Charles W. Hutchins

Discovery of ABT-267, a pan-genotypic inhibitor of HCV NS5A.

We describe here N-phenylpyrrolidine-based inhibitors of HCV NS5A with excellent potency, metabolic stability, and pharmacokinetics. Compounds with 2S,5S stereochemistry at the pyrrolidine ring provided improved genotype 1 (GT1) potency compared to the 2R,5R analogues. Furthermore, the attachment of substituents at the 4-position of the central N-phenyl group resulted in compounds with improved potency. Substitution with tert-butyl, as in compound 38 (ABT-267), provided compounds with low-picomolar EC50 values and superior pharmacokinetics. It was discovered that compound 38 was a pan-genotypic HCV inhibitor, with an EC50 range of 1.7-19.3 pM against GT1a, -1b, -2a, -2b, -3a, -4a, and -5a and 366 pM against GT6a. Compound 38 decreased HCV RNA up to 3.10 log10 IU/mL during 3-day monotherapy in treatment-naive HCV GT1-infected subjects and is currently in phase 3 clinical trials in combination with an NS3 protease inhibitor with ritonavir (r) (ABT-450/r) and an NS5B non-nucleoside polymerase inhibitor (ABT-333), with and without ribavirin.

Analgesic potential of TRPV1 antagonists

The discovery of TRPV1 antagonists as a new class of analgesic agents for the treatment of chronic pathological pain has been pursued aggressively across the pharmaceutical industry. This effort has led to the identification of several TRPV1 antagonists that have entered clinical trials, including ABT-102 (Abbott), SB-705498 (GSK), AMG-517 (Amgen), MK2295 (Merck/Neurogen), and GRC-6211 (Lilly/Glenmark). Using the published structures for ABT-102, SB-705498, AMG-517, and lead compounds representing six additional TRPV1 antagonist chemotypes, a pharmacophore model that describes the common structural features found in potent TRPV1 antagonists was established. The TRPV1 antagonist pharmacophore fits within the pore region of a TRPV1 receptor homology model, with critical hydrogen bond interactions proposed between the TRPV1 antagonist pharmacophore and Tyr 667 on helix six. In spite of the putative common binding site for all TRPV1 antagonists included in this particular TRPV1 pharmacophore, these ligands have demonstrated that they can still offer distinct pharmacological profiles, likely due to differences in their pharmacokinetic profiles. This is highlighted by differences in temperature elevation observed when comparing the clinical candidates ABT-102 and AMG-517.

Molecular Determinants of Species-Specific Activation or Blockade of TRPA1 Channels

TRPA1 is an excitatory, nonselective cation channel implicated in somatosensory function, pain, and neurogenic inflammation. Through covalent modification of cysteine and lysine residues, TRPA1 can be activated by electrophilic compounds, including active ingredients of pungent natural products (e.g., allyl isothiocyanate), environmental irritants (e.g., acrolein), and endogenous ligands (4-hydroxynonenal). However, how covalent modification leads to channel opening is not understood. Here, we report that electrophilic, thioaminal-containing compounds [e.g., CMP1 (4-methyl-N-[2,2,2-trichloro-1-(4-nitro-phenylsulfanyl)-ethyl]-benzamide)] covalently modify cysteine residues but produce striking species-specific effects [i.e., activation of rat TRPA1 (rTRPA1) and blockade of human TRPA1 (hTRPA1) activation by reactive and nonreactive agonists]. Through characterizing rTRPA1 and hTRPA1 chimeric channels and point mutations, we identified several residues in the upper portion of the S6 transmembrane domains as critical determinants of the opposite channel gating: Ala-946 and Met-949 of rTRPA1 determine channel activation, whereas equivalent residues of hTRPA1 (Ser-943 and Ile-946) determine channel block. Furthermore, side-chain replacements at these critical residues profoundly affect channel function. Therefore, our findings reveal a molecular basis of species-specific channel gating and provide novel insights into how TRPA1 respond to stimuli.

Potent, Selective Inhibitors of Protein Tyrosine Phosphatase 1B

We have previously reported a novel series of oxalyl-aryl-amino benzoic acid-based, catalytic site-directed, competitive, reversible protein tyrosine phosphatase 1B (PTP1B) inhibitors. With readily access to key intermediates, we utilized a solution phase parallel synthesis approach and rapidly identified a highly potent PTP1B inhibitor (19, K(i)=76 nM) with moderate selectivity (5-fold) over T-cell PTPase (TCPTP) through interacting with a second phosphotyrosine binding site (site 2) in the close proximity to the catalytic site.

Aryl tetrahydropyridine inhibitors of farnesyltransferase: glycine, phenylalanine and histidine derivatives.

Inhibitors of farnesyltransferase are effective against a variety of tumors in mouse models of cancer. Clinical trials to evaluate these agents in humans are ongoing. In our effort to develop new farnesyltransferase inhibitors, we have discovered a series of aryl tetrahydropyridines that incorporate substituted glycine, phenylalanine and histidine residues. The design, synthesis, SAR and biological properties of these compounds will be discussed.

Discovery and SAR of novel, potent and selective protein tyrosine phosphatase 1B inhibitors.

A salicylate second site binder was linked to three classes of phosphotyrosine mimetics to produce potent protein tyrosine phosphatase 1B (PTP1B) inhibitors which exhibit significant selectivity against other phosphatases including the most homologous member, TCPTP.

Ligand association rates to the inner-variable-domain of a dual-variable-domain immunoglobulin are significantly impacted by linker design

The DVD-IgTM protein is a dual-specific immunoglobulin. Each of the two arms of the molecule contains two variable domains, an inner variable domain and an outer variable domain linked in tandem, each with binding specificity for different targets or epitopes. One area of on-going research involves determining how the proximity of the outer variable domain affects the binding of ligands to the inner variable domain. To explore this area, we prepared a series of DVD-Ig proteins with binding specificities toward TNFα and an alternate therapeutic target. Kinetic measurements of TNFα binding to this series of DVD-Ig proteins were used to probe the effects of variable domain position and linker design on ligand on- and off-rates. We found that affinities for TNFα are generally lower when binding to the inner domain than to the outer domain and that this loss of affinity is primarily due to reduced association rate. This effect could be mitigated, to some degree, by linker design. We show several linker sequences that mitigate inner domain affinity losses in this series of DVD-Ig proteins. Moreover, we show that single chain proteolytic cleavage between the inner and outer domains, or complete outer domain removal, can largely restore inner domain TNFα affinity to that approaching the reference antibody. Taken together, these results suggest that a loss of affinity for inner variable domains in this set of DVD-Ig proteins may be largely driven by simple steric hindrance effects and can be reduced by careful linker design.

Preparation and characterization of N-(3-pyridinyl) spirocyclic diamines as ligands for nicotinic acetylcholine receptors

Several N-pyridin-3-yl spirobicyclic diamines, designed as conformationally restricted analogs of tebanicline (ABT-594), were synthesized as novel ligands for nicotinic acetylcholine receptors (nAChR). The spirocyclic compounds exhibited weaker binding affinity, than other constrained analogs in accord with a pharmacophore model. Nevertheless, some (1a, 1b) possessed (partial) agonist potencies comparable to nicotine at the alpha4beta2 subtype, but with greatly improved selectivity relative to the alpha3beta4* nAChR.

Design, synthesis, and neuraminidase inhibitory activity of GS-4071 analogues that utilize a novel hydrophobic paradigm.

Structure-based design has led to the synthesis of a novel analogue of GS-4071, an influenza neuraminidase inhibitor, in which the basic amino group has been replaced by a hydrophobic vinyl group. An X-ray co-crystal structure of the new inhibitor (K(i)=45 nM) bound to the active site shows that the vinyl group occupies the same subsite as the amino group in GS-4071.

Aryl tetrahydropyridine inhibitors of farnesyltransferase: bioavailable analogues with improved cellular potency.

Inhibitors of farnesyltransferase are effective against a variety of tumors in mouse models of cancer. Clinical trials to evaluate these agents in humans are ongoing. In our effort to develop new farnesyltransferase inhibitors, we have discovered bioavailable aryl tetrahydropyridines that are potent in cell culture. The design, synthesis, SAR and biological properties of these compounds will be discussed.