Liposome conjugates

K., Abe, O., and Saito, K. (1987). Antitumor effect of adria-mycin entrapped in liposomes conjugated with anti-human alfa-fetoprotein monoclonal antibody, Cancer Res., 47, 4471-4477. 

Native chemical ligation also can be extended to the conjugation of peptides or proteins to other molecules or surfaces. For instance, Reulen et al. (2007) prepared liposomes that contained cysteine-PEG-phospholipid derivatives and then coupled thioester-modified peptides or proteins to form a protein-liposome conjugate. Using this procedure, approximately 100 molecules of a collagen binding protein could be coupled to the cysteine-containing liposomes. 

The advantage of this approach to liposome conjugation is that the linkage between the lectin complex and the membrane bilayer is noncovalent and reversible. The addition of a saccharide containing the proper sequence or sugar type recognized by the lectin breaks the binding... 

Figure 22.17 Antibody-liposome conjugates may be used as targeting reagents for detection or therapeutic applications. The liposome may be constructed to contain fluorescent molecules for detection purposes or bioactive agents for therapy. The antibody component targets the complex for binding to specific antigenic determinants.

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

Reulen, S.W.A., Brusselaars, W.W.T., Langereis, S., Mulder, W.J.M., Breurken, M., and Merkx, M. (2007) Protein-liposome conjugates using cysteine-lipids and native chemical ligation. Bioconjugate Chem. 18(2), 590-596. 

Figure 14.17. Liposome fluoroimmunoassay depiction, in which antigen-liposome conjugates containing fluorescent dye (concentration quenched) compete with analyte antigen for antibody binding sites, followed by wash and detergent lysis, to release the fluorophore for fluorescence measurement.

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