Discovery of NMS-E973 as novel, selective and potent inhibitor of heat shock protein 90 (Hsp90).

Novel small molecule inhibitors of heat shock protein 90 (Hsp90) were discovered with the help of a fragment based drug discovery approach (FBDD) and subsequent optimization with a combination of structure guided design, parallel synthesis and application of medicinal chemistry principles. These efforts led to the identification of compound 18 (NMS-E973), which displayed significant efficacy in a human ovarian A2780 xenograft tumor model, with a mechanism of action confirmed in vivo by typical modulation of known Hsp90 client proteins, and with a favorable pharmacokinetic and safety profile.

NMS-E973, a novel synthetic inhibitor of Hsp90 with activity against multiple models of drug resistance to targeted agents, including intracranial metastases.

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 Hsp90α 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.

The generation of purinome-targeted libraries as a means to diversify ATP-mimetic chemical classes for lead finding.

The generation of novel chemotypes in support of our oncology research projects expanded in recent years from a canonical design of kinase-targeted compound libraries to a broader interpretation of purinome-targeted libraries (PTL) addressing the specificity of cancer relevant targets such as kinases and ATPases. Successful screening of structurally diverse ATP-binding targets requires compound libraries covering multiple design elements, which may include phosphate surrogate moieties in ATPase inhibitors or far reaching lipophilic residues stabilizing inactive kinase conformations. Here, we exemplify the design and preparation of drug-like combinatorial libraries and report significantly enhanced screening performance on purinomic targets. We compared overall hit rates of PTL with a simultaneously tested unbiased collection of 200,000 compounds and found consistent superiority of the targeted libraries in all cases. We also analyzed the performance of the largest targeted libraries in comparison with each other and often found striking differences in how a specific target responds to various chemotypes and to whole collections.

Inhibition of protein-protein interactions: the discovery of druglike beta-catenin inhibitors by combining virtual and biophysical screening.

The interaction between beta-catenin and Tcf family members is crucial for the Wnt signal transduction pathway, which is commonly mutated in cancer. This interaction extends over a very large surface area (4800 A(2)), and inhibiting such interactions using low molecular weight inhibitors is a challenge. However, protein surfaces frequently contain "hot spots," small patches that are the main mediators of binding affinity. By making tight interactions with a hot spot, a small molecule can compete with a protein. The Tcf3/Tcf4-binding surface on beta-catenin contains a well-defined hot spot around residues K435 and R469. A 17,700 compounds subset of the Pharmacia corporate collection was docked to this hot spot with the QXP program; 22 of the best scoring compounds were put into a biophysical (NMR and ITC) screening funnel, where specific binding to beta-catenin, competition with Tcf4 and finally binding constants were determined. This process led to the discovery of three druglike, low molecular weight Tcf4-competitive compounds with the tightest binder having a K(D) of 450 nM. Our approach can be used in several situations (e.g., when selecting compounds from external collections, when no biochemical functional assay is available, or when no HTS is envisioned), and it may be generally applicable to the identification of inhibitors of protein-protein interactions.

Potent and selective Aurora inhibitors identified by the expansion of a novel scaffold for protein kinase inhibition.

Potent and selective Aurora kinase inhibitors were identified from the combinatorial expansion of the 1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole bi-cycle, a novel and versatile scaffold designed to target the ATP pocket of protein kinases. The most potent compound reported in this study had an IC(50) of 0.027 microM in the enzymatic assay for Aur-A inhibition and IC(50)s between 0.05 microM and 0.5 microM for the inhibition of proliferation of different tumor cell lines.