ANTIBODIES AS TARGETING MOIETIES - AFFINITY MEASUREMENTS CONJUGATION CHEMISTRY AND APPLICATIONS IN IMMUNOLIPOSOMES

Monoclonal antibodies are finding increasing use in medical imaging, t herapeutics and targeted-drug delivery. Applications in drug-delivery systems involve coupling the intact IgG or its fragments to drug carri ers such as water-soluble polymers or lipid vesicles. As with the deve lopment of other new products, we believe that it is important to moni tor the activity and stability of the antibody during modification ste ps. However, these issues are often woefully neglected. In this articl e, we use immunoliposomes as a vehicle for examining affinity determin ation methods and conjugation chemistry. During the early development phase of a new drug delivery system, it is often advantageous to use a well-characterized monoclonal antibody instead of the clinically-rele vant antibody. Our favorite model system is a family of antibodies whi ch bind fluorescein. This is because fluorescein's emission spectra ch anges significantly upon binding to the antibody, which allows facile determination of antigen-binding affinity. We also describe how to use antigen-mimicking peptides to measure the affinities of clinically-re levant antibodies during later phases of development. With regard to i mmunoliposomes, we describe a novel procedure for conjugating poly(eth ylene glycol) to lipid vesicles in order to prolong their circulation half-line. Our strategy is to conjugate both antigen-binding fragments and poly(ethylene glycol) chains to pre-formed vesicles via anchor li pids in the outer leaflet.