Optimization of Pharmacokinetic and In Vitro Safety Profile of a Series of Pyridine Diamide Indirect AMPK Activators.

A set of focused analogues have been generated around a lead indirect adenosine monophosphate-activated kinase (AMPK) activator to improve the rat clearance of the molecule. Analogues were focused on inhibiting amide hydrolysis by the strategic placement of substituents that increased the steric environment about the secondary amide bond between 4-aminopiperidine and pyridine-5-carboxylic acid. It was found that placing substituents at position 3 of the piperidine ring and position 4 of the pyridine could all improve clearance without significantly impacting on-target potency. Notably, trans-3-fluoropiperidine 32 reduced rat clearance from above liver blood flow to 19 mL/min/kg and improved the hERG profile by attenuating the basicity of the piperidine moiety. Oral dosing of 32 activated AMPK in mouse liver and after 2 weeks of dosing improved glucose handling in a db/db mouse model of Type II diabetes as well as lowering fasted glucose and insulin levels.

Tuning the Reactivity of Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Activators for Optimal in Vivo Efficacy.

Dimethyl fumarate 1 is approved for the treatment of multiple sclerosis but is also associated with off-target activation of the niacin receptor. By using a tetrazolone or triazolone bioisostere approach to the fumarate and vinyl sulfone series of Nrf2 activators, we have optimized the electrophilicity of the double bond to tune the on-target Nrf2 activation with PK properties to achieve efficacy in animal models of multiple sclerosis. The study linked highly potent, highly electrophilic molecules to low plasma stability and, subsequently, limited efficacy. By contrast, a sulfonylvinyltriazolone 17 retains on-target potency but shows much weaker electrophilic potential. As a consequence, in vivo high exposures of 17 are obtained, resulting in efficacy in the EAE model similar to that observed for DMF. 17 (R079) is Ames negative, is not cytotoxic to cells, and shows little inhibition of either the niacin receptor or a panel of off-target receptors.

Structure activity relationships leading to the identification of the indirect activator of AMPK, R419.

Using an in-cell AMPK activation assay, we have developed structure-activity relationships around a hit pyridine dicarboxamide 5 that resulted in 40 (R419). A particular focus was to retain the on-target potency while also improving microsomal stability and reducing off-target activities, including hERG inhibition. We were able to show that removing a tertiary amino group from the piperazine unit of hit compound 5 improved microsomal stability while hERG inhibition was improved by modifying the substitution of the central core pyridine ring. The SAR resulted in 40, which continues to maintain on-target potency. Compound 40 was able to activate AMPK in vivo after oral administration and showed efficacy in animal models investigating activation of AMPK as a therapy for glucose control (both db/db and DIO mouse models).

Brain Permeable AMP-Activated Protein Kinase Activator R481 Raises Glycaemia by Autonomic Nervous System Activation and Amplifies the Counterregulatory Response to Hypoglycaemia in Rats.

Aim: We evaluated the efficacy of a novel brain permeable "metformin-like" AMP-activated protein kinase activator, R481, in regulating glucose homeostasis. Materials and Methods: We used glucose sensing hypothalamic GT1-7 neuronal cells and pancreatic αTC1.9 α-cells to examine the effect of R481 on AMPK pathway activation and cellular metabolism. Glucose tolerance tests and hyperinsulinemic-euglycemic and hypoglycemic clamps were used in Sprague-Dawley rats to assess insulin sensitivity and hypoglycemia counterregulation, respectively. Results: In vitro, we demonstrate that R481 increased AMPK phosphorylation in GT1-7 and αTC1.9 cells. In Sprague-Dawley rats, R481 increased peak glucose levels during a glucose tolerance test, without altering insulin levels or glucose clearance. The effect of R481 to raise peak glucose levels was attenuated by allosteric brain permeable AMPK inhibitor SBI-0206965. This effect was also completely abolished by blockade of the autonomic nervous system using hexamethonium. During hypoglycemic clamp studies, R481 treated animals had a significantly lower glucose infusion rate compared to vehicle treated controls. Peak plasma glucagon levels were significantly higher in R481 treated rats with no change to plasma adrenaline levels. In vitro, R481 did not alter glucagon release from αTC1.9 cells, but increased glycolysis. Non brain permeable AMPK activator R419 enhanced AMPK activity in vitro in neuronal cells but did not alter glucose excursion in vivo. Conclusions: These data demonstrate that peripheral administration of the brain permeable "metformin-like" AMPK activator R481 increases blood glucose by activation of the autonomic nervous system and amplifies the glucagon response to hypoglycemia in rats. Taken together, our data suggest that R481 amplifies the counterregulatory response to hypoglycemia by a central rather than a direct effect on the pancreatic α-cell. These data provide proof-of-concept that central AMPK could be a target for future drug development for prevention of hypoglycemia in diabetes.

AMPK mediates energetic stress-induced liver GDF15.

Growth differentiating factor-15 (GDF15) is an emerging target for the treatment of obesity and metabolic disease partly due to its ability to suppress food intake. GDF15 expression and secretion are thought to be regulated by a cellular integrated stress response, which involves endoplasmic reticulum (ER) stress. AMPK is another cellular stress sensor, but the relationship between AMPK, ER stress, and GDF15 has not been assessed in vivo. Wildtype (WT), AMPK ß1 deficient (AMPKß1-/- ), and CHOP-/- mice were treated with three distinct AMPK activators; AICAR, which is converted to ZMP mimicking the effects of AMP on the AMPKγ isoform, R419, which indirectly activates AMPK through inhibition of mitochondrial respiration, or A769662, a direct AMPK activator which binds the AMPKß1 isoform ADaM site causing allosteric activation. Following treatments, liver Gdf15, markers of ER-stress, AMPK activity, adenine nucleotides, circulating GDF15, and food intake were assessed. AICAR and R419 caused ER and energetic stress, increased GDF15 expression and secretion, and suppressed food intake. Direct activation of AMPK ß1 containing complexes by A769662 increased hepatic Gdf15 expression, circulating GDF15, and suppressed food intake, independent of ER stress. The effects of AICAR, R419, and A769662 on GDF15 were attenuated in AMPKß1-/- mice. AICAR and A769662 increased GDF15 to a similar extent in WT and CHOP-/- mice. Herein, we provide evidence that AMPK plays a role in mediating the induction of GDF15 under conditions of energetic stress in mouse liver in vivo.

Structures of AMP-activated protein kinase bound to novel pharmacological activators in phosphorylated, non-phosphorylated, and nucleotide-free states.

AMP-activated protein kinase (AMPK) is an attractive therapeutic target for managing metabolic diseases. A class of pharmacological activators, including Merck 991, binds the AMPK ADaM site, which forms the interaction surface between the kinase domain (KD) of the α-subunit and the carbohydrate-binding module (CBM) of the ß-subunit. Here, we report the development of two new 991-derivative compounds, R734 and R739, which potently activate AMPK in a variety of cell types, including ß2-specific skeletal muscle cells. Surprisingly, we found that they have only minor effects on direct kinase activity of the recombinant α1ß2γ1 isoform yet robustly enhance protection against activation loop dephosphorylation. This mode of activation is reminiscent of that of ADP, which activates AMPK by binding to the nucleotide-binding sites in the γ-subunit, more than 60 Å away from the ADaM site. To understand the mechanisms of full and partial AMPK activation, we determined the crystal structures of fully active phosphorylated AMPK α1ß1γ1 bound to AMP and R734/R739 as well as partially active nonphosphorylated AMPK bound to R734 and AMP and phosphorylated AMPK bound to R734 in the absence of added nucleotides at <3-Å resolution. These structures and associated analyses identified a novel conformational state of the AMPK autoinhibitory domain associated with partial kinase activity and provide new insights into phosphorylation-dependent activation loop stabilization in AMPK.

Developing DYRK inhibitors derived from the meridianins as a means of increasing levels of NFAT in the nucleus.

A structure-activity relationship has been developed around the meridianin scaffold for inhibition of Dyrk1a. The compounds have been focussed on the inhibition of kinase Dyrk1a, as a means to retain the transcription factor NFAT in the nucleus. NFAT is responsible for up-regulation of genes responsible for the induction of a slow, oxidative skeletal muscle phenotype, which may be an effective treatment for diseases where exercise capacity is compromised. The SAR showed that while strong Dyrk1a binding was possible with the meridianin scaffold the compounds have no effect on NFAT localisation, however, by moving from the indole to a 6-azaindole scaffold both potent Dyrk1a binding and increased NFAT residence time in the nucleus were obtained - properties not observed with the reported Dyrk1a inhibitors. One compound was shown to be effective in an ex vivo muscle fiber assay. The increased biological activity is thought to arise from the added interaction between the azaindole nitrogen and the lysine residue in the back pocket.

Developing structure-activity relationships from an HTS hit for inhibition of the Cks1-Skp2 protein-protein interaction.

Structure-activity relationships have been developed around 5-bromo-8-toluylsulfonamidoquinoline 1 a hit compound in an assay for the interaction of the E3 ligase Skp2 with Cks1, part of the SCF ligase complex. Disruption of this protein-protein interaction results in higher levels of CDK inhibitor p27, which can act as a tumor suppressor. The results of the SAR developed highlight the relationship between the sulfonamide and quinoline nitrogen, while also suggesting that an aryl substituent at the 5-position of the quinoline ring contributes to the potency in the interaction assay. Compounds showing potency in the interaction assay result in greater levels of p27 and have been shown to inhibit cell growth of two p27 sensitive tumor cell lines.

Global metabolite profiling of mice with high-fat diet-induced obesity chronically treated with AMPK activators R118 or metformin reveals tissue-selective alterations in metabolic pathways.

BACKGROUND: The novel small molecule R118 and the biguanide metformin, a first-line therapy for type 2 diabetes (T2D), both activate the critical cellular energy sensor 5'-AMP-activated protein kinase (AMPK) via modulation of mitochondrial complex I activity. Activation of AMPK results in both acute responses and chronic adaptations, which serve to restore energy homeostasis. Metformin is thought to elicit its beneficial effects on maintenance of glucose homeostasis primarily though impacting glucose and fat metabolism in the liver. Given the commonalities in their mechanisms of action and that R118 also improves glucose homeostasis in a murine model of T2D, the effects of both R118 and metformin on metabolic pathways in vivo were compared in order to determine whether R118 elicits its beneficial effects through similar mechanisms. RESULTS: Global metabolite profiling of tissues and plasma from mice with diet-induced obesity chronically treated with either R118 or metformin revealed tissue-selective effects of each compound. Whereas metformin treatment resulted in stronger reductions in glucose and lipid metabolites in the liver compared to R118, upregulation of skeletal muscle glycolysis and lipolysis was apparent only in skeletal muscle from R118-treated animals. Both compounds increased ß-hydroxybutyrate levels, but this effect was lost after compound washout. Metformin, but not R118, increased plasma levels of metabolites involved in purine metabolism. CONCLUSIONS: R118 treatment but not metformin resulted in increased glycolysis and lipolysis in skeletal muscle. In contrast, metformin had a greater impact than R118 on glucose and fat metabolism in liver tissue.

Exercise performance and peripheral vascular insufficiency improve with AMPK activation in high-fat diet-fed mice.

Intermittent claudication is a form of exercise intolerance characterized by muscle pain during walking in patients with peripheral artery disease (PAD). Endothelial cell and muscle dysfunction are thought to be important contributors to the etiology of this disease, but a lack of preclinical models that incorporate these elements and measure exercise performance as a primary end point has slowed progress in finding new treatment options for these patients. We sought to develop an animal model of peripheral vascular insufficiency in which microvascular dysfunction and exercise intolerance were defining features. We further set out to determine if pharmacological activation of 5'-AMP-activated protein kinase (AMPK) might counteract any of these functional deficits. Mice aged on a high-fat diet demonstrate many functional and molecular characteristics of PAD, including the sequential development of peripheral vascular insufficiency, increased muscle fatigability, and progressive exercise intolerance. These changes occur gradually and are associated with alterations in nitric oxide bioavailability. Treatment of animals with an AMPK activator, R118, increased voluntary wheel running activity, decreased muscle fatigability, and prevented the progressive decrease in treadmill exercise capacity. These functional performance benefits were accompanied by improved mitochondrial function, the normalization of perfusion in exercising muscle, increased nitric oxide bioavailability, and decreased circulating levels of the endogenous endothelial nitric oxide synthase inhibitor asymmetric dimethylarginine. These data suggest that aged, obese mice represent a novel model for studying exercise intolerance associated with peripheral vascular insufficiency, and pharmacological activation of AMPK may be a suitable treatment for intermittent claudication associated with PAD.

AMPK activation through mitochondrial regulation results in increased substrate oxidation and improved metabolic parameters in models of diabetes.

Modulation of mitochondrial function through inhibiting respiratory complex I activates a key sensor of cellular energy status, the 5'-AMP-activated protein kinase (AMPK). Activation of AMPK results in the mobilization of nutrient uptake and catabolism for mitochondrial ATP generation to restore energy homeostasis. How these nutrient pathways are affected in the presence of a potent modulator of mitochondrial function and the role of AMPK activation in these effects remain unclear. We have identified a molecule, named R419, that activates AMPK in vitro via complex I inhibition at much lower concentrations than metformin (IC50 100 nM vs 27 mM, respectively). R419 potently increased myocyte glucose uptake that was dependent on AMPK activation, while its ability to suppress hepatic glucose production in vitro was not. In addition, R419 treatment of mouse primary hepatocytes increased fatty acid oxidation and inhibited lipogenesis in an AMPK-dependent fashion. We have performed an extensive metabolic characterization of its effects in the db/db mouse diabetes model. In vivo metabolite profiling of R419-treated db/db mice showed a clear upregulation of fatty acid oxidation and catabolism of branched chain amino acids. Additionally, analyses performed using both (13)C-palmitate and (13)C-glucose tracers revealed that R419 induces complete oxidation of both glucose and palmitate to CO2 in skeletal muscle, liver, and adipose tissue, confirming that the compound increases mitochondrial function in vivo. Taken together, our results show that R419 is a potent inhibitor of complex I and modulates mitochondrial function in vitro and in diabetic animals in vivo. R419 may serve as a valuable molecular tool for investigating the impact of modulating mitochondrial function on nutrient metabolism in multiple tissues and on glucose and lipid homeostasis in diabetic animal models.

Enantioselective synthesis of cis-3-fluoropiperidin-4-ol, a building block for medicinal chemistry.

The first enantioselective route to both enantiomers of cis-1-Boc-3-fluoropiperidin-4-ol, a highly prized building block for medicinal chemistry, is reported. An enantioselective fluorination is employed, taking advantage of the methodology reported by MacMillan, which uses a modified cinchona alkaloid catalyst. In studying the fluorination reaction, we have shown that the catalyst can be replaced by commercially available primary amines, including α-methylbenzylamine, with similar levels of enantioselectivity. The piperidinols are readily crystallized to obtain enantiopure material.

The role of the 4''-hydroxyl on motilin agonist potency in the 9-dihydroerythromycin series.

The role of the erythromycin 4''-hydroxyl group has been explored on the motilin agonist potential in the 9-dihydroerythromycin series of motilides. The compounds show potencies 2- to 4-fold superior to the corresponding hydroxylated compounds. The relationship is maintained when the 9-hydroxyl is alkylated to generate the corresponding 4''-deoxy-9-O-acetamido-9-dihydroerythromycins. However, concomitant with this increase in potency is an increase in hERG inhibition.

9-Dihydroerythromycin ethers as motilin agonists--developing structure-activity relationships for potency and safety.

A series of derivatives of the amine of 9-dihydro-9-O-ethylamino-N-desmethyl-N-isopropyl erythromycin A derivatives were synthesized as motilin agonists. The compounds were developed for potency without showing antibacterial activity and inhibition of the hERG potassium channel. The formamide of the amide series was found to show the optimal combination of properties relative to carbamates, ureas, thioureas, and amines. This prompted an investigation of heterocyclic isosteres for the amide. In this series the triazole had the optimal combination of properties. From the study, two compounds met the criteria for detailed pharmacokinetic studies.

Structure-activity relationships of 9-substituted-9-dihydroerythromycin-based motilin agonists: optimizing for potency and safety.

A series of 9-dihydro-9-acetamido-N-desmethyl-N-isopropyl erythromycin A analogues and related derivatives was generated as motilin agonists. The compounds were optimized for potency while showing both minimal antibacterial activity and hERG inhibition. As the substituent on the amide was increased in lipophilicity the potency and hERG inhibition increased, while polar groups lowered potency, without significantly impacting hERG inhibition. The N-methyl acetamide 7a showed the optimal in vitro profile and was probed further by varying the chain length to the macrocycle as well as changing the macrocycle scaffold. 7a remained the compound with the best in vitro properties.

Investigating amine derivatives of ambruticin VS-5 and VS-4.

A structure-activity relationship around the amine group of the ambruticin VS series has been developed for antifungal activity. It was shown that the amine can be alkylated through reductive amination without loss of potency. However, if it is converted into either an amide, carbamate, or urea, a significant loss of potency is observed. Of the alkyl amines, small nonpolar groups are optimal for both potency and oral bioavailability. As a result of this study, one compound (KOS-2079) was taken into an animal efficacy model with success.

The structure activity relationship of discodermolide analogues.

The marine polyketide discodermolide is a member of a class of natural products that stabilize microtubules. Many analogues have been synthesized suggesting that few changes can be made to the internal carbon backbone. Both ends of the molecule, however, can be modified. The majority of analogues have been generated via modification of the lactone region. This suggests that significant simplifications can be made in this region provided that the lactone moiety is maintained.

Coumarin-derived discodermolide analogues possessing equivalent antiproliferative activity to the natural product--a further simplification of the lactone region.

Analogues of discodermolide in which the complete C-1 to C-7 fragment is replaced with a coumarin moiety display equivalent potency to that of the natural product.

A series of 23,24-dihydrodiscodermolide analogues with simplified lactone regions.

A collection of seven new 23,24-dihydrodiscodermolide analogues have been synthesized with modifications to the lactone ring, some of which show antiproliferative activities similar to discodermolide.