Abstract 3130: CYP3A5 positively regulates androgen receptor signaling in prostate cancer cells: Potential for therapeutic targeting

Abstract

Abstract Purpose: Prostate cancer is the most common malignancy and second leading cause of cancer-specific mortality in US men. The androgen receptor (AR) plays a major role in promoting growth and progression of prostate cancer and thus has been successfully targeted therapeutically. Therapeutic resistance to androgen deprivation therapy (ADT) accounts for much of the morbidity and mortality attributable to prostate cancer. Therapeutic resistance is typically accompanied by insufficient blockade of AR activation, whose initial step involves translocation of AR to the nucleus. Previously we demonstrated that CYP3A5 facilitates the nuclear translocation of AR, promoting prostate cancer growth. Targeting CYP3A5 and blocking AR nuclear translocation may override therapeutic resistance to ADT, representing a novel approach for treating men with advanced prostate cancer. This work focuses on understanding the role of CYP3A5 in regulating AR nuclear translocation process and its subsequent promotion of prostate cancer growth. Methods: AR nuclear translocation is tightly regulated through a process involving several chaperones, multiple cofactors, and kinases, including HSP90, HSP70, HSP40 and HSP27. Complexed HSP90 maintains the AR as an inactive receptor in the cytoplasm. Upon androgen binding and activation, AR associates with HSP27, then translocates to the nucleus where it activates transcription of AR regulated genes responsible for prostate cancer growth. To decipher the role of CYP3A5 in this AR translocation process we performed a series of co-immunoprecipitation experiments with CYP3A5 and components of HSP90-AR complex, at different stages of AR translocation process. We used extracts of LNCaP transfected with a CYP3A5-Flag-tagged construct with either Flag-agarose or HSP90 and AR antibodies with A/G beads for immunoprecipitation. Results: Our co-immunoprecipitation experiments using CYP3A5-Flag transfected LNCaP extracts demonstrate that CYP3A5 associates with the HSP90-AR complex that helps to maintain AR in a form that can be readily activated by androgen. Using Flag-agarose in co-immunoprecipitation experiments, we demonstrated that CYP3A5 is a component of the HSP90-AR complex, associating with AR, HSP90, HSP70 and HSP40 each which are chaperones regulating AR nuclear translocation. We further confirmed the presence of CYP3A5 in the HSP90-AR complex by co-immunoprecipitation using HSP90 and AR antibodies in combination with A/G beads instead of flag-agarose. Conclusion: Our current finding supports the notion that CYP3A5 is a part of the HSP90-AR complex and positively regulates AR nuclear translocation. Therefore, targeting CYP3A5 to block AR nuclear translocation may be a therapeutic adjunctive approach in advanced prostate cancer. Citation Format: Ranjana Mitra, Priyatham Gorjala, Oscar B. Goodman. CYP3A5 positively regulates androgen receptor signaling in prostate cancer cells: Potential for therapeutic targeting [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 3130. doi:10.1158/1538-7445.AM2017-3130