Abstract 3862: Ormeloxifene, a novel pharmacological activator of PKD1 enhances docetaxel sensitivity in prostate cancer

Background: Prostate cancer (PrCa) is the second leading cause of cancer-related deaths in American Men. Docetaxel (DTX) is a standard first-line treatment for metastatic castration-resistant PrCa after the failure of hormone therapy. However, most PrCa patients who receive DTX experience only transient benefits and rapidly develop incurable drug resistance. Protein Kinase D1 (PKD1), one of the serine threonine kinases from PKD family is highly expressed in normal prostate tissues and is suppressed during PrCa progression. Accumulative evidence suggest a tumor suppressive role of PKD1 in PrCa, while other isoforms of PKD (PKD2 and PKD3) act as oncogene. In this study, we identified pharmacological agent Ormeloxifene (ORM) which selectively activates PKD1 and inhibits metastasis associated protein 1 (MTA1), thus induces sensitivity to DTX treatment in PrCa cells. Materials and Methods: We have used androgen-independent human PrCa cells (C4-2) which show low PKD1 expression compared to other PrCa cell lines. Cells were treated with 10 and 15 μM doses of ORM for 24 hrs and various functional assays (cell proliferation, colony formation, motility and invasion) were performed. In a parallel experiment, cells were treated with ORM (10 and 15 μM) for 24 hrs protein and RNA samples isolation. Protein lysates were used to investigate the effect of ORM on PKD1, PKD2, PKD3 and MTA1 protein levels. qRT-PCR was performed to investigate the effect of ORM on PKD1, PKD2 and PKD3 expression at mRNA levels. To investigate if ORM treatment sensitizes the effects of DTX, cells were treated with ORM and DTX alone or in combination. In-silico docking studies were performed to determine the putative molecular interaction of ORM with MTA1. Results: ORM treatment inhibits proliferation and clonogenic potential of C4-2 cells. We observed that ORM significantly induces PKD1 expression at protein and mRNA level in C4-2 cells. To determine whether this PKD1 inducing effects of ORM in PrCa cells is specific, we examined the effects of ORM on PKD2 and PKD3 at mRNA and protein levels. Interestingly, we observed that ORM treatment inhibits expression of oncogenic PKD3 isoform, however, no effect PKD2 was observed. MTA1 is involved in DTX resistance and ORM treatment effectively inhibited the expression of MTA1. However, there was no effect of DTX treatment on the expression of MTA1. We also observed that ORM treatment significantly potentiates the effect of DTX on cell viability and colony formation of C4-2 cells. In-silico docking studies between ORM and MTA1 showed four potential binding sites with best score at serine 270. Conclusion: Overall, our study defines ORM as a novel PKD1 activator/modulator which also inhibits a key metastasis associated protein, MTA1 and sensitizes the PrCa cells to DTX. Based on these results, it appears that ORM may be a novel therapeutic modality for advanced stage metastatic PrCa alone or in combination with DTX. Citation Format: Aditya Ganju, Bilal Bin Hafeez, Fathi Halaweish, Wei Li, Man Mohan Singh, Murali Mohan Yallapu, Subhash Chauhan, Meena Jaggi. Ormeloxifene, a novel pharmacological activator of PKD1 enhances docetaxel sensitivity in prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3862.