Gamini Chandrasena

Comparative Metabolism of Radiolabeled Muraglitazar in Animals and Humans by Quantitative and Qualitative Metabolite Profiling

Muraglitazar (Pargluva), a dual α/γ peroxisome proliferator-activated receptor (PPAR) activator, has both glucose- and lipid-lowering effects in animal models and in patients with diabetes. This study describes the in vivo and in vitro comparative metabolism of [14C]muraglitazar in rats, dogs, monkeys, and humans by quantitative and qualitative metabolite profiling. Metabolite identification and quantification methods used in these studies included liquid chromatography/mass spectrometry (LC/MS), LC/tandem MS, LC/radiodetection, LC/UV, and a newly described mass defect filtering technique in conjunction with high resolution MS. After oral administration of [14C]muraglitazar, absorption was rapid in all species, reaching a concentration peak for parent and total radioactivity in plasma within 1 h. The most abundant component in plasma at all times in all species was the parent drug, and no metabolite was present in greater than 2.5% of the muraglitazar concentrations at 1 h postdose in rats, dogs, and humans. All metabolites observed in human plasma were also present in rats, dogs, or monkeys. Urinary excretion of radioactivity was low (<5% of the dose) in all intact species, and the primary route of elimination was via biliary excretion in rats, monkeys, and humans. Based on recovered doses in urine and bile, muraglitazar showed a very good absorption in rats, monkeys, and humans. The major drug-related components in bile of rats, monkeys, and humans were glucuronides of muraglitazar and its oxidative metabolites. The parent compound was a minor component in bile, suggesting extensive metabolism of the drug. In contrast, the parent drug and oxidative metabolites were the major components in feces, and no glucuronide conjugates were found, suggesting that glucuronide metabolites were excreted in bile and hydrolyzed in the gastrointestinal tract. The metabolites of muraglitazar resulted from both glucuronidation and oxidation. The metabolites in general had greatly reduced activity as PPARα/γ activators relative to muraglitazar. In conclusion, muraglitazar was rapidly absorbed, extensively metabolized through glucuronidation and oxidation, and mainly eliminated in the feces via biliary excretion of glucuronide metabolites in all species studied. Disposition and metabolic pathways were qualitatively similar in rats, dogs, monkeys, and humans.

Identification and optimization of a novel series of [2.2.1]-oxabicyclo imide-based androgen receptor antagonists

A novel series of [2.2.1]-oxabicyclo imide-based compounds were identified as potent antagonists of the androgen receptor. Molecular modeling and iterative drug design were applied to optimize this series. The lead compound [3aS-(3aalpha,4beta,5beta,7beta,7aalpha)]-4-(octahydro-5-hydroxy-4,7-dimethyl-1,3-dioxo-4,7-epoxy-2H-isoindol-2-yl)-2-iodobenzonitrile was shown to have potent in vivo efficacy after oral dosing in the CWR22 human prostate tumor xenograph model.

Pharmacokinetics of muraglitazar (BMS-298585), a dual peroxisome proliferator-activated receptors (PPAR) α and γ activator, in mice, rats, dogs, and monkeys

The pharmacokinetic parameters of muraglitazar, a novel dual-activator of the peroxisome proliferator-activated receptors (PPAR) α and γ, were determined in mice, rats, dogs, and monkeys after intravenous and oral administration. In the mouse, rat, and monkey the absolute oral bioavailability of muraglitazar ranged from 64 to 88%, and in the dog oral bioavailability was approximately 18%. The systemic clearance values of muraglitazar in the mouse, rat, dog, and cynomolgus monkey were 1.2, 3.0, 12.3 and 1.2 ml min−1 kg−1, respectively. The terminal elimination half-life was 2.4 h in dogs and 7.3 h in rats. The terminal elimination half-life could not be determined in the mouse and monkey because the sampling interval did not adequately cover the terminal elimination phase. Muraglitazar appears to be distributed outside of the vasculature, with the steady-state volume of distribution being approximately twofold that of the vascular volume in rats and dogs, and approximately twofold that of the total body water in mice. The systemic plasma clearance of muraglitazar in humans was predicted to be approximately 12–14 ml min−1 kg−1 based on allometry or by scaling of in vitro clearance parameters. Overall, the pharmacokinetic parameters of muraglitazar in preclinical species were acceptable for the advancement of the compound as a clinical candidate.

N-Heteroaryl glycinamides and glycinamines as potent NPY5 antagonists

Subtype specific ligands are needed to evaluate the therapeutic potential of modulating the brains neuropeptide Y system. The benzothiazepine glycinamide 1a was identified as an NPY5 antagonist lead. While having acceptable solubility, the compound was found to suffer from high clearance and poor exposure. Optimization efforts are described targeting improvements in potency, microsomal stability, and PK properties. The low microsomal stability and poor PK properties were addressed through the optimization of the sulfonyl urea and replacement of the benzothiazepinone with other N-heteroaryl glycinamides. For example, the analogous benzoxazine glycinamide 2e has improvements in both affinity (human Y5 K(i) 4 nM vs 1a 27 nM) and microsomal stability (human CL(int) 2.5 L/min vs 1a 35L/min). However the brain penetration (B/P 43/430 nM at 10 mg/kg PO) remained an unresolved issue. Further optimization by decreasing the hydrogen bond donating properties and PSA provided potent and brain penetrant NPY5 antagonists such as 5f (human Y5 K(i) 9 nM, B/P 520/840 nM 10 mg/kg PO).

Indolyl and dihydroindolyl N-glycinamides as potent and in vivo active NPY5 antagonists.

A novel series of indolyl and dihydroindolyl glycinamides were identified as potent NPY5 antagonists with in vivo activity from screen hit 1. The dihydroindolyl glycinamide 10a significantly inhibits NPY5 agonist induced feeding at a dose of 0.1 mg/kg. The indolyl glycinamide 12c also inhibits NPY5 agonist induced feeding at a dose of 1 mg/kg. Both compounds 10a and 12c represent potential tools for further investigation into the biology of the NPY5 receptor.

Radiosynthesis and in Vivo Evaluation of Neuropeptide Y5 Receptor (NPY5R) PET Tracers

Neuropeptide Y receptor type 5 (NPY5R) is a G-protein coupled receptor (GPCR) that belongs to the subfamily of neuropeptide receptors (NPYR) that mediate the action of endogenous neuropeptide Y (NPY). Animal models and preclinical studies indicate a role for NPY5R in the pathophysiology of depression, anxiety, and obesity and as a target of potential therapeutic drugs. To better understand the pathophysiological involvement of NPY5R, and to measure target occupancy by potential therapeutic drugs, it would be advantageous to measure NPY5R binding in vivo by positron emission tomography (PET). Four potent and selective NPY5R antagonists were radiolabeled via nucleophilic aromatic substitution reactions with [(18)F]fluoride. Of the four radioligands investigated, PET studies in anesthetized baboons showed that [(18)F]LuAE00654 ([(18)F]N-[trans-4-({[4-(2-fluoropyridin-3-yl)thiazol-2-yl]amino}methyl)cyclohexyl]propane-2-sulfonamide) penetrates blood brain barrier (BBB) and a small amount is retained in the brain. Slow metabolism of [(18)F]LuAE00654 was observed in baboon plasma. Blocking studies with a specific NPY5R antagonist demonstrated up to 60% displacement of radioactivity in striatum, the brain region with highest NPY5R binding. Our studies suggest that [(18)F]LuAE00654 can be a potential PET radiotracer for the quantification and occupancy studies of NPY5R drug candidates.