The effectiveness of controlled release 1-aminobenzotriazole (ABT) administration to inhibit cytochrome P450 (P450) enzymes has been evaluated in mice. To maximize the duration of P450 inhibition in vivo, ABT was administered via an osmotic pump. The degree of P450 inhibition was compared with that achieved with a single bolus dose of ABT. Two-hour prior subcutaneous treatment of mice with ABT (50 mg/kg) inhibited antipyrine clearance by 88%. A less pronounced inhibitory effect (29% reduction in clearance) was observed when ABT was administered 24-hours before antipyrine administration, indicating partial restoration of P450 activity during this longer pretreatment time. The duration of ABT in mice was very short (mean residence time = 1.7 hours) after subcutaneous bolus administration. When the inhibitor was delivered by an osmotic pump, maximum blood concentrations of the inhibitor were observed 24 hours after device implantation and were maintained at steady state for 6 days. Inhibition of P450 activity, as measured by antipyrine clearance, was confirmed at 24 hours and 120 hours after pump implantation, highlighting the utility of this method as a longerterm model for P450 inhibition in mice. The magnitude of P450 inhibition in ABT-treated mice was compared with that in hepatic P450 reductase null mice and both models were comparable. In vivo ABT administration by an osmotic pump offers an effective approach for longer-term P450 inhibition in mice and avoids the necessity for multiple dosing of the inhibitor.
Introduction1-Aminobenzotriazole (ABT) is a time-dependant inhibitor of cytochrome P450 (P450) enzymes (Ortiz de Montellano et al., 1984) and is often used as a tool compound for in vitro (Furnes and Schlenk, 2005) and in vivo (Stringer et al., 2014;Boily et al., 2015) drug metabolism studies. The utility of ABT for in vivo P450 inhibition has been evaluated in a range of species, including mice, rats, guinea pigs, dogs, and monkeys (Balani et al., 2002(Balani et al., , 2004. For each species, efficient inhibition of metabolism was demonstrated with antipyrine, a nonspecific substrate of P450 enzymes (Engel et al., 1996;Sharer and Wrighton, 1996). To avoid the need for repeated ABT administration, we have explored the use of osmotic pumps as a technology to achieve sustained release of ABT and sustained inhibition of P450 enzymes in mice.To assess the effectiveness of the in vivo ABT approach, we compared the degree of P450 inhibition using this method with that in the hepatic reductase null (HRN) mouse. The HRN mouse only has residual hepatic P450 activity as a result of a liver-specific knockout of the P450 reductase enzyme during the postnatal period (Henderson et al., 2003), and extrahepatic P450 is unaffected. Marked differences in drug disposition have been observed in HRN mice compared with wild-type mice (Pickup et al., 2012;Boggs et al., 2014;Grimsley et al., 2014). After a single bolus dose of ABT to mice, the duration of inhibitory activity was relatively short: clearance of antipyrin...