Tumor-targeted delivery of siRNA by self-assembled nanoparticles

Abstract

We have developed a self-assembled nanoparticle (NP) that efficiently delivers small interfering RNA (siRNA) to the tumor by intravenous (IV) administration. The NP was obtained by mixing carrier DNA, siRNA, protamine, and lipids, followed by post-modification with polyethylene glycol and a ligand, anisamide. Four hours after IV injection of the formulation into a xenograft model, 70-80% of injected siRNA/g accumulated in the tumor, approximately 10% was detected in the liver and approximately 20% recovered in the lung. Confocal microscopy showed that fluorescent-labeled siRNA was efficiently delivered into the cytoplasm of the sigma receptor expressing NCI-H460 xenograft tumor by the targeted NPs, whereas free siRNA and non-targeted NPs showed little uptake. Three daily injections (1.2 mg/kg) of siRNA formulated in the targeted NPs silenced the epidermal growth factor receptor (EGFR) in the tumor and induced approximately 15% tumor cell apoptosis. Forty percent tumor growth inhibition was achieved by treatment with targeted NPs, while complete inhibition lasted for 1 week when combined with cisplatin. The serum level of liver enzymes and body weight monitoring during the treatment indicated a low level of toxicity of the formulation. The carrier itself also showed little immunotoxicity (IMT).

Figure 1. Serum concentration profiles of FAM-siRNA in different formulations

Data = mean ± SD, n = 4–8. NP, nanoparticle; siRNA, small interfering RNA.

Figure 2. Tissue distribution study

(a) Fluorescence signal of FAM-siRNA in different tissues detected by the Xenogen IVIS imaging system. (b) Tissue distribution of FAM-siRNA in different formulations. Data = mean ± SD, n = 3–4. NP, nanoparticle; siRNA, small interfering RNA.

Figure 3. Tumoral uptake of FAM-siRNA in different formulations

Blue arrows indicate the extracellular space and pink arrows indicate the intracellular uptake of FAM-siRNA. Magnification = ×400 (xyz images), ×630 (xzy images). NP, nanoparticle; siRNA, small interfering RNA.

Figure 4. Immunohistochemical analysis of the tumor samples

(a) Immunohistochemical staining on tumor sections: epidermal growth factor receptor (upper), prostate apoptotic response 4 (middle), and apoptosis inducing factor (AIF) (bottom). Magnification = ×200. (b) Quantitative analysis of nuclear translocation of AIF in the tumors treated with different formulations. **indicates P < 0.01, *indicates P < 0.05. NP, nanoparticle; PBS, phosphate-buffered saline; siRNA, small interfering RNA.

Figure 5. Western blot analysis of epidermal growth factor receptor (EGFR) in the NCI-H460 xenograft tumor after treatment with different formulations

NP, nanoparticle; PBS, phosphate-buffered saline; siRNA, small interfering RNA.

Figure 6. NCI-H460 xenograft tumor growth inhibition by small interfering RNA (siRNA) in different formulations with or without the combination of cisplatin

Solid arrows indicate the intravenous administrations of siRNA (1.2 mg/kg) and dash-line arrows indicate the intra-peritoneal injections of cisplatin (3 mg/kg). Data = mean, n = 6–9. SD of the data points is not shown for clarity.

Figure 7. Serum cytokine analysis

Serum cytokine levels in the (a) athymic nude mice and (b) C57BL/6 mice 2 hours after the injection of different formulations at the dose of 1.2 mg siRNA/kg (2.4 mg DNA/kg for group F). A, phosphate-buffered saline (PBS); B, epidermal growth factor receptor (EGFR) small interfering RNA (siRNA) in PBS; C, EGFR siRNA and calf thymus DNA in non-targeted nanoparticle (NP); D, EGFR siRNA and calf thymus DNA in targeted NP; E, MDM2 siRNA and calf thymus DNA in targeted NP; F, calf thymus DNA in targeted NP (empty NP); G, EGFR siRNA and plasmid DNA in targeted NP. Data = mean ± SD, n = 3–8.