Organic cation transporter OCT6 mediates cisplatin uptake and resistance to cisplatin in lung cancer.

The purposes of this study were to determine whether organic cation transporters (OCTs) can mediate platinum uptake, and whether OCT down-regulation confers resistance against cisplatin (CDDP) in cancer cells. Two lung cancer cell lines, PC-6 and PC-14, and their CDDP-resistant derivatives, PC-6/CDDP and PC-14/CDDP, were analyzed. OCT expression levels were assayed using quantitative RT-PCR and Western blotting. Additionally, the effect of OCT6 overexpression, induced by transfection of the OCT6 gene SLC22A16 using a forced expression vector, on cellular sensitivity to CDDP and on intracellular platinum accumulation was measured using PC-14/CDDP cells. Both gene and protein expression of OCT6 were decreased in both CDDP-resistant cell lines compared with their expression in their respective parental cells. Intracellular accumulation of platinum was decreased in PC-14/CDDP cells compared with the parental cells after CDDP treatment. Furthermore, OCT6 overexpression induced by transfection of the OCT6 gene (SLC22A16) forced expression vector-sensitized PC-14/CDDP cells to CDDP and oxaliplatin (L-OHP) concomitant with increased intracellular concentration of platinum. OCT6 is a mediator of platinum uptake in cancer cells, and down-regulation of OCT6 is possibly one of the mechanisms of resistance against cisplatin in lung cancer.