CONCENTRATION-DEPENDENT AND TIME-DEPENDENT CYTOSTATIC EFFECTS OF METHOTREXATE AND ETOPOSIDE ON L1210 LEUKEMIC-CELLS IN-VITRO DEMONSTRATED BY A NEW MICROPERFUSION METHOD

For validation of a new microperfusion system to fol- low the influence of pharmacokinetic parameters of cytostatic drugs on cultured tumor cells, we investigated the effects of methotrexate (MTX) and etoposide (VP16-213) on L1210 colony growth. Inhibition kinetics of cells were compared to those obtained by suspension culture exposure. We found good correlations between the IC50 values measured with either method. Evaluation of the kinetics under constant drug concentrations (steady-state) showed that the microperfusion method is comparable to other methods. A simple HPLC column-switching method was developed to determine drug concentrations in serum-free medium. Under these conditions solutions of etoposide were found to be unstable. Its quantity decreased biphasically with a concentration-dependent first-order kinetic in the initial phase, The relevance of exposure dose (cxt) for the mode of drug action has been shown, especially for instable solutions of drugs (VP16-213). The microperfusion method might substantially improve in vitro screening assays of anticancer drugs.