DOTAP VEGF-A siRNA containing an immunostimulatory motif significantly increased anti tumoral therapy efficacy in an HCC orthotopic fibrotic tumor model

BACKGROUND/AIMS Most experimental therapy studies are performed in mice that bear subcutaneous or orthotopic hepatoma but are otherwise healthy and non-fibrotic. However, the majority of hepatocellular carcinoma develops in patients suffering from pre-existing liver fibrosis. Here we investigated the efficacy of a standard experimental therapeutic approach to interrupt the VEGF/VEGFR cascade via VEGF-A silencing in pre-fibrotic HCC mice with or without DOTAP (cationic lipid) formulation. RESULTS We could show that the treatment with naked VEGF-A siRNA (200µg/kg) was inefficient to treat HCC under this pre-fibrotic circumstance. But VEGF-A siRNA containing an immunostimulatory motif (poly U proposed by Judge et al.) in combination with DOTAP formulation, led to a significant reduction of hepatic VEGF-A expression and additionally activated the innate and adapted immune system as shown by increased intrahepatic IFN type I response (68 fold increased IFN-beta expression). We demonstrated that DOTAP VEGF-A formulated siRNA can markedly improve the VEGF-A siRNA uptake and enhance the anti-tumor response probably through synergistic effects of VEGF-A silencing and activation of the immune system. The percentage of pre-fibrotic HCC bearing mice with less then 30 surface satellites in the DOTAP VEGF-A siRNA group increased by nearly 4 fold to 82% compared to the corresponding VEGF-A siRNA sub group. CONCLUSION This study showed first time the therapeutic feasibility of using synergistic effects (silencing/immune system activation) united in one siRNA sequence with DOTAP formulation to reduce HCC growth and spread in pre-fibrotic HCC bearing mice. These results will help to improve future experimental gene silencing approaches in order to increase the therapy outcome and could lead to even more efficient anti-tumoral therapy against HCC.

DOTAP - HCC - VEGF-A - siRNA