Abstract 3976: Disrupting CD44-SPP1 interaction between tumor cells and tumor-associated macrophages (TAMs) to overcome cisplatin resistance in muscle-invasive bladder cancer (MIBC)

Introduction: Cisplatin-based chemotherapy remains a mainstay of treatment for MIBC; however, cisplatin resistance is common and is associated with poor clinical outcomes. Tumor cells actively shape the tumor microenvironment (TME), including tumor-associated macrophages (TAMs)—which comprise 50-80% of stromal cells—to support tumor growth. While TAMs are critical determinants of pro- or anti-tumor TME characteristics, the mechanisms underlying tumor-macrophage crosstalk in cisplatin resistant tumors remain poorly understood. Methods: We employed single-nucleus RNA sequencing (snRNA-seq) to analyze cell populations in cisplatin sensitive and resistant human bladder tumors. Spatial transcriptomic analysis was performed to assess the spatial organization of cell types within tumors. CRISPR-Cas9 was utilized to generate CD44-deficient bladder cancer cell lines and SPP1-deficient macrophages. Functional assays for tumor cells and macrophages were performed using direct and indirect tumor cell-macrophage co-culture systems. Phagocytosis was analyzed using live-cell imaging and flow cytometry. Finally, both immune-competent and immune -deficient mouse model was utilized to evaluate the therapeutic potential of targeting the CD44-SPP1 axis as a strategy to overcome cisplatin resistance. Results: Our analysis revealed that high CD44 expression in tumor cells is positively correlated with cisplatin in human bladder cancer patients. SPP1-expressing macrophages were spatially localized near CD44 positive tumor cells in cisplatin resistant tumors. Deleting CD44 in tumor cells increased sensitivity to cisplatin, which was more significant in the presence of macrophage-conditioned media in co-culture with bladder cancer cell lines. CD44 loss also promoted the phagocytic activity of the mouse macrophage cell line Raw264.7. We are currently using an immune-competent mouse bladder cancer model to test whether genetic deletion or pharmacological blockade of CD44 sensitizes tumors to cisplatin. Furthermore, we will utilize immune-deficient nude mice to co-implant human bladder cancer cell with human macrophages with or without SPP1 expression to evaluate whether SPP1 deficient macrophage enhance cisplatin responses and promote tumor suppression. Conclusion: Targeting the CD44-SPP1 interaction, either through genetic modification or antibody-mediated blockade, sensitizes bladder tumors to cisplatin. This approach represents a promising therapeutic strategy to overcome cisplatin resistance in MIBC. Citation Format: Yuzhen Zhou, Jihyun Lee, Hiba Siddiqui, Martin Egger, Eliezer M Van Allen, Filipe De Carvalho, Kent Mouw. Disrupting CD44-SPP1 interaction between tumor cells and tumor-associated macrophages (TAMs) to overcome cisplatin resistance in muscle-invasive bladder cancer (MIBC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3976.