Growth-inhibiting effects of MTX against parental and 7-OHMTX-resistant sublines of CEM and MOLT-4 after short-term drug exposure. (A) Parental CCRF-CEM cells (○) and CEM/7-OHMTX cells (•) and (B) parental MOLT-4 cells (□) and MOLT-4/7-OHMTX cells (▪) were incubated with a range of MTX concentrations for 4 hours, after which cells were washed and resuspended in drug-free medium for another 68 hours and monitored for inhibition of cell growth. Results are presented as the mean of 3 independent experiments ± SD.