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

Laboratory of Receptor Biology and Gene Expression, National Cancer Institute (M.-H.S., T.K., T.C.V., J.G.M., G.L.H.), Head and Neck Surgery Branch, National Institute on Deafness and Communication Disorders (L.B., Z.C., X.Y., C.V.W.), and Genetics and Molecular Biology Branch, National Human Genome Research Institute (C.S.), National Institutes of Health, Bethesda, Maryland

Nuclear factor-B (NF-B) influences the initiation, progression, and maintenance of diverse cancer types. Despite current therapeutic efforts to block hyperactive NF-B in cancer cells, the in vivo effects of a drug upon this complex pathway are unclear. We monitored NF-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--induced oscillation of NF-B was echoed by equally dynamic reporter expression rate. Bortezomib is a proteasome inhibitor whose anticancer action is partly mediated through inhibition of NF-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.

Address correspondence to: Dr. Myong-Hee Sung, Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Room B602, Bldg. 41, 41 Library Dr., Bethesda, MD 20892. E-mail: sungm{at}mail.nih.gov