Interactions of radiation and 5-fluorouracil, cyclophosphamide or methotrexate in intestinal crypt cells

The interactions of radiation and 5-fluorouracil (5-FU), cyclophosphamide (CTX), or methotrexate (MTX) in mouse jejunal crypt cells were studied using the microcolony survival assay. 5-FU given from 48 hr before to 24 hr after irradiation resulted in an almost constant, increased cell kill except at injection 6 hr after irradiation, which resulted in a more pronounced effect. CTX enhanced the radiation effect only when given simultaneously with or up to 3 hr after irradiation. The effect of MTX, extremely dependent on the sequence and interval between drug administration and irradiation, was most prominent when administered 1 hr before irradiation. At this drug-radiation interval, the D0 surprisingly increased by a factor of 2.4, whereas MTX 15 min before irradiation displaced the survival curve to the left without changing the D0. The influence of MTX on the radiation response disappeared when the drug was given either 96 hr before or 3 hr after irradiation.