​Echinomycin (quinomycin A) is a peptide antibiotic from the quinoxaline family, which has a DNA bifunctional intercalating activity and an inhibitor of hypoxia-inducible factor (HIF1α). Echinomycin was discovered in 1957 as a potent antitumor agent; however, it was not successful in clinical use due to its low water solubility and short half-life. To revitalize this potent drug, it is important to increase its aqueous solubility and bioavailability. In this study, echinomycin was loaded into PEGylated pH-sensitive liposomes (PEGLippH) and functionalized with anti-nucleolin aptamer (AptNCL) for selective targeting and pH-responsive release of echinomycin into cancer cells. Echinomycin was complexed with γ-cyclodextrin (ECγCD) to enhance its water solubility and then encapsulated into pH-sensitive liposomes (PEGLippH-ECγCD). Then, liposomes were functionalized with AptNCL (AptNCL-PEGLippH-ECγCD) and the …​