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: The data above show that PLX4720 elicits changes in matrix production and remodeling by MAFs. To test if the ECM was sufficient to modulate the response of melanoma cells to PLX4720, we varied both matrix composition and matrix stiffness. Figure S4A shows that fibronectin (FN) consistently reduces the effect of PLX4720 on both 5555 and 4434 melanoma cells. Other matrix components, including THBS1/2 and TNC, have more variable effects between the two cell lines. In addition to matrix composition, matrix stiffness affects the behavior of cancer cells. Therefore, we combined variations in matrix composition and matrix stiffness. Polyacrylamide gels ranging from 0.2 kPa (similar to adipose tissue) to 12 kPa (similar to stiff tumors or muscle) were coated with either collagen I, FN, or a combination of FN, THBS1/2, and TNC. Melanoma cells on low stiffness collagen I showed high levels of cell death following BRAF inhibition (Figures 4A and 4B). However, this was greatly abrogated if cells were cultured on FN matrices with either 3 kPa or 12 kPa stiffness, with the most impressive cell survival on 12 kPa FN-, THBS1/2-, and TNC,containing matrices (Figures 4A and 4B). These data demonstrate that an appropriate matrix composition and stiffness can render BRAF-mutant melanoma cells insensitive to PLX4720.
Affiliation: Tumor Cell Biology Laboratory, Cancer Research UK London Research Institute, London WC2A 3LY, UK.