CC chemokine ligand 2 (CCL2) promotes prostate cancer tumorigenesis and metastasis. Cytokine Growth Factor Rev. 2010;21:41-48. [PMID: 20005149 DOI: 10.1016/j.cytogfr.2009.11.009]

Cancer-promoting tumor-associated macrophages: new vistas and open questions

Tumor-associated macrophages (TAMs) are key components of the tumor macroenvironment. Cancer- and host cell-derived signals generally drive the functions of TAMs towards an M2-like polarized, tumor-propelling mode; however, when appropriately re-educated. TAMs also have the potential to elicit tumor destructive reactions. Here, we discuss recent advances regarding the immunobiology of TAMs and highlight open questions including the mechanisms of their accumulation (recruitment versus proliferation), their diversity and how to best therapeutically target these cells.

Expression of antigen processing and presenting molecules in brain metastasis of breast cancer

Defects in human leukocyte antigen class I antigen processing machinery (APM) component expression can have a negative impact on the clinical course of tumors and the response to T cell-based immunotherapy. Since brain metastases of breast cancer are of increasing clinical significance, the APM component expression levels and CD8(+) T cell infiltration patterns were analyzed in primary breast and metastatic brain lesions of breast cancer by immunohistochemistry. Comparison of unpaired 50 primary and 33 brain metastases showed lower expression of β2-microglobulin, transporter associated with antigen processing (TAP) 1, TAP2 and calnexin in the brain lesions. Although no significant differences were found in APM component scores between primary breast and brain lesions in 15 paired cases, primary breast lesions of which patients eventually developed brain metastases showed lower levels of β2-microglobulin, TAP1 and calnexin compared with breast lesions without known brain metastases. The extent of CD8(+) T cell infiltration was significantly higher in the lesions without metastasis compared with the ones with brain metastases, and was positively associated with the expression of TAP1 and calnexin. Furthermore, mouse tumor cells stably transfected with silencing hairpin (sh)RNA for TAP1 demonstrated a decreased susceptibility to cytotoxic T lymphocytes in vitro and enhanced spontaneous brain metastasis in vivo. These data support the functional significance of TAP1 expression in tumor cells. Taken together, our data suggest that patients with low or defective TAP1 or calnexin in primary breast cancers may be at higher risks for developing brain metastasis due to the defects in T cell-based immunosurveillance.

The tumor microenvironment: part 1

For years the mutated, highly proliferating neoplastic cells were presented as the only important agent in tumors; however, during the last 3–4 decades it has become clear that the microenvironment of the cancer cells plays a determinative role in the malignant evolution of neoplasia. Cancers are in fact heterogeneous entities containing, in addition to the neoplastic cell component, cells derived of multiple lineages (fibroblasts, endothelial cells lining blood and lymphatic vessels, pericytes, adipocytes and immune system cells belonging to both innate and adaptive responses), as well as the extracellular matrix, with a large variety of soluble molecules of biological importance, constituting a complex organ-like structure. The tumor microenvironment consists in a tissue that may have a predictive significance for tumor behavior and response to therapy.

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.

MicroRNAs associated with metastatic prostate cancer

Objective

Metastasis is the most common cause of death of prostate cancer patients. Identification of specific metastasis biomarkers and novel therapeutic targets is considered essential for improved prognosis and management of the disease. MicroRNAs (miRNAs) form a class of non-coding small RNA molecules considered to be key regulators of gene expression. Their dysregulation has been shown to play a role in cancer onset, progression and metastasis, and miRNAs represent a promising new class of cancer biomarkers. The objective of this study was to identify down- and up-regulated miRNAs in prostate cancer that could provide potential biomarkers and/or therapeutic targets for prostate cancer metastasis.

Methods

Next generation sequencing technology was applied to identify differentially expressed miRNAs in a transplantable metastatic versus a non-metastatic prostate cancer xenograft line, both derived from one patient's primary cancer. The xenografts were developed via subrenal capsule grafting of cancer tissue into NOD/SCID mice, a methodology that tends to preserve properties of the original cancers (e.g., tumor heterogeneity, genetic profiles).

Results

Differentially expressed known miRNAs, isomiRs and 36 novel miRNAs were identified. A number of these miRNAs (21/104) have previously been reported to show similar down- or up-regulation in prostate cancers relative to normal prostate tissue, and some of them (e.g., miR-16, miR-34a, miR-126*, miR-145, miR-205) have been linked to prostate cancer metastasis, supporting the validity of the analytical approach.

Conclusions

The use of metastatic and non-metastatic prostate cancer subrenal capsule xenografts derived from one patient's cancer makes it likely that the differentially expressed miRNAs identified in this study include potential biomarkers and/or therapeutic targets for human prostate cancer metastasis.

Recombinant VP1, an Akt inhibitor, suppresses progression of hepatocellular carcinoma by inducing apoptosis and modulation of CCL2 production

Background

The application of viral elements in tumor therapy is one facet of cancer research. Recombinant capsid protein VP1 (rVP1) of foot-and-mouth disease virus has previously been demonstrated to induce apoptosis in cancer cell lines. Here, we aim to further investigate its apoptotic mechanism and possible anti-metastatic effect in murine models of hepatocellular carcinoma (HCC), one of the most common human cancers worldwide.

Methodology/Principal Findings

Treatment with rVP1 inhibited cell proliferation in two murine HCC cell lines, BNL and Hepa1-6, with IC₅₀ values in the range of 0.1–0.2 µM. rVP1 also induced apoptosis in these cells, which was mediated by Akt deactivation and dissociation of Ku70-Bax, and resulted in conformational changes and mitochondrial translocation of Bax, leading to the activation of caspases-9, -3 and -7. Treatment with 0.025 µM rVP1, which did not affect the viability of normal hepatocytes, suppressed cell migration and invasion via attenuating CCL2 production. The production of CCL2 was modulated by Akt-dependent NF-κB activation that was decreased after rVP1 treatment. The in vivo antitumor effects of rVP1 were assessed in both subcutaneous and orthotopic mouse models of HCC in immune-competent BALB/c mice. Intratumoral delivery of rVP1 inhibited subcutaneous tumor growth as a result of increased apoptosis. Intravenous administration of rVP1 in an orthotopic HCC model suppressed tumor growth, inhibited intra-hepatic metastasis, and prolonged survival. Furthermore, a decrease in the serum level of CCL2 was observed in rVP1-treated mice.

Conclusions/Significance

The data presented herein suggest that, via inhibiting Akt phosphorylation, rVP1 suppresses the growth, migration, and invasion of murine HCC cells by inducing apoptosis and attenuating CCL2 production both in vitro and in vivo. Recombinant protein VP1 thus has the potential to be developed as a new therapeutic agent for HCC.

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.

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.

Identification of novel markers for the diagnosis of malignant pleural mesothelioma

The diagnosis of malignant pleural mesothelioma is difficult, with the most common differential diagnoses being benign pleural diseases and metastatic adenocarcinomas (ADCA). To identify novel markers that would be able to improve diagnostic accuracy, we performed a genome-wide gene expression analysis on tumor cell lines established from pleural effusions (malignant pleural mesothelioma and lung ADCA). This analysis led to the identification of genes encoding novel and pertinent cellular and soluble markers, for which the expression was validated by real-time RT-PCR. Immunohistochemical staining of tumor biopsy specimens with anti-type III collagen antibodies showed positive labeling for mesothelioma cells but not for ADCA cells. Using enzyme-linked immunosorbent assay, we showed that the C-C motif chemokine 2 (CCL2) concentration was significantly higher in pleural effusions from patients with mesothelioma (n = 61) than in subjects with ADCA (n = 25) or with benign pleural effusions (n = 15): median (interquartile range) = 2.99 ng/ml (1.76 to 6.01) vs 0.99 ng/ml (0.51 to 1.83) and 1.47 ng/ml (0.80 to 1.56), respectively, P < 0.0001. Conversely, the galectin-3 concentration was lower in mesothelioma: 11.50 ng/ml (6.73 to 23.53) vs 24.74 ng/ml (20.42 to 70.35) and 17.64 ng/ml (14.81 to 24.68), respectively, P < 0.0001. The areas under the curve for CCL2 were 0.8030 and 0.7716 for the differentiation of mesothelioma from ADCA or benign pleural effusions, respectively. Similarly, the areas under the curve obtained for galectin-3 were 0.7980 and 0.6923, respectively. In conclusion, type III collagen, CCL2, and galectin-3 are promising new diagnostic markers for mesothelioma.

GM-CSF-based fusion cytokines as ligands for immune modulation

Chromosomal translocations that combine distinct functional domains of unrelated proteins are an experiment in nature. They demonstrate how endogenous regulatory checkpoints can be overridden by altered cell biochemistry, informing a means to engineering an aberrant signal that the cell is incapable of counterregulating. Thus, our laboratory and others have synthesized fusions of GM-CSF with peptides, ILs, and chemokines, which we have termed fusokines, with the aim of inducing an enhanced immune response against cancer, aiming to overcome the maladapted biological processes causing disease. In doing so, we found that these fusokines did not behave as merely the sum of their natural unfused counterparts, but as entirely novel ligands co-opting their cognate receptor to communicate a unique message to responsive cellular targets. In this review, we discuss how fusion proteins combining different bioactive ligands can alter immune responses and briefly discuss the regulatory pathways that they circumvent.

Leukocytes as paracrine regulators of metastasis and determinants of organ-specific colonization

It is now well recognized that tumor cell-host interactions regulate all aspects of cancer development. Amongst the various host response programs that facilitate primary cancer development, an emerging body of literature points to a critical role for leukocytes and their soluble mediators as regulating discrete events during primary tumor development and metastasis. This review focuses on the multiple aspects of leukocytes and their effector molecules as regulators of the metastatic process.

Tumor infiltrating regulatory T cells: tractable targets for immunotherapy

Several studies have linked tumor-infiltration by regulatory T cells with poor patient outcome. Targeting the mechanisms by which regulatory T cells traffic to and persist in the tumor may circumvent tumor immune-escape by de-restricting T cell-mediated cytotoxicity. In this review, we describe the principle axes that govern regulatory T cell migration and the mechanisms that underpin their immunosuppressive activity in cancer. Inhibiting either the migration or function of regulatory T cells may enhance host-anti-cancer immune responses and as such are attractive and tractable targets for therapeutic intervention.

Inherited variants in the chemokine CCL2 gene and prostate cancer aggressiveness in a Caucasian cohort

PURPOSE

Though C-C chemokine ligand 2 (CCL2) has been shown to play a pivotal role in prostate cancer tumorigenesis and invasion, the role of inherited variation in the CCL2 gene in prostate cancer progression and metastases remains unanswered. This study is aimed to determine the influence of CCL2 germline variants on prostate cancer aggressiveness.

EXPERIMENTAL DESIGN

We performed an association study between six single nucleotide polymorphisms (SNP) in the CCL2 gene and prostate cancer clinicopathologic variables in a large hospital-based Caucasian patient cohort (N = 4,073).

RESULTS

Genetic variation at CCL2 is associated with markers of disease aggressiveness. Three SNPs, each in strong linkage disequilibrium, are associated with a higher (>7) biopsy Gleason score: CCL2 -1811 A/G, -2835 A/C, and +3726 T/C (P = 0.01, 0.03, and 0.04, respectively). The CCL2 -1811 G allele is additionally associated with advanced pathologic stages in patients who underwent radical prostatectomy (P = 0.04). In haplotype analysis, we found that the frequency of a common haplotype, H5, was higher among patients with D'Amico good risk features (P(permutation) = 0.04).

CONCLUSIONS

These results support the influence of CCL2 variants on prostate cancer development and progression.

The tumor-immune microenvironment and response to radiation therapy

Chemotherapy and radiation therapy (RT) are standard therapeutic modalities for patients with cancer, including breast cancer. Historic studies examining tissue and cellular responses to RT have predominantly focused on damage caused to proliferating malignant cells leading to their death. However, there is increasing evidence that RT also leads to significant alterations in the tumor microenvironment, particularly with respect to effects on immune cells infiltrating tumors. This review focuses on tumor-associated immune cell responses following RT and discusses how immune responses may be modified to enhance durability and efficacy of RT.

Inflammation-mediated promotion of invasion and metastasis

Inflammation has been suggested to represent the seventh hallmark of cancer. Myelomonocytic cells are a key component of cancer-related inflammation. Tumor-associated macrophages and their mediators affect key elements in the multistep process of invasion and metastasis, from interaction with the extracellular matrix to the construction of a pre-metastatic niche. Evidence indicating that inflammatory mediators affect genetic stability and cause persistent epigenetic alterations suggests that inflammatory components of the tumor microenvironment impacts on fundamental mechanisms responsible for the generation of metastatic variants. These results provide impetus for efforts aimed at translating cancer-related inflammation into diagnostic-prognostic markers and innovative therapeutic strategies.

Targeting chemokine (C-C motif) ligand 2 (CCL2) as an example of translation of cancer molecular biology to the clinic

Chemokines are a family of small and secreted proteins that play pleiotropic roles in inflammation-related pathological diseases, including cancer. Among the identified 50 human chemokines, chemokine (C-C motif) ligand 2 (CCL2) is of particular importance in cancer development since it serves as one of the key mediators of interactions between tumor and host cells. CCL2 is produced by cancer cells and multiple different host cells within the tumor microenvironment. CCL2 mediates tumorigenesis in many different cancer types. For example, CCL2 has been reported to promote prostate cancer cell proliferation, migration, invasion, and survival, via binding to its functional receptor CCR2. Furthermore, CCL2 induces the recruitment of macrophages and induces angiogenesis and matrix remodeling. Targeting CCL2 has been demonstrated as an effective therapeutic approach in preclinical prostate cancer models, and currently, neutralizing monoclonal antibody against CCL2 has entered into clinical trials in prostate cancer. In this chapter, targeting CCL2 in prostate cancer will be used as an example to show translation of laboratory findings from cancer molecular biology to the clinic.