Stephanie van Hoppe

102 Chapter 5 can significantly modulate the pharmacokinetic behavior, and hence the therapeutic efficacy and toxicity profile of these drugs [22]. Some studies indicated that ponatinib could modestly interact with hABCB1 and more profoundly with hABCG2 in vitro , resulting in inhibition of these transporters, and possibly transport by hABCG2 [23]. However, another study found that ponatinib was not noticeably transported by ABCB1 or ABCG2 in CML cells [24]. If these transporters could efficiently transport ponatinib in vivo , this might lead to decreased accumulation of ponatinib in transporter-expressing cancer cells, and thus pharmacotherapeutic resistance. Moreover, leukemic cells can spread outside the blood to other parts of the body, including the central nervous system (brain and spinal cord). About 7% of adult ALL patients have central nervous system (CNS) involvement at presentation [25, 26]. Given the high ABCB1 and ABCG2 expression in the BBB, these transporters could potentially limit brain accumulation of ponatinib, which might reduce therapeutic efficiency against CML and ALL CNS metastases. In this study we investigated whether ponatinib and DMP are transported substrates of ABCB1 and ABCG2 in vitro or in vivo , and how this might affect their oral plasma pharmacokinetics and brain penetration. Furthermore, ponatinib is substantially metabolized by cytochrome P450 (CYP3A4) [1, 27], indicating that induction or inhibition of this enzyme may influence ponatinib exposure. We therefore also studied the influence of CYP3A on the (oral) systemic availability and tissue exposure of ponatinib and DMP. MAT E R I A L AND ME T HOD S Chemi c a l s Ponatinib and zosuquidar were obtained fromSequoia Research Products (Pangbourne, UK). Ko143 was obtained from Tocris Bioscience (Bristol, UK). Isoflurane was purchased from Pharmachemie BV (Haarlem, The Netherlands), heparin (5000 IU ml -1 ) was from Leo Pharma (Breda, The Netherlands), and Bovine Serum Albumin (BSA) Fraction V from Roche (Mannheim, Germany). Chemicals and reference standards used for the bioanalytical assay of ponatinib and its metabolite DMP were described previously [28]. All other chemicals and reagents were obtained from Sigma-Aldrich (Steinheim, Germany). Tr an s po r t a s s ay s PolarizedMadin-Darby Canine Kidney (MDCK-II) cell lines transduced with either human (h)ABCB1, murine (m)Abcg2 or hABCG2 cDNA were cultured in DMEM plus 10% FCS and