Intravital imaging reveals how BRAF inhibition generates drug-tolerant microenvironments with high integrin β1/FAK signaling.
Bottom Line: Intravital imaging of BRAF-mutant melanoma cells containing an ERK/MAPK biosensor reveals how the tumor microenvironment affects response to BRAF inhibition by PLX4720.Fibronectin-rich matrices with 3-12 kPa elastic modulus are sufficient to provide PLX4720 tolerance.We propose that paradoxically activated MAFs provide a "safe haven" for melanoma cells to tolerate BRAF inhibition.
Affiliation: Tumor Cell Biology Laboratory, Cancer Research UK London Research Institute, London WC2A 3LY, UK.Show MeSH
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Mentions: We sought to establish a culture system that re-capitulated the PLX4720 tolerance that we observed in vivo. The behavior of pure spheroids of melanoma cells was compared with that of equivalent sized tumor pieces when embedded in a collagen matrix. Figures 2A and 2B show that pure melanoma spheroids were highly sensitive to PLX4720, with the appearance of many nuclear fragments indicating cell death. In contrast, melanoma explants from either subcutaneous tumors or experimentally established lung metastases were unresponsive to PLX4720 (Figures 2A and 2B). Even in the presence of drug, melanoma cells retained healthy nuclear architecture and invasive capability. Thus, the spheroid model recapitulates the stroma-dependent PLX4720 tolerance observed in vivo. It also formally excludes any problems relating to drug access that might confound interpretation of the in vivo data.
Affiliation: Tumor Cell Biology Laboratory, Cancer Research UK London Research Institute, London WC2A 3LY, UK.