Abstract 2748: Prostate-specific inhibition of PI3 Kinase and protein synthesis as a therapy for advanced hormone-refractory prostate cancer
Authors: Daniele Baiz, Young A Choi, Yelena Karpova, Dana Yancey, Sazzad Hassan, Michel Sadelain, Waldemar Debinski, George Kulik
Journal: Cancer Research (2012)

Abstract Prostate cancer remains the second leading cause of cancer-related death in men in the United States, as at present there are no effective treatments for advanced stage-affected patients. Recurrence usually involves hormonal androgen suppression, which typically translates into androgen-ablation insensitivity with accompanied limited or transient response to systemic chemotherapy. Our preliminary experiments have shown that it is possible to induce massive and rapid apoptosis in the hormone-refractory prostate cancer cells in vitro and in vivo, by using the PI3K inhibitor ZSTK474 in combination with a prostate cancer-selective cytotoxin J591PE38, a fusion protein between two fragments: one from the J591 antibody (that recognizes the Prostate-Specific Membrane Antigen, expressed in nearly all prostate cancers with the highest rate in poorly differentiated, metastatic and hormone-refractory cases), and the other from the Pseudomonas aeruginosa exotoxin A (PE38, that ADP-ribosylates and inhibits the Eukaryotic Elongation Factor 2). The PI3K inhibitor ZSTK474 in combination with the cytotoxin J591PE38 induces massive cell death (around 100%) in prostate cancer C4-2tetLuc and C4-2 cells monitored by Time-Lapse Video Microscopy during 24 hours, when compared to controls. Combined agents at 6 hours synergistically increases Caspase 3 activity, as confirmed by DEVD-Afc enzymatic assay (about 25 and 30 folds in C4-2tetLuc and C4-2 cells respectively, compared to control) and Western blotting (3.28 and 2.45 folds in C4-2tetLuc and C4-2 cells respectively, compared to control). Apoptosis activation was confirmed by detecting the cleaved fragments of Caspase 7 and PARP (compared to control respectively: 4.12 and 3.58 folds for C4-2tetLuc; 5.38 and 13.38 folds for C4-2 cells). No any major effects were found in the PSMA-negative prostate cancer PC-3 and breast cancer BT-549 cells treated with both agents when compared to controls, confirming the specificity of the cytotoxin J591PE38. PI3 Kinase inhibition by ZSTK474 was confirmed in all cell lines used by monitoring the phosphorylation levels of Akt (Thr308) by Western blotting. Prostate cancer C4-2tetLuc xenografts in nude mice showed a potent reduction of luminescence (around 95% at day 7) in tumors treated with a single local injection of both agents, when compared to controls. Apoptosis activation and PI3 Kinase inhibition at 6 hours were confirmed by monitoring the protein levels of cleaved-PARP and the phosphorylation levels of Akt by Western blotting. In summary, in this study we demonstrated the efficacy of a potential combinatorial approach using a specific PI3 Kinase and de novo protein synthesis inhibitor to treat hormone-refractory prostate cancer with constitutive active PI3K/Akt pathway, by generating massive and rapid apoptosis in vitro and in vivo (This work is supported by NIH/NCI grant 3R01 CA 118329 02S2). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2748. doi:1538-7445.AM2012-2748