The characteristics and consequences of folate depletion in hepatoma cells in vitro by inhibition of dihydrofolate reductase.
Growth of rat hepatoma cells in subtoxic concentrations of the DHFR inhibitor metoprine caused a marked time and concentration dependent reduction in cellular folates. As much as 75% total cellular folates can be lost without impairing growth. Increasing the concentration of metoprine into a range that causes inhibition of growth results in no further reduction in cellular folates. This effect is presumably mediated through inhibition of DHFR and several mechanisms are discussed which may account for these results. Cells grown in medium in which the concentration of folate is changed from 4 microM to 20 nM had intracellular folate levels that were reduced 85%. This is nearly the same reduction caused by treating cells grown in normal medium (4 microM folate) with continuous, subtoxic levels of metoprine. The reduction in cellular folates caused by growth in nM folic acid caused enhanced growth inhibitory activity of several antifolates. On a concentration basis metoprine was 12-fold more active under these conditions, PDDF was 37-fold more active and DDATHF was 44-fold more active. The reason for the enhanced sensitivity to PDDF and DDATHF may also be analogous to the reason for their synergism with the low concentration of metoprine and trimetrexate (12).
Galivan
J
J
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
Nimec
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Z
Rotundo
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R
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D005492:Folic Acid / Q000378:metabolism*; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D011739:Pyrimethamine / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D005493:Folic Acid Antagonists; C006308:metoprine; D005492:Folic Acid; D011739:Pyrimethamine