Complement downregulation promotes an inflammatory signature that renders colorectal cancer susceptible to immunotherapy

Advances in research on the intestinal microbiota in the mechanism and prevention of colorectal cancer (Review)

The intestinal microbiota represents a diverse population that serves a key role in colorectal cancer (CRC) and its treatment outcomes. Advancements in sequencing have revealed notable shifts in microbial composition and diversity among individuals with CRC. Concurrently, animal models have elucidated the involvement of specific microbes such as Lactobacillus fragilis, Escherichia coli and Fusobacterium nucleatum in the progression of CRC. The present review aimed to highlight contributions of intestinal microbiota to the pathogenesis of CRC, the effects of traditional treatments on intestinal microbiota and the potential for microbiota modulation as a therapeutic strategy for CRC.

Interplay between the complement system and other immune pathways in the tumor microenvironment

Tumor growth and spread are sustained by the tumor microenvironment. Inflammatory cells and pathways have a fundamental role in the tumor microenvironment, driving or conditioning the functional activation of other leukocyte subsets and favoring evasion of anti-tumor immunity. One of the inflammatory pathways contributing to cancer-related inflammation is the complement system. Complement has long been considered an immune mechanism associated with immunosurveillance. More recently it emerged as a tumor promoting pathway, due to direct effects on cancer cells or indirect effects via immunosuppression driven by myeloid cells. The role of complement in cancer is complex and ambiguous, and depends on the tumor type and stage, as well as other factors including oncogenic drivers, leukocyte infiltration, interactions with other tumor microenvironment components or tumor cells. Other factors of complexity include the source of complement molecules, its canonical or non-canonical extracellular functions, its potential intracellular activation, and the interaction with other systems, such as the coagulation or the microbiome. Preclinical studies generally demonstrate the involvement of complement activation in smouldering inflammation in cancer and promotion of an immunosuppressive environment. These studies paved the way for clinical trials aimed at enhancing the potential of immunotherapy, in particular by targeting complement-dependent myeloid-sustained immunosuppression. However, the complex role of complement in cancer and the multiplicity of complement players may represent stumbling blocks and account for failures of clinical trials, and suggest that further studies are required to identify patient subsets who may benefit from specific complement molecule targeting in combination with conventional therapies or immunotherapy. Here, we will discuss the anti- or pro-tumor role of complement activation in cancer, focusing on the interactions of complement with immune cells within the tumor microenvironment, in particular the myeloid compartment. Furthermore, we will examine the potential of complement targeting in cancer treatment, particularly in the context of macrophage reprogramming.

New insights into the role of complement system in colorectal cancer (Review)

Colorectal cancer (CRC) is one of the most common cancers worldwide. With the growing understanding of immune regulation in tumors, the complement system has been recognized as a key regulator of tumor immunity. Traditionally, the complement cascade, considered an evolutionarily conserved defense mechanism against invading pathogens, has been viewed as a crucial inhibitor of tumor progression. Complement components or activation products produced via cascade‑dependent or ‑independent processes are associated with the regulation of tumor‑associated inflammation. Various forms of complement activation products present in body fluids or inside cells, along with complement regulatory proteins and complement receptors, are involved in tumor cell growth and modulating the tumor microenvironment. In the present review, the role of the complement system in the tumor immunity of CRC is discussed. In addition, the contribution of the unconventional cascade‑independent pathway of complement activation in CRC progression is highlighted. A deeper understanding of the mechanism underlying the complement system in colitis‑associated colorectal cancer (CAC) may provide novel insights to assist the development of methods to prevent tumor progression and identify potential targets for the treatment of CAC.

Effect of colorectal cancer stem cells on the development and metastasis of colorectal cancer

The relevant mechanism of tumor-associated macrophages (TAMs) in the treatment of colorectal cancer patients with immune checkpoint inhibitors (ICIs) is discussed, and the application prospects of TAMs in reversing the treatment tolerance of ICIs are discussed to provide a reference for related studies. As a class of drugs widely used in clinical tumor immunotherapy, ICIs can act on regulatory molecules on cells that play an inhibitory role - immune checkpoints - and kill tumors in the form of an immune response by activating a variety of immune cells in the immune system. The sensitivity of patients with different types of colorectal cancer to ICI treatment varies greatly. The phenotype and function of TAMs in the colorectal cancer microenvironment are closely related to the efficacy of ICIs. ICIs can regulate the phenotypic function of TAMs, and TAMs can also affect the tolerance of colorectal cancer to ICI therapy. TAMs play an important role in ICI resistance, and making full use of this target as a therapeutic strategy is expected to improve the immunotherapy efficacy and prognosis of patients with colorectal cancer.

Complement: you gutsy thing!

Complement, traditionally perceived as a liver-derived and plasma-operative guardian against bloodborne pathogens, is increasingly recognized as a local and central player in tissue immunity. Two recent studies, by Xu et al. and Wu et al., validate this concept in the mouse gut, where extrahepatic, intestine-produced, and/or operative C3 protects against enteric infections.

An NFAT1-C3a-C3aR Positive Feedback Loop in Tumor-Associated Macrophages Promotes a Glioma Stem Cell Malignant Phenotype

Extensive infiltration by tumor-associated macrophages (TAM) in combination with myeloid-derived suppressor cells constitute the immunosuppressive microenvironment and promote the malignant phenotype of gliomas. The aggressive mesenchymal (MES)-subtype glioma stem cells (GSC) are prominent in the immunosuppressive microenvironment of gliomas. However, the underlying immune-suppressive mechanisms are still unknown. The current study showed that the antitumor immune microenvironment was activated in glioma in Nfat1-/- mice, suggesting induction of the immune-suppressive microenvironment by nuclear factor of activated T cells-1 (NFAT1). In TAMs, NFAT1 could upregulate the transcriptional activity of complement 3 (C3) and increase the secretion of C3a, which could then bind to C3aR and promote M2-like macrophage polarization by activating TIM-3. Simultaneously, C3a/C3aR activated the Ca2+-NFAT1 pathway, forming a positive feedback loop for the M2-like polarization of TAMs, which further promoted the MES transition of GSCs. Finally, disruption of this feedback loop using a C3aR inhibitor significantly inhibited glioma growth both in vitro and in vivo. The current study demonstrated that a NFAT1-C3a-C3aR positive feedback loop induces M2-like TAMs and further promotes the malignant phenotype of GSCs, which might be the potential therapeutic target for glioma.

The role of intestinal flora on tumorigenesis, progression, and the efficacy of PD-1/PD-L1 antibodies in colorectal cancer

Intestinal flora affects the maturation of the host immune system, serves as a biomarker and efficacy predictor in the immunotherapy of several cancers, and has an important role in the development of colorectal cancer (CRC). Anti-PD-1/PD-L1 antibodies have shown satisfactory results in MSI-H/dMMR CRC but performed poorly in patients with MSS/pMMR CRC. In recent years an increasing number of studies have shown that intestinal flora has an important impact on anti-PD-1/PD-L1 antibody efficacy in CRC patients. Preclinical and clinical evidence have suggested that anti-PD-1/PD-L1 antibody efficacy can be improved by altering the composition of the intestinal flora in CRC. Herein, we summarize the studies related to the influence of intestinal flora on anti-PD-1/PD-L1 antibody efficacy in CRC and discuss the potential underlying mechanism(s). We have focused on the impact of the intestinal flora on the efficacy and safety of anti-PD-1/PD-L1 antibodies in CRC and how to better utilize the intestinal flora as an adjuvant to improve the efficacy of anti-PD-1/PD-L1 antibodies. In addition, we have provided a basis for the potential of the intestinal flora as a new treatment modality and indicator for determining patient prognosis.

The Yin Yang of Complement and Cancer

Cancer-related inflammation is a crucial component of the tumor microenvironment (TME). Complement activation occurs in cancer and supports the development of an inflammatory microenvironment. Complement has traditionally been considered a mechanism of immune resistance against cancer, and its activation is known to contribute to the cytolytic effects of antibody-based immunotherapeutic treatments. However, several studies have recently revealed that complement activation may exert protumoral functions by sustaining cancer-related inflammation and immunosuppression through different molecular mechanisms, targeting both the TME and cancer cells. These new discoveries have revealed that complement manipulation can be considered a new strategy for cancer therapies. Here we summarize our current understanding of the mechanisms by which the different elements of the complement system exert antitumor or protumor functions, both in preclinical studies and in human tumorigenesis. Complement components can serve as disease biomarkers for cancer stratification and prognosis and be exploited for tumor treatment.

Improving radiotherapy in immunosuppressive microenvironments by targeting complement receptor C5aR1

An immunosuppressive microenvironment causes poor tumor T cell infiltration and is associated with reduced patient overall survival in colorectal cancer. How to improve treatment responses in these tumors is still a challenge. Using an integrated screening approach to identify cancer-specific vulnerabilities, we identified complement receptor C5aR1 as a druggable target, which when inhibited improved radiotherapy, even in tumors displaying immunosuppressive features and poor CD8+ T cell infiltration. While C5aR1 is well-known for its role in the immune compartment, we found that C5aR1 is also robustly expressed on malignant epithelial cells, highlighting potential tumor cell-specific functions. C5aR1 targeting resulted in increased NF-κB-dependent apoptosis specifically in tumors and not normal tissues, indicating that, in malignant cells, C5aR1 primarily regulated cell fate. Collectively, these data revealed that increased complement gene expression is part of the stress response mounted by irradiated tumors and that targeting C5aR1 could improve radiotherapy, even in tumors displaying immunosuppressive features.