ABSTRACT
The properties of the carrier largely influence the fate of the conjugate, and accordingly will differ from those of free drugs given by the same route.
Peptide/protein carriers can be classified as molecules with or without recognition units (e.g. antibodies, lectins, hormones, transferrin), which enable specific binding to cell surface receptor (Figure 43.1). Delivery with homing device equipped carriers are suitable for “active targeting” of entities attached to well defined acceptor/receptor structures at the
cell membrane or in the cytosol. Synthetic macromolecules such as linear or branched chain poly--amino acids, polydepsipeptides and peptide-spacer containing non-peptidic polymers (N-(2-hydroxypropyl)methacrylamide, HPMA) have also been used as soluble drug conjugates for “passive targeting” resulting in altered pharmacokinetics (e.g. accumulation in tumor), decreased non-specific toxicity and immunogenicity. Linkage between bioactive compounds and carrier molecules could combine these components directly or by insertion of a “spacer” unit to facilitate enzymatic release and/or an “intermediate carrier” to increase the number of molecules coupled to the carrier without influencing recognition (Figure 43.2).
