Gene therapy that has purposed as new treatment of incurable diseases including genetic disorders and cancer had receive attention from many researchers.Carriers including therapeutic gene is divided into two kinds, viral vector and non viral vector. Despite numerous trials to develop efficient non viral vector such as plasmid DNA, viral vector remain much more efficient vehicles.Ad-vectors (Ad type 5) are effective viral vector of delivering genes and thus they are used in clinical trials, mostly. Even though adenoviral vector induces neutralizing antibodies, and has short blood circulation half-life of adenovirus, hepatotoxicity and low selective accumulation in the target site, it has shown positive results in several clinical trials.
Despite recent progresses in the development of recombinant Ad particles, several factors present major obstacles for the better clinical application of Ad-mediated gene therapy. Adenovirus is internalized by endocytosis after Ad attachment to a primary adhesion receptor, coxsackievirus and adenovirus receptor(CAR) on the cell membrane via the Ad fiber knob. CAR receptor expression is frequently down-regulated in primary and malignant cancer cells, hampering Ad binding and transgene expression.
For overcome the limitations of adenoviral gene transfer, cationic emulsions were studied as a vehicle to improve adenovirus mediated gene transfer. Adenovirus complexed with of emulsions containing the cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) increased the potency of adenovirus mediated gene transfer efficiency as compared to DOTAP liposomes. Among the various lipid composition of cationic emulsions examined, those containing the iodized oil, Lipiodol, as an inner core and stabilized by DOTAP/cholesterol/1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy(poly- ethylene glycol)-5000 enhanced adenovirus-mediated gene transfer, mostly. Lipiodol-containing emulsions appear to be more strongly associated with adenoviral particles, exhibiting higher complex stability compared to other formulations. They provide additional cellular entry mechanism through caveolae-dependent endocytosis and increased adenovirus entry into cells. Furthermore, adenovirus complexed with emulsion significantly reduced transgene efficiency in the liver following systemic injection. These findings indicate that emulsion complexation may be a promising strategy for overcoming many of the predominant liver accumulation associated with the use of adenoviruses in gene therapy. Additionally, the observation of enhanced transgene efficiency in lung together with decreasedexpression in liver improve that the adenovirus complexed with emulsion may act as a lung-targeting adenovirus gene delivery system.
However, this lipids composition revealed cell toxicity with adv complexed with adenovirus. DOTAP caused cellular toxicity by proton sponge in target cells. For optimizing cationic emulsion composition with less cytotoxicity, amount of DOTAP was reduced and replaced with phospholipids, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Furthermore, Lipiodol oil proved that increased cellular uptake of cationic emulsion complexed with adenovirus increased dose as an inner core of optimized cationic emulsion. This optimized cationic emulsion showed that efficiently enhanced adenovirus-mediated gene transfer while it became low cytotoxicity and stabler in destabilized serum condition than former lipid composition.
Aminoclay, another cationic nanomaterials,introduced improve adv mediated gene transfer efficiency.The third study explored the potential of 3-aminopropyl functionalizedmagnesium phyllosilicate (aminoclay) as a cationic vehicle for improving Ad-mediated gene transfer without inducingcytotoxicity.
Aminoclay complexation produced a dose-dependent increase in Ad-mediated transgene expressionin both Ad infection-sensitive and -refractory cells, thereby greatly lowering the Ad dose required for transgene expression.
Unlike the case for cationic lipids (Lipofectamine) or polymers (Polybrene), the enhancing effect of aminoclaywas not accompanied by significant cytotoxicity regardless of cell lines and it was not observed for nonviral plasmidvectors. Physical characterization studies revealed that nanobiohybrid complexes formed between aminoclay and Ad particlesthrough electrostatic interactions, creating aggregates of Ad particles whose surface was shielded with aminoclaynanosheet oligomers. It appears that aminoclay complexation changes the surface charge of Ad particles from a negativeto a highly positive value and thus increases Ad binding to cellular membranes, thereby providing an additional cellularentry mechanism, namely caveolae-dependent endocytosis. Aminoclay-Ad nanobiohybrids may serve as a next-generationefficient, versatile and biocompatible gene-delivery carrier.