Janice C. Parker

Troglitazone: the discovery and development of a novel therapy for the treatment of Type 2 diabetes mellitus

Prior to the introduction of troglitazone, it had been more than 30 years since the last significant improvement in antidiabetic therapy. In view of the pressing need for more effective oral agents for the treatment of Type 2 diabetes mellitus, troglitazone was granted priority review by the FDA and was launched in the USA in 1997. The first of the thiazolidinedione insulin sensitizing agents, troglitazone was quickly followed by rosiglitazone and pioglitazone. The glitazones proved to be effective not only in lowering blood glucose, but also to have beneficial effects on cardiovascular risk. Troglitazone was subsequently withdrawn because of concerns about hepatotoxicity, which appears to be less of a problem with rosiglitazone and pioglitazone. Recent insights into the molecular mechanism of action of the glitazones, which are ligands for the peroxisome proliferator-activated receptors, open the prospect of designing more effective, selective and safer antidiabetic agents. This document will review the history of troglitazone from discovery through clinical development.

Glucose-dependent action of glucagon-like peptide-1(7-37) in vivo during short- or long-term administration

In vitro, truncated glucagon-like peptides [GLP-1(7-36)-amide and GLP-1(7-37)] increase insulin secretion in a glucose-dependent manner, and desensitization to the action of GLP-1(7-37) has been demonstrated acutely with high concentrations. The purpose of these studies was to evaluate the glucose dependency and threshold of GLP-1(7-37) action in normal rats and in a rat model of type II diabetes and to assess the effects of long-term administration in vivo. All studies were conducted in conscious catheterized rats. An intravenous (IV) infusion of GLP-1(7-37) at 0.5, 5, or 50 pmol/min/kg during the second hour of a 2-hour 11-mmol/L hyperglycemic clamp in Sprague-Dawley rats produced a dose-related enhancement of the glucose-induced increase in plasma insulin concentration. A 1-hour infusion of a submaximal dose of GLP-1(7-37) (5 pmol/min/kg IV) in fasted and fed Sprague-Dawley rats produced small transient increases in plasma insulin (incremental increases above basal, 72 +/- 27 and 96 +/- 28 pmol/L, respectively) and decreases in plasma glucose (to levels > or = 5.2 mmol/L). Infusion of GLP-1(7-37) (5 pmol/min/kg IV) during a hyperglycemic clamp at two sequentially increasing concentrations of glucose, 11 and 17 mmol/L, produced incremental increases in insulin of 600 and 1,200 pmol/L, respectively, relative to levels in clamped control rats. Similarly, infusion of GLP-1(7-37) (5 pmol/min/kg IV) in hyperinsulinemic, hyperglycemic Zucker diabetic fatty (ZDF) rats produced a transitory increase in plasma insulin concentration and normalized the plasma glucose concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the glucose transporter content of islet cell lines: Implications for glucose-stimulated insulin release

Glucose transport across the plasma membrane of mammalian cells is mediated by a family of homologous proteins. Each glucose transporter isoform has a specific tissue distribution which relates to that tissues demand for glucose. The beta-cells of pancreatic islets are known to express a distinct glucose transporter isoform, termed GLUT 2, which has a high Km for glucose. In this study, we examined the glucose transporter content of normal rat islets and three beta cell lines, beta-TC, HIT and RIN cells. We show that at the protein level, GLUT 2 is the only detectable transporter isoform in normal islets, and that all three cell lines also express detectable GLUT 2. In contrast, all three cell lines expressed high levels of GLUT 1, but this isoform was not detected in normal islets. Neither the native islets nor any of the cell lines expressed GLUT 3. The insulin-responsive glucose transporter GLUT 4 was detected at very low levels in beta-TC cells; to our knowledge, this is the only non-muscle or adipose cell line which expresses this isoform. We propose that the elevated level of GLUT 1 expression, together with a reduced expression of the high Km transporter GLUT 2, may account for the characteristic aberrant patterns of glucose-stimulated insulin release in cell lines derived from beta-cells.

(3,3-Difluoro-pyrrolidin-1-yl)-[(2S,4S)-(4-(4-pyrimidin-2-yl-piperazin-1-yl)-pyrrolidin-2-yl]-methanone: A potent, selective, orally active dipeptidyl peptidase IV inhibitor

A series of 4-substituted proline amides was synthesized and evaluated as inhibitors of dipeptidyl pepdidase IV for the treatment of type 2 diabetes. (3,3-Difluoro-pyrrolidin-1-yl)-[(2S,4S)-(4-(4-pyrimidin-2-yl-piperazin-1-yl)-pyrrolidin-2-yl]-methanone (5) emerged as a potent (IC(50) = 13 nM) and selective compound, with high oral bioavailability in preclinical species and low plasma protein binding. Compound 5, PF-00734200, was selected for development as a potential new treatment for type 2 diabetes.

Comparison of the glucose dependency of glucagon-like peptide-1(7–37) and glyburide in vitro and in vivo

The purpose of the present study was to compare the glucose dependency of the insulin secretagogue activity of the sulfonylurea, glyburide, versus that of glucagon-like peptide-1(7-37) [GLP-1(7-37)] in vitro and in vivo. In freshly isolated rat islets, maximally effective concentrations of glyburide (10 micromol/L) and GLP-1(7-37) (10 nmol/L) were equally effective in stimulating insulin secretion in the presence of 15 mmol/L glucose (2.4-fold increase relative to 15 nmol/L glucose alone). At 5 nmol/L glucose, both agents increased insulin secretion, but the effect for glyburide was threefold greater than for GLP-1(7-37) (122% and 41% increase in insulin secretion, respectively). In conscious catheterized rats infused with glucose at a variable rate to clamp plasma glucose concentration at 11 mmol/L, glyburide (1 mg/kg orally) and GLP -1(7-37) (infused intravenously [IV] at 5 pmol/min/kg) produced similar increase in insulin levels (1.8-fold relative to the respective vehicle controls) that were sustained through 60 minutes of measurement. These doses of GLP-1(7-37) and glyburide were then administered to fasted and fed rats (basal plasma glucose concentration, 5.8 and 7.3 mmol/L, respectively). Relative to the vehicle control group, GLP-1(7-37) infusion produced a transitory increase (30%) in plasma insulin concentration and a modest sustained decrease (10% to 20%) in glucose in both fasted and fed rats, whereas glyburide induced a sustained 2.4- and 1.7-fold increase in plasma insulin concentration in fasted and fed rats, respectively, and a 50% decrease in plasma glucose in both fasted and fed rats. Results of these studies demonstrate the higher glucose threshold for the insulin secretagogue activity of GLP-1(7-37) relative to glyburide in vitro and in vivo.

1-((3S,4S)-4-Amino-1-(4-substituted-1,3,5-triazin-2-yl) pyrrolidin-3-yl)-5,5-difluoropiperidin-2-one inhibitors of DPP-4 for the treatment of type 2 diabetes

A 3-amino-4-substituted pyrrolidine series of dipeptidyl peptidase IV (DPP-4) inhibitors was rapidly developed into a candidate series by identification of a polar valerolactam replacement for the lipophilic 2,4,5-trifluorophenyl pharmacophore. The addition of a gem-difluoro substituent to the lactam improved overall DPP-4 inhibition and an efficient asymmetric route to 3,4-diaminopyrrolidines was developed. Advanced profiling of a subset of analogs identified 5o with an acceptable human DPP-4 inhibition profile based on a rat PK/PD model and a projected human dose that was suitable for clinical development.

Discovery of triazolopyrimidine-based PDE8B inhibitors: Exceptionally ligand-efficient and lipophilic ligand-efficient compounds for the treatment of diabetes

PDE8B is a cAMP-specific isoform of the broader class of phosphodiesterases (PDEs). As no selective PDE8B inhibitors had been reported, a high throughput screen was run with the goal of identifying selective tools for exploring the potential therapeutic utility of PDE8B inhibition. Of the numerous hits, one was particularly attractive since it was amenable to rapid deconstruction leading to inhibitors with very high ligand efficiency (LE) and lipophilic ligand efficiency (LLE). These triazolopyrimidines were optimized for potency, selectivity and ADME properties ultimately leading to compound 42. This compound was highly potent and selective with good bioavailability and advanced into pre-clinical development.

Piperidinyl-2-phenethylamino inhibitors of DPP-IV for the treatment of Type 2 diabetes

A highly ligand efficient lead molecule was rapidly developed into a DPP-IV selective candidate series using focused small library synthesis. A significant hurdle for series advancement was genetic safety since some agents in this series impaired chromosome division that was detected using the in vitro micronucleus assay. A recently developed high-throughput imaging-based in vitro micronucleus assay enabled the identification of chemical space with a low probability of micronucleus activity. Advanced profiling of a subset within this space identified a compound with a clean safety profile, an acceptable human DPP-IV inhibition profile based on the rat PK/PD model and a projected human dose that was suitable for clinical development.

Glucagon-like peptide-1 and analogs: A structure/function analysis

Glucagon-like peptide-1 (GLP-1) is an effective insulin secretagogue with sustained efficacy, with therapeutic potential in treating diabetes [1], As a result there has been much interest is determining its’ receptor bound conformation for rational drug design. In our study, we have identified the important residues for binding by the substitution of amino acids at sites that seemed likely, from an examination of the amino acid sequence and from previously published observations. We have used NMR, using standard methods [2-4], in conjunction with measurements of functional bioactivity to define the receptor-binding structure of GLP-1.