PTEN deletion or mutation occurs in 30% to 60% of patients with glioblastoma (GBM) and is associated with poor prognosis. Efficacious therapy for this subgroup of patients is currently lacking. To identify potential target(s) to selectively suppress PTEN-deficient GBM growth, we performed a three-step synthetic lethal screen on LN18 PTEN wild-type (WT) and knockout (KO) isogeneic GBM cell lines using a library containing 606 target-selective inhibitors. A MCL1 inhibitor UMI-77 identified in the screen exhibited excellent suppression on the proliferation, colony formation, 3D spheroid, and neurosphere formation of PTEN-deficient GBM cells. Mechanistically, loss of PTEN in GBM cells led to upregulation of MCL1 in posttranslational level via inhibition of GSK3β, and consequently confer cells resistance to apoptosis. Pharmacologic inhibition or knockdown of MCL1 blocked this PI3K-GSK3β-MCL1 axis and caused reduction of several antiapoptotic proteins, finally induced massive caspase-3 cleavage and apoptosis. In both subcutaneous and orthotopic GBM models, knockdown of MCL1 significantly impaired the in vivo growth of PTEN-deficient xenografts. Moreover, the combination of UMI-77 and temozolomide synergistically killed PTEN-deficient GBM cells. Collectively, our work identified MCL1 as a promising target for PTEN-deficient GBM. For future clinical investigations, priority should be given to the development of a selective MCL1 inhibitor with efficient brain delivery and minimal in vivo toxicity.
©2020 American Association for Cancer Research.