Background: Botulinum neurotoxin inhibits muscle function by interfering with neurotransmitter release from secretory vesicles. The mechanism underlying this effect involves cleavage of SNARE proteins which are required for vesicle docking at the plasma membrane. The ability of botulinum neurotoxin serotypes to cleave SNARE proteins and inhibit secretion is being exploited for therapeutic purposes by Syntaxin Ltd with their targeted secretion inhibitor technology (TSI). A specific TSI, SXN101959 is believed to have therapeutic utility in treating acromegaly because it specifically targets pituitary somatotrophs and cleaves vesicle-bound SNAREs to inhibit GH secretion. The expression of SNARE proteins has not been previously documented in detail in human pituitary.
Methods: Sixty-six pituitary adenomas were studied. Twenty-one GH-, 5 ACTH-, 1 PRL-secreting and 39 non-functioning pituitary adenomas were dispersed and studied for vesicle-bound SNAREs (VAMP1, VAMP2 and VAMP3) and membrane-bound SNAREs (syntaxin1, SNAP-23 and SNAP-25) by immunofluorescence and/or Western blotting. In addition, mRNA expression levels of SNAREs were measured in 14 somatotrophinomas and 15 NFPAs by RT-qPCR. Six normal pituitaries from autopsy were included as controls.
Results: VAMP2 and VAMP3 were found in normal pituitary and pituitary adenomas and in some cases, VAMP1 was also shown to be present at the mRNA level. 72% of the 66 adenomas were found to be positive for VAMP2 and/or VAMP3 by immunofluorescence and /or Western blot. Syntaxin1 was detected in all pituitary samples at both the mRNA and protein level while SNAP-23 was dominant in pituitary adenomas especially in somatotrophinomas where co-localisation with GH was observed. SNAP-25 was rarely documented in adenomas but was shown to be present in the normal pituitary.
Conclusions: The present data suggest that the VAMP2&3, SNAP-23 and syntaxin1 are the predominant SNARE-proteins in somatotroph adenomas. These data provide the basis for the therapeutic use of Syntaxin Ltd.s SXN101959 in the treatment of acromegaly.
Declaration of interest: Conflict of Interest: Commercial.
Funding: Declaration of Funding: Syntaxin Ltd.