Most of the drug delivery systems approved for marketing are liposomal-or lipid-based formulations or therapeutic molecules linked to polyethylene glycol (PEG) [6, 10, 55, 56] . One such product is PEGylated liposomal doxorubicin, Figure 3 : Diagram of the molecular mechanism of peptide-conjugated liposomes on cancer therapy. These liposomes prolong circulation time in blood and improve pharmacokinetic and biodistribution of their encapsulated drugs. After intravenous administration, liposomes are large enough to be excluded from normal endothelium. In solid tumors, the angiogenic tumor vasculature becomes leakiness that particulate liposomes can extravasate and localize in the tissue interstitial space making it possible for more drug delivering liposomes to accumulate within the tumor by EPR effect. Coupling liposomes with peptides targeted to tumor cells or tumor vasculature further enhances the specificity and accumulation of liposomes in the tumor. On arrival in the tumor tissues, the liposomes are bound and internalized by tumor cells or tumor-associated endothelial cells through receptor-mediated endocytosis, fused with the low pH compartments of the endosomes, and subsequently broken down the liposomes and to release encapsulated drugs into the intracellular space of the cells.