Targeted therapy of experimental renal cell carcinoma with a novel conjugate of monoclonal antibody 138H11 and calicheamicin theta(I)

In search for a new therapeutic approach for metastasized renal cell carcin oma (RCC), we evaluated the cytotoxicity of a novel prodrug chemoimmunoconj ugate with monoclonal antibody (mAb) 138H11 and the DNA-cleaving enediyne c alicheamicin 0(1)(I), (Cam theta) in vitro and irt vivo. Previously, mAb 13 8H11, produced against human renal gamma -glutamyltransferase, stained over 99% clear cell and papillary RCC on frozen sections, showing a membranous expression of the target antigen. In contrast, in normal kidneys gamma GT w as restricted to the brush-border in the lumen of proximal tubules and not accessible to the circulation. Thus, human tumor-bearing kidneys perfused i n an extra-corporeal system with Tc-99m-138H11 revealed a high, specific up take into the tumor. In this study, fluorescence-activated cell sorting ana lysis showed binding of mAb 138H11 to RCC cell lines, whereas squamous cell carcinoma lines, fibroblasts, and the murine RENCA were negative. XTT cell proliferation assays revealed efficient killing of the Caki-1 cell line by the 138H11Cam theta conjugate using SPDP (EC50 = 5 x 10(-11) M) as a coval ent linker, For in vivo testing, five groups of eight nude mice each mere i njected with 2.5 x 10(6) Caki-1 cells s.c. and treated with the following: (a) PBS; (b) 138H11; (c) Cam theta; (6) a mixture of 138H11 and Cam theta; and (e) 138H11Cam theta conjugate. Treatment started on day 1 after tumor i nduction and was repeated three times. The data show a highly significant i nhibition of tumor growth with the 138H11-Cam theta conjugate versus PBS (P = 0.004). Only mice treated with 138H11-Cam theta showed a tumor shrinkage to minimal residues. In a second experiment, lower doses of the 138H11Cam theta conjugate were compared with an antineuroblastoma mAb (ch14.18), conf irming targeted killing of RCC by the 138H11-Cam theta conjugate at tolerab le toxicity ill vivo, In conclusion, these combined results encourage furth er studies for targeted therapy of metastatic RCC with mAb 138H11 conjugate s.