Inhibition of nuclear factor-kappaB augments antitumor activity of adenovirus-mediated melanoma differentiation-associated gene-7 against lung cancer cells via mitogen-activated protein kinase kinase kinase 1 activation.

Nuclear factor-kappaB (NF-kappaB) activation promotes cell survival and growth. Reports show that chemotherapeutic agents and cytokines that are used for cancer therapy activate NF-kappaB expression in tumor cells and its suppression enhanced the antitumor activity. We hypothesized that adenovirus-mediated overexpression of melanoma differentiation-associated gene-7/interleukin-24 (Ad-mda7/IL-24) induces NF-kappaB expression and that inhibition of this expression results in enhanced tumor cell killing. Treatment of human lung tumor (H1299 and A549) cells with Ad-mda7 resulted in NF-kappaB activation in a dose- and time-dependent manner before activation of cell death pathways. To establish that inhibition of Ad-mda7-mediated NF-kappaB activation results in enhanced tumor cell killing, H1299 cells that overexpress the dominant-negative I kappa B alpha (dnI kappa B alpha) were treated with Ad-mda7 in vitro. An enhanced growth arrest and apoptosis was observed in Ad-mda7-treated H1299-dnI kappa B alpha compared with H1299-Neo cells. This Ad-mda7-mediated enhanced killing of H1299-dnI kappa B alpha cells involved cleavage of mitogen-activated protein kinase kinase kinase 1 (MEKK1) and caspase-3 in a feedback loop mechanism. The inhibition of MEKK1 or caspase-3 cleavage in H1299-dnI kappa B alpha cells resulted in reduced Ad-mda7-mediated cell killing. In vivo, the treatment of H1299-dnI kappa B alpha s.c. tumors with Ad-mda7 resulted in increased drug sensitivity and delayed the tumor growth rate compared with Ad-mda7-treated H1299-Neo tumors. Molecular analysis of Ad-mda7-treated H1299-dnI kappa B alpha tumors showed increased MEKK1 cleavage and activation of caspase-3 compared with Ad-mda7-treated H1299-Neo tumors. Our findings thus showed that the NF-kappaB activation induced by Ad-mda7 treatment of lung cancer cells is an intrinsic survival mechanism and that the inhibition of this NF-kappaB expression results in enhanced tumor cell killing.