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The role of blood–ocular barrier transporters in retinal drug disposition: an overview

Importance of the field: Delivery of drugs to the retina remains a major challenge which needs to be addressed urgently because retinal disorders are leading causes of visual impairment and significantly affect a patient's quality of life. Systemic drug administration is one possible route for treating retinal disorders; however, retinal transfer of drugs from the circulating blood is strictly regulated by two blood–ocular barrier systems, the blood–aqueous barrier and the blood–retinal barrier. Areas covered in this review: This review summarizes the latest biological research regarding blood–ocular barrier drug transporters. What the reader will gain: The blood–ocular barrier sites and their respective roles in aqueous humor dynamics and retinal homeostasis are briefly presented. The potential impact of ATP-binding cassette (ABC) and solute carrier (SLC) drug transporters, such as ABCB, ABCC, ABCG, SLC7, SLC16, SLC19, SLCO/SLC21A, SLC22A and SLC29 transporters, on the permeability of drugs across the blood–ocular barriers is then illustrated. Take home message: As more information becomes available regarding the blood–ocular barrier transporters, we may be able to design simpler and more effective routes for drug delivery to the retina and, consequently, improve the treatment of retinal diseases.