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

Abstract

ABSTRACT 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. Recent trends in clinical investigations clearly tend toward molecularly targeted approaches that are based on mechanisms underlying the pathophysiology of the disease. Often, the goal is to block the activity of a specific pathway that has been implicated in the disease process, by targeting a key component with a small molecule or an antibody, for example. It is seldom known whether the desired "blockade" is achieved in the relevant tissue and why paradoxical outcomes occur in certain cases. Here, we show that NF-B activity in tumor cells is altered by the action of a proteasome inhibitor in a complex way that cannot sufficiently be explained by the simplistic notion of pathway blockade. NF-B/Rel is a master regulator of inflammatory processes and has a growing list of cancers and other common diseases that require its aberrant activit