Epigenetic inhibitors eliminate senescent melanoma BRAFV600E cells that survive long‑term BRAF inhibition

Abstract

It is estimated that ~50% of patients with melanoma harbour B-Raf (BRAF)V600 driver mutations, with the most common of these being BRAFV600E, which leads to the activation of mitogen-activated protein kinase proliferative and survival pathways. BRAF inhibitors are used extensively to treat BRAF-mutated metastatic melanoma; however, acquired resistance occurs in the majority of patients. The effects of long-term treatment with PLX4032 (BRAFV600 inhibitor) were studied in vitro on sensitive V600E BRAF-mutated melanoma cell lines. After several weeks of treatment with PLX4032, the majority of the melanoma cells died; however, a proportion of cells remained viable and quiescent, presenting senescent cancer stem cell-like characteristics. This surviving population was termed SUR cells, as discontinuing treatment allowed the population to regrow while retaining equal drug sensitivity to that of parental cells. RNA sequencing analysis revealed that SUR cells exhibit changes in the expression of 1,415 genes (P<0.05) compared with parental cells. Changes in the expression levels of a number of epigenetic regulators were also observed. These changes and the reversible nature of the senescence state were consistent with epigenetic regulation; thus, it was investigated as to whether the senescent state could be reversed by epigenetic inhibitors. It was found that both parental and SUR cells were sensitive to different histone deacetylase (HDAC) inhibitors, such as SAHA and MGCD0103, and to the cyclin-dependent kinase (CDK)9 inhibitor, CDKI-73, which induced apoptosis and reduced proliferation both in the parental and SUR populations. The results suggested that the combination of PLX4032 with HDAC and CDK9 inhibitors may achieve complete elimination of SUR cells that persist after BRAF inhibitor treatment, and reduce the development of resistance to BRAF inhibitors.

BRAF Gene and Melanoma: Back to the Future

“…Concerning BRAF-mutant melanoma, many studies have pointed out the role of epigenetic mechanisms, mainly through HDAC, in resistance to BRAF and MEK inhibition [ 158 , 159 ], suggesting also the possibility of preventing the onset of resistance by using HDACi [ 160 ]. Indeed, an ongoing trial is investigating the HDACi vorinostat in resistant BRAF V600-mutant advanced melanoma patients (NCT02836548).…”

Enhancing Therapeutic Approaches for Melanoma Patients Targeting Epigenetic Modifiers

“…Treatment with the HDAC inhibitor vorinostat depleted MAPK inhibitor-resistant cells by increasing reactive oxygen species, increasing drug-sensitive clones that succumbed to BRAFi [ 113 ]. Another study showed that long-term treatment with the BRAFi PXL4032 on sensitive BRAF mutant melanoma cell lines induced senescent resistant clones that portrayed a stem cell-like phenotype and had an aberrant expression of multiple epigenetic modifiers such as HDAC6 [ 114 ]. This senescent state was reversed by HDAC inhibitors such as SAHA and mocetinostat (MGCD0103) [ 114 ].…”

“…Another study showed that long-term treatment with the BRAFi PXL4032 on sensitive BRAF mutant melanoma cell lines induced senescent resistant clones that portrayed a stem cell-like phenotype and had an aberrant expression of multiple epigenetic modifiers such as HDAC6 [ 114 ]. This senescent state was reversed by HDAC inhibitors such as SAHA and mocetinostat (MGCD0103) [ 114 ].…”

Discovery of BRAF/HDAC Dual Inhibitors Suppressing Proliferation of Human Colorectal Cancer Cells

“…Increasing evidence has been reported for the synergistic and additive effects of the joint use of HDAC inhibitors and BRAF inhibitors in colon cancer and melanoma (Lai et al, 2013;Carson et al, 2015;Fu et al, 2019). The combination of PLX4032 and HDAC inhibitors have been displayed complete elimination of cancer cells, and to reduce the progress of resistance to BRAF inhibitors (Madorsky Rowdo et al, 2020). Recently, Emmons et al revealed that HDAC8 inhibitors could enhance the durability of BRAF inhibitor therapy (Mer et al, 2019).…”