Lipid-loaded macrophages as new therapeutic target in cancer.

Macrophages are main players of the innate immune system. They show great heterogeneity and play diverse functions that include support to development, sustenance of tissue homeostasis and defense against infections. Dysfunctional macrophages have been described in multiple pathologies including cancer. Indeed tumor-associated macrophages (TAMs) are abundant in most tumors and sustain cancer growth, promote invasion and mediate immune evasion. Importantly, lipid metabolism influences macrophage activation and lipid accumulation confers pathogenic features on macrophages. Notably, a subset of lipid-loaded macrophages has been recently identified in many tumor types. Lipid-loaded TAMs support tumor growth and progression and exert immune-suppressive activities. In this review, we describe the role of lipid metabolism in macrophage activation in physiology and pathology and we discuss the impact of lipid accumulation in macrophages in the context of cancer.

Lipid-loaded tumor-associated macrophages sustain tumor growth and invasiveness in prostate cancer.

Tumor-associated macrophages (TAMs) are correlated with the progression of prostatic adenocarcinoma (PCa). The mechanistic basis of this correlation and therapeutic strategies to target TAMs in PCa remain poorly defined. Here, single-cell RNA sequencing was used to profile the transcriptional landscape of TAMs in human PCa, leading to identification of a subset of macrophages characterized by dysregulation in transcriptional pathways associated with lipid metabolism. This subset of TAMs correlates positively with PCa progression and shorter disease-free survival and is characterized by an accumulation of lipids that is dependent on Marco. Mechanistically, cancer cell-derived IL-1ß enhances Marco expression on macrophages, and reciprocally, cancer cell migration is promoted by CCL6 released by lipid-loaded TAMs. Moreover, administration of a high-fat diet to tumor-bearing mice raises the abundance of lipid-loaded TAMs. Finally, targeting lipid accumulation by Marco blockade hinders tumor growth and invasiveness and improves the efficacy of chemotherapy in models of PCa, pointing to combinatorial strategies that may influence patient outcomes.

A systemically deliverable Vaccinia virus with increased capacity for intertumoral and intratumoral spread effectively treats pancreatic cancer.

BACKGROUND: Pancreatic cancer remains one of the most lethal cancers and is refractory to immunotherapeutic interventions. Oncolytic viruses are a promising new treatment option, but current platforms demonstrate limited efficacy, especially for inaccessible and metastatic cancers that require systemically deliverable therapies. We recently described an oncolytic vaccinia virus (VV), VVLΔTKΔN1L, which has potent antitumor activity, and a regime to enhance intravenous delivery of VV by pharmacological inhibition of pharmacological inhibition of PI3 Kinase δ (PI3Kδ) to prevent virus uptake by macrophages. While these platforms improve the clinical prospects of VV, antitumor efficacy must be improved. METHODS: VVLΔTKΔN1L was modified to improve viral spread within and between tumors via viral B5R protein modification, which enhanced production of the extracellular enveloped virus form of VV. Antitumor immunity evoked by viral treatment was improved by arming the virus with interleukin-21, creating VVL-21. Efficacy, functional activity and synergy with α-programmed cell death protein 1 (α-PD1) were assessed after systemic delivery to murine and Syrian hamster models of pancreatic cancer. RESULTS: VVL-21 could reach tumors after systemic delivery and demonstrated antitumor efficacy in subcutaneous, orthotopic and disseminated models of pancreatic cancer. The incorporation of modified B5R improved intratumoural accumulation of VV. VVL-21 treatment increased the numbers of effector CD8+ T cells within the tumor, increased circulating natural killer cells and was able to polarize macrophages to an M1 phenotype in vivo and in vitro. Importantly, treatment with VVL-21 sensitized tumors to the immune checkpoint inhibitor α-PD1. CONCLUSIONS: Intravenously administered VVL-21 successfully remodeled the suppressive tumor-microenvironment to promote antitumor immune responses and improve long-term survival in animal models of pancreatic cancer. Importantly, treatment with VVL-21 sensitized tumors to the immune checkpoint inhibitor α-PD1. Combination of PI3Kδ inhibition, VVL-21 and α-PD1 creates an effective platform for treatment of pancreatic cancer.

Transient Inhibition of PI3Kδ Enhances the Therapeutic Effect of Intravenous Delivery of Oncolytic Vaccinia Virus.

Tumor-targeting oncolytic viruses such as vaccinia virus (VV) are attractive cancer therapeutic agents that act through multiple mechanisms to provoke both tumor lysis and anti-tumor immune responses. However, delivery of these agents remains restricted to intra-tumoral administration, which prevents effective targeting of inaccessible and disseminated tumor cells. In the present study we have identified transient pharmacological inhibition of the leukocyte-enriched phosphoinositide 3-kinase δ (PI3Kδ) as a novel mechanism to potentiate intravenous delivery of oncolytic VV to tumors. Pre-treatment of immunocompetent mice with the PI3Kδ-selective inhibitor IC87114 or the clinically approved idelalisib (CAL-101), prior to intravenous delivery of a tumor-tropic VV, dramatically improved viral delivery to tumors. This occurred via an inhibition of viral attachment to, but not internalization by, systemic macrophages through perturbation of signaling pathways involving RhoA/ROCK, AKT, and Rac. Pre-treatment using PI3Kδ-selective inhibitors prior to intravenous delivery of VV resulted in enhanced anti-tumor efficacy and significantly prolonged survival compared to delivery without PI3Kδ inhibition. These results indicate that effective intravenous delivery of oncolytic VV may be clinically achievable and could be useful in improving anti-tumor efficacy of oncolytic virotherapy.

The Good and the Bad Side of Heme-Oxygenase-1 in the Gut.

Significance: Mucosal immunity in the gut has the important task of protecting an organism against potential danger, but at the same time of staying silent in response to harmless antigens present in the intestinal lumen. The delicate balance between immune activation and tolerance is referred to as gut homeostasis. Recent Advances: It has become clear that different types of immune cells and several factors participate in the maintenance of gut homeostasis, having as a final goal the prevention of non-necessary inflammation. Immune cells of the myeloid lineage, such as macrophages located in the lamina propria, represent the most abundant leukocyte population in the intestine and play a critical role in keeping the immune system silent, via the production of the anti-inflammatory cytokine interleukin-10. Critical Issues: Gut macrophages are an important source of the oxidative enzyme heme-oxygenase-1 (HO-1), which has crucial immune-modulatory properties. The protective role of HO-1 in the control of the intestinal inflammation, and its connection with the enteric flora have been demonstrated in experimental settings as well as in human biological samples. Future Directions: Loss of the gut homeostasis gives rise to conditions of acute inflammation that may degenerate into chronic disease, eventually leading to carcinogenesis. Understanding the mechanisms that regulate this enzyme will disclose novel therapeutic approaches that are designed to control chronic inflammation in the intestine.

Optical in vivo imaging detection of preclinical models of gut tumors through the expression of integrin αVß3.

Optical imaging and Fluorescent Molecular Tomography (FMT) are becoming increasingly important for the study of different preclinical models of cancer, providing a non-invasive method for the evaluation of tumor progression in a relatively simple and fast way. Intestinal tumors, in particular colorectal cancer (CRC), represent a major cause of cancer-related death in Western countries: despite the presence of a number of preclinical models of intestinal carcinogenesis, there is a paucity of information about the possibility to detect intestinal tumors using fluorescent probes and optical in vivo imaging. Herein, we identify the detection of integrin αvß3 by FMT and optical imaging as an effective approach to assess the occurrence and progression of intestinal carcinogenesis in genetic and chemically-induced mouse models. For this purpose, a commercially available probe (IntegriSense), recognizing integrin αvß3, was injected in APC+/min mice bearing small intestinal adenomas or CRC: FMT analysis allowed a specific tumor detection, further confirmed by subsequent ex vivo imaging or conventional histology. In addition, IntegriSense detection by FMT allowed the longitudinal monitoring of tumor growth. Taken together, our data indicate the possibility to use integrin αvß3 for the visualization of intestinal tumors in preclinical models.

Oncolytic Viral Therapy and the Immune System: A Double-Edged Sword Against Cancer.

Oncolytic viral therapy is a new promising strategy against cancer. Oncolytic viruses (OVs) can replicate in cancer cells but not in normal cells, leading to lysis of the tumor mass. Beside this primary effect, OVs can also stimulate the immune system. Tumors are an immuno-suppressive environment in which the immune system is silenced in order to avoid the immune response against cancer cells. The delivery of OVs into the tumor wakes up the immune system so that it can facilitate a strong and durable response against the tumor itself. Both innate and adaptive immune responses contribute to this process, producing an immune response against tumor antigens and facilitating immunological memory. However, viruses are recognized by the immune system as pathogens and the consequent anti-viral response could represent a big hurdle for OVs. Finding a balance between anti-tumor and anti-viral immunity is, under this new light, a priority for researchers. In this review, we provide an overview of the various ways in which different components of the immune system can be allied with OVs. We have analyzed the different immune responses in order to highlight the new and promising perspectives leading to increased anti-tumor response and decreased immune reaction to the OVs.

Oncolytic Viruses-Interaction of Virus and Tumor Cells in the Battle to Eliminate Cancer.

Oncolytic viruses (OVs) are an emerging treatment option for many cancer types and have recently been the focus of extensive research aiming to develop their therapeutic potential. The ultimate aim is to design a virus which can effectively replicate within the host, specifically target and lyse tumor cells and induce robust, long lasting tumor-specific immunity. There are a number of viruses which are either naturally tumor-selective or can be modified to specifically target and eliminate tumor cells. This means they are able to infect only tumor cells and healthy tissue remains unharmed. This specificity is imperative in order to reduce the side effects of oncolytic virotherapy. These viruses can also be modified by various methods including insertion and deletion of specific genes with the aim of improving their efficacy and safety profiles. In this review, we have provided an overview of the various virus species currently being investigated for their oncolytic potential and the positive and negative effects of a multitude of modifications used to increase their infectivity, anti-tumor immunity, and treatment safety, in particular focusing on the interaction of tumor cells and OVs.

Heme-oxygenase-1 Production by Intestinal CX3CR1+ Macrophages Helps to Resolve Inflammation and Prevents Carcinogenesis.

CX3CR1+ macrophages in the intestinal lamina propria contribute to gut homeostasis through the immunomodulatory interleukin IL10, but there is little knowledge on how these cells or the CX3CR1 receptor may affect colorectal carcinogenesis. In this study, we show that CX3CR1-deficient mice fail to resolve gut inflammation despite high production of IL10 and have increased colitis and adenomatous polyps in chemical and genetic models of colon carcinogenesis. Mechanistically, CX3CL1-mediated engagement of the CX3CR1 receptor induced upregulation of heme-oxygenase-1 (HMOX-1), an antioxidant and anti-inflammatory enzyme. CX3CR1-deficient mice exhibited significantly lower expression of HMOX-1 in their adenomatous colon tissues. Combining LPS and CX3CL1 displayed a strong synergistic effect in vitro, but HMOX-1 levels were significantly lower in KO macrophages. Cohousing of wild-type and CX3CR1-/- mice during the AOM/DSS treatment attenuated disease severity in CX3CR1-/- mice, indicating the importance of the microbiome, but did not fully reinstate HMOX-1 levels and did not abolish polyp formation. In contrast, pharmacologic induction of HMOX-1 in vivo by cobalt protoporphyrin-IX treatment eradicated intestinal inflammation and fully protected KO mice from carcinogenesis. Taken together, our results establish an essential role for the receptor CX3CR1 in gut macrophages in resolving inflammation in the intestine, where it helps protects against colitis-associated cancer by regulating HMOX-1 expression. Cancer Res; 77(16); 4472-85. ©2017 AACR.

Inflammation as target in cancer therapy.

Cells of the innate immunity infiltrating tumour tissues promote, rather than halt, cancer cell proliferation and distant spreading. Tumour-Associated Macrophages (TAMs) are abundantly present in the tumour milieu and here trigger and perpetrate a state of chronic inflammation which ultimately supports disease development and contributes to an immune-suppressive environment. Therapeutic strategies to limit inflammatory cells and their products have been successful in pre-clinical tumour models. Early clinical trials with specific cytokine and chemokine inhibitors, or with strategies designed to target TAMs, are on their way in different solid malignancies. Partial clinical responses and stabilization of diseases were observed in some patients, in the absence of significant toxicity. These encouraging results open new perspectives of combination treatments aimed at reducing cancer-promoting inflammation to maximize the anti-tumour efficacy.

The Fractalkine-Receptor Axis Improves Human Colorectal Cancer Prognosis by Limiting Tumor Metastatic Dissemination.

Human colorectal cancer (CRC) is a frequent neoplasia in Western countries, and its metastatic progression is a major cause of cancer-related death. In search of specific molecules upregulated in CRC, with possible clinical relevance, we performed a differential gene-profiling analysis in surgery-derived CRC samples and adjacent uninvolved intestinal mucosa. The chemokine CX3CL1 and its specific receptor CX3CR1 were significantly upregulated in tumors. Higher expression of CX3CL1 and CX3CR1 was confirmed by immunohistochemistry in 100 CRC tumor samples (stages I-III). Unexpectedly, high immune scores of CX3CL1 did not correlate with the density of tumor-infiltrating CD3(+) T cells or CD68(+) macrophages. Coexpression of ligand and receptor by tumor cells (axis-positive tumors) significantly associated with longer disease-free (p = 0.01) and disease-specific survival (p = 0.001). Conversely, axis-negative tumors (with low expression of both ligand and receptor) had increased risk of tumor relapse (p = 0.02), and increased likelihood of metachronous metastasis (p = 0.001), including after stage adjustment (p = 0.006). Transduction of CX3CL1 and CX3CR1 in CRC tumor cell lines induced cell aggregation that strongly inhibited in vitro migration in chemotaxis assays. In a mouse model of spleen-liver metastases, cancer dissemination to liver was dramatically reduced in CX3CL1-CX3CR1-expressing tumors, and ligand-receptor interaction was confirmed in cancer cells in vivo by fluorescence resonance energy transfer analysis. In conclusion, tumoral expression of the CX3CL1-CX3CR1 chemokine axis functions as a retention factor, increasing homotypic cell adhesion and limiting tumor spreading to metastatic sites. Lack or low levels of expression of CX3CL1-CX3CR1 by tumor cells identifies a group of CRC patients at increased risk of metastatic progression.