Raloxifene inhibits pancreatic adenocarcinoma growth by interfering with ERß and IL-6/gp130/STAT3 signaling.

PURPOSE: Currently, the exact role of estrogen receptor (ER) signaling in pancreatic cancer is unknown. Recently, we showed that expression of phosphorylated ERß correlates with a poor prognosis in patients with pancreatic ductal adenocarcinoma (PDAC). Here, we hypothesized that raloxifene, a FDA-approved selective ER modulator (SERM), may suppress PDAC tumor growth by interfering with ERß signaling. To test this hypothesis, we studied the impact of raloxifene on interleukin-6/glycoprotein-130/signal transducer and activator of transcription-3 (IL-6/gp130/STAT3) signaling. METHODS: Human PDAC cell lines were exposed to raloxifene after which growth inhibition was assessed using a BrdU assay. ER knockdown was performed using siRNAs specific for ERα and ERß. The effects of raloxifene on IL-6 expression and STAT3 phosphorylation in PDAC cells were assessed by ELISA and Western blotting, respectively. In addition, raloxifene was administered to an orthotopic PDAC tumor xenograft mouse model, after which tumor growth was monitored and immunohistochemistry was performed. RESULTS: Raloxifene inhibited the in vitro growth of PDAC cells, and this effect was reversed by siRNA-mediated knockdown of ERß, but not of ERα, indicating ER isotype-specific signaling. We also found that treatment with raloxifene inhibited the release of IL-6 and suppressed the phosphorylation of STAT3Y705 in PDAC cells. In vivo, we found that orthotopic PDAC tumor growth, lymph node and liver metastases as well as Ki-67 expression were reduced in mice treated with raloxifene. CONCLUSIONS: Inhibition of ERß and the IL-6/gp130/STAT3 signaling pathway by raloxifene leads to potent reduction of PDAC growth in vitro and in vivo. Our results suggest that ERß signaling and IL-6/gp130 interaction may serve as promising drug targets for pancreatic cancer and that raloxifene may serve as an attractive therapeutic option for PDAC patients expressing the ERß isotype.

Elevated interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) is a poor prognostic marker in pancreatic ductal adenocarcinoma.

PURPOSE: Interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) gene from IFITs family is one gene among hundreds of IFN-stimulated genes. The potential role of IFIT3 in cancer is scarcely understood. In addition, the clinical relevance of IFIT3 is not yet known in pancreatic ductal adenocarcinoma (PDAC). We evaluated the prognostic significance of this gene in PDAC patients. METHODS: The expression of IFIT3 was analyzed in pancreatic cancer cell lines with different metastatic potential (FG and L3.6pl) and one established gemcitabine resistant cell variant-L3.6plGres. Second, we analyzed the protein expression in tissue microarrays (TMA) from specimens of 254 radically resected patients with pancreatic adenocarcinoma. The prognostic relevance of IFIT3 was evaluated by the Kaplan-Meier and Cox regression analysis. RESULTS: L3.6pl cells with an aggressive capacity showed a significant higher expression of IFIT3 as compared to FG cells. IFIT3 was accumulated in gemcitabine resistant cells. Overexpression of IFIT3 increased the resistance of apoptosis against gemcitabine treatment. Patients who had high expression of IFIT3 (32%) and received chemotherapy had a statistically significant reduced survival in multivariate analysis. CONCLUSIONS: High expression of IFIT3 enhances anti-apoptotic activity and chemotherapy resistance of PDAC cells. High expression of IFIT3 was independently correlated to shorter patients' survival and may serve as a prognostic marker.

miR-221 Mediates Chemoresistance of Esophageal Adenocarcinoma by Direct Targeting of DKK2 Expression.

BACKGROUND: Chemoresistance is a main obstacle to effective esophageal cancer (EC) therapy. We hypothesize that altered expression of microRNAs (miRNAs) play a role in EC cancer progression and resistance to 5-fluorouracil (5-FU) based chemotherapeutic strategies. METHODS: Four pairs of esophageal adenocarcinoma (EAC) cell lines and corresponding 5-FU resistant variants were established. The expression levels of miRNAs previously shown to be involved in the general regulation of stem cell pathways were analyzed by qRT-PCR. The effects of selected miRNAs on proliferation, apoptosis, and chemosensitivity were evaluated both in vitro and in vivo. We identified a particular miRNA and analyzed its putative target genes in 14 pairs of human EC tumor specimens with surrounding normal tissue by qRT-PCR as well as Wnt pathway associated genes by immunohistochemistry in another 45 EAC tumor samples. RESULTS: MiR-221 was overexpressed in 5-FU resistant EC cell lines as well as in human EAC tissue. DKK2 was identified as a target gene for miR-221. Knockdown of miR-221 in 5-FU resistant cells resulted in reduced cell proliferation, increased apoptosis, restored chemosensitivity, and led to inactivation of the Wnt/ß-catenin pathway mediated by alteration in DKK2 expression. Moreover, miR-221 reduction resulted in alteration of EMT-associated genes such as E-cadherin and vimentin as well as significantly slower xenograft tumor growth in nude mice. RT profiler analysis identified a substantial dysregulation of 4 Wnt/ß-catenin signaling and chemoresistance target genes as a result of miR-221 modulation: CDH1, CD44, MYC, and ABCG2. CONCLUSION: MiR-221 controls 5-FU resistance of EC partly via modulation of Wnt/ß-catenin-EMT pathways by direct targeting of DKK2 expression. MiR-221 may serve as a prognostic marker and therapeutic target for patients with 5-FU resistant EAC.

Verapamil inhibits tumor progression of chemotherapy-resistant pancreatic cancer side population cells.

Tumor side population (SP) cells display stem-like properties that can be modulated by treatment with the calcium channel blocker verapamil. Verapamil can enhance the cytotoxic effects of chemotherapeutic drugs and multidrug resistance by targeting the transport function of the P-glycoprotein (P-gp). This study focused on the therapeutic potential of verapamil on stem-like SP tumor cells, and further investigated its chemosensitizing effects using L3.6pl and AsPC-1 pancreatic carcinoma models. As compared to parental L3.6pl cells (0.9±0.22%), L3.6pl gemcitabine-resistant cells (L3.6plGres) showed a significantly higher percentage of SP cells (5.38±0.99%) as detected by Hoechst 33342/FACS assays. The L3.6plGres SP cells showed stable gemcitabine resistance, enhanced colony formation ability and increased tumorigenicity. Verapamil effectively inhibited L3.6plGres and AsPC-1 SP cell proliferation in vitro. A pro-apoptotic effect of verapamil was observed in L3.6pl cells, but not in L3.6plGres cells, which was linked to their differential expression of P-gp and equilibrative nucleoside transporter-1 (ENT-1). In an orthotopic pancreatic cancer mouse model, both low and high dose verapamil was shown to substantially reduce L3.6plGres-SP cell tumor growth and metastasis, enhance tumor apoptosis, and reduce microvascular density.

KRAS exon 2 mutations influence activity of regorafenib in an SW48-based disease model of colorectal cancer.

AIM: To investigate the impact of KRAS mutation variants on the activity of regorafenib in SW48 colorectal cancer cells. MATERIALS & METHODS: Activity of regorafenib was evaluated in isogenic SW48 KRAS wild-type (WT) and mutant cells. Subcutaneous xenografts (KRAS WT and G12C mutant variants) in NOD/SCID mice were analyzed to elucidate the effect of regorafenib treatment in vivo. RESULTS: Compared with KRAS WT cells, all mutant variants seemed associated with some degree of resistance to regorafenib-treatment in vitro. In vivo, activation of apoptosis (TUNEL) and reduction of proliferation (Ki67) after treatment with regorafenib were more pronounced in KRAS WT tumors as compared with G12C variants. CONCLUSION: In SW48 cells, exon 2 mutations of the KRAS gene may influence antitumor effects of regorafenib.

Overexpression of IFN-induced protein with tetratricopeptide repeats 3 (IFIT3) in pancreatic cancer: cellular "pseudoinflammation" contributing to an aggressive phenotype.

Inflammation contributes to important traits that cancer cells acquire during malignant progression. Gene array data recently identified upregulation of interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) in aggressive pancreatic cancer cells. IFIT3 belongs to the group of interferon stimulated genes (ISG), can be induced by several cellular stress stimuli and by its tetratricopeptide repeats interacts with a multitude of cellular proteins. Upregulation of IFIT3 was confirmed in the aggressive pancreatic cancer cell line L3.6pl compared with its less aggressive cell line of origin, COLO357FG. Transgenic induction of IFIT3 expression in COLO357FG resulted in greater mass of orthotopic tumors and higher prevalence of metastases. Several important traits that mediate malignancy were altered by IFIT3: increased VEGF and IL-6 secretion, chemoresistance and decreased starvation-induced apoptosis. IFIT3 showed binding to JNK and STAT1, the latter being an important inducer of IFIT3 expression. Despite still being alterable by "classical" IFN or NFκB signaling, our findings indicate constitutive - possibly auto-regulated - upregulation of IFIT3 in L3.6pl without presence of an adequate inflammatory stimulus. The transcription factor SOX9, which is linked to regulation of hypoxia-related genes, was identified as a key mediator of upregulation of the oncogene IFIT3 and thereby sustaining a "pseudoinflammatory" cellular condition.

Antisense inhibition of microRNA-21 and microRNA-221 in tumor-initiating stem-like cells modulates tumorigenesis, metastasis, and chemotherapy resistance in pancreatic cancer.

Our preliminary studies identified a small population side population (SP) cells in pancreatic cancer cells with stem cell-like properties, which were able to induce fast and aggressive tumor formation in nude mice. Gene expression analysis showed a significant difference in the expression of more than 1,300 genes in SP cells, among which a highly significant difference in microRNA expression of miR-21 and miR-221 between SP and NSP cells was identified. SP cells were identified and characterized by flow cytometry using Hoechst 33342 dye staining from a highly metastatic human pancreatic cancer cell line (L3.6pl). Antagomir transfection was performed using miRNA-21 and miRNA-221 antisense oligonucleotides (ASOs) and followed by detection of cell apoptosis, cell cycle progression, chemosensitivity, and invasion. Sorted SP cells from gemcitabine-resistant L3.6pl cells (L3.6pl(Gres)-SP) cells were orthotopically implanted in nude mice with or without miRNA-21 and miRNA-221 ASOs mono- and combination therapy. The administration of antagomir-21 and antagomir-221 significantly reduced the SP cell fraction, decreased SP cell differentiation, and downstream gene regulation, and thereby induced reduction of L3.6pl cell proliferation, invasion, and chemoresistance against gemcitabine and 5-Fluorouracil. Combination of ASOs therapy against miRNA-21 and miRNA-221 significantly inhibited primary tumor growth and metastasis compared to single antagomir treatment, especially, in L3.6plGres-SP-induced pancreatic tumor growth in vivo. These findings further indicate that the inhibition of miR-21 and miR-221 appear particularly suitable to target stem-like subpopulations and address their specific biological function to promote tumor progression in pancreatic cancer.

Effect of KRAS exon 2 mutations on antitumor activity of afatinib and gefitinib.

The aim of this study was to investigate the impact of different KRAS mutations on the inhibitory potential of afatinib and gefitinib in SW48 colorectal cancer cells. The influence of afatinib/gefitinib on cell viability and cell cycle was evaluated in isogenic SW48 KRAS wild-type/mutant cells. Protein levels of phosphorylated/total EGFR, HER-2, HER-3, ERK, and AKT were compared between treated/untreated samples using western blotting. The activity of both afatinib and gefitinib was the lowest in KRAS G12C/G12S/G12D and the highest in G13D/G12A mutant subtypes. A 50% decrease in cell viability was achieved at concentrations of 3.0-7.7 µmol/l for afatinib and 5.4-19.5 µmol/l for gefitinib. The effect of both drugs on apoptosis appeared to be stronger than their influence on proliferation and was generally less pronounced in mutant cells than in wild-type cells. The average number of apoptotic cells after treatment with afatinib was 2.6 times as high as the corresponding value following treatment with gefitinib (P<0.01). Levels of pEGFR, pHER-2, pERK, and pAKT were reduced more extensively by afatinib than by gefitinib (P<0.001). Some KRAS mutations (G12C/G12S/G12D) appear to weaken the activity of afatinib and gefitinib whereas others seem to increase sensitivity to treatment (G13D/G12A) compared with the parental clone (KRAS wild-type). In SW48 colorectal cancer cells, afatinib seems to be more potent than gefitinib because of its superior efficacy in inhibiting both EGFR and HER-2, suppressing signaling along both MEK/ERK and PI3K/AKT pathways to a greater extent.

Side population cells of pancreatic cancer show characteristics of cancer stem cells responsible for resistance and metastasis.

Cancer stem cells (CSCs) have been proposed to underlie the initiation and maintenance of tumor growth and the development of chemoresistance in solid tumors. The identification and role of these important cells in pancreatic cancer remains controversial. Here, we isolate side population (SP) cells from the highly aggressive and metastatic human pancreatic cancer cell line L3.6pl and evaluate their potential role as models for CSCs. SP cells were isolated following Hoechst 33342 staining of L3.6pl cells. SP, non-SP, and unsorted L3.6pl cells were orthotopically xenografted into the pancreas of nude mice and tumor growth observed. RNA was analyzed by whole genome array and pathway mapping was performed. Drug resistant variants of L3.6pl were developed and examined for SP proportions and evaluated for surface expression of known CSC markers. A distinct SP with the ability to self-renew and differentiate into non-SP cells was isolated from L3.6pl (0.9 % ± 0.22). SP cells showed highly tumorigenic and metastatic characteristics after orthotopic injection. Transcriptomic analysis identified modulation of gene networks linked to tumorigenesis, differentiation, and metastasization in SP cells relative to non-SP cells. Wnt, NOTCH, and EGFR signaling pathways associated with tumor stem cells were altered in SP cells. When cultured with increasing concentrations of gemcitabine, the proportion of SP cells, ABCG2(+), and CD24(+) cells were significantly enriched, whereas 5-fluorouracil (5-FU) treatment lowered the percentage of SP cells. SP cells were distinct from cells positive for previously postulated pancreatic CSC markers. The Hoechst-induced side population in L3.6pl cells comprises a subset of tumor cells displaying aggressive growth and metastasization, increased gemcitabine-, but not 5-FU resistance. The cells may act as a partial model for CSC biology.

Hypoxia-independent gene expression mediated by SOX9 promotes aggressive pancreatic tumor biology.

UNLABELLED: Pancreatic cancer aggressiveness is characterized by its high capacity for local invasion, ability to promote angiogenesis, and potential to metastasize. Hypoxia is known to represent a crucial step in the development of aggressive malignant features of many human cancers. However, micrometastatic tumors are not typically subjected to hypoxic events during early stages of dissemination; therefore, it is unclear how these tumors are able to maintain their aggressive phenotype. Thus, the identification of regulators of hypoxia-related genes in aggressive/metastatic tumors represents a fundamental step for the design of future therapies to treat pancreatic cancer. To this end, transcriptomic profiles were compared between the nonmetastatic pancreatic cancer cell line FG (LMET) and its angiogenic/metastatic derivate L3.6pl (HMET) under normoxic or hypoxic conditions. Cluster analysis revealed a number of transcripts that were induced by hypoxia in nonmetastatic cancer cells. Strikingly, this cluster was determined to be constitutively activated under normoxia in the metastatic cancer cells and could not be further induced by hypoxia. A subset of these transcripts were regulated by the transcription factor SOX9 in the aggressive-metastatic cells, but driven by hypoxia-inducible factor-1α (HIF-1α) in the parental nonmetastatic cell line. Moreover, these transcripts were enriched in cancer-related networks including: WNT, CXCR4, retinoic acid, and (FAK) focal adhesion kinase, gene PTK2 signaling pathways. In functional assays, inhibition of SOX9 expression in HMET cells led to increased apoptosis and reduced migration in vitro and a significant reduction in primary tumor growth, angiogenesis, and metastasis following orthotopic tumor cell injection. At the molecular level, the control of SOX9 expression was associated with changes in the methylation status of the SOX9 promoter. Finally, SOX9 upregulation was verified in a series of tumor specimens of patients with pancreatic carcinoma. IMPLICATIONS: SOX9 represents a novel target for pancreatic cancer therapy.

Stem cell-like side populations in esophageal cancer: a source of chemotherapy resistance and metastases.

Dye-effluxing side population (SP) cells can be resistant to chemotherapy and are thought to resemble cancer stem cells. We characterized the relevance of the SP subpopulation in esophageal cancer cell lines and their relation to chemotherapy resistance and metastasis. The SP subpopulation was detected using Hoechst 33342 staining in five esophageal cancer cell lines OE19, OE21, OE33, PT1590, and LN1590. CTx-resistant cell lines were developed after long-term exposure to 5-fluorouracil (5-FU) and cisplatin and validated by analysis of resistance markers, thymidylate synthase and ERCC1. While neither LN1590 nor PT1590 had detectable SP cells, OE19, OE21, and OE33 cells were found to contain varying levels of SP cells. With increasing duration of 5-FU or cisplatin therapy, the SP subpopulation substantially emerged in PT1590 and LN1590. OE19-SP cells displayed significant higher tumorigenicity than OE19- non-SP (NSP) cells after subcutaneous tumor cell injection in vivo. SP cells isolated from OE19 and OE19/5-FUres were subsequently analyzed by an epithelial-to-mesenchymal transition (EMT) polymerase chain reaction array. Interestingly, the SP fraction of OE19/5-FUres showed a dramatic upregulation of EMT-related genes compared to the SP fraction of OE19. Our results provide evidence that (1) the proportion of SP cells is different in esophageal cancer, (2) SP cells exhibit stem cell properties and are associated to chemotherapy resistance, and (3) long-term CTx selects for SP cells with an upregulated EMT gene profile, which might be the source of systemic disease relapse. Further investigations are necessary to ideally target these EMT-associated SP cells in esophageal cancer.

Cancer stem cells and angiogenesis.

Cancer stem cells (CSCs) or tumor initiating cells were identified and characterized as a unique subpopulation with stem cell features in many types of cancer. Current CSC studies provide novel insights regarding tumor initiation, progression, angiogenesis, resistance to therapy and interplay with the tumor micro-environment. A cancer stem cell niche has been proposed based on these findings. The niche provides the soil for CSC self-renewal and maintenance, stimulating essential signaling pathways in CSCs and leading to secretion of factors that promote angiogenesis and long term growth of CSCs. We present evidence which has emerged over the past 5 years indicating interaction of CSCs with angiogenesis in the proposed "vascular niche". Based on these findings, targeting the "cancer stem cell niche" by combining an individualized anti-CSC approach with treatment of their microenvironment may represent a novel therapeutic strategy against solid tumor systems.

EFEMP1 binds the EGF receptor and activates MAPK and Akt pathways in pancreatic carcinoma cells.

The EGF-related protein EFEMP1 (EGF-containing fibulin-like extracellular matrix protein 1) has been shown to promote tumor growth in human adenocarcinoma. To understand the mechanism of this action, the signal transduction activated upon treatment with this protein has been investigated. We show that EFEMP1 binds EGF receptor (EGFR) in a competitive manner relative to epidermal growth factor (EGF), implicating that EFEMP1 and EGF share the same or adjacent binding sites on the EGFR. Treatment of pancreatic carcinoma cells with purified EFEMP1 activates autophosphorylation of EGFR at the positions Tyr-992 and Tyr-1068, but not at the position Tyr-1048. This signal is further transduced to phosphorylation of Akt at position Thr-308 and p44/p42 MAPK (mitogen-activated protein kinase) at positions Thr-202 and Tyr-204. These downstream phosphorylation events can be inhibited by treatment with the EGFR kinase inhibitor PD 153035. The observed signal transduction upon treatment with EFEMP1 can contribute to the enhancement of tumor growth shown in pancreatic carcinoma cells overexpressing EFEMP1.

EFEMP1 expression promotes in vivo tumor growth in human pancreatic adenocarcinoma.

The progression of pancreatic cancer is dependent on local tumor growth, angiogenesis, and metastasis. EFEMP1, a recently discovered member of the fibulin family, was characterized with regard to these key elements of pancreatic cancer progression. Differential gene expression was assessed by mRNA microarray hybridization in FG human pancreatic adenocarcinoma cells and L3.6pl cells, a highly metastatic variant of FG. In vivo orthotopic tumor growth of EFEMP1-transfected FG cells was examined in nude mice. To assess the angiogenic properties of EFEMP1, vascular endothelial growth factor (VEGF) production of tumor cells, endothelial cell proliferation and migration, and tumor microvessel density were analyzed in response to EFEMP1. Further, tumor cell apoptosis, cell cycle progression, and resistance to cytotoxic agents were quantitated by propidium iodide staining and flow cytometry. In microarray hybridization, EFEMP1 was shown to be significantly up-regulated in L3.6pl cells compared with FG cells. Concordantly, EFEMP1 transfection of FG cells stimulated orthotopic and metastatic tumor growth in vivo. EFEMP1 expression resulted in a stimulation of VEGF production by tumor cells and an increased number of CD31-positive microvessels. Endothelial cell proliferation and migration were not altered by EFEMP1, indicating an indirect angiogenic effect. Further, EFEMP1 expression decreased apoptosis and promoted cell cycle progression in response to serum starvation or exposure to gemcitabine, 5-fluorouracil, and irinotecan. EFEMP1 has protumorigenic effects on pancreatic cancer in vivo and in vitro mediated by VEGF-driven angiogenesis and antiapoptotic mechanisms. Hence, EFEMP1 is a promising candidate for assessing prognosis and individualizing therapy in a clinical tumor setting.

P60-c-src suppresses apoptosis through inhibition of caspase 8 activation in hepatoma cells, but not in primary hepatocytes.

BACKGROUND/AIMS: Failure to induce apoptosis triggered by members of the death receptor family has been described in hepatocellular carcinoma (HCC) and sensitization of malignant cells to pro-apoptotic molecules such as TRAIL has been proposed as an alternative cancer therapy. Limiting to this approach are the resistance of many tumor cells to TRAIL and safety concerns about the toxicity of TRAIL in normal hepatocytes. METHODS: We here explored the possibility that the protooncogene c-Src, known to be overexpressed in a variety of tumors, could be specifically responsible for the loss of response to receptor-mediated apoptosis. RESULTS: Cotreatment of several hepatoma cell lines with the Src inhibitor PP2 potently sensitized these cells to TRAIL and CD95, dramatically decreasing effective doses of TRAIL to as low as 1 ng/ml. Remarkably, Src-inhibition did not synergize with TRAIL signaling in primary hepatocytes. Specific siRNAs showed that the effect was due to blockade of p60(c-Src) and occurred through increased recruitment of caspase 8. CONCLUSIONS: We provide evidence that p60(c-Src) is an important and effective suppressor of receptor-mediated apoptosis in hepatoma cells but not in primary human hepatocytes. Inhibition of Src sensitizes tumor cells to apoptosis and decreases effective doses of TRAIL to therapeutic concentrations.