Inhibition of purified factor Xa amidolytic activity may not be predictive of inhibition of in vivo thrombosis: implications for identification of therapeutically active inhibitors.
OBJECTIVE
In this study we test the hypothesis that blood/plasma-based prothrombinase assays, rather than inhibition of purified factor Xa (fXa), are predictive of in vivo antithrombotic activity.


RESULTS
Six fXa inhibitors with equivalent nanomolar Ki were studied in thrombin generation assays using human plasma/blood and endogenous macromolecular substrate. In all assays, benzamidine inhibitors were more potent (100 to 800 nmol/L) than the aminoisoquinolines (5 to 58 micromol/L) or neutral inhibitors (3 to 10 micromol/L). A similar rank order of compound inhibition was also seen in purified prothrombinase assays as well as in a rabbit model of deep vein thrombosis.


CONCLUSIONS
Assays using prothrombinase with protein substrates are better predictors of in vivo efficacy than fXa Ki using amidolytic substrates.
Millennium Pharmaceuticals, 256 E Grand Ave, South San Francisco, Calif 94080, USA. Uma.Sinha@mpi.com
Uma
U
Sinha
Pei Hua
PH
Lin
Susan T
ST
Edwards
Paul W
PW
Wong
Bingyan
B
Zhu
Robert M
RM
Scarborough
Ting
T
Su
Zhaozhong J
ZJ
Jia
Yonghong
Y
Song
Penglie
P
Zhang
Lane
L
Clizbe
Gary
G
Park
Andrea
A
Reed
Stanley J
SJ
Hollenbach
John
J
Malinowski
Ann E
AE
Arfsten
D000818:Animals; D001550:Benzamidines / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D004791:Enzyme Inhibitors / Q000145:classification / Q000494:pharmacology*; D065427:Factor Xa Inhibitors; D005343:Fibrinolytic Agents / Q000145:classification / Q000494:pharmacology*; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology*; D008297:Male; D015394:Molecular Structure; D011516:Prothrombin / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013379:Substrate Specificity; D013917:Thrombin / Q000096:biosynthesis; D013925:Thromboplastin / Q000037:antagonists & inhibitors*; D020246:Venous Thrombosis / Q000517:prevention & control
D001550:Benzamidines; D004791:Enzyme Inhibitors; D065427:Factor Xa Inhibitors; D005343:Fibrinolytic Agents; D007546:Isoquinolines; D011516:Prothrombin; D013925:Thromboplastin; D013917:Thrombin