Perturbation of methotrexate transport by verapamil, vinblastine, taurocholate and bromosulfophthalein in rat hepatocytes.

BACKGROUND

Methotrexate (MTX) is extensively used in different combination chemotherapy regimens. More knowledge about interactions and their mechanisms in target cancer cells and normal cells is needed to improve therapeutic efficacy and reduce toxicity.

MATERIALS AND METHODS

The effect of verapamil (VRP), vinblastine (VBL), taurocholate (TAURO) and bromosulfophthalein (BSP) on MTX transport were studied in freshly isolated rat hepatocytes.

RESULTS

During 60 min, 50 microM VRP decreased the hepatocellular MTX accumulation with 29%; whereas 100 microM BSP reduced MTX entrance with 15%. 100 microM VBL and 100 microM TAURO reduced the intracellular accumulation of MTX with 36% and 23%, respectively. VRP and BSP appeared to be selective MTX influx blockers, whereas VBL and TAURO inhibited both MTX influx and efflux, however, with major inhibition on MTX influx. Dixon plot analyses for TAURO and BSP were suggestive of competitive inhibition, giving inhibition constants (Ki) values of 105 microM for TAURO, and 800 microM for BSP.

CONCLUSION

The data demonstrate for the first time a selective inhibitory effect of VRP upon MTX influx in isolated rat hepatocytes, whereas BSP, a potent MTX efflux inhibitor in malignant cells fails to achieve this effect in the normal cell type here investigated.