Jun-ichi Kasuga

Improvement of water-solubility of biarylcarboxylic acid peroxisome proliferator-activated receptor (PPAR) δ-selective partial agonists by disruption of molecular planarity/symmetry

To elucidate the molecular basis of peroxisome proliferator-activated receptor (PPAR) δ partial agonism, X-ray crystal structures of complexes of the PPARδ ligand-binding site with partial agonists are required. Unfortunately, reported PPARδ partial agonists, biphenylcarboxylic acids 1 and 2, possess insufficient aqueous solubility to allow such crystals to be obtained. To improve the aqueous solubility of 1 and 2, substituents were introduced at the 2-position of the biaryl moiety, focusing on disruption of molecular planarity and symmetry. All 2-substituted biphenyl analogs examined showed more potent PPARδ agonistic activity with greater aqueous solubility than 1 or 2. Among these biphenyls, 25 showed potent and selective PPARδ partial agonistic activity (EC(50): 5.7 nM), with adequate solubility in phosphate buffer (0.022 mg/mL). The 2-substituted pyridyl analog 27 showed weaker PPARδ partial agonistic activity (EC(50): 76 nM) with excellent solubility in phosphate buffer (2.7 mg/mL; at least 2700 times more soluble than 2). Our results indicate that two strategies to improve aqueous solubility, that is, introduction of substituent(s) to modify the dihedral angle and to disrupt molecular symmetry, may be generally applicable to bicyclic molecules. Combination of these approaches with the traditional approach of reducing the molecular hydrophobicity may be particularly effective.

Novel biphenylcarboxylic acid peroxisome proliferator-activated receptor (PPAR) δ selective antagonists

We designed and synthesized novel PPARdelta antagonists based on the crystal structure of the PPARdelta full agonist TIPP-204 bound to the PPARdelta ligand-binding domain, in combination with our nuclear receptor helix 12 folding modification hypothesis. Representative compound 3a exhibits PPARdelta-preferential antagonistic activity.

Improvement of the transactivation activity of phenylpropanoic acid-type peroxisome proliferator-activated receptor pan agonists: effect of introduction of fluorine at the linker part.

We developed a potent peroxisome proliferator-activated receptor pan agonist (a candidate drug for treatment of altered metabolic homeostasis) by introducing fluorine atoms at appropriate position(s) of the known phenylpropionic acid-type pan agonist TIPP-703.

Determination of the Critical Amino Acids Involved in the Peroxisome Proliferator‐Activated Receptor (PPAR) δ Selectivity of Phenylpropanoic Acid‐Derived Agonists

The nuclear receptors (NRs) form a superfamily of liganddependent transcription factors that control diverse aspects of numerous biological processes and systems including reproduction, development, homeostasis, and immune function. This superfamily includes the steroid and thyroid hormone receptors, the retinoid and vitamin D receptors, as well as a large number of orphan receptors. The structures of NRs are composed of several functionally important regions (designated A to F). The N-terminal A/B region contains a transcriptional activation function-1 (AF-1) motif that works independent of ligand binding. The central DNA-binding region (C) is highly conserved among the NRs and contains two zinc finger motifs that make contact with specific nucleotide sequences, termed hormone response elements. The C-terminal regions (D, E and F) are required for ligand binding and receptor dimerization. In most receptors, this region also contains a second highly conserved transcriptional activation function-2 (AF-2) motif, which is important for ligand-dependent transcription. Based on the elucidated human genome sequence, 48 NRs are speculated to exist in humans. However, ligands have been identified for only 20–25 of them. The others are socalled orphan receptors, whose endogenous ligands are not yet known. 3] Among the NRs, much attention has been focused on the peroxisome proliferator-activated receptors (PPARs) over the past two decades. PPARs are activated by endogenous saturated and unsaturated fatty acids and their metabolites and synthetic ligands. Three subtypes have been isolated to date, PPARa, PPARd and PPARg, which are differentially expressed in a tissue-specific manner. PPARa is predominantly expressed in tissues involved in lipid oxidation, such as liver, kidney, skeletal muscle, cardiac muscle and adrenal gland. PPARg is expressed in adipose tissue, macrophages and vascular smooth muscle. In contrast to the specific distributions of PPARa and PPARg, PPARd is ubiquitously expressed. Upon ligand binding, a PPAR dimerizes with a nuclear receptor partner, retinoid X receptor (RXR), and the heterodimer regulates gene expression by binding to specific consensus DNA sequences called peroxisome proliferator responsive elements. These elements are a direct repeat of the hexameric AGGTCA recognition motif, separated by one nucleotide (DR1), present in the promoter region of the target gene. The glitazone-derived antidiabetic agents, such as pioglitazone and rosiglitazone, and fibrate-derived antidyslipidemic agents, such as fenofibrate and bezafibrate, are known ligands of PPARg and PPARa, respectively. Consequently, research interest has been focused on these two metabolic NR subtypes as therapeutic targets for the treatment of type II diabetes and dyslipidemia. In contrast, research interest in PPARd has been limited, perhaps because of its ubiquitous distribution. HowACHTUNGTRENNUNGever, the availability of PPARd knockout animals and selective ACHTUNGTRENNUNGligands, in particular GW-501516 (1) developed by Glaxo ACHTUNGTRENNUNGSmithACHTUNGTRENNUNGKline (GSK) and L-165041 (2), prompted us to examine the involvement of PPARd in fatty acid metabolism, insulin resistance, reverse cholesterol transport, inflammation, and other related processes. Recent results from phase I/II clinical studies of GW-501516 demonstrated that a PPARd agonist elevated HDL cholesterol levels (phase I) and decreased triglyceride (phase I, phase I/II), total cholesterol (phase I/II), and apoB100 [a] J. Kasuga, Prof. Dr. Y. Hashimoto, Prof. Dr. H. Miyachi Institute of Molecular and Cellular Biosciences, University of Tokyo Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan) Fax: (+ 81) 3-5841-8495 E-mail : miyachi@iam.u-tokyo.ac.jp [b] Dr. T. Oyama, Prof. Dr. K. Morikawa The Takara-Bio Endowed Division Institute for Protein Research, Osaka University 6-2-3, Furuedai, Suita, Osaka 565-0874 (Japan) [c] Prof. Dr. I. Nakagome, Prof. Dr. S. Hirono School of Pharmaceutical Sciences, Kitasato University 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641 (Japan) [d] Prof. Dr. M. Makishima School of Medicine, Nihon University 30-1 Oyaguchi-kamicho, Itabashi-ku, Tokyo 173-8610 (Japan)