Loss of Vascular Endothelial Glutaminase Inhibits Tumor Growth and Metastasis, and Increases Sensitivity to Chemotherapy

Glutamine is the most abundant nonessential amino acid in blood stream; yet its concentration in tumor interstitium is markedly lower than that in the serum, reflecting the huge demand of various cell types in tumor microenvironment for glutamine. While many studies have investigated glutamine metabolism in tumor epithelium and infiltrating immune cells, the role of glutamine metabolism in tumor blood vessels remains unknown. Here, we report that inducible genetic deletion of glutaminase (GLS) specifically in host endothelium, GLS(ECKO), impairs tumor growth and metastatic dissemination in vivo. Loss of GLS decreased tumor microvascular density, increased perivascular support cell coverage, improved perfusion, and reduced hypoxia in mammary tumors. Importantly, chemotherapeutic drug delivery and therapeutic efficacy were improved in tumor-bearing GLS(ECKO) hosts or in combination with GLS inhibitor, CB-839. Mechanistically, loss of GLS in tumor endothelium resulted in decreased leptin levels, and exogenous recombinant leptin rescued tumor growth defects in GLS(ECKO) mice. Together, these data demonstrate that inhibition of endothelial glutamine metabolism normalizes tumor vessels, reducing tumor growth and metastatic spread, improving perfusion, reducing hypoxia, and enhancing chemotherapeutic delivery. Thus, targeting glutamine metabolism in host vasculature may improve clinical outcome in patients with solid tumors. SIGNIFICANCE: This study demonstrates a crucial role for glutamine metabolism in tumor endothelium, which may be exploited therapeutically to induce vascular normalization and improve drug delivery in solid tumors.