Thiazolidinediones (TZDs) constitute an exciting new class of antidiabetic compounds, which function as activating ligands for peroxisome proliferator-activated receptor ␥ (PPAR␥). Until now, there has been an excellent correlation between in vivo hypoglycemic potency and in vitro binding and activation of PPAR␥ by TZDs. We have characterized MCC-555, a novel thiazolidinedione ligand for PPAR␥ with unique functional properties. The antidiabetic potency of this compound is greater than that of other TZDs, including BRL49653, yet its binding affinity for PPAR␥ is less than 1 ⁄10 that of BRL49653. The effect of MCC-555 binding on PPAR␥ transcriptional activity is highly context-specific such that it can function as a full agonist, partial agonist, or antagonist depending on the cell type or DNA binding site. These transcriptional properties are partly explained by unique partial agonism of coactivator recruitment to PPAR␥. The properties of MCC-555 are mechanistically distinct from those of the estrogen receptor partial agonist and antagonist tamoxifen because the N terminus of PPAR␥ is not required for activation by MCC-555, and MCC-555 does not stimulate corepressor recruitment to PPAR␥. The context selectivity of MCC-555 may contribute to its enhanced hypoglycemic potency in vivo despite reduced affinity for PPAR␥ relative to other TZDs. Nuclear hormone receptors (NHRs)1 constitute a class of transcription factors with activity that is regulated by natural or synthetic lipophilic ligands (1). A number of NHRs are involved in developmental and/or metabolic processes, and modulation of NHR activity is an effective strategy in the treatment of a variety of cancers, such as breast cancer (2), prostate cancer (3), and acute promyleocytic leukemia (4), as well as metabolic diseases including thyroid disease (5) and diabetes. Non-insulin-dependent diabetes mellitus is a major cause of morbidity and mortality in industrialized nations and is characterized by a post-insulin receptor defect that has been difficult to target therapeutically until the recent discovery that thiazolidinediones (TZDs) enhance the actions of insulin at a level distal to the insulin receptor (6).The mechanism of TZD action is not completely understood, but a number of lines of evidence point to their function as ligands for a member of the NHR superfamily called peroxisome proliferator-activated receptor ␥ (PPAR␥), the natural ligand of which may be derived from or related to prostaglandin J2 (7-9). One of the most potent TZDs, BRL49653, binds to PPAR␥ with an affinity in the nanomolar range (10), and the rank order of TZD potency for in vivo plasma glucose lowering correlates well with their rank order potency for PPAR␥ activation (11, 12). Nevertheless, a number of questions remain with regard to the mechanism of TZD potentiation of insulin action. The main problem is that PPAR␥ is primarily expressed in adipose tissue (13, 14), whereas muscle is ordinarily the main site of insulin-dependent glucose disposal in mammals. This apparent paradox h...

1 We examined the e ect of chronic (21 days) oral treatment with the thiazolidinedione, MCC-555 ((+)-5-[{6-(2-¯uorbenzyl)-oxy-2-naphy}methyl]-2,4-thiazolidinedione) on metabolic status and insulin sensitivity in obese (fa/fa) Zucker rats and Zucker Diabetic Fatty (ZDF) rats which display an impaired glucose tolerance (IGT) or overt diabetic symptoms, respectively. 2 MCC-555 treatment to obese Zucker rats (10 and 30 mg kg 71 ) and diabetic ZDF rats (10 mg kg 71 ) reduced non-esteri®ed fatty acid concentrations in both rat strains and reduced plasma glucose and triglyceride concentrations in the obese Zucker rats. Liver glycogen concentrations were signi®cantly increased by chronic MCC-555 treatment in both obese Zucker rats (30 mg kg 71 day 71 ) and diabetic ZDF rats (10 mg kg 71 day 71 ), as compared with vehicle-treated lean and obese rats and there was a signi®cant increase in hepatic glycogen synthase activity in MCC-555-treated diabetic ZDF rats as compared to vehicle-treated controls. 3 During a euglycaemic hyperinsulinaemic clamp, MCC-555-treated obese Zucker rats and diabetic ZDF rats required signi®cantly higher glucose infusion rates to maintain stable glucose concentrations (2.01+0.19 mg min 71 and 6.42+1.03 mg min 71 , respectively) than vehicle-treated obese controls (0.71+0.17 mg min 71 and 2.09+0.71 mg min 71 ; P50.05), demonstrating improved insulin sensitivity in both Zucker and ZDF rats. MCC-555 treatment also enhanced insulin-induced suppression of hepatic glucose production in ZDF rats as measured using infusions of [6-3 H]-glucose under clamp conditions. 4In conclusion, we have demonstrated that MCC-555 improves metabolic status and insulin sensitivity in obese Zucker and diabetic ZDF rats. MCC-555 may prove a useful compound for alleviating the metabolic disturbances and IGT associated with insulin resistance in man.

1 Young (6-week-old) pre-diabetic Zucker Diabetic Fatty (ZDF) rats displaying impaired glucose tolerance (IGT), moderate hyperglycaemia and hyperinsulinaemia were treated with the novel thiazolidinedione, MCC-555, for 28 days, during which time b-cell failure and progression to overt diabetes occurs. 2 Treated ZDF rats exhibited consistently lower blood glucose levels than vehicle-treated diabetic controls, with a delayed rise and lower plateau levels. MCC-555 maintained plasma insulin levels throughout the treatment period, whereas these fell by 40% in untreated ZDF rats. 3 The rise in body weight was maintained in MCC-555-treated rats, whereas vehicle-treated rats exhibited blunted body weight gain after 8 weeks of age. Daily food intake was higher in diabetic, as compared to non-diabetic rats, but treatment did not modify food intake in diabetic rats. Water intake was lower in treated ZDF rats, concomitant with lowering of blood glucose. 4 The hyperinsulinaemic-euglycaemic clamp technique was applied to all rats after treatment to examine the e ects of MCC-555 on insulin sensitivity. The glucose infusion rate to maintain normoglycaemia was lower in diabetic than in non-diabetic rats, demonstrating reduced glucose entry into insulin-sensitive tissues in diabetic rats. Increased glucose infusion rates were required to maintain euglycaemia in treated diabetic rats, demonstrating increased insulin sensitivity in these animals. 5 In conclusion, chronic MCC-555 treatment of young ZDF rats displaying IGT attenuates the development of overt diabetes through improved insulin sensitivity and maintenance of b-cell function. MCC-555 may thus be bene®cial in humans with IGT, to prevent or delay the progression of diabetes.

Freshly isolated adult rat ventricular cardiomyocytes have been used to characterize the action profile of the new thiazolidinedione antidiabetic drug MCC-555. Preincubation of cells with the compound (100 microM for 30 min or 10 microM for 2 h) did not modify basal 3-O-methylglucose transport, but produced a marked sensitizing effect (2- to 3-fold increase in insulin action at 3 x 10(-11) M insulin) and a further enhancement of maximum insulin action (1.8-fold). MCC-555 did not modulate autophosphorylation of the insulin receptor and tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1). However, insulin action (10(-10) and 10(-7) M) on IRS-1-associated phosphatidylinositol (PI) 3-kinase activity was enhanced 2-fold in the presence of MCC-555. Association of the p85 adapter subunit of PI 3-kinase to IRS-1 was not modified by the drug. Immunoblotting experiments demonstrated expression of the peroxisomal proliferator-activated receptor-gamma in cardiomyocytes reaching about 30% of the abundance observed in adipocytes. The insulin-sensitizing effect of MCC-555 was lost after inhibition of protein synthesis by preincubation of the cells with cycloheximide (1 mM; 30 min). Cardiomyocytes from obese Zucker rats exhibited a completely blunted response of glucose transport at 3 x 10(-11) M insulin. MCC-555 ameliorates this insulin resistance, producing a 2-fold stimulation of glucose transport, with maximum insulin action being 1.6-fold higher than that in control cells. This drug effect was paralleled by a significant dephosphorylation of IRS-1 on Ser/Thr. In conclusion, MCC-555 rapidly sensitizes insulin-stimulated cardiac glucose uptake by enhancing insulin signaling resulting from increased intrinsic activity of PI 3-kinase. Acute activation of protein expression leading to a modulation of the Ser/Thr phosphorylation state of signaling proteins such as IRS-1 may be underlying this process. It is suggested that MCC-555 may provide a causal therapy of insulin resistance by targeted action on the defective site in the insulin signaling cascade.