The multikinase inhibitor sorafenib is the only FDA approved drug available for advanced HCC patients, and development of second\line treatment options for patients who cannot tolerate or develop resistance to sorafenib is an urgent medical need. migration and invasion abilities compared to their parental counterparts. Moreover, after long\term sorafenib treatment, HCC cells showed induction of hepatocyte growth factor (HGF) synthesis and secretion along with increased levels of c\Met kinase and its active phosphorylated form, indicating autocrine activation of HGF/c\Met signaling. Importantly, the combined treatment of the resistant cells with c\Met kinase inhibitor SU11274 and HGF neutralizing antibody significantly reversed the increased invasion ability of the cells. The combined treatment also significantly augmented sorafenib\induced apoptosis, suggesting restoration of sorafenib sensitivity. These results describe, for the first time, compensatory upregulation of HGF synthesis leading to autocrine activation of HGF/c\Met signaling as a novel cellular strategy in the acquisition of sorafenib resistance. Therefore, we suggest that combinatorial therapeutic strategies with HGF and c\Met inhibitors comprise promising candidates for overcoming sorafenib resistance. motility and invasion assays were carried out as described previously.34 Briefly, cells were cultured in DMEM with 5% FBS and treated with either 1.0 M SU11274, anti\HGF antibody (1 g/mL), or both. Cells treated with 0.1% DMSO and mouse IgG were used as controls. The number of migrated and invaded cells was counted in five areas under a bright\field inverted microscope. Fold inductions were calculated using average numbers of migrated and invaded cells from at least three replicates. Analysis of gene expression Total RNA was isolated using the RNeasy mini kit (Qiagen, Valencia, CA, USA) and RNA concentration was detected using NanoDrop (Thermo Fisher Scientific, MA, USA). One microgram of RNA was then converted to cDNA using a RevertAid First Strand cDNA Synthesis kit (Thermo Fisher Scientific, Waltham, MA, USA) with random primers. For real\time quantitative RT\PCR, expression levels were determined in triplicate on a Light Cycler instrument (Roche 480), using the SYBR Green PCR Master Mix (Applied Biosystems, Thermo Fisher Scientific, MA, USA). Relative gene expression was normalized to GAPDH and calculated by using the 2?Ct method. Primer pairs used are given in VX-661 Doc. S1. Quantitative PCR for analysis of HGF copy VX-661 number Quantitative PCR was done on genomic DNA purified from parental and soR cell lines Rabbit polyclonal to ZNF562 using the GeneJET Genomic DNA Purification Kit (Thermo Fisher Scientific). Reactions were done in VX-661 quadruplicate with 20 ng genomic DNA. Data were normalized to RNase P which encodes the RNA moiety for the RNase P enzyme and calculated by using the 2?Ct method. Primer pairs used are given in Doc. S1. Enzyme\linked immunosorbent assay Hepatocyte growth factor concentration in the supernatants of parental and soR cells was detected by an HGF Human ELISA Kit (KAC2211; Invitrogen, Carlsbad, CA, USA) following the manufacturer’s instructions. Briefly, parental and soR cells were seeded into six\well plates in 0.1% BSA. Following 48 h of cultivation, cultured media were collected and ELISA was carried out. Apoptosis assay Cells were grown in DMEM with 10% FBS containing 3 M sorafenib and treated with either 1 microMolar, anti\human HGF antibody, or both. After 48 h, cells were collected, resuspended in annexin V binding buffer, and stained using an annexin VCFITC/propidium iodide staining kit (BD Biosciences, San Jose, CA, USA) according to the manufacturer’s instructions. Cells were then immediately analyzed using a FACSCalibur flow cytometer (BD Biosciences). Statistical analysis Statistical analysis was carried out using GraphPad Prism (GraphPad Software, Inc, California, USA). Statistical methods included anova and Student’s 0.05, ** 0.001, and *** 0.0001. Results Hepatocellular carcinoma cell lines became resistant to long\term sorafenib treatment and showed upregulation of EMT markers In our previous studies, we characterized HCC cell lines into two groups as well\differentiated and poorly differentiated according to their differentiation status.36, 37 Poorly differentiated HCC cell lines show a mesenchymal phenotype VX-661 and increased invasion ability and overexpress c\Met receptor. Well\differentiated cell lines, which have limited motility and invasion ability, show an epithelial phenotype and lack c\Met expression.36, 37 For this study, we chose one HCC cell line from each group: (i) the Mahlavu cell line, which shows mesenchymal features and augmented VX-661 motility and invasion and expresses c\Met receptor; and (ii) the Huh7 cell line, which shows epithelial features and lacks invasive ability and c\Met receptor expression. For both.