Binding of taxol to plastic and glass containers and protein under in vitro conditions

This study examined the stability and protein binding of taxol in aqueous solution and tissue culture medium. After storage for 19 h in 1% methanolic aqueous solution, the concentration of taxol declined to about 40% in 1.5 mL glass vials, 67% in 1.5 mL polypropylene tubes, and 55% in 1.5 mL siliconized polypropylene tubes. There was no difference in the decline at two initial concentrations of 0.18 and 1.8 mu g/mL. The concentration declines were biphasic; the initial phase showed a half-life of 1-2 min and the second phase showed a half-life of 30-350 min. A methanol wash recovered 0%, 16%, and 31% of taxol from glass vials and unsiliconized and siliconized polypropylene tubes, respectively. In culture medium without fetal bovine serum, the concentration of taxol stored in polystyrene tissue culture plates declined to 73% after 24 h, whereas no concentration decline was observed in the presence of 9% fetal bovine serum (FBS). Protein binding of taxol in FBS-containing culture medium was saturable, varying from 79% at 0.5 mu g/mL to 20% at 15 mu g/mL. These data indicated (a) rapid and nonspecific adsorption of taxol to plastic and glass surfaces, (b) stabilization of taxol in culture medium by FBS, and (c) saturable protein binding of taxol in culture medium.