1. Introduction
dystonia, PTD, Clostridium botulinum, upper limb spasticity
DYSTONIA, OVERACTIVE BLADDER, CHRONIC MIGRAINE HEADACHE, BLEPHAROSPASM
Commercial preparations of botulinum toxin type A (BoNTA), generally derived from the Hall strain of Clostridium botulinum, have a variety of therapeutic applications, such as the treatment of cervical dystonia, upper limb spasticity, chronic migraine headaches, overactive bladder, and blepharospasm, and are widely used for aesthetic treatment of facial lines. In these indications, the product is administered via injection directly into striated or smooth muscle or dermis guided by electromyography (EMG) or ultrasound or by reference to surface anatomical landmarks. BoNTA effects are based on their highly specific and well-characterized ability to block cholinergic innervation of striated and smooth muscle, and cholinergic autonomic innervation of exocrine glands. However, as with all macromolecular biotherapeutics, BoNTAs have the potential to be immunogenic and provoke the formation of unwanted anti-drug antibodies [With respect to BoNTA therapeutics, anti-drug antibodies can potentially form to any portion of the protein complex, including the active 150-kDa core neurotoxin [DaxibotulinumtoxinA for Injection (DAXI) is a novel, highly purified BoNTA product formulated with a unique proprietary protein transduction domain (PTD)–containing excipient. Produced following the fermentation of Clostridium botulinum, the neurotoxin undergoes multiple purification steps, including three-column chromatography steps, to minimize the presence of residual bacterial proteins or genetic material and to remove the NAPs, leaving a purified 150-kDa core neurotoxin (daxibotulinumtoxinA). In place of the human serum albumin typically found in commercial BoNTAs, DAXI is stabilized with a novel proprietary peptide excipient (RTP004). RTP004 is a synthetic 5-kDa, 35 amino acid (AA) polypeptide (RKKRRQRRRGKKKKKKKKKKKKKKKGRKKRRQRRR) composed of a 15 AA poly-lysine core with a 9 AA PTD at either end, spaced by a linker amino acid. The PTD is modeled on the sequence first identified in the 100 AA transactivator of transcription (TAT) protein sequence. To our knowledge, DAXI is likely to be the first therapeutic product containing a PTD to be approved by any regulatory agency. RTP004 is highly positively charged and binds non-covalently, but tightly, to the negatively charged core neurotoxin [This article presents a comprehensive evaluation of DAXI’s immunogenicity profile following repeated administration in adults enrolled in the extensive DAXI clinical program for the treatment of glabellar lines. Based on the high degree of purity of DAXI and the low rates of immunogenicity identified with other BoNTA products, we hypothesized the overall degree of antibody formation to DAXI to be very low. Detection and characterization of serum anti-drug antibody responses against both the daxibotulinumtoxinA neurotoxin and the novel excipient peptide RTP004 were performed using validated enzyme-linked immunosorbent assays (ELISAs). Combining data from three phase 3 studies—SAKURA 1, 2, and 3—provided a unique opportunity to evaluate DAXI immunogenicity after multiple treatments in a large population, to evaluate the temporal relationship between treatment and antibody development, and to evaluate whether RTP004 exerted an effect on daxibotulinumtoxinA immunogenicity.