Amelioration of PXR-mediated CYP3A4 induction by mGluR2 modulators.

This work describes the rational amelioration of Cytochrome P450 4/5 (CYP3A4/5) induction through the Pregnane-X Receptor (PXR) pathway in a series of compounds that modulate the metabotropic glutamate Receptor 2 (mGluR2) via an allosteric mechanism. The compounds were initially shown to induce CYP3A4/5 via the gold-standard induction assay measured in primary human hepatocytes. This was followed up by testing the compounds in a PXR assay which correlated well with the assay in primary cells. Further, one of the compounds was crystallized with PXR (pdb code 6DUP). Analysis of this co-crystal structure, together with previously published PXR co-crystal structures, lead to modification ideas. The compounds synthesized based on these ideas were shown not to be CYP3A4/5 inducers. The mGluR2 activity of the resulting compounds was maintained.

Selective inhibition of mutant isocitrate dehydrogenase 1 (IDH1) via disruption of a metal binding network by an allosteric small molecule.

Cancer-associated point mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) confer a neomorphic enzymatic activity: the reduction of α-ketoglutarate to d-2-hydroxyglutaric acid, which is proposed to act as an oncogenic metabolite by inducing hypermethylation of histones and DNA. Although selective inhibitors of mutant IDH1 and IDH2 have been identified and are currently under investigation as potential cancer therapeutics, the mechanistic basis for their selectivity is not yet well understood. A high throughput screen for selective inhibitors of IDH1 bearing the oncogenic mutation R132H identified compound 1, a bis-imidazole phenol that inhibits d-2-hydroxyglutaric acid production in cells. We investigated the mode of inhibition of compound 1 and a previously published IDH1 mutant inhibitor with a different chemical scaffold. Steady-state kinetics and biophysical studies show that both of these compounds selectively inhibit mutant IDH1 by binding to an allosteric site and that inhibition is competitive with respect to Mg(2+). A crystal structure of compound 1 complexed with R132H IDH1 indicates that the inhibitor binds at the dimer interface and makes direct contact with a residue involved in binding of the catalytically essential divalent cation. These results show that targeting a divalent cation binding residue can enable selective inhibition of mutant IDH1 and suggest that differences in magnesium binding between wild-type and mutant enzymes may contribute to the inhibitors' selectivity for the mutant enzyme.

Evaluation of cancer dependence and druggability of PRP4 kinase using cellular, biochemical, and structural approaches.

PRP4 kinase is known for its roles in regulating pre-mRNA splicing and beyond. Therefore, a wider spectrum of PRP4 kinase substrates could be expected. The role of PRP4 kinase in cancer is also yet to be fully elucidated. Attaining specific and potent PRP4 inhibitors would greatly facilitate the study of PRP4 biological function and its validation as a credible cancer target. In this report, we verified the requirement of enzymatic activity of PRP4 in regulating cancer cell growth and identified an array of potential novel substrates through orthogonal proteomics approaches. The ensuing effort in structural biology unveiled for the first time unique features of PRP4 kinase domain and its potential mode of interaction with a low molecular weight inhibitor. These results provide new and important information for further exploration of PRP4 kinase function in cancer.

X-ray crystallographic structure-based design of selective thienopyrazole inhibitors for interleukin-2-inducible tyrosine kinase.

Beginning with a screening hit, unique thienopyrazole-indole inhibitors of Itk (interleukin-2-inducible tyrosine kinase) were designed, synthesized, and crystallized in the target kinase. Although initial compounds were highly active in Itk, they were not selective. Increasing the steric bulk around a tertiary alcohol at the 5-indole position dramatically improved selectivity toward Lyk and Syk, but not Txk. Substitutions at the 3- and 4-indole positions gave less active compounds that remained poorly selective. A difluoromethyl substitution at the 5-position of the thienopyrazole led to a highly potent and selective compound. Phenyl at this position reduced activity and selectivity while pushing the side-chains of Lys-391 and Asp-500 away from the binding pocket. Novel and selective thienopyrazole inhibitors of Itk were designed as a result of combining structure-based design and medicinal chemistry.

Virtual Screening and X-ray Crystallography for Human Kallikrein 6 Inhibitors with an Amidinothiophene P1 Group.

A series of compounds with an amidinothiophene P1 group and a pyrrolidinone-sulphonamide scaffold linker was identified as potent inhibitors of human kallikrein 6 by structure-based virtual screening based on the union accessible binding space of serine proteases. As the first series of potent nonmechanism-based hK6 inhibitors, they may be used as tool compounds for target validation. An X-ray structure of a representative compound complexed with hK6, resolved at a resolution of 1.88 Å, revealed that the amidinothiophene moiety bound in the S1 pocket and the pyrrolidinone-sulphonamide linker projected the aromatic tail into the S' pocket.

Fragment screening of inhibitors for MIF tautomerase reveals a cryptic surface binding site.

In the course of a fragment screening campaign by in silico docking followed by X-ray crystallography, a novel binding site for migration inhibitory factor (MIF) inhibitors was demonstrated. The site is formed by rotation of the side-chain of Tyr-36 to reveal a surface binding site in MIF that is hydrophobic and surrounded by aromatic side-chain residues. The crystal structures of two small inhibitors that bind to this site and of a quinolinone inhibitor, that spans the canonical deep pocket near Pro-1 and the new surface binding site, have been solved. These results suggest new opportunities for structure-based design of MIF inhibitors.

Discovery of novel inhibitors for DHODH via virtual screening and X-ray crystallographic structures.

Amino-benzoic acid derivatives 1-4 were found to be inhibitors for DHODH by virtual screening, biochemical, and X-ray crystallographic studies. X-ray structures showed that 1 and 2 bind to DHODH as predicted by virtual screening, but 3 and 4 were found to be structurally different from the corresponding compounds initially identified by virtual screening.

Discovery of covalent inhibitors for MIF tautomerase via cocrystal structures with phantom hits from virtual screening.

Biochemical and X-ray crystallographic studies confirmed that hydroxyquinoline derivatives identified by virtual screening were actually covalent inhibitors of the MIF tautomerase. Adducts were formed by N-alkylation of the Pro-1 at the catalytic site with a loss of an amino group of the inhibitor.