Abstract 5031: Organotypic brain explant culture as a drug evaluation system for malignant brain tumors

Abstract

Abstract Background: Inhibition of major metabolic pathways is being assessed for several intractable tumors, including glioblastoma. Following screening in 2D-systems, evaluating metabolic inhibitors in assays that include both tumor and normal brain tissue is indispensable for selecting compounds that can affect gliomas within their microenvironment. Here we asked whether organotypic brain slices from adult mice can be used to evaluate the effects of metabolic inhibitors on malignant glioma cells. Methods: Retroviral expression of H-RasV12 and dsRed in Ink4a/Arf-/- neural stem / progenitor cells was adopted to establish glioma initiating cells (GICs). GICs with different extracellular acidification potential were derived by single cell cloning and used after one in vivo passage. GICs or their clones were implanted into the forebrain of 6-weeks-old wild-type mice. Tumor-bearing brain explants were established as 200 µm coronal brain slices, treated with cisplatin, dichloroacetate or phenformin. The effects of the drugs were assessed by fluorescence microscopy of the live explants, as well as immunohistochemical staining at the end of the treatment. Results: The feasibility of assessing drug effects in brain tumor explants from adult mice was confirmed with the use of the DNA-damaging agent cisplatin. Treatment of brain slices carrying tumors formed by GICs with 50 μM cisplatin for 4 days effectively decreased the tumor burden, as shown by a significant reduction of the tumor area on fluorescence imaging and a marked increase in tumor cells positive for cleaved caspase 3 on immunohistochemical analysis. The action of metabolic inhibitors was assessed in explants with tumors formed by GIC-derived populations that predominantly use either glycolysis or mitochondrial respiration. Treatment of the brain slices with dichloroacetate, an inhibitor of pyruvate dehydrogenase kinase, resulted in a marked increase in cleaved caspase 3-positive cells in glycolytic tumors. In contrast, phenformin, which inhibits respiratory complex I, had a pronounced pro-apoptotic effect in tumors formed by cells with a high mitochondrial activity. Conclusion: Inhibitors of both glycolysis and oxidative phosphorylation effectively and selectively induced apoptosis of the targeted tumor cells in cultured brain slices. Our results suggest that brain explants from adult mice can be used to assess the effects of anti-metabolic drugs on the survival of glioma initiating cells within a syngeneic microenvironment. Explants could thus be useful in the evaluation of new metabolic inhibitors. Citation Format: Noriaki Minami. Organotypic brain explant culture as a drug evaluation system for malignant brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5031.