S100A8/S100A9 Promote Progression of Multiple Myeloma via Expansion of Megakaryocytes

Multiple myeloma is characterized by clonal proliferation of plasma cells that accumulate preferentially in the bone marrow (BM). The tumor microenvironment is one of the leading factors that promote tumor progression. Neutrophils and monocytes are a major part of the BM tumor microenvironment, but the mechanism of their contribution to multiple myeloma progression remains unclear. Here, we describe a novel mechanism by which S100A8/S100A9 proteins produced by BM neutrophils and monocytes promote the expansion of megakaryocytes supporting multiple myeloma progression. S100A8/S100A9 alone was not sufficient to drive megakaryopoiesis but markedly enhanced the effect of thrombopoietin, an effect that was mediated by Toll-like receptor 4 and activation of the STAT5 transcription factor. Targeting S100A9 with tasquinimod as a single agent and in combination with lenalidomide and with proteasome inhibitors has potent antimyeloma effect that is at least partly independent of the adaptive immune system. This newly identified axis of signaling involving myeloid cells and megakaryocytes may provide a new avenue for therapeutic targeting in multiple myeloma.

Significance

We identified a novel mechanism by which myeloid cells promote myeloma progression independently of the adaptive immune system. Specifically, we discovered a novel role of S100A8/S100A9, the most abundant proteins produced by neutrophils and monocytes, in regulation of myeloma progression via promotion of the megakaryocyte expansion and angiogenesis. Tasquinimod, an inhibitor of S100A9, has potent antimyeloma effects as a single agent and in combination with lenalidomide and with proteasome inhibitors.

PPT1 inhibition enhances the antitumor activity of anti-PD-1 antibody in melanoma

New strategies are needed to enhance the efficacy of anti–programmed cell death protein antibody (anti–PD-1 Ab) in cancer. Here, we report that inhibiting palmitoyl-protein thioesterase 1 (PPT1), a target of chloroquine derivatives like hydroxychloroquine (HCQ), enhances the antitumor efficacy of anti–PD-1 Ab in melanoma. The combination resulted in tumor growth impairment and improved survival in mouse models. Genetic suppression of core autophagy genes, but not Ppt1, in cancer cells reduced priming and cytotoxic capacity of primed T cells. Exposure of antigen-primed T cells to macrophage-conditioned medium derived from macrophages treated with PPT1 inhibitors enhanced melanoma-specific killing. Genetic or chemical Ppt1 inhibition resulted in M2 to M1 phenotype switching in macrophages. The combination was associated with a reduction in myeloid-derived suppressor cells in the tumor. Ppt1 inhibition by HCQ, or DC661, induced cyclic GMP-AMP synthase/stimulator of interferon genes/TANK binding kinase 1 pathway activation and the secretion of interferon-β in macrophages, the latter being a key component for augmented T cell–mediated cytotoxicity. Genetic Ppt1 inhibition produced similar findings. These data provide the rationale for this combination in melanoma clinical trials and further investigation in other cancers.

Inhibiting palmitoyl-protein thioesterase 1 (PPT1), a target of CQ derivatives like hydroxychloroquine (HCQ), enhances the antitumor efficacy of anti-PD-1 Ab in murine melanoma models.

Abstract A68: A casein kinase 2 inhibitor disorders myeloid cell differentiation by blocking CCAAT/enhancer-binding protein-alpha signaling pathway in tumor microenvironment

Myeloid cells are major components of the tumor microenvironment, which are known to suppress antitumor immunity. Casein kinase 2 (CK2), a serine/threonine protein kinase with diverse intracellular protein substrates, regulates several signaling pathways involved in tumor progression and cell differentiation. We examined the efficacy of a novel CK2 inhibitor on modulating the myeloid cells in the tumor microenvironment. Although CK2 inhibitors BMS-595 and BMS-211 moderately inhibited the tumor growth in LLC, 4T1, MC38 and CT26 tumor-bearing mice, these inhibitors drastically enhanced the antitumor efficacy of anti-CTLA4 antibody with 60% to 90% of complete rejection. Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) and macrophages in spleens, and tumor-associated macrophages (TAM) were found to be decreased in LLC tumor-bearing mice treated with BMS-595 for 2 weeks. Murine hematopoietic progenitor cells (HPC) from bone marrow and human progenitor cells from cord blood were cultured with BMS-595 to evaluate the differentiation. BMS-595 treatment dramatically decreased the proportion of granulocytic cells, and this decrease was not caused by the direct killing nor apoptosis. Therefore, the genes regulated by transcription factors, IRF8, C/EBPα and C/EBPβ, which are involved in PMN-MDSC differentiation, were evaluated. Many genes controlled by C/EBPα were downregulated by the BMS-595 treatment in HPCs. Active p42 subunit of C/EBPα was revealed to be reduced by the BMS-595 treatment in HPCs, which are inversely correlated with the increased level of dominant negative p30 subunit of C/EBPα, in both the cytoplasm and nucleus of HPCs. Our results suggest that CK2 inhibition leads to a reduction of immune-suppressive PMN-MDSC and TAM by inhibiting C/EBPα activity, resulting in an enormous augmentation of antitumor efficacy of immunotherapy.

Citation Format: Ayumi Hashimoto, Chan Gao, Jerome Mastio, Andrew Kossenkov, Scott I. Abrams, Ashok V. Purandare, Heshani Desilva, Susan Wee, John Hunt, Maria Jure-Kunkel, Dmitry I. Gabrilovich. A casein kinase 2 inhibitor disorders myeloid cell differentiation by blocking CCAAT/enhancer-binding protein-alpha signaling pathway in tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A68.

Dynamics of migration patterns of polymorphonuclear myeloid-derived suppressor cells during tumor progression

Although recruitment of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) to the tumor site is well documented, little is known about their migration patterns within bone marrow in tumor progression. We found that the activation of neutrophils migration in cancer is a two-phase process. The first phase was characterized by the accumulation of a previously uncharacterized population of neutrophils that lack immunosuppressive activity but display a potent ability to spontaneously migrate, whereas the later phase is associated with accumulation of neutrophils with typical features of PMN-MDSC with low migratory activity in the bone marrow of mice with various subcutaneous (ectopic) tumors and in mice with advanced orthotopic lung cancer. Mechanistically, PM-LCs displayed increased metabolic flux through oxidative phosphorylation and glycolysis and have more ATP than that of control neutrophils. However, PMN-MDSC were indistinguishable from neutrophils from tumor-free mice in their metabolic activity. In line with studies of mice, CD15+ neutrophils exhibited greater spontaneous migration than that of PMN-MDSCs from the same patient with cancer. These results elucidate the dynamic changes that neutrophils undergo in cancer.

Inhibition of Casein Kinase 2 Disrupts Differentiation of Myeloid Cells in Cancer and Enhances the Efficacy of Immunotherapy in Mice

The role of myeloid cells as regulators of tumor progression that significantly impact the efficacy of cancer immunotherapies makes them an attractive target for inhibition. Here we explore the effect of a novel, potent, and selective inhibitor of serine/threonine protein kinase casein kinase 2 (CK2) on modulating myeloid cells in the tumor microenvironment. Although inhibition of CK2 caused only a modest effect on dendritic cells in tumor-bearing mice, it substantially reduced the amount of polymorphonuclear myeloid-derived suppressor cells and tumor-associated macrophages. This effect was not caused by the induction of apoptosis, but rather by a block of differentiation. Our results implicated downregulation of CCAAT-enhancer binding protein-α in this effect. Although CK2 inhibition did not directly affect tumor cells, it dramatically enhanced the antitumor activity of immune checkpoint receptor blockade using anti-CTLA-4 antibody. These results suggest a potential role of CK2 inhibitors in combination therapies against cancer.Significance: These findings demonstrate the modulatory effects of casein kinase 2 inhibitors on myeloid cell differentiation in the tumor microenvironment, which subsequently synergize with the antitumor effects of checkpoint inhibitor CTLA4. Cancer Res; 78(19); 5644-55. ©2018 AACR.

Plasticity of myeloid-derived suppressor cells in cancer

In recent years, myeloid-derived suppressor cells (MDSC) have emerged as one of the major inhibitors of immune effector cell function in cancer. MDSC represent a heterogeneous population of largely immature myeloid cells that are characterized by a pathological state of activation and display potent immune suppressive activity. Two major subsets of MDSC have been identified: monocytic (M-MDSC) and polymorphonuclear (PMN-MDSC). PMN-MSDC share phenotypic and morphologic features with neutrophils, whereas M-MDSC are similar to monocytes and are characterized by high plasticity. Differentiation of M-MDSC to macrophages and dendritic cells is shaped by tumor microenvironment. In recent years, the mechanisms of this process start to emerge.

Abstract 3174: Retinoblastoma protein 1 implication in the monocytic - granulocytic transition

Alterations in the myeloipoiesis during cancer lead to production of myeloid-derived suppressor cells (MDSC). MDSC are comprised of two subsets: monocytic MDSC (M-MDSC) and polymorphonuclear MDSC (PMN-MDSC). Both subsets contribute to the immunosuppressive tumor microenvironment. Therefore elimination of MDSC could potentially improve the clinical success of cancer immune therapy. Direct targeting of MDSC progenitors is an attractive possibility. Our laboratory has recently discovered that M-MDSC from the bone-marrow can give rise to PMN-MDSC and that this phenomenon is mediated by the loss of retinoblastoma protein 1 (Rb1) expression. However, a full phenotypic and molecular characterization of these MDSC progenitors has not been established. To identify the subpopulation able to give rise to PMN-MDSC within the M-MDSC population, we used Rb1-GFP reporter mice to track Rb1 expression in vivo. We found that Rb1 low M-MDSC express the stem cell marker c-Kit and low levels of CD115. These Rb1 low c-Kit + M-MDSC are substantially expanded in tumor-bearing mice. Interestingly, this population is also present in naive mice, albeit at very low frequency. Rb1 low c-Kit + monocytic cells from naïve and tumor bearing mice can give rise to granulocytic cells in vitro. These preliminary results indicate that these cells are indeed granulocytic progenitor and are expanded during tumor development. Although this monocyte-granulocyte conversion is associated with a decrease in Rb1 expression, it seems that a minimal Rb1 level is required to ensure this process, at least in naïve mice. Further characterization of the phenotype and molecular profiles of this new MDSC progenitor could lead to the development of new ways to target MDSC.

Citation Format: Jerome Mastio, Thomas Condamine, Dmitry Gabrilovich. Retinoblastoma protein 1 implication in the monocytic - granulocytic transition. [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 3174. doi:10.1158/1538-7445.AM2015-3174

Increase of the final setting time of brushite cements by using chondroitin 4-sulfate and silica gel

Chondroitin 4-sulfate (C4S) is a bioactive glycosaminoglycan with inductive properties in bone and tissue regeneration. Dicalcium phosphate dehydrate cements (known as brushite) are biocompatible and resorbable materials used in bone and dental surgery. In this study we analyzed the effect of C4S on the setting of a calcium phosphate cement and the properties of the resulting material. Brushite based cement powder was synthesised by mixing monocalcium phosphate with beta-tricalcium phosphate and sodium pyrophosphate. When the concentration of C4S, in the liquid added to the cement powder, was between 1 and 8% the cement final setting time increases. Furthermore, the cement diametral tensile strength remains unaffected when solutions with concentrations of C4S below 5% were used, but decreases at higher C4S concentrations. Calorimetric analysis showed that the cements prepared with C4S alone and in combination with silica gel have a greater content of hydrated water. We concluded from our study that the addition of small amounts of C4S increases the cement setting time without affecting its diametral tensile strength and at the same time improves the cement's hydrophilicity.