Tools to study and target the Siglec-sialic acid axis in cancer.

Siglecs are widely expressed on leucocytes and bind to ubiquitously presented glycans containing sialic acids (sialoglycans). Most Siglecs carry an immunoreceptor tyrosine-based inhibition motif (ITIM) and elicit an inhibitory intracellular signal upon ligand binding. A few Siglec receptors can, however, recruit immunoreceptor tyrosine-based activation motif (ITAM)-containing factors, which activate cells. The role of hypersialylation (the enhanced expression of sialoglycans) has recently been explored in cancer progression. Mechanistic studies have shown that hypersialylation on cancer cells can engage inhibitory Siglecs on the surface of immune cells and induce immunosuppression. These recent studies strongly suggest that the Siglec-sialic acid axis can act as a potential target for cancer immunotherapy. Moreover, the use of new tools and techniques is facilitating these studies. In this review, we summarise techniques used to study Siglecs, including different mouse models, monoclonal antibodies, Siglec fusion proteins, and sialoglycan arrays. Furthermore, we discuss the recent major developments in the study of Siglecs in cancer immunosuppression, tools, and techniques used in targeting the Siglec-sialic acid axis and the possibility of clinical intervention.

DNA-dependent protein kinase: Epigenetic alterations and the role in genomic stability of cancer.

DNA-dependent protein kinase (DNA-PK), a member of phosphatidylinositol-kinase family, is a key protein in mammalian DNA double-strand break (DSB) repair that helps to maintain genomic integrity. DNA-PK also plays a central role in immune cell development and protects telomerase during cellular aging. Epigenetic deregulation due to endogenous and exogenous factors may affect the normal function of DNA-PK, which in turn could impair DNA repair and contribute to genomic instability. Recent studies implicate a role for epigenetics in the regulation of DNA-PK expression in normal and cancer cells, which may impact cancer progression and metastasis as well as provide opportunities for treatment and use of DNA-PK as a novel cancer biomarker. In addition, several small molecules and biological agents have been recently identified that can inhibit DNA-PK function or expression, and thus hold promise for cancer treatments. This review discusses the impact of epigenetic alterations and the expression of DNA-PK in relation to the DNA repair mechanisms with a focus on its differential levels in normal and cancer cells.

DNA damaging and apoptotic potentials of Bisphenol A and Bisphenol S in human bronchial epithelial cells.

DNA damage caused by environmental agents often lead to many chronic diseases, including cancer. The present study aimed to understand the relative toxicity possessed by Bisphenol A (BPA) and Bisphenol S (BPS) on human bronchial epithelial cells (BEAS-2B). The cells were exposed to either BPA or BPS and evaluated for its cytotoxicity, reactive oxygen species (ROS), DNA fragmentation, phosphorylated histone protein (γ-H2AX) and DNA tail damage levels. Further, we also studied DNA damage response (DDR) and caspase-3 mechanisms, to evaluate its mechanism of cell death processes. Exposure with 200 µM of BPA, significantly (p < 0.05) induces caspase-3-mediated cell death by inducing cytotoxicity, ROS, and DNA fragmentation. Higher levels of γ-H2AX and DNA tail damage indicated BPA's DNA damaging potential through an ATM/ATR/Chk1/p53-dependent pathway in BEAS-2B cells. Overall, in vitro data exhibited moderate toxicity for BPS in comparison with BPA suggesting the need for a thorough clinical investigation over its safety profile.

Apple Flavonoids Suppress Carcinogen-Induced DNA Damage in Normal Human Bronchial Epithelial Cells.

SCOPE: Human neoplastic transformation due to DNA damage poses an increasing global healthcare concern. Maintaining genomic integrity is crucial for avoiding tumor initiation and progression. The present study aimed to investigate the efficacy of an apple flavonoid fraction (AF4) against various carcinogen-induced toxicity in normal human bronchial epithelial cells and its mechanism of DNA damage response and repair processes. METHODS AND RESULTS: AF4-pretreated cells were exposed to nicotine-derived nitrosamine ketones (NNK), NNK acetate (NNK-Ae), methotrexate (MTX), and cisplatin to validate cytotoxicity, total reactive oxygen species, intracellular antioxidants, DNA fragmentation, and DNA tail damage. Furthermore, phosphorylated histone (γ-H2AX) and proteins involved in DNA damage (ATM/ATR, Chk1, Chk2, and p53) and repair (DNA-PKcs and Ku80) mechanisms were evaluated by immunofluorescence and western blotting, respectively. The results revealed that AF4-pretreated cells showed lower cytotoxicity, total ROS generation, and DNA fragmentation along with consequent inhibition of DNA tail moment. An increased level of γ-H2AX and DNA damage proteins was observed in carcinogen-treated cells and that was significantly (p ≤ 0.05) inhibited in AF4-pretreated cells, in an ATR-dependent manner. AF4 pretreatment also facilitated the phosphorylation of DNA-PKcs and thus initiation of repair mechanisms. CONCLUSION: Apple flavonoids can protect in vitro oxidative DNA damage and facilitate repair mechanisms.

Plant flavonoids in cancer chemoprevention: role in genome stability.

Carcinogenesis is a multistage process that involves a series of events comprising of genetic and epigenetic changes leading to the initiation, promotion and progression of cancer. Chemoprevention is referred to as the use of nontoxic natural compounds, synthetic chemicals or their combinations to intervene in multistage carcinogenesis. Chemoprevention through diet modification, i.e., increased consumption of plant-based food, has emerged as a most promising and potentially cost-effective approach to reducing the risk of cancer. Flavonoids are naturally occurring polyphenols that are ubiquitous in plant-based food such as fruits, vegetables and teas as well as in most medicinal plants. Over 10,000 flavonoids have been characterized over the last few decades. Flavonoids comprise of several subclasses including flavonols, flavan-3-ols, anthocyanins, flavanones, flavones, isoflavones and proanthocyanidins. This review describes the most efficacious plant flavonoids, including luteolin, epigallocatechin gallate, quercetin, apigenin and chrysin; their hormetic effects; and the molecular basis of how these flavonoids contribute to the chemoprevention with a focus on protection against DNA damage caused by various carcinogenic factors. The present knowledge on the role of flavonoids in chemoprevention can be used in developing effective dietary strategies and natural health products targeted for cancer chemoprevention.

Mechanism of Action of Flavonoids in Prevention of Inflammation- Associated Skin Cancer.

Skin cancer in humans represents about 30% of all new cancers and is by far the most common malignancy in the Caucasian population. Exposure to radiations especially ultraviolet-B (UV-B) radiation is the major cause for development of skin cancers along with other chemical or biological factors. The growing incidence rates of skin cancer around the world, demand the need for new treatment options. Understanding the etiology and pathogenesis of skin cancer is therefore crucial for developing an effective drug against this prevailing disease. Medicinal plants are rich with numerous secondary metabolites such as flavonoids, which are now known to treat various chronic diseases, including inflammations and cancers. Flavonoids are sub-classified in to flavones, flavonols, iosflavones, flavanones, flavanols and anthocyanidins. They act on different targets including scavenging reactive oxygen species (ROS), regulation of the cell cycle, and initiation of DNA repair mechanisms, apoptotic induction and inhibition of metastasis. Innumerable evidence suggested that an increased consumption of flavonoid-rich fruits and vegetables rendered DNA protection to normal skin exposed to carcinogens such as UV-B radiation. Flavonoids also showed the potential to induce cell death mechanisms in melanoma, the most dreadful form of skin cancer. This comprehensive review presents flavonoids and their mechanism of action in relation to inflammation and skin cancer management.

In Vitro Protective Potentials of Annona muricata Leaf Extracts Against Sodium Arsenite-induced Toxicity.

Sodium arsenite (NaAsO2) is a metalloid which is present widely in the environment and its chronic exposure can contribute to the induction of oxidative stress, resulting in disturbances in various metabolic functions including liver cell death. Hence, there is a need to develop drugs from natural sources, which can reduce arsenic toxicity. While there have been reports regarding the antioxidant and protective potentials of Annona muricataleaf extracts, our study is the first ofits kind to extend these findings by specifically evaluating its ability to render protection against sodium arsenite (NaAsO2) induced toxicity (10 µM) in WRL-68 (human hepatic cells) and human erythrocytes by employing XTT and haemolysis inhibition assays respectively. The methanolic extract exhibited higher activity than the aqueous extract in both assays. The results showed a dose-dependent decrease in arsenic toxicity in both WRL-68 cells and erythrocytes, suggesting the protective nature of Annona muricatato mitigate arsenic toxicity. Hence the bioactive extracts can further be scrutinized for the identification and characterization of their principal contributors.