Diversity and plasticity are hallmarks of cells of the monocyte-macrophage lineage. In response to IFNs, Toll-like receptor engagement, or IL-4/IL-13 signaling, macrophages undergo M1 (classical) or M2 (alternative) activation, which represent extremes of a continuum in a universe of activation states. Progress has now been made in defining the signaling pathways, transcriptional networks, and epigenetic mechanisms underlying M1-M2 or M2-like polarized activation. Functional skewing of mononuclear phagocytes occurs in vivo under physiological conditions (e.g., ontogenesis and pregnancy) and in pathology (allergic and chronic inflammation, tissue repair, infection, and cancer). However, in selected preclinical and clinical conditions, coexistence of cells in different activation states and unique or mixed phenotypes have been observed, a reflection of dynamic changes and complex tissue-derived signals. The identification of mechanisms and molecules associated with macrophage plasticity and polarized activation provides a basis for macrophage-centered diagnostic and therapeutic strategies.

/pdf/macrophage-plasticity-and-polarization-in-vivo-veritas-3j0n8qsu6m.pdf

Macrophage plasticity and polarization: in vivo veritas

Macrophage Diversity Enhances Tumor Progression and Metastasis

Tumor-associated macrophages: from mechanisms to therapy.

Macrophages are prominent in the stromal compartment of virtually all types of malignancy. These highly versatile cells respond to the presence of stimuli in different parts of tumors with the release of a distinct repertoire of growth factors, cytokines, chemokines, and enzymes that regulate tumor growth, angiogenesis, invasion, and/or metastasis. The distinct microenvironments where tumor-associated macrophages (TAM) act include areas of invasion where TAMs promote cancer cell motility, stromal and perivascular areas where TAMs promote metastasis, and avascular and perinecrotic areas where hypoxic TAMs stimulate angiogenesis. This review will discuss the evidence for differential regulation of TAMs in these microenvironments and provide an overview of current attempts to target or use TAMs for therapeutic purposes. (Cancer Res 2006; 66(2): 605-12)

https://cancerres.aacrjournals.org/content/canres/66/2/605.full.pdf

Distinct Role of Macrophages in Different Tumor Microenvironments

Functions of individual matrix metalloproteinases (MMPs) differentially expressed by tumor cells and stromal cells, are finely regulated by their spatial as well as temporal interactions with distinct cellular and extracellular components of the tumor microenvironment and also distant pre-metastatic sites. Certain aspects of MMP involvement in tumor metastasis such as tumor-induced angiogenesis, tumor invasion, and establishment of metastatic foci at the secondary site, have received extensive attention that resulted in an overwhelming amount of experimental and observational data in favor of critical roles of MMPs in these processes. In particular, dependency of tumor angiogenesis on the activity of MMPs, especially that of MMP-9, renders this step possibly the most effective target of synthetic MMP inhibitors. MMP functioning in other stages of metastasis, including the escape of individual tumor cells from the primary tumor, their intravasation, survival in circulation, and extravasation at the secondary site, have not yet received enough consideration, resulting in insufficient or controversial data. The major pieces of evidence that are most compelling and clearly determine the role and involvement of MMPs in the metastatic cascade are provided by molecular genetic studies employing knock-out or transgenic animals and tumor cell lines, modified to overexpress or downregulate a specific MMP. Findings from all of these studies implicate different functional mechanisms for both tumor and stromal MMPs during distinct steps of the metastatic cascade and indicate that MMPs can exhibit pro-metastatic as well as anti-metastatic roles depending on their nature and the experimental setting. This dual function of individual MMPs in metastasis has become a major focus of this review.

Matrix metalloproteinases and tumor metastasis

Colony-stimulating factor (CSF)-1 is the primary regulator of tissue macrophage production. CSF-1 expression is correlated with poor prognosis in breast cancer and is believed to enhance mammary tumor progression and metastasis through the recruitment and regulation of tumor-associated macrophages. Macrophages produce matrix metalloproteases (MMPs) and vascular endothelial growth factor, which are crucial for tumor invasion and angiogenesis. Given the important role of CSF-1, we hypothesized that blockade of CSF-1 or the CSF-1 receptor (the product of the c-fms proto-oncogene) would suppress macrophage infiltration and mammary tumor growth. Human MCF-7 mammary carcinoma cell xenografts in mice were treated with either mouse CSF-1 antisense oligonucleotide for 2 weeks or five intratumoral injections of either CSF-1 small interfering RNAs or c-fms small interfering RNAs. These treatments suppressed mammary tumor growth by 50%, 45%, and 40%, respectively, and selectively down-regulated target protein expression in tumor lysates. Host macrophage infiltration; host MMP-12, MMP-2, and vascular endothelial growth factor A expression; and endothelial cell proliferation within tumors of treated mice were decreased compared with tumors in control mice. In addition, mouse survival significantly increased after CSF-1 blockade. These studies demonstrate that CSF-1 and CSF-1 receptor are potential therapeutic targets for the treatment of mammary cancer.

https://cancerres.aacrjournals.org/content/canres/64/15/5378.full.pdf

Colony-Stimulating Factor-1 Blockade by Antisense Oligonucleotides and Small Interfering RNAs Suppresses Growth of Human Mammary Tumor Xenografts in Mice

The interplay between malignant and stromal cells is essential in tumorigenesis. We have previously shown that colony-stimulating factor (CSF)-1, matrix metalloprotease (MMP)-2, and vascular endothelial growth factor (VEGF)-A production by stromal cells is enhanced by CSF-1-negative SW620 colon cancer cells. In the present study, the mechanisms by which colon cancer cells up-regulate host factors to promote tumorigenesis were investigated. Profiling of tumor cell cytokine expression in SW620 tumor xenografts in nude mice showed increased human tumor necrosis factor (TNF)-alpha mRNA expression with tumor growth. Incubation of macrophages with small interfering (si) RNAs directed against TNF-alpha or TNF-alpha-depleted SW620 cell conditioned medium versus SW620 cell conditioned medium failed to support mouse macrophage proliferation, migration, and expression of CSF-1, VEGF-A, and MMP-2 mRNAs. Consistent with these results, human TNF-alpha gene silencing decreased mouse macrophage TNF-alpha, CSF-1, MMP-2, and VEGF-A mRNA expression in macrophages cocultured with human cancer cells. In addition, inhibition of human TNF-alpha or mouse CSF-1 expression by siRNA reduced tumor growth in SW620 tumor xenografts in mice. These results suggest that colon cancer cell-derived TNF-alpha stimulates TNF-alpha and CSF-1 production by macrophages, and that CSF-1, in turn, induces macrophage VEGF-A and MMP-2 in an autocrine manner. Thus, interrupting tumor cell-macrophage communication by targeting TNF-alpha may provide an alternative therapeutic approach for the treatment of colon cancer.

https://cancerres.aacrjournals.org/content/canres/67/3/1038.full.pdf

Colon Cancer Cell–Derived Tumor Necrosis Factor-α Mediates the Tumor Growth–Promoting Response in Macrophages by Up-regulating the Colony-Stimulating Factor-1 Pathway

Deregulated Rho GTPases Rac1 and Cdc42 have been discovered in various tumors, including prostate and Rac protein expression significantly increases in prostate cancer. The Rac and Cdc42 pathways promote the uncontrolled proliferation, invasion and metastatic properties of human cancer cells. We synthesized the novel compound AZA1 based on structural information of the known Rac1 inhibitor NSC23766. In the current study we investigated the effects of inhibition of these pathways by AZA1 on prostate tumorigenicity by performing preclinical studies using a xenograft mouse model of prostate cancer. In androgen-independent prostate cancer cells, AZA1 inhibited both Rac1 and Cdc42 but not RhoA GTPase activity in a dose-dependent manner and blocked cellular migration and proliferation. Cyclin D1 expression significantly decreased following Rac1/Cdc42 inhibition in prostate cancer cells. AZA1 treatment also down-regulated PAK and AKT activity in prostate cancer cells, associated with induction of the pro-apoptotic function of BAD by suppression of serine-112 phosphorylation. Daily systemic administration of AZA1 for 2 weeks reduced growth of human 22Rv1 prostate tumor xenografts in mice and improved the survival of tumor-bearing animals significantly. These data suggest a role of AZA1 in blocking Rac1/Cdc42-dependent cell cycle progression, cancer cell migration and increase of cancer cell apoptosis involving down-regulation of the AKT and PAK signaling pathway in prostate cancer cells. We therefore propose that a small-molecule inhibitor therapy targeting Rac1/Cdc42 Rho GTPase signaling pathways may be used as a novel treatment for patients with advanced prostate cancer.

/pdf/a-rac1-cdc42-gtpase-specific-small-molecule-inhibitor-5eay3zsnth.pdf

A Rac1/Cdc42 GTPase-specific small molecule inhibitor suppresses growth of primary human prostate cancer xenografts and prolongs survival in mice.

Rho GTPases play important roles in cytoskeleton organization, cell cycle progression and are key regulators of tumor progression. Strategies to modulate increased Rho GTPase activities during cancer progression could have therapeutic potential. We report here the characterization of a Cdc42-selective small-molecule inhibitor AZA197 for the treatment of colon cancer that was developed based on structural information known from previously developed compounds affecting Rho GTPase activation. We investigated the effects of AZA197 treatment on RhoA, Rac1 and Cdc42 activities and associated molecular mechanisms in colon cancer cells in vitro. Therapeutic effects of AZA197 were examined in vivo using a xenograft mouse model of SW620 human colon cancer cells. After treatment, tumors were excised and processed for Ki-67 staining, TUNEL assays and Western blotting to evaluate proliferative and apoptotic effects induced by AZA197. In SW620 and HT-29 human colon cancer cells, AZA197 demonstrated selectivity for Cdc42 without inhibition of Rac1 or RhoA GTPases from the same family. AZA197 suppressed colon cancer cell proliferation, cell migration and invasion and increased apoptosis associated with down-regulation of the PAK1 and ERK signaling pathways in vitro. Furthermore, systemic AZA197 treatment reduced tumor growth in vivo and significantly increased mouse survival in SW620 tumor xenografts. Ki-67 staining and tissue TUNEL assays showed that both inhibition of cell proliferation and induction of apoptosis associated with reduced PAK/ERK activation contributed to the AZA197-induced therapeutic effects in vivo. These data indicate the therapeutic potential of the small-molecule inhibitor AZA197 based on targeting Cdc42 GTPase activity to modulate colorectal cancer growth.

/pdf/targeting-cdc42-with-the-small-molecule-drug-aza197-jd4upgdekp.pdf

Targeting Cdc42 with the small molecule drug AZA197 suppresses primary colon cancer growth and prolongs survival in a preclinical mouse xenograft model by downregulation of PAK1 activity

The molecular mechanisms of tumor-host interactions that render neuroblastoma (NB) cells highly invasive are unclear. Cancer cells upregulate host stromal cell colony-stimulating factor-1 (CSF-1) production to recruit tumor-associated macrophages (TAMs) and accelerate tumor growth by affecting extracellular matrix remodeling and angiogenesis. By coculturing NB with stromal cells in vitro, we showed the importance of host CSF-1 expression for macrophage recruitment to NB cells. To examine this interaction in NB in vivo, mice bearing human CSF-1-expressing SK-N-AS and CSF-1-negative SK-N-DZ NB xenografts were treated with intratumoral injections of small interfering RNAs directed against mouse CSF-1. Significant suppression of both SK-N-AS and SK-N-DZ NB growth by these treatments was associated with decreased TAM infiltration, matrix metalloprotease (MMP)-12 levels and angiogenesis compared to controls, while expression of tissue inhibitors of MMPs increased following mouse CSF-1 blockade. Furthermore, Tie-2-positive and -negative TAMs recruited by host CSF-1 were identified in NB tumor tissue by confocal microscopy and flow cytometry. However, host-CSF-1 blockade prolonged survival only in CSF-1-negative SK-N-DZ NB. These studies demonstrated that increased CSF-1 production by host cells enhances TAM recruitment and NB growth and that the CSF-1 phenotype of NB tumor cells adversely affects survival.

/pdf/stromal-cell-derived-csf-1-blockade-prolongs-xenograft-z3ptruw6oi.pdf

Karin Zins

Papers

Colony-Stimulating Factor-1 Blockade by Antisense Oligonucleotides and Small Interfering RNAs Suppresses Growth of Human Mammary Tumor Xenografts in Mice

Colon Cancer Cell–Derived Tumor Necrosis Factor-α Mediates the Tumor Growth–Promoting Response in Macrophages by Up-regulating the Colony-Stimulating Factor-1 Pathway

A Rac1/Cdc42 GTPase-specific small molecule inhibitor suppresses growth of primary human prostate cancer xenografts and prolongs survival in mice.

Targeting Cdc42 with the small molecule drug AZA197 suppresses primary colon cancer growth and prolongs survival in a preclinical mouse xenograft model by downregulation of PAK1 activity

Stromal cell-derived CSF-1 blockade prolongs xenograft survival of CSF-1-negative neuroblastoma