Enrichment-triggered prodrug activation demonstrated through mitochondria-targeted delivery of doxorubicin and carbon monoxide

Controlled activation is a critical component in prodrug development. Here we report a concentration-sensitive platform approach for bioorthogonal prodrug activation by taking advantage of reaction kinetics. Using two ‘click and release’ systems, we demonstrate enrichment and prodrug activation specifically in mitochondria to demonstrate the principle of the approach. In both cases, the payload (doxorubicin or carbon monoxide) was released inside the mitochondrial matrix following the enrichment-initiated click reaction. Furthermore, mitochondria-targeted delivery yielded substantial augmentation of functional biological and therapeutic effects in vitro and in vivo when compared to controls, which did not result in enrichment. This method is thus a platform for targeted drug delivery that is amenable to conjugation with a variety of molecules and is not limited to cell-surface delivery. Taken together, these two 'click and release' pairs clearly demonstrate the concept of enrichment-triggered drug release and the critical feasibility of treating clinically relevant diseases such as acute liver injury and cancer. A new concept for targeted drug delivery based on enrichment triggered prodrug activation has been developed. Without enrichment, the activation reaction is sluggish; however, following enrichment, the increased concentration enhances the activation reaction rate, thereby leading to the release of the payload. The same approach can be used in antibody–drug conjugate applications.