ABSTRACT
BACKGROUND: Ionizing radiation (IR) is effectively used in cancer therapy. However, in subsets of patients, a few radioresistant cancer cells survive and cause disease relapse with metastatic progression. The MET oncogene encodes the hepatocyte growth factor (HGF) receptor and is known to drive "invasive growth", a regenerative and prosurvival program unduly activated in metastasis. METHODS: Human tumor cell lines (MDA-MB-231, MDA-MB-435S, U251) were subjected to therapeutic doses of IR. MET mRNA, and protein expression and signal transduction were compared in treated and untreated cells, and the involvement of the DNA-damage sensor ataxia telangiectasia mutated (ATM) and the transcription factor nuclear factor kappa B (NF-κB) in activating MET transcription were analyzed by immunoblotting, chromatin immunoprecipitation, and use of NF-κB silencing RNA (siRNA). Cell invasiveness was measured in wound healing and transwell assays, and cell survival was measured in viability and clonogenic assays. MET was inhibited by siRNA or small-molecule kinase inhibitors (PHA665752 or JNJ-38877605). Combinations of MET-targeted therapy and radiotherapy were assessed in MDA-MB-231 and U251 xenografts (n = 5-6 mice per group). All P values were from two-sided tests. RESULTS: After irradiation, MET expression in cell lines was increased up to fivefold via activation of ATM and NF-κB. MET overexpression increased ligand-independent MET phosphorylation and signal transduction, and rendered cells more sensitive to HGF. Irradiated cells became more invasive via a MET-dependent mechanism that was further enhanced in the presence of HGF. MET silencing by siRNA or inhibition of its kinase activity by treatment with PHA665752 or JNJ-38877605 counteracted radiation-induced invasiveness, promoted apoptosis, and prevented cells from resuming proliferation after irradiation in vitro. Treatment with MET inhibitors enhanced the efficacy of IR to stop the growth of or to induce the regression of xenografts (eg, at day 13, U251 xenografts, mean volume increase relative to mean tumor volume at day 0: vehicle = 438%, 5 Gy IR = 151%, 5 Gy IR + JNJ-38877605 = 76%; difference, IR vs JNJ-38877604 + IR = 75%, 95% CI = 59% to 91%, P = .01). CONCLUSION: IR induces overexpression and activity of the MET oncogene through the ATM-NF-κB signaling pathway; MET, in turn, promotes cell invasion and protects cells from apoptosis, thus supporting radioresistance. Drugs targeting MET increase tumor cell radiosensitivity and prevent radiation-induced invasiveness.
Subject(s)
Cell Cycle Proteins/metabolism , DNA Damage/radiation effects , DNA-Binding Proteins/metabolism , NF-kappa B/metabolism , Neoplasms/metabolism , Protein Serine-Threonine Kinases/metabolism , Proto-Oncogene Proteins c-met/metabolism , Receptors, Growth Factor/antagonists & inhibitors , Receptors, Growth Factor/metabolism , Signal Transduction/radiation effects , Tumor Suppressor Proteins/metabolism , Animals , Apoptosis/radiation effects , Ataxia Telangiectasia Mutated Proteins , Blotting, Northern , Cell Cycle Proteins/genetics , Cell Cycle Proteins/radiation effects , Cell Line, Tumor , Cell Movement/radiation effects , Cell Survival/radiation effects , Chromatin Immunoprecipitation , DNA-Binding Proteins/genetics , DNA-Binding Proteins/radiation effects , Enzyme-Linked Immunosorbent Assay , Gene Expression Regulation, Neoplastic/drug effects , Gene Silencing , Humans , In Situ Nick-End Labeling , Indoles/pharmacology , Mice , Mitogen-Activated Protein Kinases/metabolism , NF-kappa B/genetics , NF-kappa B/radiation effects , Neoplasm Invasiveness/prevention & control , Neoplasms/pathology , Neoplasms/radiotherapy , Phosphorylation/radiation effects , Polymerase Chain Reaction , Protein Kinase Inhibitors/pharmacology , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/radiation effects , Proto-Oncogene Proteins c-met/antagonists & inhibitors , Proto-Oncogene Proteins c-met/drug effects , Proto-Oncogene Proteins c-met/genetics , Proto-Oncogene Proteins c-met/radiation effects , RNA, Messenger/metabolism , RNA, Small Interfering , Radiation Tolerance , Radiation, Ionizing , Radiation-Sensitizing Agents/pharmacology , Receptors, Growth Factor/drug effects , Receptors, Growth Factor/genetics , Receptors, Growth Factor/radiation effects , Sulfones/pharmacology , Transcription, Genetic/radiation effects , Transplantation, Heterologous , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/radiation effects , Up-Regulation/radiation effectsABSTRACT
In this study, we investigated the protein expression of platelet-derived growth factor receptor (PDGFR), insulin like growth factor-1 receptor (IGF-1R), phosphatidylinositol 3-kinase (PI3-K) and extracellular signal-regulated kinase (ERK1/2) in five primary glioblastoma (GB), with a view to their possible use as therapeutic targets. Our results demonstrated that appreciable levels of these proteins could be detected in the analysed GB cell lines, except for a low level of PDGFR and ERK1/2 expression in one GB cell line. The small molecule inhibitors towards IGF-1R, PDGFR, PI3-K and ERK1/2 respectively, have only modest or no anti-tumour activity on GB cells and therefore their combination with other therapy modalities was analysed. The interaction between small inhibitors and radiation was mostly additive or sub-additive; synergistic interaction was found in five of forty analysed combinations. Our results showed that GB cells are in general resistant to treatment and illustrate the difficulties in predicting the treatment response in malignant gliomas.
Subject(s)
Brain Neoplasms/metabolism , Glioblastoma/metabolism , Receptors, Growth Factor/metabolism , Signal Transduction/physiology , Antineoplastic Agents/pharmacology , Blotting, Western , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Proliferation/radiation effects , Flow Cytometry , Humans , Mitogen-Activated Protein Kinase 1/drug effects , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 1/radiation effects , Mitogen-Activated Protein Kinase 3/drug effects , Mitogen-Activated Protein Kinase 3/metabolism , Mitogen-Activated Protein Kinase 3/radiation effects , Phosphatidylinositol 3-Kinases/drug effects , Phosphatidylinositol 3-Kinases/metabolism , Phosphatidylinositol 3-Kinases/radiation effects , Receptor, IGF Type 1/drug effects , Receptor, IGF Type 1/metabolism , Receptor, IGF Type 1/radiation effects , Receptors, Growth Factor/drug effects , Receptors, Growth Factor/radiation effects , Receptors, Platelet-Derived Growth Factor/drug effects , Receptors, Platelet-Derived Growth Factor/metabolism , Receptors, Platelet-Derived Growth Factor/radiation effects , Signal Transduction/drug effects , Signal Transduction/radiation effectsABSTRACT
Ultraviolet radiation, either alone or in combination with photosensitizing agents, is widely used for the treatment of skin diseases. The efficacy of photo- and photochemotherapeutic modalities is thought to result, at least in part, from the induction of immunomodulatory effects. In particular, UV radiation has been shown to affect (i) the production of soluble mediators, (ii) the expression of cell-surface receptors and (iii) to induce apoptosis in pathogenetically relevant cells. UVB radiation-induced immunomodulatory effects are limited to the epidermis, whereas UVA radiation affects both epidermal and dermal cell populations. UVB and UVA radiation can exert essentially identical immunomodulatory effects, which result, however, from different photobiological mechanisms.
