Growth Stimulation of COX-2–Negative Pancreatic Cancer by a Selective COX-2 Inhibitor

LLGL1 Regulates Gemcitabine Resistance by Modulating the ERK-SP1-OSMR Pathway in Pancreatic Ductal Adenocarcinoma

BACKGROUND & AIMS

Gemcitabine resistance is rapidly acquired by pancreatic ductal adenocarcinoma (PDAC) patients. Novel approaches that predict the gemcitabine response of patients and enhance gemcitabine chemosensitivity are important to improve patient survival. We aimed to identify genes as novel biomarkers to predict the gemcitabine response and the therapeutic targets to attenuate chemoresistance in PDAC cells.

METHODS

Genome-wide RNA interference screening was conducted to identify genes that regulated gemcitabine chemoresistance. A cell proliferation assay and a tumor formation assay were conducted to study the role of lethal giant larvae homolog 1 (LLGL1) in gemcitabine chemoresistance. Levels of LLGL1 and its regulating targets were measured by immunohistochemical staining in tumor tissues obtained from patients who received gemcitabine as a single therapeutic agent. A gene-expression microarray was conducted to identify the targets regulated by LLGL1.

RESULTS

Silencing of LLGL1 markedly reduced the gemcitabine chemosensitivity in PDAC cells. Patients had significantly shorter survival (6 months) if they bore tumors expressing low LLGL1 level than tumors with high LLGL1 level (20 months) (hazard ratio, 0.1567; 95% CI, 0.05966-0.4117). Loss of LLGL1 promoted cytokine receptor oncostatin M receptor (OSMR) expression in PDAC cells that led to gemcitabine resistance, while knockdown of OSMR effectively rescued the chemoresistance phenotype. The LLGL1-OSMR regulatory pathway showed great clinical importance because low LLGL1 and high OSMR expressions were observed frequently in PDAC tissues. Silencing of LLGL1 induced phosphorylation of extracellular signal-regulated kinase 2 and specificity protein 1 (Sp1), promoted Sp1 (pThr453) binding at the OSMR promoter, and enhanced OSMR transcription.

CONCLUSIONS

LLGL1 possessed a tumor-suppressor role as an inhibitor of chemoresistance by regulating OSMR-extracellular signal-regulated kinase 2/Sp1 signaling. The data sets generated and analyzed during the current study are available in the Gene Expression Omnibus repository (ID: GSE64681).

Nimesulide inhibits proliferation and induces apoptosis of pancreatic cancer cells by enhancing expression of PTEN

Pancreatic cancer is the fourth leading cause of cancer-associated cases of mortality worldwide. Prostaglandin-endoperoxide synthase 2 (COX-2) is considered a therapeutic target for prevention of pancreatic cancer. Nimesulide, a selective COX-2 inhibitor, can induce cell apoptosis, resulting in an anti-cancer effect. However, the mechanism underlying this effect remains to be elucidated. The present study aimed to evaluate the effects of nimesulide on proliferation of PANC-1 cells using an MTT assay. Apoptosis was evaluated by DNA laddering and Annexin V-fluorescein isothiocyanate/propidium iodide-stained flow cytometry. Furthermore, western blot analysis was used to elucidate the mechanism underlying nimesulide treatment in PANC-1 cells. It was determined that proliferation of PANC-1 cells was inhibited by nimesulide in a dose-dependent manner. Nimesulide promoted apoptosis of PANC-1 cells. Western blot analysis demonstrated that nimesulide increased expression of cleaved caspase-3 and apoptosis regulator Bax (Bcl-2 associated protein X), and decreased the expression of pro-caspase-3 and apoptosis regulator Bcl-2 (B-cell lymphoma 2). Furthermore, nimesulide enhanced expression of phosphatase and tensin homolog (PTEN), and decreased the expression level of COX-2 and vascular endothelial growth factor. In summary, the results of the present study demonstrated that nimesulide could induce apoptosis and inhibit growth of PANC-1 cells by enhancing the expression of PTEN, which indicates the potential of nimesulide to prevent tumor angiogenesis.

LW-215, a newly synthesized flavonoid, exhibits potent anti-angiogenic activity in vitro and in vivo

LW-215 is a newly synthesized flavonoid, which is the derivative of wogonin. Our group has previously confirmed that wogonin has an anti-angiogenic activity, while the anti-angiogenic effect of LW-215 is unclear. In this study, we explored whether LW-215 can inhibit angiogenesis and further probed the potential molecular mechanisms. We found that LW-215 inhibited migration and tube formation in human umbilical vein endothelial cells (HUVECs) and immortalized endothelial EA.hy926 cells without a significant decrease in cell viability. Microvessels sprouting from rat aortic ring and chicken chorioallantoic membrane (CAM) model also revealed that LW-215 could suppress angiogenesis in vivo. Western blot and ELISA analysis indicated that LW-215 could prevent VEGFR2 activation though reducing VEGF autocrine other than VEGFR1. Thus, its downstream kinases, such as Akt, ERK and p38 signaling, were inhibited. Taken together, these results fully showed that LW-215 might be a promising anti-angiogenesis agent.

Direct growth-inhibitory effects of prostaglandin E2 in pancreatic cancer cells in vitro through an EP4/PKA-mediated mechanism

BACKGROUND

There is strong evidence linking inflammation and the development of pancreatic ductal adenocarcinoma. Cyclooxygenase-2 (COX-2) and COX-2-derived PGE₂ are overexpressed in human and murine pancreatic ductal adenocarcinoma. Several studies have demonstrated an important role of COX-2-derived PGE₂ in tumor-stroma interactions; however, the direct growth effects of prostaglandin E₂ (PGE₂) on pancreatic ductal adenocarcinoma cells is less well defined. Our aim was to investigate the effects of PGE₂ on pancreatic ductal adenocarcinoma cell growth and to characterize the underlying mechanisms.

METHODS

Human pancreatic ductal adenocarcinoma cell lines, Panc-1 and MIA PaCa-2, were treated with PGE₂ in varying doses (0-10 μM). Effects on the phosphorylation of ERK1/2 were evaluated by Western blot. Colony formation was observed for cells treated with PGE₂ for 11 days. DNA synthesis was determined by (3H)-thymidine incorporation assay. Gene expression of E-type prostaglandin (EP)2/EP4 receptors and their correlation with survival in patients with pancreatic ductal adenocarcinoma were assessed using the RNA-Seq data set from The Cancer Genome Atlas Research Network.

RESULTS

PGE₂ decreased the size and number of colonies in Panc-1 but not MIA PaCa-2 cells. In the Panc-1 cells, PGE₂ activated PKA/CREB and decreased phosphorylation of ERK1/2, which was reversed by an EP4 receptor antagonist, while an EP2 receptor antagonist had no effect. In contrast, in MIA PaCa-2 cells, PGE₂ had no effect on ERK1/2 phosphorylation. Treatment of both Panc-1 and MIA PaCa-2 cells with forskolin/IBMX decreased ERK1/2 phosphorylation. Finally, PGE₂ decreased DNA synthesis only in Panc-1 cells, which was reversed by an EP4 receptor antagonist. In human pancreatic ductal adenocarcinoma, high EP2 and low EP4 gene expression was correlated to worse median overall survival (15.6 vs 20.8 months, log-rank P = .017).

CONCLUSION

Our study provides evidence that PGE₂ can inhibit directly pancreatic ductal adenocarcinoma cell growth through an EP4-mediated mechanism. Together with our gene expression and survival analysis, this observation suggests a protective role of EP4 receptors in human pancreatic ductal adenocarcinoma that expresses E-type prostaglandin receptors.

Epithelial to mesenchymal transition contributes to drug resistance in pancreatic cancer

A better understanding of drug resistance mechanisms is required to improve outcomes in patients with pancreatic cancer. Here, we characterized patterns of sensitivity and resistance to three conventional chemotherapeutic agents with divergent mechanisms of action [gemcitabine, 5-fluorouracil (5-FU), and cisplatin] in pancreatic cancer cells. Four (L3.6pl, BxPC-3, CFPAC-1, and SU86.86) were sensitive and five (PANC-1, Hs766T, AsPC-1, MIAPaCa-2, and MPanc96) were resistant to all three agents based on GI(50) (50% growth inhibition). Gene expression profiling and unsupervised hierarchical clustering revealed that the sensitive and resistant cells formed two distinct groups and differed in expression of specific genes, including several features of "epithelial to mesenchymal transition" (EMT). Interestingly, an inverse correlation between E-cadherin and its transcriptional suppressor, Zeb-1, was observed in the gene expression data and was confirmed by real-time PCR. Independent validation experiment using five new pancreatic cancer cell lines confirmed that an inverse correlation between E-cadherin and Zeb-1 correlated closely with resistance to gemcitabine, 5-FU, and cisplatin. Silencing Zeb-1 in the mesenchymal lines not only increased the expression of E-cadherin but also other epithelial markers, such as EVA1 and MAL2, and restored drug sensitivity. Importantly, immunohistochemical analysis of E-cadherin and Zeb-1 in primary tumors confirmed that expression of the two proteins was mutually exclusive (P = 0.012). Therefore, our results suggest that Zeb-1 and other regulators of EMT may maintain drug resistance in human pancreatic cancer cells, and therapeutic strategies to inhibit Zeb-1 and reverse EMT should be evaluated.

Delayed progression of pancreatic intraepithelial neoplasia in a conditional Kras(G12D) mouse model by a selective cyclooxygenase-2 inhibitor

Pancreatic ductal adenocarcinomas are thought to arise from noninvasive, intraductal precursor lesions called pancreatic intraepithelial neoplasias (PanIN). The study of PanINs holds great promise for the identification of early detection markers and effective cancer-preventing strategies. Cyclooxygenase-2 (COX-2) represents an intriguing target for therapeutic and preventive approaches in various human malignancies. The aim of the present study was to evaluate the efficacy of a selective COX-2 inhibitor to prevent the progression of PanINs in a conditional Kras(G12D) mouse model. Offspring of LSL-KRAS(G12D) x PDX-1-Cre intercrosses were randomly allocated to a diet supplemented with the selective COX-2 inhibitor nimesulide (400 ppm) or a control diet. After 10 months, animals were sacrificed. Successful recombination in the pancreas was evaluated by PCR. The pancreas of KRAS(G12D);PDX-1-Cre mice was analyzed for the presence of murine PanINs. Animals fed the COX-2 inhibitor had significantly fewer PanIN-2 and PanIN-3 lesions than control animals (P < 0.05). Ten percent of all pancreatic ducts in the nimesulide-fed animals showed PanIN-2 or PanIN-3 lesions, whereas 40% of the pancreatic ducts in the control animals had PanIN-2 or PanIN-3 lesions. Intrapancreatic prostaglandin E(2) levels were reduced in nimesulide-fed animals. Immunohistochemistry confirmed COX-2 expression in early and late PanINs. In summary, we found that the selective COX-2 inhibitor nimesulide delays the progression of pancreatic cancer precursor lesions in a preclinical animal model. These data highlight the importance of COX-2 in the development of pancreatic cancer. Inhibition of COX-2 may represent an intriguing strategy to prevent pancreatic cancer in high-risk patients.