A quantitative evaluation of the molecular binding affinity between a monoclonal antibody conjugated to a nanoparticle and an antigen by surface plasmon resonance

We have designed a site-specific drug colloidal carrier ultimately for improving pancreatic and lung cancer treatment. It is based on a nanoparticulate drug delivery system that targets tumors overexpressing H-ferritin. A monoclonal antibody, AMB8LK, specifically recognizing H-ferritin was thiolated and conjugated to maleimide-activated polylactide nanoparticles (NPs) resulting in the formation of immunonanoparticles (immunoNPs). The AMB8LK immunoNPs exhibited a mean diameter size of 112 +/- 20 nm and a density of 76 antibody molecules per NP. AMB8LK immunoNPs were evaluated for uptake and binding properties on CAPAN-1 and A-549 cell lines, using confocal microscopy. ImmunoNPs demonstrated specific binding and increased uptake of the desired cells by means of monoclonal antibodies (MAbs), compared to nonconjugated NPs. A lipophilic paclitaxel derivative, paclitaxel palmitate (pcpl), was encapsulated within the various NP formulations, and their cytotoxic effect was evaluated on A-549 cells using MTT assay. Pcpl-loaded AMB8LK immunoNPs showed a significantly increased cytotoxic effect when compared to pcpl solution and pcpl NPs. Surface plasmon resonance (SPR) was used to determine quantitatively the affinity constants of native AMB8LK and AMB8LK immunoNPs to gain insight on the affinity of the MAbs following the conjugation process onto NIPS. The results of the association/dissociation and affinity kinetics of the interaction between H-ferritin and native AMB8LK or AMB8LK immunoNPs revealed similar constant values, showing that the conjugation process of the MAb to the NPs did not alter the intrinsic specificity and affinity of the MAb to the antigen. In conclusion, at the cellular level, AMB8LK immunoNPs may carry drugs to desired overexpressing antigen cells with adequate affinity properties, potentially leading to improved drug therapy and reduced systemic adverse effects. (C) 2009 Elsevier B.V. All rights reserved.