Figure 1.

Schematic depiction of the drug delivery systems. (a) The previous drug delivery system, where a moderate affinity between DOX and pCD is capable of controlling the rate of release suitable for tumor treatment. (b) Chemical diagram and schematic depiction of DOX modified with an adamantane through a pH-degradable hydrazone linkage. (c and d) The drug delivery system developed in this study, where (c) high affinity AD group attached by pH-cleavable hydrazone bond reduces the rate of background drug release to as little as possible, whereas in (d) the low pH tumor microenvironments, the bond to the AD group is cleaved, restoring it to the moderate affinity, slow release system. (A color version of this figure is available in the online journal.)

DOX: doxorubicin; AD: adamantane; β-CD: β-cyclodextrin