LC3-associated phagocytosis of neutrophils trigger tumor ferroptotic cell death in glioblastoma

Necrosis is commonly found in various solid tumors and predicts worse outcome. Chronic ischemia can initiate tumor necrosis, but how the damaged tissue further expands is unclear. Previous studies found that neutrophils associate with necrosis and could contribute to necrosis development in glioblastoma (GBM) by transferring myeloperoxidase (MPO)-containing granules into tumor cells and inducing tumor cell ferroptosis. How the neutrophilic granule transfer occurs is unknown. Here, through an unbiased small molecule screen, we found that statins can inhibit neutrophil-induced tumor cell death by blocking the neutrophilic content transfer into tumor cells. Surprisingly, we found that neutrophils are engulfed by tumor cells before they are fragmented and release the MPO-containing contents in tumor cells. This process involves LC3-associated phagocytosis (LAP) and can be blocked by inhibiting the Vps34-UVRAG-containing PI3K complex. Inhibition of MPO or depletion of Vps34 in an orthotopic xenograft GBM mouse model reduced necrosis formation and allowed tumor-bearing mice to survive longer. Therefore, this study revealed that the neutrophilic granule transfer involves LAP-mediated neutrophil internalization, which then triggers tumor ferroptotic cell death in glioblastoma. Blocking this process may improve prognosis of GBM. Overall design: To examine gene expression changes associating with differentiation of HL-60 cells, we performed RNA-seq analysis of gene expression in parental HL-60 cells and HL-60 cells which were induced for differentiation for 7 days under the differentiation protocol as indicated in the manuscript. The gene expression changes were identified by comparing the gene expression in these two types of cells.