In vitro permeation of bevacizumab through human sclera: effect of iontophoresis application

Objectives Bevacizumab (Avastin) is a recombinant humanized monoclonal antibody used in ophthalmology (off-label) for the treatment of neovascularization in diseases such as diabetic retinopathy and age-related macular degeneration (wet form). Bevacizumab is currently administrated by repeated intravitreal injection, which can cause severe compli- cations; a non-invasive delivery route is therefore desirable. The passive permeation of bevacizumab through isolated human sclera was evaluated and the iontophoretic technique was explored as a method to enhance its transscleral transport in vitro. Methods Bevacizumab was fluorescently labelled using fluorescein isothiocyanate (FITC). Permeation experiments were conducted for 2 h in Franz-type diffusion cells using human sclera as the barrier. The donor compartment contained FITC-bevacizumab (2.5 mg/ ml) in phosphate-buffered saline at pH 7.4. In the iontophoretic experiments, a current intensity of 2.3 mA (current density 3.8 mA/cm2) was applied. The permeation samples were analysed with a fluorescence detector (excitation and emission wavelengths were 490 and 520 nm, respectively). The stability of FITC-bevacizumab conjugate was checked by thin layer chromatography. Key findings The main finding of this work is that anodal iontophoresis can significantly enhance bevacizumab transport through isolated human sclera (enhancement factor 7.5), even though the drug is essentially uncharged. Due to the relatively constant characteristics of antibodies, these results can probably be extended to other molecules of the same family. Conclusions Preliminary results indicate that anodal iontophoresis could be a promising strategy to non-invasively deliver bevacizumab through the sclera. The presence in the eye of other barriers, both static and dynamic, necessitates further evaluation of the technique on more complex ex-vivo and in-vivo models.