Figure 2: Generation of peptide-conjugated liposomes targeting tumor blood vessels. A single lipid bilayer membrane separates an internal aqueous compartment from the external medium. Doxorubicin was encapsulated in the internal compartment. Drug molecules are tightly packed (10,000 to 15,000 molecules per liposome) in a gel phase. Tumor-homing peptide ligands were coupled to NHS-PEG-DSPE [N-hydroxysuccinimido-carboxyl-polyethylene glycol-derived distearoylphosphatidylethanolamine] in a 1 : 1.5 molar ratio [13, 14, 50]. The reaction was completed and confirmed by quantifying the remaining amino groups using TNBS (Trinitrobenzenesulfonate) reagent [51]. Peptidyl-PEG-DSPE was transferred to preformed liposomes after coincubation at a temperature above the transition temperature of the lipid bilayer [52]. There were 500 peptide molecules per liposome [53]. The mean diameter of the targeting liposome is approximately 75 nm [2, 13].