Inhibition of NLRP3 inflammasome in tumor microenvironment leads to suppression of metastatic potential of cancer cells

Interleukin-1β and Cancer

Within a tumor, IL-1β is produced and secreted by various cell types, such as immune cells, fibroblasts, or cancer cells. The IL1B gene is induced after “priming” of the cells and a second signal is required to allow IL-1β maturation by inflammasome-activated caspase-1. IL-1β is then released and leads to transcription of target genes through its ligation with IL-1R1 on target cells. IL-1β expression and maturation are guided by gene polymorphisms and by the cellular context. In cancer, IL-1β has pleiotropic effects on immune cells, angiogenesis, cancer cell proliferation, migration, and metastasis. Moreover, anti-cancer treatments are able to promote IL-1β production by cancer or immune cells, with opposite effects on cancer progression. This raises the question of whether or not to use IL-1β inhibitors in cancer treatment.

NLRC4, ASC and Caspase-1 Are Inflammasome Components that Are Mediated by P2Y2R Activation in Breast Cancer Cells

The inflammasomes are reported to be associated with tumor progression. In our previous study, we determined that extracellular ATP enhances invasion and tumor growth by inducing inflammasome activation in a P2Y purinergic receptor 2 (P2Y₂R)-dependent manner. However, it is not clear which inflammasome among the diverse complexes is associated with P2Y₂R activation in breast cancer. Thus, in this study, we determined which inflammasome components are regulated by P2Y₂R activation and are involved in tumor progression in breast cancer cells and radiotherapy-resistant (RT-R)-breast cancer cells. First, we found that NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3); NLR family caspase activation and recruitment domain (CARD) containing 4 (NLRC4); apoptosis-associated speck-like protein containing a CARD complex (ASC); and caspase-1 mRNA levels were upregulated in RT-R-MDA-MB-231 cells compared to MDA-MB-231 cells, whereas tumor necrosis factor-α (TNF-α) or ATP treatment induced NLRC4, ASC, and caspase-1 but not NLRP3 protein levels. Moreover, TNF-α or ATP increased protein levels of NLRC4, ASC, and caspase-1 in a P2Y₂R-dependent manner in MDA-MB-231 and RT-R-MDA-MB-231 cells. In addition, P2Y₂R activation by ATP induced the secretion of IL-1β and VEGF-A, as well as invasion, in MDA-MB-231 and RT-R-MDA-MB-231 cells, which was inhibited by NLRC4, ASC, and caspase-1 small interfering RNA (siRNA). Taken together, this report suggests that P2Y₂R activation by ATP induces tumor invasion and angiogenesis through inflammasome activation, specifically by regulating the inflammasome components NLRC4, ASC, and caspase-1.

Anisodamine Suppressed the Growth of Hepatocellular Carcinoma Cells, Induced Apoptosis and Regulated the Levels of Inflammatory Factors by Inhibiting NLRP3 Inflammasome Activation

Introduction

Hepatocellular carcinoma (HCC) is a primary liver cancer with a 5-year incidence of over 70%. Anisodamine (ANI), an alkaloid extracted from Anisodus, has a good therapeutic effect in septic shock and morphine addiction. Our study designed to investigate the anticancer effect of anisodamine (ANI) on HCC.

Materials and Methods

HepG2 cells were subcutaneously injected into BALB/C nude mice and the tumor tissue was subcutaneously inoculated to construct the transplanted tumor. Mice were randomly divided into 10 groups (n = 5): control group, ANI-10 group, ANI-50 group, ANI-200 group, ANI-200+pcDNA-NLRP3 group, ANI-200+EV group, sh-NLRP3 group, ANI-200 + sh-NLRP3 group, normal group and normal+ANI-200 group.

Results

Studies indicated that ANI inhibited the growth of HCC xenografts and reduced liver damage in a dose-dependent manner. Besides, ANI increased the survival rate of tumor-bearing mice and suppressed the expression of NLRP3 in a dose-dependent manner. It is worth noting that NLRP3 overexpression reversed the inhibitory effect of ANI on HCC xenografts. In addition, TUNEL analysis showed that ANI-induced apoptosis of tumor cells, and NLRP3 overexpression reversed the inhibitory effect of ANI on HCC. Moreover, ANI further regulated the levels of IFN-γ, TNF-α, IL-4 and IL-27. Notably, low expression of NLRP3 enhanced the inhibitory effect of ANI on the development of HCC xenografts in mice.

Discussion

These findings indicate that ANI suppressed the growth of HCC cells, induced apoptosis and regulated the levels of inflammatory factors by inhibiting NLRP3 inflammasome activation.

Sweroside Prevents Non-Alcoholic Steatohepatitis by Suppressing Activation of the NLRP3 Inflammasome

Non-alcoholic steatohepatitis (NASH), a type of non-alcoholic fatty liver disease, is characterized as steatosis and inflammation in the liver. NLRP3 inflammasome activation is associated with NASH pathology. We hypothesized that suppressing the NLRP3 inflammasome could be effective in preventing NASH. We searched substances that could inhibit the activation of the NLRP3 inflammasome and identified sweroside as an NLRP3 inhibitor. We investigated whether sweroside can be applied to prevent the pathological symptoms associated with NASH in a methionine–choline-deficient (MCD) diet-induced NASH mouse model. The activation of the NLRP3 inflammasome was determined by detecting the production of caspase-1 and IL-1β from pro-caspase-1 and pro-IL-1β in primary mouse macrophages and mouse liver. In a NASH model, mice were fed an MCD diet for two weeks with daily intraperitoneal injections of sweroside. Sweroside effectively inhibited NLRP3 inflammasome activation in primary macrophages as shown by a decrease in IL-1β and caspase-1 production. In a MCD diet-induced NASH mouse model, intraperitoneal injection of sweroside significantly reduced serum aspartate transaminase and alanine transaminase levels, hepatic immune cell infiltration, hepatic triglyceride accumulation, and liver fibrosis. The improvement of NASH symptoms by sweroside was accompanied with its inhibitory effects on the hepatic NLRP3 inflammasome as hepatic IL-1β and caspase-1 were decreased. Furthermore, sweroside blocked de novo synthesis of mitochondrial DNA in the liver, contributing to suppression of the NLRP3 inflammasome. These results suggest that targeting the NLRP3 inflammasome with sweroside could be beneficially employed to improve NASH symptoms.

NOD2 inhibits tumorigenesis and increases chemosensitivity of hepatocellular carcinoma by targeting AMPK pathway

Nucleotide binding oligomerization domain 2 (NOD2) is a recognized innate immune sensor which can initiate potent immune response against pathogens. Many innate immune sensors have been reported to be of great importance in carcinogenesis. However, the role of NOD2 in cancer is not well understood. Here we investigated the role of NOD2 in the development of hepatocellular carcinoma (HCC). We demonstrated that NOD2 deficiency promoted hepatocarcinogenesis in N-nitrosodiethylamine (DEN)/carbon tetrachloride (CCl₄) induced HCC mice model and xenograft tumor model. In vitro investigation showed that NOD2 acted as a tumor suppressor and inhibited proliferation, colony formation and invasion of HCC cells. Clinical investigation showed that NOD2 expression was completely lost or significantly downregulated in clinical HCC tissues, and loss of NOD2 expression was significantly correlated with advanced disease stages. Further investigation showed that NOD2 exerted its anti-tumor effect through activating adenosine 5'-monophosphate (AMP) -activated protein kinase (AMPK) signaling pathway, and NOD2 significantly enhanced the sensitivity of HCC cells to sorafenib, lenvatinib and 5-FU treatment through activating AMPK pathway induced apoptosis. Moreover, we demonstrated that NOD2 activated AMPK pathway by directly binding with AMPKα-LKB1 complex, which led to autophagy-mediated apoptosis of HCC cells. Altogether, this study showed that NOD2 acted as a tumor suppressor as well as a chemotherapeutic regulator in HCC cells by directly activating AMPK pathway, which indicated a potential therapeutic strategy for HCC treatment by upregulating NOD2-AMPK signaling axis.