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

Purpose: 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.

Methods: 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.

Results: 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.

Conclusion: 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.