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PubMed2003

Anti-HIV-1 activity of leflunomide: a comparison with mycophenolic acid and hydroxyurea.

BACKGROUND: Leflunomide inhibits de novo pyrimidine synthesis by inhibiting the activity of dihydroorotic acid dehydrogenase and has other immunomodulatory properties that make it a promising candidate for an anti-HIV drug. OBJECTIVES: To compare the anti-HIV activity of leflunomide with that of the immunomodulatory drugs hydroxyurea and mycophenolic acid; to assess whether there is an additive or synergistic effect when leflunomide is used in conjunction with mycophenolic acid; and to characterize the molecular mechanism of the anti-HIV activity of leflunomide. METHODS: Anti-HIV activity was examined in peripheral blood mononuclear cells. CD4 cell survival was examined in tonsillar lymphocytes by fluorescence-activating cell sorting. RESULTS: Leflunomide decreased HIV replication by approximately 75% at concentrations that can be obtained with conventional dosing. This activity was similar to that of hydroxyurea but superior to mycophenolic acid. Leflunomide and mycophenolic acid together have modest additive anti-HIV effects. Restoration of HIV replication by uridine indicates that leflunomide's primary mechanism at lower concentrations is inhibition of dihydroorotic acid dehydrogenase while at higher concentrations additional mechanisms may be involved. CONCLUSIONS: Leflunomide's anti-HIV activity and clinical profile make it an attractive candidate for further study of its effects. Since HIV RNA levels are an effective predictor of AIDS-free survival, leflunomide's partial suppression of HIV RNA may be valuable in certain patients.

Anti-HIV Agents↗

PubMed2003

Bimonthly leucovorin, infusion 5-fluorouracil, hydroxyurea, and irinotecan (FOLFIRI-2) for pretreated metastatic colorectal cancer.

Irinotecan has shown activity in advanced colorectal cancer resistant to leucovorin and fluorouracil. Preclinical experiments on cell cultures and human tumor xenografts indicated potential synergy when combining irinotecan and fluorouracil. We designed a new regimen combining leucovorin, fluorouracil, irinotecan, and hydroxyurea (FOLFIRI-2) and conducted a phase II study to establish its efficacy and tolerance in advanced colorectal cancer refractory to fluorouracil and oxaliplatin. Treatment was repeated every 2 weeks and consisted of leucovorin 400 mg/m2 on day 1, immediately followed by 46 hours of continuous infusion of fluorouracil 2,000 mg/m2, irinotecan 180 mg/m2 on day 3, and hydroxyurea 1,500 mg the day before leucovorin, and on days 1 and 2. Treatment was continued until progression or limiting toxicity. Twenty-nine heavily pretreated patients entered the study. Five patients achieved an objective response (17%), and 12 obtained stabilization of disease or minor response (52%). Five patients failed to continue treatment (17%) because of toxicity or worsening condition. From the start of FOLFIRI-2 treatment, median progression-free survival was 4.1 months and median survival was 9.7 months. Grade III/IV National Cancer Institute-Common Toxicity Criteria toxicities were nausea 17%, diarrhea 31%, mucositis 14%, neutropenia 52%, and febrile neutropenia 14%. FOLFIRI-2 achieved a good rate of response and stabilization in heavily pretreated patients despite significant toxicity.

Adult↗

PubMed2006

The role of hydroxyurea in enhancing the virologic control achieved through structured treatment interruption in primary HIV infection: final results from a randomized clinical trial (Pulse).

BACKGROUND: Structured treatment interruptions (STIs) have been postulated to improve virologic control in primary HIV infection (PHI) by stimulating HIV-specific T-lymphocyte immunity. The addition of hydroxyurea (HU) may reduce viral production from activated CD4 cells. METHODS: Patients with PHI received a standardized antiretroviral (ARV) regimen consisting of indinavir 800 mg twice daily (BID), ritonavir 100 mg BID, didanosine 400 mg (QD), and either stavudine 40 mg BID or lamivudine 150 mg BID, for up to 12 months and were randomized to HU 500 mg BID or not. If viral suppression (<50 copies/mL) was achieved, up to 3 STIs were undertaken. Two ARV cycles were allowed after each interruption if virologic rebound to more than 5000 RNA copies/mL occurred. Treatment success was defined as maintaining viral loads below 5000 copies/mL for 6 months after ARV interruption. RESULTS: Sixty-eight male homosexual patients were randomized: 35 to ARV + HU and 33 to ARV-alone. Median baseline HIV RNA was 5.73 log10 copies/mL, and median CD4 T-lymphocyte count was 517 cells/microL. Treatment success was not significantly different between those receiving and not receiving HU, with 9 (26%) and 9 (27%), respectively, maintaining viral load at less than 5000 copies/mL in each group (P = 0.88). Virologic control was achieved by 11 (19%) of 59 after 1 STI, 1 (2%) of 41 after 2 STIs, and 6 (17%) of 36 after the third STI. Serious adverse events were recorded for 9 (26%) of 35 of patients using HU and 3 (9%) of 33 in the ARV-only group (P = 0.28). CD4 cell increases were significantly blunted for the HU group compared to the ARV-alone group after the initial treatment phase (+101 cells vs. +196 cells, respectively, P = 0.006). CONCLUSIONS: Hydroxyurea was not found to be beneficial when used in association with STIs in patients during PHI.

Adult↗

PubMed2004

Treatment of Epstein-Barr virus lymphoproliferative disease after hematopoietic stem-cell transplantation with hydroxyurea and cytotoxic T-cell lymphocytes.

Epstein-Barr virus (EBV) lymphoproliferative disease (LPD) is a potentially fatal complication that may follow allogeneic hematopoietic stem-cell transplantation (HSCT). In this article, the authors report a 2-year-old girl with Hurler's syndrome who developed multiple central nervous system (CNS) EBV LPD lesions 1 year after unrelated donor HSCT. Before this CNS occurrence, the patient had a complete response to rituximab treatment for EBV LPD of the spleen and lymph nodes; however, treatment of the CNS disease with rituximab proved ineffective. Because of reported favorable response of primary CNS EBV LPD in two human immunodeficiency virus-positive patients, the authors treated this patient with low-dose oral hydroxyurea. The patient improved clinically, with a decrease in size of multiple EBV LPD brain lesions. Subsequently, the patient received EBV-specific cytotoxic T-cell lymphocytes and remains well. The benefit and limited toxicity of hydroxyurea therapy merit its further consideration as treatment for EBV LPD.

Adult↗

PubMed1995

Hydroxyurea therapy in beta-thalassaemia intermedia: improvement in haematological parameters due to enhanced beta-globin synthesis.

The beta-thalassaemias represent a heterogenous group of diseases resulting from decreased erythroid beta-globin mRNA expression and imbalanced alpha/beta-globin chain synthesis which are manifest clinically by ineffective erythropoiesis and excessive haemolysis. Increasing levels of haemoglobin F (HbF) by pharmacological agents has been proposed to ameliorate the severity of the disease by improving the balance in globin chain synthesis. Hydroxyurea (HU), as an effective agent with low toxicity for activating gamma-globin gene, has been shown to enhance HbF synthesis in experimental animals and in patients with sickle cell anaemia. However, previous trials of HU in beta-thalassaemia patients are ambiguous, with a small number having increased HbF synthesis. In a recent study of HU effects in Chinese beta-thalassaemia patients we unexpectedly found that two unrelated patients with beta-thalassaemia intermedia demonstrated an improvement in the effectiveness of erythropoiesis reflected by an increase in haemoglobin concentration (from 4.1 to 6.3 g/dl, patient 1; from 6.5 to 9.7 g/dl, patient 2) and in red cell volume (from 68 to 104 fl, patient 1; from 68 to 85 fl, patient 2) after a period of excess of 300d of low-dosage HU treatment. These effects, however, appear to be due to increased beta-globin biosynthesis, because the percentage of HbF decreased in each patient as total Hb increased. This was reflected by changes in the beta/alpha ratio (from 0.301 to 0.581, patient 1; from 0.348 to 0.487, patient 2) with minimal changes in gamma-globin biosynthesis. We conclude that in addition to its known effects in stimulating gamma-globin production, hydroxyurea may have a more general role in augmenting globin synthesis, including beta-globin in some thalassaemia intermedia patients who maintain the capacity to express normal beta-globin chains.

Female↗

PubMed1976

Study of the effect of hydroxyurea on the erythropoietin-sensitive cells.

The response of polycythaemic mice to a standard dose of erythropoietin has been measured at various time intervals after single or repeated injections of hydroxyurea. The results exclude S phase of the cell cycle as the period responsive to erythropoietin. They suggest the existence of feedback mechanisms within the cell cycle, operating at the G1--S boundary and within the G1 phase. Hydroxyurea given to polycythaemic mice at various time intervals after erythropoietin induced characteristic changes in the response. These changes can be explained if both gradual transit of differentiated cells into the DNA synthesis (S phase) and changes in amount of the erythropoietin sensitive cells caused by the feedback mechanisms operating in the cell cycle are considered.

Animals↗

PubMed1976

Hydroxyurea: use in determining the duration of G2 in Tetrahymena.

Observation of division of individual cells in microdrops, plus autoradiographic studies using tritiated thymidine and standard cell cycle analysis techniques, reveal that hydroxyurea (10 mM) reversibly arrests the normal progression of exponentially growing Tetrahymena pyriformis through the initial 92% of S-phase while not affecting cells in the terminal 8% and in G2 and division. Thus the fraction of the population of cells that is in G2 can be approximately determined by the fraction of the population able to divide in the presence of hydroxyurea. This fraction can be related to the approximate duration of G2 by calculations which compensate for the age gradient.

Animals↗

PubMed1980

Protection of cycling CFUs against hydroxyurea by low doses of actinomycin D.

Low dose (80 micrograms/kg) Actinomycin D (AD) produced a significant but transient inhibition of proliferation of the haemopoietic stem cells (CFUs) in chimaeras or in mice regenerating after sublethal irradiation. The same dose of AD had no effect on the resting CFUs population. During the period of proliferation inhibition, CFUs proved to be insensitive to the killing effect of [3H]thymidine in vitro and hydroxyurea (HU) in vivo. In Ehrlich ascites tumour (EAT) bearing mice enhanced CFUs turnover rate was found. Eighty micrograms/kg AD produced a selective effect in these mice: it protected the proliferating CFUs population without diminishing the effect of hydroxyurea on the tumour cells.

Animals↗

PubMed1984

Different epidermal cell kinetic effects of hydroxyurea when injected at two different times of the day.

Circadian rhythms in epidermal basal cell-cycle progression in hairless mouse skin have been repeatedly demonstrated. A dose of 10 mg/animal hydroxyurea (HU), given to inhibit DNA synthesis was injected intraperitoneally to two groups of hairless mice. One group was injected at 10.00 hours MET, when the cell-cycle progression and cell division rate are relatively high, and another group was injected at 20.00 hours, when the same variables are at minimum values. Various cell kinetic methods--[3H]TdR autoradiography, DNA flow cytometry and the stathmokinetic method (Colcemid)--were used to study HU-induced alterations in cell kinetics. Hydroxyurea (HU) immediately reduced the labelling index (LI) to less than 10% of controls when injected at both times of the day, and higher then normal values were observed 8 hr later. A subsequent decrease towards normal values was steeper in the 20.00 hours injected group. The proportion of cells with S-phase DNA content was transiently reduced in both series, but the reduction was less pronounced and control values were reached earlier in the series injected at 10.00 hours. The observed alterations in LI and fraction of cells in S phase were followed by comparable alterations in the fraction of cells in G2 and in the mitotic rate. Hence the changes in G2 and mitotic rate are easily explained as consequences of the previous perturbations in the S phase. The time-dependent differences in the cell kinetic perturbations caused by HU in the S phase may be explained by a circadian-phase-dependent action of HU on the influx and efflux of cells to and from the S phase, respectively. At 10.00 hours the efflux of cells from S is most heavily inhibited; at 20.00 hours the influx is predominantly blocked. Hence, when physiological flux is high HU mainly blocks the efflux from S, but when flux normally is low, HU mainly blocks the entrance to S. Within 20 hours after the HU injection, the cell kinetic variables had approached the unperturbed circadian pattern.

Animals↗

PubMed1984

Two-step cell-death kinetics in vitro during cis-platinum, hydroxyurea and mitomycin incubation.

A human leukaemic cell line (REH) growing in suspension was incubated with cis-platinum, hydroxyurea and mitomycin C at various concentrations causing complete cell-cycle arrest. At different times the cell suspensions were harvested, diluted 1:1 with a buffer solution, stained without further treatment with a mixture of acridine orange (AO) and ethidium bromide (EB) and analysed with a biparametrical flow cytometer. Fluorescent plastic beads were introduced into the suspensions to provide an internal numerical reference for the control of cell loss. The fluorescence distributions showed three groups of cells: vital cells (V) which were only stained with AO; dead cells in which EB stained cytoplasmic components but not the nuclear DNA (D1), and dead cells which allowed EB to stain both cytoplasm and nuclear DNA (D2). The kinetics of cells entering D1 depended on drug concentration and showed equal characteristics for cis-platinum and mitomycin, but were different for hydroxyurea. The subsequent entry into D2 occurred about 15 hr later and showed no pronounced dependence on drug concentration. Parallel trypan-blue (TB) exclusion tests revealed that TB only stained D2 cells and therefore is not useful for investigating cell-death kinetics during exposure to cell-killing agents.

Antibiotics, Antineoplastic↗

PubMed1986

Effects of hydroxyurea on the mitotic activity and the G2 phase in hairless mouse epidermis.

Hairless mice were given 5 mg hydroxyurea (HU) intraperitoneally (i.p.) followed by 0.15 mg Colcemid at various times after HU. The animals were killed at 2 and 4 hr after Colcemid, the epidermal mitotic counts in dorsal skin were determined and the mitotic rates calculated. These were compared with the normal mitotic rates, and the ratios between the results from HU-treated and -untreated animals were calculated. Hydroxyurea caused a considerable reduction in the mitotic rate with a trough at 6 hr, followed by a wave of increased mitotic rate with a peak at 14 hr, followed by a secondary drop at 20 hr, and then a return to normal. Another group of mice were given HU only, and the fraction of epidermal cells in G2 was measured by flow cytometry. From these animals, without previous injection of Colcemid, we also determined the mitotic counts and calculated the mitotic durations. Cells piled up in G2 for the first 6 hr after HU injection, then the G2 compartment was emptied. The results are discussed in relation to previous results from this department showing the effect of the same dose of HU on DNA synthesis in the same mouse strain. It is concluded that HU not only blocks or retards DNA synthesis in epidermal cells, but also affects the movement of cells through G2 and M. The cell kinetic effects of HU thus seem to be very complex.

Animals↗

PubMed1991

Deoxyribonucleotide metabolism in hydroxyurea-resistant V79 hamster cells.

V79 hamster cells were made resistant against hydroxyurea by continuous culture at stepwise increasing drug concentrations. Two cell lines were cloned, resistant to 0.4 mM (V79/H0.4) and 4 mM (V79/H4) hydroxyurea, with a fivefold and a 20-fold increase in soluble ribonucleotide reductase activity. We investigated how the increased amount of enzyme affected the in situ activity of ribonucleotide reductase and deoxyribonucleotide metabolism, in particular substrate cycles between pyrimidine deoxyribonucleosides and their 5'-phosphates. The in situ activity of the reductase was only moderately elevated (1.3-fold in V79/H4 cells). In the fully resistant line, the steady-state level of dATP was increased fourfold, and that of dTTP twofold. These nucleotides are negative allosteric effectors of the reductase and we propose that the increased pools inhibit the enzyme and thereby maintain the in situ activity of the reductase at only a slightly increased level. The surplus deoxyribonucleotides was excreted from the cells as thymidine and deoxycytidine via substrate cycles. The data support and extend our previous model for the regulation of deoxyribonucleotide synthesis via the allosteric properties of ribonucleotide reductase and substrate cycles that link salvage and degradation of deoxyribonucleotides.

Animals↗

PubMed2005

Hydroxychloroquine, hydroxyurea and didanosine as initial therapy for HIV-infected patients with low viral load: safety, efficacy and resistance profile after 144 weeks.

OBJECTIVES: To evaluate the long-term safety and efficacy of the combination of hydroxychloroquine, hydroxyurea and didanosine. METHODS: We recruited antiretroviral-naive patients with viral loads less than 100 000 HIV-1 RNA copies/mL and CD4 counts greater than 150 cells/microL. All patients received hydroxychloroquine (200 mg), hydroxyurea (500 mg) and didanosine (125-200 mg) twice daily. Clinical and laboratory safety assessments and measurements of viral load and CD4 count were made at regular intervals, and genotypic resistance testing was performed on samples with detectable viral load at 48, 96 and 144 weeks. RESULTS: Fourteen of the 17 patients who commenced therapy remained on treatment at 144 weeks. Treatment was well tolerated but caused neutropenia, usually mild and transient, in 12 patients (71%). Mean viral load was reduced by 1.6 log(10) copies/mL below baseline (P<0.001), eight patients (47%) had undetectable viral load (<400 copies/mL), and two patients (12%) had detectable viral load but no detectable resistance mutations at week 144. Four patients (24%) had detectable viral load together with major resistance mutations (three with both 74 V and 184 V, and one with both 62 V and 65R) at week 144, but still had viral load suppression below baseline. Mean CD4 count was increased by 106 cells/microL above baseline (P=0.07) at week 144. CONCLUSIONS: This novel and well-tolerated combination controls viral replication during long-term follow up, with development of few resistance mutations. With careful monitoring it may be a useful strategy for delaying highly active antiretroviral therapy (HAART) and associated toxicity in selected patients with low initial viral loads.

Adult↗

PubMed1977

Effects of hydroxyurea pretreatment of donor rats on growth of haematopoietic diffusion chamber colonies in mice.

A single dose of hydroxyurea (HU) (400 mg/kg body weight) was injected i.p. into rats. Hydroxyurea, a potent DNA synthesis inhibitor, killed bone marrow cells in the S-phase of the cell cycle. 9-10 h after HU administration, the rat bone marrow contained large numbers of necrotic cells and appeared predominantly lymphoid. Within 24-48 h of HU injection, resumption of normal haematopoiesis was observed. Rat bone marrow, 9-10 h following HU administration, was implanted in peritoneal diffusion chambers (DC) in irradiated mice. The results obtained suggest that pretreatment of donor rats with HU increases the bone marrow content of progenitor cells. The stem cell-enriched marrow was conductive to enhanced growth of DC colonies in irradiated mice.

Animals↗

PubMed1990

Reversal of myelofibrosis by hydroxyurea.

Bone marrow morphology in 39 symptomatic patients with myeloproliferative disorders (polycythaemia vera 15, essential thrombocythaemia 14, idiopathic myelofibrosis 9, myeloproliferative syndrome 1) and elevated platelet counts was studied before and after a median of 18 months of continuous treatment with hydroxyurea. We found a significant reduction of bone marrow fibrosis, believed to be mediated by suppression of thrombopoiesis by hydroxyurea.

Bone Marrow↗

PubMed1999

Detection of nitrosyl hemoglobin in venous blood in the treatment of sickle cell anemia with hydroxyurea.

The clinical efficacy of hydroxyurea (HU) in the treatment of sickle cell anemia has mainly been attributed to increased levels of fetal hemoglobin (HbF), which reduces the tendency for sickle hemoglobin to polymerize, thereby reducing the frequency of the vaso-occlusive phenomena associated with the disease. However, benefits from HU treatment in patients have been reported in advance of increased HbF levels. Thus, it has been suggested that other hydroxyurea-dependent mechanisms may, in part, account for its clinical efficacy. We have previously demonstrated that HU is metabolized in rats to release nitric oxide and, therefore, postulated the same to occur in humans. However, to our knowledge, evidence of nitric oxide production from HU metabolism in humans has yet to be demonstrated. Here we report that oral administration of HU for the treatment of sickle cell anemia produced detectable nitrosyl hemoglobin. The nitrosyl hemoglobin complex could be detected as early as 30 min after administration and persisted up to 4 h. Our observations support the hypothesis that the ability of HU to ease the vaso-occlusive phenomena may, in part, be attributed to vasodilation and/or decreased platelet activation induced by HU-derived nitric oxide well in advance of increased HbF levels.

Adult↗

PubMed2001

Bystander effects of cancer cell lines transduced with the multisubstrate deoxyribonucleoside kinase of Drosophila melanogaster and synergistic enhancement by hydroxyurea.

The multisubstrate deoxyribonucleoside kinase of Drosophila melanogaster (Dm-dNK) can be expressed in human cells with retained enzymatic activity. The cells expressing Dm-dNK exhibit increased sensitivity to several cytotoxic nucleoside analogs. In this study, we further evaluated Dm-dNK as a potential novel suicide gene in combination with (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) as the prodrug. We used two human cancer cell lines transduced with a retrovirus encoding the Dm-dNK cDNA and investigated whether the cells expressing the enzyme can induce cell death of untransduced cells, a phenomenon known as the "bystander effect". A bystander effect was observed in a thymidine kinase-deficient human osteosarcoma cell line but not in the MIA PaCa-2 human pancreatic adenocarcinoma cell line. The cytotoxicity of BVDU increased in both cell lines when the compound was used in combination with subtoxic concentrations of hydroxyurea. Hydroxyurea also enhanced the bystander effect in the osteosarcoma cells, but not in the MIA PaCa-2 cells, treated with BVDU. These findings indicate that BVDU phosphorylated by Dm-dNK in transduced cancer cells may also induce bystander cell death in certain cell lines.

Animals↗

PubMed1964

HYDROXYUREA: INHIBITORY EFFECT ON DNA METABOLISM.

Hydroxyurea, hydroxyurethane, and dihydroxyurea inhibit incorporation of thymidine into the DNA of monolayers of HeLa cells. They do not affect incorporation of uridine into RNA or of leucine into protein. In contrast, hydroxylamine inhibits cellular incorporation of all three precursors: thymidine, uridine, and leucine. Hydroxyurea does not affect thymidine kinase, thymidylate kinase, or DNA polymerase reactions, but it does inhibit incorporation of cytidylic and guanylic acids into DNA in cell-free supernatants.

Antineoplastic Agents↗