RESUMO
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.
RESUMO
AIM: To investigate the expression of DNA repair genes and the impact of the breast cancer 1, early onset (BRCA1) protein on chemoresistance of hepatocellular carcinoma (HCC). METHODS: Microarray gene expression datasets were analyzed using the gene set enrichment analysis method. BRCA1 protein was tested by Western blotting. Response of HCC cells to interstrand cross-links was investigated by cell viability assay following exposure to mitomycin C, cisplatin, and melphalan. Effects of BRCA1 ectopic expression were studied in HepG2 cells with BRCA1-expression plasmids. Effects of BRCA1 downregulation were studied in SNU449 cells with BRCA1-specific siRNAs. Response of transfected SNU449 cells to mitomycin C was analyzed by cell viability tests and cell cycle analysis using flow cytometry. RESULTS: Expression of Fanconi anemia and double-stranded DNA break repair genes was significantly upregulated in HCC tumors. This upregulation displayed a gradual amplification during tumor progression. BRCA1 and BRCA2 genes were among consistently upregulated genes. Epithelial-like HCC cells had low BRCA1 expression and low chemoresistance, whereas mesenchymal-like HCC cells had high BRCA1 expression and increased chemoresistance. Ectopic expression of BRCA1 increased the chemoresistance of epithelial-like HepG2 cells. Conversely, BRCA1 knockdown chemosensitized mesenchymal-like SNU449 cells. Chemosensitization of SNU449 cells was due to cell cycle arrest at 4N stage. CONCLUSION: Increased expression of Fanconi anemia and double-stranded DNA repair genes such as BRCA1 is a novel mechanism of HCC chemoresistance. However, functional inactivation of BRCA1 expression is sufficient to reverse such chemoresistance.
