Daniel R. Kennedy

Isoquercetin and Zafirlukast Cooperatively Suppress Tumor Growth and Thromboinflammatory Signaling in a Xenograft Model of Ovarian Cancer

ABSTRACT Cancer‐associated thrombosis (CAT), encompassing both venous thromboembolism and arterial thrombosis, contributes to up to 14% of cancer‐related mortality and remains difficult to treat due to the bleeding risks of conventional anticoagulants. Protein disulfide isomerase (PDI) and its family member ERp57 (PDIA3) are thiol isomerases that regulate both arterial and venous thrombosis and are also upregulated in tumors, where they promote growth, metastasis, and immune evasion. Here, we evaluated the therapeutic potential of two thiol isomerase inhibitors—isoquercetin (ISOQ), a selective PDI inhibitor, and zafirlukast (ZAF), a broad‐spectrum inhibitor of thiol isomerases such as PDI and ERp57—individually and in combination, in a xenograft model of ovarian cancer. ISOQ inhibited both platelet aggregation and Factor Xa generation induced by tumor cells and significantly suppressed tumor growth, thromboinflammatory markers, and expression of tissue factor, VEGF, TMEM176B, and PD‐L1. ISOQ also potentiated standard cisplatin/gemcitabine chemotherapy. Notably, the combination of low‐dose ISOQ plus ZAF achieved ≥ 80% inhibition of key tumor‐associated markers at one‐third the monotherapy dose and outperformed either agent alone. These findings support ISOQ and ZAF as promising agents for the treatment of cancer and CAT and establish thiol isomerase inhibition as a strategy to simultaneously target thrombosis, tumor progression, and immune escape.

Targeting thiol isomerase activity with zafirlukast to treat ovarian cancer from the bench to clinic

Abstract 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 IC 50 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.