Controlled activation is a critical component in prodrug development. Herein 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 this approach. In both cases, the payload (doxorubicin or carbon monoxide) was released inside the mitochondrial matrix upon the enrichment-initiated click reaction. Furthermore, mitochondria-targeted delivery yielded substantial augmentation of functional biological and therapeutic effects in vitro and in vivo, as compared to controls that did not result in enrichment. This method is thus a platform for targeted drug delivery amenable to conjugation with a variety of molecules and not limited to cell-surface delivery. Taken together, these two click and release pairs clearly demonstrate the concept of enrichment-triggered drug release and critical feasibility of treating clinically relevant diseases such as acute liver injury and cancer.

This review summarizes recent developments in using bioorthogonal chemistry in prodrug design for the delivery of traditional small molecule- and gasotransmitter-based therapeutics.

Carbon monoxide is an intrinsic signaling molecule with importance on par with that of nitric oxide. During the past decade, pharmacological studies have amply demonstrated the therapeutic potential of carbon monoxide. However, such studies were mostly based on CO inhalation and metal-based CO releasing molecules (CO-RMs). The field is now at the stage that a major effort is needed to develop pharmaceutically acceptable forms of CO for delivery via various routes such as oral, injection, infusion, or topical applications. This review examines the state of the art, discusses existing hurdles to overcome, and proposes developmental strategies necessary to address remaining drug delivery issues.

Prodrugs that release hydrogen sulfide upon esterase-mediated cleavage of an ester group followed by lactonization are described herein. By modifying the ester group and thus its susceptibility to esterase, and structural features critical to the lactonization rate, H2S release rates can be tuned. Such prodrugs directly release hydrogen sulfide without the involvement of perthiol species, which are commonly encountered with existing H2S donors. Additionally, such prodrugs can easily be conjugated to another non-steroidal anti-inflammatory agent, leading to easy synthesis of hybrid prodrugs. As a biological validation of the H2S prodrugs, the anti-inflammatory effects of one such prodrug were examined by studying its ability to inhibit LPS-induced TNF-α production in RAW 264.7 cells. This type of H2S prodrugs shows great potential as both research tools and therapeutic agents.

Abstract:Hydrogen sulfide (H 2 S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to the gasotransmitter family and plays important roles in mammals as a signaling molecule. Many studies have also shown the various therapeutic effects of H 2 S, which include protection against myocardial ischemia injury, cytoprotection against oxidative stress, mediation of neurotransmission, inhibition of insulin signaling, regulation of inflammation, inhibition of the hypoxia-inducible pathway, and dilation of blood vessels. One major challenge in the development of H 2 S-based therapeutics is its delivery. In this manuscript, we assess the various drug delivery strategies in the context of being used research tools and eventual developability as therapeutic agents.