Gephyromycin C, a novel small-molecule inhibitor of heat shock protein Hsp90, induces G2/M cell cycle arrest and apoptosis in PC3 cells in vitro

Abstract

Gephyromycin C (GC), a natural compound isolated from a marine-derived actinomycete Streptomyces sp. SS13I, which exerts anti-proliferative effect on PC3 cells. However, its underlying mechanism of the anti-cancer effect remains unknown. The results of SRB assays showed that GC inhibited the proliferation of PC3 cells with an IC₅₀ value of 1.79 ± 0.28 μM. GC also induced G2/M cell cycle arrest which was accompanied by declining levels of cyclin proteins. Possible mechanisms were investigated and it was found that GC bound to Hsp90 and caused the degradation of Hsp90 client proteins (AKT, CHK1, P53, CDK4, Raf-b, and Raf-1). The fluorescent polarization assay with FITC-labeled geldanamycin (FITC-GA) demonstrated that GC was able to compete with FITC-GA in binding to wild type Hsp90 with an IC₅₀ of 2.15 μM. Results of a docking study also suggested that GC interacted with the N-terminal domain of Hsp90. Our results showed that GC could bind to Hsp90, which resulted in down-regulation of Hsp90 client proteins and G2/M arrest in PC3 cells. Since the antitumor effects of this kind of angucycline via targeting Hsp90 has not been reported before, our results indicate that GC is a novel inhibitor of Hsp90 from marine resources and worthy of further study.

Keywords: Antitumor activity; G2/M arrest; Gephyromycin C(GC); Hsp90 inhibitor; Prostate cancer.