Received for publication October 24, 2006.
Revised March 1, 2007.
Accepted for publication March 6, 2007.

Pharmacokinetics of ML3403, a 4-pyridinylimidazole-type p38 MAP kinase inhibitor

Abstract

The p38 mitogen-activated protein kinase (MAPK) is a key mediator in cytokine-induced signalling events that are activated in response to a variety of extracellular stimuli such as stress factors, apoptosis and proliferation. Therefore the MAPK family plays an integral role in disease states including oncogenesis, autoimmune diseases and inflammatory processes. Inhibition of these protein kinases represents an attractive strategy for therapeutic intervention. Especially one class of p38 MAP kinase inhibitors - the pyridinyl imidazole derivatives - are intensely investigated by several industrial groups but so far no studies concerning the metabolism of these structurally related substances seem to be available. The objective of our examinations was the preclinical characterization of ML3403, {4-[5-(4-fluorophenyl)-2-methylsulfanyl-3H-imidazol-4-yl]-pyridin-2-yl}-(1-phenylethyl)-amine a potent inhibitor of p38 MAP kinase - comprising the basic pyridinyl imidazole structure. In human hepatic microsomal incubations, the sulfoxidation to ML3603 and M-sulfone was found to be the predominant metabolic transformation. In addition, oxidative removal of the phenylethyl moiety, pyridine N-oxidation and hydroxylation reactions were observed. Incubations were carried out with hepatic microsomes from various species and with recombinant human CYP isoenzymes, showing that CYP1A2, CYP2C19, CYP2D6 and CYP3A4 are the prominent enzymes in the metabolism of ML3403. Michaelis-Menten kinetics of ML3603 formation by these recombinant isoenzymes showed that CYP3A4 plays a pivotal role in the sulfoxidation reaction. Additionally, pharmacokinetics of ML3403 were evaluated in male and female Wistar rats after oral gavage, showing a fast and high conversion to its active sulfoxide metabolite ML3603. A remarkable gender-specific difference in the systemic exposure to ML3403 and ML3603 was found in rats. No gender-specific difference was detected in incubations with human liver microsomes.

Key words: analytical pharmacology/toxicology, CYP inhibition, cytochrome P450 isoforms, drug development, kinetic modeling, kinetics, metabolite kinetics, pharmacokinetics