A Novel Slow Release Solid Bevacizumab Tissue Tablet Prevents Scarring Following Experimental Glaucoma Filtration Surgery (GFS)

Abstract

Purpose: : Antibodies are increasingly being used for ocular and systemic applications. Administration of bevacizumab following glaucoma filtration surgery (GFS) results in enhanced experimental bleb survival. A major disadvantage is the need for regular administration due to rapid subconjunctival clearance. This results in dose dumping, a sub-optimal therapeutic dose and the need for repeat dosing. Our aims were (i) to develop an antibody-based tissue tablet for use in the subconjunctival space that would remain biologically active while displaying prolonged pharmacokinetics and (ii) to examine the anti-fibrotic effect of the bevacizumab tissue tablet.

Methods: : Bevacizumab (Avastin, Genentech) was incorporated into an implantable solid form as a tissue tablet (3 x 0.8 mm). The in vitro release profile of bevacizumab was measured using a flow rig. The quality of the released-antibody was examined by size exclusion chromatography (SEC), gel electrophoresis, three-dimensional co-culture (fibroblast and endothelial cells), and surface plasmon resonance (SPR). Our in vivo model of GFS (rabbit scarring model) was then used. Groups (n=6) were 1) bevacizumab injection (avastin, 1.25 mg), 2) water sponge, 3) MMC, 4) IgG tissue tablet and 5) bevacizumab tissue tablet (1.25 mg). The clinical examination including IOP measurement was carried out on days 1,4,7,9,12,15,18,21,24,27,30 post operatively.

Results: : Bevacizumab was released from our tissue tablet over a period of approximately 150 hours with near first order kinetics for the first 50 hours. In vitro assays confirmed no protein aggregation or loss of bioactivity. The in vivo study showed a significant increase in bleb survival of the bevacizumab tissue tablet compared with all other groups including MMC. All the tissue tablets dissolved during the 30 day experiment. No capsule formation or foreign body reaction was found in the histology.

Conclusions: : The new solid bevacizumab tissue tablet displayed prolonged release of active antibody in vitro with no significant loss of activity or protein aggregation, and an in vivo study showed a substantially prolonged bleb survival compared to MMC. This novel antibody tissue tablet has the potential to prolong local antibody release and exert a significant biological effect.

Keywords: wound healing • conjunctiva • vascular endothelial growth factor