Abstract
Ample evidence indicates that the cytotoxicity of MTX depends on an increase in [dUTP]/[dTTP], uracil misincorporation into DNA, and uracil excision without adequate repair. The result is extensive DNA fragmentation and cell death. In a survey of many cell lines we found notable differences in their levels of dUTPase activity. When 7 cell lines selected for their wide differences in dUTPase content were assayed for (1) misincorporation of uracil due to MTX, (2) sensitivity to growth inhibition by MTX, and (3) effect of MTX on [dUTP]/[dTTP], the data suggested an apparent inverse correlation between dUTPase levels and sensitivity to MTX. The evidence that low dUTPase level may be associated with higher MTX sensitivity led to a search for dUTPase inhibitors that would enhance the cytotoxicity of MTX. Studies were performed on 44 uracil analogues (mainly 5- and 6-substituted derivatives). Many inhibited dUTPase in cells and sonicates at concentrations of 0.25-3.0 mM. A few were effective inhibitors at 0.1 mM. The most interesting compounds did enhance MTX cytotoxicity as measured by cell growth, uracil misincorporation, and alkaline elution of DNA fragments. No uracil analogue tested inhibited purified dUTPase but added ATP increased inhibition of dUTPase by analogues in sonicates. Thus active inhibitors are probably nucleotide derivatives of uracil analogues.
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Beck, W., Wright, G., Nusbaum, N. et al. ENHANCEMENT OF MTX CYTOTOXICITY BY URACIL ANALOGUES THAT INHIBIT CELLULAR dUTPase ACTIVITY: 10. Pediatr Res 19, 745 (1985). https://doi.org/10.1203/00006450-198507000-00030
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DOI: https://doi.org/10.1203/00006450-198507000-00030