Synergistic Tumor Suppression by Adenovirus-Mediated Inhibitor of Growth 4 and Interleukin-24 Gene Cotransfer in Hepatocarcinoma Cells

Inhibitor of growth 4 (ING4) is a novel member of ING tumor suppressor family and has apparent tumor-suppressive effect. Interleukin-24 (IL-24) as a unique cytokine-tumor suppressor displays ubiquitous antitumor property and tumor-specific killing activity. Multigene-based combination therapy may be an effective practice in cancer gene therapy. The therapeutic potential of a conjunction of ING4 and IL-24 for cancers is still elusive. This study evaluated the combined effect on SMMC-7721 and HepG2 human hepatocarcinoma cells by adenovirus-mediated ING4 and IL-24 coexpression (Ad-ING4-IL-24) and also elucidated its underlying molecular mechanism. It was demonstrated that Ad-ING4-IL-24 induced synergistic growth inhibition, apoptosis, invasion suppression, as well as an enhanced effect on upregulation of P21, P27, Fas, FasL, FADD, Bad, Bax, Bak, cleaved Bid, cleaved Caspase-8, -9, and -3, and cleaved PARP, downregulation of Bcl-2, Bcl-XL, matrix metalloproteinase (MMP)-2, 9, vascular endothelial growth factor (VEGF), IL-8, CD34, and microvessel density, and cytochrome c release from mitochondria into cytosol in in vitro SMMC-7721 and HepG2 hepatocarcinoma cells and/or in vivo SMMC-7721 hepatocarcinoma subcutaneous xenografted tumors in athymic nude mice. The in vitro and in vivo synergistic antitumor activity elicited by Ad-ING4-IL-24 was closely associated with the cooperative activation of extrinsic and intrinsic apoptotic pathways and reduced proangiogenic factors' production of VEGF and IL-8, leading to synergistic inhibition of tumor angiogenesis. Thus, results indicate that cancer gene therapy combining two or more tumor suppressors such as ING4 and IL-24 may constitute a novel and effective therapeutic strategy for hepatocarcinoma and other cancers.