BACKGROUND: The outcome of hepatocellular carcinoma (HCC) is limited by its complex molecular characteristics and changeable tumor microenvironment (TME). Here we focused on elucidating the functional consequences of Maternal embryonic leucine zipper kinase (MELK) in the tumorigenesis, progression and metastasis of HCC, and exploring the effect of MELK on immune cell regulation in the TME, meanwhile clarifying the corresponding signaling networks.
METHODS: Bioinformatic analysis was used to validate the prognostic value of MELK for HCC. Murine xenograft assays and HCC lung metastasis mouse model confirmed the role of MELK in tumorigenesis and metastasis in HCC. Luciferase assays, RNA sequencing, immunopurification-mass spectrometry (IP-MS) and coimmunoprecipitation (CoIP) were applied to explore the upstream regulators, downstream essential molecules and corresponding mechanisms of MELK in HCC.
RESULTS: We confirmed MELK to be a reliable prognostic factor of HCC and identified MELK as an effective candidate in facilitating the tumorigenesis, progression, and metastasis of HCC; the effects of MELK depended on the targeted regulation of the upstream factor miR-505-3p and interaction with STAT3, which induced STAT3 phosphorylation and increased the expression of its target gene CCL2 in HCC. In addition, we confirmed that tumor cell-intrinsic MELK inhibition is beneficial in stimulating M1 macrophage polarization, hindering M2 macrophage polarization and inducing CD8 + T-cell recruitment, which are dependent on the alteration of CCL2 expression. Importantly, MELK inhibition amplified RT-related immune effects, thereby synergizing with RT to exert substantial antitumor effects. OTS167, an inhibitor of MELK, was also proven to effectively impair the growth and progression of HCC and exert a superior antitumor effect in combination with radiotherapy (RT).
CONCLUSIONS: Altogether, our findings highlight the functional role of MELK as a promising target in molecular therapy and in the combination of RT therapy to improve antitumor effect for HCC.

Ubiquitination and deubiquitination are important forms of posttranslational modification that govern protein homeostasis. Deubiquitinating enzymes (DUBs), a protein superfamily consisting of more than 100 members, deconjugate ubiquitin chains from client proteins to regulate cellular homeostasis. However, the dysregulation of DUBs is reportedly associated with several diseases, including cancer. The tumor microenvironment (TME) is a highly complex entity comprising diverse noncancerous cells (e.g., immune cells and stromal cells) and the extracellular matrix (ECM). Since TME heterogeneity is closely related to tumorigenesis and immune evasion, targeting TME components has recently been considered an attractive therapeutic strategy for restoring antitumor immunity. Emerging studies have revealed the involvement of DUBs in immune modulation within the TME, including the regulation of immune checkpoints and immunocyte infiltration and function, which renders DUBs promising for potent cancer immunotherapy. Nevertheless, the roles of DUBs in the crosstalk between tumors and their surrounding components have not been comprehensively reviewed. In this review, we discuss the involvement of DUBs in the dynamic interplay between tumors, immune cells, and stromal cells and illustrate how dysregulated DUBs facilitate immune evasion and promote tumor progression. We also summarize potential small molecules that target DUBs to alleviate immunosuppression and suppress tumorigenesis. Finally, we discuss the prospects and challenges regarding the targeting of DUBs in cancer immunotherapeutics and several urgent problems that warrant further investigation.

BACKGROUND: Lactate has emerged as a critical regulator within the tumor microenvironment, including glioma. However, the precise mechanisms underlying how lactate influences the communication between tumor cells and tumor-associated macrophages (TAMs), the most abundant immune cells in glioma, remain poorly understood. This study aims to elucidate the impact of tumor-derived lactate on TAMs and investigate the regulatory pathways governing TAM-mediated tumor-promotion in glioma.
METHODS: Bioinformatic analysis was conducted using datasets from TCGA and CGGA. Single-cell RNA-seq datasets were analyzed by using UCSC Cell Browser and Single Cell Portal. Cell proliferation and mobility were evaluated through CCK8, colony formation, wound healing, and transwell assays. Western blot and immunofluorescence staining were applied to assess protein expression and cell distribution. RT-PCR and ELISA were employed to identify the potential secretory factors. Mechanistic pathways were explored by western blotting, ELISA, shRNA knockdown, and specific inhibitors and activators. The effects of pathway blockades were further assessed using subcutaneous and intracranial xenograft tumor models in vivo.
RESULTS: Elevated expressions of LDHA and MCT1 were observed in glioma and exhibited a positive correlation with M2-type TAM infiltration. Lactate derived from glioma cells induced TAMs towards M2-subtype polarization, subsequently promoting glioma cells proliferation, migration, invasion, and mesenchymal transition. GPR65, highly expressed on TAMs, sensed lactate-stimulation in the TME, fueling glioma cells malignant progression through the secretion of HMGB1. GPR65 on TAMs triggered HMGB1 release in response to lactate stimulation via the cAMP/PKA/CREB signaling pathway. Disrupting this feedback loop by GPR65-knockdown or HMGB1 inhibition mitigated glioma progression in vivo.
CONCLUSIONS: These findings unveil the intricate interplay between TAMs and tumor cells mediated by lactate and HMGB1, driving tumor progression in glioma. GPR65, selectively highly expressed on TAMs in glioma, sensed lactate stimulation and fostered HMGB1 secretion via the cAMP/PKA/CREB signaling pathway. Blocking this feedback loop presents a promising therapeutic strategy for GBM.

Tumor-associated macrophages (TAMs) are among the most abundant infiltrating leukocytes in the tumor microenvironment (TME). Reprogramming TAMs from protumor M2 to antitumor M1 phenotype is a promising strategy for remodeling the TME and promoting antitumor immunity; however, the development of an efficient strategy remains challenging. Here, a genetically modified bacterial biomimetic vesicle (BBV) with IFN-γ exposed on the surface in a nanoassembling membrane pore structure was constructed. The engineered IFN-γ BBV featured a nanoscale structure of protein and lipid vesicle, the existence of rich pattern-associated molecular patterns (PAMPs), and the costimulation of introduced IFN-γ molecules. In vitro, IFN-γ BBV reprogrammed M2 macrophages to M1, possibly through NF-κB and JAK-STAT signaling pathways, releasing nitric oxide (NO) and inflammatory cytokines IL-1β, IL-6, and TNF-α and increasing the expression of IL-12 and iNOS. In tumor-bearing mice, IFN-γ BBV demonstrated a targeted enrichment in tumors and successfully reprogrammed TAMs into the M1 phenotype; notably, the response of antigen-specific cytotoxic T lymphocyte (CTL) in TME was promoted while the immunosuppressive myeloid-derived suppressor cell (MDSC) was suppressed. The tumor growth was found to be significantly inhibited in both a TC-1 tumor and a CT26 tumor. It was indicated that the antitumor effects of IFN-γ BBV were macrophage-dependent. Further, the modulation of TME by IFN-γ BBV produced synergistic effects against tumor growth and metastasis with an immune checkpoint inhibitor in an orthotopic 4T1 breast cancer model which was insensitive to anti-PD-1 mAb alone. In conclusion, IFN-γ-modified BBV demonstrated a strong capability of efficiently targeting tumor and tuning a cold tumor hot through reprogramming TAMs, providing a potent approach for tumor immunotherapy.

In a recent study, Kerzel et al. report a novel therapeutic strategy to engineer tumor-associated macrophages (TAMs) in vivo by inducing the expression of IFNα in these cells. This approach enables improved antigen presentation and T cell activation, leading to controlled tumor growth in multiple murine models of liver metastasis.

BACKGROUND: Tumor cell-induced platelet aggregation (TCIPA) is not only a recognized mechanism for paraneoplastic thrombocytosis but also a potential breakthrough alternative for a low response to immune checkpoint inhibitors (ICIs) in hematogenous metastasis of malignant melanoma (MM). However, there is no TCIPA-specific model for further investigation of the relationship among TCIPA, the tumor immune microenvironment (TIME), and metastasis.
METHODS: We developed a TCIPA metastatic melanoma model with advanced hematogenous metastasis and enhanced TCIPA characteristics. We also investigated the pathway for TCIPA in the TIME.
RESULTS: We found that TCIPA triggers the recruitment of tumor-associated macrophages (TAMs) to lung metastases by secreting B16 cell-educated platelet-derived chemokines such as CCL2, SDF-1, and IL-1β. Larger quantities of TAMs in the TCIPA model were polarized to the M2 type by B16 cell reprocessing, and their surface programmed cell death 1 ligand 1 (PD-L1) expression was upregulated, ultimately assisting B16 cells in escaping host immunity and accelerating MM hematogenous metastasis.
CONCLUSIONS: TCIPA accelerates MM lung metastasis via tumor-educated platelets (TEPs), triggering TAM recruitment, promoting TAM polarization (M2), and remodeling the suppressive TIME in lung metastases.

Tumor-associated macrophages (TAMs), as a major and essential component of tumor microenvironment (TME), play a critical role in orchestrating pancreatic cancer (PaC) tumorigenesis from initiation to angiogenesis, growth, and systemic dissemination, as well as immunosuppression and resistance to chemotherapy and immunotherapy; however, the critical intrinsic factors responsible for TAMs reprograming and function remain to be identified. By performing single-cell RNA sequencing, transforming growth factor-beta-induced protein (TGFBI) was identified as TAM-producing factor in murine PaC tumors. TAMs express TGFBI in human PaC and TGFBI expression is positively related with human PaC growth. By inducing TGFBI loss-of-function in macrophage (MΦs) in vitro with siRNA and in vivo with Cre-Lox strategy in our developed TGFBI-floxed mice, we demonstrated disruption of TGFBI not only inhibited MΦ polarization to M2 phenotype and MΦ-mediated stimulation on PaC growth, but also significantly improved anti-tumor immunity, sensitizing PaC to chemotherapy in association with regulation of fibronectin 1, Cxcl10, and Ccl5. Our studies suggest that targeting TGFBI in MΦ can develop an effective therapeutic intervention for highly lethal PaC.

Cancer stem cells (CSCs) have emerged as key contributors to tumor initiation, growth, and metastasis. In addition, CSCs play a significant role in inducing immune evasion, thereby compromising the effectiveness of cancer treatments. The reciprocal communication between CSCs and the tumor microenvironment (TME) is observed, with the TME providing a supportive niche for CSC survival and self-renewal, while CSCs, in turn, influence the polarization and persistence of the TME, promoting an immunosuppressive state. Consequently, these interactions hinder the efficacy of current cancer therapies, necessitating the exploration of novel therapeutic approaches to modulate the TME and target CSCs. In this review, we highlight the intricate strategies employed by CSCs to evade immune surveillance and develop resistance to therapies. Furthermore, we examine the dynamic interplay between CSCs and the TME, shedding light on how this interaction impacts cancer progression. Moreover, we provide an overview of advanced therapeutic strategies that specifically target CSCs and the TME, which hold promise for future clinical and translational studies in cancer treatment.

UNASSIGNED: Glioblastoma (Gb) is the most common primary malignant tumor of brain with poor prognosis. Immune cells are the main factors affecting the prognosis of Gb, tumor-associated macrophages (TAMs) are the predominant infiltrating immune cell population in the immune microenvironment of Gb. Analyzing the relationship between magnetic resonance imaging (MRI) features and TAMs of Gb, and using imaging features to characterize the infiltration level of TAMs in tumor tissue may provide indicators for clinical decision-making and prognosis evaluation of Gb.
UNASSIGNED: Data from 140 in patients with isocitrate dehydrogenase (IDH) wild-type Gb diagnosed via histopathology and molecular diagnosis in the Second Hospital of Lanzhou University from January 2018 to April 2022 were collected in this retrospective, cross-sectional study. MRI images were reviewed for lesion location, cyst, necrosis, hemorrhage, contrast-enhanced T1-weighted MRI signal intensity, average apparent diffusion coefficient (ADCmean), and minimum apparent diffusion coefficient (ADCmin). Immunohistochemical staining with anti-CD163 and anti-CD68 antibodies was employed for macrophage detection. The positive cell percentage was estimated in 9 microscopic fields at 400× magnification per whole-slide image with ImageJ software (National Institutes of Health). Additionally, the relationship between MRI features, molecular, states and the positive CD68 and CD163 expression was analyzed.
UNASSIGNED: Our study discovered that the mean or median values of CD68+ and CD163+ TAMs were 7.39% and 14.98%, respectively. There was an obvious correlation between CD163+ TAMs and CD68+ TAMs (r=0.497; P=0.000). CD68+ and CD163+ macrophage infiltration correlated with age at diagnosis in patients with Gb (CD68+: r=0.230, P=0.006; CD163+: r=0.172, P=0.042). The levels of Gb TAM infiltration in different tumor locations varied, with the temporal lobe having the highest CD163+ macrophage and CD68+ macrophage infiltration (18.58% and 9.46%, respectively). CD163+ macrophage infiltration was positively correlated with ADCmean (r=0.208; P=0.014). The infiltration of CD68+ macrophages differed significantly between groups with varying degrees of tumor enhancement (H =4.228; P=0.017). There was a significant difference in CD68+ TAMs and CD163+ TAMs between the wild-type and mutant-type telomerase reverse transcriptase (TERT) types (P=0.004 and P=0.031, respectively).
UNASSIGNED: Age, location of the tumor, degree of tumor enhancement, ADC value, and TERT mutation status were associated with macrophage infiltration. These findings may serve as an effective tool for characterizing the tumor microenvironment in patients with Gb.

Tumor-associated macrophage (TAM) affects the intrinsic properties of tumor cells and the tumor microenvironment (TME), which can stimulate tumor cell proliferation, migration, and genetic instability, and macrophage diversity includes the diversity of tumors with different functional characteristics. Macrophages are now a central drug target in various diseases, especially in the TME, which, as \"tumor promoters\" and \"immunosuppressors\", have different responsibilities during tumor development and accompany by significant dynamic alterations in various subpopulations. Remodelling immunosuppression of TME and promotion of pre-existing antitumor immune responses is critical by altering TAM polarization, which is relevant to the efficacy of immunotherapy, and uncovering the exact mechanism of action of TAMs and identifying their specific targets is vital to optimizing current immunotherapies. Hence, this review aims to reveal the triadic interactions of macrophages with programmed death and oncotherapy, and to integrate certain relationships in cancer treatment.