Background: Docetaxel remains the first-line therapeutic intervention for metastatic and castration-resistant (CR) prostate cancer (PCa). However, the therapeutic efficacy is limited due to unresponsiveness, toxicity, and drug-resistance. The availability of additional therapies increases the PCa patient survival modestly, but the development of cross-resistance limit the therapeutic efficacy. Hence, there is a need to understand the mechanisms of resistance and identify a novel target for the better management of CR PCa patients. Methods: Docetaxel resistant 22Rv1, LNCaP C-81, and PC3 PCa cells were established, and its resistance phenotype was determined by cell growth inhibition (MTT assay), apoptosis markers (western blot), tumor sphere assay, drug efflux property (SP analysis by FACS), auto fluorescence (FACS). qRT-PCR, western blot, and confocal microscopic analysis were also performed to confirm the drug-resistant marker phenotype. Additional experiments were performed to determine the underlying molecular mechanisms of docetaxel resistance. Results: The docetaxel resistant PCa cells grew well at the higher concentration of docetaxel (120, 15 and 50 nM of docetaxel, respectively) and did not result in apoptosis as measured by cPARP and caspase-3 cleavage. Docetaxel resistant PCa cells confer cross-resistance to second-generation chemotherapeutic agent cabazitaxel and show altered cell proliferation and invasion. Blocking by the ABCB1 specific inhibitor enhances docetaxel-induced cell death on par with parental cells. Side population analysis by flow cytometry confirms the acquired drug efflux property. Side population, autofluorescence and tumor sphere analyses confirmed the drug-resistance and stem-like cell phenotype. qRT-PCR, western blot and confocal microscopy show the abundant expression levels of the drug transporters, ABCB1 and ABCG2. Further, the docetaxel resistant PCa cells show higher stem cell network proteins such as PAF1, POU5F1, NANOG and SOX9 expression levels compared to age-matched control cells. Conversely, Tet-inducible PAF1 knockdown reduces embryonic stem cell network proteins and reverses docetaxel-resistance phenotype. Conclusions: Collectively, our study suggests that the stem cell factors such as PAF1 play a major role in docetaxel resistance and aggressiveness to PCa cells. Understanding the associated mechanisms and targeting these factors could lead a better management approach for CRPCa patients.

Citation Format: Sakthivel Muniyan, Rama Krishna Nimmakayala, Saswati Karmakar, Satyanarayana Rachagani, Jawed A. Siddiqui, Parthasarathy Seshacharyulu, Ming-Fong Lin, Kaustubh Datta, Moorthy P. Ponnusamy, Surinder K. Batra. Role of polymerase II associated factor 1, PAF1, in docetaxel resistant prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5897.