Jin Chen

Distant metastasis is the leading cause of mortality in many cancers. Although metabolic reprogramming is recognized as a hallmark of cancer, how tumor-intrinsic metabolic enzymes regulate tumor-immune crosstalk during metastatic progression remains poorly understood. Here, using a high-throughput functional CRISPR-Cas9 screen targeting metabolic genes in an orthotopic 4T1 murine mammary carcinoma model of spontaneous lung metastasis, we identify a selective enrichment of arginase 2 (ARG2)-deficient tumor cells in metastatic lungs of immunocompetent but not RAG1-deficient mice, indicating a lymphocyte-dependent mechanism. Loss of ARG2 enhances spontaneous lung metastasis without affecting primary tumor growth. Further, metastatic outgrowth in the lung is not affected when tumor cells are injected intravenously, indicating that ARG2 regulates an early stage of the metastatic cascade. Mechanistically, ARG2 deficiency upregulates nitric oxide synthase 2 (NOS2), resulting in increased nitric oxide production, accumulation of cytosolic DNA, and activation of the cGAS-STING-NF-κB pathway, leading to upregulation of inflammatory cytokines. ARG2-deficient tumors exhibit an immunosuppressive tumor microenvironment characterized by enrichment of Th17 cells and reduced anti-tumor immune populations. Functionally, Th17 cells enhance tumor cell migration in vitro and promote spontaneous lung metastasis in vivo . Genetic deletion of NOS2 attenuates cytosolic DNA accumulation, reduces STING-NF-κB activation, restores anti-tumor immunity, and suppresses ARG2 deficiency-driven metastatic burden in vivo . Collectively, these findings define a tumor cell-intrinsic ARG2-NOS2 axis that regulates inflammatory signaling and the tumor microenvironment to promote metastasis, highlighting a targetable vulnerability in metastatic breast cancer.

Targeted therapies have improved survival for lung adenocarcinoma patients. However, similar advances are lacking for lung squamous carcinoma (LUSC). Advances in immunotherapy have shown some promise, but the overall response rate remains low in LUSC. Here, we demonstrate that the mTORC2 signaling pathway represents an actionable target in LUSC to improve anti-tumor immune responses. We show that genetic alterations affecting the mTORC2 pathway are common among patients with LUSC tumors, and targeting mTORC2 reduces LUSC tumor growth in mouse models. Transcriptomics reveal that mTORC2-deficient LUSC cells exhibit reduced expression of glycolytic and hypoxia-related genes. In agreement, loss of mTORC2 signaling decreases lactate levels in tumor-interstitial fluid, creating reduced acidity within the tumor microenvironment. Interestingly, mTORC2-deficient LUSC cells also exhibited reduced expression of the pH-sensitive VISTA ligand PSGL-1 in a HIF-2α dependent mechanism. LUSC patients, but not those with LUAD, display a positive correlation in expression between HIF-2α and PSGL-1, suggesting a distinct association among mTORC2, HIF-2α, and immune responses in LUSC. Indeed, mTORC2 loss-of-function enhanced CD8⁺ T cell activation in tumors, while use of anti-VISTA immunotherapy reduced LUSC tumor burden only in the presence of intact mTORC2 signaling. Collectively, these data describe an important role of mTORC2 signaling in LUSC tumors and demonstrate the therapeutic potential of targeting the mTORC2/PSGL-1/VISTA axis in patients that are non-responsive to current therapies.

Targeted therapies have improved survival for lung adenocarcinoma patients. However, similar advances are lacking for lung squamous carcinoma (LUSC). Advances in immunotherapy have shown some promise, but the overall response rate remains low in LUSC. Here, we demonstrate that the mTORC2 signaling pathway represents an actionable target in LUSC to improve anti-tumor immune responses. We show that genetic alterations affecting the mTORC2 pathway are common among patients with LUSC tumors, and targeting mTORC2 reduces LUSC tumor growth in mouse models. Transcriptomics reveal that mTORC2-deficient LUSC cells exhibit reduced expression of glycolytic and hypoxia-related genes. In agreement, loss of mTORC2 signaling decreases lactate levels in tumor-interstitial fluid, creating reduced acidity within the tumor microenvironment. Interestingly, mTORC2-deficient LUSC cells also exhibited reduced expression of the pH-sensitive VISTA ligand PSGL-1 in a HIF-2α dependent mechanism. LUSC patients, but not those with LUAD, display a positive correlation in expression between HIF-2α and PSGL-1, suggesting a distinct association among mTORC2, HIF-2α, and immune responses in LUSC. Indeed, mTORC2 loss-of-function enhanced CD8 ⁺ T cell activation in tumors, while use of anti-VISTA immunotherapy reduced LUSC tumor burden only in the presence of intact mTORC2 signaling. Collectively, these data describe an important role of mTORC2 signaling in LUSC tumors and demonstrate the therapeutic potential of targeting the mTORC2/PSGL-1/VISTA axis in patients that are non-responsive to current therapies.

Metastatic outgrowth in distant microscopic niches requires sufficient nutrients, including fatty acids (FAs), to support tumor growth and to generate an immunosuppressive tumor microenvironment (TME). However, despite the important role of FAs in metastasis, the regulation of FA supply in metastatic niches has not been defined. In this report, we show that tumor endothelium actively promotes outgrowth and restricts antitumor cytolysis by transferring FAs into developing metastatic tumors. We describe a process of transendothelial FA delivery via endosomes that requires mTORC1 activity. Thus, endothelial cell–specific targeted deletion of Raptor ( Rptor ^ECKO ), a unique component of the mTORC1 complex, significantly reduced metastatic tumor burden that was associated with improved markers of T cell cytotoxicity. Low-dose everolimus that selectively inhibited endothelial mTORC1 improves immune checkpoint responses in metastatic disease models. This work reveals the importance of transendothelial nutrient delivery to the TME, highlighting a future target for therapeutic development.

Endothelial cells (ECs) that line blood vessels act as gatekeepers and shape the metabolic environment of every organ system. In normal conditions, endothelial cells are relatively quiescent with organ-specific expression signatures and metabolic profiles. In cancer, ECs are metabolically reprogrammed to promote the formation of new blood vessels to fuel tumor growth and metastasis. In addition to EC’s role on tumor cells, the tortuous tumor vasculature contributes to an immunosuppressive environment by limiting T lymphocyte infiltration and activity while also promoting the recruitment of other accessory pro-angiogenic immune cells. These elements aid in the metastatic spreading of cancer cells and contribute to therapeutic resistance. The concept of restoring a more stabilized vasculature in concert with cancer immunotherapy is emerging as a potential approach to overcoming barriers in cancer treatment. This review summarizes the metabolism of endothelial cells, their regulation of nutrient uptake and delivery, and their impact in shaping the tumor microenvironment and anti-tumor immunity. We highlight new therapeutic approaches that target the tumor vasculature and harness the immune response. Appreciating the integration of metabolic state and nutrient levels and the crosstalk among immune cells, tumor cells, and ECs in the TME may provide new avenues for therapeutic intervention.

Tumor metastasis, the main cause of death in cancer patients, requires outgrowth of tumor cells after their dissemination and residence in microscopic niches. Nutrient sufficiency is a determinant of such outgrowth ¹ . Fatty acids (FA) can be metabolized by cancer cells for their energetic and anabolic needs but impair the cytotoxicity of T cells in the tumor microenvironment (TME) ^{2, 3} , thereby supporting metastatic progression. However, despite the important role of FA in metastatic outgrowth, the regulation of intratumoral FA is poorly understood. In this report, we show that tumor endothelium actively promotes tumor growth and restricts anti-tumor cytolysis by transferring FA into developing metastatic tumors. This process uses transendothelial fatty acid transport via endosome cargo trafficking in a mechanism that requires mTORC1 activity. Thus, tumor burden was significantly reduced upon endothelial-specific targeted deletion of Raptor, a unique component of the mTORC1 complex (Rptor ^ECKO ). In vivo trafficking of a fluorescent palmitic acid analog to tumor cells and T cells was reduced in Rptor ^ECKO lung metastatic tumors, which correlated with improved markers of T cell cytotoxicity. Combination of anti-PD1 with RAD001/everolimus, at a low dose that selectively inhibits mTORC1 in endothelial cells ⁴ , impaired FA uptake in T cells and reduced metastatic disease, corresponding to improved anti-tumor immunity. These findings describe a novel mechanism of transendothelial fatty acid transfer into the TME during metastatic outgrowth and highlight a target for future development of therapeutic strategies.

Most cancer-related deaths are caused by the metastases, which commonly develop at multiple organ sites including the brain, bone, and lungs. Despite longstanding observations that the spread of cancer is not random, our understanding of the mechanisms that underlie metastatic spread to specific organs remains limited. However, metabolism has recently emerged as an important contributor to metastasis. Amino acids are a significant nutrient source to cancer cells and their metabolism which can serve to fuel biosynthetic pathways capable of facilitating cell survival and tumor expansion while also defending against oxidative stress. Compared to the primary tumor, each of the common metastatic sites exhibit vastly different nutrient compositions and environmental stressors, necessitating the need of cancer cells to metabolically thrive in their new environment during colonization and outgrowth. This review seeks to summarize the current literature on amino acid metabolism pathways that support metastasis to common secondary sites, including impacts on immune responses. Understanding the role of amino acids in secondary organ sites may offer opportunities for therapeutic inhibition of cancer metastasis.

The tumor-associated vasculature imposes major structural and biochemical barriers to the infiltration of effector T cells and effective tumor control. Correlations between stimulator of interferon genes (STING) pathway activation and spontaneous T cell infiltration in human cancers led us to evaluate the effect of STING-activating nanoparticles (STANs), which are a polymersome-based platform for the delivery of a cyclic dinucleotide STING agonist, on the tumor vasculature and attendant effects on T cell infiltration and antitumor function. In multiple mouse tumor models, intravenous administration of STANs promoted vascular normalization, evidenced by improved vascular integrity, reduced tumor hypoxia, and increased endothelial cell expression of T cell adhesion molecules. STAN-mediated vascular reprogramming enhanced the infiltration, proliferation, and function of antitumor T cells and potentiated the response to immune checkpoint inhibitors and adoptive T cell therapy. We present STANs as a multimodal platform that activates and normalizes the tumor microenvironment to enhance T cell infiltration and function and augments responses to immunotherapy.