Liposomal vectors

Filion, M.C., and Philips, N.C., Toxicity and immunomodulatory activity of liposomal vectors formulated with cationic lipids toward immune effector cells, Biochimica et Biophysica Acta, 1997, 1329, 345-356. 

Once assimilated by the cell, the exogenous nucleic acid must now travel/be delivered to the nucleus. In some cases, the mechanism by which this transfer occurs is understood, at least in part (e.g. in the case of retroviral vectors). In other cases (e.g. use of liposome vectors or naked DNA), this process is less well understood. At a practical level, gene therapy protocols may entail one of three different strategies (Figure 14.3). 

Peptides can also help overcome the most significant drawback to using liposome vectors when compared to viral vectors, which is lower transfection efficiency. Additional benefits include promotion of compaction, assisting cellular uptake of the DNA. Even peptides derived from viruses themselves can be used to compensate this deficit (e.g., adenovirus p protein and the HIV TAT). 

Several vectors have been used in an attempt to deliver the cf gene to the airway epithelial cells of sufferers. The most notable systems include adenoviruses and cationic liposomes. Vector delivery to the target cells can be achieved directly by aerosol technology. Delivery of cftr cDNA to airway epithelial cells (and subsequent gene expression) has been demonstrated with the use of both vector types. However, in order to be of therapeutic benefit, it is essential that 5-10% of the target cell population receive and express the cftr gene. This level of integration has not been... 

Reddy, J.A., Dean, D., Kennedy, M.D. and Low, P.S. (1999) Optimization of folate-conjugated liposomal vectors for folate receptor-mediated gene therapy. J. Pharm. Sci., 88, 1112-1118. 

The first human gene therapy trial using cationic liposomes was conducted in 1992 (Huang et al. 1999). The trial used 3t)(/V-(/V, /V -dimethylaminoethane)-carbamoyl) cholesterol (DC-chol)/DOPE cationic liposomes to deliver the transgene of interest. Currently 13% of gene therapy trials in progress worldwide employ nonviral liposomal vectors for transgene delivery [30]. 

Cationic liposomes composed of 3(3- [ N- (N N-dimethylaminoethane (carbamoyl] cholesterol (DC-Chol) and dioleoylphosphatidylethanolamine (DOPE) (DC-Chol/DOPE liposome, molar ratio, 1 1 or 3 2) prepared by the dry-film method have been often used as non-vtral gene delivery vectors. We have shown that a more efficient transfection in medium with serum was achieved using DC-Chol/DOPE liposomes (molar ratio, 1 2) than those (3 2), and preparation method by a modified ethanol injection than the dry-film. The most efficient DC-Chol/DOPE liposome for gene transfer was molar ratio (1 2) and prepared by a modified ethanol injection method. The enhanced transfection is related to an increase in the release of DNA in the cytoplasm by the large lipoplex during incubation in opti-MEM 1 reduced-serum medium (optiMEM), not to an increased cellular association with the lipoplex. Cationic liposomes rich in DOPE prepared by a modified ethanol injection method will help to improve the efficacy of liposome vector systems for gene delivery. 

Hydroxyethylated cationic cholesterol derivatives in liposome vectors promote gene expression in the lung. Int J Pharm. 354 196-203 doi 10.1016/j.ijpharm.2007.10.051... 

Li W, Ishida T, Tachibana R, Almofti MR, Wang X, Kiwada H (2004) Cell type-specific gene expression, mediated by TFL-3, a cationic liposomal vector, is controlled by a posttranscription process of delivered plasmid DNA. Int J Pharm 276 67-74... 

Currently, transport of exogenous DNA to cells can be achieved using viral and nonviral vectors or as naked DNA. The simplest nonviral gene delivery system simply uses naked DNA. The overall level of expression is much lower with naked DNA than with either viral or liposomal vectors. Naked DNA is also unsuitable for systemic administration due to the presence of serum nucleases. 

Ramesh R, Saeki T, Templeton NS, et al. Successful treatment ofprimaiy and disseminated human lung cancers by systemic delivery of tumor suppressor genes using an improved liposome vector. Mol Ther 2001 3 337-350. 

Cationic liposomes complexed with plasmid DNA encoding for cystic fibrosis transmembrane conductance regulator (CFTR) have been administered to nasal epithelium and to airways of patients with mild cystic fibrosis (76,95-97). However, only low levels of gene expression or activity were detected. Moreover, administration of the vectors provoked local and systemic inflammatory responses in several patients (76,96). It is not known whether the inflammatory environment in the CF airways degraded or inactivated the liposomal vectors. 

Sputum from CF patients has been demonstrated to inhibit cationic liposomal vector-mediated transfection of cultured cells and cultured sheep trachea (2,5). There has been little study of airway administration of polyplexes to more acutely injured lungs. 

IV vector administration is more likely to be itseful for diseases affecting the pulmortary vascular endothelium such as pulmonary hypertension (66). The endothelium may also be a good locus for transgene- mediated expression of soluble mediators for use in acute luttg injury. However, this has been less well explored (66). The only two vectors that have received significant study for targeting limg after IV delivery ate the adenoviral and eationic liposomal vectors. 

The use of perflubron and other PFC liquids during vector administration has been demonstrated to enhance adenovirus-mediated gene expression in intubated, ventilated rabbits and adenovirus, AAV-2, and cationic liposomal vector-... 

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