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PubMed2003

Sustained long-term hematologic efficacy of hydroxyurea at maximum tolerated dose in children with sickle cell disease.

Hydroxyurea improves hematologic parameters for children with sickle cell disease (SCD), but its long-term efficacy at maximum tolerated dose (MTD) has not been determined. Between 1995 and 2002, hydroxyurea therapy was initiated for 122 pediatric patients with SCD including 106 with homozygous sickle cell anemia (HbSS), 7 with sickle hemoglobin C (HbSC), 7 with sickle/beta-thalassemia (HbS/ beta-thalassemia [6 HbS/beta0, 1 HbS/beta+]), and 2 with sickle hemoglobin OArab (HbS/OArab). Median age at initiation of therapy was 11.1 years. Hydroxyurea was escalated to MTD, with an average dose of 25.4 +/- 5.4 mg/kg per day; the average duration of hydroxyurea therapy has been 45 +/- 24 months (range, 6-101 months). Hydroxyurea was discontinued for 15 (12%) children with poor compliance. Mild transient neutropenia occurred, but no hepatic or renal toxicity was noted. Hydroxyurea therapy led to significant increases in hemoglobin level, mean corpuscular volume, and fetal hemoglobin (HbF) level, whereas significant decreases occurred in reticulocyte, white blood cell, and platelet counts and serum bilirubin levels. Children with variant SCD genotypes also had hematologic responses to hydroxyurea. HbF induction has been sustained for up to 8 years without adverse effects on growth or increased numbers of acquired DNA mutations. Long-term hydroxyurea therapy at MTD is well tolerated by pediatric patients with SCD and has sustained hematologic efficacy with apparent long-term safety.

Adolescent↗

PubMed1997

Hydroxyurea for treatment of unresectable and recurrent meningiomas. I. Inhibition of primary human meningioma cells in culture and in meningioma transplants by induction of the apoptotic pathway.

Meningiomas, which invade intracranial bone structures and the adjacent connective tissue, are frequently unresectable because of their aggressive and recalcitrant growth behavior. They have a high recurrence rate, and in approximately 10% of these tumors there is an increased risk of malignancy. Significant morbidity and mortality rates associated with recurrent meningiomas demand nonsurgical approaches. To date, adjuvant hormonal treatment has not proven beneficial. The anticancer drug hydroxyurea was therefore tested for its potential use in the treatment of meningiomas. Early-passaged cell cultures were established from 20 different meningiomas. The addition of 5 x 10(-4) and 10(-3) M hydroxyurea over a period of 5 to 9 days resulted in a remarkable decrease in cell proliferation and even blocked tumor cell growth when compared with untreated cells. A significant arrest of meningioma cell growth in the S phase of the cell cycle was revealed on DNA flow cytometry. Electron micrographs of hydroxyurea-treated tumor cells showed ultrastructural features consistent with apoptosis, and light microscopy demonstrated DNA fragmentation by in situ DNA strand break labeling. Short-term treatment of meningioma cell cultures with hydroxyurea for 24 to 48 hours resulted in discrete oligonucleosomal fragments (DNA ladder), another characteristic sign of apoptosis. In addition to the in vitro studies, tissue from five different meningiomas was transplanted into nude mice followed by treatment with 0.5 mg/g body weight hydroxyurea over 15 days. In situ DNA strand break labeling demonstrated DNA fragmentation in distinct regions with different tumor cell densities in all hydroxyurea-treated meningioma transplants. These data provide evidence that hydroxyurea is a powerful inhibitor of meningioma cell growth, most likely by causing apoptosis in the tumor cells. Thus, hydroxyurea may be a suitable chemotherapeutic agent for the long-term treatment of unresectable or semi- to malignant meningiomas, or for preventing recurrent growth of meningiomas after resection.

Animals↗

PubMed1998

Hydroxyurea-induced leg ulceration in 14 patients.

BACKGROUND: Hydroxyurea is an antineoplastic agent commonly used to treat myeloproliferative disorders and other nonneoplastic conditions. OBJECTIVE: To further define the typical features of hydroxyurea-related cutaneous ulcers of the leg. DESIGN: Retrospective, descriptive study of the medical records of patients who developed leg ulcers while receiving hydroxyurea therapy. SETTING: A tertiary care medical center. PATIENTS: Patients with myeloproliferative disorders who were treated with hydroxyurea. RESULTS: 14 patients with extremely painful leg ulcers were identified. The most common ulcer site was the malleoli. Multiple ulcers were seen in 64% of patients. Patients had received hydroxyurea for an average of 6 years before ulcers developed. All ulcers healed after discontinuation of hydroxyurea treatment, and 2 patients developed ulcers after treatment was restarted. CONCLUSION: Hydroxyurea induces painful leg ulcers that are usually difficult to treat and require cessation of hydroxyurea therapy.

Adult↗

PubMed1998

Hydroxyurea: mechanisms of HIV-1 inhibition.

Hydroxyurea inhibits cellular ribonucleotide reductase, resulting in decreased pools of dNTPs and thus inhibition of DNA synthesis. Studies in vitro have shown that hydroxyurea reduces dNTP pools in cells infected with human immunodeficiency virus type 1 (HIV-1), inhibiting HIV-1 DNA synthesis in infected quiescent and activated primary human lymphocytes and macrophages. Hydroxyurea also potentiates the activity of nucleoside reverse transcriptase inhibitors (NRTIs): the activated triphosphate forms of NRTIs compete with naturally occurring dNTPs for incorporation into nascent viral DNA during reverse transcription. A synergistic effect is observed between hydroxyurea and didanosine (2',3'-dideoxyinosine; DDI). This combination exerts persistent suppression of HIV-1 replication without evidence of viral rebound for over 1 year in HIV-1-infected patients. Didanosine-resistant HIV-1 mutants retain sensitivity to didanosine in the presence of hydroxyurea. The incorporation of didanosine triphosphate by resistant reverse transcriptase is increased in the context of the hydroxyurea-induced depletion of dATP. Although hydroxyurea has a reduced effect on dNTPs competing with the triphosphate forms of pyrimidine NRTIs, it appears to augment the anti-HIV-1 activity of these agents by increasing their intracellular phosphorylation; this may be of particular interest for salvage strategies given recent data indicating disruption of NRTI phosphorylation with specific NRTI treatment regimens. Finally, by exerting a cytostatic effect on CD4 and CD8 T lymphocytes, hydroxyurea may (i) reduce HIV-1 replication by decreasing CD4 T cell proliferation; and (ii) prevent the exhaustion of CD8 T cell populations that may occur as a result of excessive activation in the context of HIV-1 infection.

Deoxyribonucleotides↗

PubMed2001

[Multiple skin and mouth squamous cell carcinomas related to long-term treatment with hydroxyurea].

INTRODUCTION: Cutaneous side-effects of hydroxyurea treatment are frequently observed. Squamous cell carcinomas are the most severe among them. We report a patient with skin and mouth carcinomas after hydroxyurea treatment. To the best of our knowledge, this is the first case reported. OBSERVATION: A 83-year-old woman had been treated with hydroxyurea from 1985 to 1998 for polycythemia vera. She was referred to our institution in 1998 for painful erosions of both hands. Clinical examination revealed a squamous cell carcinoma leading to amputation of a finger. Hydroxyurea was stopped at this time, and the patient underwent treatment with pipobroman. From May 1998 to March 2000, the patient developed numerous skin keratoses and four squamous cell carcinomas on both hands. In September 2000 and October 2000, two additional skin carcinomas and two mouth carcinomas were diagnosed. DISCUSSION: Cutaneous carcinomas are severe side effects of hydroxyurea therapy. They usually occur after several years of treatment and their outcome may be lethal. The chronology and clinical signs are in favour of implicating hydroxyurea in the development of skin and mouth carcinomas. Despite a bibliographic research using Medline and Embase data bases, we could not find another case-report with simultaneous occurrence of skin and mouth carcinomas after hydroxyurea therapy. This observation emphasizes the need of a long term follow-up in patients receiving hydroxyurea.

Aged↗

PubMed2000

[The apoptosis of K562 cells induced by IL-3 and hydroxyurea cooperatively].

The effect of IL-3 and hydroxyurea on human erythroleukemia cell line (K562 cells) was demonstrated by using the electro-microscopy and flow cytometry. Our data showed that neither IL-3 nor hydroxyurea could induce the apoptosis of K562 cells alone. However, the IL-3 and hydroxyurea could induce the apoptosis of K562 cells cooperatively. Analysis with flow cytometry showed that the percentage of apoptotic cells was about 31.90% after K562 cells were induced by IL-3 and hydroxyurea cooperatively for 5 days, and the sub-G1 peak (apoptotic peak) was detected in the induced K562 cells. Meanwhile, the percentage of S-phase in the IL-3 and hydroxyurea induced K562 cells was increased, and the proliferation of the induced K562 cells was inhibited significantly. Furthermore, the IL-3 and hydroxyurea induced K562 cells showed chromatin condensation with regular crescents at the nuclear edges and apoptotic bodies. It suggested that IL-3 could enhance the sensitivity of K562 cells to hydroxyurea and the apoptosis of K562 cells could be induced by IL-3 and hydroxyurea cooperatively.

Apoptosis↗

PubMed1986

Elevated glucocorticoid receptor binding in cultured human lymphoblasts following hydroxyurea treatment: lack of effect on steroid responsiveness.

While studying the effects of chemotherapy on glucocorticoid receptor (GR) binding levels in hematological malignancies, we observed a sizable increase in nuclear GR binding of [3H]dexamethasone in peripheral leukocytes from a chronic basophilic leukemia patient following treatment with hydroxyurea plus prednisone, but not after prednisone alone. This apparent clinical effect of hydroxyurea led to an examination of hydroxyurea effects on GR binding and sensitivity in the glucocorticoid-sensitive human lymphoblast cell line GM4672A. GR binding levels in GM4672A cells were measured following a 3-day exposure to 50 microM hydroxyurea, a concentration chosen to have a minimal but measurable effect on cellular growth rates with little or no effect on cellular viability. Under these conditions, nuclear [3H]dexamethasone receptor binding measured by Scatchard analysis using a whole-cell assay was elevated 2.4-fold over control values (P less than 0.05), while cytosolic residual receptor binding (measured at 37 degrees C) remained unchanged. Thus, the total cellular content of measurable GR was increased, and this increase was totally accounted for by GR capable of nuclear binding. Hydroxyurea treatment of GM4672A cells had no effect on the affinity of nuclear or cytosolic GR for [3H]dexamethasone. The increase in measurable nuclear-bound receptors occurred in a time-dependent manner over a period of 3 days and was fully reversible within 3 days following removal of hydroxyurea. The increase in receptor binding could not be explained by the slight alterations in cell cycle kinetics which occur at this low level of hydroxyurea. Despite increased receptor binding, cellular glucocorticoid responsiveness was unaltered as assessed by dexamethasone inhibition of cell growth and dexamethasone inhibition of a urokinase-like plasminogen activator. Thus, increased nuclear and total cellular GR binding levels in hydroxyurea-treated GM4672A cells are not associated with increased glucocorticoid responsiveness.

Cell Cycle↗

PubMed1999

Leg ulcers and hydroxyurea: forty-one cases.

BACKGROUND: Hydroxyurea is an antitumor agent used to treat chronic myeloproliferative disorders. Leg ulcerations have been reported in patients undergoing long-term hydroxyurea therapy for myeloproliferative diseases. To better define this dermatological adverse effect of hydroxyurea therapy and to try to understand the pathophysiological process of this disease, we collected medical information for such patients in a multicenter retrospective study. OBSERVATIONS: Forty-one patients (mean age, 67 years) developed leg ulcerations while undergoing hydroxyurea therapy (mean therapy duration, 5 years). The sex ratio was 1, and there was no underlying vascular disease. Hematologic abnormalities were identified. Complete recovery from the ulcerations occurred quickly after withdrawal of treatment in 33 (80%) of the cases. CONCLUSIONS: This longest-reported series of patients confirms the role of hydroxyurea therapy in the onset of leg ulcerations. Healing or improvement requires cessation of treatment. Cutaneous atrophy and impaired wound healing may explain the relationship between hydroxyurea and leg ulcers. In addition, the megaloblastic erythrocytes resulting from the presence of hydroxyurea may circulate poorly through the capillary network. A prospective study in hematologic centers would be valuable.

Adult↗

PubMed2004

Concomitant hydroxyurea plus radiotherapy versus radiotherapy for carcinoma of the uterine cervix.

BACKGROUND: A number of randomised studies suggest hydroxyurea given alongside radiotherapy improves survival in patients with locally advanced cervix cancer. Following publication of five large randomised trials in 1999 and 2000 concomitant chemoradiotherapy has become standard treatment for these patients. In two of the studies hydroxyurea was given to patients in both control and experimental arms. The precise role of this orally administered cytotoxic drug is not known. OBJECTIVES: To assess the effectiveness (survival and toxicity) of concomitant radiation and hydroxyurea compared with radiotherapy alone in treating locally advanced cervix cancer. SEARCH STRATEGY: We searched the following:Cochrane Gynaecological Cancer Group's Specialised RegisterCENTRAL (Cochrane Library on CD ROM, issue 4, 2002) MEDLINE (Silver Platter, from 1970 to 2001) EMBASE (from 1980 to 2001) CANCERLIT (from 1970 to 2001) PDQ (search for open and closed trials) LILACSMeta-register (ongoing trials)Searches were not language or publication restricted. Investigators of relevant trials were contacted for further information. SELECTION CRITERIA: Randomized controlled trials comparing concomitant radiotherapy (+/- surgery) with hydroxyurea versus radiotherapy (+/- surgery) for locally advanced cervix cancer. DATA COLLECTION AND ANALYSIS: Two authors independently reviewed trials for inclusion and extracted data. Discussions on all aspects of data collection and analysis took place among all the authors at regular intervals. MAIN RESULTS: Seven studies were found to be suitable for inclusion from 33 identified as relevant. None of the trials provided adequate evidence to support the use of hydroxyurea owing to small sample size, large numbers of post-randomisation exclusions and questionable rules for censoring, particularly a failure to include treatment-related deaths in the survival analysis. Details of statistical analysis were limited and often confusing, and we felt meta-analysis would lead to unreliable and invalid conclusions. Most studies appeared to be double blind placebo-controlled studies but none give details of power calculations or reasons for stopping recruitment. Only two studies had more than 50 patients. Patients were excluded from analysis in most trials for treatment-related reasons; in one, less than half those recruited were used in the analysis, the remainder having been excluded because of tumour progression or treatment-related conditions e.g. septicaemia, worsening renal/hepatic function. In another trial five out of 20 in the hydroxyurea group died of treatment-related complications but the five-year survival group was presented as 94%. REVIEWER'S CONCLUSIONS: We found no evidence to support the use of hydroxyurea in addition to radiotherapy in the routine treatment of cervix cancer.

Antineoplastic Agents↗

PubMed1996

Pharmacokinetics of hydroxyurea in patients infected with human immunodeficiency virus type I.

In a prospective, randomized, controlled, three-arm study, the pharmacokinetics of hydroxyurea administered as an antiviral agent in patients infected with human immunodeficiency virus type 1 (HIV-1) were evaluated. The three arms of the study consisted of azidothymidine (AZT) 250 mg twice daily, hydroxyurea 500 mg twice daily, or a combination of the two. Nine patients receiving hydroxyurea in monotherapy (n = 4) or in combination with AZT (n = 5) agreed to undergo multiple venipunctures for pharmacokinetic analysis. Sample collection was performed at steady-state conditions and serum concentration-time data for hydroxyurea were fitted using a one-compartment model. Mean (+/- standard deviation) peak concentration (Cmax) was 0.135 +/- 0.06 mmol/L and mean trough level (Cmin) was 0.0085 +/- 0.003 mmol/L. Mean concentration at steady state was 0.045 +/- 0.006 mmol/L. Apparent clearance (Cl/F) was 0.18 +/- 0.005 L/hr/kg, and half-life (t1/2) was 2.5 +/- 0.5 hours. Hydroxyurea given orally to patients infected with HIV-1 was well absorbed from the gastrointestinal tract, with a tmax of 0.85 to 0.96 hours after ingestion. Serum levels of hydroxyurea ranged from 0.01 to 0.13 mmol/L. These values are similar to the concentrations (between 0.01 and 0.1 mmol/L) demonstrated to inhibit HIV-1 in vitro. Our data show that hydroxyurea given at a dosage of 500 mg twice daily is sufficient to yield serum concentrations potentially useful for in vivo inhibition of HIV-1.

Adult↗

PubMed1987

Deoxyribonucleotide metabolism and cyclic AMP resistance in hydroxyurea-resistant S49 T-lymphoma cells.

We investigated the cell cycle regulation of deoxyribonucleoside triphosphate (dNTP) metabolism in hydroxyurea-resistant (HYUR) murine S49 T-lymphoma cell lines. Cell lines 10- to 40-fold more hydroxyurea-resistant were selected in a stepwise manner. These HYUR cells exhibited increased CDP reductase activity (5- to 8-fold) and increased dNTP pools (up to 5-fold) that appeared to result from increased activity of the M2 subunit (binding site of hydroxyurea) of ribonucleotide reductase. These characteristics remained stable when the cells were grown in the absence of hydroxyurea for up to 2 years. In both wild type and hydroxyurea-resistant cell populations synchronized by elutriation, dCTP and dTTP pools increased in S phase, whereas dATP and dGTP pools generally remained the same or decreased, suggesting that allosteric effector mechanisms were operating to regulate pool sizes. Additionally, CDP reductase activity measured in permeabilized cells increased in S phase in both wild type and hydroxyurea-resistant cells, suggesting a nonallosteric mechanism of increased ribonucleotide reductase activity during periods of active DNA synthesis. While wild type S49 cells could be arrested in the G1 phase of the cell cycle by dibutyryl cyclic AMP, hydroxyurea-resistant cell lines could not be arrested in the G1 phase by exogenous cyclic AMP or agents that elevate the concentration of endogenous cyclic AMP. These data suggest that cyclic AMP-generated G1 arrest in S49 cells might be mediated by the M2 subunit of ribonucleotide reductase.

Animals↗

PubMed1997

Pharmacokinetics and toxicity of 120-hour continuous-infusion hydroxyurea in patients with advanced solid tumors.

A group of 18 patients with advanced cancer were entered on a phase I study of a 120-h continuous intravenous infusion of hydroxyurea. The dose of hydroxyurea was escalated in cohorts of patients from 1 to 2 to 3.2 g/ m2 per day. The primary dose-limiting toxicity was neutropenia, often accompanied by leukopenia, thrombocytopenia and generalized skin rash. Prophylactic treatment of patients with dexamethasone and diphenhydramine hydrochloride prevented the skin rash, but not the hematopoietic toxicities. The pharmacokinetics of hydroxyurea were studied in all patients. The steady-state concentrations of hydroxyurea were linearly correlated with the dose (R2 = 0.71, n = 18, P < 0.0001). The mean +/- SE concentrations were 93 +/- 16, 230 +/- 6 and 302 +/- 27 microM at 1, 2 and 3.2 g/m2 per day, respectively. The mean +/- SE renal and nonrenal clearances of hydroxyurea were 2.14 +/- 0.18 and 3.39 +/- 0.28 l/h per m2 (n = 16), neither of which correlated with the dose. The concentration of hydroxyurea in plasma decayed monoexponentially with a mean +/- SE half-life of 3.25 +/- 0.18 h (n = 17). The steady-state concentration of hydroxyurea was > 200 microM in all nine patients treated at 2 g/m2 per day, a dose which was well tolerated for 5 days. We recommend this dose for phase II trials in combination with other antineoplastic agents.

Adult↗

PubMed1992

EPR stopped-flow studies of the reaction of the tyrosyl radical of protein R2 from ribonucleotide reductase with hydroxyurea.

The reaction of the functional tyrosyl radical in protein R2 of ribonucleotide reductase from E. coli and mouse with the enzyme inhibitor hydroxyurea has been studied by EPR stopped-flow techniques at room temperature. The rate of disappearance of the tyrosyl radical in E. coli protein R2 is k2 = 0.43 M-1 s-1 at 25 degrees C. The reaction follows pseudo-first-order kinetics up to 450 mM hydroxyurea indicating that no saturation by hydroxyurea takes place even at this high concentration. Transient nitroxide-like radicals from hydroxyurea have been detected for the first time in the reaction of hydroxyurea with protein R2 from E. coli and mouse, indicating that 1-electron transfer from hydroxyurea to the tyrosyl radical is the dominating mechanism in the inhibitor reaction. The hydroxyurea radicals appear in low steady-state concentrations during 2-3 half-decay times of the tyrosyl radical and disappear thereafter.

Animals↗

PubMed2004

Prevention of secondary stroke and resolution of transfusional iron overload in children with sickle cell anemia using hydroxyurea and phlebotomy.

OBJECTIVE: Transfusions prevent secondary stroke in children with sickle cell anemia (SCA) but also cause iron overload. Alternatives for stroke prophylaxis with effective therapy to reduce iron burden are needed. STUDY DESIGN: For 35 children with SCA and stroke, transfusions were prospectively discontinued. Hydroxyurea was prescribed for stroke prophylaxis, and phlebotomy removed excess iron. Initial patients discontinued transfusions before hydroxyurea therapy, but later patients overlapped transfusions with hydroxyurea until tolerating full-dose therapy. RESULTS: Children received hydroxyurea for 42 +/- 30 months (range, 3-104 months). Hydroxyurea (26.7 +/- 4.8 mg/kg per day) led to mild neutropenia (3.9 +/- 2.3 x 10(9)/L) with significant increases in hemoglobin concentration, mean corpuscular volume, and fetal hemoglobin. Stroke recurrence rate was 5.7 events per 100 patient-years, but children receiving overlapping hydroxyurea therapy had only 3.6 events per 100 patient-years. For 26 children with >6 months of phlebotomy, 14,311 +/- 12,459 mL blood (315 +/- 214 mL/kg) was removed, with serum ferritin decreasing from a median of 2722 to 298 ng/mL. Among patients completing phlebotomy, liver biopsy documented normal histology and no excess iron deposition. CONCLUSIONS: For children with SCA and stroke, hydroxyurea effectively prevents secondary stroke and serial phlebotomy leads to complete resolution of transfusional iron overload.

Adolescent↗

PubMedDate not supplied

[Leg ulcer in a patient treated with hydroxyurea for polycythemia vera].

INTRODUCTION: Causes of leg ulcers vary widely, although venous insufficiency and peripheral arteriopathy are most common. Ulcers are much rarer in patients treated by hydroxyurea. CASE: A 66-year-old woman who had been treated with hydroxyurea for polycythemia vera for four years came to our consultation a month after ulceration of the left lateral malleolus had begun. Symmetric peripheral pulses were present and there was no patent venous insufficiency. After two months of local symptomatic treatment, the size of the ulcer had increased. The possible involvement of hydroxyurea in the genesis and maintenance of this leg ulcer was then considered. Hydroxyurea was stopped, and the ulcer progressively grew smaller, finally healing completely two months later. DISCUSSION: We conclude that hydroxyurea was the primary cause of the malleolar ulcer, for it healed rapidly when this treatment stopped. Hydroxyurea causes cutaneous atrophy; when followed by microtrauma, associated with deterioration in DNA repair mechanisms, it may lead to the formation of persistent cutaneous ulcers. Hydroxyurea can also affect the microcirculation and induce tissular anoxia, which may also explain both the occurrence of cutaneous ulcers after microtrauma and their often painful character.

Aged↗

PubMed2001

Systematic review of combination antiretroviral therapy with didanosine plus hydroxyurea: a partial solution to Africa's HIV/AIDS problem?

Effective antiretroviral therapy remains beyond the reach of most human immunodeficiency virus (HIV)-infected persons living in the third world because of its tremendous cost. The cancer drug, hydroxyurea, inhibits HIV-1 replication in vitro and, when combined with didanosine (ddI), results in significant antiretroviral synergy. In vivo, hydroxyurea specifically targets quiescent lymphocytes and macrophages, important cellular reservoirs for HIV-1, and the combination of ddI plus hydroxyurea effectively reduces plasma HIV-1 RNA levels. Combination ddI-hydroxyurea costs about one-eighth as much as currently recommended triple drug combinations, and several countries in Africa are exploring the feasibility of widescale use of ddI-hydroxyurea for their HIV-infected populations. Intrigued by its potential relevance for Africa, the authors reviewed the literature on the in vitro and clinical efficacy of ddI plus hydroxyurea against HIV. The combination of ddI plus hydroxyurea is an effective and potentially more affordable regimen for HIV-infected persons living in poorer countries.

Africa↗

PubMed1988

Molecular mechanisms responsible for the drug-induced posttranscriptional modulation of ribonucleotide reductase levels in a hydroxyurea-resistant mouse L cell line.

Ribonucleotide reductase, which catalyzes the formation of deoxyribonucleotides from ribonucleoside diphosphate precursors, is the rate-limiting enzyme in DNA synthesis. The enzyme consists of two nonidentical subunits called M1 and M2, both of which are required for activity. Hydroxyurea, a specific inhibitor of DNA synthesis, acts by destroying the unique tyrosyl free radical of protein M2. Previously, we have described a mouse L cell line which exhibited a stable resistance to high concentrations of hydroxyurea. This mutant cell line contains elevated quantities of both proteins M1 and M2 as a result of corresponding increases in the levels of mRNAs for both subunits. Interestingly, both M1 and M2 protein levels were further elevated when mutant cells were cultured in the presence of hydroxyurea, and this elevation was not accompanied by increases in their corresponding mRNAs. These results indicated that hydroxyurea can modulate ribonucleotide reductase expression posttranscriptionally. In this report, we show that the level of both subunits of ribonucleotide reductase responds to hydroxyurea in a drug concentration dependent manner. Furthermore, results from kinetic studies indicate that protein M2 levels rise much more rapidly than protein M1. Pulse-chase experiments indicated that the half-lives of both the M1 and M2 polypeptides are increased by approximately 2-fold when the mutant cells are cultured in the presence of hydroxyurea. We also present evidence indicating that exposure of these cells to hydroxyurea leads to a relatively slow but specific increase in the rate of biosynthesis of both proteins M1 and M2, as assayed by pulse labeling.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

Comparison of busulphan, hydroxyurea and allogeneic bone marrow transplantation (BMT) in chronic myeloid leukaemia: BMT prolongs survival.

INTRODUCTION: Whether busulphan-treated patients develop blastic transformation earlier than hydroxyurea treated has been a controversial issue. In a randomised prospective study, we examined the busulphan versus hydroxyurea influence on time to blast crisis and on survival. When we opened our study in 1984, the clinical benefit of allogeneic bone marrow transplantation (BMT) was not well known; to follow up the long-time outcome of this treatment was therefore of great interest. MATERIALS AND METHODS: Previously untreated CML patients were randomly started on either hydroxyurea (30 mg/kg/day) or busulphan (0.1 mg/kg/day). The end points of the study were overall survival and time to blast crisis. A total of 26 patients subsequently underwent BMT. RESULTS: A total of 179 patients were randomised, 90 of hydroxyurea, and 89 to busulphan treatment. There was no significant difference in survival between hydroxyurea- and busulphan-treated patients (P = 0.46); median survival was 3.5 and 3.2 years, respectively. In all, 85 of the patients were subsequently diagnosed with blast crisis, 41 in the busulphan and 44 in the hydroxyurea group. There was no significant difference between the two groups (P = 0.91). The 26 patients who were allotransplanted survived significantly longer than those who were not transplanted (P = 0.0001). The 5-year-survival rates were 50 and 22% and the 10-year-survival rates were 46 and 2%, respectively. The median survival was 4.7 years for the transplanted and 3.3 years for the nontransplanted patients. CONCLUSION: We did not find any difference between hydroxyurea and busulphan treatment, either in overall survival or in blast crisis-free survival; transplanted patients survived significantly longer than nontransplanted patients.

Adolescent↗