In Vitro Evaluation of Excipients as Inhibitors of Human Intestinal P‐glycoprotein

Abstract

P‐glycoprotein (P‐gp) is one of the major barriers to oral bioavailability and contributes to the interindividual variability observed in intestinal absorption of P‐gp substrates. A well characterized source of variable P‐gp function in the intestine is inhibition by co‐administered drugs. However, the potential interplay between intestinal P‐gp and pharmaceutical excipients used in orally administered drug products has not been systematically studied and is the focus of this investigation. A fluorescence assay using calcein AM (5 mM), which served as a model substrate for P‐gp, was used to assess inhibition of P‐gp transport function by 130 excipients in HEK293 cells stably expressing human P‐gp or transfected with an empty vector (control). Specific inhibition of P‐gp‐mediated calcein AM efflux by excipients was expressed as a ratio of inhibition observed in P‐gp overexpressing cells over control cells. An inhibition screen was performed at an excipient concentration of 200 mM where possible, or at 50 mM where excipient solubility was limiting. Six potential inhibitors (inhibition ratio >1.3) were identified, including five dyes (D&C Red #6, D&C Brown#1, Naphthol blue black, Acid blue 9, Light green CF yellowish) and one suspending agent (Butylparaben). None of these potential inhibitors achieved >30% inhibition of calcein‐AM efflux at concentrations up to 300 mM. Intestinal concentrations of these potential inhibitors estimated from the maximum amount of each excipient allowed per unit dose (http://excipients.ucsf.bkslab.org/) ranged from 0.50–2.3 mM, with the exception of light green CF yellowish (214 mM). While these in vitro findings indicate minimal inhibition of human P‐gp at intestinal excipient concentrations typically expected from marketed drugs, further studies are needed to assess the impact of these excipients on the oral bioavailability of P‐gp substrates.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.