Recent efforts in brain tumor research have been directed towards the modulation of the immune system for therapeutic interventions. Several human cancers, including gliomas, are infiltrated with immune cell types—including neutrophils and myeloid-derived suppressor cells—that contribute to tumor progression, invasiveness, and treatment resistance. The role of tumor-associated neutrophils and myeloid-derived suppressor cells in cancer biology remains elusive, as these cells can exert a multitude of pro-tumor and antitumor effects. In this review, we provide the current understanding and novel insights on the role of neutrophils and myeloid-derived suppressor cells in glioma progression and treatment resistance, as well as the mechanisms of pleiotropic behaviors in these cells during disease progression, with an emphasis on possible strategies to reprogram these cells towards their antitumor actions.
Glioblastoma (GBM) is the most common, highly aggressive and lethal primary brain tumor in adults, and has a median overall survival ranging from 12 to 15 months. Several human cancers including glioma are infiltrated with numerous immune cell types which play a critical role in tumor growth, invasion and resistance to treatment. Previous studies, including our group, have shown that resistance to anti-VEGF therapy is associated with myeloid cell infiltration and mesenchymal transition in GBM. Notably, most glioma patients have shown increase in CD68+ cells due to overproduction of colony stimulating factor 1 (CSF-1) by tumor cells, a growth factor for macrophages. Therefore, we hypothesized that CSF-1 inhibition may reduce macrophage and/or myeloid cell infiltration in glioma, thereby increasing animal survival as monotherapy or in combination with VEGF inhibitors in xenograft GBM mouse models. We tested two CSF-1R inhibitors (AZD 7507 and JNJ-28312141) alone and in combination with VEGF inhibition to prevent macrophage infiltration in xenograft GBM mouse models. CSF-1R and VEGF inhibitors reduced macrophage infiltration (F4/80 staining), tumor volume, and mesenchymal transition (YKL-40 staining), and there was a marginal survival benefit in this model. Interestingly, despite significant reduction in tumor macrophages, we observed a significant increase in neutrophil infiltration and hypoxia (HIF1α staining), particularly in the combinatorial treated. Considering these observations, we further evaluated tumor-associated neutrophil (TAN) infiltration in GBM patient tumors by fluorescence-activated cell sorting (FACS). FACS-isolated TANs were identified as CD11b+/CD15+/CD66b+ triple positive. Our results shown that the infiltrating TAN population vary from 0.5 to 5% in GBM patient tumors. Detailed characterization of TAN population and polarization in patient tumors are ongoing. Our findings revealed that CSF-1 and VEGF inhibition reduced macrophage infiltration and tumor growth, but significantly increased TAN infiltration which will likely hamper the potential therapeutic benefit of anti-CSF1-directed inhibitors.
The complement system is a vital part of the innate immune system which plays a critical role in immune surveillance and inflammatory processes. Malignant and host cells express various complement inhibitory proteins on their surface to protect against complement mediated cytotoxicity. Imbalanced complement activation triggers inflammation and alters the tumor microenvironment. Complement activation has been shown to induce proliferation and migration of breast, ovarian and lung cancer cells. At this time, the expression and functional role of the complement cascade in glioblastoma (GBM) remain elusive. Here, we investigated the role of complement proteins and their receptor expression in human primary glioma stem-like cells (GSCs) and human GBM tissues. Western blot data demonstrated a high level of expression of central complement components and their receptors in GSCs. RT-PCR data further confirmed the high expression of complement genes which was similar or higher to normal human astrocytes (HA), a cell with high baseline expression levels of complement genes. Flow cytometry analysis revealed that almost 95% of GSCs expressed the anaphylatoxin complement receptors C3aR and C5aR on their cell surfaces which was consistent with our immunohistochemistry analysis of freshly resected GBM tissues. Furthermore, anaphylatoxin C5a exposure increased the proliferation of a subgroup of GSCs while reduced in another subset. Interestingly, C5a exposure was found to increase the expression of various pro-inflammatory markers in GSCs with reduced proliferation. Fluorescence-activated cell sorting (FACS) analysis of freshly isolated human GBM tissue revealed predominant expression of C5aR on cancer cells (CD11b-/CD45- cells) rather than on immune cells. RT-PCR analysis also demonstrated high expression levels of complement genes with concomitant decrease in complement inhibitory genes in human GBM tissue. Evaluation of the differential role of the complement system in GSCs along with their role in in vivo glioma models is ongoing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.