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Faculty Victor A Zammit
Cell Biochemistry, Hannah Research Institute, Ayr, KA6 5HL, Scotland v.zammit@hri.ac.uk Aetiology of type-2 diabetes and the role of carbohydrate-fatty acid interactions Type-2 diabetes is diagnosed with respect to the concentration of plasma glucose, e.g. after an overnight fast or ingestion of a standard glucose load. However, it is really a disease that arises as a result of altered fatty acid-glucose interactions, with fatty acids, and more complex lipids that incorporate them, playing a major role in determining the onset and progression of the condition, as well as the success of its treatment. The basic biochemical mechanisms involved in these interactions between fatty acid- and glucose-metabolism are remarkably similar in different tissues, although the outcome of the resulting metabolic derangement depends on the individual cell-type. It is the variety of physiological responses of these different cell-types that gives rise to the constellation of symptoms that became known as the Metabolic Syndrome, and latterly as the Insulin Resistance Syndrome. Insulin resistance is generally associated with the development of type-2 diabetes, and is initially accompanied by a compensatory hypersecretion of insulin by the pancreatic ß-cells. Controversy has long centred on “what comes first” in the debate about the identity of the primary defect that leads to the development of type-2 diabetes. But it is becoming increasingly evident that a combination of insulin resistance, including that of the pancreatic ß-cell itself, coupled to a genetic pre-disposition for insensitivity of the insulin-secretory response to glucose, combine to bring about the progression to frank diabetes. Fatty acids affect glucose metabolism, insulin-signalling and insulin-secretion at several levels. Moreover, the structure of the fatty acids is crucial to the type of effect they have. In general, delivery of saturated fatty acids to a tissue in excess to its ability to oxidise them, results in the formation of molecular species (e.g. ceramides, diacylglycerides) that interfere with insulin signalling. This has been best elucidated for muscle, for which the association between the accumulation of intramyocellular triglyceride is a marker for whole-body insulin resistance. However, other mechanisms, such as the up-regulation of the glucosamine pathway, may also be involved. The interactions in the ß-cell may be more complex, as the generation of fatty acid-derived intermediates may be involved both in normal ß-cell function and in its dysfunction (including increased apoptosis under conditions of gluco-lipotoxicity). Central to the genetic propensity for, and the physiological control and pharmacological treatment of, these conditions is the capacity for fatty acid ß-oxidation in such diverse tissues as the hypothalamus and the pancreas. Andreas Köpke Devgen N.V., Belgium andreas.kopke@devgen.com From worm models of insulin resistance to novel drugs for the treatment of type II diabetes and obesity C. elegans is the best understood animal on earth and features the advantage of being a micro organism that is amenable to liquid handling and micro plate format. Devgen has industrialised the application of this model organism to investigate genes contributing to the pathogenesis of a number of human diseases. The validity of genes identified is confirmed using mammalian and human tissue culture models. The insulin-signalling pathway was in part discovered in C. elegans and later verified in mammalian organisms, including humans. The degree of conservation is significant and enables the establishment of disease models for diabetes and obesity. A temperature sensitive C. elegans mutant was used to attenuate insulin signalling at certain phases of its life cycle. Devgen’s model for diabetes exploits an early reduction of insulin signalling that results in the development of a “dauer” phenotype. A reduction in insulin signalling later in the life cycle of C. elegans enables the generation of “fat” worms that accumulate fat droplets in their bodies, representing a model of obesity. Devgen has used its proprietary whole genome RNAi library to knock down every single gene in C. elegans. This enabled the identification of genes that, upon knockdown, reverse the two described “disease” phenotypes. Consequently druggable genes identified in these screens could be considered as novel pharmacological targets. The advantage of this approach compared with expression profiling (e.g. by DNA chips or proteomics) is the indication of an important functional role of such potential targets for the reversal of the disease. Devgen has identified two targets with a role in diabetes and obesity: Kinase 1 and Kinase 2, which have been screened using the Devgen library of almost 100.000 compounds. Lead molecules have been identified and the structure activity relationship of these scaffolds is currently under investigation. Additional validation for the roles of these targets in diabetes and obesity and their potential as drug targets has been provided by knock-out experiments in mice and experiments on human cellular responses in tissue culture experiments. In this presentation Devgen’s abilities and the two ongoing programs will be presented. Pr Philippe Froguel Imperial College Genome Centre and Genomic Medicine, London, UK p.froguel@imperial.ac.uk Genomics and the identification of drug targets. Type 2 diabetes is multifactorial disease due to interaction between susceptibility genetic risk factors and environmental factors. Although most patients with T2D are obese, only a minority of overweight subjects will develop diabetes during their lifetime. Indeed, there is a large body of evidence for inherited defects in both insulin secretion and action as well as in mitochondria function in normoglycemic offspring’s of T2D subjects. In this regard, obesity triggers T2D in those who carry susceptibility alleles in T2D associated genes. Human genetics and animal genomics have brought breakthrough in the understanding of molecular determinants of glucose homeostasis and of T2D: about 75% of monogenic forms of T2D (5% of all diabetes cases) and around 1/3 of the genetic background of common forms of T2D are already known, which will make possible in the next years the establishment of genetic profiles of at risk individuals, first step towards individualized medicine. The first T2D gene, Glucokinase was identified in 1992 by a familial linkage approach in extended pedigrees with monogenic form of T2D, names Maturity Onset Diabetes of the Young. As GCK is a glucoses sensor in both pancreatic beta-cells and in hepatocytes, hyperglycemia associated with GCK mutations (about 200 known so far) is due to both insulin secretion defects and increased glucose production from the liver. In addition, few overactive mutations in GCK associated with hypoglycemia due to unregulated excessive insulin production. Careful genotypic-phenotypic characterization in human and also in animal using gene targeting (gene deletion and chemical mutagenesis) and transgenics have permitted a very precise understanding of the mechanisms of action of this enzyme, making possible for at least 2 drug companies to discover new compounds activating GCK with major potential to treat T2D as shown in preclinical and phase 1 trials. Integrated genomic and genetic approaches have been developed in the last years to identify and to validate drug targets for T2D and also for associated obesity: interesting results have been obtained for several proteins involved in insulin resistance such as SHIP2, PTB-1B...and also in insulin secretion such as KIR 6.2, HNF 4 alpha… Although high throughput genomic approaches (for instance based on transcriptomics in animal models) can provide quite a large number of potential interesting genes which are dysregulated in diabetes states, it is quite difficult to prioritize the most interesting molecules for drug target validation and for drug development. Human genetics can powerfully complement this effort by showing which gene contains DNA variants which are primarily associated with modulation of the weight, insulin secretion or sensitivity and/or with increased risk for T2D. More targeted approaches focused on likely drug targets but with uncertain function (such as Nuclear Receptors, G coupled transmembrane receptors…) may also provide very important results in order to speed up the search of new drugs of diabesity. In this regard, alliances between academic centres of excellence in the field, biotech able to develop high throughput technologies and bioinformatics and big pharmas having significant interest for translational research and system biology are required to make significant breakthrough in the treatment of T2D and associated diseases. Dr Matthew Coghlan AstraZeneca, Diabetes Drug Discovery, CV & GI Research Area, Macclesfield, Cheshire matthew.coghlan@astrazeneca.com Small molecule Glucokinase Activators as novel anti-diabetic agents Glucokinase (GK) plays a critical role in whole body glucose homeostasis. GK expression is restricted to specific cell types most notably the pancreatic b-cell and liver cells. GK is rate limiting for glucose utilization in these cells and therefore acts as a “glucose sensor” that controls glucose stimulated insulin secretion and hepatic glucose utilization. The hyperglycaemia that characterizes Type 2 Diabetes Mellitus is caused in part by defective insulin secretion and impaired hepatic glucose utilization. The importance of GK in the control of blood glucose homeostasis in humans is evident from the impact of mutations in the GK gene. Heterozygous loss-of-function mutations in the GK gene cause Maturity Onset Diabetes of the Young – Type 2 (MODY2). Conversely, activating mutations cause hyperinsulinaemia and hypoglycaemia. Studies in rodents also support a critical role for GK in glucose homeostasis. Mice that are homozygous for disruption of the GK gene die from diabetes within days of birth whereas the heterozygotes are more midly hyperglycaemic. Mice that express additional copies of the GK gene have improved glucose tolerance, mild hypoglycaemia and resistance to diet induced diabetes. We have recently attempted to identify low molecular weight activators of GK (GK activators or GKAs) that may offer a novel therapeutic strategy for Type 2 Diabetes Mellitus. A screening approach was used and compounds were selected based on activation of human GK and stimulation of glucose metabolism in primary rat hepatocytes. This work, and other data emerging in the literature, shall be presented. Joel P. Berger, Ph.D. Senior Investigator, Merck Research Laboratories, RY80N-C31, NJ 07065 joel_berger@merck.com Beyond TZDs and fibrates- PPAR mechanisms and novel ligands. Thiazolidinedione (TZD) PPARg agonists have proven to be efficacious in the treatment of type II diabetes (T2DM) in humans for a number of years. However, major side effects associated with TZDs, including weight gain, edema, and cardiac risks, prevent their more widespread use. In an effort to circumvent these adverse effects we have identified novel selective PPARg modulators (SPPARgMs). Here, we describe highly selective and potent SPPARgMs that display unique properties in vitro as well as in preclinical animals relative to TZDs. In addition, dual PPAR a/g ?agonists which can effectively treat hyperglycemia and dyslipidemia will be discussed. Our results suggest that compounds such as those described here have the potential to be safer and more effective than presently available TZDs and fibrates in the treatment of T2DM patients. Furthermore, in the course of developing novel PPAR effectors, we have deepened our knowledge of molecular pathways that may be deranged in T2DM and positively affected by such ligands. Examples of such progress will be presented. 1. Chemokines in allergic airway disease. CM Lloyd, SM Rankin. Current Opinion in Pharmacology, 2002, 3, 1-6. Serge Halazy Serono Pharmaceutical Research Institute, Geneva, Switzerland serge.halazy@serono.com PTP1B inhibitors: a new approach to the treatment of diabetes PTP1B has emerged only four years ago as a new drug target for the treatment of diabetes and, possibly, obesity. The enzyme belongs to a ~90 member gene family of tyrosine phosphatases. Interestingly, this target has very gradually come into focus, following 19th century observations that vanadium salts are of therapeutic utility in diabetes, and the biochemical discovery that vanadate is a potent, non-selective inhibitor of phosphatases. By the mid-1980's it was understood that blocking one or more phosphatases could enhance the phosphorylation state of the insulin receptor kinaseb subunit, or of its downstream signalling partners, and revert the resistance to insulin which characterizes type II diabetes patients. The discovery in 1999, independently confirmed a year later, that PTP1B knockout mice represent a phenotype that closely mimics the useful effects of vanadate treatment spurred a vivid interest in PTP1B as a drug target for diabetes and, possibly, obesity. The presentation will briefly review the biology of PTP1B relevant to its identification as a drug target and discuss current prospects and hurdles for the development of PTP1B-selective inhibitors, as illustrated with examples from our own research. James. E Foley Ph.D. Exec. Dir. Global Clinical Development & Medical Affairs, Novartis Pharmaceutical Corp. One Health Plaza, East Hanover, NJ USA james.foley@pharma.novartis.com DPP-4 Inhibition: A new therapeutic approach for the treatment of type 2 diabetes. The Novartis (Sandoz) DDP-4 program was originally conceived in the early 1990s. We anticipated the positive outcomes of the DCCT and the UKPDS with regards to the importance of tight glucose control. In addition, we had appreciated that importance of balancing the demand for insulin with the ability of the ß-cell to supply insulin achieving tight control. Our assumptions have been that this demand for insulin can come from inappropriate glucagon secretion and insulin resistance due to high CHO intake, chronic nutrition and hyperglycemia. We have also assumed that early in progression to type 2 diabetes that increased demand with insulin that was not met by adequate ß-cell function resulted in glucose intolerance and that further progression was associated with progressive loss of ß-cell function. Combinations of currently available drugs can deal with many of these metabolic problems. These drugs are usually about as efficacious as each other when adjusted to the same glycemic baseline, and often additive which each other. Although safety and tolerability issues exist with all these drugs they are often not considered important limitations by prescribers. The real issue appears to be the lack of durability of drugs as evidenced by the UKPDS. In early 1990s we also appreciated the therapeutic potential of the incretin hormones to get patients close to normal glycemia and were especially interested in the multi-mechanism attributes of GLP-1 that may engender durability. We had incorrectly assumed that injecting peptides was a not viable option and in 1993 first discussed inhibiting the enzyme which inactivates GLP-1, dipeptidyl-peptidase-4 (DPP-4). In 1995 when the DPP-4 inhibitor valine-pyrrolidide was shown to inhibit the inactivation of GLP-1 we validated that valine-pyrrolidide improved glucose tolerance in rodents and monkeys and immediately initiated a combichem effort around valine-pyrrolidide leading to DPP-728 in 1996 and LAF237 as longer acting inhibitor in 1998. Both DPP-728 and LF237 have been in man and LAF237 is currently in phase III development. At this point (end of Phase II) we can say that LAF237 is well tolerated, but long term safety and tolerability can only be assessed from phase III results. Phase II data indicate that LAF237 is effective in lowering HbA1c both alone or in combination with metformin and extension data are consistent with durability for one year in combination with metformin. Mechanistically the data to date indicate that LAF237 enhances the active levels of both GLP-1 and GIP; that basal insulin secretion tone is enhanced, and that glucagon levels are decreased during meals. There are other DPP-4 inhibitors in development: the structures and information about their relative safety and activity are not in the public domain. Lotte Bjerre Knudsen L. on behalf of Novo Nordisk GLP-1 research and development teams, Denmark lbkn@novonordisk.com Acylated Analogues of Glucagon-Like Peptide-1 – a New Class of Drugs for the Treatment of Type 2 Diabetes. Glucagon-Like Peptide-1 (GLP-1) is the hormone from which a new promising class of compounds for the treatment of type 2 diabetes is emerging. This class promises effective glucose control, weight control and b-cell rescue. Analogues of GLP-1 show improved pharmacokinetic properties but still have to be dosed a least two or three times daily. In contrast, fatty acid acylated analogues have half-lives making once daily dosing possible without any protracted formulation. These analogues bind to albumin, are stable against degradation and are released slowly from the injection site. A relationship has been shown between structure and receptor potency, and half-life in pigs. Different spacers have been used between the peptide and the fatty acid. Several potent compounds may be selected with half-lives suitable for once daily dosing. Liraglutide has been selected for clinical development and has shown a promising activity profile in a once daily dosing regime (t½ 13h) in several phase 2 studies. Currently, liraglutide has completed phase 2 clinical testing. |
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