FDA Approval Summary: Vemurafenib for the Treatment of Patients with Erdheim-Chester Disease with the BRAFV600 Mutation.

On November 6, 2017, the U.S. Food and Drug Administration (FDA) granted regular approval to vemurafenib for the treatment of adult patients with Erdheim-Chester disease (ECD) with BRAFV600 mutation. ECD is a type of histiocytosis, a rare disorder characterized by an abnormal accumulation and behavior of cells of the mononuclear phagocytic system, which includes antigen-processing cells, dendritic cells, monocytes, or macrophages. Recently published data confirm a frequency of 54% of BRAFV600E mutations in patients with ECD.Approval was based on a cohort of 22 patients who received 960 mg of vemurafenib twice daily within the VE Basket Trial (MO28072), a single-arm, multicenter, multiple cohort study. Patients in the ECD cohort had histologically confirmed ECD with BRAFV600 mutations that were refractory to standard therapy. The ECD cohort achieved an overall response rate of 54.5% (95% confidence interval: 32.2-75.6), with a complete response rate of 4.5%. With a median duration of follow-up of 26.6 months, the median duration of response has not been reached. The most frequently reported adverse reactions (>50%) in the ECD cohort were arthralgia, rash maculo-papular, alopecia, fatigue, electrocardiogram QT interval prolonged, and skin papilloma. The median treatment duration for ECD patients in this study was 14.2 months. This article describes the FDA review of the vemurafenib efficacy supplement for patients with ECD with BRAFV600 mutations. IMPLICATIONS FOR PRACTICE: Vemurafenib, an oral monotherapy targeting a mutation in BRAF, is the first U.S. Food and Drug Administration approval for the treatment of Erdheim-Chester disease (ECD). ECD is an extremely rare hematopoietic neoplasm that represents clonal proliferation of myeloid progenitor cells. ECD may involve bone and one or more organ systems, primarily affecting adults in their 5th and 7th decades of life, with a slight male predominance. This approval provides an effective and reasonably safe therapy for patients with a serious and life-threatening condition for which no approved therapy exists.

High levels of GDF15 in thalassemia suppress expression of the iron regulatory protein hepcidin.

In thalassemia, deficient globin-chain production during erythropoiesis results in anemia. Thalassemia may be further complicated by iron overload (frequently exacerbated by blood transfusion), which induces numerous endocrine diseases, hepatic cirrhosis, cardiac failure and even death. Accumulation of iron in the absence of blood transfusions may result from inappropriate suppression of the iron-regulating peptide hepcidin by an erythropoietic mechanism. To test this hypothesis, we examined erythroblast transcriptome profiles from 15 healthy, nonthalassemic donors. Growth differentiation factor 15 (GDF15), a member of the transforming growth factor-beta superfamily, showed increased expression and secretion during erythroblast maturation. Healthy volunteers had mean GDF15 serum concentrations of 450 +/- 50 pg/ml. In comparison, individuals with beta-thalassemia syndromes had elevated GDF15 serum levels (mean 66,000 +/- 9,600 pg/ml; range 4,800-248,000 pg/ml; P < 0.05) that were positively correlated with the levels of soluble transferrin receptor, erythropoietin and ferritin. Serum from thalassemia patients suppressed hepcidin mRNA expression in primary human hepatocytes, and depletion of GDF15 reversed hepcidin suppression. These results suggest that GDF15 overexpression arising from an expanded erythroid compartment contributes to iron overload in thalassemia syndromes by inhibiting hepcidin expression.

Cytokine-mediated increases in fetal hemoglobin are associated with globin gene histone modification and transcription factor reprogramming.

Therapeutic regulation of globin genes is a primary goal of translational research aimed toward hemoglobinopathies. Signal transduction was used to identify chromatin modifications and transcription factor expression patterns that are associated with globin gene regulation. Histone modification and transcriptome profiling were performed using adult primary CD34(+) cells cultured with cytokine combinations that produced low versus high levels of gamma-globin mRNA and fetal hemoglobin (HbF). Embryonic, fetal, and adult globin transcript and protein expression patterns were determined for comparison. Chromatin immunoprecipitation assays revealed RNA polymerase II occupancy and histone tail modifications consistent with transcriptional activation only in the high-HbF culture condition. Transcriptome profiling studies demonstrated reproducible changes in expression of nuclear transcription factors associated with high HbF. Among the 13 genes that demonstrated differential transcript levels, 8 demonstrated nuclear protein expression levels that were significantly changed by cytokine signal transduction. Five of the 8 genes are recognized regulators of erythropoiesis or globin genes (MAFF, ID2, HHEX, SOX6, and EGR1). Thus, cytokine-mediated signal transduction in adult erythroid cells causes significant changes in the pattern of globin gene and protein expression that are associated with distinct histone modifications as well as nuclear reprogramming of erythroid transcription factors.

Acute chest syndrome: sickle cell disease.

Acute chest syndrome (ACS) is a common complication and reason for hospital admission in patients with sickle cell disease (SCD). It is also the most common cause of death in this patient population. Most of the time, the trigger for ACS in an individual patient cannot be identified. However, although infection is the most common identifiable cause for ACS, other important triggers are vaso-occlusive crisis (VOC) and asthma. This comprehensive review will focus on the pathogenesis, clinical characteristics, complications and treatment available to manage ACS. But importantly, this review will highlight new possible etiologies, with the goal of improving oxygenation and, therefore, a reduction in sickling and lung damage in this patient population.

Inhibition of erythroblast growth and fetal hemoglobin production by ribofuranose-substituted adenosine derivatives.

In vivo, inhibition of fetal hemoglobin (HbF) expression in humans around the time of birth causes the clinical manifestation of sickle cell and beta-thalassemia syndromes. Inhibition of HbF among cultured cells was recently described by the adenosine derivative molecule named SQ22536. Here, a primary cell culture model was utilized to further explore the inhibition of HbF by adenosine derivative molecules. SQ22536 demonstrated down-regulation of growth and HbF expression among erythroblasts cultured from fetal and adult human blood. The effects upon HbF were noted in a majority of cells, and quantitative PCR analysis demonstrated a transcriptional mechanism. Screening assays demonstrated that two additional molecules named 5'-deoxy adenosine and 2',3'-dideoxy adenosine had effects on HbF comparable to SQ22536. Other adenosine derivative molecules, adenosine receptor binding ligands, and cAMP-signaling regulators failed to inhibit HbF in matched cultures. These results suggest that structurally related ribofuranose-substituted adenosine analogues act through an unknown mechanism to inhibit HbF expression in fetal and adult human erythroblasts.

Multicenter COMPACT study of COMplications in patients with sickle cell disease and utilization of iron chelation therapy.

BACKGROUND: Over the past few decades, lifespans of sickle cell disease (SCD) patients have increased; hence, they encounter multiple complications. Early detection, appropriate comprehensive care, and treatment may prevent or delay onset of complications. OBJECTIVE: We collected longitudinal data on sickle cell disease (SCD) complication rates and associated resource utilization relative to blood transfusion patterns and iron chelation therapy (ICT) use in patients aged ≥16 years to address a gap in the literature. RESEARCH DESIGN AND METHODS: Medical records of 254 SCD patients ≥16 years were retrospectively reviewed at three US tertiary care centers. MAIN OUTCOME MEASURES: We classified patients into cohorts based on cumulative units of blood transfused and ICT history: <15 units, no ICT (Cohort 1 [C1]), ≥15 units, no ICT (Cohort 2 [C2]), and ≥15 units with ICT (Cohort 3 [C3]). We report SCD complication rates per patient per year; cohort comparisons use rate ratios (RRs). RESULTS: Cohorts had 69 (C1), 91 (C2), and 94 (C3) patients. Pain led to most hospitalizations (76%) and emergency department (ED) (82%) visits. Among transfused patients (C2+C3), those receiving ICT were less likely to experience SCD complications than those who did not (RR [95% CI] C2 vs. C3: 1.33 [1.25-1.42]). Similar trends (RR [95% CI]) were observed in ED visits and hospitalizations associated with SCD complications (C2 vs. C3, ED: 1.94 [1.70-2.21]; hospitalizations: 1.61 [1.45-1.78]), but not in outpatient visits. CONCLUSIONS: Although the most commonly reported SCD complication among all patients was pain, patients who received ICT were less likely to experience pain and other complications than those who did not. These results highlight the need for increased patient and provider education on the importance of comprehensive disease management.

Sepsis caused by Mycobacterium terrae complex in a patient with sickle cell disease.

Infections are a significant cause of morbidity and mortality in patients with sickle cell disease. Loss of splenic function in these patients makes them highly susceptible to some bacterial infections. Non-tuberculous mycobacterial infections in patients with sickle cell disease are extremely rare and only two cases have been reported previously. We describe a case of sepsis caused by non-tuberculous mycobacterium, Mycobacterium terrae complex in a patient with febrile sickle cell disease. M terrae complex is a rare clinical pathogen and this is the first reported case of sepsis secondary to this organism in a patient with sickle cell disease. The patient responded to imipenem and amikacin therapy.

Fetal hemoglobin silencing in humans.

Interruption of the normal fetal-to-adult transition of hemoglobin expression should largely ameliorate sickle cell and beta-thalassemia syndromes. Achievement of this clinical goal requires a robust understanding of gamma-globin gene and protein silencing during human development. For this purpose, age-related changes in globin phenotypes of circulating human erythroid cells were examined from 5 umbilical cords, 99 infants, and 5 adult donors. Unexpectedly, an average of 95% of the cord blood erythrocytes and reticulocytes expressed HbA and the adult beta-globin gene, as well as HbF and the gamma-globin genes. The distribution of hemoglobin and globin gene expression then changed abruptly due to the expansion of cells lacking HbF or gamma-globin mRNA (silenced cells). In adult reticulocytes, less than 5% expressed gamma-globin mRNA. These data are consistent with a "switching" model in humans that initially results largely from gamma- and beta-globin gene coexpression and competition during fetal development. In contrast, early postnatal life is marked by the rapid accumulation of cells that possess undetectable gamma-globin mRNA and HbF. The silencing phenomenon is mediated by a mechanism of cellular replacement. This novel silencing pattern may be important for the development of HbF-enhancing therapies.