Synthesis, Binding Mode, and Antihyperglycemic Activity of Potent and Selective (5-Imidazol-2-yl-4-phenylpyrimidin-2-yl)[2-(2-pyridylamino)ethyl]amine Inhibitors of Glycogen Synthase Kinase 3.

In an effort to identify new antidiabetic agents, we have discovered a novel family of (5-imidazol-2-yl-4-phenylpyrimidin-2-yl)[2-(2-pyridylamino)ethyl]amine analogues which are inhibitors of human glycogen synthase kinase 3 (GSK3). We developed efficient synthetic routes to explore a wide variety of substitution patterns and convergently access a diverse array of analogues. Compound 1 (CHIR-911, CT-99021, or CHIR-73911) emerged from an exploration of heterocycles at the C-5 position, phenyl groups at C-4, and a variety of differently substituted linker and aminopyridine moieties attached at the C-2 position. These compounds exhibited GSK3 IC50s in the low nanomolar range and excellent selectivity. They activate glycogen synthase in insulin receptor-expressing CHO-IR cells and primary rat hepatocytes. Evaluation of lead compounds 1 and 2 (CHIR-611 or CT-98014) in rodent models of type 2 diabetes revealed that single oral doses lowered hyperglycemia within 60 min, enhanced insulin-stimulated glucose transport, and improved glucose disposal without increasing insulin levels.

Mechanism of Action and Pharmacology of Patiromer, a Nonabsorbed Cross-Linked Polymer That Lowers Serum Potassium Concentration in Patients With Hyperkalemia.

Hyperkalemia is a potentially life-threatening condition, and patients who have chronic kidney disease, who are diabetic, or who are taking renin-angiotensin-aldosterone system inhibitors are at increased risk. Therapeutic options for hyperkalemia tend to have limited effectiveness and can be associated with serious side effects. Colonic potassium secretion can increase to compensate when urinary potassium excretion decreases in patients with renal impairment, but this adaptation is insufficient and hyperkalemia still results. Patiromer is a novel, spherical, nonabsorbed polymer designed to bind and remove potassium, primarily in the colon, thereby decreasing serum potassium in patients with hyperkalemia. Patiromer has been found to decrease serum potassium in patients with hyperkalemia having chronic kidney disease who were on renin-angiotensin-aldosterone system inhibitors. Results of nonclinical studies and an early phase clinical study are reported here. Two studies with radiolabeled drug, one in rats and the other in dogs, confirmed that patiromer was not absorbed into the systemic circulation. Results of an in vitro study showed that patiromer was able to bind 8.5 to 8.8 mEq of potassium per gram of polymer at a pH similar to that found in the colon and had a much higher potassium-binding capacity compared with other resins, including polystyrene sulfonate. In a study in hyperkalemic rats, a decrease in serum potassium was observed via an increase in fecal potassium excretion. In a clinical study in healthy adult volunteers, a significant increase in fecal potassium excretion and a significant decrease in urinary potassium excretion were observed. Overall, patiromer is a high-capacity potassium binder, and the chemical and physical characteristics of patiromer may lead to good clinical efficacy, tolerability, and patient acceptance.

Therapeutic applications of cell-penetrating peptides.

Since the discovery over 15 years ago of a protein transcription factor that possessed the ability to cross the plasma membrane, cell-penetrating peptides (CPPs) have been evaluated for the ability to transport diverse cargoes into cells, tissues, and organs. Certain CPPs have been used for the intracellular delivery of information-rich molecules to modulate protein-protein interactions and thereby inhibit key cellular mechanisms of disease. The ability to introduce drugs into cells allows the conventional biodistribution of drugs to be altered in order to favorably impact toxicity, patient compliance, and other treatment factors. In this monograph, we present the current status and future prospects for the application of CPPs to the development of human therapeutics. We discuss some of the advantages and disadvantages of using CPPs in the in vivo setting, and review the current status of a number of preclinical and human clinical studies of CPP-mediated delivery of therapeutics. These include CPP-conjugated moieties directed against a growing variety of targets and disease areas, including cancer, cardiology, pain, and stroke. Our discussion focuses on those therapeutics that have been tested in humans, including a CPP conjugate for the treatment of acute myocardial infarction. The promising results obtained in a number of these studies indicate that CPPs may have an important role in the development of novel therapeutics.

Glycogen synthase kinase 3beta inhibitor Chir025 reduces neuronal death resulting from oxygen-glucose deprivation, glutamate excitotoxicity, and cerebral ischemia.

The serine/threonine kinase, glycogen synthase kinase 3beta (GSK3beta), is abundant in CNS and is neuron specific. GSK3beta plays a pivotal role in the regulation of numerous cellular functions. GSK3beta phosphorylates and thereby regulates many metabolic, signaling, and structural proteins which can influence cell survival. Increased GSK3beta correlates with increased cell death, whereas reduced GSK3beta expression correlates with increased cell survival. We report that the GSK3beta inhibitor Chir025 is neuroprotective in vitro and in vivo. First, Chir025 reduced cultured hippocampal neuron death following glutamate exposure by 15-20% versus vehicle-treated controls. Second, Chir025 significantly reduced cultured cortical neuron death following oxygen-glucose deprivation (OGD) by approximately 50%. Third, Chir025 reduced infarct size following focal cerebral ischemia by nearly 20%. There were no significant differences in the number of TUNEL-positive neurons or in caspase-3 and -9 activities between Chir025- and vehicle-treated rats, although Chir025 elevated cytosolic Bcl-2 expression. These data show that Chir025-mediated inhibition of GSK3beta is neuroprotective and that the mechanism is probably not anti-apoptotic.

Selective glycogen synthase kinase 3 inhibitors potentiate insulin activation of glucose transport and utilization in vitro and in vivo.

Insulin resistance plays a central role in the development of type 2 diabetes, but the precise defects in insulin action remain to be elucidated. Glycogen synthase kinase 3 (GSK-3) can negatively regulate several aspects of insulin signaling, and elevated levels of GSK-3 have been reported in skeletal muscle from diabetic rodents and humans. A limited amount of information is available regarding the utility of highly selective inhibitors of GSK-3 for the modification of insulin action under conditions of insulin resistance. In the present investigation, we describe novel substituted aminopyrimidine derivatives that inhibit human GSK-3 potently (K(i) < 10 nmol/l) with at least 500-fold selectivity against 20 other protein kinases. These low molecular weight compounds activated glycogen synthase at approximately 100 nmol/l in cultured CHO cells transfected with the insulin receptor and in primary hepatocytes isolated from Sprague-Dawley rats, and at 500 nmol/l in isolated type 1 skeletal muscle of both lean Zucker and ZDF rats. It is interesting that these GSK-3 inhibitors enhanced insulin-stimulated glucose transport in type 1 skeletal muscle from the insulin-resistant ZDF rats but not from insulin-sensitive lean Zucker rats. Single oral or subcutaneous doses of the inhibitors (30-48 mg/kg) rapidly lowered blood glucose levels and improved glucose disposal after oral or intravenous glucose challenges in ZDF rats and db/db mice, without causing hypoglycemia or markedly elevating insulin. Collectively, our results suggest that these selective GSK-3 inhibitors may be useful as acute-acting therapeutics for the treatment of the insulin resistance of type 2 diabetes.

Modulation of muscle insulin resistance by selective inhibition of GSK-3 in Zucker diabetic fatty rats.

A role for elevated glycogen synthase kinase-3 (GSK-3) activity in the multifactorial etiology of insulin resistance is now emerging. However, the utility of specific GSK-3 inhibition in modulating insulin resistance of skeletal muscle glucose transport is not yet fully understood. Therefore, we assessed the effects of novel, selective organic inhibitors of GSK-3 (CT-98014 and CT-98023) on glucose transport in insulin-resistant muscles of Zucker diabetic fatty (ZDF) rats. Incubation of type IIb epitrochlearis and type I soleus muscles from ZDF rats with CT-98014 increased glycogen synthase activity (49 and 50%, respectively, P < 0.05) but did not alter basal glucose transport (2-deoxyglucose uptake). In contrast, CT-98014 significantly increased the stimulatory effects of both submaximal and maximal insulin concentrations in epitrochlearis (37 and 24%) and soleus (43 and 26%), and these effects were associated with increased cell-surface GLUT4 protein. Lithium enhanced glycogen synthase activity and both basal and insulin-stimulated glucose transport in muscles from ZDF rats. Acute oral administration (2 x 30 mg/kg) of CT-98023 to ZDF rats caused elevations in GSK-3 inhibitor concentrations in plasma and muscle. The glucose and insulin responses during a subsequent oral glucose tolerance test were reduced by 26 and 34%, respectively, in the GSK-3 inhibitor-treated animals. Thirty minutes after the final GSK-3 inhibitor treatment, insulin-stimulated glucose transport was significantly enhanced in epitrochlearis (57%) and soleus (43%). Two hours after the final treatment, insulin-mediated glucose transport was still significantly elevated (26%) only in the soleus. These results indicate that specific inhibition of GSK-3 enhances insulin action on glucose transport in skeletal muscle of the insulin-resistant ZDF rat. This unique approach may hold promise as a pharmacological treatment against insulin resistance of skeletal muscle glucose disposal.

Regulation of Wnt signaling during adipogenesis.

We have identified Wnt10b as a potent inhibitor of adipogenesis that must be suppressed for preadipocytes to differentiate in vitro. Here, we demonstrate that a specific inhibitor of glycogen synthase kinase 3, CHIR 99021, mimics Wnt signaling in preadipocytes. CHIR 99021 stabilizes free cytosolic beta-catenin and inhibits adipogenesis by blocking induction of CCAAT/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma. Preadipocyte differentiation is inhibited when 3T3-L1 cells are exposed to CHIR 99021 for any 24 h period during the first 3 days of adipogenesis. Consistent with this time frame of inhibition, expression of Wnt10b mRNA is suppressed upon induction of differentiation, with a 50% decline by 6 h and complete inhibition by 36 h. Of the agents used to induce differentiation, exposure of 3T3-L1 cells to methyl-isobutylxanthine or cAMP is sufficient to suppress expression of Wnt10b mRNA. Inhibition of adipogenesis by Wnt10b is likely mediated by Wnt receptors, Frizzled 1, 2, and/or 5, and co-receptors low density lipoprotein receptor-related proteins 5 and 6. These receptors, like Wnt10b, are highly expressed in preadipocytes and stromal vascular cells. Finally, we demonstrate that disruption of extracellular Wnt signaling by expression of secreted Frizzled related proteins causes spontaneous adipocyte conversion.