EFFECT OF METHOTREXATE (MTX) ON NAD(P)(-CELLS - MALIC ENZYME, 2-OXOGLUTARATE AND ISOCITRATE DEHYDROGENASES() DEHYDROGENASES OF HELA)

The effects of methotrexate (MTX) on oxygen uptake by permeabilized He La cells were evaluated. MTX did not inhibit state III respiration whe n the oxidizable substrate was succinate, but when the substrates were 2-oxoglutarate or isocitrate the respiration decreased about 50 per c ent at 1.0 mM concentration of the drug. This effect was explained by inhibition of 2-oxoglutarate and isocitrate dehydrogenases by MTX. No effect was observed on succinate dehydrogenase. An evaluation of the e ffects of MTX on malic enzyme activity as measured by pyruvate plus la ctate production in intact cells supplied with malate showed a decreas e of about 40 per cent in metabolite production using 0.4 mM MTX. HeLa cell malic enzyme, as observed for other tumour cells, is compartment alized in mitochondria and cytosol, and is another example of a dehydr ogenase inhibited by MTX. (C) 1997 John Wiley & Sons, Ltd.