The Luciferase-Expressing Glioma-261 Murine Models Elicit an Immune-Mediated Antitumor Response

INTRODUCTION: Preclinical models that accurately recapitulate the immunosuppressive properties of human gliomas are essential to assess immune therapeutics. Glioma-261 (GL261) murine glioma cells are widely used as an in Vivo model of glioma. Our group has previously shown that the red-shifted luciferase-expressing cell line, GL261 Red-FLuc, creates an inflammatory response when implanted intracranially in C57BL/6 mice. However, it remains unclear if this is particular to GL261 Red-Fluc or any GL261 cell line transfected with luciferase-expressing genes. For this reason, we have additionally explored the inflammatory response of stably transfected, monoclonal GL261-luc2 cells. METHODS: To evaluate the characteristics of these various cell lines, C57BL/6 mice (n = 10 in each group) underwent stereotaxic, intracranial implantation with GL261, GL261 Red-FLuc, or GL261-Luc2 cells at doses of 5 × 104 cells/5 μL or 3 × 105 cells/5 μL. Immunohistochemistry and flow cytometry of sacrificed mouse brains assess the frequency of immune cell populations. Magnetic resonance imaging (MRI) scans were also performed to monitor relative tumor growth. Finally, in Vitro cytokine profiles were evaluated by proteome microarray. RESULTS: Kaplan-Meier survival analysis demonstrated that the median survival for mice implanted with GL261 cells at 5 × 104 cells/5 μL was 21 d. However, even at a higher tumor dose (3 × 105 cells/5 μL), the GL261-Red FLuc implanted mice did not reach median survival. Mice injected with the newly transfected GL261-Luc2 cells at 3 × 105 cells/5 μL reached median survival at 23 d, but median survival was not reached for GL261-Luc2 implanted mice at 5 × 104 cells/5 μL. MRI analysis reveals clear differences in tumor growth that correspond well with the onset of clinical symptoms and median survival. In addition, proteomic analysis reveals significantly elevated inflammatory cytokines such as IFNgamma, IL-7, and TNF-alpha in the supernatant of the GL261 Red-FLuc cells and upregulated IL-1alpha in GL261-Luc2 cells. Further immune characterization is ongoing. CONCLUSION: Our data suggest that both GL261 Red-FLuc and GL261-luc2 murine models create an undesirable microenvironment for tumor growth by increasing proinflammatory modulators.