971. New Generation Conditionally Replicative Adenovirus for Hormone-Refractory Prostate Cancer

Abstract

Top of pageAbstract Although anti-androgen therapy is initially effective for advanced prostate cancer, all patients eventually progress to hormone-refractory (HR) prostate cancer (PC) due to biological selection. In this stage, a median survival is only 6-12 months. Therefore, new therapeutic approaches for hormone-refractory prostate carcinoma (HRPC) are needed. Conditionally replicative adenoviruses (CRAds) are attractive anti-cancer agents. These agents are designed to replicate specifically in tumor cells followed by spread of the viral progeny to neighboring cancer cells. We used the cyclooxygenase-2 (COX-2) promoter for transcriptional targeting of tumor, which is active in many cancers but minimally active in normal tissues, including the liver. The COX-2 promoter (-1432/+59: COX-2L) was tested with luciferase (Luc) expression vectors in PC-3, Du-145, and LnCap prostate cancer cell lines. Very strong COX-2 promoter activity comparable to the CMV promoter was observed in PC-3 and Du-145 HRPC cell lines. We next examined infectivity enhancement in the PC cells by using fiber modification of Ad5 vectors, including incorporation of an RGD4C motif into the HI loop (RGD) and replacement of the Ad5 knob region with the Ad3 knob (Ad5/3 chimera),. Three CMV promoter driven Luciferase expression vectors with the wild type fiber (Ad5Luc1), RGD insertion (AdRGDLuc1), and Ad5/3 chimera fiber (Ad5/3Luc1) were used. The RGD-modified vector did not show enhanced infectivity in either of these PC cell lines, while the Ad5/3 chimera demonstrated significantly higher levels of infection in PC-3 and Du-145 HRPC cells. To analyze the effect of fiber modification on the cytocidal effect of CRAds we constructed COX-2 CRAds with wild type, RGD-modified, and Ad5/3 chimeric fibers, respectively. All COX-2 CRAds showed replication and subsequent oncolytic killing in both PC-3 and Du-145 cell lines while the COX-2 negative LnCap cell line was not affected. Ad5/Ad3 chimera CRAds demonstrated the strongest cytocidal effect among COX-2 CRAds in PC3 and Du-145 cell lines. Analysis of in vivo anti-tumor efficacy was performed using Du-145 prostate carcinoma subcutaneous xenografts. COX-2 CRAd agents with unmodified, RGD-modified, or Ad5/3 chimera fibers as well as wild type Ad5 and a non-replicative E1 deleted vector were used for intratumoral administration (5×109 vp/tumor). Our data indicate that the anti-tumor effect of COX-2 CRAd with Ad5/3 chimera fiber was better than unmodified or RGD-modified CRAds. The present results demonstrate that selective replication of CRAd under the control of the COX-2 promoter and infectivity enhancement with Ad5/3 chimeric fiber may be combined to generate promising viral therapeutic agents for the treatment of hormone refractory prostate carcinomas.