Gemcitabine is an active metabolite of the gemcitabine prodrugs NUC-1031 and gemcitabine elaidate and a prodrug form of gemcitabine di- and triphosphates. Gemcitabine is phosphorylated by intracellular kinases to the intermediate metabolite gemcitabine monophosphate and the active di- and triphosphate forms.It is cytotoxic to HepG2 hepatocellular carcinoma and A549 non-small cell lung cancer (NSCLC) cells (IC50s = 5.2 and 16 nM, respectively) and inhibits tumor growth in various breast, colon, lung, and pancreatic cancer mouse xenograft models. Gemcitabine (12 mg/kg) sensitizes tumors to antibodies targeting programmed cell death protein 1 (PD-1), decreases the number of tumor-infiltrating regulatory T cells (Tregs), and increases survival in an MC-38 syngeneic mouse model of colon carcinoma. Formulations containing gemcitabine have been used in the treatment of cancer.