Amy L. Cox

Novel Small Molecule Glucagon-like Peptide-1 Receptor Agonist Stimulates Insulin Secretion in Rodents and from Human Islets

OBJECTIVE The clinical effectiveness of parenterally-administered glucagon-like peptide-1 (GLP-1) mimetics to improve glucose control in patients suffering from type 2 diabetes strongly supports discovery pursuits aimed at identifying and developing orally active, small molecule GLP-1 receptor agonists. The purpose of these studies was to identify and characterize novel nonpeptide agonists of the GLP-1 receptor. RESEARCH DESIGN AND METHODS Screening using cells expressing the GLP-1 receptor and insulin secretion assays with rodent and human islets were used to identify novel molecules. The intravenous glucose tolerance test (IVGTT) and hyperglycemic clamp characterized the insulinotropic effects of compounds in vivo. RESULTS Novel low molecular weight pyrimidine-based compounds that activate the GLP-1 receptor and stimulate glucose-dependent insulin secretion are described. These molecules induce GLP-1 receptor-mediated cAMP signaling in HEK293 cells expressing the GLP-1 receptor and increase insulin secretion from rodent islets in a dose-dependent manner. The compounds activate GLP-1 receptor signaling, both alone or in an additive fashion when combined with the endogenous GLP-1 peptide; however, these agonists do not compete with radiolabeled GLP-1 in receptor-binding assays. In vivo studies using the IVGTT and the hyperglycemic clamp in Sprague Dawley rats demonstrate increased insulin secretion in compound-treated animals. Further, perifusion assays with human islets isolated from a donor with type 2 diabetes show near-normalization of insulin secretion upon compound treatment. CONCLUSIONS These studies characterize the insulinotropic effects of an early-stage, small molecule GLP-1 receptor agonist and provide compelling evidence to support pharmaceutical optimization.

Hybrid insulin cocrystals for controlled release delivery

The ability to tailor the release profile of a drug by manipulating its formulation matrix offers important therapeutic advantages. We show here that human insulin can be cocrystallized at preselected ratios with the fully active lipophilically modified insulin derivative octanoyl-Nε-LysB29–human insulin (C8-HI). The cocrystal is analogous to the NPH (neutral protamine Hagedorn) crystalline complex formed with human insulin, which is commonly used as the long-acting insulin component of diabetes therapy. The in vitro and in vivo release rates of the cocrystal can be controlled by adjusting the relative proportions of the two insulin components. We identified a cocrystal composition comprising 75% C8-HI and 25% human insulin that exhibits near-ideal basal pharmacodynamics in somatostatin-treated beagle dogs. The dependence of release rate on cocrystal ratio provides a robust mechanism for modulating insulin pharmacodynamics. These findings show that a crystalline protein matrix may accommodate a chemical modification that alters the dissolution rate of the crystal in a therapeutically useful way, yet that is structurally innocuous enough to preserve the pharmaceutical integrity of the original microcrystalline entity and the pharmacological activity of the parent molecule.

Farnesoid X receptor agonist reduces serum asymmetric dimethylarginine levels through hepatic dimethylarginine dimethylaminohydrolase-1 gene regulation.

The farnesoid X receptor (FXR, NR1H4) is a bile acid-responsive nuclear receptor that plays critical roles in the transcriptional regulation genes involved in cholesterol, bile acid, triglyceride, and carbohydrate metabolism. By microarray analysis of hepatic genes from female Zucker diabetic fatty (ZDF) rats treated with the FXR agonist GW4064, we have identified dimethylarginine dimethylaminohydrolase-1 (DDAH1) as an FXR target gene. DDAH1 is a key catabolic enzyme of asymmetric dimethylarginine (ADMA), a major endogenous nitric-oxide synthase inhibitor. Sequence analysis of the DDAH1 gene reveals the presence of an FXR response element (FXRE) located 90 kb downstream of the transcription initiation site and within the first intron. Functional analysis of the putative FXRE demonstrated GW4064 dose-dependent transcriptional activation from the element, and we have demonstrated that the FXRE sequence binds the FXR-RXR heterodimer. In vivo administration of GW4064 to female ZDF rats promoted a dose-dependent and >6-fold increase in hepatic DDAH1 gene expression. The level of serum ADMA was reduced concomitantly. These findings provide a mechanism by which FXR may increase endothelium-derived nitric oxide levels through modulation of serum ADMA levels via direct regulation of hepatic DDAH1 gene expression. Thus, beneficial clinical outcomes of FXR agonist therapy may include prevention of atherosclerosis and improvement of the metabolic syndrome.

β-Cell Glucagon-Like Peptide-1 Receptor Contributes to Improved Glucose Tolerance After Vertical Sleeve Gastrectomy

Vertical sleeve gastrectomy (VSG) produces high rates of type 2 diabetes remission; however, the mechanisms responsible for this remain incompletely defined. Glucagon-like peptide-1 (GLP-1) is a gut hormone that contributes to the maintenance of glucose homeostasis and is elevated after VSG. VSG-induced increases in postprandial GLP-1 secretion have been proposed to contribute to the glucoregulatory benefits of VSG; however, previous work has been equivocal. In order to test the contribution of enhanced β-cell GLP-1 receptor (GLP-1R) signaling we used a β-cell-specific tamoxifen-inducible GLP-1R knockout mouse model. Male β-cell-specific Glp-1r(β-cell+/+) wild type (WT) and Glp-1r(β-cell-/-) knockout (KO) littermates were placed on a high-fat diet for 6 weeks and then switched to high-fat diet supplemented with tamoxifen for the rest of the study. Mice underwent sham or VSG surgery after 2 weeks of tamoxifen diet and were fed ad libitum postoperatively. Mice underwent oral glucose tolerance testing at 3 weeks and were euthanized at 6 weeks after surgery. VSG reduced body weight and food intake independent of genotype. However, glucose tolerance was only improved in VSG WT compared with sham WT, whereas VSG KO had impaired glucose tolerance relative to VSG WT. Augmentation of glucose-stimulated insulin secretion during the oral glucose tolerance test was blunted in VSG KO compared with VSG WT. Therefore, our data suggest that enhanced β-cell GLP-1R signaling contributes to improved glucose regulation after VSG by promoting increased glucose-stimulated insulin secretion.

Fully Implantable Arterial Blood Glucose Device for Metabolic Research Applications in Rats for Two Months

Background: Chronic continuous glucose monitoring options for animal research have been very limited due to various technical and biological challenges. We provide an evaluation of a novel telemetry device for continuous monitoring of temperature, activity, and plasma glucose levels in the arterial blood of rats for up to 2 months. Methods: In vivo testing in rats including oral glucose tolerance tests (OGTTs) and intraperitoneal glucose tolerance tests (IPGTTs) and ex vivo waterbath testing were performed to evaluate acute and chronic sensor performance. Animal studies were in accordance with the guidelines for the care and use of laboratory animals and approved by the corresponding animal care and use committees (Data Sciences International, Eli Lilly). Results: Results demonstrated the ability to record continuous measurements for 75 days or longer. Bench testing demonstrated a high degree of linearity over a range of 20-850 mg/dL with R2 = .998 for linear fit and .999 for second order fit (n = 8 sensors). Evaluation of 6 rats over 28 days with 52 daily and OGTT test strip measurements each resulted in mean error of 3.8% and mean absolute relative difference of 16.6%. Conclusions: This device provides significant advantages in the quality and quantity of data that can be obtained relative to existing alternatives such as intermittent blood sampling. These devices provide the opportunity to expand the understanding of both glucose metabolism and homeostasis and to work toward improved therapies and cures for diabetes.

Specific Reduction of Hepatic Glucose 6-Phosphate Transporter-1 Ameliorates Diabetes while Avoiding Complications of Glycogen Storage Disease

d-Glucose-6-phosphatase is a key regulator of endogenous glucose production, and its inhibition may improve glucose control in type 2 diabetes. Herein, 2′-O-(2-methoxy)ethyl-modified phosphorothioate antisense oligonucleotides (ASOs) specific to the glucose 6-phosphate transporter-1 (G6PT1) enabled reduction of hepatic d-Glu-6-phosphatase activity in diabetic ob/ob mice. Treatment with G6PT1 ASOs decreased G6PT1 expression, reduced G6PT1 activity, blunted glucagon-stimulated glucose production, and lowered plasma glucose concentration in a dose-dependent manner. In contrast to G6PT1 knock-out mice and patients with glycogen storage disease, excess hepatic and renal glycogen accumulation, hyperlipidemia, neutropenia, and elevations in plasma lactate and uric acid did not occur. In addition, hypoglycemia was not observed in animals during extended periods of fasting, and the ability of G6PT1 ASO-treated mice to recover from an exogenous insulin challenge was not impaired. Together, these results demonstrate that effective glucose lowering by G6PT1 inhibitors can be achieved without adversely affecting carbohydrate and lipid metabolism.

Comparative pharmacokinetics studies of immediate- and modified-release formulations of glipizide in pigs and dogs.

The utility of pigs as preclinical animals for pharmaceutical development was assessed by evaluating the pharmacokinetics and pharmacodynamics of glipizide (Glucotrol®) following oral administration of immediate-release (IR) and modified-release (MR) formulations. Doses of 10 and 30 mg were administered to six male pigs in a crossover design. Blood samples were collected at selected time-points up to 48 h after dose. Relative to the IR formulation, the time to reach the maximum concentration (t(max) ) was delayed with the MR formulation from 1.3 to 8.7 h with the 10 mg dose and to 6.2 h with the 30 mg dose. The relative bioavailability (BA) was approximately 92% at 10 mg and 79% at 30 mg dose. The area under the curve of the plasma concentration versus time curve (AUC) increased nearly proportionally with the dose. Interanimal coefficient of variation (CV) in AUC ranged from approximately 40% to 60%. Blood glucose results suggest that pigs demonstrate formulation-dependent response to glipizide. Compared with the pigs, the 10 mg MR formulation in dogs showed a higher AUC CV of approximately 80%, a t(max) of 5.5 h, and a lower relative BA of 18%. These data indicate that the MR formulation performed less consistently in dogs as compared with humans, whereas the porcine absorption kinetics and BA were consistent with published clinical data.

Insulin-XTEN® Exhibits a Size-Dependent Alteration in Tissue Action in Rats

To optimize the action of exogenously administered insulin, we employed XTEN® technology to create insulins with variably sized XTEN amino acid polymers. Recombinant fusions of XTEN polymers linked to insulin lispro with an A21G mutation were prepared in various amino acid lengths. Insulin-XTEN molecules demonstrated 15-fold lower potency in binding and receptor phosphorylation than insulin lispro but did not differ from each other. These insulin-XTEN molecules were equally effective in lowering blood glucose at a 100nmol/kg dose in diabetic Sprague-Dawley rats. Furthermore, the larger insulin-XTEN molecules had a longer duration of glucose lowering. Insulin-XTENs were compared to insulin lispro in rat euglycemic clamp studies, using insulin doses that would elicit steady plasma insulin concentrations and equivalent increases in glucose infusion rate. Insulin-mediated suppression of endogenous glucose production was not significantly different among any of the administered insulins. However, plasma free fatty acids and soleus muscle glucose uptake were significantly decreased in an XTEN size-dependent manner when compared to insulin lispro. Additional studies demonstrated equal hepatic pAkt accumulation in rats treated with insulin lispro or any of the insulin-XTENs, but revealed a significant XTEN size-dependent reduction in skeletal muscle pAkt in rats administered insulin-XTENs compared to insulin lispro. These data suggest a possible XTEN size-dependent regulation of insulin action and that the differing sizes of the XTEN polymer may convey preferential tissue action. In conclusion, XTEN technology may permit “tuning” of the glucodynamic effects of the insulin, leading to an enhanced time extension and improved hepatic and peripheral pharmacodynamic action that could more closely mimic the action of endogenously secreted insulin into the portal circulation. Disclosure M.E. Christe: Employee; Self; Eli Lilly and Company. D. Konkol: None. J. Friedrich: None. J. Jacobs: None. E. Hawkins: Employee; Self; Eli Lilly and Company. J. Moyers: Employee; Self; Eli Lilly and Company. Stock/Shareholder; Self; Eli Lilly and Company. C. Zhang: Employee; Self; Eli Lilly and Company. S.D. Kahl: Employee; Self; Eli Lilly and Company. H.E. Baker: None. A.L. Cox: None. R.J. Hansen: Employee; Self; Eli Lilly and Company. Stock/Shareholder; Self; Eli Lilly and Company. A. Sperry: Employee; Self; Eli Lilly and Company. Stock/Shareholder; Self; Eli Lilly and Company. M. Michael: Employee; Self; Eli Lilly and Company. Stock/Shareholder; Self; Eli Lilly and Company. Employee; Spouse/Partner; Eli Lilly and Company. Stock/Shareholder; Spouse/Partner; Eli Lilly and Company. V. Schellenberger: None. D. Baldwin: None. J.M. Beals: Employee; Self; Eli Lilly and Company. A. Korytko: None.