Inhibition of NF-κB, clonogenicity, and radiosensitivity of human cancer cells

Background: Activation of the transcription factor NF-kappa B is part of the immediate early response of tissues to ionizing irradiation. This pathway has been shown to protect cells from tumor necrosis factor-alpha, chemotherapy, and radiation therapy-induced apoptosis (programmed cell death). However, because the role of NF-kappa B as a modifier of the intrinsic radiosensitivity of cancer cells is less clear, we have studied the impact of NF-kappa B on the intrinsic radiosensitivity of human cancer cells. Methods: We used PC3 prostate cancer cells and HD-MyZ Hodgkin's lymphoma cells transduced with an adenovirus vector that contains a gene encoding a form of I kappa B (an inhibitor of NF-kappa B) that cannot be phosphorylated. This form of I kappa B v9ill remain bound to NF-kappa B; thus, NF-kappa B cannot be activated. We monitored NF-kappa B activity with a gel-shift assay and used a colony-forming assay to assess clonogenicity and radiosensitivity, Results: Constitutive DNA-binding: activity of NF-kappa B was dramatically decreased in PC3 cells transduced with the I kappa B super-repressor gene. The clonogenicity of transduced PC3 cells declined to 19.6% of that observed for untreated control cells, a finding similar to one we have previously demonstrated for I kappa B-transduced HD-MyZ cells. However, inhibition of NF-kappa B activity in the surviving PC3 and HD-MyZ cells failed to alter their intrinsic radiosensitivity, Conclusions: We conclude that activation of NF-kappa B does not determine the intrinsic radiosensitivity of cancer cells, at least for the cell lines tested in this study.