Oral etoposide and zosuquidar bioavailability in rats: Effect of co-administration and in vitro-in vivo correlation of P-glycoprotein inhibition

Abstract

P-glycoprotein inhibitors, like zosuquidar, have widely been used to study the role of P-glycoprotein in oral absorption. Still, systematic studies on the inhibitor dose-response relationship on intestinal drug permeation are lacking. In the present study, we investigated the effect of 0.79 nM-2.5 μM zosuquidar on etoposide permeability across Caco-2 cell monolayers. We also investigated etoposide pharmacokinetics after oral or IV administration to Sprague Dawley rats with co-administration of 0.063–63 mg/kg zosuquidar, as well as the pharmacokinetics of zosuquidar itself. Oral zosuquidar bioavailability was 2.6–4.2%, while oral etoposide bioavailability was 5.5 ± 0.9%, which increased with increasing zosuquidar doses to 35 ± 5%. The intestinal zosuquidar concentration required to induce a half-maximal increase in bioavailability was estimated to 180 μM. In contrast, the IC 50 of zosuquidar on etoposide permeability in vitro was only 5–10 nM, and a substantial in vitro-in vivo discrepancy of at least four orders of magnitude was thereby identified. Overall, the present study provides valuable insights for future formulation development that applies fixed dose combinations of P-glycoprotein inhibitors to increase the absorption of poorly permeable P-glycoprotein substrate drugs.

Combinational Inhibition of P-Glycoprotein-Mediated Etoposide Transport by Zosuquidar and Polysorbate 20

“…For series 2 (MDCKII-MDR1), initial TEER values ranged from 71–95 Ω × cm 2 and on average dropped by 19% during the experiment, and no single filter displayed a drop of more than 34%. These changes were consistent with our previous studies [ 5 , 21 ], and cell monolayers were considered intact.…”

“…Therefore, the aim was also to assess oral etoposide absorption in Sprague Dawley rats after coadministration with combinations of zosuquidar and polysorbate 20. During the experimental work for the present publication and a previous publication [ 5 ], it was discovered that zosuquidar unexpectedly elicited low solubility and nonspecific adsorption to labware surfaces. Polysorbate 20 may affect the solubility or adsorption behaviour of zosuquidar.…”

“…Test solutions were either prepared by conventional serial dilution for series (1)–(2) or by a spike method for series (3). The spike method was described previously [ 5 ]. Briefly, the spike method consisted of preparing 100-times-concentrated zosuquidar and/or polysorbate 20 solutions in pure methanol and spiking these solutions into the donor and receiver buffers in the relevant compartments of the Transwell plate and inserts at the start of the experiment.…”

“…Therefore, there is a need to develop drug formulations that can increase the intestinal absorption and oral bioavailability of P-gp substrates. The third-generation inhibitor zosuquidar has been used to increase P-gp-limited oral absorption of etoposide [ 5 ]. Likewise, certain nonionic surfactants such as polysorbate 20, polysorbate 80, Cremophor ® EL, and Pluronic ® P85 also inhibit P-gp-mediated transport in vitro as well as in vivo, increasing the oral absorption of etoposide when coadministered together (reviewed by Al-Ali et al [ 6 ]).…”

“…Etoposide is useful as a model drug for P-gp substrates, as its bioavailability is limited by P-gp, which was exemplified by increased oral bioavailability in mdr1a knockout rats [ 7 ]. Moreover, bioanalytical methods are available [ 5 , 7 , 8 ], with one drawback to using etoposide being its cytotoxic properties [ 9 ]. Several formulation approaches have been attempted to increase oral etoposide absorption by either inhibiting P-gp with inhibitors or increasing the solubility of etoposide in the intestine to saturate P-gp.…”