Inhibition of nuclear factor-KB 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-KB (NF-KB) activation promotes cell survival and growth. Reports show that chemotherapeutic agents and cytokines that are used for cancer therapy activate NF-KB 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 (Admda7/IL-24) induces NF-KB 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-KB activation in a doseand time-dependent manner before activation of cell death pathways. To establish that inhibition of Ad-mda7– mediated NF-KB activation results in enhanced tumor cell killing, H1299 cells that overexpress the dominantnegative IKBA (dnIKBA) were treated with Ad-mda7 in vitro. An enhanced growth arrest and apoptosis was observed in Ad-mda7–treated H1299-dnIKBA compared with H1299-Neo cells. This Ad-mda7–mediated enhanced killing of H1299-dnIKBA 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 H1299dnIKBA cells resulted in reduced Ad-mda7–mediated cell killing. In vivo, the treatment of H1299-dnIKBA s.c. tumors with Ad-mda7 resulted in increased drug sensitivity and delayed the tumor growth rate compared with Admda7–treated H1299-Neo tumors. Molecular analysis of Ad-mda7–treated H1299-dnIKBA 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-KB activation induced by Ad-mda7 treatment of lung cancer cells is an intrinsic survival mechanism and that the inhibition of this NF-KB expression results in enhanced tumor cell killing. [Mol Cancer Ther 2007;6(4):1440–9]