ABSTRACT
BACKGROUND AND PURPOSE: The major obstacles to treatment of pancreatic cancer are the highly invasive capacity and resistance to chemo- and radiotherapy. Glycogen synthase kinase 3ß (GSK3ß) regulates multiple cellular pathways and is implicated in various diseases including cancer. Here we investigate a pathological role for GSK3ß in the invasive and treatment resistant phenotype of pancreatic cancer. METHODS: Pancreatic cancer cells were examined for GSK3ß expression, phosphorylation and activity using Western blotting and in vitro kinase assay. The effects of GSK3ß inhibition on cancer cell survival, proliferation, invasive ability and susceptibility to gemcitabine and radiation were examined following treatment with a pharmacological inhibitor or by RNA interference. Effects of GSK3ß inhibition on cancer cell xenografts were also examined. RESULTS: Pancreatic cancer cells showed higher expression and activity of GSK3ß than non-neoplastic cells, which were associated with changes in its differential phosphorylation. Inhibition of GSK3ß significantly reduced the proliferation and survival of cancer cells, sensitized them to gemcitabine and ionizing radiation, and attenuated their migration and invasion. These effects were associated with decreases in cyclin D1 expression and Rb phosphorylation. Inhibition of GSK3ß also altered the subcellular localization of Rac1 and F-actin and the cellular microarchitecture, including lamellipodia. Coincident with these changes were the reduced secretion of matrix metalloproteinase-2 (MMP-2) and decreased phosphorylation of focal adhesion kinase (FAK). The effects of GSK3ß inhibition on tumor invasion, susceptibility to gemcitabine, MMP-2 expression and FAK phosphorylation were observed in tumor xenografts. CONCLUSION: The targeting of GSK3ß represents an effective strategy to overcome the dual challenges of invasiveness and treatment resistance in pancreatic cancer.
Subject(s)
Glycogen Synthase Kinase 3/metabolism , Neoplasm Invasiveness , Pancreatic Neoplasms/pathology , Animals , Antineoplastic Agents/therapeutic use , Blotting, Western , Deoxycytidine/analogs & derivatives , Deoxycytidine/therapeutic use , Drug Resistance, Neoplasm , Fluorescent Antibody Technique , Glycogen Synthase Kinase 3/antagonists & inhibitors , Glycogen Synthase Kinase 3 beta , Humans , Immunohistochemistry , Mice , Pancreatic Neoplasms/drug therapy , Pancreatic Neoplasms/enzymology , Pancreatic Neoplasms/radiotherapy , Phosphorylation , Xenograft Model Antitumor Assays , GemcitabineABSTRACT
Development and progression of pancreatic cancer involves general metabolic disorder, local chronic inflammation, and multistep activation of distinct oncogenic molecular pathways. These pathologic processes result in a highly invasive and metastatic tumor phenotype that is a major obstacle to curative surgical intervention, infusional gemcitabine-based chemotherapy, and radiation therapy. Many clinical trials with chemical compounds and therapeutic antibodies targeting growth factors, angiogenic factors, and matrix metalloproteinases have failed to demonstrate definitive therapeutic benefits to refractory pancreatic cancer patients. Glycogen synthase kinase 3ß (GSK3ß), a serine/threonine protein kinase, has emerged as a therapeutic target in common chronic and progressive diseases, including cancer. Here we review accumulating evidence for a pathologic role of GSK3ß in promoting tumor cell survival, proliferation, invasion, and resistance to chemotherapy and radiation in pancreatic cancer. We also discuss the putative involvement of GSK3ß in mediating metabolic disorder, local inflammation, and molecular alteration leading to pancreatic cancer development. Taken together, we highlight potential therapeutic as well as preventive effects of GSK3ß inhibition in pancreatic cancer.
ABSTRACT
BACKGROUND: Pancreatic cancer is obstinate and resistant to gemcitabine, a standard chemotherapeutic agent for the disease. We previously showed a therapeutic effect of glycogen synthase kinase-3ß (GSK3ß) inhibition against gastrointestinal cancer and glioblastoma. Here, we investigated the effect of GSK3ß inhibition on pancreatic cancer cell sensitivity to gemcitabine and the underlying molecular mechanism. METHODS: Expression, phosphorylation, and activity of GSK3ß in pancreatic cancer cells (PANC-1) were examined by Western immunoblotting and in vitro kinase assay. The combined effect of gemcitabine and a GSK3ß inhibitor (AR-A014418) against PANC-1 cells was examined by isobologram and PANC-1 xenografts in mice. Changes in gene expression in PANC-1 cells following GSK3ß inhibition were studied by cDNA microarray and reverse transcription (RT)-PCR. RESULTS: PANC-1 cells showed increased GSK3ß expression, phosphorylation at tyrosine 216 (active form), and activity compared with non-neoplastic HEK293 cells. Administration of AR-A014418 at pharmacological doses attenuated proliferation of PANC-1 cells and xenografts, and significantly sensitized them to gemcitabine. Isobologram analysis determined that the combined effect was synergistic. DNA microarray analysis detected GSK3ß inhibition-associated changes in gene expression in gemcitabine-treated PANC-1 cells. Among these changes, RT-PCR and Western blotting showed that expression of tumor protein 53-induced nuclear protein 1, a gene regulating cell death and DNA repair, was increased by gemcitabine treatment and substantially decreased by GSK3ß inhibition. CONCLUSIONS: The results indicate that GSK3ß inhibition sensitizes pancreatic cancer cells to gemcitabine with altered expression of genes involved in DNA repair. This study provides insight into the molecular mechanism of gemcitabine resistance and thus a new strategy for pancreatic cancer chemotherapy.
