2 research outputs found
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Zafirlukast is a broad-spectrum thiol isomerase inhibitor that inhibits thrombosis without altering bleeding times
Background and purpose
Multiple members of the thiol isomerase (TI) family of enzymes are present in, and released by platelets. Inhibition of these enzymes results in diminished platelet responses including aggregation, adhesion and thrombus formation. In recent years, the therapeutic potential of TI inhibition has been recognised and drug-development technologies used to identify selective small molecule inhibitors. To date, few pan-TI inhibitors have been characterised and the most studied, bacitracin is known to be nephrotoxic which prohibits its systemic therapeutic usage.
Experimental approach
We therefore sought to identify novel broad-spectrum inhibitors of these enzymes and test their effects in vivo. 3641 compounds were screened for inhibitory effects on the redox activity of ERp5, PDI, ERp57, ERp72 and thioredoxin (TRX) in an insulin turbidity assay. Of the lead compounds identified, zafirlukast (ZFL) was selected for further investigation.
Key results
When applied to platelets, ZFL diminished platelet responses in vitro. ZFL was antithrombotic in murine models of thrombosis but did not impair responses in a model of haemostasis. Since thiol isomerases are known to modulate adhesion receptor function, we explored the effects of ZFL on cell migration. This was inhibited independently of cysteinyl leukotriene receptor expression and was associated with modulation of cell-surface free thiol levels consistent with alterations in redox activity on the cell surface.
Conclusion and implications
We identify zafirlukast to be a novel, potent, broad-spectrum TI inhibitor, with wide ranging effects on platelet function, thrombosis and integrin-mediated cell migration. ZFL is antithrombotic but does not cause bleeding
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Targeting thiol isomerase activity with zafirlukast to treat ovarian cancer from the bench to clinic
Thiol isomerases, including PDI, ERp57, ERp5, and ERp72, play important and distinct roles in cancer progression, cancer cell signaling, and metastasis. We recently discovered that zafirlukast, an FDA-approved medication for asthma, is a pan-thiol isomerase inhibitor. Zafirlukast inhibited the growth of multiple cancer cell lines with an IC50 in the low micromolar range, while also inhibiting cellular thiol isomerase activity, EGFR activation, and downstream phosphorylation of Gab1. Zafirlukast also blocked the procoagulant activity of OVCAR8 cells by inhibiting tissue factor-dependent Factor Xa generation. In an ovarian cancer xenograft model, statistically significant differences in tumor size between control vs treated groups were observed by Day 18. Zafirlukast also significantly reduced the number and size of metastatic tumors found within the lungs of the mock-treated controls. When added to a chemotherapeutic regimen, zafirlukast significantly reduced growth, by 38% compared with the mice receiving only the chemotherapeutic treatment, and by 83% over untreated controls. Finally, we conducted a pilot clinical trial in women with tumor marker-only (CA-125) relapsed ovarian cancer, where the rate of rise of CA-125 was significantly reduced following treatment with zafirlukast, while no severe adverse events were reported. Thiol isomerase inhibition with zafirlukast represents a novel, well-tolerated therapeutic in the treatment of ovarian cancer