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Methods for Determining the Parameters of Receptor-Ligand Interactions on the Model of Concanavalin A and Mannosylated Chitosans Promising Carriers for Drug Delivery to Alveolar Macrophages

Abstract-The search for mannosylated molecules forming strong complexes with the model mannose receptor, concanavalin A (ConA), is an important step for the creation of targeted drug carriers. The goal of this work was to develop an accurate and reproducible method for determining the parameters of lectin-ligand interactions to assess the affinity of concanavalin A to chitosan and its mannosylated derivatives. It was shown that the use of UV spectroscopy, as well as fluorescence quenching, makes it possible to determine the parameters of ligand-receptor complexation at reagent concentrations 1-2 orders of magnitude lower than those described in the literature and obtained, including by isothermal calorimetry. UV spectroscopy also opens up the possibility of analyzing a wide range of ligands and makes the process less laborious. Comparative characteristics of the above methods are given. It was proposed to use chitosans as carriers for drug delivery to macrophages due to their biocompatibility, mucoadhesiveness, as well as the ability to reduce the toxicity of antibacterial agents and enhance their absorption by macrophages. Unmodified chitosans bind to ConA relatively weakly (Kd ≈ 10-4 M). With an increase in the molecular weight, the degree of modification of chitosans with mannose, as well as with the introduction of a spermidine spacer into their molecule, the strength of complexation of the carrier with the model mannosylated receptor ConA increases significantly; Kd values are in the range of 10-6-10-7 M, which is almost an order of magnitude lower than for the natural ligand, trimannoside. The effect is achieved due to the high clustering of mannose residues (Man). Taking into account such criteria of drugs as safety and immunogenicity, we believe that among the studied chitosan molecules, a spacer-containing high-mannosylated chitosan polymer with a molecular weight of 5 kDa should be considered the optimal carrier for drug delivery to macrophages.

Key words: mannose receptors, chitosan, concanavalin A, UV spectroscopy, fluorescence quenching, dissociation constant, macrophages