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Abstract Many intracellular signaling events remain poorly characterized due to a general lack of tools to interfere with “undruggable” targets. Antibodies have the potential to elucidate intracellular mechanisms via targeted disruption of cell signaling cascades because of their ability to bind to a target with high specificity and affinity. However, due to their size and chemical composition, antibodies cannot innately cross the cell membrane, and thus access to the cytosol with these macromolecules has been limited. Herein we describe strategies for accessing the intracellular space with recombinant antibodies mediated by cationic lipid nanoparticles to selectively disrupt intracellular signaling events. Together, our results demonstrate the use of recombinantly produced antibodies, delivered at concentrations of 10 nM, to selectively interfere with signaling driven by a single posttranslational modification. Efficient intracellular delivery of engineered antibodies opens up possibilities for modulation of previously “undruggable” targets, including for potential therapeutic applications. 

Abstract Therapeutic antibodies, due to their high affinity and specificity toward their biological targets, may demonstrate reduced harmful side effects compared with traditional drug moieties. While most of the as‐yet clinically approved antibody therapeutics have targeted extracellular or membrane‐bound domains, the ability to target intracellular antigens with antibodies opens up tremendous opportunities for imaging, diagnosis, and therapeutic applications. Generally, delivery concerns have limited the ability to target intracellular antigens, as many antibodies cannot easily cross the cell membrane due to their size and surface chemistry. Delivery platforms have been explored to address this issue, including physical methods, fusion protein/peptide techniques, and synthetic carrier‐based systems. This review summarizes the progress of carrier‐based intracellular antibody delivery systems employing synthetic lipids, polymers, and inorganic nanomaterials. Antibodies targeting various epitopes have been loaded through adsorption, conjugation, or physical encapsulation strategies. Successful intracellular deliveries have been demonstrated largely through fluorescence imaging using dye‐labeled antibody cargos. Specific synthetic delivery platforms have great potential for ex vivo and in vivo therapeutic applications. Challenges and opportunities are further discussed for material scientists to explore in this research area.