The Natural Inhibitor of DNA Topoisomerase I, Camptothecin, Modulates HIF-1 Activity by Changing miR Expression Patterns in Human Cancer Cells

MicroRNAs and Chinese Medicinal Herbs: New Possibilities in Cancer Therapy

In recent decades Chinese medicine has been used worldwide as a complementary and alternative medicine to treat cancer. Plenty of studies have shown that microRNAs (miRNAs) play fundamental roles in many pathological processes, including cancer, while the anti-cancer mechanisms of Chinese medicinal herbs targeting miRNAs also have been extensively explored. Our previous studies and those of others on Chinese medicinal herbs and miRNAs in various cancer models have provided a possibility of new cancer therapies, for example, up-regulating the expression of miR-23a may activate the positive regulatory network of p53 and miR-23a involved in the mechanism underlying the anti-tumor effect of berberine in hepatocellular carcinoma (HCC). In this review, we survey the role of Chinese medicinal herbal products in regulating miRNAs in cancer and the use of mediating miRNAs for cancer treatment. In addition, the controversial roles of herb-derived exogenous miRNAs in cancer treatment are also discussed. It is expected that targeting miRNAs would provide a novel therapeutic approach in cancer therapy by improving overall response and survival outcomes in cancer treatment, especially when combined with conventional therapeutics and Chinese medicinal herbal products.

MicroRNA-18a regulates invasive meningiomas via hypoxia-inducible factor-1α

The aim of the present study was to investigate the effects of microRNA-18a (miR-18a) on the invasiveness and metastasis of invasive meningiomas and the underlying mechanism. A total of 69 patients with meningiomas (30 patients in the invasive meningioma group and 39 patients in the non-invasive meningioma group) and 48 cases in the control group were enrolled. Samples of meningioma tissues, serum and cerebrospinal fluid were collected. Reverse transcription-quantitative polymerase chain reaction was performed to quantify the expression levels of hypoxia-inducible factor-1α (HIF-1α) mRNA and miR-18a. Western blot analysis was used to determine protein expression levels of HIF-1α. The expression levels of HIF-1α mRNA and protein in all three types of sample from the invasive meningioma group were significantly higher compared with those in the control and non-invasive meningioma groups (P<0.05), and the expression levels of HIF-1α mRNA in the serum and cerebrospinal fluid of the non-invasive meningioma group were significantly higher compared with those in the control group (P<0.05). The expression levels of miR-18a in the invasive meningioma group were significantly reduced compared with those in the control and non-invasive meningioma groups (P<0.05), whereas the levels of miR-18a in the non-invasive meningioma group were significantly lower compared with those in the control group (P<0.05). The expression of HIF-1α is significantly upregulated in patients with invasive meningiomas, possibly due to the downregulation of miR-18a expression. Therefore, miR-18a may regulate invasive meningiomas via HIF-1α.

Interactional role of microRNAs and bHLH-PAS proteins in cancer (Review)

MicroRNAs (miRNAs) are recognized as an emerging class of master regulators that regulate human gene expression at the post-transcriptional level and are involved in many normal and pathological cellular processes. Mammalian basic HLH (helix-loop-helix)-PER-ARNT-SIM (bHLH-PAS) proteins are heterodimeric transcriptional regulators that sense and respond to environmental signals (such as chemical pollutants) or to physiological signals (for instance hypoxia). In the normal state, bHLH-PAS proteins are responsible for multiple critical aspects of physiology to ensure the cell accurate homeostasis, but dysregulation of these proteins has been shown to contribute to carcinogenic events such as tumor initiation, promotion, and progression. Increasing epidemiological and experimental studies have shown that bHLH-PAS proteins regulate a panel of miRNAs, whereas some miRNAs also target bHLH-PAS proteins. The interaction between miRNAs and certain bHLH-PAS proteins [hypoxia-inducible factor (HIF) and aryl hydrocarbon receptor (AHR)] is relevant to many vital events associated with tumorigenesis. This review will summarize recent findings on the interesting and complicated underlying mechanisms that miRNAs interact with HIFs or AHR in tumors, hopefully to benefit the discovery of novel drug-interfering targets for cancer therapy.

Modulation of microRNAs by phytochemicals in cancer: underlying mechanisms and translational significance

MicroRNAs (miRNAs) are small, endogenous noncoding RNAs that regulate a variety of biological processes such as differentiation, development, and survival. Recent studies suggest that miRNAs are dysregulated in cancer and play critical roles in cancer initiation, progression, and chemoresistance. Therefore, exploitation of miRNAs as targets for cancer prevention and therapy could be a promising approach. Extensive evidence suggests that many naturally occurring phytochemicals regulate the expression of numerous miRNAs involved in the pathobiology of cancer. Therefore, an understanding of the regulation of miRNAs by phytochemicals in cancer, their underlying molecular mechanisms, and functional consequences on tumor pathophysiology may be useful in formulating novel strategies to combat this devastating disease. These aspects are discussed in this review paper with an objective of highlighting the significance of these observations from the translational standpoint.

Novel DNA topoisomerase IIα inhibitors from combined ligand- and structure-based virtual screening

DNA topoisomerases are enzymes responsible for the relaxation of DNA torsional strain, as well as for the untangling of DNA duplexes after replication, and are important cancer drug targets. One class of topoisomerase inhibitors, “poisons”, binds to the transient enzyme-DNA complex which occurs during the mechanism of action, and inhibits the religation of DNA. This ultimately leads to the accumulation of DNA double strand breaks and cell death. Different types of topoisomerases occur in human cells and several poisons of topoisomerase I and II are widely used clinically. However, their use is compromised by a variety of side effects. Recent studies confirm that the inhibition of the α-isoform of topoisomerase II is responsible for the cytotoxic effect, whereas the inhibition of the β-isoform leads to development of adverse drug reactions. Thus, the discovery of agents selective for topoisomerase IIα is an important strategy for the development of topoisomerase II poisons with improved clinical profiles. Here, we present a computer-aided drug design study leading to the identification of structurally novel topoisomerase IIα poisons. The study combines ligand- and structure-based drug design methods including pharmacophore models, homology modelling, docking, and virtual screening of the National Cancer Institute compound database. From the 8 compounds identified from the computational work, 6 were tested for their capacity to poison topoisomerase II in vitro: 4 showed selective inhibitory activity for the α- over the β-isoform and 3 of these exhibited cytotoxic activity. Thus, our study confirms the applicability of computer-aided methods for the discovery of novel topoisomerase II poisons, and presents compounds which could be investigated further as selective topoisomerase IIα inhibitors.

microRNA-18a is a genetic marker for the early diagnosis of cerebral injury induced by type 2 diabetes

The present study aimed to investigate the value of microRNA (miRNA)-18a for the early diagnosis of cerebral injury in patients with type 2 diabetes. Blood samples were collected from patients with type 2 diabetes, admitted to hospital between January and December 2013. The patients were randomly divided into three groups, which included one control and two experimental groups of severely and mildly diabetic patients (33 individuals per group). The levels of biochemical indicators in the serum, including S100 protein, neuron-specific enolase, myelin basic protein and endothelin-1, were determined. The mRNA and protein expression levels of hypoxia-inducible factor (HIF)-1α in the serum were measured by quantitative polymerase chain reaction (qPCR) and western blot analysis, respectively. In addition, the serum expression levels of miRNA-18a were determined by qPCR. The concentrations of the biochemical indicators in the severe diabetes group were significantly higher compared with those from the other two groups. Furthermore, the mRNA and protein expression levels of HIF-1α in the severe diabetes group were significantly upregulated compared with the other groups. However, the levels of miRNA-18a in the severe diabetes group were significantly downregulated compared with the other groups. The present study demonstrated that the elevation of biochemical indicators in the serum and the upregulation of HIF-1α mRNA and protein expression are associated with the downregulation of miRNA-18a. Therefore, miRNA-18a may be a potential genetic marker for the early diagnosis of cerebral injury induced by type 2 diabetes.