Continuous Irradiation of P388F Lymphomain VitroSensitization by 5-iodo-2′-deoxyuridine

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Abstract
P388F lymphoma cells in vitro were exposed to non-cytotoxic concentrations of IUdR (5-iodo-2′-deoxyuridine), either as a 30 min pulse, or continuously for 20 days. Both treatments caused an increase in sensitivity (increase in doubling time) to continuous irradiation. Sensitization, reduction in extrapolation number, to acute doses of 300 kvp x-rays was demonstrated after 16 days growth in low IUdR concentrations (up to 0·28 µM). Populations given 30 min treatments (5·6 µM IUdR) and subsequently grown in normal medium were also more sensitive to acute doses of x-rays. There was again a decrease in extrapolation number with no change in the D0 value. This increased sensitivity was still demonstrable in two of the treated populations after 20 days' growth and in a third after 30 days' growth in normal medium. Sensitization, after 30 min treatments, was not due to a change in the relative proportions of the stages of the cell-cycle as shown by the rate of increase of labelled cells and labelled mitoses.