Drug release and cell penetration of the drug/ONB conjugates. (A) The drug release profile of Dox from Dox/ONB conjugates. (B) Cell penetration of the Dox + ONB mixture in MDA-MB-231 cells. Various lipid ratios (1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG-2000-Amine), and DSPE-PEG-2000-Biotin) were used to synthesize ONBs to assess their penetration effect, and were evaluated using the fluorescence intensity of Dox. (C) Cell penetration of FITC-conjugated ONBs in MDA-MB-231 cells evaluated using the fluorescence intensity of fluorescein (FITC) (D) Cell penetration of Dox/ONB was evaluated and compared to those of Dox only and Dox + ONB mixture in MDA-MB-231 cells. ** indicates p-value < 0.01, *** indicates p-value < 0.001, and **** indicates p-value < 0.0001. ns: no significant difference.