Amethopterin Transport in Ehrlich Ascites Carcinoma and L1210 Cells1

Accumulation of amethopterin by L1210 and Ehrlich ascites cells in miro was mediated by a slow, temperature-sensitive, and partly saturable process. The structural specificity of the proc ess could be measured by competition studies; differences were found between the two cell lines. At physiologic drug levels, i.e., those found in vivo during drug therapy, concentrativi uptake of amethopterin was found in L1210 but not in Ehrlich cells. This may explain the sensitivity of L1210 to amethopterin and the lack of sensitivity of the Ehrlich cells. A correlation was found between affinity of several amethopterin derivatives for the L1210 transport process and the effectiveness of these com pounds in inhibition of tumor growth in vivo.