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OBJECTIVES: Hospital death is comparatively common in people with haematological cancers, but little is known about patient preferences. This study investigated actual and preferred place of death, concurrence between these and characteristics of preferred place discussions. METHODS: Set within a population-based haematological malignancy patient cohort, adults (≥18 years) diagnosed 2004-2012 who died 2011-2012 were included (n=963). Data were obtained via routine linkages (date, place and cause of death) and abstraction of hospital records (diagnosis, demographics, preferred place discussions). Logistic regression investigated associations between patient and clinical factors and place of death, and factors associated with the likelihood of having a preferred place discussion. RESULTS: Of 892 patients (92.6%) alive 2 weeks after diagnosis, 58.0% subsequently died in hospital (home, 20.0%; care home, 11.9%; hospice, 10.2%). A preferred place discussion was documented for 453 patients (50.8%). Discussions were more likely in women (p=0.003), those referred to specialist palliative care (p<0.001), and where cause of death was haematological cancer (p<0.001); and less likely in those living in deprived areas (p=0.005). Patients with a discussion were significantly (p<0.05) less likely to die in hospital. Last recorded preferences were: home (40.6%), hospice (18.1%), hospital (17.7%) and care home (14.1%); two-thirds died in their final preferred place. Multiple discussions occurred for 58.3% of the 453, with preferences varying by proximity to death and participants in the discussion. CONCLUSION: Challenges remain in ensuring that patients are supported to have meaningful end-of-life discussions, with healthcare services that are able to respond to changing decisions over time.
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Muerte , Neoplasias Hematológicas/mortalidad , Prioridad del Paciente/estadística & datos numéricos , Cuidado Terminal/estadística & datos numéricos , Adulto , Anciano , Estudios de Cohortes , Femenino , Servicios de Atención de Salud a Domicilio/estadística & datos numéricos , Hospitales para Enfermos Terminales/estadística & datos numéricos , Hospitales/estadística & datos numéricos , Humanos , Modelos Logísticos , Masculino , Persona de Mediana Edad , Cuidado Terminal/métodos , Cuidado Terminal/psicología , Reino UnidoRESUMEN
DNA-PK is a key component within the DNA damage response, as it is responsible for recognizing and repairing double-strand DNA breaks (DSBs) via non-homologous end joining. Historically it has been challenging to identify inhibitors of the DNA-PK catalytic subunit (DNA-PKcs) with good selectivity versus the structurally related PI3 (lipid) and PI3K-related protein kinases. We screened our corporate collection for DNA-PKcs inhibitors with good PI3 kinase selectivity, identifying compound 1. Optimization focused on further improving selectivity while improving physical and pharmacokinetic properties, notably co-optimization of permeability and metabolic stability, to identify compound 16 (AZD7648). Compound 16 had no significant off-target activity in the protein kinome and only weak activity versus PI3Kα/γ lipid kinases. Monotherapy activity in murine xenograft models was observed, and regressions were observed when combined with inducers of DSBs (doxorubicin or irradiation) or PARP inhibition (olaparib). These data support progression into clinical studies (NCT03907969).
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Proteína Quinasa Activada por ADN/antagonistas & inhibidores , Inhibidores de Proteínas Quinasas/uso terapéutico , Purinas/uso terapéutico , Piranos/uso terapéutico , Triazoles/uso terapéutico , Animales , Antineoplásicos/síntesis química , Antineoplásicos/farmacocinética , Antineoplásicos/uso terapéutico , Línea Celular Tumoral , Fosfatidilinositol 3-Quinasa Clase Ib/metabolismo , Perros , Descubrimiento de Drogas , Humanos , Ratones , Estructura Molecular , Neoplasias/tratamiento farmacológico , Inhibidores de Proteínas Quinasas/síntesis química , Inhibidores de Proteínas Quinasas/farmacocinética , Purinas/síntesis química , Purinas/farmacocinética , Piranos/síntesis química , Piranos/farmacocinética , Ratas , Receptores de Factor Estimulante de Colonias de Granulocitos y Macrófagos/antagonistas & inhibidores , Relación Estructura-Actividad , Triazoles/síntesis química , Triazoles/farmacocinética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
PURPOSE: Patients with haematological malignancies are more likely to die in hospital, and less likely to access palliative care than people with other cancers, though the reasons for this are not well understood. The purpose of our study was to explore haematology nurses' perspectives of their patients' places of care and death. METHOD: Qualitative description, based on thematic content analysis. Eight haematology nurses working in secondary and tertiary hospital settings were purposively selected and interviewed. Transcriptions were coded and analysed for themes using a mainly inductive, cross-comparative approach. RESULTS: Five inter-related factors were identified as contributing to the likelihood of patients' receiving end of life care/dying in hospital: the complex nature of haematological diseases and their treatment; close clinician-patient bonds; delays to end of life discussions; lack of integration between haematology and palliative care services; and barriers to death at home. CONCLUSIONS: Hospital death is often determined by the characteristics of the cancer and type of treatment. Prognostication is complex across subtypes and hospital death perceived as unavoidable, and sometimes the preferred option. Earlier, frank conversations that focus on realistic outcomes, closer integration of palliative care and haematology services, better communication across the secondary/primary care interface, and an increase in out-of-hours nursing support could improve end of life care and facilitate death at home or in hospice, when preferred.
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Actitud del Personal de Salud , Neoplasias Hematológicas/terapia , Hematología , Personal de Enfermería en Hospital/psicología , Cuidado Terminal , Comunicación , Humanos , Cuidados Paliativos , Percepción , Investigación Cualitativa , Reino UnidoRESUMEN
BACKGROUND: People with haematological malignancies have different end-of-life care patterns from those with other cancers and are more likely to die in hospital. Little is known about patient and relative preferences at this time and whether these are achieved. AIM: To explore the experiences and reflections of bereaved relatives of patients with leukaemia, lymphoma or myeloma, and examine (1) preferred place of care and death; (2) perceptions of factors influencing attainment of preferences; and (3) changes that could promote achievement of preferences. DESIGN: Qualitative interview study incorporating 'Framework' analysis. SETTING/PARTICIPANTS: A total of 10 in-depth interviews with bereaved relatives. RESULTS: Although most people expressed a preference for home death, not all attained this. The influencing factors include disease characteristics (potential for sudden deterioration and death), the occurrence and timing of discussions (treatment cessation, prognosis, place of care/death), family networks (willingness/ability of relatives to provide care, knowledge about services, confidence to advocate) and resource availability (clinical care, hospice beds/policies). Preferences were described as changing over time and some family members retrospectively came to consider hospital as the 'right' place for the patient to have died. Others shared strong preferences with patients for home death and acted to ensure this was achieved. No patients died in a hospice, and relatives identified barriers to death in this setting. CONCLUSION: Preferences were not always achieved due to a series of complex, interrelated factors, some amenable to change and others less so. Death in hospital may be preferred and appropriate, or considered the best option in hindsight.
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Actitud Frente a la Muerte , Aflicción , Familia/psicología , Neoplasias Hematológicas/mortalidad , Características de la Residencia , Cuidado Terminal , Adulto , Anciano , Femenino , Humanos , Entrevistas como Asunto , Masculino , Persona de Mediana Edad , Investigación CualitativaRESUMEN
B-cell lymphoma 6 (BCL6) inhibition is a promising mechanism for treating hematological cancers but high quality chemical probes are necessary to evaluate its therapeutic potential. Here we report potent BCL6 inhibitors that demonstrate cellular target engagement and exhibit exquisite selectivity for BCL6 based on mass spectrometry analyses following chemical proteomic pull down. Importantly, a proteolysis-targeting chimera (PROTAC) was also developed and shown to significantly degrade BCL6 in a number of diffuse large B-cell lymphoma (DLBCL) cell lines, but neither BCL6 inhibition nor degradation selectively induced marked phenotypic response. To investigate, we monitored PROTAC directed BCL6 degradation in DLBCL OCI-Ly1 cells by immunofluorescence and discovered a residual BCL6 population. Analysis of subcellular fractions also showed incomplete BCL6 degradation in all fractions despite having measurable PROTAC concentrations, together providing a rationale for the weak antiproliferative response seen with both BCL6 inhibitor and degrader. In summary, we have developed potent and selective BCL6 inhibitors and a BCL6 PROTAC that effectively degraded BCL6, but both modalities failed to induce a significant phenotypic response in DLBCL despite achieving cellular concentrations.
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Antineoplásicos/farmacología , Proteínas Proto-Oncogénicas c-bcl-6/antagonistas & inhibidores , Quinolonas/farmacología , Talidomida/análogos & derivados , Talidomida/farmacología , Proteínas Adaptadoras Transductoras de Señales , Antineoplásicos/síntesis química , Antineoplásicos/metabolismo , Línea Celular Tumoral , Células HEK293 , Humanos , Ligandos , Linfoma de Células B Grandes Difuso/tratamiento farmacológico , Péptido Hidrolasas/metabolismo , Unión Proteica , Proteolisis , Proteínas Proto-Oncogénicas c-bcl-6/química , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Quinolonas/síntesis química , Quinolonas/metabolismo , Talidomida/síntesis química , Talidomida/metabolismo , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
BACKGROUND: Haematological malignancies (leukaemias, lymphomas and myeloma) are complex cancers that are relatively common, affect all ages and have divergent outcomes. Although the symptom burden of these diseases is comparable to other cancers, patients do not access specialist palliative care (SPC) services as often as those with other cancers. To determine the reasons for this, we asked SPC practitioners about their perspectives regarding the barriers and facilitators influencing haematology patient referrals. METHODS: We conducted a qualitative study, set within the United Kingdom's (UK's) Haematological Malignancy Research Network (HMRN: www.hmrn.org ), a population-based cohort in the North of England. In-depth, semi-structured interviews were conducted with 20 SPC doctors and nurses working in hospital, community and hospice settings between 2012 and 2014. Interviews were digitally audio-recorded, transcribed and analysed for thematic content using the 'Framework' method. RESULTS: Study participants identified a range of barriers and facilitators influencing the referral of patients with haematological malignancies to SPC services. Barriers included: the characteristics and pathways of haematological malignancies; the close patient/haematology team relationship; lack of role clarity; late end of life discussions and SPC referrals; policy issues; and organisational issues. The main facilitators identified were: establishment of inter-disciplinary working patterns (co-working) and enhanced understanding of roles; timely discussions with patients and early SPC referral; access to information platforms able to support information sharing; and use of indicators to 'flag' patients' needs for SPC. Collaboration between haematology and SPC was perceived as beneficial and desirable, and was said to be increasing over time. CONCLUSIONS: This is the first UK study to explore SPC practitioners' perceptions concerning haematology patient referrals. Numerous factors were found to influence the likelihood of referral, some of which related to the organisation and delivery of SPC services, so were amenable to change, and others relating to the complex and unique characteristics and pathways of haematological cancers. Further research is needed to assess the extent to which palliative care is provided by haematology doctors and nurses and other generalists and ways in which clinical uncertainty could be used as a trigger, rather than a barrier, to referral.
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Actitud del Personal de Salud , Neoplasias Hematológicas/terapia , Hematología/métodos , Cuidados Paliativos , Percepción , Derivación y Consulta/normas , Neoplasias Hematológicas/psicología , Hematología/tendencias , Cuidados Paliativos al Final de la Vida , Humanos , Entrevistas como Asunto , Cuidados Paliativos/métodos , Cuidados Paliativos/normas , Investigación Cualitativa , Calidad de Vida/psicología , Derivación y Consulta/tendencias , Reino Unido , Recursos HumanosRESUMEN
Inhibition of the protein-protein interaction between B-cell lymphoma 6 (BCL6) and corepressors has been implicated as a therapeutic target in diffuse large B-cell lymphoma (DLBCL) cancers and profiling of potent and selective BCL6 inhibitors are critical to test this hypothesis. We identified a pyrazolo[1,5-a]pyrimidine series of BCL6 binders from a fragment screen in parallel with a virtual screen. Using structure-based drug design, binding affinity was increased 100000-fold. This involved displacing crystallographic water, forming new ligand-protein interactions and a macrocyclization to favor the bioactive conformation of the ligands. Optimization for slow off-rate constant kinetics was conducted as well as improving selectivity against an off-target kinase, CK2. Potency in a cellular BCL6 assay was further optimized to afford highly selective probe molecules. Only weak antiproliferative effects were observed across a number of DLBCL lines and a multiple myeloma cell line without a clear relationship to BCL6 potency. As a result, we conclude that the BCL6 hypothesis in DLBCL cancer remains unproven.
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Mapas de Interacción de Proteínas/efectos de los fármacos , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Pirazoles/química , Pirazoles/farmacología , Piridinas/química , Piridinas/farmacología , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Diseño de Fármacos , Humanos , Linfoma de Células B Grandes Difuso/tratamiento farmacológico , Simulación del Acoplamiento Molecular , Proteínas Proto-Oncogénicas c-bcl-6/antagonistas & inhibidoresAsunto(s)
Anemia Mielopática/etiología , Intoxicación por Plomo/complicaciones , Trastornos de la Personalidad/etiología , Anemia Mielopática/sangre , Terapia por Quelación , Humanos , Intoxicación por Plomo/sangre , Intoxicación por Plomo/tratamiento farmacológico , Masculino , Persona de Mediana EdadRESUMEN
BACKGROUND: The reasons patients with haematological malignancies die in hospital more often than those with other cancers is the subject of much speculation. We examined variations in place of death by disease sub-type and time from diagnosis to death, to identify groups of 'at-risk' patients. METHODS: The study is based in the United Kingdom within the infrastructure of the Haematological Malignancy Research Network (HMRN), a large on-going population-based cohort including all patients newly diagnosed with haematological malignancies in the north of England. Diagnostic, demographic, prognostic, treatment and outcome data are collected for each patient and individuals are 'flagged' for death. This study includes all adults (≥18 years) diagnosed 1st September 2004 to 31st August 2010 (n = 10,325), focussing on those who died on/before 31st August 2012 (n = 4829). RESULTS: Most deaths occurred in hospital (65.9%), followed by home (15.6%), nursing home (11%) and hospice (7.5%) and there was little variation by diagnostic sub-type overall. Differences in place of death were, however, observed by time from diagnosis to death, and this was closely related to sub-type; 87.7% of deaths within a month of diagnosis happened in hospital and these largely occurred in patients with acute myeloid leukaemia, diffuse large B-cell lymphoma and myeloma. Patients surviving longer, and particularly beyond 1 year, were less likely to die in hospital and this corresponded with an increase in the proportion of home deaths. CONCLUSIONS: Time from diagnosis to death was clearly a major determinant of place of death and many patients that died within three months of diagnosis did so in hospital. This was closely related to disease sub-type, with early deaths occurring most notable in the more aggressive diseases. This is likely to be due to a combination of factors including acute presentation, rapid disease progression without transition to a palliative approach to care and complications of treatment. Nonetheless, hospital deaths also occurred frequently in indolent diseases, suggesting that other factors were likely to contribute to the large proportion of hospital deaths overall. More evidence is needed to fully understand these complex cancers.
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Haematological malignancies are complex diseases, affecting the entire age spectrum, and having marked differences in presentation, treatment, progression and outcome. Patients have a significant symptom burden and despite treatment improvements for some sub-types, many patients die from their disease. We carried out a systematic review and meta-analysis to examine the proportion of patients with haematological malignancies that received any form of specialist palliative or hospice care. Twenty-four studies were identified, nine of which were suitable for inclusion in the meta-analysis. Our review showed that patients with haematological malignancies were far less likely to receive care from specialist palliative or hospice services compared to other cancers (Risk Ratio 0.46, [95% confidence intervals 0.42-0.50]). There are several possible explanations for this finding, including: ongoing management by the haematology team and consequent strong bonds between staff and patients; uncertain transitions to a palliative approach to care; and sudden transitions, leaving little time for palliative input. Further research is needed to explore: transitions to palliative care; potential unmet patient needs; where patients want to be cared for and die; existing practices in the delivery of palliative and end-of-life care; and barriers to specialist palliative care and hospice referral and how these might be overcome.
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Neoplasias Hematológicas , Cuidados Paliativos al Final de la Vida/estadística & datos numéricos , Cuidados Paliativos/organización & administración , Manejo de Atención al Paciente/organización & administración , Derivación y Consulta/normas , Actitud del Personal de Salud , Costo de Enfermedad , Humanos , Metaanálisis como Asunto , Calidad de Vida , Derivación y Consulta/tendencias , Especialización , Nivel de AtenciónRESUMEN
BACKGROUND: Haematological malignancies are a common, heterogeneous and complex group of diseases that are often associated with poor outcomes despite intensive treatment. Research surrounding end-of-life issues, and particularly place of death, is therefore of paramount importance, yet place of death has not been formally reviewed in these patients. METHODS: A systematic literature review and meta-analysis was undertaken using PubMed to identify all studies published between 1966 and 2010. Studies examining place of death in adult haematology patients, using routinely compiled morbidity and mortality data and providing results specific to this disease were included. 21 studies were identified with descriptive and/or risk-estimate data; 17 were included in a meta-analysis. RESULTS: Compared to other cancer deaths, haematology patients were more than twice as likely to die in hospital (Odds Ratio 2.25 [95% Confidence Intervals, 2.07-2.44]). CONCLUSION: Home is generally considered the preferred place of death but haematology patients usually die in hospital. This has implications for patients who may not be dying where they wish, and also health commissioners who may be funding costly end-of-life care in inappropriate acute hospital settings. More research is needed about preferred place of care for haematology patients, reasons for hospital deaths, and how these can be avoided if home death is preferred.
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OBJECTIVE: The identification of signaling pathways involved in megakaryocytopoiesis is essential for development of novel therapeutics to treat hematological disorders. Following our previous findings that megakaryocytes express functional channel-forming N-methyl-D-aspartate-type glutamate receptors, here we aimed to determine the glutamate release capacity in undifferentiated and differentiated megakaryocytes and the role of soluble N-ethyl maleimide-sensitive factor attachment protein receptor (SNARE) proteins that are known to be associated with vesicular exocytosis. MATERIALS AND METHODS: Using the megakaryocytic cell line MEG-01, primary megakaryocytes, and tissue sections of bone marrow, reverse transcription polymerase chain reaction, Western blot analysis, and immunolocalization were employed to detect factors required for vesicular glutamate release. Vesicle recycling was monitored by acridine orange and FM1-43 staining and glutamate release activity was assessed by an enzyme-linked fluorimetric assay. Genetically modified MEG-01 cells, with deletion or overexpression of SNARE and vesicular proteins, were also examined for glutamate release activity. RESULTS: We demonstrated that megakaryocytes express numerous proteins required for vesicular glutamate release, including core SNARE proteins, vesicle-associated membrane protein, soluble N-ethyl maleimide-sensitive factor attachment protein-23, and syntaxin, as well as specific glutamate-loading vesicle proteins, VGLUT1 and VGLUT2. Moreover, active vesicle recycling and differentiation-dependent glutamate release were observed in megakaryocytes. Vesicle-associated membrane protein-deficient MEG-01 cells, which are impaired in vesicle recycling, showed a 30% decrease in released glutamate, whereas overexpression of VGLUT1 exhibited up to a 2.2-fold increase in glutamate release. CONCLUSION: These data show that glutamate release from megakaryocytes occurs in a SNARE-dependent, exocytotic manner and is increased during differentiation, suggesting that manipulation of glutamate signaling could influence megakaryocytopoiesis and, therefore, offer a suitable target for the treatment of thrombosis and other hematological disorders.
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Ácido Glutámico/metabolismo , Megacariocitos/metabolismo , Proteínas SNARE/fisiología , Animales , Secuencia de Bases , Western Blotting , Diferenciación Celular , Línea Celular , Cartilla de ADN , Exocitosis , Humanos , Megacariocitos/citología , RatonesRESUMEN
The aetiology of haemolytic disease is diverse and the diagnosis often relies on laboratory testing. We describe a case of intravascular haemolysis, which illustrates that significant intravascular haemolysis can occur in the absence of any abnormal haematological findings. Despite gross haemoglobinuria at presentation, the haemoglobin and reticulocyte counts were both within reference limits and a normal blood film was observed. Subsequently, acute tubular necrosis occurred secondary to haemolysis, and acute renal failure was evident by day 2. However, the haemoglobin decreased slowly reaching a nadir of 75 g/L on day 6 (reference interval 130-180 g/L). A diagnosis of paroxysmal cold haemoglobinuria secondary to mycoplasma infection was subsequently made. Biochemical analysis was useful in this case to confirm that the gross pigmentation in the samples received could be attributable to intravascular haemolysis.
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Hemoglobinuria Paroxística/diagnóstico , Lesión Renal Aguda/diagnóstico , Lesión Renal Aguda/patología , Hemoglobinas/análisis , Hemoglobinuria Paroxística/patología , Humanos , Masculino , Infecciones por Mycoplasma/diagnóstico , Infecciones por Mycoplasma/patología , Adulto JovenAsunto(s)
Células Dendríticas/patología , Leucemia de Células Plasmáticas/patología , Infiltración Leucémica/patología , Piel/patología , Anciano , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Ciclofosfamida/uso terapéutico , Doxorrubicina/uso terapéutico , Humanos , Leucemia de Células Plasmáticas/tratamiento farmacológico , Masculino , Prednisolona/uso terapéutico , Vincristina/uso terapéuticoRESUMEN
The true incidence and prognosis of autoimmune thrombocytopenic purpura (ITP) in adults is unknown. We present the results of a prospective study in a population-based cohort of newly presenting adults (> or = 16 years) with ITP and platelet count of < 50 x 109/l, which took place between 1 January 1993 and 31 December 1999 in the former Northern Health Region in the UK (population 3.08 million). A total of 245 cases were confirmed by bone marrow examination with a median follow-up of 60 months (range 6-78 months). There were 134 females/111 males (1.2:1). Overall incidence was 1.6 per 105 per annum. Absolute incidence was similar for both sexes, with highest age-specific incidence in those aged > 60 years. Thirty patients (12%) presented with frank bleeding, and 28% were asymptomatic. Forty-five patients (18%) received no treatment, and 135 (55%) received first-line treatment only. Thirty patients (12%) underwent splenectomy. There were four deaths (1.6%) from bleeding and/or the complications of therapy in this cohort, but only one was in the acute phase of the illness. The majority of patients (155 out of 245) achieved remission (platelet count > 100 x 109/l), with a further 59 (24%) in partial remission with no symptoms (platelet count 30-100 x 109/l). This population-based study suggests that the traditional view of adult ITP as being a predominantly chronic disease that preferentially affects females needs to be modified.
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Púrpura Trombocitopénica Idiopática/epidemiología , Adolescente , Adulto , Distribución por Edad , Anciano , Anciano de 80 o más Años , Causas de Muerte , Inglaterra/epidemiología , Femenino , Estudios de Seguimiento , Hemorragia/etiología , Humanos , Incidencia , Infecciones/complicaciones , Masculino , Persona de Mediana Edad , Recuento de Plaquetas , Pronóstico , Estudios Prospectivos , Púrpura Trombocitopénica Idiopática/complicaciones , Púrpura Trombocitopénica Idiopática/terapia , Remisión Espontánea , Distribución por Sexo , Esplenectomía , Resultado del TratamientoAsunto(s)
Inmunoglobulinas/análisis , Leucemia Linfocítica Crónica de Células B/patología , Linfocitos/patología , Colorantes , Cristalización , Técnica del Anticuerpo Fluorescente , Humanos , Cadenas Pesadas de Inmunoglobulina/análisis , Inmunoglobulina M , Cadenas lambda de Inmunoglobulina/análisisRESUMEN
Identification of the regulatory inputs that direct megakaryocytopoiesis and platelet production is essential for the development of novel therapeutic strategies for the treatment of thrombosis and related hematologic disorders. We have previously shown that primary human megakaryocytes express the N-methyl-d-aspartate acid (NMDA) receptor 1 (NR1) subunit of NMDA-type glutamate receptors, which appear to be pharmacologically similar to those identified at neuronal synapses, responsible for mediating excitatory neurotransmission in the central nervous system. However, the functional role of NMDA receptor signaling in megakaryocytopoiesis remains unclear. Here we provide evidence that demonstrates the fundamental importance of this signaling pathway during human megakaryocyte maturation in vitro. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of RNA extracted from CD34+-derived megakaryocytes identified expression of NR2A and NR2D receptor subunits in these cells, as well as the NMDA receptor accessory proteins, Yotiao and postsynaptic density protein 95 (PSD-95). In functional studies, addition of a selective NMDA receptor antagonist, MK-801 inhibited proplatelet formation, without affecting proliferation or apoptosis. Exposure of CD34+ cells to MK-801 cultured for 14 days in the presence of thrombopoietin induced a decrease in expression of the megakaryocyte cell surface markers CD61, CD41a, and CD42a compared with controls. At an ultrastructural level, MK-801-treated cells lacked alpha-granules, demarcated membranes, and multilobed nuclei, which were prominent in untreated mature megakaryocyte controls. Using immunohistochemistry on sections of whole tibiae from c-Mpl knockout mice we demonstrated that megakaryocytic NMDA receptor expression was maintained following c-Mpl ablation. These data support a fundamental role for glutamate signaling in megakaryocytopoiesis and platelet production, which is likely to be independent of thrombopoietin-mediated effects.