Inhibition of BACE1 Facilitates Macrophage-based Immunotherapy to Suppress Malignant Growth of Glioblastoma

Abstract Malignant tumors, including glioblastoma (GBM), contain abundant tumor-associated macrophages (TAMs) that mainly promote tumor growth and therapeutic resistance. Reprograming tumor-promoting TAMs (pTAMs) into tumor-suppressive TAMs (sTAMs) represents an attractive therapeutic strategy. We discovered that inhibition of the β-site amyloid precursor protein cleaving enzyme 1 (BACE1) by MK-8931 potently redirects pTAMs into sTAMs and promotes macrophage phagocytosis of glioma cells to suppress the malignant growth of GBM. Moreover, low doses of radiation markedly enhance TAM infiltration and synergize with MK-8931 treatment. BACE1 is preferentially expressed by pTAMs in human GBMs and is required for maintaining pTAM polarization through trans-IL-6/sIL-6R/STAT3 signaling. As several BACE1 inhibitors, including MK-8931, previously developed for Alzheimer's disease, were shown in clinical trials to be safe for humans, repurposing these inhibitors for cancer therapy should be straightforward. Collectively, this study offers a promising therapeutic approach, through inhibition of BACE1, to facilitate the macrophage-based tumor immunotherapy.