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. 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. 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. 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.

One new metabolite 3,7-dimethyl-9-(-2,2,5,5-tetramethyl-1,3-dioxolan-4-yl)nona-1,6-dien-3-ol, together with nine known compounds, were isolated from the strain Xylaria sp., an endophytic fungus of Taxus mairei. Their structures were deduced from 1D and 2D NMR data. In vitro cytotoxicity and antibacterial activity of these compounds were evaluated. Some of them exhibited substantial activity.

Heat shock protein 90 (Hsp90) is a fascinating target for cancer therapy due to its significant role in the crossroad of multiple signaling pathways associated with cell proliferation and regulation. Hsp90 inhibitors have the potential to be developed into anti-cancer drugs. Here, we identified nicotinic-mycoepoxydiene (NMD), a structurally novel compound as Hsp90 inhibitor to perform the anti-tumor activity. The compound selectively bound to the Hsp90 N-terminal domain, and degraded the Hsp90 client protein Akt. The degradation of Akt detained Bad in non-phosphorylation form. NMD-associated apoptosis was characterized by the formation of fragmented nuclei, poly(ADP-ribose) polymerase cleavage, cytochrome c release, caspase-3 activation, and the increased proportion of sub-G1 phase cells. Interestingly, the apoptosis was accompanied with autophagy, by exhibiting the increased expression of LC-3 and the decrease of lysosome pH value. Our findings provide a novel cellular mechanism by which Hsp90 inhibitor adjusts cell apoptosis and autophagy in vitro, suggesting that NMD not only has a potential to be developed into a novel anti-tumor pharmaceutical, but also exhibits a new mechanism in regulating cancer cell apoptosis and autophagy via Hsp90 inhibition.