Differences in Uptake and Intracellular Fate between Bevacizumab and Aflibercept after Repetitive Long-Term Treatment in the Retinal Pigment Epithelium

Both bevacizumab and aflibercept display a distinctive time-dependent uptake in the RPE cells and are stored in actin-covered accumulations for extended periods of time. When normalized and quantified, less aflibercept can be found in RPE cells, while more aflibercept is co-localized with Lamp2. Our data suggest that bevacizumab is differently processed by RPE cells than aflibercept.

Experiments were conducted in primary porcine retinal pigment epithelium (RPE) cells in first passage and in ARPE-19 cell line. Cells were treated with 250 µg/mL bevacizumab, aflibercept, or, as a non-VEGF inhibiting antibody, rituximab once a week for 1 day, 7 days, 4, and 12 weeks. Cell survival was evaluated with methyl thiazolyl tetrazolium assay. Uptake and localization of compounds were investigated with immunofluorescence microscopy. Selective intracellular proteins were stained with specific respective primary antibodies; actin cytoskeleton was stained with phalloidin. For quantitative analysis, intracellular signals were normalized to light intensity and exposure time. Intracellular association with lysosomes (Lamp2) and exosomes (CD63) was also quantified. In addition, subcellular fractions (nucleus, plasma, membrane, and cytoskeleton) were generated and analyzed in Western blot.

Weekly treatment up to 12 weeks displayed no toxic effects on RPE cells in any substance tested. Intracellular signal of bevacizumab and aflibercept was strongest after 1 day, decreased after 1 and 4 weeks but increased again after 12 weeks. The signal of intracellular bevacizumab was significantly stronger than of aflibercept. In addition, in primary RPE, aflibercept was significantly more associated with Lamp2, indicating degradation of aflibercept. At all time points, the respective therapeutics could be detected at the cytoskeleton. In primary RPE cells, co-localization with exosome marker CD63 showed a maximum after 1 day for bevacizumab and after 12 weeks for aflibercept. Actin-encapsulated therapeutics can be found at any time point tested.