Abstract/Summary

Background: Thiol isomerases including PDI, ERp57, ERp72 and ERp5 play essential and distinct roles in thrombosis, cancer progression, cancer cell signalling and metastasis. Thiol isomerase inhibitors constitute a class of agents to combat these complications where they generally have been studied to combat either thrombosis or cancer but not both. Recently, our lab has identified the FDA approved leukotriene receptor antagonist, zafirlukast, as a broad-spectrum thiol isomerase inhibitor able to inhibit platelet aggregation and thrombus formation. Aims: The aims of this thesis begin with the goal to improve the efficacy of zafirlukast for thrombotic inhibition via the exploration of zafirlukast analogues. It continues by exploring how zafirlukast fairs against and ovarian cancer model, and whether its effects can be improved by combining it with a standard chemotherapy regimen or with another thiol isomerase inhibitor, isoquercetin. It concludes by exploring the mechanistic effects of thiol isomerase inhibition, and pathways affected through zafirlukast and isoquercetin treatment. Results: One of 35 zafirlukast analogues, termed compound 21, demonstrated greater potency than zafirlukast and was able to better inhibit platelet aggregation, P-selectin exposure and thrombus formation. Both zafirlukast and compound 21 demonstrated reversibility of thiol isomerase inhibition and demonstrated no cytotoxicity towards cultured lung liver and kidney cells. Although compound 21 was a better inhibitor overall, it only held a 2.5-fold increase in potency, so to explore the effects of zafirlukast on cancer inhibition I remained with the parent compound, which demonstrated inhibition of cancer growth in an ovarian xenograft model. With this data we performed a pilot clinical trial of zafirlukast’s anticancer effects in ovarian cancer patients. These results however were inconclusive; therefore, I tried improving the efficacy of zafirlukast by combining it with isoquercetin or cisplatin/gemcitabine. When combined with isoquercetin in low doses the effects were similar to that of a high dose of zafirlukast on its own. Then when zafirlukast was combined with cisplatin/gemcitabine a greater inhibition was seen than just the chemotherapy on its own. Finally, in addition to inhibiting thiol isomerases zafirlukast and isoquercetin were able to inhibit factors involved in cancer induced thrombosis, angiogenesis and inflammation including tissue factor, VEGF, TMEM176B and PD-L1. Conclusions: One conclusion drawn from this thesis is that thiol isomerase inhibitors, such as zafirlukast, are able to act as both anti-thrombotic and anti-cancer agents, making zafirlukast an interesting drug to continue exploring in combination with chemotherapeutic drugs to potentially combat cancer induced thrombosis. Another conclusion is that it is possible to alter zafirlukast to perform better as an inhibitor, where it can continue to be explored for even better analogue development. Additionally, zafirlukast in combination with another thiol isomerase inhibitor, such as isoquercetin can also improve efficacy and target other pathways beyond thiol isomerases.