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Hydroxyurea induces fetal hemoglobin by the nitric oxide-dependent activation of soluble guanylyl cyclase.

Hydroxyurea treatment of patients with sickle-cell disease increases fetal hemoglobin (HbF), which reduces hemoglobin S polymerization and clinical complications. Despite its use in the treatment of myeloproliferative diseases for over 30 years, its mechanism of action remains uncertain. Recent studies have demonstrated that hydroxyurea generates the nitric oxide (NO) radical in vivo, and we therefore hypothesized that NO-donor properties might determine the hemoglobin phenotype. We treated both K562 erythroleukemic cells and human erythroid progenitor cells with S-nitrosocysteine (CysNO), an NO donor, and found similar dose- and time-dependent induction of gamma-globin mRNA and HbF protein as we observed with hydroxyurea. Both hydroxyurea and CysNO increased cGMP levels, and the guanylyl cyclase inhibitors ODQ, NS 2028, and LY 83,538 abolished both the hydroxyurea- and CysNO-induced gamma-globin expression. These data provide strong evidence for an NO-derived mechanism for HbF induction by hydroxyurea and suggest possibilities for therapies based on NO-releasing or -potentiating agents.

Cyclic GMP↗

Hydroxyurea-induced fever: case report and review of the literature.

OBJECTIVE: To describe a patient with hydroxyurea-induced fever. CASE SUMMARY: A patient with essential thrombocythemia developed a fever 12 hours after beginning hydroxyurea therapy. The diagnosis of drug fever was established by resolution of the fever after withdrawal of hydroxyurea and its recurrence on reexposure to the drug. DISCUSSION: Hydroxyurea-induced fever is rare. In the present case, a short lag period between commencement of hydroxyurea therapy and appearance of fever may suggest either direct toxicity or an idiosyncratic reaction. In previous reports, a hypersensitivity drug reaction was implicated. CONCLUSIONS: The mechanism of hydroxyurea-induced fever remains unclear. Clinicians should be aware of this rare adverse effect.

Fever↗

Hydroxyurea induces the eNOS-cGMP pathway in endothelial cells.

Hydroxyurea is a cell-cycle-specific drug that has been used to treat myeloproliferative diseases and sickle cell anemia. We have recently shown that hydroxyurea, like nitric oxide (NO)-donor compounds, increased cGMP levels in human erythroid cells. We show now that hydroxyurea increases endothelial-cell production of NO; this induction of NO in human umbilical vein endothelial cells (HUVECs) and human bone marrow endothelial cell line (TrHBMEC) is blocked by competitive inhibitors of NO synthase (NOS), such as NG-nitro-L-arginine-methyl ester (L-NAME) and NG-nitro-L-arginine. It is dependent on cAMP-dependent protein kinase (PKA) and protein kinase B (PKB/Akt) activity. We found that hydroxyurea dose- and time-dependently induced rapid and transient phosphorylation of eNOS at Ser1177 in a PKA-dependent manner; inhibitors of PKB/Akt could partially abrogate this effect. In addition, hydroxyurea induced cAMP and cGMP levels in a dose-dependent manner, as well as levels of intracellular calcium in HUVECs. These studies established an additional mechanism by which rapid and sustained effects of hydroxyurea may affect cellular NO levels and perhaps enhance the effect of NO in myeloproliferative diseases.

Androstadienes↗

Hydroxyurea versus misonidazole with radiation in cervical carcinoma: long-term follow-up of a Gynecologic Oncology Group trial.

PURPOSE: Long-term follow-up data of a randomized trial that compared hydroxyurea and the hypoxic-cell radiosensitizer to misonidazole as adjuncts to standard radiation therapy in locally advanced carcinoma of the cervix are reported. PATIENTS AND METHODS: Three hundred eight women were entered, and all 294 eligible patients are assessable as randomized. Eighty-one percent of patients have been monitored for 5 years or to death. RESULTS: There was an advantage for hydroxyurea in progression-free interval and survival (P = .05 and P = .066, respectively). There was no significant difference in the distribution of sites of failure between the regimens. For the 39% of patients with stages III to IVA disease, the advantage in progression-free interval for hydroxyurea was significant (47.8% v 33.6%). More leukopenia occurred on the hydroxyurea regimen than on the misonidazole regimen. CONCLUSION: In summary, these data provide stronger evidence than our previous analysis that hydroxyurea is superior to misonidazole as an adjunct to radiation therapy. For patients with locally advanced carcinoma of the cervix, hydroxyurea continues to be the adjunct of choice with radiation.

Adult↗

Hydroxyurea in the treatment of HIV-1.

OBJECTIVE: To describe the role of hydroxyurea in the treatment of HIV-1. DATA SOURCES: Published clinical studies using hydroxyurea in HIV treatment were accessed through MEDLINE (January 1994-March 1999) and conference abstracts. All relevant studies were evaluated. DATA SYNTHESIS: Adherence, expense, and resistance limit the pharmacotherapeutic options in the management of patients with HIV. Hydroxyurea may be an alternative to conventional HIV treatments. CONCLUSIONS: Several potential advantages of adding hydroxyurea to antiretroviral treatment regimens include the drug's well-documented toxicity, convenient dosing, good tolerability and low cost, and its unique mechanism of action. Hydroxyurea may have synergistic effects that prove promising in initial and salvage therapy antiretroviral regimens. Larger, well-controlled clinical studies are needed to adequately define the role of hydroxyurea in the treatment of HIV.

Acquired Immunodeficiency Syndrome↗

Acute tumor lysis syndrome secondary to hydroxyurea in acute myeloid leukemia.

OBJECTIVE: To report 2 cases of acute tumor lysis syndrome (ATLS) associated with hydroxyurea treatment. CASE SUMMARY: A 79-year-old woman diagnosed with chronic lymphocytic leukemia presented with an acute blastic transformation. She was promptly hydrated, started on allopurinol, and treated with hydroxyurea. About 24 hours later, her biochemistry panel showed parameters consistent with ATLS when compared with pretreatment levels. The second case was a 76-year-old man newly diagnosed with acute myeloid leukemia presenting with high blast fraction. He was given appropriate hydration and allopurinol prophylaxis, and was started on high-dose hydroxyurea treatment. He became symptomatic after 12 hours and results of his blood work were consistent with ATLS. DISCUSSION: ATLS is a well-known metabolic disturbance that occurs after cell destruction of rapidly growing tumors. In standard doses, hydroxyurea leads to cell death in the S phase and is not thought to cause significant cell lysis. However, in large doses, it possibly acts by a different mechanism and had a direct cytolytic effect associated with ATLS in our patients. CONCLUSIONS: Although ATLS caused by hydroxyurea appears to be rare, patients at risk should be closely monitored for this complication. An objective causality assessment using the Naranjo probability scale revealed that the adverse drug reaction was probable between ATLS and hydroxyurea therapy in these 2 patients.

Aged↗

Stabilization of disease progression by hydroxyurea in patients with recurrent or unresectable meningioma.

OBJECT: The management of certain meningiomas of the skull base and those involving the dural venous sinuses remains a challenge. In recent reports it has been suggested that hydroxyurea chemotherapy can cause regression of unresectable and recurrent meningiomas. The authors report their experience in using hydroxyurea for the treatment of patients with recurrent or unresectable meningiomas. METHODS: Hydroxyurea was administered at a dosage of approximately 20 mg/kg/day to 11 women and nine men (median age 59 years, range 31-75 years) with recurrent or unresectable intracranial meningiomas (12 basal, two parasagittal, and six multiple). In 16 patients the meningiomas were benign, in three they had atypical features, and in one the meningioma was malignant. All patients had measurable residual disease. Four patients with benign meningiomas had previously received radiotherapy (two were treated with conventional fractionated radiotherapy and two with stereotactic radiosurgery), three with atypical meningiomas received conventional fractionated radiotherapy, and the one with a malignant meningioma received conventional radiotherapy with additional stereotactic radiosurgery. Tumor enlargement was documented in all patients on neuroimages obtained before initiation of hydroxyurea therapy. All patients were evaluable for response to therapy. In 12 patients with benign meningiomas, the disease had stabilized on neuroimages obtained posttreatment (median duration of treatment 122 weeks, range 8-151 weeks), and two of these showed clinical improvement. One patient with a benign meningioma experienced a minor partial response that was noted after 39 weeks of treatment and was confirmed on neuroimaging and clinical evaluations. In three others with benign meningiomas, progression was confirmed on neuroimages obtained after 41, 55, and 66 weeks, respectively: the 1-year freedom from progression rate was 0.93 (standard error 0.07) in patients with benign meningiomas. In three patients with atypical meningiomas, the tumors had progressed on neuroimages obtained after 12, 19, and 45 weeks, respectively. In the patient with a malignant meningioma, progression was confirmed on neuroimages obtained at 24 weeks. Hydroxyurea has been reasonably well tolerated, although one patient discontinued therapy because of moderate myelosuppression. CONCLUSIONS: Although tumor regression appears uncommon, these results indicate that hydroxyurea may arrest progression of unresectable or recurrent benign meningiomas.

Adult↗

Hydroxyurea toxicity combined with didanosine (ddl) in HIV-1-seropositive asymptomatic individuals.

OBJECTIVE: Hydroxyurea, a carbamate compound widely used for the treatment of myeloproliferative disorders, has been investigated in several clinical trials conducted in the setting of HIV infection, where it is given in combination regimens almost always containing didanosine (ddI). Hydroxyurea mainly acts as a ribonucleotide reductase inhibitor and can positively modulate the activity of several pyrimidine and purine analogues. Due to its inhibition of DNA synthesis, the main side-effect of hydroxyurea is represented by myelosuppression. DESIGN: The toxicity profile of hydroxyurea plus didanosine (ddI) has been investigated in 40 asymptomatic HIV-positive patients with a baseline CD4+ absolute count between 250 and 500 cells/microl. Bone marrow function tests and adverse events occurring during the trial were analyzed. RESULTS: No major toxic event according to WHO classification was registered. At the dosage of 500 mg twice a day, hydroxyurea could be safely administered for at least 40 weeks of therapy. Minimal reversible bone marrow depression was noted in 2 patients. Even though reductions observed in white blood cell count, lymphocyte count and hemoglobin were statistically significant, they did not have any clinical relevance. CONCLUSIONS: Hydroxyurea seems to be well-tolerated and devoid of severe toxicity effects when used in asymptomatic HIV-positive subjects.

Adult↗

Clinical use of hydroxyurea in HIV-1 infected patients.

Emerging drug resistance and side effects complicate the clinical care of HIV-infected patients. Accumulating data from basic science and clinical studies suggest that hydroxyurea-based regimens are effective treatment options for patients at various stages of disease. Review of the clinical studies confirms that hydroxyurea-based regimens produce potent and sustained viral suppression, with an unexpected high degree of tolerability, in patients with primary and chronic HIV infection. Hydroxyurea, the first antiretroviral drug targeting a cellular factor, represents a novel and inexpensive approach to combination therapy for HIV infection. Hydroxyurea is not prone to resistance while impeding resistance to reverse transcriptase inhibitors. The cytostatic properties of hydroxyurea may contribute to its immunomodulatory effects while reducing activated HIV target cells. These characteristics make hydroxyurea a good candidate for long-term treatment of HIV infected individuals. Future studies including those that evaluate optimal dosing a long-term use will continue to define the role for this agent in the treatment of HIV infection.

Anti-HIV Agents↗

[Acute interstitial pneumopathy with fever caused by hydroxyurea].

BACKGROUND: Hydroxyurea has few side effects excepting the known bone marrow toxicity. Fever with or without pneumonia has occasionally been reported. CASE REPORT: A patient given hydroxyurea for polycythemia suddenly developed severe interstitial pneumonia with fever and hypoxemia. All bacteriological tests were negative and an empirical antibiotic regimen was ineffective. Fever recurred after reintroducing hydroxyurea and definitive cure was achieved after its withdrawal. The clinical course was rapidly favorable without the need for corticosteroids. DISCUSSION: Fever, and in some cases interstitial pneumonia, in patients given hydroxyurea generally suggests an infection. However, 15 cases of pneumonia have been reported as caused by hydroxyurea in patients treated for a myeloproliferative syndrome. Delay to onset is 3 to 8 weeks after initiating treatment. The course is favorable after withdrawal, with or without corticosteroids. Fever may be the only sign of a drug reaction, resolving with withdrawal and recurring at re-challenge. The underlying mechanism remains unknown. Definitive cure can be achieved by discontinuing hydroxyurea, avoiding the need for further investigations.

Aged↗

[Treatment of polycythemia. II.--Comparison of hydroxyurea with pipobroman in 294 patients less than 65 years of age].

AIMS: To compare by a prospective study in low risk polycythemia vera (PV) patients alone two drugs: hydroxyurea and pipobroman. Toxicity, efficiency, and leukemogenic potential were studied. PATIENTS: 294 patients with a documented PV, aged less than 65 years, have been included since 1980 in a prospective study comparing hydroxyurea and pipobroman. Blood cell counts were performed every two months and a clinical evaluation by a specialist was obtained every four or six months. RESULTS: Hematologic toxicity of both drugs was higher than expected, requiring strict surveillance. These drugs were tolerated in some (gastric pain and diarrhea on pipobroman, buccal aphtosis and chronic leg ulcers on hydroxyurea), leading to a change of arm in 10% of the cases. Hydroxyurea did not control the megakaryocitic hyperplasia in 40% of the cases, which probably explains a high rate of progression to myelofibrosis with myeloid metaplasia in this arm. Both drugs were leukemogenic with an actuarial risk of about 15% at the 15th year, not significantly lower than that observed in the 32P treated patients. A significant risk of cutaneous malignancy was observed in the hydroxyurea arm. The mean expectancy of life cannot yet be accurately evaluated, but seems significantly lower than that of the reference population. CONCLUSION: The treatment of PV by hydroxyurea or pipobroman has to account for these results less optimistic than those traditionally well-known to hematologists and internists.

Adult↗

Evaluation of the mutagenic activity of hydroxyurea on the G1-S-G2 phases of the cell cycle: an in vitro study.

Hydroxyurea is considered an antineoplastic drug, which also plays an important role in the treatment of sickle cell anemia patients. We evaluated and compared the clastogenic and cytotoxic effects of hydroxyurea, using chromosomal aberrations and mitotic index, respectively, as endpoints. In vitro short-term cultures of lymphocytes were exposed to several concentrations of this drug, at various cell cycle phases. There was a significant increase in the cytotoxicity of hydroxyurea at G1 and G1/S as well in the G2 phase of the cell cycle. Hydroxyurea did not significantly increase chromosome aberrations. There was an S-dependent cytotoxic effect of hydroxyurea, which is expected based on the known activity of hydroxyurea as an inhibitor of ribonucleotide reductase.

Analysis of Variance↗

Effects of hydroxyurea on the membrane of erythrocytes and platelets in sickle cell anemia.

BACKGROUND AND OBJECTIVES: Adhesion molecules on the surface of erythrocytes, leukocytes and platelets are involved in vascular occlusion in sickle cell anemia. Hydroxyurea treatment of sickle cell anemia patients leads to clinical improvement and reduces the incidence of vaso-occlusive episodes. It has been previously demonstrated that hydroxyurea treatment also reduces the expression of adhesion molecules on the surface of erythrocytes. Phosphatidylserine (PS) exposure on the surface of erythrocytes has been considered to be the main determinant of altered erythrocyte adhesion in sickle cell anemia. In this study we examine the expression of PS on the surface of erythrocytes and platelets of sickle cell anemia patients before and during treatment with hydroxyurea. DESIGN AND METHODS: Blood samples from 15 sickle cell anemia patients were analyzed before and during treatment with hydroxyurea. The profile of PS expression was examined by flow cytometry. RESULTS: Hydroxyurea was effective, as determined by the patients clinical improvement and increased hemoglobin (8.3 vs 9.1 g/dL, p< 0.005), F cells (15.9% vs 37.1%, p< 0.005) and mean corpuscular volume ( 82 fL vs 101 fL, p< 0.005). PS expression on the surface of erythrocytes and platelets decreased from 6.27% to 2.96% (p< 0.005) and from 13.5% to 4.7% (p< 0.005), respectively. INTERPRETATION AND CONCLUSIONS: Hydroxyurea treatment reduces PS expression on the surface of erythrocytes and platelets, thus contributing to the favorable effects of this therapy.

Adolescent↗

Hydroxyurea: overview of clinical data and antiretroviral and immunomodulatory effects.

Data from comparative trials involving more than 500 patients indicate that hydroxyurea is safe and augments suppression of HIV-1 replication when used in combination with didanosine or didanosine/stavudine as initial therapy or in patients without extensive antiretroviral experience. Additional studies will determine the optimum dosage and schedule for hydroxyurea and its effects when used with other agents and in patients with advanced disease or extensive pretreatment. Activities of hydroxyurea include inhibition of HIV-1 in active and resting CD4 lymphocytes and macrophages, potentiation of the activity of nucleoside reverse transcriptase inhibitors (NRTIs), compensation for resistance to adenosine analogue NRTIs, and potential increased phosphorylation of pyrimidine NRTIs. Recent attention, however, has focused on the potential immunomodulatory effects of hydroxyurea. The cytostatic effect of this agent on both CD4 and CD8 T cells may provide immunological benefits by reducing immune system overactivation, thus preventing both CD8 T cell exhaustion and CD4 T cell depletion. Accumulating evidence indicates that hydroxyurea-containing regimens may be associated with decreased levels of activated CD8 T cells, increased levels of naive CD4 and CD8 T cells, and preservation of the HIV-1-specific immune response. Further study of the potential for beneficial immunomodulation with hydroxyurea-containing regimens is needed to ascertain the clinical implications of these initial findings.

Anti-HIV Agents↗

The place of hydroxyurea in the treatment of primary brain tumors.

Hydroxyurea has been used since the early 1970s to potentiate the effects of radiation in the treatment of primary gliomas. In the only randomized study, a statistically significant increase in time to tumor progression for glioblastoma patients was noted for those receiving hydroxyurea. In other studies, hydroxyurea has been used as a cell-cycle phase-specific agent to improve survival in patients with recurrent gliomas and, in combination with 5-fluorouracil, to increase cell kill and as a potential DNA polymerase inhibitor. Other protocols have used hydroxyurea during radiation therapy in medulloblastoma and in combination chemotherapy for metastatic brain tumors as well. While widely used in the treatment of primary and secondary brain tumors, hydroxyurea trials usually have not been randomized or otherwise controlled; most have been nonrandomized, phase II activity studies. With the conclusion of some current trials, it is conceivable that the use of hydroxyurea may be more clearly defined in the treatment of tumors affecting the nervous system.

Antineoplastic Combined Chemotherapy Protocols↗

Increased ferritin gene expression is associated with increased ribonucleotide reductase gene expression and the establishment of hydroxyurea resistance in mammalian cells.

In the present study, we show that hydroxyurea-inactivated ribonucleotide reductase protein M2 has a destabilized iron center, which readily releases iron. In addition, evidence is presented which indicates that single or multistep selection for hydroxyurea resistance, in a variety of mammalian cell lines, leads to alterations in the expression of the gene for the iron storage protein, ferritin. In all hydroxyurea-resistant cell lines examined, including human, hamster, rat, and mouse, there was an elevation in ferritin heavy (H)- and/or light (L)-mRNA levels, but no change in the corresponding gene copy number. A detailed analysis of ferritin expression in a hydroxyurea-resistant mouse L cell line showed that when compared to its wild type counterpart, there was an increase in H subunit concentration but no significant change in L subunit levels. The increased H/L subunit ratio was not brought about by specific changes in the rates of ferritin subunit biosynthesis, but rather resulted from changes in the post-translational stability of H subunits relative to L subunits in the resistant cell line compared to its parental wild type. Also, we show that treatment of cells with hydroxyurea results in an increased rate of ferritin biosynthesis in the absence of changes in H- or L-mRNA levels. These results indicate that the development of even low level hydroxyurea resistance in mammalian cells may require alterations in ferritin gene expression, and they show an interesting relationship between the expressions of two highly regulated activities, ribonucleotide reductase and ferritin.

Animals↗

In vitro cytotoxicity of caracemide alone and in combination with hydroxyurea or iron-chelating agents in human chronic myeloid leukemia cells and murine tumors.

The cytotoxic effect of caracemide and hydroxyurea was compared in human chronic myeloid leukemia cells. Caracemide was found to be about twelve times more effective than hydroxyurea. The combined effect of caracemide, hydroxyurea and hydrophobic iron-chelating agents at relatively nontoxic concentrations was studied. Hydroxyurea, 2,2'-bipyridine and 1,10-phenanthroline combined with caracemide synergistically inhibited DNA synthesis, while Desferal did not show any such effect. Fe++ partially reversed the cytotoxicity of caracemide in combination with 2,2'-bipyridine, while it had no effect on the cytotoxicity of caracemide alone. Caracemide was found to have a stronger inhibitory effect on DNA synthesis in P388 lymphocytic leukemia and Ehrlich ascites carcinoma cells than hydroxyurea. However, bipyridine, phenanthroline and Desferal in combination with caracemide did not induce any synergistic inhibition. These data indicate the value of human tumor cells to predict drug responsiveness and suggest the further evaluation of caracemide and its combination with hydroxyurea and iron-chelating agents in the treatment of human leukemias.

2,2'-Dipyridyl↗

Chromosomal changes without DNA overproduction in hydroxyurea-treated mammalian cells: implications for gene amplification.

It has been reported that a 6-h incubation of early S-phase Chinese hamster cells with hydroxyurea promotes DNA overproduction, i.e., replication of DNA a second time within a single cell cycle, and that this could be the basis for gene amplification in drug-treated mammalian cells. When we incubated methotrexate-resistant Chinese hamster cells that were approximately 2 h into the S phase with hydroxyurea for 6 h, DNA that had been replicated before the incubation with hydroxyurea (early S-phase DNA) was replicated again within 11 h after the hydroxyurea treatment. However, incubation with colchicine or Colcemid after hydroxyurea treatment virtually abolished this overreplication, as well as that of the amplified dihydrofolate reductase genes in these cells, indicating that the second replication had occurred in a second cell cycle. Cells collected in the first mitosis after incubation with hydroxyurea never contained overreplicated DNA but did contain abundant chromosome aberrations. Early S-phase DNA replicated again on schedule during the first few hours after mitosis. Asymmetric segregation of chromosome fragments or unequal sister chromatid exchange may be the actual basis for gene amplification in drug-treated mammalian cells.

Animals↗