Ziconotide

Ziconotide is the synthetic equivalent of omega-conotoxin MVIIA, a 25-amino-acid peptide found in the venom of the fish-hunting cone snail Conus magus. Its structure is stabilised by three disulfide bonds that form a compact inhibitor cystine knot. The conotoxin family was characterised largely through the work of Baldomero Olivera and colleagues at the University of Utah, whose studies of cone-snail venoms revealed hundreds of peptides with exquisite selectivity for ion channels and receptors.

Ziconotide was approved by the FDA in 2004 and by the EMA in 2005, marketed as Prialt, for severe chronic pain in narrowly defined circumstances. It was the first venom-derived peptide approved in its class and remains a landmark for marine natural product pharmacology. Its use is limited by a narrow therapeutic window and by neuropsychiatric adverse effects reported in clinical studies, which has kept it a specialist agent. For researchers, ziconotide is a reference blocker of N-type calcium channels and a prototype for non-opioid analgesic mechanisms, and it continues to inspire efforts to engineer more tractable conotoxin analogues.

Ziconotide selectively and reversibly blocks N-type voltage-gated calcium channels, known as Cav2.2. These channels are concentrated on the central terminals of primary afferent nociceptors in the dorsal horn of the spinal cord. When an action potential arrives, calcium entry through Cav2.2 triggers release of neurotransmitters such as glutamate, substance P and calcitonin gene-related peptide. By occluding the channel pore, ziconotide reduces this release and dampens transmission of nociceptive signals to second-order neurons. Its mechanism is independent of opioid receptors, so it does not produce opioid tolerance in experimental models, a property that underpins much of the research interest.