A METHOD TO ATTACH LECTINS TO THE SURFACE OF SPERMINE ALGINATE MICROCAPSULES BASED ON THE AVIDIN-BIOTIN INTERACTION

To serve as model cell or tissue specific drug delivery systems spermi ne alginate capsules were surface modified by attachment of proteins w ith carbohydrate specific binding properties, i.e. lectins. In the fir st of a two step process avidin was covalently bound to the capsule su rfaces using a hydroxy-succinimide catalysed carbodiimide reagent. Sur face bound avidin was quantitated by lysing the capsules in hypertonic phosphate buffered saline (PBS) and measuring the change in absorbanc e at 500 nm in the interaction with 2-(4'hydroxyazobenzene) benzoic ac id. A time course study of the avidin-binding reaction showed avidin s urface concentrations averaged 5.4 nM/cm(2) after 16 h. In the second step avidin-coated capsules were incubated in aqueous solutions of bio tinylated-lectin derivatives. To quantitate lectin uptake, avidin-coat ed capsules were lysed in PBS and titrated to the turbidance endpoint with ten different biotinylated lectins. Lectin surface concentrations ranged from 2.0 to 6.8 nM/cm(2), well below the theoretical limit of 4 biotinylated ligands per molecule of avidin. Individual lectins boun d to capsular surfaces retained their respective ligand specific bindi ng properties as demonstrated by measurement of the selective saturabl e uptake of radiolabeled ligands when incubated with variously lectin coated capsules. The presence of porcine gastric mucin in concentratio ns up to 4% w/v did not inhibit binding of C-14-labelled mannose or ga lactose by concanavalin A-coated capsules.