Ferroptosis, necroptosis, and pyroptosis in anticancer immunity

Abstract

In recent years, cancer immunotherapy based on immune checkpoint inhibitors (ICIs) has achieved considerable success in the clinic. However, ICIs are significantly limited by the fact that only one third of patients with most types of cancer respond to these agents. The induction of cell death mechanisms other than apoptosis has gradually emerged as a new cancer treatment strategy because most tumors harbor innate resistance to apoptosis. However, to date, the possibility of combining these two modalities has not been discussed systematically. Recently, a few studies revealed crosstalk between distinct cell death mechanisms and antitumor immunity. The induction of pyroptosis, ferroptosis, and necroptosis combined with ICIs showed synergistically enhanced antitumor activity, even in ICI-resistant tumors. Immunotherapy-activated CD8+ T cells are traditionally believed to induce tumor cell death via the following two main pathways: (i) perforin-granzyme and (ii) Fas-FasL. However, recent studies identified a new mechanism by which CD8+ T cells suppress tumor growth by inducing ferroptosis and pyroptosis, which provoked a review of the relationship between tumor cell death mechanisms and immune system activation. Hence, in this review, we summarize knowledge of the reciprocal interaction between antitumor immunity and distinct cell death mechanisms, particularly necroptosis, ferroptosis, and pyroptosis, which are the three potentially novel mechanisms of immunogenic cell death. Because most evidence is derived from studies using animal and cell models, we also reviewed related bioinformatics data available for human tissues in public databases, which partially confirmed the presence of interactions between tumor cell death and the activation of antitumor immunity.

Keywords: Anticancer immunity; Ferroptosis; Necroptosis; Pyroptosis.

Fig. 1

Pathways controlling ferroptosis, necroptosis, and pyroptosis. Xc-complex imports cystine, which is used to synthesize glutathione. Glutathione is used by GPX4 to prevent lipid reactive oxygen species accumulation. In this context, the normal expression and function of Xc-complex and GPX4 are essential for the inhibition of ferroptosis under physiological conditions. Gasdermins form membrane pores to cause pyroptosis. The following three pathways have been confirmed to induce pyroptosis in mammals: (1) NLRP3/ASC/caspase-1/GSDMD axis, (2) caspase-4/5/11/GSDMD axis, and (3) caspase-3/GSDME axis. Membrane-associated MLKL induces necroptosis. When the function of caspase-8 is inhibited, the binding of TNF-α and its receptor could promote the assembly of a RIPK1-RIPK3-MLKL signaling complex. RIPK3-mediated phosphorylation of MLKL leads to MLKL translocation to the plasma membrane to trigger membrane damage. As a result of membrane damage, potassium ion outflow could further activate NLRP3 through NEK7, which may be a crosstalk with pyroptosis pathway

Fig. 2

Crosstalk between necroptosis and antitumor immunity. Two strategies have been reported to trigger antitumor immunity through necroptosis. (1) Vaccination with necroptotic tumor cells: DAMPs released from tumor cells undergoing necroptosis promote the maturation of BMDCs, cross-priming of effector T cells, and subsequent cytotoxic effects. Excessive IFN-γ production is observed during this process, likely representing another anticancer approach used by CD8+ T cells. (2) Vaccination with fibroblasts: necroptotic cells release NF-κB-derived signals, further leading to DC activation, increased antigen loading, and robust CD8+ T cell-mediated tumor control. In this context, DAMPs do not appear to be involved in the activation of antitumor immunity. Tumor clearance is increased by the concomitant administration of PD1 inhibitors

Fig. 3

Crosstalk between ferroptosis and pyroptosis and antitumor immunity. Pyroptosis in less than 15% of tumor cells is sufficient to clear an entire tumor graft, suggesting that robust anticancer immunity plays an important role in pyroptosis-initiated tumor killing. On the one hand, tumor cells undergoing pyroptosis facilitate the recruitment of anticancer immune cells, including CD8+ T cells and NK cells, by releasing danger signals. However, the level of infiltration of tumor-promoting cells, such as MDSCs, is significantly decreased during this process. On the other hand, CD8+ T cells and NK cells induce cancer cell pyroptosis by secreting GzmA and GzmB, which are enzymes capable of cleaving GSDMB and GSDME, respectively. Activated macrophage-derived IL-1β is required for the antitumor immunity induced by tumor cell pyroptosis. Similarly, CD8+ T cells induce tumor cell ferroptosis by secreting IFN-γ, which mediates the downregulation of SLC7A11 and leads to the accumulation of lipid ROS. Notably, PD1/PDL-1 inhibitors exert an obvious synergistic effect with pyroptosis/ferroptosis inducers on tumor inhibition

Fig. 4

Bioinformatic evidence of the effects of necroptosis, ferroptosis, and pyroptosis on T cell dysfunction and CD8+ T cell infiltration based on molecular signatures. a The effects of necroptosis, ferroptosis, and pyroptosis on T cell dysfunction and CD8+ T cell infiltration were evaluated based on the molecular signatures of four sets with 37 independent cohorts (core cohorts, immunotherapy datasets, CRISPR screen datasets, and datasets of immunosuppressive cell types). The core cohorts consisted of the five most confident results obtained using gene expression data, and a high z-score (red) suggests that the indicated gene promotes T cell dysfunction. The immunotherapy datasets consisted of 12 datasets of patients who received either ICIs or ACT. In this set, a high z-score (red) represents an unfavorable role of the indicated gene in improving the effects of immunotherapy. CRISPR screening of mouse cancer cells identified genes whose knockout enhanced the efficacy of T cell-mediated tumor cell killing based on 17 cohorts; in these studies, a z-score < 0 (blue) reflects the downregulation of the indicated gene after an increase in either T cell function or the efficacy of immunotherapy, suggesting the negative effects of the indicated gene on immunotherapy outcomes. Immunosuppressive cells restrict the tumor infiltration of T cells, including cancer-associated fibroblasts (CAFs), myeloid-derived suppressor cells (MDSCs), and the M2 subtype of tumor-associated macrophages (TAMs). This section presents the gene expression levels in these T cell exclusion signatures, and a high z-score (red) indicates that the specified gene is overexpressed in immunosuppressive cells. b An example of the evaluation of T cell dysfunction. A considerable amount of CTL infiltration predicts prolonged survival only in tumor samples from patients with low SLC7A11 expression, suggesting that SLC7A11 potentially promotes T cell dysfunction. c The effects of necroptosis, ferroptosis, and pyroptosis on CD8+ T cell infiltration based on molecular signatures are shown

Fig. 5

Correlations among ferroptosis-, pyroptosis-, and necroptosis-related genes; microsatellite instability (MSI); and the tumor mutation burden (TMB) across 33 cancers. The correlations among ferroptosis-, pyroptosis-, and necroptosis-related genes, MSI, and TMB were visualized as a heatmap. The colors of the up-pointing triangles reflect the correlation strength between the expression levels of ferroptosis-, pyroptosis-, and necroptosis-related genes and MSI. The colors of the down-pointing triangles reflect the correlation strength between the expression levels of ferroptosis-, pyroptosis-, and necroptosis-related genes and TMB. The correlations between GSDMC and MSI or TMB were further visualized as a radar map