Research Paper Involvement of P-glycoprotein, Multidrug Resistance Protein 2 and Breast Cancer Resistance Protein in the Transport of Belotecan and Topotecan in Caco-2 and MDCKII Cells Hong Li, 1 Hyo-Eon Jin, 1 Wooyoung Kim, 1 Yong-Hae Han, 2 Dae-Duk Kim, 1 Suk-Jae Chung, 1 and Chang-Koo Shim 1,3 Received February 27, 2008; accepted June 25, 2008; published online July 25, 2008 Purpose. To investigate the underlying mechanism of low bioavailabilities of the water-soluble camptothecin derivatives, belotecan and topotecan. Methods. The bioavailability of belotecan and topotecan in rats was determined following oral administration of each drug at a dose of 5 mg/kg body weight. The vectorial transport of each drug was measured in Caco-2 and engineered MDCK II cells. Results. The bioavailability of belotecan (11.4%) and topotecan (32.0%) in rats was increased to 61.5% and 40.8%, respectively, by the preadministration of CsA at a dose of 40 mg/kg. Contrary to the absorptive transport, the secretory transport of these drugs across the Caco-2 cell monolayer was concentration-dependent, saturable, and significantly inhibited by the cis presence of verapamil (a P-gp substrate), MK-571 (an MRP inhibitor), bromosulfophthalein (BSP, an MRP2 inhibitor), fumitremorgin C (FTC, a BCRP inhibitor) and cyclosporine A (CsA, an inhibitor of P-gp and BCRP, and a substrate of P-gp) suggesting the involvement of these transporters, which could be further confirmed in MDCKII/P- gp, MDCKII/MRP2 and MDCKII/BCRP cells. Conclusion. The involvement of secretory transporters P-gp, MRP2 and BCRP, particularly for belotecan, as well as a low passive permeability, appears to be responsible for the low bioavailability of belotecan and topotecan. KEY WORDS: BCRP; belotecan; bioavailability; MRP2; P-gp; topotecan. INTRODUCTION 20-(s)-Camptothecin (CPT), a plant alkaloid isolated from a tree native to China (Camptotheca accuminata), is a novel antitumor agent that exerts its activity exclusively by inhibition of topoisomerase I (1–3). Although, clinical evalu- ation of CPT was discontinued due to its unpredictably severe toxicity and poor water-solubility, recent development of several semisynthetic CPT analogues including topotecan (Fig. 1A) have succeeded (4,5). Topotecan, a water soluble analogue of CPT, was approved by the FDA for treatment of advanced small cell lung cancers (6). Since then, other CPT analogues are being evaluated in clinical trials. In 2004, a novel water-soluble camptothecin analogue, (20s)-7-(2-iso- propylamino)ethylcamptothecin·HCl, also known as belote- can (Fig. 1B), was developed by Chong Kun Dang Pharmaceutical Co. (Seoul, Korea). Belotecan currently is marketed in Korea as Camtobell \ for the treatment of ovarian and small cell lung cancers (7,8) based on a series of successful clinical trials (9). CPTs are cell-cycle-specific and are most effective during the S-phase, which is a relatively short phase of the cell cycle. Therefore, prolonged or repetitive exposure to these drugs is needed for efficient killing of malignant cells. Preclinical and clinical studies have shown that prolonged exposure to CPTs, through either continuous intravenous (iv) infusion or repeti- tive oral (po) administration, results in optimal therapeutic activity (10–12). The oral delivery route is generally preferred 2601 0724-8741/08/1100-2601/0 # 2008 Springer Science + Business Media, LLC Pharmaceutical Research, Vol. 25, No. 11, November 2008 ( # 2008) DOI: 10.1007/s11095-008-9678-0 Hong Li and Hyo-Eon Jin have contributed equally to this work. 1 National Research Laboratory for Transporters Targeted Drug Design, Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul 151-742, Republic of Korea. 2 Department of Metabolism and Pharmacokinetics, Pharmaceutical Candidate Optimization, Bristol-Myers Squibb R&D, Princeton( New Jersey, USA. 3 To whom correspondence should be addressed. (e-mail: shimck@snu.ac.kr) ABBREVIATIONS: ABC, ATP-binding cassette; BCRP, breast cancer resistance protein; BSP, bromosulfophtahlein; CPT, 20-(s)- camptothecin; CsA, cyclosporine A; DMEM, Dulbecco’s modified Eagle’s medium; FTC, fumitremorgin; HBSS, Hank’s balanced salt solution; HEPES, N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid; MDCK, Mardine–Darby canine kidney; MK-571, 3-([{3-(2-[7- chloro-2-quinolinyl]ethyl)phenyl}-{(3-dimethylamino-3-oxopropyl)- thio}-methyl]-thio) propanoic acid; MRP2, multidrug resistance protein 2; P-gp, P-glycoprotein; SD, Sprague–Dawley; TEER, transepithelial electrical resistance.