BRAF inhibitor rechallenge in patients with advanced BRAF V600-mutant melanoma

Pro-Apoptotic Activity of MCL-1 Inhibitor in Trametinib-Resistant Melanoma Cells Depends on Their Phenotypes and Is Modulated by Reversible Alterations Induced by Trametinib Withdrawal

BACKGROUND

Although BRAFV600/MEK inhibitors improved the treatment of melanoma patients, resistance is acquired almost inevitably.

METHODS

Trametinib withdrawal/rechallenge and MCL-1 inhibition in trametinib-resistance models displaying distinct p-ERK1/2 levels were investigated.

RESULTS

Trametinib withdrawal/rechallenge caused reversible changes in ERK1/2 activity impacting the balance between pro-survival and pro-apoptotic proteins. Reversible alterations were found in MCL-1 levels and MCL-1 inhibitors, BIM and NOXA. Taking advantage of melanoma cell dependency on MCL-1 for survival, we used S63845. While it was designed to inhibit MCL-1 activity, we showed that it also significantly reduced NOXA levels. S63845-induced apoptosis was detected as the enhancement of Annexin V-positivity, caspase-3/7 activation and histone H2AX phosphorylation. Percentages of Annexin V-positive cells were increased most efficiently in trametinib-resistant melanoma cells displaying the p-ERK1/2low/MCL-1low/BIMhigh/NOXAlow phenotype with EC50 values at concentrations as low as 0.1 μM. Higher ERK1/2 activity associated with increased MCL-1 level and reduced BIM level limited pro-apoptotic activity of S63845 further influenced by a NOXA level.

CONCLUSIONS

Our study supports the notion that the efficiency of an agent designed to target a single protein can largely depend on the phenotype of cancer cells. Thus, it is important to define appropriate phenotype determinants to stratify the patients for the novel therapy.

Efficacy and Safety of Rechallenge with BRAF/MEK Inhibitors in Advanced Melanoma Patients: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aims to evaluate the efficacy and safety of rechallenging advanced melanoma patients with BRAFi/MEKi. Seven studies, accounting for 400 patients, were included. Most patients received immunotherapy before the rechallenge, and 79% underwent rechallenge with the combination of BRAFi/MEKi. We found a median progression-free survival of 5 months and overall survival of 9.8 months. The one-year survival rate was 42.63%. Regarding response, ORR was 34% and DCR 65%. There were no new or unexpected safety concerns. Rechallenge with BRAFi/MEKi can improve outcomes in advanced melanoma patients with refractory disease. These findings have significant implications for clinical practice, particularly in the setting of progressive disease in later lines and limited treatment options.

Trametinib-Resistant Melanoma Cells Displaying MITFhigh/NGFRlow/IL-8low Phenotype Are Highly Responsive to Alternating Periods of Drug Withdrawal and Drug Rechallenge

Despite significant advances in targeted therapies against the hyperactivated BRAF^V600/MEK pathway for patients with unresectable metastatic melanoma, acquired resistance remains an unsolved clinical problem. In this study, we focused on melanoma cells resistant to trametinib, an agent broadly used in combination therapies. Molecular and cellular changes were assessed during alternating periods of trametinib withdrawal and rechallenge in trametinib-resistant cell lines displaying either a differentiation phenotype (MITF^high/NGFR^low) or neural crest stem-like dedifferentiation phenotype (NGFR^high/MITF^low). Neither drug withdrawal nor drug rechallenge induced cell death, and instead of loss of fitness, trametinib-resistant melanoma cells adapted to altered conditions by phenotype switching. In resistant cells displaying a differentiation phenotype, trametinib withdrawal markedly decreased MITF level and activity, which was associated with reduced cell proliferation capacity, and induced stemness assessed as NGFR-positive cells and senescence features, including IL-8 expression and secretion. All these changes could be reversed by trametinib re-exposure, which emphasizes melanoma cell plasticity. Trametinib-resistant cells displaying a dedifferentiation phenotype were less responsive presumably due to the already low level of MITF, a master regulator of the melanoma phenotype. Considering new directions of the development of anti-melanoma treatment, our study suggests that the phenotype of melanomas resistant to targeted therapy might be a crucial determinant of the selection of second-line therapy for melanoma patients.

Tolerability of BRAF and MEK Inhibitors for Metastasized Melanoma after Intra-Class Switch: A Multicenter, Retrospective Study

Targeted therapy with BRAF and MEK inhibitors (BRAFi, MEKi) is one of the mainstays of melanoma treatment. When dose-limiting toxicity (DLT) is observed, an option represents the intra-class switch to a different BRAFi+MEKi combination. Currently, there is scarce evidence for this procedure. This is a multicenter, retrospective analysis from six German skin cancer centers of patients who received two different combinations of BRAFi and MEKi. In total, 94 patients were included: 38 patients (40%) were re-exposed with a different combination because of previous unacceptable toxicity, 51 (54%) were re-exposed after progression, and 5 (5%) were included for other reasons. Of the 44 patients with a DLT during their first BRAFi+MEKi combination, only five (11%) experienced the same DLT during their second combination. A new DLT was experienced by 13 patients (30%). Six patients (14%) had to discontinue the second BRAFi treatment due to its toxicity. Compound-specific adverse events were avoided in the majority of patients by switching to a different combination. Efficacy data were similar to historical cohorts of BRAFi+MEKi rechallenge, with an overall response rate of 31% for patients who had previously progressed to treatment. We conclude that switching to a different BRAFi+MEKi combination if dose-limiting toxicity occurs is a feasible and rational approach in patients with metastatic melanoma.

The Fra-1/AP-1 Oncoprotein: From the "Undruggable" Transcription Factor to Therapeutic Targeting

The genetic and epigenetic changes affecting transcription factors, coactivators, and chromatin modifiers are key determinants of the hallmarks of cancer. The acquired dependence on oncogenic transcriptional regulators, representing a major determinant of cancer cell vulnerability, points to transcription factors as ideal therapeutic targets. However, given the unavailability of catalytic activities or binding pockets for small-molecule inhibitors, transcription factors are generally regarded as undruggable proteins. Among components of the AP-1 complex, the FOS-family transcription factor Fra-1, encoded by FOSL1, has emerged as a prominent therapeutic target. Fra-1 is overexpressed in most solid tumors, in response to the BRAF-MAPK, Wnt-beta-catenin, Hippo-YAP, IL-6-Stat3, and other major oncogenic pathways. In vitro functional analyses, validated in onco-mouse models and corroborated by prognostic correlations, show that Fra-1-containing dimers control tumor growth and disease progression. Fra-1 participates in key mechanisms of cancer cell invasion, Epithelial-to-Mesenchymal Transition, and metastatic spreading, by driving the expression of EMT-inducing transcription factors, cytokines, and microRNAs. Here we survey various strategies aimed at inhibiting tumor growth, metastatic dissemination, and drug resistance by interfering with Fra-1 expression, stability, and transcriptional activity. We summarize several tools aimed at the design and tumor-specific delivery of Fra-1/AP-1-specific drugs. Along with RNA-based therapeutics targeting the FOSL1 gene, its mRNA, or cognate regulatory circRNAs, we will examine the exploitation of blocking peptides, small molecule inhibitors, and innovative Fra-1 protein degraders. We also consider the possible caveats concerning Fra-1 inhibition in specific therapeutic contexts. Finally, we discuss a recent suicide gene therapy-based approach, aimed at selectively killing the Fra-1-overexpressing neoplastic cells.

Mitogen-activated protein kinase blockade in melanoma: intermittent versus continuous therapy, from preclinical to clinical data

PURPOSE OF REVIEW

Although targeted therapy provides a high response rate and rapid disease control in advanced melanoma, most patients experience disease progression due to acquired resistance mechanisms leading to reactivation of mitogen-activated protein kinase pathway. The purpose of this article is to review the recently published data on the impact of an intermittent versus continuous dosing schedule of BRAF and MEK inhibition in advanced melanoma to determine the best approach in clinical practice.

RECENT FINDINGS

Some preclinical studies have highlighted the concept that drug-resistant cells may also display drug dependency, such that intermittent dosing of targeted therapy may prevent the emergence of lethal drug resistance. Moreover, clinical observations have suggested that repeated treatment after a break or an intervening therapy may provide clinical benefit. However, recent preclinical and clinical studies have also failed to demonstrate an advantage of intermittent dosing and showed a similar efficacy of the intermittent versus continuous regimens of BRAF and MEK inhibitors in mice models and phase 2 clinical trial.

SUMMARY

Owing to these discordant results, continuous dosing of BRAF and MEK inhibitors remains the optimal therapeutic approach until additional clinical data demonstrate the superiority of another combination or dosing regimen.

BRAF and MEK inhibitors rechallenge as effective treatment for patients with metastatic melanoma

Despite considerable progress made in the treatment of patients with advanced melanoma, the majority of the patients treated with BRAF and mitogen-activated protein inhibitors (BRAFi and MEKi) experience a disease progression due to acquired resistance. Currently, ongoing studies explore the possibility to overcome or reverse this process. Our multicenter retrospective analysis included 51 patients with metastatic BRAF-mutated melanoma who had previously progressed on BRAFi/MEKi than had progressed on immunotherapy (anti-progression disease-1 or anti-cytotoxic T-lymphocyte-associated protein 4) and next were rechallenged with BRAFi/MEKi. Median age at BRAFi/MEKi rechallenge was 56 (range: 31-82 y/o). Median overall survival from the start of the first BRAFi/MEKi therapy and from rechallenge BRAFi/MEKi treatment was 29.7 and 9.3 months, respectively, whereas median progression-free survival was 10.5 and 5.9 months, respectively. Six-month, annual, and 2-year overall survival rates on both treatments were: 98% and 55%, 92% and 29%, and 69% and 2%, respectively. A response rate to treatment was higher in the group receiving BRAFi/MEKi for the first time as compared with the group receiving BRAFi/MEKi rechallenge and was overall response rate 72% and 27%; disease control rate 92% and 63%. Time interval between the end of the first BRAFi/MEKi treatment and the beginning of BRAFi/MEKi rechallenge did not influence median overall survival or progression-free survival. A lower toxicity rate was noted with BRAFi/MEKi rechallenge. BRAFi/MEKi rechallenge treatment remains clinically important and is associated with the lower toxicity. BRAFi/MEKi rechallenge efficacy is higher in patients who are in good performance status, with normal lactate dehydrogenase, and without brain metastases.

Decreased survival in patients treated by chemotherapy after targeted therapy compared to immunotherapy in metastatic melanoma

Background

Cytotoxic chemotherapy (CC) is currently used in metastatic melanoma after patients have developed resistance to immune checkpoint inhibitors (ICI) and/or Mitogen‐Activated Protein Kinase inhibitors (MAPKi). We sought to evaluate if a previous treatment by ICI or MAPKi influences clinical outcomes in patients treated by CC in metastatic melanoma.

Methods

Eighty‐eight patients with a metastatic melanoma, treated by CC after a previous treatment by ICI or MAPKi between January 2009 and October 2019, were retrospectively analyzed. Progression‐Free‐Survival (PFS), Overall Survival (OS), Overall Response Rate (ORR), and Disease Control Rate (DCR) were evaluated in patients treated by CC according to their prior treatment by ICI or MAPKi.

Results

Patients treated by CC after ICI tended to have a better median PFS (2.81 months (2.39–5.30) versus 2.40 months (0.91–2.75), p = 0.023), median OS (6.03 months (3.54–11.54) versus 4.44 months (1.54–8.59), p = 0.27), DCR (26.0% vs. 10.5%, p = 0.121) and ORR (22.0% vs. 7.9% p = 0.134) than those previously treated by MAPKi.

Conclusions

A prior treatment by an MAPKi may be associated with a worse response to CC than ICI, and further investigations should be performed to confirm if there is a clinical benefit to propose CC in this setting.

Mechanisms of Resistance to BRAF-Targeted Melanoma Therapies

About half of all cutaneous melanomas harbor activating mutations in the BRAF oncogene. Dependence on this pathway makes the tumors vulnerable to BRAF (and downstream MEK) inhibition, and three drug combinations are approved to target this vulnerability in advanced melanomas with BRAFV600 mutations. Responses to BRAF/MEK inhibitors are usually fast, but durability of response can be limited. Five-year data from BRAF/MEK inhibitors show long-term survival benefit for a third of the patients. There is a wide variety of known mechanisms of resistance to BRAF/MEK inhibition, such as mitogen-activated protein kinase reactivation, activation of parallel pathways, alterations in cell-cycle regulation, and non-genetic resistance mechanisms. Strategies that have been explored to overcome these mechanisms include alternative dosing regimens, addition of another kinase inhibitor, and use of anti-PD-1 immunotherapy either in combination or post-relapse on BRAF/MEK inhibitor therapies.

The positive correlation between drug addiction and drug dosage in vemurafenib-resistant melanoma cells is underpinned by activation of ERK1/2-FRA-1 pathway

Malignant melanoma is a kind of highly invasive and deadly diseases. The BRAF inhibitor (BRAFi) such as vemurafenib could achieve a high response rate in melanoma patients with BRAF mutation. However, melanoma cells could easily develop resistance as well as addiction to BRAFi. Based on the drug addiction, intermittent treatment has been proposed to select against BRAFi-resistant melanoma cells. Because different dosages of BRAFi might be used in patients, it is necessary to know about the relationship between drug dosage and the degree of addiction. To address the problem, four drug-resistant melanoma cell sublines (A375/R0.5, A375/R2.0, M14/R0.5 and M14/R2.0) were established by continuously exposure of melanoma A375 or M14 cells to 0.5 or 2.0 μM vemurafenib. Vemurafenib withdrawal resulted in much stronger suppression on clone formation in A375/R2.0 and M14/R2.0, compared with A375/R0.5 and M14/R0.5, respectively. Meanwhile, stronger upregulation of ERK1/2-FRA-1 pathway could be observed in A375/R2.0 and M14/R2.0. Further detection showed that some proinflammatory cytokines downstream of ERK1/2-FRA-1 pathway were upregulated after drug withdrawal, and the conditioned medium collected from the resistant A375 cells could inhibit clone formation. Furthermore, vemurafenib withdrawal resulted in suppressed cell proliferation rather than cell senescence, with stronger effect on A375/R2.0 compared with A375/R0.5. This study suggested that the depth of vemurafenib addiction in resistant melanoma cells is positively correlated to the drug dosage, which might be underpinned by the ERK1/2-FRA-1 pathway and the related cytokines.

ESMO consensus conference recommendations on the management of metastatic melanoma: under the auspices of the ESMO Guidelines Committee

The European Society for Medical Oncology (ESMO) held a consensus conference on melanoma on 5-7 September 2019 in Amsterdam, The Netherlands. The conference included a multidisciplinary panel of 32 leading experts in the management of melanoma. The aim of the conference was to develop recommendations on topics that are not covered in detail in the current ESMO Clinical Practice Guideline and where available evidence is either limited or conflicting. The main topics identified for discussion were (i) the management of locoregional disease; (ii) targeted versus immunotherapies in the adjuvant setting; (iii) targeted versus immunotherapies for the first-line treatment of metastatic melanoma; (iv) when to stop immunotherapy or targeted therapy in the metastatic setting; and (v) systemic versus local treatment for brain metastases. The expert panel was divided into five working groups to each address questions relating to one of the five topics outlined above. Relevant scientific literature was reviewed in advance. Recommendations were developed by the working groups and then presented to the entire panel for further discussion and amendment before voting. This manuscript presents the results relating to the management of metastatic melanoma, including findings from the expert panel discussions, consensus recommendations and a summary of evidence supporting each recommendation. All participants approved the final manuscript.

Metabolic imaging using hyperpolarized 13 C-pyruvate to assess sensitivity to the B-Raf inhibitor vemurafenib in melanoma cells and xenografts

Nearly all melanoma patients with a BRAF‐activating mutation will develop resistance after an initial clinical benefit from BRAF inhibition (BRAFi). The aim of this work is to evaluate whether metabolic imaging using hyperpolarized (HP) ¹³C pyruvate can serve as a metabolic marker of early response to BRAFi in melanoma, by exploiting the metabolic effects of BRAFi. Mice bearing human melanoma xenografts were treated with the BRAFi vemurafenib or vehicle. In vivo HP ¹³C magnetic resonance spectroscopy was performed at baseline and 24 hours after treatment to evaluate changes in pyruvate‐to‐lactate conversion. Oxygen partial pressure was measured via electron paramagnetic resonance oximetry. Ex vivo qRT‐PCR, immunohistochemistry and WB analysis were performed on tumour samples collected at the same time‐points selected for in vivo experiments. Similar approaches were applied to evaluate the effect of BRAFi on sensitive and resistant melanoma cells in vitro, excluding the role of tumour microenvironment. BRAF inhibition induced a significant increase in the HP pyruvate‐to‐lactate conversion in vivo, followed by a reduction of hypoxia. Conversely, the conversion was inhibited in vitro, which was consistent with BRAFi‐mediated impairment of glycolysis. The paradoxical increase of pyruvate‐to‐lactate conversion in vivo suggests that such conversion is highly influenced by the tumour microenvironment.

Intracranial antitumor activity with encorafenib plus binimetinib in patients with melanoma brain metastases: A case series

Background

Sixty percent of patients with stage IV melanoma may develop brain metastases, which result in significantly increased morbidity and a poor overall prognosis. Phase 3 studies of melanoma usually exclude patients with untreated brain metastases; therefore, clinical data for intracranial responses to treatments are limited.

Methods

A multicenter, retrospective case series investigation of consecutive BRAF‐mutant patients with melanoma brain metastases (MBMs) treated with a combination of BRAF inhibitor encorafenib and MEK inhibitor binimetinib was conducted to evaluate the antitumor response. Assessments included the intracranial, extracranial, and global objective response rates (according to the modified Response Evaluation Criteria in Solid Tumors, version 1.1); the clinical benefit rate; the time to response; the duration of response; and safety.

Results

A total of 24 patients with stage IV BRAF‐mutant MBMs treated with encorafenib plus binimetinib in 3 centers in the United States were included. Patients had received a median of 2.5 prior lines of treatment, and 88% had prior treatment with BRAF/MEK inhibitors. The intracranial objective response rate was 33%, and the clinical benefit rate was 63%. The median time to a response was 6 weeks, and the median duration of response was 22 weeks. Among the 21 patients with MBMs and prior BRAF/MEK inhibitor treatment, the intracranial objective response rate was 24%, and the clinical benefit rate was 57%. Similar outcomes were observed for extracranial and global responses. The safety profile for encorafenib plus binimetinib was similar to that observed in patients with melanoma without brain metastases.

Conclusions

Combination therapy with encorafenib plus binimetinib elicited intracranial activity in patients with BRAF‐mutant MBMs, including patients previously treated with BRAF/MEK inhibitors. Further prospective studies are warranted and ongoing.

All clinical trials to date with encorafenib and binimetinib (US Food and Drug Administration–approved in June 2018 for BRAF‐mutated metastatic melanoma) have excluded untreated melanoma brain metastases. This case series provides the first clinical evidence of intracranial activity of the combination of encorafenib plus binimetinib in patients with BRAF‐mutant melanoma with active brain metastases. Intracranial clinical activity is observed for the first time in patients previously treated with BRAF/MEK inhibitors, a population that has not been previously investigated.

Severe Drug-Induced Liver Injury from Combination Encorafenib/Binimetinib

Encorafenib/binimetinib is a new combination BRAF/MEK inhibitor used in the treatment of advanced or metastatic BRAFV600-mutant melanoma. Though generally tolerated well, mild to moderate aminotransferase elevations are common. However, significant liver injury has not been demonstrated in the literature. Here, we report the first case of severe hepatic injury associated with encorafenib/binimetinib in a 58-year-old gentleman requiring admission and extensive workup. He was successfully treated by withdrawing the combination therapy, and liver function returned to normal range.

The efficacy of re-challenge with BRAF inhibitors after previous progression to BRAF inhibitors in melanoma: A retrospective multicenter study

BRAF and MEK inhibition is efficient in patients with BRAF V600-mutated metastatic melanoma, but due to acquired resistance the duration of response (DoR) is often only short-lived. In this retrospective multicenter study with 60 patients suffering from inoperable or metastatic melanoma we evaluated the efficacy of re-challenge with a BRAF inhibitor (BRAF2) with or without MEK-inhibition after progressive disease upon previous treatment with a BRAF inhibitor (BRAF1) with or without MEK inhibition.

Treatment with BRAF1 led to a disease control rate (DCR) of 90% with 12% complete responses (CR), 58% partial responses (PR) and 20% stable diseases (SD), the median progression-free survival (PFS) was 9.9 and DoR 10.7 months. BRAF2 with (68%) or without (32%) additional MEK inhibition was initiated after a median interval of 3.4 months. DCR after re-challenge with BRAF2 was 57%, 8% CR, 20% PR and 28% SD, median PFS was 5.0 and DoR 14.0 months. The duration of the treatment interval or the treatment in the interval did not influence the DCR or PFS to BRAF2. The only predictive factor for response to BRAF2 was previous response to BRAF1; all patients with CR to BRAF1 achieved disease control with BRAF2, but only 60% of the patients with PR to BRAF1 (p=0.002). Addition of MEK inhibition to BRAF2 after treatment with BRAF1 as monotherapy did not significantly increase the DCR or PFS compared to patients treated solely with mono- or combination therapy.

In conclusion re-challenge with a BRAF inhibitor is a meaningful therapeutic option for patients with BRAF V600-mutated metastatic melanoma.

Dabrafenib plus trametinib rechallenge in four melanoma patients who previously progressed on this combination

In unresectable or metastatic melanoma with a BRAF V600 mutation, combined BRAF/MEK targeted therapy improves clinical outcomes. Yet, disease progression because of acquired resistance occurs in the majority of patients. There is emerging evidence that resistance to BRAF-inhibitor-based targeted therapy can be reversible in some cases. We retrospectively analyzed four patients with BRAF-mutant stage IV cutaneous melanoma who were treated with dabrafenib plus trametinib and rechallenged with the same combination after previously experiencing progression. At initial treatment with dabrafenib plus trametinib, three patients achieved a partial response and one patient achieved a complete response. Progression-free survival varied from 9.9 to 24.3 (median 19.8) months. The targeted therapy-free interval ranged from 2.3 to 11.7 (median 8.8) months. At rechallenge, all four patients had a partial response, with progression-free survival ranging from 3.6 to 6.8 (median 5.2) months. Clinical benefit and a second radiological response can be obtained upon readministration of dabrafenib plus trametinib after previously acquiring resistance to this combination. A better understanding of the biological underpinnings of genomic and nongenomic mechanisms of resistance to BRAF-inhibitor-based targeted therapy is needed to identify patients who may benefit from this rechallenge approach.

Clinical outcome of concomitant vs interrupted BRAF inhibitor therapy during radiotherapy in melanoma patients

Background:

Concomitant radiation with BRAF inhibitor (BRAFi) therapy may increase radiation-induced side effects but also potentially improve tumour control in melanoma patients.

Methods:

A total of 155 patients with BRAF-mutated melanoma from 17 European skin cancer centres were retrospectively analysed. Out of these, 87 patients received concomitant radiotherapy and BRAFi (59 vemurafenib, 28 dabrafenib), while in 68 patients BRAFi therapy was interrupted during radiation (51 vemurafenib, 17 dabrafenib). Overall survival was calculated from the first radiation (OS_RT) and from start of BRAFi therapy (OS_BRAFi).

Results:

The median duration of BRAFi treatment interruption prior to radiotherapy was 4 days and lasted for 17 days. Median OS_RT and OS_BRAFi in the entire cohort were 9.8 and 12.6 months in the interrupted group and 7.3 and 11.5 months in the concomitant group (P=0.075/P=0.217), respectively. Interrupted vemurafenib treatment with a median OS_RT and OS_BRAFi of 10.1 and 13.1 months, respectively, was superior to concomitant vemurafenib treatment with a median OS_RT and OS_BRAFi of 6.6 and 10.9 months (P=0.004/P=0.067). Interrupted dabrafenib treatment with a median OS_RT and OS_BRAFi of 7.7 and 9.8 months, respectively, did not differ from concomitant dabrafenib treatment with a median OS_RT and OS_BRAFi of 9.9 and 11.6 months (P=0.132/P=0.404). Median local control of the irradiated area did not differ in the interrupted and concomitant BRAFi treatment groups (P=0.619). Skin toxicity of grade ≥2 (CTCAE) was significantly increased in patients with concomitant vemurafenib compared to the group with treatment interruption (P=0.002).

Conclusions:

Interruption of vemurafenib treatment during radiation was associated with better survival and less toxicity compared to concomitant treatment. Due to lower number of patients, the relevance of treatment interruption in dabrafenib treated patients should be further investigated. The results of this analysis indicate that treatment with the BRAFi vemurafenib should be interrupted during radiotherapy. Prospective studies are desperately needed.

Exploiting Drug Addiction Mechanisms to Select against MAPKi-Resistant Melanoma

Melanoma resistant to MAPK inhibitors (MAPKi) displays loss of fitness upon experimental MAPKi withdrawal and, clinically, may be resensitized to MAPKi therapy after a drug holiday. Here, we uncovered and therapeutically exploited the mechanisms of MAPKi addiction in MAPKi-resistant BRAFMUT or NRASMUT melanoma. MAPKi-addiction phenotypes evident upon drug withdrawal spanned transient cell-cycle slowdown to cell-death responses, the latter of which required a robust phosphorylated ERK (pERK) rebound. Generally, drug withdrawal-induced pERK rebound upregulated p38-FRA1-JUNB-CDKN1A and downregulated proliferation, but only a robust pERK rebound resulted in DNA damage and parthanatos-related cell death. Importantly, pharmacologically impairing DNA damage repair during MAPKi withdrawal augmented MAPKi addiction across the board by converting a cell-cycle deceleration to a caspase-dependent cell-death response or by furthering parthanatos-related cell death. Specifically in MEKi-resistant NRASMUT or atypical BRAFMUT melanoma, treatment with a type I RAF inhibitor intensified pERK rebound elicited by MEKi withdrawal, thereby promoting a cell death-predominant MAPKi-addiction phenotype. Thus, MAPKi discontinuation upon disease progression should be coupled with specific strategies that augment MAPKi addiction.Significance: Discontinuing targeted therapy may select against drug-resistant tumor clones, but drug-addiction mechanisms are ill-defined. Using melanoma resistant to but withdrawn from MAPKi, we defined a synthetic lethality between supraphysiologic levels of pERK and DNA damage. Actively promoting this synthetic lethality could rationalize sequential/rotational regimens that address evolving vulnerabilities. Cancer Discov; 8(1); 74-93. ©2017 AACR.See related commentary by Stern, p. 20This article is highlighted in the In This Issue feature, p. 1.

BRAF Fusion as a Novel Mechanism of Acquired Resistance to Vemurafenib in BRAFV600E Mutant Melanoma

Purpose: Many patients with BRAF^V600E mutant melanoma treated with BRAF inhibitors experience a rapid response, but ultimately develop resistance. Insight into the mechanism of resistance is critical for development of more effective treatment strategies.Experimental Design: Comprehensive genomic profiling of serial biopsies was performed in a patient with a BRAF^V600E mutant metastatic melanoma who developed resistance to vemurafenib. An AGAP3-BRAF fusion gene, identified in the vemurafenib-resistant tumor, was expressed in BRAF^V600E melanoma cell lines, and its effect on drug sensitivity was evaluated.Results: Clinical resistance to vemurafenib in a melanoma harboring a BRAF^V600E mutation was associated with acquisition of an AGAP3-BRAF fusion gene. Expression of the AGAP3-BRAF fusion in BRAF^V600E mutant melanoma cells induced vemurafenib resistance; however, these cells remained relatively sensitive to MEK inhibitors. The patient experienced clinical benefit following treatment with the combination of a BRAF and a MEK inhibitor. Rebiopsy of the tumor at a later time point, after BRAF and MEK inhibitors had been discontinued, showed loss of the AGAP3-BRAF fusion gene. Mixing experiments suggest that cells harboring both BRAF^V600E and AGAP3-BRAF only have a fitness advantage over parental BRAF^V600E cells during active treatment with a BRAF inhibitor.Conclusions: We report acquisition of a BRAF fusion as a novel mechanism of acquired resistance to vemurafenib in a patient with melanoma harboring a BRAF^V600E mutation. The acquisition and regression of clones harboring this fusion during the presence and absence of a BRAF inhibitor are consistent with rapidly evolving clonal dynamics in melanoma. Clin Cancer Res; 23(18); 5631-8. ©2017 AACR.

Successful retreatment with combined BRAF/MEK inhibition in metastatic BRAFV600-mutated melanoma

BACKGROUND

The combination treatment with BRAF and MEK inhibitors is amongst the current standard of care for stage IIIC/IV BRAF-mutated melanoma. However, therapeutic options are limited once patients have progressed upon both targeted and immunotherapy.

OBJECTIVE

To investigate whether retreatment with BRAF and MEK inhibitor combination is an option for patients with metastatic BRAF-mutated melanoma upon previous progression on kinase inhibitors.

METHODS

Two patients with metastatic BRAF-mutated melanoma were rechallenged with BRAF and MEK inhibitor combination after progression on targeted therapy and subsequent immunotherapy with anti-CTLA-4 and anti-PD-1 antibodies.

RESULTS

Both patients responded to retreatment. Responses were limited to a few months and associated with a considerable increase in quality of life.

CONCLUSION

Retreatment with BRAF and MEK inhibitors may present a feasible treatment option upon progression on both kinase inhibitors and immunotherapy, and should be considered when all other treatment options have been exhausted.

Combination of dabrafenib plus trametinib for BRAF and MEK inhibitor pretreated patients with advanced BRAFV600-mutant melanoma: an open-label, single arm, dual-centre, phase 2 clinical trial

BACKGROUND

Patients with BRAF^V600-mutant melanoma benefit from treatment with the combination of BRAF and MEK inhibitors, but resistance and disease progression develops in most patients. Preclinical studies and case studies have indicated that acquired resistance to BRAF inhibition can be reversible. We aimed to assess the anti-tumour activity of rechallenge with BRAF plus MEK inhibition in a prospective clinical trial.

METHODS

In this open-label, single arm, dual-centre, phase 2 academic study in Belgium, patients aged 18 years or older with BRAF^V600-mutant melanoma who had previously progressed on BRAF inhibitors (with or without MEK inhibitors) and were off-treatment for at least 12 weeks, were treated with dabrafenib 150 mg orally twice per day plus trametinib 2 mg orally once per day. The primary endpoint was the proportion of patients with investigator-assessed overall response at any time (defined as complete response or partial response according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 confirmed on two occasions, at least 28 days after the first response was recorded). Analyses were done in the intention-to-treat population. The study is ongoing but no longer recruiting patients. This trial is registered with ClinicalTrials.gov, number NCT02296996.

FINDINGS

Between April 5, 2014, and Feb 2, 2016, 25 patients were enrolled and initiated treatment in our study. A partial response was documented in eight (32%) of 25 patients (95% CI 15-54; six patients had progressed on previous treatment with dabrafenib plus trametinib and two patients had progressed on previous BRAF inhibitor monotherapy). Stable disease was noted in ten patients (40%; 95% CI 21-61). Rechallenge with dabrafenib plus trametinib was well tolerated. There were no unexpected or grade 4 or 5 treatment-related adverse events. Grade 3 adverse events occurred in two patients (8%; panniculitis [n=1] and pyrexia [n=1]). Serious adverse events which occurred on study were one patient with an Addison crisis triggered by grade 2 pyrexia symptoms that resolved after discontinuation of dabrafenib and trametinib. No patients died as a result of study treatment.

INTERPRETATION

Rechallenge with dabrafenib plus trametinib showed anti-tumour activity in patients who had previously progressed on BRAF inhibitors and as such, rechallenge represents a potential new treatment option for these patients.

FUNDING

Vlaamse Liga Tegen Kanker, Novartis.

Therapeutic approach to treating patients with BRAF-mutant lung cancer: latest evidence and clinical implications

Lung adenocarcinoma is known for its high rate of somatic mutations and genomic rearrangements. The identification of epidermal growth factor receptor (EGFR) mutations and anaplastic lymphoma kinase (ALK) rearrangements that sensitize tumors to specific drugs has changed the therapeutic approach and prognosis in these molecularly-defined subgroups. Several other key genetic alterations have been identified, of which BRAF mutations are found in 4% of non-small cell lung cancer (NSCLC) cases. Targeted drugs against BRAF and downstream MEK were recently approved for the treatment of BRAF-positive melanoma and have entered clinical evaluation in NSCLC. In this review we discuss the latest evidence on the treatment of BRAF-mutated NSCLC, including tumor biology, targeted treatment with BRAF and MEK inhibitors, therapeutic resistance and strategies to overcome resistance.