Inhibition of dipeptidyl peptidase-4 (DPP-4) activity has been shown to improve glycemic control in patients with type 2 diabetes by prolonging and potentiating the actions of incretin hormones. This study is designed to determine the effects of the DPP-4 inhibitor sitagliptin on improving islet function in a mouse model of insulin resistance and insulin secretion defects. ICR mice were pre-treated with high fat diet and a low dose of streptozotocin to induce insulin resistance and impaired insulin secretion respectively. Diabetic mice were treated with sitagliptin or the sulfonylurea agent glipizide as admixture to high fat diet for ten weeks. Sustained reduction of blood glucose, HbA(1c), circulating glucagon and improvement in oral glucose tolerance were observed in mice treated with sitagliptin. In contrast, glipizide improved glycemic control only during the early weeks and to a lesser degree compared to sitagliptin, and had no effect on circulating glucagon levels or glucose tolerance. The improvement in glycemic control in sitagliptin-treated mice was associated with a significant increase in glucose-dependent insulin secretion in both perfused pancreas and isolated islets. Importantly, in contrast to the lack of effect by glipizide, sitagliptin significantly restored beta and alpha cell mass as well as alpha/beta cell ratio. These data indicate that DPP-4 inhibition by sitagliptin provided better overall improvement of glycemic control compared to glipizide in the high fat diet / streptozotocin mouse model. The ability of sitagliptin to enhance islet cell function may offer insight into the potential for disease modification.

Dipeptidyl-peptidase IV (DPP-4) inhibitors inhibit the degradation of the incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). The first available DPP-4 inhibitors are sitagliptin and vildagliptin. These compounds are orally active and have been shown to be efficacious and well tolerated. Two additional DPP-4 inhibitors are under review, and there are several others in clinical development. This article gives an overview on the mechanism of action of DPP-4 inhibitors and focuses on their development and their important physiological actions with regard to the treatment of type 2 diabetes.

A new series of DPP-4 inhibitors derived from piperidine-fused benzimidazoles and imidazopyridines is described. Optimization of this class of DPP-4 inhibitors led to the discovery of imidazopyridine 34. The potency, selectivity, cross-species DMPK profiles, and in vivo efficacy of 34 is reported.

Probing with tool molecules, and by modeling and X-ray crystallography the binding modes of two structurally distinct series of DPP-4 inhibitors led to the discovery of a rare aromatic fluorine H-bond and the spatial requirement for better biaryl binding in the DPP-4 enzyme active site. These newly found binding elements were successfully incorporated into novel DPP-4 inhibitors.

Objectives: Acute activation of G protein-coupled Receptor 40 (GPR40) by free fatty acids (FFAs) or synthetic GPR40 agonists enhances insulin secretion. However, it is still a matter of debate if activation of GPR40 would be beneficial for the treatment of type 2 diabetes since chronic exposure to FFAs impairs islet function. We sought to evaluate the specific role of GPR40 in islets and its potential as a therapeutic target using compounds that specifically activate GPR40. Research Design and Methods: We developed a series of GPR40 selective small molecule agonists and studied their acute and chronic effects on glucose-dependent insulin secretion (GDIS) in isolated islets, as well as effects on blood glucose levels during intraperitoneal glucose tolerance tests (IPGTT) in wild-type (WT) and in GPR40 knock-out mice (GPR40-/-). Results: Small molecule GPR40 agonists significantly enhanced GDIS in isolated islets and improve glucose tolerance in WT mice, but not in GPR40-/- mice. While a 72-hour exposure to FFA in tissue culture significantly impaired GDIS in islets from both WT and GPR40-/- mice, similar exposure to the GPR40 agonist did not impair GDIS in islets from WT mice. Furthermore, the GPR40 agonist enhanced insulin secretion in perfused pancreata from neonatal streptozotocin-induced diabetic rats, and improved glucose levels in high fat diet-induced obese mice acutely and chronically. Conclusions: GPR40 does not mediate the chronic toxic effects of FFAs on islet function. Pharmacological activation of GPR40 may potentiate GDIS in humans and be beneficial on overall glucose control in patients with type 2 diabetes mellitus.

The synthesis, selectivity, rat pharmacokinetic profile, and drug metabolism profiles of a series of potent fluoroolefin-derived DPP-4 inhibitors (4) are reported. A radiolabeled fluoroolefin 33 was shown to possess a high propensity to form reactive metabolites, thus revealing a potential liability for this class of DPP-4 inhibitors.

Identification and validation of novel drug targets continues to be a major bottleneck in drug development, particularly for polygenic complex diseases such as type 2 diabetes. Here, the authors describe an approach that allows researchers to rapidly identify and validate potential drug targets by combining chemical tools and RNA interference technology. As a proof-of-concept study, the known mechanism Sigma LOPAC library was used to screen for glucose-dependent insulin secretion (GDIS) in INS-1 832/13 cells. In addition to several mechanisms that are known to regulate GDIS (such as cyclic adenosine monophosphate-specific phosphodiesterases, adrenoceptors, and Ca<Sup>2+</Sup> channels), the authors find that several of the dopamine receptor (DRD) antagonists significantly enhance GDIS, whereas DRD agonists profoundly inhibit GDIS. Subsequent siRNA studies in the same cell line indicate that knockdown of DRD2 enhanced GDIS. Furthermore, selective DRD2 antagonists and agonists also enhance or suppress, respectively, GDIS in isolated rat islets. The data support that the approach described here offers a rapid and effective way for target identification and validation.(Journal of Biomolecular Screening XXXX;xx-xx).

A series of substituted imidazopiperidine amides has been prepared and evaluated for inhibition of dipeptidyl peptidase IV (DPP-4). Substitution at the 1- and 3-positions produced increased selectivity for DPP-4 relative to DPP-8 and DPP-9. Compounds in this series had IC(50) values as low as 5.8nM for inhibition of DPP-4.

A novel series of 4-arylcyclohexylalanine DPP-4 inhibitors was synthesized and tested for inhibitory activity as well as selectivity over the related proline-specific enzymes DPP-8 and DPP-9. Optimization of this series led to 28 (DPP-4 IC(50)=4.8nM), which showed an excellent pharmacokinetic profile across several preclinical species. Evaluation of 28 in an oral glucose tolerance test demonstrated that this compound effectively reduced glucose excursion in lean mice.

Various beta-amino amides containing triazolopiperazine heterocycles have been prepared and evaluated as potent, selective, orally active dipeptidyl peptidase IV (DPP-4) inhibitors. These compounds display excellent oral bioavailability and good overall pharmacokinetic profiles in preclinical species. Moreover, in vivo efficacy in an oral glucose tolerance test in lean mice is demonstrated.