title: Competitive inhibition by genistein and ATP dependence of daunorubicin transport in intact MRP overexpressing human small cell lung cancer cells.
abstract: In several multidrug resistant tumor cell lines without overexpression of P-glycoprotein (non-Pgp MDR), a decreased accumulation of drugs has been shown to contribute to resistance. We have recently reported that daunorubicin (DNR) accumulation was decreased in the multidrug resistance-associated protein overexpressing GLC4/ADR non-Pgp MDR small cell lung cancer cell line due to an enhanced energy-dependent efflux which could be inhibited by the isoflavonoid genistein. The purpose of this work was 2-fold: (i) to investigate the mechanism by which genistein inhibits the DNR efflux in the GLC4/ADR cells; and (ii) to characterize the dependence of DNR transport on ATP concentration in intact GLC4/ADR cells. The active transport of DNR in GLC4/ADR cells appeared to be a saturable process with an apparent Km of DNR of 1.4 +/- 0.4 microM. Genistein increased the apparent Km value of DNR, suggesting that this agent is a competitive inhibitor of DNR transport. These data provide additional evidence that energy-dependent DNR transport in GLC4/ADR cells is a protein-mediated process. In addition, genistein decreased cellular ATP concentration in a dose-dependent manner in sensitive as well as in resistant cells. Marked inhibition of DNR transport activity in intact GLC4/ADR cells was found when cellular ATP concentration was decreased below 2 mM by sodium azide or 2-deoxy-D-glucose. Thus, since DNR transport in intact GLC4/ADR is already inhibited at modest cellular ATP depletion, a limitation in ATP supply might open ways to make MDR cells more susceptible to drug toxicity.
authors.affiliation: Department of Medical Oncology, Free University Hospital, Amsterdam, The Netherlands.
authors.forename: C H
authors.initials: CH
authors.lastname: Versantvoort
authors.forename: H J
authors.initials: HJ
authors.lastname: Broxterman
authors.forename: J
authors.initials: J
authors.lastname: Lankelma
authors.forename: N
authors.initials: N
authors.lastname: Feller
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
mesh_terms: D000255:Adenosine Triphosphate / Q000172:deficiency / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D018288:Carcinoma, Small Cell / Q000378:metabolism; D003630:Daunorubicin / Q000378:metabolism* / Q000494:pharmacology; D004351:Drug Resistance; D019833:Genistein; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D007529:Isoflavones; D000255:Adenosine Triphosphate; D019833:Genistein; D003630:Daunorubicin