Metabolism of artelinic acid to dihydroqinghaosu by human liver cytochrome P4503A

1. Artelinic acid (AL), a water-soluble artemisinin analogue for treatment of multidrug resistant malaria, is metabolized to the active metabolite dihydroqinghaosu (DQHS) solely by CYP3A4/5. Although AL is not metabolized by CYP2C9, it does inhibit diclofenac 4-hydroxylase activity with an IC50= 115 mu M. Interestingly, AL activates CYP2D6-mediated bufuralol metabolism in human liver microsomes but not recombinant CYP2D6-Val by similar to 30% at AL concentrations up to 100 mu M. 2. In human liver microsomes, AL is metabolized to DQHS with a K-m, = 157 +/- 44 mu M I and V-max = 0.77+/-0.56 nmol DQHS/min/mg protein. Human recombinant CYP3A4 catalysed the conversion of AL to DQHS with a K-m,= 102+/-23 mu M and a I 1.96+/-0.38 nmol DQHS/min/nmol P450. The kinetic parameters (K-m and V-max) for DQHS formation from CYP3A5 were 189+/-19 mu M and 3.60+/-0.42 nmol DQHS/min/nmol P450 respectively. 3. Inhibition studies suggest that azole antifungals and calcium channel blockers may present clinically significant drug-drug interactions. In human liver microsomes, ketoconazole and miconazole were potent competitive inhibitors of DQHS formation with a K-1 = 0.028 and 0.124 mu M respectively. Verapamil is a non-competitive inhibitor of DQHS formation in human liver microsomes with a K-m = 15 mu M.