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PubMed2002

Nitric oxide and cyclic GMP levels in sickle cell patients receiving hydroxyurea.

Recent studies suggest that nitric oxide (NO) may partly be responsible for the beneficial effect of hydroxyurea (HU) in sickle cell disease (SCD) patients. NO stimulates cyclic guanosine monophosphate (cGMP) production, which mediates vasodilatation. We investigated the association between NO, cGMP and fetal haemoglobin (HbF) levels after HU administration. Our data showed that chronic HU significantly increased NO, cGMP, and HbF levels in SCD. Recently it was shown that HbF production was stimulated by cGMP-dependent protein kinase. Our results suggest that NO stimulates cGMP production, which then activates a protein kinase and increases the production of HbF.

Adult↗
PubMed2002

Hydroxyurea exerts bi-modal dose-dependent effects on erythropoiesis in human cultured erythroid cells via distinct pathways.

Hydroxyurea (HU) has been shown to increase the proportion of fetal haemoglobin (HbF) in most sickle cell patients. A low-dosage regimen increased total haemoglobin (Hb) levels in some thalassaemia intermedia patients by preferentially increasing beta-globin biosynthesis. To further characterize these apparent dose-dependent effects of HU, we examined erythroid cells exposed to HU (5-100 micro mol/l) in two-phase liquid culture. Low doses (from 5 to 25 micro mol/l) increased Hb levels by up to 2.7-fold, and a high dose (100 micro mol/l) increased Hb levels when added at d 3-6 of phase II, with no significant changes in response to HU during the late stage of phase II culture (> or = 9 d). HU exposure during d 0-3 of phase II culture increased the number of erythroid colonies to a maximum of fivefold at 5 micro mol/l HU. GATA-1 mRNA was downregulated at a high dose and GATA-2 was dose dependently upregulated over a lower dosage range. Treatment with 100 micro mol/l HU dramatically upregulated the death receptor DR-5, caspase 3, as determined by cDNA microarray analysis. In contrast, 10 micro mol/l HU modestly upregulated mRNA levels of the early growth response gene. Our results suggest that HU exerts concentration-dependent effects on HbF production and erythropoiesis and that these two effects are mediated by distinct molecular mechanisms.

Adult↗
PubMed2003

Oxidative stress is involved in hydroxyurea-induced erythroid differentiation.

Hydroxyurea (HU), an inhibitor of DNA synthesis, can also induce haemoglobinization in certain erythroid cell lines. In this study, we report that intracellular peroxides levels were increased in HU-treated murine erythroleukaemia (MEL) cells and that l-acetyl-N-cysteine (LNAC), a potent reducing reagent, had a significant inhibitory effect on the HU-mediated induction of beta-globin, delta-aminolaevulinate synthase mRNA expression and haemoglobinization of MEL cells. In contrast, the addition of LNAC to dimethyl sulphoxide (DMSO)-treated MEL cells had a much smaller effect on the number of haemoglobinized cells. These findings suggest that oxidative stress is involved in HU-mediated induction of erythroid differentiation and that HU induces MEL cell differentiation by a mechanism different to that involved in DMSO-mediated differentiation. Our findings also suggest that the induction of MEL cell differentiation by HU does not involve RAS-MAP (mitogen-activated protein) kinase signalling.

Blotting, Western↗
PubMed2000

Hydroxyurea inhibits the transactivation of the HIV-long-terminal repeat (LTR) promoter.

HIV-1 gene expression is regulated by the promoter/enhancer located within the U3 region of the proviral 5' LTR that contains multiple potential cis-acting regulatory sites. Here we describe that the inhibitor of the cellular ribonucleoside reductase, hydroxyurea (HU), inhibited phorbol myristate acetate- or tumour necrosis factor-alpha-induced HIV-1-LTR transactivation in both lymphoid and non-lymphoid cells in a dose-dependent manner within the first 6 h of treatment, with a 50% inhibitory concentration of 0.5 mM. This inhibition was found to be specific for the HIV-1-LTR since transactivation of either an AP-1-dependent promoter or the CD69 gene promoter was not affected by the presence of HU. Moreover, gel-shift assays in 5.1 cells showed that HU prevented the binding of the NF-kappaB to the kappaB sites located in the HIV-1-LTR region, but it did not affect the binding of both the AP-1 and the Sp-1 transcription factors. By Western blots and cell cycle analyses we detected that HU induced a rapid dephosphorylation of the pRB, the product of the retinoblastoma tumour suppressor gene, and the cell cycle arrest was evident after 24 h of treatment. Thus, HU inhibits HIV-1 promoter activity by a novel pathway that implies an inhibition of the NF-kappaB binding to the LTR promoter. The present study suggests that HU may be useful as a potential therapeutic approach for inhibition of HIV-1 replication through different pathways.

Antigens, CD↗
PubMed1997

Pleural effusion secondary to extramedullary haemopoiesis in a patient with idiopathic myelofibrosis responding to pleurodesis and hydroxyurea.

A case of idiopathic myelofibrosis presenting with a pleural effusion secondary to extramedullary haemopoeisis is described. Approximately 2 years following the diagnosis of his myeloprolioferative disorder the patient presented with dyspnoea. Physical signs were consistent with a pleural effusion which was confirmed radiologically. Cytology of the effusion fluid demonstrated myeloid precursors, including megakaryocytes. The effusion required repeated draining and a pleurodesis was undertaken in an attempt to prevent reaccumulation of the fluid. The procedure was successful and follow up over a period of 5 months demonstrated no recurrence of the pleural effusion on that side of the chest. An effusion later occurred on the other side but was managed conservatively by drainage. Hydroxyurea was introduced at that stage, but shortly afterwards the patient died from an unrelated cause. We review the literature on this uncommon complication of myelofibrosis and discuss the options available to treat the disorder.

Hematopoiesis, Extramedullary↗
PubMed2000

The absence of ribonuclease H1 or H2 alters the sensitivity of Saccharomyces cerevisiae to hydroxyurea, caffeine and ethyl methanesulphonate: implications for roles of RNases H in DNA replication and repair.

BACKGROUND: RNA of RNA-DNA hybrids can be degraded by ribonucleases H present in all organisms including the eukaryote Saccharomyces cerevisiae. Determination of the number and roles of the RNases H in eukaryotes is quite feasible in S. cerevisiae. RESULTS: Two S. cerevisiae RNases H, related to Escherichia coli RNase HI and HII, are not required for growth under normal conditions, yet, compared with wild-type cells, a double-deletion strain has an increased sensitivity to hydroxyurea (HU) and is hypersensitive to caffeine and ethyl methanesulphonate (EMS). In the absence of RNase H1, RNase H2 activity increases, and cells are sensitive to EMS but not HU and are more tolerant of caffeine; the latter requires RNase H2 activity. Cells missing only RNase H2 exhibit increased sensitive to HU and EMS but not caffeine CONCLUSIONS: Mutant phenotypes infer that some RNA-DNA hybrids are recognized by both RNases H1 and H2, while other hybrids appear to be recognized only by RNase H2. Undegraded RNA-DNA hybrids have an effect when DNA synthesis is impaired, DNA damage occurs or the cell cycle is perturbed by exposure to caffeine suggesting a role in DNA replication/repair that can be either beneficial or detrimental to cell viability.

Caffeine↗
PubMed1999

Sequence of a mosquito ribonucleotide reductase cDNA and evidence for gene amplification in hydroxyurea-resistant cells.

Ribonucleotide reductase is essential for production of the deoxyribonucleotide substrates required for DNA synthesis in all eukaryotic cells. The full-length cDNA encoding a mosquito ribonucleotide reductase R2 subunit was obtained from Aedes albopictus cells using a polymerase chain reaction (PCR)-based approach. The cDNA contained 1197 nucleotides, and encoded a 398 amino acid R2 protein. Overall, mosquito R2 shared approximately 70% amino acid sequence identity with R2 proteins from vertebrates, but conservation at the N-terminus of the protein was relatively low. The sequence of R2 cDNA was identical in hydroxyurea-resistant mosquito cells and in wild-type cells, while the R2 gene copy number was increased ten to twentyfold in resistant cells.

Aedes↗
PubMed2002

Leg ulcers and hydroxyurea: report of three cases with essential thrombocythemia.

CASE 1: A 65-year-old woman with essential thrombocythemia (ET) had been taking oral hydroxyurea (HU), 1,000 mg daily, for 7 years. Six months ago, she developed an ulcer on the outer part of her left ankle, which healed spontaneously within 2 months. She presented with a new, tender, shallow ulcer, 2 cm x 2 cm in size, at the same site. Doppler examination revealed thrombosis of the left common femoral vein and a calcified atheroma plaque of the left common femoral artery. The dosage of HU was decreased to 500 mg daily when the platelet counts were found to be within normal levels. The ulcer completely healed within 2 months with occlusive wound dressings, and has not recurred within the follow-up period of 1 year. CASE 2: A 56-year-old women presented with multiple, painful, leg ulcers of 1 year duration. She had been diagnosed as having ET and had been on HU therapy, 1,500 mg/day, for the past 5 years. Interferon-alpha-2b was started 3 months ago, in addition to HU, which was tapered to 1,000 mg daily. She had suffered from hypertension for 20 years treated with nifedipine and enalapril, and had recently been diagnosed with diabetes mellitus which was controlled by diet. Examination revealed three ulcers located on the lateral aspects of both ankles and right distal toe. Arterial and venous Doppler examinations were within normal limits. Histopathology of the ulcer revealed nonspecific changes with a mixed inflammatory cell infiltrate around dermal vessels. The ulcers completely healed within 10 weeks with topical hydrocolloid dressings. After healing, she was lost to follow-up. A year later, it was learned that she had developed a new ulcer at her right heel, 3 months after her last visit (by phone call). This ulcer persisted for 8 months until HU was withdrawn. CASE 3: A 64-year-old woman with ET presented with a painful leg ulcer of 6 months' duration. She had been taking oral HU for 5 years. She had a 20-year history of hypertension treated with lisinopril. Examination revealed a punched-out ulcer of 2 cm x 2 cm over the right lateral malleolus. Doppler examination of the veins revealed insufficiency of the right greater saphenous and femoral veins. Angiography showed multiple stenoses of the right popliteal and femoral arteries. As her platelet count remained high, HU was continued. During the follow-up period of 13 months, the ulcer showed only partial improvement with local wound care.

Aged↗
PubMed2004

[Longitudinal melanonychia induced by hydroxyurea therapy].

UNLABELLED: Four case reports of patients with myeloproliferative syndrome receiving therapy with hydroxycarbamide (synonymous: hydroxyurea) and developing streaky longitudinal pigmentation appeared in fingernails and toenails several months after starting this therapy. BACKGROUND: Pigmentation of finger- and toenails presents a wide range of differential diagnostic considerations. They can be of infectious, melanocytic or exogenous origin or caused by metabolic disorders. PATIENTS AND METHODS: Three women and one man, ranging in age from 62 and 87 years, were treated with hydroxycarbamide for myeloproliferative syndrome or chronic myelogenous leukemia for five to twelve years. All four patients were Fitzpatrick skin types II. RESULTS: Several months after starting this therapy, they developed streaky longitudinal pigmentation of their fingernails and toenails. In two patients, these findings were diagnosed by chance, whereas two patients sought dermatological advice because of nail pigmentation. In two of the patients the longitudinal pigmentation disappeared a few month after discontinuation of hydroxycarbamide. The melanonychia persisted in another patient, while the fourth was lost to follow-up. CONCLUSIONS: When melanonychia is identified in hematology-oncology patients, a careful medical history should be obtained. A list of medications is crucial, since hydroxycarbamide causes nail pigmentation. In each case of nail pigmentation, an acral lentiginous melanoma must be excluded.

Aged↗
PubMed1999

Hydroxyurea-induced nail pigmentation in HIV patients.

Hydroxyurea (HU), a cytotoxic agent used in myeloproliferative disorders, has recently been introduced as an adjunct to combination anti-retroviral therapy. We describe abnormal nail pigmentation in four HIV-seropositive patients treated with HU and discuss the likely factors associated with its development.

Adult↗
PubMed2004

Polycythemia vera and pregnancy: a case report with the use of hydroxyurea in the first trimester.

Polycythemia vera (PV) is rarely associated with pregnancy. A 34-year-old patient treated with hydroxyurea for PV became pregnant and was referred to our clinic. At the patient's request, pregnancy was continued. The patient's hematocrit level remained below 45% without any treatment throughout her pregnancy, and a healthy male infant (without any congenital malformations or complications) was delivered at 37 weeks. This case report suggests that normal pregnancy and delivery is possible in patients with PV.

Adult↗
PubMed2002

Nail pigmentation caused by hydroxyurea: report of 9 cases.

We report a series of 9 patients, 6 men and 3 women, who presented nail hyperpigmentation arising between 6 and 24 months from the start of hydroxyurea therapy. The most commonly observed clinical pattern was that of longitudinal melanonychia. In only 1 patient, who was affected in all 20 nails, we observed longitudinal melanonychia, diffuse melanonychia, and hyperpigmentation of the skin.

Adult↗
PubMed1999

Induction by adozelesin and hydroxyurea of origin recognition complex-dependent DNA damage and DNA replication checkpoints in Saccharomyces cerevisiae.

DNA damaging agents induce a conserved intra-S-phase checkpoint that inhibits DNA replication in eukaryotic cells. To better understand this checkpoint and its role in determining the efficacy of antitumor drugs that damage DNA, we examined the effects of adozelesin, a DNA-alkylating antitumor agent that has a profound inhibitory effect on initiation of DNA replication in mammals, on the replication of Saccharomyces cerevisiae chromosomes. Adozelesin inhibited initiation of S. cerevisiae DNA replication by inducing an intra-S-phase DNA damage checkpoint. This inhibitory effect was abrogated in orc2-1 cells containing a temperature-sensitive mutation in a component of the origin recognition complex (ORC) that also causes a defect in initiation. The orc2-1 mutation also caused a defect in a checkpoint that regulates the activation of origins in late S phase in cells treated with hydroxyurea. Defects in both initiation and checkpoint regulation in the orc2-1 strain were suppressed by deletion of a gene encoding a putative acetyltransferase, SAS2. Adozelesin also induced a cellular response that requires a function of ORC in G(1). A similar G(1)-specific response in mammals may contribute to the cytotoxic and antitumor properties of this and other DNA-damaging drugs.

Antineoplastic Agents, Alkylating↗
PubMed2003

Hydroxyurea arrests DNA replication by a mechanism that preserves basal dNTP pools.

The relationship between dNTP levels and DNA synthesis was investigated using alpha factor-synchronized yeast treated with the ribonucleotide reductase inhibitor hydroxyurea (HU). Although HU blocked DNA synthesis and prevented the dNTP pool expansion that normally occurs at G1/S, it did not exhaust the levels of any of the four dNTPs, which dropped to about 80% of G1 levels. When dbf4 yeast that are ts for replication initiation were allowed to preaccumulate dNTPs at 37 degrees C before being released to 25 degrees C in the presence of HU, they synthesized 0.3 genome equivalents of DNA and then arrested as dNTPs approached sub-G1 levels. Accumulation of dNTPs at G1/S was not a prerequisite for replication initiation, since dbf4 cells incubated in HU at 25 degrees C were able to replicate when subsequently switched to 37 degrees C in the absence of HU. The replication arrest mechanism was not dependent on the Mec1/Rad53 pathway, since checkpoint-deficient rad53 cells also failed to exhaust basal dNTPs when incubated in HU. The persistence of basal dNTP levels in HU-arrested cells and partial bypass of the arrest in cells that had preaccumulated dNTPs suggest that cells have a mechanism for arresting DNA chain elongation when dNTP levels are not maintained above a critical threshold.

DNA Replication↗
PubMed2006

Hydroxyurea and interleukin-6 synergistically reactivate HIV-1 replication in a latently infected promonocytic cell line via SP1/SP3 transcription factors.

The existence of viral latency limits the success of highly active antiretroviral therapy. With the therapeutic intention of reactivating latent virus to induce a cure, in this study we assessed the impact of cell synchronizers on HIV gene activation in latently infected U1 cells and investigated the molecular mechanisms responsible for such effect. Latently infected U1 cells were treated with 10 drugs including hydroxyurea (HU) and HIV-1 replication monitored using a p24 antigen capture assay. We found that HU was able to induce HIV-1 replication by 5-fold. HU has been used in the clinical treatment of HIV-1-infected patients in combination with didanosine; therefore, we investigated the impact of HU on HIV-1 activation in the presence of the proinflammatory cytokines, interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha). IL-6 or TNF-alpha alone induced HIV replication by 18- and approximately 500-fold, respectively. Of interest, in the presence of HU, IL-6-mediated HIV-1 activation was enhanced by >90-fold, whereas TNF-alpha-mediated activation was inhibited by >30%. A reporter gene assay showed that HU and IL-6 synergized to activate HIV promoter activity via the Sp1 binding site. Electrophoretic mobility shift and supershift assays revealed increased binding of the Sp1 and Sp3 transcription factors to this region. Western blot analysis showed that HU and IL-6 co-stimulation resulted in increased levels of Sp1 and Sp3 proteins. In contrast, treatment with HU plus TNF-alpha down-regulated the expression of NF-kappaB. These findings suggest that Sp1/Sp3 is involved in controlling the HU/IL-6-induced reactivation of HIV-1 in latently infected cells.

Cell Line, Tumor↗
PubMed2001

Hodgkin's disease in a child with sickle cell disease treated with hydroxyurea.

Hydroxyurea (HU) is an oral drug that ameliorates the clinical course of sickle cell anemia by increasing the levels of fetal hemoglobin and decreasing the adhesion of red cells to endothelium. Although HU has minimal short-term toxicity, few data are available about the long-term safety and the potential risk for carcinogenesis or leukemogenesis. An 8-year-old child with sickle cell/beta 0-thalassemia who received HU treatment for painful crises is described. Six months after the initiation of the HU treatment he developed Hodgkin's disease, lymphocyte predominance subtype. Chemotherapy induced a complete remission. After discontinuation of chemotherapy the painful crises recurred and bone marrow transplantation was decided at the age of 12 years. Two years after the bone marrow transplantation, the child is in complete remission without painful crises. Although the authors suggest that the development of Hodgkin's disease is a coexisting event, questions arise about the safety of HU treatment in childhood.

Anemia, Sickle Cell↗
PubMed2004

Clinical response and adverse events in young patients with sickle cell disease treated with hydroxyurea.

The authors studied the long-term clinical and hematological response to hydroxyurea (HU) therapy in young patients, with either S/beta-thalassemia (beta(thal)) (8 patients) or SS (6 patients). All patients with S/beta(thal) responded well to treatment. Longitudinal evaluation of Hb, HbF, and MCV showed a significant increase compared to baseline levels, but the pattern of HbF changes varied among patients. Changes in HbF and Hb correlated well with baseline HbF. Favorable clinical responses, as documented by decline in hospitalization days for vasoocclusive crisis and transfused units of packed red blood cells, were also noted. During treatment, 1 patient was diagnosed with Hodgkin's lymphoma and 2 patients developed bilateral avascular necrosis of the femoral head. HU seems to be effective in a high proportion of young patients with sickle cell disease and in particular with S/beta(thal), but cannot eliminate occurrence of serious adverse events.

Adolescent↗