The discovery of two classes of heterocyclic dipeptidyl peptidase IV (DPP-4) inhibitors, pyrimidinones and pyrimidinediones, is described. After a single oral dose, these potent, selective, and noncovalent inhibitors provide sustained reduction of plasma DPP-4 activity and lowering of blood glucose in animal models of diabetes. Compounds 13a, 27b, and 27j were selected for development.

We used a number of receptor antagonists to determine which receptors mediate the effect of arginine vasopressin (AVP) and oxytocin (OT) on insulin release. We found that OT (10(-7) M) and AVP (10(-8) M) increased insulin release from the perfused rat pancreas with similar magnitude. The antagonist with potent V1b receptor-blocking activity, dP[Tyr(Me)2]AVP (10(-7) M), abolished the effect of OT and AVP, whereas the highly selective OT receptor antagonist L-366,948 (10(-6) M) did not change the effect of OT, nor did a V1a receptor antagonist, d(CH2)5[Tyr(Me)2]AVP (10(-7) M), change the effect of AVP. The insulin-releasing potency of OT was estimated as 9-fold less than that of AVP in RINm5F cells. Selected AVP and OT antagonists were used to study their antagonism on AVP- and OT-induced insulin release from RINm5F cells, and the order of potencies of antagonists was estimated as dP[Tyr(Me)2]AVP > d(CH2)5[D-Phe2,Ile4]AVP > SR-49059 > d(CH2)5[Tyr(Me)2]AVP > desGly9d(CH2)5[Tyr(Et)2]VAVP (WK-3-6) approximately L-366,948. These results were consistent with the V1b receptor antagonistic activities of the antagonists. d[D-3-Pal]VP, a V1b receptor agonist, increased insulin release dose dependently (10(-9) to 10(-6) M), and this effect was antagonized by dP[Tyr(Me)2]AVP but not by WK-3-6 (10(-6) M). These results suggested that the stimulatory effect of both OT and AVP on insulin release from beta-cells may be mediated by V1b, but not by V1a or OT receptors.

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؉ . We show that inhibition of the mNCE enhances mitochondrial oxidative metabolism and increases glucose-stimulated insulin secretion in rat islets and INS-1 cells. The benzothiazepine CGP37157 inhibited mNCE activity in INS-1 cells (50% inhibition at IC 50 ‫؍‬ 1.5 mol/l) and increased the glucose-induced rise in mitochondrial Ca 2؉ ([Ca 2؉ ] m ) 2.1 times. Cellular ATP content was increased by 13% in INS-1 cells and by 49% in rat islets by CGP37157 (1 mol/l). Krebs cycle flux was also stimulated by CGP37157 when glucose was present. Insulin secretion was increased in a glucosedependent manner by CGP37157 in both INS-1 cells and islets. In islets, CGP37157 increased insulin secretion dose dependently (half-maximal efficacy at EC 50 ‫؍‬ 0.06 mol/l) at 8 mmol/l glucose and shifted the glucose dose response curve to the left. In perifused islets, mNCE inhibition had no effect on insulin secretion at 2.8 mmol/l glucose but increased insulin secretion by 46% at 11 mmol/l glucose. The effects of CGP37157 could not be attributed to interactions with the plasma membrane sodium calcium exchanger, L-type calcium channels, ATP-sensitive K ؉ channels, or [Ca 2؉ ] m uniporter. In hyperglycemic clamp studies of Wistar rats, CGP37157 increased plasma insulin and C-peptide levels only during the hyperglycemic phase of the study. These results illustrate the potential utility of agents that affect mitochondrial metabolism as novel insulin secretagogues. Diabetes 52:965-973, 2003 M itochondrial oxidative metabolism plays an important role in the insulin secretory process in pancreatic ␤-cells. Stimulus-secretion coupling in the ␤-cell depends on the metabolism of glucose and the subsequent mitochondrial oxidative phosphorylation that generates ATP. ATP closes ATPsensitive K ϩ (K ATP ) channels, causing depolarization of the ␤-cell membrane, opening of voltage-dependent calcium channels, and Ca 2ϩ influx (1,2). Although two main processes, glycolysis and oxidative phosphorylation, are responsible for ATP synthesis during glucose metabolism, oxidative phosphorylation is the predominant pathway in the pancreatic ␤-cell (3,4). Insulin secretion induced by other secretagogues, such as leucine and glyceraldehydes, is also mediated by the production of ATP (5,6). The critical regulatory role of oxidative ATP production in glucose-stimulated insulin secretion (GSIS) is underscored by the observation that disrupting mitochondrial oxidative metabolism blocks nutrient-mediated insulin secretion. For example, inhibition of oxidative phosphorylation (7,8), blockade of NADH transport into mitochondria (9,10), or elimination of mitochondrial DNA from ␤-cells in vitro (11-15) or in vivo (16) all prevent GSIS. We tested the hypothesis that enhancing oxidative ATP production in response to glucose can increase insulin secretion. The normal feed-forward regulatory role of mitochondrial Ca 2ϩ ([Ca 2ϩ ] m ) in the ␤-cell was exploited to enhance oxidative metabolism.The influx of calcium into the cytoplasm of the ␤-cell in response to a nutrient l...