Synthetic lethal CRISPR screen identifies a cancer cell-intrinsic role of PD-L1 in regulation of vulnerability to ferroptosis.

Despite the success of programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1) inhibition in tumor therapy, many patients do not benefit. This failure may be attributed to the intrinsic functions of PD-L1. We perform a genome-wide CRISPR synthetic lethality screen to systematically explore the intrinsic functions of PD-L1 in head and neck squamous cell carcinoma (HNSCC) cells, identifying ferroptosis-related genes as essential for the viability of PD-L1-deficient cells. Genetic and pharmacological induction of ferroptosis accelerates cell death in PD-L1 knockout cells, which are also more susceptible to immunogenic ferroptosis. Mechanistically, nuclear PD-L1 transcriptionally activates SOD2 to maintain redox homeostasis. Lower reactive oxygen species (ROS) and ferroptosis are observed in patients with HNSCC who have higher PD-L1 expression. Our study illustrates that PD-L1 confers ferroptosis resistance in HNSCC cells by activating the SOD2-mediated antioxidant pathway, suggesting that targeting the intrinsic functions of PD-L1 could enhance therapeutic efficacy.

PD-1/CD80+ small extracellular vesicles from immunocytes induce cold tumours featured with enhanced adaptive immunosuppression.

Only a minority of cancer patients benefit from immune checkpoint blockade therapy. Sophisticated cross-talk among different immune checkpoint pathways as well as interaction pattern of immune checkpoint molecules carried on circulating small extracellular vesicles (sEV) might contribute to the low response rate. Here we demonstrate that PD-1 and CD80 carried on immunocyte-derived sEVs (I-sEV) induce an adaptive redistribution of PD-L1 in tumour cells. The resulting decreased cell membrane PD-L1 expression and increased sEV PD-L1 secretion into the circulation contribute to systemic immunosuppression. PD-1/CD80+ I-sEVs also induce downregulation of adhesion- and antigen presentation-related molecules on tumour cells and impaired immune cell infiltration, thereby converting tumours to an immunologically cold phenotype. Moreover, synchronous analysis of multiple checkpoint molecules, including PD-1, CD80 and PD-L1, on circulating sEVs distinguishes clinical responders from those patients who poorly respond to anti-PD-1 treatment. Altogether, our study shows that sEVs carry multiple inhibitory immune checkpoints proteins, which form a potentially targetable adaptive loop to suppress antitumour immunity.

Targeting CMTM6 Suppresses Stem Cell-Like Properties and Enhances Antitumor Immunity in Head and Neck Squamous Cell Carcinoma.

CMTM6, a regulator of PD-L1 expression, also modulates tumor immunity. Little is known about the function of CMTM6 and its mechanism of action in head and neck squamous cell carcinoma (HNSCC). In this study, we found by IHC analysis that CMTM6 overexpression predicted a poor prognosis for patients with HNSCC. We discovered that CMTM6 expression was correlated with increased activity through the Wnt/ß-catenin signaling pathway, which is essential for tumorigenesis, maintenance of cancer stem cells (CSC), and the epithelial-to-mesenchymal transition (EMT) characteristic of multiple cancers. We used short hairpin RNA to eliminate expression of CMTM6, which led, in HNSCC cells, to reduced expression of nuclear ß-catenin as well as inhibition of stem cell-like properties, TGFß-induced EMT, and cell proliferation. Consistent with these results, we identified a significant positive correlation between expression of CMTM6 and EMT- and CSC-related genes in The Cancer Genome Atlas (TCGA). We found positive correlations for both RNA and protein between expression of CMTM6 and immune checkpoint components. CMTM6 silencing-induced PD-L1 downregulation delayed SCC7 tumor growth and increased CD8+ and CD4+ T-cell infiltration. The proportions of PD-1+, TIM-3+, VISTA+, LAG-3+, and B7-H3+ exhausted T cells were decreased significantly in the CMTM6 knockdown group. CMTM6 thus regulates stemness, EMT, and T-cell dysfunction and may be a promising therapeutic target in the treatment of HNSCC.

Specific blockade CD73 alters the "exhausted" phenotype of T cells in head and neck squamous cell carcinoma.

The adenosine-induced immunosuppression hampers the immune response toward tumor cells and facilitates the tumor cells to evade immunosurveillance. CD73, an ecto-5-nucleotidase, is the ectoenzyme dephosphorylating extracellular AMP to adenosine. Here, using immunocompetent transgenic head and neck squamous cell carcinoma (HNSCC) mouse model, immune profiling showed high expression of CD73 on CD4+ and CD8+ T cells was associated with an "exhausted" phenotype. Further, treatment with anti-CD73 monoclonal antibody (mAb) significantly blunted the tumor growth in the mouse model, and the blockade of CD73 reversed the "exhausted" phenotype of CD4+ and CD8+ T cells through downregulation of total expression of PD-1 and CTLA-4 on T cells. Whereas the population of CD4+ CD73hi /CD8+ CD73hi T cells expressed higher CTLA-4 and PD-1 as compared to untreated controls. In addition, the human tissue microarrays showed the expression of CD73 is upregulated on tumor infiltrating immune cells in patients with primary HNSCC. Moreover, CD73 expression is an independent prognostic factor for poor outcome in our cohort of HNSCC patients. Altogether, these findings highlight the immunoregulatory role of CD73 in the development of HNSCC and we propose that CD73 may prove to be a promising immunotherapeutic target for the treatment of HNSCC.

γ-Secretase inhibitor reduces immunosuppressive cells and enhances tumour immunity in head and neck squamous cell carcinoma.

Immune evasion is a hallmark feature of cancer, and it plays an important role in tumour initiation and progression. In addition, tumour immune evasion severely hampers the desired antitumour effect in multiple cancers. In this study, we aimed to investigate the role of the Notch pathway in immune evasion in the head and neck squamous cell carcinoma (HNSCC) microenvironment. We first demonstrated that Notch1 signaling was activated in a Tgfbr1/Pten-knockout HNSCC mouse model. Notch signaling inhibition using a γ-secretase inhibitor (GSI-IX, DAPT) decreased tumour burden in the mouse model after prophylactic treatment. In addition, flow cytometry analysis indicated that Notch signaling inhibition reduced the sub-population of myeloid-derived suppressor cells (MDSCs), tumour-associated macrophages (TAMs) and regulatory T cells (Tregs), as well as immune checkpoint molecules (PD1, CTLA4, TIM3 and LAG3), in the circulation and in the tumour. Immunohistochemistry (IHC) of human HNSCC tissues demonstrated that elevation of the Notch1 downstream target HES1 was correlated with MDSC, TAM and Treg markers and with immune checkpoint molecules. These results suggest that modulating the Notch signaling pathway may decrease MDSCs, TAMs, Tregs and immune checkpoint molecules in HNSCC.

TRAF6 regulates tumour metastasis through EMT and CSC phenotypes in head and neck squamous cell carcinoma.

Epithelial-mesenchymal transition (EMT) is associated with metastasis formation, generation and maintenance of cancer stem cells (CSCs). However, the regulatory mechanisms of CSCs have not been clarified. This study aims to investigate the role of TNF receptor-associated factor 6 (TRAF6) on EMT and CSC regulation in squamous cell carcinoma of head and neck (SCCHN). We found TRAF6 was overexpressed in human SCCHN tissues, and high TRAF6 expression was associated with lymphatic metastasis and resulted in poor prognosis in patients with SCCHN. In addition, elevated TRAF6 expression was observed in several HNSCC cell lines, and wound healing and transwell assay results showed that TRAF6 knockdown inhibited the migration and invasion ability of the SCCHN cells. Moreover, the expression of Vimentin, Slug and N-cadherin was down-regulated and that of E-cadherin was elevated after TRAF6 knockdown but decreased by transforming growth factor beta 1 (TGF-ß1) and CAL27 similar to mesenchymal cells formed after TGF-ß1 induction. In addition, the expression levels of CD44, ALDH1, KLF4 and SOX2 were inhibited after TRAF6 knockdown, and the anchor-dependent colony formation number and sphere number were remarkably reduced. Flow cytometry showed TRAF6 knockdown reduced ALDH1-positive cancer stem cells. We also demonstrated that TRAF6 is closely associated with EMT process and cancer stem cells using a Tgfbr1/Pten 2cKO mice SCCHN model and human SCCHN tissue microarray. Our findings indicate that TRAF6 plays a role in EMT phenotypes, the generation and maintenance of CSCs in SCCHN, suggesting that TRAF6 is a potential therapeutic target for SCCHN.

Inhibition of JAK2/STAT3 reduces tumor-induced angiogenesis and myeloid-derived suppressor cells in head and neck cancer.

Angiogenesis is an essential event in tumor growth and metastasis, and immune system also contributes to the tumor evasion. Emerging evidences have suggested the bidirectional link between angiogenesis and immunosuppression. Myeloid-derived suppressor cell (MDSC) is a kind of immunosuppressive cells and plays an important role in this process. However, the actual regulatory mechanisms of angiogenesis and MDSCs in head and neck squamous cell carcinoma (HNSCC) were unclear. In this study, through analyzing the immunohistochemistry staining of human HNSCC tissue microarray, we found that the microvascular density (MVD) was significantly increased in HNSCC patients. We also characterized angiogenic factors p-STAT3, VEGFA, CK2, and MDSCs marker CD11b in HNSCC tissue array, and found the close expression correlation among these markers. To determine the role of JAK2/STAT3 pathway in tumor microenvironment of HNSCC, we utilized AG490 (an inhibitor of JAK2/STAT3) for further research. Results showed that inhibition of JAK2/STAT3 suppressed angiogenesis by decreasing VEGFA and HIF1-α both in vitro and vivo. Moreover, in HNSCC transgenic mouse model, inhibiting JAK2/STAT3 not only suppressed angiogenesis but also reduced MDSCs in the tumor microenvironment through suppressing VEGFA and CK2. Our findings demonstrated the close relationship between angiogenesis and MDSCs in HNSCC, and inhibition of JAK2/STAT3 could reduce tumor-induced angiogenesis and decrease MDSCs.

Blockage of the NLRP3 inflammasome by MCC950 improves anti-tumor immune responses in head and neck squamous cell carcinoma.

The NLRP3 inflammasome is a critical innate immune pathway responsible for producing active interleukin (IL)-1ß, which is associated with tumor development and immunity. However, the mechanisms regulating the inflammatory microenvironment, tumorigenesis and tumor immunity are unclear. Herein, we show that the NLRP3 inflammasome was over-expressed in human HNSCC tissues and that the IL-1ß concentration was increased in the peripheral blood of HNSCC patients. Additionally, elevated NLRP3 inflammasome levels were detected in tumor tissues of Tgfbr1/Pten 2cKO HNSCC mice, and elevated IL-1ß levels were detected in the peripheral blood serum, spleen, draining lymph nodes and tumor tissues. Blocking NLRP3 inflammasome activation using MCC950 remarkably reduced IL-1ß production in an HNSCC mouse model and reduced the numbers of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) and tumor-associated macrophages (TAMs). Moreover, inhibiting NLRP3 inflammasome activation increased the numbers of CD4+ and CD8+ T cells in HNSCC mice. Notably, the numbers of exhausted PD-1+ and Tim3+ T cells were significantly reduced. A human HNSCC tissue microarray showed that NLRP3 inflammasome expression was correlated with the expression of CD8 and CD4, the Treg marker Foxp3, the MDSC markers CD11b and CD33, and the TAM markers CD68 and CD163, PD-1 and Tim3. Overall, our results demonstrate that the NLRP3 inflammasome/IL-1ß pathway promotes tumorigenesis in HNSCC and inactivation of this pathway delays tumor growth, accompanied by decreased immunosuppressive cell accumulation and an increased number of effector T cells. Thus, inhibition of the tumor microenvironment through the NLRP3 inflammasome/IL-1ß pathway may provide a novel approach for HNSCC therapy.

NLRP3 inflammasome activation promotes inflammation-induced carcinogenesis in head and neck squamous cell carcinoma.

BACKGROUND: NLRP3 inflammasome acts as a danger signal sensor that triggers and coordinates the inflammatory response. However, the roles of NLRP3 inflammasome in the tumorigenesis and development of cancer stem cells (CSCs) of squamous cell carcinoma of the head and neck (SCCHN) remain ambiguous. METHODS: In our study, tissue microarrays, ELISA, sphere-forming assay, colony formation assay and Western blot analysis were performed to evaluate the effect of NLRP3 inflammasome on the development of CSCs in human SCCHN tissue specimen, cell lines, and transgenic mouse SCCHN model. RESULTS: The components of NLRP3 inflammasome, namely, NLRP3, ASC, Caspase-1, and IL-18 were correlated with CSCs markers BMI1, ALDH1 and CD44 in human SCCHN specimens. Moreover, NLRP3, Caspase-1, IL-1ß, and IL-18 were highly expressed in SCCHN cell lines. NLRP3 inflammasome activated by LPS and ATP promoted sphere-forming and colony formation capacities along with an upregulation of BMI1, ALDH1 and CD44. In addition, NLRP3 inflammasome blockade by NLRP3 inhibitor MCC950 reduced sphere and colony number, also decreased the expression of BMI1, ALDH1 and CD44 in SCCHN cell lines. Expression of NLRP3, ASC, Caspase-1, IL-1ß, IL-18, BMI1, ALDH1 and CD44 was upregulated in Tgfbr1/Pten 2cKO mouse SCCHN model, and NLRP3 inflammasome expression was closely related to those CSCs makers in mice SCCHN. However, MCC950 treatment reduced the expression of NLRP3 inflammasome, CSCs markers BMI1, ALDH1 and CD44 in Tgfbr1/Pten 2cKO mice SCCHN. In addition, blockade of NLRP3 inflammasome can also delayed the tumor-burdened speed in SCCHN mice. CONCLUSIONS: Our study demonstrates that NLRP3 inflammasome was upregulated and associated with the carcinogenesis and CSCs self-renewal activation in SCCHN. NLRP3 inflammasome can be a potential target in the development of novel approaches for head and neck squamous cell carcinoma therapy.

Targeting phosphorylation of STAT3 delays tumor growth in HPV-negative anal squamous cell carcinoma mouse model.

Although conventional chemoradiotherapy is effective for most anal squamous cell carcinoma (ASCC) patients, HPV-negative ASCC patients respond poorly to this treatment and new therapeutic approach is required. Our group has previously established an HPV-negative ASCC mouse model and demonstrated that signal transducer and activation of transcription 3 (STAT3) is hyper-activated in the model. Here, we show that in vivo inhibition of STAT3 by S3I-201 effectively delays tumor growth in ASCC mouse model indicated by significantly smaller tumor size and burden in the treatment group compared with control group at the same point. Further analysis shows that survivin and Ki67, important biomarkers for tumor cell survival and proliferation, are significantly reduced after S3I-201 treatment. Additionally, flow cytometry and immunohistofluorescent assays reveal decreased Myeloid-derived suppressor cell (MDSC) and tumor-associated macrophage (TAM) populations in the S3I-201 treatment group, which indicates a reversion of the immunosuppressive environment, unraveling the potential role for S3I-201 in immunosuppression in ASCC. Together these results for the first time demonstrated the anti-tumor effects of STAT3 inhibitor S3I-201 in HPV-negative ASCC mouse model and its multiple effects on cancer cells and immune system. Thus we conclude that S3I-201 may be a novel therapeutic approach for HPV-negative ASCC patients.

Expression and associations of TRAF1, BMI-1, ALDH1, and Lin28B in oral squamous cell carcinoma.

Tumor necrosis factor receptor-associated factor 1, an adaptor protein of tumor necrosis factor 2, is involved in classical nuclear factor (NF)-κB activation and lymphocyte recruitment. However, less is known about the expression and association of tumor necrosis factor receptor-associated factor 1 with cancer stem cell markers in oral squamous cell carcinoma. This study aimed to investigate the expression of tumor necrosis factor receptor-associated factor 1 and stem cell characteristic markers (lin28 homolog B, B cell-specific Moloney murine leukemia virus integration site 1, and aldehyde dehydrogenase 1) in oral squamous cell carcinoma and analyze their relations. Paraffin-embedded tissues of 78 oral squamous cell carcinomas, 39 normal oral mucosa, and 12 oral dysplasia tissues were employed in tissue microarrays, and the expression of tumor necrosis factor receptor-associated factor 1, B cell-specific Moloney murine leukemia virus integration site 1, aldehyde dehydrogenase 1, and lin28 homolog B was measured by immunohistostaining and digital pathological analysis. The expression of tumor necrosis factor receptor-associated factor 1 was higher in the oral squamous cell carcinoma group as compared with the expression in the oral mucosa (p < 0.01) and oral dysplasia (p < 0.001) groups. In addition, the expression of tumor necrosis factor receptor-associated factor 1 was associated with those of B cell-specific Moloney murine leukemia virus integration site 1, aldehyde dehydrogenase 1, and lin28 homolog B (p = 0.032, r2 = 0.109; p < 0.0001, r2 = 0.64; and p < 0.001, r2 = 0.16) in oral squamous cell carcinoma. The patient survival rate was lower in the highly expressed tumor necrosis factor receptor-associated factor 1 group, although the difference was not significant. The clustering analysis showed that tumor necrosis factor receptor-associated factor 1 was most related to aldehyde dehydrogenase 1. These findings suggest that tumor necrosis factor receptor-associated factor 1 has potential direct/indirect regulations with the cancer stem cell markers in oral squamous cell carcinoma, which may help in further analysis of the cancer stem cell characteristics.

AGR2 promotes the proliferation, migration and regulates epithelial-mesenchymal transition in salivary adenoid cystic carcinoma.

Salivary adenoid cystic carcinoma (AdCC) is a common head and neck cancer with the propensity for local spread and distant metastasis. In our previous study, elevated expression of Anterior gradient 2 (AGR2) was detected in head and neck squamous cell carcinoma (HNSCC), associated with epithelial-mesenchymal transition (EMT) and cancer stemness. However, to date, the expression and function of AGR2 in AdCC has yet to be elucidated. In the present study, human AdCC tissue microarrays including 18 cases of normal salivary gland (NSG), 12 cases of pleomorphic adenoma (PMA) and 72 cases of AdCC were employed for immunohistochemical staining analysis. Results indicated that AGR2, which was remarkably correlated with Ki-67, transforming growth factor beta-1 (TGF-ß1) and CD147, was significantly elevated in human salivary AdCC tissues. Knockdown of AGR2 significantly repressed the proliferation and migration of human SACC-83 and SACC-LM cell lines. Additionally, AGR2 silencing obviously reversed the EMT phenomena induced by TGF-ß1. Taken together, our present study revealed the potential pro-metastasis role of AGR2 in AdCC, indicating that AGR2 might be a novel therapeutic target of AdCC with distant metastasis.

T-cell immunoglobulin mucin 3 blockade drives an antitumor immune response in head and neck cancer.

T-cell immunoglobulin mucin 3 (TIM3) contributes to immune suppression during progression of many cancers, but the precise role of TIM3 in head and neck squamous cell carcinoma (HNSCC) is not clearly understood. In this study, we report that TIM3 expression was significantly up-regulated in patients with HNSCC and associated with lymph node metastasis. Additionally, TIM3 expression was increased in patients with recurrent HNSCC and patients with preradiotherapy or prechemotherapy. We also characterized CD8+ T cells and CD11b+ CD33+ myeloid-derived suppressor cells (MDSCs) in human HNSCC, and found that their expression was positively correlated with TIM3 expression. To determine the underlying mechanism of TIM3 in immune response during HNSCC progression, we utilized the Tgfbr1/Pten 2cKO HNSCC mouse model with TIM3 overexpression. Treatment with anti-TIM3 monoclonal antibody effectively suppressed tumor growth through restoring effector T-cell function by targeting CD4+ TIM3+ cells and CD8+ TIM3+ cells and decreasing MDSCs. Our findings demonstrate TIM3 expression in patients with HNSCC and suggest anti-TIM3 immunotherapy as a novel therapeutic approach for effective treatment of HNSCC.

PAK2 promotes migration and proliferation of salivary gland adenoid cystic carcinoma.

P21 activated kinase 2 (PAK2) is a member of Group I PAKs family and highly expressed in various cancers. Current studies have demonstrated that PAK2 played a pivotal role in tumor progression. However, the role of PAK2 in salivary adenoid cystic carcinoma is still unclear. This study aims to explore the expression and the function of PAK2 in AdCC. Human salivary gland tissue microarray, including 18 normal salivary glands (NSG), 12 pleomorphic adenoma (PMA) and 72 AdCC, and immunohistochemistry were used to evaluate the expression of PAK2. The result showed that PAK2 was significantly increased in AdCC compared with NSG and PMA. Then the Pearson correlation analysis using serial tissue sections showed a close correlation of PAK2 with Cyclin D1, Phospho-STAT3 at Tyrosine 705 (p-STAT3) and Ki-67. Further in vitro study utilizing PAK2 knockdown via siRNA transfection revealed significantly reduced migration and proliferation of AdCC cell lines compared with control group. Knockdown of PAK2 decreased the expression of Cyclin D1 in AdCC cell lines. In addition, the inhibition of STAT3 reduced the expression of PAK2 in AdCC cell lines. These findings suggested that PAK2 promotes AdCC cell migration and proliferation and may be a potential therapeutic target.

Dihydromyricetin promotes autophagy and apoptosis through ROS-STAT3 signaling in head and neck squamous cell carcinoma.

Chemotherapy is an effective weapon in the battle against cancer, but numerous cancer patients are either not sensitive to chemotherapy or develop drug resistance to current chemotherapy regimens. Therefore, an effective chemotherapy mechanism that enhances tumor sensitivity to chemotherapeutics is urgently needed. The aim of the present study was to determine the antitumor activity of dihydromyricetin (DHM) on head and neck squamous cell carcinoma (HNSCC) and its underlying mechanisms. We demonstrated that DHM can markedly induce apoptotic cell death and autophagy in HNSCC cells. Meanwhile, increased autophagy inhibited apoptosis. Pharmacological or genetic inhibition of autophagy further sensitized the HNSCC cells to DHM-induced apoptosis. Mechanistic analysis showed that the antitumor of DHM may be due to the activation phosphorylation of signal transducer and activator of transcription 3 (p-STAT3), which contributed to autophagy. Importantly, DHM triggered reactive oxygen species (ROS) generation in the HNSCC cells and the levels of ROS decreased with N-acetyl-cysteine (NAC), a ROS scavenger. Moreover, NAC abrogated the effects of DHM on STAT3-dependent autophagy. Overall, the following critical issues were observed: first, DHM increased the p-STAT3-dependent autophagy by generating ROS-signaling pathways in head and neck squamous cell carcinoma. Second, inhibiting autophagy could enhance DHM-induced apoptosis in head and neck squamous cell carcinoma.

Role of 5-aminolevulinic acid in the salinity stress response of the seeds and seedlings of the medicinal plant Cassia obtusifolia L.

BACKGROUND: Soil salinity, one of the major abiotic stresses affecting germination, crop growth, and productivity, is a common adverse environmental factor. The possibility of enhancing the salinity stress tolerance of Cassia obtusifolia L. seeds and seedlings by the exogenous application of 5-aminolevulinic acid (ALA) was investigated. RESULT: To improve the salinity tolerance of seeds, ALA was applied in various concentrations (5, 10, 15, and 20 mg/L). To improve the salinity tolerance of seedlings, ALA was applied in various concentrations (10, 25, 50, and 100 mg/L). After 10 mg/L ALA treatment, physiological indices of seed germination (i.e., germination vigor, germination rate, germination index, and vigor index) significantly improved. At 25 mg/L ALA, there was a significant protection against salinity stress compared with non-ALA-treated seedlings. Chlorophyll content, total soluble sugars, free proline, and soluble protein contents were significantly enhanced. Increased thiobarbituric acid reactive species and membrane permeability levels were also inhibited with the ALA treatment. With the treatments of ALA, the levels of chlorophyll fluorescence parameters, i.e., the photochemical efficiency of photosystem II (Fv/Fm), photochemical efficiency (Fv'/Fm'), PSII actual photochemical efficiency (ΦPSII), and photochemical quench coefficient (qP), all significantly increased. In contrast, the non-photochemical quenching coefficient (NPQ) decreased. ALA treatment also enhanced the activities of superoxide dismutase, peroxidase, and catalase in seedling leaves. The highest salinity tolerance was obtained at 25 mg/L ALA treatment. CONCLUSION: The plant growth regulator ALA could be effectively used to protect C. obtusifolia seeds and seedlings from the damaging effects of salinity stress without adversely affecting plant growth.