*2.2. Cell Culture*

For the cellular accumulation and cytotoxicity studies, HeLa (human cervical cancer) cells were cultured in Dulbecco's modified Eagle's medium (DMEM; Welgene Inc., Daegu, Korea) supplemented with 10% fetal bovine serum (FBS; Welgene Inc., Daegu, Korea) and 100 U/mL penicillin–100 µg/mL streptomycin at 37 ◦C in a humidified incubator with 5% CO2. For the bi-directional transport study, previously established human BCRP-overexpressing MDCKII cells [27] were used. Briefly, a plasmid construct containing cDNA for human BCRP was transfected into wildtype MDCKII cells to functionally express the transporter. MDCKII cells were grown in DMEM containing 10% FBS, 1% nonessential amino acid solution, 100 units/mL penicillin, and 0.1 mg/mL streptomycin under a humidified atmosphere containing 5% CO<sup>2</sup> at 37 ◦C.
