A radio-sensitizing pyrimidine nucleoside with potential antineoplastic activity. Cytochlor is metabolized first to a phosphate derivative, CldCMP, by the enzyme deoxycytidine kinase and then to the active uracyl derivative, CldUMP, by the enzyme dCMP deaminase; deoxycytidine kinase and dCMP deaminase have been found in abnormally high concentrations in most cancers. CldUMP, the active metabolite, incorporates into DNA and, upon exposure to radiation, induces the formation of uracil radicals and double-strand DNA breaks. (NCI04)