Sensitizing immune unresponsive colorectal cancers to immune checkpoint inhibitors through MAVS overexpression

A targeted MAVS fusion protein for controlled innate immune activation and antitumor therapy

Targeted therapies leveraging the innate immune system are emerging as promising cancer treatments. The mitochondrial antiviral signaling protein (MAVS) plays a crucial role in initiating innate immune responses, but its clinical use is limited by the risk of uncontrolled activation and systemic toxicity. To address this, we developed a novel therapeutic agent, the truncated interferon activation switch (TRIAS), combining MAVS truncates with a tumor antigen-targeting single-chain variable fragment (scFv). This design ensures antigen-dependent, controlled activation. Lentiviral delivery of TRIAS induced significant antitumor responses, including complete tumor regression in some cases. Flow cytometry (FCM) analysis further confirmed that tumor cells were the predominant population expressing the transgene. TRIAS-expressing tumor cells exhibited enhanced antitumor activity, likely due to increased cytokine release and upregulated major histocompatibility complex (MHC) expression, enabling tumor cells to function as antigen-presenting cells. This activated other immune cells, driving adaptive immune responses. Additionally, TRIAS promoted a proinflammatory shift in the tumor microenvironment (TME). In conclusion, TRIAS was validated as an innovative immunotherapeutic agent with MAVS-like immune-activating properties and tightly controlled mechanisms, offering a safer and more effective approach for clinical cancer immunotherapy.

ETS2 aggravate allergic airway inflammation by regulating ANT2-mediated cytosolic mitochondrial DsRNA levels

BACKGROUND

ETS2 has been identified as a pivotal regulator in the development of human inflammatory diseases. Nevertheless, the functional aspects of ETS2 in asthma remain inadequately characterized. The release of mitochondrial dsRNA is recognized as an initiator of innate immune responses and implicated in intensifying inflammation triggered by alternative immunogens. The interplay between these mechanisms remains poorly understood, and only a limited number of direct targets that underpin the pro-inflammatory role of ETS2 have been identified.

METHODS

The expression of ETS2 in epithelial cells under immune responses was analyzed, and its effects on asthma progression were examined through clinical specimens, human bronchial epithelial cells, and an allergic asthma mouse model. Additionally, the potential involvement of adenine nucleotide translocase-2 in mediating the immune responses regulated by ETS2 was explored.

RESULTS

Increased expression of ETS2 in lung epithelial cells was observed in both asthma patients and ovalbumin (OVA)-induced asthma mice. The deficiency of ETS2 resulted in a substantial decline in inflammatory cell infiltration and markedly diminished IL-6, IL-5, and IL-13 levels in epithelial cells. Mechanistically, ETS2 overexpression was associated with elevated cytosolic mitochondrial RNA levels, whereas knockdown resulted in their suppression. Furthermore, adenine nucleotide translocase-2 (ANT2) expression was robustly upregulated by ETS2 through direct promoter binding. The advantageous effects of ETS2 on asthma development were abrogated in ANT2-deficient mice.

CONCLUSIONS

The findings collectively underscore the role of ETS2 as an exacerbating factor in allergic airway inflammation during asthma progression, primarily by inducing ANT2 expression. Therapeutic targeting of epithelial ETS2 could represent a novel approach to asthma management.

CLINICAL TRIAL NUMBER

Not applicable.

Loss of histone deubiquitinase Bap1 triggers anti-tumor immunity

PURPOSE

Immunotherapy using PD-L1 blockade is effective in only a small group of cancer patients, and resistance is common. This emphasizes the importance of understanding the mechanisms of cancer immune evasion and resistance.

METHODS

A genome-scale CRISPR-Cas9 screen identified Bap1 as a regulator of PD-L1 expression. To measure tumor size and survival, tumor cells were subcutaneously injected into both syngeneic WT mice and immunocompromised mice. The phenotypic and transcriptional characteristics of Bap1-deleted tumors were examined using flow cytometry, RNA-seq, and CUT&Tag-seq analysis.

RESULTS

We found that loss of histone deubiquitinase Bap1 in cancer cells activates a cDC1-CD8+ T cell-dependent anti-tumor immunity. The absence of Bap1 leads to an increase in genes associated with anti-tumor immune response and a decrease in genes related to immune evasion. As a result, the tumor microenvironment becomes inflamed, with more cDC1 cells and effector CD8+ T cells, but fewer neutrophils and regulatory T cells. We also found that the elimination of Bap1-deleted tumors depends on the tumor MHCI molecule and Fas-mediated CD8+ T cell cytotoxicity. Our analysis of TCGA data further supports these findings, showing a reverse correlation between BAP1 expression and mRNA signatures of activated DCs and T-cell cytotoxicity in various human cancers.

CONCLUSION

The histone deubiquitinase Bap1 could be used as a biomarker for tumor stratification and as a potential therapeutic target for cancer immunotherapies.

Cellular mechanisms of combining innate immunity activation with PD-1/PD-L1 blockade in treatment of colorectal cancer

PD-1/PD-L1 blockade therapies have displayed extraordinary clinical efficacy for melanoma, renal, bladder and lung cancer; however, only a minority of colorectal cancer (CRC) patients benefit from these treatments. The efficacy of PD-1/PD-L1 blockade in CRC is limited by the complexities of tumor microenvironment. PD-1/PD-L1 blockade immunotherapy is based on T cell-centered view of tumor immunity. However, the onset and maintenance of T cell responses and the development of long-lasting memory T cells depend on innate immune responses. Acknowledging the pivotal role of innate immunity in anti-tumor immune response, this review encapsulates the employment of combinational therapies those involve PD-1/PD-L1 blockade alongside the activation of innate immunity and explores the underlying cellular mechanisms, aiming to harnessing innate immune responses to induce long-lasting tumor control for CRC patients who received PD-1/PD-L1 blockade therapy.

Dual inhibitors of DNMT and HDAC remodels the immune microenvironment of colorectal cancer and enhances the efficacy of anti-PD-L1 therapy

Colorectal cancer is the second most prevalent and deadly cancer worldwide. The emergence of immune checkpoint therapy has provided a revolutionary strategy for the treatment of solid tumors. However, less than 5 % of colorectal cancer patients respond to immune checkpoint therapy. Thus, it is of great scientific significance to develop "potentiators" for immune checkpoint therapy. In this study, we found that knocking down different DNMT and HDAC isoforms could increase the expression of IFNs in colorectal cancer cells, which can enhance the effectiveness of immune checkpoint therapy. Therefore, the combined inhibition of DNMT and HDAC cloud synergistically enhance the effect of immunotherapy. We found that dual DNMT and HDAC inhibitors C02S could inhibit tumor growth in immunocompetent mice but not in immunocompromised nude mice, which indicates that C02S exerts its antitumor effects through the immune system. Mechanistically, C02S could increase the expression of ERVs, which generated the intracellular levels of dsRNA in tumor cells, and then promotes the expression of IFNs through the RIG-I/MDA5-MAVS signaling pathway. Moreover, C02S increased the immune infiltration of DCs and T cells in microenvironment, and enhanced the efficacy of anti-PD-L1 therapy in MC38 and CT26 mice model. These results confirmed that C02S can activate IFNs through the RIG-I/MDA5-MAVS signaling pathway, remodel the tumor immune microenvironment and enhance the efficacy of immune checkpoint therapy, which provides new evidence and solutions for the development of "potentiator" for colorectal cancer immunotherapy.

ANT2 functions as a translocon for mitochondrial cross-membrane translocation of RNAs

Bidirectional transcription of mammalian mitochondrial DNA generates overlapping transcripts that are capable of forming double-stranded RNA (dsRNA) structures. Release of mitochondrial dsRNA into the cytosol activates the dsRNA-sensing immune signaling, which is a defense mechanism against microbial and viral attack and possibly cancer, but could cause autoimmune diseases when unchecked. A better understanding of the process is vital in therapeutic application of this defense mechanism and treatment of cognate human diseases. In addition to exporting dsRNAs, mitochondria also export and import a variety of non-coding RNAs. However, little is known about how these RNAs are transported across mitochondrial membranes. Here we provide direct evidence showing that adenine nucleotide translocase-2 (ANT2) functions as a mammalian RNA translocon in the mitochondrial inner membrane, independent of its ADP/ATP translocase activity. We also show that mitochondrial dsRNA efflux through ANT2 triggers innate immunity. Inhibiting this process alleviates inflammation in vivo, providing a potential therapeutic approach for treating autoimmune diseases.

Activation of insulin-like growth factor-1 receptor (IGF-1R) promotes growth of colorectal cancer through triggering the MEX3A-mediated degradation of RIG-I

Insulin-like growth factor-1 receptor (IGF-1R) has been made an attractive anticancer target due to its overexpression in cancers. However, targeting it has often produced the disappointing results as the role played by cross talk with numerous downstream signalings. Here, we report a disobliging IGF-1R signaling which promotes growth of cancer through triggering the E3 ubiquitin ligase MEX3A-mediated degradation of RIG-I. The active β-arrestin-2 scaffolds this disobliging signaling to talk with MEX3A. In response to ligands, IGF-1Rβ activated the basal βarr2 into its active state by phosphorylating the interdomain domain on Tyr64 and Tyr250, opening the middle loop (Leu130‒Cys141) to the RING domain of MEX3A through the conformational changes of βarr2. The models of βarr2/IGF-1Rβ and βarr2/MEX3A could interpret the mechanism of the activated-IGF-1R in triggering degradation of RIG-I. The assay of the mutants βarr2^Y64A and βarr2^Y250A further confirmed the role of these two Tyr residues of the interlobe in mediating the talk between IGF-1Rβ and the RING domain of MEX3A. The truncated-βarr2 and the peptide ATQAIRIF, which mimicked the RING domain of MEX3A could prevent the formation of βarr2/IGF-1Rβ and βarr2/MEX3A complexes, thus blocking the IGF-1R-triggered RIG-I degradation. Degradation of RIG-I resulted in the suppression of the IFN-I-associated immune cells in the TME due to the blockade of the RIG-I-MAVS-IFN-I pathway. Poly(I:C) could reverse anti-PD-L1 insensitivity by recovery of RIG-I. In summary, we revealed a disobliging IGF-1R signaling by which IGF-1Rβ promoted cancer growth through triggering the MEX3A-mediated degradation of RIG-I.

The Therapeutic Landscape for KRAS-Mutated Colorectal Cancers

Colorectal cancer is one of the world's most prevalent and lethal cancers. Mutations of the KRAS gene occur in ~40% of metastatic colorectal cancers. While this cohort has historically been difficult to manage, the last few years have shown exponential growth in the development of selective inhibitors targeting KRAS mutations. Their foremost mechanism of action utilizes the Switch II binding pocket and Cys12 residue of GDP-bound KRAS proteins in G12C mutants, confining them to their inactive state. Sotorasib and Adagrasib, both FDA-approved for the treatment of non-small cell lung cancer (NSCLC), have been pivotal in paving the way for KRAS G12C inhibitors in the clinical setting. Other KRAS inhibitors in development include a multi-targeting KRAS-mutant drug and a G12D mutant drug. Treatment resistance remains an issue with combination treatment regimens including indirect pathway inhibition and immunotherapy providing possible ways to combat this. While KRAS-mutant selective therapy has come a long way, more work is required to make this an effective and viable option for patients with colorectal cancer.

The lncRNAs involved in regulating the RIG-I signaling pathway

Understanding the targets and interactions of long non-coding RNAs (lncRNAs) related to the retinoic acid-inducible gene-I (RIG-I) signaling pathway is essential for developing interventions, which would enable directing the host inflammatory response regulation toward protective immunity. In the RIG-I signaling pathway, lncRNAs are involved in the important processes of ubiquitination, phosphorylation, and glycolysis, thus promoting the transport of the interferon regulatory factors 3 and 7 (IRF3 and IRF7) and the nuclear factor kappa B (NF-κB) into the nucleus, and activating recruitment of type I interferons (IFN-I) and inflammatory factors to the antiviral action site. In addition, the RIG-I signaling pathway has recently been reported to contain the targets of coronavirus disease-19 (COVID-19)-related lncRNAs. The molecules in the RIG-I signaling pathway are directly regulated by the lncRNA-microRNAs (miRNAs)-messenger RNA (mRNA) axis. Therefore, targeting this axis has become a novel strategy for the diagnosis and treatment of cancer. In this paper, the studies on the regulation of the RIG-I signaling pathway by lncRNAs during viral infections and cancer are comprehensively analyzed. The aim is to provide a solid foundation of information for conducting further detailed studies on lncRNAs and RIG-I in the future and also contribute to clinical drug development.