Targeting of MPEG-protected polyamino acid carrier to human E-selectin in vitro

Summary.  Targeted diagnostic agents are expected to have a significant impact in molecular imaging of cell-surface associated markers of proliferation, inflammation and angiogenesis. In this communication, we describe a new class of targeted polyamino acid-based protected graft copolymers (PGC) of poly-(L-lysine) and methyl poly-(ethylene glycol) (PGC) covalently conjugated with a monoclonal antibody fragment, F(ab′)₂. We utilized targeted PGC conjugates as carriers of near-infrared indocyanine fluorophores (Cy5.5) for optical imaging of endothelial cell populations expressing IL-1β inducible proinflammatory marker E-selectin. We compared two conjugation chemistries, involving either introduction of sulfhydryl group to F(ab′)₂, or via direct attachment of the antibody fragment directly to the chemically activated PGC. Both PGC-based targeted agents demonstrated high binding specificity (20–30 fold over non-specific uptake) and were utilized for imaging E-selectin expression on human endothelial cells activated with IL-1β. Received June 29, 2001 Accepted August 8, 2001 Published online August 9, 2002