Abstract 4167: Co-targeting the stress survival proteins LEDGF/p75 and clusterin to resensitize chemoresistant prostate cancer cells to docetaxel

Prostate cancer (PCa) is the most commonly diagnosed male cancer and the second leading cause of cancer deaths in U.S. men. Late-stage PCa is characterized by metastasis followed by castration resistant PCa (mCRPC), for which there is no cure. Docetaxel (DTX) is the first-line chemotherapeutic drug for late-stage PCa, and resistance to this drug is inevitable. Our group has previously reported the elevated expression of the stress oncoprotein lens epithelium-derived growth factor (LEDGF/p75) in PCa cells and tissues, and this upregulation promotes resistance to DTX-induced non-apoptotic lysosomal cell death. Another stress oncoprotein, clusterin (CLU), is also upregulated in DTX-resistant PCa, and protects cells from DTX-induced mitochondrial-triggered apoptosis. In this study we observed that targeting LEDGF/75 with siRNAs partially resensitized DTX-resistant (DR) mCRPC cell lines to DTX treatment in clonogenic assays. Similarly, other groups have shown that knockdown of CLU in mCRPC-DR cells resensitizes them to treatment with taxanes. However, recent clinical trials targeting CLU have not been effective, suggesting that blocking this protein alone is insufficient to overcome DTX resistance. We hypothesized that simultaneous knockdown or inhibition of both LEDGF/p75 and CLU could be more effective in resensitizing chemoresisant PCa cells to taxane therapy than targeting each protein alone. Because of LEDGF/p75’s role as a stress transcription co-activator, we first sought to determine if this protein contributes to CLU expression by performing siRNA-mediated knockdown of LEDGF/p75 on the taxane-sensitive and -resistant mCRPC cell lines PC3 and DU145. Western blotting revealed that CLU protein expression was not downregulated by LEDGF/p75 knockdown, compared to treatment with scrambled siRNA control. Similarly, CLU knockdown in these cell lines did not downregulate LEDGF/p75. These results indicated that CLU expression is independent of LEDGF/p75, consistent with previous observations that these two proteins promote chemoresistance via distinct, possibly redundant, mechanisms. We then performed siRNA-mediated knockdown of LEDGF/p75 and CLU, separately or together, in PC3 DR and DU145 DR cells, in the presence and absence of varying concentrations of DTX. MTT and clonogenic assays were used to determine cell death viability and clonogenicity, respectively. Simultaneous knockdown of LEDGF/p75 and CLU, in combination with DTX treatment, resulted in increased sensitization to DTX than single knockdown of each protein. These findings suggest that co-targeting LEDGF/p75 and CLU could be an effective strategy for ameliorating chemoresistance in mCRPC, and set the foundation for combinatorial therapies targeting multiple stress pathways linked to taxane resistance together with taxane chemotherapy for treatment of late-stage PCa. Citation Format: Christina K. Cajigas-Du Ross, Leslimar Rios-Colon, Leanne Woods-Burnham, Carlos A. Casiano. Co-targeting the stress survival proteins LEDGF/p75 and clusterin to resensitize chemoresistant prostate cancer cells to docetaxel [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4167. doi:10.1158/1538-7445.AM2017-4167