Compartmentalization of adriamycin and daunomycin in cultured chick cardiac myocytes. Effects on synthesis of contractile and cytoplasmic proteins.

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Abstract
The affinity of two anthracycline antineoplastics [( 14C]adriamycin and [14C]daunomycin) for cultured embryonic chick heart cells was determined by measuring their uptake, compartmentalization into subcellular fractions, and effects on the synthesis of cytoplasmic and cytoskeletal proteins. Both drugs, at micromolar concentrations, were readily uptaken by myocytes and found to be concentrated in a light-buoyant-density fraction containing no lysosomes. Nuclear 14C drug content accounted for 20-25% of the drug incorporated. Binding of adriamycin was saturable within 90 minutes of drug exposure, and the uptake of [14C]adriamycin was inhibited 50% by verapamil and adenosine triphosphate. Uptake of [14C]daunomycin was not influenced by these compounds. Cytosolic and contractile protein synthesis measured by [35S]methionine incorporation into proteins was blocked 70% overall in each fraction after 6 hours of incubation with 2 microM adriamycin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography and quantitative densitometry, revealed that actin synthesis was the least affected of the major proteins. Cardiac myocytes incubated for short periods of time with 2 microM adriamycin revealed subtle cytoplasmic changes in their organelles with the appearance of clear zones of cytoplasm containing short unorganized microfilaments. The deleterious effects of anthracyclines in heart cells are manifested early by rapid drug incorporation into myocytes and inhibition of cytoplasmic protein synthesis.