Androgen Receptor and Prostate Cancer Stem Cells: Biological Mechanisms and Clinical Implications

Abstract

Prostate cancer (PCa) contains phenotypically and functionally distinct cells, and this cellular heterogeneity poses clinical challenges as the distinct cell types likely respond differently to various therapies. Clonal evolution, driven by genetic instability, and intra-clonal cancer cell diversification, driven by cancer stem cell (CSCs), together, create tumor cell heterogeneity. In this review, we first discuss prostate cancer stem cells (PCSCs) and heterogeneity of androgen receptor (AR) expression in primary, metastatic and treatment-failed PCa. Based on literature reports and our own studies, we hypothesize that whereas PCSCs in primary and untreated tumors and models are mainly AR ⁻, PCSCs in CRPCs could be either AR ⁺ or AR ^−/lo. We illustrate the potential mechanisms whereby AR ⁺ and AR ⁻ PCSCs may employ to propagate PCa at the population level, mediate therapy resistance, and metastasize. As a result, targeting AR alone may not be able to achieve long-lasting therapeutic efficacy. Elucidating the roles of AR and PCSCs should provide important clues to designing novel personalized combinatorial therapeutic protocols targeting both AR ⁺ and AR ⁻ PCa cells.