Engineered biopolymeric hydrogels for in vitro modeling of equine sarcoid tumors in comparative oncology.

Developing advanced preclinical in vitro cancer models is essential for understanding tumor biology, improving drug discovery, and enhancing the clinical translation of new therapies. Papillomaviruses (PVs) cause diverse lesions in humans and animals; notably, bovine papillomavirus (BPV) is the main cause of equine sarcoid, the most common skin tumor in horses. Its pathogenesis involves viral infection, fibroblast transformation, and extracellular matrix (ECM) remodeling. These processes highlight the limitations of conventional two-dimensional (2D) culture systems, which fail to replicate the structural and biochemical complexity of the tumor microenvironment (TME). To overcome these limitations, this study presents, to the best of our knowledge, the first three-dimensional (3D) in vitro models of equine sarcoid based on chitosan (CHITO) and chitosan-collagen (CHITO-COL) hydrogels. Results showed that collagen incorporation did not alter the thermogelation process and structural integrity of chitosan. Both hydrogels displayed porosity, and stiffness values within the physiological range of native sarcoid tissue. The MTT assay revealed increased metabolic activity at days in vitro (DIV) 10, indicating active proliferation. Compared with 2D cultures, 3D models better preserved and upregulated key mesenchymal markers (Vimentin and CDH2). Our findings show how these biomimetic 3D platforms better replicate sarcoid TME, offering a promising tool for comparative oncology and PV-related human cancers.