Analysis of the sustained release ability of bevacizumab-loaded tetra-PEG gel

Multiple intravitreal injections, which are painful and costly, are often required in the treatment of retinal disorders. Therefore, a novel drug delivery system using hydrogels is currently being evaluated as an alternative. This study aimed to evaluate the ability of tetra-armed polyethylene glycol (tetra-PEG) gel for sustained release in vitro. Bevacizumab-loaded tetra-PEG gel and 5-Carboxyfluorescein N-succinimidyl ester (FAM-NHS)-labeled IgG-loaded tetra-PEG gel were prepared by mixing tetra-PEG with thiol termini (tetra-PEG-SH) solution, maleimide termini (tetra-PEG-MA) solution, and bevacizumab or FAM-NHS labeled IgG. The gels were prepared with three different polymer concentrations of 1.5%, 5%, and 10%, then an in vitro release study performed to assess the sustained release ability of the drug-loaded tetra-PEG gels. High performance liquid chromatography (HPLC) was used to test the structural stability of the bevacizumab released from the tetra-PEG gel. The binding of bevacizumab to tetra-PEG-SH or MA was assessed using SDS-polyacrylamide gel electrophoresis (PAGE). The bioactivity of released bevacizumab was tested using KDR/NFAT-RE HEK293 cells. In addition, in vitro degradation and swelling studies were also performed. The in vitro release analysis showed that the release of bevacizumab was slower in the 5% and 10% tetra-PEG gels than that of 1.5% tetra-PEG gels. Similarly, the release of FAM-NHS-labeled IgG was slowest in the 1.5%, 5%, and 10% tetra-PEG gels, in that order. The 5% and 10% tetra-PEG gels released bevacizumab and FAM-NHS-labeled IgG over a period of 1-2 weeks. Both bevacizumab and FAM-NHS-labeled IgG were not fully released in 2 weeks. HPLC analysis showed that the retention time of the samples released from the bevacizumab-loaded tetra-PEG gel was similar to that of the bevacizumab standard. The SDS-PAGE analysis showed that bevacizumab binds to tetra-PEG-MA. The bioactivity assay test revealed no decrease in the bioactivity of the released bevacizumab. In vitro degradation and swelling studies revealed that 1.5%, 5%, and 10% tetra-PEG gels expanded by approximately 1.4-, 2-, and 3-fold, respectively. Based on the results of the release and swelling tests, 5% tetra-PEG gels are considered good candidates for controlled release systems for therapeutic antibodies such as bevacizumab. The binding of PEG to the therapeutic antibodies may reduce the availability of therapeutic antibodies that can be released.