Radiosensitization of a Mammalian Cell Line with 5-Bromodeoxyuridine

Abstract

Incubation of H.Ep. #1 cells (derived from a human cervical carcinoma) in the presence of 6/[mu]g/ml of 5-bromodeoxyuridine (BUDR) for 3.5 days resulted in 1% incorporation of BUDR into cell DNA. Studies were made on the ability of these cells to form macroscopic colonies following X-ray or thermal neutron irradia-tion. A two-fold increase in X-ray sensitivity of cells incorporating 1% BUDR (compared with cells not treated with the analog) was observed. Extrapolation or hit numbers of survival curves were 10 and 30 for analog-free and exposed cells, respectively. In contrast, an enhanced sensitivity of only 1.2 was found following thermal neutron irradiation with identical treatment of cells with the analog. Extrapolation numbers were 2.2 and 1.0 for unexposed and analog-exposed cells, respectively. Theoretical calculations on X-ray energy absorbed by BUDR-exposed cells demonstrates a negligible increase in absorbed energy by cells having incorporated 1% BUDR, as compared to cells having normal DNA. Enhanced X-ray sensitivity does not appear to be due to a possible increase in energy absorbed per cell associated with the high absorption cross-section of bromine. Observations on a change in survival in analog-exposed cells with time after cell plating, which was not seen for unexposed cells are also described.