Methotrexate Cytotoxicity as Related to Irreversible S Phase Arrest in Mouse L1210 Leukemia Cells

Abstract

The association between cytotoxicity and cell cycle perturbation caused by methotrexate (MTX) was investigated in mouse L1210 leukemia cells by flow cytometric bromodeoxyuridine/DNA assay. In the range of concentrations of MTX from 10(-7) M to 10-6) M, in vitro exposure to the drug for 6 h caused a dose-dependent suppression of clonal growth of the tumor cells and S phase arrest in the cycle progression, resulting in an accumulation of cells in early S phase, in which they showed no definite increase of DNA content above G1 levels. The surviving fraction of the clonogenic cells corresponded with the fraction of cells which recovered from the S phase arrest in MTX-free medium. In mice bearing L1210 ascites tumors, a bolus injection of MTX caused the S phase arrest of the tumor cells as shown in suspension cultures, and cytokinetic recovery was observed in parallel with the regrowth of the tumor. These results showed that irreversible S phase arrest is a critical cytokinetic event associated with the cytotoxicity of MTX.