In Vivo Metabolic Tagging and targeting of Long-Circulating Biomembranes - Project Summary The native biomembrane of red blood cells (RBCs) has long been considered an attractive engineering target for drug delivery, immune modulation, hemostasis, vaccination, and many other applications due to the natural abundance, long life-span, and excellent tissue accessibility of RBCs. However, current RBC membrane engineering approaches are only applicable to isolated RBCs under in vitro conditions, and there is a lack of effective methods for in vivo tagging or modification of circulating RBCs under physiological conditions. Here we propose to develop an innovative platform technology for in vivo metabolic tagging of RBC membrane and subsequent targeting of molecular imaging and therapeutic cargos via efficient click chemistry. The proposed work builds upon our preliminary data that RBCs can metabolize unnatural sugars and express chemical tags (e.g., azido groups) in the form of glycoproteins and glycolipids. This finding is somewhat counter-intuitive considering the RBC’s nucleus-free structure and low metabolic activities, but it is not surprising since glycoproteins and glycolipids are essential components of RBC membranes, so there must be some active pathways for metabolism and glyco-synthesis associated with RBCs. We further hypothesize that intravenous administration of unnatural sugars could also result in metabolic labeling of circulating RBCs with chemical tags, which would then allow direct conjugation and targeting of various imaging and therapeutic agents via click chemistry. Thus, the proposed work has three specific aims. In Aim 1, we will elucidate the fundamental mechanisms of metabolic glycan labeling, optimize its efficiency, evaluate the effects of metabolic glycan labeling on RBC structure and functions, and investigate the conjugation efficiency and membrane retention of cargos on chemically tagged RBCs. In Aim 2, we will explore metabolic glycan labeling in vivo, measure the in vivo conjugation efficiency of DBCO-molecules of different sizes to azido-labeled RBCs, and determine in vivo retention of the conjugated molecules. In vivo labeling of RBCs in dogs will also be studied. In Aim 3, we will demonstrate the promise of our membrane labeling and targeting technology to enable (1) long-term magnetic resonance imaging (MRI) with one dose of contrast agent, and (2) enhanced blood circulation and pharmacokinetics of drugs such as insulin. If successful, the proposed tagging technology is expected to have a broad range of biomedical applications including molecular imaging, long-acting drug delivery, and immune modulation.
