Table 2

Relationships among MTA influx, growth inhibition, and intracellular accumulation in RFC1-defective L1210 variants

Cells were grown in complete RPMI 1640 containing 2.2 μm folic acid or were transferred to, and grown in, folate-free medium supplemented with 25 nm 5-CHO-THF for at least 1 week, but no more than 3 weeks, before measurements were made. For MTA accumulation, cells were exposed to 50 nm[ 3H]MTA for 3 days in the presence of 200μ m glycine, 100 μm adenosine, and 10μ m thymidine. All data are the mean ± SE of three separate experiments.

Cell lineMTA influxMTA IC50MTX IC50Total MTA accumulation
nmol/g dry weight/min%anmFoldΔbnmFoldΔbnmol/g dry weight%a
Folic acid as the sole folate source
L12101.7 ± 0.110012 ± 11  7c125 ± 2100
L1210-G1a0.16 ± 0.019.470 ± 85.8 85c126.6 ± 0.526
MTXTA0.072 ± 0.0024.2260 ± 3022500c712.6 ± 0.210
5-CHO-THF as the sole folate source
L12100.98 ± 0.0310013 ± 2114 ± 3128 ± 3100
L1210-G1a0.17 ± 0.001742 ± 33.2150 ± 171013 ± 146
MTXTA0.11 ± 0.011131 ± 62.4160 ± 10118.0 ± 0.929
  • a Percentage of the level in L1210 cells.

  • b Fold change as compared to L1210 cells.

  • c From Ref. 20 .