Nanoparticles are used to solve the current drug delivery problem. We present a high-performance method for efficient and selective action on nucleic acid target in cells using unique TiO₂·PL-DNA nanocomposites (polylysine-containing DNA fragments noncovalently immobilized onto TiO₂ nanoparticles capable of transferring DNA). These nanocomposites were used for inhibition of human influenza A (H3N2) virus replication in infected MDCK cells. They showed a low toxicity (TC₅₀ ≈ 1800 μg/ml) and a high antiviral activity (>99.9% inhibition of the virus replication). The specificity factor (antisense effect) appeared to depend on the delivery system of DNA fragments. This factor for nanocomposites is ten-times higher than for DNA in the presence of lipofectamine. IC₅₀ for nanocomposites was estimated to be 1.5 μg/ml (30 nM for DNA), so its selectivity index was calculated as ~1200. Thus, the proposed nanocomposites are prospective for therapeutic application.

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