George J. Dover

Design of the multicenter study of hydroxyurea in sickle cell anemia

The Multicenter Study of Hydroxyurea in Sickle Cell Anemia is a randomized double-blind placebo-controlled trial to test whether hydroxyurea can reduce the rate of painful crises in adult patients who have at least three painful crises per year. The sample size of 299 patients yields at least 90% power to detect a 50% or greater reduction in crisis rate. Dosage starts at 15 mg/kg/day and is titrated to the patients maximum tolerated dose up to 35 mg/kg/day. Placebo dosage is titrated in similar fashion to maintain blinding. Attempts are made to ascertain medical contacts for at least 2 years after study entry. The Core Laboratory, Treatment Distribution Center, and Data Coordinating Center collaborate to provide standardized monitoring for toxicity and dose adjustments. The Core Laboratory also reduces the possibility of inadvertent unmasking of treatment assignment during review of hematologic data in clinical centers. An independent Crisis Review Committee classifies clinical events to assure that outcome evaluations are standardized and unbiased by knowledge of treatment assignments. The Data and Safety Monitoring Board assures scientific integrity of the study, as well as the safety and ethical treatment of study patients. We expect the study to determine whether or not treatment with hydroxyurea can offer significant clinical benefit to patients with the most common hereditary disorder among African-Americans in the United States.

Erythropoietic activity in patients with sickle cell anaemia before and after treatment with hydroxyurea

In this project we have prospectively studied the erythropoietic activity in patients with sickle cell anaemia (SS) before and after treatment with hydroxyurea (HU). Some of the patients were enrolled in a double‐blind placebo controlled trial of HU in patients with SS and others were enrolled in an open label study. Determinants of erythropoietic activity included the reticulocyte count, red blood cell (RBC) survival by the 51Cr method, plasma 59Fe clearance, plasma iron turnover (PIT), erythron transferrin uptake (ETU), RBC production/destruction rate, and RBC Fe utilization. Therapy with HU increased the mean corpuscular volume (MCV), haemoglobin (Hb)F, RBC survival and t1/259Fe clearance; it decreased the reticulocyte count, the white blood cell (WBC) count, ETU, and the PIT. Most of the changes in parameters of erythropoiesis could be explained by the increase in 51Cr RBC survival after therapy with HU. Together the data showed that in selected patients the net effect of HU on Hb level was a function of the difference between the suppressive effect of HU (decreased RBC production) and the increase in RBC survival. In the majority of patients who responded to HU, there was a preferential effect on RBC survival.

Fetal hemoglobin in sickle cell anemia: a glass half full?

Fetal hemoglobin (HbF) modulates the phenotype of sickle cell anemia by inhibiting deoxy sickle hemoglobin (HbS) polymerization. The blood concentration of HbF, or the number of cells with detectable HbF (F-cells), does not measure the amount of HbF/F-cell. Even patients with high HbF can have severe disease because HbF is unevenly distributed among F-cells, and some cells might have insufficient concentrations to inhibit HbS polymerization. With mean HbF levels of 5%, 10%, 20%, and 30%, the distribution of HbF/F-cell can greatly vary, even if the mean is constant. For example, with 20% HbF, as few as 1% and as many as 24% of cells can have polymer-inhibiting, or protective, levels of HbF of ∼10 pg; with lower HbF, few or no protected cells can be present. Only when the total HbF concentration is near 30% is it possible for the number of protected cells to approach 70%. Rather than the total number of F-cells or the concentration of HbF in the hemolysate, HbF/F-cell and the proportion of F-cells that have enough HbF to thwart HbS polymerization is the most critical predictor of the likelihood of severe sickle cell disease.

Sickle cell disease: no longer a single gene disorder.

Patients who are homozygous for the sickle hemoglobin mutation can present with remarkably different clinical courses, varying from death in childhood, to recurrent painful vasoocclusive crises and multiple organ damage in adults, to being relatively well even until old age. Increasing numbers of genetic loci have now been identified that can modulate sickle cell disease phenotype, from nucleotide motifs within the beta-globin gene cluster, to genes located on different chromosomes. With recent success of the human genome project, it is anticipated that many more genetic modifiers of sickle cell disease will be discovered that can lead to the development of more effective therapeutic approaches. The multigenic origin of the variable phenotype in sickle cell disease will serve as a paradigm for the study of variation in phenotypes of all single gene disorders in man.

Sustained increase in haemoglobin and RBC following long-term administration of recombinant human erythropoietin to patients with homozygous beta-thalassaemia

Summary. Recombinant human erythropoietin (rHuEPO) was given subcutaneously three times per week in an escalating dose from 500u/kg to 950u/kg together with ferrous fumarate 305 mg and folic acid 5mg/d, to 10 patients from four unrelated Arab families with homozygous /3‐thaIassaemia. Six splenectomized patients showed a mean (istandard error) increase in haemoglobin from 7‐1 – 0‐1 to 9‐3 – 0‐1 g/dl (P = 0‐0001), in RBC from 4‐0 to 5‐0 × 1012/1 (P = 0‐0001) and in nucleated RBC from 32 – 7 × 1010/1 to 82–6 × 1010/1 while receiving 750u/kg three times per week which persisted for 4‐11 months. In two patients there was no need for further blood transfusions. In three out of four unsplenectomized patients there were no changes in Hb and RBC despite dose escalation. There were no significant changes in MVC, MCH and reticulocyte count, serum bilirubin, LDH, malonyldialdehyde (MDA) and vitamin E levels. After 13 weeks of rHuEPO there was a mean increase in the percentage of F cells from 31 –10% to 86 –6% (P< 0‐003) in three splenectomized patients and in one unsplenectomized patient from 56‐4% to 80% without changes in the levels of Hb F. Globin chain synthesis ratios did not change in four responding patients. Mean serum iron and transferrin saturation index did not change, whereas mean serum ferritin increased from 299–45/ng/I to 480–20/ig/l (P< 0‐001). In seven responding patients an accelerated linear growth was indicated by positive changes in height standard deviation score for chronological age. Side‐effects were minimal throughout the treatment period.

Prevalence of impaired growth in children with homozygous sickle cell anemia

The prevalence of impaired growth was evaluated in 63 patients with homozygous sickle cell anemia. Twenty-five percent of the children studied were less than the fifth percentile of National Center for Health Statistics growth standards for either height/age, weight/age, or weight/height. Significantly more 11− to 18-year-old children were less than the fifth percentile for weight/height compared with earlier age ranges. No differences due to gender were found. Nutritional intervention may improve growth in selected children.

Induction of fetal hemoglobin synthesis in children with sickle cell anemia on low-dose oral sodium phenylbutyrate therapy.

This study was designed to determine if low doses of oral sodium phenylbutyrate (SPB) induce hemoglobin F (HbF) synthesis in children with hemoglobin SS (HbSS). We treated 8 children with HbSS over a period of 5–30 weeks. The initial dose (1.0 g/d) was increased weekly (by 1.0 g/d) until F-reticulocytes doubled. All patients showed an increase in F-reticulocytes (P = 0.002) that was dose-dependent (P = 0.001). Three of 5 patients who continued oral SPB for more than 10 weeks had substantial increases in HbF. We conclude that lower dose SPB is effective in inducing HbF synthesis in some children with HbSS. Further trials are warranted to determine the optimal treatment regimen.

Hemoglobin Switching Protocols in Thalassemia: Experience with Sodium Phenylbutyrate and Hydroxyurea

Abstract: Homozygous β thalassemia affects thousands of people around the world. Current management of this condition includes regular transfusion of red cells, which leads to transfusional iron overload requiring chelation therapy: increasing hemoglobin levels while decreasing or eliminating iron overload is therefore a major therapeutic goal in the treatment of thalassemia. Bone marrow transplantation may achieve this goal, but it is not an option for most patients. This study reports on efforts to increase γ‐globin transcription and HbF production using sodium phenylbutyrate (SPB) and hydroxyurea (HU). It was found that 36% (4/11) of all patients or 50% (4/8) of non‐transfused patients responded to SPB (increase in Hb levels of 1g/dL). A positive correlation between baseline serum erythropoietin level and likelihood of response to SPB was observed. Since HU may also increase HbF production, evaluation of combination therapy with these drugs is underway and preliminary results are reported.

Pulsed-dosing with oral sodium phenylbutyrate increases hemoglobin F in a patient with sickle cell anemia.

Increasing hemoglobin F (HbF) appears to be beneficial for patients with sickle cell anemia. We previously demonstrated that daily, oral sodium phenylbutyrate (OSPB) induces HbF synthesis in pediatric and adult patients with hemoglobin SS (HbSS). The high doses and need for daily therapy, however, have limited its use. Here, we report a patient treated with pulsed‐dosing of OSPB for over 3 years. This patient developed a modest, but sustained elevation in HbF over the course of therapy without side effects. Although larger studies are needed, this case demonstrates that pulsed‐dosing with OSPB enhances HbF synthesis. Pediatr Blood Cancer 2008;50:357–359.

Progress toward increasing fetal hemoglobin production in man: experience with 5-azacytidine and hydroxyurea.

Increased fetal hemoglobin (Hb F) production may potentially benefit individuals with thalassemia and sickle cell disease. Before 1982, significantly increased levels of Hb F production beyond genetically determined adult levels were only associated with recovery from marrow hypoplasia or sudden erythropoietic tress.-^ Although many different genetic disorders are associated with elevated steady-state levels of Hb F production in adults, no clear understanding of how one might alter Hb F production was apparent from detailed analysis of these mutations: Furthermore, erythroid culture systems seemed to suggest that the capacity for adult erythroid precursors to produce Hb F decreased during differentiation? In culture, very primitive erythroid precursor (BFU-E) produced colonies containing more Hb F than more mature precursors (CFU-E). The inference was that increased Hb F production during marrow recovery or erythropoietic stress was the result of selective premature differentiation of early erythroid precursors (BFU-E).6 The origin of the small number of Hb Fcontaining erythrocytes (F cells) in normal adults without evidence of erythropoietic stress was unclear.