ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine]: a novel, orally effective analgesic acting via neuronal nicotinic acetylcholine receptors: I. In vitro characterization.
The discovery of (+/-)-epibatidine, a naturally occurring neuronal nicotinic acetylcholine receptor (nAChR) agonist with antinociceptive activity 200-fold more potent than that of morphine, has renewed interest in the potential role of nAChRs in pain processing. However, (+/-)-epibatidine has significant side-effect liabilities associated with potent activity at the ganglionic and neuromuscular junction nAChR subtypes which limit its potential as a clinical entity. ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine] is a novel, potent cholinergic nAChR ligand with analgesic properties (see accompanying paper by Bannon et al., 1998b) that shows preferential selectivity for neuronal nAChRs and a consequently improved in vivo side-effect profile compared with (+/-)-epibatidine. ABT-594 is a potent inhibitor of the binding of [3H](-)-cytisine to alpha 4 beta 2 neuronal nAChRs (Ki = 37 pM, rat brain; Ki = 55 pM, transfected human receptor). At the alpha 1 beta 1 delta gamma neuromuscular nAChR labeled by [125I] alpha-bungarotoxin (alpha-Btx), ABT-594 has a Ki value of 10,000 nM resulting in a greater than 180,000-fold selectivity of the compound for the neuronal alpha 4 beta 2 nAChR. In contrast, (+/-)-epibatidine has Ki values of 70 pM and 2.7 nM at the alpha 4 beta 2 and alpha 1 beta 1 delta gamma nAChRs, respectively, giving a selectivity of only 38-fold. The S-enantiomer of ABT-594, A-98593 has activity at the neuronal alpha 4 beta 2 nAChR identical with ABT-594 (Ki = 34-39 pM), which demonstrates a lack of stereospecific binding similar to that reported previously for (+/-)-epibatidine. A similar lack of stereoselectivity is seen at the human alpha 7 receptor. However, A-98593 is 3-fold more potent at the neuromuscular nAChR (Ki = 3420 nM) and the brain alpha-Btx-sensitive nAChR (Ki = 4620 nM) than ABT-594. ABT-594 has weak affinity in binding assays for adrenoreceptor subtypes alpha-1B (Ki = 890 nM), alpha-2B (Ki = 597 nM) and alpha-2C (Ki = 342 nM), and it has negligible affinity (Ki > 1000 nM) for approximately 70 other receptors, enzyme and transporter binding sites. Functionally, ABT-594 is an agonist. At the transfected human alpha 4 beta 2 neuronal nAChR (K177 cells), with increased 86Rb+ efflux as a measure of cation efflux, ABT-594 had an EC50 value of 140 nM with an intrinsic activity (IA) compared with (-)-nicotine of 130%; at the nAChR subtype expressed in IMR-32 cells (sympathetic ganglion-like), an EC50 of 340 nM (IA = 126%); at the F11 dorsal root ganglion cell line (sensory ganglion-like), an EC50 of 1220 nM (IA = 71%); and via direct measurement of ion currents, an EC50 value of 56,000 nM (IA = 83%) at the human alpha 7 homooligimeric nAChR produced in oocytes. A-98593 is 2- to 3-fold more potent and displays approximately 50% greater intrinsic activity than ABT-594 in all four functional assays. In terms of potency, ABT-594 is 8- to 64-fold less active than (+/-)-epibatidine and also has less IA in these functional assays. ABT-594 (30 microM) inhibits the release of calcitonin gene-related peptide from C-fibers terminating in the dorsal horn of the spinal cord, an effect mediated via nAChRs. Pharmacologically, ABT-594 has an in vitro profile distinct from that of the prototypic nicotinic analgesic (+/-)-epibatidine, with the potential for substantially reduced side-effect liability and, as such, represents a potentially novel therapeutic approach to pain management.
Donnelly-Roberts
D L
DL
Pharmaceutical Products Division, Abbott Laboratories, Illinois, USA.
Puttfarcken
P S
PS
Kuntzweiler
T A
TA
Briggs
C A
CA
Anderson
D J
DJ
Campbell
J E
JE
Piattoni-Kaplan
M
M
McKenna
D G
DG
Wasicak
J T
JT
Holladay
M W
MW
Williams
M
M
Arneric
S P
SP
D000284:Administration, Oral; D000470:Alkaloids / Q000378:metabolism; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000818:Animals; D001384:Azetidines / Q000494:pharmacology*; D001392:Azocines; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002038:Bungarotoxins / Q000378:metabolism; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006801:Humans; D008297:Male; D018722:Nicotinic Agonists / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology*; D011807:Quinolizines; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000502:physiology; D014982:Xenopus laevis; D000093843:Quinolizidine Alkaloids
D000470:Alkaloids; D018712:Analgesics, Non-Narcotic; D001384:Azetidines; D001392:Azocines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002038:Bungarotoxins; D015740:Calcitonin Gene-Related Peptide; D002118:Calcium; D018722:Nicotinic Agonists; D011725:Pyridines; D011807:Quinolizines; D011978:Receptors, Nicotinic; C109763:5-(2-azetidinylmethoxy)-2-chloropyridine; C004712:cytisine; D000093843:Quinolizidine Alkaloids; C082748:epibatidine