RT Journal Article SR Electronic T1 EFFECT OF CYP3A5 POLYMORPHISM ON TACROLIMUS METABOLIC CLEARANCE IN VITRO JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 836 OP 847 DO 10.1124/dmd.105.008680 VO 34 IS 5 A1 Dai, Yang A1 Hebert, Mary F. A1 Isoherranen, Nina A1 Davis, Connie L. A1 Marsh, Christopher A1 Shen, Danny D. A1 Thummel, Kenneth E. YR 2006 UL http://dmd.aspetjournals.org/content/34/5/836.abstract AB Previous investigations of solid organ transplant patients treated with tacrolimus showed that individuals carrying a CYP3A5*1 allele have lower dose-adjusted trough blood concentrations compared with homozygous CYP3A5*3 individuals. The objective of this investigation was to quantify the contribution of CYP3A5 to the hepatic and renal metabolic clearance of tacrolimus. Four primary tacrolimus metabolites, 13-O-desmethyl tacrolimus (13-DMT) (major), 15-O-desmethyl tacrolimus, 31-O-desmethyl tacrolimus (31-DMT), and 12-hydroxy tacrolimus (12-HT), were generated by human liver microsomes and heterologously expressed CYP3A4 and CYP3A5. The unbound tacrolimus concentration was low (4–15%) under all incubation conditions. For CYP3A4 and CYP3A5, Vmax was 8.0 and 17.0 nmol/min/nmol enzyme and Km,u was 0.21 and 0.21 μM, respectively. The intrinsic clearance of CYP3A5 was twice that of CYP3A4. The formation rates of 13-DMT, 31-DMT, and 12-HT were ≥1.7-fold higher, on average, in human liver microsomes with a CYP3A5*1/*3 genotype compared with those with a homozygous CYP3A5*3/*3 genotype. Tacrolimus disappearance clearances were 15.9 ± 9.8 ml/min/mg protein and 6.1 ± 3.6 ml/min/mg protein, respectively, for the two genotypes. In vitro to in vivo scaling using both liver microsomes and recombinant enzymes yielded higher predicted in vivo tacrolimus clearances for patients with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. In addition, formation of 13-DMT was 13.5-fold higher in human kidney microsomes with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. These data suggest that CYP3A5 contributes significantly to the metabolic clearance of tacrolimus in the liver and kidney. The American Society for Pharmacology and Experimental Therapeutics