Piggybacking on the Cholera Toxin: Identification of a Toxoid-binding Protein as an Approach for Targeted Delivery of Proteins to Motor Neurons

A significant unmet need exists for the delivery of biologic drugs such as polypeptides or nucleic acids, to the central nervous system (CNS) for the treatment and understanding of neurodegenerative diseases. Naturally occurring toxoids have been considered as tools to meet this need. However, due to the complexity of tethering macromolecular drugs to toxins, and the inherent dangers of working with large quantities of recombinant toxin, no such route has been successfully exploited. Developing a method where toxoid and drug can be assembled immediately prior to in vivo administration has the potential to circumvent some of these issues. Using a phage-display screen, we identified two antibody mimetics, Anti-Cholera Toxoid Affimer (ACTA) -A2 and ACTA-C6 that non-covalently associate with the non-binding face of the cholera toxin B-subunit. In a first step toward the development of a non-viral motor neuron drug-delivery vehicle, we show that Affimers can be selectively delivered to motor neurons in vivo . ### Competing Interest Statement The authors have declared no competing interest. * ACTA : anti-cholera toxoid Affimer ALS : amyotrophic lateral sclerosis CNS : central nervous system CPP : cell-penetrating petides CTB : cholera toxin B-subunit HRP : horse-radish peroxidase ELISA : enzyme-linked immunosorbent assay ALBA : Affimer-lectin binding assay LTB : heat-labile enterotoxin B subunit ITC : isothermal titration calorimetry.