PP2A-based triple-strike therapy overcomes mitochondrial apoptosis resistance in brain cancer cells

Area of Science:

• Oncology
• Molecular Biology
• Cancer Metabolism

Background:

• Malignant brain tumors exhibit hallmarks of mitochondrial glycolysis and phosphatidylinositol 3-kinase-protein kinase B (AKT) pathway hyperactivity.
• Previous clinical trials targeting AKT (AKTi) or pyruvate dehydrogenase kinase (PDKi) individually have shown limited success in brain tumor patients.

Purpose of the Study:

• To investigate the efficacy of combined AKT and PDK inhibition in brain tumor models.
• To evaluate a novel triplet therapy combining AKT and PDK inhibition with protein phosphatase 2A (PP2A) reactivation for brain tumors.

Main Methods:

• Utilized heterogeneous glioblastoma (GB) and medulloblastoma (MB) cell lines.
• Assessed cytostatic and apoptotic responses to combined AKTi and PDKi, and triplet therapy (AKTi + PDKi + PP2A reactivator).
• Performed in vivo efficacy studies in intracranial GB and MB models.

Main Results:

• Combined AKT and PDK inhibition resulted in cytostatic responses, pathway shutdown, and apoptosis priming but not cell death.
• Triplet therapy, including PP2A reactivation, demonstrated sensitivity across all tested brain tumor cell models.
• In vivo studies confirmed the brain-penetrant triplet therapy's efficacy in intracranial models.

Conclusions:

• PP2A reactivation is crucial for converting cytostatic responses to cytotoxic apoptosis in brain tumors.
• The triplet therapy mechanism involves PP2A-mediated shutdown of mitochondrial oxidative phosphorylation and increased proton leakage.
• These findings support the development of triple-strike strategies targeting mitochondrial metabolism to overcome brain tumor therapy resistance.