The use of DNA sequence-specific therapies is recognized as a way to treat diseases in a truly specific way, but the approaches to reach the goal of gene-specific DNA eradication are very few. To be useful, the therapeutic agent will have to be able to remove unwanted DNA on a cell by cell basis, in a mature organism. Such an approach has to be highly sequence-specific and inducible/controllable. TiO2-oligonucleotide nanocomposites developed by our group (Paunesku et al., 2003) are an attempt to develop a universal tool for targeted, sequence-specific removal of “unwanted” DNA (e.g., oncogenes obligatory for cancer maintenance). TiO2-oligonucleotide nanocomposites can be used to recognize any nucleic acid and hybridize with it in a sequence specific way (due to the presence of the oligonucleotide) and cause degradation of the target sequence in a highly localized fashion (due to the presence of the semiconductor), thereby fulfilling the requirements needed for removal of unwanted DNA such as an oncogene etc. We are developing for intracellular use a new type of bio-nanocomposite that has new functional properties inside cells and in vitro. These nanocomposites are composed of metal oxide (TiO2) nanoparticles (4.5 nm in size, surface coated with glycidyl isopropyl ether) conjugated to DNA oligonucleotides via dopamine. TiO2 nanocomposites exhibit semiconducting properties through both constituents (Rajh et al., 2002; Rajh et al., 1999). Exposure of TiO2 to electromagnetic radiation of energy above the band gap of anatase TiO2 (3.2 eV, corresponding to 385 nm) results in charge separation in the nanocomposite. Electrons accumulate in metal oxide. Electropositive holes become trapped in the sugar molecules of the DNA phosphodiester backbone leading to the cleavage of the DNA (Paunesku et al., 2003). This endonuclease activity is: i) excitable by a factor not naturally encountered by the cells in vivo (electromagnetic radiation of energy higher than 3.2 eV); and ii) highly sequence specific-it can be directed toward a single target in a whole genome (due to the high specificity of long oligonucleotide base-pairing). Therefore, the complete titanium dioxide-oligonucleotide nanocomposites act as inducible nucleic acid endonucleases. The data we have generated so far demonstrate that TiO2-oligonucleotide nanocomposites i) conduct restriction endonuclease-like activity, cleaving DNA in a sequence-specific manner, and ii) can be introduced successfully into mammalian cells and retained in specific subcellular compartments (mitochondria, nucleoli). Possible applications of TiO2-oligonucleotide nanocomposites include gene surgery, development of nano-devices for intracellular manipulations and platforms for intracellular structural studies, development of nano-sized diagnostic devices, and highly localized delivery of agents loaded onto the nanocomposites.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]