Designing a Cleavable Cell Surface Protein for Cytotherapy and Drug Delivery Applications

Many cytotherapy applications focus on delivering a therapeutic molecule or nanoparticle to a disease site. One challenging step in this delivery is releasing the therapeutic molecule from the delivery cell upon arrival at the delivery sight. Here a protein is designed and expressed that can bind a biotin-labeled cargo and release that cargo in response to the presence of urokinase plasminogen activator. A gene was designed that coded for a protein that contained a streptavidin domain for binding biotin-labeled cargo, a urokinase cleavage domain for release by urokinase plasminogen activator, and a PLAP domain for cell-surface expression. The utility of the resultant protein was tested with biotin (5-fluorescein) and a biotinylated PLGA nanoparticle to test the performance of the delivery systems with models for small molecule drugs and nanoformulations. When expressed in neural progenitor cells (C17.2), the designed protein was able to bind both the biotin (5-fluorescein) and the biotinylated PLGA nanoparticles and was able to release the biotin (5-fluorescein) in response to urokinase plasminogen activator. This designed, multi-domain protein may prove useful as a method for specifically releasing a cargo from delivery cells at a target site.