The recent discovery of genes that play a role in the development of life-threatening diseases, including cancer and certain viral infections has significantly stimulated the research into new treatment options based on genes and recently also "small interfering" RNAs (siRNAs). Genes and siRNAs have a great therapeutic potential, but when after administration to patients they are unable to reach the desired cells and cannot penetrate into these cells the likelihood of a therapeutic effect is nil. The development of genes and siRNA as a new class of drugs depends therefore on the availability of safe and effective delivery systems for therapeutic nucleic acids. The in vitro evaluation and development of new non-viral gene delivery systems and siRNA's since 1997 is a major theme within the research of the Ghent promoters. This in vitro study is in a stage where information about the in vivo behavior of the nucleic acid delivery systems containing therapeutic genes or siRNA needs to be evaluated. This brings us to the goal of this research project being the in vivo evaluation of promising therapeutic genes developed within the research of the Ghent promoters. The evaluation is performed in vivo using imaging techniques (MicroSPECT and BLI) in collaboration with the VUB team.