Ocular drug delivery is limited both by patient acceptability and by the limited time that the dosage form is retained within the precorneal region. The aim of this investigation was to identify lectin receptors within the precorneal region as potential targets for a lectin containing ocular dosage form, thus facilitating prolonged drug delivery. Initial ex-vivo studies evaluated the binding, after 15 min contact with intact (unfixed) rat corneal and conjunctival epithelia, of a panel of 36 lectins of varying sugar specificities. Tissues were sectioned and examined using light microscopy. Lectin binding was identified using a standard histological procedure involving the avidin-biotin reaction, and the formation of a brown precipitate from a 3,3'-diaminobenzidine tetrahydrochloride (DAB) solution. All lectins were observed to bind to both the cornea and conjunctiva to varying degrees. There was little evidence of a specific receptor or structural type of lectin that particularly favoured binding. The lectins fromSolanum tuberosum(potato) andHelix pomatia(edible snail) which are specific for the terminal sugar residuesN-acetyl-D-glucosamine andN-acetyl-D-galactosamine respectively, appeared to be the most promising and displayed clear visual evidence of binding to ocular tissues after only 10 s contact. The stability of binding of these two lectins was assessed using a video microscopy method of evaluation, and binding in a second species investigated using unfixed porcine cornea. Both lectins were found to show rapid, substantial and stable binding ex-vivo, and these will be taken forward in future work for quantitative in vivo studies and toxicological evaluation.
