NMS-E973, a Novel Synthetic Inhibitor of Hsp90 with Activity against Multiple Models of Drug Resistance to Targeted Agents, Including Intracranial Metastases

Abstract

Purpose: Recent developments of second generation Hsp90 inhibitors suggested a potential for development of this class of molecules also in tumors that have become resistant to molecular targeted agents. Disease progression is often due to brain metastases, sometimes related to insufficient drug concentrations within the brain. Our objective was to identify and characterize a novel inhibitor of Hsp90 able to cross the blood-brain barrier (BBB).Experimental Design: Here is described a detailed biochemical and crystallographic characterization of NMS-E973. Mechanism-based anticancer activity was described in cell models, including models of resistance to kinase inhibitors. Pharmacokinetics properties were followed in plasma, tumor, liver, and brain. In vivo activity and pharmacodynamics, as well as the pharmacokinetic/pharmacodynamic relationships, were evaluated in xenografts, including an intracranially implanted melanoma model.Results: NMS-E973, representative of a novel isoxazole-derived class of Hsp90 inhibitors, binds Hsp90a with subnanomolar affinity and high selectivity towards kinases, as well as other ATPases. It possesses potent antiproliferative activity against tumor cell lines and a favorable pharmacokinetic profile, with selective retention in tumor tissue and ability to cross the BBB. NMS-E973 induces tumor shrinkage in different human tumor xenografts, and is highly active in models of resistance to kinase inhibitors. Moreover, consistent with its brain penetration, NMS-E973 is active also in an intracranially implanted melanoma model.Conclusions: Overall, the efficacy profile of NMS-E973 suggests a potential for development in different clinical settings, including tumors that have become resistant to molecular targeted agents, particularly in cases of tumors which reside beyond the BBB.

ATP Acyl Phosphate Reactivity Reveals Native Conformations of Hsp90 Paralogs and Inhibitor Target Engagement

“…In clinical trials, Hsp90 inhibitors have suffered from several types of toxicities, including hepatic, gastrointestinal, and ocular. 37 The reasons for these toxicities are not fully understood. While certain examples, like the hepatotoxicity of 17-AAG, are unlikely to be related to PMS2 inhibition based on our work, the prospect of off-target inhibition leading to other cases of toxicity warrants consideration.…”

Sparse labeling of proteins: Structural characterization from long range constraints

“…There are crystal structures of full length bacterial homologs, [25] [26] yeast homologs,[27] a canine ER homolog,[28] and a recently determined structure of the zebrafish TRAP1 (Lavery et al, 2013, under revision), as well as a number of individual domain structures including those of the human cytosolic homologs. [29–32] However, structures of full length proteins remain rare and structural characterization of domain reorganization on client binding remains a challenge[33, 34] (See Figure 1A for a homology model of TRAP1). Expression in a bacterial host with perdeuteration is possible, but the dimer, even without a client present, pushes the resolution limits of uniform labeling approaches.…”

Sulphoxythiocarbamates modify cysteine residues in HSP90 causing degradation of client proteins and inhibition of cancer cell proliferation

“…Activation of the heat shock response is a common feature of HSP90 inhibitors as HPSP90 is the major negative regulator of HSF1, and presents a major challenge in the development of HSP90 inhibitors and their clinical implementation as anticancer agents. Nonetheless, the destabilisation of mutant p53 and oncogenic kinases, which are overexpressed in tumours with high frequencies, represents an important mechanism of action of HSP90 inhibitors that have been shown to inhibit tumour growth in numerous preclinical cancer models, such as pancreatic, breast, lung, and melanoma, including intracranial metastases (Neckers, 2002; Williams et al , 2007; Moser et al , 2012; Fogliatto et al , 2013; Garon et al , 2013; Haarberg et al , 2013). The increased dependence on HSP90 and higher sensitivity to HSP90 inhibition of cancer cells in comparison with normal cells suggests a paradigm whereby HSP90 inhibitors may selectively target cancer cells while enhancing protection in normal cells via the upregulation of HSF1- and NRF2-dependent genes, collectively termed vitagenes (Calabrese et al , 2011).…”