Discovery and preclinical development of AR453588 as an anti-diabetic glucokinase activator.

Glucose flux through glucokinase (GK) controls insulin release from the pancreas in response to high levels of glucose. Flux through GK is also responsible for reducing hepatic glucose output. Since many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, identifying compounds that can activate GK could provide a therapeutic benefit. Herein we report the further structure activity studies of a novel series of glucokinase activators (GKA). These studies led to the identification of pyridine 72 as a potent GKA that lowered post-prandial glucose in normal C57BL/6J mice, and after 14d dosing in ob/ob mice.

A Next-Generation TRK Kinase Inhibitor Overcomes Acquired Resistance to Prior TRK Kinase Inhibition in Patients with TRK Fusion-Positive Solid Tumors.

Larotrectinib, a selective TRK tyrosine kinase inhibitor (TKI), has demonstrated histology-agnostic efficacy in patients with TRK fusion-positive cancers. Although responses to TRK inhibition can be dramatic and durable, duration of response may eventually be limited by acquired resistance. LOXO-195 is a selective TRK TKI designed to overcome acquired resistance mediated by recurrent kinase domain (solvent front and xDFG) mutations identified in multiple patients who have developed resistance to TRK TKIs. Activity against these acquired mutations was confirmed in enzyme and cell-based assays and in vivo tumor models. As clinical proof of concept, the first 2 patients with TRK fusion-positive cancers who developed acquired resistance mutations on larotrectinib were treated with LOXO-195 on a first-in-human basis, utilizing rapid dose titration guided by pharmacokinetic assessments. This approach led to rapid tumor responses and extended the overall duration of disease control achieved with TRK inhibition in both patients.Significance: LOXO-195 abrogated resistance in TRK fusion-positive cancers that acquired kinase domain mutations, a shared liability with all existing TRK TKIs. This establishes a role for sequential treatment by demonstrating continued TRK dependence and validates a paradigm for the accelerated development of next-generation inhibitors against validated oncogenic targets. Cancer Discov; 7(9); 963-72. ©2017 AACR.See related commentary by Parikh and Corcoran, p. 934This article is highlighted in the In This Issue feature, p. 920.

5-Alkyl-2-urea-Substituted Pyridines: Identification of Efficacious Glucokinase Activators with Improved Properties.

Two 1-(4-aryl-5-alkyl-pyridin-2-yl)-3-methylurea glucokinase activators were identified with robust in vivo efficacy. These two compounds possessed higher solubilities than the previously identified triaryl compounds (i.e., AM-2394). Structure-activity relationship studies are presented along with relevant pharmacokinetic and in vivo data.

Novel Series of Potent Glucokinase Activators Leading to the Discovery of AM-2394.

Glucokinase (GK) catalyzes the phosphorylation of glucose to glucose-6-phosphate. We present the structure-activity relationships leading to the discovery of AM-2394, a structurally distinct GKA. AM-2394 activates GK with an EC50 of 60 nM, increases the affinity of GK for glucose by approximately 10-fold, exhibits moderate clearance and good oral bioavailability in multiple animal models, and lowers glucose excursion following an oral glucose tolerance test in an ob/ob mouse model of diabetes.

C5-Alkyl-2-methylurea-Substituted Pyridines as a New Class of Glucokinase Activators.

Glucokinase (GK) activators represent a class of type 2 diabetes therapeutics actively pursued due to the central role that GK plays in regulating glucose homeostasis. Herein we report a novel C5-alkyl-2-methylurea-substituted pyridine series of GK activators derived from our previously reported thiazolylamino pyridine series. Our efforts in optimizing potency, enzyme kinetic properties, and metabolic stability led to the identification of compound 26 (AM-9514). This analogue showed a favorable combination of in vitro potency, enzyme kinetic properties, acceptable pharmacokinetic profiles in preclinical species, and robust efficacy in a rodent PD model.

Discovery of 2-pyridylureas as glucokinase activators.

Glucokinase (GK) is the rate-limiting step for insulin release from the pancreas in response to high levels of glucose. Flux through GK also contributes to reducing hepatic glucose output. Since many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, identifying compounds that can allosterically activate GK may address this issue. Herein we report the identification and initial optimization of a novel series of glucokinase activators (GKAs). Optimization led to the identification of 33 as a compound that displayed activity in an oral glucose tolerance test (OGTT) in normal and diabetic mice.

Characterization of a novel glucokinase activator in rat and mouse models.

Glucokinase (GK) is a hexokinase isozyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate. Glucokinase activators are being investigated as potential diabetes therapies because of their effects on hepatic glucose output and/or insulin secretion. Here, we have examined the efficacy and mechanisms of action of a novel glucokinase activator, GKA23. In vitro, GKA23 increased the affinity of rat and mouse glucokinase for glucose, and increased glucose uptake in primary rat hepatocytes. In vivo, GKA23 treatment improved glucose homeostasis in rats by enhancing beta cell insulin secretion and suppressing hepatic glucose production. Sub-chronic GKA23 treatment of mice fed a high-fat diet resulted in improved glucose homeostasis and lipid profile.

Identification of a new class of glucokinase activators through structure-based design.

Glucose flux through glucokinase (GK) controls insulin release from the pancreas in response to high glucose concentrations. Glucose flux through GK also contributes to reducing hepatic glucose output. Because many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, compounds that can activate GK may serve as effective treatments for type 2 diabetes. Herein we report the identification and initial optimization of a novel series of allosteric glucokinase activators (GKAs). We discovered an initial thiazolylamino pyridine-based hit that was optimized using a structure-based design strategy and identified 26 as an early lead. Compound 26 demonstrated a good balance of in vitro potency and enzyme kinetic parameters and demonstrated blood glucose reductions in oral glucose tolerance tests in both C57BL/6J mice and high-fat fed Zucker diabetic fatty rats.

ARRY-520, a novel KSP inhibitor with potent activity in hematological and taxane-resistant tumor models.

AIM: Profiling the efficacy and pharmacodynamic activity of the kinesin spindle protein (KSP) inhibitor ARRY-520 will aid the identification of responsive tumor types and pharmacodynamic profiles that correlate with activity. MATERIALS AND METHODS: In vivo activity was evaluated in a diverse panel of 16 different tumor xenograft models. Pharmacodynamic activity was evaluated in selected models. RESULTS: ARRY-520 had low nanomolar antiproliferative activity in tumor cell lines. Monopolar spindles were formed at active potencies. Partial or complete responses were observed in 13/16 xenograft models. Hematological tumors were particularly sensitive, with a 100% complete response rate in some models. Maintenance of mitotic block for a sufficient length of time for cells to lose survival signals and progress to apoptosis was a key component of the mechanism of activity. ARRY-520 was also active in several taxane resistant models. CONCLUSION: The data provide a rationale for clinical evaluation of the activity of ARRY-520 in hematological carcinomas and taxane-resistant tumors.

Synthesis, in vitro and in vivo activity of thiamine antagonist transketolase inhibitors.

Tumor cells extensively utilize the pentose phosphate pathway for the synthesis of ribose. Transketolase is a key enzyme in this pathway and has been suggested as a target for inhibition in the treatment of cancer. In a pharmacodynamic study, nude mice with xenografted HCT-116 tumors were dosed with 1 ('N3'-pyridyl thiamine'; 3-(6-methyl-2-amino-pyridin-3-ylmethyl)-5-(2-hydroxy-ethyl)-4-methyl-thiazol-3-ium chloride hydrochloride), an analog of thiamine, the co-factor of transketolase. Transketolase activity was almost completely suppressed in blood, spleen, and tumor cells, but there was little effect on the activity of the other thiamine-utilizing enzymes alpha-ketoglutarate dehydrogenase or glucose-6-phosphate dehydrogenase. Synthesis and SAR of transketolase inhibitors is described.

Non-charged thiamine analogs as inhibitors of enzyme transketolase.

Inhibition of the thiamine-utilizing enzyme transketolase (TK) has been linked with diminished tumor cell proliferation. Most thiamine antagonists have a permanent positive charge on the B-ring, and it has been suggested that this charge is required for diphosphorylation by thiamine pyrophosphokinase (TPPK) and binding to TK. We sought to make neutral thiazolium replacements that would be substrates for TPPK, while not necessarily needing thiamine transporters (ThTr1 and ThTr2) for cell penetration. The synthesis, SAR, and structure-based rationale for highly potent non-thiazolium TK antagonists are presented.

Prodrug thiamine analogs as inhibitors of the enzyme transketolase.

Transketolase, a key enzyme in the pentose phosphate pathway, has been suggested as a target for inhibition in the treatment of cancer. Compound 5a ('N3'-pyridyl thiamine'; 3-(6-methyl-2-amino-pyridin-3-ylmethyl)-5-(2-hydroxy-ethyl)-4-methyl-thiazol-3-ium chloride hydrochloride), an analog of the transketolase cofactor thiamine, is a potent transketolase inhibitor but suffers from poor pharmacokinetics due to high clearance and C(max) linked toxicity. An efficient way of improving the pharmacokinetic profile of 5a is to prepare oxidized prodrugs which are slowly reduced in vivo yielding longer, sustained blood levels of the drug. The synthesis of such prodrugs and their evaluation in rodent models is reported.

The kinetic model of the shikimate pathway as a tool to optimize enzyme assays for high-throughput screening.

Four-enzyme section of the shikimate pathway (Aro B, D, E, and K) of Streptococcus pneumoniae has been studied. Kinetic properties of the individual enzymes and three- and four-enzyme linked reactions have been characterized in vitro. On the basis of the data measured in spectrophotometric and LC-MS experiments, kinetic mechanisms of the enzymes have been suggested and all kinetic parameters have been identified. Kinetic models for these three- and four-enzyme sections of the shikimate pathway have been constructed and validated. The model of the four-enzyme section of shikimate pathway has been employed to design an inhibition-sensitive reconstituted pathway for a high-throughput screening effort on the shikimate pathway. It was demonstrated that using the model it was possible to optimize this reconstituted pathway in such a way to provide equal sensitivity of the enzymes to inhibition.

Indole naphthyridinones as inhibitors of bacterial enoyl-ACP reductases FabI and FabK.

Bacterial enoyl-ACP reductase (FabI) is responsible for catalyzing the final step of bacterial fatty acid biosynthesis and is an attractive target for the development of novel antibacterial agents. Previously we reported the development of FabI inhibitor 4 with narrow spectrum antimicrobial activity and in vivo efficacy against Staphylococcus aureus via intraperitoneal (ip) administration. Through iterative medicinal chemistry aided by X-ray crystal structure analysis, a new series of inhibitors has been developed with greatly increased potency against FabI-containing organisms. Several of these new inhibitors have potent antibacterial activity against multidrug resistant strains of S. aureus, and compound 30 demonstrates exceptional oral (po) in vivo efficacy in a S. aureus infection model in rats. While optimizing FabI inhibitory activity, compounds 29 and 30 were identified as having low micromolar FabK inhibitory activity, thereby increasing the antimicrobial spectrum of these compounds to include the FabK-containing pathogens Streptococcus pneumoniae and Enterococcus faecalis. The results described herein support the hypothesis that bacterial enoyl-ACP reductases are valid targets for antibacterial agents.

Characterization of Streptococcus pneumoniae enoyl-(acyl-carrier protein) reductase (FabK).

The enoyl-(acyl-carrier protein) (ACP) reductase catalyses the last step in each cycle of fatty acid elongation in the type II fatty acid synthase systems. An extensively characterized NADH-dependent reductase, FabI, is widely distributed in bacteria and plants, whereas the enoyl-ACP reductase, FabK, is a distinctly different member of this enzyme group discovered in Streptococcus pneumoniae. We were unable to delete the fabK gene from Strep. pneumoniae, suggesting that this is the only enoyl-ACP reductase in this organism. The FabK enzyme was purified and the biochemical properties of the reductase were examined. The visible absorption spectrum of the purified protein indicated the presence of a flavin cofactor that was identified as FMN by MS, and was present in a 1:1 molar ratio with protein. FabK specifically required NADH and the protein activity was stimulated by ammonium ions. FabK also exhibited NADH oxidase activity in the absence of substrate. Strep. pneumoniae belongs to the Bacillus / Lactobacillus / Streptococcus group that includes Staphylococcus aureus and Bacillus subtilis. These two organisms also contain FabK-related genes, suggesting that they may also express a FabK-like enoyl-ACP reductase. However, the genes did not complement a fabI (Ts) mutant and the purified flavoproteins were unable to reduce enoyl-ACP in vitro and did not exhibit NAD(P)H oxidase activity, indicating they were not enoyl-ACP reductases. The restricted occurrence of the FabK enoyl-ACP reductase may be related to the role of substrate-independent NADH oxidation in oxygen-dependent anaerobic energy metabolism.

Defining and combating the mechanisms of triclosan resistance in clinical isolates of Staphylococcus aureus.

The MICs of triclosan for 31 clinical isolates of Staphylococcus aureus were 0.016 micro g/ml (24 strains), 1 to 2 micro g/ml (6 strains), and 0.25 micro g/ml (1 strain). All the strains for which triclosan MICs were elevated (>0.016 micro g/ml) showed three- to fivefold increases in their levels of enoyl-acyl carrier protein (ACP) reductase (FabI) production. Furthermore, strains for which triclosan MICs were 1 to 2 micro g/ml overexpressed FabI with an F204C alteration. Binding studies with radiolabeled NAD(+) demonstrated that this change prevents the formation of the stable triclosan-NAD(+)-FabI complex, and both this alteration and its overexpression contributed to achieving MICs of 1 to 2 micro g/ml for these strains. Three novel, potent inhibitors of FabI (50% inhibitory concentrations, < or =64 nM) demonstrated up to 1,000-fold better activity than triclosan against the strains for which triclosan MICs were elevated. None of the compounds tested from this series formed a stable complex with NAD(+)-FabI. Consequently, although the overexpression of wild-type FabI gave rise to an increase in the MICs, as expected, overexpression of FabI with an F204C alteration did not cause an additional increase in resistance. Therefore, this work identifies the mechanisms of triclosan resistance in S. aureus, and we present three compounds from a novel chemical series of FabI inhibitors which have excellent activities against both triclosan-resistant and -sensitive clinical isolates of S. aureus.

Discovery of a novel and potent class of FabI-directed antibacterial agents.

Bacterial enoyl-acyl carrier protein (ACP) reductase (FabI) catalyzes the final step in each elongation cycle of bacterial fatty acid biosynthesis and is an attractive target for the development of new antibacterial agents. High-throughput screening of the Staphylococcus aureus FabI enzyme identified a novel, weak inhibitor with no detectable antibacterial activity against S. aureus. Iterative medicinal chemistry and X-ray crystal structure-based design led to the identification of compound 4 [(E)-N-methyl-N-(2-methyl-1H-indol-3-ylmethyl)-3-(7-oxo-5,6,7,8-tetrahydro-1,8-naphthyridin-3-yl)acrylamide], which is 350-fold more potent than the original lead compound obtained by high-throughput screening in the FabI inhibition assay. Compound 4 has exquisite antistaphylococci activity, achieving MICs at which 90% of isolates are inhibited more than 500 times lower than those of nine currently available antibiotics against a panel of multidrug-resistant strains of S. aureus and Staphylococcus epidermidis. Furthermore, compound 4 exhibits excellent in vivo efficacy in an S. aureus infection model in rats. Biochemical and genetic approaches have confirmed that the mode of antibacterial action of compound 4 and related compounds is via inhibition of FabI. Compound 4 also exhibits weak FabK inhibitory activity, which may explain its antibacterial activity against Streptococcus pneumoniae and Enterococcus faecalis, which depend on FabK and both FabK and FabI, respectively, for their enoyl-ACP reductase function. These results show that compound 4 is representative of a new, totally synthetic series of antibacterial agents that has the potential to provide novel alternatives for the treatment of S. aureus infections that are resistant to our present armory of antibiotics.

Discovery of aminopyridine-based inhibitors of bacterial enoyl-ACP reductase (FabI).

Bacterial enoyl-ACP reductase (FabI) catalyzes the final step in each cycle of bacterial fatty acid biosynthesis and is an attractive target for the development of new antibacterial agents. Our efforts to identify potent, selective FabI inhibitors began with screening of the GlaxoSmithKline proprietary compound collection, which identified several small-molecule inhibitors of Staphylococcus aureus FabI. Through a combination of iterative medicinal chemistry and X-ray crystal structure based design, one of these leads was developed into the novel aminopyridine derivative 9, a low micromolar inhibitor of FabI from S. aureus (IC(50) = 2.4 microM) and Haemophilus influenzae (IC(50) = 4.2 microM). Compound 9 has good in vitro antibacterial activity against several organisms, including S. aureus (MIC = 0.5 microg/mL), and is effective in vivo in a S. aureus groin abscess infection model in rats. Through FabI overexpressor and macromolecular synthesis studies, the mode of action of 9 has been confirmed to be inhibition of fatty acid biosynthesis via inhibition of FabI. Taken together, these results support FabI as a valid antibacterial target and demonstrate the potential of small-molecule FabI inhibitors for the treatment of bacterial infections.