Innovative In Vitro-In Silico Platform for Dose-Response Modeling in Canine Bladder Cancer: A 3D Organoid- and Mathematics-Based Approach.

Approximately 25% of human urothelial carcinoma (UC) cases progress to high-grade, muscle-invasive bladder cancer (MIBC), for which treatment response remains difficult to predict. To address the need for more predictive platforms, we developed an integrated in vitro-in silico system using canine UC derived organoids, which closely mirror human MIBC at the histological, molecular, and clinical levels. Organoids were irradiated at doses of 0, 5, 9, or 15 Gy and cisplatin was administered at concentrations of 0, 10, 25, 50, or 100 μM at 24 and 72 h post-plating, respectively. Cell viability was assessed one week later using a PrestoBlue metabolic activity assay. Combined effects of radiation and cisplatin were estimated using a two-dimensional Hill model, which disentangles synergism in magnitude of effect (efficacy) and potency, with directly interpretable parameters. Implementation within a Bayesian hierarchical model accommodated both between-subject and between-assay variation. The model showed inter-patient variability in response to both radiation and cisplatin, with varying potency for the radiation dose (posterior median ED50: 0.55-7.6 Gy) and cisplatin concentration (posterior median EC50: 40-174 μM), although in some cases the maximum effect fell outside the observed data range. Radiation had a generally greater contribution to the combined inhibitory effect than cisplatin. In selected cases, synergistic effects of chemoradiation were also identified, primarily in the efficacy dimension. These preliminary results establish a robust in vitro platform for assessing chemoradiation efficacy and potency, and provide essential data for the future development of personalized and optimized chemoradiation strategies in canine and human. UC.