Abstract #5342: The aging suppressor klotho: A tumor suppressor and modulator of the IGF-I pathway in human pancreatic cancer
Authors: Lilach Abramovitz, Tami Rubinek, Hagai Ligumsky, Michal Shulman, Iris Barshak, Ido Wolf
Journal: Cancer Research (2009)

Klotho is an anti-aging transmembrane protein, which is expressed in the brain and kidney, and also in various endocrine-related tissues including the pancreas. We have recently identified klotho as a tumor suppressor and a modulator of the insulin-like growth factor (IGF)-1 and the fibroblast growth factor (FGF) pathways in breast cancer. Pancreatic adenocarcinoma is one of the most lethal of human cancers, with less than 5% 5-year survival. The IGF-1 pathway plays an important role in the pathogenesis of pancreatic cancer. IGF-I and IGF-I receptor (IGF-IR) are overexpressed in human pancreatic tumors and cell lines. Inhibition of the IGF-1R suppresses tumorigenicity in vitro and in vivo and increases sensitivity of pancreatic tumors to radiation and chemotherapy-induced apoptosis. Thus, the IGF pathway may serve as an attractive target for novel therapies against pancreatic cancer. As klotho inhibits the IGF-I pathway and is expressed in normal pancreas, we aimed to study its expression and activities in pancreatic cancer. Immunohistochemistry was used to analyze klotho expression in pancreatic tissues and revealed high klotho expression in normal pancreas, but only in 2 out of 12 pancreatic cancer samples. Overexpression of klotho markedly reduced colony formation and proliferation of Panc1, Colo357 and Mia-PaCa2 pancreatic cancer cell lines, but not of the human non-cancer cells, HEK-293 and treatment of Panc1 cells with soluble klotho (5nM) caused a reduction of more than 50% in cell viability. Moreover, soluble klotho increased Panc1 sensitivity to the chemotherapeutic drug 5-fluorouracil (5-FU). While 5-FU alone reduced viability by 50%, the combination reduced viability by 75%. Both overexpressed and soluble klotho inhibited ligand-dependent activation of IGF-I pathway in pancreatic cancer cells, resulting in reduced phosphorylation of the IGF-IR and its downstream targets IRS-1, AKT1, ERK1/2. The in vivo activity of klotho was tested using a xenograft model. Panc1 cells were injected into both flanks of athymic mice and treated with daily intraperitoneal injections of either a control vehicle, 10µg/kg or 25µg/kg soluble klotho (5 mice in each group). Treatment reduced tumor size by 30% to 50% respectively. Notably, klotho administration did not affect weight or general health of the mice. Our data indicate klotho, for the first time, as a potential tumor suppressor gene in pancreatic cancer. Klotho levels are reduced in pancreatic cancer and expression of it in pancreatic cancer cells, or treatment with its soluble form, slows their growth and inhibits the IGF-1 pathway. Moreover, daily treatment of mice with soluble klotho was safe and effectively reduced growth of pancreatic cancer cells. As klotho is an endogenous hormone, its use as a novel therapeutic model may be feasible and should be further explored.  Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5342.