Figure 4.

Diagram of nucleotide metabolism involved in cancer radioresistance and its radiosensitizers. DNA damage repair is one of the major mechanisms by which tumor cells develop radioresistance, requiring the accumulation of a large amount of nucleotides. To promote tumor cell survival during radiotherapy, activated glucose metabolism (e g. glycolysis, PPP) and amino acid metabolism (e g. glutamate, asparagine, serine) provide sufficient substrates and energy to accelerate purine and pyrimidine synthesis. Simultaneously, related enzymes in the de novo nucleotide synthesis pathway (e g. TS/PPAT/IMPDH) have been shown to be targets for radiosensitization.