• Biomolecules & Therapeutics
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• v.23 no.4
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• pp.320-326
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• 2015

The clinical benefits of oncogenic BRAF inhibitor therapies are limited by the emergence of drug resistance. In this study, we investigated the role of a negative regulator of the MAPK pathway, Spry2, in acquired resistance using BRAF inhibitor-resistant derivatives of the BRAF-V600E melanoma (A375P/Mdr). Real-time RT-PCR analysis indicated that the expression of Spry2 was higher in A375P cells harboring the BRAF V600E mutation compared with wild-type BRAF-bearing cells (SK-MEL-2) that are resistant to BRAF inhibitors. This result suggests the ability of BRAF V600E to evade feedback suppression in cell lines with BRAF V600E mutations despite high Spry2 expression. Most interestingly, Spry2 exhibited strongly reduced expression in A375P/Mdr cells with acquired resistance to BRAF inhibitors. Furthermore, the overexpression of Spry2 partially restored sensitivity to the BRAF inhibitor PLX4720 in two BRAF inhibitor-resistant cells, indicating a positive role for Spry2 in the growth inhibition induced by BRAF inhibitors. On the other hand, long-term treatment with PLX4720 induced pERK reactivation following BRAF inhibition in A375P cells, indicating that negative feedback including Spry2 may be bypassed in BRAF mutant melanoma cells. In addition, the siRNA-mediated knockdown of Raf-1 attenuated the rebound activation of ERK stimulated by PLX4720 in A375P cells, strongly suggesting the positive role of Raf-1 kinase in ERK activation in response to BRAF inhibition. Taken together, these data suggest that RAF signaling may be released from negative feedback inhibition through interacting with Spry2, leading to ERK rebound and, consequently, the induction of acquired resistance to BRAF inhibitors.

• Biomolecules & Therapeutics
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• v.29 no.4
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• pp.434-444
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• 2021

BRAF inhibitors are insufficient monotherapies for BRAF-mutated cancer; therefore, we investigated which inhibitory pathway would yield the most effective therapeutic approach when targeted in combination with BRAF inhibition. The oncogenic BRAF inhibitor, PLX4720, increased basal autophagic flux in BRAF-mutated cells compared to wild-type (WT) BRAF cells. Interestingly, early autophagy inhibition improved the effectiveness of PLX4720 regardless of BRAF mutation, whereas late autophagy inhibition did not. Although ATG5 knockout led to PLX4720 resistance in both WT and BRAF-mutated cells, the MEK inhibitor trametinib exhibited a synergistic effect on PLX4720 sensitivity in WT BRAF cells but not in BRAF-mutated cells. Conversely, the prolonged inhibition of endoplasmic reticulum (ER) stress reduced basal autophagy in BRAF-mutated cells, thereby increasing PLX4720 sensitivity. Taken together, our results suggest that the combined inhibition of ER stress and BRAF may simultaneously suppress both pro-survival ER stress and autophagy, and may therefore be suitable for treatment of BRAF-mutated tumors whose autophagy is increased by chronic ER stress. Similarly, for WT BRAF tumors, therapies targeting MEK signaling may be a more effective treatment strategy. Together, this study presents a rational combination treatment strategy to improve the efficacy of BRAF inhibitors depending on BRAF mutation status.

• Biomolecules & Therapeutics
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• v.27 no.3
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• pp.302-310
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• 2019

Melanoma cells have been shown to respond to BRAF inhibitors; however, intrinsic and acquired resistance limits their clinical application. In this study, we performed RNA-Seq analysis with BRAF inhibitor-sensitive (A375P) and -resistant (A375P/Mdr with acquired resistance and SK-MEL-2 with intrinsic resistance) melanoma cell lines, to reveal the genes and pathways potentially involved in intrinsic and acquired resistance to BRAF inhibitors. A total of 546 differentially expressed genes (DEGs), including 239 up-regulated and 307 down-regulated genes, were identified in both intrinsic and acquired resistant cells. Gene ontology (GO) analysis revealed that the top 10 biological processes associated with these genes included angiogenesis, immune response, cell adhesion, antigen processing and presentation, extracellular matrix organization, osteoblast differentiation, collagen catabolic process, viral entry into host cell, cell migration, and positive regulation of protein kinase B signaling. In addition, using the PAN-THER GO classification system, we showed that the highest enriched GOs targeted by the 546 DEGs were responses to cellular processes (ontology: biological process), binding (ontology: molecular function), and cell subcellular localization (ontology: cellular component). Ingenuity pathway analysis (IPA) network analysis showed a network that was common to two BRAF inhibitorresistant cells. Taken together, the present study may provide a useful platform to further reveal biological processes associated with BRAF inhibitor resistance, and present areas for therapeutic tool development to overcome BRAF inhibitor resistance.

• Korean Journal of Head & Neck Oncology
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• v.30 no.2
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• pp.53-61
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• 2014

Background and Objectives : Anaplastic thyroid carcinoma(ATC) is a rare but highly aggressive thyroid malignancy that is associated with an extremely poor survival despite the best multidisciplinary care. BRAF(V600E) mutation is detected in about a quarter of ATC, but unlike its high treatment response to selective BRAF inhibitor (PLX4032) in metastatic melanoma, the treatment response of ATC is reported to be low. The purpose of this study is to investigate the innate resistance mechanism responsible for this low treatment response to BRAF inhibitor and its effect on epithelial-mesenchymal transition(EMT). Materials and Methods : Two ATP cell lines, 8505C and FRO were selected and treated with PLX4032 and its drug sensitivity and effects on cell migration and EMT were examined and compared. Further investigation on the changes in signals responsible for the different treatment response to PLX4032 was carried out and the same experiment was performed on both orthotopic and ectopic xenograft mouse models. Results : FRO cell line was more sensitive to PLX4032 treatment compared to 8505C cell line. The resistance to BRAF inhibition in 8505C was due to increased expression of EGFR. Effective inhibition of both EGFR and p-AKT was achieved after dual treatment with BRAF inhibitor(PLX4032) and EGFR inhibitor(Erlotinib). Similar results were confirmed on in vivo study. Conclusion : EGFR-mediated reactivation of the PI3K/AKT pathway and MAPK pathway contributes to the relative insensitivity of BRAF(V600E) mutant ATC cells to PLX4032. Dual inhibition of BRAF and EGFR leads to sustained treatment response including cell invasiveness.

• Genomics & Informatics
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• v.19 no.1
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• pp.2.1-2.10
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• 2021

BRAF inhibitors (e.g., vemurafenib) are widely used to treat metastatic melanoma with the BRAF V600E mutation. The initial response is often dramatic, but treatment resistance leads to disease progression in the majority of cases. Although secondary mutations in the mitogen-activated protein kinase signaling pathway are known to be responsible for this phenomenon, the molecular mechanisms governing acquired resistance are not known in more than half of patients. Here we report a genome- and transcriptome-wide study investigating the molecular mechanisms of acquired resistance to BRAF inhibitors. A microfluidic chip with a concentration gradient of vemurafenib was utilized to rapidly obtain therapy-resistant clones from two melanoma cell lines with the BRAF V600E mutation (A375 and SK-MEL-28). Exome and transcriptome data were produced from 13 resistant clones and analyzed to identify secondary mutations and gene expression changes. Various mechanisms, including phenotype switching and metabolic reprogramming, have been determined to contribute to resistance development differently for each clone. The roles of microphthalmia-associated transcription factor, the master transcription factor in melanocyte differentiation/dedifferentiation, were highlighted in terms of phenotype switching. Our study provides an omics-based comprehensive overview of the molecular mechanisms governing acquired resistance to BRAF inhibitor therapy.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.2
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• pp.699-705
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• 2015

Vemurafenib has recently been used as drug for treatment of melanomas with $BRAF^{V600E}$ mutation. Unfortunately, treatment with only vemurafenib has not been sufficiently effective, with recurrence after a short period. In this study, three vemurafenib-resistant $BRAF^{V600E}$ melanoma cell lines, $A375P^R$, $A375M^R$ and SKMEL-$28^R$, were established from the original A375P, A375M and SKMEL-28 cell lines. Examination of the molecular mechanisms showed that the phosphorylation levels of MEK and ERK, which play key roles in the RAS/RAF/MEK/ERK signaling pathway, were reduced in these three cell lines, with increased phosphorylation levels of pAKTs limited to SKMEL-$28^R$ cells. Treatment of SKMEL-$28^R$ cells with 100 nM paclitaxel resulted in increased apoptosis and decreased cellular proliferation, invasion and colony formation via reduction of expression levels of EGFR and pAKTs. Moreover, vemurafenib-induced pAKTs in SKMEL-$28^R$ were decreased by treatment with an AKT inhibitor, MK-2206. Taken together, our results revealed that resistance mechanisms of $BRAF^{V600E}$-mutation melanoma cells to vemurafenib depended on the cell type. Our results suggested that paclitaxel should be considered as a drug in combination with vemurafenib to treat melanoma cells.

• Journal of the Korean Medical Association
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• v.61 no.11
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• pp.662-669
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• 2018

The cutaneous melanoma has been regarded as rare disease entity in Korea for long time but it shows a silent growth recently. Furthermore the management of cutaneous melanoma including staging system, surgical principle, sentinel lymph node biopsy and subsequent complete node dissection and, most importantly, immunotherapy and target therapy against cutaneous melanoma recently. The incidence of cutaneous melanoma is steadily increasing in Korea but its increase is rapid recent 2 decades to 4.3 times and should be greater soon according to the steeper increase of life expectancy. New staging system proposed by American Joint Committee on Cancer (2017) includes changes in individual TNM category and stage groups, particularly from a prognostic viewpoint. Dermoscopy has been successfully introduced in the differential diagnosis of pigmented skin lesion focusing on cutaneous melanoma by non-invasive simple diagnostic tool. Sentinel lymph node biopsy was a issue of long debate whether survival benefit is real or not. Temporary conclusion about this question is reached after two large scale studies and immediate complete node dissection should be performed in a certain situations. Most important change is drug therapy focusing on immunotherapy and target therapy. Braf- and MEK-inhibitor, immune checkpoint inhibitor and PD-1 blocker has been proved to be effective as a sole or combination regimen against advanced and/or high-risk adjuvant setting of cutaneous melanoma. In conclusion, these remarkable changes will be reviewed shortly here.

• BMB Reports
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• v.54 no.12
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• pp.608-613
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• 2021

Melanoma, the most serious type of skin cancer, exhibits a high risk of metastasis. Although chemotherapeutic treatment for metastatic melanoma improves disease outcome and patient survival, some patients exhibit resistance or toxicity to the drug treatment regime. OTUB1 is a deubiquitinating enzyme overexpressed in several cancers. In this study, we investigated the effects of inhibiting OTUB1 expression on melanoma-cell proliferation and viability and identified the underlying molecular mechanism of action of OTUB1. We did endogenous OTUB1 knockdown in melanoma cells using short interfering RNA, and assessed the resulting phenotypes via MTT assays, Western blotting, and cell-cycle analysis. We identified differentially expressed genes between OTUB1-knockdown cells and control cells using RNA sequencing and confirmed them via Western blotting and reverse transcription polymerase chain reaction. Furthermore, we investigated the involvement of apoptotic and cell survival signaling pathways upon OTUB1 depletion. OTUB1 depletion in melanoma cells decreased cell viability and caused simultaneous accumulation of cells in the sub-G1 phase, indicating an increase in the apoptotic-cell population. RNA sequencing of OTUB1-knockdown cells revealed an increase in the levels of the apoptosis-inducing protein TRAIL. Additionally, OTUB1-knockdown cells exhibited increased sensitivity to PLX4032, a BRAF inhibitor, implying that OTUB1 and BRAF act collectively in regulating apoptosis. Taken together, our findings show that OTUB1 induces apoptosis of melanoma cells in vitro, likely by upregulating TRAIL, and suggest that approaches targeting OTUB1 can be developed to provide novel therapeutic strategies for treating melanoma.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.5
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• pp.2369-2374
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• 2014

Background and Aim: Selumetinib is a promising and interesting targeted therapy agent as it may reverse radioiodine uptake in patients with radioiodine-refractory differentiated thyroid cancer. We conduct this metaanalysis to compare the efficacy and safety of selumetinib with current therapies in patients with advanced cancer. Methods: An electronic search was conducted using PubMed/ Medicine, EMBASE and Cochrane library databases. Statistical analyses were carried out using either random-effects or fixed-effects models according to the heterogeneity of eligible studies. Results: Six eligible trials involved 601 patients were identified. Compared with current therapies, treatment schedules with selumetinib did not improve progression free survival (hazard ratio, 0.91; 95%CI 0.70-1.17, P= 0.448), but did identify better clinical benefits (odds ratio, 1.24; 95%CI 0.69-2.24, P = 0.472) and less disease progression (hazard ratio, 0.72; 95%CI 0.51-1.00, P = 0.052) though its impact was not statistically significant. Sub-group analysis resulted in significantly improved progression free survival (hazard ratio, 0.61; 95%CI 0.49-0.57, P = 0.00), clinical benefits (odds ratio, 3.04; 95%CI 1.60-5.77, P = 0.001) and reduced disease progression (hazard ratio, 0.35; 95%CI 0.18-0.67, P = 0.001) in patients administrated selumetinib. Dermatitis acneiform (risk ratio, 9.775; 95%CI 3.143-30.395, P = 0.00) and peripheral edema (risk ratio, 2.371; 95%CI 1.690-3.327, P = 0.00) are the most frequently observed adverse effects associated with selumetinib. Conclusions: Compared with current chemotherapy, selumetinib has modest clinical activity as monotherapy in patients with advanced cancer, but combinations of selumetinib with cytotoxic agents in patients with BRAF or KRAS mutations hold great promise for cancer treatment. Dermatitis acneiform and peripheral edema are the most frequently observed adverse effects in patients with selumetinib.