p38 MAPK Inhibition Mitigates Hypoxia-Induced AR Signaling in Castration-Resistant Prostate Cancer.

BACKGROUND: Aberrant androgen receptor (AR) signaling is a major driver of castration-resistant prostate cancer (CRPC). Tumor hypoxia increases AR signaling and is associated with treatment resistance in prostate cancer. Heat shock protein 27 (Hsp27) is a molecular chaperone that is activated in response to heat shock and hypoxia. Hsp27 has previously been reported to facilitate AR nuclear translocation in a p38 mitogen-activated protein kinase (MAPK) dependent manner in castration-sensitive prostate cancer cell lines. Here, we evaluated the potential for inhibiting p38 MAPK/Hsp27 mediated AR signaling under normoxia and hypoxia in experimental models of CRPC. METHODS: We inhibited p38 MAPK with SB203580 in prostate cancer cell lines and measured Hsp27 phosphorylation, AR activity, cell proliferation, and clonogenicity under normoxia and hypoxia. AR activity was measured using an androgen response element driven reporter assay and qPCR to measure expression of AR target genes. Xenograft-bearing mice were treated with SB203580 to measure tumor growth and serum prostate specific antigen (PSA). RESULTS: Our results indicate that p38 MAPK and Hsp27 are activated under normoxia and hypoxia in response to androgens in CRPC cells. p38 MAPK inhibition diminished Hsp27 activation and the hypoxia-mediated increase in AR activity. Additionally, inhibition of p38 MAPK activity decreased proliferation and survival of CRPC cells in vitro and prolonged the survival of tumor-bearing mice. CONCLUSIONS: These results suggest that p38 MAPK inhibition may represent a therapeutic strategy to disrupt AR signaling in the heterogeneous CRPC tumor microenvironment.