Lipid metabolism in tumor microenvironment: novel therapeutic targets

Inhibition of PCSK9: A Promising Enhancer for Anti-PD-1/PD-L1 Immunotherapy

Immune checkpoint therapy, such as programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) blockade, has achieved remarkable results in treating various tumors. However, most cancer patients show a low response rate to PD-1/PD-L1 blockade, especially those with microsatellite stable/mismatch repair-proficient colorectal cancer subtypes, which indicates an urgent need for new approaches to augment the efficacy of PD-1/PD-L1 blockade. Cholesterol metabolism, which involves generating multifunctional metabolites and essential membrane components, is also instrumental in tumor development. In recent years, inhibiting proprotein convertase subtilisin/kexin type 9 (PCSK9), a serine proteinase that regulates cholesterol metabolism, has been demonstrated to be a method enhancing the antitumor effect of PD-1/PD-L1 blockade to some extent. Mechanistically, PCSK9 inhibition can maintain the recycling of major histocompatibility protein class I, promote low-density lipoprotein receptor-mediated T-cell receptor recycling and signaling, and modulate the tumor microenvironment (TME) by affecting the infiltration and exclusion of immune cells. These mechanisms increase the quantity and enhance the antineoplastic effect of cytotoxic T lymphocyte, the main functional immune cells involved in anti-PD-1/PD-L1 immunotherapy, in the TME. Therefore, combining PCSK9 inhibition therapy with anti-PD-1/PD-L1 immunotherapy may provide a novel option for improving antitumor effects and may constitute a promising research direction. This review concentrates on the relationship between PCSK9 and cholesterol metabolism, systematically discusses how PCSK9 inhibition potentiates PD-1/PD-L1 blockade for cancer treatment, and highlights the research directions in this field.

Overlap in oncogenic and pro-inflammatory pathways associated with areca nut and nicotine exposure

Background

Betel nut/areca nut/Areca catechu is one of the most commonly used psychoactive substance, and is also a major preventable cause of cancer. Unlike other psychoactive substances, such as nicotine, the mechanisms underlying addiction to areca nuts and related oncogenesis remain elusive. Recent reports suggest a possible overlap in the mechanisms of action of nicotine and areca nuts in the human body. Thus, this study aimed to investigate the interactome of human proteins associated with areca nut exposure and the intricate similarities and differences in the effects of the two psychoactive substances on humans.

Methods

A list of proteins associated with areca nut use was obtained from the available literature using terms from Medical Subject Headings (MeSH). Protein-protein interaction (PPI) networks and functional enrichment were analyzed. The results obtained for both psychoactive substances were compared.

Results

Given the limited number of common proteins (36/226, 16%) in the two sets, a substantial overlap (612/1176 nodes, 52%) was observed in the PPI networks, as well as in Gene Ontology. Areca nuts mainly affect signaling pathways through three hub proteins (alpha serine/threonine-protein kinase, tumor protein 53, and interleukin-6), which are common to both psychoactive substances, as well as two unique hub proteins (epidermal growth factor receptor and master regulator of cell cycle entry and proliferative metabolism). Areca nut-related proteins are associated with unique pathways, such as extracellular matrix organization, lipid storage, and metabolism, which are not found in nicotine-associated proteins.

Conclusions

Areca nuts affect regulatory mechanisms, leading to systemic toxicity and oncogenesis. Areca nuts also affect unique pathways that can be studied as potential markers of exposure, as well as targets for anticancer therapeutic agents.

Elucidating the Role of Lipid-Metabolism-Related Signal Transduction and Inhibitors in Skin Cancer

Lipids, as multifunctional molecules, play a crucial role in a variety of cellular processes. These include regulating membrane glycoprotein functions, controlling membrane trafficking, influencing apoptotic pathways, and affecting drug transport. In addition, lipid metabolites can alter the surrounding microenvironment in ways that might encourage tumor progression. The reprogramming of lipid metabolism is pivotal in promoting tumorigenesis and cancer progression, with tumors often displaying significant changes in lipid profiles. This review concentrates on the essential factors that drive lipid metabolic reprogramming, which contributes to the advancement and drug resistance in melanoma. Moreover, we discuss recent advances and current therapeutic strategies that employ small-molecule inhibitors to target lipid metabolism in skin cancers, particularly those associated with inflammation and melanoma.

Unique lipid composition maintained by extracellular blockade leads to prooncogenicity

Lipid-mediated inflammation is involved in the development and malignancy of cancer. We previously demonstrated the existence of a novel oncogenic mechanism utilizing membrane lipids of extracellular vesicles in Epstein-Barr virus (EBV)-positive lymphomas and found that the lipid composition of lymphoma cells is skewed toward ω-3 fatty acids, which are anti-inflammatory lipids, suggesting an alteration in systemic lipid composition. The results showed that arachidonic acid (AA), an inflammatory lipid, was significantly reduced in the infected cells but detected at high levels in the sera of EBV-positive patients lead to the finding of the blockade of extracellular AA influx by downregulating FATP2, a long-chain fatty acid transporter that mainly transports AA in EBV-infected lymphoma cells. Low AA levels in tumor cells induced by downregulation of FATP2 expression confer resistance to ferroptosis and support tumor growth. TCGA data analysis and xenograft models have demonstrated that the axis plays a critical role in several types of cancers, especially poor prognostic cancers, such as glioblastoma and melanoma. Overall, our in vitro, in vivo, in silico, and clinical data suggest that several cancers exert oncogenic activity by maintaining their special lipid composition via extracellular blockade.

ADAM9 drives the immunosuppressive microenvironment by cholesterol biosynthesis-mediated activation of IL6-STAT3 signaling for lung tumor progression

Chronic inflammation associated with lung cancers contributes to immunosuppressive tumor microenvironments, reducing CD8+ T-cell function and leading to poor patient outcomes. A disintegrin and metalloprotease domain 9 (ADAM9) promotes cancer progression. Here, we aim to elucidate the role of ADAM9 in the immunosuppressive tumor microenvironment. A bioinformatic analysis of TIMER2.0 was used to investigate the correlation of ADAM9 and to infiltrate immune cells in the human lung cancer database and mouse lung tumor samples. Flow cytometry, immunohistochemistry, and RNA sequencing (RNA-seq) were performed to investigate the ADAM9-mediated immunosuppressive microenvironment. The coculture system of lung cancer cells with immune cells, cytokine array assays, and proteomic approach was used to investigate the mechanism. By analyzing the human LUAD database and the mouse lung cancer models, we showed that ADAM9 was associated with the immunosuppressive microenvironment. Additionally, ADAM9 released IL6 protein from cancer cells to inhibit IL12p40 secretion from dendritic cells, therefore leading to dendritic cell dysfunction and further affecting T-cell functions. Proteomic analysis indicated that ADAM9 promoted cholesterol biosynthesis and increased IL6-STAT3 signaling. Mechanistically, ADAM9 reduced the protein stability of LDLR, resulting in reduced cholesterol uptake and induced cholesterol biosynthesis. Moreover, LDLR reduction enhanced IL6-STAT3 activation. We reveal that ADAM9 has a novel biological function that drives the immunosuppressive tumor microenvironment by linking lung cancer's metabolic and signaling axes. Thus, by targeting ADAM9 an innovative and promising therapeutic opportunity was indicated for regulating the immunosuppression of lung cancer.

Adipocyte‑rich microenvironment promotes chemoresistance via upregulation of peroxisome proliferator‑activated receptor gamma/ABCG2 in epithelial ovarian cancer

The effects of adipocyte‑rich microenvironment (ARM) on chemoresistance have garnered increasing interest. Ovarian cancer (OVCA) is a representative adipocyte‑rich associated cancer. In the present study, epithelial OVCA (EOC) was used to investigate the influence of ARM on chemoresistance with the aim of identifying novel targets and developing novel strategies to reduce chemoresistance. Bioinformatics analysis was used to explore the effects of ARM‑associated mechanisms contributing to chemoresistance and treated EOC cells, primarily OVCAR3 cells, with human adipose tissue extracts (HATES) from the peritumoral adipose tissue of patients were used to mimic ARM in vitro. Specifically, the peroxisome proliferator‑activated receptor γ (PPARγ) antagonist GW9662 and the ABC transporter G family member 2 (ABCG2) inhibitor KO143, were used to determine the underlying mechanisms. Next, the effect of HATES on the expression of PPARγ and ABCG2 in OVCAR3 cells treated with cisplatin (DDP) and paclitaxel (PTX) was determined. Additionally, the association between PPARγ, ABCG2 and chemoresistance in EOC specimens was assessed. To evaluate the effect of inhibiting PPARγ, using DDP, a nude mouse model injected with OVCAR3‑shPPARγ cells and a C57BL/6 model injected with ID8 cells treated with GW9662 were established. Finally, the factors within ARM that contributed to the mechanism were determined. It was found that HATES promoted chemoresistance by increasing ABCG2 expression via PPARγ. Expression of PPARγ/ABCG2 was related to chemoresistance in EOC clinical specimens. GW9662 or knockdown of PPARγ improved the efficacy of chemotherapy in mice. Finally, angiogenin and oleic acid played key roles in HATES in the upregulation of PPARγ. The present study showed that the introduction of ARM‑educated PPARγ attenuated chemoresistance in EOC, highlighting a potentially novel therapeutic adjuvant to chemotherapy and shedding light on a means of improving the efficacy of chemotherapy from the perspective of ARM.

Targeting Fatty Acid Desaturase I Inhibits Renal Cancer Growth Via ATF3-mediated ER Stress Response

Monounsaturated fatty acids (MUFAs) play a pivotal role in maintaining endoplasmic reticulum (ER) homeostasis, an emerging hallmark of cancer. However, the role of polyunsaturated fatty acid (PUFAs) desaturation in persistent ER stress driven by oncogenic abnormalities remains elusive. Fatty Acid Desaturase 1 (FADS1) is a rate-limiting enzyme controlling the bioproduction of long-chain PUFAs. Our previous research has demonstrated the significant role of FADS1 in cancer survival, especially in kidney cancers. We explored the underlying mechanism in this study. We found that pharmacological inhibition or knockdown of the expression of FADS1 effectively inhibits renal cancer cell proliferation and induces cell cycle arrest. The stable knockdown of FADS1 also significantly inhibits tumor formation in vivo. Mechanistically, we show that while FADS1 inhibition induces ER stress, its expression is also augmented by ER-stress inducers. Notably, FADS1-inhibition sensitized cellular response to ER stress inducers, providing evidence of FADS1's role in modulating the ER stress response in cancer cells. We show that, while FADS1 inhibition-induced ER stress leads to activation of ATF3, ATF3-knockdown rescues the FADS1 inhibition-induced ER stress and cell growth suppression. In addition, FADS1 inhibition results in the impaired biosynthesis of nucleotides and decreases the level of UPD-N-Acetylglucosamine, a critical mediator of the unfolded protein response. Our findings suggest that PUFA desaturation is crucial for rescuing cancer cells from persistent ER stress, supporting FADS1 as a new therapeutic target.

Altered tumor signature and T-cell profile after chemotherapy reveal new therapeutic opportunities in high-grade serous ovarian carcinoma

Chemotherapy combined with debulking surgery is the standard treatment protocol for high-grade serous ovarian carcinoma (HGSOC). Nonetheless, a significant number of patients encounter relapse due to the development of chemotherapy resistance. To better understand and address this resistance, we conducted a comprehensive study investigating the transcriptional alterations at the single-cell resolution in tissue samples from patients with HGSOC, using single-cell RNA sequencing and T-cell receptor sequencing techniques. Our analyses unveiled notable changes in the tumor signatures after chemotherapy, including those associated with epithelial-mesenchymal transition and cell cycle arrest. Within the immune compartment, we observed alterations in the T-cell profiles, characterized by naïve or pre-exhausted populations following chemotherapy. This phenotypic change was further supported by the examination of adjoining T-cell receptor clonotypes in paired longitudinal samples. These findings underscore the profound impact of chemotherapy on reshaping the tumor landscape and the immune microenvironment. This knowledge may provide clues for the development of future therapeutic strategies to combat treatment resistance in HGSOC.

The combination of the low immunohistochemical expression of peroxiredoxin 4 and perilipin 2 predicts longer survival in pancreatic ductal adenocarcinoma with peroxiredoxin 4 possibly playing a main role

Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease with poor prognosis. Therefore, indicators that can be used for the early prediction of the prognosis of PDAC are needed. Peroxiredoxin (PRDX) 4 is a secretion-type antioxidant enzyme located in the cytoplasmic endoplasmic reticulum. Recent studies have reported that it is closely related to the development and prognosis of many types of cancer. Perilipin (PLIN) 2 is a lipid droplet coating protein. The high expression of PLIN2 is known to be an indicator of some types of cancer and oxidative stress management. It is highly suggestive of the interplay between PRDX4 and PLIN2 to some degree. In this study, we collected 101 patients' clinical data and paraffin-embedded specimens with PDAC and analyzed them with immunohistochemical staining of PRDX4 and PLIN2. We found that the low expression of PRDX4 predicts longer survival and a better clinical condition in PDAC patients. Moreover, when the low expression of PRDX4 is combined with the low expression of PLIN2, the 3-year survival is significantly improved. Univariate and multivariate Cox proportional hazard analyses showed that the PRDX4 expression in PDAC was an independent prognostic factor for survival. Taken together, between PRDX4 and PLIN2, PRDX4 plays a main role in prognosis and has the potential to become a clinical prognostic indicator of PDAC.

Lipid metabolic vulnerabilities of multiple myeloma

Multiple myeloma (MM) is the second most common hematological malignancy worldwide, characterized by abnormal proliferation of malignant plasma cells within a tumor-permissive bone marrow microenvironment. Metabolic dysfunctions are emerging as key determinants in the pathobiology of MM. In this review, we highlight the metabolic features of MM, showing how alterations in various lipid pathways, mainly involving fatty acids, cholesterol and sphingolipids, affect the growth, survival and drug responsiveness of MM cells, as well as their cross-talk with other cellular components of the tumor microenvironment. These findings will provide a new path to understanding the mechanisms underlying how lipid vulnerabilities may arise and affect the phenotype of malignant plasma cells, highlighting novel druggable pathways with a significant impact on the management of MM.

Lipid metabolism as a target for cancer drug resistance: progress and prospects

Cancer is the world's leading cause of human death today, and the treatment process of cancer is highly complex. Chemotherapy and targeted therapy are commonly used in cancer treatment, and the emergence of drug resistance is a significant problem in cancer treatment. Therefore, the mechanism of drug resistance during cancer treatment has become a hot issue in current research. A series of studies have found that lipid metabolism is closely related to cancer drug resistance. This paper details the changes of lipid metabolism in drug resistance and how lipid metabolism affects drug resistance. More importantly, most studies have reported that combination therapy may lead to changes in lipid-related metabolic pathways, which may reverse the development of cancer drug resistance and enhance or rescue the sensitivity to therapeutic drugs. This paper summarizes the progress of drug design targeting lipid metabolism in improving drug resistance, and providing new ideas and strategies for future tumor treatment. Therefore, this paper reviews the issues of combining medications with lipid metabolism and drug resistance.

Identification of genetic mechanisms underlying lipid metabolism-mediated tumor immunity in head and neck squamous cell carcinoma

OBJECTIVE

To identify the genetic mechanisms underlying lipid metabolism-mediated tumor immunity in head and neck squamous carcinoma (HNSC).

MATERIALS AND METHODS

RNA sequencing data and clinical characteristics of HNSC patients were procured from The Cancer Genome Atlas (TCGA) database. Lipid metabolism-related genes were collected from KEGG and MSigDB databases. Immune cells and immune-related genes were obtained from the TISIDB database. The differentially expressed genes (DEGs) in HNSC were identified and weighted correlation network analysis (WGCNA) was performed to identify the significant gene modules. Lasso regression analysis was performed to identify hub genes. The differential gene expression pattern, diagnostic values, relationships with clinical features, prognostic values, relationships with tumor mutation burden (TMB), and signaling pathways involved, were each investigated.

RESULTS

One thousand six hundred sixty-eight DEGs were identified as dysregulated between HNSC tumor samples and healthy control head and neck samples. WGCNA analysis and Lasso regression analysis identified 8 hub genes, including 3 immune-related genes (PLA2G2D, TNFAIP8L2 and CYP27A1) and 5 lipid metabolism-related genes (FOXP3, IL21R, ITGAL, TRAF1 and WIPF1). Except CYP27A1, the other hub genes were upregulated in HNSC as compared with healthy control samples, and a low expression of these hub genes indicated a higher risk of death in HNSC. Except PLA2G2D, all other hub genes were significantly and negatively related with TMB in HNSC. The hub genes were implicated in several immune-related signaling pathways including T cell receptor signaling, Th17 cell differentiation, and natural killer (NK) cell mediated cytotoxicity.

CONCLUSION

Three immune genes (PLA2G2D, TNFAIP8L2, and CYP27A1) and immune-related pathways (T cell receptor signaling, Th17 cell differentiation, and natural killer (NK) cell mediated cytotoxicity) were predicted to play significant roles in the lipid metabolism-mediated tumor immunity in HNSC.

Mechanism of Cytotoxic Action of Gold Nanorods Photothermal Therapy for A549 Cell

Photothermal therapy has developed into an important field of tumor treatment research, and numerous studies have focused on the preparation of photothermal therapeutic agents, tumor targeting, diagnosis, and treatment integration. However, there are few studies on the mechanism of photothermal therapy acting on cancer cells. Here we investigated the metabolomics of lung cancer cell A549 during gold nanorod (GNR) photothermal treatment by high-resolution LC/MS, and several differential metabolites and corresponding metabolic pathways during photothermal therapy were found. The main differential metabolites contained 18-hydroxyoleate, beta-alanopine and cis-9,10-epoxystearic acid, and phosphorylcholine. Pathway analysis also showed metabolic changes involving cutin, suberine, and wax biosynthesis, pyruvate and glutamic acid synthesis, and choline metabolism. Analysis also showed that the photothermal process of GNRs may induce cytotoxicity by affecting pyruvate and glutamate synthesis, normal choline metabolism, and ultimately apoptosis.