Dendrimers as Delivery Systems in Gene Silencing Studies I. Waczulíková *1 , M. Bryszewska 2 , B. Klajnert 2 , R. Gomez-Ramirez 3 , J. de la Mata 3 , M. Ionov 2 , Z. Garaiová 1 , D. Wróbel 2 , T. Hianik 1 1 Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dol. F1, 842 48, Bratislava, Slovakia 2 Department of General Biophysics, University of Lodz, Banacha 12/16, 90-237, Lodz, Poland 3 Departamento Química Inorgánica, Universidad de Alcalá de Henares, CIBER-BBN Alcalá de Henares, Spain Abstract: RNA interference (RNAi) is a natural defence pathway in a variety of species, which leads to the posttranscriptional gene silencing - degradation of target messenger RNAs in a gene-dependent manner. This phenomenon has been employed to manipulate gene expression by introduction of small interfering RNA (siRNA) into the cell. Researchers are now developing RNAi-based interventions for the prevention and treatment of human diseases such as viral infection, tumors and metabolic disorders. However, RNAi-based drugs require usage of efficient carriers to permit the genetic material to cross the plasma membranes of target cells. In this review, we will define key terms of this breakthrough technology and mention some prerequisites of the RNAi-based therapy that must be fulfilled for this treatment to work. We will also point at some unique properties of dendrimers as carriers for targeting nucleic-acid materials and introduce carbosilane dendrimers that are currently being studied by our research team. Keywords: Dendrimers, Carriers, RNA interference, Gene therapy, Biomembranes *Corresponding author: waczulikova@fmph.uniba.sk (I. Waczulikova) 1. Introduction Nano-sized particles exhibit unique chemical, biological, electrical and mechanical prop- erties. Recently much attention has been devoted toward using nanotechnologies for medi- cal application (nanomedicine), since there is a growing evidence that nanomedicine has the potential to cure diseases and repair tissues by manipulating individual cells at the mo- lecular level. An experimental way of using nanotechnologies to treat or prevent disease is a gene therapy approach. The gene therapy is mostly aimed at replacing an abnormal dis- ease-causing gene or inactivating a mutated gene that is not working properly (or at activat- ing a gene that should work but it does not). The method requires using a carrier called a vector in order to bring the new gene into the body’s cells [1]. Acta Physica Universitatis Comenianae Vol. LII (2011) 3-8