Mitochondria Targeting Non-Isocyanate-Based Polyurethane Nanocapsules for Enzyme-Triggered Drug Release

Surface engineering of nanocarriers allows fine-tuning of their interactions with biological organisms, potentially forming the basis of devices for the monitoring of intracellular events or for intracellular drug delivery. In this context, biodegradable nanocarriers or nanocapsules capable of carrying bioactive molecules or drugs into the mitochondrial matrix could offer new capabilities in treating mitochondrial diseases. Nanocapsules with a polymeric backbone that undergoes programmed rupture in response to a specific chemical or enzymatic stimulus with subsequent release of the bioactive molecule or drug at mitochondria would be particularly attractive for this function. With this goal in mind, we have developed biologically benign nanocapsules using polyurethane-based, polymeric backbone that incorporates repetitive ester functionalities. The resulting nanocapsules are found to be highly stable and monodispersed in size. Importantly, a new non-isocyanate route is adapted for the synthesis of these non-isocyanate polyurethane nanocapsules (NIPU). The embedded ester linkages of these capsules' shells have facilitated complete degradation of the polymeric backbone in response to a stimulus provided by an esterase enzyme. Hydrophilic payloads like rhodamine or doxorubicin can be loaded inside these nanocarriers during their synthesis by an interfacial polymerization reaction. The postgrafting of the nanocapsules with phosphonium ion, a mitochondria-targeting receptor functionality, has helped us achieve the site-specific release of the drug. Co-localization experiments with commercial mitotracker green as well as mitotracker deep red confirmed localization of the cargo in mitochondria. Our in vitro studies confirm that specific release of doxorubicin within mitochondria causes higher cytotoxicity and cell death compared to free doxorubicin. Endogenous enzyme triggered nanocapsule rupture and release of the encapsulated dye is also demonstrated in a zebrafish model. The results of this proof-of-concept study illustrate that NIPU nanocarriers can provide a site-specific delivery vehicle and improve the therapeutic efficacy of a drug or be used to produce organelle-specific imaging studies.