| Summary: | Indazole carboxamide synthetic cannabinoid, AB-PINACA, has been placed into Schedule I of the Controlled Substances Act by the US Drug Enforcement Administration since 2015. Despite the possibility of AB-PINACA exposure in drug abusers, the interactions between AB-PINACA and drug-metabolizing enzymes and transporters that play crucial roles in the pharmacokinetics and efficacy of various substrate drugs have not been investigated. This study was performed to investigate the inhibitory effects of AB-PINACA on eight clinically important human major cytochrome P450s (CYPs) and six uridine 5′-diphospho-glucuronosyltransferases (UGT) in human liver microsomes and the activities of six solute carrier transporters and two efflux transporters in transporter-overexpressing cells. AB-PINACA reversibly inhibited the metabolic activities of CYP2C8 (<i><b>K</b><sub>i</sub></i>, 16.9 µM), CYP2C9 (<i><b>K</b><sub>i</sub></i>, 6.7 µM), and CYP2C19 (<i><b>K</b><sub>i</sub></i>, 16.1 µM) and the transport activity of OAT3 (<i><b>K</b><sub>i</sub></i>, 8.3 µM). It exhibited time-dependent inhibition on CYP3A4 (<i><b>K</b><sub>i</sub></i>, 17.6 µM; <i><b>k</b><sub>inact</sub></i>, 0.04047 min<sup>−1</sup>). Other metabolizing enzymes and transporters such as CYP1A2, CYP2A6, CYP2B6, CYP2D6, UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7, OAT1, OATP1B1, OATP1B3, OCT1, OCT2, P-glycoprotein, and BCRP, exhibited only weak interactions with AB-PINACA. These data suggest that AB-PINACA can cause drug-drug interactions with CYP3A4 substrates but that the significance of drug interactions between AB-PINACA and CYP2C8, CYP2C9, CYP2C19, or OAT3 substrates should be interpreted carefully.
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