Febuxostat Enhances the Antitumor Efficacy of 2-Fluoroadenine and 5'-Methylthioadenosine in MTAP-Deleted Cancer

Homozygous deletion of the methylthioadenosine phosphorylase (MTAP) gene is a frequent genetic alteration in cancer. The MTAP enzyme, which creates adenine from 5'-methylthioadenosine (MTA), is constitutively expressed in all tissues throughout the body. Previously, we described a novel strategy to specifically target MTAP-deleted cancer cells by combining the antipurine prodrug 2-fluoroadenine (2FA) with MTA. In vitro, this combination efficiently kills MTAP- cancer cells while leaving MTAP+ cells unharmed. However, in vivo, the combination was less effective at tumor cell killing, resulting in slower growth but not tumor regression. In this study, we show that this effectiveness difference is associated with a large difference in the amount of 2FA that is incorporated into 2FA-containing nucleotides. To explain this observation, we tested the hypothesis that 2FA was a target for the purine metabolic enzyme xanthine oxidase (XO), which is found in various extracellular fluids. In vitro, the addition of XO protein to culture media effectively abolishes killing by 2FA, and this effect can be fully reversed by the addition of febuxostat (FX), a XO inhibitor. In vivo, the addition of FX to 2FA results in increased cell killing and toxicity, and a 1,000% increase in the amount of 2FA that is converted to its active form, 2FA-monophosphate. Xenograft studies using MTAP- HT1080 and MiaPaCa-2 cell lines show that a 2FA/MTA/FX cocktail can cause tumor regression in vivo. These studies suggest that a combination of 2FA/MTA/FX may be useful in treating MTAP- cancer.

Deletion of the MTAP gene is one of the most frequent genetic alterations in cancer, making it a potentially good target for cancer therapy. Previously, we demonstrated that a combination of 2FA and MTA could specifically target MTAP- cells. In this study, we show that the addition of FX substantially increases the potency of 2FA/MTA in vivo.