Molecular Radiobiology of Human Cell Lines: V. Comparative Radiosensitizing Properties of 5-Halodeoxycytidines and 5-Halodeoxyuridines

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Abstract
Under identical conditions, 5-bromo derivatives of deoxyuridine (BUdR) and deoxycytidine (BCdR) are incorporated to the same extent into the DNA of the human cell line D98/AG, producing approximately equal degrees of radiosensitization. An analogous conclusion holds true for 5-iododeoxyuridine (IUdR) and 5-iododeoxycytidine (ICdR), although the iodo analogs are less effectively incorporated into DNA than the bromo analogs. For the same degree of thymidine replacement, bromo derivatives are only slightly better ultraviolet light sensitizers than the iodo derivatives; on the other hand, the latter are much better X-ray sensitizers than the former. For all the compounds, but especially for the bromo analogs, the sensitization toward ultraviolet light is more pronounced than toward X-rays. The X-ray sensitization by halo analogs does not seem to depend on the comparatively higher photoelectric absorption cross section of the halogen atoms, since the degree of sensitization is independent of the energy of the X-rays.