Positive allosteric interaction of structurally diverse T-type calcium channel antagonists.
Low-voltage-activated (T-type) calcium channels play a role in diverse physiological responses including neuronal burst firing, hormone secretion, and cell growth. To better understand the biological role and therapeutic potential of the target, a number of structurally diverse antagonists have been identified. Multiple drug interaction sites have been identified for L-type calcium channels, suggesting a similar possibility exists for the structurally related T-type channels. Here, we radiolabel a novel amide T-type calcium channel antagonist (TTA-A1) and show that several known antagonists, including mibefradil, flunarizine, and pimozide, displace binding in a concentration-dependent manner. Further, we identify a novel quinazolinone T-type antagonist (TTA-Q4) that enhanced amide radioligand binding, increased affinity in a saturable manner and slowed dissociation. Functional evaluation showed these compounds to be state-dependent antagonists which show a positive allosteric interaction. Consistent with slowing dissociation, the duration of efficacy was prolonged when compounds were co-administered to WAG/Rij rats, a genetic model of absence epilepsy. The development of a T-type calcium channel radioligand has been used to demonstrate structurally distinct TTAs interact at allosteric sites and to confirm the potential for synergistic inhibition of T-type calcium channels with structurally diverse antagonists.
Uebele
Victor N
VN
Department of Depression and Circadian Disorders, Merck Research Laboratories, West Point, PA 19486, USA. victor_uebele@merck.com
Nuss
Cindy E
CE
Fox
Steven V
SV
Garson
Susan L
SL
Cristescu
Razvan
R
Doran
Scott M
SM
Kraus
Richard L
RL
Santarelli
Vincent P
VP
Li
Yuxing
Y
Barrow
James C
JC
Yang
Zhi-Qiang
ZQ
Schlegel
Kelly-Ann S
KA
Rittle
Kenneth E
KE
Reger
Thomas S
TS
Bednar
Rodney A
RA
Lemaire
Wei
W
Mullen
Faith A
FA
Ballard
Jeanine E
JE
Tang
Cuyue
C
Dai
Ge
G
McManus
Owen B
OB
Koblan
Kenneth S
KS
Renger
John J
JJ
D000494:Allosteric Regulation / Q000187:drug effects; D000495:Allosteric Site / Q000187:drug effects; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D008297:Male; D015394:Molecular Structure; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type