Improvement of Drug Release from an Aptamer Drug Conjugate Using Reductive-sensitive Linkers for Tumor-targeted Drug Delivery

The selective delivery of small molecule compounds such as Gemcitabine to tumor cells is a promising methodology for enhancing therapeutic efficacy and attenuating the side effects of anticancer drugs. Aptamers are useful as target-directed ligands for tumor-selective drug delivery due to their ability to bind specific proteins. However, the drug must be released from the aptamer after the conjugate is taken up by the cell to exert its pharmacological effect. In this study, we designed and synthesized a conjugate in which a linker cleaved by glutathione, which is highly expressed in tumor cells, was inserted between the aptamer (AS1411) and Gemcitabine. Almost all Gemcitabine was released from the conjugate after 30 min in the presence of 6 mM glutathione. AS1411 is known to bind to nucleolin, which is highly expressed on tumor cells. The cytotoxicity of the AS1411 and Gemcitabine conjugate with a disulfide bond on A549 cells was higher than that of the conjugate without a disulfide bond. Furthermore, the cytotoxicity of the disulfide-linked conjugate of AS1411 and Gemcitabine was higher in A549 cells than in MCF10A cells, which were used as the model of normal cells. These results indicate that disulfide conjugation enhanced the tumor cell-selective cytotoxicity of Gemcitabine with AS1411.