Abstract PS5-03-24: Thromboxane A2-Prostanoid Receptor (TPR) Blockade with Ifetroban Disrupts Platelet-Tumor Cell Interactions to Reduce Metastasis in Triple-Negative Breast Cancer

Abstract Platelets play a central role in tumor metastasis by promoting circulating tumor cell (CTC) survival, vascular arrest, and extravasation. Thromboxane A2 (TXA2), a key platelet activation mediator, drives these processes via its receptor (TPr). Here, we investigate the therapeutic potential of the TPr antagonist ifetroban to disrupt platelet-tumor cell crosstalk and suppress metastasis in triple-negative breast cancer (TNBC). In vitro, ifetroban significantly reduced platelet activation and binding to MDA-MB-231 cells. Co-culture assays showed U46619 (TPr agonist) increased platelet-tumor cell interactions by 160%, while ifetroban pretreatment reduced binding by 65% (p<0.05). Flow cytometry confirmed decreased CD62P expression (activation marker) in ifetroban-treated platelets, supporting the established antiplatelet effect of TPr blockade. The in vivo zebrafish model results revealed that ifetroban reduced MDA-MB-231 xenograft metastasis without attenuating platelet (CD41+) recruitment. Murine studies demonstrated ifetroban’s efficacy across TNBC models: 4T1 subcutaneous tumor model (1x106 cells) showed higher lung and liver metastatic foci in control animals, while ifetroban treatment (50 mg/kg BW, oral dosing, pretreatment for 2 weeks before tumor induction and continued until the end) resulted in significantly lower (p<0.05) numbers of lung and liver metastases and lower circulating levels of TXA2 metabolite, TXB2. Additionally, a decrease in tumor volume and weight was observed in ifetroban-treated animals, although ifetroban (up to 500 µM) did not show any direct toxic effects on tumor cell lines (MDA-MB-231 and 4T1), suggesting an indirect anticancer effect. Further confirmation came from a xenograft model using Athymic nude mice induced with MDA-MB-231 RFP cells (1x106 cells, subcutaneous injection). The treatment regime was similar (50 mg/kg BW, oral dosing, pretreatment for 2 weeks before tumor induction and continued until the end), and results from in vivo imaging system (IVIS) studies showed a significant (p<0.05) reduction in MDA-MB-231 cell metastasis to the liver and lungs compared to the control. Tumor weight and volume reductions were consistent with previous animal studies, demonstrating ifetroban's therapeutic efficacy in different TNBC models. Histopathological analysis of lungs and liver confirmed findings in both mouse models. Mechanistically, ifetroban suppressed circulating TXB2 (TXA2 metabolite) and disrupted platelet-mediated CTC protection. Notably, tumor volume/weight reductions occurred without direct tumor cell toxicity, implicating immune-modulatory effects. These findings highlight ifetroban’s ability to target platelet-driven metastatic niches by blocking TXA2-TPr signaling. Our data provide preclinical evidence for repurposing ifetroban as an adjuvant therapy to reduce metastasis in TNBC, offering a novel strategy to counteract platelet-supported metastatic progression. Citation Format: V. Toragall, A. Rester, S. Begum, O. Shofolawe-Bakare, K. Hulugalla, J. Monroe, Y. Gibert, T. Werfel. Thromboxane A2-Prostanoid Receptor (TPR) Blockade with Ifetroban Disrupts Platelet-Tumor Cell Interactions to Reduce Metastasis in Triple-Negative Breast Cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-03-24.