Cytocidal effect of gossypol on cultured murine erythroleukemia cells is prevented by serum protein

The interaction of gossypol (G) with cultured murine erythroleukemia cells (MELC) was studied in vitro. G was cytocidal (inhibited growth greater than 90%) to MELC at greater than 10 microM, but not at less than 5 microM in medium supplemented with 10 and 15% fetal calf serum (FCS). Five micromolar of G 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 microM) was removed after 1 h but not after 24 h. Uptake of [14C]G by MELC (approximately 10(6) cells/ml) was saturable with half-maximal uptake at 8 microM 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 (approximately 2%) and serum albumin (approximately 0.03%), the accumulation of [14C]G (10 microM) by MELC was decreased approximately 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 approximately 10(-7) M. Visible absorption spectra for G in the presence of serum albumin exhibited batho- and hyperchromic shifts of the maxima at approximately 380 nm. These studies demonstrate that: 1) G, at pharmacologically relevant concentrations, is cytocidal for MELC; 2) serum protein, e.g., albumin, can reduce both the cytocidal effects of G and the uptake of [14C]G by MELC; and 3) these effects are probably the result of G binding to serum protein, e.g., albumin, which reduces the free effective concentration of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)