Rational design, synthesis, and biological evaluation of novel C6-modified geldanamycin derivatives as potent Hsp90 inhibitors and anti-tumor agents

Heat shock protein 90(Hsp90) is an appealing anticancer drug target that provoked a tremendous wave of investigations. Geldanamycin(GA) is the first identified Hsp90 inhibitor that exhibited potent anticancer activity, but the off-target toxicity associated with the benzoquinone moiety hampered its clinical application. Until now, structure optimization of GA is still in need to fully exploit the therapeutic value of Hsp90. Due to the structural complexity and synthetic challenge of this compound family, conventional optimization is bound to be costly but high efficiency is expected to be reachable by combining the art of rational design and total synthesis. Described in this paper is our first attempt at this approach aiming at rational modification of the C6-position of GA. The binding affinities towards Hsp90 of compound 1(C6-ethyl) and 2(C6-methyl) were designed and predicted by using Discovery Studio. These compounds were synthesized and further subjected to a thorough in vitro biological evaluation. We found that compounds1 and 2 bind to Hsp90 protein with the IC_(50) of 34.26 nmol/L and 163.7 nmol/L, respectively. Both compounds showed broad-spectrum antitumor effects. Replacing by ethyl, compound 1 exhibited more potent bioactivity than positive control GA, such as in G2/M cell cycle arrest, cell apoptosis and client proteins degradations. The results firstly indicated that the docking study is able to provide a precise prediction of Hsp90 affinities of GA analogues, and the C6 substituent of GA is not erasable without affecting its biological activity.

PGK1-coupled HSP90 stabilizes GSK3βexpression to regulate the stemness of breast cancer stem cells

Objective:Glycogen synthase kinase-3β(GSK3β)has been recognized as a suppressor of Wnt/β-catenin signaling,which is critical for the stemness maintenance of breast cancer stem cells.However,the regulatory mechanisms of GSK3βprotein expression remain elusive.Methods:Co-immunoprecipitation and mass spectral assays were performed to identify molecules binding to GSK3β,and to characterize the interactions of GSK3β,heat shock protein 90(Hsp90),and co-chaperones.The role of PGK1 in Hsp90 chaperoning GSK3βwas evaluated by constructing 293T cells stably expressing different domains/mutants of Hsp90α,and by performing a series of binding assays with bacterially purified proteins and clinical specimens.The influences of Hsp90 inhibitors on breast cancer stem cell stemness were investigated by Western blot and mammosphere formation assays.Results:We showed that GSK3βwas a client protein of Hsp90.Hsp90,which did not directly bind to GSK3β,interacted with phosphoglycerate kinase 1 via its C-terminal domain,thereby facilitating the binding of GSK3βto Hsp90.GSK3β-bound PGK1 interacted with Hsp90 in the“closed”conformation and stabilized GSK3βexpression in an Hsp90 activity-dependent manner.The Hsp90 inhibitor,17-AAG,rather than HDN-1,disrupted the interaction between Hsp90 and PGK1,and reduced GSK3βexpression,resulting in significantly reduced inhibition ofβ-catenin expression,to maintain the stemness of breast cancer stem cells.Conclusions:Our findings identified a novel regulatory mechanism of GSK3βexpression involving metabolic enzyme PGK1-coupled Hsp90,and highlighted the potential for more effective cancer treatment by selecting Hsp90 inhibitors that do not affect PGK1-regulated GSK3βexpression.

A novel derivative of geldanamycin and its antitumor activity

A new derivative of geldanamycin was synthesized by introducing the 6-cinnamamido-hexyl-amino group into the 17-site of geldanamycin, a heat shock protein 90 （Hsp90） inhibitor, to obtain 17-（6-cinnamamido-hexylamino）-17-demethoxygel-danamycin （CNDG）. Its in vitro and in vivo antitumor effects were evaluated by MTT assay and xenograft in nude mice.

Discovery and development of natural heat shock protein 90 inhibitors in cancer treatment

Heat shock protein 90(Hsp90)is a highly conserved molecular chaperone that plays a vital role in the signal transduction of cancers.Hsp90 inhibitors are able to inhibit Hsp90 or the complex of Hsp90 and co-chaperones resulting in the degradation of Hsp90-dependent client proteins through the ubiqui tina tion-proteasome pathway,thereby leading to the growth inhibition of tumor cells.This review will briefy discuss the molecular structure and biological function of Hsp90,and focus on a summary of recent progress in the development and testing of natural Hsp90 inhibitors and their different means by which they interact with Hsp90.

4,5,6,7-Tetrahydro-[1,2,3]triazolo[1,5-a]pyrazine as a new scaffold for heat shock protein 90 inhibitors

Heat shock protein 90（hsp90） is a promising anticancer drug target. A library of 2,4-dihydroxyphenyl（resorcinol） substituted 4,5,6,7-tetrahydro-[1,2,3]triazolo[1,5-a]pyrazine compounds that target this protein were designed and prepared based on our earlier study. The compounds were tested in five cancer cell lines and seven of them showed notable anticancer activity（IC_（50）2-10 mmol/L）. The active subset compounds were further subjected to a polarized fluorescent assay and exhibited high binding affinity toward purified hsp90（IC_（50）60-100 nmol/L）. These results indicated that the tetrahydrotriazolopyrazine motif of the molecules may represent a novel scaffold for the development of hsp90 inhibitors.

Simplified aminocoumarin analogues as anticancer agents:Amino isosteric replacement in the noviose moiety resulted in substantial enhancement of antiproliferative activity

Simplified aminocoumarin analogues,either noviosylated or simple basic heterocycle attached 3-amido-coumarin compounds,are known to be promising anticancer agents targeting the C-terminal ATP-binding site of Hsp90.In this study,3＇-amino isosteric replacement in the noviose moiety of two known noviose containing Hsp90 C-terminal inhibitors was synthetically realized for the first time.In vitro evaluation of these compounds suggested that the introduction of a basic amino group into the noviose subunit resulted in significant improvement of their cytotoxicities.