First published January 17, 2019 - More info
Background: Protein disulfide isomerase (PDI) is a thiol isomerase secreted by vascular cells that is required for thrombus formation. Quercetin flavonoids inhibit PDI activity and block platelet accumulation and fibrin generation at the site of a vascular injury in mouse models but the clinical effect of targeting extracellular PDI in humans has not been studied.
Methods: We conducted a multi-center phase 2 trial of sequential dosing cohorts to evaluate the efficacy of targeting PDI with isoquercetin to reduce hypercoagulability in cancer patients at high risk for thrombosis. Patients received isoquercetin at 500 mg (cohort A, N=28) or 1000 mg (cohort B, N=29) daily for 56 days with laboratory assays performed at baseline and end-of-study, along with bilateral lower extremity compression ultrasound. The primary efficacy endpoint was a reduction in D-dimer and the primary clinical endpoint included pulmonary embolism or proximal deep vein thrombosis.
Results: The administration of isoquercetin 1000 mg decreased D-dimer plasma concentrations by a median of -21.9% (P=0.0002). There were no primary VTE events or major hemorrhages observed in either cohort. Isoquercetin increased PDI inhibitory activity in plasma (37.0% in cohort A, N=25, P<0.001; 73.3% in cohort B, N=22, P<0.001, respectively). Corroborating the antithrombotic efficacy, we also observed a significant decrease in platelet-dependent thrombin generation (cohort A median decrease -31.1%, P=0.007; cohort B median decrease -57.2%, P=0.004) and circulating soluble P-selectin at the 1000 mg isoquercetin dose (median decrease -57.9%, P<0.0001).
Conclusions: Isoquercetin represents first-in-class inhibitor of PDI demonstrating efficacy in improving markers of coagulation in advanced cancer patients.
Trial Registration: Clinicaltrials.gov NCT02195232