(409d) Developing Modified Oxalate-Based Doxorubicin (OX-Dox) Prodrugs for Reactive Oxygen Species (ROS) Responsive Drug Delivery

While chemotherapy is a top option for treating metastatic breast cancer, reducing the side effects along with maximizing the therapeutic efficacy remain as major challenges. A prodrug design with a stimulus-responsive linker can address the adverse off-target side effects by deactivating potent but toxic drugs upon conjugation to a linker and reactivating them upon release triggered by a stimulus-response mechanism. Reactive oxygen species (ROS) play a pivotal physiological role in intracellular signaling of any living organism. Due to the elevated levels of ROS in cancerous cells compared to normal cells, an increasing number of ROS-responsive probes and prodrugs have been fabricated in the fight against cancer.

Here, we have developed a modified oxalate-based Doxorubicin (OX-Dox) prodrug by conjugating a benzene ring to one side of the oxalate backbone and a doxorubicin molecule to the other side using an amide bond. Further modification of the functional group on the para position of the benzene ring resulted in a stable but highly specific ROS-responsive OH-OX-Dox prodrug. While the Dox release in PBS was less than 20% within 24 hrs, it was more than 90% after stimulating the production of intracellular ROS by the addition of 50 µM of H₂O₂ and horseradish peroxidase (HRP). An MTS assay result showed that MDA-MB-231 and MDA-MB-468 cells responded to our Dox prodrug in a dose-dependent but less cytotoxic manner compared to free Dox. Also, the addition of L-Buthionine-sulfoximine (BSO), which can enhance the ROS level in cells by inhibiting cellular glutathione (GSH), increased the toxicity of the Dox prodrug towards the aforementioned cell lines that further confirmed the ROS responsiveness of our prodrug. This design has potential to deliver Dox in a sustained manner during systemic circulation at low ROS level while achieving controlled drug release at solid tumor sites at high ROS level.