PTEN-loss confers dependence on the guanylate synthesis enzyme IMPDH in T-cell acute lymphoblastic leukemia

Loss of the tumor suppressor PTEN is common in T-cell acute lymphoblastic leukemia (T-ALL), and is associated with poor prognosis. PTEN-loss drives robust activation of AKT/mTORC1 signaling to promote leukemic cell growth. We find that PTEN-loss in T-ALL confers dependence on the guanylate nucleotide synthesis enzyme inosine 5-monophosphate dehydrogenase (IMPDH) for cell growth and viability. This metabolic vulnerability is dependent on sustained mTORC1 signaling and can be exploited using clinically approved IMPDH inhibitors to selectively kill PTEN-deficient T-ALL cells, and extend survival in genetic and xenograft T-ALL models in mice. Mechanistically, IMPDH inhibitors cause early DNA replication stress, followed by DNA damage. In contrast to treatment with mTORC1 inhibitors, these events culminate in robust and selective cell death in PTEN-deficient T-ALL cells. These findings reveal a targetable metabolic vulnerability in T-ALL, which could provide rationale for repurposing clinically approved IMPDH inhibitors. Statement of SignificanceWe find that the IMPDH inhibitors mycophenolic acid and mizoribine, which are currently used as well-tolerated immunosuppressants, exert anti-leukemic activity in an aggressive molecular subset of T-ALL cells that are associated with poor prognosis. The use of clinically approved compounds to exploit this vulnerability could lead to rapid drug repurposing.