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UTILITY OF THE MURINE ERYTHROLEUKEMIC CELL (MELC) IN ASSESSING MECHANISMS OF ACTION OF DNA-ACTIVE DEVELOPMENTAL TOXICANTS: APPLICATION TO 5-FLUOROURACIL
Citation:
Elstein, K., R. Zucker, D. Shuey, C. Lau, N. Chernoff, AND J. Rogers. UTILITY OF THE MURINE ERYTHROLEUKEMIC CELL (MELC) IN ASSESSING MECHANISMS OF ACTION OF DNA-ACTIVE DEVELOPMENTAL TOXICANTS: APPLICATION TO 5-FLUOROURACIL. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-93/386 (NTIS PB93236651).
Description:
Murine erythroleukemic cells (MELC) exposed to 2-deoxy-5-azacytidine (D-AZA) or to the active cyclophosphamide (CP) metabolites phosphoramide mustard (PAM) and 4-hydroxycyclo-phosphamide (OHCP) reveal cell-cycle perturbations similar to those seen in limb bud nuclei of gestation day (GD) 10 CD-1 mouse embryos exposed in utero to D-AZA or CP, respectively. he similarities in response suggest MELC may be a useful model for determining mechanisms of action of DNA-active developmental toxicants. or such investigations, MELC offer several advantages: they grow in suspension (which simplifies FCM analysis), are easily synchronized (for studying cell-cycle-dependent effects), and can be assayed for growth kinetics. o test the utility of this model, we used MELC to investigate the mechanism of action of 5-fluorouracil (5-FU), a thymidylate synthetase (TS) inhibitor that induced in GD 14 rat fetuses an apparent S-phase accumulation in limb bud cells 8 hr after in utero exposure, but S-phase depletion in liver cells 24 hr postexposure. ELC timed recovery and synchronization studies suggest that in all proliferative tissues, 5-FU induces an early S-phase accumulation followed by a synchronous, concentration-dependent delay in progression through the cell cycle. onsequently, it is the tissue-specific rate of retardation, and not different mechanisms of action, that results in apparent tissue-specific perturbations. oreover, growth and cell-cycle data suggest that calls entering S-phase (when TS activity is greatest) are the most sensitive to 5-FU toxicity. ssays of the TS activity of recovering MELC reveal that although the extent of TS inhibition is not concentration-dependent, the time to recovery is suggesting that the rate of S-phase progression is limited by TS activity. ogether, the induction of similar cell-cycle perturbations in embryonic/fetal tissues and MELC following exposure to CP, D-AZA, or 5-FU, an well as the adaptability of MELC to a variety of kinetic assays suggests that, for those developmental toxicants suspected of inducing call-cycle perturbations in embryonic/fetal tissues, MELC may prove useful for elucidating mechanisms of action.
