Leukotriene B4 Rezeptor 2 (BLT2) — ein spezifischer Marker und Promoter in der Pankreaskarzinogenese?

Abstract

Introduction: Pancreatic cancer has an abysmal prognosis because of its late diagnosis and lack of response to available therapeutics. Incidence almost equals mortality. Pancreatic intraepithelial neoplasias (PanINs) and intraductal papillary mucinous neoplasias (IPMNs) are precursor lesions which could be an ideal target for chemoprevention. Obesity and high fat intake are risk factors for the development of pancreatic cancer. The arachidonic acid pathway plays a key role. Overexpression of cyclooxygenase-2 (COX-2) in transgenic mice promotes the development of pancreatic cancer, a process inhibited by COX-2 inhibitors. Furthermore, 5-lipoxygenase (5-LOX) is pro-tumorigenic and overexpressed in PanINs, IPMNs and pancreatic adenocarcinoma. Leukotriene B4 (LTB4) as a product of the 5-LOX metabolism stimulates tumor cell growth and insulin secretion. The expression and role of the second LTB4 receptor (BLT2) was unknown and therefore, aim of this study. Materials and Methods: Expression of BLT2 was investigated in pancreatic cancer cell lines and human pancreatic tissues (10 normal pancreas, 10 chronic pancreatitis, 10 pancreatic adenocarcinoma and 38 IPMNs) by real time RT-PCR and immunohistochemistry. Cell proliferation was studied by cell counting and Wst-1 assay in Colo357, Panc-1 and AsPC1 cells after stable transfection with BLT2 to cause overexpression of this receptor and after treatment with siRNA, Compound A as an agonist and LY255283 as an antagonist. Results: BLT2 is expressed in all pancreatic cancer cell lines. Results from real-time RT-PCR revealed significant overexpression of BLT2 in malignant IPMNs and pancreatic adenocarcinoma. Intense staining for BLT2 was evident in infiltrating tumor cells and advanced PanINs (> PanIN-1b) in 10/10 cancer and 1/10 pancreatitis tissues but not in normal ductal cells or PanIN-1a lesions (9 pancreatitis and 10 normal tissues). BLT2 was expressed in all IPMNs. Specificity of the antibody was demonstrated by using a blocking peptide. Overexpression of BLT2 as well as stimulation of Colo357, Panc-1 and AsPC1 cells with Compound A caused a significant increase in tumor cell proliferation, an effect reversed after siRNA treatment. Blocking BLT2 with LY255283 also significantly inhibited tumor cell growth. Conclusion: This study demonstrates for the first time expression of BLT2 in the pancreas and overexpression in pancreatic cancers and malignant IPMNs in particular. Furthermore, up-regulation of BLT2 is already evident in precursor lesions (PanINs, IPMNs). Overexpressing this receptor or stimulation of BLT2 enhances proliferation of cancer cells. In contrast, the BLT2 antagonist LY255283 inhibits tumor cell growth. These findings provide evidence that BLT2 serves as a specific marker and tumor promoter in pancreatic carcinogenesis. BLT2 antagonists may be a new tool for prevention and therapy in the fight against pancreatic cancer.