Altered cytotoxicity of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea in human glioma cell lines SK-MG-1 and SKI-1 correlates with differential transport kinetics.
Resistance to (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU), an experimental anticancer compound, was investigated in the chloroethylnitrosourea-sensitive Mer- SK-MG-1 and -resistant Mer- SKI-1 human glioma cell lines. The transport of [3H]SarCNU was examined in suspension. The uptake of [3H]SarCNU was found to be temperature dependent in SK-MG-1 and SKI-1, but less so in SKI-1. At 37 degrees C, uptake of 50 microM [3H]SarCNU was linear up to 4 s in both cell lines, with uptake being significantly faster in SK-MG-1 than in SKI-1 under initial rate conditions. There was no significant difference in the rate of influx at 22 degrees C between both cell lines. Equilibrium was approached after 1 min at 22 and 37 degrees C. At 37 degrees C, steady state accumulation of SarCNU at 30 min was reduced significantly (35%) in SKI-1 cells compared with SK-MG-1 cells, although accumulation was similar at 22 degrees C. In SK-MG-1 cells, uptake of [3H]SarCNU at 37 degrees C was found to be saturable, but uptake in SKI-1 cells was not saturable over a 1000-fold range of concentrations. Analysis of efflux in cells preloaded with 50 microM [3H]SarCNU revealed that the rate of efflux was equivalent in both cell lines but that the efflux rate was more rapid at 37 degrees C compared with 22 degrees C. Metabolism of SarCNU at 37 degrees C was not different in either cell line after a 60-min incubation, as determined by thin layer chromatography. SKI-1 cells, compared with SK-MG-1 cells, were 3-fold more resistant to SarCNU at 37 degrees C but only 2-fold more resistant at 22 degrees C, a temperature at which SarCNU accumulation was similar in both cell lines. The 2-fold resistance at 22 degrees C was similar to that of 1,3-bis(2-chloroethyl)-1-nitrosourea at 37 and 22 degrees C. These findings indicate that increased cytotoxicity in SK-MG-1 cells is associated with a greater accumulation of SarCNU via an epinephrine-sensitive carrier that is not detectable in SKI-1 cells. However, part of the chloroethylnitrosourea resistance in SKI-1 cells is not secondary to decreased accumulation.