Magic™ Anti-Avidin monoclonal antibody, clone N29723FH4

Biotin is well known to be bound with exceptional strength by the avidin class of proteins. This ability comes from a match between the biotin-binding pocket of the protein and the structural elements of biotin, including its ureido and thiolane rings. Here we investigate the solvation shell of biotin in water as revealed by classical force field molecular dynamics with GAFF force field. Snapshots from the classical molecular dynamics were then used to generate microsolvated structures. Details of hydrogen bonding patterns present in these microsolvated structures were studied by symmetry-adapted perturbation theory (SAPT). Interaction energy values for small models of biotin hydrated by 5 or 6 water molecules show that the cooperativity constitutes 15-22% of the total interaction energy and corresponds roughly to formation of one additional hydrogen bond to biotin. The SAPT analysis shows the differences underlying hydrogen bonds of similar strength (with oxygen or sulfur atoms as the hydrogen bond acceptors, and with nitrogen atom playing a dual role of the donor and acceptor).

Oxidized form of avidin, named AvidinOX, provides stable fixation of biotinylated molecules in tissues thus representing a breakthrough in topical treatment of cancer. AvidinOX proved to be a stable receptor for radiolabeled biotin, biotinylated antibodies and cells. In order to expand applicability of the AvidinOX-based delivery platform, in the present study we investigated the possibility to hold biotinylated chemotherapeutics in AvidinOX-treated sites. A novel biotinylated gimatecan-derived camptothecin, coded ST8161AA1, was injected at suboptimal doses into human tumors xenografted in mice alone or pre-complexed to AvidinOX. Significantly higher growth inhibition was observed when the drug was anchored to AvidinOX suggesting the potential utility of this delivery modality for the local treatment of inoperable tumors.