Development of drug resistance is an inevitable phenomenon in
castration-resistant
prostate cancer (CRPC) cells requiring novel therapeutic approaches. In this study, efficacy and toxicity of
Rhizochalinin (Rhiz) - a novel
sphingolipid-like marine compound - was evaluated in
prostate cancer models, resistant to currently approved standard
therapies. In vitro activity and mechanism of action of Rhiz were examined in the human
prostate cancer cell lines PC-3, DU145, LNCaP, 22Rv1, and VCaP. Rhiz significantly reduced cell viability at low micromolar concentrations showing most pronounced effects in
enzalutamide and
abiraterone resistant AR-V7 positive cells. Caspase-dependent apoptosis, inhibition of pro-survival autophagy, downregulation of AR-V7, PSA and
IGF-1 expression as well as inhibition of
voltage-gated potassium channels were identified as mechanisms of action. Remarkably, Rhiz re-sensitized AR-V7 positive cells to
enzalutamide and increased efficacy of
taxanes.In vivo activity and toxicity were evaluated in PC-3 and 22Rv1 NOD SCID mouse xenograft models using i.p. administration. Rhiz significantly reduced growth of PC-3 and 22Rv1
tumor xenografts by 27.0% (p = 0.0156) and 46.8% (p = 0.047) compared with controls with an increased fraction of
tumor cells showing apoptosis secondary to Rhiz exposure. In line with the in vitro data, Rhiz was most active in AR-V7 positive xenografts in vivo. In animals, no severe side effects were observed.In conclusion, Rhiz is a promising novel marine-derived compound characterized by a unique combination of anticancer properties. Its further clinical development is of high impact for patients suffering from
drug resistant
prostate cancer especially those harboring AR-V7 mediated resistance to
enzalutamide and
abiraterone.