Expression and effects of inhibition of type I insulin-like growth factor receptor tyrosine kinase in mantle cell lymphoma

Type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase induces significant oncogenic effects. Strategies to block IGF-IR signaling are being tested in clinical trials that include patients with aggressive solid malignancies. Mantle cell lymphoma is a B-cell neoplasm with poor prognosis and a tendency to develop resistance. The expression and potential significance of IGF-IR in mantle cell lymphoma are not known. We used reverse transcriptase polymerase chain reaction, quantitative real-time polymerase chain reaction, immunoprecipitation, western blotting, flow cytometry, and immunohistochemistry to analyze the expression of IGF-IR mRNA, and IGF-IR and pIGF-IR proteins in mantle cell lymphoma cell lines and patients' specimens. Selective and specific blockade of IGF-IR was achieved using picropodophyllin and short-interfering RNA, respectively. Cell viability, apoptosis, cell cycle, cellular morphology, cell proliferation, and target proteins were then analyzed. We detected the expression of IGF-IR and pIGF-IR in mantle cell lymphoma cell lines. Notably, IGF-IR molecules/cell were markedly increased in mantle cell lymphoma cell lines compared with human B-lymphocytes. IGF-IR and pIGF-IR were also detected in 78% and 74%, respectively, of 23 primary mantle cell lymphoma specimens. Treatment of serum-deprived mantle cell lymphoma cell lines with IGF-I salvaged these cells from apoptosis. Selective inhibition of IGF-IR by picropodophyllin decreased the viability and proliferation of mantle cell lymphoma cell lines, and induced apoptosis and cell cycle arrest. Selective inhibition of IGF-IR was associated with caspase-3, caspase-8, caspase-9, and PARP cleavage, cytochrome c release, up-regulation of cyclin B1, and down-regulation of cyclin D1, pCdc2, pIRS-1, pAkt, and pJnk. Similar results were obtained by using IGF-IR short-interfering RNA. In addition, picropodophyllin decreased the viability and proliferation of primary mantle cell lymphoma cells that expressed IGF-IR. IGF-IR is up-regulated and frequently activated in mantle cell lymphoma. Our data suggest that IGF-IR could be a molecular target for the treatment of mantle cell lymphoma.