Gene Transfer with Multivalent Synthetic Vectors

Development of an ultra-high-performance liquid chromatography-charged aerosol detection/UV method for the quantitation of linear polyethylenimines in oligonucleotide polyplexes

Linear polyethylenimines are polycationic excipients that have found many pharmaceutical applications, including as a delivery vehicle for gene therapy through formation of polyplexes with oligonucleotides. Accurate quantitation of linear polyethylenimines in both starting solution and formulation containing oligonucleotide/polyethylenimine polyplexes is critical. Existing methods using spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry time-of-flight, or nuclear magnetic resonance are either complex or suffer from low selectivity. Here, the development and performance of a simple analytical method is described whereby linear polyethylenimines are resolved by ultra-high-performance liquid chromatography and quantified using either a charged aerosol detector or an ultraviolet detector. For formulated oligonucleotide/polyethylenimine polyplexes, sample preparation through decomplexation/digestion by trifluoroacetic acid was necessary to eliminate separation interference. The method can be used not only to support formulation development but also to monitor the synthesis/purification and characterization of linear polyethylenimines.

Characterization of commercially available and synthesized polyethylenimines for gene delivery

Five new polyethylenimines (PEI) were synthesized by polymerization of aziridine in aqueous solution and compared to several commercially available PEI used for gene transfer. Polymers were characterized by 13C NMR spectroscopy, capillary viscosimetry, potentiometric titration and Cu(II) complex formation to gain insight into structural and functional properties. 13C NMR analysis revealed differences in the extent of branching based on the ratio of primary, secondary and tertiary amino groups. An amino group ratio 1 degrees :2 degrees :3 degrees =1:2:1 was obtained for the synthesized PEI, whereas commercially available PEI generally showed a higher degree of branching (1:1:1). Capillary viscosimetry of aqueous PEI solutions with a sufficient amount of salt gave Mark-Houwink parameters of alpha=0.26 and K(V)=1.00 cm(3)/g for the commercially available polymers. In case of the synthesized polymers, variation of reaction conditions yielded viscosity average molar masses (M(v)) in the range of 8000-24000 g/mol. PEI solutions were investigated by potentiometric titration analysis showing that their buffer capacity was not significantly influenced by molar mass or polymer structure. The pK(a) values (8.18-9.94) and the buffer capacity beta (0.08-0.014 mol/l) were of comparable magnitude. This study highlights the necessity of more detailed characterization methods for PEI used in gene transfer protocols since physico-chemical properties do not reflect the vast differences found in transfection efficiencies.

Co-polymer of histidine and lysine markedly enhances transfection efficiency of liposomes

Development of nonviral delivery systems is progressing toward a transfection efficiency sufficient to affect metabolic and neoplastic diseases in humans. Nevertheless, inadequate transfection efficiency of target cells with current nonviral systems still limits the utility of this therapy. In the current study, we have determined that a co-polymer of histidine and lysine (H-K) enhances the transfection efficiency of liposomes, a leading nonviral system. We found that in the absence of serum, the addition of this polymer increased transfection as much as 10-fold in comparison with the liposome:DNA complex alone. More impressively, the co-polymer in the presence of serum increased transfection efficiency up to 100-fold. Furthermore, in vivo expression of luciferase in a tumor increased 15-fold with the addition of H-K polymer to the liposome:plasmid DNA complexes. Without liposomes, the H-K polymer had little to no effect on transfection efficiency. We anticipate that further modifications of this co-polymer will yield molecules with both increased complexity and transfection efficiency.

Polynucleotide vaccines: potential for inducing immunity in animals

Polynucleotide immunization has been described as the Third Revolution in Vaccinology. Early studies suggest the potential benefits of this form of immunization including: long-lived immunity, a broad-spectrum of immune responses (both cell mediated immunity, and humoral responses) and the simultaneous induction of immunity to a variety of pathogens through the use of multivalent vaccines. Using a murine model, we studied methods to enhance and direct the immune response to polynucleotide vaccines. We demonstrated the ability to modulate the magnitude and direction of the immune response by co-administration of plasmid encoded cytokines and antigen. Also, we clearly demonstrated that the cellular components (cytosolic, membrane-anchored, or extracellular) to which the expressed antigen is delivered determines the types of immune responses induced. Since induction of immunity at mucosal surfaces (route of entry for many pathogens) is critical to prevent infection, various methods of delivering polynucleotide vaccines to mucosal surfaces have been attempted and are described. Expansion of studies in various species, using natural models, should be extremely helpful in demonstrating the universality of this approach to immunization and more importantly, accurately identify parameters that are critical for the development of protective immunity.