Discovery of novel pyridinones as MGAT2 inhibitors for the treatment of metabolic disorders

Inhibition of monoacylglycerol transferase 2 (MGAT2) has recently emerged as a potential therapeutic strategy for the treatment of metabolic diseases such as obesity, diabetes and non-alcoholic steatohepatitis (NASH). Metabolism studies with our clinical lead (1) suggested variability in in vitro glucuronidation rates in liver microsomes across species, which made projection of human doses challenging. In addition, the observation of deconjugation of the C3-C4 double bond in the dihydropyridinone ring of 1 in solution had the potential to complicate its clinical development. This report describes our lead optimization efforts in a novel pyridinone series, exemplified by compound 33, which successfully addressed both of these potential issues.

Optimization of Physicochemical Properties of Pyrrolidine GPR40 AgoPAMs Results in a Differentiated Profile with Improved Pharmacokinetics and Reduced Off-Target Activities

GPR40 AgoPAMs are highly effective antidiabetic agents that have a dual mechanism of action, stimulating both glucose-dependent insulin and GLP-1 secretion. The early lipophilic, aromatic pyrrolidine and dihydropyrazole GPR40 AgoPAMs from our laboratory were highly efficacious in lowering plasma glucose levels in rodents but possessed off-target activities and triggered rebound hyperglycemia in rats at high doses. A focus on increasing molecular complexity through saturation and chirality in combination with reducing polarity for the pyrrolidine AgoPAM chemotype resulted in the discovery of compound 46, which shows significantly reduced off-target activities as well as improved aqueous solubility, rapid absorption, and linear PK. In vivo, compound 46 significantly lowers plasma glucose levels in rats during an oral glucose challenge yet does not demonstrate the reactive hyperglycemia effect at high doses that was observed with earlier GPR40 AgoPAMs.

Screening Hit to Clinical Candidate: Discovery of BMS-963272, a Potent, Selective MGAT2 Inhibitor for the Treatment of Metabolic Disorders

MGAT2 inhibition is a potential therapeutic approach for the treatment of metabolic disorders. High-throughput screening of the BMS internal compound collection identified the aryl dihydropyridinone compound 1 (hMGAT2 IC₅₀ = 175 nM) as a hit. Compound 1 had moderate potency against human MGAT2, was inactive vs mouse MGAT2 and had poor microsomal metabolic stability. A novel chemistry route was developed to synthesize aryl dihydropyridinone analogs to explore structure-activity relationship around this hit, leading to the discovery of potent and selective MGAT2 inhibitors 21f, 21s, and 28e that are stable to liver microsomal metabolism. After triaging out 21f due to its inferior in vivo potency, pharmacokinetics, and structure-based liabilities and tetrazole 28e due to its inferior channel liability profile, 21s (BMS-963272) was selected as the clinical candidate following demonstration of on-target weight loss efficacy in the diet-induced obese mouse model and an acceptable safety and tolerability profile in multiple preclinical species.

Unique pharmacology of a novel allosteric agonist/sensitizer insulin receptor monoclonal antibody

Objective

Insulin resistance is a key feature of Type 2 Diabetes (T2D), and improving insulin sensitivity is important for disease management. Allosteric modulation of the insulin receptor (IR) with monoclonal antibodies (mAbs) can enhance insulin sensitivity and restore glycemic control in animal models of T2D.

Methods

A novel human mAb, IRAB-A, was identified by phage screening using competition binding and surface plasmon resonance assays with the IR extracellular domain. Cell based assays demonstrated agonist and sensitizer effects of IRAB-A on IR and Akt phosphorylation, as well as glucose uptake. Lean and diet-induced obese mice were used to characterize single-dose in vivo pharmacological effects of IRAB-A; multiple-dose IRAB-A effects were tested in obese mice.

Results

In vitro studies indicate that IRAB-A exhibits sensitizer and agonist properties distinct from insulin on the IR and is translated to downstream signaling and function; IRAB-A bound specifically and allosterically to the IR and stabilized insulin binding. A single dose of IRAB-A given to lean mice rapidly reduced fed blood glucose for approximately 2 weeks, with concomitant reduced insulin levels suggesting improved insulin sensitivity. Phosphorylated IR (pIR) from skeletal muscle and liver were increased by IRAB-A; however, phosphorylated Akt (pAkt) levels were only elevated in skeletal muscle and not liver vs. control; immunochemistry analysis (IHC) confirmed the long-lived persistence of IRAB-A in skeletal muscle and liver. Studies in diet-induced obese (DIO) mice with IRAB-A reduced fed blood glucose and insulinemia yet impaired glucose tolerance and led to protracted insulinemia during a meal challenge.

Conclusion

Collectively, the data suggest IRAB-A acts allosterically on the insulin receptor acting non-competitively with insulin to both activate the receptor and enhance insulin signaling. While IRAB-A produced a decrease in blood glucose in lean mice, the data in DIO mice indicated an exacerbation of insulin resistance; these data were unexpected and suggested the interplay of complex unknown pharmacology. Taken together, this work suggests that IRAB-A may be an important tool to explore insulin receptor signaling and pharmacology.

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A novel anti-insulin receptor monoclonal antibody (IRAB-A) was identified that has both agonist and sensitizing activities.

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IRAB-A increases the receptor's affinity for insulin by binding to an allosteric site and does not compete with insulin.

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Mice injected once with IRAB-A show improved glycemia and reduced insulinemia, indicative of enhanced insulin sensitivity.

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In diet induced obese mice, the insulin sensitizing effect of IRAB-A appears to depend on the degree of insulin resistance.

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Chronic treatment of obese mice showed mixed effects on glucose homeostasis under normal fed or meal challenged conditions.

SGLT2 knockout prevents hyperglycemia and is associated with reduced pancreatic β-cell death in genetically obese mice

Inhibition of the sodium-glucose co-transporter type 2 (SGLT2) has received growing acceptance as a novel, safe and effective means to improve glycemic control in patients with type 2 diabetes. Inhibition of SGLT2 lowers the renal glucose threshold and reduces plasma glucose by promoting glucose excretion in urine. Both animal studies and clinical trials in man suggest that SGLT2 inhibition has the potential to improve pancreatic β-cell function by reducing glucose toxicity. However, there is limited data exploring how reducing glucotoxicity via SGLT2 inhibition affects rates of β-cell proliferation and death throughout life in the context of insulin resistance and type 2 diabetes. SGLT2^-/- mice were backcrossed to the db/db strain to produce littermate control db/db-SGLT2^+/+ and experimental db/db-SGLT2^-/- mice. Mice were euthanized at 5, 12 and 20 weeks of age to collect plasma for glucose, insulin, lipid and cytokine measures, and pancreata for histological analysis including determination of β-cell mass and rates of proliferation and death. SGLT2 deletion in db/db mice reduced plasma glucose as early as 5 weeks of age and continued throughout life without changes in plasma lipids or cytokines. Reduced plasma glucose levels occurred in parallel with an increase in the relative β-cell volume and reduced frequency of β-cell death, and no apparent change in rates of β-cell proliferation. These data add to a growing body of evidence demonstrating that improved glycemic control achieved through SGLT2 inhibition can preserve β-cell function and endogenous insulin secretion by reducing glucose toxicity and rates of β-cell death.

Discovery of Pyrrolidine-Containing GPR40 Agonists: Stereochemistry Effects a Change in Binding Mode

A novel series of pyrrolidine-containing GPR40 agonists is described as a potential treatment for type 2 diabetes. The initial pyrrolidine hit was modified by moving the position of the carboxylic acid, a key pharmacophore for GPR40. Addition of a 4-cis-CF₃ to the pyrrolidine improves the human GPR40 binding K_i and agonist efficacy. After further optimization, the discovery of a minor enantiomeric impurity with agonist activity led to the finding that enantiomers (R,R)-68 and (S,S)-68 have differential effects on the radioligand used for the binding assay, with (R,R)-68 potentiating the radioligand and (S,S)-68 displacing the radioligand. Compound (R,R)-68 activates both G_q-coupled intracellular Ca²⁺ flux and G_s-coupled cAMP accumulation. This signaling bias results in a dual mechanism of action for compound (R,R)-68, demonstrating glucose-dependent insulin and GLP-1 secretion in vitro. In vivo, compound (R,R)-68 significantly lowers plasma glucose levels in mice during an oral glucose challenge, encouraging further development of the series.

Novel Monoclonal Antibody Is an Allosteric Insulin Receptor Antagonist That Induces Insulin Resistance

A hallmark of type 2 diabetes is impaired insulin receptor (IR) signaling that results in dysregulation of glucose homeostasis. Understanding the molecular origins and progression of diabetes and developing therapeutics depend on experimental models of hyperglycemia, hyperinsulinemia, and insulin resistance. We present a novel monoclonal antibody, IRAB-B, that is a specific, potent IR antagonist that creates rapid and long-lasting insulin resistance. IRAB-B binds to the IR with nanomolar affinity and in the presence of insulin efficiently blocks receptor phosphorylation within minutes and is sustained for at least 3 days in vitro. We further confirm that IRAB-B antagonizes downstream signaling and metabolic function. In mice, a single dose of IRAB-B induces rapid onset of hyperglycemia within 6 h, and severe hyperglycemia persists for 2 weeks. IRAB-B hyperglycemia is normalized in mice treated with exendin-4, suggesting that this model can be effectively treated with a GLP-1 receptor agonist. Finally, a comparison of IRAB-B with the IR antagonist S961 shows distinct antagonism in vitro and in vivo. IRAB-B appears to be a powerful tool to generate both acute and chronic insulin resistance in mammalian models to elucidate diabetic pathogenesis and evaluate therapeutics.

Carcinogenicity risk assessment supports the chronic safety of dapagliflozin, an inhibitor of sodium-glucose co-transporter 2, in the treatment of type 2 diabetes mellitus

INTRODUCTION

Dapagliflozin is a selective inhibitor of the sodium-glucose co-transporter 2 (SGLT2) that increases urinary glucose excretion to reduce hyperglycemia in the treatment of type 2 diabetes mellitus. A robust carcinogenicity risk assessment was undertaken to assess the chronic safety of dapagliflozin and SGLT2 inhibition.

METHODS

Genotoxicity potential of dapagliflozin and its metabolites was assessed in silico, in vitro, and in vivo. Dapagliflozin was administered daily by oral gavage to mice, rats, and dogs to evaluate carcinogenicity risks, including the potential for tumor promotion. SGLT2(-/-) mice were observed to evaluate the effects of chronic glucosuria. The effects of dapagliflozin and increased glucose levels on a panel of human bladder transitional cell carcinoma (TCC) cell lines were also evaluated in vitro and in an in vivo xenograft model.

RESULTS

Dapagliflozin and its metabolites were not genotoxic. In CD-1 mice and Sprague-Dawley rats treated for up to 2 years at ≥100× human clinical exposures, dapagliflozin showed no differences versus controls for tumor incidence, time to onset for background tumors, or urinary bladder proliferative/preneoplastic lesions. No tumors or preneoplastic lesions were observed in dogs over 1 year at >3,000× the clinical exposure of dapagliflozin or in SGLT2(-/-) mice observed over 15 months. Transcription profiling in Zucker diabetic fatty rats showed that 5-week dapagliflozin treatment did not induce tumor promoter-associated or cell proliferation genes. Increasing concentrations of glucose, dapagliflozin, or its primary metabolite, dapagliflozin 3-O-glucuronide, did not affect in vitro TCC proliferation rates and dapagliflozin did not enhance tumor growth in nude mice heterotopically implanted with human bladder TCC cell lines.

CONCLUSION

A multitude of assessments of tumorigenicity risk consistently showed no effects, suggesting that selective SGLT2 inhibition and, specifically, dapagliflozin are predicted to not be associated with increased cancer risk.

Nonclinical Toxicology Assessments Support the Chronic Safety of Dapagliflozin, a First-in-Class Sodium-Glucose Cotransporter 2 Inhibitor

Dapagliflozin, a first-in-class, selective inhibitor of sodium-glucose cotransporter 2 (SGLT2), promotes urinary glucose excretion to reduce hyperglycemia for the treatment of type 2 diabetes. A series of nonclinical studies were undertaken to evaluate dapagliflozin in species where it was shown to have pharmacologic activity comparable with that in humans at doses that resulted in supratherapeutic exposures. In vitro screening (>300 targets; 10 μmol/L) indicated no significant off-target activities for dapagliflozin or its primary human metabolite. Once daily, orally administered dapagliflozin was evaluated in Sprague-Dawley rats (≤6 months) and in beagle dogs (≤1 year) at exposures >5000-fold those observed at the maximum recommended human clinical dose (MRHD; 10 mg). Anticipated, pharmacologically mediated effects of glucosuria, osmotic diuresis, and mild electrolyte loss were observed, but there were no adverse effects at clinically relevant exposures, including in the kidneys or urogenital tract. The SGLT2−/− mice, which show chronic glucosuria, and dapagliflozin-treated, wild-type mice exhibited similar safety profiles. In rats but not dogs, dapagliflozin at >2000-fold MRHD exposures resulted in tissue mineralization and trabecular bone accretion. Investigative studies suggested that the effect was not relevant to human safety, since it was partially related to off-target inhibition of SGLT1, which was observed only at high doses of dapagliflozin and resulted in intestinal glucose malabsorption and increased intestinal calcium absorption. The rigorous assessment of supra- and off-target dapagliflozin pharmacology in nonclinical species allowed for a thorough evaluation of potential toxicity, providing us with confidence in its safety in patients with diabetes.

Targeting the kidney and glucose excretion with dapagliflozin: preclinical and clinical evidence for SGLT2 inhibition as a new option for treatment of type 2 diabetes mellitus

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a novel class of glucuretic, antihyperglycemic drugs that target the process of renal glucose reabsorption and induce glucuresis independently of insulin secretion or action. In patients with type 2 diabetes mellitus, SGLT2 inhibitors have been found to consistently reduce measures of hyperglycemia, including hemoglobin A1c, fasting plasma glucose, and postprandial glucose, throughout the continuum of disease. By inducing the renal excretion of glucose and its associated calories, SGLT2 inhibitors reduce weight and have the potential to be disease modifying by addressing the caloric excess that is believed to be one of the root causes of type 2 diabetes mellitus. Additional benefits, including the possibility for combination with insulin-dependent antihyperglycemic drugs, a low potential for hypoglycemia, and the ability to reduce blood pressure, were anticipated from the novel mechanism of action and have been demonstrated in clinical studies. Mechanism-related risks include an increased incidence of urinary tract and genital infections and the possibility of over-diuresis in volume-sensitive patients. Taken together, the results of Phase III clinical studies generally point to a positive benefit-risk ratio across the continuum of diabetes patients. To date, data on dapagliflozin, a selective SGLT2 inhibitor in development, demonstrate that the kidney is an efficacious and safe target for therapy, and that SGLT2 inhibition may have benefits for patients with type 2 diabetes mellitus beyond glycemic control.

SGLT2 deletion improves glucose homeostasis and preserves pancreatic beta-cell function

OBJECTIVE

Inhibition of the Na(+)-glucose cotransporter type 2 (SGLT2) is currently being pursued as an insulin-independent treatment for diabetes; however, the behavioral and metabolic consequences of SGLT2 deletion are unknown. Here, we used a SGLT2 knockout mouse to investigate the effect of increased renal glucose excretion on glucose homeostasis, insulin sensitivity, and pancreatic β-cell function.

RESEARCH DESIGN AND METHODS

SGLT2 knockout mice were fed regular chow or a high-fat diet (HFD) for 4 weeks, or backcrossed onto the db/db background. The analysis used metabolic cages, glucose tolerance tests, euglycemic and hyperglycemic clamps, as well as isolated islet and perifusion studies.

RESULTS

SGLT2 deletion resulted in a threefold increase in urine output and a 500-fold increase in glucosuria, as well as compensatory increases in feeding, drinking, and activity. SGLT2 knockout mice were protected from HFD-induced hyperglycemia and glucose intolerance and had reduced plasma insulin concentrations compared with controls. On the db/db background, SGLT2 deletion prevented fasting hyperglycemia, and plasma insulin levels were also dramatically improved. Strikingly, prevention of hyperglycemia by SGLT2 knockout in db/db mice preserved pancreatic β-cell function in vivo, which was associated with a 60% increase in β-cell mass and reduced incidence of β-cell death.

CONCLUSIONS

Prevention of renal glucose reabsorption by SGLT2 deletion reduced HFD- and obesity-associated hyperglycemia, improved glucose intolerance, and increased glucose-stimulated insulin secretion in vivo. Taken together, these data support SGLT2 inhibition as a viable insulin-independent treatment of type 2 diabetes.

Quantitative PCR tissue expression profiling of the human SGLT2 gene and related family members

SGLT2 (for "Sodium GLucose coTransporter" protein 2) is the major protein responsible for glucose reabsorption in the kidney and its inhibition has been the focus of drug discovery efforts to treat type 2 diabetes. In order to better clarify the human tissue distribution of expression of SGLT2 and related members of this cotransporter class, we performed TaqMan™ (Applied Biosystems, Foster City, CA, USA) quantitative polymerase chain reaction (PCR) analysis of SGLT2 and other sodium/glucose transporter genes on RNAs from 72 normal tissues from three different individuals. We consistently observe that SGLT2 is highly kidney specific while SGLT5 is highly kidney abundant; SGLT1, sodium-dependent amino acid transporter (SAAT1), and SGLT4 are highly abundant in small intestine and skeletal muscle; SGLT6 is expressed in the central nervous system; and sodium myoinositol cotransporter is ubiquitously expressed across all human tissues.

The novel sodium glucose transporter 2 inhibitor dapagliflozin sustains pancreatic function and preserves islet morphology in obese, diabetic rats

AIMS

To investigate whether glucose lowering with the selective sodium glucose transporter 2 (SGLT2) inhibitor dapagliflozin would prevent or reduce the decline of pancreatic function and disruption of normal islet morphology.

METHODS

Female Zucker diabetic fatty (ZDF) rats, 7-8 weeks old, were placed on high-fat diet. Dapagliflozin (1 mg/kg/day, p.o.) was administered for ∼33 days either from initiation of high-fat diet or when rats were moderately hyperglycaemic. Insulin sensitivity and pancreatic function were evaluated using a hyperglycaemic clamp in anaesthetized animals (n = 5-6); β-cell function was quantified using the disposition index (DI) to account for insulin resistance compensation. Pancreata from a matched subgroup (n = 7-8) were fixed and β-cell mass and islet morphology investigated using immunohistochemical methods.

RESULTS

Dapagliflozin, administered from initiation of high-fat feeding, reduced the development of hyperglycaemia; after 24 days, blood glucose was 8.6 ± 0.5 vs. 13.3 ± 1.3 mmol/l (p < 0.005 vs. vehicle) and glycated haemoglobin 3.6 ± 0.1 vs. 4.8 ± 0.26% (p < 0.003 vs. vehicle). Dapagliflozin improved insulin sensitivity index: 0.08 ± 0.01 vs. 0.02 ± 0.01 in obese controls (p < 0.03). DI was improved to the level of lean control rats (dapagliflozin 0.29 ± 0.04; obese control 0.15 ± 0.01; lean 0.28 ± 0.01). In dapagliflozin-treated rats, β-cell mass was less variable and significant improvement in islet morphology was observed compared to vehicle-treated rats, although there was no change in mean β-cell mass with dapagliflozin. Results were similar when dapagliflozin treatment was initiated when animals were already moderately hyperglycaemic.

CONCLUSION

Sustained glucose lowering with dapagliflozin in this model of type 2 diabetes prevented the continued decline in functional adaptation of pancreatic β-cells.

Eleven amino acid glucagon-like peptide-1 receptor agonists with antidiabetic activity

Glucagon-like peptide 1 (GLP-1) is a 30 or 31 amino acid peptide hormone that contributes to the physiological regulation of glucose homeostasis and food intake. Herein, we report the discovery of a novel class of 11 amino acid GLP-1 receptor agonists. These peptides consist of a structurally optimized 9-mer, which is closely related to the N-terminal 9 amino acids of GLP-1, linked to a substituted C-terminal biphenylalanine (BIP) dipeptide. SAR studies resulted in 11-mer GLP-1R agonists with similar in vitro potency to the native 30-mer. Peptides 21 and 22 acutely reduced plasma glucose excursions and increased plasma insulin concentrations in a mouse model of diabetes. These peptides also showed sustained exposures over several hours in mouse and dog models. The described 11-mer GLP-1 receptor agonists represent a new tool in further understanding GLP-1 receptor pharmacology that may lead to novel antidiabetic agents.

In vitro characterization and pharmacokinetics of dapagliflozin (BMS-512148), a potent sodium-glucose cotransporter type II inhibitor, in animals and humans

(2S,3R,4R,5S,6R)-2-(3-(4-Ethoxybenzyl)-4-chlorophenyl)-6-hydroxymethyl-tetrahydro-2H-pyran-3,4,5-triol (dapagliflozin; BMS-512148) is a potent sodium-glucose cotransporter type II inhibitor in animals and humans and is currently under development for the treatment of type 2 diabetes. The preclinical characterization of dapagliflozin, to allow compound selection and prediction of pharmacological and dispositional behavior in the clinic, involved Caco-2 cell permeability studies, cytochrome P450 (P450) inhibition and induction studies, P450 reaction phenotyping, metabolite identification in hepatocytes, and pharmacokinetics in rats, dogs, and monkeys. Dapagliflozin was found to have good permeability across Caco-2 cell membranes. It was found to be a substrate for P-glycoprotein (P-gp) but not a significant P-gp inhibitor. Dapagliflozin was not found to be an inhibitor or an inducer of human P450 enzymes. The in vitro metabolic profiles of dapagliflozin after incubation with hepatocytes from mice, rats, dogs, monkeys, and humans were qualitatively similar. Rat hepatocyte incubations showed the highest turnover, and dapagliflozin was most stable in human hepatocytes. Prominent in vitro metabolic pathways observed were glucuronidation, hydroxylation, and O-deethylation. Pharmacokinetic parameters for dapagliflozin in preclinical species revealed a compound with adequate oral exposure, clearance, and elimination half-life, consistent with the potential for single daily dosing in humans. The pharmacokinetics in humans after a single dose of 50 mg of [(14)C]dapagliflozin showed good exposure, low clearance, adequate half-life, and no metabolites with significant pharmacological activity or toxicological concern.

Aglycone exploration of C-arylglucoside inhibitors of renal sodium-dependent glucose transporter SGLT2

Inhibition of sodium-dependent glucose transporter 2 (SGLT2), the transporter that is responsible for renal re-uptake of glucose, leads to glucosuria in animals. SGLT-mediated glucosuria provides a mechanism to shed excess plasma glucose to ameliorate diabetes-related hyperglycemia and associated complications. The current study demonstrates that the proper relationship of a 4'-substituted benzyl group to a beta-1C-phenylglucoside is important for potent and selective SGLT2 inhibition. The lead C-arylglucoside (7a) demonstrates superior metabolic stability to its O-arylglucoside counterpart (4) and it promotes glucosuria when administered in vivo.

Dapagliflozin, a selective SGLT2 inhibitor, improves glucose homeostasis in normal and diabetic rats

OBJECTIVE

The inhibition of gut and renal sodium-glucose cotransporters (SGLTs) has been proposed as a novel therapeutic approach to the treatment of diabetes. We have identified dapagliflozin as a potent and selective inhibitor of the renal sodium-glucose cotransporter SGLT2 in vitro and characterized its in vitro and in vivo pharmacology.

RESEARCH DESIGN AND METHODS

Cell-based assays measuring glucose analog uptake were used to assess dapagliflozin's ability to inhibit sodium-dependent and facilitative glucose transport activity. Acute and multi-dose studies in normal and diabetic rats were performed to assess the ability of dapagliflozin to improve fed and fasting plasma glucose levels. A hyperinsulinemic-euglycemic clamp study was performed to assess the ability of dapagliflozin to improve glucose utilization after multi-dose treatment.

RESULTS

Dapagliflozin potently and selectively inhibited human SGLT2 versus human SGLT1, the major cotransporter of glucose in the gut, and did not significantly inhibit facilitative glucose transport in human adipocytes. In vivo, dapagliflozin acutely induced renal glucose excretion in normal and diabetic rats, improved glucose tolerance in normal rats, and reduced hyperglycemia in Zucker diabetic fatty (ZDF) rats after single oral doses ranging from 0.1 to 1.0 mg/kg. Once-daily dapagliflozin treatment over 2 weeks significantly lowered fasting and fed glucose levels at doses ranging from 0.1 to 1.0 mg/kg and resulted in a significant increase in glucose utilization rate accompanied by a significant reduction in glucose production.

CONCLUSIONS

These data suggest that dapagliflozin has the potential to be an efficacious treatment for type 2 diabetes.

Discovery of dapagliflozin: a potent, selective renal sodium-dependent glucose cotransporter 2 (SGLT2) inhibitor for the treatment of type 2 diabetes

The C-aryl glucoside 6 (dapagliflozin) was identified as a potent and selective hSGLT2 inhibitor which reduced blood glucose levels in a dose-dependent manner by as much as 55% in hyperglycemic streptozotocin (STZ) rats. These findings, combined with a favorable ADME profile, have prompted clinical evaluation of dapagliflozin for the treatment of type 2 diabetes.

Alternate choice of initiation codon produces a biologically active product of the von Hippel Lindau gene with tumor suppressor activity

The VHL tumor suppressor gene has previously been reported to encode a protein of 213 amino acid residues. Here we report the identification of a second major VHL gene product with an apparent molecular weight of 18 kD, pVHL18, which appears to arise from alternate translation initiation at a second AUG codon (codon 54) within the VHL open reading frame. In vitro and in vivo studies indicate that the internal codon in the VHL mRNA is necessary and sufficient for production of pVHL18. pVHL18 can bind to elongin B, elongin C, and Hs-CUL2. When reintroduced into renal carcinoma cells that lack a wild-type VHL allele, pVHL18 suppresses basal levels of VEGF expression, restores hypoxia-inducibility of VEGF expression, and inhibits tumor formation in nude mice. These data strongly support the existence of two distinct VHL gene products in VHL tumor suppression.

The von Hippel-Lindau tumor suppressor protein is required for proper assembly of an extracellular fibronectin matrix

Fibronectin coimmunoprecipitated with wild-type von Hippel-Lindau protein (pVHL) but not tumor-derived pVHL mutants. Immunofluorescence and biochemical fractionation experiments showed that fibronectin colocalized with a fraction of pVHL associated with the endoplasmic reticulum, and cold competition experiments suggested that complexes between fibronectin and pVHL exist in intact cells. Assembly of an extracellular fibronectin matrix by VHL-/- renal carcinoma cells, as determined by immunofluorescence and ELISA assays, was grossly defective compared with VHL+/+ renal carcinoma cells. Reintroduction of wildtype, but not mutant, pVHL into VHL-/- renal carcinoma cells partially corrected this defect. Finally, extracellular fibronectin matrix assembly by VHL-/- mouse embryos and mouse embryo fibroblasts (MEFs), unlike their VHL+/+ counterparts, was grossly impaired. These data support a direct role of pVHL in fibronectin matrix assembly.

Tau protein in cerebrospinal fluid as an aid in the diagnosis of Alzheimer's disease

Neurofibrillary tangles and dystrophic neurites are characteristic pathological features found in the brains of Alzheimer's disease (AD) patients. A major constituent of these lesions is the cytoskeletal protein tau. This study examined whether the measurement of tau in cerebral spinal fluid (CSF) has value in the diagnosis of AD. Seventy-seven subjects were enrolled in this prospective study: These included AD (N = 24), Neurological Controls (dementing diseases/syndromes, N = 26), Normal Controls (N = 14), and Others (N = 13). CSF was obtained by lumbar puncture, and tau concentrations (pg/mL) were determined using a dual monoclonal antibody microplate immunoassay. The mean tau value for AD subjects (1,430 +/- 739) was significantly different from Neurological Control subjects (790 +/- 579) (p < 0.001) and Normal Control subjects (816 +/- 355) (p < 0.001). Tau values were elevated in two Neurological Control subjects, one with Binswanger's disease (age 75) and one with depression (age 90). Tau values were also elevated in three Normal Control subjects; two were subjects with a family history of AD. Tau concentrations did not correlate significantly with age in AD subjects (r = 0.05, p = 0.82) or in Normal Control subjects (r = -0.49, p = 0.08). Tau also did not correlate with severity of cognitive impairment in AD subjects (r = -0.03, p = 0.91) or duration of AD symptoms (r = 0.16, p = 0.52). Based on these results and others, CSF levels of tau protein may provide a useful biochemical marker to aid in the clinical diagnosis of AD.

Cloning and characterization of a mouse gene with homology to the human von Hippel-Lindau disease tumor suppressor gene: implications for the potential organization of the human von Hippel-Lindau disease gene

The human von Hippel-Lindau disease (VHL) gene has recently been identified and, based on the nucleotide sequence of a partial cDNA clone, has been predicted to encode a novel protein with as yet unknown functions [F. Latif et al., Science (Washington DC), 260: 1317-1320, 1993]. The length of the encoded protein and the characteristics of the cellular expressed protein are as yet unclear. Here we report the cloning and characterization of a mouse gene (mVHLh1) that is widely expressed in different mouse tissues and shares high homology with the human VHL gene. It predicts a protein 181 residues long (and/or 162 amino acids, considering a potential alternative start codon), which across a core region of approximately 140 residues displays a high degree of sequence identity (98%) to the predicted human VHL protein. High stringency DNA and RNA hybridization experiments and protein expression analyses indicate that this gene is the most highly VHL-related mouse gene, suggesting that it represents the mouse VHL gene homologue rather than a related gene sharing a conserved functional domain. These findings provide new insights into the potential organization of the VHL gene and nature of its encoded protein.

Germ-line mutations in the von Hippel-Lindau tumor-suppressor gene are similar to somatic von Hippel-Lindau aberrations in sporadic renal cell carcinoma

von Hippel-Lindau (VHL) disease is a hereditary tumor syndrome predisposing to multifocal bilateral renal cell carcinomas (RCCs), pheochromocytomas, and pancreatic tumors, as well as angiomas and hemangioblastomas of the CNS. A candidate gene for VHL was recently identified, which led to the isolation of a partial cDNA clone with extended open reading frame, without significant homology to known genes or obvious functional motifs, except for an acidic pentamer repeat domain. To further characterize the functional domains of the VHL gene and assess its involvement in hereditary and nonhereditary tumors, we performed mutation analyses and studied its expression in normal and tumor tissue. We identified germline mutations in 39% of VHL disease families. Moreover, 33% of sporadic RCCs and all (6/6) sporadic RCC cell lines analyzed showed mutations within the VHL gene. Both germ-line and somatic mutations included deletions, insertions, splice-site mutations, and missense and nonsense mutations, all of which clustered at the 3' end of the corresponding partial VHL cDNA open reading frame, including an alternatively spliced exon 123 nt in length, suggesting functionally important domains encoded by the VHL gene in this region. Over 180 sporadic tumors of other types have shown no detectable base changes within the presumed coding sequence of the VHL gene to date. We conclude that the gene causing VHL has an important and specific role in the etiology of sporadic RCCs, acts as a recessive tumor-suppressor gene, and appears to encode important functional domains within the 3' end of the known open reading frame.

Comparative study of p53 gene and protein alterations in human astrocytic tumors

The p53 gene is a tumor suppressor gene involved in many common malignancies, including astrocytomas. Genetic analysis of the p53 gene and immunohistochemistry of the p53 protein have each been used to screen astrocytomas. To compare these methods, we performed immunohistochemistry with the monoclonal antibody PAb 1801 and single-strand conformational polymorphism (SSCP) with sequence analysis on 34 astrocytic tumors (WHO grades II, III and IV). Seven cases had detectable p53 protein and gene mutations, while twelve cases had neither detectable protein nor gene mutations. Four tumors had frameshift mutations in the p53 gene that were not revealed by immunohistochemistry. One tumor had a genetic polymorphism and no detectable p53 protein. Ten tumors had p53 protein accumulation but no mutations by SSCP; these cases may represent p53 mutations outside of the conserved exons or elevated levels of wild-type p53 protein. Thus, some p53 mutations are missed with PAb 1801 immunohistochemistry alone. p53 immunohistochemistry, however, may reveal p53 accumulation independent of mutations in the conserved portions of the gene. Finally, we suggest that glioblastomas with p53 mutations in the conserved region of the gene may be a subset that are more common in women and in younger patients.

Cytogenetic and molecular studies of a familial renal cell carcinoma

In a previously studied family with inherited renal cell carcinoma (RCC), RCC was shown to segregate with a constitutional balanced t(3;8)(p14.2;q24.1). In addition, we recently showed that in a RCC tumor from this family the constitutional translocation became unbalanced, suggesting a genetic mechanism that may be associated with the primary genetic events of tumorigenesis. We now report that the RCC tumor cells from this case showed additional cytogenetic alterations, possibly related to tumor progression, which include an additional tumor-specific translocation involving band 14 of chromosome 13. Because this band contains the retinoblastoma (RB) gene, we examined the tumor for aberrations in the RB gene using DNA sequence polymorphism analysis and pulsed-field gel electrophoresis (PFGE), but did not detect alterations in the RB gene.

Efficient mutation induction by 125I and 131I decays in DNA of human cells

To examine the role of radiation energy deposition in DNA on cellular effects, we investigated the ability of 125IdUrd and 131IdUrd to kill cells and induce mutations at the hprt locus. We employed human lymphoblastoid cells proficient (TK6) or deficient (SE30) in the ability to incorporate a thymidine analog into DNA by way of the thymidine kinase (TK) scavenger pathway. Iodine-125 releases a shower of low-energy Auger electrons upon decay which deposit most of their energy within 20 nm of the decay site, whereas 131I is a high-energy beta/gamma emitter that is generally considered to emit sparsely ionizing radiation. Although 125IdUrd incorporated into cellular DNA was very effective at producing toxic and mutagenic effects in TK6 cells, virtually no effect was seen in TK-deficient cells incubated with similar levels of 125IdUrd in the extracellular medium. In response to 131IdUrd treatment, 0.45 X 10(-6) mutants were induced per centigray dose deposited within the nucleus in TK-proficient cells, whereas few mutations were induced in TK-deficient cells at doses up to 38 cGy from 131I decays occurring in the medium. The differences in biological response between TK6 and SE30 cells cannot be explained by differential radiosensitivity or IdUrd sensitization of the cell lines involved. We conclude that both 125I and 131I decays occurring while incorporated into DNA are more effective at inducing cell killing and mutations in human cells than either nonincorporated decays or low-LET radiations. These results suggest that localized energy deposition is an important factor in producing biologically important damage by both of these isotopes, and that residual lesions following the decay of DNA-incorporated radioisotopes may contribute to the toxic and mutagenic effects observed in TK-proficient cells. Furthermore, they emphasize that certain beta/gamma-emitting isotopes such as 131I may be particularly hazardous when incorporated into DNA.

Chromosome 17p deletions and p53 gene mutations associated with the formation of malignant neurofibrosarcomas in von Recklinghausen neurofibromatosis

von Recklinghausen neurofibromatosis (NF1) is a common hereditary disorder characterized by neural crest-derived tumors, particularly benign neurofibromas whose malignant transformation to neurofibrosarcomas can be fatal. The NF1 gene has been mapped to a small region of chromosome 17q, but neither the nature of the primary defect nor the mechanisms involved in tumor progression are understood. We have tested whether NF1 might be caused by the inactivation of a tumor suppressor gene on 17q, analogous to that on chromosome 22 in NF2, by searching for deletions of chromosome 17 in NF1-derived tumor specimens. Both neurofibrosarcomas from patients with "atypical" NF and 5 of 6 neurofibrosarcomas from NF1 patients displayed loss of alleles for polymorphic DNA markers on chromosome 17. However, the common region of deletion was on 17p and did not include the NF1 region of 17q. Since no loss of markers on chromosome 17 was observed in any of 30 benign tumors from NF1 patients, the 17p deletions seen in neurofibrosarcomas are probably associated with tumor progression and/or malignancy. This region contains a candidate gene for tumor progression, p53, which has recently been implicated in the progression of a broad array of human cancers. In a preliminary search for p53 aberrations by direct sequencing of polymerase chain reaction-amplified DNA from 7 neurofibrosarcomas, 2 tumors that contained point mutations in exon 4 of the p53 gene were found, suggesting a role for this gene in at least some neurofibrosarcomas. Thus the formation of malignant neurofibrosarcomas may result from several independent genetic events including mutation of the NF1 gene, whose mechanism of tumorigenesis remains uncertain, and subsequent loss of a "tumor suppressor" gene on 17p, most likely p53.

Mutation induction by 125iodoacetylproflavine, a DNA-intercalating agent, in human cells

Survival and the induction of mutations at the hprt and tk loci were measured in TK6 human lymphoblastoid cells following treatment with the DNA-intercalating agent 125iodoacetylproflavine (125IAP). 125IAP was readily taken up into the cells, was localized to the nucleus, and was released rapidly following resuspension of the cells in fresh medium. Treatment with 125IAP for 24 h yielded a D0 of 110 decays/cell and an induced mutant fraction of 0.13 x 10(-6) per decay at the hprt locus and 0.4 x 10(-6) per decay at the tk locus. Molecular analyses of 125IAP-induced hprt mutants by Southern blot revealed a high proportion of large-scale changes at this locus. When these results are compared with those observed with 125IdUrd, 125IAP shows a reduced effectiveness per decay, related perhaps to the non-covalent nature of intercalator binding, resulting in reduced energy deposition in the DNA.

Molecular characterization of hprt mutants induced by low- and high-LET radiations in human cells

Southern blotting techniques were employed to examine the spectrum of molecular alterations in DNA induced by internally emitting iodine isotopes and X-rays at and around the hprt locus in a human lymphoblastoid cell line. We analyzed 165 mutant clones using a cDNA probe for the human hprt locus, and 3 anonymous sequence probes for regions of the X chromosome which are linked to hprt. The results were compared with those for 35 spontaneously arising mutant clones. The majority of ionizing radiation-induced mutants showed changes in the normal restriction patterns at the hprt locus, whereas very few alterations were seen at linked markers along the X chromosome. Total hprt coding sequence deletions comprised 30-48% of the changes observed at this locus, while partial deletions and rearrangements comprised 14-54% of the observed changes. In the case of mutants induced by [125I]dUrd, a densely ionizing radiation, the spectrum of alterations was dose-dependent; at low doses it was not significantly different from that seen after sparsely ionizing X-ray exposure, whereas a higher proportion of gene deletions and rearrangements occurred after high doses of this incorporated isotope. Changes were rarely observed in the 3 linked markers examined. Overall, these results indicate that the distribution of mutational events at the hprt locus in irradiated human cells may not only be LET-dependent but dose-dependent, and that deletions involving large regions of the X chromosome surrounding the hprt locus are rare events.