Table 6: Commonly used ligands in drug delivery.

Sl. no.Name of the ligandDefinitionCharacteristics

(1)SugarAny of a class of sweet, soluble, crystalline carbohydrates, white when pureThe specificity of carbohydrate-protein interactions is much larger than that of many other ligand-binding systems, through its great ability to undergo site-specific modification. Use of carbohydrate ligands to target protein receptors at sites of localization, termed “glycotargeting,” exploits the highly specific interactions of endogenous lectins with carbohydrates

(2)Folic acidA water-soluble vitamin, yellowish-orange, (C19 H19 N7 O6) belonging to the B-complex group of vitaminsEmployed as a targeting moiety for anticancer drugs through covalent conjugation to drugs; the folate receptor-α is overexpressed in several human tumors, including ovarian, lung, brain, head and neck, and breast tumors

(3)PeptideNatural or synthetic, short polymer chain compound, containing two or more amino acids linked by the carboxyl group of one amino acid to the amino group of anotherEGF-R peptide ligand (D4: Leu-Ala-Arg-Leu-Leu-Thr) is conjugated with a polyethylene glycol (PEG) lipid, and the lipid moiety of the peptide-PEG-lipid conjugate is inserted into liposome membranes by a postmodification process. D4 peptide-conjugated liposomes bind to and enter cells by endocytosis specifically and efficiently in vitro in a process apparently mediated by EGF-R high-expressing cancer cells (H1299) [20]

(4)AntibodyAn immunoglobulin, a specialized immune protein, generally found in the blood that detects and destroys invaders, like bacteria, and so forth; produced because of the introduction of an antigen into the bodyanti-CEA (Carcinoembryonic Antigen) half-antibody conjugated lipid-polymer hybrid nanoparticles show enhanced cancer killing effect compared to the corresponding nontargeted nanoparticles [21]