Inverse agonism of SQ 29,548 and Ramatroban on Thromboxane A2 receptor.
G protein-coupled receptors (GPCRs) show some level of basal activity even in the absence of an agonist, a phenomenon referred to as constitutive activity. Such constitutive activity in GPCRs is known to have important pathophysiological roles in human disease. The thromboxane A2 receptor (TP) is a GPCR that promotes thrombosis in response to binding of the prostanoid, thromboxane A2. TP dysfunction is widely implicated in pathophysiological conditions such as bleeding disorders, hypertension and cardiovascular disease. Recently, we reported the characterization of a few constitutively active mutants (CAMs) in TP, including a genetic variant A160T. Using these CAMs as reporters, we now test the inverse agonist properties of known antagonists of TP, SQ 29,548, Ramatroban, L-670596 and Diclofenac, in HEK293T cells. Interestingly, SQ 29,548 reduced the basal activity of both, WT-TP and the CAMs while Ramatroban was able to reduce the basal activity of only the CAMs. Diclofenac and L-670596 showed no statistically significant reduction in basal activity of WT-TP or CAMs. To investigate the role of these compounds on human platelet function, we tested their effects on human megakaryocyte based system for platelet activation. Both SQ 29,548 and Ramatroban reduced the platelet hyperactivity of the A160T genetic variant. Taken together, our results suggest that SQ 29,548 and Ramatroban are inverse agonists for TP, whereas, L-670596 and Diclofenac are neutral antagonists. Our findings have important therapeutic applications in the treatment of TP mediated pathophysiological conditions.
Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada ; Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada.
Raja
R
Chakraborty
Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada.
Rajinder P
RP
Bhullar
Departments of Pediatrics, Physiology, University of Manitoba, Winnipeg, Manitoba, Canada ; Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada.
Shyamala
S
Dakshinamurti
Department of Internal Medicine (Cardiology), Cardiovascular Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America.
John
J
Hwa
Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada ; Departments of Pediatrics, Physiology, University of Manitoba, Winnipeg, Manitoba, Canada ; Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada.
Prashen
P
Chelikani
D019943:Amino Acid Substitution; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D020013:Calcium Signaling / Q000187:drug effects; D002227:Carbazoles / Q000494:pharmacology*; D004353:Drug Evaluation, Preclinical; D005231:Fatty Acids, Unsaturated; D057809:HEK293 Cells; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*
D019086:Bridged Bicyclo Compounds, Heterocyclic; D002227:Carbazoles; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013449:Sulfonamides; D015544:Inositol 1,4,5-Trisphosphate; C045749:SQ 29548; C063119:ramatroban