Gene Delivery Using Physical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 88

Figure 3.1 EP cell.

DNA
solution

Electrodes

Target tissue

+ -

wide variety of macromolecules such as proteins, DNA, and drugs can be introduced
into the exposed cells by local electrophoretic effect. EP is one of the most widely
used methods of DNA transfection because of its flexibility and versatility with dif-
ferent cell types, including primary cells from tissue isolates, plant protoplasts, bac-
terial cells, and, most importantly, mammalian and murine eukaryotic culture cells,
which have been shown to be transfected with similar efficiency ( Figure 3.1 ).
The eukaryotic cells are transfected in vitro by EP, using a special cuvette con-
nected to a power supply. The cells and the buffered DNA solution are suspended in
the cuvette, and an electric field is applied to the cells. The process of EP is applied
to multiple cell types with highly efficient, reproducible, and appropriate transient
and stable transfections, as required . The strength of the electric field and the dura-
tion of cell exposure are varied for optimizing the transfection efficiency for every
cell type. The variables influencing the success of EP include state of cell growth
at the time of EP, type of cell to be transfected, amount of transfecting DNA, size
of the capacitor used to store the charge, voltage of the electrical charge delivered
to the cells, and duration of electric field application. The use of dimethylsulphox-
ide (DMSO) in mammalian cells has demonstrated increased EP efficiency of the
DNA [34] .
However, the method also suffers from the disadvantage that it can only be applied
to suspension cells; but this disadvantage has been overcome using a procedure for in
situ EP of cells grown on microporous membranes of polyethylene terephthalate or
polyester [35] .
The transfection efficiency after EP has also been dependent on the electrode
design used in the experiment. With a change in electrode design, change in transfec-
tion efficiency has been observed, probably because of change in the distribution pat-
tern of DNA within the cells. The caliper and meander electrodes have shown slightly
variable DNA transfection in skin, but the meander electrode was found to be more
patient-friendly because it avoids the need to pinch the skin between the calipers [36] .
The plate and needle electrode has been used in EP of the liver and muscles. The plate
electrodes have demonstrated a more uniform electric field, with highly improved
transfection efficiency in small animals, but have been inconsistent in DNA electro-
transfer in large animals because higher electrical fields are required [36] . To over-
come the inability of electrodes to electroporate in large animals, including humans,