Analysis of radiation effects in two irradiated tumor spheroid models.

Multicellular spheroids have proven suitable as three-dimensional in vivo-like models of non-vascularized micrometastases. Unlike monolayer-based models, spheroids mirror the cellular milieu and the pathophysiological gradients inside tumor nodules. However, there is limited knowledge of the radiation effects at the molecular level in spheroids of human origin. The present study is a presentation of selected cell biological processes that may easily be analyzed with methods available at routine pathology laboratories. Using gamma irradiated pancreatic neuroendocrine BON1 and colonic adenocarcinoma HCT116 spheroids as model systems, the present study assessed the radiobiological response in these models. Spheroid growth after irradiation was followed over time and molecular responses were subsequently assessed with immunohistochemistry (IHC) staining for descriptive analyses and semi-automatic grading of apoptosis, G2-phase and senescence in thin sections of the spheroids. Growth studies demonstrated the BON1 spheroids were slower growing and less sensitive to radiation compared with the HCT116 spheroids. IHC staining for G2-phase was primarily observed in the outer viable P-cell layers of the spheroids, with the 6 Gy irradiated HCT116 spheroids demonstrating a very clear increase in staining intensity compared with unirradiated spheroids. Apoptosis staining results indicated increased apoptosis with increasing radiation doses. No clear association between senescence and radiation exposure in the spheroids were observed. The present results demonstrate the feasibility of the use of multicellular spheroids of human origin in combination with IHC analyses to unravel radiobiological responses at a molecular level. The present findings inspire further investigations, including other relevant IHC-detectable molecular processes in time- and radiation dose-dependent settings.

Intra-image referencing for simplified assessment of HER2-expression in breast cancer metastases using the Affibody molecule ABY-025 with PET and SPECT.

PURPOSE: In phase I/II-studies radiolabelled ABY-025 Affibody molecules identified human epidermal growth factor receptor 2 (HER2) expression in breast cancer metastases using PET and SPECT imaging. Here, we wanted to investigate the utility of a simple intra-image normalization using tumour-to-reference tissue-ratio (T/R) as a HER2 status discrimination strategy to overcome potential issues related to cross-calibration of scanning devices. METHODS: Twenty-three women with pre-diagnosed HER2-positive/negative metastasized breast cancer were scanned with [111In]-ABY-025 SPECT/CT (n = 7) or [68Ga]-ABY-025 PET/CT (n = 16). Uptake was measured in all metastases and in normal spleen, lung, liver, muscle, and blood pool. Normal tissue uptake variation and T/R-ratios were established for various time points and for two different doses of injected peptide from a total of 94 whole-body image acquisitions. Immunohistochemistry (IHC) was used to verify HER2 expression in 28 biopsied metastases. T/R-ratios were compared to IHC findings to establish the best reference tissue for each modality and each imaging time-point. The impact of shed HER2 in serum was investigated. RESULTS: Spleen was the best reference tissue across modalities, followed by blood pool and lung. Spleen-T/R was highly correlated to PET SUV in metastases after 2 h (r = 0.96, P < 0.001) and reached an accuracy of 100% for discriminating IHC HER2-positive and negative metastases at 4 h (PET) and 24 h (SPECT) after injection. In a single case, shed HER2 resulted in intense tracer retention in blood. In the remaining patients shed HER2 was elevated, but without significant impact on ABY-025 biodistribution. CONCLUSION: T/R-ratios using spleen as reference tissue accurately quantify HER2 expression with radiolabelled ABY-025 imaging in breast cancer metastases with SPECT and PET. Tracer binding to shed HER2 in serum might affect quantification in the extreme case.

Good manufacturing practice production of [(68)Ga]Ga-ABY-025 for HER2 specific breast cancer imaging.

Therapies targeting human epidermal growth factor receptor type 2 (HER2) have revolutionized breast cancer treatment, but require invasive biopsies and rigorous histopathology for optimal patient stratification. A non-invasive and quantitative diagnostic method such as positron emission tomography (PET) for the pre-therapeutic determination of the presence and density of the HER2 would significantly improve patient management efficacy and treatment cost. The essential part of the PET methodology is the production of the radiopharmaceutical in compliance with good manufacturing practice (GMP). The use of generator produced positron emitting (68)Ga radionuclide would provide worldwide accessibility of the agent. GMP compliant, reliable and highly reproducible production of [(68)Ga]Ga-ABY-025 with control over the product peptide concentration and amount of radioactivity was accomplished within one hour. Two radiopharmaceuticals were developed differing in the total peptide content and were validated independently. The specific radioactivity could be kept similar throughout the study, and it was 6-fold higher for the low peptide content radiopharmaceutical. Intrapatient comparison of the two peptide doses allowed imaging optimization. The high peptide content decreased the uptake in healthy tissue, in particular liver, improving image contrast. The later imaging time points enhanced the contrast. The combination of high peptide content radiopharmaceutical and whole-body imaging at 2 hours post injection appeared to be optimal for routine clinical use.

Measuring HER2-Receptor Expression In Metastatic Breast Cancer Using [68Ga]ABY-025 Affibody PET/CT.

PURPOSE: Positron Emission Tomography (PET) imaging of HER2 expression could potentially be used to select patients for HER2-targed therapy, predict response based on uptake and be used for monitoring. In this phase I/II study the HER2-binding Affibody molecule ABY-025 was labeled with (68)Ga-gallium ([(68)Ga]ABY-025) for PET to study effect of peptide mass, test-retest variability and correlation of quantified uptake in tumors to histopathology. EXPERIMENTAL DESIGN: Sixteen women with known metastatic breast cancer and on-going treatment were included and underwent FDG PET/CT to identify viable metastases. After iv injection of 212±46 MBq [(68)Ga]ABY-025 whole-body PET was performed at 1, 2 and 4 h. In the first 10 patients (6 with HER2-positive and 4 with HER2-negative primary tumors), [(68)Ga]ABY-025 PET/CT with two different doses of injected peptide was performed one week apart. In the last six patients (5 HER2-positive and 1 HER2-negative primary tumors), repeated [(68)Ga]ABY-025 PET were performed one week apart as a test-retest of uptake in individual lesions. Biopsies from 16 metastases in 12 patients were collected for verification of HER2 expression by immunohistochemistry and in-situ hybridization. RESULTS: Imaging 4h after injection with high peptide content discriminated HER2-positive metastases best (p<0.01). PET SUV correlated with biopsy HER2-scores (r=0.91, p<0.001). Uptake was five times higher in HER2-positive than in HER2-negative lesions with no overlap (p=0.005). The test-retest intra-class correlation was r=0.996. [(68)Ga]ABY-025 PET correctly identified conversion and mixed expression of HER2 and targeted treatment was changed in 3 of the 16 patients. CONCLUSION: [(68)Ga]ABY-025 PET accurately quantifies whole-body HER2-receptor status in metastatic breast cancer.

Biodistribution and Radiation Dosimetry of the Anti-HER2 Affibody Molecule 68Ga-ABY-025 in Breast Cancer Patients.

UNLABELLED: (68)Ga-ABY-025 is a radiolabeled Affibody molecule for in vivo diagnosis of human epidermal growth factor receptor 2 (HER2)-positive breast cancer tumors with PET. The aim of the present work was to measure the biodistribution and estimate the radiation dosimetry of (68)Ga-ABY-025 for 2 different peptide mass doses in a single group of patients using dynamic and serial whole-body PET/CT. METHODS: Eight patients with metastatic breast cancer were included. Each patient underwent an abdominal 45-min dynamic and 3 whole-body PET/CT scans at 1, 2, and 4 h after injection of a low peptide dose (LD) and a high peptide dose (HD), with approximately the same amount of radioactivity, in separate investigations 1 wk apart. As input to the absorbed dose calculations, volumes of interest were drawn on all clearly identifiable source organs: liver, kidneys, spleen, descending aorta, and upper large intestine. Absorbed doses were calculated using OLINDA/EXM, version 1.1. RESULTS: Of the major organs, the highest radionuclide uptake at 1, 2, and 4 h after injection was observed in the kidneys and liver. The highest absorbed organ doses were seen in the kidneys, followed by the liver for both LD and HD (68)Ga-ABY-025. Absorbed doses to liver and kidneys were slightly but significantly higher for LD. Total effective dose was 0.030 ± 0.003 mSv/MBq for LD and 0.028 ± 0.002 mSv/MBq for HD. CONCLUSION: The effective dose for a typical 200-MBq administration of (68)Ga-ABY-025 is 6.0 mSv for LD and 5.6 mSv for HD. Therefore, from a radiation dosimetry point of view, HD is preferred for PET/CT evaluation of HER2-expressing breast cancer tumors. These effective doses are somewhat higher than earlier published values for other (68)Ga-labeled tracers, such as 0.021 ± 0.003 mSv/MBq for (68)Ga-DOTATATE and (68)Ga-DOTATOC, mainly because of higher uptake in liver and kidney.

EGFR-expression in primary urinary bladder cancer and corresponding metastases and the relation to HER2-expression. On the possibility to target these receptors with radionuclides.

BACKGROUND: There is limited effect of tyrosine kinase inhibitors or "naked" antibodies binding EGFR or HER2 for therapy of metastasized urinary bladder cancer and these methods are therefore not routinely used. Targeting radio-nuclides to the extracellular domain of the receptors is potentially a better possibility. METHODS: EGFR- and HER2-expression was analyzed for primary tumors and corresponding metastases from 72 patients using immunohistochemistry and the internationally recommended HercepTest. Intracellular mutations were not analyzed since only the receptors were considered as targets and intracellular abnormalities should have minor effect on radiation dose. RESULTS: EGFR was positive in 71% of the primary tumors and 69% of corresponding metastases. Local and distant metastases were EGFR-positive in 75% and 66% of the cases, respectively. The expression frequency of HER2 in related lesions was slightly higher (data from previous study). The EGFR-positive tumors expressed EGFR in metastases in 86% of the cases. The co-expression of EGFR and HER2 was 57% for tumors and 53% for metastases. Only 3% and 10% of the lesions were negative for both receptors in tumors and metastases, respectively. Thus, targeting these receptors with radionuclides might be applied for most patients. CONCLUSIONS: At least one of the EGFR- or HER2-receptors was present in most cases and co-expressed in more than half the cases. It is therefore interesting to deliver radionuclides for whole-body receptor-analysis, dosimetry and therapy. This can hopefully compensate for resistance to other therapies and more patients can hopefully be treated with curative instead of palliative intention.

HER2 expression in primary gastric cancers and paired synchronous lymph node and liver metastases. A possible road to target HER2 with radionuclides.

Resistance has been reported to human epidermal growth factor receptor 2 (HER2)-targeted therapy with the tyrosine kinase inhibitor lapatinib and the antibody trastuzumab in metastatic gastric cancer. An alternative or complement might be to target the extracellular domain of HER2 with therapy-effective radionuclides. The fraction of patients with HER2 expression in primary tumors and major metastatic sites, e.g., lymph nodes and liver, was analyzed to evaluate the potential for such therapy. Samples from primary tumors and lymph node and liver metastases were taken from each patient within a few hours, and to our knowledge, such sampling is unique. The number of analyzed cases was therefore limited, since patients that had received preoperative radiotherapy, chemotherapy, or HER2-targeted therapy were excluded. From a large number of considered patients, only 29 could be included for HER2 analysis. Intracellular mutations were not analyzed since they are assumed to have no or minor effect on the extracellular binding of molecules that deliver radionuclides. HER2 was positive in nearly 52 % of the primary tumors, and these expressed HER2 in corresponding lymph node and liver metastases in 93 and 100 % of the cases, respectively. Similar values for primary tumors and also good concordance with metastases have been indicated in the literature. Thus, relevant radionuclides and targeting molecules for nuclear medicine-based noninvasive, whole-body receptor analysis, dose planning, and therapy can be applied for many patients; see "Discussion" Hopefully, more patients can then be treated with curative instead of palliative intention.

First-in-human molecular imaging of HER2 expression in breast cancer metastases using the 111In-ABY-025 affibody molecule.

UNLABELLED: The expression status of human epidermal growth factor receptor type 2 (HER2) predicts the response of HER2-targeted therapy in breast cancer. ABY-025 is a small reengineered Affibody molecule targeting a unique epitope of the HER2 receptor, not occupied by current therapeutic agents. This study evaluated the distribution, safety, dosimetry, and efficacy of (111)In-ABY-025 for determining the HER2 status in metastatic breast cancer. METHODS: Seven patients with metastatic breast cancer and HER2-positive (n = 5) or -negative (n = 2) primary tumors received an intravenous injection of approximately 100 µg (∼ 140 MBq) of (111)In-ABY-025. Planar γ-camera imaging was performed after 30 min, followed by SPECT/CT after 4, 24, and 48 h. Blood levels of radioactivity, antibodies, shed serum HER2, and toxicity markers were evaluated. Lesional HER2 status was verified by biopsies. The metastases were located by (18)F-FDG PET/CT 5 d before (111)In-ABY-025 imaging. RESULTS: Injection of (111)In-ABY-025 yielded a mean effective dose of 0.15 mSv/MBq and was safe, well tolerated, and without drug-related adverse events. Fast blood clearance allowed high-contrast HER2 images within 4-24 h. No anti-ABY-025 antibodies were observed. When metastatic uptake at 24 h was normalized to uptake at 4 h, the ratio increased in HER2-positive metastases and decreased in negative ones (P < 0.05), with no overlap and confirmation by biopsies. In 1 patient, with HER2-positive primary tumor, (111)In-ABY-025 imaging correctly suggested a HER2-negative status of the metastases. The highest normal-tissue uptake was in the kidneys, followed by the liver and spleen. CONCLUSION: (111)In-ABY-025 appears safe for use in humans and is a promising noninvasive tool for discriminating HER2 status in metastatic breast cancer, regardless of ongoing HER2-targeted antibody treatment.

Potential for clinical radionuclide-based imaging and therapy of common cancers expressing EGFR-family receptors.

High expression of epidermal growth factor receptor (EGFR)-family receptors, especially EGFR, HER2, and HER3, makes them interesting for targeted radionuclide-based imaging and therapy of disseminated cancer. The expression in some commonly occurring cancers such as breast, prostate, colorectal, and urinary bladder cancers is summarized. Possible strategies for radionuclide-based imaging and therapy are briefly discussed, especially in relation to the receptor expression in metastases.

Quantification of internalization of EGFR-binding Affibody molecules: Methodological aspects.

Tumor cell internalization of targeting agents is of interest, since internalization influences the local retention time of a radionuclide and thereby imaging quality in PET and SPECT and effects of radionuclide therapy. In cases where nuclear methods are not applicable at the cellular level, quantitative fluorescent techniques are useful as described in this article. Two fluorescence-based methods to study cellular internalization were applied: the CypHer and the Alexa488-quenching methods, both utilized in fluorescence microscopy and flow cytometry. Two EGFR-binding Affibody molecules were analyzed in A431 cells: the monomer Z1907 and the dimer (Z1907)2. EGF, cetuximab and non-specific Affibody molecules were used as controls. For comparison, internalization of 111In-labeled Z1907 was studied with the acid wash internalization assay. The Cypher method is straightforward, but requires equal labeling of all compounds for accurate quantification. The Alexa488-quenching method is preferable since it is independent of the dye-to-protein ratio. According to this method, about 45% of EGF and 19-24% of the bound Affibody molecules and cetuximab were internalized within one hour. Similar results were seen with 111In-Z1907 in the acid wash method, while (Z1907)2 was not removed by acid and thus could not be studied this way. The fluorescence-based Alexa488-quenching method is well suited to quantitatively analyze internalization of targeting agents, also those that resist acid wash. The internalized fraction showed that both the monomeric and dimeric Affibody molecules are expected to give good uptake and thereby good retention of metallic radionuclides which will render good tumor to background values.

Nuclisome: a novel concept for radionuclide therapy using targeting liposomes.

PURPOSE: For the treatment of cancer, the therapeutic potential of short-range, low-energy Auger-electron emitters, such as (125)I, is getting progressively wider recognition. The potency of Auger-electron emitters is strongly dependent on their location in close vicinity to DNA. We have developed a new two-step targeting strategy to transport (125)I into cancer-cell nuclei using PEG-stabilized tumour-cell targeting liposomes named "Nuclisome-particles". METHODS: In the present study, epidermal growth factor (EGF) was used as a tumour-cell-specific agent to target the EGF-receptor (EGFR) and the liposomes were loaded with (125)I-Comp1, a recently synthesized daunorubicin derivative. RESULTS: As analysed with cryo-TEM, the derivative precipitates inside liposomes at a drug-to-lipid molar ratio of 0.05:1. Receptor-specific uptake in cultured U-343MGaCl2:6 tumour cells of EGFR-targeting liposomes increased with time while non-specific and receptor-blocked uptake remained low. Nuclisome-particles were able to target single U-343MGaCl2:6 cells circulating in human blood during 4 h, with low uptake in white blood cells, as demonstrated in an ex vivo system using a Chandler loop. Autoradiography of targeted cells indicates that the grains from the radiolabelled drug are mainly co-localized with the cell nuclei. The successful targeting of the nucleus is shown to provide high-potency cell killing of cultured U-343MGaCl2:6 cells. At the concentration used, Nuclisome-particles were up to five orders of magnitude more effective in cell killing than EGFR-targeting liposomes loaded with doxorubicin. CONCLUSION: The results thus provide encouraging evidence that our two-step targeting strategy for tumour cell DNA has the potential to become an effective therapy against metastasizing cancer cells in the bloodstream.

Engineering and characterization of a bispecific HER2 x EGFR-binding affibody molecule.

HER2 (human epidermal-growth-factor receptor-2; ErbB2) and EGFR (epidermal-growth-factor receptor) are overexpressed in various forms of cancer, and the co-expression of both HER2 and EGFR has been reported in a number of studies. The simultaneous targeting of HER2 and EGFR has been discussed as a strategy with which to potentially increase efficiency and selectivity in molecular imaging and therapy of certain cancers. In an effort to generate a molecule capable of bispecifically targeting HER2 and EGFR, a gene fragment encoding a bivalent HER2-binding affibody molecule was genetically fused in-frame with a bivalent EGFR-binding affibody molecule via a (G4S)3 [(Gly4-Ser)3]-encoding gene fragment. The encoded 30 kDa affibody construct (ZHER2)2-(G4S)3-(ZEGFR)2, with potential for bs (bispecific) binding to HER2 and EGFR, was expressed in Escherichia coli and characterized in terms of its binding capabilities. The retained ability to bind HER2 and EGFR separately was demonstrated using both biosensor technology and flow-cytometric analysis, the latter using HER2- and EGFR-overexpressing cells. Furthermore, simultaneous binding to HER2 and EGFR was demonstrated in: (i) a sandwich format employing real-time biospecific interaction analysis where the bs affibody molecule bound immobilized EGFR and soluble HER2; (ii) immunofluorescence microscopy, where the bs affibody molecule bound EGFR-overexpressing cells and soluble HER2; and (iii) a cell-cell interaction analysis where the bs affibody molecule bound HER2-overexpressing SKBR-3 cells and EGFR-overexpressing A-431 cells. This is, to our knowledge, the first reported bs affinity protein with potential ability for the simultaneous targeting of HER2 and EGFR. The potential future use of this and similar constructs, capable of bs targeting of receptors to increase the efficacy and selectivity in imaging and therapy, is discussed.

Dimeric HER2-specific affibody molecules inhibit proliferation of the SKBR-3 breast cancer cell line.

HER2-specific affibody molecules in different formats have previously been shown to be useful tumor targeting agents for radionuclide-based imaging and therapy applications, but their biological effect on tumor cells is not well known. In this study, two dimeric ((Z(HER2:4))(2) and (Z(HER2:342))(2)) and one monomeric (Z(HER2:342)) HER2-specific affibody molecules are investigated with respect to biological activity. Both (Z(HER2:4))(2) and (Z(HER2:342))(2) were found to decrease the growth rate of SKBR-3 cells to the same extent as the antibody trastuzumab. When the substances were removed, the cells treated with the dimeric affibody molecules continued to be growth suppressed while the cells treated with trastuzumab immediately resumed normal proliferation. The effects of Z(HER2:342) were minor on both proliferation and cell signaling. The dimeric (Z(HER2:4))(2) and (Z(HER2:342))(2) both reduced growth of SKBR-3 cells and may prove therapeutically useful either by themselves or as carriers of radionuclides or other cytotoxic agents.

Effects of radiation on growth of two human tumour cell lines surviving a previous high dose, low dose-rate, radionuclide exposure.

Effects of radiation on growth of two human tumour cell lines that survived a previous high dose, low dose-rate radionuclide exposure simulating intensive radionuclide therapy, were analyzed. The purpose was to investigate whether the survivors gained therapy induced changes in growth and radiation response. The U118MG, ParRes (parental resistant), and U373MG, ParSen (parental sensitive), glioma cells were used because they are known to be low dose-rate radiation resistant and sensitive, respectively. These cells were initially exposed to high dose, low dose-rate radiation for 24 h and surviving U118MG and U373MG cells formed new cultures called SurRes (surviving resistant) and SurSen (surviving sensitive), respectively. All four cell types were then exposed to graded acute radiation doses, 0-8 Gy, and analyzed for radiation induced growth disturbances. They were also analyzed regarding DNA-content and cell cycle distributions. The SurRes cells regained in most cases the same growth rate, had the same growth delays and showed generally a similar response as the original ParRes cells to the 0-8 Gy exposures. In contrast, the SurSen cells had in all cases slower growth rate and longer growth delays than the original ParSen cells after the 0-8 Gy exposures. There were no signs of radiation-induced radioresistance. The slow growing SurSen cells contained about 80% more DNA and had more cells in G1 and fewer in G2 than the ParSen cells. The conclusion is that tumour cells surviving high dose, low dose-rate, radionuclide therapy, afterwards can react differently to a new radiation exposure.

EGFR, HER2, and HER3 expression in laryngeal primary tumors and corresponding metastases.

BACKGROUND: There are several substances available to target members of the epidermal growth factor receptor (EGFR) family, both for imaging in nuclear medicine and for various forms of therapy. The level and stability of expression in both primary tumors and corresponding metastases is crucial in the assessment of a receptor as a target in systemic tumor therapy. To date, the expression of EGFR family members has only been determined in primary laryngeal carcinomas, and we have not found published data regarding the receptor status in corresponding metastatic lesions. METHODS: Expression of EGFR, HER2, and HER3 was investigated immunohistochemically in both lymph node metastases and corresponding primary laryngeal squamous carcinomas (n = 40). RESULTS: EGFR overexpression (2+ or 3+) was found in 87.5% (35/40) of the laryngeal primary tumors and 82.5% (33/40) of the corresponding lymph node metastases. There was a good agreement between the primary tumors and the paired metastases regarding EGFR expression. HER2 overexpression was found in only four cases (10.5%) of the studied primary tumors and in all cases the HER2 expression was retained in the paired metastases. Another two metastases gained HER2 status when compared to the corresponding primary tumors. Strong HER3 staining was found in 26.7% of both the primary tumors and the corresponding metastases. CONCLUSIONS: The high frequency and stability in EGFR expression is encouraging for efforts to use EGFR targeting agents (e.g. Iressa, Tarceva, Erbitux or radiolabeled antibodies) for therapy of laryngeal carcinoma. For a few laryngeal carcinoma patients with HER2 overexpression, anti-HER2 agents could possibly be used.

Differences in radiosensitivity between three HER2 overexpressing cell lines.

PURPOSE: HER2 is a potential target for radionuclide therapy, especially when HER2 overexpressing breast cancer cells are resistant to Herceptin(R) treatment. Therefore, it is of interest to analyse whether HER2 overexpressing tumour cells have different inherent radiosensitivity. METHODS: The radiosensitivity of three often used HER2 overexpressing cell lines, SKOV-3, SKBR-3 and BT-474, was analysed. The cells were exposed to conventional photon irradiation, low linear energy transfer (LET), to characterise their inherent radiosensitivity. The analysis was made with clonogenic survival and growth extrapolation assays. The cells were also exposed to alpha particles, high LET, from (211)At decays using the HER2-binding affibody molecule (211)At-(Z(HER2:4))(2) as targeting agent. Assays for studies of internalisation of the affibody molecule were applied. RESULTS: SKOV-3 cells were most radioresistant, SKBR-3 cells were intermediate and BT-474 cells were most sensitive as measured with the clonogenic and growth extrapolation assays after photon irradiation. The HER2 dependent cellular uptake of (211)At was qualitatively similar for all three cell lines. However, the sensitivity to the alpha particles from (211)At differed; SKOV-3 was most resistant, SKBR-3 intermediate and BT-474 most sensitive. These differences were unexpected because it is assumed that all types of cells should have similar sensitivity to high-LET radiation. The sensitivity to alpha particle exposure correlated with internalisation of the affibody molecule and with size of the cell nucleus. CONCLUSION: There can be differences in radiosensitivity, which, if they also exist between patient breast cancer cells, are important to consider for both conventional radiotherapy and for HER2-targeted radionuclide therapy.

Cellular studies of binding, internalization and retention of a radiolabeled EGFR-binding affibody molecule.

INTRODUCTION: The cellular binding and processing of an epidermal growth factor receptor (EGFR) targeting affibody molecule, (Z(EGFR:955))(2), was studied. This new and small molecule is aimed for applications in nuclear medicine. The natural ligand epidermal growth factor (EGF) and the antibody cetuximab were studied for comparison. METHODS: All experiments were made with cultured A431 squamous carcinoma cells. Receptor specificity, binding time patterns, retention and preliminary receptor binding site localization studies were all made after (125)I labeling. Internalization was studied using Oregon Green 488, Alexa Fluor 488 and CypHer5E markers. RESULTS: [(125)I](Z(EGFR:955))(2) and [(125)I]cetuximab gave a maximum cellular uptake of (125)I within 4 to 8 h of incubation, while [(125)I]EGF gave a maximum uptake already after 2 h. The retention studies showed that the cell-associated fraction of (125)I after 48 h of incubation was approximately 20% when delivered as [(125)I](Z(EGFR:955))(2) and approximately 25% when delivered as [(125)I]cetuximab. [(125)I]EGF-mediated delivery gave a faster (125)I release, where almost all cell-associated radioactivity had disappeared within 24 h. All three substances were internalized as demonstrated with confocal microscopy. Competitive binding studies showed that both EGF and cetuximab inhibited binding of (Z(EGFR:955))(2) and indicated that the three substances competed for an overlapping binding site. CONCLUSION: The results gave information on cellular processing of radionuclides when delivered with (Z(EGFR:955))(2) in comparison to delivery with EGF and cetuximab. Competition assays suggested that [(125)I](Z(EGFR:955))(2) bind to Domain III of EGFR. The affibody molecule (Z(EGFR:955))(2) can be a candidate for EGFR imaging applications in nuclear medicine.

EGFR, HER2 and HER3 expression in esophageal primary tumours and corresponding metastases.

The expression of EGFR, HER2 and HER3 receptors were analyzed in immunohistochemical preparations from primary esophageal tumours and corresponding lymph node metastases. The goal was to evaluate whether any of these receptors are suitable as targets for radionuclide based imaging and therapy. The receptor expressions were evaluated in parallel samples, primary tumour and metastasis, from each patient (n=51). The majority of the cases were esophageal squamous cell carcinomas, ESCC (n=40). The HercepTest scoring was used for the analysis of both HER2 and EGFR expression (0, 1+, 2+ or 3+). HER3 was only evaluated as negative, weak or strong staining. EGFR overexpression (2+/3+) was found in 67.5% (27/40) of both the ESCC primary tumours and the corresponding lymph node metastases. There were only a few changes in these EGFR-scores: two cases from 2+/3+ to 0/1+ when the primary tumours were compared to the corresponding metastases and 2 changes the other way around. HER2 overexpression (2+/3+) was found in only 3 of the primary ESCC tumours and 2 of the lymph node metastases. EGFR and HER2 stainings were found mainly in the cell membranes. The HER3 staining (weak or strong) was mainly cytoplasmic and granular and was observed in about half (20/39) of the cases, for both the ESCC primary tumours and the corresponding lymph node metastases. It was concluded that ESCC lymph node metastases generally have a strong expression of EGFR in their cell membranes and to the same extent as in the primary tumours. The stability in EGFR expression is encouraging for efforts to develop radionuclide based EGFR imaging agents. It is also possible that EGFR targeting agents (e.g. Iressa, Tarceva, Erbitux or radiolabelled antibodies) can be applied for therapy of ESCC.

Application of the multicellular tumour spheroid model to screen PET tracers for analysis of early response of chemotherapy in breast cancer.

INTRODUCTION: Positron emission tomography (PET) is suggested for early monitoring of treatment response, assuming that effective anticancer treatment induces metabolic changes that precede morphology alterations and changes in growth. The aim of this study was to introduce multicellular tumour spheroids (MTS) to study the effect of anticancer drugs and suggest an appropriate PET tracer for further studies. METHODS: MTS of the breast cancer cell line MCF7 were exposed to doxorubicin, paclitaxel, docetaxel, tamoxifen or imatinib for 7 days for growth pattern studies and for 3 or 5 days for PET tracer studies. The effect on growth was computed using the semi-automated size determination method (SASDM). The effect on the uptake of PET tracers [18F]3'-deoxy-3'-fluorothymidine (FLT), [1-11C]acetate (ACE), [11C]choline (CHO), [11C]methionine (MET), and 2-[18F]fluoro-2-deoxyglucose (FDG) was calculated in form of uptake/viable volume of the MTS at the end of the drug exposures, and finally the uptake was related to effects on growth rate. RESULTS: The drugs paclitaxel, docetaxel and doxorubicin gave severe growth inhibition, which correlated well with inhibition of the FLT uptake. FLT had, compared with ACE, CHO, MET and FDG, higher sensitivity in monitoring the therapy effects. CONCLUSION: SASDM provides an effective, user-friendly, time-saving and accurate method to record the growth pattern of the MTS, and also to calculate the effect of the drug on PET tracer uptake. This study demonstrate the use of MTS and SASDM in combination with PET tracers as a promising approach to probe and select PET tracer for treatment monitoring of anticancer drugs and that can hopefully be applied for optimisation in breast cancer treatment.

Biodistribution of 211At labeled HER-2 binding affibody molecules in mice.

The size of affibody molecules makes them suitable as targeting agents for targeted radiotherapy with the alpha-emitter 211At, since their biokinetic properties match the short physical half-live of 211At. In this study, the potential for this approach was investigated in vivo. Two different HER-2 binding affibody molecules were radiolabeled with 211At using both the linker PAB (N-succinimidyl-para-astatobenzoate) and a decaborate-based linker, and the biodistribution in tumor-bearing nude mice was investigated. The influence of L-lysine and Na-thiocyanate on the 211At uptake in normal tissues was also studied. Based on the biokinetic information obtained, the absorbed dose was calculated for different organs. Compared with a previous biodistribution with 125I, the 211At biodistribution using the PAB linker showed higher uptake in lungs, stomach, thyroid and salivary glands, indicating release of free 211At. When the decaborate-based linker was used, the uptake in those organs was decreased, but instead, high uptake in kidneys and liver was found. The uptake, when using the PAB linker, could be significantly reduced in some organs by the use of L-lysine and/or Na-thiocyanate. In conclusion, affibody molecules have suitable blood-kinetics for targeted radionuclide therapy with 211At. However, the labeling chemistry affects the distribution in normal organs to a high degree and needs to be improved to allow clinical use.