(607g) The Sound of Silence. Multiscale Molecular Simulations and Experiments in Developing Nanocarrier/Nucleic Acid Systems

Although the use of DNA and/or potent, sequence-specific small interfering RNAs (siRNAs) to suppress expression of specific gene transcripts was originally a useful technique for probing gene functions in vitro, their successful application in vivo in animal models against a spectrum of diseases, including cancer, has spurred interest in developing this approach for nucleic acid-based therapeutics. However, there are still significant obstacles to be overcome before these models can be used in the clinic as, for instance, anticancer agents. Perhaps, foremost among these is the issue of delivery. The in vivo use of DNA/siRNA effective against cancer hinges on the availability of a delivery vehicle that can be systematically administered to reach both primary and metastatic tumor cells. Moreover, because sufficient intact, functional genetic material must be delivered into cells to reach an effective intracellular concentration, and to limit potential side effects due to a randomized, general transfection of normal, non-target tissues, it is also crucial to develop means of directing such a delivery vehicle specifically to the target cells. Injected nano-scale drug delivery systems, or nanovectors, are ideal candidates to provide breakthrough solutions to the time-honored problem of optimizing therapeutic index for a treatment. Even modest amounts of progress towards this goal have historically engendered substantial benefits across multiple fields of medicine, with the translability from, for example, a subfield of oncology to a field as distant as the treatment of infectious diseases being granted by the fact that the progresses had a single common denominator in the underlying technological platform. In this study, we combined multiscale molecular simulations and experimental approaches to define mode and molecular requirements of the interaction of nucleic acid-based therapeutics and dendrimer/dendron-based delivery agents. In details, the interaction of DNA and different siRNA sequences were complexed with different type of dendrimeric nanovectors. Their binding processes were characterized by a combination of experimental and molecular simulations techniques, and the effects of siRNA sequences, dendrimer generations, and other molecular parameters such as nanocarrier flexibility upon binding, multivalency effects, microstructure formation and phase diagram, complex stability, transfection ability, and silencing efficiency of these systems were rationalized on the basis of the resulting evidences. This type of investigation can provide valuable information to devise optimal delivery systems that would increase the efficacy of DNA/siRNA therapeutics in cells and laboratory animals and move them toward clinical applications.