Inhibiting autophagy selectively prunes dysfunctional tumor vessels and optimizes the tumor immune microenvironment.

Abstract

Dysfunctional tumor vasculature, hypoxia, and an immunosuppressive microenvironment are significant barriers to effective cancer therapy. Autophagy, which is critical for maintaining cellular homeostasis and apoptosis resistance, is primarily triggered by hypoxia and nutrient deprivation, conditions prevalent in dysfunctional tumor vessels due to poor circulation. However, the role of autophagy in dysfunctional tumor endothelial cells and its impact on treatment and the tumor microenvironment (TME) remain poorly understood. Methods: We used multiplex immunofluorescence and transgene-based imaging to characterize autophagy in endothelial cells from clinical tumor samples, zebrafish xenograft tumors, and murine models. Using a zebrafish xenograft vasculature platform, we analyzed the effects of autophagy inhibitors on the structure and function of the tumor vasculature. In mice, we investigated autophagy inhibition via endothelial-specific autophagy gene knockout (Atg7 ^iECKO) and the autophagy inhibitor SBI-0206965 and evaluated the synergistic effects of combining SBI-0206965 with low-dose chemotherapy (5-fluorouracil, 5-FU) or PD-1 antibody. Human umbilical vein endothelial cells (HUVECs) were cultured in vitro under hypoxic, glucose-deprived, and serum-free conditions to simulate dysfunctional tumor endothelial cells and to explore the mechanisms by which autophagy inhibition optimizes tumor vasculature. Results: Elevated autophagy was observed in tumor endothelial cells within the dysfunctional vasculature. Autophagy inhibition, through either genetic knockout or pharmacological inhibition, selectively prunes dysfunctional vessels and improves vascular function. It also stimulates the formation of a perivascular immune niche, thereby optimizing the tumor immune microenvironment (TiME). Furthermore, combining the autophagy inhibitor SBI-0206965 with low-dose 5-FU or PD-1 antibody potentiated the anti-tumor effects. Mechanistic studies have indicated that autophagy acts as a protective response to the hypoxic and nutrient-deprived TME, while its inhibition, mediated by p53 activation, promotes tumor endothelial cell apoptosis in dysfunctional tumor vessels, further optimizing the structure and function of the tumor vasculature. Conclusions: Targeting endothelial cell autophagy is a promising strategy for remodeling the dysfunctional tumor vasculature, optimizing the TiME, and boosting the efficacy of chemotherapy and immunotherapy.