RAS pathway mutations as a predictive biomarker for treatment adaptation in pediatric B-cell precursor acute lymphoblastic leukemia

RAS pathway mutations have been linked to relapse and chemotherapy resistance in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). However, comprehensive data on the frequency and prognostic value of subclonal mutations in well-defined subgroups using highly sensitive and quantitative methods are lacking. Targeted deep sequencing of 13 RAS pathway genes was performed in 461 pediatric BCP-ALL cases at initial diagnosis and in 19 diagnosis-relapse pairs. Mutations were present in 44.2% of patients, with 24.1% carrying a clonal mutation. Mutation frequencies were highest in high hyperdiploid, infant t(4;11)-rearranged, BCR-ABL1-like and B-other cases (50-70%), whereas mutations were less frequent in ETV6-RUNX1-rearranged, and rare in TCF3-PBX1- and BCR-ABL1-rearranged cases (27-4%). RAS pathway-mutated cells were more resistant to prednisolone and vincristine ex vivo. Clonal, but not subclonal, mutations were linked to unfavorable outcome in standard- and high-risk-treated patients. At relapse, most RAS pathway mutations were clonal (9 of 10). RAS mutant cells were sensitive to the MEK inhibitor trametinib ex vivo, and trametinib sensitized resistant cells to prednisolone. We conclude that RAS pathway mutations are frequent, and that clonal, but not subclonal, mutations are associated with unfavorable risk parameters in newly diagnosed pediatric BCP-ALL. These mutations may designate patients eligible for MEK inhibitor treatment.

The Dual MEK/FLT3 Inhibitor E6201 Exerts Cytotoxic Activity against Acute Myeloid Leukemia Cells Harboring Resistance-Conferring FLT3 Mutations

Fms-like tyrosine kinase 3 (FLT3) inhibition has elicited encouraging responses in acute myeloid leukemia (AML) therapy. Unfortunately, unless combined with a bone marrow transplant, disease relapse is frequent. In addition to the acquired point mutations in the FLT3 kinase domain that contribute to FLT3 inhibitor resistance, MEK/ERK signaling is persistently activated in AML cells even when FLT3 phosphorylation is continually suppressed. Thus, concomitant targeting of FLT3 and MAPK may potentially exert synergistic activity to counteract the resistance of AML cells to FLT3-targeted therapy. In this study, we investigated the antileukemia activity of a MEK1 and FLT3 dual inhibitor, E6201, in AML cells resistant to FLT3 inhibition. We found that E6201 exerted profound apoptogenic effects on AML cells harboring resistance-conferring FLT3 mutations. This activity appeared to be p53 dependent, and E6201-induced cytotoxicity was retained under hypoxic culture conditions and during coculture with mesenchymal stem cells that mimic the AML microenvironment. Furthermore, E6201 markedly reduced leukemia burden and improved the survival of mice in a human FLT3-mutated AML model. Collectively, our data provide a preclinical basis for the clinical evaluation of E6201 in AML patients harboring FLT3 mutations, including those who relapse following FLT3-targeted monotherapy.

MEK1 and MEK2 inhibitors and cancer therapy: the long and winding road

The role of the ERK signalling pathway in cancer is thought to be most prominent in tumours in which mutations in the receptor tyrosine kinases RAS, BRAF, CRAF, MEK1 or MEK2 drive growth factor-independent ERK1 and ERK2 activation and thence inappropriate cell proliferation and survival. New drugs that inhibit RAF or MEK1 and MEK2 have recently been approved or are currently undergoing late-stage clinical evaluation. In this Review, we consider the ERK pathway, focusing particularly on the role of MEK1 and MEK2, the 'gatekeepers' of ERK1/2 activity. We discuss their validation as drug targets, the merits of targeting MEK1 and MEK2 versus BRAF and the mechanisms of action of different inhibitors of MEK1 and MEK2. We also consider how some of the systems-level properties (intrapathway regulatory loops and wider signalling network connections) of the ERK pathway present a challenge for the success of MEK1 and MEK2 inhibitors, discuss mechanisms of resistance to these inhibitors, and review their clinical progress.

Allo-SCT for myelofibrosis: reversing the chronic phase in the JAK inhibitor era?

At present, allo-SCT is the only curative treatment for patients with myelofibrosis (MF). Unfortunately, a significant proportion of candidate patients are considered transplant ineligible due to their poor general condition and advanced age at the time of diagnosis. The approval of the first JAK inhibitor, ruxolitinib, for patients with advanced MF in 2011 has had a qualified impact on the treatment algorithm. The drug affords substantial improvement in MF-associated symptoms and splenomegaly but no major effect on the natural history. There has, therefore, been considerable support for assessing the drug's candidacy in the peritransplant period. The drug's precise impact on clinical outcome following allo-SCT is currently not known; nor are the drug's long-term efficacy and safety known. Considering the rarity of MF and the small proportion of patients who undergo allo-SCT, well designed collaborative efforts are required. In order to address some of the principal challenges, an expert panel of laboratory and clinical experts in this field was established, and an independent workshop held during the 54th American Society of Hematology Annual Meeting in New Orleans, USA on 6 December 2013, and the European Hematology Association's Annual Meeting in Milan, Italy on 13 June 2014. This document summarizes the results of these efforts.

Translational hematology

Translational research is scientific research that helps to make findings from basic science useful for practical applications in the clinic. The successful use of a drug that interferes with the specific molecular pathophysiology of cancer remains the ultimate vision in cancer medicine. Translational research is a multistep process including the discovery of a cytogenetic/molecular aberration as well as the demonstration of its pathophysiological relevance and its druggability by in vitro experiments and in vivo animal models. Information obtained from preclinical research paves the way for clinical trials in which a drug of interest is developed until its clinical application. Modern pathophysiology-oriented anticancer drugs that have been developed by translational research are available for clinical applications since the beginning of this millennium. By using these drugs higher efficacy and lower toxicity could be achieved as compared with previous treatments. In this article, we will present some of the most prominent examples of this translational approach.

Trametinib: first global approval

Trametinib is an orally bioavailable mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor with antineoplastic activity. The compound specifically binds to MEK1 and MEK2, resulting in inhibition of growth factor-mediated cell signalling and cellular proliferation in various cancers. Originally developed by Japan Tobacco, GlaxoSmithKline has licensed exclusive worldwide rights to the compound and conducted development in a number of different cancer types. Trametinib, as a monotherapy, has been approved in the US for the treatment of unresectable or metastatic malignant melanoma with BRAF V600E or V600K mutations, as detected by an FDA-approved test. The compound, as a monotherapy, has also been submitted for regulatory review in the EU for BRAF mutation-positive malignant melanoma, and is in phase III development in Europe, Argentina, Canada and Oceania. Phase II development is underway for pancreatic cancer, non-small cell lung cancer and relapsed or refractory leukaemias. GlaxoSmithKline is also developing trametinib for use in combination with dabrafenib in BRAF V600 mutation-positive metastatic cutaneous melanoma; the combination is at the preregistration stage in the EU and a phase III clinical programme is underway worldwide. Phase II development for this combination is also underway in colorectal cancer. Several phase I trials have also been initiated to evaluate trametinib in combination with other drugs for the treatment of various solid tumours and haematological malignancies. A paediatric oral solution formulation has been assessed against the oral tablet formulation in a phase I trial. This article summarizes the milestones in the development of trametinib leading to this first approval for unresectable or metastatic BRAF mutation-positive malignant melanoma.

MEK inhibitors as a chemotherapeutic intervention in multiple myeloma

The Ras/Raf/MEK/extracellular signal regulated kinase (ERK) (Ras/mitogen-activated protein kinases (MAPK)) signal transduction pathway is a crucial mediator of many fundamental biological processes, including cellular proliferation, survival, angiogenesis and migration. Aberrant signalling through the Ras/MAPK cascade is common in a wide array of malignancies, including multiple myeloma (MM), making it an appealing candidate for the development of novel targeted therapies. In this review, we explore our current understanding of the Ras/MAPK pathway and its role in MM. Additionally, we summarise the current status of small molecule inhibitors of MEK under clinical evaluation, and discuss future approaches required to optimise their use.