Selective inhibition of mTORC1 in tumor vessels increases antitumor immunity.

Shan Wang,Rebecca Cook,Siyuan Zhang,Eileen Shiuan,Margaret M Allaman,Jin Chen,Ariel Raybuck,Keith T Wilson,Deanna Edwards,Qingfei Wang,James Nathan,Mark Boothby,Sung Hoon Cho,David Denardo,Dana M Brantley-Sieders

doi:10.1172/jci.insight.139237

Abstract

A tumor blood vessel is a key regulator of tissue perfusion, immune cell trafficking, cancer metastasis, and therapeutic responsiveness. mTORC1 is a signaling node downstream of multiple angiogenic factors in the endothelium. However, mTORC1 inhibitors have limited efficacy in most solid tumors, in part due to inhibition of immune function at high doses used in oncology patients and compensatory PI3K signaling triggered by mTORC1 inhibition in tumor cells. Here we show that low-dose RAD001/everolimus, an mTORC1 inhibitor, selectively targets mTORC1 signaling in endothelial cells (ECs) without affecting tumor cells or immune cells, resulting in tumor vessel normalization and increased antitumor immunity. Notably, this phenotype was recapitulated upon targeted inducible gene ablation of the mTORC1 component Raptor in tumor ECs (RaptorECKO). Tumors grown in RaptorECKO mice displayed a robust increase in tumor-infiltrating lymphocytes due to GM-CSF–mediated activation of CD103+ dendritic cells and displayed decreased tumor growth and metastasis. GM-CSF neutralization restored tumor growth and metastasis, as did T cell depletion. Importantly, analyses of human tumor data sets support our animal studies. Collectively, these findings demonstrate that endothelial mTORC1 is an actionable target for tumor vessel normalization, which could be leveraged to enhance antitumor immune therapies.

Highlights

A rapidly growing tumor requires blood vessels to support the increased demands for nutrients and oxygen
Phospho–flow cytometry analysis revealed that low-dose RAD001 treatment inhibited p-S6, a downstream target of mTORC1 signaling, in CD31+ endothelial cells (ECs) (Figure 1C), but not in CD45–CD31– populations and CD45+ immune cells (Figure 1D), suggesting that low doses of RAD001 primarily target ECs within the tumor microenvironment
Given our finding that upregulation of GM-CSF in RaptorECKO tumors increased the proportion of CD103+ DCs and IFN-γ+CD8+ T cells, we examined if GM-CSF has an impact on antitumor immunity in clinical lung (n = 1129) and breast cancer (n = 1218) data sets curated by The Cancer Genome Atlas (TCGA)

Summary

Introduction

A rapidly growing tumor requires blood vessels to support the increased demands for nutrients and oxygen. Unlike vessels in healthy tissues, tumor blood vessels are highly dysfunctional, characterized by chaotic networks of leaky, tortuous, and uneven endothelial tubules without pericyte support These vascular abnormalities cause sluggish blood flow, vascular leakiness, and poor perfusion in tumors. Immune responses and leukocyte trafficking may be affected by poor tumor perfusion, as well as by the hypoxic microenvironment created by the faulty vessels [4, 5]. Constant vessel remodeling in tumors contributes to spontaneous hemorrhage and increased interstitial fluid pressure, which blocks drug delivery and enhances a malignant tumor phenotype, including metastasis [6]. The abnormal nature of the tumor vasculature enhances tumor metastasis, immune escape, and poor therapeutic response.

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Conclusion