Definition

A synthetic pyrimidine nucleoside analogue with biomodulating activity. Tetrahydrouridine increases the efficacy of the radiosensitizer cytochlor (5-chloro-2′-deoxycytidine) by inhibiting the enzyme deoxycytidine monophosphate (dCMP) deaminase and preventing the premature deamination of the cytochlor metabolite 5-chloro-2′-deoxycytidine monophosphate (CldCMP) to 5-chloro-2′-deoxyuridine monophosphate (CldUMP); in turn, this increases tumor concentrations of CldUMP which is then further anabolized and incorporated selectively into tumor DNA as CldU (5-chloro-2′-deoxyuridine).