Targeting DDR1 and DDR2 overcomes matrix-mediated melanoma cell adaptation to BRAF-targeted therapy

Resistance to BRAF/MEK inhibitor therapy in BRAFV600-mutated advanced melanoma remains a major obstacle that limits patient benefit. Microenvironment components including the extracellular matrix (ECM) can support tumor cell adaptation and tolerance to targeted therapy, however the underlying mechanisms remain poorly understood. Here, we investigated the process of matrix-mediated drug resistance (MMDR) in response to BRAFV600 pathway inhibition in melanoma. We demonstrate that physical and structural cues from fibroblast-derived ECM abrogate anti-proliferative responses to BRAF/MEK inhibition. MMDR is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2, two tyrosine kinase collagen receptors. Depletion and pharmacological targeting of DDR1 and DDR2 overcome ECM-mediated resistance to BRAF-targeted therapy. In xenografts, targeting DDR with Imatinib enhances BRAF inhibitor efficacy, counteracts drug-induced collagen remodeling and delays tumor relapse. Mechanistically, DDR-dependent MMDR fosters a targetable pro-survival NIK/IKKα/NF-κB2 pathway. These findings reveal a novel role for a collagen-rich matrix and DDR in tumor cell adaptation and resistance. They also provide important insights into environment-mediated drug resistance and a pre-clinical rationale for targeting DDR signaling in combination with targeted therapy in melanoma.