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In vivo non-invasive molecular imaging techniques have potential to improve clinical research and practices in nephrology. Here, the authors discuss the benefits and challenges of preclinical and clinical applications of molecular imaging to acute kidney injury and chronic kidney disease, transplantation and kidney cancer.In nephrology, differential diagnosis or assessment of disease activity largely relies on the analysis of glomerular filtration rate, urinary sediment, proteinuria and tissue obtained through invasive kidney biopsies. However, currently available non-invasive functional parameters, and most serum and urine biomarkers, cannot capture intrarenal molecular disease processes specifically. Moreover, although histopathological analyses of kidney biopsy samples enable the visualization of pathological morphological and molecular alterations, they only provide information about a small part of the kidney and do not allow longitudinal monitoring. These limitations not only hinder understanding of the dynamics of specific disease processes in the kidney, but also limit the targeting of treatments to active phases of disease and the development of novel targeted therapies. Molecular imaging enables non-invasive and quantitative assessment of physiological or pathological processes by combining imaging technologies with specific molecular probes. Here, we discuss current preclinical and clinical molecular imaging approaches in nephrology. Non-invasive visualization of the kidneys through molecular imaging can be used to detect and longitudinally monitor disease activity and can therefore provide companion diagnostics to guide clinical trials, as well as the safe and effective use of drugs.

Carbonic anhydrase IX (CAIX) is a transmembranous enzyme that is present in multiple carcinomas, including clear cell renal cell carcinoma (ccRCC). CAIX is a validated cell marker for hypoxia, an important asset in the prediction of radiotherapeutic efficacy. CAIX expression in ccRCC is high and homogenous, the consequence of mutations in the von Hippel Lindau gene, leading to a pseudohypoxic phenotype. CAIX is recognized, amongst others, by the monoclonal antibody G250. The high expression of CAIX in the most common malignant renal cancer in combination with very limited expression in normal tissue endorses CAIX as a promising candidate for multiple antibody-based applications in this disease. This chapter explores potential clinical applications, including the guidance of clinical decision making in case of diagnostic dilemmas concerning ccRCC suspicion, the use of real-time monitoring of surgical margins during renal surgery, the development of novel therapeutic options in patients with advanced ccRCC, and the use of CAIX imaging in hypoxic tumors.

Renal cell carcinoma (RCC) accounts for approximately 85% to 90% of all primary kidney malignancies, with clear cell RCC (ccRCC) constituting approximately 70% to 85% of all RCCs. This study describes an innovative multimodal imaging and detection strategy that uses 124I-labeled chimeric monoclonal antibody G250 (124I-cG250) for accurate preoperative and intraoperative localization and confirmation of extent of disease for both laparoscopic and open surgical resection of ccRCC. Two cases presented herein highlight how this technology can potentially guide complete surgical resection and confirm complete removal of all diseased tissues. This innovative 124I-cG250 (ie, 124I-girentuximab) multimodal imaging and detection approach, which would be clinically very useful to urologic surgeons, urologic medical oncologists, nuclear medicine physicians, radiologists, and pathologists who are involved in the care of ccRCC patients, holds great potential for improving the diagnostic accuracy, operative planning and approach, verification of disease resection, and monitoring for evidence of disease recurrence in ccRCC patients.

Objectives In tumors, hypoxia stimulates angiogenesis and correlates with treatment resistance and poor prognosis. We have previously demonstrated hypoxia in human renal cell carcinoma (RCC) via direct oxygen probe measurements. Carbonic anhydrase IX (CA IX) is a protein stimulated by hypoxia and involved in angiogenesis, and is a potential tumor target for imaging and therapies using cG250, a monoclonal antibody that recognizes CAIX. Our objectives were to characterize intratumoral hypoxia in a human RCC xenograft model using oxygen probe measurements; investigate if 124 I-cG250 targets RCC correlating uptake on noninvasive positron emission tomography-computerized tomography (PET-CT) against traditional biodistribution studies, and investigate CAIX expression in this RCC model. Methods BALB/c nude mice had human RCC (SK-RC-52) subcutaneously xenografted with oxygen levels measured by probe. Positron emission tomography (PET/CT) and biodistribution studies ( 124 I-cG250) were correlated with oxygen measurements. Immunohistochemistry and autoradiography were performed on selected tumors to confirm CAIX expression Results Oxygen tension in normal tissue (muscle) was 35.08 ± 2.41 mmHg (mean ± 95% CI), significantly greater compared to xenograft SK-RC-52 tumors at 5.02 ± 1.12 mmHg. Biodistribution studies of 124 I-cG250 demonstrated isotope uptake in SK-RC-52 xenografts peaking at 23.45 ± 5.07% ID/g (mean ± SD) 48 hours after antibody injection, which was maintained for a further 2 days (19.43 ± 4.31 and 10.64 ± 5.64 % ID/g, respectively). PET studies demonstrated excellent localization of 124 I-cG250 in tumor, and a significant correlation between SUVmean, SUVmax, and %/ID 124 I-cG250. CAIX expression was present in all groups studied but there was no significant correlation between it and any oxygen parameter studied. Conclusion Intratumoral hypoxia does exist within a human RCC xenograft model using invasive oxygen probe measurements. 124 I-cG250 targets RCC with correlation between uptake on noninvasive PET-CT studies and traditional biodistribution studies opening the possibility of using PET/CT in future studies. Finally, CAIX expression was not related to hypoxia in this model, supporting the hypothesis that cell lines may subvert known hypoxia mechanisms in hypoxic environments.

Carbonic anhydrase IX (CAIX) has long been recognized as a relevant target for clear cell renal cell carcinoma (ccRCC). It has shown value as biomarker and monoclonal antibody G250 (mAbG250), recognizing a conformational determinant on CAIX, and has shown remarkable targeting ability in RCC patients. The addition of CAIX expression to nomograms can further stratify ccRCC patients, but unfortunately lack of commercially available agents has thus far prevented implementation. Indirect evidence suggests that therapy with unmodified mAbG250 can be beneficial in a subgroup of patients, but randomized trials are needed to substantiate this claim. The main value of the antibody at present appears to be as diagnostic and also as a delivery vehicle for radioimmunotherapy. Whether mAbG250 can be combined with tyrosine-kinase inhibitors or mTOR inhibitors remains to be established.

Metastases from renal cell carcinomas (RCC) are resistant to radiation and chemotherapy but are relatively immunogenic. We have investigated the possibility to eliminate human RCC micrometastases using MAb G250. G250 penetrates human micrometastases completely in a spheroid model and induces complement deposition rapidly on the outmost cell layers. However, complement dependent cytotoxicity (CDC) was barely detected using either 51 chromium release assays or confocal microscopy, due to relatively low expression of the G250 antigen and the effect of membrane bound complement regulatory proteins. Addition of blocking anti-CD59 MAbs enhanced formation of C5b-9 and consequently complement mediated lysis (13%). Complement assisted cellular cytotoxicity (CACC) was not detectable, although the iC3b ligand and CR3 receptor were present on respectively target and effector cells. Addition of soluble -glucan induced the killing of MAb and iC3b opsonized spheroids by effector cells (6 –21%). Despite a lower affinity for G250 antigen, a bispecific anti-G250*anti-CD55 MAb enhanced cell killing in spheroids comparable to the parental G250 MAb. Our results suggest that complement-activating G250 in combination with anti-mCRP MAbs is able to kill human RCC cells in micrometastasis in vitro. For CACC the presence of CR3-priming -glucan seems to be obligatory. In vivo, bi-MAb may be more effective as therapeutic agent due to its increased C5a generating properties. © 2004 Wiley-Liss, Inc.

After nephrectomy for renal cell carcinoma (RCC), a significant number of patients develop recurrent disease. In order to improve the prognosis of these patients, the role of adjuvant immunotherapy should be clarified; the appropriate selection of patients is especially crucial. For this purpose, the search for prognostic factors is important to identify at-risk patients. Known factors such as stage, grade, and microvascular invasion can be used for appropriate selection. Other molecular markers, such as cadherin-6 and G250 antigen, may become important. So far, adjuvant immunotherapy in RCC has not shown improved survival data, but the results may be hampered by inadequate recruitment and follow-up. Adequate selection of patients and the search for less toxic and more effective immunotherapy approaches are of importance. Therefore, the use of monoclonal antibody G250 or dendritic cell vaccinations, alone or together with cytokines, may be advantageous and is currently used. Today, adjuvant protocols are open for recruitment of patients to elucidate the important question as to whether this approach should be implemented in the treatment of RCC. In this article, an update is given in the field of adjuvant immunotherapy in patients with RCC.

G250 (Girentuximab) is a chimeric IgG1 monoclonal antibody (MAb) currently being evaluated as an immunotherapy for kidney cancer. It targets carbonic anhydrase protein (CA Ⅸ), a transmembrane carbonic anhydrase (CA) isoform, which is regulated by VHL/HIF pathway and hence expressed in the majority of renal cell carcinomas (RCCs) as well as in hypoxic non‑RCC tumours. CA Ⅸ functions in pH regulation and cell migration/invasion, and supports tumour cell survival in hypoxia and/or acidosis. It contains a highly active extracellular catalytic domain (CA) extended N-terminally with a proteoglycan-like region and C-terminally with short transmembrane and intracellular regions. Here we characterize the binding and internalization properties of G250, as well as its therapeutic effects in animal model, and discuss the impact of G250‑mediated immunotherapy in non‑RCC tumours. We demonstrated that G250 MAb recognizes a conformational epitope in the CA domain, detects the soluble CA Ⅸ ectodomain (ECD), but not the splicing variant, and does not cross-react with CA Ⅰ, Ⅱ, and Ⅻ isoforms. We showed that G250 internalizes via clathrin-coated vesicles, escapes degradation in lysosomes and enters the recycling pathway via the perinuclear compartment. This results in long intracellular persistence and enables consecutive internalization cycles. Moreover, the recycled antibody maintains an intact Fc portion potentially capable of continuous induction of antibody-dependent cell-mediated cytotoxicity (ADCC) response, thus explaining its therapeutic efficacy. Finally, we showed that G250 treatment is effective against HT-29 colorectal carcinoma xenografts that differ from RCC by more heterogeneous, hypoxia-related expression of CA Ⅸ. These results suggest potential therapeutic usefulness of the G250 MAb in non-RCC tumours.

PURPOSE Pharmacokinetics, biodistribution, immunogenicity, and imaging characteristics of iodine 131 (131I)-labeled chimeric monoclonal antibody (mAb) G250 (cG250) were studied in patients with renal cell carcinoma (RCC) to determine the therapeutic potential of this antibody. PATIENTS AND METHODS Sixteen patients with RCC received a single intravenous (IV) infusion of 6 mCi 131I-labeled cG250. Five protein dose levels were investigated (2 to 50 mg). Planar scintigraphic images were acquired, and normal tissue biopsies and tumor samples were obtained of surgery (7 days postinjection). The immunogenicity of cG250 was investigated using a sandwich enzyme-linked immunosorbent assay (ELISA) and dosimetric analysis was performed. RESULTS In all patients with antigen-positive tumors (n = 13), the primary tumors and all known metastases were clearly visualized. Overall uptake, expressed as the percentage of the injected dose (%ID), in the primary tumors ranged from 2.4 to 9.0. Focally, 131I-cG250 uptake as high as 0.52% ID/g was observed. However, intratumoral uptake was highly heterogeneous. 131I-cG250 uptake in nontumorous tissues remained low. Dosimetric analysis showed that up to .48 Gy/mCi was guided to the primary tumors. Selected "hot areas" within these tumors received up to .72 Gy/mCi. A bone metastasis received .23 Gy/mCi and regional lymph node metastases received .20 Gy/mCi. Minimal human antichimeric antibody (HACA) levels were detected in two of 16 patients. CONCLUSION 131I-cG250 tumor uptake is among the highest reported in clinical studies with antitumor antibodies in solid tumors. Since tumor-sterilizing levels may be guided to the tumor when high doses 131I-cG250 are administered (> 100 mCi) and cG250 appears to be immunosilent, cG250 is a promising vehicle for radioimmunotherapy in RCC.

Item does not contain fulltext Autologous T cells genetically modified to express a chimeric antibody receptor (CAR) against carboxy-anhydrase-IX (CAIX) were administered to 12 patients with CAIX-expressing metastatic renal cell carcinoma (RCC). Patients were treated in three cohorts with a maximum of 10 infusions of a total of 0.2 to 2.1 x 10(9) CAR T cells. CTC grade 2-4 liver enzyme disturbances occurred at the lowest CAR T cell doses, necessitating cessation of treatment in four out of eight patients in cohorts 1 and 2. Examination of liver biopsies revealed CAIX expression on bile duct epithelium with infiltration of T cells, including CAR T cells. Subsequently four patients were pre-treated with CAIX monoclonal antibody (mAb) G250 to prevent CAR-specific toxicity and showed no liver toxicities and indications for enhanced peripheral T cell persistence. No clinical responses were recorded. This report shows that CAIX-targeting CAR T cells exerted antigen-specific effects in vivo and induced liver toxicity at the lowest dose of 0.2 x 10(9) T cells applied, illustrating the potency of receptor-modified T cells. We provide in-patient proof that the observed "on-target" toxicity is antigen-directed and can be prevented by blocking antigenic sites in off-tumor organs and allowing higher T cell doses.

Contains fulltext : 117856.pdf (Publisher’s version ) (Open Access) Monoclonal antibody G250 (mAbG250) recognizes a determinant on carbonic anhydrase IX (CAIX). CAIX is expressed by virtually all renal cell carcinomas of the clear cell type (ccRCC), but expression in normal tissues is restricted. The homogeneous CAIX expression in ccRCC and excellent targeting capability of mAbG250 in animal models led to the initiation of the clinical evaluation of mAbG250 in (metastatic) RCC (mRCC) patients. Clinical studies confirmed the outstanding targeting ability of mAbG250 and cG250 PET imaging, as diagnostic modality holds great promise for the future, both in detecting localized and advanced disease. Confirmation of the results obtained in the non-randomized clinical trials with unmodified cG250 is needed to substantiate the value of cG250 treatment in mRCC. cG250-Based radio immuno-therapy (RIT) holds promise for treatment of patients with small-volume disease, and adjuvant treatment with unmodified cG250 may be of value in selected cases. In the upcoming years, ongoing clinical trials should provide evidence for these assumptions. Lastly, whether cG250-based RIT can be combined with tyrosine kinase inhibitors, which constitutes the current standard treatment for mRCC, needs to be established.

Because renal-cell carcinoma (RCC) is considered relatively resistant to radio- and chemotherapy, RCC patients may benefit from new treatment modalities, e.g. immunotherapy. In vitro and in vivo studies suggest that combinations of cytokines such as interferon gamma or interferon alpha (IFN-gamma, IFN-alpha) and tumor necrosis factor alpha (TNF-alpha) may act synergistically. In this study we tested whether a monoclonal antibody (MAb) G250, reactive with a RCC-associated antigen, showed anti-tumor effects in vivo in nude mice with established s.c. human RCC xenografts, and also whether this MAb could enhance the anti-tumor effect of combinations of IFNs and TNF-alpha. Treatment with combinations of IFN-alpha/TNF-alpha or IFN-gamma/TNF-alpha, or with MAb G250 alone, resulted in a significant inhibition of tumor growth. Treatment with MAb G250, in combination with IFN-gamma/TNF-alpha, did not result in an improve anti-tumor effect as compared to that of either treatment alone. In contrast, MAb G250 combined with IFN-alpha/TNF-alpha resulted in a significantly enhanced anti-tumor response. In one experiment, 3 out of 10 mice showed complete tumor regression, with no recurrence after 90 days. Large numbers of infiltrating macrophages were found surrounding viable and necrotic tumor tissue after treatment with G250 combined with IFN-alpha/TNF-alpha. These results suggest that combination therapy, consisting of IFN-alpha, TNF-alpha and MAbs, may have therapeutic value in the treatment of RCC.

Purpose: A study was designed to define the therapeutic efficacy, safety, and toxicity of two sequential high-dose treatments of radioimmunotherapy with [131I]cG250 in patients with metastasized renal cell carcinoma. Here, we report the dosimetric analysis and the relationship between the development of a human antichimeric antibody response and altered pharmacokinetics. Experimental Design: Patients (n = 29) with progressive metastatic renal cell carcinoma received a low dose (222 MBq) of [131I]cG250 for dosimetric analysis, followed by the first radioimmunotherapy with 2,220 MBq/m2 [131I]cG250 (n = 27) 1 week later. If no grade 4 hematologic toxicity was observed, a second low dose of [131I]cG250 (n = 20) was given 3 months later. Provided that no accelerated blood clearance was observed, a second radioimmunotherapy of [131I]cG250 was administered at an activity-dose level of 1,110 MBq/m2 (n = 3) or 1,665 MBq/m2 (n = 16). After each administration, whole-body images were obtained and the pharmacokinetics and the development of human antichimeric antibody responses were determined. Radiation-absorbed doses were calculated for whole body, red marrow, organs, and metastases. Results: No correlation was found between hematologic toxicity and radiation-absorbed dose to the whole body or bone marrow, nor administered activity (MBq and MBq/kg). The tumor-absorbed doses varied largely. An inverse relation between tumor size and radiation-absorbed dose was found. Most tumor lesions received 50 Gy. A relatively high number of patients developed a human antichimeric antibody response (8 of 27) with altered pharmacokinetics, hampering additional radioimmunotherapies in four of these patients. Conclusions: Dosimetric analysis did not adequately predict the degree of bone marrow toxicity. When human antichimeric antibody developed, the rapid clearance of radioactivity from the blood and body prohibited further treatment. According to the calculated absorbed dose in metastatic lesions, future radioimmunotherapy studies with radiolabeled cG250 should aim at treatment of small-volume disease or treatment in an adjuvant setting.

Contains fulltext : 57114.pdf (Publisher’s version ) (Closed access) Chimeric monoclonal antibody G250 (WX-G250) binds to a cell surface antigen found on >90% of renal cell carcinoma (RCC). A multicentre phase II study was performed to evaluate the safety and efficacy of WX-G250 in metastatic RCC (mRCC) patients. In all, 36 patients with mRCC were included. WX-G250 was given weekly by intravenous infusion for 12 weeks. Patients with stable disease (SD) or response were eligible to receive additional treatment for 8 weeks. None of the 36 enrolled patients experienced any drug-related grade III or IV toxicity. Only three patients had grade II toxicity possibly related to the study medication. In all, 10 patients had SD and received extended treatment. One complete response and a significant regression was observed during the follow-up of the treatment. Five patients with progressive disease at study entry were stable for more than 6 months after study entry. The median survival after treatment start was 15 months. The weekly schedule of WX-G250 was well tolerated. With a median survival of 15 months after the start of this treatment and two late clinical responses, WX-G250 seems to be able to modulate mRCC. To improve the activity of WX-G250-specific antibody-dependent cellular cytotoxicity and the clinical response rate, currently combinations of WX-G250 with cytokines are in phase II trials.

Item does not contain fulltext Monoclonal antibody G250 treatment may have a role in the management of metastatic RCC; however, particular subgroups who are more prone to benefit from this treatment must be delineated. High-risk patients may benefit from adjuvant treatment with this nontoxic treatment modality. Large cohort studies are needed to investigate this possibility.

In radioimmunotherapy of solid tumors substantial gain might be achieved by carefully selecting the radionuclide and the linker connecting it to the antibody. In contrast to 131I, radiometals such as 90Y and 111In may be retained in the tumor cell after internalization of the antibody, thereby enhancing the radiation dose to the tumor. The physical properties of 186Re with 1.08 MeV beta-emission (71%) and 137 keV gamma-emission (10%) seem ideal for radioimmunotherapy. In this study we investigated in nude mice with s.c. renal cell carcinoma xenografts the biodistribution and the retention in the tumor of 186Re-MAG3 labeled monoclonal antibody (mAb) G250 as compared to 111In-DTPA-G250, to 125I-G250 and to 131I-MN14 (non-specific control mAb). Radiolabeled antibody preparations were i.v. injected. Seventy two hours p.i. the biodistribution of the radiolabel was determined. Blood levels of all mAb G250 preparations were remarkably low (mean: 2.38, 1.40 and 1.43% ID/g for 125I, 111In and 186Re respectively) whereas blood levels of mAb MN14 were significantly higher (mean: 12.3% ID/g), indicating tumor processing of mAb G250. Retention of 111In in the tumor was significantly higher than of 186Re and 125I whereas retention in the tumor of 186Re and 125I did not differ significantly.In contrast to other radiometals such as 111In and 90Y, 186Re is not retained in the tumor cell. Therefore 186Re has no additional advantage for radioimmunotherapy with respect to retention in the tumor.

The monoclonal antibody G250 (mAbG250) raised against a human renal cell carcinoma (RCC) has been shown to react with a large number of RCCs. Recently, G250 antigen was isolated and found to be homologous to the MN/CA9 gene originally identified in HeLa cells. To determine whether G250 antigen (MN/CA IX/G250) could be a potential therapeutic target and a tumour marker, a total of 147 cases of RCC were investigated immunohistochemically as well as by reverse transcriptase polymerase chain reaction (RT-PCR) analysis. In addition, total RNAs extracted from patients' peripheral blood samples were analysed for MN/CA9/G250 mRNA signals. Immunohistochemistry demonstrated strong expression in 128/147 (87.1%) of RCCs, in contrast to the lack of expression observed in normal tissues. RT-PCR analyses of frozen specimens resulted in the clear detection of MN/CA9/G250 mRNA signals in 137/147 (93.2%), and despite subtle differences the results were almost identical to those for immunohistochemistry. Although high-grade and -stage tumours exhibited significantly lower expression than low-grade and -stage tumours, a large proportion of tumours expressed MN/G250 protein as well as mRNA. RT-PCR analysis of patients' blood samples revealed the presence of circulating MN/CA9/G250 expressing cells. These findings suggest that this antigen may be a potential therapeutic target as well as diagnostic marker for RCCs. © 1999 Cancer Research Campaign

In previous studies, highly heterogeneous uptake of 131I-labelled chimeric monoclonal antibody G250 ([131I]cG250) in primary renal cell carcinomas has been observed (intratumoral differences > factor 100). In this study, we investigated a possible correlation between intratumoral antibody uptake and four immunohistochemically determined parameters: G250 antigen expression, blood vessel density, neovascularization and percentage of viable tumour cells. Whole tumour slices of four different tumours were cut into 1-cm3 cubes, and in each cube the [131I]cG250 uptake was determined. The correlation between [131I]cG250 uptake and each individual parameter was determined in a multiple regression analysis. Additionally, the data were reanalysed after introducing arbitrary cut-off values for each parameter. If a sample showed expression of a parameter above the introduced threshold value, this sample fulfilled one condition. Subsequently, the Pearson correlation coefficients were calculated from [131I]cG250 uptake and the number of fulfilled conditions (0-3). All tumour samples with high [131I]cG250 uptake [> 0.1% of the injected dose per gram (ID g(-1))] showed high antigen expression (> 50%). However, not all samples with high antigen expression displayed high uptake. A statistically significant correlation between [131I]cG250 uptake and antigen expression was found (beta = 0.44, 0.69 and 0.74) in three out of four tumours analysed. Of the other determined parameters, no consistent correlation with [131I]cG250 uptake was found; only the percentage of viable tumour cells correlated significantly in two out of four tumours (beta = 0.80 and 0.26). Calculation of the Pearson correlation coefficients showed a statistically significant correlation between [131I]cG250 uptake and an increased number of fulfilled conditions in all tumours, indicating that each of the individual parameters contribute to the uptake of [131I]cG250. These observations indicate that high antigen expression is a prerequisite for high antibody uptake. However, regional differences in antibody uptake within a tumour cannot be explained by antigen expression alone. Images Figure 1 Figure 2 Figure 3

1. Bray-Ward, P., Menninger, J., Lieman, J., Desai, T., Mokady, N., Banks, A., and Ward, C. (1996). Integration of cytogenetic, genetic, and physical maps of the human genome by FISH mapping of CEPH YAC clones. Genomics 32: 1–14. 2. Oosterwijk, E., Ruiter, D. J., Hoedemaeker, P. J., Pauwels, E. K. J., Jonas, U., Zwartendijk, J., and Warnaar, S. O. (1986). Monoclonal antibody G250 recognizes a determinant present in renal-cell carcinoma and absent from normal kidney. Int. J. Cancer 38: 489–494. 3. Pastorek, J., Pastorekova, S., Callebaut, I., Mornon, J. P., Zelnik, V., Opavsky, R., Zat’ovicova, M., Liao, S., Pertetelle, D., Stanbridge, E. J., Zavada, J., Burny, A., and Kettmann, R. (1994). Cloning and characterization of MN, a human tumorassociated protein with a domain homologous to carbonic anhydrase and a putative helix–loop–helix DNA binding segment. Oncogene 9: 2877–2888. 4. Pastorekova, S., Zavadova, Z., Kost’al, M., Babusikova, O., and Zavada, J. (1992). A novel quasi-viral agent, TaTu, is a twocomponent system. Virology 187: 620–626. 5. Zavada, J., Zavadova, Z., Malir, A., and Kocent, A. (1972). VSV pseudotype produced in cell line derived from human mammary carcinoma. Nat. New Biol. 240: 124–125.

The current status of iodine 131-radiolabeled monoclonal antibody G250 (mAb G250) in renal-cell carcinoma (RCC) is described. This mAb recognizes a tumor-associated antigen that is expressed on the cell surface of almost all RCC but is not expressed on normal tissues, with the exception of gastric mucosa and larger bile ducts. On the basis of these favorable characteristics, this mAb seemed a prime candidate for clinical investigations. Preclinical animal studies and ex vivo perfusion experiments in tumor-bearing kidneys showed excellent targeting of mAb G250 to RCC tumors. Supported by these investigations, a phase I study was initiated to define the imaging and biodistribution characteristics of 131I-labeled mAb G250 in RCC patients. Specific localized of [131I]-mAb G250 to G250-antigen-positive primary and metastatic RCC was observed. In several patients, [131I]-mAb G250 imaging revealed thus far unrecognized, i.e., occult, disease. Values obtained for [131I]-mAb G250 uptake, relative as well as absolute, were among the highest reported for tumor biopsies obtained 8 days after intravenous mAb administration. The specific localization and high accumulation encouraged us to begin a phase I/II radiotherapy trial with [131I]-mAb G250. The maximal tolerable dose was reached at 90 mCi/m2 [131I]-mAb G250. In the subsequent phase I/II radiotherapy study, we observed stable disease in a great number of patients as well as minor responses in a small number of patients. Multiple treatments seemed necessary to achieve better response rates. However, anti-mouse responses prevented multiple dosing with the murine mAb G250. Therefore, we developed a chimeric version of mAb G250 (cG250), in which constant regions of the mouse immunoglobulin have been exchanged for human immunoglobulin regions. A phase I clinical trial with cG250 is ongoing and very encouraging. The general imaging and targeting characteristics of cG250 seem comparable with those of murine mAb G250. In the near future the (radio)therapeutic possibilities of this promising mAb will be investigated.

We have previously isolated and characterized 6 anti-idiotype antibodies (Ab2s) directed against monoclonal antibody G250 (MAbG250) which reacts with a tumor-associated antigen (TAA) expressed in a large proportion of human renal-cell carcinomas (RCC). These 6 Ab2s (NUH31, 51, 71, 82, 91: IgG1, NUH44: IgG2a) showed MAbG250 binding site specificity and induction of anti-TAA antibody resembling MAbG250 (so-called Ab l') in rabbits, indicating that they are internal image antibodies. To investigate whether these Ab2s could induce G250-TAA-specific cell-mediated immunity, delayed-type hypersensitivity (DTH) tests were carried out with G250 antigen-positive and/or -negative cells in the ears of BALB/c mice. Mice primed with Ab2 showed antigen-specific DTH responses, whereas no significant DTH response was observed with G250-negative cells. This antigen-specific DTH could be transferred to naive mice by lymphocytes harvested from Ab2-sensitized mice. In addition to the classical DTH responses observed 24 and 48 hr after tumor challenge, an early-phase antigen-specific hypersensitivity response was seen 2 hr after challenge. This early component of the specific hypersensitivity reaction but not the classical DTH could be transferred to naive mice by serum from Ab2-sensitized mice, indicating that the early reaction was due to serum factors. These findings demonstrate that all Ab2s induced tumor-specific cellular immune responses directed against human RCC, and suggest that they may be useful as RCC-TAA surrogates, i.e., as tumor vaccines for RCC patients.

PURPOSE To define the imaging and biodistribution characteristics of iodine 131-labeled monoclonal antibody (mAb) G250 (131I-mAbG250), which recognizes a cell-surface antigen expressed by human renal cell carcinoma (RCC). PATIENTS AND METHODS G250 is a cell-surface antigen recognized by mAbG250 expressed by RCC but not detected in normal kidney. Clear-cell RCC, the most frequent form of RCC, shows homogeneous expression of G250, whereas non-clear-cell RCC and cancers derived from other organs generally do not express G250. Expression in normal tissues is highly restricted and limited to large bile ducts and gastric epithelium. 131I-mAbG250 was administered intravenously (IV) to 16 patients with RCC 7 to 8 days before surgery at five dose levels, with at least three patients entered at each dose level. RESULTS Clear tumor images were observed in 12 patients with G250-positive tumors and in one of three patients with G250-negative tumors. Imaged lesions in the peritoneal cavity were confirmed at surgery. The smallest lesion visualized was 8 mm in diameter. The specificity of 131I-mAbG250 localization to tumor tissue was established by radioactivity measurements, autoradiography, and immunohistochemistry of biopsied tissues, and technetium 99-human serum albumin blood-flow studies. The fraction of the injected 131I-mAbG250 dose per gram tumor (%ID/g tumor) localized in G250-positive tumors showed a broad range, but reached levels as high as 0.02% to 0.12%. CONCLUSION 131I-mAbG250 localized specifically to G250 antigen-positive RCC and seems to have considerable potential as an imaging agent in RCC patients. 131I-mAbG250 uptake in the tumors, relative as well as absolute, are among the highest reported for tumor biopsies obtained 8 days after IV mAb administration. Based on the specific localization and high accumulation, mAb G250 may have therapeutic potential.

A study was made of the relative effects of size and binding strength of various forms of the monoclonal antibody (MAb) G250, reacting with primary and metastatic human renal-cell carcinoma (RCC), on the localization in human RCC xenografts in nude mice. Preferential tumor localization was demonstrated after injection of 1251-labelled intact IgG, with increasing tumor/non-tumor ratios in time. Approximately 27.4% of the injected dose/gram (%ID/g) was localized in the xenograft 24 hr post-injection. A control MAb did not preferentially localize in xenografts. With F(ab′), fragments, higher tumor/blood ratios were obtained, although a lower percentage of injected dose per gram was bound to the tumor, 24 and 48 hr post-injection. Using a bispecific MAb CD3/G250 F(ab′)2 fragment, which reacts with CD3 on human T lymphocytes and binds monovalently to RCC, an enhanced accumulation in tumor tissue was also observed. The %ID/g tumor obtained with bispecific CD3/G250 F(ab′)2 was comparable with %ID/g tumor found with G250 F(ab′)2. The 10-fold lower binding affinity to RCC compared with intact IgG or F(ab′)2 had only marginal effects on %ID/g tumor. These results show that MAb G250 preferentially localizes to RCC xenografts. Because injection of F(ab′)2 fragments resulted in higher tumor/non-tumor ratios, G250 F(ab′)2 may therefore be more suitable for diagnostic evaluation of RCC in patients. The tumor uptake is more dependent on size than on affinity. Furthermore, the data obtained with bispecific MAb CD3/G250 F(ab′)2 support the hypothesis that this bispecific MAb may be able to target cytotoxic T lymphocytes to RCC in humans to mediate destruction of RCC.

This report describes a monoclonal antibody designated G 250, subclass IgGl, that recognizes an antigen preferentially expressed on cell membranes of renal-cell carcinoma cells (RCC) and not expressed in normal proximal tubular epithelium. G 250 antibody reacted with 46 of 47 primary RCC, with 7 of 8 RCC metastases and with a few other malignant tumors. The staining pattern of G 250 differs from that of other RCC-related antibodies described. Preliminary experiments show that this antibody can be used to visualize RCC xenografts in nude mice by immunoscintigraphy.