| Summary: | Victor Jeannot,1,2 Benoit Busser,1–3 Laetitia Vanwonterghem,1,2 Sophie Michallet,1,2 Sana Ferroudj,1,2 Murat Cokol,4 Jean-Luc Coll,1,2 Mehmet Ozturk,1,2,5 Amandine Hurbin1,2 1INSERM U1209, Department Cancer Targets and Experimental Therapeutics, Grenoble, France; 2University Grenoble Alpes, Institute for Advanced Biosciences, Grenoble, France; 3Department of Biochemistry, Toxicology and Pharmacology, Grenoble University Hospital, Grenoble, France; 4Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey; 5Faculty of Medicine, Dokuz Eyul University, Izmir Biomedicine and Genome Center, Izmir, Turkey Abstract: Development of drug resistance limits the efficacy of targeted therapies. Alternative approaches using different combinations of therapeutic agents to inhibit several pathways could be a more effective strategy for treating cancer. The effects of the approved epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (gefitinib) or a multi-targeted kinase inhibitor (sorafenib) in combination with a histone deacetylase inhibitor (vorinostat) on cell proliferation, cell cycle distribution, apoptosis, and signaling pathway activation in human lung adenocarcinoma and hepatocarcinoma cells with wild-type EGFR and mutant KRAS were investigated. The effects of the synergistic drug combinations were also studied in human lung adenocarcinoma and hepatocarcinoma cells in vivo. The combination of gefitinib and vorinostat synergistically reduced cell growth and strongly induced apoptosis through inhibition of the insulin-like growth factor-1 receptor/protein kinase B (IGF-1R/AKT)-dependent signaling pathway. Moreover, the gefitinib and vorinostat combination strongly inhibited tumor growth in mice with lung adenocarcinoma or hepatocarcinoma tumor xenografts. In contrast, the combination of sorafenib and vorinostat did not inhibit cell proliferation compared to a single treatment and induced G2/M cell cycle arrest without apoptosis. The sorafenib and vorinostat combination sustained the IGF-1R-, AKT-, and mitogen-activated protein kinase-dependent signaling pathways. These results showed that there was synergistic cytotoxicity when vorinostat was combined with gefitinib for both lung adenocarcinoma and hepatocarcinoma with mutant KRAS in vitro and in vivo but that the combination of vorinostat with sorafenib did not show any benefit. These findings highlight the important role of the IGF-1R/AKT pathway in the resistance to targeted therapies and support the use of histone deacetylase inhibitors in combination with EGFR-tyrosine kinase inhibitors, especially for treating patients with mutant KRAS resistant to other treatments. Keywords: targeted therapy, combined treatments, non-small cell lung cancer, hepatocarcinoma
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