IN-VITRO AND IN-VIVO EFFECTS OF THE ARYLAMINE HUMAN-IMMUNODEFICIENCY-VIRUS PROTEASE INHIBITOR -BETA,7-BETA)-1-[(3-(1-IMIDAZOYLCARBAMONYL)PHENYL) AMINOPHENYL)METHYL]HEXAHYDRO-5,6-DIHYDROXY-4,7-BIS (PHENYLMETHYL)-2H-1,3-DIAZEPIN-2-ONE (SD894) ON RAT HEPATIC CYTOCHROME-P450 2B AND 3A

The human immunodeficiency virus-1 protease inhibitor SD894 was evalua ted as an inhibitor and inducer of cytochromes P450 (CYPs) in rats, Af ter addition of 10 mu M SD894 and 2 mM NADPH to liver microsomes from dexamethasone-treated rats, a type ii spectrum appeared. Within 2 min, it was replaced by a type ill spectrum, with absorbance maxima at 426 and 456 nm, similar to those observed with alkylamines (SKF-525A) and arylamines (p-chloroaniline). Preincubation of microsomes from dexame thasone-treated rats with SD894 and NADPH resulted in a time-dependent inhibition of testosterone 6 beta-hydroxylation (CYP 3A1/2 activity), which was decreased to 25% of controls after 30 min, Testosterone 16 beta-hydroxylation (CYP 2B1/2 activity) was unaffected under these con ditions. Testosterone 6 beta-hydroxylation rates in liver microsomes f rom pregnenolone 16 alpha-carbonitrile-treated rats incubated with 10 mu M SD894 and NADPH, washed, and reisolated by ultra centrifugation w ere reduced by 71%, whereas 16 beta-hydroxylation was unaffected by SD 894. Immunoblots of liver microsomes from rats dosed iv with SD894 or ip with TAO displayed increased CYP 2B1 and CYP 3A1 levels, respective ly, Testosterone 6 beta-hydroxylase activity in microsomes from TAO-tr eated rats was greater than controls, Preincubation of these microsome s with potassium ferricyanide produced an additional 50% increase, con sistent with disruption of a metabolite-GYP complex. Microsomes from S D894-treated rats displayed a 3-fold increase in testosterone 16 beta- hydroxylation. Potassium ferricyanide preincubation did not increase a ctivity. Thus, although SD894 appears to inhibit CYP in vitro in a man ner typical of other amine-containing, mechanism-based inhibitors, in vivo induction by 10 mg/kg daily doses of SD894 affects a different is ozyme than does inhibition. The mechanism of induction is unknown.