7-[(1R,2S,3S,5R)-6,6-dimethyl-3-(4- iodobenzenesulfonylamino)bicyclo[3.1.1]hept-2-yl]-5(Z)-heptenoic acid: a novel high-affinity radiolabeled antagonist for platelet thromboxane A2/prostaglandin H2 receptors.
A high-affinity thromboxane (TX)A2/prostaglandin (PG) H2 receptor antagonist, I-SAP [7-[(1R,2S,3S,5R)-6,6-dimethyl-3-(4- iodobenzenesulfonylamino)bicyclo[3.1.1]hept-2-yl]-5(Z)-heptenoic acid] and its radiolabeled analog [125I]SAP (Mais et al., 1991) are characterized in the present study. I-SAP antagonized I-BOP ([1S-(1 alpha, 2 beta(5Z),3 alpha(1E,3R*),4 alpha)]-7-[3-(3-hydroxy-4- (4'-iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1]heptan-2y l]-5'heptenoic acid) and U46619 [15S-hydroxy-11 alpha,9 alpha-(epoxymethano)-prosta-5Z,13E-dienoic acid)], two different TXA2/PGH2 mimetics, induced aggregation of washed human platelets in a similar manner (pA2 of 8.11 +/- 0.09, Kd = 7.8 nM, n = 3; pA2 = 8.01 +/- 0.05, Kd = 9.7 nM, n = 8, respectively). I-SAP also had agonistic activity, producing platelet shape change (EC50 = 9.7 nM +/- 0.6 nM at pH 7.4, n = 3) which was blocked by pretreatment of platelets with SQ29548 ([1S-(1 alpha,2 beta(5Z),3 beta,4 alpha)]-7-[3-[[2- [(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept- 2-yl]-5-heptenoic acid), a TXA2/PGH2 receptor antagonist. Radioligand binding studies were performed with [125I]SAP using washed human platelets. Competition of three agonists and four antagonists for binding with [125I]SAP was determined. The compounds showed the appropriate rank order potencies, including stereoselective competition by a pair of stereoisomeric antagonists. In washed human platelets, the Kd for I-SAP was 468 +/- 49 pM and the maximum binding (Bmax) was 2057 +/- 156 sites/platelet at pH 7.4 (n = 6). The Bmax was significantly increased 49% to 3072 +/- 205 sites/platelet at pH 6.5 (P less than .01 but the Kd was unchanged (490 +/- 18 pM, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
Naka
M
M
Medical University of South Carolina, Department of Cell and Molecular Pharmacology, Charleston.
Mais
D E
DE
Morinelli
T A
TA
Hamanaka
N
N
Oatis
J E
JE
Halushka
P V
PV
D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000378:metabolism* / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism* / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D011982:Receptors, Prostaglandin / Q000187:drug effects* / Q000378:metabolism; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors*
D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; D010975:Platelet Aggregation Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; C061750:7-(3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo(2.2.1)heptan-2-yl)-5-heptenoic acid; C076030:7-(6,6-dimethyl-3-(4-iodobenzenesulfonylamino)bicyclo(3.1.1.)hept-2-yl)-5-heptenoic acid; D013928:Thromboxane A2