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PubMed2004

Mutations in the R2 subunit of ribonucleotide reductase that confer resistance to hydroxyurea.

Ribonucleotide reductase is an essential enzyme that catalyzes the reduction of ribonucleotides to deoxyribonucleotides for use in DNA synthesis. Ribonucleotide reductase from Escherichia coli consists of two subunits, R1 and R2. The R2 subunit contains an unusually stable radical at tyrosine 122 that participates in catalysis. Buried deep within a hydrophobic pocket, the radical is inaccessible to solvent although subject to inactivation by radical scavengers. One such scavenger, hydroxyurea, is a highly specific inhibitor of ribonucleotide reductase and therefore of DNA synthesis; thus it is an important anticancer and antiviral agent. The mechanism of radical access remains to be established; however, small molecules may be able to access Tyr-122 directly via channels from the surface of the protein. We used random oligonucleotide mutagenesis to create a library of 200,000 R2 mutants containing random substitutions at five contiguous residues (Ile-74, Ser-75, Asn-76, Leu-77, Lys-78) that partially comprise one side of a channel where Tyr-122 is visible from the protein surface. We subjected this library to increasing concentrations of hydroxyurea and identified mutants that enhance survival more than 1000-fold over wild-type R2 at high drug concentrations. Repetitive selections yielded S75T as the predominant R2 mutant in our library. Purified S75TR2 exhibits a radical half-life that is 50% greater than wild-type R2 in the presence of hydroxyurea. These data represent the first demonstration of R2 protein mutants in E. coli that are highly resistant to hydroxyurea; elucidation of their mechanism of resistance may provide valuable insight into the development of more effective inhibitors.

Antineoplastic Agents↗

PubMed2004

Hydroxyurea chemotherapy for meningiomas: enlarged cohort with extended follow-up.

Meningiomas account for 18-20% of all intracranial tumours and often recur despite surgical resection. Hydroxyurea is under evaluation as adjuvant therapy of meningiomas. In the authors' initial report of 17 patients with meningioma, hydroxyurea demonstrated modest efficacy, with a median time to progression (TTP) of 80 weeks. In the current study, 21 patients with meningioma have been placed on hydroxyurea (20 mg/kg/day orally), with extended follow-up of the original cohort. Eighteen of 20 evaluable patients (90%) responded with stable disease ranging from 20 to 328 + weeks (median TTP 176 weeks; 11 patients censored). Five of the stabilized patients progressed after 20, 56, 36, 216 and 56 weeks, respectively. Two patients had progressive disease after 10 weeks. Toxicity was mainly haematological. Hydroxyurea has modest activity against meningiomas and should be considered for patients who are poor surgical candidates, have unresectable or large residual meningiomas, or have progressed after surgical resection or irradiation, or both.

Adult↗

PubMed2003

Development of large genital ulcer due to hydroxyurea treatment in a patient with chronic myeloid leukemia and Behcet's disease.

Chronic myeloid leukemia (CML) is a myeloproliferative disease arising from abnormal stem cells and associated with splenomegaly and leukocytosis. Hydroxyurea and interferon alpha are used in treatment very frequently. Behcet's disease (BD) is a chronic, repetitive disease of unknown etiology and associated with mucocutaneous, ocular, vascular and central nervous system involvement. Cases with symptoms of BD have been reported during interferon alpha treatment of CML. However, similar symptoms due to hydroxyurea treatment have been reported in only one case until now. A 32-year-old female patient under follow up because of CML and BD, developed a large genital ulcer during hydroxyurea treatment. Ulcers due to hydroxyurea treatment and the co-existence of these two diseases has been reported in only one case in the literature while large genital ulcers have not been reported previously.

Adult↗

PubMed2006

Platelet aggregation profile as a marker of hydroxyurea bioavailability through nitric oxide generation in chronic myelogenous leukemia.

Platelet aggregation profiles were studied in chronic myelogenous leukemia patients who were undergoing hydroxyurea therapy. Nitric oxide (NO) generation induced by hydroxyurea was measured from the altered aggregatory response, in which the platelet suspension exhibits a de-aggregatory behaviour. NO caused platelet de-aggregation by generation of cyclic guanidine monophosphate through the activation of soluble guanylate cyclase (SGC). The fact that the observed response is specific to NO was confirmed by the reversal of the de-aggregatory behaviour in the presence of (1)H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of SGC. Among the subjects studied, one subset showed an hydroxyurea-induced de-aggregatory effect that was inhibited by ODQ, whereas another subset did not show any such effect. The observed inter-individual variability in platelet aggregometric response after the ingestion of drugs may be an indicator for NO generation from hydroxyurea, and this may help to explain the drug efficacy encountered in such cases.

Adult↗

PubMed2001

Clinical and hematological responses to hydroxyurea in Sicilian patients with Hb S/beta-thalassemia.

Although, several reports have detailed that hydroxyurea can ameliorate the clinical course of adult and pediatric patients with sickle cell anemia (Hb S or beta(S)), few clinical studies have been carried out in patients with beta(S)/beta-thalassemia. In a two-year clinical study, we evaluated the efficacy of hydroxyurea in a group of 22 adult Sicilian patients with beta(S)/beta-thalassemia with severe phenotypes. Among the 20 patients evaluated during 2 years of treatment, we observed a very good clinical response with a 93% reduction of the annual number of crises (median 7 versus 0.5 crises per year; P < 0.001) and of days in hospital (mean 22+/- 21.9 versus 1.2 +/- 2.3; P < 0.001), a significant increase in Hb F (7.5 +/- 5.3% versus 25.2 +/- 5.2%; P < 0.001) and in MCV (73.1 +/- 4.8 fL versus 96.4 +/- 7.2 fL; P < 0.001), and no significant modifications in Hb (9.6 +/- 1.3 g/dL versus 10.0 +/- 1.5 g/dL; P > 0.05) and in WBC (11.4 +/- 3.9 x 10(9)/L versus 10.2 +/- 3.9 x 10(9)/L; P > 0.05). Twelve patients had no crises from the first month of treatment; 16 patients showed a 2-3-fold increase over baseline in Hb F. During the study no severe complications and no important side effects of hydroxyurea were observed. Our data suggest that hydroxyurea efficacy in patients with beta(S)/beta-thalassemial may be greater than that described in patients with sickle cell disease. This pattern and durability of response will need to be confirmed in a larger, randomized, clinical trial.

Adult↗

PubMed2005

Imatinib and hydroxyurea in pretreated progressive glioblastoma multiforme: a patient series.

BACKGROUND: Grade IV malignancies of the brain, such as glioblastoma multiforme (GBM), are associated with a dismal prognosis. Autocrine and paracrine loops of platelet-derived growth factor (PDGF) signaling, as well as other signal transduction pathways, have been postulated to play a role in glioblastoma transformation, and molecules involved in these pathways can potentially serve as targets for therapeutic inhibitory agents. Imatinib, an inhibitor of PDGF receptors alpha and beta, as well as other selected tyrosine kinases, is indicated for treatment of chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor (GIST). Unfortunately, imatinib, as with many conventional chemotherapeutic agents, has limited efficacy as monotherapy in GBM. In preclinical studies, the chemotherapeutic agent hydroxyurea is demonstrated to have cytotoxic effects additive with imatinib. PATIENTS AND METHODS: We tested the combination of hydroxyurea and imatinib in 30 grade IV progressive GBM patients refractory to chemo- and radiotherapy. All 30 patients were evaluable after a median 19 weeks observation time. RESULTS: Combination therapy with imatinib and hydroxyurea resulted in a 20% response rate, including complete and partial responses. Patients experiencing response or stable disease yielded a combined clinical benefit rate of 57%. Median time to progression was 10 weeks and median overall survival was 19 weeks. Three patients continue to survive on combination therapy, with the shortest duration being 106 weeks. Six-month and 2-year progression-free survival rates were 32% and 16%, respectively. CONCLUSION: The efficacy results, combined with findings that imatinib and hydroxyurea were well tolerated, suggest that this combination shows promise as therapy for GBM.

Adolescent↗

PubMed1988

Hydroxyurea and etoposide: in vitro synergy and phase I clinical trial.

L1210 murine leukemia cells were treated with hydroxyurea (10-200 microM) for 24 hours and/or etoposide (0.17-3.4 microM) for 2 hours. Combination treatments used a fixed molar hydroxyurea:etoposide ratio of 58.9:1, and drug-drug interactions were quantitated according to the median effect principle. Hydroxyurea and etoposide were antagonistic at low doses at which the survival fraction was greater than 0.5 and synergistic at higher doses at which the survival fraction was less than 0.25. In a phase I clinical trial, 19 patients were treated with the two drugs at one of three dose levels. The dose-limiting toxic effect was myelosuppression. Doses of 100 mg of etoposide/m2 per day by continuous infusion and 500 mg of hydroxyurea orally every 4 hours, both for 3 days, are recommended for phase II trials.

Adult↗

PubMed1994

Hydroxyurea-induced acute interstitial lung disease.

Hydroxyurea is a cytotoxic agent that is being increasingly used for a number of malignant and nonmalignant systemic diseases. This agent is particularly well tolerated, with dose-related myelosuppression being the primary side effect. We describe a patient who had patchy interstitial infiltrates with cavitation 2 months after the start of therapy with hydroxyurea. After hydroxyurea therapy was discontinued and empiric corticosteroid therapy was given, the pulmonary infiltrates resolved. This is a case of presumed hydroxyurea-induced lung disease, the first with supportive lung biopsy material. It is essential for physicians to be aware of this potentially life-threatening toxicity.

Acute Disease↗

PubMedDate not supplied

Cutaneous manifestations of hydroxyurea therapy in childhood: case report and review.

Hydroxyurea is commonly used in the treatment of various myeloproliferative disorders. In conventional pediatric clinical practice, its use is limited to benign hematologic conditions such as sickle cell disease and thalassemia. Long-term hydroxyurea use is associated with various adverse mucocutaneous effects including hyperpigmentation, alopecia, leg ulcers, and lichenoid eruptions. We report a 10-year-old boy with chronic myelogenous leukemia who presented with hyperpigmentation of the skin and nails 3 months after the start of hydroxyurea therapy. Melanonychia of all 20 nails with involvement of all three mucocutaneous areas (skin, nails, and mucosa) at presentation was a unique feature in our patient. With the recently increasing pediatric use of hydroxyurea in a variety of disorders, its benign and not so uncommon cutaneous adverse effects are emphasized here.

Antineoplastic Agents↗

PubMedDate not supplied

Cutaneous adverse reactions to hydroxyurea in patients with intermediate thalassemia.

Although the cutaneous effects of hydroxyurea have been described for patients with sickle cell anemia, myeloproliferative disorders, and psoriasis, there are no reports of cutaneous adverse effects from hydroxyurea when used for patients with intermediate thalassemia. Therefore 43 patients with intermediate thalassemia treated with hydroxyurea were examined by a dermatologist, and pertinent cutaneous findings were recorded. These patients had received hydroxyurea for a mean of 15.5 months. Nineteen had cutaneous hyperpigmentation, eight had xerosis, and three were found to have one cafe au lait macule each. Eleven patients had nail abnormalities, including nail ridging, partial leukonychia, and longitudinal melanonychia. There were no cases of leg ulceration. It was concluded that the risk of developing leg ulcers and pigmentary disorders appears to be related to the underlying disease being treated, as well as to a patient's age, gender, and pigmentation.

Adolescent↗

PubMed1975

Induction of phage production in the lysogenic Escherichia coli by hydroxyurea.

1) Hydroxyurea, a reversible DNA synthesis inhibitor, was used to study the mechanism of prophage lambda induction in Escherichia coli K12. Induction of prophage was judged on two criteria: increase of phage-producing cells and loss of colony-forming ability of the cells. 2) Hydroxyurea induced an increase of phage-producing cells only in lysogenic strains known to be inducible with ultraviolet irradiation for prophage development and not in strains such as E. coli K12 (lambdaind-) or E. coli K12 recA (lambda+). 3) When protein synthesis was inhibited, hydroxyurea did not increase phage-producing cells of lysogenic strains; it showed a bacteriocidal effect on lysogenic recA+ strains, but not on nonlysogenic strains. 4) The sensitivity of E. coli K12 recA to hydroxyurea was independent of whether or not the cells were lysogenic. 5) From the results it is suggested that certain steps leading to loss of colony-forming ability (i.e. prophage induction) do not require de novo protein synthesis but require the presence of the host recA+ gene.

Bacterial Proteins↗

PubMed1989

Hydroxyurea in the management of therapy resistant psoriasis.

Eighty-five patients with extensive chronic plaque psoriasis, unresponsive to conventional topical therapy, were treated with long-term hydroxyurea in a dose of 0.5-1.5 g daily. Fifty-two (61%) had a satisfactory remission during treatment without significant adverse effects. Treatment was discontinued in 33 patients (39%), due to an inadequate response or significant relapse during treatment and because of adverse reactions (19%). Four (4.7%) patients on hydroxyurea developed actinic psoriasis. Significant haematological abnormalities occurred in 30 patients (35%), but these became normal following a reduction in the dose of hydroxyurea or temporarily stopping the drug. In only six was it considered necessary to discontinue treatment because of bone marrow suppression. Our experience suggests that hydroxyurea is an effective long-term treatment for psoriasis that is refractory to conventional topical therapy and that the incidence of serious adverse effects compares favourably with other cytotoxic drugs.

Adult↗

PubMed1995

Hydroxyurea-induced dermatomyositis-like eruption.

Hydroxyurea is frequently used to treat myeloproliferative syndromes. Cutaneous lesions resembling those seen in dermatomyositis have rarely been reported in the course of treatment with hydroxyurea. We report six additional patients with this unusual adverse effect. All of the patients had a very typical and similar cutaneous eruption, with scaly, linear erythema on the dorsa of the hands. Leg ulceration occurred in two cases. Muscle involvement was never observed. One patient had unexplained lung disease. In all the others the disorder pursued a benign course, even when hydroxyurea was not withdrawn. Dermatomyositis-like lesions seem to be a not infrequent and characteristic adverse reaction to hydroxyurea. Investigations are not required, and the course is usually benign.

Aged↗

PubMed2005

Hydroxyurea and splenic irradiation-induced tumour lysis syndrome: a case report and review of the literature.

Therapeutic agents for chronic myeloid leukaemia (CML) in the chronic phase include hydroxyurea, interferon alpha, allogeneic stem cell transplantation and the tyrosine kinase inhibitor imatinib (STI 571, Gleevec). For elderly patients, oral hydroxyurea is suitable for the relief of symptoms caused by hyperleukocytosis, and splenic irradiation would be considered if abdominal discomfort or fullness induced by splenomegaly were present. Tumour lysis syndrome (TLS) is seldom seen in the treatment for CML, and TLS caused by hydroxyurea or splenic irradiation is rarely observed. Herein, we report an elderly CML patient who received treatment with hydroxyurea, allopurinol, hydration and splenic irradiation. After 3 days, acute TLS developed. Aggressive supportive treatment, including haemodialysis, stabilized the condition.

Aged↗

PubMed1994

Cutaneous manifestations of long-term hydroxyurea therapy.

Skin changes associated with long term hydroxyurea therapy have only rarely been reported and are not widely known. This report concerns a patient in whom extensive and debilitating skin changes developed secondary to hydroxyurea therapy. In addition to previously reported manifestations such as ichthyosis, a dermatomyositis-like eruption on the dorsal hands, facial erythema and accelerated development of premalignant and malignant skin lesions, the patient developed an erosive eruption on the glans penis. He also developed a rapidly enlarging viral wart which clinically resembled a squamous cell carcinoma and histologically showed marked cytological atypia. It is possible that hydroxyurea caused accelerated photoageing and also contributed to the rapid growth of the viral wart and the atypical histological features. The time course of the clinical changes suggests that they result from direct toxicity of hydroxyurea on the basal layer of the epidermis and mucosal surfaces.

Drug Eruptions↗

PubMed1998

Aqueous stability of SB 210661: kinetics and primary degradation mechanisms of an N-hydroxyurea-containing 5-lipoxygenase inhibitor.

SB 210661, (S)-N-hydroxy-N-[2,3-dihydro-6-(2,6-difluorophenylmethoxy)-3-benzo furanyl]urea, is a potent and selective inhibitor of 5-lipoxygenase. Its aqueous stability was primarily evaluated to support development of analytical methods and formulations. The results also add to the growing database on the stability of N-hydroxyurea compounds. Comparison of the stability of SB 210661 with that of two other N-hydroxyurea-containing compounds, zileuton and Abbott-79175, supported a common primary degradative pathway at pH > 5 and different degradative pathways at pH < 5. The pathway at pH > 5 is consistent with the hydrolysis of the N-hydroxyurea group, whereas for SB 210661, the pathway at pH < 5 is consistent with specific acid-catalysed nucleophilic displacement of the N-hydroxyurea group by water.

Benzofurans↗

PubMed1968

Effect of nalidixic acid and hydroxyurea on division ability of Escherichia coli fil+ and lon- strains.

Short periods of incubation in medium containing nalidixic acid or hydroxyurea, followed by a return to normal growth conditions, induced filament formation in Escherichia coli B (fil(+)) and AB1899NM (lon(-)) but not in B/r (fil(-)) and AB1157 (lon(+)). These drugs reversibly stopped deoxyribonucleic acid (DNA) synthesis with little or no effect on ribonucleic acid (RNA) synthesis or mass increase. The initial imbalance caused by incubation in these drugs was the same for B and B/r as was macromolecular synthesis following a return to normal growth conditions. DNA degradation caused by nalidixic acid was measured and found to be the same for B and B/r. Hydroxyurea caused no DNA degradation in these two strains. Survival curves as determined under various conditions by colony formation suggested that the property of filament formation was responsible for the extrasensitivity of fil(+) and lon(-) strains to either nalidixic acid or hydroxyurea. E. coli B was more sensitive to either drug than was B/r or B(s-1). Pantoyl lactone or liquid holding treatment aided division and colony formation of nalidixic acid-treated B but had no effect on B/r. Likewise, the filament-former AB1899NM was more sensitive to nalidixic acid than was the non-filament-former AB1157. The sensitivity of B/r and B(s-1) to nalidixic acid was nearly the same except at longer times in nalidixic acid, when B(s-1) appeared more resistant. Even though nalidixic acid, hydroxyurea, and ultraviolet light may produce quite different molecular alterations in E. coli, they all cause a metabolic imbalance resulting in a lowered ratio of DNA to RNA and protein. We propose that it is this imbalance per se rather than any specific primary chemical or photochemical alterations which leads to filament formation by some genetically susceptible bacterial strains such as lon(-) and fil(+).

Bacterial Proteins↗

PubMed1973

Hydroxyurea-induced accumulation of short fragments during polyoma DNA replication. II. Behavior during incubation of isolated nuclei.

The synthesis of polyoma DNA was studied in isolated nuclei from hydroxyurea-inhibited 3T6 cells infected with polyoma virus. During incubation of nuclei under conditions suitable for polyoma DNA synthesis in vitro, the short DNA fragments with a sedimentation coefficient of 4S formed in vivo (hydroxyurea fragments) became associated with preformed, replicating DNA strands. Centrifugation in dye-buoyant density gradients showed that the fragments formed part of the structure of the replicative intermediate of polyoma DNA. The proportion of "young" replicative intermediates was larger after hydroxyurea inhibition than in uninhibited controls. Hydroxyurea fragments appear to be closely related to the 4S fragments formed as normal intermediates during discontinuous synthesis of polyoma DNA.

Animals↗