Comparison of adriamycin- and ouabain-induced cytotoxicity and inhibition of 86rubidium transport in wild-type and ouabain-resistant C3H/10T1/2 mouse fibroblasts.

Ouabain (OUA) inhibited 86Rb uptake (50% inhibitory concentration = 0.8 X 10(-4) M) over concentration ranges close to those at which it caused a reversible cytotoxicity (50% lethal dose = 2.5 X 10(-4) M) in growing wild-type C3H/10T1/2 cells. On the other hand, Adriamycin (ADM) inhibited 86Rb uptake (50% inhibitory concentration = 2 X 10(-3) M) but at concentrations 10(4)-fold higher than those causing irreversible cytotoxicity in growing wild-type cells (50% lethal dose = 3 X 10(-8) M). While OUA inhibited 86Rb uptake more in wild-type cells than in a OUA-resistant mutant, ADM inhibited 86Rb uptake to the same extent in confluent wild-type and OUA-resistant cells. Further, three OUA-resistant mutants were not cross-resistant to ADM- or daunomycin (DM)-induced cytotoxicity during log phase or to ADM-induced cytotoxicity at confluence. In addition, ADM, DM, or 5-iminodaunomycin did not displace the cardiac glycosides digoxin or digitoxin from their respective antibody complexes. The order of potency of anthracycline derivatives in inhibiting 86Rb uptake in confluent wild-type cells was the same as their order of inhibiting the growth of wild-type cells and in detaching confluent wild-type cells (DM > ADM > 5-iminodaunomycin) but did not correlate with their cardiotoxic potentials (ADM > DM > 5-iminodaunomycin). Therefore, in this model system, ADM cytotoxicity is mediated differently from OUA cytotoxicity. Further, we find no biological evidence consistent withADM binding to the OUA site on the cell surface (Na+-K+) adenosine triphosphatase and therefore no evidence in this model system that ADM cardiotoxicity could be a digitalis-type toxicity per se.