Diet-induced obesity accelerates oral carcinogenesis by recruitment and functional enhancement of myeloid-derived suppressor cells

Effects of dietary intervention on human diseases: molecular mechanisms and therapeutic potential

Diet, serving as a vital source of nutrients, exerts a profound influence on human health and disease progression. Recently, dietary interventions have emerged as promising adjunctive treatment strategies not only for cancer but also for neurodegenerative diseases, autoimmune diseases, cardiovascular diseases, and metabolic disorders. These interventions have demonstrated substantial potential in modulating metabolism, disease trajectory, and therapeutic responses. Metabolic reprogramming is a hallmark of malignant progression, and a deeper understanding of this phenomenon in tumors and its effects on immune regulation is a significant challenge that impedes cancer eradication. Dietary intake, as a key environmental factor, can influence tumor metabolism. Emerging evidence indicates that dietary interventions might affect the nutrient availability in tumors, thereby increasing the efficacy of cancer treatments. However, the intricate interplay between dietary interventions and the pathogenesis of cancer and other diseases is complex. Despite encouraging results, the mechanisms underlying diet-based therapeutic strategies remain largely unexplored, often resulting in underutilization in disease management. In this review, we aim to illuminate the potential effects of various dietary interventions, including calorie restriction, fasting-mimicking diet, ketogenic diet, protein restriction diet, high-salt diet, high-fat diet, and high-fiber diet, on cancer and the aforementioned diseases. We explore the multifaceted impacts of these dietary interventions, encompassing their immunomodulatory effects, other biological impacts, and underlying molecular mechanisms. This review offers valuable insights into the potential application of these dietary interventions as adjunctive therapies in disease management.

Dietary fat and lipid metabolism in the tumor microenvironment

Metabolic reprogramming has been considered a core hallmark of cancer, in which excessive accumulation of lipids promote cancer initiation, progression and metastasis. Lipid metabolism often includes the digestion and absorption of dietary fat, and the ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment. Among multiple cancer risk factors, obesity has a positive association with multiple cancer types, while diets like calorie restriction and fasting improve health and delay cancer. Impact of these diets on tumorigenesis or cancer prevention are generally studied on cancer cells, despite heterogeneity of the tumor microenvironment. Cancer cells regularly interact with these heterogeneous microenvironmental components, including immune and stromal cells, to promote cancer progression and metastasis, and there is an intricate metabolic crosstalk between these compartments. Here, we focus on discussing fat metabolism and response to dietary fat in the tumor microenvironment, focusing on both immune and stromal components and shedding light on therapeutic strategies surrounding lipid metabolic and signaling pathways.

Depletion of Gr1+ myeloid cells attenuates high-fat-diet-aggravated esophageal squamous cell carcinoma in mice

Obesity is a leading cause of multiple cancers, but whether it promotes esophageal squamous cell carcinoma (ESCC) and its underlying cancer-promoting mechanism remains unclear. To evaluate the effect of a high-fat diet (HFD) on ESCC and explore the role and mechanism of myeloid-derived suppressor cells (MDSCs) in HFD-induced ESCC, C57BL/6J mice were treated with 4-nitroquinoline 1-oxide (4NQO) to induce ESCC and randomly assigned to an HFD or a normal-fat diet. An anti-Gr1 monoclonal antibody was used to deplete MDSCs in the context of experimental diets and ESCC induction. The expression of MDSC markers CD11b and Gr1 and immune checkpoints (ICs) PD1, TIM3, and VISTA in lesions were detected by immunohistochemistry. The correlation between myeloid cell markers (CD11b and CD33) and ICs and their relationship with ESCC patient prognosis were further analyzed using the The Cancer Genome Atlas dataset. The results showed that HFD accelerated esophageal carcinogenesis, induced MDSC expansion, and upregulated IC expression, whereas depletion of Gr1+ myeloid cells significantly suppressed tumor growth, decreased the number of MDSCs, and downregulated IC expression in HFD mice. PD1, TIM3, and VISTA expressions were positively correlated with myeloid cell marker expression in human ESCC. Moreover, the high expression of IC molecules was associated with poor survival in patients with ESCC. These data indicate that HFD promotes the initiation and development of ESCC. Gr1+ myeloid cell targeting significantly inhibited ESCC formation in HFD mice, which may be associated with IC downregulation.

KRAS mutations upregulate Runx1 to promote occurrence of head and neck squamous cell carcinoma

Gene mutations play an important role in head and neck squamous cell carcinoma (HNSCC) by not only promoting the occurrence and progression of HNSCC but also affecting sensitivity to treatment and prognosis. KRAS is one of the most frequently mutated oncogenes, which has been reported to have a mutation rate from 1.7% to 12.7% and may lead to poor prognosis in HNSCC, but its role remains unclear. Here, we found that the KRAS mutation can promote HNSCC generation through synergism with 4-Nitroquinoline-1-Oxide(4NQO). Mechanistically, KRAS mutations can significantly upregulate Runx1 to promote oral epithelial cell proliferation and migration and inhibit apoptosis. Runx1 inhibitor Ro 5-3335 can effectively inhibit KRAS-mutated HNSCC progression both in vitro and in vivo. These findings suggest that the KRAS mutation plays an important role in HNSCC and that Runx1 may be a novel therapeutic target for KRAS-mutated HNSCC.

Targeting adipocyte-immune cell crosstalk to control breast cancer progression

Adipocytes are crucial components of breast cancer and are involved in regulating the progression, therapeutic efficacy, and prognosis of breast cancer patients. Characterized by storing energy and producing a variety of secretory factors, adipocytes are responsible for inducing obesity and regulating the tumor immune activity. Adipocytes communicate with tumor infiltrating immune cells through the secreted adipokines, cytokines, and exosomes in the breast cancer TIME, which shapes the tumor supporting environment to facilitate the immune escape of tumor cells. In-depth studies of the crosstalk between adipocytes and TIME can not only provide a more comprehensive regulatory landscape of TIME, but also be conducive to screening novel targets for future precision targeted therapy. The aim of this review is to discuss recent studies for understanding the role of crosstalk between adipocytes and immune cells in shaping the breast cancer immune microenvironment.

Targeting PCSK9 reduces cancer cell stemness and enhances antitumor immunity in head and neck cancer

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been demonstrated to play a critical role in regulating cholesterol homeostasis and T cell antitumor immunity. However, the expression, function, and therapeutic value of PCSK9 in head and neck squamous cell carcinoma (HNSCC) remain largely unexplored. Here, we found that the expression of PCSK9 was upregulated in HNSCC tissues, and higher PCSK9 expression indicated poorer prognosis in HNSCC patients. We further found that pharmacological inhibition or siRNA downregulating PCSK9 expression suppressed the stemness-like phenotype of cancer cells in an LDLR-dependent manner. Moreover, PCSK9 inhibition enhanced the infiltration of CD8⁺ T cells and reduced the myeloid-derived suppressor cells (MDSCs) in a 4MOSC1 syngeneic tumor-bearing mouse model, and it also enhanced the antitumor effect of anti-PD-1 immune checkpoint blockade (ICB) therapy. Together, these results indicated that PCSK9, a traditional hypercholesterolemia target, may be a novel biomarker and therapeutic target to enhance ICB therapy in HNSCC.

The Role of IL-17 in the Pathogenesis of Oral Squamous Cell Carcinoma

Elucidating the inflammatory mechanisms underlying formation and progression of oral squamous cell carcinoma (OSCC) is crucial for discovering new targeted therapeutics. The proinflammatory cytokine IL-17 has proven roles in tumor formation, growth, and metastasis. The presence of IL-17 is demonstrated in both in vitro and in vivo models, and in OSCC patients, is mostly accompanied by enhanced proliferation and invasiveness of cancer cells. Here we review the known facts regarding the role of IL-17 in OSCC pathogenesis, namely the IL-17 mediated production of proinflammatory mediators that mobilize and activate myeloid cells with suppressive and proangiogenic activities and proliferative signals that directly induce proliferation of cancer cells and stem cells. The possibility of a potential IL-17 blockade in OSCC therapy is also discussed.

Alteration of the tumor microenvironment by pharmacological inhibition of EZH2 in hepatocellular carcinoma

Enhancer of zeste homolog 2 (EZH2), a core component of polycomb repressive component 2 is overexpressed in a variety of cancers and recognized as a therapeutic target molecule. However, EZH2 possesses immunomodulatory functions in the tumor microenvironment (TME). The impact of EZH2 on TME of hepatocellular carcinoma (HCC) using immunocompetent mouse model was evaluated in the present study. UNC1999, an EZH2 inhibitor, impaired growth of the murine HCC cells (H22 cells) and induced apoptosis in a dose-dependent manner. Although UNC1999 significantly inhibited the growth of H22 cells-derived and Hepa1-6 cells-derived tumors in nonobese diabetic/severe combined immunodeficiency mice, its antitumor effect was diminished in allogenic BALB/c and C57BL/6 mice. Flow cytometric analyses of TME cells in BALB/c mice demonstrated a significant decrease in the number of interferon‑γ⁺ CD8⁺ T cells and regulatory T cells and a significant increase in the number of myeloid-derived suppressor cells (MDSCs). Administration of Gr-1 neutralizing antibody concomitant with UNC1999 restored antitumor effect accompanied by an increase in the number of CD8⁺ T cells followed by a decrease in the number of MDSCs. Chemokine antibody array demonstrated an enhanced expression of chemokines responsible for MDSCs recruitment such as C5a, CCL8, and CCL9. In conclusion, the study results demonstrated that EZH2 inhibitor contributed to attenuation of tumor immunity caused by TME arrangement. Combination therapy with EZH2 inhibitors and agents that reduce MDSCs might represent a novel therapeutic strategy for HCC.

The role of lipids in cancer progression and metastasis

Lipids have essential biological functions in the body (e.g., providing energy storage, acting as a signaling molecule, and being a structural component of membranes); however, an excess of lipids can promote tumorigenesis, colonization, and metastatic capacity of tumor cells. To metastasize, a tumor cell goes through different stages that require lipid-related metabolic and structural adaptations. These adaptations include altering the lipid membrane composition for invading other niches and overcoming cell death mechanisms and promoting lipid catabolism and anabolism for energy and oxidative stress protective purposes. Cancer cells also harness lipid metabolism to modulate the activity of stromal and immune cells to their advantage and to resist therapy and promote relapse. All this is especially worrying given the high fat intake in Western diets. Thus, metabolic interventions aiming to reduce lipid availability to cancer cells or to exacerbate their metabolic vulnerabilities provide promising therapeutic opportunities to prevent cancer progression and treat metastasis.

MDSCs might be "Achilles heel" for eradicating CSCs

During tumor initiation and progression, the complicated role of immune cells in the tumor immune microenvironment remains a concern. Myeloid-derived suppressor cells (MDSCs) are a group of immune cells that originate from the bone marrow and have immunosuppressive potency in various diseases, including cancer. In recent years, the key role of cancer stemness has received increasing attention in cancer development and therapy. Several studies have demonstrated the important regulatory relationship between MDSCs and cancer stem cells (CSCs). However, there is still no clear understanding regarding the complex interacting regulation of tumor malignancy, and current research progress is limited. In this review, we summarize the complicated role of MDSCs in the modulation of cancer stemness, evaluate the mechanism of the relationship between CSCs and MDSCs, and discuss potential strategies for eradicating CSCs with respect to MDSCs.

The World of Oral Cancer and Its Risk Factors Viewed from the Aspect of MicroRNA Expression Patterns

Oral cancer is one of the leading causes of death worldwide, with a reported 5-year survival rate of around 50% after treatment. Epigenetic modifications are considered to have a key role in oral carcinogenesis due to histone modifications, aberrant DNA methylation, and altered expression of miRNAs. MicroRNAs (miRNAs) are small non-coding RNAs that have a key role in cancer development by regulating signaling pathways involved in carcinogenesis. MiRNA deregulation identified in oral cancer has led to the idea of using them as potential biomarkers for early diagnosis, prognosis, and the development of novel therapeutic strategies. In recent years, a key role has been observed for risk factors in preventing and treating this malignancy. The purpose of this review is to summarize the recent knowledge about the altered mechanisms of oral cancer due to risk factors and the role of miRNAs in these mechanisms.