Laura Raccosta

Tumor-mediated liver X receptor-[alpha] activation inhibits CC chemokine receptor-7 expression on dendritic cells and dampens antitumor responses

Sterol metabolism has recently been linked to innate and adaptive immune responses through liver X receptor (LXR) signaling. Whether products of sterol metabolism interfere with antitumor responses is currently unknown. Dendritic cells (DCs) initiate immune responses, including antitumor activity after their CC chemokine receptor-7 (CCR7)-dependent migration to lymphoid organs. Here we report that human and mouse tumors produce LXR ligands that inhibit CCR7 expression on maturing DCs and, therefore, their migration to lymphoid organs. In agreement with this observation, we detected CD83+CCR7− DCs within human tumors. Mice injected with tumors expressing the LXR ligand–inactivating enzyme sulfotransferase 2B1b (SULT2B1b) successfully controlled tumor growth by regaining DC migration to tumor-draining lymph nodes and by developing overt inflammation within tumors. The control of tumor growth was also observed in chimeric mice transplanted with bone marrow from mice lacking the gene encoding LXR-α (Nr1h3−/− mice) Thus, we show a new mechanism of tumor immunoescape involving products of cholesterol metabolism. The manipulation of this pathway could restore antitumor immunity in individuals with cancer.

The oxysterol–CXCR2 axis plays a key role in the recruitment of tumor-promoting neutrophils

Tumor-derived oxysterols recruit protumor neutrophils in an LXR-independent, CXCR2-dependent manner, thus favoring tumor growth by promoting neoangiogenesis and immunosuppression.

Peripheral blood lymphocytes genetically modified to express the self/tumor antigen MAGE-A3 induce antitumor immune responses in cancer patients

Dendritic cell (DC) targeting in vivo has recently been shown to confer strong and protective cytotoxic T lymphocyte (CTL)-based immunity in tumor murine models. Our group has recently demonstrated in preclinical models that the infusion of genetically modified lymphocytes (GMLs) expressing the self/tumor antigen TRP-2 is able to elicit functional TRP-2-specific effectors with antitumor activity by targeting DCs in vivo. Here we have analyzed vaccine- and tumor-specific immune responses of 10 melanoma patients treated with autologous GMLs expressing the cancer germline gene MAGE-A3. Three of 10 patients treated with MAGE-A3-GML showed an increase of circulating anti-MAGE-A3 T cells, and developed skin delayed-type hypersensitivity to MAGE-A3. Interestingly, in 2 of these patients, with progressive and measurable tumors at study entry, anti-MAGE-A3 T cells were detected not only in the blood but also within tumors resected after vaccination. These results demonstrate that the infusion of MAGE-A3-GML elicits antitumor T cells, which are capable of trafficking to inflamed tissues and of infiltrating tumors. Clinical studies on a larger group of patients are needed to evaluate the clinical efficacy of such a strategy.

Selected natural and synthetic retinoids impair CCR7- and CXCR4-dependent cell migration in vitro and in vivo

Dendritic cell (DC) migration to secondary lymphoid organs is a crucial step to initiate adaptive immune responses. This step requires the expression of a functional CCR7 chemokine receptor on DC undergoing maturation. Here, we show that the natural retinoid 9‐cis retinoic acid (9cRA) and the synthetic retinoid fenretinide (4‐HPR) specifically inhibit the functional up‐regulation of CCR7 on maturing human DCs, without affecting early steps of DC maturation. As a consequence, mature DCs do not migrate in vitro toward the chemokine CCL19. Importantly, 4‐HPR and 9cRA by inhibiting the expression of CCR7 on bone marrow‐derived murine DCs dampen their in vivo migration to draining lymph nodes. 4‐HPR also inhibits the expression of the chemokine receptors CXCR4, therefore, impairing in vitro migration of human DCs to CXCL12 and inhibiting in vivo the CXCR4‐dependent migration of the posterior lateral line primordium (PLLp) in zebrafish embryos. Taken together, these data highlight a novel function of retinoids and suggest the possibility of using retinoids to treat inflammatory or autoimmune diseases.

Lymphocytes genetically modified to express tumor antigens target DCs in vivo and induce antitumor immunity

The exploitation of the physiologic processing and presenting machinery of DCs by in vivo loading of tumor-associated antigens may improve the immunogenic potential and clinical efficacy of DC-based cancer vaccines. Here we show that lymphocytes genetically modified to express self/tumor antigens, acting as antigen carriers, efficiently target DCs in vivo in tumor-bearing mice. The infusion of tyrosinase-related protein 2-transduced (TRP-2-transduced) lymphocytes induced the establishment of protective immunity and long-term memory in tumor-bearing mice. Analysis of the mechanism responsible for the induction of such an immune response allowed us to demonstrate that cross-presentation of the antigen mediated by the CD11c(+)CD8alpha(+) DC subset had occurred. Furthermore, we demonstrated in vivo and in vitro that DCs had undergone activation upon phagocytosis of genetically modified lymphocytes, a process mediated by a cell-to-cell contact mechanism independent of CD40 triggering. Targeting and activation of secondary lymphoid organ-resident DCs endowed antigen-specific T cells with full effector functions, which ultimately increased tumor growth control and animal survival in a therapeutic tumor setting. We conclude that the use of transduced lymphocytes represents an efficient method for the in vivo loading of tumor-associated antigens on DCs.

Cholesterol metabolites and tumor microenvironment: the road towards clinical translation

Abstract Targeting the tumor microenvironment focusing on immune cells has recently become a standard of care for some tumors. Indeed, antibodies blocking immune checkpoints (e.g., anti-CTLA-4 and anti-PD1 mAbs) have been approved by regulatory agencies for the treatment of some solid tumors based upon successes in many clinical trials. Although tumor metabolism has always attracted the attention of tumor biologists, only recently have oncologists renewed their interest in this field of tumor biology research. This has highlighted the possibility to pharmacologically target rate-limiting enzymes along key metabolic pathways of tumor cells, such as lipogenesis and aerobic glycolysis. Altered tumor metabolism has also been shown to influence the functionality of the tumor microenvironment as a whole, particularly the immune cell component of thereof. Cholesterol, oxysterols and Liver X receptors (LXRs) have been investigated in different tumor models. Recent in vitro and in vivo results point to their involvement in tumor and immune cell biology, thus making the LXR/oxysterol axis a possible target for novel antitumor strategies. Indeed, the possibility to target both tumor cell metabolism (i.e., cholesterol metabolism) and tumor-infiltrating immune cell dysfunctions induced by oxysterols might result in a synergistic antitumor effect generating long-lasting memory responses. This review will focus on the role of cholesterol metabolism with particular emphasis on the role of the LXR/oxysterol axis in the tumor microenvironment, discussing mechanisms of action, pros and cons, and strategies to develop antitumor therapies based on the modulation of this axis.

24-hydroxycholesterol participates in pancreatic neuroendocrine tumor development

Significance Oxysterols promote tumor growth directly or through the dampening of tumor-infiltrating immune cells. Whether oxysterols contribute to pancreatic neuroendocrine tumor (pNET) development and how they are generated within the pNET microenvironment are currently unknown. Here, we show that the 24S-hydroxycholesterol (24S-HC) oxysterol-generating enzyme Cyp46a1 is overexpressed during the angiogenic switch in rat insulin promoter 1–T-antigen 2 (RIP1-Tag2) pNET formation. Moreover, we report that Cyp46a1 overexpression requires hypoxia inducible factor-1a (HIF-1α). Importantly, we show that pharmacologic blockade and genetic inactivation of 24S-HC delays angiogenic switch and therefore tumor formation in RIP1-Tag2. Overexpression of Cyp46a1 transcripts in some human pNET samples suggests that targeting this axis in patients affected by pancreatic neuroendocrine tumors may be an effective therapeutic strategy. Cells in the tumor microenvironment may be reprogrammed by tumor-derived metabolites. Cholesterol-oxidized products, namely oxysterols, have been shown to favor tumor growth directly by promoting tumor cell growth and indirectly by dampening antitumor immune responses. However, the cellular and molecular mechanisms governing oxysterol generation within tumor microenvironments remain elusive. We recently showed that tumor-derived oxysterols recruit neutrophils endowed with protumoral activities, such as neoangiogenesis. Here, we show that hypoxia inducible factor-1a (HIF-1α) controls the overexpression of the enzyme Cyp46a1, which generates the oxysterol 24-hydroxycholesterol (24S-HC) in a pancreatic neuroendocrine tumor (pNET) model commonly used to study neoangiogenesis. The activation of the HIF-1α–24S-HC axis ultimately leads to the induction of the angiogenic switch through the positioning of proangiogenic neutrophils in proximity to Cyp46a1+ islets. Pharmacologic blockade or genetic inactivation of oxysterols controls pNET tumorigenesis by dampening the 24S-HC–neutrophil axis. Finally, we show that in some human pNET samples Cyp46a1 transcripts are overexpressed, which correlate with the HIF-1α target VEGF and with tumor diameter. This study reveals a layer in the angiogenic switch of pNETs and identifies a therapeutic target for pNET patients.

The administration of drugs inhibiting cholesterol/oxysterol synthesis is safe and increases the efficacy of immunotherapeutic regimens in tumor-bearing mice.

Tumor-derived metabolites dampen tumor-infiltrating immune cells and antitumor immune responses. Among the various metabolites produced by tumors, we recently showed that cholesterol oxidized products, namely oxysterols, favor tumor growth through the inhibition of DC migration toward lymphoid organs and by promoting the recruitment of pro-tumor neutrophils within the tumor microenvironment. Here, we tested different drugs capable of blocking cholesterol/oxysterol formation. In particular, we tested efficacy and safety of different administration schedules, and of immunotherapy-based combination of a class of compounds, namely zaragozic acids, which inhibit cholesterol pathway downstream of mevalonate formation, thus leaving intact the formation of the isoprenoids, which are required for the maturation of proteins involved in the immune cell function. We show that zaragozic acids inhibit the in vivo growth of the RMA lymphoma and the Lewis lung carcinoma (LLC) without inducing side effects. Tumor growth inhibition requires an intact immune system, as immunodeficient tumor-bearing mice do not respond to zaragozic acid treatment. Of note, the effect of zaragozic acids is accompanied by a marked reduction in the LXR target genes Abcg1, Mertk, Scd1 and Srebp-1c in the tumor microenvironment. On the other hand, zoledronate, which blocks also isoprenoid formation, did not control the LLC tumor growth. Finally, we show that zaragozic acids potentiate the antitumor effects of active and adoptive immunotherapy, significantly prolonging the overall survival of tumor-bearing mice treated with the combo zaragozic acids and TAA-loaded DCs. This study identifies zaragozic acids as new antitumor compounds exploitable for the treatment of cancer patients.

Oxysterols recruit tumor-supporting neutrophils within the tumor microenvironment: The many facets of tumor-derived oxysterols.

By binding to the liver X receptor (LXR), oxysterols inhibit the expression of chemokine (C-C motif) receptor 7 (CCR7), hence impairing the migration of dendritic cells to secondary lymphoid organs and inhibiting antitumor immune responses. We have recently identified a new tumor-supporting activity of oxysterols, which recruit neutrophils within tumor microenvironment by a chemokine (C-X-C motif) receptor 2 (CXCR2)-dependent, LXR-independent mechanism.

Enzymatic Inactivation Of Oxysterols In Breast Tumor Cells Constraints Metastasis Formation By Reprogramming The Metastatic Lung Microenvironment

Recent evidence indicates that immune cells contribute to the formation of tumor metastases by regulating the pre-metastatic niche. Whether tumor-derived factors involved in primary tumor formation play a role in metastasis formation is poorly characterized. Oxysterols act as endogenous regulators of lipid metabolism through the interaction with the nuclear Liver X Receptors-(LXR)α and LXRβ. In the context of tumor development, they establish a pro-tumor environment by dampening antitumor immune responses, and by recruiting pro-angiogenic and immunosuppressive neutrophils. However, the ability of LXR/oxysterol axis to promote tumor invasion and metastasis by exploiting immune cells, is still up to debate. In this study we provide evidence that oxysterols participate in the primary growth of orthotopically implanted 4T1 breast tumors by establishing a tumor-promoting microenvironment. Furthermore, we show that oxysterols are involved in the metastatic spread of 4T1 breast tumors, since their enzymatic inactivation mediated by the sulfotransferase 2B1b, reduces the number of metastatic cells in the lungs of tumor-bearing mice. Finally, we provide evidence that oxysterols support the metastatic cascade by modifying the lung metastatic niche, particularly allowing the recruitment of tumor-promoting neutrophils. These results identify a possible new metastatic pathway to target in order to prevent metastasis formation in breast cancer patients.