PI3Kγ inhibition suppresses microglia/TAM accumulation in glioblastoma microenvironment to promote exceptional temozolomide response

Abstract

Precision medicine in oncology leverages clinical observations of exceptional response. Towards an understanding of the molecular features that define this response, we applied an integrated, multi-platform analysis of RNA profiles derived from clinically annotated glioblastoma samples. This analysis suggested that specimens from exceptional responders are characterized by decreased accumulation of microglia/macrophages in the glioblastoma microenvironment. Glioblastoma-associated microglia/macrophages secreted interleukin 11 (IL11) to activate STAT3-MYC signaling in glioblastoma cells. This signaling induced stem cell states that confer enhanced tumorigenicity and resistance to the standard-of-care chemotherapy, temozolomide (TMZ). Targeting a myeloid cell restricted isoform of PI3K, PI3K{gamma}, by pharmacologic inhibition or genetic inactivation, disrupted this signaling axis by suppressing microglia/macrophage accumulation and associated IL11 secretion in the tumor microenvironment. Mirroring the clinical outcomes of exceptional responders, PI3K{gamma} inhibition synergistically enhanced the anti-neoplastic effects of TMZ in orthotopic murine glioblastoma models. Moreover, inhibition or genetic inactivation of PI3K{gamma} in murine glioblastoma models recapitulated expression profiles observed in clinical specimens isolated from exceptional responders. Our results suggest key contributions from tumor-associated microglia/macrophages in exceptional responses and highlight the translational potential for PI3K{gamma} inhibition as a glioblastoma therapy. Significance StatementUnderstanding the basis for exceptional responders represents a key pillar in the framework of precision medicine. In this study, we utilized distinct informatics platforms to analyze the expression profiles of clinically annotated tumor specimens derived from patients afflicted with glioblastoma, the most common form of primary brain cancer. These analyses converged on prognostic contributions from glioblastoma-associated microglia/macrophages. Glioblastoma-associated microglia secreted interleukin 11 (IL11) to activate a STAT3-MYC signaling axis in glioblastoma cells, facilitating resistance to the standard-of-care chemotherapy, temozolomide. Microglia recruitment and IL11 secretion were dependent on the myeloid specific phosphoinositide-3-kinase gamma isoform (PI3K{gamma}). Inhibition or genetic inactivation of PI3K{gamma} in murine glioblastoma models recapitulated expression profiles observed in specimens derived from exceptional responders, suggesting potential for clinical translation.