Comparative Preclinical Drug Metabolism and Pharmacokinetic Evaluation of Novel 4-Aminoquinoline Anti-Malarials CHARLES B. DAVIS, 1 RAMESH BAMBAL, 1 GANESH S. MOORTHY, 1 ERIN HUGGER, 1 HONG XIANG, 1 BRIAN KEVIN PARK, 2 ALLISON E. SHONE, 3 PAUL M. O’NEILL, 4 STEPHEN A. WARD 3 1 Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Drug Discovery, 1250 South Collegeville Rd, Collegeville, Pennsylvania 19426 2 Department of Pharmacology and Therapeutics, University of Liverpool, Liverpool L693GE, UK 3 Molecular and Biochemical Parasitology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L35QA, UK 4 Department of Chemistry, University of Liverpool, Liverpool L697ZD, UK Received 27 March 2008; accepted 12 May 2008 Published online 18 June 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.21469 ABSTRACT: The disposition of three 4-aminoquinoline leads, namely isoquine (ISO), des-ethyl isoquine (DEI) and N-tert-butyl isoquine (NTBI), were studied in a range of in vivo and in vitro assays to assist in selecting an appropriate candidate for further development. Analogous to amodiaquine (ADQ), ISO undergoes oxidative N-dealkylation to form DEI in vivo. Blood clearance of DEI was as much as 10-fold lower than that of ISO in animals and after oral administration, metabolite exposure exceeded that of parent by as much as 14-fold. Replacement of the N-ethyl with an N-tert-butyl substituent substantially reduced N-dealkylation as blood clearance of NTBI was 2 to 3-fold lower than DEI in mouse, rat, dog and monkey. Mean NTBI oral bioavailability was generally higher than the other leads (68%). Blood cell association was substantial for NTBI, particularly in dog and monkey, where blood to plasma concentration ratios >4 were observed. Human plasma protein binding was similar for NTBI, DEI, and des-ethyl amodiaquine (DEA). Allometric scaling predicted human blood clearance (CL) for NTBI to be low (12% liver blood flow). All the 4-aminoquinolines inhibited recombinant human cytochrome P450 2D6 with similar potency; DEI also inhibited 1A2. On balance, NTBI appeared the most promising lead to progress towards full development. ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:362–377, 2009 Keywords: preclinical pharmacokinetics; drug design; pro-drugs; ADME; cyto- chrome P450; MDCK cells; protein binding; blood partitioning; anti-malarials; bioactivation INTRODUCTION Malaria is endemic to the poorest countries in the world, causing more than 1 million deaths each year. More than 90% of the deaths occur in Sub- Saharan Africa and nearly all the deaths are in children under the age of 5 years. The morbidity and mortality from malaria have been increasing over the last several decades due to deterioration in health systems, growing drug and insecticide Abbreviations used: CL, in vivo clearance; V ss , volume of distribution at steady-state; t 1/2 , apparent terminal half-life; AUC, area under the concentration-time curve; F, oral bioa- vailability; CLi, intrinsic clearance; P-gp, P-glycoprotein; MDR1, multidrug resistance 1; MDCKII, Madin Darby Canine Kidney Type II; NTBI, N-tert-butyl isoquine, ISO, isoquine; DEI, des-ethyl isoquine; ADQ, amodiaquine; DEA, des-ethyl amodiaquine. Correspondence to: Charles B. Davis (Telephone: 610-917- 5601; Fax: 610-917-7005; E-mail: charles.b.davis@gsk.com) Journal of Pharmaceutical Sciences, Vol. 98, 362–377 (2009) ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association 362 JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009