Advancing photocytotoxicity evaluation of nitric oxide derivative-ruthenium complex in 3D biofabricated breast cancer models

Cancer remains a major health challenge, emphasizing the need for innovative therapies. Photodynamic therapy (PDT) uses light-activated photosensitizers (PSs) to induce targeted cancer cell death, but clinical translation is limited by low tumor specificity, toxicity, and inadequate in vitro models. Three-dimensional (3D) tumor models provide physiologically relevant platforms that enhance translational predictability. Here, we evaluated a promising photoactivated ruthenium-based PS, {TPyP [Ru(NO 2 ) (bpy) 2 ] 4 }(PF 6 ) 4 complex (RuNO 2 TPyP), across 3D cancer models of increasing complexity, including free-standing spheroids, bioprinted spheroids within hydrogel matrix, and bioprinted patient-derived organoids (PDOs). The RuNO 2 TPyP complex triggered significant cell death and apoptosis while reducing tumor aggressiveness following PDT. Its efficacy was model-dependent: effective at 0.19 μM in free-standing spheroids, requiring higher concentrations (0.78 μM) in bioprinted spheroids embedded within a hydrogel matrix that mimics the tumor extracellular microenvironment, and showing substantial resistance in bioprinted PDOs (1.56 μM). These findings underscore the significance of bioprinted 3D models and establish a basis for future investigations of this and related PSs in personalized cancer therapy.