Enhancing anticancer activity of macrophages through rational drug combinations.

Targeting tumor-associated macrophages (TAMs) is an emerging approach being tested in multiple clinical trials. TAMs, depending on their differentiation state, can exhibit pro- or antitumorigenic functions. For example, the M2-like phenotype represents a protumoral state that can stimulate tumor growth, angiogenesis, metastasis, therapy resistance, and immune evasion by expressing immune checkpoint proteins. In this issue of the JCI, Vaccaro and colleagues utilized an innovative drug screen approach to demonstrate that targeting driver oncogenic signaling pathways concurrently with anti-CD47 sensitizes tumor cells, causing them to undergo macrophage-induced phagocytosis. The combination treatment altered expression of molecules on the tumor cells that typically limit phagocytosis. It also reprogrammed macrophages to an M1-like antitumor state. Moreover, the approach was generalizable to tumor cells with different oncogenic pathways, opening the door to precision oncology-based rationale combination therapies that have the potential to improve outcomes for patients with oncogene-driven lung cancers and likely other cancer types.

Modulation of the tumor microenvironment and mechanism of immunotherapy-based drug resistance in breast cancer.

Breast cancer, the most frequent female malignancy, is often curable when detected at an early stage. The treatment of metastatic breast cancer is more challenging and may be unresponsive to conventional therapy. Immunotherapy is crucial for treating metastatic breast cancer, but its resistance is a major limitation. The tumor microenvironment (TME) is vital in modulating the immunotherapy response. Various tumor microenvironmental components, such as cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs), are involved in TME modulation to cause immunotherapy resistance. This review highlights the role of stromal cells in modulating the breast tumor microenvironment, including the involvement of CAF-TAM interaction, alteration of tumor metabolism leading to immunotherapy failure, and other latest strategies, including high throughput genomic screening, single-cell and spatial omics techniques for identifying tumor immune genes regulating immunotherapy response. This review emphasizes the therapeutic approach to overcome breast cancer immune resistance through CAF reprogramming, modulation of TAM polarization, tumor metabolism, and genomic alterations.

Regulating Tumor-Associated Macrophage Polarization by Cyclodextrin-Modified PLGA Nanoparticles Loaded with R848 for Treating Colon Cancer.

Purpose: This study aimed to develop a novel and feasible modification strategy to improve the solubility and antitumor activity of resiquimod (R848) by utilizing the supramolecular effect of 2-hydroxypropyl-beta-cyclodextrin (2-HP-ß-CD). Methods: R848-loaded PLGA nanoparticles modified with 2-HP-ß-CD (CD@R848@NPs) were synthesized using an enhanced emulsification solvent-evaporation technique. The nanoparticles were then characterized in vitro by several methods, such as scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, particle size analysis, and zeta potential analysis. Then, the nanoparticles were loaded with IR-780 dye and imaged using an in vivo imaging device to evaluate their biodistribution. Additionally, the antitumor efficacy and underlying mechanism of CD@R848@NPs in combination with an anti-TNFR2 antibody were investigated using an MC-38 colon adenocarcinoma model in vivo. Results: The average size of the CD@R848@NPs was 376 ± 30 nm, and the surface charge was 21 ± 1 mV. Through this design, the targeting ability of 2-HP-ß-CD can be leveraged and R848 is delivered to tumor-supporting M2-like macrophages in an efficient and specific manner. Moreover, we used an anti-TNFR2 antibody to reduce the proportion of Tregs. Compared with plain PLGA nanoparticles or R848, CD@R848@NPs increased penetration in tumor tissues, dramatically reprogrammed M1-like macrophages, removed tumors and prolonged patient survival. Conclusion: The new nanocapsule system is a promising strategy for targeting tumor, reprogramming tumor -associated macrophages, and enhancement immunotherapy.

Discovery of a Novel CSF-1R Inhibitor with Highly Improved Pharmacokinetic Profiles and Superior Efficacy in Colorectal Cancer Immunotherapy.

Blocking CSF-1/CSF-1R pathway has emerged as a promising strategy to remodel tumor immune microenvironment (TME) by reprogramming tumor-associated macrophages (TAMs). In this work, a novel CSF-1R inhibitor C19 with a highly improved pharmacokinetic profile and in vivo anticolorectal cancer (CRC) efficiency was successfully discovered. C19 could effectively reprogram M2-like TAMs to M1 phenotype and reshape the TME by inducing the recruitment of CD8+ T cells into tumors and reducing the infiltration of immunosuppressive Tregs/MDSCs. Deeper mechanistic studies revealed that C19 facilitated the infiltration of CD8+ T cells by enhancing the secretion of chemokine CXCL9, thus significantly potentiating the anti-CRC efficiency of PD-1 blockade. More importantly, C19 combined with PD-1 mAb could induce durable antitumor immune memory, effectively overcoming the recurrence of CRC. Taken together, our findings suggest that C19 is a promising therapeutic option for sensitizing CRC to anti-PD-1 therapy.

Activation of M2 macrophage autophagy by rapamycin increases the radiosensitivity of colorectal cancer xenografts.

BACKGROUND: Tumor-associated macrophages (TAMs) are intimately involved in cancer radiochemotherapy resistance. However, the mechanism by which macrophages affect radiosensitivity through autophagy remains unclear. The purpose of our study was to investigate how activating autophagy in type-II macrophages (M2) by using rapamycin (RAP) would affect the radiosensitivity of colorectal cancer (CRC) xenografts. MATERIALS AND METHODS: A nude mouse CRC model was established by injecting LoVo CRC cells. After tumor formation, supernatant from M2 cells (autophagy-unactivated), autophagy-activated M2 cells, or autophagy-downregulated M2 cells was injected peritumorally. All tumor-bearing mice were irradiated with 8-Gy X-rays twice, and the radiosensitivity of CRC xenografts was analyzed in each group. RESULTS: The mass, volume, and microvessel density (MVD) of tumors in the autophagy-unactivated M2 group significantly increased; however, supernatant from M2 cells that were autophagy-activated by rapamycin significantly decreased tumor weight, volume, and MVD compared with negative control. Combining bafilomycin A1 (BAF-A1) with RAP treatment restored the ability of the M2 supernatant to increase tumor mass, volume, and MVD. Immunohistochemical and Western blot results showed that compared with the negative control group, supernatant from M2 cells that were not activated by autophagy downregulated the expression of Livin and Survivin in tumor tissues; activation of M2 autophagy further downregulated the protein levels. CONCLUSIONS: Therefore, autophagy-activated M2 supernatant can downregulate the expression of the antiapoptotic genes Livin and Survivin in CRC xenografts, improving the radiosensitivity of CRC by inducing apoptosis in combination with radiotherapy and inhibiting the growth of transplanted tumors.

Enhancing Glioblastoma Immunotherapy with Integrated Chimeric Antigen Receptor T Cells through the Re-Education of Tumor-Associated Microglia and Macrophages.

Glioblastoma (GBM) is an aggressive brain cancer that is highly resistant to treatment including chimeric antigen receptor (CAR)-T cells. Tumor-associated microglia and macrophages (TAMs) are major contributors to the immunosuppressive GBM microenvironment, which promotes tumor progression and treatment resistance. Hence, the modulation of TAMs is a promising strategy for improving the immunotherapeutic efficacy of CAR-T cells against GBM. Molecularly targeting drug pexidartinib (PLX) has been reported to re-educate TAMs toward the antitumorigenic M1-like phenotype. Here, we developed a cell-drug integrated technology to reversibly conjugate PLX-containing liposomes (PLX-Lip) to CAR-T cells and establish tumor-responsive integrated CAR-T cells (PLX-Lip/AZO-T cells) as a combination therapy for GBM. We used a mouse model of GBM to show that PLX-Lip was stably maintained on the surface of PLX-Lip/AZO-T cells in circulation and these cells could transmigrate across the blood-brain barrier and deposit PLX-Lip at the tumor site. The uptake of PLX-Lip by TAMs effectively re-educated them into the M1-like phenotype, which in turn boosted the antitumor function of CAR-T cells. GBM tumor growth was completely eradicated in 60% of the mice after receiving PLX-Lip/AZO-T cells and extended their overall survival time beyond 50 days; in comparison, the median survival time of mice in other treatment groups did not exceed 35 days. Overall, we demonstrated the successful fusion of CAR-T cells and small-molecule drugs with the cell-drug integrated technology. These integrated CAR-T cells provided a superior combination strategy for GBM treatment and presented a reference for the construction of integrated cell-based drugs.

Superparamagnetic Iron Oxide Nanoparticles Reprogram the Tumor Microenvironment and Reduce Lung Cancer Regrowth after Crizotinib Treatment.

ALK-positive NSCLC patients demonstrate initial responses to ALK tyrosine kinase inhibitor (TKI) treatments, but eventually develop resistance, causing rapid tumor relapse and poor survival rates. Growing evidence suggests that the combination of drug and immune therapies greatly improves patient survival; however, due to the low immunogenicity of the tumors, ALK-positive patients do not respond to currently available immunotherapies. Tumor-associated macrophages (TAMs) play a crucial role in facilitating lung cancer growth by suppressing tumoricidal immune activation and absorbing chemotherapeutics. However, they can also be programmed toward a pro-inflammatory tumor suppressive phenotype, which represents a highly active area of therapy development. Iron loading of TAMs can achieve such reprogramming correlating with an improved prognosis in lung cancer patients. We previously showed that superparamagnetic iron oxide nanoparticles containing core-cross-linked polymer micelles (SPION-CCPMs) target macrophages and stimulate pro-inflammatory activation. Here, we show that SPION-CCPMs stimulate TAMs to secrete reactive nitrogen species and cytokines that exert tumoricidal activity. We further show that SPION-CCPMs reshape the immunosuppressive Eml4-Alk lung tumor microenvironment (TME) toward a cytotoxic profile hallmarked by the recruitment of CD8+ T cells, suggesting a multifactorial benefit of SPION-CCPM application. When intratracheally instilled into lung cancer-bearing mice, SPION-CCPMs delay tumor growth and, after first line therapy with a TKI, halt the regrowth of relapsing tumors. These findings identify SPIONs-CCPMs as an adjuvant therapy, which remodels the TME, resulting in a delay in the appearance of resistant tumors.

Optical controlled and nuclear targeted CECR2 competitor to downregulate CSF-1 for metastatic breast cancer immunotherapy.

The crosstalk between breast cancer cells and tumor associated macrophages (TAMs) greatly contributes to tumor progression and immunosuppression. In this work, cat eye syndrome chromosome region candidate 2 (CECR2) is identified to overexpress in breast cancer patients, which can recognize v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) and activate nuclear factor κB (NF-κB) to release colony stimulating factor-1 (CSF-1). Pharmacological inhibition of CECR2 by the bromodomain competitor (Bromosporine, Bro) can downregulate CSF-1 to inhibit M2 type TAMs. To amplify the immunotherapeutic effect, a chimeric peptide-based and optical controlled CECR2 competitor (designated as N-PB) is constructed to enhance the nuclear targeted delivery of Bro and initiate an immunogenic cell death (ICD). In vivo results indicate a favorable breast cancer targeting ability and primary tumor suppression effect of N-PB under optical irradiation. Importantly, N-PB downregulates CSF-1 by competitive inhibition of CECR2 and NF-κB(RelA) interactions, thus inhibiting immunosuppressive M2-like TAMs while improving the antitumorigenic M1-like phenotype. Ultimately, the systemic anti-tumor immunity is activated to suppress the metastatic breast cancer in an optical controlled manner. This study provides a promising therapeutic target and reliable strategy for metastatic breast cancer treatment by interrupting immunosuppressive crosstalk between tumor cells and macrophages.

Arenobufagin modulation of PCSK9-mediated cholesterol metabolism induces tumor-associated macrophages polarisation to inhibit hepatocellular carcinoma progression.

BACKGROUND: The tumor microenvironment (TME) of hepatocellular carcinoma is heterogeneous enough to be prone to drug resistance and multidrug resistance during treatment, and reprogramming of cholesterol metabolism in TME mediates tumor-associated macrophages (TAMs) polarization, which has an impact on the regulation of malignant tumor progression. Arenobufagin (ARBU) was extracted and isolated from toad venom (purity ≥98 %), which is the main active ingredient of the traditional Chinese medicine Chan'su with good anti-tumor effects. PURPOSE: To investigate the regulatory effect of ARBU on lipid metabolism in tumor microenvironment, interfere with macrophage polarization, and determine its mechanism of action on liver cancer progression. METHODS: In this study, the inhibitory effect of ARBU on the proliferation of Hepa1-6 in C57 mice and the safety of administration were evaluated by establishing a transplanted tumor model of Hepa1-6 hepatocellular carcinoma mice and using 5-FU as a positive control drug. In addition, we constructed a co-culture system of Hepa1-6 cells and primary mouse macrophages to study the effects of ARBU on the polarization phenotypic transformation of macrophages and the proliferation and migration of hepatoma cells. The influence of ARBU on the metabolism of lipids in the hepatocellular carcinoma mouse model was investigated by combining it with lipidomics technology. The influence of ARBU on the PCSK9/LDL-R signaling pathway and macrophage polarization, which regulate cholesterol metabolism, was tested by using qRT-PCR, gene editing, IF, and WB. CONCLUSION: ARBU significantly inhibited the proliferation of Hepa1-6 in vivo and in vitro, regulated cholesterol metabolism, and promoted the M1-type polarization of macrophages in the tumor microenvironment. ARBU inhibits cholesterol synthesis in the TME through the PCSK9/LDL-R signaling pathway, thereby blocking macrophage M2 polarization, promoting apoptosis of the tumor cells, and inhibiting their proliferation and migration.

F1 fraction isolated from Mesobuthus eupeus scorpion venom induces macrophage polarization toward M1 phenotype and exerts anti-tumoral effects on the CT26 tumor cell line.

Scorpion venoms identified as agents with anti-tumor and anti-angiogenic features. Tumor microenvironment (TME) plays a pivotal role in the process of tumorigenesis, tumor development, and polarization of M2 phenotype tumor associated macrophages (TAMs). M2 polarized cells are associated with tumor growth, invasion, and metastasis. The fractionation process was performed by gel filtration chromatography on a Sephadex G50 column. To elucidate whether scorpion venom can alter macrophage polarization, we treated interleukin (IL)-4-polarized M2 cells with isolated fractions from Mesobuthus eupeus. Next, we evaluated the cytokine production and specific markers expression for M2 and M1 phenotype using enzyme linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (PCR), respectively. The phagocytic capacity of macrophages was also assessed. In addition, the migration assay and MTT analysis were performed to investigate the effects of reprogrammed macrophages on the CT-26 colon cancer cells. The results indicated that F1 fraction of venom significantly upregulated the levels and expression of M1-associated cytokines and markers, including tumor necrosis factor-alpha (TNF-α) (p < 0.001), IL-1 (p < 0.01), interferon regulatory factor 5 (IRF5) (p < 0.0001), induced nitric oxide synthase (iNOS) (p < 0.0001), and CD86 (p < 0.0001), and downregulated M2-related markers, including transforming growth factor-beta (TGF-ß) (p < 0.05), IL-10 (p < 0.05), Fizz1 (p < 0.0001), arginase-1 (Arg-1) (p < 0.0001), and CD206 (p < 0.001). The macrophage phagocytic capacity was enhanced after treatment with F1 fraction (p < 0.01). Moreover, incubation of CT-26 cell line with conditioned media of F1-treated macrophages suppressed migration (p < 0.0001) and proliferation (p < 0.01) of tumor cells. In conclusion, our findings demonstrated the potential of Mesobuthus eupeus venom in M2-to-M1 macrophage polarization as a promising therapeutic approach against proliferation and metastasis of colon cancer cells.

Lentinan inhibits cell invasion via M2 polarization of tumor-associated macrophages and Wnt/ß-catenin signaling in non-small cell lung cancer.

Non-small cell lung cancer (NSCLC) is an aggressive and devastating cancer due to its metastasis induced by increased invasion. Lentinan is a polysaccharide exerting antitumor roles in multiple cancers, including lung cancer. However, the influence of lentinan on cell invasion in NSCLC remains unclear. Cell invasion was detected by transwell analysis. Matrix metallopeptidase 9 (MMP9) levels were measured through immunofluorescence staining. The markers arginase-1 (Arg-1), CD206 and interleukin (IL)-10 (IL-10) of M2 macrophages, Wnt3a, and ß-catenin levels were measured by western blot or enzyme linked immunosorbent assay. Lentinan did not affect cell viability and proliferation in NSCLC cells. Lentinan suppressed cell invasion and reduced the expression and secretion of MMP9. Lentinan attenuated also M2 polarization of tumor-associated macrophages. Moreover, lentinan mitigated the M2 macrophage conditioned medium-mediated cell invasion and MMP9 alterations in NSCLC cells. Lentinan inhibited the activation of the Wnt/ß-catenin signaling in NSCLC cells. The activated Wnt/ß-catenin pathway reversed the suppressive effects of lentinan on cell invasion and MMP9 level in NSCLC cells. In conclusion, lentinan reduces cell invasion in NSCLC cells by inhibiting the M2 polarization of tumor-associated macrophages and the Wnt/ß-catenin signaling.

Momordicine-I Suppresses Head and Neck Cancer Growth by Reprogrammimg Immunosuppressive Effect of the Tumor-Infiltrating Macrophages and B Lymphocytes.

Head and neck cancer (HNC) is prevalent worldwide, and treatment options are limited. Momordicine-I (M-I), a natural component from bitter melon, shows antitumor activity against these cancers, but its mechanism of action, especially in the tumor microenvironment (TME), remains unclear. In this study, we establish that M-I reduces HNC tumor growth in two different immunocompetent mouse models using MOC2 and SCC VII cells. We demonstrate that the anticancer activity results from modulating several molecules in the monocyte/macrophage clusters in CD45+ populations in MOC2 tumors by single-cell RNA sequencing. Tumor-associated macrophages (TAM) often pose a barrier to antitumor effects, but following M-I treatment, we observe a significant reduction in the expression of Sfln4, a myeloid cell differentiation factor, and Cxcl3, a neutrophil chemoattractant, in the monocyte/macrophage populations. We further find that the macrophages must be in close contact with the tumor cells to inhibit Sfln4 and Cxcl3, suggesting that these TAMs are impacted by M-I treatment. Coculturing macrophages with tumor cells shows inhibition of Agr1 expression following M-I treatment, which is indicative of switching from M2 to M1 phenotype. Furthermore, the total B-cell population in M-I-treated tumors is significantly lower, whereas spleen cells also show similar results when cocultured with MOC2 cells. M-I treatment also inhibits PD1, PD-L1, and FoxP3 expression in tumors. Collectively, these results uncover the potential mechanism of M-I by modulating immune cells, and this new insight can help to develop M-I as a promising candidate to treat HNCs, either alone or as adjuvant therapy.

Etomidate inhibits tumor growth of glioblastoma by regulating M1 macrophage polarization.

Glioblastoma (GBM) is a common primary central nervous system tumor. Although the multimodal integrated treatment for GBM has made great progress in recent years, the overall survival time of GBM is still short. Thus, novel treatments for GBM are worth further investigation and exploration. This study aimed to investigate the effects of etomidate on GBM tumor growth and the underlying mechanism. A xenograft tumor model was established and treated with etomidate to assess tumor growth. Immunohistochemistry (IHC) assay evaluated the positive rate of Ki67 cells in tumor tissues. Cell counting kit (CCK)-8 and EdU assays accessed the cell viability and proliferation. Immunofluorescence (IF) staining detected the distribution of macrophage markers in tumor tissues. The percentages of M1- and M2-like macrophages in tumor-associated macrophages (TAMs) and co-culture system (macrophages and GBM cells) were detected using flow cytometry. Macrophage polarization-related genes were measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Etomidate treatment inhibited the tumor growth, and increased the CD86+ cells but decreased the CD206+ cells in TAMs. The gene expression of M1 markers was increased in TAMs of etomidate-treated mice, whereas that of M2 markers was decreased. Moreover, etomidate treatment increased the number of CD86+ M1-like macrophages co-cultured with tumor cells but decreased that of CD206+ M2-like macrophages, with the upregulation of M1 markers and downregulation of M2 markers. Etomidate inhibited GBM tumor growth by promoting M1 macrophage polarization, suggesting a new insight into the clinical treatment of GBM.

The BCL-2 inhibitor APG-2575 resets tumor-associated macrophages toward the M1 phenotype, promoting a favorable response to anti-PD-1 therapy via NLRP3 activation.

The main challenges in the use of immune checkpoint inhibitors (ICIs) are ascribed to the immunosuppressive tumor microenvironment and the lack of sufficient infiltration of activated CD8+ T cells. Transforming the tumor microenvironment (TME) from "cold" to "hot" and thus more likely to potentiate the effects of ICIs is a promising strategy for cancer treatment. We found that the selective BCL-2 inhibitor APG-2575 can enhance the antitumor efficacy of anti-PD-1 therapy in syngeneic and humanized CD34+ mouse models. Using single-cell RNA sequencing, we found that APG-2575 polarized M2-like immunosuppressive macrophages toward the M1-like immunostimulatory phenotype with increased CCL5 and CXCL10 secretion, restoring T-cell function and promoting a favorable immunotherapy response. Mechanistically, we demonstrated that APG-2575 directly binds to NF-κB p65 to activate NLRP3 signaling, thereby mediating macrophage repolarization and the activation of proinflammatory caspases and subsequently increasing CCL5 and CXCL10 chemokine production. As a result, APG-2575-induced macrophage repolarization could remodel the tumor immune microenvironment, thus improving tumor immunosuppression and further enhancing antitumor T-cell immunity. Multiplex immunohistochemistry confirmed that patients with better immunotherapeutic efficacy had higher CD86, p-NF-κB p65 and NLRP3 levels, accompanied by lower CD206 expression on macrophages. Collectively, these data provide evidence that further study on APG-2575 in combination with immunotherapy for tumor treatment is required.

An AMPK agonist suppresses the progress of colorectal cancer by regulating the polarization of TAM to M1 through inhibition of HIF-1α and mTOR signal pathway.

OBJECTIVE: This study aimed to evaluate the impact of an adenosine monophosphate-activated protein kinase (AMPK) agonist, metformin (MET), on the antitumor effects of macrophages and to determine the underlying mechanism involved in the process. MATERIALS AND METHODS: M0 macrophages were derived from phorbol-12-myristate-13-acetate-stimulated THP-1 cells. RESULTS: The levels of tumor necrosis factor-alpha (TNF-α) and human leukocyte antigen-DR (HLA-DR) were decreased in macrophages incubated with HCT116 cells, whereas those of arginase-1 (Arg-1), CD163, and CD206 were elevated; these effects were reversed by MET. The transfection of small interfering (si) RNA abrogated the influence of MET on the expression of the M1/M2 macrophage biomarkers. MET significantly suppressed the proliferation and migration abilities of HCT116 cells incubated with M0 macrophages; these actions were reversed by siRNA transfection against AMPK. The hypoxia-inducible factor 1-alpha (HIF-1α), phosphorylated protein kinase B (p-AKT), and phosphorylated mammalian target of rapamycin (p-mTOR) levels were reduced by the introduction of MET and promoted by siRNA transfection against AMPK. In addition, the levels of HIF-1α, p-AKT, and p-mTOR suppressed by MET were markedly increased following the transfection of siRNA against AMPK. CONCLUSION: These findings indicate that MET can repress the progression of colorectal cancer by transforming tumor-associated macrophages to the M1phenotype via inhibition of the HIF-1α and mTOR signaling pathways.

Tumor-associated macrophages: Potential therapeutic targets and diagnostic markers in cancer.

Macrophages are plastic and functionally diverse, present in all tissues, and play a key role in organisms from development, homeostasis and repair, to immune responses to pathogens. They are central to many disease states and have emerged as important therapeutic targets for many diseases. Tumor-associated macrophages (TAMs) are the most abundant immune cells in the tumor microenvironment (TME) and are key factors influencing cancer progression, metastasis and tumor recurrence. TAMs can be derived from different sources and exert different pro- or anti-tumor effects based on the type, stage and immune composition of the tumor. TAMs are highly heterogeneous and diverse, and have multiple functional phenotypes. There is still a great deal of controversy regarding the relationship between TAMs and prognosis of cancer patients. In this review, we summarize the characteristics of common markers of TAMs as well as explore the prognostic role of TAMs in different cancers including lung, breast, gastric, colorectal, esophageal and ovarian cancers.

Interaction of tumor-associated microglia/macrophages and cancer stem cells in glioma.

Glioma is the most common tumor of the primary central nervous system, and its malignant phenotype has been shown to be closely related to glioma stem cells (GSCs). Although temozolomide has significantly improved the therapeutic outcome of glioma with a high penetration rate of the blood-brain barrier, resistance is often present in patients. Moreover, evidence has shown that the crosstalk between GSCs and tumor-associated microglia/macrophages (TAMs) affect the clinical occurrence, growth, and multi-tolerance of chemoradiotherapy in gliomas. Here, we highlight its vital roles in the maintenance of the stemness of GSCs and the ability of GSCs to recruit TAMs to the tumor microenvironment and promote their polarization into tumor-promoting macrophages, hence providing groundwork for future research into new treatment strategies of cancer.

Dynamic increase of M2 macrophages is associated with disease progression of colorectal cancers following cetuximab-based treatment.

We aimed to investigate the dynamic changes of gene expression profiles and immune microenvironment linked to resistance to cetuximab-based treatments in patients with metastatic colorectal cancer (mCRC). A total of 106 patients with RAS-wild type mCRC who were treated with cetuximab-based treatments were included as the study population. RNA-sequencing and multiplexed immunohistochemistry were performed using paired or unpaired pre-treatment and post-treatment tumor tissues. Differentially expressed gene analysis of paired pre-treatment and post-treatment tumor tissues that develop acquired resistance (AR) identified the AR signature. Gene ontology analysis of the AR signature indicated enrichment of immune-related pathway genes. Among the immune subsets whose abundance was estimated by CIBERSORT, M2 macrophages showed the most prominent positive correlation with the expression of the AR signature. Among the post-treatment samples, progressive disease (PD) tumors showed a significantly higher abundance of M2 macrophages compared to non-PD tumors. These findings were validated by multiplexed immunohistochemistry analysis: the density of CD68+CD206+ M2 macrophages significantly increased at the time of PD following cetuximab-based treatment, whereas it did not consistently change in the tumor pairs of non-PD. In conclusion, a dynamic increase of M2 macrophages is associated with disease progression during cetuximab-based treatment of mCRCs. Targeting M2 macrophages is a promising immunotherapeutic strategy in this clinical context.

Methylglyoxal produced by tumor cells through formaldehyde-enhanced Warburg effect potentiated polarization of tumor-associated macrophages.

Environmental exposure to formaldehyde is known to be associated with cancers and many other diseases. Although formaldehyde has been classified as a group I carcinogen, the molecular mechanisms of its carcinogenicity are still not fully understood. Formaldehyde is also involved in the folate-driven one­carbon metabolism, and excess amount of formaldehyde was found to interfere with other metabolic pathways including glycolysis, which can enhance Warburg effect and induce immunosuppression in tumor microenvironment. Therefore, different tumor cells and THP-1 derived macrophages were utilized to explore the metabolism-related effects induced by formaldehyde at environmentally relevant concentrations. Significant increases of glucose uptake, glycolysis levels, HIF-1α signaling and methylglyoxal production were observed in tumor cells treated with 20 and 50 µM formaldehyde for 24 h, and the overproduced methylglyoxal in the conditioned medium collected from the tumor cells treated with formaldehyde triggered macrophage polarization towards M2 cells. Myricetin, a flavonol scavenging methylglyoxal, reversed the polarization of macrophages induced by methylglyoxal at 50 µM. These results not only provided essential evidences to reveal the molecular mechanisms of Warburg effect and metabolism-related immunosuppression related to formaldehyde exposure, but also indicated that methylglyoxal could be utilized as a target for therapeutic treatment or prevention of formaldehyde-induced immunotoxicity.

TAMpepK Suppresses Metastasis through the Elimination of M2-Like Tumor-Associated Macrophages in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) accounts for approximately 10-15% of all breast cancer cases and is characterized by high invasiveness, high metastatic potential, relapse proneness, and poor prognosis. M2-like tumor-associated macrophages (TAMs) contribute to tumorigenesis and are promising targets for inhibiting breast cancer metastasis. Therefore, we investigated whether melittin-conjugated pro-apoptotic peptide (TAMpepK) exerts therapeutic effects on breast cancer metastasis by targeting M2-like TAMs. TAMpepK is composed of M2-like TAM binding peptide (TAMpep) and pro-apoptotic peptide d(KLAKLAK)2 (dKLA). A metastatic mouse model was constructed by injecting 4T1-luc2 cells either orthotopically or via tail vein injection, and tumor burden was quantified using a bioluminescence in vivo imaging system. We found that TAMpepK suppressed lung and lymph node metastases of breast cancer by eliminating M2-like TAMs without affecting the viability of M1-like macrophages and resident macrophages in the orthotopic model. Furthermore, TAMpepK reduced pulmonary seeding and the colonization of tumor cells in the tail vein injection model. The number of CD8+ T cells in contact with TAMs was significantly decreased in tumor nodules treated with TAMpepK, resulting in the functional activation of cytotoxic CD8+ T cells. Taken together, our findings suggest that TAMpepK could be a novel therapeutic agent for the inhibition of breast cancer metastasis by targeting M2-like TAMs.