Project description:Rapid resistance to BRAF inhibitors in BRAFV600-mutant metastatic melanoma has produced an urgent need for new treatment options. BRAF inhibitor resistance commonly involves reactivation of mitogen-activated protein kinase (MAPK) signaling and yet inhibition of downstream kinases has not circumvented resistance, partly because MAPK is regulated via a complex network of feedback mechanisms that influence pathway rebound. To examine the transcriptome responses of melanoma cells to MAPK inhibition, a panel of 11 BRAFV600-mutant melanoma cell lines were treated with control (DMSO), 100nM dabrafenib alone (i.e BRAF inhibitor monotherapy) or 100nM dabrafenib + 10nM trametinib (i.e combination BRAF + MEK inhibition) for 24h.
Project description:We identify a profoundly remodelled TME in targeted therapy resistant (RTT) tumours. We provide bulk transcriptomic data of targeted therapy naive (NTT) and RTT tumours of 3 murine models. Additionally, we provide low-input sequencing of CD103+ dendritic cells and T cells from NTT and RTT Braf/Pten tumours. We identified that in RTT cell lines the MAPK pathway is reactivated and provide SLAM-seq data to determine transcriptional targets of MAPK pathway inhibition in NTT and RTT cell lines. We also provide ATAC-Seq data of NTT and RTT cell lines sorted from tumors of the Braf/Pten melanoma model.
Project description:Recent trials with MAPK inhibitors have shown promising results in many patients with metastatic melanoma; however, nearly all responding patients experience disease relapse. We describe here how melanoma cells respond to MAPK inhibition in a phenotype-specific manner, suggesting that slow cycling invasive phenotype cells provide a treatment-resistant pool from which disease relapse may be derived. The implication is that while MAPK inhibition may successfully treat proliferating cells, another cell population needs to be addressed at the same time. 12 samples
Project description:Preclinical and clinical data implicate the transcriptional co-activator YAP1 in resistance to multiple targeted therapies, including BRAF and MEK inhibitors. However, tumor subtypes driven by YAP1 activity and associated vulnerabilities are poorly defined. Here, we show particularly high YAP1 activity in the MITFlow/AXLhigh subset of melanoma cell lines and patient tumors characterized by resistance to MAPK pathway inhibition and broad receptor tyrosine kinase activity. To uncover genetic dependencies of melanoma cells with high YAP1 activity, we used a genome-wide CRISPR/Cas9 functional screen and identified SLC35B2, the 3′-phosphoadenosine-5′-phosphosulfate transporter of the Golgi apparatus, as an essential gene for YAP1-mediated drug resistance. SLC35B2 expression correlates with tumor progression, and its loss decreases heparan sulfate expression, reduces receptor tyrosine kinase activity, and sensitizes resistant melanoma cells to BRAF inhibition in vitro and in vivo. Thus, SLC35B2 is a target in YAP1-driven BRAF mutant melanoma for overcoming drug resistance to MAPK pathway inhibitors.
Project description:Survival kinase MELK has been shown to be important for proliferation of several tumors such as brain, breast or prostate. MELK expression is elevated in cutaneous melanoma, therefore, we analyzed the role of MELK in melanoma. Inhibition of MELK in melanoma cell lines resulted in decreased proliferation, increased cell death and decreased invasion. MELK expression is regulated through MAP kinase pathway and inhibition of MAPK pathway leads to diminished MELK expression. Finally, inhibition of MELK reduces tumor size in nude mice.
Project description:Inhibitors of the MAPKs, BRAF and MEK, induce tumor regression in the majority of patients with BRAF-mutant metastatic melanoma. The clinical benefit of MAPK inhibitors is restricted by the development of acquired resistance with half of those who benefit having progressed by 6-7 months and long-term responders uncommon. There remains no agreed treatment strategy on disease progression in these patients. Without published evidence, fears of accelerated disease progression on inhibitor withdrawal have led to the continuation of drugs beyond formal disease progression. We now demonstrate that treatment with MAPK inhibitors beyond disease progression can provide significant clinical benefit, and the withdrawal of these inhibitors led to a marked increase in the rate of disease progression in two patients. We also show that MAPK inhibitors retain partial activity in acquired resistant melanoma by examining drug-resistant clones generated to dabrafenib, trametinib or the combination of these drugs. All resistant sublines displayed a markedly slower rate of proliferation when exposed to MAPK inhibitors, and this coincided with a reduction in MAPK signalling, decrease in BrdU incorporation and S-phase inhibition. This cytostatic effect was also associated diminished levels of cyclin D1 and p-pRb.. Two short-term melanoma cultures generated from resistant tumour biopsies also responded to MAPK inhibition with comparable inhibitory changes in proliferation and MAPK signalling. These data provide a rationale for the continuation of BRAF and MEK inhibitors after disease progression and support the development of clinical trials to examine this strategy. Total RNA obtained from melanooma cell lines treated for 24h with dabrafenib, trametinib or combination of dabrafenib and trametinib
Project description:Current therapeutic management of advanced melanoma patients largely depends on their BRAF mutation status. However, the vast heterogeneity of the tumors hampers the success of therapies targeting the MAPK/ERK pathway alone. Dissecting this heterogeneity will contribute to identifying key players in the oncogenic progression to tailor more effective therapies. We performed a comprehensive molecular and phenotypic characterization of a panel of patient-derived BRAFV600E-positive melanoma cell lines. Transcriptional profiling was used to identify groups of coregulated genes whose expression relates to an increased migratory potential and a higher resistance. A decrease in sensitivity to MAPK/ERK pathway inhibition with vemurafenib or trametinib corresponded with an increasing quiescence and migratory properties of the cells. This was accompanied by the loss of transcriptional signatures of melanocytic differentiation, and the gain of stem cell features that conferred highly-resistant/mesenchymal-like cells with increased xenobiotic efflux capacity. Nevertheless, targeting of the implicated ABC transporters did not improve the response to vemurafenib, indicating that incomplete BRAF inhibition due to reduced drug uptake is not a main driver of resistance. Rather, indifference to MAPK/ERK pathway inhibition arose from the activation of compensatory signaling cascades. The PI3K/AKT pathway in particular showed a higher activity in mesenchymal-like cells, conferring a lower dependency on MAPK/ERK signaling and supporting stem-like properties that could be reverted by dual PI3K/mTOR inhibition with dactolisib. In case of MAPK/ERK independency, therapeutic focus may be shifted to the PI3K/AKT pathway to overcome late-stage resistance in melanoma tumors that have acquired a mesenchymal phenotype.
Project description:Small-molecule inhibitors targeting the most commonly activated pathway in melanoma, MAPK pathway (either alone or in combination) are already given to melanoma patients for few years, and initially reduce tumour burden dramatically, eventually melanomas become resistant and tumours progress while on treatment. Resistance to this treatment occurs by acquisition of additional mutations or other alterations that affect the mitogen-activated protein kinase (MAPK) pathway by either direct or indirect signalling. Many resistance mechanisms somehow lead to reactivation of extracellular signal-regulated kinase (ERK), thereby restoring signalling of the oncogenic BRAF/MEK/ERK pathway. In addition, PI3K pathway activation contributes to resistance to BRAF inhibition. Less frequent but equally important to the phenomenon of targeted drug resistance is the observation that B15–20% of BRAF mutant melanoma patients fail to respond to BRAF inhibition already early on treatment, owing to intrinsic resistance. These patients have little therapeutic options, unless immunotherapy can be given. To better understand the resistance mechanisms in MAPK inhibitor-treated melanoma patients and melanoma biology, our lab generated a big panel of MAPK inhibitor resistant melanoma cell lines by continuous drug exposure. The understanding of the genetic landscape and gene expression as well as cross resistance to other treatment regimens, and other aspects of melanoma biology such as phenotype switch, will allow us to better exploit new therapeutic strategies for melanoma patients.
Project description:Combined therapy with anti-BRAF plus anti-MEK is currently used as first-line treatment of patients with metastatic melanomas harboring the somatic BRAF V600E mutation. However, the main issue with targeted therapy is the acquisition of tumor cell resistance. In 70% of resistant melanoma cells, the resistant process consists in epithelial-to-mesenchymal transition (EMT). This process called phenotype switching makes melanoma cells more invasive. Its signature is characterized by MITF low, AXL high, and actin cytoskeleton reorganization through RhoA activation. In parallel of this phenotype switching phase, the resistant cells exhibit an anarchic cell proliferation due to hyper-activation of the MAP kinase pathway. We show that a majority of human melanoma overexpress discoidin domain receptor 2 (DDR2) after treatment. The same result was found in resistant cell lines presenting phenotype switching compared to the corresponding sensitive cell lines. We demonstrate that DDR2 inhibition induces a decrease in AXL expression and reduces stress fiber formation in resistant melanoma cell lines. In this phenotype switching context, we report that DDR2 control cell and tumor proliferation through the MAP kinase pathway in resistant cells in vitro and in vivo. Therefore, inhibition of DDR2 could be a new and promising strategy for countering this resistance mechanism.