Targeting Prostate Cancer Subtype 1 by Forkhead Box M1 Pathway Inhibition

Purpose: Prostate cancer was recently classified to three clinically relevant subtypes (PCS) demarcated by unique pathway activation and clinical aggressiveness. In this preclinical study, we investigated molecular targets and therapeutics for PCS1, the most aggressive and lethal subtype, with no treatment options available in the clinic.Experimental Design: We utilized the PCS1 gene set and our model of enzalutamide (ENZ^R) castration-resistant prostate cancer (CRPC) to identify targetable pathways and inhibitors for PCS1. The findings were evaluated in vitro and in the ENZ^R CRPC xenograft model in vivoResults: The results revealed that ENZ^R CRPC cells are enriched with PCS1 signature and that Forkhead box M1 (FOXM1) pathway is the central driver of this subtype. Notably, we identified Monensin as a novel FOXM1-binding agent that selectively targets FOXM1 to reverse the PCS1 signature and its associated stem-like features and reduces the growth of ENZ^R CRPC cells and xenograft tumors.Conclusions: Our preclinical data indicate FOXM1 pathway as a master regulator of PCS1 tumors, namely in ENZ^R CRPC, and targeting FOXM1 reduces cell growth and stemness in ENZ^R CRPC in vitro and in vivo These preclinical results may guide clinical evaluation of targeting FOXM1 to eradicate highly aggressive and lethal PCS1 prostate cancer tumors. Clin Cancer Res; 23(22); 6923-33. ©2017 AACR.