there is provided an imaging agent for use in a method of visualization of HER2 expression in a human patient, said method comprising an administration of the imaging agent to the patient in a dose of 400-700 μg and subsequently a scanning of the patient to detect, visualize and/or quantify HER2 expression. Similarly, there is provided a method of visualization of HER2 expression in a human patient, said method comprising an administration of an imaging agent to the patient in a dose of 400-700 μg and subsequently a scanning of the patient to visualize HER2 expression,
There is also provided a unit dose comprising an imaging agent in an amount of 400-700 μg
The imaging agent referred to above is a conjugate comprising a radionuclide and a HER2-binding protein (HBP), wherein the HBP comprises or consists of an amino acid sequence selected from
i) LAX3AKX6TX8X9Y HLX13X14X15GVX18DX20 YKX23LIDKX28KT VEX33VX35AX37YX39X40 ILX43ALP (SEQ ID NO:18), wherein, independently of each other,
In an embodiment, the radionuclide is coupled to a terminal end of the HBP, such as the N-terminal end of the HBP. The imaging agent may further comprise a linking amino acid sequence, wherein the radionuclide is coupled to the terminal end of the HBP via the linking amino acid sequence.
In an embodiment, the number of amino acid residues of the linking amino acid sequence is 5-30, such as 5-20.
In an embodiment, at least part of the linking amino acid sequence forms a chelator for the radionuclide. The chelator may comprise the sequence HHHHHH (SEQ ID NO:3).
In an embodiment, the linking amino acid sequence distances any chelator or other radionuclide-binding moiety from the HBP by at least five amino acid residues, such as at least six amino acid residues.
In an embodiment of amino acid sequence i):
In an embodiment, the HBP comprises or consists of an amino acid sequence selected from the group consisting of:
In an embodiment, the HBP comprises or consist of an amino acid sequence selected from the group consisting of:
In an embodiment, the radionuclide is selected from the group consisting of 18F, 124I, 76Br, 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y, 110mIn, 123I, 131I, 99mTc, 111In and 67Ga.
In an embodiment, the radionuclide is selected from the group consisting of 18F, 68Ga, 99mTc and 111In.
In an embodiment, the radionuclide is selected from the group consisting of 18F, 124I, 76Br, 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y and 110mIn and the scanning is PET.
In an embodiment, the radionuclide is 18F or 68Ga and the scanning is PET.
In an embodiment, the radionuclide is conjugated to the HBP by means of a chelator or a prosthetic group forming a covalent bond to the radionuclide.
In an embodiment, the imaging agent comprises less than 73 amino acid residues, such as less than 68 amino acid residues.
In an embodiment, the imaging agent is administered by intravenously.
In an embodiment, the above-mentioned scanning is carried out within 4 hours of the administration of the imaging agent, such as within 3 hours of the administration of the imaging agent.
In an embodiment, the above-mentioned scanning is carried out between 1 and 3 hours after the administration of the imaging agent, such as between 1.5 and 2.5 hours after the administration of the imaging agent.
In an embodiment, the radionuclide is selected from the group consisting of 18F, 124I, 76Br, 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y and 110mIn and the scanning is PET carried out between 1 and 3 hours after the administration of the imaging agent, such as between 1.5 and 2.5 hours after the administration of the imaging agent.
In an embodiment, the patient suffers from a breast cancer or a gastroesophageal cancer.
In an embodiment, the above-mentioned dose is 400-600 μg, such as 450-550 μg, such as about 500 μg. Similarly, the amount the imaging agent in the unit dose may be 400-600 μg, such as 450-550 μg, such as about 500 μg.
In an embodiment, the imaging agent is formulated in a composition adapted for intravenous administration. The volume of the composition may be 1-15 ml, such as 1-10 ml, such as 8-10 ml. The composition may be water-based, such as saline-based. The water-based composition may be buffered, such as phosphate-buffered.
There is also provided a product comprising a container and the above-mentioned unit dose, wherein the unit dose is contained in the container. The container may be a vial or ampoule. The volume of the container may be 1-15 ml, such as 1-10 ml, such as 8-10 ml.
As a first aspect of the present disclosure, there is provided an imaging agent for use in a method of visualization of HER2 expression in a human patient, which patient typically suffers from a breast cancer or a gastroesophageal cancer. It may also be a patient with suspected recurrent breast or gastroesophageal cancer.
The method comprises an administration of the imaging agent to the patient in a dose of 400-700 μg. Preferably, the dose is 400-600 μg, such as 450-550 μg, such as about 500 μg. The route of administration is typically intravenous.
Subsequent to the administration of the imaging agent, the patient is scanned to detect, visualize and/or quantify HER2 expression. The imaging agent of the present disclosure provides for high-contrast imaging relatively quickly, which reduces the time the patient has to stay in the clinic (which in turn reduces costs and improve the patient's quality of life). Hence, the patient is patient is preferably scanned within 4 hours of the administration of the imaging agent, such as within 3 hours of the administration of the imaging agent. In an embodiment, the scanning is carried out between 1 and 3 hours after the administration of the imaging agent, such as between 1.5 and 2.5 hours after the administration of the imaging agent. The scanning is typically a tomography, preferably positron emission tomography (PET) or single-photon emission computed tomography (SPECT). For the latter, a CZT-based camera technology may be used.
The imaging agent is a conjugate comprising a radionuclide and a HER2-binding protein (HBP).
In an embodiment, the radionuclide is selected from the group consisting of 18F, 124I, 76Br, 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y, 110mIn, 123I, 131I, 99mTc, 111In and 67Ga. A preferred group consists of 18F, 68Ga, 99mTc and 111In. Another preferred group consists of 18F, 68Ga and 111In.
For radiolabelling with 18F, a prosthetic group (forming a covalent bond to 18F) may be coupled to the HBP (optionally via the linking amino acid sequence discussed below). Examples of resulting structures are N-(2-(4-[18F]-fluorobenzamido)ethyl)maleimido ([18F]FBEM), 4-[18F]-fluorobenzaldehyde ([18F]-FBA) and [18F]-fluorophenyloxadiazole methylsulfone ([18F]-FPOS. Another option is [18F]aluminium monofluoride in combination with a triaza chelator.
Also in case of radiolabeling with 123I, 124I, 131I and 76Br, a prosthetic group may be used. Examples of resulting structures are iodo-/bromo-benzoate and iodo-/bromo-hydroxyphenylethyl maleimide.
For radiolabeling with 68Ga, 67Ga, 66Ga, 44Sc, 55Co, 41Ti, 86Y, 110mIn and 111In, it is preferred to couple a chelator to the HBP (optionally via the linking amino acid sequence discussed below). Examples of chelators are DOTA, NOTA, NODAGA and DOTAGA and their derivatives.
For 61Cu and 64Cu, a cross-bridged chelator, such as CB-TE2A, is a better option.
For radiolabelling with 99mTc, a variety of chelators can be used, such as hexahistidine (H6) and chelators based on a cysteine- or mercaptoacetyl-containing peptide.
In case of 18F, 124I, 76Br, 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y or 110mIn, the scanning technique is preferably PET.
In case of 123I, 131I, 99mTc, 111In or 67Ga, the scanning technique preferably comprises SPECT, e.g. using a CZT-based camera.
The radionuclide is preferably coupled to a terminal end of the HBP, such as the N-terminal end of the HBP. In an embodiment, the imaging agent further comprises a linking amino acid sequence and the radionuclide is coupled to the terminal end of the HBP via the linking amino acid sequence. The number of amino acid residues of the linking amino acid sequence is typically 5-30, preferably 5-25 or 5-20.
In an embodiment, at least part of the linking amino acid sequence forms a chelator for the radionuclide. As an example, the chelator-forming part may comprise the sequence HHHHHH (SEQ ID NO:3), which can bind 99mTc. An alternative to HHHHHH is HEHEHE (SEQ ID NO:5).
The linking amino acid sequence preferably distances any chelator or other radionuclide-binding moiety from the HBP, e.g. by at least five amino acid residues, such as at least six amino acid residues. Thereby, any interference with the HER2-binding may be avoided or at least reduced. In an embodiment, the linking amino acid sequence comprises the sequence DEAVDANS (SEQ ID NO:4) on the C-terminal side of the chelator or radionuclide-binding moiety for such distancing. Accordingly, linking amino acid sequence may comprise both SEQ ID NO:3 and SEQ ID NO:4, e.g. forming SEQ ID NO:2.
The HBP comprises or consists of an amino acid sequence selected from i) LAX3AKX6TX8X9Y HLX13X14X15GVX18DX20 YKX23LIDKX28KT VEX33VX35AX37YX39X40 ILX43ALP, wherein, independently of each other,
Data supporting binding activity of i) and ii) to HER2 is presented in WO2014076179, Nilvebrant 2014 and the Examples section below.
In a preferred embodiment of the amino acid sequence i)
In another preferred embodiment, the HBP comprises or consists of an amino acid sequence selected from the group consisting of:
A particularly preferred group consists of SEQ ID NO:6, SEQ ID NO:9 and SEQ ID NO:13. SEQ ID NO:9 and 13 were identified by both phage display and FACS in Nilvebrant 2014, which the inventors consider to be beneficial. SEQ ID NO:6 is used in the Examples section below. The HBP and the above-mentioned linking amino acid sequence may be fused to consist of SEQ ID NO:1.
In an embodiment, the imaging agent comprises less than 73 amino acid residues, such as less than 68 amino acid residues. Such a relatively small size facilitates high tumor uptake (further discussed below) and thus high-contrast imaging. The total molecular weight of the therapeutic conjugate is preferably below 12.0 kDa, preferably below 8.0 kDa, such as below 7.1 kDa.
In an embodiment, the HER2 expression in the patient is quantified subsequent to the scanning and if the quantified HER2 expression is found to be above a clinically relevant reference value, a HER2-targeting treatment is applied. If the quantified HER2 expression is below the reference value, the decision may be to refrain from the HER2-targeting treatment.
As a second aspect of the present disclosure, there is provided a unit dose comprising the imaging agent of the first aspect in an amount of 400-700 μg. Preferably, the amount is 400-600 μg, such as 450-550 μg, such as about 500 μg. The embodiments of the first aspect apply to the second aspect mutatis mutandis. The unit dose of the second aspect facilitates the method of the first aspect.
The imaging agent of the second aspect is preferably formulated in a composition adapted for intravenous administration.
The composition is typically water-based, such as saline-based. The water-based composition may be buffered, such as phosphate-buffered. Accordingly, the composition may comprise phosphate-buffered saline (PBS). As an example, a PBS-based buffer is a suitable buffer when the radionuclide is 99mTc. As another example, the pH of the composition is preferably about 5 when the radionuclide is 111In.
The unit dose of the second aspect may be ready for administration, preferably intravenous administration. Alternatively, the unit dose may be subjected to purification prior to administration. Such a purification is typically carried out in or in close connection to the clinic.
Whether or not the purification is required may depend to the nature of the radiolabel. Radiohalogens usually require the purification. A labelling using radiometals might be optimized to such extent that purification of a product is not required. Examples of radiometals for which purification is generally not required are 68Ga, 44Sc, 61Cu, 64Cu, 89Zr, 55Co, 41Ti, 66Ga, 86Y, 110mIn, 99mTc, 111In and 67Ga.
The purification may comprise the steps of: loading of a solution of the imaging agent on a disposable sterilizable size-exclusion column (cartridge) followed by elution with an appropriate solvent, for example PBS. The column (cartridge) should be pre-calibrated to determine the dead volume and the volume of eluent necessary for elution of the high-molecular weight fraction without the low-molecular weight fraction. The eluate containing the high-molecular-weight fraction is collected.
The volume to be administrated is typically 1-15 ml, such as 1-10 ml, such as 8-10 ml. Accordingly, the volume of the composition may be 1-15 ml, such as 1-10 ml, such as 8-10 ml, in particular when no purification is required.
The embodiments of the second aspect apply to the first aspect mutatis mutandis.
As a third aspect of the present disclosure, there is provided a product comprising a container and the unit dose of the second aspect, wherein the unit dose is contained in the container. Such a product, which is typically a single-use product (one product per patient and visualization), facilitates the procedures in the clinic. The container is typically a vial or ampoule. The volume of the container may be 1-15 ml, such as 1-10 ml, such as 8-10 ml.
As a fourth aspect of the present disclosure, there is provided a method of visualization of HER2 expression in a human patient, said method comprising an administration of an imaging agent to the patient in a dose of 400-700 μg and subsequently a scanning of the patient to visualize HER2 expression. The imaging agent is the same as in the first aspect. Embodiments of the fourth aspect are derived from the above description of the first aspect.
In an in-human study, an imaging agent (referred to as “99mTc-ADAPT6” below) has been evaluated in patients with primary HER2-positive and HER2-negative breast cancer.
The primary objectives of the study were:
A secondary objective was to compare the tumor imaging data with the data concerning HER2 expression obtained by immunohistochemistry (IHC) or fluorescent in situ hybridization (FISH) analysis of biopsy samples.
In the study, human patients were injected with 250, 500 or 1000 μg of 99mTc-ADAPT6. Evaluations through planar scintigraphy and PET imaging were carried out 2, 4, 6 and 24 h after injection. However, the patients injected with 250 μg were only evaluated after 2 h.
Patients
This was a prospective, open-label, non-randomized Phase I diagnostic study in patients with untreated primary breast cancer. The protocol was approved by the Scientific Council of Cancer Research Institute, Tomsk National Research Medical Center of the Russian Academy of Sciences. All patients signed a written informed consent. Twenty-eight (28) patients were enrolled (Table 1).
99mTc-ADAPT6.
Biopsy samples of primary tumors were collected, and the level of HER2 expression was determined by immunohistochemistry (IHC) using Herceptest (DAKO). For the tumors with a score of 2+ or in a case of questionable results, a HER2 amplification was assessed using fluorescent in situ hybridization (FISH). The tumors were classified as HER2-positive (HercepTest score 3+ or HercepTest score 2+ and FISH-positive) or HER2-negative (HercepTest score 0 or 1+, or score 2+ but FISH-negative) according to the guidelines of the American Society of Clinical Oncology (Wolff 2013).
As a local standard of care, a mammography (Giotto Image), a bone scan (Siemens E.Cam 180) using 99mTc-pyrophosphate, a chest CT (Siemens Somatom Emotions 16 ECO) and an ultrasound (GE LOGIQ E9) imaging were performed for all patients. For patient 4, an additional MRI (Siemens Magnetom Essenza 1.5T) examination was performed.
Imaging Protocol
Labeling of ADAPT6 was performed in aseptic conditions according to a method described earlier (Lindbo 2016). Briefly, 99mTc was converted to 99mTc(H2O)3(CO)3+ using a CRS (Center for Radiopharmaceutical Sciences) kit. PBS (100 μL) and 99mTc(H2O)3(CO)3+ (400 μL, 1.3±0.3 GBq) were added to vials containing either 250, 500 or 1000 μg freeze-dried protein having the sequence GSSHHHHHHD EAVDANSLAA AKETALYHLD RLGVADAYKD LIDKAKTVEG VKARYFEILH ALP (SEQ ID NO:1), which is ADAPT6 (SEQ ID NO:6) with the N-terminal extension GSSHHHHHHD EAVDANS (SEQ ID NO:2). In the N-terminal extension sequence, the hexahistidine (HHHHHH (SEQ ID NO:3)) subsequence is a chelator for the radionuclide (99mTc). The DEAVDANS (SEQ ID NO:4) subsequence acts as a spacer between the chelating moiety and the HER2-binding protein. Further, it facilitates production of the protein. The vials were incubated for 60 min at 50° C., and radiolabeled protein (“99mTc-ADAPT6”) was purified by size-exclusion chromatography. The yield was 77±9%, and radiochemical purity was 99±1%.
99mTc-ADAPT6 was injected as an intravenous bolus (a high-molecular-weight fraction from size-exclusion purification (solution in PBS) that had been diluted with sterile saline to a volume of 10 ml). Patients 1-11 were injected with 500 μg ADAPT6 (416±135 MBq), and patients 12-22 with 1000 μg (349±133 MBq) Imaging was performed using (Siemens E.Cam 180) scanner. Planar whole-body imaging and SPECT scans were performed at 2, 4, 6 and 24 h. Patients 23-28 were injected with 250 μg (165±29 MBq), and planar whole-body imaging and SPECT scans were performed at 2 h.
Monitoring of vital signs and possible side effects was performed during imaging study (0-24 h after injection) and 3-7 days after injection. Blood and urine analyses were performed 5 and 14 days after injection.
Assessment of Distribution and Dosimetry
Regions of interest (ROI) were drawn over organs of interest and the whole body, on the anterior and posterior whole-body images of patients injected with 500 and 1000 μg 99mTc-ADAPT6; a geometric mean at 2, 4, 6 and 24 h was calculated for each ROI. For quantification, a counting of known activity of 99mTc in a water-filled phantom in combination with Chang's correction was used. To assess the kinetics in blood, an ROI was placed over the heart content. The data were fitted by a single exponential function, and residence time was calculated as an area under the fitted curve using Prism 8 for window software (GraphPad Software, LLC). Absorbed doses were calculated by OLINDA/EXM 1.1 using Adult Female phantom.
To calculate the tumor-to-contralateral breast and the tumor-to-liver ratios, a 3.5-cm3 volume of interest (VOI) was drawn on a tomographic image in the area of the highest tumor uptake, and the counts were recorded. Thereafter, this VOI was copied to a contralateral breast and liver to obtain counts in the reference areas.
Statistics
Values are reported as a mean±standard deviation. The significance of the differences between uptake in organs at different time points was analyzed using 1-way ANOVA. The significance of the differences between tumor-to-contralateral breast and tumor-to-liver ratio values for HER2-positive and HER2-negative tumors was analyzed using the nonparametric Mann-Whitney U test. A 2-sided P value of less than 0.05 was considered significant.
Safety and Tolerability
99mTc-ADAPT6 was administered in twenty-eight patients. The administration was well tolerated. No drug-related adverse reactions or changes in vital signs were observed during imaging or the follow-up period. No changes in blood or urine analyses were detected.
Distribution and Dosimetry
The highest uptake in normal organs was observed in the kidneys, liver and lungs (
1.4 ± 0.5b
1.2 ± 0.4b
aSignificantly (p < 0.05) lower uptake in the intestines content after injection of 500 μg compared to 1000 μg;
bSignificantly (p < 0.05) lower uptake in the lungs at 24 h after injection compared to 2 and 4 h;
cSignificantly (p < 0.05) lower uptake in the lungs at 6 h after injection compared to 2 h.
The blood kinetics of 99mTc-ADAPT6 is shown in
Estimated absorbed doses are presented in Table 3. The highest absorbing organ was kidney. Absorption in adrenal, gall bladder wall, liver, spleen and pancreas were also noticeable, although they were several-fold lower than the renal dose. Doses to adrenals, stomach wall, spleen, thyroid and uterus were significantly (p<0.05) higher for 1000 μg, but absolute difference was prominent only for adrenal and thyroid. Total effective dose was 0.009±0.002 mSv/MBq for 500 μg and 0.010±0.003 mSv/MBq for 1000 μg. For a typical injected activity in this study, 380 MBq, this would result in an effective dose of 3.4 and 3.8 mSv.
Discrimination Between Tumors with High and Low HER2 Expression
Unexpectedly, all tumors and involved lymph nodes with both high and low HER2 expression were clearly visualized already 2 h after injection of 250, 500 or 1000 μg 99mTc-ADAPT6, and remained visible throughout the study (
Also unexpectable, the best discrimination between tumors with high and low HER2 expression was provided in the case of injection of 500 μg 99mTc-ADAPT6. The mean value of tumor-to-contralateral breast ratio value for HER2-positive tumors already 2 h after injection was 37±19, which was significantly (p<0.001, Mann-Whitney test) higher than the value for HER2-negative tumors (5±2) (
Patient 17 was enrolled in this study because the initial IHC evaluation of the analyzed biopsy suggested a 3+ expression level. However, the image showed unusually low tumor-to-contralateral breast ratio (1.33 at 2 h). The biopsy samples were further evaluated and were found FISH-negative. As a consequence, the treatment was adjusted and the HER2-targeting therapy was cancelled.
Imaging of patient 4 revealed, besides a primary tumor and auxiliary metastases, a site of accumulation in rib 5 and two sites at vertebra Th 8 and Th9 (
Injections of 99mTc-ADAPT6 resulted in higher uptake in tumors than in liver, regardless of the injected dose (
The results of the present study demonstrate that injections of 99mTc-ADAPT6 are safe and well tolerated. The mean effective dose of 0.010 mSv/MBq in this study corresponds to 3.8 mSv per patient. This is slightly lower compared to doses reported from imaging using 68Ga-ABY25 affibody molecule (5.6 mSv) (Sandström 2016) or 68Ga-nanobody (4.6 mSv) (Keyaerts 2016), and appreciably lower than effective doses for 89Zr-trastuzumab (18-38 mSv) (Dijkers 2010; Laforest 2016) or 89Zr-pertuzumab (39 mSv) (Ulaner 2018). Noteworthy is that clear discrimination between HER2-positive and HER2-negative tumors already 2 h after injection might permit further two-fold reduction of injection activity.
Discrimination between HER2-positive and HER2-negative lesions is the ultimate goal of molecular imaging. However, the term “HER2-negative”, i.e. unsuitable for treatment with HER2-targeting therapies, is deceptive. Breast tumors with IHC score of 2+ (and FISH negative) are considered as HER2-negative, but they may express up to 500 000 HER2 receptors per cell (Ross 2004). Thus, some accumulation of imaging probes is expected even in HER2-negative lesions. Studies in mice have demonstrated that an increase of the injected dose of 68Ga-labeled ADAPT6 from 1 to 15 μg improved discrimination between human xenografts with high and low HER2 expression, although at the cost of slightly lower uptake in tumors with high expression (Garousi 2015). However, the translation from mice to humans is quite unpredictable. Therefore, injections of 99mTc-ADAPT6 at different dose levels were evaluated. Surprisingly, 500 μg provided excellent discrimination already 2 h after injection (
PET is considered to be the imaging modality that provides the best resolution and sensitivity. However, the modern PET/CT facilities are mainly installed in Europe and North America, while SPECT is the most common imaging modality in Asia and South America. Therefore, there is a need for 99mTc-labeled targeting proteins and peptides in these regions (Briganti 2019). Moreover, the development of CZT-based cameras improves SPECT imaging in terms of resolution and sensitivity appreciably (Desmonts 2020; Goshen 2018). Hence, an increased use of CZT SPECT for molecular imaging even in Europe and US can be foreseen. The imaging method of the present disclosure is a viable option for such applications.
For the reasons set out below, it is expected that a dose of around 500 μg will be optimal also in case 99mTc is replaced with another radionuclide.
The major factors determining the tumor uptake are: injected protein dose; extravasation rate in tumors; diffusion rate in tumors; clearance rate of imaging agent that is not bound to a tumor or HER2 in normal tissue; binding to HER2 in tumor; and binding to HER2 expressed in normal hepatocytes in liver. Extravasation, diffusion and clearance rates are determined mainly by the size of the agent. The type of radiolabel does not affect the size to any significant extent. The binding to HER2 (in tumor or hepatocytes) is determined by affinity, which is primarily determined by the HER2-binding protein. In is not expected that the type of radiolabel has any major impact on the affinity, in particular when the radionuclide is separated from the HER2-binding region by a spacer region.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/061735 | 4/30/2020 | WO |
