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PubMed2006

Hydroxyurea induces vasopressin release and cytokine gene expression in the rat hypothalamus.

We previously showed that the cytostatic drug hydroxyurea (HU) activates the hypothalamo-pituitary-adrenal (HPA) axis in intact rats, whereas it is lethal in rats with impaired HPA function. In these animals, HU toxicity is mediated by increased circulating levels of proinflammatory cytokines, whose secretion cannot be counteracted by glucocorticoids, suggesting that HPA activation blunts HU toxicity. Here we investigated the mechanisms through which HU activates the HPA axis, looking at the direct effects of the drug on the isolated hypothalamus. We found that HU significantly increases the release of arginine vasopressin but not that of corticotrophin-releasing hormone in short-term incubation experiments. The levels of arginine vasopressin are also increased in the hypothalamus and systemic circulation 2 h after the in vivo administration of the drug. Furthermore, HU increased significantly the expression of interleukin-6 and, to a lesser extent, interleukin-1beta in the hypothalamus. Interestingly, experiments with HU on primary cultures of rat microglia and astrocytes suggested that the increase in cytokine gene expression observed in hypothalamic explants is not accounted for by glial cells. Since both vasopressin and cytokines can activate the HPA axis, our present findings provide a reasonable explanation of the HPA activation elicited by HU in vivo in the rat.

Animals↗

PubMed2005

Molecular mechanisms of hydroxyurea(HU)-induced apoptosis in the mouse fetal brain.

Hydroxyurea (HU), a potent mammalian teratogen, affects proliferating embryonic cells and inhibits DNA synthesis. The teratogenic potential of HU has been well known in experimental animals for several decades. In this study, we investigated molecular mechanisms of HU-induced apoptosis in the telencephalon of the fetal brain by exposing pregnant mice to HU on day 13 of gestation. The number of TUNEL-positive cells began to increase at 3 h, peaked at 12 h, and rapidly decreased at 24 h. Although changes of p53 mRNA expression were not observed by RT-PCR, a p53-positive reaction was detected immunohistochemically in the nuclei of neuroepithelial cells from 1 h to 6 h, and p53-protein expression was simultaneously identified by Western blot analysis. The expression of p53-target genes was detected at both the mRNA and protein. The mRNA levels of apotosis-related genes (fas, fasL, and bax) and cell cycle-related genes (mdm2 and p21) were significantly elevated, and the degree to and sequence in which these target genes expressed was similar to those for fas, fasL, mdm2 and p21. Flow-cytometric and Western blot analyses of cell cycle-related proteins suggested that neuroepithelial cells are arrested at the S checkpoint from 3 to 6 h and at the G2/M checkpoint at 12 h, respectively. HU-induced apoptosis is considered to be mediated by p53 in the fetal brain.

Animals↗

PubMed2026

Association of hydroxyurea use and sickle cell retinopathy: A systematic review and meta-analysis.

Hydroxyurea (HU) is prescribed to reduce systemic complications of sickle cell disease; however, its association with sickle cell retinopathy (SCR) remains unclear. This meta-analysis (PROSPERO: CRD420251079006) evaluates the pooled association between HU use and SCR. In the primary analysis, HU use was not associated with a statistically significant reduction in SCR (OR = 0.90, 95% CI [0.41, 1.97], p = 0.79; I² = 77%). In a prespecified leave-one-out analysis, exclusion of the outlier study did not produce a statistically significant association, although the estimate shifted toward a stronger protective effect with reduced heterogeneity (OR = 0.70, 95% CI [0.39, 1.27], p = 0.25; I² = 67%). In a subgroup analysis excluding high-risk-of-bias studies, HU use was also not associated with a statistically significant reduction in SCR (OR = 0.84, 95% CI [0.39, 1.82], p = 0.66; I² = 77%). In post hoc analyses, HU use was not associated with a statistically significant reduction in SCR in non-adult populations (OR = 1.14, 95% CI [0.43, 3.05], p = 0.79; I² = 81%) or genotype-restricted analyses (OR = 1.22, 95% CI [0.81, 1.84], p = 0.35; I² = 0%). In post hoc analyses restricting studies to retinopathy phenotype, however, HU was associated with statistically significant lower odds of non-proliferative SCR (OR = 0.73, 95% CI [0.54, 0.98], p = 0.04; I² = 0%) and proliferative SCR (OR = 0.24, 95% CI [0.09, 0.60], p = 0.002; I² = 12%). Very low-certainty evidence suggests mixed associations between HU and SCR. Prospective studies are needed to clarify its role in SCR prevention.

Humans↗

PubMed2003

Toxic interaction between hydroxyurea and 1-beta-D-arabino-furanosylcytosine on the DNA of a human hepatoma cell line (HEPG2).

Hydroxyurea (HU) and 1-beta-D-arabino-furanosylcytosine (AraC) are two compounds used to inhibit DNA repair in the comet assay and thereby increase its sensitivity. We used RNA synthesis and comet assays to assess the cytotoxic and genotoxic effects of HU and AraC in the HepG2 cells after 1, 5, or 21 h of exposure to concentrations used to inhibit DNA repair. HU was genotoxic between 2 and 10 mM after 1 h of exposure and cytotoxic after 21 h. The presence of AraC (10, 50, or 100 microM) increased the DNA damage caused by HU (10 mM) suggesting a potentiation of the genotoxic effect. The interaction between the two inhibitors started after 5 h but was not dependent on the concentrations of AraC. Consequently, careful attention is required when employing a combination of HU and AraC, as their mechanisms of action could interfere with the interpretation of the data from genotoxicity assays.

Carcinoma, Hepatocellular↗

PubMed2001

The additive in vitro anti-HIV-1 effect of chloroquine, when combined with zidovudine and hydroxyurea.

The 4-aminoquinoline chloroquine and its analogue hydroxychloroquine are endowed with anti-HIV-1 activity both in vitro and in vivo. We previously reported that the addition of CQ (chloroquine) to the combination of HU (hydroxyurea) and ddI (didanosine) provides additive anti-HIV-1 activity. We here extended this in vitro investigation by studying whether the addition of CQ also resulted in additive anti-HIV-1 activity when combined with HU plus AZT (zidovudine). The same effect was found, whether CQ was added to HU plus AZT or to HU plus ddI, in recently infected H-9 and U-937 cells or primary T cells and monocytes, as well as in immunologically or oxidatively stimulated ACH-2 and U-1 cells. At concentrations where CQ exerts its anti-HIV-1 effect in combination with the other drugs, CQ addition does not result in either cell toxicity or apoptosis.

Anti-HIV Agents↗

PubMed1994

Pharmacologic treatment of thalassemia intermedia with hydroxyurea.

Three adult patients with beta-thalassemia intermedia were treated with hydroxyurea. Each had a significant but transient rise in total hemoglobin level associated with a variable increase in hemoglobin F.

Administration, Oral↗

PubMed2003

Cell kinetics-dependent antitumor effect of irinotecan hydrochloride induced by the synchronizing effect of hydroxyurea: cell kinetics and dosing time.

Influence of hydroxyurea (HU) on the antitumor effect of irinotecan hydrochloride (CPT-11) was investigated in ICR male mice transplanted with sarcoma 180 cells (S-180). A single dose of CPT-11 (100 mg/kg) was injected at various times after a single dose of HU (300 mg/kg). The relative tumor weight varied significantly depending on the timing of CPT-11 injection after HU injection (P < 0.01). The higher antitumor effect of CPT-11 was observed when DNA synthesis of S-180 cells increased (20 hr), and the lower effect was observed when the DNA synthesis decreased (0 hr). The loss of body weight also varied significantly depending on the timing of CPT-11 injection after HU injection (P < 0.01). The toxicity of CPT-11 was higher when the inhibitory effect of HU on DNA synthesis of bone marrow cells was stronger (15 hr), and the lower toxicity was observed when the inhibitory effect was not observed (0 hr). The plasma SN-38 concentration at 2 hr after CPT-11 injection was higher at 20 hr after HU injection than at 0 hr after HU injection. The difference in plasma esterase activity between 0 hr and 20 hr after HU injection was regarded as the mechanism underlying the dosing time-dependent difference of the SN-38 concentration. These experiments suggest that HU can produce a different phase of cell cycle between tumor cells and normal cells. This leads to increase the antitumor effect of CPT-11 without increasing the adverse effect of the drug. It is essential to consider the dosing time in the two-drug combination therapy.

Animals↗

PubMed1986

Aneuploidy and other genetic effects induced by hydroxyurea in Saccharomyces cerevisiae.

Hydroxyurea induces mitotic gene conversion, mitotic crossing-over, reverse mutation, respiration-deficient petite mutants and aneuploidy in growing cultures of Saccharomyces cerevisiae. Evidence is presented indicating that induction rather than selection is responsible for the increase in frequency of the genetic end points measured. Complications concerning the detection of aneuploidy in the presence of other genetic effects are described, and the need for following the complete protocol for confirmation of the aneuploids in any chemical screening program is emphasized.

Aneuploidy↗

PubMed2003

A randomized study comparing interferon (IFN alpha) plus low-dose cytarabine and interferon plus hydroxyurea (HU) in early chronic-phase chronic myeloid leukemia (CML).

This multicenter randomized phase III study was designed to compare the efficacy and toxicity of IFN alpha-2c (3.5 MU/d) in combination with either araC (10 mg/m(2) d1-10) or hydroxyurea (HU: 25 mg/kg per day) in newly diagnosed CML patients. A total of 114 patients were randomized. Following a median observation period of 36 (range 1-73) months the major cytogenetic response rates were 25 and 27% and the 4-year survival probabilities 62.5 and 63% for the araC and HU group, respectively. While the overall toxicity profile was comparable between both groups, patients in the HU arm exhibited a slightly higher degree of WHO grades 3 and 4 non-hematological toxicities.

Adult↗

PubMed1997

Salvage therapy for relapsed or refractory childhood acute lymphocytic leukemia by alternative administration a lymphoid- and myeloid-directed chemotherapeutic regimen consisting of dual modulation of ara-C, hydroxyurea, and etoposide.

Risk-directed chemotherapeutic regimens in recent use have improved the prognosis of children with acute lymphocytic leukemia (ALL). However, many patients relapse during or shortly after cessation of the initial continuation chemotherapy. Since achievement of a second complete remission (CR) is the initial step in successful retreatment effort, it is important to develop salvage protocols for children with relapsed or refractory ALL. In the present study, we developed a new salvage protocol (MLL-93) and applied the concept of dual chemical modulation of cytarabine, hydroxyurea, and etoposide with the alternative administration of high doses of myeloid- and lymphoid-directed agents. We also planned to perform allogeneic bone marrow transplantation (BMT) following a CR if patients had HLA-identical donor(s). The six patients treated with the MLL-93 protocol achieved a second CR. One patients in CR died of interstitial pneumonia after an unrelated allogeneic BMT. The other five patients have been in CR for 12-41 months. We suggest that the concepts of alternative administration of lymphoid- and myeloid-directed drugs and biochemical modulation are useful in the treatment of children with relapsed or refractory ALL.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2002

Suppression of retrovirus-induced immunodeficiency disease (murine AIDS) by trimidox and didox: novel ribonucleotide reductase inhibitors with less bone marrow toxicity than hydroxyurea.

Recently, the use of the ribonucleotide reductase (RR) inhibitor hydroxyurea (HU) in combination with nucleoside analogs has gained attention as a potential strategy for anti-HIV-1 therapy. However, appeal for the long-term use of HU in HIV-1 infection may be limited by its propensity to induce hematopoietic toxicity. We report a comparison of the efficacy and bone marrow toxicity of HU (400 and 200 mg/kg/day) with the novel RR inhibitors and free radical-scavenging compounds didox (DX; 3,4-dihydroxybenzohydroxamic acid; 350 mg/kg/day) and trimidox (TX; 3,4,5-trihydroxybenzamidoxime; 175 mg/kg/day) in the murine AIDS (LPBM5 MuLV) model of retrovirus infection. Infected mice received daily drug treatment for 8 weeks. Efficacy was determined by measuring drug effects on retroviral-induced disease progression (i.e. development of splenomegaly and hypergammaglobulinemia) and by evaluating splenic levels of proviral DNA. Bone marrow toxicity was evaluated by measuring peripheral blood indices (WBC, hematocrit and reticulocyte counts), femoral cellularity and by determining the numbers of hematopoietic progenitor cells (CFU-GM, BFU-E) per femur and spleen. Compared to infected controls receiving no drug treatment, disease progression was significantly suppressed by TX, DX and HU. However, HU was associated with mortality and induced significant hematopoietic toxicity in a time- and dose-dependent manner. Conversely, TX and DX effectively inhibited retrovirus-induced disease but did not induce hematopoietic toxicity. These results suggest that due to their reduced hematopoietic toxicity and ability to inhibit disease progression in murine AIDS, TX and DX may offer effective alternatives to HU therapy in HIV-1 infection.

Animals↗

PubMed1999

Expression and cellular localization of ribonucleotide reductase small subunit M2 protein in hydroxyurea-resistant Leishmania mexicana amazonensis.

We raised a specific antiserum against the recombinant M2 subunit protein of ribonucleotide reductase of Leishmania mexicana amazonensis in rabbit. This antiserum was used to study the expression and cellular location of the M2 protein in wildtype as well as hydroxyurea-resistant variants (HuR) of the parasite. The protein increased with increasing dose of the drug used for selection of resistance. The increase in protein level was accompanied by an increase in the copy numbers of mRNA of the M2 gene in the variants. In contrast to mammalian cells, the M2 protein of Leishmania is located in the nucleus rather than in the cytoplasm. The number of cells expressing M2 protein is also different in mammalian cells versus Leishmania. In mammalian cells, expression of M2 protein is a strictly S-phase-correlated event and in exponentially growing cells only approximately 50% of the cells are in S-phase and only these cells synthesize M2 protein. In L. m. amazonensis, however, almost all exponentially growing cells are positive for M2 protein. This makes it unlikely that M2 protein expression in Leishmania is S-phase dependent. In view of these findings, a fresh look in the future into the regulatory mechanisms of synthesis and the site of action of RNR in L. m. amazonensis is warranted.

Animals↗

PubMed2003

The role of hydroxyurea in the management of sickle cell disease.

Sickle cell disease (SCD) is one of the most common genetic diseases with some 250,000 new births each year. Most patients suffer intermittent pain crises and life-threatening events while life expectancy is considerably reduced. Until the last decade management was purely preventative or supportive aimed at symptom control. Apart from stem cell transplant, there is no cure but the oral chemotherapeutic drug hydroxyurea (HU) has now established a role in ameliorating the disease and improving life expectancy for most patients. There are side effects and risks of HU treatment in SCD but for moderate and severely affected patients, the benefits can be significant.

Anemia, Sickle Cell↗

PubMed1997

Fever caused by hydroxyurea: a report of three cases and review of the literature.

Hydroxyurea (HU) is generally regarded as an effective and well-tolerated drug for the treatment of the chronic myeloproliferative syndromes. It has rarely been implicated as a cause of drug fever. We report two patients with primary thrombocythaemia and one patient with polycythaemia vera who developed fever and shaking chills during treatment with HU. Infection was highly suspected and all patients were examined extensively. The fever subsided after discontinuation of therapy with this drug. However, the fever recurred within 1 day after rechallenge. The mechanism of HU-induced fever remained unclear, but the experience in our patients and the reviewed cases in the literature are highly suggestive of a hypersensitivity reaction. Clinicians should be aware of this rare adverse effect.

Aged↗

PubMed2002

Maternal protein-and-energy restriction reduces the developmental toxicity of cyclophosphamide and hydroxyurea in rats.

In this study, we examined the relationship between maternal weight gain deficits induced by protein-and-energy restriction (PER) and pregnancy outcome. We also evaluated whether PER would potentiate the developmental toxicity of cyclophosphamide (CP) and hydroxyurea (HU). Two independent experiments--employing two different methods of inducing protein-and-energy malnourishment-were performed. In the first experiment, well-nourished (fed ad libitum, normal diet, 22% of protein, 11.9 kJ/g) and food restricted (fed approximately half of ad libitum food intake, i.e. 12 g/day) rats received CP (0, 5 and 7.5 mg/kg sc) on pregnancy day 11. In the second experiment, well-nourished (normal diet, 24% of protein, 12.4 kJ/g) and malnourished (protein-and-energy deficient diet, 8% of protein, 6.2 kJ/g) rats received HU (0, 300 and 500 mg/kg ip) on pregnancy day 11. PER alone caused pronounced reductions of pregnancy weight gain and low fetal body weight, but induce no embryolethality and, except for a few sternum anomalies, no malformation. PER attenuated embryolethal and teratogenic effects of CP. PER reduced teratogenicity but did not alter effects of HU on embryolethality and fetal body weight. Therefore severe maternal weight gain deficits are not necessarily associated to embryolethality and terata and PER attenuates the teratogenic effects of CP and HU.

Animals↗

PubMed2000

The reactions of myoglobin, normal adult hemoglobin, sickle cell hemoglobin and hemin with hydroxyurea.

The kinetics of the reaction of hydroxyurea (HU) with myoglobin (Mb), hemin, sickle cell hemoglobin (HbS), and normal adult hemoglobin (HbA) were determined using optical absorption spectroscopy as a function of time, wavelength, and temperature. Each reaction appeared to follow pseudo-first order kinetics. Electron paramagnetic resonance spectroscopy (EPR) experiments indicated that each reaction produced an FeNO product. Reactions of hemin and the ferric forms of HbA, HbS, and myoglobin with HU also formed the NO adduct. The formation of methemoglobin and nitric oxide-hemoglobin from these reactions may provide further insight into the mechanism of how HU benefits sickle cell patients.

Adult↗

PubMed2003

Combined use of nonmyelosuppressive nitrosourea analogues with hydroxyurea in the induction of F-cell production in a human erythroleukemic cell line.

OBJECTIVE: Although hydroxyurea (HU) has been used clinically to treat patients with sickle cell disease (SCD), not all patients benefit from HU treatment due to its toxicity. The objective of this study was to investigate the effectiveness of the use of two new Hb F-inducing nitrosourea analogues, 2-[3-(2-methyl, 2-nitroso) ureido]-2-deoxy-D-glucopyranose (MNGU) and 2-[3-(2-chloroethyl) ureido]-2-deoxy-D-glucopyranose (CGU), in combination with HU in K562 cells or erythroid progenitors. MATERIALS AND METHODS: After K562 cells were cultured with different concentrations of HU with CGU or MNGU, aliquots of the cells were obtained to determine the total (benzidine-positive) hemoglobin level, number of F cells, and Hb F level. Erythroid progenitor cells of SCD patients and healthy donors were cultured with the optimal drug concentrations, and the number of BFU-E and Hb F level were determined. RESULTS: Our results showed that the combined use of HU with CGU or MNGU increased the number of both benzidine-positive normoblasts and F cells in a synergistic manner. Further, a lower concentration of HU was required to induce a significant level of Hb F synthesis when combined with either of the two compounds in comparison with treatment with HU alone. On day 4, the number of benzidine-positive cells was 4.5- to 6.5-fold and the number of F cells was 5.0- to 8.0-fold higher than the respective numbers in the untreated K562 cells. Similarly, a 3.2- to 14.3-fold induction of Hb F was obtained when human erythroid progenitors from SCD patients were treated with the same drug combinations. CONCLUSION: Based on these results, the use of CGU or MNGU in combination with HU might offer substantial benefits to patients with SCD and other hemoglobinopathies.

Cell Division↗

PubMed1999

Uptake of glucose analogues by colonic tumour cells during growth and after treatment with hydroxyurea.

SW620 cells were grown in tissue culture flasks to various cell densities producing populations of cells with a range of proliferative indices. The uptake of the two glucose analogues, deoxy-D-glucose (DG) and 3-O-methylglucose (OMG) was determined and found to be associated with S-phase fraction. The strong correlation between DG and OMG uptakes suggested that proliferation-related changes in transmembrane transport accounted for the association with S-phase fraction. Treatment of SW620 cells with the cell cycle inhibitor hydroxyurea was found to increase the uptake of DG and OMG in a time-dependent manner.

3-O-Methylglucose↗