1. Elaborate studies of cholesteryl ester transfer protein (CETP) polymorphisms and genetic deficiency in humans suggest direct links between CETP, high-density lipoprotein cholesterol (HDL-c) levels and coronary heart diseases. The hypothesis that CETP inhibition by small molecule inhibitors raises HDL-c has been validated clinically with structurally-diverse CETP inhibitors such as torcetrapib, anacetrapib, dalcetrapib and evacetrapib. 2. Despite promising phase 2 results with respect to HDL-c elevation, torcetrapib was discontinued in phase 3 trials due to increased mortality rates in the cardiovascular outcomes study. Emerging evidence for the adverse effects hints at off-target chemotype-specific cardiovascular toxicity, possibly related to the pressor effects of torcetrapib, since structurally diverse CETP inhibitors such as anacetrapib, evacetrapib and dalcetrapib are not associated with blood pressure increases in humans. Nonclinical follow-up studies showed that torcetrapib induces aldosterone biosynthesis and secretion in vivo and in vitro, an effect which is not observed with other CETP inhibitors in clinical development. 3. As part of ongoing efforts to identify novel CETP inhibitors devoid of pressor effects, strategies were implemented towards the design of compounds, which lack the 1,2,3,4-tetrahydroquinoline (THQ) scaffold present in torcetrapib. In this article, we disclose results of structure-activity relationship studies for a series of novel non-THQ CETP inhibitors, which resulted in the identification of a novel isonipecotic acid derivative 10 (also referred to as PF-04445597) with vastly improved oral pharmacokinetic properties mainly as a result of improved aqueous solubility. This feature is attractive in that, it bypasses significant investments needed to develop compatible solubilizing formulation(s) for oral drug delivery of highly lipophilic and poorly soluble compounds; attributes, which are usually associated with small molecule CETP inhibitors. PF-04445597 was also devoid of aldosterone secretion in human H295R adrenal carcinoma cells.

The role of transporters in the disposition of (+)-2-[4-({[2-(benzo[1,3]dioxol-5-yloxy)-pyridine-3-carbonyl]-amino}-methyl)-3-fluoro-phenoxy]-propionic acid (CP-671,305), an orally active inhibitor of phosphodiesterase-4, was examined. In bile duct-exteriorized rats, a 7.4-fold decrease in the half-life of CP-671,305 was observed, implicating enterohepatic recirculation. Statistically significant differences in CP-671,305 pharmacokinetics (clearance and area under the curve) were discernible in cyclosporin A- or rifampicin-pretreated rats. Considering that cyclosporin A and rifampicin inhibit multiple uptake/efflux transporters, the interactions of CP-671,305 with major human hepatic drug transporters, multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2), breast cancer resistant protein (BCRP), and organic anion-transporting polypeptide (OATPs) were evaluated in vitro. CP-671,305 was identified as a substrate of MRP2 and BCRP, but not MDR1. CP-671,305 was a substrate of human OATP2B1 with a high affinity (Km = 4 microM) but not a substrate for human OATP1B1 or OATP1B3. Consistent with these results, examination of hepatobiliary transport of CP-671,305 in hepatocytes indicated active uptake followed by efflux into bile canaliculi. Upon examination as a substrate for major rat hepatic Oatps, CP-671,305 displayed high affinity (Km = 12 microM) for Oatp1a4. The role of rat Mrp2 in the biliary excretion was also examined in Mrp2-deficient rats. The observations that CP-671,305 pharmacokinetics were largely unaltered suggested that compromised biliary clearance of CP-671,305 was compensated by increased urinary clearance. Overall, these studies suggest that hepatic transporters play an important role in the disposition and clearance of CP-671,305 in rat and human, and as such, these studies should aid in the design of clinical drug-drug interaction studies.

The disposition of 6-(4-(2,5-difluorophenyl)oxazol-5-yl)-3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine (1), a potent and selective inhibitor of mitogen activated protein (MAP) kinase p38α, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 1 demonstrated generally favorable pharmacokinetic properties in all species examined. Following intravenous (i.v.) administration, 1 exhibited low volumes of distribution at steady state (Vdss) ranging from 0.4–1.3 l/kg (2.4–26 l/m2) in the rat, dog and monkey. Systemic plasma clearance was low in cynomolgus monkeys (6.00 ml/min/kg, 72.0 ml/min/m2) and Sprague-Dawley rats (7.65±1.08 ml/min/kg, 45.9±6.48 ml/min/m2 in male rats and 3.15±0.27 ml/min/kg, 18.9±1.62 ml/min/m2 in female rats) and moderate in beagle dogs (12.3±5.1 ml/min/kg, 246±102 ml/min/m2) resulting in plasma half-lives ranging from 1 to 5 h in preclinical species. Moderate to high bioavailability of 1 was observed in rats (30–65%), dogs (87%) and monkeys (40%) after oral (p.o.) dosing consistent with the in vitro absorption profile of 1 in the Caco-2 permeability assay. In rats, the oral pharmacokinetics were dose dependent over the dose range studied (5, 50 and 100 mg/kg). The principal route of clearance of 1 in rat, dog, monkey and human liver microsomes and in vivo in preclinical species involved oxidative metabolism mediated by cytochrome P450 enzymes. The major metabolic fate of 1 in preclinical species and humans involved hydroxylation on the isopropyl group to yield the tertiary alcohol metabolite 2. In human liver microsomes, this transformation was catalysed by CYP3A4 as judged from reaction phenotyping analysis using isozyme-specific inhibitors and recombinant CYP enzymes. Metabolite 2 was also shown to possess inhibitory potency against p38α in a variety of in vitro assays. 1 as well as the active metabolite 2 were moderately to highly bound to plasma proteins (fu∼0.1–0.33) in rat, mouse, dog, monkey and human. 1 as well as the active metabolite 2 did not exhibit competitive inhibition of the five major cytochrome P450 enzymes namely CYP1A2, 2C9, 2C19, 2D6 and 3A4 (IC50>50 µM). Overall, these results indicate that the absorption, distribution, metabolism and excretion (ADME) profile of 1 is relatively consistent across preclinical species and predict potentially favorable pharmacokinetic properties in humans, supporting its selection for toxicity/safety assessment studies and possible investigations in humans as an anti-inflammatory agent. Copyright © 2006 John Wiley & Sons, Ltd.

Clinical Pharmacology & TherapeuticsVolume 77, Issue 3 p. 225-226 Letter to the Editor Disposition of Cisapride Appears to be Influenced by P-glycoprotein in the Mouse Edna F. Choo PhD, Edna F. Choo PhD Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorKarthik Venkatakrishnan PhD, Karthik Venkatakrishnan PhD Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorHeather L. Hatch MA, Heather L. Hatch MA Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorSandhya Rahematpura BSc, Sandhya Rahematpura BSc Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this author Edna F. Choo PhD, Edna F. Choo PhD Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorKarthik Venkatakrishnan PhD, Karthik Venkatakrishnan PhD Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorHeather L. Hatch MA, Heather L. Hatch MA Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this authorSandhya Rahematpura BSc, Sandhya Rahematpura BSc Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Groton, ConnSearch for more papers by this author First published: 07 March 2005 https://doi.org/10.1016/j.clpt.2004.10.009Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References 1Lowry, J. A., Kearns, G. L., Abdel-Rahman, S. M., Nafziger, A. N., Khan, I. S. and Kashuba, A. D. M. et al. (2003). Cisapride: a potential model substrate to assess cytochrome P4503A4 activity in vivo. Clin Pharmacol Ther. 73: 209–222. 2Kim, R. B., Fromm, M. F., Wandel, C., Leake, B., Wood, A. J. J. and Roden, D. M. et al. (1998). The drug transporter P-glycoprotein limits oral absorption and brain entry of HIV-1 protease inhibitors. J Clin Invest. 101: 289–294. 3Gottesman, M. M. and Pastan, I. (1993). Biochemistry of multidrug resistance mediated by the multidrug transporter. Annu Rev Biochem. 62: 385–427. 4Cordon-Cardo, C., O'Brien, J. P., Casals, D., Rittman-Grauer, L., Biedler, J. L. and Melamed, M. R. et al. (1989). Multidrug-resistance gene (P-glycoprotein) is expressed by endothelial cells at blood-brain barrier sites. Proc Natl Acad Sci U S A. 86: 695–698. 5Michalets, E. L. and Williams, C. R. (2000). Drug interactions with cisapride: clinical implications. Clin Pharmacokinet. 39: 49–75. Volume77, Issue3March 2005Pages 225-226 ReferencesRelatedInformation