“Intravital imaging reveals how stroma dictates heterogeneous responses to targeted therapy”
1The Francis Crick Institute, London, UK
The Ras-MAPK pathway is mutated in the majority of melanoma, with BRAF mutations being most common. Tumours with BRAF mutations show an initial response to BRAF inhibitors before genetic resistance emerges. However little is known about the spatio-temporal response to BRAF inhibitors in vivo and how this relates to the failure of targeted therapy. In this study, we have used both intravial ratiometic FRET and FLIM of an ERK/MAP kinase biosensor to investigate heterogeneity in signalling in melanoma models. We have longitudinally monitored responses to targeted therapy and identified areas that become refractory to drug action. BRAF mutant melanoma cells can rapidly become tolerant to PLX4720 in areas of high stroma. The rapid kinetics of this process indicate that it is not caused by genetic events. We demonstrate that PLX4720 has an unexpected effect on the tumour stroma leading to enhanced matrix remodelling. The remodelled matrix then provides signals that enable melanoma cells to tolerate PLX4720. We propose that this safe haven enhances the population of cancer cells from which genetically resistance emerges.