Tetrahydrocannabinol and Its Major Metabolites Are Not (or Are Poor) Substrates or Inhibitors of Human P-Glycoprotein [ATP-Binding Cassette (ABC) B1] and Breast Cancer Resistance Protein (ABCG2)

Abstract

(-)-Δ⁹-Tetrahydrocannabinol (THC) is the primary psychoactive constituent of cannabis. In humans, 11-hydroxy-THC (11-OH-THC) and 11-nor-9-carboxy-THC (THC-COOH) are psychoactive and nonpsychoactive circulating metabolites of THC, respectively. Whether these cannabinoids are substrates or inhibitors of human P-glycoprotein (P-gp) or breast cancer resistance protein (BCRP) is unknown. Previous animal studies suggest that THC and its metabolites could be substrates of these transporters. Therefore, we performed Transwell, cellular accumulation, and vesicular transport assays, at pharmacologically relevant concentrations of these cannabinoids, using Madin-Darby canine kidney (MDCK) II cells or plasma membrane vesicles overexpressing human P-gp or BCRP. Neither THC nor 11-OH-THC was found to be a substrate or inhibitor of P-gp or BCRP. The efflux ratio of THC-COOH in MDCKII-BCRP cells was 1.6, which was significantly decreased to 1.0 by the BCRP inhibitor Ko143. Likewise, cellular accumulation of THC-COOH was significantly increased 1.6-fold in the presence versus absence of Ko143. THC-COOH also significantly inhibited BCRP-mediated transport of Lucifer yellow, a BCRP substrate; however, THC-COOH was neither a substrate nor an inhibitor of P-gp. Collectively, these results indicate that THC and 11-OH-THC are not substrates or inhibitors (at pharmacologically relevant concentrations) of either P-gp or BCRP. THC-COOH is a weak substrate and inhibitor of BCRP, but not of P-gp. Accordingly, we predict that P-gp/BCRP will not modulate the disposition of these cannabinoids in humans. In addition, use of these cannabinoids will not result in P-gp- or BCRP-based drug interactions. SIGNIFICANCE STATEMENT: This study systematically investigated whether Δ⁹-tetrahydrocannabinol (THC) and its major metabolites, 11-hydroxy-THC and 11-nor-9-carboxy-THC, are substrates and/or inhibitors of human P-gp and BCRP at pharmacologically relevant concentrations. The results obtained are highly valuable for mechanistic understanding and prediction of the roles of P-gp and BCRP in determining the human pharmacokinetics, tissue distribution, and drug interactions of cannabinoids.

Fig. 1.

Cellular accumulation of THC, 11-OH-THC, or THC-COOH in MDCKII-P-gp cells in a representative experiment. Cellular accumulation of 5 µM THC (A), 0.3 µM 11-OH-THC (B), 2.5 µM THC-COOH (C), and 2 µM quinidine (D) in MDCKII-P-gp cells in the absence (solid circles) or presence (solid squares) of 5 µM tariquidar in a representative experiment. Data shown are means ± S.D. of triplicates. Differences in cellular accumulation in the absence and presence of tariquidar were analyzed using two-way ANOVA followed by the Šidák’s post hoc test. *P < 0.05.

Fig. 2.

Transwell transport of THC-COOH by BCRP in MDCKII-BCRP cells. Shown are the Transwell transport data of 2.5 µM THC-COOH (A and B) and 3 µM prazosin (C and D) in MDCKII-BCRP cells in the absence (solid circles for A→B, and solid squares for B→A) or presence (open circles for A→B, and open squares for B→A) of 5 µM Ko143. Data shown are means ± S.D. of triplicates. Differences in transport between the A→B and B→A directions at each time point were analyzed using paired two-way ANOVA followed by the Tukey’s post hoc test. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

Fig. 3.

Cellular accumulation of THC, 11-OH-THC, and THC-COOH in MDCKII-BCRP cells in a representative experiment. Shown are cellular accumulation data for 5 µM THC (A), 0.3 µM 11-OH-THC (B), 2.5 µM THC-COOH(C), and 3 µM prazosin (D) in MDCKII-BCRP cells in the absence (solid circles) or presence (solid squares) of 5 µM Ko143 in a representative experiment with triplicates. Data shown are means ± S.D. from triplicates in the experiment. Differences in cellular accumulation between the absence and presence of Ko143 were analyzed using two-way ANOVA followed by the Šidák’s post hoc test. *P < 0.05; **P < 0.01.

Fig. 4.

Inhibition of P-gp– or BCRP-mediated vesicular transport by THC, 11-OH-THC, or THC-COOH. Inhibition of P-gp– or BCRP-mediated vesicular transport by THC, 11-OH-THC, or THC-COOH at pharmacologically relevant concentrations was assessed using inside-out plasma membrane vesicles overexpressing human P-gp (A) or BCRP (B). Data shown are means ± S.D. of triplicates with duplicate in each experiment. The final concentrations of NMQ (P-gp probe substrate) and LY (BCRP probe substrate) were 1 µM and 50 µM, respectively. Statistically significant differences between all treatment groups were evaluated using paired one-way ANOVA followed by the Dunnett’s post hoc test for multiple comparisons. * P < 0.05; ** P < 0.01; *** P < 0.001.