Abstract
Human diploid fibroblasts grown in the presence of methotrexate (MTX) accumulated the drug and metabolized it to poly-γ-glutamyl metabolites (polyglutamates). After 15 min incubation in 1 μM MTX, the non-diffusable component of MTX in these cells was 58 pg MTX equivalent/mg cell protein, none of which consisted of polyglutamates. Accumulation of polyglutamates was linear with time so that after 6 h the cells contained 285 pg/mg of which 45 pg/mg was MTX, 162 pg/mg was MTX monoglutamate and 78 pg/mg was MTX diglutamate. It has been suggested that the continued presence of a component of intracellular MTX in excess of that bound to intracellular binders is required for the inhibition by MTX of deoxyuridine (dU) incorporation into DNA. When fibroblasts were preincubated for 1 h in 1 μM MTX-containing medium and then transferred into MTX-free medium, there was complete recovery of their ability to incorporate dU into DNA. However when the pre-incubation was increased to 4 and 6 h, the 24 h incorporation of dU decreased from 65.5 nM dU/gm cell protein to 17.5 and 4.9 nM/gm respectively. Thus inhibition by MTX of dU incorporation into DNA after the longer incubations was not dependent on the continued presence of MTX in the culture medium and was associated with a rise both in total intracellular MTX derivatives and most particularly in MTX polyglutamates.
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Rosenblatt, D., Whitehead, V., Puttier, A. et al. 654 TEMPORAL RELATIONSHIP BETWEEN ACCUMULATION OF METHOTREXATE POLYSLUTAMATES AND PROLONGED INHIBITION OF DNA SYNTHESIS. Pediatr Res 12 (Suppl 4), 472 (1978). https://doi.org/10.1203/00006450-197804001-00659
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DOI: https://doi.org/10.1203/00006450-197804001-00659