Table 1 Different types of targeting ligands available

Antibodies

Aminoacids (high molecular weight)

Strong binding affinity; High specificity

High production cost; Large size;

Immunogenicity

Antibody-drug conjugates approved;

NPs with antibodies as targeting ligand in Clinical Trials

(SGT-94)

[24,25,26,27,28,29]

Proteins

Aminoacids (high molecular weight)

High specificity

High production cost;

Large size

In Clinical Trials

(MBP-426, 2B3-101, CALAA-01, 2B3-101)

[30,31,32,33,34]

Peptides

Aminoacids (low molecular weight)

Simple to produce;

Small size;

High affinity

May be cleaved by proteases in circulation

In Clinical Trials

(BT1718, CEND-1)

[35,36,37,38]

Aptamers

Synthetic structural RNA/DNA

High specificity;

Small size;

Customizable for any target

High production cost;

May be cleaved by nucleases in circulation

In pre-clinical development

(Sgc8,

A-10, AS1411, TTA 1)

[39,40,41,42,43,44]

Small Molecules

Chemical elements (carbon, oxygen, sulfur, etc.)

Low production cost;

Small size

Target specificity reduced

In Clinical Trials

(SEL-068, BIND-014)

[23, 45,46,47,48]