Flavoprotein-dependent
reactive oxygen species (ROS) play a critical role in
cytokine-mediated signal transduction in normal tissues and
tumor cells. The flavoenzyme inhibitors
diphenylene iodonium (DPI) and
di-2-thienyliodonium (DTI) have been used to inhibit membrane-bound,
flavoprotein-containing
NADPH oxidases, including epithelial and leukocyte
NADPH oxidases (Nox1-5 and Duox 1 and 2). Recent evidence suggests that DPI can decrease
tumor cell proliferation; however, the molecular mechanisms involved remain poorly defined. To explore the mechanisms underlying DPI- and DTI-related
tumor cell growth delay, we examined growth inhibition patterns produced by both agents in the NCI-60
tumor panel, and determined expression levels of Nox gene family members across these cell lines. Possible molecular targets were predicted using the COMPARE program. DPI was more potent than DTI (GI(50): 10nM versus 10μM); DPI and DTI exposure produced unique patterns of growth inhibition when evaluated against the small molecule anticancer database of the National Cancer Institute. Growth inhibition profiling of DPI revealed a modest positive correlation with Nox1 levels; novel mechanisms of DPI and DTI action, including alterations in Stat, Erk1/2, and Akt pathways, were inferred by correlation with NCI-60 Affymetrix(®) array data. Exposure of HT-29
colon cancer cells, which express Nox1, to DPI and DTI confirmed their inhibitory effects on steady state ROS levels, and demonstrated decreased Stat, Erk1/2, and Akt signaling mediated by
IL-4,
IL-6,
IL-13, and
IL-22, possibly due to a concomitant increase in
tumor cell
phosphatase activity. These findings suggest that DPI and DTI may act therapeutically by altering ROS-related signal transduction.