Quercetin-induced miR-200b-3p regulates the mode of self-renewing divisions in pancreatic cancer.

BACKGROUND: Cancer stem cells are suggested to contribute to the extremely poor prognosis of pancreatic ductal adenocarcinoma and dysregulation of symmetric and asymmetric stem cell division may be involved. Anticancer benefits of phytochemicals like the polyphenol quercetin, present in many fruits, nuts and vegetables, could be expedited by microRNAs, which orchestrate cell-fate decisions and tissue homeostasis. The mechanisms regulating the division mode of cancer stem cells in relation to phytochemical-induced microRNAs are poorly understood. METHODS: Patient-derived pancreas tissue and 3 established pancreatic cancer cell lines were examined by immunofluorescence and time-lapse microscopy, microRNA microarray analysis, bioinformatics and computational analysis, qRT-PCR, Western blot analysis, self-renewal and differentiation assays. RESULTS: We show that symmetric and asymmetric division occurred in patient tissues and in vitro, whereas symmetric divisions were more extensive. By microarray analysis, bioinformatics prediction and qRT-PCR, we identified and validated quercetin-induced microRNAs involved in Notch signaling/cell-fate determination. Further computational analysis distinguished miR-200b-3p as strong candidate for cell-fate determinant. Mechanistically, miR-200b-3p switched symmetric to asymmetric cell division by reversing the Notch/Numb ratio, inhibition of the self-renewal and activation of the potential to differentiate to adipocytes, osteocytes and chondrocytes. Low miR-200b-3p levels fostered Notch signaling and promoted daughter cells to become symmetric while high miR-200b-3p levels lessened Notch signaling and promoted daughter cells to become asymmetric. CONCLUSIONS: Our findings provide a better understanding of the cross talk between phytochemicals, microRNAs and Notch signaling in the regulation of self-renewing cancer stem cell divisions.

[Corrigendum] Dexamethasone-induced inhibition of miR-132 via methylation promotes TGF-ß-driven progression of pancreatic cancer.

Subsequently to the publication of the above article, an interested reader drew to the authors' attention that two pairs of the culture plate images in Fig. 4A-C on p. 60 appeared to be the same, although the images were shown in different orientations; moreover, the 'NC/0 and DEX+miR132' and 'DEX and miR132' pairings of images in the scratch-wound assay experiments shown in Fig. 4B also appeared to be overlapping, such that these were apparently derived from the same original source where the results of differently performed experiments were intended to have been portrayed. After re­examining their original data, the authors have realized that some of the data in Fig. 4A and B were inadvertently assembled incorrectly. The revised version of Fig. 4, showing all the correct data for the culture plate images in Fig. 4A-C (specifically, the images fifth along on the right for Fig. 4B and C have been revised) and the correct images for 'NC/0' and 'DEX/0' in Fig. 4D is shown on on the next page. The authors are grateful to the Editor of International Journal of Oncology for allowing them this opportunity to publish a Corrigendum, and all the authors agree with its publication. Furthermore, the authors apologize to the readership for any inconvenience caused. [International Journal of Oncology 54: 53­64, 2019; DOI: 10.3892/ijo.2018.4616].

Dexamethasone-induced inhibition of miR-132 via methylation promotes TGF-ß-driven progression of pancreatic cancer.

Glucocorticoids (GCs) such as dexamethasone (DEX) are administered as cancer co­treatment for palliative purposes due to their pro­apoptotic effects in lymphoid cancer and limited side effects associated with cancer growth and chemotherapy. However, there is emerging evidence that GCs induce therapy resistance in most epithelial tumors. Our recent data reveal that DEX promotes the progression of pancreatic ductal adenocarcinoma (PDA). In the present study, we examined 1 primary and 2 established PDA cell lines, and 35 PDA tissues from patients who had received (n=14) or not received (n=21) GCs prior to surgery. Through microRNA microarray analysis, in silico, and RT­qPCR analyses, we identified 268 microRNAs differentially expressed between DEX­treated and untreated cells. With a focus on cancer progression, we selected miR­132 and its target gene, transforming growth factor-ß2 (TGF­ß2), as top candidates. miR­132 mimics directly bound to the 3' untranslated region (3'UTR) of a TGF­ß2 luciferase construct and enhanced expression, as shown by increased luciferase activity. By contrast, DEX inhibited miR­132 expression via promoter methylation. miR­132 mimics also reduced DEX­induced clonogenicity, migration and expression of vimentin and E­cadherin in vitro and in tumor xenografts. In patients, GC intake prior to surgery enhanced global hypermethylation and expression of TGF­ß2 in tissues; expression of miR­132 was detected but could not be quantified. Our results demonstrate that DEX­mediated inhibition of miR­132 is a key mediator in the progression of pancreatic cancer, and the findings provide a foundation for miRNA­based therapies.

Simvastatin inhibits sonic hedgehog signaling and stemness features of pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDA) has poor therapeutic options. Recent patient studies indicate that cholesterol-lowering statins have anti-tumor capacities. We examined several established and primary PDA and normal cell lines as well as PDA patient tissues (n = 68). We found that simvastatin inhibited viability, stemness, tumor growth and metastasis and that it enhanced the efficacy of gemcitabine. These changes were associated with modulation of Shh-related gene expression. Overexpression of Shh prevented the anti-cancer effect of simvastatin, and inhibition of Shh mimicked the simvastatin effect. In PDA tissues, expression levels of Shh, downstream mediators of Shh and progression markers, namely, cMet, CxCR4 and Vimentin, were lower when patients were prescribed statin medication prior to surgery. These results suggested that statins are cost effective and well-tolerated drugs for prevention and co-treatment of PDA.

Dexamethasone mediates pancreatic cancer progression by glucocorticoid receptor, TGFß and JNK/AP-1.

Glucocorticoids such as dexamethasone are widely co-prescribed with cytotoxic therapy because of their proapoptotic effects in lymphoid cancer, reduction of inflammation and edema and additional benefits. Concerns about glucocorticoid-induced therapy resistance, enhanced metastasis and reduced survival of patients are largely not considered. We analyzed dexamethasone-induced tumor progression in three established and one primary human pancreatic ductal adenocarcinoma (PDA) cell lines and in PDA tissue from patients and xenografts by FACS and western blot analysis, immunohistochemistry, MTT and wound assay, colony and spheroid formation, EMSA and in vivo tumor growth and metastasis of tumor xenografts on chicken eggs and mice. Dexamethasone in concentrations observed in plasma of patients favored epithelial-mesenchymal transition, self-renewal potential and cancer progression. Ras/JNK signaling, enhanced expression of TGFß, vimentin, Notch-1 and SOX-2 and the inhibition of E-cadherin occurred. This was confirmed in patient and xenograft tissue, where dexamethasone induced tumor proliferation, gemcitabine resistance and metastasis. Inhibition of each TGFß receptor-I, glucocorticoid receptor or JNK signaling partially reversed the dexamethasone-mediated effects, suggesting a complex signaling network. These data reveal that dexamethasone mediates progression by membrane effects and binding to glucocorticoid receptor.

Up-regulation of microRNA let-7c by quercetin inhibits pancreatic cancer progression by activation of Numbl.

Pancreatic Ductal Adenocarcinoma (PDA) is a highly malignant tumor with poor prognosis. MicroRNAs (miRs) may offer novel therapeutic approaches to treatment. The polyphenol quercetin, present in many fruits and vegetables, possesses anti-carcinogenic properties. To unravel the effect of quercetin to miR signaling we performed miR profiling in PDA cells before and after quercetin treatment, followed by biostatistical analysis. miR let-7c was among the top up-regulated candidates after quercetin treatment, as measured by qRT-PCR and confirmed in two established and one primary PDA cell lines. By computational analysis we identified the Notch-inhibitor Numbl as let-7c target gene. This was strengthened by luciferase assays, where lipofected let-7c mimics induced a Numbl 3-UTR wild type construct, but not the mutated counterpart. Let-7c induced Numbl mRNA and protein expression but inhibited Notch just like quercetin. It also inhibited colony formation, wound healing, and protein expression of progression markers. In vivo xenotransplantation of PDA cells and subsequent intravenous injection of let-7c resulted in a significant decrease in tumor mass without obvious toxic effects in the fertilized chick egg model. The delivery rate of the miR mimics to the tumor mass was 80%, whereas minor amounts were present in host tissue. By immunohistochemistry we demonstrated that let-7c inhibited Notch and progression markers but up-regulated Numbl. These findings show that quercetin-induced let-7c decreases tumor growth by posttranscriptional activation of Numbl and indirect inhibition of Notch.

MicroRNA-101-3p reverses gemcitabine resistance by inhibition of ribonucleotide reductase M1 in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDA) is among the most lethal malignancies and resistance to chemotherapy prevents the therapeutic outcome. MicroRNAs provide a novel therapeutic strategy. Here, the established and primary human PDA cell lines PANC-1, AsPC-1, MIA-PaCa2, AsanPaCa, BxPC-3 and three gemcitabine-resistant subclones were examined. A gene expression profiling revealed that the ribonucleotide reductase M1 (RRM1) was upregulated in gemcitabine-resistant cells, which was confirmed by qRT-PCR, Western blot analysis and immunostaining. Inhibition of RRM1 by lipotransfection of siRNA reduced its expression and reversed gemcitabine resistance. The expression of RRM1 correlated to gemcitabine resistance in vitro and was higher in malignant patient pancreas tissue compared to non-malignant pancreas tissue. By microRNA expression profiling, we identified microRNA-101-3p as top-downregulated candidate. Lipotransfection of microRNA-101-3p mimics inhibited the expression of RRM1, reduced the luciferase activity of its 3'UTR and sensitized for gemcitabine-induced cytotoxicity. These results underline the relevance of microRNA-101-3p-driven regulation of RRM1 in drug resistance and suggest the co-delivery of microRNA-101-3p and gemcitabine for more effective therapy outcome.

Inhibition of glucose turnover by 3-bromopyruvate counteracts pancreatic cancer stem cell features and sensitizes cells to gemcitabine.

According to the cancer stem cell (CSC) hypothesis, the aggressive growth and early metastasis of pancreatic ductal adenocarcinoma (PDA) is due to the activity of CSCs, which are not targeted by current therapies. Otto Warburg suggested that the growth of cancer cells is driven by a high glucose metabolism. Here, we investigated whether glycolysis inhibition targets CSCs and thus may enhance therapeutic efficacy. Four established and 3 primary PDA cell lines, non-malignant cells, and 3 patient-tumor-derived CSC-enriched spheroidal cultures were analyzed by glucose turnover measurements, MTT and ATP assays, flow cytometry of ALDH1 activity and annexin positivity, colony and spheroid formation, western blotting, electrophoretic mobility shift assay, xenotransplantation, and immunohistochemistry. The effect of siRNA-mediated inhibition of LDH-A and LDH-B was also investigated. The PDA cells exhibited a high glucose metabolism, and glucose withdrawal or LDH inhibition by siRNA prevented growth and colony formation. Treatment with the anti-glycolytic agent 3-bromopyruvate almost completely blocked cell viability, self-renewal potential, NF-κB binding activity, and stem cell-related signaling and reverted gemcitabine resistance. 3-bromopyruvate was less effective in weakly malignant PDA cells and did not affect non-malignant cells, predicting minimal side effects. 3-bromopyruvate inhibited in vivo tumor engraftment and growth on chicken eggs and mice and enhanced the efficacy of gemcitabine by influencing the expression of markers of proliferation, apoptosis, self-renewal, and metastasis. Most importantly, primary CSC-enriched spheroidal cultures were eliminated by 3-bromopyruvate. These findings propose that CSCs may be specifically dependent on a high glucose turnover and suggest 3-bromopyruvate for therapeutic intervention.

Sulforaphane counteracts aggressiveness of pancreatic cancer driven by dysregulated Cx43-mediated gap junctional intercellular communication.

The extreme aggressiveness of pancreatic ductal adenocarcinoma (PDA) has been associated with blocked gap junctional intercellular communication (GJIC) and the presence of cancer stem cells (CSCs). We examined whether disturbed GJIC is responsible for a CSC phenotype in established and primary cancer cells and patient tissue of PDA using interdisciplinary methods based in physiology, cell and molecular biology, histology and epigenetics. Flux of fluorescent dyes and gemcitabine through gap junctions (GJs) was intact in less aggressive cells but not in highly malignant cells with morphological dysfunctional GJs. Among several connexins, only Cx43 was expressed on the cell surface of less aggressive and GJIC-competent cells, whereas Cx43 surface expression was absent in highly malignant, E-cadherin-negative and GJIC-incompetent cells. The levels of total Cx43 protein and Cx43 phosphorylated at Ser368 and Ser279/282 were high in normal tissue but low to absent in malignant tissue. si-RNA-mediated inhibition of Cx43 expression in GJIC-competent cells prevented GJIC and induced colony formation and the expression of stem cell-related factors. The bioactive substance sulforaphane enhanced Cx43 and E-cadherin levels, inhibited the CSC markers c-Met and CD133, improved the functional morphology of GJs and enhanced GJIC. Sulforaphane altered the phosphorylation of several kinases and their substrates and inhibition of GSK3, JNK and PKC prevented sulforaphane-induced CX43 expression. The sulforaphane-mediated expression of Cx43 was not correlated with enhanced Cx43 RNA expression, acetylated histone binding and Cx43 promoter de-methylation, suggesting that posttranslational phosphorylation is the dominant regulatory mechanism. Together, the absence of Cx43 prevents GJIC and enhances aggressiveness, whereas sulforaphane counteracts this process, and our findings highlight dietary co-treatment as a viable treatment option for PDA.