10779/crick.12746111.v1 Eishu Hirata Eishu Hirata Maria Romina Girotti Maria Romina Girotti Amaya Viros Amaya Viros Steven Hooper Steven Hooper Bradley Spencer-Dene Bradley Spencer-Dene Michiyuki Matsuda Michiyuki Matsuda James Larkin James Larkin Richard Marais Richard Marais Erik Sahai Erik Sahai Intravital imaging reveals how BRAF inhibition generates drug-tolerant microenvironments with high integrin β1/FAK signaling The Francis Crick Institute 2020 Animals Cell Line, Tumor Drug Resistance, Neoplasm Focal Adhesion Protein-Tyrosine Kinases Humans Indoles Integrin beta1 Melanoma Mice Mice, Inbred C57BL Proto-Oncogene Proteins B-raf Signal Transduction Sulfonamides Tumor Microenvironment Sahai HP BRF-ack Oncology & Carcinogenesis 1112 Oncology and Carcinogenesis 1109 Neurosciences 2020-07-31 12:51:53 Journal contribution https://crick.figshare.com/articles/journal_contribution/Intravital_imaging_reveals_how_BRAF_inhibition_generates_drug-tolerant_microenvironments_with_high_integrin_1_FAK_signaling/12746111 Intravital imaging of BRAF-mutant melanoma cells containing an ERK/MAPK biosensor reveals how the tumor microenvironment affects response to BRAF inhibition by PLX4720. Initially, melanoma cells respond to PLX4720, but rapid reactivation of ERK/MAPK is observed in areas of high stromal density. This is linked to "paradoxical" activation of melanoma-associated fibroblasts by PLX4720 and the promotion of matrix production and remodeling leading to elevated integrin β1/FAK/Src signaling in melanoma cells. Fibronectin-rich matrices with 3-12 kPa elastic modulus are sufficient to provide PLX4720 tolerance. Co-inhibition of BRAF and FAK abolished ERK reactivation and led to more effective control of BRAF-mutant melanoma. We propose that paradoxically activated MAFs provide a "safe haven" for melanoma cells to tolerate BRAF inhibition.