​Impacts of endothelial cell autophagy inhibition on tumorigenesis

Metastasis is the leading cause of cancer related mortality, and this burden is particularly severe in breast cancers lacking hormone receptor expression. These patients have limited treatment options and poorer outcomes. Endothelial cells are important regulators of metastasis, as they control vascular integrity and migration of circulating tumor cells into other tissues. Inhibition of autophagy, a conserved degradative process which promotes metabolic adaptation in tumor cells, is being tested as a targeted therapy for breast and other cancers. However, the impact of autophagy inhibition on the tumor vasculature and metastasis is poorly understood. To determine how endothelial autophagy influences breast tumor progression, we generated endothelial cell specific Atg12 and Atg5 knockout (ECKO) mice driven by the Cdh5CreER vascular endothelial cadherin promoter. In orthotopic transplantation of MMTV-PyMT tumor organoids and genetic crosses to PyMT mice, Atg12 ECKO mice displayed delayed primary tumor growth compared to controls. Mid- stage Atg12 ECKO tumors exhibited increased apoptosis, whereas proliferation and necrosis were unchanged at endpoint, indicating that endothelial cell autophagy promotes efficient tumor cell survival during mid-stage cancer progression. Despite increased CD31 + vascular density, Atg12 ECKO tumors demonstrated elevated HIF1-alpha, consistent with impaired vascular function and hypoxia. Following surgical resection of primary tumors, Atg12 ECKO mice demonstrated higher rates of tumor recurrence and lung metastasis, and tail vein injection of PyMT cells into tumor naïve mice confirmed enhanced metastatic outgrowth. To test whether these effects were tumor type specific, we used the Rat insulin promoter-SV40 Large T antigen (RIP-Tag) model of pancreatic neuroendocrine tumors, which are highly vascular and sensitive to anti-angiogenic therapy. Neither early nor late endothelial deletion of Atg12 altered primary tumor burden or survival, in contrast to the PyMT findings. However, Atg12 ECKO mice displayed increased liver micrometastasis, indicating that the effects of endothelial autophagy loss are highly context specific. These results highlight the context dependent roles of endothelial autophagy in shaping tumor growth and metastasis, underscoring the need to consider strategies to limit changes to metastasis with autophagy inhibition strategies in cancer therapy.