Targeting Drug Efflux Pump Chemoresistance with Regorafenib in a 3D Tissue-Engineered Model of Osteosarcoma

Treatment strategies for osteosarcoma (OS), the predominant primary bone tumor in the pediatric patient population, have witnessed minimal progress over the past four decades. 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 osteosarcoma tumor microenvironment, particularly cell interactions with the extracellular matrix (ECM). This study uses a novel in vitro model of osteosarcoma to investigate the cell-response to collagen type I, the primary component of the osteosarcoma ECM. After seven days of culture within three-dimensional (3D) collagen hydrogels, osteosarcoma cells displayed a more elongated cellular morphology and reduced sensitivity to the standard chemotherapy used for osteosarcoma treatment compared to cells grown on two-dimensional (2D) substrates. We identified the overexpression of an ATP-binding cassette transporter, ABCG2, as a mechanism of chemoresistance within the 3D culture, and developed a metronomic treatment regimen with regorafenib, a tyrosinase kinase inhibitor used for relapsed OS, to counteract cell-matrix induced chemoresistance. 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 a novel approach to its treatment.