Background: Sorafenib has a well known efficacy in patients with advanced hepatocellular carcinoma (HCC). Sorafenib displays antiangiogenic effects by targeting receptors for VEGF (VEGFR2 and VEGFR3) and PDGF (PDGFRβ) and blocks cancer cell proliferation by targeting RAF/MEK/ERK signalling. However, disease-stabilizing effects are eventually followed by emergence of resistance in patients. The aim of the present work was to describe mechanisms associated with acquired resistance to sorafenib.

Materials and Methods: Cell proliferation and clonogenic survival were evaluated in sorafenib-sensitive and -resistant HCC models. Invasiveness of cells was determined by Matrigel invasion assay. qRT-PCR and western blot assays were used to assess a panel of genes and proteins. In vivo sorafenib efficacy was determined in SCID mice bearing SK-HEP1 xenografts. The drug was administered orally, once daily at dose levels of 10 and 30 mg/kg until sorafenib-resistance appearance, starting when tumors were detectable (100-300mm3).

Results: The SK-sora cell line was established from the parental SK-HEP1 cell line using a stepwise exposure to increasing sorafenib concentrations for more than 6 months. Exposure to 48-hour sorafenib led to IC50s of 8.3 and 15.9 µM in SK-HEP1 and SK-sora cells, respectively. Clonogenic assay also indicated a significant sorafenib resistance in SK-sora cells. Sorafenib-resistant cells did not display cross-resistance to sunitinib, another multitarget inhibitor. In addition, 30 days sorafenib withdrawal did not restore the sensitive to the drug in Sk-sora cells. Protracted exposure to sorafenib led to a 3-fold increase mRNA expression of VEGFA, VEGFD, erbb4, IGFR1, CXCL12 (SDF-1α) and MIF in SK-sora respect to parental SK-HEP1 cells. In addition we observed a basal up regulation of MAPK and AKT survival signalling pathways as measured by p-ERK1/2, p-AKT and p-S6rp levels in SK-sora cells. Matrigel assay revealed a 3 fold (p<0.05) increase in the number of invasive SK-sora cells respect to SK-HEP1 cells. Current in vivo studies point out that sorafenib (30 mg/kg/day) significantly suppressed SK-HEP1 xenograft tumor growth (34.6%; p<0.05) after 25 days of treatment. Mechanisms associated with resistance to sorafenib in mice will be explored.

Conclusions: Our data show that acquired resistance to sorafenib is associated with the activation of the AKT and MAPKs pathways together with an increased invasion in HCC cells. The role of CXCR4/CXCL12 axis in this model will be explored.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4266. doi:10.1158/1538-7445.AM2011-4266