Fluorine- and rhenium-containing geldanamycin derivatives as leads for the development of molecular probes for imaging Hsp90

LZY3016, a novel geldanamycin derivative, inhibits tumor growth in an MDA-MB-231 xenograft model

A novel geldanamycin derivative LZY3016 was synthesized as an antitumor agent. Compound LZY3016 exhibited potent anti-proliferation activity toward MDA-MB-231 (IC₅₀ = 0.06 μM), which was more effective than positive drug 17-AAG. In vivo hepatotoxicity assay displayed that serum AST/ALT levels in LZY3016-treated mice were both significantly less than those in the geldanamycin (GA) group. LZY3016 showed potent antitumor activity in an MDA-MB-231 xenograft mouse model, suggesting LZY3016 is an up-and-coming antitumor candidate. The theoretical binding mode between LZY3016 and Hsp90 was obtained by molecular dynamics simulation.

Synthesis, structure and anticancer activity of new geldanamycin amine analogs containing C(17)- or C(20)- flexible and rigid arms as well as closed or open ansa-bridges

The nucleophilic attack of amines at C(17) or C(17)/C(20) positions of geldanamycin's (GDM) benzoquinone, via initial 1,4-Michael conjugate addition mechanism, yield new analogs with closed or open ansa-bridges (1-31), respectively. X-ray structures of analogs 22 and 24 reveals an unexpected arrangement of the ansa-bridge in solid (conformer B), that is located between those of conformers A, prevailing in solution (trans-lactam), and C, crucial at binding to Hsp90 (cis-lactam). The structure of a new-type conformer B allows to better understand the molecular recognition mechanism between the GDM analogs and the target Hsp90. Combined analysis of: anticancer test results (SKBR-3, SKOV-3, PC-3, U-87, A-549) and those performed in normal cells (HDF), K_D values and docking modes at Hsp90 as well as clogP parameters, reveals that the rigid C(17)-arm (piperidyl, cyclohexyl) with a H-bond acceptor as carbonyl group together with a lipophilicity clogP∼3 favor high potency of analogs, even up to IC₅₀ ∼0.08 μM, at improved selectivity (SI_HDF > 30), when compared to GDM. The most active 25 show higher anticancer potency than 17-AAG (in SKOV-3 and A-549) as well as reblastatin (in SKBR-3 and SKOV-3). Opening of the ansa-bridge within GDM analogs, at the best case, decreases activity (IC₅₀∼2 μM) and toxicity in HDF cells (SI_HDF∼2-3), relative to GDM.

The conserved NxNNWHW motif in Aha-type co-chaperones modulates the kinetics of Hsp90 ATPase stimulation

Hsp90 is a dimeric molecular chaperone that is essential for the folding and activation of hundreds of client proteins. Co-chaperone proteins regulate the ATP-driven Hsp90 client activation cycle. Aha-type co-chaperones are the most potent stimulators of the Hsp90 ATPase activity but the relationship between ATPase regulation and in vivo activity is poorly understood. We report here that the most strongly conserved region of Aha-type co-chaperones, the N terminal NxNNWHW motif, modulates the apparent affinity of Hsp90 for nucleotide substrates. The ability of yeast Aha-type co-chaperones to act in vivo is ablated when the N terminal NxNNWHW motif is removed. This work suggests that nucleotide exchange during the Hsp90 functional cycle may be more important than rate of catalysis.

Synthesis and biological evaluation of geldanamycin–ferulic acid conjugate as a potent Hsp90 inhibitor

A novel geldanamycin–ferulic acid conjugate LZY228 was prepared and evaluated for anti-proliferation activity on human cancer cell line MDA-MB-231. Compound LZY228 exhibited potent cytotoxicity with IC₅₀ value of 0.27 μM, which was more potent than 17-AAG. Hepatotoxicity test in mice demonstrated that the levels of both AST and ALT of LZY228-treated group were lower than that of GA-treated group, indicating that LZY228 was a promising antitumor candidate. In addition, excellent in vivo antitumor potency of LZY228 was observed in MDA-MB-231 xenograft model, which was superior to reference drug 17-AAG. Docking and MD refinement of the Hsp90-LZY228 complex give us an explanation of theoretical binding model of 17-ferulamido-17-demethoxygeldanamycins at molecular level.

Compared to 17-AAG, LZY228 exhibited higher Hsp90 inhibitory activity in vitro and better antitumor activity in human breast carcinoma (MDA-MB-231) xenograft nude mice.

The Mechanism of Hsp90 ATPase Stimulation by Aha1

Hsp90 is a dimeric molecular chaperone responsible for the folding, maturation, and activation of hundreds of substrate proteins called ‘clients’. Numerous co-chaperone proteins regulate progression through the ATP-dependent client activation cycle. The most potent stimulator of the Hsp90 ATPase activity is the co-chaperone Aha1p. Only one molecule of Aha1p is required to fully stimulate the Hsp90 dimer despite the existence of two, presumably identical, binding sites for this regulator. Using ATPase assays with Hsp90 heterodimers, we find that Aha1p stimulates ATPase activity by a three-step mechanism via the catalytic loop in the middle domain of Hsp90. Binding of the Aha1p N domain to the Hsp90 middle domain exerts a small stimulatory effect but also drives a separate conformational rearrangement in the Hsp90 N domains. This second event drives a rearrangement in the N domain of the opposite subunit and is required for the stimulatory action of the Aha1p C domain. Furthermore, the second event can be blocked by a mutation in one subunit of the Hsp90 dimer but not the other. This work provides a foundation for understanding how post-translational modifications regulate co-chaperone engagement with the Hsp90 dimer.

Natural Product Inspired N-Terminal Hsp90 Inhibitors: From Bench to Bedside?

The 90 kDa heat shock proteins (Hsp90) are responsible for the conformational maturation of nascent polypeptides and the rematuration of denatured proteins. Proteins dependent upon Hsp90 are associated with all six hallmarks of cancer. Upon Hsp90 inhibition, protein substrates are degraded via the ubiquitin-proteasome pathway. Consequentially, inhibition of Hsp90 offers a therapeutic opportunity for the treatment of cancer. Natural product inhibitors of Hsp90 have been identified in vitro, which have served as leads for the development of more efficacious inhibitors and analogs that have entered clinical trials. This review highlights the development of natural product analogs, as well as the development of clinically important inhibitors that arose from natural products.

Targeting heat-shock-protein 90 (Hsp90) by natural products: geldanamycin, a show case in cancer therapy

Covering 2005 to 2013. In this review recent progress in the development of heat shock proteins (Hsp90) in oncogenesis is illuminated. Particular emphasis is put on inhibitors such as geldanamycin and analogues that serve as a natural product show case. Hsp90 has emerged as an important target in cancer therapy and/or against pathogenic cells which elicit abnormal Hsp patterns. Competition for ATP by geldanamycin and related compounds abrogate the chaperone function of Hsp90. In this context, this account pursues three topics in detail: a) Hsp90 and its biochemistry, b) Hsp90 and its role in oncogenesis and c) strategies to create compound libraries of structurally complex inhibitors like geldanamycin on which SAR studies and the development of drugs that are currently in different stages of clinical testing rely.