Armed antibodies targeted to STEAP1 inhibit growth of human prostate xenografts in vivo

4468 Highly restricted expression patterns for cell surface antigens make them ideal candidates for targeted delivery of cytotoxic agents by specific monoclonal antibodies (′armed′ antibodies). STEAP1, six transmembrane epithelial antigen of the prostate, is one such antigen whose expression is highly localized to the prostate with minimal expression in other normal tissues. An antibody generated against the extracellular epitopes of STEAP1 recognizes STEAP1 on the cell surface of prostate cancer cell lines. This antibody, when armed with the auristatin microtubule destabilizing agents MMAE or MMAF, demonstrated potent efficacy in multiple established mouse xenograft models derived from prostate cancer cell lines or from patient derived prostate models. These results suggest that armed STEAP1 antibodies may be a promising therapeutic for the treatment of prostate cancer.