Dendrimer-mediated transfection

Kukowska-Latallo JF, Chen C, Eichman J, et al. Enhancement of dendrimer-mediated transfection using synthetic lung surfactant exosurf neonatal in vitro. Biochem Biophys Res Commun 1999 264(1) 253—261. 

Fig. 3. Comparison of transfection efficiencies obtained using PolyFect Reagent, a dendrimer-based transfection reagent, and a calcium phosphate-mediated procedure. COS-7 and HeLa cells were transfected in srx-weU plates with a /3-galactosidase expression plasmid using the appropriate protocol. For the calcium phosphate-mediated transfection, 6 pg of plasmid DNA was used and the medium was changed after 5 h incubation. Transfections were performed in triplicate, and transfection efficiency was measured by monitoring the /3-galactosidase activity of extracts obtained from the transfected cells. The amoimt of /3-galactosidase activity in the extracts correlates with the transfection efficiency. Cells were harvested 48 h post-trans-fection...

This increase has two-fold implications. First, it implies that the fractured dendrimer is more flexible than the intact dendrimer and second, that the fractured dendrimer may expand due to an increase in positive charge at lower pH, a quantity that was described as essential for PEI mediated transfection. Indeed, when branched PEI was subjected to the same set of experiments, the same three-fold increase in viscosity was observed, lending support to the idea that PAMAM dendrimers act as proton sponges. Evidence of lysosomal buffering capability of PAMAM dendrimers was shown by Kukowska-Latallo et al. (1996) when they observed that the efficiency of G5-EDA dendrimers was enhanced by the addition of chloroquine, while the same molecule could not enhance transfection of G10-EDA dendrimers, which contain 40-fold more surface amine groups for proton absorption. 

The structure of cationic lipids and polymers is readily amenable to chemical modification [35, 36] allowing the exploration of a virtually unlimited number of combinations and strategies at the mercy of chemists creative abilities. Various reviews have been focused on cationic lipids, dendrimers and polymers in terms of their chemical structures and their transfection properties [36—41], in an attempt to shed some light on the chemical requirements necessary to mediate gene delivery. The focus of this chapter will be to explore these carriers from a synthetic perspective, with a description of the chemical strategies used for the preparation via synthetic organic chemistry (excluding polymer synthesis) of cationic lipids and dendrimers. 

To date, a variety of methods have been developed for the efficient delivery of QDs into cells [204, 205]. These include nonspecific endocytosis [206-209] or receptor-mediated endocytosis that involves QDs decorated with transfection reagents (peptides [210-215], proteins [65, 216-219], cationic liposomes [204], dendrimers [204], polymers [220,221] or small molecules [222,223]) that were used for the intracellular delivery of QDs. Physical techniques such as, electroporation [204, 224] or microinjection [204, 225, 226] have also been employed to deliver QDs into cells. 

Szoka and Haensler investigated the application of PAMAM dendrimers as non-viral vectors for in vitro gene transfer. Their study demonstrated that complexes consisting of G5 PAMAM dendrimers and DNA expression plasmids enhanced transfection efficiency over naked plasmid DNA in many cells, particularly cell lines derived from monkey and human neoplasms. PAMAM cascade polymers mediate efficient transfection of cells in culture. The efficiency of intact dendrimers as synthetic vectors for the delivery of genetic material into cells has also been demonstrated. 

Three generations of peptoid-based dendrimers were synthesized by Diaz-Mochon et al. (2008) through solid-phase methods, using N-Fmoc-N-(6-N -Fmoc-aminohexyl)-glycine as both the initiator core and the monomer unit. It offers an unusual dendrimeric periphery composed of both secondary and primary amines. The third generation compound (dendrimer) proved to be an efficient mediator of transfection while displaying minimal cytotoxicity... 

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