Local and Systemic Immune Dysregulation Alters Glioma Growth in Hyperglycemic Mice.

Abstract

Unlike most cancers, no clear epidemiological correlation between diabetes (Db) and malignant glioma progression exists. Because hyperglycemia activates proinflammatory pathways through the receptor for advanced glycation endproducts (RAGE), we hypothesized that Db can also promote malignant glioma progression. We compared the growth of two phenotypically diverse syngeneic glioma models in control and diabetic mice. Tumor growth and antitumor immune responses were evaluated in orthotopic and heterotopic models and correlated to RAGE and RAGE ligand expression. Irrespective of tumor implantation site, growth of a "classical" glioma model, GL261, increased in hyperglycemic mice and was mediated by upregulation of RAGE and its ligand, HMGB1. However, growth of a "mesenchymal" glioma subtype, K-Luc, depended on tumor implantation site. Whereas heterotopic K-Luc tumors progressed rapidly in Db mice, intracranial K-Luc tumors grew slower. We further showed that hyperglycemia inhibited the innate antitumor inflammatory responses in both models. Although this contributed to the accelerated growth of heterotopic tumors, suppression of tumor inflammatory responses dampened the growth of orthotopic K-Luc gliomas. Hyperglycemia may enhance glioma growth through promotion of RAGE expression and suppression of antitumor immune responses. However, abrogation of the proinflammatory milieu in tumors may also dampen the growth of inflammatory glioma subtypes in the brains of diabetic mice. This dichotomy in glioma growth response to hyperglycemia may partly explain why conflicting epidemiological studies show both an increased risk and a protective effect of Db in patients with malignant gliomas.