INCREASED AVAILABILITY OF PHOSPHORIBOSYL PYROPHOSPHATE AS THE BASIS FOR ENHANCED 6-MERCAPTOPURINE INCORPORATION BY METHOTREXATE, IN CULTURED HUMAN LYMPHOBLASTS: 52

摘要

In this study we have examined the inhibition of purine de novo synthesis by methotrexate (MTX), with concommitant increase of intracellular PRPP concentrations and enhancement of 6-mercaptopurine (6MP) incorporation. We found a significant elevation of PRPP concentrations in three cultured human leukemic cell lines (Molt-4, Raji, KM3), treated with 0.2 μM and 0.02 μM MTX, respectively. The maximal increase of the intracellular PRPP concentrations occured after distinct time intervals, dependent on both the MTX concentration and the cell type used.During incubation with MTX, samples were taken at various time points and the cells were studied on the availability to incorporate [8-14 C] -6MP. Enhanced 6MP incorporation was observed in time after treatment. At the time points measured, the enhancement of 6MP incorporation correlated well with the increased PRPP levels.