ADENOSINE TRIPHOSPHATE-DEPENDENT TRANSPORT OF LEUKOTRIENE C-4 BY MEMBRANE-VESICLES PREPARED FROM CISPLATIN-RESISTANT HUMAN EPIDERMOID CARCINOMA TUMOR-CELLS

Background: Cisplatin accumulation is decreased in many cisplatin-resistant cells. An active efflux pump far cisplatin exists in cisplatin-resistant human epidermoid carcinoma cells (called KB cells). A previous study has suggested that the adenosine triphosphate (ATP)-dependent glutathione S-conjugate export pump (GS-X pump), which exports the bis-(glutathionato) platinum (II) (GS-platinum) complex, could contribute to cellular resistance to cisplatin, Purpose: In this study, we examined whether the active efflux pump for cisplatin in the cisplatin-resistant KB cells is the GS-X pump and tested its activity by using an endogenous substrate, [H-3]leukotriene C-4 ([H-3]LTC(4)). Methods: Membrane vesicles were prepared from KB-3-1 (clone from parental KB cells) cells and from cisplatin-resistant KCP-4 (a mutant clone derived from KB-3-1 cells) cells. Using a filtration technique, we measured the uptake and transport of [H-3]LTC(4), a substrate for the GS-X pump, into membrane vesicles at 37 degrees C. Results: The uptake of [H-3]LTC(4) in the membrane vesicles from both the KB-3-1 and KCP-4 cells was ATP-dependent. In contrast, the ATP-dependent transport of [H-3]LTC(4) was observed only in KCP-4 membrane vesicles but not in KB-3-1 membrane vesicles. The ATP-dependent transport was vanadate sensitive and was inhibited by GS-platinum complex but only marginally by cisplatin and glutathione and not by vincristine or verapamil. The nucleotide triphosphates, guanosine triphosphate, cytidine triphosphate, uridine triphosphate, and deoxythymidine triphosphate could be substituted for ATP but were less efficient. A nonhydrolyzable ATP analogue, adenosine 5'-(beta,gamma-methylene) triphosphate, was not effective. Conclusions: The transport of LTC(4) in membrane vesicles prepared from KCP-4 cells was facilitated by an ATP-dependent pump that appeared very similar to the GS-X pump. Implications: Our study suggests that the GS-X pump is involved in the decreased accumulation of cisplatin in KCP-4 cells.