C05 • ROS-Sensitive 1,2,3- Diazaborinine Prodrugs for Targeted Chemotherapy
Targeted drug delivery represents a cornerstone of modern pharmaceutical technology, particularly in the field of chemotherapy. Anticancer agents need to be safely transported to their target site and exert their cytotoxic effect only where desired: within tumor tissue. Several sophisticated delivery systems have been proposed to achieve this intricate balance, incorporating either particular active targeting moieties or more indirect stimuli-responsive elements.
In the present project, we propose a modular pharmaceutical delivery design that involves both approaches. Using advanced main-group chemistry synthetic techniques, we will synthesize a structurally diverse library of 1,2,3-diazaborinine prodrugs for the model anticancer agent camptothecin (CPT). When caged, i.e., conjugated to this boron-containing moiety, the drug remains inactive. However, at sufficiently high levels of reactive oxygen species (ROS), CPT is de-caged in a cage-structure-dependent manner, releasing the cytotoxic cargo. Paradoxically, we envision selecting the most stable candidates from this library that will remain inactive at ROS levels relevant for cells, thereby effectively circumventing any systemic toxicity and ensuring drug safety.
Biochemically, caged compounds will then be linked to another module: the arginine-depleting enzyme Aplysia punctata ink toxin (APIT) that locally increases ROS levels (H2O2 ↑) in tumor cells, thereby reaching the conditions necessary for de-caging CPT out of even the most stable prodrugs. Conjugation will be achieved either by direct attachment to lysines or enzymatically, through installing substrate sequences into both modules that allow cross-linking by transglutaminases (TGs). ROS-increasing APIT will finally be engineered to conjugate a model recognition element specific for the oncogenic human epidermal growth factor receptor (HER2).
Our chemical/biochemical pas de deux (APIT ↑ = ROS ↑ = boron de-caging ↑ = safety and efficacy ↑) will then be realized and studied in detail in-vivo, by administering the recombinantly engineered, modularly-designed constructs that incorporate the most promising selection of boron cages from our library. For this purpose, we will analyze the biodistribution and efficacy of conjugates in a zebrafish cancer model. Exchanging CPT in our drug module with a diagnostic chromophore will allow direct imaging of the constructs’ fate in vivo. By further obtaining activation patterns using tandem mass spectrometry, our screening approach will enable us to experimentally gain structure-based insights into the efficacy and safety of 1,2,3-diazaborinine cages. This will also be complemented by their in silico characterization, allowing for a direct correlation of physicochemical cage properties and in vitro measurements with our pharmacodynamic and pharmacokinetic results. Therefore, we will be able to postulate rational design guidelines for optimal boron-based drug cages in our modular delivery system.
