In agreement with the aforementioned in vitro results, early studies reported that NA cotreatment abolished the antitumor effects of FK866, GNE-617, and GMX1777 in mice bearing xenografts of NAPRT-proficient tumors (ML-2 and HCT-116) [190,203,204], while not affecting the efficacy of GMX1777 (24 h IV infusion 150 mg/kg and 650 mg/kg) or LSN3154567 (20 mg/kg; BID) in xenografts of NAPRT-deficient cancer cells (HT-1080 and NCI-H1155) [115,203]. This evidence concerns the gene NAPRT and cancer.