Unmasking the Dynamic Interplay between Intestinal P-Glycoprotein and CYP3A4

TLDR

Intestinal P‑glycoprotein reduces oral bioavailability of many CYP3A4 substrates by efflux. The study hypothesizes that P‑glycoprotein and CYP3A4 interaction at the apical membrane enhances drug metabolism. The authors employed CYP3A4‑transfected Caco‑2 cells to measure transport, metabolism, and intracellular levels of K77 (a P‑glycoprotein and CYP3A4 substrate) and felodipine (a CYP3A4 substrate only) while inhibiting P‑glycoprotein with GG918 or both enzymes with cyclosporine. K77 showed reduced apical‑to‑basolateral extraction ratios and increased absorption when P‑glycoprotein was inhibited, whereas felodipine’s extraction ratios were largely unchanged by GG918 but decreased by cyclosporine, demonstrating that P‑glycoprotein modulates intestinal drug metabolism by prolonging drug exposure to CYP3A4.

Abstract

Drug efflux by intestinal P-glycoprotein (P-gp) is known to decrease the oral bioavailability of many CYP3A4 substrates. We hypothesized that the interplay occurring between P-gp and CYP3A4 at the apical membrane would increase the opportunity for drug metabolism. To define the roles of P-glycoprotein (P-gp) and CYP3A4 in controlling the extent of intestinal absorption and metabolism, two substrates were tested. The transport, metabolism, and intracellular levels of<i>N-</i>methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K77, a cysteine protease inhibitor; P-gp and CYP3A4 substrate) and felodipine (CYP3A4 substrate only) were measured across CYP3A4-transfected Caco-2 cells in the presence of an inhibitor of CYP3A4 and P-gp, cyclosporine (CsA), or an inhibitor of P-gp and not CYP3A4, GG918 (<i>N</i>-{4-[2-(1,2,3,4-tetrahydro-6,7- dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamine). The extent of metabolism was measured by calculating the extraction ratio (ER) across the cells, while accounting for intracellular changes occurring with P-gp inhibition. The (A)pical to (B)asolateral and B→A ERs for K77 were 0.33 and 0.06, respectively. These changed with GG918 to 0.14 and 0.12 and with CsA to 0.06 and 0.04. Felodipine ERs were similar in both directions, 0.26 and 0.24 (A→B and B→A), and were unchanged in the presence of GG918 but decreased with CsA (0.14 and 0.11). The K77 absorption rate was increased 5 and 4.2-fold in the presence of CsA and GG918, respectively, whereas no change was observed for felodipine absorption. The decreased A→B ER and increased absorption of K77 with GG918 suggest that P-gp influences the extent of drug metabolism in the intestine via prolonging the access of drugs to CYP3A4 near the apical membrane and decreasing transport across the cells.