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PubMed1981

A comparison of hydroxyurea, methyl-chloroethyl-cyclohexy-nitrosourea and cyclophosphamide in patients with advanced carcinoma of the prostate.

This is the fifth completed randomized clinical trial of the National Prostatic Cancer Project. There were 125 patients with histologically confirmed relapsing clinical stage D prostatic cancer randomized to receive hydroxyurea, methyl-chloroethyl-cyclohexy-nitrosourea or cyclophosphamide. All patients had received and failed previous hormonal therapy. Patients whose disease progressed after 12 weeks on the initial therapy were crossed over or randomized to receive an alternate drug. There were 98 patients available for comparison of treatments. Objective responses included patients with complete or partial regression as well as stable disease. The response rates were 35 per cent for cyclophosphamide, 30 per cent for methyl-chloroethyl-cyclohexy-nitrosourea and 15 per cent for hydroxyurea. Subjective response parameters included improvement in performance status and relief of pain. Pain was improved in a fifth of the patients on each treatment area. Methyl-chloroethyl-cyclohexy-nitrosourea and hydroxyurea showed activity in advanced prostatic cancer patients but at the expense of excessive toxicity. Cyclophosphamide continues to be the most active single agent in this type of patient, particularly with regard to duration of response and survival. There was a statistically demonstrable advantage for cyclophosphamide over hydroxyurea and a marginal advantage over methyl-chloroethyl-cyclohexy-nitrosourea in survival experience.

Acid Phosphatase↗

PubMed1998

Leg ulcers associated with long-term hydroxyurea therapy.

Hydroxyurea is commonly used in the treatment of various hematologic disorders, e.g., chronic myelogenous leukemia (CML), polycythemia vera, and occasionally, at lower doses, for severe psoriasis vulgaris. Cutaneous side effects such as alopecia, diffuse hyperpigmentation, poikiloderma, atrophy of the skin, or nail changes occur, especially with long-term treatment. Painful leg ulcers in association with hydroxyurea have only rarely been reported. We describe 2 patients who developed spontaneous painful leg ulcers during long-term hydroxyurea therapy for a myeloproliferative disorder; these ulcers healed only after hydroxyurea was withdrawn.

Aged↗

PubMed1999

The reaction of deoxy-sickle cell hemoglobin with hydroxyurea.

In addition to its capacity to increase fetal hemoglobin levels, other mechanisms are implicated in hydroxyurea's ability to provide beneficial effects to patients with sickle cell disease. We hypothesize that the reaction of hemoglobin with hydroxyurea may play a role. It is shown that hydroxyurea reacts with deoxy-sickle cell hemoglobin (Hb) to form methemoglobin (metHb) and nitrosyl hemoglobin (HbNO). The products of the reaction as well as the kinetics are followed by absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Analysis of the kinetics shows that the reaction can be approximated by a pseudo-first order rate constant of 3.7x10(-4) (1/(s.M)) for the disappearance of deoxy-sickle cell hemoglobin. Further analysis shows that HbNO is formed at an observed average rate of 5.25x10(-5) (1/s), three to four times slower than the rate of formation of metHb. EPR spectroscopy is used to show that the formation of HbNO involves the specific transfer of NO from the NHOH group of hydroxyurea. The potential importance of this reaction is discussed in the context of metHb and HbNO being able to increase the delay time for sickle cell hemoglobin polymerization and HbNO's vasodilating capabilities through conversion to S-nitrosohemoglobin.

Antisickling Agents↗

PubMed1997

Determination of hydroxyurea in plasma and peritoneal fluid by high-performance liquid chromatography using electrochemical detection.

A sensitive method has been developed for the determination of hydroxyurea in plasma and peritoneal fluid using reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. Plasma or peritoneal fluid samples were treated with acetonitrile to precipitate proteins then injected to the HPLC. A C18 analytical column was used to separate hydroxyurea from interfering substances in the biological matrix. The mobile phase, consisting of 0.2 M sodium perchlorate-methanol (95:5, v/v) adjusted to pH 5.0, was delivered isocratically at a flow-rate of 1 ml/min and hydroxyurea was detected using a glassy-carbon electrode operating at an applied potential of +800 mV. Hydroxyurea eluted with a retention time of 3 min. The cycle time for analysis is short and the assay precision is acceptable (C.V. plasma=1.4-3.9%. C.V. peritoneal fluid=2.1-9.7%). The method has been validated and is linear from 25 to 400 ng/ml in plasma and 5 to 30 ng/ml in peritoneal fluid. The method has been shown to be applicable for pharmacokinetic studies.

Antineoplastic Agents↗

PubMed1983

Rearrangements of chromatin structure in newly repaired regions of deoxyribonucleic acid in human cells treated with sodium butyrate or hydroxyurea.

The rate and extent of redistribution of repair-incorporated nucleotides within chromatin during very early times (10-45 min) after ultraviolet irradiation were examined in normal human fibroblasts treated with 20 mM sodium butyrate, or 2-10 mM hydroxyurea, and compared to results for untreated cells. Under these conditions, DNA replicative synthesis is reduced to very low levels in each case. However, DNA repair synthesis is stimulated by sodium butyrate and partially inhibited by hydroxyurea. Furthermore, in the sodium butyrate treated cells, the core histones are maximally hyperacetylated. Using methods previously described by us, it was found that treatment with sodium butyrate had little or no effect on either the rate or the extent of redistribution of repair-incorporated nucleotides during this early time interval. On the other hand, there was a 1.7-2.5-fold decrease in the rate of redistribution of these nucleotides in cells treated with hydroxyurea; the extent of redistribution was unchanged in these cells. Since hydroxyurea has been shown to decrease the rate of completion of "repair patches" in mammalian cells, these results indicate that nucleosome rearrangement in newly repaired regions of DNA does not occur until after the final stages of the excision repair process are completed. Furthermore, hyperacetylation of the core histones in a large fraction of the total chromatin prior to DNA damage and repair synthesis does not appear to alter the rate or extent of nucleosome core formation in newly repaired regions of DNA.

Butyrates↗

PubMed2002

Horseradish peroxidase catalyzed nitric oxide formation from hydroxyurea.

Hydroxyurea represents an approved treatment for sickle cell anemia and a number of cancers. Chemiluminescence and electron paramagnetic resonance spectroscopic studies show horseradish peroxidase catalyzes the formation of nitric oxide from hydroxyurea in the presence of hydrogen peroxide. Gas chromatographic headspace analysis and infrared spectroscopy also reveal the production of nitrous oxide in this reaction, which provides evidence for nitroxyl, the one-electron reduced form of nitric oxide. These reactions also generate carbon dioxide, ammonia, nitrite, and nitrate. None of these products form within 1 h in the absence of hydrogen peroxide or horseradish peroxidase. Electron paramagnetic resonance spectroscopy and trapping studies show the intermediacy of a nitroxide radical and a C-nitroso species during this reaction. Absorption spectroscopy indicates that both compounds I and II of horseradish peroxidase act as one-electron oxidants of hydroxyurea. Nitroxyl, generated from Angeli's salt, reacts with ferric horseradish peroxidase to produce a ferrous horseradish peroxidase-nitric oxide complex. Electron paramagnetic resonance experiments with a nitric oxide specific trap reveal that horseradish peroxidase is capable of oxidizing nitroxyl to nitric oxide. A mechanistic model that includes the observed nitroxide radical and C-nitroso compound intermediates has been forwarded to explain the observed product distribution. These studies suggest that direct nitric oxide producing reactions of hydroxyurea and peroxidases may contribute to the overall pharmacological properties of this drug.

Catalysis↗

PubMed1987

Quantitative analysis of hydroxyurea and urea by proton nuclear magnetic resonance (NMR) spectroscopy.

Quantitative 1H-nuclear magnetic resonance (NMR) procedures are described for measuring hydroxyurea and urea. Dimethylsulfoxide-d6 is used as the solvent for both assays; the internal standards employed are urea and p-dichlorobenzene for hydroxyurea and urea, respectively. The analysis for hydroxyurea is based on the comparison of the area of the -NH2 peak of hydroxyurea with the area of the urea -NH2 peak area. The analysis of urea is based on the comparison of the -NH2 peak of urea with the area of the p-dichlorobenzene singlet. The 1H-NMR assays yield results that are precise and agree well with results of the more cumbersome and less specific USP procedures.

Hydroxyurea↗

PubMed2005

Acute myocardial infarction in sickle cell disease: a possible complication of hydroxyurea treatment.

We describe a 28-year-old man treated with hydroxyurea for sickle cell anemia, who was admitted to the University Hospital with an acute myocardial infarction. The patient had evolved high hematocrit values during his long-term hydroxyurea treatment, suggesting a correlation between a possible increment in blood viscosity and the coronary occlusion without previous lesions. Indeed, several studies associate vasocclusive episodes and severe clinical course with high viscosity. Although hydroxyurea is considered an effective therapeutic option for these patients, care should be taken to monitor hematocrit levels and possible complications. Hematocrit and hemoglobin values of above 30% and 10.5 g/dl in SS patients on hydroxyurea therapy should be avoided or closely monitored.

Adult↗

PubMed1992

The gene for a novel protein, a member of the protein disulphide isomerase/form I phosphoinositide-specific phospholipase C family, is amplified in hydroxyurea-resistant cells.

Cell lines selected in multiple steps for increasing resistance to hydroxyurea have been shown to have corresponding increases in ribonucleotide reductase activity. We have isolated a number of cDNA clones from a cDNA library constructed from a highly hydroxyurea-resistant hamster cell line, 600H, in which the activity of ribonucleotide reductase is elevated more than 80-fold. These clones correspond to genomic DNA sequences amplified in the 600H cell line compared with the V79 parental line. One of these cDNA clones, termed P5, codes for a 50 kDa protein detected by in vitro translation of poly(A)+ RNA isolated by hybridization/selection. The cDNA sequence contains a single open reading frame of 1317 nucleotides which encodes a polypeptide of 439 amino acids. The amino acid sequence deduced from the cDNA insert contains two copies of the 11-amino-acid sequence Val-Glu-Phe-Tyr-Ala-Pro-Trp-Cys-Gly-His-Cys. Duplicate copies of this sequence also occur in the active site of rat and human protein disulphide isomerase (also known as the beta-subunit of human prolyl 4-hydroxylase, tri-iodothyronine-binding protein) and in Form I phosphoinositide-specific phospholipase C, indicating that P5 falls into this newly defined superfamily of proteins. Genomic sequences similar to the cDNA clone are amplified 10-20-fold in hamster cells selected for resistance to increasing concentrations of hydroxyurea, a phenomenon observed earlier with cDNA clones for the M2 subunit of ribonucleotide reductase and ornithine decarboxylase. RNA blots probed with P5 cDNA show two poly(A)+ RNA species which are elevated in hydroxyurea-resistant cells.

Amino Acid Sequence↗

PubMed2002

Mucocutaneous adverse effects of hydroxyurea: a prospective study of 30 psoriasis patients.

Hydroxyurea is an anti-tumour agent most commonly used to treat chronic myeloproliferative disorders in doses up to 4 g per day. Dermatological adverse effects reported so far have been observed predominantly in these patients. As we are treating selected psoriasis patients with low dose hydroxyurea we attempted to define the spectrum and chronology of dermatological adverse effects in this group of patients prospectively. Of the 29 evaluable patients, 19 (65.5%) developed a mucocutaneous adverse reaction after a mean duration of 6.4 weeks of treatment. Pigmentation of nails, skin or mucosa was the most common observation and was seen in 17 (58.6%) patients. Other less common findings were xerosis, diffuse alopecia, oedema of the legs, oral ulcers and actinic psoriasis. Adverse effects subsided in 11 (57.9%) patients during a mean follow up of 18 weeks. Three hitherto unreported side-effects - scleral pigmentation, acquired ichthyosis and pigmentation of lunula of the nails - were noted. This first study of dermatological adverse effects of hydroxyurea therapy on Asian psoriatic patients reveals several new findings. Pigmentation of skin, nails and mucosa appears to be very common and occurs early. Serious dermatological side-effects probably do not occur with low dose (up to 1.5 g per day) hydroxyurea in patients with psoriasis.

Adult↗

PubMed1998

Regression of extramedullary haemopoiesis and augmentation of fetal haemoglobin concentration during hydroxyurea therapy in beta thalassaemia.

Hydroxyurea increases fetal haemoglobin in many patients with sickle cell anaemia, but its effectiveness in thalassaemia appears to be less consistent. We describe the response to hydroxyurea in an adult male with homozygous beta thalassaemia, symptomatic paraspinal extramedullary haemopoiesis, bone pain, and progressive tissue iron loading. Prior to therapy with hydroxyurea the circulating haemoglobin (Hb) concentration was 7.0 g/dl and absolute fetal haemoglobin concentration was 5.0 g/dl. Administration of sodium phenylbutyrate had induced no increase in either parameter. Subsequent therapy with hydroxyurea was associated with increases in total haemoglobin to 9.0 g/dl, and in fetal haemoglobin to 7.6 g/dl. Ineffective erythropoiesis was reduced and extramedullary haemopoiesis regressed during therapy.

Adult↗

PubMed2001

Resveratrol, a natural dietary phytoalexin, possesses similar properties to hydroxyurea towards erythroid differentiation.

Resveratrol, a natural dietary polyphenol, has been postulated to be implicated in the cardioprotective effect of red wine and the low incidence of breast and prostate cancers among vegetarians and Orientals respectively. This compound inhibits ribonucleotide reductase as does hydroxyurea, the first therapeutic agent used in the treatment of sickle cell disease. Using the human erythroleukaemic K562 cell line as an in vitro model, we show here that 50 micromol/l of resveratrol induced a higher haemoglobin production (sevenfold) in K562 cells than 500 micromol/l of hydroxyurea (3.5-fold). This erythroid differentiation was linked to a dose- and time-dependent inhibition of cell proliferation associated with an equivalent increased expression of p21 mRNA, but with a higher increased level of p21 protein (sixfold) for cells treated with resveratrol than for those treated with hydroxyurea (1.5-fold). We also show that 50 micromol/l of resveratrol and 25 micromol/l of hydroxyurea induced variable but similar enhancements of fetal haemoglobin synthesis in cultured erythroid progenitors for the majority of the sickle cell patients studied. These inductions were linked to, but not correlated with, a variable decrease in erythroid burst-forming unit clone number. Taken together, these results show that resveratrol merits further investigations in sickle cell disease therapy.

Anemia, Sickle Cell↗

PubMed1999

Dermatomyositis-like eruption and leg ulceration caused by hydroxyurea in a patient with psoriasis.

We report the case of an elderly woman who had been on hydroxyurea for long-standing widespread psoriasis. After approximately 5 years's treatment with hydroxyurea, she developed a symmetrical dermatomyositis-like eruption on her hands, together with bilateral leg ulceration. Although similar skin eruptions have been reported after long-term hydroxyurea treatment, all of the previous patients were being treated for myeloproliferative disorders. A dermatomyositis-like eruption has not previously been reported to occur as a consequence of hydroxyurea treatment for psoriasis. Its recognition is important to prevent unnecessary investigation or treatment withdrawal.

Aged↗

PubMed2000

The cutaneous side-effects of hydroxyurea.

The cutaneous side-effects of long-term hydroxyurea therapy are not widely known and only rarely reported. We report on a patient who developed widespread skin changes, including the recently recognized hydroxyurea dermopathy, during long-term treatment with hydroxyurea for polycythaemia rubra vera. The time course of the clinical changes suggests that they result from direct toxicity of hydroxyurea on the basal layer of the epidermis and mucosal surfaces. We aim to increase clinical awareness of this problem.

Aged↗

PubMed2001

Rediscovering hydroxyurea: its role in recalcitrant psoriasis.

BACKGROUND: There is an acute paucity of second-line systemic agents for the treatment of extensive chronic plaque psoriasis (CPP). Recent studies using hydroxyurea in patients with HIV infection and sickle cell anemia have rekindled interest in this old drug and have provided more data regarding safety and dosage. OBJECTIVE: We wanted to test the efficacy and tolerability of hydroxyurea in patients with extensive CPP who had to discontinue first-line oral agents for any reason. METHODS: The study was a prospective nonrandomized series. Thirty-one patients, including 26 with prior history of systemic antipsoriatic therapy were given hydroxyurea 1-1.5 g per day for a median duration of 36 weeks. They were followed up for a mean period of 36.1 +/- 13.8 weeks. RESULTS: Almost 75% of the patients showed an adequate response (35% reduction in Psoriasis Area and Severity Index at or before 8 weeks) with over half showing more than 70% reduction in PASI score. All adverse effects were mild and reversible and none of the patients required cessation of therapy. CONCLUSION: Hydroxyurea is an effective, very safe but relatively slower acting alternative for patients with extensive CPP over the short-to-medium term.

Adult↗

PubMed1995

Hydroxyurea for patients with essential thrombocythemia and a high risk of thrombosis.

BACKGROUND: Abnormalities in the number and function of platelets may contribute to thromboembolic complications in patients with essential thrombocythemia. We assessed whether maintaining the platelet count below 600,000 per cubic millimeter with hydroxyurea reduces the incidence of thrombosis in patients with essential thrombocythemia and a high risk of thrombosis. METHODS: A total of 114 patients with essential thrombocythemia (77 women and 37 men; median age, 68 years; range, 40 to 85) and a median platelet count of 788,000 per cubic millimeter (range, 533,000 to 1,240,000 per cubic millimeter) were randomly assigned to receive hydroxyurea (56 patients) or no myelosuppressive therapy (58 patients). Ninety-seven (85 percent) were over 60 years old, and 52 (46 percent) had had thrombosis. The two groups were matched for age, sex, and platelet count at randomization. Antiplatelet prophylaxis with aspirin or ticlopidine was not stopped. Follow-up lasted a median of 27 months in both groups. RESULTS: Two patients (3.6 percent) treated with hydroxyurea had thrombotic episodes (one stroke and one myocardial infarction), whereas 14 patients (24 percent) in the control group had thrombotic episodes (one stroke, five transient ischemic attacks, five peripheral arterial occlusions, one deep-vein thrombosis, and two cases of superficial thrombophlebitis). The difference (20.4 percentage points; 95 percent confidence interval, 8.5 to 32 percent) was statistically significant (chi-square with Yates' correction, 8.3; 1 df; P = 0.003). CONCLUSIONS: Hydroxyurea is effective in preventing thrombosis in high-risk patients with essential thrombocythemia.

Adult↗

PubMed1981

Overproduction of the free radical of ribonucleotide reductase in hydroxyurea-resistant mouse fibroblast 3T6 cells.

Hydroxyurea inhibits the activity of ribonucleotide reductase (ribonucleoside-diphosphate reductase; 2'-deoxy-ribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) in bacteria and mammalian cells. The reductase from Escherichia coli consists of two nonidentical subunits (B1 and B2) and hydroxyurea acts by specifically destroying a tyrosine free radical of B2 required for enzyme activity. The mammalian enzyme also consists of two nonidentical subunits (M1 and M2), only one of which (M1) has been obtained in pure form. By continuous culture at stepwise increasing drug concentrations, we have now obtained a 3T6 mouse fibroblast cell line with a 100-fold increased resistance to hydroxyurea. Extracts from resistant cells showed a 3- to 15-fold increase in reductase activity. The amount of M1 protein was not increased. The amount of M2 protein could not be measured directly, but the M2 activity in extracts from resistant cells (but not normal cells) showed an EPR spectrum very similar to that of the tyrosine radical of the bacterial B2 subunit. We propose that resistance to hydroxyurea is caused either by overproduction of the complete M2 subunit or by increased generation of the tyrosine radical within the M2 protein. It seems that either alternative mirrors a possible normal regulatory mechanism for the activity of the reductase.

Animals↗

PubMed1995

Disparate actions of hydroxyurea in potentiation of purine and pyrimidine 2',3'-dideoxynucleoside activities against replication of human immunodeficiency virus.

We and other groups have recently reported the potentiation by ribonucleotide reductase inhibitors such as hydroxyurea of the anti-human immunodeficiency virus type 1 (HIV-1) activity of purine and pyrimidine 2',3'-dideoxynucleosides in both resting and phytohemagglutinin-stimulated peripheral blood mononuclear cells. Little agreement prevails, however, as to the mechanism of the synergistic effects described. We report here that in phytohemagglutinin-stimulated peripheral blood mononuclear cells, two mechanisms exist for the potentiation of the anti-HIV-1 activity by low-dose hydroxyurea of the purine-based dideoxynucleoside 2',3'-dideoxyinosine and the pyrimidine-based dideoxynucleosides 3'-azido-3'-deoxythymidine and 2',3'-dideoxycytidine. For 2',3'-dideoxyinosine, the enhancement arises from a specific depletion of dATP by hydroxyurea, resulting in a favorable shift of the 2',3'-dideoxyadenosine 5'-triphosphate/dATP ratio. For the pyrimidine dideoxynucleosides 3'-azido-3'-deoxythymidine and 2',3'-dideoxycytidine, the more modest anti-HIV enhancement results from hydroxyurea-induced increases of pyrimidine kinase activities in the salvage pathway and, hence, increased 5'-phosphorylation of these drugs, while depletion of the corresponding deoxynucleoside 5'-triphosphates (dTTP and dCTP) plays no significant role.

Adenosine Kinase↗