Effect of raloxifene on human pancreatic adenocarcinoma growth in vitro and in vivo

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Background: The role of estrogen receptor (ER) signaling in pancreatic cancer is unknown. Recently, we demonstated that expression of the isoform ER beta correlates with an adverse prognosis in patients with pancreatic cancer. Here, we show that raloxifene, a specific estrogen receptor modulator (SERM), suppresses in vitro and in vivo tumor growth by interfering with ER beta signaling in human pancreatic adenocarcinoma.

Methods: The human pancreatic adenocarcinoma cell line L3.6pl was cultured and exposed to raloxifene in vitro, and cell proliferation was determined by the BrdU assay. To analyze the specificity of raloxifene induced effects, ER knockdown was performed using siRNA specific for ER alpha and ER beta. In an in vivo model of orthotopic tumor xenografts in nude mice, raloxifene was administered daily, and tumor growth was monitored. Expression of ER beta and the proliferation marker Ki-67 were determined by immunohistochemistry.

Results: Raloxifene treatment resulted in a potent, dose dependent reduction of proliferation in vitro over a nanomolar dose range. This effect was completely reversed by siRNA knockdown of ER beta, but not ER alpha, indicating an ER isotype specific signaling. In vivo, orthotopic tumor growth, as well as lymph node and liver metastases, was significantly suppressed in raloxifene treated mice. Analogous to the in vitro data, Ki-67 expression in vivo was significantly reduced in raloxifene treated mice, while ER beta expression was not changed in vivo.

Conclusions: Inhibition of ER beta signaling by raloxifene results in a potent reduction of human pancreatic adenocarcinoma growth in vitro and in vivo. Treatment with SERMs may be an attractive therapeutic option in subjects expressing the ER beta isotype.

No significant financial relationships to disclose.

Src tyrosine kinase inhibition suppresses lymphangiogenesis in vitro and in vivo

PURPOSE

The close association of lymphatic and blood vessels and their coordinated development in vivo suggest that there are parallel mechanisms regulating hemangiogenesis and lymphangiogenesis. Here, we hypothesize that inhibition of the Src tyrosine kinase, apart from anti-hemangiogenic effects, results in a suppression of lymphangiogenesis.

EXPERIMENTAL DESIGN

The ability of the Src kinase inhibitor PP2 to block Src in isolated lymphatic endothelial cells (LECs) was analyzed by Western Blot. The effects of PP2 on LEC proliferation, migration, and sprouting were assessed by MTT, Boyden chamber, and spheroid assays, respectively. The level of VEGF-C secreted by L3.6pl pancreatic carcinoma cells was measured by ELISA. For in vivo assessment of lymphangiogenesis, Src kinase inhibitor AZM475271 was used in mouse corneal micropocket and lymphangioma models.

RESULTS

VEGF-C stimulation of isolated LECs led to an increased phosphorylation of Src kinase that was abrogated by PP2. Treatment with PP2 inhibited spheroid sprouting of LECs at even lower concentrations than suggested by the proliferation assay. Src inhibition significantly reduced the level of VEGF-C in L3.6pl supernatant. Treatment with PP2 also resulted in a significant reduction in the migratory activity of LECs. In vivo, Src inhibition reduced de novo formation of lymphangiomas and corneal neovascularization.

CONCLUSIONS

Inhibition of Src kinase shows strong anti-lymphangiogenic activity in vitro and in vivo. Together with anti-angiogenic effects mediated by Src inhibition, this strategy may be attractive in the treatment of lymphatic and hematogeneous metastasis of cancer.

The RON receptor tyrosine kinase promotes MSP-independent cell spreading and survival in breast epithelial cells

The recepteur d’origne nantais (RON) is a receptor tyrosine kinase (RTK) in the scatter factor family, which includes the c-Met receptor. RON exhibits increased expression in a significant number of human breast cancer tissues as well as in many established breast cancer cell lines. Recent studies have indicated that in addition to ligand-dependent signaling events, RON also promotes signals in the absence of its only known ligand, the macrophage stimulating protein, when expressed in epithelial cells. In the current study, we found that when expressed in MCF-10A breast epithelial cells, RON exhibits both MSP-dependent and MSP-independent signaling, which lead to distinct biological outcomes. In the absence of MSP, RON signaling promotes cell survival, increased cell spreading and enhanced migration in response to other growth factors. However, both RON-mediated proliferation and migration require the addition of MSP in MCF-10A cells. Both MSP-dependent and MSP-independent signaling by RON is mediated in part by Src-family kinases. These data suggest that RON has two alternative modes of signaling that can contribute to oncogenic behavior in normal breast epithelial cells.

FTY720 inhibits tumor growth and angiogenesis

De novo malignancies and recurrence of tumors are some of the biggest threats to allograft recipients subjected to chronic immunosuppression. FTY720, a synthetic myriocin analogue, is an immunosuppressant that induces apoptosis of activated lymphocytes and prevents infiltration of lymphocytes into allografts, thereby prolonging allograft survival in a dose-dependent manner. Additionally, FTY720 was shown to prevent tumor growth and metastasis. Therefore, we examined the effect of FTY720 on angiogenesis in a HUVEC spheroid model. To substantiate our in vitro findings the effect of FTY720 was also tested in C57/B16 mice subcutaneously injected with Lewis Lung Carcinoma (LLC1) cells. After establishment of a palpable tumor the animals were treated daily with either saline or 1, 5, or 10 mg/kg FTY720. Subsequently, the tumor size was measured, periodically. In our experiments FTY720 showed a strong antiangiogenic effect, overcoming the stimulating effect of VEGF (20 ng/mL) even at subnanomolar concentrations. In vivo, FTY720 showed a dose-dependent inhibition of subcutaneous tumors, and the tumor size of animals treated with 10 mg/kg FTY720 was less than half of the size of tumors in control animals. In conclusion, FTY-720 demonstrated a strong antiangiogenic effect in vitro and a substantial antitumor effect in vivo. Presumably, the stabilizing effect of surrounding pericytes limits the effect of FTY720 in our mouse model. Therefore, a combination of FTY720 with an mTOR inhibitor might be the most favorable immunosuppressive drug combination for allograft recipients at risk for tumor development.

Fibroblast growth factor receptor 3 induces gene expression primarily through Ras-independent signal transduction pathways

Fibroblast growth factor receptors (FGFR) are widely expressed in many tissues and cell types, and the temporal expression of these receptors and their ligands play important roles in the control of development. There are four FGFR family members, FGFR-1-4, and understanding the ability of these receptors to transduce signals is central to understanding how they function in controlling differentiation and development. We have utilized signal transduction by FGF-1 in PC12 cells to compare the ability of FGFR-1 and FGFR-3 to elicit the neuronal phenotype. In PC12 cells FGFR-1 is much more potent in the induction of neurite outgrowth than FGFR-3. This correlated with the ability of FGFR-1 to induce robust and sustained activation of the Ras-dependent mitogen-activated protein kinase pathways. In contrast, FGFR-3 could not induce strong sustained Ras-dependent signals. In this study, we analyzed the ability of FGFR-3 to induce the expression of sodium channels, peripherin, and Thy-1 in PC12 cells because all three of these proteins are known to be induced via Ras-independent pathways. We determined that FGFR-3 was capable of inducing several Ras-independent gene expression pathways important to the neuronal phenotype to a level equivalent of that induced by FGFR-1. Thus, FGFR-3 elicits phenotypic changes primarily though activation of Ras-independent pathways in the absence of robust Ras-dependent signals.

Identification of the cytoplasmic regions of fibroblast growth factor (FGF) receptor 1 which play important roles in induction of neurite outgrowth in PC12 cells by FGF-1

Fibroblast growth factor 1 (FGF-1) induces neurite outgrowth in PC12 cells. Recently, we have shown that the FGF receptor 1 (FGFR-1) is much more potent than FGFR-3 in induction of neurite outgrowth. To identify the cytoplasmic regions of FGFR-1 that are responsible for the induction of neurite outgrowth in PC12 cells, we took advantage of this difference and prepared receptor chimeras containing different regions of the FGFR-1 introduced into the FGFR-3 protein. The chimeric receptors were introduced into FGF-nonresponsive variant PC12 cells (fnr-PC12 cells), and their ability to mediate FGF-stimulated neurite outgrowth of the cells was assessed. The juxtamembrane (JM) and carboxy-terminal (COOH) regions of FGFR-1 were identified as conferring robust and moderate abilities, respectively, for induction of neurite outgrowth to FGFR-3. Analysis of FGF-stimulated activation of signal transduction revealed that the JM region of FGFR-1 conferred strong and sustained tyrosine phosphorylation of several cellular proteins and activation of MAP kinase. The SNT/FRS2 protein was demonstrated to be one of the cellular substrates preferentially phosphorylated by chimeras containing the JM domain of FGFR-1. SNT/FRS2 links FGF signaling to the MAP kinase pathway. Thus, the ability of FGFR-1 JM domain chimeras to induce strong sustained phosphorylation of this protein would explain the ability of these chimeras to activate MAP kinase and hence neurite outgrowth. The role of the COOH region of FGFR-1 in induction of neurite outgrowth involved the tyrosine residue at amino acid position 764, a site required for phospholipase C gamma binding and activation, whereas the JM region functioned primarily through a non-phosphotyrosine-dependent mechanism. In contrast, assessment of the chimeras in the pre-B lymphoid cell line BaF3 for FGF-1-induced mitogenesis revealed that the JM region did not play a role in this cell type. These data indicate that FGFR signaling can be regulated at the level of intracellular interactions and that signaling pathways for neurite outgrowth and mitogenesis use different regions of the FGFR.

Characterization of changes in gene expression associated with malignant transformation by the NF-kappaB family member, v-Rel

In this study, alterations in gene expression patterns have been examined in v-Rel-transformed avian bone marrow cells. Using a conditional v-Rel estrogen receptor chimera (v-RelER) which transforms cells in an estrogen-dependent manner, we constructed subtraction cDNA libraries from v-RelER-transformed bone marrow cells. Several different sequences were identified whose expression was altered upon hormone activation of v-RelER. These include two genes related to the MIP-1 chemokine family (mip-1beta and a tca3 homologue), a cell surface antigen sca-2 and the transcription factor nfkb1. The expression of each gene was assayed in a number of wild-type and mutant v-Rel-expressing fibroblast and hematopoietic cells. All v-Rel-transformed hematopoietic cells tested express high levels of nfkb1 and sca-2. In fibroblasts, wild-type v-Rel induced expression of mip-1beta and nfkb1, while nontransforming mutants of v-Rel failed to do so, suggesting a role for these two genes in v-Rel mediated transformation. Finally, these genes are expressed at high levels in cells overexpressing wild-type and truncated forms of c-Rel, implying that v-Rel transforms, in part, by induction of c-Rel target genes.

Distinct roles of the receptor tyrosine kinases c-ErbB and c-Kit in regulating the balance between erythroid cell proliferation and differentiation

In the bone marrow, multipotent and committed hematopoietic progenitors have to closely regulate their balance between sustained proliferation without differentiation (self renewal) and entering a terminal differentiation pathway. A useful model to analyze this regulation at the molecular level is committed avian erythroid progenitors. These are induced to undergo long-term self renewal by the ligand-activated receptor tyrosine kinase (RTK) c-ErbB, in cooperation with steroid hormone receptors. This self-renewal induction by c-ErbB even occurs in the presence of differentiation factors (erythropoietin and insulin). Under the same conditions, the RTK c-Kit is unable to sustain erythroid progenitor self renewal, stimulating cell proliferation without arresting terminal differentiation. Two mechanisms are involved in these differential activities of c-Kit and c-ErbB. The first one, differential regulation of receptor expression, proved to be of minor importance, because c-Kit was unable to induce self renewal, even if exogenously expressed from a retrovirus at high levels. Rather our results support the second mechanism, i.e., that receptor-specific signal transduction is responsible for the differential biological activity of c-Kit and c-ErbB: (a) specific tyrosine kinase inhibitors (tryphostins) were found which selectively inhibited the biological function of either c-Kit or c-ErbB in erythroblasts but did not affect ligand-induced autophosphorylation of either RTK; and (b) c-ErbB selectively induced SHC phosphorylation and STAT5 activation. The Ras pathway was similarly activated by c-Kit and c-ErbB. The c-ErbB-specific tyrphostin AG30 specifically blocked STAT5 activation, implicating this signal transducer in c-ErbB-induced self renewal.

Isolation of a cDNA encoding a novel chicken chemokine homologous to mammalian macrophage inflammatory protein-1 beta

A cDNA encoding a novel chicken chemokine homologous to mammalian chemokine macrophage inflammatory protein 1 beta (MIP-1 beta) was isolated and characterised. The cDNA encodes a protein which is 75-80% homologous to human and mouse MIP-1 beta. All conserved amino acids characteristic of the mammalian chemokine family have been evolutionarily preserved in chicken MIP-1 beta, suggesting similar protein folding patterns and functional properties.