Uridine kinase activity in human tumors.

The activity of uridine kinase, a key enzyme in the salvage pathway for pyrimidine bases and nucleosides and for the activation of the corresponding chemotherapeutic analogs, varied 10-fold in a series of human colon adenosarcomas; similar variations were observed with other tumor types. In contrast to the leukemias where only the adult isozyme appears to be present, both the adult and embryonic forms were present in the solid tumors examined. The qualitative and quantitative differences may account, in part, for differences in the innate (initial) sensitivity of the tumors to pyrimidine base and nucleoside analogs.