Mechanism of action of a nanomolar potent, allosteric antagonist of the thyroid-stimulating hormone receptor.
OBJECTIVE
Graves' disease (GD) is an autoimmune disease in which the thyroid is overactive, producing excessive amounts of thyroid hormones, caused by thyroid-stimulating hormone (TSH) receptor-stimulating immunoglobulins (TSIs). Many GD patients also suffer from thyroid eye disease (Graves' ophthalmopathy or GO), as TSIs also activate TSH receptors in orbital tissue. We recently developed low molecular weight (LMW) TSH receptor antagonists as a novel therapeutic strategy for the treatment of GD and GO. Here, we determined the molecular pharmacology of a prototypic, nanomolar potent LMW TSH receptor antagonist, Org 274179-0.


METHODS
Using CHO cells heterogeneously expressing human TSH receptors and rat FRTL-5 cells endogenously expressing rat TSH receptors, we determined the potency and efficacy of Org 274179-0 at antagonizing TSH- and TSI-induced TSH receptor signalling and its cross-reactivity at related follicle-stimulating hormone and luteinizing hormone receptors. We analysed the allosteric mode of interaction of Org 274179-0 and determined whether it is an inverse agonist at five naturally occurring, constitutively active TSH receptor mutants.


RESULTS
Nanomolar concentrations of Org 274179-0 completely inhibited TSH (and TSI)-mediated TSH receptor activation with little effect on the potency of TSH, in accordance with an allosteric mechanism of action. Conversely, increasing levels of TSH receptor stimulation only marginally reduced the antagonist potency of Org 274179-0. Org 274179-0 fully blocked the increased basal activity of all the constitutively active TSH receptor mutants tested with nanomolar potencies.


CONCLUSIONS
Nanomolar potent TSH receptor antagonists like Org 274179-0 have therapeutic potential for the treatment of GD and GO.
Department of Molecular Pharmacology, Medicinal Chemistry Early Clinical Research, Merck Research Laboratories, the Netherlands. chris.vankoppen@online.de
Chris J
CJ
van Koppen
Marcel E
ME
de Gooyer
Willem-Jan
WJ
Karstens
Ralf
R
Plate
Paolo G M
PG
Conti
Tanja A E
TA
van Achterberg
Monique G A
MG
van Amstel
Jolanda H G M
JH
Brands
Jesse
J
Wat
Rob J W
RJ
Berg
J Robert D
JR
Lane
Andre M M
AM
Miltenburg
C Marco
CM
Timmers
D000262:Adenylyl Cyclases / Q000378:metabolism; D000634:Aminoquinolines / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004353:Drug Evaluation, Preclinical; D006111:Graves Disease / Q000188:drug therapy / Q000276:immunology; D006801:Humans; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D051381:Rats; D011989:Receptors, Thyrotropin / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D013972:Thyrotropin / Q000378:metabolism
D000634:Aminoquinolines; C573712:N-(1-acetyl-4-methyl-4-phenyl-1,2,3,4-tetrahydro-quinolin-6-yl)-3-(3-trifluoromethyl-phenyl)propionamide; D011989:Receptors, Thyrotropin; D011994:Recombinant Proteins; D013972:Thyrotropin; D000262:Adenylyl Cyclases