Nonviral gene delivery vectors now show good therapeutic potential: however, detailed characterization of the composition and macromolecular organization of such particles remains a challenge. This paper describes experiments to elucidate the structure of a ternary, targeted, lipopolyplex synthetic vector, the LID complex. This consists of a lipid component, Lipofectin (L) (1:1 DOTMA:DOPE), plasmid DNA (D), and a dual-function, cationic peptide component (I) containing DNA condensation and integrin-targeting sequences. Fluorophore-labeled lipid, peptide, and DNA components were used to formulate the vector, and the stoichiometry of the particles was established by fluorescence correlation spectroscopy (FCS). The size of the complex was measured by FCS, and the sizes of LID, L, LD, and ID complexes were measured by dynamic light scattering (DLS). Fluorescence quenching experiments and freeze-fracture electron microscopy were then used to demonstrate the arrangement of the lipid, peptide, and DNA components within the complex. These experiments showed that the cationic portion of the peptide, I, interacts with the plasmid DNA, resulting in a tightly condensed DNA-peptide inner core; this is surrounded by a disordered lipid layer, from which the integrin-targeting sequence of the peptide partially protrudes.

Improving the buffer and serum stability of non‐viral gene delivery vectors, and increasing their circulation time in vivo, is an important focus of current research in gene therapy. The most successful strategies to date have involved shielding the complexes with large polydisperse PEG adducts. However, this approach is accompanied by a fall in transfection efficiency. In this paper we describe the solid‐phase synthesis of a series of bifunctional peptides bearing short PEG spacers of defined structure as components of lipopolyplex gene delivery vectors. Short, high‐yielding routes to a series of PEG‐amino acids are described: these PEG‐amino acids can be used in varying combinations to afford bifunctional peptides with varying lengths of PEG spacers by using standard solid‐phase synthesis techniques. A series of lipopolyplexes were formulated using these bifunctional peptides, and their transfection properties assessed. Dynamic light scattering measurements on the complex with the best transfection properties showed that in phosphate‐buffered saline this complex was considerably more stable, and aggregated more slowly, than a complex formulated using a similar peptide lacking the short PEG spacer.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Concerns with insertional mutagenesis for retrovirus and immunogenicity for adenovirus have motivated research into development of non-viral vectors that can safely deliver desired gene constructs to target cells in tissues and organs. Many non-viral vectors suffer from unacceptably poor in vivo cell transfection and low transgene expression. Evidence suggests that cell transfection is linked to particle size - vector particles below about 200 nm are considered desirable. Experimental measurements indicate, however, that vector particles are susceptible to significant aggregation under most conditions of pH and ionic strength, including physiological conditions, although there are currently no means of predicting the kinetics of aggregation. The present paper addresses this challenge by presenting a mathematical framework based on the Monte Carlo simulation techniques for modelling the dynamics of aggregation. The approach is used to simulate the evolution of particle-size distribution for an integrin-targeting lipid-peptide-DNA vector system in buffers of different pH and ionic strength. The simulations required two input parameters, including the initial-size distribution of the particles and a fitting parameter (alpha). Comparison of simulations with experimental data showed that alpha was closely related to the zeta potential of the particles in the buffer medium, making simulations fully predictive. The modelling approach may be used in other vector systems.