Stimulation of cis-diamminedichloroplatinum(II) accumulation by modulation of passive permeability with genistein: an altered responce in accumulation-defective resistant cells.

The effect of the tyrosine kinase inhibitor genistein onthe accumulation of cisplatin (DDP) was investigated inDDP-sensitive and -resistant human 2008 ovarian cardnomacell lines. DDP accumulation after a 1-h exposure wasmaximally increased by concurrent 40 piM genistein. Themaximal stimulation of accumulation was observed after 2 hof total genistein exposure and was 83 ± 13% (n = 5) higherthan controls. With resistant C13* cells, however, the stimulationof accumulation was delayed until 4 h and wasincreased only 46 ± 18% compared to controls. RevertantRH4 cells that retained the accumulation defect behaved likethe C13 cells. Genistein stimulated [3H]mannitol accumulation(a marker of passive permeability) by 43 ± 9% (n =3) in 2008 cells, and the effect was maximal after 2 h of totalgenistein exposure. Changes in [3Hjmannitol accumulationin 2008 parent cells were highly correlated with DDP accumulation(r = 0.9010). These experiments also revealed that[3H]mannitol accumulation after 2 h in C13* cells was reduced38% compared to 2008 cells, a decrease that reflectedthe DDP accumulation defect. Fluid-phase pinocytosis determinedwith lucifer yellow CH as a marker showed nodifference between 2008 and C13* cells and no effect ofgenistein. Genistein was demonstrated to clearly inhibit protein-tyrosine phosphorylation initiated by the epidermalgrowth factor receptor kinase. Differences were noted in thephosphotyrosine pattern between the 2008 and C13* cells.Under the conditions that had the maximal effect on DDPaccumulation in 2008 cells, genistein decreased the IC50 ofDDP 8.2-fold in 2008 cells and 4.7-fold in C13* cells. Weconclude that: (a) genistein stimulates DDP accumulation bymodulating the passive permeability of the plasma membrane;(b) C13* cells are less permeable to passively diffusingsmall molecules, which offers a mechanism for the DDPaccumulation defect without invoking carrier proteins; (C)the effect of tyrosine kinase inhibition on passive permeabilityis altered in C13 cells; and (d) pinocytosis contributes insignificantly to DDP accumulation. Genistein, a dietaryisoflavone, thus seems to be a promising clinical candidatefor combination with DDP.