Chronic inflammation caused by persistent infections and metabolic disorders is thought to contribute to the increased cancer risk and the accelerated cancer progression. Oppositely, acute inflammation induced by bacteria-based vaccines or that is occurring after cancer selectively inhibits cancer progression and metastasis. However, the interaction between inflammation and cancer may be more complex than the current explanations for the relationship between chronic and acute inflammation and cancer. In this review, we described the impact of inflammation on cancer on the basis of three perspectives, including inflammation with different durations (chronic and acute inflammation), different scopes (systemic and local inflammation) and different occurrence sequences (inflammation occurring after and before cancer). In addition, we also introduced bacteria/virus-based cancer immunotherapies. We perceive that inflammation may be a double-edged sword with cancer-promoting and cancer-suppressing functions in certain cases. We expect to further improve the understanding of the relationship between inflammation and cancer and provide a theoretical basis for further research on their complex interaction.

In recent years, the role of cancer immunotherapy has become increasingly important compared to traditional cancer treatments, including surgery, chemotherapy and radiotherapy. Of note, the clinical successes of immune checkpoint blockade, such as PD-1 and CTLA-4, represent a landmark event in cancer immunotherapy development. Therefore, further exploration of how immune checkpoints are regulated in the tumor microenvironment will provide key insights into checkpoint blockade therapy. In this review, we discuss in details about the regulation of immune checkpoints mediated by immune cells, oncolytic viruses, epigenetics, and gut microbiota and mutual regulation by co-expressed checkpoints. Finally, predictions are made for future personalized cancer immunotherapy based on different checkpoint modulations.

Introduction: Previous studies have produced controversial results regarding whether mesenchymal stem cells (MSCs) promote or inhibit tumor development. Given the dual role of MSCs in inflammation and cancer, in this study the colitis-associated colorectal cancer (CAC) model was used to examine whether umbilical cord tissue-derived MSCs could prevent neoplasm by inhibiting chronic inflammation. Methods: MSCs were obtained and identified using flow cytometry. Colitis-associated colorectal cancer model was induced using azoxymethane (AOM) and dextran sulfate sodium (DSS) and MSCs were injected intravenously twice. Levels of immune cells in mesenteric lymph node including regulatory T (Treg) cells were detected using flow cytometry. Naïve T cells and Jurkat cells were co-cultured with MSCs and the effect of MSCs on Treg cells differentiation was evaluated. Results: After injection through tail vein, MSCs could migrate to colon and suppress colitis-related neoplasm. This tumor suppressive effect was characterized by longer colon length, decreased tumor numbers and decreased expression of Ki-67. Moreover, MSCs alleviated the pathology of inflammation in the colitis stage of CAC model and inhibited inflammation cytokines both in colon and serum. Furthermore, Treg cells were accumulated in mesenteric lymph node of MSCs-treated mice while the percentage of T helper cells 2 (Th2) and Th17 were not changed. Of note, MSCs secreted transforming growth factor-β (TGF-β) enhanced the induction of Treg cells from naïve T cells. The conditioned medium of MSCs also activated Smad2 signaling, which has been reported to regulate Treg cells. Conclusions: These results proved that MSCs could migrate to colon tissues and induce the differentiation of Treg cells via Smad2 as so to inhibit the colitis and suppress the development of CAC.

Due to chemotherapeutic drug resistance, tumor recurrence is common in patients with colorectal cancer (CRC) and chemo-resistant patients are often accompanied by defects in the mismatch repair system (MMR). Our previous study has shown that Candida tropicalis (C. tropicalis) is closely related to the occurrence and development of colorectal cancer, but whether this conditional pathogenic fungus is involved in chemotherapy needs further investigation. Here we found that C. tropicalis promoted chemotherapy resistance of colon cancer to oxaliplatin. Compared with oxaliplatin-treated group, the expression of functional MMR proteins in tumors were decreased in C.tropicalis/oxaliplatin -treated group, while the glycolysis level of tumors was up-regulated and the production of lactate was significantly increased in C.tropicalis/oxaliplatin -treated group. Inhibiting lactate production significantly alleviated the chemoresistance and rescued the decreased expression of MMR caused by C. tropicalis. Furthermore, we found that lactate down-regulated the expression of MLH1 through the GPR81-cAMP-PKA-CREB axis. This study clarified that C. tropicalis promoted chemoresistance of colon cancer via producing lactate and inhibiting the expression of MLH1, which may provide novel ideas for improving CRC chemotherapy effect.

There is increasing evidence that gut fungi dysbiosis plays a crucial role in the development and progression of colorectal cancer (CRC). It has been reported that gut fungi exacerbate the severity of CRC by regulating tumor immunity. Our previous studies have shown that the opportunistic pathogenic fungal pathogen, Candida tropicalis (C. tropicalis) promotes CRC progression by enhancing the immunosuppressive function of MDSCs and activating the NLRP3 inflammasome of MDSCs. However, the relationship between IL-1β produced by NLRP3 inflammasome activation and the immunosuppressive function of MDSCs enhanced by C. tropicalis in CRC remains unclear. The TCGA database was used to analyze the relationship between IL-1β and genes related to immunosuppressive function of MDSCs in human CRC. The expression of IL-1β in human CRC tissues was detected by immunofluorescence staining. The proteomic analysis was performed on the culture supernatant of C. tropicalis-stimulated MDSCs. The experiments of supplementing and blocking IL-1β as well as inhibiting the NLRP3 inflammasome activation were conducted. A mouse colon cancer xenograft model was established by using MC38 colon cancer cell line. Analysis of CRC clinical samples showed that the high expression of IL-1β was closely related to the immunosuppressive function of tumor-infiltrated MDSCs. The results of in vitro experiments revealed that IL-1β was the most secreted cytokine of MDSCs stimulated by C. tropicalis. In vitro supplementation of IL-1β further enhanced the immunosuppressive function of C. tropicalis-stimulated MDSCs and NLRP3-IL-1β axis mediated the immunosuppressive function of MDSCs enhanced by C. tropicalis. Finally, blockade of IL-1β secreted by MDSCs augmented antitumor immunity and mitigated C. tropicalis-associated colon cancer. C. tropicalis promotes excessive secretion of IL-1β from MDSCs via the NLRP3 inflammasome. IL-1β further enhances the immunosuppressive function of MDSCs to inhibit antitumor immunity, thus promoting the progression of CRC. Therefore, targeting IL-1β secreted by MDSCs may be a potential immunotherapeutic strategy for the treatment of CRC.

Aim: Quxie capsule (QX), a compound of 21 kinds of Traditional Chinese Medicine (TCM) herbs, has been used to treat patients with metastatic colorectal cancer (mCRC) and could suppress the growth of colon cancer. However, the mechanisms of QX inhibiting colorectal cancer remain unclear. In current study, we attempted to determine the anti-colorectal cancer (CRC) effects of QX and the mechanisms of QX in alleviating colorectal cancer. Methods: A colitis-associated colon cancer (CAC) model was established by intraperitoneally injecting mice with AOM followed by 3 cycles of 2% DSS in water. During establishment of CAC model, we orally gavaged mice with QX. Hematoxylin and eosin (H&E) and immunohistochemistry were performed to assess lesion of the colonic tumors. The expression of pro-inflammatory cytokines in colonic tumors was measured by qPCR. The proportion of immune cells in colonic tumors was analyzed by flow cytometry. Internal transcribed spacer (ITS) sequencing and 16S rRNA gene sequencing were performed to detect intestinal microbiota. The expression of glycolytic related enzymes, lactate production, and extracellular acidification rate (ECAR) were used to assess the level of aerobic glycolysis. Results: QX markedly inhibited intestinal tumorigenesis by decreasing the expression of pro-inflammatory cytokines and the proportion of myeloid-derived suppressor cells (MDSCs), and increasing the proportion of CD8⁺ T cells in colon tumors. Fecal microbiota sequencing revealed that QX increased the relative abundances of intestinal symbiotic probiotics, such as, Lactobacillus, Bifidobacterium and Faecalibacterium genera. What’s more, opportunistic pathogens, Bacteroides genera and Aspergillus- Aspergillus fumigatus, exhibited remarkably reduced abundances in mice treated with QX compared with untreated CAC mice. Further experiments showed that QX significantly reduced glycolysis of colon tumor and suppressed A. fumigatus-induced glycolytic metabolism of colon cancer cells. Conclusions: QX alleviates the development of CRC at least in part through modulating intestinal microbiota and reducing A. fumigatus-induced aerobic glycolysis of colon cancer cells.