Pharmacokinetics and metabolism of a cysteinyl leukotriene-1 receptor antagonist from the heterocyclic chromanol series in rats: in vitro-in vivo correlation, gender-related differences, isoform identification, and comparison with metabolism in human hepatic tissue

CP-199,331 is a potent antagonist of the cysteinyl leukotriene-1 (LT(1)) receptor, targeted for the treatment of asthma. The pharmacokinetic/metabolism properties of CP-199,331 were studied in rats and compared with those in human liver microsomes/hepatocytes. In vitro biotransformation of CP-199,331 in rat and human hepatocytes was similar, consisting primarily of CP-199,331 O-demethylation. Marked sex-related differences in plasma clearance (CL(p)) of CP-199,331 were observed in rats: 51 and 1.2 ml/min/kg in males and females, respectively. This difference in CL(p) was attributed to gender differences in metabolizing capacity because V(max) and K(m) values for CP-199,331 metabolism were 30-fold higher and 8-fold lower, respectively, in male rat liver microsomes compared with female microsomes. Scale-up of the in vitro microsomal data predicted hepatic clearance (CL(h)) of 64 and 2.5 ml/min/kg in male and female rats, respectively. These values were in close agreement with the in vivo CL(p), suggesting that CP-199,331 CL(p) in male and female rats was entirely due to hepatic metabolism. Studies with rat recombinant cytochromes P450 and anti-rat cytochrome P450 (CYP) antibodies revealed the involvement of male rat-specific CYP2C11 in the metabolism of CP-199,331. In contrast, CP-199,331 metabolism in human liver microsomes was principally mediated by CYP3A4. The projected human clearance in liver microsomes and hepatocytes varied 6-fold from low to moderate, depending on CYP3A4 activity. Considering that O-demethylation is the major route of elimination in humans, the in vivo clearance of CP-199,331 may exhibit moderate variability, depending on CYP3A4 abundance in the human population.

Discovery of CP-199,330 and CP-199,331: two potent and orally efficacious cysteinyl LT1 receptor antagonists devoid of liver toxicity

CP-199,330 (3) and CP-199,331 (4) are cysLT1 receptor antagonists that are equipotent to marketed cysLT1 receptor antagonists zafirlukast and pranlukast, show good pharmacokinetics in rats and monkeys, and are devoid of liver toxicity in monkeys as seen in CP-85,958 (1).

Development of 2,2-dimethylchromanol cysteinyl LT1 receptor antagonists

A new series of cysLT1 receptor antagonists represented by CP-288,886 (7) and CP-265,298 (8) were developed which are equipotent to clinical cysLT1 receptor antagonists Zafirlukast (1) and Pranlukast (2).

Discovery of the hemifumarate and (alpha-L-alanyloxy)methyl ether as prodrugs of an antirheumatic oxindole: prodrugs for the enolic OH group

Ether, ester, and carbonate derivatives of the antirheumatic oxindole 1 were prepared and screened as potential prodrugs of 1. This effort led to the discovery of the (alpha-L-alanyloxy)-methyl ether and hemifumarate derivatives of 1 which deliver the drug efficiently into the circulation of test animals, are stable in the solid state, and possess good stability in solution at low pH as required to ensure gastric stability. Success in achieving acceptable bioavailabilities of 1 across species (rats, dogs, and monkeys) followed the inclusion of ionizable functionality within the promoiety to compensate for masking the polar enolic OH group of the free drug. However, the introduction of ionizable functionality was often associated with decreased stability, as demonstrated by the hemisuccinate, hemiadipate, hemisuberate, and alpha-amino ester derivatives of 1 which could not be isolated. A clear exception was the hemifumarate derivative of 1 which was not only isolable but actually more stable at neutral pH than the nonionizable ester analogues. The solution and solid state stability of the hemifumarate, together with its activity as a prodrug of 1, suggests that hemifumarate be considered as an alternative to hemisuccinate as a prodrug derivative for alcohols, particularly in situations where solution state stability is an issue.