Abstract
Over the years, gene therapy has gained much attention across the field of research. The ability to deliver genes into cells offers the opportunities to treat various human genetic disease which results from mutation or deletion of gene(s). Effective gene delivery is highly dependent on its stability and ability to transfect across cell membrane and interferes with the host DNA. However, DNA is easily susceptible to enzymatic degradation and its large size and highly negatively charged surface are barriers towards successful transfection (1). Therefore, DNA has to be protected from degradation, neutralised and condensed into appropriate size for effective gene delivery. Currently, non-viral vectors are the preferred carrier systems as they are safer, and easier to manufacture. In this research, the use of β and γ-cyclodextrin as non-viral vectors with the incorporation of two different excipients (Pluronic-F127 and folic acid) at different concentrations to stabilise the formulation was investigated. These formulations were characterised in fresh and freeze dried forms. The freeze dried and fresh solutions of DNA were prepared with cyclodextrins (β or γ), folic acid and Pluronic-F127 as excipients in different ratios [(3:3:1, 10:10:1 and 20:10:1) excipient : cyclodextrin : DNA]. The DNA stability in the formulations was tested by determining the stability of DNA against enzymatic degradation (DNase test) using ultraviolet-visible spectroscopy. The degree of DNA inclusion into cyclodextrins was investigated using fluorescence spectroscopy. Fourier Transform Infrared Spectroscopy (FTIR) was employed to study the interaction between DNA and excipients. Scanning Electron Microscope (SEM) was used in observing the surface morphology and uniformity of formed freeze dried particles and thermal behaviour was studied using Differential Scanning Calorimetry (DSC).The formulations were also stored in high humidity (RH=76%) over 5 weeks to access storage stability. In addition, charge measurement was conducted to figure out the transfection efficiency in vivo. It was observed that incorporation of Pluronic-F127 produced the most stable formulations regarding enzymatic degradation, particularly in the freeze dried formulations. These formulations also show high percentage inclusion (>40%). Shift of peaks in FTIR data, appearance of uniform particulate as detected by SEM and changing in the denaturation temperature as demonstrated by DSC data for Pluronic-F127 containing formulations confirms clear interaction between Pluronic-F127 and the cyclodextrin/DNA complex which exhibits positive overall charge. DNA/cyclodextrin formulations containing Pluronic-F127 also showed high stability and protection for the DNA after storage at 76%RH. Overall, it was noted γ-cyclodextrin provide better protection and inclusion compared to β-cyclodextrin. In summary, Pluronic-F127 with β or γ -cyclodextrins is a promising combination to improve stability and delivery of DNA.
Highlights
The ability of gene(s) to treat various human genetic diseases has expanded the field of research over the past few years
F127 or folic acid as excipients has dramatically affected the stability of the gene formulations
The addition of Pluronic®-F127 into the Deoxyribonucleic acid (DNA) formulations improved the overall stability while conflicting results were observed with folic acid containing formulations
Summary
The ability of gene(s) to treat various human genetic diseases has expanded the field of research over the past few years. The concept of gene therapy arose since the late 1960s and early 1970s and this has led to many new developments in the field of genetics. Gene therapy is described as the new age in medicine where application of genetic testing and pharmacogenomics are believed to direct treatment based on each person’s own genetic makeup (Niidome, 2002). It is a suitable substitute for conventional protein therapy because problems such as bioavailability, systemic toxicity, manufacturing cost and in vivo clearance rate can be overcame (Wong et al 2007). The concept of gene therapy looks promising, but current and ongoing clinical trials are unable to prove its efficacy. This is mainly due to challenges associated with safety of delivery systems, specificity of cell targeting, regulation of gene expression and efficiency of gene transfer and the stability of the gene itself (Park et al 2006)
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