Identification of Bexarotene as a PPAR γ

The retinoid x receptors (RXRs) are the pharmacological target of Bexarotene, an antineoplastic agent indicated for the treatment of cutaneous T cell lymphoma (CTCL). The RXRs form heterodimers with several nuclear receptors (NRs), including peroxisome proliferator-activated receptor gamma (PPARγ), to regulate target gene expression through cooperative recruitment of transcriptional machinery. Here we have applied hydrogen/deuterium exchange (HDX) mass spectrometry to characterize the effects of Bexarotene on the conformational plasticity of the intact RXRα:PPARγ heterodimer. Interestingly, addition of Bexarotene to PPARγ in the absence of RXRα induced protection from solvent exchange, suggesting direct receptor binding. This observation was confirmed using a competitive binding assay. Furthermore, Bexarotene functioned as a PPARγ antagonist able to alter rosiglitazone induced transactivation in a cell based promoter:reporter transactivation assay. Together these results highlight the complex polypharmacology of lipophilic NR targeted small molecules and the utility of HDX for identifying and characterizing these interactions

Ligand and Receptor Dynamics Contribute to the Mechanism of Graded PPARγ Agonism

SummaryLigand binding to proteins is not a static process, but rather involves a number of complex dynamic transitions. A flexible ligand can change conformation upon binding its target. The conformation and dynamics of a protein can change to facilitate ligand binding. The conformation of the ligand, however, is generally presumed to have one primary binding mode, shifting the protein conformational ensemble from one state to another. We report solution nuclear magnetic resonance (NMR) studies that reveal peroxisome proliferator-activated receptor γ (PPARγ) modulators can sample multiple binding modes manifesting in multiple receptor conformations in slow conformational exchange. Our NMR, hydrogen/deuterium exchange and docking studies reveal that ligand-induced receptor stabilization and binding mode occupancy correlate with the graded agonist response of the ligand. Our results suggest that ligand and receptor dynamics affect the graded transcriptional output of PPARγ modulators

Varieties of export-oriented entrepreneurship in Asia

This paper explores differences in the proportion of export-oriented early-stage entrepreneurial activity in 12 Asian countries. Drawing on varieties of capitalism theory, we find that Asian countries with high quality institutions are more likely to have higher proportions of young export-oriented firms. However, analysis on a 51 country data set indicates that Asian countries have significantly fewer young export-oriented firms than do non-Asian countries. Furthermore, the multi-country study reveals that countries with higher proportions of export-oriented entrepreneurial activity tend to have flexible industrial relations, high quality vocational training, and confrontational labor-employer relations, however the proportion of export-oriented new ventures is not related to the quality of corporate governance and inter-firm relations

Synthetic RORγt Agonists Enhance Protective Immunity

The T cell specific RORγ isoform RORγt has been shown to be the key lineage-defining transcription factor to initiate the differentiation program of T_H17 and T_C17 cells, cells that have demonstrated antitumor efficacy. RORγt controls gene networks that enhance immunity including increased IL17 production and decreased immune suppression. Both synthetic and putative endogenous agonists of RORγt have been shown to increase the basal activity of RORγt enhancing T_H17 cell proliferation. Here, we show that activation of RORγt using synthetic agonists drives proliferation of T_H17 cells while decreasing levels of the immune checkpoint protein PD-1, a mechanism that should enhance antitumor immunity while blunting tumor associated adaptive immune resistance. Interestingly, putative endogenous agonists drive proliferation of T_H17 cells but do not repress PD-1. These findings suggest that synthetic agonists of RORγt should activate T_C17/T_H17 cells (with concomitant reduction in the Tregs population), repress PD-1, and produce IL17 <i>in situ</i> (a factor associated with good prognosis in cancer). Enhanced immunity and blockage of immune checkpoints has transformed cancer treatment; thus such a molecule would provide a unique approach for the treatment of cancer

Antidiabetic actions of a non-agonist PPARγ ligand blocking Cdk5-mediated phosphorylation

PPARγ is the functioning receptor for the thiazolidinedione (TZD) class of antidiabetes drugs including rosiglitazone and pioglitazone. These drugs are full classical agonists for this nuclear receptor, but recent data have shown that many PPARγ-based drugs have a separate biochemical activity, blocking the obesity-linked phosphorylation of PPARγ by Cdk5. Here we describe novel synthetic compounds that have a unique mode of binding to PPARγ, completely lack classical transcriptional agonism and block the Cdk5-mediated phosphorylation in cultured adipocytes and in insulin-resistant mice. Moreover, one such compound, SR1664, has potent antidiabetic activity while not causing the fluid retention and weight gain that are serious side effects of many of the PPARγ drugs. Unlike TZDs, SR1664 also does not interfere with bone formation in culture. These data illustrate that new classes of antidiabetes drugs can be developed by specifically targeting the Cdk5-mediated phosphorylation of PPARγ

Design, Synthesis, and Biological Evaluation of Indole Biphenylcarboxylic Acids as PPARγ Antagonists

The thiazolidinediones (TZD) typified by rosiglitazone are the only approved therapeutics targeting PPARγ for the treatment of type-2 diabetes (T2DM). Unfortunately, despite robust insulin sensitizing properties, they are accompanied by a number of severe side effects including congestive heart failure, edema, weight gain, and osteoporosis. We recently identified PPARγ antagonists that bind reversibly with high affinity but do not induce transactivation of the receptor, yet they act as insulin sensitizers in mouse models of diabetes (SR1664). This Letter details our synthetic exploration around this novel series of PPARγ antagonists based on an <i>N</i>-biphenylmethylindole scaffold. Structure–activity relationship studies led to the identification of compound <b>46</b> as a high affinity PPARγ antagonist that exhibits antidiabetic properties following oral administration in diet-induced obese mice