Mechanisms of Acquired Resistance to Anti-VEGF Therapy for Neovascular Eye Diseases

PURPOSE. The purpose of this study was to evaluate clinical reports of response-loss in patients with neovascular eye diseases, such as neovascular age-related macular degener-ation (AMD) and diabetic macular edema (DME), after repeated anti-vascular endothelial growth factor (VEGF) therapy. To assess experimental evidence of associations of other angiogenic growth factors and endothelial glycolytic pathways with the diseases and to propose the underlying mechanisms. METHODS. Review of published clinical studies and experimental investigations. RESULTS. Intravitreal injection of anti-VEGF biologic drugs (e.g. bevacizumab, ranibizumab, and aflibercept) is the front-line treatment for neovascular AMD and DME, and acts by halting the progression of excess blood vessel growth and leakage. Despite favorable clinical results, exudation returns in a number of patients after repeated admin-istrations over time. Patients suffering from disease recurrence may have developed an acquired resistance to anti-VEGF therapy. We have analyzed clinical and preclinical find-ings on changes to angiogenic signaling pathways following VEGF-targeted treatment and hypothesize that switching to alternative pathways could potentially bypass VEGF blockade, accounting for development of resistance to anti-VEGF therapy. We have also discussed potential reprogramming of ocular endothelial glycolysis in response to VEGF antagonism and proposed that metabolic adaptations could impair blood-retinal barrier function, counteracting the clinical efficacy of VEGF-targeted therapies and contributing to a decline of response to them. CONCLUSIONS. Future studies of the mechanisms proposed in this review may shed some light on how these adaptations result in the development of acquired resistance to anti-VEGF therapy, which should help discover new therapeutic strategies for overcoming anti-VEGF resistance and improving clinical efficacy.