Defining a Population of Stem-like Human Prostate Cancer Cells That Can Generate and Propagate Castration-Resistant Prostate Cancer.

Purpose: We have shown that the phenotypically undifferentiated (PSA −/lo ) prostate cancer cell population harbors long-term self-renewing cancer stem cells (CSC) that resist castration, and a subset of the cells within the PSA −/lo population bearing the ALDH hi CD44 + α2β1 + phenotype (Triple Marker + /TM + ) is capable of robustly initiating xenograft tumors in castrated mice. The goal of the current project is to further characterize the biologic properties of TM + prostate cancer cell population, particularly in the context of initiating and propagating castration-resistant prostate cancer (CRPC). Experimental Design: The in vivo CSC activities were measured by limiting-dilution serial tumor transplantation assays in both androgen-dependent and androgen-independent prostate cancer xenograft models. In vitro clonal, clonogenic, and sphere-formation assays were conducted in cells purified from xenograft and patient tumors. qPCR, Western blot, lentiviral-mediated gene knockdown, and human microRNA arrays were performed for mechanistic studies. Results: By focusing on the LAPC9 model, we show that the TM + cells are CSCs with both tumor-initiating and tumor-propagating abilities for CRPC. Moreover, primary patient samples have TM + cells, which possess CSC activities in “castrated” culture conditions. Mechanistically, we find that (i) the phenotypic markers are causally involved in CRPC development; (ii) the TM + cells preferentially express castration resistance and stem cell–associated molecules that regulate their CSC characteristics; and (iii) the TM + cells possess distinct microRNA expression profiles and miR-499-5p functions as an oncomir. Conclusions: Our results define the TM + prostate cancer cells as a population of preexistent stem-like cancer cells that can both mediate and propagate CRPC and highlight the TM + cell population as a therapeutic target. Clin Cancer Res; 22(17); 4505–16. ©2016 AACR .