Use of circular dichroism spectroscopy in determining the conformation of a monoclonal antibody prior to its incorporation in an immunoliposome.

Attachment of antibodies to liposomes endows target specificity to liposomes for a certain cell or organ that express the targeted antigenic determinant. These so-called immunoliposomes hold high promise as targeted drug carriers. One approach of immunoliposome preparation involves conjugating antibodies to hydrophobic anchors (e.g. fatty acids or phospholipid molecules) for incorporation into the liposome membrane. Often, these conjugation reactions are harsh and may result in undesirable chemical and structural changes in the antibody molecule. This necessitates confirmation of the target specificity of the derivatized antibody prior to its incorporation into the liposome. Our approach to this problem is to utilize circular dichroism spectroscopy, which can detect subtle structural differences in proteins with high reproducibility and accuracy in relatively short period of time. In addition, circular dichroism is a non-destructive technique. In this study, we demonstrate the ability of circular dichroism to confirm the conformation of a model antibody, HYB-241, conjugated to N-glutarylphosphatidylethanolamine, prior to its mixing with dioleoylphosphatidylethanolamine/dioleoylphosphatidic acid to form a target-sensitive immunoliposome.