Properties of the initial reaction of bleomycin and several of its metal complexes with Ehrlich cells

Characteristics of the reaction of bleomycin-A2 (BLM) and several of its metal complexes with Ehrlich cells in culture are described. Short incubation of BLM and Fe(III)-, Cu-, Zn-, and CdBLM with Ehrlich cells effectively inhibits cell proliferation. There is a sharp break at 30 min in the dependence of cytotoxicity upon time of exposure of cells to these forms of the drug. Qualitatively, the same curve can be generated by sequential additions of CoCl2 to cells during their first hour of incubation with BLM or Fe(III)BLM. The cobalt salt has less effect on CuBLM. The kinetics of initiation of the effect are directly correlated with the rapid kinetics of uptake of [3H]BLM by cells. Measurements of the initial rate of association of drug with cells as a function of extracellular BLM concentration suggest that a binding step is involved, for the rate of association approaches a maximal velocity at large concentrations of BLM. Uptake leads to both specific and nonspecific binding of tritium label; however, very little BLM gets into these cells. The internal concentration is estimated to be less than that in the external medium. BLM and its Fe(III) and copper complexes are taken up by Ehrlich cells to the same general extent after 60 min incubation; the cellular uptake of CoBLM is 25-50 times higher. Even the distributions of Fe(III)-, Cu-, and metal-free BLM within cytosol are comparable. A fraction binds to macromolecules; the rest appears unbound in low molecular weight fractions. The binding of [3H]BLM to cells cannot be reversed by incubation of labeled cells in drug-free medium or in media containing large concentrations of cold BLM.