Differential Impact of P-Glycoprotein (ABCB1) and Breast Cancer Resistance Protein (ABCG2) on Axitinib Brain Accumulation and Oral Plasma Pharmacokinetics

Abstract

ABSTRACT:The second-generation tyrosine kinase inhibitor and anticancer drug axitinib is a potent, orally active inhibitor of the vascular endothelial growth factor receptors 1, 2, and 3. Axitinib has clinical activity against solid tumors such as metastatic renal cell carcinoma and advanced pancreatic cancer. We studied axitinib transport using Madin-Darby canine kidney II cells overexpressing human ABCB1 or ABCG2 or murine Abcg2. Axitinib was a good substrate of ABCB1 and Abcg2, whereas transport activity by ABCG2 was moderate. These transporters may therefore contribute to axitinib resistance in tumor cells. Upon oral administration of axitinib, Abcg2(؊/؊) and Abcb1a/1b;Abcg2(؊/؊) mice displayed 1.7-and 1.8-fold increased axitinib areas under the plasma concentration-time curve from 0 to 4 compared with those of wild-type mice. Plasma concentrations in Abcb1a/1b(؊/؊) mice were not significantly increased. In contrast, relative brain accumulation of axitinib in Abcb1a/1b(؊/؊) and Abcb1a/1b;Abcg2(؊/؊) mice was, respectively, 6.8-and 13.9-fold higher than that in wild-type mice at 1 h and 4.9-and 20.7-fold at 4 h after axitinib administration. In Abcg2(؊/؊) mice, we found no significant differences in brain accumulation compared with those in wild-type mice. Thus, Abcb1 strongly restricts axitinib brain accumulation and completely compensates for the loss of Abcg2 at the blood-brain barrier, whereas Abcg2 can only partially take over Abcb1-mediated axitinib efflux. Hence, Abcg2 has a stronger impact on axitinib oral plasma pharmacokinetics, whereas Abcb1 is the more important transporter at the blood-brain barrier. These findings illustrate that in vitro transport data for ABCB1 and ABCG2 cannot always be simply extrapolated to the prediction of the relative impact of these transporters on oral availability versus brain penetration. IntroductionThe ATP-binding cassette (ABC) transporters P-glycoprotein (Pgp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) affect the disposition of a variety of endogenous and exogenous compounds, including many anticancer drugs. Both transporters are expressed at the apical membranes of enterocytes, hepatocytes, and renal tubular epithelial cells, where they potentially limit gastrointestinal absorption or mediate direct intestinal, hepatic, or renal excretion of their substrates. Moreover, ABCB1-and ABCG2-mediated efflux activity in brain endothelial capillary cells of the blood-brain barrier (BBB) is crucial for the protection of the central nervous system from harmful compounds (Schinkel and Jonker, 2003;Vlaming et al., 2009). In addition, ABC transporters are expressed in many tumor types, mediating multidrug resistance against anticancer drugs (Borst and Oude Elferink, 2002).Only recently, the combined role of ABCB1 and ABCG2 at the BBB in limiting brain accumulation of shared substrates has been studied in detail using Abcb1a/1b;Abcg2(Ϫ/Ϫ) combination knockout mice. It was found that brain penetration of topotecan and several tyrosine kinase inhibitors (TKIs) includ...

In Vitro Characterization of Axitinib Interactions with Human Efflux and Hepatic Uptake Transporters: Implications for Disposition and Drug Interactions

“…Our finding that axitinib is at most only a weak substrate for MDR1 and not a BCRP substrate is in contrast to the recent publication by Poller et al (2011), which identified axitinib as a good and moderate substrate for MDR1 and BCRP, respectively. We found that, over a concentration range of axitinib from 1 to 5 mM, the P-gp mediated efflux ratio in the MDR1-MDCK was #1.45, and our positive control substrate, digoxin, exhibited an efflux ratio of 24.…”

“…It is possible that axitinib is a substrate for canine P-gp and that the MDR1-MDCK and BCRP-MDCK cell lines used by Poller et al (2011) may contain higher levels of canine P-gp than our cell lines, resulting in the contrasting results between the two laboratories. Additionally, it was previously demonstrated that P-gp activity differs between species (Tang-Wai et al, 1995).…”

“…7) with the results obtained by Poller et al (2011) where the parent drug was specifically measured. We confirmed their finding that axitinib has restricted mouse brain distribution, as the level of axitinib radioactive equivalents present in the brain was markedly lower than in whole blood or other tissues.…”

“…We investigated the role of efflux and uptake transporters in the disposition and drug interaction potential of axitinib. Poller et al (2011) previously demonstrated that axitinib is a substrate for P-gp and BCRP in rodent knockout and cell-based in vitro models. Early studies conducted in our laboratory suggested differing results for these efflux transporters, and the work herein attempts to understand this discrepancy as well as examine other transporter-related characteristics.…”

“…We confirmed their finding that axitinib has restricted mouse brain distribution, as the level of axitinib radioactive equivalents present in the brain was markedly lower than in whole blood or other tissues. Poller et al (2011) went on to study the brain disposition of axitinib in abcg2 2/2 , abcb1a/b 2/2 , and triple knockout mice. These results showed no effect of abcg2 2/2 , a marked increase in brain exposure in abcb1a/b 2/2 , and an even greater increase in the triple knockout.…”