Impaired tumor growth in colony-stimulating factor 1 (CSF-1)-deficient, macrophage-deficient op/op mouse: evidence for a role of CSF-1-dependent macrophages in formation of tumor stroma

A temporal perspective for tumor-associated macrophage identities and functions

Cancer is a progressive disease that can develop and evolve over decades, with inflammation playing a central role at each of its stages, from tumor initiation to metastasis. In this context, macrophages represent well-established bridges reciprocally linking inflammation and cancer via an array of diverse functions that have spurred efforts to classify them into subtypes. Here, we discuss the intertwines between macrophages, inflammation, and cancer with an emphasis on temporal dynamics of macrophage diversity and functions in pre-malignancy and cancer. By instilling temporal dynamism into the more static classic view of tumor-associated macrophage biology, we propose a new framework to better contextualize their significance in the inflammatory processes that precede and result from the onset of cancer and shape its evolution.

MAFB shapes human monocyte-derived macrophage response to SARS-CoV-2 and controls severe COVID-19 biomarker expression

Monocyte-derived macrophages, the major source of pathogenic macrophages in COVID-19, are oppositely instructed by macrophage CSF (M-CSF) or granulocyte macrophage CSF (GM-CSF), which promote the generation of antiinflammatory/immunosuppressive MAFB+ (M-MØ) or proinflammatory macrophages (GM-MØ), respectively. The transcriptional profile of prevailing macrophage subsets in severe COVID-19 led us to hypothesize that MAFB shapes the transcriptome of pulmonary macrophages driving severe COVID-19 pathogenesis. We have now assessed the role of MAFB in the response of monocyte-derived macrophages to SARS-CoV-2 through genetic and pharmacological approaches, and we demonstrate that MAFB regulated the expression of the genes that define pulmonary pathogenic macrophages in severe COVID-19. Indeed, SARS-CoV-2 potentiated the expression of MAFB and MAFB-regulated genes in M-MØ and GM-MØ, where MAFB upregulated the expression of profibrotic and neutrophil-attracting factors. Thus, MAFB determines the transcriptome and functions of the monocyte-derived macrophage subsets that underlie pulmonary pathogenesis in severe COVID-19 and controls the expression of potentially useful biomarkers for COVID-19 severity.

A phase I/II study of LY3022855 with BRAF/MEK inhibition in patients with Melanoma

BRAF/MEK targeted therapies and immune checkpoint inhibition have dramatically improved disease control and survival of patients with advanced melanoma. However, most patients do not have durable benefit from either of these therapies. BRAF targeted therapy often has a limited duration of efficacy due to the development of resistance. Pre-clinical data suggest that one possible way to overcome resistance to BRAF/MEK targeted therapy may be the addition of CSF1R inhibition. In this phase I/II study we evaluated the safety and efficacy of LY3022855, an anti-colony stimulating factor-1 receptor (CSF-1R) monoclonal antibody in combination with the BRAF inhibitor vemurafenib and the MEK inhibitor cobimetinib in patients with BRAF V600E/K mutant metastatic melanoma. The trial was terminated early due to discontinuation of the development program for LY3022855 by the sponsor. Between August 2017 and May 2018 five pts were enrolled. Three patients experienced grade 3 events that were deemed possibly related to LY3022855. There were no grade 4 or grade 5 events related to LY3022855. One of the 5 patients had a complete response (CR), whereas the other 4 had progressive disease (PD). Median progression free survival was 3.9 months (90% CI: 1.9-37.2 mos). CSF1R inhibition with LY3022855 in combination with BRAF/MEK inhibition with vemurafenib and cobimetinib was difficult to tolerate in a small melanoma population. One response was observed in this small sample of patients suggesting this combination might be worthy of further exploration.

A phase I/II study of MCS110 with BRAF/MEK inhibition in patients with melanoma after progression on BRAF/MEK inhibition

BACKGROUND

Prognosis for patients with metastatic melanoma has been improved dramatically with the development of BRAF/MEK directed therapy and immune checkpoint inhibition. However, resistance to therapy remains a challenge, particularly with BRAF/MEK targeted therapy which often has a limited duration of efficacy. Pre-clinical data suggest that adding CSF1 inhibition to BRAF/MEK targeted therapy may reduce resistance and increase efficacy.

METHODS

We performed a phase I/II study to determine the safety and efficacy of CSF1 inhibition with MCS110 in combination with BRAF/MEK inhibition with dabrafenib/trametinib in patients with BRAF V600E/K mutant metastatic melanoma. The trial was terminated early due to a decision by the study sponsor to cease further development of MCS110.

RESULTS

Between September 2018 to July 2019 six patients were enrolled on the study. Patients were evenly split between female (50%) and male (50%) with a median age of 59.5 yrs. (26-71). Five patients experienced grade 3 toxicities that were possibly related to one of the therapies, there were no grade 4 or grade 5 events. One patient had a partial response (PR) by RECIST 1.1, one patient had stable disease (SD), 3 patients had disease progression (PD). Median progression free survival was 2.3 months (90% CI: 1.3 mos to not reached).

CONCLUSION

MCS110 in combination with dabrafenib and trametinib was reasonably well tolerated in a small melanoma population. One response was observed in this small sample of patients suggesting this combination might be worthy of further exploration.

Inhibition of LXR controls the polarization of human inflammatory macrophages through upregulation of MAFB

Monocyte-derived macrophages contribute to pathogenesis in inflammatory diseases and their effector functions greatly depend on the prevailing extracellular milieu. Whereas M-CSF primes macrophages for acquisition of an anti-inflammatory profile, GM-CSF drives the generation of T cell-stimulatory and pro-inflammatory macrophages. Liver X Receptors (LXRα and LXRβ) are nuclear receptors that control cholesterol metabolism and regulate differentiation of tissue-resident macrophages. Macrophages from rheumatoid arthritis and other inflammatory pathologies exhibit an enriched LXR pathway, and recent reports have shown that LXR activation raises pro-inflammatory effects and impairs the acquisition of the anti-Inflammatory profile of M-CSF-dependent monocyte-derived macrophages (M-MØ). We now report that LXR inhibition prompts the acquisition of an anti-inflammatory gene and functional profile of macrophages generated within a pathological environment (synovial fluid from Rheumatoid Arthritis patients) as well as during the GM-CSF-dependent differentiation of human monocyte-derived macrophages (GM-MØ). Mechanistically, inhibition of LXR results in macrophages with higher expression of the v-Maf Avian Musculoaponeurotic Fibrosarcoma Oncogene Homolog B (MAFB) transcription factor, which governs the macrophage anti-inflammatory profile, as well as over-expression of MAFB-regulated genes. Indeed, gene silencing experiments on human macrophages evidenced that MAFB is required for the LXR inhibitor to enhance the anti-inflammatory nature of human macrophages. As a whole, our results demonstrate that LXR inhibition prompts the acquisition of an anti-inflammatory transcriptional and functional profile of human macrophages in a MAFB-dependent manner, and propose the use of LXR antagonists as potential therapeutic alternatives in macrophage re-programming strategies during inflammatory responses.

Activation of LXR Nuclear Receptors Impairs the Anti-Inflammatory Gene and Functional Profile of M-CSF-Dependent Human Monocyte-Derived Macrophages

Liver X Receptors (LXR) control cholesterol metabolism and exert anti-inflammatory actions but their contribution to human macrophage polarization remains unclear. The LXR pathway is enriched in pro-inflammatory macrophages from rheumatoid arthritis as well as in tumors-associated macrophages from human tumors. We now report that LXR activation inhibits the anti-inflammatory gene and functional profile of M-CSF-dependent human macrophages, and prompts the acquisition of a pro-inflammatory gene signature, with both effects being blocked by an LXR inverse agonist. Mechanistically, the LXR-stimulated macrophage polarization shift correlates with diminished expression of MAFB and MAF, which govern the macrophage anti-inflammatory profile, and with enhanced release of activin A. Indeed, LXR activation impaired macrophage polarization in response to tumor-derived ascitic fluids, as well as the expression of MAF- and MAFB-dependent genes. Our results demonstrate that LXR activation limits the anti-inflammatory human macrophage polarization and prompts the acquisition of an inflammatory transcriptional and functional profile.

Cancer Therapy Targeting CD47/SIRPα

Simple Summary

The interaction between cluster of differentiation 47 (CD47) on cancer cells and signal regulatory protein alpha (SIRPα) on immune cells, such as macrophages and dendritic cells, generates a “don’t eat me” signal. This is a common mechanism that provides cancer cells an escape from the innate immune system. Several therapeutics directed to CD47 or SIRPα have entered early clinical trials in recent years. In this article, we review the role of CD47/SIRPα axis in cancer, and summarize the literature on the efficacy and safety of therapeutics targeting CD47 or SIRPα. We also discuss the future implementation of these therapeutics in the treatments of various cancer types.

Abstract

In the past decade, the field of cancer immunotherapy has rapidly advanced, establishing a crucial role for immune checkpoint blockers in the treatment of a variety of cancer types. In parallel with these remarkable clinical developments, further efforts have focused on ways of unleashing adaptive immune responses against cancer. CD47, a cell surface molecule overexpressed by several cancer types that facilitates immune escape from macrophages, dendritic cells and natural killer cells, and its ligand SIRPα, have emerged as potential therapeutic targets. A number of agents directed to CD47/SIRPα have been developed and demonstrated preclinical activity. Early phase clinical trials are investigating CD47/SIRPα directed agents with available data, suggesting safety and preliminary activity. Herein, we provide an overview of the mechanistic rationale of targeting CD47/SIRPα axis and associated clinical evidence.

Myeloid cell-derived PROS1 inhibits tumor metastasis by regulating inflammatory and immune responses via IL-10

Stimulation of TAM (TYRO3, AXL, and MERTK) receptor tyrosine kinases promotes tumor progression through numerous cellular mechanisms. TAM cognate ligands GAS6 and PROS1 (for TYRO3 and MERTK) are secreted by host immune cells, an interaction which may support tumor progression. Here, we revealed an unexpected antimetastatic role for myeloid-derived PROS1: suppressing metastatic potential in lung and breast tumor models. Pros1 deletion in myeloid cells led to increased lung metastasis, independent of primary tumor infiltration. PROS1-cKO bone marrow-derived macrophages (BMDMs) led to elevated TNF-α, IL-6, Nos2, and IL-10 via modulation of the Socs3/NF-κB pathway. Conditioned medium from cKO BMDMs enhanced EMT, ERK, AKT, and STAT3 activation within tumor cells and promoted IL-10-dependent invasion and survival. Macrophages isolated from metastatic lungs modulated T cell proliferation and function, as well as expression of costimulatory molecules on DCs in a PROS1-dependent manner. Inhibition of MERTK kinase activity blocked PROS1-mediated suppression of TNF-α and IL-6 but not IL-10. Overall, using lung and breast cancer models, we identified the PROS1/MERTK axis within BMDMs as a potent regulator of adaptive immune responses with a potential to suppress metastatic seeding and revealed IL-10 regulation by PROS1 to deviate from that of TNF-α and IL-6.

Immunomodulatory Activity of a Colony-stimulating Factor-1 Receptor Inhibitor in Patients with Advanced Refractory Breast or Prostate Cancer: A Phase I Study

PURPOSE

Tumor-associated macrophages correlate with increased invasiveness, growth, and immunosuppression. Activation of the colony-stimulating factor-1 receptor (CSF-1R) results in proliferation, differentiation, and migration of monocytes/macrophages. This phase I study evaluated the immunologic and clinical activity, and safety profile of CSF-1R inhibition with the mAb LY3022855.

PATIENTS AND METHODS

Patients with advanced refractory metastatic breast cancer (MBC) or metastatic castration-resistant prostate cancer (mCRPC) were treated with LY3022855 intravenously in 6-week cycles in cohorts: (A) 1.25 mg/kg every 2 weeks (Q2W); (B) 1.0 mg/kg on weeks 1, 2, 4, and 5; (C) 100 mg once weekly; (D)100 mg Q2W. mCRPC patients were enrolled in cohorts A and B; patients with MBC were enrolled in all cohorts. Efficacy was assessed by RECIST and Prostate Cancer Clinical Trials Working Group 2 criteria.

RESULTS

Thirty-four patients (22 MBC; 12 mCRPC) received ≥1 dose of LY3022855. At day 8, circulating CSF-1 levels increased and proinflammatory monocytes CD14^DIMCD16^BRIGHT decreased. Best RECIST response was stable disease in five patients with MBC (23%; duration, 82-302 days) and three patients with mCRPC (25%; duration, 50-124 days). Two patients with MBC (cohort A) had durable stable disease >9 months and a third patient with MBC had palpable reduction in a nontarget neck mass. Immune-related gene activation in tumor biopsies posttreatment was observed. Common any grade treatment-related adverse events were fatigue, decreased appetite, nausea, asymptomatic increased lipase, and creatine phosphokinase.

CONCLUSIONS

LY3022855 was well tolerated and showed evidence of immune modulation. Clinically meaningful stable disease >9 months was observed in two patients with MBC.

Stromal CCL2 Signaling Promotes Mammary Tumor Fibrosis through Recruitment of Myeloid-Lineage Cells

Obesity is correlated with breast tumor desmoplasia, leading to diminished chemotherapy response and disease-free survival. Obesity causes chronic, macrophage-driven inflammation within breast tissue, initiated by chemokine ligand 2 (CCL2) signaling from adipose stromal cells. To understand how CCL2-induced inflammation alters breast tumor pathology, we transplanted oncogenically transformed human breast epithelial cells with breast stromal cells expressing CCL2 or empty vector into murine mammary glands and examined tumor formation and progression with time. As tumors developed, macrophages were rapidly recruited, followed by the emergence of cancer-associated fibroblasts (CAFs) and collagen deposition. Depletion of CD11b + myeloid lineage cells early in tumor formation reduced tumor growth, CAF numbers, and collagen deposition. CCL2 expression within developing tumors also enhanced recruitment of myeloid progenitor cells from the bone marrow into the tumor site. The myeloid progenitor cell population contained elevated numbers of fibrocytes, which exhibited platelet-derived growth factor receptor-alpha (PDGFRα)-dependent colony formation and growth in vitro. Together, these results suggest that chronic inflammation induced by CCL2 significantly enhances tumor growth and promotes the formation of a desmoplastic stroma through early recruitment of macrophages and fibrocytes into the tumor microenvironment. Fibrocytes may be a novel target in the tumor microenvironment to reduce tumor fibrosis and enhance treatment responses for obese breast cancer patients.

Folate Receptor β (FRβ) Expression in Tissue-Resident and Tumor-Associated Macrophages Associates with and Depends on the Expression of PU.1

As macrophages exhibit a huge functional plasticity under homeostasis and pathological conditions, they have become a therapeutic target for chronic inflammatory diseases. Hence, the identification of macrophage subset-specific markers is a requisite for the development of macrophage-directed therapeutic interventions. In this regard, the macrophage-specific Folate Receptor β (FRβ, encoded by the FOLR2 gene) has been already validated as a target for molecular delivery in cancer as well as in macrophage-targeting therapeutic strategies for chronic inflammatory pathologies. We now show that the transcriptome of human macrophages from healthy and inflamed tissues (tumor; rheumatoid arthritis, RA) share a significant over-representation of the “anti-inflammatory gene set”, which defines the gene profile of M-CSF-dependent IL-10-producing human macrophages (M-MØ). More specifically, FOLR2 expression has been found to strongly correlate with the expression of M-MØ-specific genes in tissue-resident macrophages, tumor-associated macrophages (TAM) and macrophages from inflamed synovium, and also correlates with the presence of the PU.1 transcription factor. In fact, PU.1-binding elements are found upstream of the first exon of FOLR2 and most M-MØ-specific- and TAM-specific genes. The functional relevance of PU.1 binding was demonstrated through analysis of the proximal regulatory region of the FOLR2 gene, whose activity was dependent on a cluster of PU.1-binding sequences. Further, siRNA-mediated knockdown established the importance of PU.1 for FOLR2 gene expression in myeloid cells. Therefore, we provide evidence that FRβ marks tissue-resident macrophages as well as macrophages within inflamed tissues, and its expression is dependent on PU.1.

Inflammatory Responses during Tumour Initiation: From Zebrafish Transgenic Models of Cancer to Evidence from Mouse and Man

The zebrafish is now an important model organism for cancer biology studies and provides unique and complementary opportunities in comparison to the mammalian equivalent. The translucency of zebrafish has allowed in vivo live imaging studies of tumour initiation and progression at the cellular level, providing novel insights into our understanding of cancer. Here we summarise the available transgenic zebrafish tumour models and discuss what we have gleaned from them with respect to cancer inflammation. In particular, we focus on the host inflammatory response towards transformed cells during the pre-neoplastic stage of tumour development. We discuss features of tumour-associated macrophages and neutrophils in mammalian models and present evidence that supports the idea that these inflammatory cells promote early stage tumour development and progression. Direct live imaging of tumour initiation in zebrafish models has shown that the intrinsic inflammation induced by pre-neoplastic cells is tumour promoting. Signals mediating leukocyte recruitment to pre-neoplastic cells in zebrafish correspond to the signals that mediate leukocyte recruitment in mammalian tumours. The activation state of macrophages and neutrophils recruited to pre-neoplastic cells in zebrafish appears to be heterogenous, as seen in mammalian models, which provides an opportunity to study the plasticity of innate immune cells during tumour initiation. Although several potential mechanisms are described that might mediate the trophic function of innate immune cells during tumour initiation in zebrafish, there are several unknowns that are yet to be resolved. Rapid advancement of genetic tools and imaging technologies for zebrafish will facilitate research into the mechanisms that modulate leukocyte function during tumour initiation and identify targets for cancer prevention.

Cerebrospinal fluid penetration of the colony-stimulating factor-1 receptor (CSF-1R) inhibitor, pexidartinib

PURPOSE

Pexidartinib (PLX3397) is a colony-stimulating factor-1 receptor (CSF-1R) inhibitor under clinical evaluation for potential CNS tumor treatment. This study aims to evaluate plasma pharmacokinetic parameters and estimate CNS penetrance of pexidartinib in a non-human primate (NHP) cerebrospinal fluid (CSF) reservoir model.

METHODS

Five male rhesus macaques, each with a previously implanted subcutaneous CSF ventricular reservoir and central venous lines, were used. NHPs received a single dose of 40 mg/kg pexidartinib (human equivalent dose of 800 mg/m²), administered orally as 200 mg tablets. Serial paired samples of blood and CSF were collected at 0-8, 24, 48, and 72 h. Pexidartinib concentrations were assayed by Integrated Analytical Solutions, Inc. (Berkeley, CA, USA) using HPLC/MS/MS. Pharmacokinetic (PK) analysis was performed using noncompartmental methods.

RESULTS

Samples from four NHPs were evaluable. Average (± SD) plasma PK parameters were as follows: C_max = 16.50 (± 6.67) μg/mL; T_max = 5.00 (± 2.58) h; AUC_last = 250.25 (± 103.76) h*μg/mL; CL = 0.18 (± 0.10) L/h/kg. In CSF, pexidartinib was either quantifiable (n = 2), with C_max values of 16.1 and 10.1 ng/mL achieved 2-4 h after plasma T_max, or undetected at all time points (n = 2, LLOQ_CSF = 5 ng/mL).

CONCLUSION

Pexidartinib was well-tolerated in NHPs, with no Grade 3 or Grade 4 toxicities. The CSF penetration of pexidartinib after single-dose oral administration to NHPs was limited.

Immunosurveillance and Immunoediting of Lung Cancer: Current Perspectives and Challenges

The immune system plays a dual role in tumor evolution-it can identify and control nascent tumor cells in a process called immunosurveillance and can promote tumor progression through immunosuppression via various mechanisms. Thus, bilateral host-protective and tumor-promoting actions of immunity are integrated as cancer immunoediting. In this decade, immune checkpoint inhibitors, specifically programmed cell death 1 (PD-1) pathway inhibitors, have changed the treatment paradigm of advanced non-small cell lung cancer (NSCLC). These agents are approved for the treatment of patients with NSCLC and demonstrate impressive clinical activity and durable responses in some patients. However, for many NSCLC patients, the efficacy of immune checkpoint inhibitors is limited. To optimize the full utility of the immune system for eradicating cancer, a broader understanding of cancer immunosurveillance and immunoediting is essential. In this review, we discuss the fundamental knowledge of the phenomena and provide an overview of the next-generation immunotherapies in the pipeline.

The Yin and Yang of Cytoreductive SBRT in Oligometastases and Beyond

Background: Oligometastatic disease has emerged as a possibly distinct metastatic phenotype in numerous cancer histologies. With the advancement in treatment modalities including stereotactic body radiation therapy (SBRT), certain patients may derive benefits from local ablative therapy. SBRT alone has already shown to have potential benefits in certain oligometastatic disease types. However, more understanding of the immunologic modulation and microenvironment is needed to guide which patients may benefit from SBRT alone or with combination therapy, if at all. Purpose: The purpose of this review is to offer an update on the emerging data testing SBRT combined with immunotherapy, review the pro-inflammatory and immunosuppressive effects of the tumor microenvironment, discuss novel molecular targets used to augment the immune response, and review potential methods used to decrease toxicity in order to improve the therapeutic ratio.

Tumor-Associated Macrophages and Dendritic Cells as Prototypic Type II Polarized Myeloid Populations

Environmental signals polarize mononuclear phagocytes which can express different functional programmes. Fully polarized type I and type II (or alternatively activated) macrophages are the extremes of a continuum of functional states. Tumor-derived and T cell-derived cytokines stimulate tumor associated macrophages (TAM) to acquire a polarized type II phenotype. These functionally polarized cells, and similarly oriented or immature dendritic cells present in tumors, play a key role in subversion of adaptive immunity and in inflammatory circuits which promote tumor growth and progression.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in "distant" pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in “distant” pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

The Role of CSF-1 in Normal Physiology of Mammary Gland and Breast Cancer: An Update

Colony stimulating factor (CSF-1) and its receptor (CSF-1R, product of c-fms proto-oncogene) were initially implicated as essential for normal monocyte development as well as for trophoblastic implantation. However, studies have demonstrated that CSF-1 and CSF-1R have additional roles in mammary gland development during pregnancy and lactation. This apparent role for CSF-1/CSF-1R in normal mammary gland development is very intriguing because this receptor/ligand pair has also been found to be important in the biology of breast cancer in which abnormal expression of CSF-1 and its receptor correlates with tumor cell invasiveness and adverse clinical prognosis. Recent findings also implicate tumor-produced CSF-1 in promotion of bone metastasis in breast cancer, and a certain membrane-associated form of CSF-1 appears to induce immunity against tumors. This review aims to summarize recent findings on the role of CSF-1 and its receptor in normal and neoplastic mammary development that may elucidate potential relationships of growth factor–induced biological changes in the breast during pregnancy and tumor progression.

The Ontogeny and Microenvironmental Regulation of Tumor-Associated Macrophages

SIGNIFICANCE

Tumor progression is supported by non-cancerous stromal cells, of which tumor-associated macrophages (TAMs) are prominent constituents. These cells could be considered promising therapeutic targets, but this requires a better understanding of their heterogeneity under the influence of tumor microenvironmental cues and/or ontogenic differences. Recent Advances: The availability of oxygen is an important regulator of the TAM phenotype, as well as of its access to myelopoietic growth factors. Very recent evidence also demonstrated that macrophages can be derived from embryonal precursors or from monocytes post-birth, introducing yet another level of heterogeneity among macrophages.

CRITICAL ISSUES

The relative contribution of ontogenically distinct macrophages to tumor characteristics is, to a large extent, still an open question. In addition, further knowledge on the role of tumor microenvirontal cues that shape TAMs is warranted.

FUTURE DIRECTIONS

More detailed insights into the TAM-regulating factors will provide new opportunities for therapeutic intervention. Interference with the phenotypes of TAM, which are known to be immunosuppressive and to contribute to dysfunctional tumor blood vessels, is anticipated to be beneficial in combination with chemotherapy and/or immunotherapy. Antioxid. Redox Signal. 25, 775-791.

Anticancer Effects of Targeting Hsp70 in Tumor Stromal Cells

The stress-induced chaperone protein Hsp70 enables the initiation and progression of many cancers, making it an appealing therapeutic target for development. Here, we show that cancer cells resistant to Hsp70 inhibitors in vitro remain sensitive to them in vivo, revealing the pathogenic significance of Hsp70 in tumor stromal cells rather than tumor cells as widely presumed. Using transgenic mouse models of cancer, we found that expression of Hsp70 in host stromal cells was essential to support tumor growth. Furthermore, genetic ablation or pharmacologic inhibition of Hsp70 suppressed tumor infiltration by macrophages needed to enable tumor growth. Overall, our results illustrate how Hsp70 inhibitors mediate the anticancer effects by targeting both tumor cells and tumor stromal cells, with implications for the broad use of these inhibitors as tools to ablate tumor-associated macrophages that enable malignant progression. Cancer Res; 76(20); 5926-32. ©2016 AACR.

Glioblastoma-derived Macrophage Colony-stimulating Factor (MCSF) Induces Microglial Release of Insulin-like Growth Factor-binding Protein 1 (IGFBP1) to Promote Angiogenesis

Glioblastoma (grade IV glioma/GBM) is the most common primary adult malignant brain tumor with poor prognosis. To characterize molecular determinants of tumor-stroma interaction in GBM, we profiled 48 serum cytokines and identified macrophage colony-stimulating factor (MCSF) as one of the elevated cytokines in sera from GBM patients. Both MCSF transcript and protein were up-regulated in GBM tissue samples through a spleen tyrosine kinase (SYK)-dependent activation of the PI3K-NFκB pathway. Ectopic overexpression and silencing experiments revealed that glioma-secreted MCSF has no role in autocrine functions and M2 polarization of macrophages. In contrast, silencing expression of MCSF in glioma cells prevented tube formation of human umbilical vein endothelial cells elicited by the supernatant from monocytes/microglial cells treated with conditioned medium from glioma cells. Quantitative proteomics based on stable isotope labeling by amino acids in cell culture showed that glioma-derived MCSF induces changes in microglial secretome and identified insulin-like growth factor-binding protein 1 (IGFBP1) as one of the MCSF-regulated proteins secreted by microglia. Silencing IGFBP1 expression in microglial cells or its neutralization by an antibody reduced the ability of supernatants derived from microglial cells treated with glioma cell-conditioned medium to induce angiogenesis. In conclusion, this study shows up-regulation of MCSF in GBM via a SYK-PI3K-NFκB-dependent mechanism and identifies IGFBP1 released by microglial cells as a novel mediator of MCSF-induced angiogenesis, of potential interest for developing targeted therapy to prevent GBM progression.

Modulating the tumor microenvironment with RNA interference as a cancer treatment strategy

The tumor microenvironment is composed of accessory cells and immune cells in addition to extracellular matrix (ECM) components. The stromal compartment interacts with cancer cells in a complex crosstalk to support tumor development. Growth factors and cytokines produced by stromal cells support the growth of tumor cells and promote interaction with the vasculature to enhance tumor progression and invasion. The activation of autocrine and paracrine oncogenic signaling pathways by growth factors, cytokines, and proteases derived from both tumor cells and the stromal compartment is thought to play a major role in assisting tumor cells during metastasis. Consequently, targeting tumor-stroma interactions by RNA interference (RNAi)-based approaches is a promising strategy in the search for novel treatment modalities in human cancer. Recent advances in packaging technology including the use of polymers, peptides, liposomes, and nanoparticles to deliver small interfering RNAs (siRNAs) into target cells may overcome limitations associated with potential RNAi-based therapeutics. Newly developed nonviral gene delivery approaches have shown improved anticancer efficacy suggesting that RNAi-based therapeutics provide novel opportunities to elicit significant gene silencing and induce regression of tumor growth. This chapter summarizes our current understanding of the tumor microenvironment and highlights some potential targets for therapeutic intervention with RNAi-based cancer therapeutics.

Melanoma brain metastasis globally reconfigures chemokine and cytokine profiles in patient cerebrospinal fluid

The aggressiveness of melanoma is believed to be correlated with tumor–stroma-associated immune cells. Cytokines and chemokines act to recruit and then modulate the activities of these cells, ultimately affecting disease progression. Because melanoma frequently metastasizes to the brain, we asked whether global differences in immunokine profiles could be detected in the cerebrospinal fluid (CSF) of melanoma patients and reveal aspects of tumor biology that correlate with patient outcomes. We therefore measured the levels of 12 cytokines and 12 chemokines in melanoma patient CSF and the resulting data were analyzed to develop unsupervised hierarchical clustergrams and heat maps. Unexpectedly, the overall profiles of immunokines found in these samples showed a generalized reconfiguration of their expression in melanoma patient CSF, resulting in the segregation of individuals with melanoma brain metastasis from nondisease controls. Chemokine CCL22 and cytokines IL1α, IL4, and IL5 were reduced in most samples, whereas a subset including CXCL10, CCL4, CCL17, and IL8 showed increased expression. Further, analysis of clusters identified within the melanoma patient set comparing patient outcome suggests that suppression of IL1α, IL4, IL5, and CCL22, with concomitant elevation of CXCL10, CCL4, and CCL17, may correlate with more aggressive development of brain metastasis. These results suggest that global immunokine suppression in the host, together with a selective increase in specific chemokines, constitute a predominant immunomodulatory feature of melanoma brain metastasis. These alterations likely drive the course of this disease in the brain and variations in the immune profiles of individual patients may predict outcomes.

Myeloid cells in cancer-related inflammation

Myeloid cells are key elements of the cancer-related inflammation with the potential to support not only tumor growth but also invasion and metastasis. Tumor-derived factors affect myeloid cell differentiation inducing a phenotype that supports tumor growth, inducing immunosuppression, angiogenesis and tissue remodeling. Soluble mediators, produced at primary tumor site, can also act in a remote mode inducing the release from bone marrow of myeloid cells that have immunosuppressive activities in tumor-draining lymphoid organs and can predispose to colonization when migrate to metastatic organs. We will here review current knowledge on the contribution of tumor-derived signals that affect polarized activation of myeloid cells, their bone marrow release and recruitment to metastatic sites with a particular focus on the role of chemokines.

Macrophage colony-stimulating factor plays a pivotal role in chemically induced hepatocellular carcinoma in mice

AIM

The specific purpose of this study was to investigate the role of macrophage colony-stimulating factor (M-CSF) in initiation and progression of hepatocellular carcinoma using M-CSF-deficient mice.

METHODS

M-CSF-deficient (osteopetrotic: op/op) and their littermate (LM) mice were i.p. injected with diethylnitrosamine (DEN) to induce hepatocellular carcinoma. Twenty-eight weeks after DEN administration, the tumor incidence rate and serum M-CSF levels were assessed. Furthermore, distribution of the activated macrophages and the mRNA expression of CD163 and CD204 were evaluated. Moreover, angiogenesis was analyzed in tumors. In another set of experiments, apoptosis and proliferation of the hepatocytes were examined in the acute phase after DEN administration. Isolated hepatic macrophages were cultured with or without M-CSF, and vascular endothelial growth factor (VEGF) production was assessed by enzyme-linked immunoassay.

RESULTS

Tumor incidence was significantly reduced in the op/op compared with the LM mice. Serum M-CSF levels were increased in the carcinogenesis models of the LM mice. Hepatic macrophages were found only in tumors in the op/op but in both normal liver tissue and tumors in the LM mice. In the op/op group, the mRNA expression of inflammatory cytokines was significantly lower compared with the LM mice. Furthermore, apoptosis was significantly increased in the op/op than the LM mice. Angiogenesis increased in liver tumors from the LM compared with the op/op mice. Production of VEGF was greater in the hepatic macrophages incubated with M-CSF compared with those without M-CSF.

CONCLUSION

Thus, M-CSF is involved in the progression of chemically induced hepatocarcinogenesis.

Optimized nonclinical safety assessment strategies supporting clinical development of therapeutic monoclonal antibodies targeting inflammatory diseases

An increasing number of immunomodulatory monoclonal antibodies (mAbs) and IgG Fc fusion proteins are either approved or in early-to-late stage clinical trials for the treatment of chronic inflammatory conditions, autoimmune diseases and organ transplant rejection. The exquisite specificity of mAbs, in combination with their multi-functional properties, high potency, long half-life (permitting intermittent dosing and prolonged pharamcological effects), and general lack of off-target toxicity makes them ideal therapeutics. Dosing with mAbs for these severe and debilitating but often non life-threatening diseases is usually prolonged, for several months or years, and not only affects adults, including sensitive populations such as woman of child-bearing potential (WoCBP) and the elderly, but also children. Immunosuppression is usually a therapeutic goal of these mAbs and when administered to patients whose treatment program often involves other immunosuppressive therapies, there is an inherent risk for frank immunosuppression and reduced host defence which when prolonged increases the risk of infection and cancer. In addition when mAbs interact with the immune system they can induce other adverse immune-mediated drug reactions such as infusion reactions, cytokine release syndrome, anaphylaxis, immune-complex-mediated pathology and autoimmunity. An overview of the nonclinical safety assessment and risk mitigation strategies utilized to characterize these immunomodulatory mAbs and Fc fusion proteins to support first-in human (FIH) studies and futher clinical development in inflammatory disease indications is provided. Specific emphasis is placed on the design of studies to qualify animal species for toxicology studies, early studies to investigate safety and define PK/PD relationships, FIH-enabling and chronic toxicology studies, immunotoxicity, developmental, reproductive and juvenile toxicity studies and studies to determine the potential for immunosuppression and reduced host defence against infection and cancer. Nonclinical strategies to facilitate clinical and market entry in the most efficient timeframe are presented.

Mechanisms driving macrophage diversity and specialization in distinct tumor microenvironments and parallelisms with other tissues

Macrophages are extremely versatile cells that adopt a distinct phenotype in response to a changing microenvironment. Consequently, macrophages are involved in diverse functions, ranging from organogenesis and tissue homeostasis to recognition and destruction of invading pathogens. In cancer, tumor-associated macrophages (TAM) often contribute to tumor progression by increasing cancer cell migration and invasiveness, stimulating angiogenesis, and suppressing anti-tumor immunity. Accumulating evidence suggests that these different functions could be exerted by specialized TAM subpopulations. Here, we discuss the potential underlying mechanisms regulating TAM specialization and elaborate on TAM heterogeneity in terms of their ontogeny, activation state, and intra-tumoral localization. In addition, parallels are drawn between TAM and macrophages in other tissues. Together, a better understanding of TAM diversity could provide a rationale for novel strategies aimed at targeting the most potent tumor-supporting macrophages.

The role of inflammation in gastric cancer

Gastric cancer, despite its declining incidence rate, is still the second cause of cancer-related death worldwide, killing 750,000 people each year and remaining the second common type of cancer. The best examples of inflammation-associated cancer in human beings may be gastric cancer. Understanding the molecular mechanism of the inflammation in gastric carcinogenesis is important for developing new strategies against gastric cancer.

Tumor-associated macrophages are involved in tumor progression in papillary renal cell carcinoma

Tumor-associated macrophages (TAMs) play a key role in cancer development. Especially, the immunosuppressive M2 phenotype is associated with increased tumor growth, invasiveness and metastasis. The differentiation of macrophages to the alternative phenotype M2 is mediated, inter alia, by macrophage colony-stimulating factor (M-CSF). Papillary renal cell carcinoma (RCC) represents a rare tumor type which, based upon histological criteria, can be subdivided into two subtypes (I and II), of which type II is associated with poor prognosis. In both subtypes, typically, a dense infiltrate of macrophages is found. In the present study, the expression of CD68, CD163, M-CSF, Ki-67, and CD31 was examined in 30 type I and 30 type II papillary RCCs (n = 60). Both types of papillary RCCs contained an equally dense infiltrate of CD68-positive macrophages. Nearly all macrophages in papillary RCC type II expressed CD163, a characteristic for M2 macrophages. In type I papillary RCC, less than 30 % of macrophages expressed CD163. Furthermore, tumor cells in type II papillary RCC expressed significantly more M-CSF and showed increased (Ki-67 expression defined) proliferative activity in comparison with type I papillary RCC. In addition, the (CD31 defined) capillary density was higher in type II than in type I papillary RCC. A dense infiltrate of M2 phenotype TAM and high M-CSF expression in tumor cells are key features of type II papillary RCC. These findings might explain why the prognosis of papillary RCC type II is worse than that of type I.

Elevated CSF1 serum concentration predicts poor overall survival in women with early breast cancer

Colony-stimulating factor 1 (CSF1) is a key regulator of mammary gland development, and a modulator of tissue macrophages. Expression of the CSF1 receptor gene C-FMS (CSF1R) is strongly associated with poor outcome in breast cancer and results in tumor cell invasiveness and pro-metastatic behavior in vitro. However, CSF1's role as a predictive factor in breast cancer remains unclear. We have prospectively measured circulating CSF1 using ELISA in 572 women with early breast cancer and in 688 women with benign breast lesions, and correlated these concentrations with overall survival (OS), nodal status, and other clinical and histological parameters. Serum CSF1 concentrations were significantly elevated in patients with early breast cancer when compared with those with benign tumors (P<0.0001). Within breast cancer patients, CSF1 was higher in women with axillary lymph nodes (P=0.03). Serum CSF1 correlated with tumor size (P=0.002), age (P<0.001), and Ki67 expression (P=0.006). Log CSF1 serum concentrations were predictive of poor survival in both univariate (hazard ratio (HR): 3.77, 95% CI: 1.65-8.65, P=0.002) and multivariate analyses (HR: 3.1, 95% CI: 1.03-9.33, P=0.04). Post- but not premenopausal women with CSF1 serum concentrations >873  pg/ml experienced a significantly poorer outcome (P=0.004 log-rank test). Serum CSF1 concentrations are elevated in women with malignant breast tumors. In early breast cancer, elevated serum CSF1 is associated with nodal involvement, and in postmenopausal women also with poor OS.

MerTK inhibition in tumor leukocytes decreases tumor growth and metastasis

MerTK, a receptor tyrosine kinase (RTK) of the TYRO3/AXL/MerTK family, is expressed in myeloid lineage cells in which it acts to suppress proinflammatory cytokines following ingestion of apoptotic material. Using syngeneic mouse models of breast cancer, melanoma, and colon cancer, we found that tumors grew slowly and were poorly metastatic in MerTK-/- mice. Transplantation of MerTK-/- bone marrow, but not wild-type bone marrow, into lethally irradiated MMTV-PyVmT mice (a model of metastatic breast cancer) decreased tumor growth and altered cytokine production by tumor CD11b+ cells. Although MerTK expression was not required for tumor infiltration by leukocytes, MerTK-/- leukocytes exhibited lower tumor cell-induced expression of wound healing cytokines, e.g., IL-10 and growth arrest-specific 6 (GAS6), and enhanced expression of acute inflammatory cytokines, e.g., IL-12 and IL-6. Intratumoral CD8+ T lymphocyte numbers were higher and lymphocyte proliferation was increased in tumor-bearing MerTK-/- mice compared with tumor-bearing wild-type mice. Antibody-mediated CD8+ T lymphocyte depletion restored tumor growth in MerTK-/- mice. These data demonstrate that MerTK signaling in tumor-associated CD11b+ leukocytes promotes tumor growth by dampening acute inflammatory cytokines while inducing wound healing cytokines. These results suggest that inhibition of MerTK in the tumor microenvironment may have clinical benefit, stimulating antitumor immune responses or enhancing immunotherapeutic strategies.

Molecular profiling predicts the existence of two functionally distinct classes of ovarian cancer stroma

Although stromal cell signaling has been shown to play a significant role in the progression of many cancers, relatively little is known about its importance in modulating ovarian cancer development. The purpose of this study was to investigate the process of stroma activation in human ovarian cancer by molecular analysis of matched sets of cancer and surrounding stroma tissues. RNA microarray profiling of 45 tissue samples was carried out using the Affymetrix (U133 Plus 2.0) gene expression platform. Laser capture microdissection (LCM) was employed to isolate cancer cells from the tumors of ovarian cancer patients (Cepi) and matched sets of surrounding cancer stroma (CS). For controls, ovarian surface epithelial cells (OSE) were isolated from the normal (noncancerous) ovaries and normal stroma (NS). Hierarchical clustering of the microarray data resulted in clear separations between the OSE, Cepi, NS, and CS samples. Expression patterns of genes encoding signaling molecules and compatible receptors in the CS and Cepi samples indicate the existence of two subgroups of cancer stroma (CS) with different propensities to support tumor growth. Our results indicate that functionally significant variability exists among ovarian cancer patients in the ability of the microenvironment to modulate cancer development.

Recruitment of monocytes/macrophages in different tumor microenvironments

After emigration from the bone marrow into the peripheral blood, monocytes enter tissues and differentiate into macrophages. Monocytes/macrophages have many roles in immune regulation, angiogenesis, and tumor metastasis and invasion. In addition, studies have revealed that these cells are essential to tumor progression. Recently, an accumulation of evidence has indicated that macrophages in distinct regions of tumor masses have distinct origins. For instance, classical monocytes appear to be a major source of macrophages in tumor epithelial, perivascular, and hypoxic regions. In contrast, non-classical monocytes are an important source of macrophages in the tumor perivascular region. During the past century, it has been demonstrated that several chemoattractants can regulate the recruitment of monocytes/macrophages to tumor sites. Despite the importance of monocytes/macrophages in tumor progression, there had been, until recently, no efforts to summarize receptor-ligand pairs between tumor-derived chemokines and corresponding receptors in monocytes in different microenvironments. In this review, we present a cohesive view of the distinct expression patterns of chemokine receptors in two different monocyte subsets (classical and non-classical monocytes) and describe their roles in monocyte/macrophage recruitment into distinct tumor microenvironments. This review provides insight into the behavior of monocytes/macrophages in different tumor microenvironments.

Reciprocal interactions between tumor-associated macrophages and CD44-positive cancer cells via osteopontin/CD44 promote tumorigenicity in colorectal cancer

PURPOSE

CD44 is of functional importance for tumor initiation and progression in colorectal cancer, but how this molecule benefits cancer cells from the tumor microenvironment, especially tumor-associated macrophages (TAM), remains poorly defined.

EXPERIMENTAL DESIGN

In vivo tumorigenic assays were conducted to assess the role of murine TAMs in the tumorigenesis of human colorectal cancer cells. Both in vitro and in vivo osteopontin (OPN) expression levels in TAMs were examined by immunohistochemistry, quantitative PCR, and Western blotting. Soft agar colony formation assays were used to estimate the clonogenicity of colorectal cancer cells that had received different treatments. The relationships between the expression levels of OPN, CD44v6, and CD68 and clinical prognosis were evaluated by tissue microarray analysis.

RESULTS

We found that macrophages, when coinjected or cocultured with CD44-positive colorectal cancer cells, were able to produce higher levels of OPN, which in turn facilitated the tumorigenicity and clonogenicity of the colorectal cancer cells. The knockdown of CD44 or treatment with blocking antibodies to CD44 attenuated OPN secretion. OPN, through binding to its receptor CD44, activated c-jun-NH(2)-kinase signaling and promoted the clonogenicity of colorectal cancer cells. Moreover, tissue microarray data have shown that OPN expression, in combination with CD44v6, has a negative correlation with colorectal cancer patient survival.

CONCLUSIONS

These results suggest that the OPN-CD44 interaction is important for colorectal cancer progression and could serve as a potential therapeutic target for the treatment of colorectal cancer.

Gastric carcinogenesis

Gastric cancer is the second most common cancer worldwide and the second most common cause of cancer-related deaths. Despite complete resection of gastric cancer and lymph node dissection, as well as improvements in chemotherapy and radiotherapy, there are still 700 000 gastric cancer-related deaths per year worldwide and more than 80% of patients with advanced gastric cancer die of the disease or recurrent disease within 1 year after diagnosis. None of the treatment modalities we have been applying today can influence the overall survival rates: at present, the overall 5-year relative survival rate for gastric cancer is about 28%. Cellular metaplasia due to chronic inflammation, injury and repair are the most documented processes for neoplasia. It appears that chronic inflammation stimulates tumor development and plays a critical role in initiating, sustaining and advancing tumor growth. It is also evident that not all inflammation is tumorigenic. Additional mutations can be acquired, and this leads to the cancer cell gaining a further growth advantage and acquiring a more malignant phenotype. Intestinalization of gastric units, which is called “intestinal metaplasia”; phenotypic antralization of fundic units, which is called “spasmolytic polypeptide-expressing metaplasia”; and the development directly from the stem/progenitor cell zone are three pathways that have been described for gastric carcinogenesis. Also, an important factor for the development of gastrointestinal cancers is peritumoral stroma. However, the initiating cellular event in gastric metaplasia is still controversial. Understanding gastric carcinogenesis and its precursor lesions has been under intense investigation, and our paper attempts to highlight recent progress in this field of cancer research.

The interaction between Siglec-15 and tumor-associated sialyl-Tn antigen enhances TGF-β secretion from monocytes/macrophages through the DAP12-Syk pathway

We previously demonstrated that Siglec-15, a member of the Siglec family of glycan-recognition proteins, is expressed on a subset of macrophages and preferentially recognizes the sialyl-Tn (sTn) antigen, a tumor-associated glycan structure. In this study, we report on the biological significance of the Siglec-15-mediated interaction between monocytes/macrophages and cancer cells. Siglec-15 is expressed on tumor-associated macrophages (TAMs) in various human tumor tissues. We further demonstrated that its expression is substantially elevated in macrophage colony-stimulating factor-induced M2-like macrophages, which produced more transforming growth factor-β (TGF-β) in response to sTn-positive cells than to negative cells. We designed a co-culture model of THP-1 (human monocytic leukemia) cells and H157 (human lung carcinoma) cells mimicking the interaction between monocytes/macrophages and cancer cells that recapitulated the enhanced TGF-β production in Siglec-15 expressing THP-1 cells by the cellular interaction with sTn expressing H157 cells. The enhanced TGF-β production required a direct interaction between the two cell lines through sialic acids. Siglec-15 associates with adaptor protein DNAX activation protein of 12 kDa (DAP12) at the binding determinant Lys(274) in the transmembrane domain and transduces a signal to spleen tyrosine kinase (Syk). The enhanced TGF-β secretion was significantly attenuated by Syk inhibitor treatment of THP-1 cells or by substitution of the Siglec-15 Lys(274) to Ala, which disrupts the molecular interaction between Siglec15 and DAP12. These findings indicate that Siglec-15 recognizes the tumoral sTn antigen and transduces a signal for enhanced TGF-β secretion in TAMs and further suggest that Siglec-15 on macrophages may contribute to tumor progression by the TGF-β-mediated modulation of intratumoral microenvironments.

The apoptotic function analysis of p53, Apaf1, Caspase3 and Caspase7 during the spermatogenesis of the Chinese fire-bellied newt Cynops orientalis

BACKGROUND

Spontaneous and stress-induced germ cell apoptosis during spermatogenesis of multicellular organisms have been investigated broadly in mammals. Spermatogenetic process in urodele amphibians was essentially like that in mammals in spite of morphological differences; however, the mechanism of germ cell apoptosis in urodele amphibians remains unknown. The Chinese fire-belly newt, Cynops orientalis, was an excellent organism for studying germ cell apoptosis due to its sensitiveness to temperature, strong endurance of starvation, and sensitive skin to heavy metal exposure.

METHODOLOGY/PRINCIPAL FINDINGS

TUNEL result showed that spontaneous germ cell apoptosis took place in normal newt, and severe stress-induced apoptosis occurred to spermatids and sperm in response to heat shock (40°C 2 h), cold exposure (4°C 12 h), cadmium exposure (Cd 36 h), and starvation stress. Quantitative reverse transcription polymerase chain reactions (qRT-PCR) showed that gene expression of Caspase3 or Caspase7 was obviously elevated after stress treatment. Apaf1 was not altered at its gene expression level, and p53 was significantly decreased after various stress treatment. Caspase assay demonstrated that Caspase-3, -8, -9 enzyme activities in newt testis were significantly elevated after heat shock (40°C 2 h), cold exposure (4°C 12 h), and cadmium exposure (Cd 36 h), while Caspase3 and Caspase8 activities were increased with Caspase9 significantly decreased after starvation treatment.

CONCLUSIONS/SIGNIFICANCE

Severe germ cell apoptosis triggered by heat shock, cold exposure, and cadmium exposure was Caspase3 dependent, which probably involved both extrinsic and intrinsic pathways. Apaf1 may be involved in this process without elevating its gene expression. But starvation-induced germ cell apoptosis was likely mainly through extrinsic pathway. p53 was probably not responsible for stress-induced germ cell apoptosis in newt testis. The intriguing high occurrence of spermatid and sperm apoptosis probably resulted from the sperm morphology and unique reproduction policy of Chinese fire-belly newt, Cynops orientalis.

FMS Kinase Inhibitors: Current Status and Future Prospects

FMS, first discovered as the oncogene responsible for Feline McDonough Sarcoma, is a type III receptor tyrosine kinase that binds to the macrophage or monocyte colony-stimulating factor (M-CSF or CSF-1). Signal transduction through that binding results in survival, proliferation, and differentiation of monocyte/macrophage lineage. Overexpression of CSF-1 and/or FMS has been implicated in a number of disease states such as the growth of metastasis of certain types of cancer, in promoting osteoclast proliferation in bone osteolysis, and many inflammatory disorders. Inhibition of CSF-1 and/or FMS may help treat these pathological conditions. This article reviews FMS gene, FMS kinase, CSF-1, IL-34, and their roles in bone osteolysis, cancer biology, and inflammation. Monoclonal antibodies, FMS crystal structure, and small molecule FMS kinase inhibitors of different chemical scaffolds are also reviewed.

Tumor lymphangiogenesis as a potential therapeutic target

Metastasis the spread of cancer cells to distant organs, is the main cause of death for cancer patients. Metastasis is often mediated by lymphatic vessels that invade the primary tumor, and an early sign of metastasis is the presence of cancer cells in the regional lymph node (the first lymph node colonized by metastasizing cancer cells from a primary tumor). Understanding the interplay between tumorigenesis and lymphangiogenesis (the formation of lymphatic vessels associated with tumor growth) will provide us with new insights into mechanisms that modulate metastatic spread. In the long term, these insights will help to define new molecular targets that could be used to block lymphatic vessel-mediated metastasis and increase patient survival. Here, we review the molecular mechanisms of embryonic lymphangiogenesis and those that are recapitulated in tumor lymphangiogenesis, with a view to identifying potential targets for therapies designed to suppress tumor lymphangiogenesis and hence metastasis.

Therapeutic applications of macrophage colony-stimulating factor-1 (CSF-1) and antagonists of CSF-1 receptor (CSF-1R) signaling

Macrophage-colony stimulating factor (CSF-1) signaling through its receptor (CSF-1R) promotes the differentiation of myeloid progenitors into heterogeneous populations of monocytes, macrophages, dendritic cells, and bone-resorbing osteoclasts. In the periphery, CSF-1 regulates the migration, proliferation, function, and survival of macrophages, which function at multiple levels within the innate and adaptive immune systems. Macrophage populations elicited by CSF-1 are associated with, and exacerbate, a broad spectrum of pathologies, including cancer, inflammation, and bone disease. Conversely, macrophages can also contribute to immunosuppression, disease resolution, and tissue repair. Recombinant CSF-1, antibodies against the ligand and the receptor, and specific inhibitors of CSF-1R kinase activity have been each been tested in a range of animal models and in some cases, in patients. This review examines the potential clinical uses of modulators of the CSF-1/CSF-1R system. We conclude that CSF-1 promotes a resident-type macrophage phenotype. As a treatment, CSF-1 has therapeutic potential in tissue repair. Conversely, inhibition of CSF-1R is unlikely to be effective in inflammatory disease but may have utility in cancer.

Glycosaminoglycan mimicry by COAM reduces melanoma growth through chemokine induction and function

Chlorite-oxidized oxyamylose (COAM), a glycosaminoglycan mimetic and potent antiviral agent, provided significant growth reduction of syngeneic murine B16-F1 melanoma tumors. A single early dose (100 μg, into the site of tumor cell inoculation) was sufficient to establish a persistent effect over 17 days (resected tumor volume of 78.3 mm(3) in COAM-treated mice compared to 755.2 mm(3) in the control cohort, i.e., 89.6% reduction of tumor volumes). COAM was a much better antitumoral agent than the polyanionic glycosaminoglycan heparin. COAM retained its antitumoral effect in lymphopenic mice, reinforcing the idea of myeloid cell involvement. Massive recruitment of myeloid cells into dermal air pouches in response to COAM and their increased presence in early-treated tumors indicated that mainly CD11b(+) GR-1(+) myeloid cells were attracted by COAM to exert antitumoral effects. Leukocyte chemotaxis was mediated by the chemokine system through the induction in B16-F1 cells of mouse granulocyte chemotactic protein-2/CXCL6 upon COAM treatment. Thus, COAM constitutes a novel tool to study the role of innate immune cells in the initial stages of tumor development and an example that innate immunostimulating glycosaminoglycan mimicry may be exploited therapeutically.

Leukocyte complexity predicts breast cancer survival and functionally regulates response to chemotherapy

Immune-regulated pathways influence multiple aspects of cancer development. In this article we demonstrate that both macrophage abundance and T-cell abundance in breast cancer represent prognostic indicators for recurrence-free and overall survival. We provide evidence that response to chemotherapy is in part regulated by these leukocytes; cytotoxic therapies induce mammary epithelial cells to produce monocyte/macrophage recruitment factors, including colony stimulating factor 1 (CSF1) and interleukin-34, which together enhance CSF1 receptor (CSF1R)-dependent macrophage infiltration. Blockade of macrophage recruitment with CSF1R-signaling antagonists, in combination with paclitaxel, improved survival of mammary tumor-bearing mice by slowing primary tumor development and reducing pulmonary metastasis. These improved aspects of mammary carcinogenesis were accompanied by decreased vessel density and appearance of antitumor immune programs fostering tumor suppression in a CD8+ T-cell-dependent manner. These data provide a rationale for targeting macrophage recruitment/response pathways, notably CSF1R, in combination with cytotoxic therapy, and identification of a breast cancer population likely to benefit from this novel therapeutic approach.

SIGNIFICANCE

These findings reveal that response to chemotherapy is in part regulated by the tumor immune microenvironment and that common cytotoxic drugs induce neoplastic cells to produce monocyte/macrophage recruitment factors, which in turn enhance macrophage infiltration into mammary adenocarcinomas. Blockade of pathways mediating macrophage recruitment, in combination with chemotherapy, significantly decreases primary tumor progression, reduces metastasis, and improves survival by CD8+ T-cell-dependent mechanisms, thus indicating that the immune microenvironment of tumors can be reprogrammed to instead foster antitumor immunity and improve response to cytotoxic therapy.

Inflammatory alterations of the extracellular matrix in the tumor microenvironment

Complex interactions between cancer cells and host stromal cells result in the formation of the "tumor microenvironment", where inflammatory alterations involve the infiltration of tumor-associated fibroblasts and inflammatory leukocytes that contribute to the acquisition of malignant characteristics, such as increased cancer cell proliferation, invasiveness, metastasis, angiogenesis, and avoidance of adaptive immunity. The microenvironment of a solid tumor is comprised not only of cellular compartments, but also of bioactive substances, including cytokines, growth factors, and extracellular matrix (ECM). ECM can act as a scaffold for cell migration, a reservoir for cytokines and growth factors, and a signal through receptor binding. During inflammation, ECM components and their degraded fragments act directly and indirectly as inflammatory stimuli in certain cases and regulate the functions of inflammatory and immune cells. One such ECM component, hyaluronan, has recently been implicated to modulate innate immune cell function through pattern recognition toll-like receptors and accelerate the recruitment and activation of tumor-associated macrophages in inflamed cancers. Here, we will summarize the molecular mechanism linking inflammation with ECM remodeling in the tumor microenvironment, with a particular emphasis on the role of hyaluronan in controlling the inflammatory response.

MRI of tumor-associated macrophages with clinically applicable iron oxide nanoparticles

PURPOSE

The presence of tumor-associated macrophages (TAM) in breast cancer correlates strongly with poor outcome. The purpose of this study was to develop a clinically applicable, noninvasive diagnostic assay for selective targeting and visualization of TAMs in breast cancer, based on magnetic resonanceI and clinically applicable iron oxide nanoparticles.

EXPERIMENTAL DESIGN

F4/80-negative mammary carcinoma cells and F4/80-positive TAMs were incubated with iron oxide nanoparticles and were compared with respect to magnetic resonance signal changes and iron uptake. MMTV-PyMT transgenic mice harboring mammary carcinomas underwent nanoparticle-enhanced magnetic resonance imaging (MRI) up to 1 hour and 24 hours after injection. The tumor enhancement on MRIs was correlated with the presence and location of TAMs and nanoparticles by confocal microscopy.

RESULTS

In vitro studies revealed that iron oxide nanoparticles are preferentially phagocytosed by TAMs but not by malignant tumor cells. In vivo, all tumors showed an initial contrast agent perfusion on immediate postcontrast MRIs with gradual transendothelial leakage into the tumor interstitium. Twenty-four hours after injection, all tumors showed a persistent signal decline on MRIs. TAM depletion via αCSF1 monoclonal antibodies led to significant inhibition of tumor nanoparticle enhancement. Detection of iron using 3,3'-diaminobenzidine-enhanced Prussian Blue staining, combined with immunodetection of CD68, localized iron oxide nanoparticles to TAMs, showing that the signal effects on delayed MRIs were largely due to TAM-mediated uptake of contrast agent.

CONCLUSION

These data indicate that tumor enhancement with clinically applicable iron oxide nanoparticles may serve as a new biomarker for long-term prognosis, related treatment decisions, and the evaluation of new immune-targeted therapies.

Macrophages, PPARs, and Cancer

Mononuclear phagocytes often function as control switches of the immune system, securing the balance between pro- and anti-inflammatory reactions. For this purpose and depending on the activating stimuli, these cells can develop into different subsets: proinflammatory classically activated (M1) or anti-inflammatory alternatively activated (M2) macrophages. The expression of the nuclear peroxisome proliferator-activated receptors (PPARs) is regulated by M1- or M2-inducing stimuli, and these receptors are generally considered to counteract inflammatory M1 macrophages, while actively promoting M2 activation. This is of importance in a tumor context, where M1 are important initiators of inflammation-driven cancers. As a consequence, PPAR agonists are potentially usefull for inhibiting the early phases of tumorigenesis through their antagonistic effect on M1. In more established tumors, the macrophage phenotype is more diverse, making it more difficult to predict the outcome of PPAR agonism. Overall, in our view current knowledge provides a sound basis for the clinical evaluation of PPAR ligands as chemopreventive agents in chronic inflammation-associated cancer development, while cautioning against the unthoughtful application of these agents as cancer therapeutics.

Mononuclear phagocyte heterogeneity in cancer: different subsets and activation states reaching out at the tumor site

Mononuclear phagocytes are amongst the most versatile cells of the body, contributing to tissue genesis and homeostasis and safeguarding the balance between pro- and anti-inflammatory reactions. Accordingly, these cells are notoriously heterogeneous, functioning in distinct differentiation forms (monocytes, MDSC, macrophages, DC) and adopting different activation states in response to a changing microenvironment. Accumulating evidence exists that mononuclear phagocytes contribute to all phases of the cancer process. These cells orchestrate the inflammatory events during de novo carcinogenesis, participate in tumor immunosurveillance, and contribute to the progression of established tumors. At the tumor site, cells such as tumor-associated macrophages (TAM) are confronted with different tumor microenvironments, leading to TAM subsets with specialized functions. A better refinement of the molecular and functional heterogeneity of tumor-associated mononuclear phagocytes might pave the way for novel cancer therapies that directly target these tumor-supporting cells.

Leukocyte complexity predicts breast cancer survival and functionally regulates response to chemotherapy

Immune-regulated pathways influence multiple aspects of cancer development. In this article we demonstrate that both macrophage abundance and T-cell abundance in breast cancer represent prognostic indicators for recurrence-free and overall survival. We provide evidence that response to chemotherapy is in part regulated by these leukocytes; cytotoxic therapies induce mammary epithelial cells to produce monocyte/macrophage recruitment factors, including colony stimulating factor 1 (CSF1) and interleukin-34, which together enhance CSF1 receptor (CSF1R)-dependent macrophage infiltration. Blockade of macrophage recruitment with CSF1R-signaling antagonists, in combination with paclitaxel, improved survival of mammary tumor-bearing mice by slowing primary tumor development and reducing pulmonary metastasis. These improved aspects of mammary carcinogenesis were accompanied by decreased vessel density and appearance of antitumor immune programs fostering tumor suppression in a CD8+ T-cell-dependent manner. These data provide a rationale for targeting macrophage recruitment/response pathways, notably CSF1R, in combination with cytotoxic therapy, and identification of a breast cancer population likely to benefit from this novel therapeutic approach.

SIGNIFICANCE

These findings reveal that response to chemotherapy is in part regulated by the tumor immune microenvironment and that common cytotoxic drugs induce neoplastic cells to produce monocyte/macrophage recruitment factors, which in turn enhance macrophage infiltration into mammary adenocarcinomas. Blockade of pathways mediating macrophage recruitment, in combination with chemotherapy, significantly decreases primary tumor progression, reduces metastasis, and improves survival by CD8+ T-cell-dependent mechanisms, thus indicating that the immune microenvironment of tumors can be reprogrammed to instead foster antitumor immunity and improve response to cytotoxic therapy.