Adenovirus-Mediated Suicide Gene Transduction: Feasibility in Lens Epithelium and in Prevention of Posterior Capsule Opacification in Rabbits

Abstract

The most common complication of cataract surgery is the development of posterior capsule opacification (PCO). Hyperplasia of the lens epithelium is one of the main cellular events following phacoemulsification, and has been found to be an important feature contributing to opacification of the posterior capsule. Adenoviral vector-mediated transfer is a suitable method for transducing the herpes simplex virus thymidine kinase gene (HSV-tk) into proliferating cells, allowing for the selective killing of these cells by ganciclovir (GCV) treatment. To determine the potential of gene transduction for lens epithelial cells, we studied the transduction of rabbit lens epithelial cells with adenoviral vectors containing either the Escherichia coli beta-galactosidase (lacZ) gene or the HSV-tk gene in vitro and in vivo in an experimental model of PCO. The efficiency of lacZ gene transfer in rabbit lens epithelial cells was at least 95% both in vitro and in vivo. In vivo transduction with HSV-tk adenoviral vector followed by GCV treatment significantly inhibited the development of PCO (p<0.001). These results suggest that adenoviral vector-mediated transfer of HSV-tk into the proliferating lens epithelial cells is feasible and may provide a novel therapeutic strategy for PCO.

Prevention of posterior capsule opacification by the induction of therapeutic apoptosis of residual lens cells

“…9 Four vectors were constructed ( Figure 1b) expressing proteins involved in three apoptotic pathways: activation of the caspase pathway through the activation of members of the TNF-R family (AdTRAIL, AdCaspase-3), release of apoptotic molecules such as cytochrome c into the cytosol (mitochondrial pathway) (AdBax and AdCaspase 3), and the p53 pathway (Adp53). We hypothesized that manipulation of any of these three steps of the apoptotic pathway by gene therapy may result in induction of therapeutic apoptosis of residual lens cells and prevention of PCO in vivo.…”

“…Considering that PCO develops from residual lens cells and that this cell proliferation process can be observed immediately post surgery, we reported previously that it was possible to lower the incidence of PCO by killing lens cells using GCV after transduction with an Ad vector encoding HSV-tk. 8,9 This provided the first proof-of-concept study on the use of gene transfer as a potential treatment for PCO. However, as mentioned, there are clinical drawbacks.…”

“…Ad vectors were chosen because they can transduce 100% of lens cells in vitro and in vivo, 9 and there is essentially no insertion of the vector into the host genome (epigenomic). Ad vectors encoding the proapoptotic genes were used in vitro (rabbit lens cells), ex vivo (human lens cells from capsular bag), or in vivo (rabbit model of phacoemulsification).…”

“…Secondary cataract was evaluated after pupil dilatation using a slit lamp biomicroscope, and an operating microscope. The evaluation of secondary cataract was quantified considering the surface of the regenerated opacified area according to Gwon et al 26 We used a scoring system ranging from 0 to IV, as described previously 9 and shown in Figure 4a.…”

“…[5][6][7] The prototype for this approach is herpes simplex virus 1 thymidine kinase (HSV-tk), which converts the dideoxynucleoside prodrug ganciclovir (GCV) into its phosphorylated form, leading to DNA chain termination and cell death. We previously demonstrated the efficacy of this suicide gene to prevent PCO in a rabbit model 8,9 but there are three major weaknesses for its clinical use: (i) the need for repeated intraocular injections of GCV, which reduces the possibility of treating patients, (ii) a significant although partial efficacy (probably due to the fact that not all of the residual epithelial cells divide immediately after phacoemulsification), and (iii) toxic side effects due to a high concentration of GCV. We thus suggested that this strategy could be improved by using an apoptosis inducer gene to remove the residual lens epithelial cells.…”