DCK and cancer: Even though DI-39 showed promising results as a single agent and more prominently as combination therapy with other inhibitors of pyrimidine de novo synthesis in ALL cancer cells and mouse models, DI-39 has limited solubility and metabolic stability due to a short half-life in vivo leading to the development of additional dCK inhibitors with DI-87 being the most promising candidate (Figure 2B,D) [73,74].