Imaging of prostate cancer with immuno-PET and immuno-SPECT using a radiolabeled anti-EGP-1 monoclonal antibody.

UNLABELLED: hRS7 is a humanized IgG1 monoclonal antibody directed against the epithelial glycoprotein-1 (EGP-1; also known as TROP2). This antigen is found in many epithelial cancers, including prostate cancer, and therefore this antibody could be suitable for targeting this cancer. In this study, the characteristics of hRS7 for targeting prostate cancer were examined. The potential for immuno-PET with (89)Zr-hRS7 and immuno-SPECT with (111)In-hRS7 was assessed using nude mice with human prostate cancer xenografts. METHODS: EGP-1 expression was assessed by immunohistology in human primary and metastatic prostate cancer samples and in PC3 xenografts. The optimal antibody protein dose for prostate cancer targeting was examined in nude mice with subcutaneous PC3 xenografts, and then the biodistribution of (111)In-, (125)I-, and (89)Zr-labeled hRS7 was determined in subcutaneous PC3 xenografts at 1, 3, and 7 d after injection. Immuno-PET and immuno-SPECT were performed with (89)Zr-hRS7 and (111)In-hRS7 in mice with subcutaneous and intraprostatic PC3 xenografts, respectively. RESULTS: Immunohistochemical analysis showed abundant EGP-1 expression in human primary and metastatic prostate cancers and in PC3 xenografts. (111)In-hRS7 and (89)Zr-hRS7 preferentially and specifically accumulated in PC3 xenografts, with tumor uptake as high as 60% injected dose per gram at a protein dose of 0.1 µg per mouse. PC3 tumors in nude mice were clearly visualized with both tracers with immuno-PET and immuno-SPECT. CONCLUSION: hRS7 shows excellent in vivo tumor targeting in human prostate cancer xenografts. Therefore, hRS7 is a potential vehicle for targeting prostate cancer.

Targeting of adenovirus to human renal cell carcinoma cells.

OBJECTIVES: The use of recombinant adenoviruses in cancer gene therapy is limited by the widespread expression of the coxsackievirus and adenovirus receptor on normal human cells. Targeting adenoviral vectors to renal cell carcinoma (RCC) cells may improve their potential in cancer gene therapy of patients with metastatic RCC. The G250 protein, also known as the carbonic anhydrase IX protein, is membranously expressed in all cases of clear cell RCC, and clinical studies have demonstrated exceptional tumor targeting with a G250 monoclonal antibody. METHODS: A recombinant bispecific single-chain antibody directed against the RCC-associated G250 protein and the adenovirus fiber knob domain was constructed and used to retarget recombinant adenovirus expressing the green fluorescent protein under control of the cytomegalovirus promoter. G250-specific adenoviral transduction of cells was examined by flow cytometric analysis of green fluorescent protein expression. RESULTS: G250-positive RCC cells displayed enhanced susceptibility for transduction by the green fluorescent protein recombinant adenovirus complexed with the G250-directed bispecific single-chain antibody when compared with native adenovirus. This enhanced transduction was restricted to G250-positive RCC cells and could be abolished completely in the presence of excess G250 protein. CONCLUSIONS: The results of this study demonstrate the feasibility of immunologic retargeting of adenovirus to RCC cells with the highly tumor-specific G250 protein as the target. This strategy may provide the possibility of improving cancer gene therapy for patients with RCC.

Renal cell carcinoma-associated antigen G250 encodes a naturally processed epitope presented by human leukocyte antigen-DR molecules to CD4(+) T lymphocytes.

We previously identified an HLA-A2.1-restricted epitope within the RCC-associated antigen G250 that is recognized by CTLs. Using DCs of healthy individuals, which were loaded with overlapping 20 mer G250-derived peptides, we here report the induction of CD4(+) T cells that recognize the G250 peptide of amino acids 249-268. Moreover, naturally processed G250 protein is readily recognized by these G250-specific CD4(+) T cells in the context of HLA-DR molecules. Interestingly, peptide G250:249-268 overlaps the previously identified HLA-A2.1-restricted G250 epitope recognized by CTLs. These data and the high prevalence of G250 in RCC patients make peptide G250:249-268 a potential target in peptide-based vaccines to induce both CD4(+) and CD8(+) T-cell responses in patients.