(10) Modeling transporter cooperativity in cells transfected with the ATP-binding cassette transporters ABCB1 and ABCG2

     Throughout medical history, cancer has remained a disease for which developing effective treatments has been prioritized. The phenomenon of multidrug resistance (MDR) has jeopardized the success of treatment with... [ view full abstract ]

     Throughout medical history, cancer has remained a disease for which developing effective treatments has been prioritized. The phenomenon of multidrug resistance (MDR) has jeopardized the success of treatment with chemotherapy as cells with MDR overexpress proteins from the family of ATP-binding cassette (ABC) transporters. Together the ABC transporters ABCB1 (P-glycoprotein) and ABCG2 function to protect the integrity of the blood-brain barrier, using their overlapping substrate specificity to eliminate chemotherapy agents from the cell. In the disease-state, these transporters are upregulated and pump out anticancer drugs before they can impart their toxicity in the cancer cell. In this study, the cooperativity of ABCB1 and ABCG2 was characterized using Human Embryonic Kidney – 293 cells that were transfected with either an empty vector or a vector containing ABCB1, ABCG2, or both. A surface expression, or FACS, analysis was used to confirm similar expression of ABCB1 and ABCG2 in singly and doubly transfected cell lines. Various drugs, including Mitoxantrone, Etoposide, NSC73306, and Camptothecin, were utilized in cell cytotoxicity assays with Cell-Titer Glow. A Rhodamine efflux assay was used to determine ABCB1 inhibition using tariquidar. It was found that tariquidar is a strong inhibitor of ABCB1 and a substrate for ABCG2. Transfected cells showed cross-resistance to drugs that were substrates for one or both transporters. In the future, this experiment should be performed in LLCPK1 cells, as these are capable of establishing a polarized monolayer similar to the one characterized in the blood-brain barrier.