Do complexing proteins provide mechanical protection for botulinum neurotoxins?

Area of Science:

• Biochemistry
• Pharmacology
• Neuroscience

Background:

• Botulinum toxin (BT) is a complex biological agent used therapeutically.
• Botulinum neurotoxin can be formulated with or without complexing proteins (CPs).
• The role of CPs in the mechanical stability and therapeutic efficacy of BT formulations is not fully understood.

Purpose of the Study:

• To compare the mechanical stability of a CP-containing BT (onabotulinumtoxinA) versus a CP-free BT (incobotulinumtoxinA).
• To investigate whether CPs provide mechanical protection to botulinum neurotoxin.
• To assess the necessity of CPs for the therapeutic application of botulinum toxin.

Main Methods:

• OnabotulinumtoxinA (ONA) and incobotulinumtoxinA (INCO) were reconstituted under conditions with (WS) and without (NS) mechanical stress.
• A novel stress test was employed to generate mechanical stress.
• The potency of both BT formulations under NS and WS was measured using the mouse diaphragm assay, determining paralysis times (PTs).

Main Results:

• Mechanical stress significantly increased the paralysis time (potency) of ONA by 35.0% (p=0.002), indicating inactivation.
• Mechanical stress resulted in a smaller, non-significant increase in the paralysis time of INCO by 13.2% (p=0.129).
• CP-free INCO demonstrated superior mechanical stability compared to CP-containing ONA.

Conclusions:

• Complexing proteins (CPs) do not protect botulinum neurotoxin from mechanical stress-induced inactivation.
• Mechanical stress negatively impacts the potency of CP-containing botulinum toxin formulations.
• The findings support the view that CPs are not essential for the therapeutic use of botulinum toxin.