Design, synthesis and evaluation of MCH receptor 1 antagonists--Part III: Discovery of pre-clinical development candidate BI 186908.

Although overweight and obesity are highly prevalent conditions, options to treat them are still very limited. As part of our search for safe and effective MCH-R1 antagonists for the treatment of obesity, two series of pyridones and pyridazinones were evaluated. Optimization was aimed at improving DMPK properties by increasing metabolic stability and improving the safety profile by reducing inhibition of the hERG channel and reducing the potential to induce phospholipidosis. Steric shielding of a labile keto moiety with an ortho-methyl group and fine-tuning of the polarity in several parts of the molecule resulted in BI 186908 (11 g), a potent and selective MCH-R1 antagonist with favorable DMPK and CMC properties. Chronic administration of BI 186908 resulted in significant body weight reduction comparable to sibutramine in a 4 week diet-induced obesity model in rats. Based on its favorable safety profile, BI 186908 was advanced to pre-clinical development.

Design, synthesis and evaluation of MCH receptor 1 antagonists--Part II: Optimization of pyridazines toward reduced phospholipidosis and hERG inhibition.

Despite recent success there remains a high therapeutic need for the development of drugs targeting diseases associated with the metabolic syndrome. As part of our search for safe and effective MCH-R1 antagonists for the treatment of obesity, a series of 3,6-disubstituted pyridazines was evaluated. During optimization several issues of the initial lead structures had to be resolved, such as selectivity over related GPCRs, inhibition of the hERG channel as well as the potential to induce phospholipidosis. Utilizing property-based design, we could demonstrate that all parameters can significantly be improved by consequently increasing the polarity of the compounds. By this strategy, we succeeded in identifying potent and orally available MCH-R1 antagonists with good selectivity over M1 and 5-HT2A and an improved safety profile with respect to hERG inhibition and phospholipidosis.

Crystal structure of the human liver X receptor beta ligand-binding domain in complex with a synthetic agonist.

LXRbeta belongs to the nuclear hormone receptor superfamily of ligand-activated transcription factors. Its natural ligands are supposed to be oxidised derivatives of cholesterol. Stimulation of LXRbeta by agonists activates a number of genes that are involved in the regulation of lipid metabolism and cholesterol efflux from cells. Therefore, LXRbeta may represent a novel therapeutic target for the treatment of dyslipidemia and atherosclerosis.Here, we report the X-ray crystal structure of the LXRbeta ligand-binding domain in complex with a synthetic agonist, T-0901317. This compound occupies the ligand-binding pocket of the receptor, forms numerous lipophilic contacts with the protein and one crucial hydrogen bond to His435 and stabilises the agonist conformation of the receptor ligand-binding domain. The recruitment of the AF2-region of the protein is not achieved via direct polar interactions of the ligand with protein side-chains of this helical segment, but rather via few hydrophobic contacts and probably more importantly via indirect effects involving the pre-orientation of side-chains that surround the ligand-binding pocket and form the interface to the AF2-helix. On the basis of these results we propose a binding mode and a mechanism of action for the putative natural ligands, oxidised derivatives of cholesterol.

Scavenger receptor BI (SR-BI) mediates a higher selective cholesteryl ester uptake from LpA-I compared with LpA-I:A-II lipoprotein particles.

Scavenger receptor class B, type I (SR-BI) mediates the selective uptake of high-density lipoprotein- (HDL-) associated cholesteryl esters (CE), i.e. lipid uptake independent from HDL holo-particle internalisation. This pathway contributes to the HDL-mediated CE delivery to the liver. From human plasma HDL, two major lipoprotein subfractions can be isolated: one contains apolipoprotein (apo) A-I and apo A-II (LpA-I:A-II) as dominant protein components, whereas in the other population apo A-II is absent (LpA-I). In this investigation the role of SR-BI in selective CE uptake from HDL, LpA-I and LpA-I:A-II was explored. HDL(3) (d=1.125-1.21 g/ml), LpA-I and LpA-I:A-II were isolated from human plasma and radiolabeled in the protein (125I) as well as in the CE moiety ([3H]). Baby hamster kidney (BHK) cells were stably transfected with the full-length human SR-BI cDNA and these cells demonstrate SR-BI expression in immunoblots. In contrast, no SR-BI protein was detectable in control BHK cells (vector). To investigate lipoprotein uptake, cells incubated (37 degrees C, 4 h) in medium containing radiolabeled HDL(3), LpA-I or LpA-I:A-II and finally cellular tracer content was determined. For both types of BHK cells, the rate of apparent lipoprotein particle uptake according to the lipid tracer ([3H]) was in substantial excess over that due to the protein tracer (125I) demonstrating selective CE uptake ([3H]-(125)I) from HDL(3), LpA-I and LpA-I:A-II. SR-BI expression increased cellular selective CE uptake from labeled HDL(3) up to 24-fold. In BHK cells without SR-BI expression, selective CE uptake was higher from LpA-I compared with LpA-I:A-II. Analogously, in BHK cells with SR-BI expression, the rate of selective CE uptake was higher from LpA-I compared with LpA-I:A-II. In summary, SR-BI significantly increases selective CE uptake from HDL(3), LpA-I and LpA-I:A-II. Concerning HDL subfractions, the rate of SR-BI-mediated selective CE uptake is greater from LpA-I compared with LpA-I:A-II and this result suggests that SR-BI preferentially facilitates the CE transfer from LpA-I lipoprotein particles to cells.