FW-04-806 inhibits proliferation and induces apoptosis in human breast cancer cells by binding to N-terminus of Hsp90 and disrupting Hsp90-Cdc37 complex formation

Background: Heat shock protein 90 (HSP90) is a promising therapeutic target and inhibition of HSP90 will presumably result in suppression of multiple signaling pathways. FW-04-806, a bis-oxazolyl Macrolide compound extracted from China-native Streptomyces FIM-04-806, was reported to be identical in structure to the polyketide Conglobatin.

Methods: We adopted the methods of chemproteomics, computational docking, immunoprecipitation, siRNA gene knock down, Quantitative Real-Time PCR and xenograft models on the research of FW-04-806 antitumor mechanism, through the HER2-overexpressing breast Cancer SKBR3 and HER2-underexpressing breast Cancer MCF-7 cell line.

Results: We have verified the direct binding of FW-04-806 to the N-terminal domain of HSP90 and found that FW-04-806 inhibits HSP90/cell division cycle protein 37 (Cdc37) chaperone/co-chaperone interactions, but does not affect ATP-binding capability of HSP90, thereby leading to the degradation of multiple HSP90 client proteins via the Proteasome pathway. In breast Cancer cell lines, FW-04-806 inhibits cell proliferation, caused G2/M cell cycle arrest, induced Apoptosis, and downregulated HSP90 client proteins HER2, Akt, Raf-1 and their phosphorylated forms (p-HER2, p-Akt) in a dose and time-dependent manner. Importantly, FW-04-806 displays a better anti-tumor effect in HER2-overexpressed SKBR3 tumor xenograft model than in HER2-underexpressed MCF-7 model. The result is consistent with cell proliferation assay and in vitro Apoptosis assay applied for SKBR-3 and MCF-7. Furthermore, FW-04-806 has a favorable toxicity profile.

Conclusions: As a novel HSP90 Inhibitor, FW-04-806 binds to the N-terminal of HSP90 and inhibits HSP90/Cdc37 interaction, resulting in the disassociation of HSP90/Cdc37/client complexes and the degradation of HSP90 client proteins. FW-04-806 displays promising antitumor activity against breast Cancer cells both in vitro and in vivo, especially for HER2-overexpressed breast Cancer cells.