Absence of BRAF-V600E in the human cell lines BONNA-12, ESKOL, HAIR-M, and HC-1 questions their origin from hairy cell leukemia

A cyanine-based NIR fluorescent Vemurafenib analog to probe BRAFV600E in cancer cells

BRAF represents one of the most frequently mutated protein kinase genes and BRAF^V600E mutation may be found in many types of cancer, including hairy cell leukemia (HCL), anaplastic thyroid cancer (ATC), colorectal cancer and melanoma. Herein, a fluorescent probe, based on the structure of the highly specific BRAF^V600E inhibitor Vemurafenib (Vem, 1) and featuring the NIR fluorophore cyanine-5 (Cy5), was straightforwardly synthesized and characterized (Vem-L-Cy5, 3), showing promising spectroscopic properties. Biological validation in BRAF^V600E-mutated cancer cells evidenced the ability of 3 to penetrate inside the cells, specifically binding to its elective target BRAF^V600E with high affinity, and inhibiting MEK phosphorylation and cell growth with a potency comparable to that of native Vem 1. Taken together, these data highlight Vem-L-Cy5 3 as a useful tool to probe BRAF^V600E mutation in cancer cells, and suitable to acquire precious insights for future developments of more informed BRAF inhibitors-centered therapeutic strategies.

Misidentified biomedical resources: Journal guidelines are not a quick fix

Biomedical researchers routinely use a variety of biological models and resources, such as cultured cell lines, antibodies and laboratory animals. Unfortunately, these resources are not flawless: cell lines can be misidentified; for antibodies, problems with specificity, lot-to-lot consistency and sensitivity are common; and the reliability of animal models is questioned due to poor translation of animal studies to human clinical trials. In some cases, these problems can render the results of a study meaningless. As a response, some journals have implemented guidelines regarding the use and reporting of cell lines, antibodies and laboratory animals. In our study we use a portfolio of existing and newly created datasets to investigate identification and authentication information of cell lines, antibodies and organisms before and after guideline introduction, compared to journals without guidelines. We observed a general improvement of reporting quality over time, which the implementation of guidelines accelerated only in some cases. We therefore conclude that the effectiveness of journal guidelines is likely to be context dependent, affected by factors such as implementation conditions, research community support and monitoring and resource availability. Hence, journal reporting guidelines in themselves are not a quick fix to repair shortcomings in biomedical resource documentation, even though they can be part of the solution.

How I treat refractory/relapsed hairy cell leukemia with BRAF inhibitors

Hairy cell leukemia (HCL) responds very well to frontline chemotherapy with purine analogs (cladribine and pentostatine). However, approximately half of patients experience 1 or more relapses, which become progressively resistant to these myelotoxic and immunosuppressive agents. At progression, standard therapeutic options include a second course of purine analogs alone or in combination with rituximab and, upon second relapse, therapy with the anti-CD22 immunotoxin moxetumomab pasudotox. Furthermore, blockade of the mutant BRAF-V600E kinase (the pathogenetic hallmark of HCL) through orally available specific inhibitors (vemurafenib or dabrafenib) effaces the peculiar morphologic, phenotypic, and molecular identity of this disease and its typical antiapoptotic behavior and is emerging as an attractive chemotherapy-free strategy in various clinical scenarios. These include patients with, or at risk of, severe infections and, in a highly effective combination with rituximab, patients with relapsed or refractory HCL. Other treatments explored in clinical trials are BTK inhibition with ibrutinib and co-inhibition of BRAF (through dabrafenib or vemurafenib) and its downstream target MEK (through trametinib or cobimetinib). Here, we focus on our experience with BRAF inhibitors in clinical trials and as off-label use in routine practice by presenting 3 challenging clinical cases to illustrate their management in the context of all available treatment options.

In Vitro Sensitivity to Venetoclax and Microenvironment Protection in Hairy Cell Leukemia

Current standard treatment of patients with hairy cell leukemia (HCL), a chronic B-cell neoplasia of low incidence that affects the elderly, is based on the administration of purine analogs such as cladribine. This chemotherapy approach shows satisfactory responses, but the disease relapses, often repeatedly. Venetoclax (ABT-199) is a Bcl-2 inhibitor currently approved for the treatment of chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) in adult patients ineligible for intensive chemotherapy. Given that HCL cells express Bcl-2, our aim was to evaluate venetoclax as a potential therapy for HCL. We found that clinically relevant concentrations of venetoclax (0.1 and 1 µM) induced primary HCL cell apoptosis in vitro as measured by flow cytometry using Annexin V staining. As microenvironment induces resistance to venetoclax in CLL, we also evaluated its effect in HCL by testing the following stimuli: activated T lymphocytes, stromal cells, TLR-9 agonist CpG, and TLR-2 agonist PAM3. We found decreased levels of venetoclax-induced cytotoxicity in HCL cells exposed for 48 h to any of these stimuli, suggesting that leukemic B cells from HCL patients are sensitive to venetoclax, but this sensitivity can be overcome by signals from the microenvironment. We propose that the combination of venetoclax with drugs that target the microenvironment might improve its efficacy in HCL.

"Hairiness" is a Facsimile of Reorganized Cytoskeletons: A Cytopathic Effect of Coxiella burnetii

In 1993, I reported that Coxiella burnetii transforms human B cells into hairy cells (cbHCs), the first hairy cell reported outside of hairy cell leukemia (HCL). Over last few decades, advances in molecular biology have provided evidence supporting that C. burnetii induces hairiness and inhibits the apoptosis of host cells. The present review summarizes new information in support of cbHC. C. burnetii was shown to induce reorganization of the cytoskeleton and to inhibit apoptosis in host cells. Peritoneal B1a cells were found to be permissive for virulent C. burnetii Nine Mile phase I (NMI) strains in mice. C. burnetii severely impaired E-cad expression in circulating cells of Q fever patients. B-cell non-Hodgkin lymphoma was linked to C. burnetii. Mutation of BRAF V600E was pronounced in HCL, but "hairiness" was not linked to the mutation. Risk factors shared among coxiellosis and HCL in humans and animals were reported in patients with Q-fever. Accordingly, I propose that C. burnetii induces reorganization of the cytoskeleton and inhibits apoptosis as cytopathic effects that are not target cell specific. The observed hairiness in cbHC appears to be a fixed image of dynamic nature, and hairy cells in HCL are distinct among lymphoid cells in circulation. As the cytoskeleton plays key roles in maintaining cell structural integrity in health and disease, the pathophysiology of similar cytopathic effects should be addressed in other diseases, such as myopathies, B-cell dyscrasias, and autoimmune syndromes.

New treatment options in hairy cell leukemia with focus on BRAF inhibitors

Hairy cell leukemia (HCL) responds initially very well to chemotherapy with purine analogues. However, up to 50% of patients relapse, often multiple times, and become progressively less sensitive to these myelotoxic and immune-suppressive drugs. At progression, viable therapeutic strategies include addition of rituximab to purine analogues, and treatment with the anti-CD22 immunotoxin moxetumomab pasudotox, which has been recently approved by the FDA in HCL patients after at least two prior therapies. Identification of the BRAF-V600E kinase mutation as the genetic cause of HCL has opened the way, in the relapsed/refractory experimental setting, to targeted and non-myelotoxic effective strategies that are based on inhibition of BRAF with vemurafenib, co-inhibition of BRAF and its target MEK with dabrafenib and trametinib, and BRAF inhibition with vemurafenib combined with anti-CD20 immunotherapy. In particular, vemurafenib plus rituximab is emerging as a short, safe, chemotherapy-free regimen able to induce deep complete remissions in most HCL patients refractory to, or relapsed multiple times, after chemo(immuno)therapy.

New generation sequencing of targeted genes in the classical and the variant form of hairy cell leukemia highlights mutations in epigenetic regulation genes

Classical hairy cell leukemia (HCL-c) is a rare lymphoid neoplasm. BRAF^V600E mutation, detected in more than 80% of the cases, is described as a driver mutation, but additional genetic abnormalities appear to be necessary for the disease progression. For cases of HCL-c harboring a wild-type BRAF gene, the differential diagnosis of the variant form of HCL (HCL-v) or splenic diffuse red pulp lymphoma (SDRPL) is complex. We selected a panel of 21 relevant genes based on a literature review of whole exome sequencing studies (BRAF, MAP2K1, DUSP2, MAPK15, ARID1A, ARID1B, EZH2, KDM6A, CREBBP, TP53, CDKN1B, XPO1, KLF2, CXCR4, NOTH1, NOTCH2, MYD88, ANXA1, U2AF1, BCOR, and ABCA8). We analyzed 20 HCL-c and 4 HCL-v patients. The analysis of diagnostic samples mutations in BRAF (n = 18), KLF2 (n = 4), MAP2K1 (n = 3), KDM6A (n = 2), CDKN1B (n = 2), ARID1A (n = 2), CREBBP (n = 2) NOTCH1 (n = 1) and ARID1B (n = 1). BRAF^V600E was found in 90% (18/20) of HCL-c patients. In HCL-c patients with BRAF^V600E, other mutations were found in 33% (6/18) of cases. All 4 HCL-v patients had mutations in epigenetic regulatory genes: KDM6A (n = 2), CREBBP (n = 1) or ARID1A (n = 1). The analysis of sequential samples (at diagnosis and relapse) from 5 patients (2 HCL-c and 3 HCL-v), showed the presence of 2 new subclonal mutations (BCOR^E1430X and XPO1^E571K) in one patient and variations of the mutated allele frequency in 2 other cases. In the HCL-v disease, we described new mutations targeting KDM6A that encode a lysine demethylase protein. This opens new perspectives for personalized medicine for this group of patients.

Genomics of Hairy Cell Leukemia

Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the discovery of its underlying genetic cause, the BRAF-V600E kinase-activating mutation, which is somatically and clonally present in almost all patients through the entire disease spectrum and clinical course. By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior. Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis. Conversely, BRAF-V600E is absent in other B-cell neoplasms, including mimickers of HCL that require different treatments (eg, HCL-variant and splenic marginal zone lymphoma). Thus, testing for BRAF-V600E allows for a genetics-based differential diagnosis between HCL and HCL-like tumors, even noninvasively in routine blood samples. BRAF-V600E also represents a new therapeutic target. Patients' leukemic cells exposed ex vivo to BRAF inhibitors are spoiled of their HCL identity and then undergo apoptosis. In clinical trials of patients with HCL who have experienced multiple relapses after purine analogs or who are refractory to purine analogs, a short course of the oral BRAF inhibitor vemurafenib produced an almost 100% response rate, including complete remission rates of 35% to 42%, without myelotoxicity. To further improve on these results, it will be important to clarify the mechanisms of incomplete leukemic cell eradication by vemurafenib and to explore chemotherapy-free combinations of a BRAF inhibitor with other targeted agents (eg, a MEK inhibitor and/or an anti-CD20 monoclonal antibody).

Somatic mutations in solid tumors: a spectrum at the service of diagnostic armamentarium or an indecipherable puzzle? The morphological eyes looking for BRAF and somatic molecular detections on cyto-histological samples

This review article deals with the analysis and the detection of the morphological features associated with somatic mutations, mostly BRAFV600E mutation, on both cytological and histological samples of carcinomas. Few authors demonstrated that some architectural and specific cellular findings (i.e. polygonal eosinophilic cells defined as "plump cells" and sickle-shaped nuclei) are able to predict BRAF V600E mutation in both cytological and histological samples of papillary thyroid carcinoma (PTC) as well as in other carcinomas. In the current review article we evaluated the first comprehensive analysis of the morphological prediction of BRAFV600E and other somatic mutations in different malignant lesions with the description of the possible mechanisms beneath these morphologic features. The detection of predictive morphological features, mostly on FNAC, may add helpful information to the stratification of the malignant risk and personalized management of cancers. Additionally, the knowledge of the molecular mechanism of different oncogenic drivers can lead to the organ-specific triaging selection of cases and can provide significant insight for targeted therapies in different malignant lesions.

BRAF V600E mutation in hairy cell leukemia: from bench to bedside

Hairy cell leukemia (HCL) is a distinct clinicopathological entity whose underlying genetic lesion has remained a mystery for over half a century. The BRAF V600E mutation is now recognized as the causal genetic event of HCL because it is somatic, present in the entire tumor clone, detectable in almost all cases at diagnosis (encompassing the whole disease spectrum), and stable at relapse. BRAF V600E leads to the constitutive activation of the RAF-MEK-extracellular signal-regulated kinase (ERK) signaling pathway which represents the key event in the molecular pathogenesis of HCL. KLF2 and CDNK1B (p27) mutations may cooperate with BRAF V600E in promoting leukemic transformation. Sensitive molecular assays for detecting BRAF V600E allow HCL (highly responsive to purine analogs) to be better distinguished from HCL-like disorders, which are treated differently. In vitro preclinical studies on purified HCL cells proved that BRAF and MEK inhibitors can induce marked dephosphorylation of MEK/ERK, silencing of RAF-MEK-ERK pathway transcriptional output, loss of the HCL-specific gene expression profile signature, change of morphology from “hairy” to “smooth,” and eventually apoptosis. The overall response rate of refractory/relapsed HCL patients to the BRAF inhibitor vemurafenib approached 100%, with 35% to 40% complete remissions (CRs). The median relapse free-survival was about 19 months in patients who had achieved CR and 6 months in those who had obtained a partial response. Future therapeutic perspectives include: (1) combining BRAF inhibitors with MEK inhibitors or immunotherapy (anti-CD20 monoclonal antibody) to increase the percentage of CRs and (2) better understanding of the molecular mechanisms underlying resistance of HCL cells to BRAF inhibitors.

Potential role of AKT/mTOR signalling proteins in hairy cell leukaemia: association with BRAF/ERK activation and clinical outcome

The potential role of AKT/mTOR signalling proteins and its association with the Raf-MEK-ERK pathway was investigated in hairy cell leukaemia (HCL). BRAFV600E expression and activated forms of AKT, mTOR, ERK1/2, p70S6k and 4E-BP1 were immunohistochemically assessed in 77 BM biopsies of HCL patients and correlated with clinicopathological and BM microvascular characteristics, as well as with c-Caspase-3 levels in hairy cells. Additionally, we tested rapamycin treatment response of BONNA-12 wild-type cells or transfected with BRAFV600E. Most HCL cases expressed p-p70S6K and p-4E-BP1 but not p-mTOR, being accompanied by p-ERK1/2 and p-AKT. AKT/mTOR activation was evident in BONNA-12 cells irrespective of the presence of BRAFV600E mutation and was implicated in cell proliferation enhancement. In multivariate analysis p-AKT/p-mTOR/p-4E-BP1 overexpression was an adverse prognostic factor for time to next treatment conferring earlier relapse. When p-AKT, p-mTOR and p-4E-BP1 were examined separately only p-4E-BP1 remained significant. Our findings indicate that in HCL, critical proteins up- and downstream of mTOR are activated. Moreover, the strong associations with Raf-MEK-ERK signalling imply a possible biologic interaction between these pathways. Most importantly, expression of p-4E-BP1 alone or combined with p-AKT and p-mTOR is of prognostic value in patients with HCL.

BRAF inhibitors reverse the unique molecular signature and phenotype of hairy cell leukemia and exert potent antileukemic activity

Hairy cell leukemia (HCL) shows unique clinicopathological and biological features. HCL responds well to purine analogs but relapses are frequent and novel therapies are required. BRAF-V600E is the key driver mutation in HCL and distinguishes it from other B-cell lymphomas, including HCL-like leukemias/lymphomas (HCL-variant and splenic marginal zone lymphoma). The kinase-activating BRAF-V600E mutation also represents an ideal therapeutic target in HCL. Here, we investigated the biological and therapeutic importance of the activated BRAF-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) pathway in HCL by exposing in vitro primary leukemic cells purified from 26 patients to clinically available BRAF (vemurafenib; dabrafenib) or MEK (trametinib) inhibitors. Results were validated in vivo in samples from vemurafenib-treated HCL patients within a phase 2 clinical trial. BRAF and MEK inhibitors caused, specifically in HCL (but not HCL-like) cells, marked MEK/ERK dephosphorylation, silencing of the BRAF-MEK-ERK pathway transcriptional output, loss of the HCL-specific gene expression signature, downregulation of the HCL markers CD25, tartrate-resistant acid phosphatase, and cyclin D1, smoothening of leukemic cells' hairy surface, and, eventually, apoptosis. Apoptosis was partially blunted by coculture with bone marrow stromal cells antagonizing MEK-ERK dephosphorylation. This protective effect could be counteracted by combined BRAF and MEK inhibition. Our results strongly support and inform the clinical use of BRAF and MEK inhibitors in HCL.

Hairy cell leukemia: short review, today's recommendations and outlook

Hairy cell leukemia (HCL) is part of the low-grade non-Hodgkin lymphoma family and represents approximately 2% of all leukemias. Treatment with splenectomy and interferon-α historically belonged to the first steps of therapeutic options, achieving partial responses/remissions (PR) in most cases with a median survival between 4 and 6 years in the 1980s. The introduction of the purine analogs (PA) pentostatin and cladribine made HCL a well-treatable disease: overall complete response rates (CRR) range from 76 to 98%, with a median disease-free survival (DFS) of 16 years a normal lifespan can be reached and HCL-related deaths are rare. However, insufficient response to PA with poorer prognosis and relapse rates of 30–40% after 5–10 years of follow-up may require alternative strategies. Minimal residual disease can be detected by additional examinations of bone marrow specimens after treatment with PA. The use of immunotherapeutic monoclonal antibodies (mAB) like rituximab as a single agent or in combination with a PA or more recently clinical trials with recombinant immunotoxins (RIT) show promising results to restrict these problems. Recently, the identification of the possible disease-defining BRAF V600E mutation may allow the development of new therapeutic targets.

BRAF--a new player in hematological neoplasms

BRAF oncogenic kinase has become a target for specific therapy in oncology. Genetic characterization of a predominant V600E mutation in melanoma, thyroid cancer, and other tumors became a focus for developing specific inhibitors, such as vemurafenib or dabrafenib. Our knowledge regarding the role of mutated BRAF in hematological malignancies has grown quickly as a result of new genetic techniques such as next-generation sequencing. This review summarizes current knowledge regarding the role of BRAF in lymphoid and myeloid neoplasms, with a focus on hairy-cell leukemia, Langerhans cell histiocytosis, and Erdheim-Chester disease.