Role of the Androgen-Androgen Receptor Axis in the Treatment Resistance of Advanced Prostate Cancer: From Androgen-Dependent to Castration Resistant and Further

After the introduction of prostate-specific antigen (PSA) screening, prostate cancer diagnosis has shifted to early and curative stages, although 10-20% of patients still present with metastatic and incurable cancer. Prostate cancer is androgen-dependent, and most patients with prostate cancer initially respond to androgen deprivation therapy (ADT). After 1-2 years of the treatment, advanced prostate cancer eventually progresses to castration resistant prostate cancer (CRPC). A variety of mechanisms of progression from androgen-dependent prostate cancer to CRPC under ADT have been postulated, and the key pathway is re-activation of the androgen-androgen receptor (AR) axis, for example, caused by AR mutation/overexpression/splice variants, altered expression of AR cofactors, and increased production of androgens. Recently approved new agents, such as the hormonal agents abiraterone and enzalutamide and the chemotherapeutic agent cabazitaxel, have demonstrated survival benefit in men with CRPC. However, the prolongation of survival times provided with these agents is limited because of the treatment resistance. Androgen-AR axis still plays a pivotal role in the resistance to the new agents for CRPC. To improve the prognosis of patients with CRPC, intensive research to identify effective agents, treatment strategies, and useful predictive biomarkers to select the patients who can benefit from such treatments are required. Additional clinical data, with a better understanding of the biology of CRPC, may provide better CRPC treatment outcomes. This article reviews the underlying mechanisms of treatment resistance and future direction of CRPC treatments.

Novel and next-generation androgen receptor-directed therapies for prostate cancer: Beyond abiraterone and enzalutamide

The approval of abiraterone and enzalutamide for the treatment of advanced castration-resistant prostate cancer heralded a paradigm shift in the management of this disease. Nevertheless, new and improved treatments are needed since the disease remains incurable for the majority of these patients. In this article, we review the biology of castration-resistant disease as well as emerging therapeutic compounds directed at the androgen receptor, including galeterone, VT-464, ARN-509, and ODM-201. Mechanisms of action, early clinical data, and ongoing clinical studies for these compounds are all reviewed. The need to find optimal sequencing and combination strategies as well as the need for predictive biomarkers of response to these agents is discussed.