Targeting Cell‐Matrix Induced Chemoresistance With Regorafenib in a <scp>3D</scp> Model of Osteosarcoma

Over the past four decades, there has been little advancement in treatment strategies for osteosarcoma (OS), the predominant primary bone tumor in the pediatric patient population. Current therapy involves multiple rounds of chemotherapy and surgical resection, which are associated with significant morbidity and suboptimal survival rates. A key challenge in developing new treatments is the difficulty in replicating the OS tumor microenvironment, particularly cell interactions with the extracellular matrix (ECM). This study uses an in vitro model of OS to investigate the cell response to collagen (COL) type I, the primary component of the OS ECM. After 7 days of culture within three-dimensional COL hydrogels, OS cells displayed a more elongated cellular morphology and reduced sensitivity to the standard chemotherapy used for OS treatment compared to cells grown on two-dimensional substrates. To test whether this model could be used to study treatment strategies used for high-risk OS patients, we applied a metronomic regimen combining regorafenib, a multi-tyrosine kinase inhibitor, with front-line chemotherapy to overcome cell-matrix induced chemoresistance. We identified overexpression of the ATP-binding cassette transporter ABCG2, a drug efflux pump, as a potential mechanism of resistance in 3D culture. Regorafenib's inhibitory effect on ABCG2 suggests a mechanistic basis for its ability to restore chemosensitivity in 3D culture. Altogether, these findings highlight the importance of cell-matrix interactions in in vitro OS models, provide valuable insights into a matrix-induced mechanism of OS chemoresistance, and suggest an approach to its treatment.