Produced by Clostridium botulinum, a gram-positive anaerobic bacterium, the botulinum neurotoxin (BoNT) proteins prevent the release of acetylcholine at the cholinergic ends of the peripheral nerves of the skeletal and autonomic nervous system. This weakens the neuromuscular junction and causes flaccid paralysis of the injected muscles for a period of time. Of the eight toxin subtypes (A through H), only toxins A and B are FDA approved for therapeutic use with BoNT-A the most used.1
Since its initial approval in 1989 for the treatment of blepharospasm and other facial spasms, BoNT-A has evolved into a therapeutic modality for a variety of neurological and non-neurological disorders. BoNT-A has been reported to be effective for the treatment of cervical dystonia, bruxism, tremors, tics, myoclonus, restless legs syndrome, tardive dyskinesia, spasticity, chronic migraines, hypersalivation, spinal cord injuries and a variety of symptoms associated with Parkinson’s disease. Research is ongoing for potential CNS applications in the treatment of neurodegenerative disorders.2
In addition to neurological applications, BoNT-A is also used in aesthetics to relax muscles and smooth the upper facial lines such as glabellar lines, forehead wrinkles and crow’s feet.
Treatments have an onset of a few days with a peak effect two weeks after injection. Although treatment duration is 3-4 months, the effect decreases progressively after 1-2 months necessitating regular injections. This is especially relevant in therapeutics indications. When symptoms reoccur they impact quality of life and the ability to function.
“A key goal is to improve toxin performance, and, notably, to increase the duration,” says Mickael Machicoane, PhD, VP Research at Fastox Pharma. “An easy way to achieve this is to inject higher doses; however, a plateau effect is reached quickly. The increase in duration is not proportional to the injected amount.”
Improvement in Durability
Lausanne-based Fastox has developed a lead candidate, FTP-501, that speeds up onset and allows the treatment to reach a higher response and greater durations of 50%-100% when injected in combination with BoNT-A. Experimental data show that at each time point the response is higher with the combination than with the toxin alone.
Results have been demonstrated in two recognized animal model tests – the digit abduction score (DAS) and the free running wheel – using virtually all BoNT-A formulations. “FTP-501 enhances the key toxins on the market today including Botox®, Dysport®, Xeomin® and Alluzience®, the new liquid toxin in Europe,” says Machicoane.
The typical BoNT-A toxin, which has a slow onset and a moderate duration, is combined with the booster FTP-501, which acts postsynaptically to inhibit the muscle contraction, and potentiate the action of the toxin. “We call this molecule a postsynaptic inhibitor (POSI),” explains Machicoane. “Our patented LAST technology is a new paradigm. To our knowledge, we are the only company doing postsynaptic investigations. Other companies focus on trying to improve the presynaptic behavior with toxin engineering or formulation with less success.”
Mechanism of Action (MOA)
To perform its inhibitory function the BoNT needs to enter the motoneuron. It does so by hijacking the natural exo/endocytic machinery of the neuron, which releases and recycles neurotransmitters in the synaptic cleft. BoNT uses these vesicles as entry doors into the motoneuron.
“The addition of POSI first rapidly blocks the muscle,” says Machicoane. “This blockade is sensed by the motoneuron that gets frustrated because of the absence of response in the muscle and increases its release of neurotransmitters. This increase in exocytosis allows more BoNT to enter the neuron quicker leading to faster onset and longer duration. We plan to enter clinical trials later this year.”
Fastox collaborates with the team of Ornella Rossetto, PhD, associate professor, and Marco Pirazzini, PhD, assistant professor, at the Neuroparalysis and Neuroregeneration Laboratory of the University of Padova. These experts have pioneered the discovery of fundamental mechanisms of clostridium toxins and developed tools to monitor the activity of BoNT within motoneurons that permit the exploration of the MOA of the combination of BoNT with POSI.
It was previously known that BoNT-A toxin performs its inhibitory function by cleaving SNAP-25, a key component for the neuron to release neurotransmitters for signaling to the muscle. This collaborative work has shown that the combination of BoNT-A and POSI enables the cleavage of SNAP-25 inside the neuron more quickly than with the toxin alone.
Currently focusing on FTP-501, their lead candidate, Fastox has a pipeline of other candidates.
Rocka A, Piędel F, Jasielski PP, Piwek M, Petit V, Rejdak K. Botulinum in Selected Neurological Disorders – Review. Journal of Pre-Clinical and Clinical Research 2021, Vol 15, No 4, 176-183.
Anandan, C and Jankovic, J. Botulinum Toxin in Movement Disorders: An Update. Toxins 2021, 13, 42.