Environmental Toxicology and Pharmacology 23 (2007) 272–278 Di(2-ethylhexyl)phthalate leached from medical PVC devices serves as a substrate and inhibitor for the P-glycoprotein Joon-Ho Kim a,b , Jisoo Yun a , Jae-Kyung Sohng c , Jin-Myeong Cha d , Bum-Chae Choi e , Ho-Jong Jeon f , Sang-Hyun Kim g , Cheol-Hee Choi a,b,∗ a Research Center for Resistant Cells, Chosun University, Gwangju 501-759, Republic of Korea b Department of Pharmacology, Chosun University Medical School, Gwangju 501-759, Republic of Korea c Department of Chemistry, SunMoon University, Asan 336-840, Republic of Korea d DrugsLife Inc., Hwasoon, Jeonnam 519-831, Republic of Korea e Creation & Love Women’s Hospital, Gwangju 502-800, Republic of Korea f Department of Pathology, Chosun University Medical School, Gwangju 501-759, Republic of Korea g Department of Pharmacology, School of Medicine, Kyungpook National University, Daegu 700-422, Republic of Korea Received 27 June 2006; received in revised form 28 October 2006; accepted 7 November 2006 Available online 12 November 2006 Abstract A di(2-ethylhexyl)phthalate (DEHP) was accidentally extracted from plastics in the process of purification of chemosensitizers reversing P- glycoprotein (Pgp)-mediated multidrug resistance (MDR). The purpose of this study was to investigate the Pgp-reversal activities of phthalates, which are endocrine-disrupting chemicals, by utilizing the Pgp-overexpressing leukemic cell line AML-2/D100. The phthalates includes DEHP, diethyl phthalate (DEP) and dibutyl phthalate (DBP). Of the tested phthalates, DEHP showed the highest Pgp-reversal activity and DEP the most potent drug-accumulating activity. On the other hand, they did not show any chemosensitizing activity against multidrug resistance associated protein-mediated MDR. The complete inhibition of Pgp by verapamil increased the cytotoxicity of DEHP, but neither DEP nor DBP had this effect, suggesting that DEHP alone may be a possible substrate for the Pgp. DEHP showed higher hydrophobicity than the other phthalates when determined by reverse phase-HPLC. In addition, DEHP, but not the others increased the ATPase activity in a concentration-dependent manner. This is the first report that phthalates can reverse Pgp-mediated MDR by increasing drug accumulation, as well as serving as substrates for the Pgp. It is thought that the hydrophobic characteristics of phthalates could play an important role in Pgp-inhibitory activity. Therefore, pharmaco- and toxicokinetic interactions between phthalates leached from medical PVC devices and substrates for the Pgp should be kept in mind. © 2006 Elsevier B.V. All rights reserved. Keywords: Di(2-ethylhexyl)phthalate; Chemosensitizers; P-glycoprotein; Multidrug resistance; ATPase 1. Introduction The acquisition of multidrug resistance (MDR) by tumor cells is a major obstacle for the successful cancer chemotherapy, and several mechanisms responsible for multidrug resistance (MDR) have been described. Multidrug resistance 1 (MDR1) P-glycoprotein (Pgp), multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) are members of the ATP-binding-cassette (ABC) superfamily of membrane transporters (Maliepaard et al., 1999; Riordan and ∗ Corresponding author. Tel.: +82 62 230 6336; fax: +82 62 232 4045. E-mail address: chchoi@chosun.ac.kr (C.-H. Choi). Ling, 1979; Vernhet et al., 1999). These proteins are thought to function as the energy-dependent efflux pumps for a vari- ety of structurally diverse chemotherapeutic agents, and so they decrease the intracellular drug accumulation. As a result, over- expression of these proteins confers MDR to cancer cells by allowing the cells to evade the cytotoxic effects of drugs. Of these, a mechanism that has been most extensively investigated is the Pgp that acts as an efflux pump for a number of commonly used cytotoxic agents, e.g. doxorubicin, vincristine, vinblastine, paclitaxel, colhicine, actinomycin D and mitomycin C (Endicott and Ling, 1989). Differential compounds have been shown to reverse Pgp- mediated MDR, including verapamil (Tsuruo et al., 1981) and cyclosporin A (Twentyman et al., 1987). MDR cells can be 1382-6689/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.etap.2006.11.001