(615a) High Throughput Screening For Inhibitors Of Coagulation Factor Xia And Factor Xiia

Factor XIa (FXIa) and factor XIIa (FXIIa) are blood coagulation enzymes involved in activation of enzymes leading to thrombin production. While the exact in vivo role of FXIIa is unclear, it has been shown to be a risk factor for pathologic thrombus formation, as is FXIa. Thus, these two enzymes may play roles in fine regulation of coagulation processes and are attractive targets for anticoagulant therapy. HTS was performed using 63K compounds of the NIH Molecular Libraries Screening Center Network (MLSCN) library combined as mixtures of 10 orthogonally pooled compounds totaling 2.5mM, which were diluted 50-fold into 10μl 384 well assay plates (final concentration 5μM each compound). The assay used to test for percent inhibition was a fluorescence assay utilizing hydrolysis of Boc-EAR-AMC (FXIa), or Boc-QGR-AMC (FXIIa). Hits with >20% inhibition in both wells of the mixture plates were retested in complete IC50 curves (FXIa hit rate: 0.19%, FXIIa: 0.15%). A dose-response assay was performed on the hits from the mixture assays, with compound concentrations between 50μM and 1.52nM, with an active retest rate of 25% for FXIa and 18% for FXIIa. IC50s of FXIa inhibitory compounds were between 524nM and 30μM, with 5 compounds showing an IC50 < 2μM. For FXIIa inhibitors, IC50s ranged between 103nM and 6.3μM, with 15 compounds showing an IC50 < 1μM. These results show that high affinity inhibitors against these proteases are present in the MLSCN mixture library. Phenotypic testing in whole blood will allow for further characterization of these compounds.