IMPDH and GTP Metabolism in Cancer: Mechanisms, Regulation, and Translational Scope.

Guanosine triphosphate (GTP) is increasingly recognized as a critical actor in cancer cell proliferation, yet its regulatory mechanism remains incompletely defined. A key contributor to elevated GTP levels in tumors is inosine monophosphate dehydrogenase 2 (IMPDH2), a rate-limiting enzyme in the de novo guanine nucleotide biosynthetic pathway. Although IMPDH inhibitors, mycophenolic acid (MPA) and mycophenolate mofetil (MMF), have shown potential in cancer therapies, their success has been limited due to their immunosuppressive side effects and several unresolved regulatory mechanisms, including paradoxical control of IMPDH activity by GTP. This review provides a systematic summary of the current understanding of IMPDH biology, emphasizing its complex regulation and therapeutic relevance in cancer. We will outline key unresolved questions, including isozyme-specific roles and mechanisms for escaping regulation, and propose mechanistic and translational strategies to design IMPDH-targeted cancer therapies.