Dynamic Effect of Bortezomib on Nuclear Factor-κB Activity and Gene Expression in Tumor Cells

Nuclear factor-kappa B (NF-kappa B) influences the initiation, progression, and maintenance of diverse cancer types. Despite current therapeutic efforts to block hyperactive NF-kappa B in cancer cells, the in vivo effects of a drug upon this complex pathway are unclear. We monitored NF-kappa B activity and a fast-expressing reporter level simultaneously in head and neck squamous carcinoma cells by quantitative live microscopy. The real-time single cell assay revealed the tumor necrosis factor-alpha-induced oscillation of NF-kappa B was echoed by equally dynamic reporter expression rate. Bortezomib is a proteasome inhibitor whose anticancer action is partly mediated through inhibition of NF-kappa B. When administered to preactivated cells, the drug gave rise to distinct inhibition dynamics, with discrete pulses of reporter induction remaining for hours. These findings suggest that, contrary to a simplistic presumption for a pathway blockade, the network dynamics and the intracellular pharmacokinetics of the inhibitor must be critically evaluated in developing strategies for optimal intervention of oncogenic pathways.