title: A rational chemical intervention strategy to circumvent bioactivation liabilities associated with a nonpeptidyl thrombopoietin receptor agonist containing a 2-amino-4-arylthiazole motif.
abstract: The current study examined the bioactivation potential of a nonpeptidyl thrombopoietin receptor agonist, 1-(3-chloro-5-((4-(4-fluoro-3-(trifluoromethyl)phenyl)thiazol-2-yl)carbamoyl)pyridine-2-yl)piperidine-4-carboxylic acid (1), containing a 2-carboxamido-4-arylthiazole moiety in the core structure. Toxicological risks arising from P450-catalyzed C4-C5 thiazole ring opening in 1 via the epoxidation-->diol sequence were alleviated, since mass spectrometric analysis of human liver microsome and/or hepatocyte incubations of 1 did not reveal the formation of reactive acylthiourea and/or glyoxal metabolites, which are prototypic products derived from thiazole ring scission. However, 4-(4-fluoro-3-(trifluoromethyl)phenyl)thiazol-2-amine (2), the product of hydrolysis of 1 in human liver microsomes, hepatocytes, and plasma, underwent oxidative bioactivation in human liver microsomes, since trapping studies with glutathione led to the formation of two conjugates derived from the addition of the thiol nucleophile to 2 and a thiazole- S-oxide metabolite of 2. Mass spectral fragmentation and NMR analysis indicated that the site of attachment of the glutathionyl moiety in both conjugates was the C5 position in the thiazole ring. Based on the structures of the glutathione conjugates, two bioactivation pathways are proposed, one involving beta-elimination of an initially formed hydroxylamine metabolite and the other involving direct two-electron oxidation of the electron-rich 2-aminothiazole system to electrophilic intermediates. This mechanistic insight into the bioactivation process allowed the development of a rational chemical intervention strategy that involved blocking the C5 position with a fluorine atom or replacing the thiazole ring with a 1,2,4-thiadiazole group. These structural changes not only abrogated the bioactivation liability associated with 1 but also resulted in compounds that retained the attractive pharmacological and pharmacokinetic attributes of the prototype agent.
authors.affiliation: Pharmacokinetics, Dynamics and Metabolism Department, Pfizer Global Research and Development, Groton, Connecticut 06340, USA. amit.kalgutkar@pfizer.com
authors.forename: Amit S
authors.initials: AS
authors.lastname: Kalgutkar
authors.forename: James
authors.initials: J
authors.lastname: Driscoll
authors.forename: Sabrina X
authors.initials: SX
authors.lastname: Zhao
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Walker
authors.forename: Richard M
authors.initials: RM
authors.lastname: Shepard
authors.forename: John R
authors.initials: JR
authors.lastname: Soglia
authors.forename: James
authors.initials: J
authors.lastname: Atherton
authors.forename: Linning
authors.initials: L
authors.lastname: Yu
authors.forename: Abdul E
authors.initials: AE
authors.lastname: Mutlib
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Munchhof
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Reiter
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Jones
authors.forename: Johnathan L
authors.initials: JL
authors.lastname: Doty
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Trevena
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Shaffer
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Ripp
mesh_terms: D000818:Animals; D001682:Biological Availability; D001711:Biotransformation; D002460:Cell Line; D004355:Drug Stability; D005978:Glutathione / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism; D015394:Molecular Structure; D011725:Pyridines / Q000097:blood / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053628:Receptors, Thrombopoietin / Q000819:agonists* / Q000235:genetics; D013844:Thiazoles / Q000097:blood / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection
chemical_list: C527070:1-(3-chloro-5-((4-(4-fluoro-3-(trifluoromethyl)phenyl)thiazol-2-yl)carbamoyl)pyridine-2-yl)piperidine-4-carboxylic acid; D011725:Pyridines; D053628:Receptors, Thrombopoietin; D013844:Thiazoles; C082218:MPL protein, human; D005978:Glutathione