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Most tumors, including brain tumors, are sporadic. However, a small subset of CNS tumors are associated with hereditary cancer conditions like Lynch Syndrome (LS). Here, we present a case of an oligodendroglioma, IDH-mutant and 1p/19q-codeleted, and LS with a germline pathogenic PMS2 mutation. To our knowledge, this has only been reported in a few cases in the literature. While the family history is less typical of LS, previous studies have indicated the absence of a significant family history in patient cohorts with PMS2 mutations due to its low penetrance. Notably, only a handful of studies have worked on characterizing PMS2 mutations in LS, and even fewer have looked at these mutations in the context of brain tumor development. This report aims to add to the limited literature on germline PMS2 mutations and oligodendrogliomas. It highlights the importance of genetic testing in neuro-oncology.

BACKGROUND Glioblastoma (GBM) is the most aggressive and lethal type of brain tumor. Activation of PI3K/mTOR pathway along with the loss of its primary negative regulator, phosphatase and tensin homolog (PTEN), occurs in nearly 50% of GBM patients. As PTEN is known to promote DNA damage repair deficiency, here we investigated whether PTEN deficiency presents a vulnerability to a simultaneous induction of DNA damage and suppression of repair mechanisms by combining topoisomerase I (TOP1) and PARP inhibitors. METHODS We used patient-derived GBM cells and stem-like cells to determine response to LMP400 (Indotecan), a novel non-camptothecin TOP1 inhibitor, and the PARP inhibitors Olaparib or Niraparib. Treatment efficacy was also determined using cell viability, cell cycle, DNA damage, repair, and apoptosis assays in a pair of isogenic PTEN-null and PTEN-WT glioma cell lines derived from a genetically engineered mouse GBM model. RNAseq analysis was performed to identify treatment-induced dysregulated pathways. RESULTS PTEN-deficient cells are highly sensitive to LMP400 and PTEN rescue lessens sensitivity to the treatment. Combining LMP400 with PARP inhibitors, Olaparib or Niraparib, leads to synergistic cytotoxicity. LMP400/Niraparib combination induces G2/M cell cycle arrest, DNA damage, suppression of homologous recombination (HR)-related proteins and activation of caspase 3/7 activity significantly more in PTEN-null cells compared to isogenic PTEN-WT cells. Gene set enrichment analysis revealed suppression of cell cycle and DNA damage repair as well as activation of cell death pathways. Finally, CRISPR-Cas9 KO screening suggests that LMP400 is not likely to be a substrate for ABC transporters, suggesting the brain penetration and supporting the use in brain tumor patients. CONCLUSION Combined inhibition of TOP1 and PARP induces synergistic antiglioma effects selectively in PTEN-null glioblastoma cells, providing a strong scientific premise for a clinical trial of combined treatment with LMP400 and Niraparib in a subset of GBM with PTEN deficiency.

BACKGROUND IDH mutations are common in diffuse gliomas and confer an increased dependency on oxidative mitochondrial function. Zotiraciclib, a multi-kinase inhibitor, not only suppresses CDK9-mediated gene transcription process but also causes mitochondrial dysfunction in preclinical models. We investigated the selective activity of zotiraciclib in IDH-mutant gliomas. METHODS Cytotoxicity of zotiraciclib was determined in patient-derived glioma cells with/without IDH mutations. Immunoblotting and flow cytometry were used to evaluate the cell death pathways. Real-time ATP production was measured by Seahorse assay. RESULTS The EC50 of zotiraciclib in IDH-wt cells was twice as high as in IDH-mutant cells. In low-dose zotiraciclib (15nM)-treated IDH-mutant cells, RNA Pol II phosphorylation and expression of antiapoptotic proteins, including XIAP, MCL-1 and survivin were decreased significantly. Cleaved caspase 3/7, 8, 9 and LC3B were also detected in treated IDH-mutant cells but not in IDH-wt cells, suggesting activation of intrinsic and extrinsic cell apoptosis pathways, and subsequent autophagy of IDH-mutant cells. Low-dose treated IDH-mutant, but not IDH-wt cells, induced decreased expression of a panel of mitochondrial respiration genes, and mitochondrial respiration complexes, cellular ATP depletion and increased ROS production, suggesting a greater disruption of mitochondrial function in zotiraciclib-treated IDH-mutant cells. Zotiraciclib treatment prolonged the survival in mice bearing intracranial IDH-mutant gliomas (30 days in DMSO-treated group vs 33 days in zotiraciclib-treated group, p = 0.01), but not in mice with glioma established with the isogenic IDH-wt glioma cells (18 days in DMSO-treated vs 20 days in zotiraciclib-treated group, p = 0.10). CONCLUSIONS There is selective activity of zotiraciclib in IDH-mutated glioma. Low-dose exposure of zotiraciclib induces cell death and suppresses transcriptional process and mitochondrial biogenesis in IDH-mutant glioma, not in IDH-wt tumors. These findings support a clinical trial testing zotiraciclib in IDH-mutated glioma. The treatment efficacy seen even at low concentrations further supports testing it as a single agent, thereby reducing toxicity concerns.