5-Azacitidine restores and amplifies the bicalutamide response on preclinical models of androgen receptor expressing or deficient prostate tumors

BACKGROUND. Epigenetic modifications play a key role in the in prostate cancer (Pca) progression to a hormone refractory state (HRPC) and the current use of agents targeting epigenetic changes has become a topic of intense interest in cancer research. In this regard, 5-Azacitine (5-Aza) represents a promising epigenetic modulator. This study tested the hypothesis that 5-Aza may restore and enhance the responsiveness of HRPC cells to antihormonal therapy on Androgen receptor (AR) expressing (22rv1) and AR-deficient (PC3) cells. METHODS. The effects were studied in vitro and in vivo models. This sequential treatment induced in vitro cell cycle arrest and apoptosis both in 22rv1 and PC3 tumor cell lines. RESULTS. This combined treatment up-regulated the expression of FasL, phospho-FADD, p16^INKA, Bax, Bak, and p21^WAF1, and inhibited FLIP, Bcl-2, and Bcl-XL expression. The re-activation of hormonal response of AR-negative PC3 cell line was partially due to the AR re-expression mediated by 5-Aza treatment. In contrast, the increase in the response to antiandrogenic therapy in 22rv1 did not correlate with AR expression levels. Furthermore, xenograft studies revealed that the combined treatment of 5-Aza with AR-antagonist Bicalutamide had additive/synergistic effects in repressing tumor growth in vivo and the underlying mechanisms responsible for these effects seem to be in part mediated by induction of apoptosis. CONCLUSIONS. So, this study strongly suggests a therapeutic potential of 5-Aza in combination with anti-androgen therapy in patients with in AR expressing and AR-deficient HRPC.