HSP90 Mediates IFNγ-Induced Adaptive Resistance to Anti-PD-1 Immunotherapy

The aryl hydrocarbon receptor controls IFN-γ-induced immune checkpoints PD-L1 and IDO via the JAK/STAT pathway in lung adenocarcinoma

While immunotherapy has shown some efficacy in lung adenocarcinoma (LUAD) patients, many respond only partially or not at all. One limitation in improving outcomes is the lack of a complete understanding of immune checkpoint regulation. Here, we investigated a possible link between an environmental chemical receptor implicated in lung cancer and immune regulation, the AhR, a known but counterintuitive mediator of immunosuppression (interferon (IFN)-γ), and regulation of two immune checkpoints (PD-L1 and IDO). AhR gene-edited LUAD cell lines, a syngeneic LUAD mouse model, bulk and scRNA sequencing of LUADs and tumor-infiltrating T cells were used to map out a signaling pathway leading from IFN-γ through the AhR to JAK/STAT, PD-L1, IDO, and tumor-mediated immunosuppression. The data demonstrate that: (1) IFN-γ activation of the JAK/STAT pathway leading to PD-L1 and IDO1 up-regulation is mediated by the AhR in murine and human LUAD cells, (2) AhR-driven IDO1 induction results in the production of Kynurenine (Kyn), an AhR ligand, which likely mediates an AhR→IDO1→Kyn→AhR amplification loop, (3) transplantation of AhR-knockout LUAD cells results in long-term tumor immunity in most recipients. (4) The 23% of AhR-knockout tumors that do grow do so at a much slower pace than controls and exhibit higher densities of CD8+ T cells expressing markers of immunocompetence, increased activity, and increased cell-cell communication. The data definitively link the AhR to IFN-γ-induced JAK/STAT pathway and immune checkpoint-mediated immunosuppression and support the targeting of the AhR in the context of LUAD.

Glutamine deprivation confers immunotherapy resistance by inhibiting IFN-γ signaling in cancer cells

Glutamine metabolism is emerging as a target for improving immunotherapy efficacy. However, the outcomes remain inconclusive. Given that the tumor-intrinsic response to interferon-γ (IFN-γ) is a key determinant of immunotherapy efficacy, we investigated whether and how glutamine deprivation in cancer cells affects their response to IFN-γ. By using human lung cancer cell lines, patient-derived tumor explants, and a syngeneic mouse model of lung cancer, we demonstrated that glutamine deprivation reduced the IFN-γ-driven response in cancer cells by promoting autophagy-dependent IFN-γ receptor (IFNGR1) degradation and rendering tumors resistant to anti-PD-1 or anti-PD-L1 therapy. Treatment with V9302, an inhibitor of the alanine-serine-cysteine transporter (ASCT2), enhanced the IFN-γ-driven response of cancer cells and increased the efficacy of PD-1 blockade therapy. Mechanistic analysis revealed that V9302 inhibited autophagy by impairing lysosomal activity independent of glutamine deprivation, likely because of its physiochemical properties, thereby preventing IFNGR1 degradation. Moreover, V9302 also increased Glut1 expression through the inhibition of lysosomal pathway-dependent degradation of Glut1 and consequently increased cancer cell glucose uptake, in turn retaining the levels of intracellular alpha-ketoglutarate (α-KG) and ATP, which are involved in maintaining IFN-γ signal transduction in cancer cells. In support of these findings, targeting lysosomal activity with chloroquine (CQ) also increased IFNGR1 expression and the IFN-γ-driven response in cancer cells. The administration of CQ increased the sensitivity of ASCT2-deficient tumors to anti-PD-L1 therapy. Glutamine deprivation per se leads to resistance to immunotherapy, whereas V9302 treatment results in increased immunotherapy efficacy through impaired lysosomal activity, which is independent of glutamine deprivation.

OSGIN1 promotes ferroptosis resistance by directly enhancing GCLM activity

Oxidative stress induced growth inhibitor 1 (OSGIN1) is a tumor protein p53 (TP53)-target gene involved in the oxidative stress response and promotes apoptosis. Here, we present the first evidence that OSGIN1 functions conversely by inhibiting ferroptosis, a distinct form of oxidative cell death driven by excessive lipid peroxidation. OSGIN1 expression is upregulated by pharmacological ferroptosis inducers in an NFE2 like BZIP transcription factor 2 (NFE2L2)-dependent manner, rather than through the TP53 pathway, in human pancreatic ductal adenocarcinoma (PDAC) cells. Genetic depletion of OSGIN1 or NFE2L2 similarly promotes ferroptosis, while re-expression of OSGIN1 rescues ferroptosis resistance in NFE2L2-knockout cells, both in vitro and in animal models. Mechanistically, immunoprecipitation combined with mass spectrometry revealed that OSGIN1 interacts with glutamate-cysteine ligase modifier subunit (GCLM), enhancing glutathione production and thereby mitigating oxidative stress. Additionally, OSGIN1 expression shows a positive correlation with NFE2L2 expression in pancreatic tumors, which is linked to poorer prognosis in PDAC patients. Collectively, these findings establish a novel defense mechanism that regulates ferroptosis and may influence tumor suppression in PDAC.

NFE2L2 and SLC25A39 drive cuproptosis resistance through GSH metabolism

Cuproptosis is a recently discovered form of regulated cell death triggered by mitochondrial copper accumulation and proteotoxic stress. Here, we provide the first evidence that glutathione (GSH), a major non-protein thiol in cells, acts as a cuproptosis inhibitor in pancreatic ductal adenocarcinoma (PDAC) cells. Mechanistically, GSH inhibits cuproptosis by chelating copper, contrasting its role in blocking ferroptosis by inhibiting lipid peroxidation. The classical cuproptosis inducer, ES-Cu (elesclomol plus copper), increases the protein stability of the transcription factor NFE2L2 (also known as NRF2), leading to the upregulation of gene expression of glutamate-cysteine ligase modifier subunit (GCLM) and glutamate-cysteine ligase catalytic subunit (GCLC). GCLM and GCLC are rate-limiting enzymes in GSH synthesis, and increased GSH is transported into mitochondria via the solute carrier family 25 member 39 (SLC25A39) transporter. Consequently, genetic inhibition of the NFE2L2-GSH-SLC25A39 pathway enhances cuproptosis-mediated tumor suppression in cell culture and in mouse tumor models. These findings not only reveal distinct mechanisms of GSH in inhibiting cuproptosis and ferroptosis, but also suggest a potential combination strategy to suppress PDAC tumor growth.

Mechanism of immune checkpoint inhibitor resistance in colorectal cancer patients and its interventional strategies

The remarkable efficacy demonstrated by immune checkpoint inhibitors (ICIs) in melanoma treatment has driven their widespread use in the treatment of a variety of solid tumours, and they have now become one of the mainstays of oncology treatment, especially in the field of colorectal cancer, where they have demonstrated great potential. However, in long-term large-sample studies, it was found that the response to ICIs is low, and there are problems of primary and acquired resistance, which seriously affect their therapeutic effect. In this paper, we will review the mechanism of resistance to ICIs in patients with colorectal cancer and the progress in research of interventional strategies for ICI resistance, aiming to provide new ideas for the solution of the problem of clinical drug resistance to ICIs.

Cetylpyridinium chloride triggers paraptosis to suppress pancreatic tumor growth via the ERN1-MAP3K5-p38 pathway

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive solid malignancy with low 5-year survival and limited treatment options. We conducted an unbiased screening using FDA-approved drug and demonstrated that cetylpyridinium chloride (CPC), a component commonly found in mouthwash and known for its robust bactericidal and antifungal attributes, exhibits anticancer activity against human PDAC cells. CPC inhibited PDAC cell growth and proliferation by inducing paraptosis, rather than apoptosis. Mechanistically, CPC induced paraptosis through the initiation of endoplasmic reticulum stress, leading to the accumulation of misfolded proteins. Subsequently, the endoplasmic reticulum stress to nucleus signaling 1 (ERN1)-mitogen-activated protein kinase kinase kinase 5 (MAP3K5)-p38 mitogen-activated protein kinase (MAPK) signaling pathway was activated, ultimately culminating in the induction of paraptosis. In vivo experiments, including those involving patient-derived xenografts, orthotopic models, and genetically engineered mouse models of PDAC, provided further evidence of CPC's effectiveness in suppressing the growth of pancreatic tumors.

The Aryl Hydrocarbon Receptor Controls IFNγ-Induced Immune Checkpoints PD-L1 and IDO via the JAK/STAT Pathway in Lung Adenocarcinoma

While immunotherapy has shown efficacy in lung adenocarcinoma (LUAD) patients, many respond only partially or not at all. One limitation in improving outcomes is the lack of a complete understanding of immune checkpoint regulation. Here, we investigated a possible link between an environmental chemical receptor implicated in lung cancer and immune regulation, (the aryl hydrocarbon receptor/AhR), a known but counterintuitive mediator of immunosuppression (IFNγ), and regulation of two immune checkpoints (PD-L1 and IDO). AhR gene-edited LUAD cell lines, a syngeneic LUAD mouse model, bulk- and scRNA sequencing of LUADs and tumor-infiltrating leukocytes were used to map out a signaling pathway leading from IFNγ through the AhR to JAK/STAT, PD-L1, IDO, and tumor-mediated immunosuppression. The data demonstrate that: 1) IFNγ activation of the JAK/STAT pathway leading to PD-L1 and IDO1 upregulation is mediated by the AhR in murine and human LUAD cells, 2) AhR-driven IDO1 induction results in the production of Kynurenine (Kyn), an AhR ligand, which likely mediates an AhR→IDO1→Kyn→AhR amplification loop, 3) transplantation of AhR-knockout LUAD cells results in long-term tumor immunity in most recipients. 4) The 23% of AhR-knockout tumors that do grow do so at a much slower pace than controls and exhibit higher densities of CD8+ T cells expressing markers of immunocompetence, increased activity, and increased cell-cell communication. The data definitively link the AhR to IFNγ-induced JAK/STAT pathway and immune checkpoint-mediated immunosuppression and support the targeting of the AhR in the context of LUAD.

Heat shock protein 90α reduces CD8+ T cell exhaustion in acute lung injury induced by lipopolysaccharide

CD8+ T-cell exhaustion is a promising prognostic indicator of sepsis-induced acute respiratory distress syndrome (ARDS). Patients with sepsis-related ARDS had reduced levels of HSP90AA1. However, whether the changes in CD8+ T cells were related to HSP90α, encoded by the HSP90AA1 gene, was unclear. This study aimed to examine the regulatory mechanism of HSP90α and its impact on CD8+ T-cell exhaustion in lipopolysaccharide (LPS)-induced acute lung injury (ALI). In this study, by conducting a mouse model of ALI, we found that one week after LPS-induced ALI, CD8+ T cells showed exhaustion characteristics. At this time, proliferation and cytokine release in CD8+ T cells were reduced. The inhibitory costimulatory factors PD-1 and Tim-3, on the other hand, were enhanced. Meanwhile, the expression of HSP90α and STAT1 decreased significantly. The in vitro studies showed that HSP90α stimulation or inhibition affected the CD8+ T-cell exhaustion phenotype. Interference with STAT1 reduced the expression of HSP90α and impaired its regulation of CD8+ T cells. The Co-Immunoprecipitation results indicated that HSP90α can directly or indirectly bind to TOX to regulate TOX expression and downstream signal transduction. In summary, by inhibiting TOX-mediated exhaustion signaling pathways, HSP90α inhibited CD8+ T-cell exhaustion in ALI. The participation of STAT1 in the regulation of HSP90α was required.

Tumor-specific GPX4 degradation enhances ferroptosis-initiated antitumor immune response in mouse models of pancreatic cancer

Lipid peroxidation-dependent ferroptosis has become an emerging strategy for tumor therapy. However, current strategies not only selectively induce ferroptosis in malignant cells but also trigger ferroptosis in immune cells simultaneously, which can compromise anti-tumor immunity. Here, we used In-Cell Western assays combined with an unbiased drug screening to identify the compound N6F11 as a ferroptosis inducer that triggered the degradation of glutathione peroxidase 4 (GPX4), a key ferroptosis repressor, specifically in cancer cells. N6F11 did not cause the degradation of GPX4 in immune cells, including dendritic, T, natural killer, and neutrophil cells. Mechanistically, N6F11 bound to the RING domain of E3 ubiquitin ligase tripartite motif containing 25 (TRIM25) in cancer cells to trigger TRIM25-mediated K48-linked ubiquitination of GPX4, resulting in its proteasomal degradation. Functionally, N6F11 treatment caused ferroptotic cancer cell death that initiated HMGB1-dependent antitumor immunity mediated by CD8+ T cells. N6F11 also sensitized immune checkpoint blockade that targeted CD274/PD-L1 in advanced cancer models, including genetically engineered mouse models of pancreatic cancer driven by KRAS and TP53 mutations. These findings may establish a safe and efficient strategy to boost ferroptosis-driven antitumor immunity.

Targeting leucine-rich repeat serine/threonine-protein kinase 2 sensitizes pancreatic ductal adenocarcinoma to anti-PD-L1 immunotherapy

Pancreatic ductal adenocarcinoma (PDAC) is not sensitive to immune checkpoint blockade therapy, and negative feedback of tumor immune evasion might be partly responsible. We isolated CD8+ T cells and cultured them in vitro. Proteomics analysis was performed to compare changes in Panc02 cell lines cultured with conditioned medium, and leucine-rich repeat kinase 2 (LRRK2) was identified as a differential gene. LRRK2 expression was related to CD8+ T cell spatial distribution in PDAC clinical samples and upregulated by CD8+ T cells via interferon gamma (IFN-γ) simulation in vitro. Knockdown or pharmacological inhibition of LRRK2 activated an anti-pancreatic cancer immune response in mice, which meant that LRRK2 acted as an immunosuppressive gene. Mechanistically, LRRK2 phosphorylated PD-L1 at T210 to inhibit its ubiquitination-mediated proteasomal degradation. LRRK2 inhibition attenuated PD-1/PD-L1 blockade-mediated, T cell-induced upregulation of LRRK2/PD-L1, thus sensitizing the mice to anti-PD-L1 therapy. In addition, adenosylcobalamin, the activated form of vitamin B12, which was found to be a broad-spectrum inhibitor of LRRK2, could inhibit LRRK2 in vivo and sensitize PDAC to immunotherapy as well, which potentially endows LRRK2 inhibition with clinical translational value. Therefore, PD-L1 blockade combined with LRRK2 inhibition could be a novel therapy strategy for PDAC.

Activating an Adaptive Immune Response with a Telomerase-Mediated Telomere Targeting Therapeutic in Hepatocellular Carcinoma

A select group of patients with hepatocellular carcinomas (HCC) benefit from surgical, radiologic, and systemic therapies that include a combination of anti-angiogenic and immune-checkpoint inhibitors. However, because HCC is generally asymptomatic in its early stages, this not only leads to late diagnosis, but also to therapy resistance. The nucleoside analogue 6-thio-dG (THIO) is a first-in-class telomerase-mediated telomere-targeting anticancer agent. In telomerase expressing cancer cells, THIO is converted into the corresponding 5'-triphosphate, which is efficiently incorporated into telomeres by telomerase, activating telomere damage responses and apoptotic pathways. Here, we show how THIO is effective in controlling tumor growth and, when combined with immune checkpoint inhibitors, is even more effective in a T-cell-dependent manner. We also show telomere stress induced by THIO increases both innate sensing and adaptive antitumor immunity in HCC. Importantly, the extracellular high-mobility group box 1 protein acts as a prototypical endogenous DAMP (Damage Associated Molecular Pattern) in eliciting adaptive immunity by THIO. These results provide a strong rationale for combining telomere-targeted therapy with immunotherapy.

FOXO3a-dependent up-regulation of HSP90 alleviates cisplatin-induced apoptosis by activating FUNDC1-mediated mitophagy in hypoxic osteosarcoma cells

Hypoxia-induced decrease in cisplatin (CDDP) sensitivity in human osteosarcoma (OS) is a significant obstacle to effective chemotherapy. Recently, mitophagy has been shown to be associated with CDDP sensitivity. However, whether it regulates hypoxia-induced decreases in CDDP sensitivity in OS and the underlying mechanisms remain unknown. In this study, we found that hypoxia activated mitophagy and suppressed mitophagy with specific inhibitors, mitochondrial division inhibitor-1 (Mdivi-1) or lysosome inhibitor chloroquine (CQ), which inhibited CDDP-induced apoptosis in hypoxic U-2OS and MG-63 cells. In addition, hypoxia upregulated the phosphorylation level of FUN14 domain-containing protein 1 (FUNDC1), whereas the activation of mitophagy and decreased CDDP sensitivity were inhibited by transfection with FUNDC1 small interfering RNA (siRNA). Hypoxia treatment also led to the up-regulation of heat shock protein 90 (HSP90), whereas HSP90 siRNA inhibited FUNDC1-mediated activation of mitophagy and decreased CDDP sensitivity. Furthermore, activation of Unc-51 like autophagy activating kinase 1 (Ulk1) was found in U-2OS and MG-63 cells after induction of hypoxia. Overexpression of Ulk1 prevented the inhibitory effect of HSP90 siRNA on the activation of FUNDC1 and mitophagy and decreased CDDP sensitivity in hypoxic U-2OS and MG-63 cells. Finally, hypoxia induced the activation of forkhead box transcription factor 3a (FOXO3a), whereas FOXO3a siRNA inhibited hypoxia-induced HSP90 up-regulation, Ulk1 activation, and FUNDC1-mediated activation of mitophagy, and decreased CDDP sensitivity in U-2OS and MG-63 cells. Using a chromatin immunoprecipitation (ChIP) assay, we confirmed that FOXO3a binds to the HSP90 promoter region. In conclusion, our findings suggest that hypoxia alleviates CDDP-induced apoptosis by activating mitophagy through the FOXO3a/HSP90/Ulk1/FUNDC1 signaling pathway in OS cells.

HSP90 mediates the connection of multiple programmed cell death in diseases

Heat shock protein (HSP) 90, an important component of the molecular chaperone network, is closely concerned with cellular signaling pathways and stress response by participating in the process of maturation and activation of client proteins, playing a crucial role both in the normal and abnormal operation of the organism. In functionally defective tissues, programmed cell death (PCD) is one of the regulable fundamental mechanisms mediated by HSP90, including apoptosis, autophagy, necroptosis, ferroptosis, and others. Here, we show the complex relationship between HSP90 and different types of PCD in various diseases, and discuss the possibility of HSP90 as the common regulatory nodal in multiple PCD, which would provide a new perspective for the therapeutic approaches in disease.

Targeting Heat-Shock Protein 90 in Cancer: An Update on Combination Therapy

Heat-shock protein 90 (HSP90) is an important molecule chaperone associated with tumorigenesis and malignancy. HSP90 is involved in the folding and maturation of a wide range of oncogenic clients, including diverse kinases, transcription factors and oncogenic fusion proteins. Therefore, it could be argued that HSP90 facilitates the malignant behaviors of cancer cells, such as uncontrolled proliferation, chemo/radiotherapy resistance and immune evasion. The extensive associations between HSP90 and tumorigenesis indicate substantial therapeutic potential, and many HSP90 inhibitors have been developed. However, due to HSP90 inhibitor toxicity and limited efficiency, none have been approved for clinical use as single agents. Recent results suggest that combining HSP90 inhibitors with other anticancer therapies might be a more advisable strategy. This review illustrates the role of HSP90 in cancer biology and discusses the therapeutic value of Hsp90 inhibitors as complements to current anticancer therapies.

The V-ATPases in cancer and cell death

Transmembrane ATPases are membrane-bound enzyme complexes and ion transporters that can be divided into F-, V-, and A-ATPases according to their structure. The V-ATPases, also known as H⁺-ATPases, are large multi-subunit protein complexes composed of a peripheral domain (V1) responsible for the hydrolysis of ATP and a membrane-integrated domain (V0) that transports protons across plasma membrane or organelle membrane. V-ATPases play a fundamental role in maintaining pH homeostasis through lysosomal acidification and are involved in modulating various physiological and pathological processes, such as macropinocytosis, autophagy, cell invasion, and cell death (e.g., apoptosis, anoikis, alkaliptosis, ferroptosis, and lysosome-dependent cell death). In addition to participating in embryonic development, V-ATPase pathways, when dysfunctional, are implicated in human diseases, such as neurodegenerative diseases, osteopetrosis, distal renal tubular acidosis, and cancer. In this review, we summarize the structure and regulation of isoforms of V-ATPase subunits and discuss their context-dependent roles in cancer biology and cell death. Updated knowledge about V-ATPases may enable us to design new anticancer drugs or strategies.