Effects of the 6-alkyl substitution of ellipticine on the uptake by NIH-3T3 cells and on the cytotoxicity.

New ellipticine derivatives of the 2-methyl ellipticinium (NME) series, i.e. 2,6-dimethylellipticinium (6-Me-NME) and 2-methyl-6-n-propylellipticinium (6-Pr-NME), have been studied as cytotoxic compounds. Their uptake by NIH-3T3 cells and efflux have been measured by a sensitive and specific high performance liquid chromatographic assay. These compounds are equitoxic if we compare their cytotoxicity by two methods: growth inhibition and cloning efficiency. However, they accumulate in NIH-3T3 cells at different steady state levels and the efflux rates are not similar. This raises the question of the mode of action of these drugs.