Abstract 1080: Kras downregulation by nanoparticle delivery of siRNA reduces tumor growth in mice
Authors: Strand Matthew , Pan Hua , Zhang Xiuli , Grossman Julie , Goedegebuure Peter , Fleming Timothy , Gillanders William E. , Wickline Samuel A. , Fields Ryan C. 
Published: July 2016

Abstract
Introduction
Small-interfering RNA (siRNA) is an attractive option for delivering precision therapy to cancer patients because of the potential for highly-specific control of gene expression. Attempts to utilize siRNA in vivo have been hampered by its short circulating half-life, limited cellular uptake, and cellular confinement within endosomes. To overcome these barriers, we packaged siRNA within serum-stable, cell-penetrating, and endosomolytic peptide-based nanoparticles (NPs) to deliver siRNA to human and mouse pancreas and colorectal cancers. In a small pilot study, twice weekly administration of KRAS siRNA-NP to mice bearing human colorectal cancers significantly reduced tumor growth compared to controls.
Methods
NP uptake was assessed in cell lines utilizing fluorescent siRNA-NPs in combination with fluorescence microscopy and flow cytometry. Cell lines were incubated with KRAS-siRNA NP and KRAS knockdown was assessed by quantitative PCR. Mice bearing tumors derived from these cell lines were injected intravenously with fluorescent NP, and localization and uptake were assessed with an in vivo imaging system (IVIS) and flow cytometry. Immune deficient mice were inoculated subcutaneously with a human colorectal cancer and half were treated for 4 weeks with twice weekly IV injections of KRAS siRNA-NP (1 nmol KRAS siRNA per dose).
Results
On average, fluorescent siRNA was detected in more than 93% of human and mouse pancreas and colorectal cancer cells (n = 5 cell lines) after 24 hours of incubation. Exposure of colorectal cancer cells to KRAS siRNA-NP in vitro produced a conservatively-estimated 70% downregulation of KRAS. Tumors derived from all cell lines were strongly fluorescent 2 hours after IV injection of fluorescent NP and signal persisted beyond 30 hours. The liver and kidneys also expressed fluorescent signal by IVIS. 86% of tumor cells derived from tumors exposed to fluorescent-NP by IV injection expressed fluorescent signal 24 hours post-injection. Only 18% and 14% of liver and kidney cells, respectively, were fluorescent. Compared to control mice, tumor size was reduced in mice bearing colorectal cancer that received KRAS-siRNA NP IV injections. Eighteen days after initiation of treatment, tumor volumes in the control and treatment groups were 229.5 mm3 and 460.25 mm3 respectively (p &lt; 0.05). Hematologic, liver and kidney function tests revealed no differences between the treatment and control groups.
Conclusions
Peptide NPs are rapidly and efficiently taken up by human and mouse pancreas and colorectal cancer cells both in vitro and in vivo. Incubation of cancer cells with peptide NP-packaged KRAS-siRNA reduces KRAS expression in vitro. Treatment of tumor-bearing mice with KRAS-siRNA NP leads to a statistically significant reduction in tumor growth compared to control mice. This delivery platform overcomes traditional limitations of siRNA and may be generalizable to target other putative drivers of tumor progression.
Citation Format: Matthew Strand, Hua Pan, Xiuli Zhang, Julie Grossman, Peter Goedegebuure, Timothy Fleming, William E. Gillanders, Samuel A. Wickline, Ryan C. Fields. Kras downregulation by nanoparticle delivery of siRNA reduces tumor growth in mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1080.