Non-benzoquinone geldanamycin analogs trigger various forms of death in human breast cancer cells

Background: hsp90 proteins are important therapeutic targets for many anti-cancer drugs in clinical trials. geldanamycin (ga) was identified as the first natural inhibitor of hsp90,increasing evidence suggests that ga was not a good choice for clinical trials. in this study,we investigated two new non-benzoquinone geldanamycin analogs of hsp90 inhibitors,dhq3 and 17-demethoxy-reblastatin (17-dr),to explore the molecular mechanisms of their anti-cancer activity in vivo and vitro. methods: mtt and colony formation assays were used to measure cell viability. flow cytometry,dapi staining,atp assay,electron microscopy,western blots,sirnas transfection and immunofluorescence were used to determine the molecular mechanism of dhq3- or 17-dr-induced different forms of death in human breast cancer mda-mb-231 cells. malachite green reagent was used to measure atpase activity of the analogs. results: dhq3 and 17-dr presented efficiently inhibitory effect in mda-mb-231 cell lines,and dhq3 induced necroptosis by activation of the rip1-rip3-mlkl necroptosis cascade. and dhq3-induced cell death was inhibited by a necroptosis inhibitor,necrostatin-1 (nec-1),but not by a caspase inhibitor z-vad-fmk. on the other hand,17-dr induced apoptosis in mda-mb-231 cells,indicating a caspase-dependent killing mechanism. we further demonstrated that down-regulation of rip1 and rip3 by sirna protected against dhq3 but not 17-dr induced cell death. these results were confirmed by electron microscopy. dhq3 and 17-dr induced the degradation of hsp90 client proteins,and they showed strong antitumor effects in mda-mb-231 cell-xenografted nude mice. conclusions: these findings supported that dhq3 and 17-dr induce different forms of death in some cancer cell line via activation of different pathways. all of the results provided evidence for its anti-tumorigentic action with low hepatotoxicity in vivo,making them promising anti-breast cancer agents. © 2016 the author(s).