Ramakanth Sarabu

Peptidomimetic compounds that inhibit antigen presentation by autoimmune disease-associated class II major histocompatibility molecules

We have identified a heptapeptide with high affinity to rheumatoid arthritis–associated class II major histocompatibility (MHC) molecules. Using a model of its interaction with the class II binding site, a variety of mimetic substitutions were introduced into the peptide. Several unnatural amino acids and dipeptide mimetics were found to be appropriate substituents and could be combined into compounds with binding affinities comparable to that of the original peptide. Compounds were designed that were several hundred-fold to more than a thousand-fold more potent than the original peptide in inhibiting T-cell responses to processed protein antigens presented by the target MHC molecules. Peptidomimetic compounds of this type could find therapeutic use as MHC-selective antagonists of antigen presentation in the treatment of autoimmune diseases.

Glucokinase activators as new type 2 diabetes therapeutic agents

Background: Small molecule glucokinase activators (GKAs) represent a new strategy to treat type 2 diabetes. Glucokinase (GK) primarily exerts its effect through modulatory actions in the pancreatic β-cells and the liver. It couples insulin secretion in the pancreas with plasma glucose concentration, and improves glucose utilization in the liver, thus affecting two key aspects of glucose homeostasis. Objective and method: To review currently disclosed GKA structures and to classify them based on the key structural features. For this purpose, the data from patent disclosures and publications are used. Also, published in vitro findings on related lead GKAs are used to compare their effect on GK kinetics. Results and conclusion: The most common GKA pharmacophore consists of a center, which can be a carbon or an aromatic ring, and three attachments. Two of these are hydrophobic groups, with at least one of them being an aromatic ring. The third attachment, without exception, consists of an H-bond donor–acceptor pair in the form of a heterocyclic amine, or an N-acyl urea. These structurally diverse GKAs show important differences in their effects on the kinetic properties of GK.

Glucokinase activators for diabetes therapy: May 2010 status report.

Type 2 diabetes is characterized by elevated blood glucose levels resulting from a pancreatic β-cell secretory insufficiency combined with insulin resistance, most significantly manifested in skeletal muscle and liver (1). If untreated, diabetic complications develop that cause loss of vision, peripheral neuropathy, impaired kidney function, heart disease, and stroke. The disease has a polygenic basis because numerous genes (the latest count exceeding 20) participate in its pathogenesis, but modern lifestyle characterized by limited physical activity and excessive caloric intake are critical precipitating factors for the current epidemic of type 2 diabetes worldwide (2). It appears that available treatments, including attempts at lifestyle alterations and drug therapies including insulin, are insufficient to stem the tide. Therefore, new approaches, including the development of therapeutic agents with novel mechanisms of action, are needed. Selection of new drug targets to treat type 2 diabetes has to be guided primarily by consideration of established physiological chemistry of glucose homeostasis and of prevailing views about the pathophysiology of type 2 diabetes because the genetics of the disease that could serve as another guiding principle remain prohibitively perplexing. The glucose-phosphorylating enzyme glucokinase (GK) was identified as an outstanding drug target for developing antidiabetic medicines because it has an exceptionally high impact on glucose homeostasis because of its glucose sensor role in pancreatic β-cells and as a rate-controlling enzyme for hepatic glucose clearance and glycogen synthesis, both processes that are impaired in type 2 diabetes (3). Milestones in the 45-year history of GK research are listed in Supplementary Table 1 (Supplementary References S1–S27). In the mid-1990s, Hoffmann La-Roche scientists conducted a high-throughput screen in search of small molecules that could reverse the inhibition of GK by its regulatory protein (GKRP, see further discussion below) and identified a hit molecule that reversed GKRP inhibition by directly stimulating GK (4 …

Discovery of Piragliatin—First Glucokinase Activator Studied in Type 2 Diabetic Patients

Glucokinase (GK) activation as a potential strategy to treat type 2 diabetes (T2D) is well recognized. Compound 1, a glucokinase activator (GKA) lead that we have previously disclosed, caused reversible hepatic lipidosis in repeat-dose toxicology studies. We hypothesized that the hepatic lipidosis was due to the structure-based toxicity and later established that it was due to the formation of a thiourea metabolite, 2. Subsequent SAR studies of 1 led to the identification of a pyrazine-based lead analogue 3, lacking the thiazole moiety. In vivo metabolite identification studies, followed by the independent synthesis and profiling of the cyclopentyl keto- and hydroxyl- metabolites of 3, led to the selection of piragliatin, 4, as the clinical lead. Piragliatin was found to lower pre- and postprandial glucose levels, improve the insulin secretory profile, increase β-cell sensitivity to glucose, and decrease hepatic glucose output in patients with T2D.

Research and Development of Glucokinase Activators for Diabetes Therapy: Theoretical and Practical Aspects

Glucokinase Glucokinase (GK GK ; EC 2.7.1.1.) phosphorylates and regulates glucose metabolism in insulin-producing pancreatic beta-cells, hepatocytes, and certain cells of the endocrine and nervous systems allowing it to play a central role in glucose homeostasis glucose homeostasis . Most importantly, it serves as glucose sensor glucose sensor in pancreatic beta-cells mediating glucose-stimulated insulin biosynthesis and release and it governs the capacity of the liver to convert glucose to glycogen. Activating and inactivating mutations of the glucokinase gene cause autosomal dominant hyperinsulinemic hypoglycemia and hypoinsulinemic hyperglycemia in humans, respectively, illustrating the preeminent role of glucokinase in the regulation of blood glucose and also identifying the enzyme as a potential target for developing antidiabetic drugs antidiabetic drugs . Small molecules called glucokinase activators (GKAs) glucokinase activators (GKAs) which bind to an allosteric activator allosteric activator site of the enzyme have indeed been discovered and hold great promise as new antidiabetic agents. GKAs increase the enzymes affinity for glucose and also its maximal catalytic rate. Consequently, they stimulate insulin biosynthesis and secretion, enhance hepatic glucose uptake, and augment glucose metabolism and related processes in other glucokinase-expressing cells. Manifestations of these effects, most prominently a lowering of blood glucose, are observed in normal laboratory animals and man but also in animal models of diabetes and patients with type 2 diabetes mellitus (T2DM T2DM ) type 2 diabetes mellitus (T2DM) . These compelling concepts and results sustain a strong R&D effort by many pharmaceutical companies to generate GKAs with characteristics allowing for a novel drug treatment of T2DM.

Novel glucokinase activators: a patent review (2008 – 2010)

Importance of the field: Small molecule glucokinase activators (GKAs) continue to represent a potential strategy to treat type 2 diabetes (T2D). Glucokinase (GK) primarily exerts its effect through modulatory actions in pancreatic β-cells and hepatocytes. It couples insulin secretion in the pancreas with plasma glucose concentration and improves glucose utilization in the liver, thus, affecting two key aspects of glucose homeostasis. There has been an intense interest in GKAs within the pharmaceutical industry ever since the first report of a low molecular mass activator in 2003. The key drivers for this interest are the robust glucose lowering activity observed with GKAs in preclinical T2D animal models and early reports of efficacy in T2D patients. Areas covered in this review: The objective is to review GKA structures disclosed during the 2008 – 2010 period and classify them based on key structural features. For this purpose, only compound data from patent disclosures were used. What the reader will gain: The reader would gain a detailed view of structural diversity of the GKA field disclosed during the review period. Take home message: There continues to be a high level of interest within the pharmaceutical industry in novel GKAs. Several new and highly potent structure types were reported for the first time in the past 3 years. Common features of all of them include a hydrogen bond donor–acceptor pair that makes contact with the backbone CO- and NH- bonds of Arg 63 residue on GK and two hydrophobic groups. During this review period, several GKAs progressed to Phase II clinical testing and the data on their safety and efficacy profiles are eagerly awaited.

Discovery, structure-activity relationships, pharmacokinetics, and efficacy of glucokinase activator (2R)-3-cyclopentyl-2-(4-methanesulfonylphenyl)-N-thiazol-2-yl-propionamide (RO0281675).

Glucokinase (GK) is a glucose sensor that couples glucose metabolism to insulin release. The important role of GK in maintaining glucose homeostasis is illustrated in patients with GK mutations. In this publication, identification of the hit molecule 1 and its SAR development, which led to the discovery of potent allosteric GK activators 9a and 21a, is described. Compound 21a (RO0281675) was used to validate the clinical relevance of targeting GK to treat type 2 diabetes.

Recent Advances in Therapeutic Approaches to Type 2 Diabetes

Publisher Summary This chapter presents the recent advances in therapeutic approaches to type 2 diabetes (T2D). The developments discussed in this chapter, can be broadly classified into (1) enhancers of insulin release, (2) enhancers of insulin action, (3) inhibitors of hepatic glucose production, and (4) inhibitors of glucose absorption from the gut. Major current therapies for T2D include sulfonylureas, metformin, and TZDs. Each of these therapies has limitations with regard to their efficacy or side-effect profile. Among the targets discussed in this chapter, the most advanced are those based on glucagon-like peptide 1 (GLP-1) agonist activity—that is, Exenatide, and DPPIV (dipeptidyl peptidase IV )inhibitors. Both strategies are directed to potentiate the actions of GLP-1 on insulin secretion and have shown promise in Phase II/III clinical trials. These agents may avoid complications related to hypoglycemia and also may limit the potential for weight gain, thus complementing existing therapies. The discovery of potent Protein tyrosine phosphatase 1B (PTP1B) inhibitors remains a challenge; however, progress is being made and effective PTP1B inhibitors are expected to show beneficial effects in reducing insulin resistance and modulating weight gain. Glucokinase activation is the newest strategy disclosed.

Mutational analysis of allosteric activation and inhibition of glucokinase.

GK (glucokinase) is activated by glucose binding to its substrate site, is inhibited by GKRP (GK regulatory protein) and stimulated by GKAs (GK activator drugs). To explore further the mechanisms of these processes we studied pure recombinant human GK (normal enzyme and a selection of 31 mutants) using steady-state kinetics of the enzyme and TF (tryptophan fluorescence). TF studies of the normal binary GK-glucose complex corroborate recent crystallography studies showing that it exists in a closed conformation greatly different from the open conformation of the ligand-free structure, but indistinguishable from the ternary GK-glucose-GKA complex. GKAs did activate and GKRP did inhibit normal GK, whereas its TF was doubled by glucose saturation. However, the enzyme kinetics, GKRP inhibition, TF enhancement by glucose and responsiveness to GKA of the selected mutants varied greatly. Two predominant response patterns were identified accounting for nearly all mutants: (i) GK mutants with a normal or close to normal response to GKA, normally low basal TF (indicating an open conformation), some variability of kinetic parameters (k(cat), glucose S(0.5), h and ATP K(m)), but usually strong GKRP inhibition (13/31); and (ii) GK mutants that are refractory to GKAs, exhibit relatively high basal TF (indicating structural compaction and partial closure), usually show strongly enhanced catalytic activity primarily due to lowering of the glucose S(0.5), but with reduced or no GKRP inhibition in most cases (14/31). These results and those of previous studies are best explained by envisioning a common allosteric regulator region with spatially non-overlapping GKRP- and GKA-binding sites.

Design, synthesis, and three-dimensional structural characterization of a constrained Ω-loop excised from interleukin-1α

Abstract The cyclic peptide 1 , containing a 2,7-disubstituted naphthalene spacer, was designed to mimic an exposed Ω-loop present in interleukin-1α, an important mediator of immune and inflammatory responses. The synthesis of this cyclic peptide was accomplished via solution phase fragment condensation methodology. The three dimensional characterization using 2D-NMR techniques revealed it to be an excellent mimic for the Ω-loop sequence 41–48 in interleukin -1α.