Table 1.

Receptor & protein mediated targeting peptides.

Peptides	*Properties	References
Transferrin and anti transferrin antibody	Iron binding proteins found in vertebrates. Enables 2-fold increase in tissue accumulation of non-specific antibody conjugated liposome.	[39,40,60–62]
Herceptin™/Trastuzumab	Antibody against HER2. Showed increased internalization of carrier and a 6-fold increase in internalization.	[50,64,65]
GE11 peptide	Ligand for human epidermal growth factor receptor. Contains the peptide sequence ‘YHWYGYTPQNVI.’	[49,51]
Albumin	Human plasma protein soluble in water. Assists in transporting hydrophobic molecules. Used as a carrier for anticancer therapy.	[12,57,72,147]
HIV TAT peptide	The TAT protein enters cells when added exogenously. The transduction domain responsible for this property is RKKRRQRRR,’ which can be appended to other systems.	[148–150]
NGR peptide	This motif has 2 distinct binding sites 1) Aminopeptidase N (CD13) 2) αvβ3 Integrin. Plays a major role in cell adhesion.	[69,71]
RGD peptide	This motif is a recognized by integrins and is important for cell adhesion.	[66–68,151]
GFLG peptide	Acts as a cleavable peptide linker sensitive to proteolyses by lysosomal cathepsin B.	[73]
ALAL peptide	Acts as a cleavable peptide linker sensitive to proteolyses by lysosomal cathepsin B.	[72]
GPQGaAGQR peptide	Where a = Leucine, Isoleucine or Valine. This peptide sequence acts as a substrate for MMP-2,9 and can be used as a linker/trigger for drug release from polymer conjugates or drug carriers.	[76,79]

^*A=Alanine, F=Phenylalanine, G=Glycine, H=Histidine, I=Isoleucine, K=Lysine, L=Leucine, N=Asparaginine, P=Proline, Q=Glutamine, R=Arginine, T=Theronine, V=Valine, W=Tryptophan Y=Tyrosine.