Ongoing Response in BRAF V600E-Mutant Melanoma After Cessation of Intermittent Vemurafenib Therapy: A Case Report

On minimising tumoural growth under treatment resistance

Drug resistance is a major challenge for curative cancer treatment, representing the main reason of death in patients. Evolutionary biology suggests pauses between treatment rounds as a way to delay or even avoid resistance emergence. Indeed, this approach has already shown promising preclinical and early clinical results, and stimulated the development of mathematical models for finding optimal treatment protocols. Due to their complexity, however, these models do not lend themself to a rigorous mathematical analysis, hence so far clinical recommendations generally relied on numerical simulations and ad-hoc heuristics. Here, we derive two mathematical models describing tumour growth under genetic and epigenetic treatment resistance, respectively, which are simple enough for a complete analytical investigation. First, we find key differences in response to treatment protocols between the two modes of resistance. Second, we identify the optimal treatment protocol which leads to the largest possible tumour shrinkage rate. Third, we fit the "epigenetic model" to previously published xenograft experiment data, finding excellent agreement, underscoring the biological validity of our approach. Finally, we use the fitted model to calculate the optimal treatment protocol for this specific experiment, which we demonstrate to cause curative treatment, making it superior to previous approaches which generally aimed at stabilising tumour burden. Overall, our approach underscores the usefulness of simple mathematical models and their analytical examination, and we anticipate our findings to guide future preclinical and, ultimately, clinical research in optimising treatment regimes.

Inflammation across tissues: can shared cell biology help design smarter trials?

Immune-mediated inflammatory diseases (IMIDs) are responsible for substantial global disease burden and associated health-care costs. Traditional models of research and service delivery silo their management within organ-based medical disciplines. Very often patients with disease in one organ have comorbid involvement in another, suggesting shared pathogenic pathways. Moreover, different IMIDs are often treated with the same drugs (including glucocorticoids, immunoregulators and biologics). Unlocking the cellular basis of these diseases remains a major challenge, leading us to ask why, if these diseases have so much in common, they are not investigated in a common manner. A tissue-based, cellular understanding of inflammation might pave the way for cross-disease, cross-discipline basket trials (testing one drug across two or more diseases) to reduce the risk of failure of early-phase drug development in IMIDs. This new approach will enable rapid assessment of the efficacy of new therapeutic agents in cross-disease translational research in humans.

Molecular Alterations Associated with Acquired Drug Resistance during Combined Treatment with Encorafenib and Binimetinib in Melanoma Cell Lines

Combination treatment using BRAF/MEK inhibitors is a promising therapy for patients with advanced BRAF^V600E/K mutant melanoma. However, acquired resistance largely limits the clinical efficacy of this drug combination. Identifying resistance mechanisms is essential to reach long-term, durable responses. During this study, we developed six melanoma cell lines with acquired resistance for BRAFi/MEKi treatment and defined the molecular alterations associated with drug resistance. We observed that the invasion of three resistant cell lines increased significantly compared to the sensitive cells. RNA-sequencing analysis revealed differentially expressed genes that were functionally linked to a variety of biological functions including epithelial-mesenchymal transition, the ROS pathway, and KRAS-signalling. Using proteome profiler array, several differentially expressed proteins were detected, which clustered into a unique pattern. Galectin showed increased expression in four resistant cell lines, being the highest in the WM1617^E+BRes cells. We also observed that the resistant cells behaved differently after the withdrawal of the inhibitors, five were not drug addicted at all and did not exhibit significantly increased lethality; however, the viability of one resistant cell line (WM1617^E+BRes) decreased significantly. We have selected three resistant cell lines to investigate the protein expression changes after drug withdrawal. The expression patterns of CapG, Enolase 2, and osteopontin were similar in the resistant cells after ten days of "drug holiday", but the Snail protein was only expressed in the WM1617^E+BRes cells, which showed a drug-dependent phenotype, and this might be associated with drug addiction. Our results highlight that melanoma cells use several types of resistance mechanisms involving the altered expression of different proteins to bypass drug treatment.

Clinical Implications of Acquired BRAF Inhibitors Resistance in Melanoma

Understanding the role of mitogen-activated protein kinase (MAPK) pathway-activating mutations in the development and progression of melanoma and their possible use as therapeutic targets has substantially changed the management of this neoplasm, which, until a few years ago, was burdened by severe mortality. However, the presence of numerous intrinsic and extrinsic mechanisms of resistance to BRAF inhibitors compromises the treatment responses’ effectiveness and durability. The strategy of overcoming these resistances by combination therapy has proved successful, with the additional benefit of reducing side effects derived from paradoxical activation of the MAPK pathway. Furthermore, the use of other highly specific inhibitors, intermittent dosing schedules and the association of combination therapy with immune checkpoint inhibitors are promising new therapeutic strategies. However, numerous issues related to dose, tolerability and administration sequence still need to be clarified, as is to be expected from currently ongoing trials. In this review, we describe the clinical results of using BRAF inhibitors in advanced melanoma, with a keen interest in strategies aimed at overcoming resistance.

Successful BRAF/MEK inhibition in a patient with BRAF V600E-mutated extrapancreatic acinar cell carcinoma

Pancreatic acinar cell carcinoma (PAC) is a rare disease with a poor prognosis. Treatment options for metastatic PAC are limited and often follow chemotherapeutic regimens for pancreatic ductal adenocarcinoma. Although recurrent genomic alterations, such as BRAF fusions and defects in genes involved in homologous recombination DNA repair, have been described in PAC, data on the clinical efficacy of molecularly guided, targeted treatment are scarce. Here we describe the case of a 27-yr-old patient with BRAF^V600E-mutated PAC who was successfully treated with a combination of BRAF and MEK inhibitors. The patient presented to our clinic with abdominal pain and weight loss. Imaging showed extensive retroperitoneal disease as well as mediastinal lymphadenopathy. Because of elevated α-fetoprotein (AFP) levels and inconclusive histologic findings, a germ cell tumor was suspected; however, PEI chemotherapy was unsuccessful. A repeat biopsy yielded the diagnosis of PAC and treatment with FOLFIRINOX was initiated. Comprehensive molecular profiling within the MASTER (Molecularly Aided Stratification for Tumor Eradication Research) precision oncology program revealed a somatic BRAF^V600E mutation and a germline PALB2 stop-gain mutation. Therapy was therefore switched to BRAF/MEK inhibition, resulting in almost complete remission and disease control for 12 mo and a remarkable improvement in the patient's general condition. These results indicate that BRAF alterations are a valid therapeutic target in PAC that should be routinely assessed in this patient population.

Molecular alterations associated with acquired resistance to BRAFV600E targeted therapy in melanoma cells

Selective inhibition of the mutant BRAF protein is a highly promising therapeutic approach for melanoma patients carrying the BRAF mutation. Despite the remarkable clinical response, most patients develop resistance and experience tumour regrowth. To clarify the molecular background of BRAF inhibitor resistance, we generated four drug-resistant melanoma cell lines from paired primary/metastatic cell lines using a vemurafenib analogue PLX4720. Three of the resistant cell lines showed decreased proliferation after drug withdrawal, but the proliferation of one cell line (WM278) increased notably. Furthermore, we observed opposite phenomena in which a 'drug holiday' could not only be beneficial but also contribute to tumour progression. Using genomic and proteomic approaches, we found significantly different alterations between the sensitive and resistant cell lines, some of which have not been reported previously. In addition to several other changes, copy number gains were observed in all resistant cell lines on 8q24.11-q24.12 and 8q21.2. Gene expression analysis showed that most genes upregulated in the resistant cell lines were associated with cell motility and angiogenesis. Increased expression of six proteins (ANGPLT4, EGFR, Endoglin, FGF2, SerpinE1 and VCAM-1) and decreased expression of two proteins (osteopontin and survivin) were observed consistently in all resistant cell lines. In summary, we identified new genomic alterations and characterized the protein expression patterns associated with the resistant phenotype. Although several proteins have been shown to be associated with BRAF resistance, our study is the first to describe the association of VCAM-1 and osteopontin with BRAF resistance.

Acquired resistance to BRAFi reverses senescence-like phenotype in mutant BRAF melanoma

Targeting MAPK pathway in mutant BRAF melanoma with the specific BRAF inhibitor vemurafenib showed robust initial responses in the majority of patients followed by relapses due to acquired resistance to the drug. In ^V600EBRAF melanoma cell lines, senescence-associated β-galactosidase activity is often encountered in a constitutive manner or induced after MAPK inhibition. However, the link between the senescence-like phenotype and the resistance to BRAF inhibition is not fully understood yet. Our data validate a senescence-like phenotype (low cell proliferation, high cell volume, and high β-Gal activity) in mutant BRAF cells. Vemurafenib increased β-Gal activity in 4 out of 5 sensitive lines and in 2 out of 5 lines with intrinsic resistance to the drug. Interestingly, the 3 lines with acquired resistance to vemurafenib became depending on the drug for proliferation. In absence of drug, these lines showed a lower cell proliferation rate together with a substantial increase of β-Gal activity both in vitro and in vivo. In all settings, the senescence-like phenotype was significantly associated with an inhibition of pRB and cyclin D1, explaining the inhibition of cell proliferation. In conclusion, β-Gal activity is increased by ^V600EBRAF inhibition in the majority of sensitive and intrinsically resistant melanoma cells. Acquired resistance to vemurafenib is associated with a dependence to the drug for cell proliferation and tumor growth, and, in this case, drug removal stimulate β-Gal activity suggesting that the senescence-like phenotype could contribute to the acquired resistance to BRAF inhibition.

The safety and efficacy of dabrafenib and trametinib for the treatment of melanoma

INTRODUCTION

The introduction of BRAF and MEK inhibitors into clinical practice improved the prognosis of metastatic melanoma patients. The combination of BRAF inhibitor dabrafenib with MEK inhibitor trametinib has shown its superiority to single agent therapy and is characterized by a tolerable spectrum of adverse events which shows a decrease in incidence over time on treatment. Areas covered: The current scientific literature on safety and adverse events (AEs) related to BRAF and MEK-inhibition has been investigated with special focus on the large phase 3 studies (COMBI-v, COMBI-d and CoBRIM) as well as recent updates presented at oncology and melanoma meetings. Additionally, published case series/case reports were screened for information on AEs. Expert opinion: Even though almost every patient (98%) under combination therapy with dabrafenib and trametinib experiences at least one adverse event, these are generally mild to moderate, reversible and can be managed with dose reductions or interruptions. However, due to an increased life expectancy, there is a substantial need to prevent and treat also mild adverse events, as they play a central role for the quality of life of patients. Ongoing clinical trials will have to demonstrate the efficacy as well as safety of triple combination with anti-PD-1/anti-PD-L1 antibodies.

Cancer drug addiction is relayed by an ERK2-dependent phenotype switch

Drug addiction denotes the dependency of tumors on the same therapeutic drugs to which they have acquired resistance. Observations from cultured cells1–3, animal models4 and patients5–7 raise the possibility that cancer drug addiction can instigate a potential cancer vulnerability, which may be used therapeutically. However, for this trait to become of clinical interest, it is imperative to first define the underlying mechanism. Therefore, we performed an unbiased CRISPR-Cas9 knockout screen to functionally mine the genome of melanoma cells that are both resistant and addicted to BRAF inhibition for “addiction genes”. Here, we describe a signaling pathway comprising ERK2, JUNB and FRA1, disruption of which allows tumor cells to reverse addiction and survive upon treatment discontinuation. This occurred both in culture and mice, and was irrespective of the acquired drug resistance mechanism. In melanoma and lung cancer cells, death induced by drug withdrawal was preceded by a specific ERK2-dependent phenotype switch, alongside transcriptional reprogramming reminiscent of EMT. In melanoma, this caused shutdown of the lineage survival oncoprotein MITF, restoration of which reversed both phenotype switching and drug addiction-associated lethality. In melanoma patients who had progressed on BRAF inhibition, treatment cessation was followed by increased expression of the phenotype switch-associated receptor tyrosine kinase AXL. Drug discontinuation synergized with the melanoma chemotherapeutic dacarbazine by further suppressing MITF and its prosurvival target BCL2 while inducing DNA damage. Our results uncover a pathway driving cancer drug addiction, which may guide alternating therapeutic strategies for enhanced clinical responses of drug-resistant cancers.

BRAF inhibitors: resistance and the promise of combination treatments for melanoma

Identification of mutations in the gene encoding the serine/threonine-protein kinase, BRAF, and constitutive activation of the mitogen-activated protein kinase (MAPK) pathway in around 50% of malignant melanomas have led to the development and regulatory approval of targeted pathway inhibitor drugs. A proportion of patients are intrinsically resistant to BRAF inhibitors, and most patients who initially respond, acquire resistance within months. In this review, we discuss pathway inhibitors and their mechanisms of resistance, and we focus on numerous efforts to improve clinical benefits through combining agents with disparate modes of action, including combinations with checkpoint inhibitor antibodies. We discuss the merits of combination strategies based on enhancing immune responses or overcoming tumor-associated immune escape mechanisms. Emerging insights into mechanisms of action, resistance pathways and their impact on host-tumor relationships will inform the design of optimal combinations therapies to improve outcomes for patients who currently do not benefit from recent treatment breakthroughs.