Tumor-Derived Prostaglandin E2 Promotes p50 NF-κB-Dependent Differentiation of Monocytic MDSCs

Myeloid-derived suppressor cells (MDSC) include immature monocytic (M-MDSC) and granulocytic (PMN-MDSC) cells that share the ability to suppress adaptive immunity and to hinder the effectiveness of anticancer treatments. Of note, in response to IFNγ, M-MDSCs release the tumor-promoting and immunosuppressive molecule nitric oxide (NO), whereas macrophages largely express antitumor properties. Investigating these opposing activities, we found that tumor-derived prostaglandin E2 (PGE2) induces nuclear accumulation of p50 NF-κB in M-MDSCs, diverting their response to IFNγ toward NO-mediated immunosuppression and reducing TNFα expression. At the genome level, p50 NF-κB promoted binding of STAT1 to regulatory regions of selected IFNγ-dependent genes, including inducible nitric oxide synthase (Nos2). In agreement, ablation of p50 as well as pharmacologic inhibition of either the PGE2 receptor EP2 or NO production reprogrammed M-MDSCs toward a NOS2^low/TNFα^high phenotype, restoring the in vivo antitumor activity of IFNγ. Our results indicate that inhibition of the PGE2/p50/NO axis prevents MDSC-suppressive functions and restores the efficacy of anticancer immunotherapy. SIGNIFICANCE: Tumor-derived PGE2-mediated induction of nuclear p50 NF-κB epigenetically reprograms the response of monocytic cells to IFNγ toward an immunosuppressive phenotype, thus retrieving the anticancer properties of IFNγ. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/13/2874/F1.large.jpg.

Nicotinamide Phosphoribosyltransferase Acts as a Metabolic Gate for Mobilization of Myeloid-Derived Suppressor Cells

Cancer induces alteration of hematopoiesis to fuel disease progression. We report that in tumor-bearing mice the macrophage colony-stimulating factor elevates the myeloid cell levels of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD salvage pathway, which acts as negative regulator of the CXCR4 retention axis of hematopoietic cells in the bone marrow. NAMPT inhibits CXCR4 through a NAD/Sirtuin 1-mediated inactivation of HIF1α-driven CXCR4 gene transcription, leading to mobilization of immature myeloid-derived suppressor cells (MDSC) and enhancing their production of suppressive nitric oxide. Pharmacologic inhibition or myeloid-specific ablation of NAMPT prevented MDSC mobilization, reactivated specific antitumor immunity, and enhanced the antitumor activity of immune checkpoint inhibitors. Our findings identify NAMPT as a metabolic gate of MDSC precursor function, providing new opportunities to reverse tumor immunosuppression and to restore clinical efficacy of immunotherapy in patients with cancer. SIGNIFICANCE: These findings identify NAMPT as a metabolic gate of MDSC precursor function, providing new opportunities to reverse tumor immunosuppression and to restore clinical efficacy of immunotherapy in cancer patients.

RORC1 Regulates Tumor-Promoting "Emergency" Granulo-Monocytopoiesis

Cancer-driven granulo-monocytopoiesis stimulates expansion of tumor promoting myeloid populations, mostly myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). We identified subsets of MDSCs and TAMs based on the expression of retinoic-acid-related orphan receptor (RORC1/RORγ) in human and mouse tumor bearers. RORC1 orchestrates myelopoiesis by suppressing negative (Socs3 and Bcl3) and promoting positive (C/EBPβ) regulators of granulopoiesis, as well as the key transcriptional mediators of myeloid progenitor commitment and differentiation to the monocytic/macrophage lineage (IRF8 and PU.1). RORC1 supported tumor-promoting innate immunity by protecting MDSCs from apoptosis, mediating TAM differentiation and M2 polarization, and limiting tumor infiltration by mature neutrophils. Accordingly, ablation of RORC1 in the hematopoietic compartment prevented cancer-driven myelopoiesis, resulting in inhibition of tumor growth and metastasis.

Abstract 393: Nicotinamide phosphoribosyl transferase (NAMPT) inhibitors: novel modulators of antitumor immunity

Nicotinamide phosphoribosyltransferase (NAMPT), an essential enzyme involved in NAD metabolism, is a pleiotropic player in cell signalling and is implicated in a number of diseases, including cancer, inflammatory and metabolic disorders. NAMPT inhibitors (e.g. FK866 and CHS828) have been shown to be potentially effective in cancer therapy and have entered clinical trials in oncology. NAMPT could represent a putative link between metabolism, inflammation and cancer. This study investigated the role of NAMPT in cancer-related inflammation.

A mouse model of transplantable MNMCA1 fibrosarcoma was utilized. WT Mice or NAMPTflox CrelysM+/- mice were injected with 10^4 MN-MNCA1 or G217R MNMCA1 (NAMPT inhibitors resistant cell line) cells and subsequently treated or not with 10 mg/kg of NAMPT inhibitors. Next, tumor growth, metastasis formation, tumor angiogenesis and the inflammatory infiltrate were estimated. In addition, monocytic (M-MDSCs) and granulocytic (G-MDSCs) myeloid derived-suppressor cells (MDSCs), isolated from the spleen of tumour bearing mice (untreated and treated with NAMPT inhibitors), or differentiated in vitro from bone marrow precursors, were analysed for their suppressive activity, nitric oxide (NO) production, gene profile and expression of enzymes involved in cancer-associated immunosuppression (e.g. iNOS, ARG1, NOX2).

In the fibrosarcoma mouse model, NAMPT inhibitors inhibited tumor growth, tumor vessel formation and delay metastasis formation. Phenotypic analysis of the immune infiltrate revealed that the number of macrophages and dendritic cells was not affected by NAMPT inhibition. However MDSCs displayed a marked decreased in blood, spleen and primary tumour, which was associated with an increase number of both CD4+ and CD8+ T lymphocytes. On the contrary an increase number of MDSCs have been found in the bone marrow. A detail analysis of CXCR4 expression revealed that NAMPT inhibitors affect MDSCs migration in vivo. Moreover, in NAMPTflox CrelysM+/- mice fibrosarcoma growth is reduced.

Expression analysis revealed that NAMPT was up-regulated in MDSCs in response to M1-stimulation, suggesting a role of this enzyme during inflammatory process. Moreover, NAMPT inhibitors blocked the NO-mediated T cell suppressive activity induced by IFNγ in M-MDSC. Preliminary evidences indicate a role of both AMPK and SIRT 1/3 in the inhibition of M-MDSC suppressive activity operated by NAMPT inhibitors. Furthermore, both M-MDSCs isolated from spleen of NAMPT inhibitors treated mice and MDSCs isolated from NAMPTflox CrelysM+/- mice display a reduced T-cell suppression activity.

Here, we demonstrate for the first time a role of NAMPT metabolism in the functional differentiation of suppressive M-MDSCs associated with cancer development and suggest that pharmacological inhibition of NAMPT may prevent cancer-associated immunosuppression, restoring adaptive antitumor immunity.

Citation Format: Cristina Travelli, Sara Morlacchi, Ubaldina Galli, Gian Cesare Tron, Armando A Genazzani, Antonio Sica. Nicotinamide phosphoribosyl transferase (NAMPT) inhibitors: novel modulators of antitumor immunity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 393. doi:10.1158/1538-7445.AM2015-393

Abstract 1871: Targeting nicotinamide phosphoribosyltransferase (NAMPT) in cancer therapy

Nicotinamide adenine dinucleotide (NAD) metabolism has been emerged as a new target pathway in developing new cancer therapies. NAD has principal two functions in cells: (i) cofactor in redox reactions and (ii) substrate of several classes of NAD-dependent enzymes (i.e. PARPs, sirtuins). When NAD is a redox carrier, its not consumed by cells, however NAD-utilizing enzymes degrade NAD, inducing a decrease of the intracellular NAD pool. Therefore, to re-establish NAD levels in cells, the so called “NAD salvage pathway” exists. In this pathway, nicotinamide phosphoribosyltransferase (NAMPT) plays a crucial role; this enzyme is able to convert nicotinamide (Nam), released by NAD-dependent enzymes, into nicotinamide mononucleotide (NMN), which is finally converted to NAD by NMNAT.

Different expression and activity of NAMPT have been correlated with a number of pathologies, and cancer is not an exception. For example, NAMPT has been found up-regulated in several types of cancer.

To date, two potent NAMPT inhibitors (FK866 and CHS828) have been discovered and are now in phase I and II of trials in different types of solid and non-solid cancers. However, the results of the trials are still unpublished. Moreover, NAMPT has been also described as a cytokine, also called visfatin, released by adipocytes and several types of activated immune cells. However the function of visfatin and the possible release of this cytokine by cancer cells are still unknown.

We have investigated (i) the action of NAMPT inhibitors in two different types of cancer (neuroblastoma and melanoma) that differ in NAMPT expression and (ii) the contribution of extracellular form of NAMPT (visfatin) in tumour.

We found a positive correlation between NAMPT expression and responsiveness to NAMPT inhibitors. In particular neuroblastoma cells, which express normal levels of NAMPT, are sensitive to FK866, contrary melanoma cells, which over-expressed NAMPT are refractory to FK866 treatment. Therefore, these data may suggest that in melanoma cells NAMPT may have not only an enzymatic activity but may have another function. We found that these cells are able to release NAMPT in a time-dependent manner, suggesting that NAMPT could act also as a cytokine in melanoma cell culture. Since cytokines are involved in inflammation, and that inflammation is a critical component of tumour progression, we decided to investigate the possible role of NAMPT and visfatin in tumour-related inflammation. Our preliminary results show that NAMPT altered the activity of myeloid-derived suppressor cells (MDSC), a heterogeneous population of early myeloid progenitors that facilitate tumour progression. Our results could be a starting point for future direction in targeting NAMPT to interfere with tumour-related inflammation.

Citation Format: Cristina Travelli, Sara Morlacchi, Antonio Caldarelli, Antonio Sica, Armando A. Genazzani. Targeting nicotinamide phosphoribosyltransferase (NAMPT) in cancer therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1871. doi:10.1158/1538-7445.AM2013-1871

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Hypoxia-mediated regulation of macrophage functions in pathophysiology

Oxygen availability affects cell differentiation, survival and function, with profound consequences on tissue homeostasis, inflammation and immunity. A gradient of oxygen levels is present in most organs of the body as well as in virtually every site of inflammation, damaged or pathological tissue. As a consequence, infiltrating leukocytes, macrophages in particular, are equipped with the capacity to shift their metabolism to anaerobic glycolysis, to generate ATP and induce the expression of factors that increase the supply of oxygen and nutrients. Strikingly, low oxygen conditions (hypoxia) and inflammatory signals share selected transcriptional events, including the activation of members of both the hypoxia-inducible factor and nuclear factor κB families, which may converge to activate specific cell programs. In the pathological response to hypoxia, cancer in particular, macrophages act as orchestrators of disease evolution and their number can be used as a prognostic marker. Here we review mechanisms of macrophage adaptation to hypoxia, their role in disease as well as new perspectives for their therapeutic targeting.

Origin and Functions of Tumor-Associated Myeloid Cells (TAMCs)

The construction of an inflammatory microenvironment provides the fuel for cancer development and progression. Hence, solid tumors promote the expansion and the recruitment of leukocyte populations, among which tumor-associated myeloid cells (TAMCs) represent a paradigm for cancer-promoting inflammation. TAMCs group heterogeneous phagocytic populations stemming from a common myeloid progenitor (CMP), that orchestrate various aspects of cancer, including: diversion and skewing of adaptive responses; immunosuppression; cell growth; angiogenesis; matrix deposition and remodelling; construction of a metastatic niche and actual metastasis. Several evidence indicate that TAMCs show plasticity and/or functional heterogeneity, suggesting that tumour-derived factors promote their functional "reprogramming" towards protumoral activities. While recent studies have attempted to address the role of microenvironment signals, the interplay between cancer cells, innate and adaptive immunity is now emerging as a crucial step of the TAMCs reprogramming. Here we discuss the evidence for the differentiation of TAMCs during the course of tumor progression and the molecular mechanisms that regulate such event.

Syntaxin 4 is required for acid sphingomyelinase activity and apoptotic function

Acid sphingomyelinase (A-SMase) is an important enzyme in sphingolipid metabolism and plays key roles in apoptosis, immunity, development, and cancer. In addition, it mediates cytotoxicity of cisplatin and some other chemotherapeutic drugs. The mechanism of A-SMase activation is still undefined. We now demonstrate that, upon CD95 stimulation, A-SMase is activated through translocation from intracellular compartments to the plasma membrane in an exocytic pathway requiring the t-SNARE protein syntaxin 4. Indeed, down-regulation of syntaxin 4 inhibits A-SMase translocation and activation induced by CD95 stimulation. This leads to inhibition of the CD95-triggered signaling events, including caspase 3 and 9 activation and apoptosis, activation of the survival pathway involving the protein kinase Akt, and important changes in cell cycle and proliferation. The molecular interaction between A-SMase and syntaxin 4 was not known and clarifies the mechanism of A-SMase activation. The novel actions of syntaxin 4 in sphingolipid metabolism and exocytosis we describe here define signaling mechanisms of broad relevance in cell pathophysiology.