ABSTRACT: Tumorigenesis is a complex and dynamic process in which the tumor microenvironment (TME) plays a central role. In solid tumors, the TME contributes to key mechanisms of tumor progression, including metastasis, immune evasion, and resistance to therapies. One major challenge in preclinical cancer research is the development of reliable three-dimensional (3D) in vitro models, which more accurately replicate the in vivo tumor architecture and microenvironmental conditions, such as hypoxia and extracellular matrix (ECM) organization. However, reproducing functional vascular networks and neo-angiogenesis within these models remains a key challenge. In this study, an advanced 3D tumor model, referred to as angiotumoroids, was developed by co-culturing primary murine breast tumor cells (PTCs) with species-specific adipose-derived microvascular fragments (MVFs). Angiotumoroids successfully integrated MVFs, resulting in the formation of vasculature-like structures and demonstrated robust structural organization with a dynamic modulation of matrix metalloproteinase 9 (MMP9). Formation of neovasculature was visualized through sprouting and branching, driven by both direct PTC–MVF interactions and PTC-conditioned media, underscoring the importance of juxtacrine and paracrine signaling in vascular development within the tumor model. To further characterize these structures, high-resolution proteomic profiling was performed, revealing distinct patterns associated with angiogenesis, ECM composition, and remodeling. Angiotumoroids exhibited a unique proteomic signature, including differential expression of several angiogenic factors. ECM analysis confirmed the presence of collagen types I and IV and elevated expression of MMPs, highlighting active ECM remodeling. Additionally, the proteomic data revealed increased levels of ATP-binding cassette (ABC) transporters, particularly ABCB1 (P-glycoprotein), potential mechanisms of drug efflux. Functionally, angiotumoroids exhibited reduced sensitivity to doxorubicin compared to PTC spheroids, maintaining structural integrity and higher cell viability post-treatment. Time-course analysis of doxorubicin uptake revealed preferential accumulation in MVF-enriched regions, as confirmed by colocalization with CD31, pointing to a spatially regulated drug distribution pattern mediated by the vascular compartment. Collectively, these findings establish angiotumoroids as a robust and physiologically relevant in vitro model for investigating tumor vascularization, ECM dynamics, and therapeutic response. This platform holds significant promise for predictive cancer research and preclinical drug screening, bridging the gap between traditional in vitro systems and in vivo models
Margot Lo Pinto 
