Selection of COP1 4/7siRNA for in vivo application based on the inhibition of tumor cell growth and minimal cytokine induction. A, Inhibition of Huh7-luc+ cell growth after transfection of SNALP-formulated COP1-1 (native) or COP1 4/7 siRNA (a modified variant). The siRNA transfectants were examined by MTT assay at 4 days after treatment. B, Real-Time RT-PCR analysis of COP1 gene expression in Huh7-luc+ cells treated with the indicated siRNA. **, P < 0.01 (n=3) by Bootstrap t-test. C, Quantification of cytokines after luciferase (LUC) or COP1 targeting. Culture supernatants of Flt3L-derived dendrocytes were assayed for IFN-α and IL-6 using ELISA at 24 h after siRNA treatment. Data are shown are the means ± SD of triplicate experiments. D, Serum levels of IFN-β and downregulation of COP1 protein levels in Huh7-derived tumors (inset) 48 h after a single i.v. administration of encapsulated siRNA (2 mg/kg) targeting β-galactosidase (β gal) or COP1 into immunodeficient mice. Each bar represents the mean picogram of IFN-β ± SD of duplicate experiments. NS, normal serum, S, SNALP.