On-Demand Drug Release from Click-Refillable Drug Depots.

Stimuli-responsive, on-demand release of drugs from drug-eluting depots could transform the treatment of many local diseases, providing intricate control over local dosing. However, conventional on-demand drug release approaches rely on locally implanted drug depots, which become spent over time and cannot be refilled or reused without invasive procedures. New strategies to noninvasively refill drug-eluting depots followed by on-demand release could transform clinical therapy. Here we report an on-demand drug delivery paradigm that combines bioorthogonal click chemistry to locally enrich protodrugs at a prelabeled site and light-triggered drug release at the target tissue. This approach begins with introduction of the targetable depot through local injection of chemically reactive azide groups that anchor to the extracellular matrix. The anchored azide groups then capture blood-circulating protodrugs through bioorthogonal click chemistry. After local capture and retention, active drugs can be released through external light irradiation. In this report, a photoresponsive protodrug was constructed consisting of the chemotherapeutic doxorubicin (Dox), conjugated to dibenzocyclooctyne (DBCO) through a photocleavable ortho-nitrobenzyl linker. The protodrug exhibited excellent on-demand light-triggered Dox release properties and light-mediated in vitro cytotoxicity in U87 glioblastoma cell lines. Furthermore, in a live animal setting, azide depots formed in mice through intradermal injection of activated azide-NHS esters. After i.v. administration, the protodrug was captured by the azide depots with intricate local specificity, which could be increased with multiple refills. Finally, doxorubicin could be released from the depot upon light irradiation. Multiple rounds of depot refilling and light-mediated release of active drug were accomplished, indicating that this system has the potential for multiple rounds of treatment. Taken together, these in vitro and in vivo proof of concept studies establish a novel method for in vivo targeting and on-demand delivery of cytotoxic drugs at target tissues.