Checkpoints are present in all phases of the cell cycle and

Substituted guanines and pyrimidines were tested as inhibitors of cyclin B1/CDK1 and cyclin A3/CDK2 and soaked into crystals of monomeric CDK2. O6-Cyclohexylmethylguanine (NU2058) was a competitive inhibitor of CDK1 and CDK2 with respect to ATP (Ki values: CDK1, 5 +/- 1 microM; CDK2, 12 +/- 3 microM) and formed a triplet of hydrogen bonds (i.e., NH-9 to Glu 81, N-3 to Leu 83, and 2-NH2 to Leu 83). The triplet of hydrogen bonding and CDK inhibition was reproduced by 2,6-diamino-4-cyclohexylmethyloxy-5-nitrosopyrimidine (NU6027, Ki values: CDK1, 2.5 +/- 0.4 microM; CDK2, 1.3 +/- 0.2 microM). Against human tumor cells, NU2058 and NU6027 were growth inhibitory in vitro (mean GI50 values of 13 +/- 7 microM and 10 +/- 6 microM, respectively), with a pattern of sensitivity distinct from flavopiridol and olomoucine. These CDK inhibition and chemosensitivity data indicate that the distinct mode of binding of NU2058 and NU6027 has direct consequences for enzyme and cell growth inhibition.

BPT inhibitors can sensitize a resistant B. fragilis clinical isolate expressing metallo-beta-lactamase to the antibiotics imipenem or penicillin G but not to rifampicin.

S-Adenosyl-L-methionine (SAM) is an enzyme cofactor used in methyl transfer reactions and polyamine biosynthesis. The biosynthesis of SAM from ATP and L-methionine is performed by the methionine adenosyltransferase enzyme family (Mat; EC 2.5.1.6). Human methionine adenosyltransferase 2A (Mat2A), the extrahepatic isoform, is often deregulated in cancer. We identified a Mat2A inhibitor, PF-9366, that binds an allosteric site on Mat2A that overlaps with the binding site for the Mat2A regulator, Mat2B. Studies exploiting PF-9366 suggested a general mode of Mat2A allosteric regulation. Allosteric binding of PF-9366 or Mat2B altered the Mat2A active site, resulting in increased substrate affinity and decreased enzyme turnover. These data support a model whereby Mat2B functions as an inhibitor of Mat2A activity when methionine or SAM levels are high, yet functions as an activator of Mat2A when methionine or SAM levels are low. The ramification of Mat2A activity modulation in cancer cells is also described.

The conventional protein kinase C isoform, PKCII, is a signaling kinase activated during the hyperglycemic state and has been associated with the development of microvascular abnormalities associated with diabetes. PKCII, therefore, has been identified as a therapeutic target where inhibitors of its kinase activity are being pursued for treatment of microvascular-related diabetic complications. In this report, we describe the crystal structure of the catalytic domain of PKCbetaII complexed with an inhibitor at 2.6 A resolution. The kinase domain of PKCbetaII was cleaved and purified from full-length PKCbetaII expressed in baculovirus-infected insect cells. The overall kinase domain structure follows the classical bilobal fold and is in its fully activated conformation with three well-defined phosphorylated residues: Thr-500, Thr-641, and Ser-660. Different from the crystal structures of nonconventional PKC isoforms, the C-terminus of the PKCbetaII catalytic domain is almost fully ordered and features a novel alpha helix in the turn motif. An ATP-competitive inhibitor, 2-methyl-1H-indol-3-yl-BIM-1, was crystallized with the PKCbetaII catalytic domain as a dimer of two enzyme-inhibitor complexes. The bound inhibitor adopts a nonplanar conformation in the ATP-binding site, with the kinase domain taking on an intermediate, open conformation. This PKCbetaII-inhibitor complex represents the first structural description of any conventional PKC kinase domain. Given the pathogenic role of PKCbetaII in the development of diabetic complications, this structure can serve as a template for the rational design of inhibitors as potential therapeutic agents.

Protein kinase inhibitors represent an important and still emerging class of targeted therapeutic agents. Drug discovery and development strategies have explored numerous approaches to target the inhibition of protein kinase signaling. This review will highlight some of the strategies that have led to the successful clinical development of therapeutic protein kinase inhibitors, particularly as anticancer drugs. Some notable advances have been made in the development of novel protein and oligonucleotide-based biologics that target growth factor or receptor tyrosine kinases. Also, advances have been made in the rational design of small-molecule inhibitors that target unique kinase conformational forms and binding sites, and have specific kinase selectivity profiles. A review will also be given of some of the potential clinical toxicities and adverse side-effects associated with these kinase-targeted drugs. Therapeutic protein kinase inhibitors have been highly beneficial to cancer patients and offer the promise of future therapies for other diseases as well.

The free energies of dimer dissociation of the retroviral proteases (PRs) of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) were determined by measuring the effects of denaturants on the protein fluorescence upon the unfolding of the enzymes. HIV-1 PR was more stable to denaturation by chaotropes and extremes of pH and temperature than SIV PR, indicating that the former enzyme has greater conformational stability. The urea unfolding curves of both proteases were sigmoidal and single phase. The midpoints of the transition curves increased with increasing protein concentrations. These data were best described by and fitted to a two-state model in which folded dimers were in equilibrium with unfolded monomers. This denaturation model conforms to cases in which protein unfolding and dimer dissociation are concomitant processes in which folded monomers do not exist [Bowie, J. U., & Sauer, R. T. (1989) Biochemistry 28, 7140-7143]. Accordingly, the free energies of unfolding reflect the stabilities of the protease dimers, which for HIV-1 PR and SIV PR were, respectively, delta GuH2O = 14 +/- 1 kcal/mol (Ku = 39 pM) and 13 +/- 1 kcal/mol (Ku = 180 pM). The binding of a tight-binding, competitive inhibitor greatly stabilized HIV-1 PR toward urea-induced unfolding (delta GuH2O = 19.3 +/- 0.7 kcal/mol, Ku = 7.0 fM). There were also profound effects caused by adverse pH on the protein conformation for both HIV-1 PR and SIV PR, resulting in unfolding at pH values above and below the respective optimal ranges of 4.0-8.0 and 4.0-7.0

O(6)-substituted guanines are adenosine 5'-triphosphate (ATP) competitive inhibitors of CDK1/cyclin B1 and CDK2/cyclin A, the O(6) substituent occupying the kinase ribose binding site. Fifty-eight O(6)-substituted guanines were prepared to probe the ribose pocket, and the structures of four representative compounds bound to monomeric CDK2 were determined by X-ray crystallography. Optimum binding occurs with a moderately sized aliphatic O(6) substituent that packs tightly against the hydrophobic patch presented by the glycine loop, centered on Val18, an interaction promoted by the conformational restraints imposed in a cyclohexylmethyl or cyclohexenylmethyl ring. Structure-based design generated (R)-(2-amino-9H-purin-6-yloxymethyl)pyrrolidin-2-one (56), which reproduces the reported hydrogen bonds formed between ATP and Asp86 and Gln131 but failed to improve inhibitory potency. Thus, the parent compound O(6)-cyclohexylmethylguanine (NU2058, 25) is the preferred starting point for exploring other areas of the kinase active site.