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Sirtuin Inhibitors: An Overview from Medicinal Chemistry Perspective

Yoon YK, Oon CE

Anticancer Agents Med Chem, 2016;16(8):1003-1016.
PMID: 26961318 DOI: 10.2174/1871520616666160310141622

The role of sirtuins in age-related diseases is an area of rapidly expanding investigation. Sirtuins are NAD+ -dependent class III histone deacetylases (HDACs) that share extensive homologies with the yeast HDAC Sir2. Class I and class II HDACs inhibitors have been identified as potential anticancer agents and are in clinical studies, but much less is known about class III HDAC inhibitors. However, inhibitors of sirtuins are currently being targeted as potential therapeutic agents for disease such as cancer, neurodegenerative disease and other disorders as sirtuins are discovered to regulate numerous downstream enzymes. Given the link between sirtuins and cancer, understanding the functionality of these enzymes may ultimately have significant impact in cancer prevention or cancer treatment. This review gives an updated overview regarding the regulation of sirtuin enzymes, their implications in cancer, various sirtuin inhibitor scaffolds and their insights in drug design.
How glycosylation aids tumor angiogenesis: An updated review

Cheng WK, Oon CE

Biomed Pharmacother, 2018 Jul;103:1246-1252.
PMID: 29864905 DOI: 10.1016/j.biopha.2018.04.119

Glycosylation is an enzymatic process in which a carbohydrate is attached to a functional group from another molecule. Glycosylation is a crucial post translational process in protein modification. The tumor microenvironment produces altered glycans that contribute to cancer progression and aggressiveness. Abnormal glycosylation is widely observed in tumor angiogenesis. Despite many attempts to decipher the role of glycosylation in different aspects of cancer, little is known regarding the roles of glycans in angiogenesis. The blood vessels in tumors are often used to transport oxygen and nutrients for tumor progression and metastasis. The crosstalk within the tumor microenvironment can induce angiogenesis by manipulating these glycans to hijack the normal angiogenesis process, thus promoting tumor growth. Abnormal glycosylation has been shown to promote tumor angiogenesis by degrading the extracellular matrix to activate the angiogenic signaling pathways. This review highlights the latest update on how glycosylation can contribute to tumor angiogenesis that may affect treatment outcomes.
Natural pro-oxidants: an alternative remedy to explore as novel cancer therapeutic agents

Jothy SL, Oon CE, Sasidharan S

Asian Pac J Cancer Prev, 2014;15(3):1501.
PMID: 24606490
Molecular targeted therapy: Treating cancer with specificity

Lee YT, Tan YJ, Oon CE

Eur J Pharmacol, 2018 Sep 05;834:188-196.
PMID: 30031797 DOI: 10.1016/j.ejphar.2018.07.034

Molecular targeted therapies are revolutionized therapeutics which interfere with specific molecules to block cancer growth, progression, and metastasis. Many molecular targeted therapies approved by the Food and Drug Administration (FDA), have demonstrated remarkable clinical success in the treatment of a myriad of cancer types including breast, leukemia, colorectal, lung, and ovarian cancers. This review provides an update on the different types of molecular targeted therapies used in the treatment of cancer, focusing on the fundamentals of molecular targeted therapy, its mode of action in cancer treatment, as well as its advantages and limitations.
Fulltext Benzimidazole and its derivatives as cancer therapeutics: The potential role from traditional to precision medicine

Lee YT, Tan YJ, Oon CE

Acta Pharm Sin B, 2023 Feb;13(2):478-497.
PMID: 36873180 DOI: 10.1016/j.apsb.2022.09.010

Cancer is the second leading cause of mortality globally which remains a continuing threat to human health today. Drug insensitivity and resistance are critical hurdles in cancer treatment; therefore, the development of new entities targeting malignant cells is considered a high priority. Targeted therapy is the cornerstone of precision medicine. The synthesis of benzimidazole has garnered the attention of medicinal chemists and biologists due to its remarkable medicinal and pharmacological properties. Benzimidazole has a heterocyclic pharmacophore, which is an essential scaffold in drug and pharmaceutical development. Multiple studies have demonstrated the bioactivities of benzimidazole and its derivatives as potential anticancer therapeutics, either through targeting specific molecules or non-gene-specific strategies. This review provides an update on the mechanism of actions of various benzimidazole derivatives and the structure‒activity relationship from conventional anticancer to precision healthcare and from bench to clinics.
Fulltext BZD9L1 Differentially Regulates Sirtuins in Liver-Derived Cells by Inducing Reactive Oxygen Species

Lee YT, Tan YJ, Oon CE

Biomedicines, 2023 Nov 15;11(11).
PMID: 38002059 DOI: 10.3390/biomedicines11113059

Growing evidence has highlighted that mitochondrial dysfunction contributes to drug-induced toxicities and leads to drug attrition and post-market withdrawals. The acetylation or deacetylation of mitochondrial proteins can affect mitochondrial functions as the cells adapt to various cellular stresses and other metabolic challenges. SIRTs act as critical deacetylases in modulating mitochondrial function in response to drug toxicity, oxidative stress, reactive oxygen species (ROS), and energy metabolism. We previously showed that a recently characterised SIRT inhibitor (BZD9L1) is non-toxic in rodents in a short-term toxicity evaluation. However, the impact of BZD9L1 on mitochondrial function is unknown. This work aims to determine the effects of BZD9L1 on mitochondrial function in human normal liver and kidney-derived cell lines using the Agilent Seahorse Cell Mito Stress Test to complement our short-term toxicity evaluations in vivo. The Mito Stress assay revealed that BZD9L1 could potentially trigger oxidative stress by inducing ROS, which promotes proton leak and reduces coupling efficiency in liver-derived THLE cells. However, the same was not observed in human kidney-derived HEK293 cells. Interestingly, BZD9L1 had no impact on SIRT3 protein expression in both cell lines but affected SOD2 and its acetylated form at 72 h in THLE cells, indicating that BZD9L1 exerted its effect through SIRT3 activity rather than protein expression. In contrast, BZD9L1 reduced SIRT1 protein expression and impacted the p53 protein differently in both cell lines. Although BZD9L1 did not affect the spare respiratory capacity in vitro, these findings call for further validation of mitochondrial function through assessment of other mitochondrial parameters to evaluate the safety of BZD9L1.
SIRT1 inhibition in pancreatic cancer models: contrasting effects in vitro and in vivo

Oon CE, Strell C, Yeong KY, Östman A, Prakash J

Eur J Pharmacol, 2015 Jun 15;757:59-67.
PMID: 25843411 DOI: 10.1016/j.ejphar.2015.03.064

Gemcitabine remains the standard treatment for pancreatic cancer, although most patients acquire resistance to the therapy. Up-regulated in pancreatic cancer, SIRT1 is involved in tumorigenesis and drug resistance. However the mechanism through which SIRT1 regulates drug sensitivity in cancer cells is mainly unknown. We hypothesise that inhibiting SIRT1 activity may increase sensitivity of pancreatic cancer cells to gemcitabine treatment through the regulation of apototic cell death, cell cycle, epithelial-mesenschymal-transition (EMT) and senescence. We demonstrate that gemcitabine or 6-Chloro-2,3,4,9-tetrahydro-1 H-Carbazole-1-carboxamide (EX527) SIRT1 inhibitor reduces PANC-1 cell proliferation in vitro. EX527 enhanced sensitivity of PANC-1 cells to gemcitabine treatment through increased apoptosis. However, EX527 displayed no beneficial effect either as a monotreatment or in combination with gemcitabine in the modulation of cell cycle progression. Combination treatment did not reverse the two phenomena known to affect drug sensitivity, namely EMT and senescence, which are both induced by gemcitabine. Unexpectedly, EX527 promoted PANC-1 xenograft tumour growth in SCID mice compared to control group. Dual tX527 and gemcitabine displayed no synergistic effect compared to gemcitabine alone. The study reveals that SIRT1 is involved in chemoresistance and that inhibiting SIRT1 activity with EX527 sensitised PANC-1 cells to gemcitabine treatment in vitro. Sensitisation of cells is shown to be mainly through induction of micronuclei formation as a result of DNA damage and apoptosis in vitro. However, the absence of positive combinatorial effects in vivo indicates possible effects on cells of the tumor microenvironment and suggests caution regarding the clinical relevance of tissue culture findings with EX527.
Rapamycin induces apoptosis when autophagy is inhibited in T-47D mammary cells and both processes are regulated by Phlda1

Moad AI, Muhammad TS, Oon CE, Tan ML

Cell Biochem Biophys, 2013 Jul;66(3):567-87.
PMID: 23300026 DOI: 10.1007/s12013-012-9504-5

Autophagy is an evolutionarily conserved lysosomal degradation pathway and plays a critical role in the homeostatic process of recycling proteins and organelles. Functional relationships have been described between apoptosis and autophagy. Perturbations in the apoptotic machinery have been reported to induce autophagic cell deaths. Inhibition of autophagy in cancer cells has resulted in cell deaths that manifested hallmarks of apoptosis. However, the molecular relationships and the circumstances of which molecular pathways dictate the choice between apoptosis and autophagy are currently unknown. This study aims to identify specific gene expression of rapamycin-induced autophagy and the effects of rapamycin when the autophagy process is inhibited. In this study, we have demonstrated that rapamycin is capable of inducing autophagy in T-47D breast carcinoma cells. However, when the autophagy process was inhibited by 3-MA, the effects of rapamycin became apoptotic. The Phlda1 gene was found to be up-regulated in both autophagy and apoptosis and silencing this gene was found to reduce both activities, strongly suggests that Phlda1 mediates and positively regulates both autophagy and apoptosis pathways.
Polyalthia longifolia Methanolic Leaf Extracts (PLME) induce apoptosis, cell cycle arrest and mitochondrial potential depolarization by possibly modulating the redox status in hela cells

Vijayarathna S, Oon CE, Chen Y, Kanwar JR, Sasidharan S

Biomed Pharmacother, 2017 May;89:499-514.
PMID: 28249252 DOI: 10.1016/j.biopha.2017.02.075

Medicinal plants have been accepted as a gold mine, with respect to the diversity of their phytochemicals. Many medicinal plants extracts are potential anticancer agents. Polyalthia longifolia var. angustifolia Thw. (Annonaceae) is one of the most significant native medicinal plants and is found throughout Malaysia. Hence, the present study was intended to assess the anticancer properties of P. longifolia leaf methanolic extract (PLME) and its underlying mechanisms. The Annexin V/PI flow cytometry analysis showed that PLME induces apoptosis in HeLa cells in dose-dependent manner whereas the PI flow cytometric analysis for cell cycle demonstrated the accumulation of cells at sub G0/G1, G0/G1 and G2/M phases. Investigation with JC-1 flow cytometry analysis indicated increase in mitochondria membrane potential depolarisation corresponding to increase in PLME concentrations. PLME was also shown to influence intracellular reactive oxygen species (ROS) by exerting anti-oxidant (half IC50) and pro-oxidant (IC50and double IC50) affect against HeLa cells. PLME treatment also displayed DNA damage in HeLa cells in concentration depended fashion. The proteomic profiling array exposed the expression of pro-apoptotic and anti-apoptotic proteins upon PLME treatment at IC50concentration in HeLa cells. Pro-apoptotic proteins; BAX, BAD, cytochrome c, caspase-3, p21, p27 and p53 were found to be significantly up-regulated while anti-apoptotic proteins; BCL-2 and BCL-w were found to be significantly down-regulated. This investigation postulated the role of p53 into mediating apoptosis, cell cycle arrest and mitochondrial potential depolarisation by modulating the redox status of HeLa cells.
BZD9L1 sirtuin inhibitor: Identification of key molecular targets and their biological functions in HCT 116 colorectal cancer cells

Tan YJ, Lee YT, Mancera RL, Oon CE

Life Sci, 2021 Nov 01;284:119747.
PMID: 34171380 DOI: 10.1016/j.lfs.2021.119747

BZD9L1 was previously described as a SIRT1/2 inhibitor with anti-cancer activities in colorectal cancer (CRC), either as a standalone chemotherapy or in combination with 5-fluorouracil. BZD9L1 was reported to induce apoptosis in CRC cells; however, the network of intracellular pathways and crosstalk between molecular players mediated by BZD9L1 is not fully understood. This study aimed to uncover the mechanisms involved in BZD9L1-mediated cytotoxicity based on previous and new findings for the prediction and identification of related pathways and key molecular players. BZD9L1-regulated candidate targets (RCTs) were identified using a range of molecular, cell-based and biochemical techniques on the HCT 116 cell line. BZD9L1 regulated major cancer pathways including Notch, p53, cell cycle, NFκB, Myc/MAX, and MAPK/ERK signalling pathways. BZD9L1 also induced reactive oxygen species (ROS), regulated apoptosis-related proteins, and altered cell polarity and adhesion profiles. In silico analyses revealed that most RCTs were interconnected, and were involved in the modulation of catalytic activity, metabolism and transcription regulation, response to cytokines, and apoptosis signalling pathways. These RCTs were implicated in p53-dependent apoptosis pathway. This study provides the first assessment of possible associations of molecular players underlying the cytotoxic activity of BZD9L1, and establishes the links between RCTs and apoptosis through the p53 pathway.
Fulltext Key Molecular Events in Cervical Cancer Development

Balasubramaniam SD, Balakrishnan V, Oon CE, Kaur G

Medicina (Kaunas), 2019 Jul 17;55(7).
PMID: 31319555 DOI: 10.3390/medicina55070384

Cervical cancer is the fourth most common cancer among women. Infection by high-risk human papillomavirus (HPV) is the main aetiology for the development of cervical cancer. Infection by high-risk human papillomavirus (HPV) and the integration of the HPV genome into the host chromosome of cervical epithelial cells are key early events in the neoplastic progression of cervical lesions. The viral oncoproteins, mainly E6 and E7, are responsible for the initial changes in epithelial cells. The viral proteins inactivate two main tumour suppressor proteins, p53, and retinoblastoma (pRb). Inactivation of these host proteins disrupts both the DNA repair mechanisms and apoptosis, leading to rapid cell proliferation. Multiple genes involved in DNA repair, cell proliferation, growth factor activity, angiogenesis, as well as mitogenesis genes become highly expressed in cervical intraepithelial neoplasia (CIN) and cancer. This genomic instability encourages HPV-infected cells to progress towards invasive carcinoma. The key molecular events involved in cervical carcinogenesis will be discussed in this review.
MicroRNAs: biogenesis, roles for carcinogenesis and as potential biomarkers for cancer diagnosis and prognosis

Kavitha N, Vijayarathna S, Jothy SL, Oon CE, Chen Y, Kanwar JR, et al.

Asian Pac J Cancer Prev, 2014;15(18):7489-97.
PMID: 25292018

MicroRNAs (miRNAs) are short non-coding RNAs of 20-24 nucleotides that play important roles in carcinogenesis. Accordingly, miRNAs control numerous cancer-relevant biological events such as cell proliferation, cell cycle control, metabolism and apoptosis. In this review, we summarize the current knowledge and concepts concerning the biogenesis of miRNAs, miRNA roles in cancer and their potential as biomarkers for cancer diagnosis and prognosis including the regulation of key cancer-related pathways, such as cell cycle control and miRNA dysregulation. Moreover, microRNA molecules are already receiving the attention of world researchers as therapeutic targets and agents. Therefore, in-depth knowledge of microRNAs has the potential not only to identify their roles in cancer, but also to exploit them as potential biomarkers for cancer diagnosis and identify therapeutic targets for new drug discovery.
MicroRNA pathways: an emerging role in identification of therapeutic strategies

Vijayarathna S, Oon CE, Jothy SL, Chen Y, Kanwar JR, Sasidharan S

Curr Gene Ther, 2014;14(2):112-20.
PMID: 24588707

For years researchers have exerted every effort to improve the influential roles of microRNA (miRNA) in regulating genes that direct mammalian cell development and function. In spite of numerous advancements, many facets of miRNA generation remain unresolved due to the perplexing regulatory networks. The biogenesis of miRNA, eminently endures as a mystery as no universal pathway defines or explicates the variegation in the rise of miRNAs. Early evidence in biogenesis ignited specific steps of being omitted or replaced that eventuate in the individual miRNAs of different mechanisms. Understanding the basic foundation concerning how miRNAs are generated and function will help with diagnostic tools and therapeutic strategies. This review encompasses the canonical and the non-canonical pathways involved in miRNA biogenesis, while elucidating how miRNAs regulate genes at the nuclear level and also the mechanism that lies behind circulating miRNAs.
Epigenetics: The master control of endothelial cell fate in cancer

V Subramaniam A, Yehya AHS, Cheng WK, Wang X, Oon CE

Life Sci, 2019 Sep 01;232:116652.
PMID: 31302197 DOI: 10.1016/j.lfs.2019.116652

The development of new blood vessels from pre-existing vasculature is called angiogenesis. The growth of tumors depends on a network of supplying vessels that provide them with oxygen and nutrients. Pro-angiogenic factors that are secreted by tumors will trigger the sprouting of nearby existing blood vessels towards themselves and therefore researchers have developed targeted therapy towards these pro-angiogenic proteins to inhibit angiogenesis. However, certain pro-angiogenic proteins tend to bypass the inhibition. Thus, instead of targeting these expressed proteins, research towards angiogenesis inhibition had been focused on a deeper scale, epigenetic modifications. Epigenetic regulatory mechanisms are a heritable change in a sequence of stable but reversible gene function modification yet do not affect the DNA primary sequence directly. Methylation of DNA, modification of histone and silencing of micro-RNA (miRNA)-associated gene are currently considered to initiate and sustain epigenetic changes. Recent findings on the subject matter have provided an insight into the mechanism of epigenetic modifications, thus this review aims to present an update on the latest studies.
Identification of genes involved in the regulation of 14-deoxy-11,12-didehydroandrographolide-induced toxicity in T-47D mammary cells

Tan ML, Tan HK, Oon CE, Kuroyanagi M, Muhammad TS

Food Chem Toxicol, 2012 Feb;50(2):431-44.
PMID: 22101062 DOI: 10.1016/j.fct.2011.11.001

14-Deoxy-11,12-didehydroandrographolide is one of the principle compounds of the medicinal plant, Andrographis paniculata Nees. This study explored the mechanisms of 14-deoxy-11,12-didehydroandrographolide-induced toxicity and non-apoptotic cell death in T-47D breast carcinoma cells. Gene expression analysis revealed that 14-deoxy-11,12-didehydroandrographolide exerted its cytotoxic effects by regulating genes that inhibit the cell cycle or promote cell cycle arrest. This compound regulated genes that are known to reduce/inhibit cell proliferation, induce growth arrest and suppress cell growth. The growth suppression activities of this compound were demonstrated by a downregulation of several genes normally found to be over-expressed in cancers. Microscopic analysis revealed positive monodansylcadaverine (MDC) staining at 8h, indicating possible autophagosomes. TEM analysis revealed that the treated cells were highly vacuolated, thereby suggesting that 14-deoxy-11,12-didehydroandrographolide may cause autophagic morphology in these cells. This morphology may be correlated with the concurrent expression of genes known to affect lysosomal activity, ion transport, protein degradation and vesicle transport. Interestingly, some apoptotic-like bodies were found, and these bodies contained multiple large vacuoles, suggesting that this compound is capable of eliciting a combination of apoptotic and autophagic-like morphological characteristics.
Comparative transcriptomic profiling in HPV-associated cervical carcinogenesis: Implication of MHC class II and immunoglobulin heavy chain genes

Balasubramaniam SD, Wong KK, Oon CE, Balakrishnan V, Kaur G

Life Sci, 2020 Sep 01;256:118026.
PMID: 32615187 DOI: 10.1016/j.lfs.2020.118026

AIM: We aimed to determine the biological processes and pathways involved in cervical carcinogenesis associated with high-risk human papillomavirus (HPV) infection.
MATERIALS AND METHODS: Total RNA was extracted from three formalin-fixed paraffin-embedded (FFPE) samples each of normal cervix, HPV-infected low-grade squamous intraepithelial lesion (LSIL), high-grade SIL (HSIL) and squamous cell carcinoma (SCC). Transcriptomic profiling by microarrays was conducted followed by downstream Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses.
RESULTS: We examined the difference in GOs enriched for each transition stage from normal cervix to LSIL, HSIL, and SCC, and found 307 genes to be differentially expressed. In the transition from normal cervix to LSIL, the extracellular matrix (ECM) genes were significantly downregulated. The MHC class II genes were significantly upregulated in the LSIL to HSIL transition. In the final transition from HSIL to SCC, the immunoglobulin heavy locus genes were significantly upregulated and the ECM pathway was implicated.
CONCLUSION: Deregulation of the immune-related genes including MHC II and immunoglobulin heavy chain genes were involved in the transitions from LSIL to HSIL and SCC, suggesting immune escape from host anti-tumour response. The extracellular matrix plays an important role during the early and late stages of cervical carcinogenesis.
Nuclear and stromal expression of Manic fringe in renal cell carcinoma

Cheng WK, Kaur G, Sjöberg E, Frödin M, Egevad L, Harmenberg U, et al.

Exp Mol Pathol, 2021 Aug 08;122:104667.
PMID: 34371013 DOI: 10.1016/j.yexmp.2021.104667

Renal cell carcinoma (RCC) is the most common type of kidney cancer and has the highest mortality rate among genitourinary cancers. Despite the advances in molecular targeted therapies to treat RCC, the inevitable emergence of resistance has delineated the need to uncover biomarkers to prospectively identify patient response to treatment and more accurately predict patient prognosis. Fringe is a fucose specific β1, 3N-acetylglucosaminyltransferase that modifies the Notch receptors. Given the link between its function and aberrant Notch activation in RCC, Fringe may be implicated in this disease. The Fringe homologs comprise of Lunatic fringe (LFng), Manic fringe (MFng) and Radical fringe (RFng). MFng has been reported to play a role in cancer. MFng is also essential in the development of B cells. However, the expression profile and clinical significance of MFng, and its association with B cells in RCC are unknown. CD20 is a clinically employed biomarker for B cells. This pilot study aimed to determine if MFng protein expression can be utilized as a prospective biomarker for therapeutics and prognosis in RCC, as well as to determine its association with CD20+ B cells. Analysis of publicly available MFng gene expression datasets on The Cancer Genome Atlas Netlwork (TCGA) identified MFng gene expression to be up-regulated in Kidney Clear Cell Renal Carcinoma (KIRC) patients. However there was no significant association between the patient survival probability and the level of MFng expression in this cohort. Immunohistochemistry performed on a tissue microarray containing cores from 64 patients revealed an elevated MFng protein expression in the epithelial and stromal tissues of RCC compared to the normal kidney, suggesting a possible role in tumorigenesis. Our study describes for the first time to our knowledge, the protein expression of MFng in the nuclear compartment of normal kidney and RCC, implicating a prospective involvement in gene transcription. At the cellular level, cytoplasmic MFng was also abundant in the normal kidney and RCC. However, MFng protein expression in the malignant epithelial and stromal tissue of RCC had no positive correlation with the patients' overall survival, progression-free survival and time to metastasis, as well as the gender, age, tumor stage and RCC subtype, indicating that MFng may not be an appropriate prognostic marker. The association between CD20+ B cells and epithelial MFng was found to approach borderline insignificance. Nonetheless, these preliminary findings may provide valuable information on the suitability of MFng as a potential therapeutic molecular marker for RCC, thus warrants further investigation using a larger cohort.
Anticancer activities of a benzimidazole compound through sirtuin inhibition in colorectal cancer

Tan YJ, Lee YT, Yeong KY, Petersen SH, Kono K, Tan SC, et al.

Future Med Chem, 2018 Sep 01;10(17):2039-2057.
PMID: 30066578 DOI: 10.4155/fmc-2018-0052

AIM: This study aims to investigate the mode of action of a novel sirtuin inhibitor (BZD9L1) and its associated molecular pathways in colorectal cancer (CRC) cells.
MATERIALS & METHODS: BZD9L1 was tested against metastatic CRC cell lines to evaluate cytotoxicity, cell cycle and apoptosis, senescence, apoptosis related genes and protein expressions, as well as effect against major cancer signaling pathways.
RESULTS & CONCLUSION: BZD9L1 reduced the viability, cell migration and colony forming ability of both HCT 116 and HT-29 metastatic CRC cell lines through apoptosis. BZD9L1 regulated major cancer pathways differently in CRC with different mutation profiles. BZD9L1 exhibited anticancer activities as a cytotoxic drug in CRC and as a promising therapeutic strategy in CRC treatment.
Functional Analysis of Circular RNAs

Shanmugapriya, Huda HA, Vijayarathna S, Oon CE, Chen Y, Kanwar JR, et al.

Adv Exp Med Biol, 2018 9 28;1087:95-105.
PMID: 30259360 DOI: 10.1007/978-981-13-1426-1_8

Circular RNAs characterize a class of widespread and diverse endogenous RNAs which are non-coding RNAs that are made by back-splicing events and have covalently closed loops with no polyadenylated tails. Various indications specify that circular RNAs (circRNAs) are plentiful in the human transcriptome. However, their participation in biological processes remains mostly undescribed. To date thousands of circRNAs have been revealed in organisms ranging from Drosophila melanogaster to Homo sapiens. Functional studies specify that these transcripts control expression of protein-coding linear transcripts and thus encompass a key component of gene expression regulation. This chapter provide a comprehensive overview on functional validation of circRNAs. Furthermore, we discuss the recent modern methodologies for the functional validation of circRNAs such as RNA interference (RNAi) gene silencing assay, luciferase reporter assays, circRNA gain-of-function investigation via overexpression of circular transcript assay, RT-q-PCR quantification, and other latest applicable assays. The methods described in this chapter are demonstrated on the cellular model.
Fulltext Minichromosome Maintenance Complex (MCM) Genes Profiling and MCM2 Protein Expression in Cervical Cancer Development

Kaur G, Balasubramaniam SD, Lee YJ, Balakrishnan V, Oon CE

Asian Pac J Cancer Prev, 2019 Oct 01;20(10):3043-3049.
PMID: 31653153 DOI: 10.31557/APJCP.2019.20.10.3043

OBJECTIVE: Minichromosome maintenance complex (MCM) proteins are essential for the process of DNA replication and cell division. This study aimed to evaluate MCM genes expression profiles and MCM2 protein in HPV-associated cervical carcinogenesis.
METHODOLOGY: MCM2, 4, 5 and 7 genes expression profiles were evaluated in three cervical tissue samples each of normal cervix, human papillomavirus (HPV)-infected low grade squamous intraepithelial lesion (LSIL), high grade squamous intraepithelial lesion (HSIL) and squamous cell carcinoma (SCC), using Human Transcriptome Array 2.0 and validated by nCounter® PanCancer Pathway NanoString Array. Immunohistochemical expression of MCM2 protein was semi-quantitatively assessed by histoscore in tissue microarrays containing 9 cases of normal cervix, 10 LSIL, 10 HSIL and 42 cases of SCC.
RESULTS: MCM2, 4, 5 and 7 genes expressions were upregulated with increasing fold change during the progression from LSIL to HSIL and the highest in SCC. MCM2 gene had the highest fold change in SCC compared to normal cervix. Immunohistochemically, MCM2 protein was localised in the nuclei of basal cells of normal cervical epithelium and dysplastic-neoplastic cells of CIN and SCC. There was a significant difference in MCM2 protein expression between the histological groups (P = 0.039), and histoscore was the highest in HSIL compared to normal cervix (P = 0.010).
CONCLUSION: The upregulation of MCM genes expressions in cervical carcinogenesis reaffirms MCM as a proliferative marker in DNA replication pathway, whereby proliferation of dysplastic and cancer cells become increasingly dysregulated and uncontrolled. A strong expression of MCM2 protein in HSIL may aid as a concatenated screening tool in detecting pre-cancerous cervical lesions.

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