EPIBATIDINEThe toxicology and prospective pharmacology of a toxin derived from Epipedobates anthoyi.

By: Kriti Mishra, Aaron Marks, Bikal Wagle, & Carlos Garcia

What is Epibatidine?• A toxic substance derived

from the skin of the poison dart frog, Epipedobates anthoyi.• Ecuadorian natives use

the toxin on their darts to kill big game.• It was discovered by John

Daly in 1974.• It has stronger analgesic

properties than morphine.

Why Epibatidine? • Morphine is an opioid analgesic used in the medical

field with a high potential for addiction, psychological dependence, and tolerance.• Epibatidine binds to a different receptor than

morphine.• Epibatidine is a strong contender to take the place of

morphine without being addictive.• On the other hand, the effective dose of epibatidine is

very close to the lethal dose. Narrow safety margin!• Less lethal derivatives of epibatidine are being

researched.

What will you learn?• Mechanism of action• Past research• Implications of the research conducted• Future research

Don’t even think about touching

me.

DATA: Where does Epibatidine Bind?• Epibatidine does not bind to

opioid receptors like morphine.• Epibatidine has a Ki of 0.12 (high

binding affinity) for nicotinic acetylcholine receptors (nAChr).• nACHr’s are specific receptors of

skeletal muscle

• Naloxone is an antagonist of opioid receptors.• When mice were injected with

BOTH naloxone and epibatidine, the mice were fully influenced by the effects of epibatidine. • KEY POINT: Epibatidine does not

bind to opioid receptors.

DATA: Where does Epibatidine Bind?

DATA: Straub Reaction Tests• In a Straub reaction test, the

tail of an animal becomes rigid in an S-shaped curve in response to a neuronal effector.• The left column epibatidine

requires a much smaller administered dose (mg/kg) to elicit Straub response compared to morphine.• The right column indicates

that epibatidine has a very low affinity for opioid receptors.

DATA: Hot Plate Analgesia Tests• Hot plate analgesia is a behavioral model of

nociception.• Nociception is the perception of painful stimuli.• Behaviors such as jumping and hind paw-licking are

elicited following placing a live sample with a noxious thermal stimulus.

• Mice injected with epibatidine stay longer on the hot plates due to a greater analgesic effect than mice injected with morphine.• Epibatidine was reported to be a 200 times

more potent analgesic than morphine.

DATA: CNS and PNS Specificity• In vivo testing with mice models shows that

epibatidine binds to the Central Nervous System (CNS) AND the Peripheral Nervous System (PNS).

1.CNS: Epibatidine binds to nAChr’s of the CNS tissue and elicits an analgesic effect.• This has been hypothesized that Epibatidine binding induces neurotransmitter

release of dopamine and norepinephrine.

2.PNS: Epibatidine ALSO simultaneously binds to nAChr’s of the the neuromuscular junction of skeletal muscle causing muscular PARALYSIS (Sullivan et al. 1994).

What are the Upsides? • Epibatidine has a much stronger analgesic effect

than opioids like morphine and codeine.• Epibatidine binds nAChr’s in the central nervous

system tissue causing analgesic effects.• It does not bind to opioid receptors.

What are the Downsides?• Epibatidine is too toxic for clinical use.• Epibatidine binding to the peripheral nervous

system, specifically skeletal muscle nAChr’s, causes paralysis.

Implications:• Epibatidine medicinal research is still very promising!• The idea: Find the pharmacophore of the molecule, and

modify it so that is safe for human consumption while still maintaining is powerful analgesic properties by targeting only the CNS.• Pharmacophore: the region of the molecule that has an

active effect in binding with the receptor.• A new class of analgesic drugs can be developed that

mitigate the negative side effects of opioid analgesics while having superior analgesic properties.

The Future of Epibatidine:• A pharmacophore called ABT-594 was discovered by

Abbott industries.• ABT-594 is also known as Tebanicline or Ebanicline.• It is a non-opioid drug and does not produce the

negative side-effects of morphine: respiratory depression, tolerance, and addiction in a mouse model.• ABT-594 is effective against acute, chronic, and

neuropathic pain.• It selectively inhibits afferent pain signal transmission without other sensory modalities such as touch.

The Future of ABT-594:• ABT-594 seems to be a miracle replacement for morphine

without the ill-effects of morphine.• Nicotine is very addictive and is similar in structure to ABT-594.• The presence of addictive effects of ABT-594 in human models

are unknown.• Mouse physiology is certainly different from human; there have

been accounts of promising drugs that fail in human trials.• Future research needs to be conducted to find the possible addictive effects of ABT-594 in humans.

Summary:• WHAT?• Epibatidine

• WHERE?• Found on the skin of a poison dart frog found in the

Ecuadorian Forests• HOW?• Binds to nAChr’s and provides analgesic properties

stronger than that of morphine without addictive effects

References:• Badio, Barbara, and John Daly. "Epibatidine, a Potent Analgetic and Nicotinic Agonist."

Molecular Pharmacology 45 (1994): 563-569.• Bannon, A.W., Decker, M.W., Holladay, M. W., Curzon, P>, Donnelly-Roberts, D.,Porsolt, R.D.,

Williams, M., Arneric, S.P. Broad-Spectrum, Non-Opioid Analgesic Activity by Selective Modulation of Neuronal Nicotinic Acetylcholine Receptors. Science 2 January 1998: vol. 279, No. 5347, pp. 77-80.

• Bonhaus, D. W., Bley, K. R., Broka, C. A., Fontana, D. J., Leung, E., Lewis, R., ... & Wong, E. H. (1995). Characterization of the electrophysiological, biochemical and behavioral actions of epibatidine. Journal of Pharmacology and Experimental Therapeutics, 272(3), 1199-1203.

• Spande, T. F., Garraffo, H. M., Edwards, M. W., Yeh, H. J., Pannell, L., & Daly, J. W. (1992). Epibatidine: a novel (chloropyridyl) azabicycloheptane with potent analgesic activity from an Ecuadoran poison frog. Journal of the American Chemical Society, 114(9), 3475-3478.

• Strong, Suzanne. "Altering Chemistry: Epibatidine a Novel Alkaloid."Sjbr/strong/1998. 1 Jan. 1998. Web. 16 Apr. 2015. <http://wwwchem.csustan.edu/chem4400/sjbr/strong98.htm>.

• Sullivan JP, Decker MW, Brioni JD, Roberts-Donnelly D, Anderson DJ, Bannon A, Gopalakrishnan M, Piattoni-Kaplan M, Adams P, Buckley MJ, Kang CH, Williams M, Arneric SP (1994) Pharmacological properties of (±)-epibatidine: A potent nicotinic acetylcholine receptor ligand. J Pharmacol Exp Ther 271:624–631

• Traynor, J. R. (1998). Epibatidine and pain. British journal of anaesthesia, 81(1), 69-76.