A botulinum toxin–derived targeted secretion inhibitor downregulates the GH/IGF1 axis
Emmanuel Somm, … , Richard Jones, Michel L. Aubert
Emmanuel Somm, … , Richard Jones, Michel L. Aubert
Published August 1, 2012
Citation Information: J Clin Invest. 2012;122(9):3295-3306. https://doi.org/10.1172/JCI63232.
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Research Article Endocrinology

A botulinum toxin–derived targeted secretion inhibitor downregulates the GH/IGF1 axis

Abstract

Botulinum neurotoxins (BoNTs) are zinc endopeptidases that block release of the neurotransmitter acetylcholine in neuromuscular synapses through cleavage of soluble N-ethylmaleimide-sensitive fusion (NSF) attachment protein receptor (SNARE) proteins, which promote fusion of synaptic vesicles to the plasma membrane. We designed and tested a BoNT-derived targeted secretion inhibitor (TSI) targeting pituitary somatotroph cells to suppress growth hormone (GH) secretion and treat acromegaly. This recombinant protein, called SXN101742, contains a modified GH-releasing hormone (GHRH) domain and the endopeptidase domain of botulinum toxin serotype D (GHRH-LHN/D, where HN/D indicates endopeptidase and translocation domain type D). In vitro, SXN101742 targeted the GHRH receptor and depleted a SNARE protein involved in GH exocytosis, vesicle-associated membrane protein 2 (VAMP2). In vivo, administering SXN101742 to growing rats produced a dose-dependent inhibition of GH synthesis, storage, and secretion. Consequently, hepatic IGF1 production and resultant circulating IGF1 levels were reduced. Accordingly, body weight, body length, organ weight, and bone mass acquisition were all decreased, reflecting the biological impact of SXN101742 on the GH/IGF1 axis. An inactivating 2–amino acid substitution within the zinc coordination site of the endopeptidase domain completely abolished SXN101742 inhibitory actions on GH and IGF1. Thus, genetically reengineered BoNTs can be targeted to nonneural cells to selectively inhibit hormone secretion, representing a new approach to treating hormonal excess.

Authors

Emmanuel Somm, Nicolas Bonnet, Alberto Martinez, Philip M.H. Marks, Verity A. Cadd, Mark Elliott, Audrey Toulotte, Serge L. Ferrari, René Rizzoli, Petra S. Hüppi, Elaine Harper, Shlomo Melmed, Richard Jones, Michel L. Aubert

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Figure 6

SXN101742 dose dependently inhibits bone mass acquisition in juvenile rats (experiment no. 2).

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SXN101742 dose dependently inhibits bone mass acquisition in juvenile ra...
(A) Femur length (mm). *P < 0.001 versus control group. (B) Femur cross-section area (mm2). *P < 0.05 versus control group. (C) Femur trabecular number (mm–1). *P < 0.01 versus control group. n = 6 animals per group for A–C. (D) Images of tridimensional reconstruction of distal trabecular structure (top panel), longitudinal sections (middle panel), and transversal sections (bottom panel) of femurs. (E) Growth plate thickness (μm). *P < 0.001 versus control group; #P < 0.01 versus 0.1 mg/kg group. n = 5 animals per group. (F) Growth plate histology (toluidine blue staining). Note the shortening of the proliferative cell layer without any change in the differentiating cell layer. (G) MAR (μm/d), *P < 0.002 versus control group. n = 5 animals per group. (H) Radial growth histology (calcein double-labeling method). Note the inhibitory effect of SXN101742 on the periosteal surface (Ps) development with no change in the endocortical compartment (Ec). Results are expressed as mean ± SEM. Original magnification, ×20 (F); ×10 (H).