Abstract 2169: TTK/PLK1 dual antagonist BAL0891 synergizes with pembrolizumab in a vascularized 3D tumor microenvironment model

Abstract Introduction: BAL0891, a first-in-class dual TTK/PLK1 inhibitor, activates the cGAS/STING pathway and induces a senescence-associated secretory phenotype (SASP), resulting in increased PD-L1 expression and pro-inflammatory cytokine production in cancer cells. These changes enhance tumor susceptibility to immunotherapies. However, evaluating the synergy between BAL0891 and immune checkpoint inhibitors like pembrolizumab (PD-1 inhibitor) is challenging in traditional preclinical models, which lack human immune cells and key features of the tumor microenvironment. To address these limitations, Qureator’s advanced 3D tumor microenvironment (TME) model, incorporating perfusable vessels, human primary cells, and patient-derived organoids (PDOs) was utilized. This physiologically relevant system enabled a detailed investigation of BAL0891's mechanism of action (MOA) and its combination with pembrolizumab across multiple cancer types, aiming to guide clinical trial design and patient stratification. Methods: Vascularized TME models were developed by co-culturing endothelial cells, fibroblasts, and PDOs derived from renal cell carcinoma, triple-negative breast cancer, gastric cancer, and colorectal cancer within Qureator’s Microphysiological System (MPS). Following vasculature formation, models were primed with BAL0891 for two days and then treated with PBMCs and pembrolizumab or isotype control antibodies. Tumor growth, immune infiltration, and tumor cell killing were assessed via live cell imaging and immunofluorescence staining. Post-treatment immuno-profiling included flow cytometry to analyze macrophage polarization and T cell activation/exhaustion. Multiplex secretome analysis was performed to characterize chemokine and cytokine profiles associated with BAL0891 and the combination therapy. Results: BAL0891 priming sensitized a subset of PDOs to pembrolizumab, demonstrating synergistic anti-tumor activity in the vascularized TME model. Responsive PDOs exhibited significant organoid shrinkage, increased immune cell infiltration, enhanced T cell activation, and macrophage polarization towards an anti-tumoral phenotype. Cytokine and chemokine analysis revealed a shift to a pro-inflammatory microenvironment. Conversely, non-responders showed limited immune infiltration and minimal activation. Conclusion: Qureator’s vascularized TME model provided a robust platform to evaluate the synergy between BAL0891 and pembrolizumab. The study demonstrated BAL0891's ability to reshape the tumor immune landscape and enhance the efficacy of the immune checkpoint inhibitor. These findings offer valuable insights into the MOA of BAL0891 within this highly representative tumor model, supporting its further clinical development in combination with checkpoint inhibitors. Citation Format: Junfeng Wang, MinKyung Kang, Byungjun Lee, Delaney Donnelly, Jihye Baek, Bushra Rajput, Tsung-Li Liu, Hyeon-geun Park, Yunha Shin, Aneesh Sathe, Yangji Kim, Kyusuk Baek, Sanghee Yoo, Salman Ahmed, Jae Jung Lee, Seunghyun Ma. TTK/PLK1 dual antagonist BAL0891 synergizes with pembrolizumab in a vascularized 3D tumor microenvironment model [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 2169.