Abstract
BACKGROUND: Intracellular Zn(2+) levels decrease during prostate cancer progression and agents that modulate intracellular Zn(2+) are cytotoxic to prostate cancer cells by an incompletely described mechanism. F10 is a new polymeric fluoropyrimidine drug-candidate that displays strong activity with minimal systemic toxicity in pre-clinical models of prostate cancer and other malignancies. The effects of exogenous Zn(2+) or Zn(2+) chelation for enhancing F10 cytotoxicity are investigated as is the role of Omi/HtrA2, a serine protease that promotes apoptosis in response to cellular stress. METHODS: To test the hypothesis that the pro-apoptotic effects of F10 could be enhanced by modulating intracellular Zn(2+) we investigated cell-permeable and cell-impermeable Zn(2+) chelators and exogenous Zn(2+) and evaluated cell viability and apoptosis in cellular models of castration-resistant prostate cancer (CRPC; PC3, C4-2). The role of Omi/HtrA2 for modulating apoptosis was evaluated by pharmacological inhibition and Western blotting. RESULTS: Exogenous Zn(2+) initially reduced prostate cancer cell viability but these effects were transitory and were ineffective at enhancing F10 cytotoxicity. The cell-permeable Zn(2+) -chelator tetrakis-(2-pyridylmethl) ethylenediamine (TPEN) induced apoptosis in prostate cancer cells and enhanced the pro-apoptotic effects of F10. The pro-apoptotic effects of Zn(2+) -chelation in combination with F10 treatment were enhanced by inhibiting Omi/HtrA2 implicating this serine protease as a novel target for prostate cancer treatment. CONCLUSIONS: Zn(2+) -chelation enhances the pro-apoptotic effects of F10 and may be useful for enhancing the effectiveness of F10 for treatment of advanced prostate cancer. The serine protease Omi/HtrA2 modulates Zn(2+) -dependent apoptosis in prostate cancer cells and represents a new target for treatment of CRPC. Prostate 75:360-369, 2015. © 2014 Wiley Periodicals, Inc.