Mechanical Stiffening Promotes Growth, Invasion, and Mitogen-Activated Protein Kinase Kinase (MEK) Inhibitor Resistance in 3D Plexiform Neurofibroma Cultures

Plexiform neurofibromas with neurofibromatosis type I (pNF1s) are benign peripheral nerve sheath tumors caused by <i>NF1</i> loss, leading to dysregulated RAS/mitogen-activated protein kinase (MAPK) signaling. While mitogen-activated protein kinase kinase (MEK) inhibitors, selumetinib and mirdametinib, can reduce tumor volume, surgical resection remains the primary treatment for immediate debulking and symptom relief. Complete removal is often limited by tumor infiltration along nerve plexuses, and residual tumors may undergo postsurgical tissue remodeling, producing localized regions of stiffened extracellular matrix (ECM). The impact of ECM stiffness on pNF1 progression and drug response is unknown. Using patient-derived pNF1 tumor cells cultured in 3D hydrogels with defined stiffness (1.5 kPa soft, 7 kPa stiff), we found that stiff ECM promoted spread morphology, increased growth, and progressive intracellular softening. Stiff ECM reduced lysyl oxidase (LOX) expression, reflecting mechanoadaptive ECM remodeling, and upregulated P-glycoprotein, leading to decreased sensitivity to selumetinib. These results provide the first evidence that ECM stiffening, such as that arising from postsurgical remodeling, directly drives pNF1 progression and therapeutic resistance. Our findings highlight mechanobiology as a key regulator of tumor behavior and support targeting ECM mechanics to improve clinical outcomes in NF1 patients.