Perturbation of methotrexate transport by verapamil, vinblastine, taurocholate and bromosulfophthalein in rat hepatocytes
Smeland, E.; Bremnes, R.M.; Fuskevåg, O.M.; Aarbakke, J.
Anticancer Research 15(1): 45-50
1995
ISSN/ISBN: 0250-7005 PMID: 7733639 Document Number: 446407
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 mu-M VRP decreased the hepatocellular MTX accumulation with 29%, whereas 100 mu-M BSP reduced MTX entrance with 15%. 100 mu-M VBL and 100 mu-M 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 (K-i) values of 105 mu-M for TAURO, and 800 mu-M for BSP. Conclusion: The data demonstrate for the first time a selective inhibitory effect of VPP 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.