Abstract
BackgroundVemurafenib (PLX4032) is one of the most frequently used treatments for late-stage melanoma patients with the BRAFV600E mutation; however, acquired resistance to the drug poses as a major challenge. It remains to be determined whether off-target effects of vemurafenib on normal stroma components could reshape the tumor microenvironment in a way that contributes to cancer progression and drug resistance.MethodsBy using temporally-resolved RNA- and ATAC-seq, we studied the early molecular changes induced by vemurafenib in human dermal fibroblast (HDF), a main stromal component in melanoma and other tumors with high prevalence of BRAFV600 mutations.ResultsTranscriptomics analyses revealed a stepwise up-regulation of proliferation signatures, together with a down-regulation of autophagy and proteolytic processes. The gene expression changes in HDF strongly correlated in an inverse way with those in BRAFV600E mutant malignant melanoma (MaMel) cell lines, consistent with the observation of a paradoxical effect of vemurafenib, leading to hyperphosphorylation of MEK1/2 and ERK1/2. The transcriptional changes in HDF were not strongly determined by alterations in chromatin accessibility; rather, an already permissive chromatin landscape seemed to facilitate the early accessibility to MAPK/ERK-regulated transcription factor binding sites. Combinatorial treatment with the MEK inhibitor trametinib did not preclude the paradoxical activation of MAPK/ERK signaling in HDF. When administered together, vemurafenib partially compensated for the reduction of cell viability and proliferation induced by trametinib. These paradoxical changes were restrained by using the third generation BRAF inhibitor PLX8394, a so-called paradox breaker compound. However, the advantageous effects on HDF during combination therapies were also lost.ConclusionsVemurafenib induces paradoxical changes in HDF, enabled by a permissive chromatin landscape. These changes might provide an advantage during combination therapies, by compensating for the toxicity induced in stromal cells by less specific MAPK/ERK inhibitors. Our results highlight the relevance of evaluating the effects of the drugs on non-transformed stromal components, carefully considering the implications of their administration either as mono- or combination therapies.AvTAQshbXYn1EX7N3vKt_-Video
Highlights
Vemurafenib (PLX4032) is one of the most frequently used treatments for late-stage melanoma patients with the B RAFV600E mutation; acquired resistance to the drug poses as a major challenge
Dynamic transcriptional changes lead to an enhanced proliferation of fibroblasts after vemurafenib treatment To determine whether vemurafenib exerts off-target effects that could reshape the tumor microenvironment, we focused on understanding the dynamic transcriptional changes induced in non-transformed human dermal fibroblasts as a major stromal component [15, 16]
Principal component analysis (PCA) did not reveal a strong segregation of the transcriptomes based on the drug treatment; rather, the majority of the variance in gene expression was mainly driven by the stimulation time (Fig. 1A), suggesting that the short-term effects of vemurafenib on non-transformed human dermal fibroblast (HDF) are likely mild
Summary
Vemurafenib (PLX4032) is one of the most frequently used treatments for late-stage melanoma patients with the B RAFV600E mutation; acquired resistance to the drug poses as a major challenge. In 2011, the FDA approved the use of PLX4032, known as vemurafenib (short for V600E mutated BRAF inhibitor), as treatment of late-stage melanoma [5] This drug blocks the activation of the mitogen-activated protein kinase kinase (MAPK/ERK kinase; MEK) through an ATP-competitive inhibition of the kinase domain of BRAF with the mutations V600E and, to a minor extent, V600K [6], providing a median progression-free survival (PFS) of about seven months [7,8,9]
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