Inhibition of human erythrocyte inositol lipid metabolism by adriamycin.

Incubation of human erythrocytes with Adriamycin prevented their morphological transition from discocytes to echinocytes when they were either depleted of ATP or loaded with calcium. This effect was dependent upon drug concentration and cell density. Adriamycin (10(-5) M) prevented, by greater than 90%, the echinocytosis of 10(7) cells/ml (S. B. Chahwala and J. A. Hickman, Cancer Res., 45: 4986-4989, 1985), and 5 X 10(-4) M prevented that of 10(9) cells/ml. There was a poor correlation between the effects of Adriamycin as a modulator of this morphological transition and its potency as an inhibitor of calmodulin. Using inside-out red blood cell vesicles, Adriamycin inhibited calmodulin dependent Ca2+ uptake with a 50% inhibitory concentration of 5 X 10(-4) M. Adriamycin thus differs from other amphipathic drugs, such as those of the phenothiazine class, where inhibition of calmodulin correlated well with effects on erythrocyte morphology (G. A. Nelson, M. L. Andrews, and M. J. Karnovsky, J. Cell Biol., 96: 730-735, 1983). After 12 h of ATP depletion, levels of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] extracted from 10(9) erythrocytes/ml fell by 57% and after 48 h they fell by 97%, changes which were coincident with a 100% transition of morphology to echinocytes. Adriamycin, 5 X 10(-4) M-1 X 10(-3) M, maintained 10(9) cells/ml in a discocyte morphology and maintained PtdIns(4,5)P2 levels at 60-70% of the time zero controls, independently of the size of the fall in PtdIns(4,5)P2 levels. The data suggested that Adriamycin inhibited a discrete pool of PtdIns(4,5)P2 which may be responsible for the maintenance of a discocyte morphology. Neomycin, 10(-3) M, had no effect on the ATP depletion-induced discocyte-echinocyte transition of 10(9) erythrocytes/ml or on the fall in PtdIns(4,5)P2 levels. Adriamycin, like neomycin, prevented the calcium-induced breakdown of erythrocyte membrane vesicle PtdIns(4,5)P2 to inositol trisphosphate (50% inhibitory concentration, 7 X 10(-4) M) but, unlike neomycin (50% inhibitory concentration, 4.25 X 10(-4) M) it was able to inhibit breakdown by 100% at higher concentrations.