Abstract 2888: Lipid nanoparticle-mediated delivery of siRNA to extrahepatic tumors

Abstract

Abstract While lipid nanoparticles (LNPs) proved to be effective in delivering siRNA to the liver and hepatocellular carcinoma (HCC) via systemic administration, they showed inferior or no efficacy in the extrahepatic tumor models. To understand the underlying mechanism for LNP activity in delivering siRNA to extrahepatic tumors, we determined siRNA biodistribution and gene-silencing activity of the LNP-siRNA nanoparticles containing different percentages of a polyethylene glycol (PEG) lipid, distinct PEG lipids with a short (C-14) or long (C-18) alkyl chain, or an identical composition with different particle sizes in mouse subcutaneous tumor xenograft models derived from either human HCC (Hep3B) or colon cancer (HT29 or HCT116) cells. We show that the LNPs containing C-18 DSA PEG exhibited a higher retention of siRNA in both Hep3B and HT29 tumors than those with C-14 DMA PEG following an intravenous administration. Intriguingly, LNPs containing 2% of DSA or DMA PEG resulted in similar levels (∼50%) of target knockdown in Hep3B tumors while those containing 6% of DSA or DMA PEG caused no target silencing. Also, none of these LNPs reduced target expression in HT29 tumors despite the retention of siRNA in tumor tissues. When LNPs with an identical composition (2% DMG PEG) but different particle sizes (80 nm vs. 120 nm) were tested, we observed a comparable and moderate suppression of target expression in Hep3B tumors, but no target knockdown in HCT116 tumors. This is despite the fact that the expression of low density lipid receptor, which is shown to be involved in mediating LNP efficacy, is detected in HT29 and HCT116 tumors. Finally, intratumor injection of LNPs only induced minimal target silencing in subcutaneous tumors while provoking significant target knockdown in the liver. Together, enhanced tumor retention of siRNA might not be readily translated to target silencing activity in tumors. Other factors such as the efficiency of transfecting tumor cells and the passive targeting effect through opsonization could impact on LNP efficacy in extrahepatic tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2888. doi:1538-7445.AM2012-2888