Zvi G. Fridlender

Phenotypic Diversity and Plasticity in Circulating Neutrophil Subpopulations in Cancer

Controversy surrounds neutrophil function in cancer because neutrophils were shown to provide both pro- and antitumor functions. We identified a heterogeneous subset of low-density neutrophils (LDNs) that appear transiently in self-resolving inflammation but accumulate continuously with cancer progression. LDNs display impaired neutrophil function and immunosuppressive properties, characteristics that are in stark contrast to those of mature, high-density neutrophils (HDNs). LDNs consist of both immature myeloid-derived suppressor cells (MDSCs) and mature cells that are derived from HDNs in a TGF-β-dependent mechanism. Our findings identify three distinct populations of circulating neutrophils and challenge the concept that mature neutrophils have limited plasticity. Furthermore, our findings provide a mechanistic explanation to mitigate the controversy surrounding neutrophil function in cancer.

Transcriptomic Analysis Comparing Tumor-Associated Neutrophils with Granulocytic Myeloid-Derived Suppressor Cells and Normal Neutrophils

The role of myeloid cells in supporting cancer growth is well established. Most work has focused on myeloid-derived suppressor cells (MDSC) that accumulate in tumor-bearing animals, but tumor-associated neutrophils (TAN) are also known to be capable of augmenting tumor growth. However, little is known about their evolution, phenotype, and relationship to naïve neutrophils (NN) and to the granulocytic fraction of MDSC (G-MDSC). In the current study, a transcriptomics approach was used in mice to compare these cell types. Our data show that the three populations of neutrophils are significantly different in their mRNA profiles with NN and G-MDSC being more closely related to each other than to TAN. Structural genes and genes related to cell-cytotoxicity (i.e. respiratory burst) were significantly down-regulated in TAN. In contrast, many immune-related genes and pathways, including genes related to the antigen presenting complex (e.g. all six MHC-II complex genes), and cytokines (e.g. TNF-α, IL-1-α/β), were up-regulated in G-MDSC, and further up-regulated in TAN. Thirteen of the 25 chemokines tested were markedly up-regulated in TAN compared to NN, including striking up-regulation of chemoattractants for T/B-cells, neutrophils and macrophages. This study characterizes different populations of neutrophils related to cancer, pointing out the major differences between TAN and the other neutrophil populations.

Tumor-associated neutrophils (TAN) develop pro-tumorigenic properties during tumor progression

Abstract The role and characteristics of tumor-associated neutrophils (TAN) in cancer are poorly defined. We have recently shown that TAN can have anti-tumorigenic (N1) or pro-tumorigenic (N2) functions. An interesting unanswered question is how the phenotype of TAN is influenced by the ongoing evolvement of tumor microenvironment. We therefore studied the phenotype and effects of TAN at different time points during tumor progression. We used two models of murine tumor cancer cell lines—Lewis lung carcinoma (LLC) and AB12 (mesothelioma). Neutrophils were studied at early and late stages and compared to each other and to neutrophils from bone marrow/periphery of naïve mice. Although there was no difference in the number of neutrophils entering the tumor, we found that at early stages of tumor development, neutrophils were almost exclusively at the periphery of the tumor. Only at later stages, neutrophils were also found scattered among the tumor cells. We further found that TAN from early tumors are more cytotoxic toward tumor cells and produce higher levels of TNF-α, NO and H2O2. In established tumors, these functions are down-regulated and TAN acquire a more pro-tumorigenic phenotype. In line with this phenotype, only depletion of neutrophils at later stages of tumor development inhibited tumor growth, possibly due to their central location in the tumor. Our work adds another important layer to the understanding of neutrophils in cancer by further characterizing the changes in TAN during time. Additional research on the functional role of TAN and differences between subsets of TAN is currently underway.

CCL2 Blockade Augments Cancer Immunotherapy

Altering the immunosuppressive microenvironment that exists within a tumor will likely be necessary for cancer vaccines to trigger an effective antitumor response. Monocyte chemoattractant proteins (such as CCL2) are produced by many tumors and have both direct and indirect immunoinhibitory effects. We hypothesized that CCL2 blockade would reduce immunosuppression and augment vaccine immunotherapy. Anti-murine CCL2/CCL12 monoclonal antibodies were administered in three immunotherapy models: one aimed at the human papillomavirus E7 antigen expressed by a non-small cell lung cancer (NSCLC) line, one targeted to mesothelin expressed by a mesothelioma cell line, and one using an adenovirus-expressing IFN-alpha to treat a nonimmunogenic NSCLC line. We evaluated the effect of the combination treatment on tumor growth and assessed the mechanism of these changes by evaluating cytotoxic T cells, immunosuppressive cells, and the tumor microenvironment. Administration of anti-CCL2/CCL12 antibodies along with the vaccines markedly augmented efficacy with enhanced reduction in tumor volume and cures of approximately half of the tumors. The combined treatment generated more total intratumoral CD8+ T cells that were more activated and more antitumor antigen-specific, as measured by tetramer evaluation. Another important potential mechanism was reduction in intratumoral T regulatory cells. CCL2 seems to be a key proximal cytokine mediating immunosuppression in tumors. Its blockade augments CD8+ T-cell immune response to tumors elicited by vaccines via multifactorial mechanisms. These observations suggest that combining CCL2 neutralization with vaccines should be considered in future immunotherapy trials.

Systemic blockade of transforming growth factor-beta signaling augments the efficacy of immunogene therapy.

Locally produced transforming growth factor-beta (TGF-beta) promotes tumor-induced immunosuppression and contributes to resistance to immunotherapy. This article explores the potential for increased efficacy when combining immunotherapies with TGF-beta suppression using the TGF-beta type I receptor kinase inhibitor SM16. Adenovirus expressing IFN-beta (Ad.IFN-beta) was injected intratumorally once in established s.c. AB12 (mesothelioma) and LKR (lung cancer) tumors or intratracheally in a Kras orthotopic lung tumor model. Mice bearing TC1 (lung cancer) tumors were vaccinated with two injections of adenovirus expressing human papillomavirus-E7 (HPV-E7; Ad.E7). SM16 was administered orally in formulated chow. Tumor growth was assessed and cytokine expression and cell populations were measured in tumors and spleens by real-time PCR and flow cytometry. SM16 potentiated the efficacy of both immunotherapies in each of the models and caused changes in the tumor microenvironment. The combination of SM16 and Ad.IFN-beta increased the number of intratumoral leukocytes (including macrophages, natural killer cells, and CD8(+) cells) and increased the percentage of T cells expressing the activation marker CD25. SM16 also augmented the antitumor effects of Ad.E7 in the TC1 flank tumor model. The combination did not increase HPV-E7 tetramer-positive CD8(+) T cells in the spleens but did induce a marked increase in the tumors. Tumors from SM16-treated mice showed increased mRNA and protein for immunostimulatory cytokines and chemokines, as well as endothelial adhesion molecules, suggesting a mechanism for the increased intratumoral leukocyte trafficking. Blockade of the TGF-beta signaling pathway augments the antitumor effects of Ad.IFN-beta immune-activating or Ad.E7 vaccination therapy. The addition of TGF-beta blocking agents in clinical trials of immunotherapies may increase efficacy.

Monocyte chemoattractant protein-1 blockade inhibits lung cancer tumor growth by altering macrophage phenotype and activating CD8+ cells.

The role of chemokines in the pathogenesis of lung cancer has been increasingly appreciated. Monocyte chemoattractant protein-1 (MCP-1, also known as CCL2) is secreted from tumor cells and associated tumor stromal cells. The blockade of CCL2, as mediated by neutralizing antibodies, was shown to reduce tumorigenesis in several solid tumors, but the role of CCL2 in lung cancer remains controversial, with evidence of both protumorigenic and antitumorigenic effects. We evaluated the effects and mechanisms of CCL2 blockade in several animal models of non-small-cell lung cancer (NSCLC). Anti-murine-CCL2 monoclonal antibodies were administered in syngeneic flank and orthotopic models of NSCLC. CCL2 blockade significantly slowed the growth of primary tumors in all models studied, and inhibited lung metastases in a model of spontaneous lung metastases of NSCLC. In contrast to expectations, no significant effect of treatment was evident in the number of tumor-associated macrophages recruited into the tumor after CCL2 blockade. However, a change occurred in the polarization of tumor-associated macrophages to a more antitumor phenotype after CCL2 blockade. This was associated with the activation of cytotoxic CD8(+) T lymphocytes (CTLs). The antitumor effects of CCL2 blockade were completely lost in CB-17 severe combined immunodeficient mice or after CD8 T-cell depletion. Our data from NSCLC models show that CCL2 blockade can inhibit the tumor growth of primary and metastatic disease. The mechanisms of CCL2 blockade include an alteration of the tumor macrophage phenotype and the activation of CTLs. Our work supports further evaluation of CCL2 blockade in thoracic malignancies.

The HDAC inhibitor panobinostat (LBH589) inhibits mesothelioma and lung cancer cells in vitro and in vivo with particular efficacy for small cell lung cancer

Lung cancer is the leading cause of cancer deaths in the United States. Current therapies are inadequate. Histone deacetylase inhibitors (HDACi) are a recently developed class of anticancer agents that cause increased acetylation of core histones and nonhistone proteins leading to modulation of gene expression and protein activity involved in cancer cell growth and survival pathways. We examined the efficacy of the HDACi panobinostat (LBH589) in a wide range of lung cancers and mesotheliomas. Panobinostat was cytotoxic in almost all 37 cancer cell lines tested. IC50 and LD50 values were in the low nmol/L range (4–470 nmol/L; median, 20 nmol/L). Small cell lung cancer (SCLC) cell lines were among the most sensitive lines, with LD50 values consistently <25 nmol/L. In lung cancer and mesothelioma animal models, panobinostat significantly decreased tumor growth by an average of 62% when compared with vehicle control. Panobinostat was equally effective in immunocompetent and severe combined immunodeficiency mice, indicating that the inhibition of tumor growth by panobinostat was not due to direct immunologic effects. Panobinostat was, however, particularly effective in SCLC xenografts, and the addition of the chemotherapy agent etoposide augmented antitumor effects. Protein analysis of treated tumor biopsies revealed elevated amounts of cell cycle regulators such as p21 and proapoptosis factors, such as caspase 3 and 7 and cleaved poly[ADP-ribose] polymerase, coupled with decreased levels of antiapoptotic factors such as Bcl-2 and Bcl-XL. These studies together suggest that panobinostat may be a useful adjunct in the treatment of thoracic malignancies, especially SCLC. [Mol Cancer Ther 2009;8(8):2221–31]

Changes in the local tumor microenvironment in recurrent cancers may explain the failure of vaccines after surgery

Each year, more than 700,000 people undergo cancer surgery in the United States. However, more than 40% of those patients develop recurrences and have a poor outcome. Traditionally, the medical community has assumed that recurrent tumors arise from selected tumor clones that are refractory to therapy. However, we found that tumor cells have few phenotypical differences after surgery. Thus, we propose an alternative explanation for the resistance of recurrent tumors. Surgery promotes inhibitory factors that allow lingering immunosuppressive cells to repopulate small pockets of residual disease quickly. Recurrent tumors and draining lymph nodes are infiltrated with M2 (CD11b+F4/80hiCD206hi and CD11b+F4/80hiCD124hi) macrophages and CD4+Foxp3+ regulatory T cells. This complex network of immunosuppression in the surrounding tumor microenvironment explains the resistance of tumor recurrences to conventional cancer vaccines despite small tumor size, an intact antitumor immune response, and unaltered cancer cells. Therapeutic strategies coupling antitumor agents with inhibition of immunosuppressive cells potentially could impact the outcomes of more than 250,000 people each year.

B-cell depletion using an anti-CD20 antibody augments antitumor immune responses and immunotherapy in nonhematopoetic murine tumor models.

The role played by B cells in cancer biology is complex and somewhat controversial. Previous studies using genetically engineered mice suggest that B cells may be immunosuppressive and inhibit tumor rejection. However, the effects of B-cell depletion employing an antibody in mice bearing solid tumors has not been tested owing to difficulties in making an effective antimouse CD20 antibody (similar to rituximab). Injection of a newly developed antimouse CD20 antibody was effective in depleting circulating B cells from blood and lymph nodes, although depletion was less complete in the spleen. B-cell depletion slowed the growth of new solid tumors (not expressing CD20) and retarded the growth of established tumors but did not induce tumor regression. However, when the antibody was combined with an active immunotherapy approach using an adenovirus vaccine expressing the human papilloma virus-E7 gene (Ad.E7) in mice bearing TC1 tumors (murine lung cancer cells expressing human papilloma virus-E7), we noted enhanced antitumor effects and increased numbers of tetramer+/CD8+ T cells within the spleens and activated CD8+ T cells within tumors. B-cell depletion using an anti-CD20 antibody was thus effective in retarding tumor growth in multiple solid tumor models and augmenting immunotherapy in a tumor vaccine model. These studies raise the possibility that B-cell depletion may be a useful adjunct in human immunotherapy trials.

Telomerase activity in bleomycin-induced epithelial cell apoptosis and lung fibrosis.

Epithelial cell injury and apoptosis are recognised as early features in idiopathic pulmonary fibrosis and bleomycin-induced fibrosis in mice. Telomerase is a known apoptosis-alleviating factor. The role of telomerase was studied during bleomycin-induced lung epithelial cell (LEC) apoptosis in vitro in a mouse LEC line, and in vivo in LECs isolated from bleomycin-treated mice. The current authors evaluated changes in murine telomerase reverse transcriptase (mTERT) mRNA levels and changes in telomerase activity with the TRAPeze Detection Kit, telomeric length with the TeloTTAGGG Telomere Length Kit, and LEC apoptosis with FACScan and 4,6-diamino-2-phenylindole dihydrochloride stain. There was a significant elevation in mTERT mRNA and a transient 41% increase in telomerase activity 24 h after in vitro bleomycin treatment. At 72 h, telomerase activity had fallen to 26% below levels in untreated cells. Reduction of telomerase activity over time, or by direct inhibition, significantly elevated LEC apoptosis. No change in average telomeric length was noted. In vivo, telomerase activity of LECs from bleomycin-treated mice increased at 7 and 14 days. In conclusion, telomerase activity may play a protective role against robust bleomycin-induced lung epithelial cell apoptosis. Moreover, stabilising telomerase activity may decrease epithelial cell apoptosis and the resulting lung fibrosis.