Upon exposure to Botulinum neurotoxin (BoNT), the toxin enters the body and migrates to motor neurons, internalizes and delivers a protease which inactivates nerve function leading to flaccid paralysis and, in serious cases, death. Once the toxin is inside neurons, antitoxins become ineffective and no therapy exists beyond palliative care. The protease can persist within neurons for many months resulting in long term paralysis. While this is a desirable trait for therapeutic applications, BoNT persistence is problematic when the exposure is accidental or malicious. The Department of Infectious Disease and Global Health is developing biomolecular antidotes for botulism that enter motor neurons and promote the rapid destruction of the intoxicating protease. The antidote strategy has been successfully tested in neuronal cells, and if successful, similar treatments may become possible for diseases caused by some other intracellular pathogens.
The Department of Infectious Disease and Global Health's strategy for botulism antidote development (see Kuo et al) employs camelid antitoxin heavy-chain-only Ab VH (VHH) binding domains that specifically recognize and neutralize intoxicating BoNT proteases. These VHHs are genetically fused to an F-box domain to create a ‘targeted F-box’ or TFB which promotes the rapid degradation of the VHH-bound BoNT protease using the cell’s own natural protein turnover system. Our current research, funded by NIH NIAID grants, is focused on the development of vehicles that will specifically deliver TFBs to BoNT intoxicated motor neurons within a patient. Vehicles being tested include several toxins, such as BoNT itself, which are evolved to have the ability to deliver their cargo into cells. The toxins are modified to eliminate toxicity while retaining the ability to deliver cargo such as a TFB. This research is performed through a NIAID Partnership in Biodefense award in collaboration with Synaptic Research LLC. A second TFB delivery vehicle being tested, in collaboration with Dr. David Curiel at Washington University in St. Louis, are viruses that are modified to eliminate pathogenicity and targeted to infect neuronal cells.