CYTOCIDAL EFFECT OF GOSSYPOL ON CULTURED MURINE ERYTHROLEUKEMIA-CELLS IS PREVENTED BY SERUM-PROTEIN

Abstract

The interaction of gossypol (G) with cultured murine erythroleukemia cells (MELC) was studied in vitro. G was cytocidal (inhibited growth > 90%) to MELC at > 10 .mu.M, but not at < 5 .mu.M in medium supplemented with 10 and 15% fetal calf serum (FCS). G (5 .mu.M was cytocidal in 2 and 5% FCS. Serum albumin (2%) also decreased the effective cytocidal dose of G. This inhibition was reversible if extracellular drug (30 .mu.M) was removed after 1 h but not after 24 h. Uptake of [14C]G by MELC (.apprx. 10-6 cells/ml) was saturable with half-maximal uptake at 8 .mu.M in the absence of FCS. This uptake was concentrative, i.e., 75-fold relative to the total [14C]G concentration. In the presence of both FCS (.apprx. 2%) and serum albumin (.apprx. 0.03%), the accumulation of [14C]G (10 .mu.M) by MELC was decreased .apprx. 50%. Direct binding of G to albumin, assayed by quenching of intrinsic fluorescence, was stoichiometric with respect to micromolar albumin content suggesting an apparent affinity of .apprx. 10-7 M. Visible absorption spectra for G in the presence of serum albumin exhibited batho- and hyperchromic shifts of the maxima at .apprx. 380 nm. G, at pharmacologically relevant concentrations, is cytocidal for MELC. Serum protein, e.g., albumin, can reduce both the cytocidal effects of G and the uptake of [14C]G by MELC. These effects are probably the result of G binding to serum protein, e.g., albumin, which reduces the free effective concentration of the drug. Implications of these findings for the pharmacokinetics and contraceptive actions of G in vivo are discussed.