Mitogenic and progenitor gene programmes in single pilocytic astrocytoma cells.

Pilocytic astrocytoma (PA), the most common childhood brain tumor, is a low-grade glioma with a single driver BRAF rearrangement. Here, we perform scRNAseq in six PAs using methods that enabled detection of the rearrangement. When compared to higher-grade gliomas, a strikingly higher proportion of the PA cancer cells exhibit a differentiated, astrocyte-like phenotype. A smaller proportion of cells exhibit a progenitor-like phenotype with evidence of proliferation. These express a mitogen-activated protein kinase (MAPK) programme that was absent from higher-grade gliomas. Immune cells, especially microglia, comprise 40% of all cells in the PAs and account for differences in bulk expression profiles between tumor locations and subtypes. These data indicate that MAPK signaling is restricted to relatively undifferentiated cancer cells in PA, with implications for investigational therapies directed at this pathway.

ER stress in temozolomide-treated glioblastomas interferes with DNA repair and induces apoptosis.

Glioblastoma multiforme (GBM) is a deadly grade IV brain tumor. Radiation in combination with temozolomide (TMZ), the current chemotherapeutic for GBMs, only provides 12-14 months survival post diagnosis. Because GBMs are dependent on both activation of the DNA damage pathway and the endoplasmic reticulum (ER) stress response, we asked if a novel ER stress inducing agent, JLK1486, increases the efficacy of TMZ.We found that the combination of TMZ+JLK1486 resulted in decreased proliferation in a panel of adherent GBM cells lines and reduced secondary sphere formation in non-adherent and primary lines. Decreased proliferation correlated with increased cell death due to apoptosis. We found prolonged ER stress in TMZ+JLK1486 treated cells that resulted in sustained activation of the unfolded protein response (UPR) through increased levels of BiP, ATF4, and CHOP. In addition, TMZ+JLK1486 treatment caused decreased RAD51 levels, impairing DNA damage repair. Furthermore, we found delayed time to tumor doubling in TMZ+JLK1486 treated mice.Our data shows that the addition of JLK1486 to TMZ increases the efficaciousness of the treatment by decreasing proliferation and inducing cell death. We propose increased cell death is due to two factors. One, prolonged ER stress driving the expression of the pro-apoptotic transcription factor CHOP, and, second, unresolved DNA double strand breaks, due to decreased RAD51 levels. The combination of TMZ+JLK1486 is a potential novel therapeutic combination and suggests an inverse relationship between unresolved ER stress and the DNA damage response pathway.

Glioblastoma multiforme therapy and mechanisms of resistance.

Glioblastoma multiforme (GBM) is a grade IV brain tumor characterized by a heterogeneous population of cells that are highly infiltrative, angiogenic and resistant to chemotherapy. The current standard of care, comprised of surgical resection followed by radiation and the chemotherapeutic agent temozolomide, only provides patients with a 12-14 month survival period post-diagnosis. Long-term survival for GBM patients remains uncommon as cells with intrinsic or acquired resistance to treatment repopulate the tumor. In this review we will describe the mechanisms of resistance, and how they may be overcome to improve the survival of GBM patients by implementing novel chemotherapy drugs, new drug combinations and new approaches relating to DNA damage, angiogenesis and autophagy.