Table 1: Comparison of recent, improved targeted delivery systems.

NP* type Increase to NT** Decrease to NT*** Efficacy of targeted delivery system BIVs + small molecules + reversible masking 200-fold None Complete elimination of aggressive, orthotopic pancreatic cancers after 5 iv injections administered once a week [9] RTNs with endosomally cleavable PEG 2-fold None 75% reduction in subcutaneous neuroblastoma tumor size after 7 iv injections administered every 48 h [10, 11] MEND + pH-sensitive fusogenic peptide or a cell penetrating peptide + cleavable PEG None 2-fold None reported [12, 13] FRT + cleavable PEG 1-fold None None reported [14] Copolymers + cleavable PEG None None None reported [15] Liposomes + cell penetrating peptide + cleavable PEG 1.3-fold None None reported [16, 17]

*Nanoparticle (NP). **Nontargeted (NT); increased delivery of the targeted NP to the target compared with the corresponding nontargeted formulation. ***Nontargeted (NT); decreased delivery of the targeted NP to the target compared with the corresponding nontargeted formulation.