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. Author manuscript; available in PMC: 2014 Sep 1.
Published in final edited form as: Cancer Chemother Pharmacol. 2013 Jul 24;72(3):597–606. doi: 10.1007/s00280-013-2231-9

Table 1. Comparison of the free intracellular pralatrexate and MTX levels.

Tritiated drug levels were assessed at extracellular concentrations of 0.05 and 0.5 M in HeLa cells grown in medium supplemented with 100 M folic acid to minimize formation of polyglutamate derivatives. At one hour total antifolate levels were measured following which the cells were washed in 0°C buffer, resuspended into antifolate-free HBS at 37°C, and the intracellular drug levels monitored. The difference between the total and DHFR-bound levels is considered the free intracellular drug concentrations. The gradient is the ratio between the extracellular and intracellular free drug concentration. Data are the mean ± SEM from four independent experiments.

Extracellular concentration 0.05 M 0.5 M
pralatrexate MTX pralatrexate MTX
Total drug (μM) 0.49 ± 0.07 0.39 ± 0.04 1.25 ± 0.10 1.04 ± 0.08
DHFR-bound (μM) 0.31 ± 0.05 0.33 ± 0.04 0.44 ± 0.02 0.59 ± 0.06
Free intracellular drug (μM) 0.17 ± 0.08 0.05 ± 0.04* 0.81 ± 0.12 0.45 ± 0.10**
Free intracellular/extracellular drug 3.4 1 1.6 0.9
*

P-value of 0.04,

**

P-value of 0.01, for the difference between pralatrexate and MTX.