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PubMed2003

Metastatic squamous cell carcinoma of the skin in chronic myeloid leukaemia: complication of hydroxyurea therapy.

Hydroxyurea is a ribonucleotide diphosphate reductase inhibitor used in the treatment of patients with myeloproliferative disorders. Hydroxyurea has some dermatological side-effects. It has recently been recognized that hydroxyurea can induce squamous cell and basal cell carcinomas of skin. We present the case of an elderly man with chronic myeloid leukaemia who was treated with hydroxyurea for 4 years, with good control of his disease. However, in addition to the appearance of various skin lesions and cutaneous squamous cell carcinoma after 3 years of therapy, he was found to have a metastatic squamous cell carcinoma after 4 years. Hydroxyurea was discontinued, and he underwent surgery and radiotherapy. The patient subsequently died of ventricular fibrillation. We present this case to draw attention to the association between hydroxyurea and secondary skin cancers and to emphasize the need for dermatological examination before and during the course of hydroxyurea therapy.

Aged↗

PubMed1981

Synergistic interaction between 1-beta-D-arabinofuranosylcytosine, thymidine, and hydroxyurea against human B cells and leukemic blasts in vitro.

Isobologram analysis was used to examine the interaction between 1-beta-D-arabinofuranosylcytosine (Ara-C), thymidine (dThd), and hydroxyurea. All three pairs of drugs, as well as the triple combination, were synergistic against a human B cell line in vitro across a broad range of concentrations. Synergy was associated with an increase in the Ara-C nucleotide pool and Ara-C triphosphate concentration. dThd increased, and hydroxyurea decreased, the incorporation of Ara-C into trichloroacetic acid-insoluble macromolecules per unit time. Hydroxyurea was more effective than dThd at equimolar concentrations in increasing the acid-soluble Ara-C pool. Maximal stimulation of Ara-C triphosphate formation by dThd occurred at 1 mM and was associated with reduction of the deoxycytidine triphosphate pool to 31% of control. At the same concentration, hydroxyurea increased Ara-C triphosphate formation to a greater extent but increased deoxycytidine triphosphate to 116% of control. When tested at clinically achievable concentrations on blasts from patients with acute leukemia, hydroxyurea increased the Ara-C nucleotide pool in all six cases studied, whereas dThd decreased the Ara-C nucleotide pool. These results indicate that in SB cells dThd and hydroxyurea work by different mechanisms to augment the Ara-C nucleotide pool and that hydroxyurea may be more effective than dThd as a modulator of Ara-C activity in patients with acute leukemia.

Animals↗

PubMed2000

Rationale for the use of hydroxyurea as an anti-human immunodeficiency virus drug.

Hydroxyurea has been extensively used in medical practice, mainly for treating chronic myelogenous leukemia, sickle cell anemia, and other diseases. In light of its ability to inhibit DNA synthesis and to induce cell cycle arrest through inhibition of ribonucleotide reductase, the effects of hydroxyurea on replication of human immunodeficiency virus type 1 (HIV-1) have been investigated. In vitro hydroxyurea has been shown to block HIV-1 reverse transcription and/or replication in quiescent peripheral blood mononuclear cells (PBMC) and macrophages. Hydroxyurea was also found to be synergistic with the nucleoside reverse transcriptase inhibitor didanosine and to inhibit HIV-1 replication in activated PBMC; this inhibition may be due to a reduction in deoxynucleoside triphosphate pool sizes. Finally, hydroxyurea has been shown to sensitize didanosine-resistant mutants. Hydroxyurea may therefore be useful for limiting the spread of didanosine-resistant HIV-1 variants. The favorable toxicity profile of hydroxyurea and the lack of significant overlapping toxicities with some of the nucleoside reverse transcriptase inhibitors, as well as their distinct mechanisms of action, have provided further rationale for use of these agents in combination therapies.

Anti-HIV Agents↗

PubMed2005

Lowering the dose of hydroxyurea minimizes toxicity and maximizes anti-HIV potency.

The goal of this study was to optimize the hydroxyurea dosage in HIV-infected patients, and to minimize the toxicity and maximize the antiviral efficacy of the hydroxyurea-didanosine combination. In a randomized, open-label study (RIGHT 702, a multicenter trial performed in private and institutional practices), three daily doses (600 microg, 800-900 microg, and 1200 microg) of hydroxyurea were administered in combination with didanosine and stavudine to 115 chronically HIV-infected patients, one-third antiretroviral drug naive, with viremia between 5000 and 200,000 copies/ml regardless of CD4+ cell count. The primary efficacy end point was the proportion of patients with plasma HIV-1 RNA levels below 400 copies/ml after 24 weeks of therapy. In the RIGHT 702 intent-to-treat population the lowest (600 mg) dose of hydroxyurea was better tolerated, associated with fewer adverse events, and more potent by all efficacy parameters, including the primary end point (76 versus 60% patients with viremia<400 copies/ml at week 24 for the 600-mg and 800- to 900-mg dose groups, respectively; p=0.027), the mean area under the curve (60.3 versus 65.8; p=0.016), and the mean log10 decrease (-1.95 versus -0.77; p=0.001). Patients receiving 600 mg of hydroxyurea daily also had the highest CD4+ cell count, CD4+/CD8+ cell ratio, and lowest CD8+ cell count and percentage (p=0.035). The RIGHT 702 trial provides an explanation for the increased toxicity and decreased efficacy of hydroxyurea when it was used at high dosage (1200 mg daily). At the optimal dosage of 600 mg daily, hydroxyurea, in combination with didanosine, deserves reevaluation for the long-term management of HIV/AIDS worldwide, because of its excellent resistance profile, durability, and affordability.

Anti-HIV Agents↗

PubMedDate not supplied

Hydroxyurea in children with sickle cell disease: impact on splenic function and compliance with therapy.

PURPOSE: Hydroxyurea therapy reduces clinical complications in sickle cell disease. While evaluating the clinical and laboratory responses to hydroxyurea in children with sickle cell disease, we concurrently objectively monitored, for the first time during such treatment, compliance with therapy. Because most deaths in affected children are related to infection, we also evaluated the impact of hydroxyurea on splenic function, estimated by the percentage of red cells containing endocytic vacuoles ("pitted" cells) over 1 year of therapy. PATIENTS AND METHODS: Seventeen children with a history of > or = 3 hospital admissions in the previous year, aged (mean +/- standard error of mean) 12.3 +/- 1.2 years, were treated with hydroxyurea. Clinical and laboratory assessments monitored efficacy and toxicity. Compliance was monitored using computerized pill bottles containing cap microprocessors which monitor the frequency of bottle openings. RESULTS: Over 18.5 +/- 2.1 months, compliance with hydroxyurea (as determined by percent of the prescribed drug actually taken) was 96 +/- 2%, resulting in increases in mean fetal hemoglobin from 7.7 +/- 1.6% to 16.7 +/- 1.8% (p < 0.005). In 11 patients who reached maximum tolerated doses, an increase to 18.8 +/- 2.5% (p = 0.0001) was observed. Pitted red cell counts did not change. Annual rates of vaso-occlusive crisis (p = 0.0105), acute chest syndrome (p = 0.0417), transfusions administered (p = 0.0168), and days in hospital (p = 0.0017) all decreased significantly. CONCLUSIONS: Hydroxyurea in children is associated with sustained excellent compliance and monitoring this compliance is uncomplicated. Splenic function in most hydroxyurea-treated children did not change over 1 year of therapy.

Adolescent↗

PubMed1982

Analysis of the effect of hydroxyurea on stem cell (CFU-s) kinetics.

Hydroxyurea induces profound changes in the pluripotential haemopoietic stem cell (CFU-s) kinetics. The main feature of these changes is a synchronous entry of resting G0 CFU-s into the cell cycle. The analysis of the passage of the CFU-s cohort through the cell cycle has been largely based on the examination of the fraction of CFU-s which synthesize DNA in the S phase of the cell cycle. This analysis has, however, been hampered by the fact that both the sensitivity of the S phase CFU-s to hydroxyurea and their sensitivity in the [3H]thymidine suicide technique vary as the cells pass through the S phase. Methods which overcome these difficulties have been used in the experiments presented in this paper. It was demonstrated that hydroxyurea kills only about 80% of the S phase CFU-s. The sensitivity to hydroxyurea gradually decreases as the cells approach the middle part of the S phase and increases again as the cells enter the late portions of the S phase. The degree of CFU-s synchrony at the point of entry into and exit from, the S phase has been established. Mathematical analysis of the available data suggests that CFU-s pass through the S phase with a mean transit time of 4.79 hr (standard deviation, 1.45 hr). Hydroxyurea, administered in vivo, blocks CFU-s in the late G1 phase. The duration of this G1-S block, induced by a dose of 1000 mg of hydroxyurea per kg body weight, is approximately 2 hr. The CFU-s in the middle of the S phase, which survive hydroxyurea administration, are also blocked in their passage through the S phase. These cells, however, seem to finish the S phase with a delay of approximately 2 hr.

Animals↗

PubMed2006

Leg ulcer in a patient associated with hydroxyurea therapy.

Hydroxyurea is a hydroxylated derivate of urea commonly used in the treatment of various hematologic disorders. Cutaneous side-effects such as alopecia, diffuse hyperpigmentation, scaling, poikiloderma, atrophy of the skin and subcutaneous tissues or nail changes can develop after long-term treatment with hydroxyurea. Painful leg ulcers in association with hydroxyurea have only rarely been reported. We present a report of a 52-year-old patient with essential thrombocythemia suffering from painful leg ulcers 3 years after starting therapy with hydroxyurea. We decided to treat the leg ulcers following a modern phase-adapted wound-healing strategy and continued hydroxyurea therapy until complete healing of the ulcers. In conclusion, cutaneous ulceration of the leg is one adverse effect in patients with essential thrombocythemia during hydroxyurea therapy. Healing does not necessarily require discontinuation of the drug. Therefore, therapists should first optimize a conservative and systematic wound-healing strategy. If these interventions fail, discontinuation of hydroxyurea therapy is advisable.

Alginates↗

PubMed1997

In vivo production of nitric oxide in rats after administration of hydroxyurea.

The metabolism of nitrovasodilators such as glyceryl trinitrate and nitroprusside provides the active moiety of these drugs (that is, nitric oxide). This process is not limited to the known nitrovasodilators, but also occurs with nitroaromatic antimicrobials. Here we report that the administration of hydroxyurea, an antitumor drug, to rats at pharmacological doses formed detectable nitrosyl hemoglobin, which increased with dose. At higher doses, nitrosyl hemoprotein complexes could also be detected in liver tissue. [15N]hydroxyurea was synthesized and compared with [14N]hydroxyurea. These observations verified that nitric oxide detected as nitrosyl hemoglobin or nitrosyl hemoprotein complexes in rats was the result of the metabolism of hydroxyurea. The time course and dose-dependence of nitric oxide generation were also investigated. Hydroxyurea's antineoplastic activity is caused by its direct action on ribonucleotide reductase, the rate-limiting enzyme in DNA synthesis. Because nitric oxide also inhibits ribonucleotide reductase, this metabolite may supplement this action of hydroxyurea. In addition, the known ability of hydroxyurea to ease the pain of sickle cell anemia patients may be the result of vasodilation by the drug-derived nitric oxide.

Animals↗

PubMed1999

Differential regulation of DNA synthesis by nitric oxide and hydroxyurea in vascular smooth muscle cells.

We investigated the influence of nitrovasodilators on DNA synthesis in cultured human aortic smooth muscle cells and explored the hypothesis that nitric oxide (NO) is directly involved in mediating the inhibitory effects of hydroxyurea on DNA synthesis. Both NO and hydroxyurea inhibited ongoing DNA synthesis and S phase progression in our cells. Exogenous deoxynucleosides partially reversed this inhibition, suggesting that ribonucleotide reductase is a primary target for both NO and hydroxyurea. Nitrovasodilators inhibited DNA synthesis by releasing NO, as detected by chemiluminescence and as shown by the reversal of DNA synthesis inhibition by NO scavengers. This inhibition appears to occur via a cGMP-independent mechanism. In contrast, hydroxyurea did not produce a detectable NO signal, and NO scavengers had no influence on its inhibition of DNA synthesis, suggesting that NO does not mediate the inhibitory action of hydroxyurea in our system. Furthermore, the action of nitrovasodilators and hydroxyurea on DNA synthesis differed according to redox sensitivity. The redox agents N-acetyl-L-cysteine and ascorbate reversed NO inhibition of DNA synthesis and had no effect on DNA synthesis inhibition caused by hydroxyurea.

Antioxidants↗

PubMed2005

Long-term hydroxyurea therapy for infants with sickle cell anemia: the HUSOFT extension study.

The long-term efficacy and toxicity of hydroxyurea for infants are undefined, and its role in preventing organ dysfunction is unknown. Short-term feasibility of hydroxyurea administration, toxicities, hematologic effects, and effect on spleen function in infants with sickle cell anemia (SCA) were reported (Hydroxyurea Safety and Organ Toxicity [HUSOFT] trial). These infants completing 2 years of hydroxyurea therapy (20 mg/kg/d) were offered study extension with dose escalation to 30 mg/kg/d. Patients were monitored with laboratory tests and biannual imaging studies. Hematologic indices were compared with predicted age-specific values and event rates compared with historic rates. All 21 subjects completing the original trial enrolled in the extension study: median age, 3.4 years old (range, 2.6 to 4.4 years); 12 females; 20 with Hb SS, 1 with Hb S/beta0-thalassemia. Seventeen patients completed 4 years of hydroxyurea, and 11 completed 6 years. After 4 years, hydroxyurea was associated with increased hemoglobin concentration, percentage of fetal hemoglobin (Hb F), and mean corpuscular volume (MCV) and decreased reticulocytes, white blood cells (WBCs), and platelets (P < .01). Patients experienced 7.5 acute chest syndrome (ACS) events per 100 person-years, compared with 24.5 events per 100 person-years among historic controls (P = .001). Treated patients had better spleen function than expected and improved growth rates. Infants with SCA tolerate prolonged hydroxyurea therapy with sustained hematologic benefits, fewer ACS events, improved growth, and possibly preserved organ function.

Anemia, Sickle Cell↗

PubMed2002

Predictors of fetal hemoglobin response in children with sickle cell anemia receiving hydroxyurea therapy.

In the phase I/II pediatric hydroxyurea safety trial (HUG-KIDS), school-aged children with sickle cell anemia receiving hydroxyurea at the maximally tolerated dose (MTD) had variable increases in the percentage of fetal hemoglobin (%HbF). To identify predictors of the HbF response to hydroxyurea therapy, baseline clinical and laboratory values (age, sex, hemoglobin concentration, %HbF, reticulocytes, white blood cell [WBC], platelets, and serum chemistries), as well as treatment variables (number of toxicities, noncompliance, MTD dose, and MTD blood counts) were analyzed in 53 HUG-KIDS children who achieved MTD. Baseline %HbF values (P =.001), baseline hemoglobin concentration (P =.01), MTD dose (P =.02), and compliance (P =.02) were significantly associated with a higher %HbF at MTD; in contrast, age, sex, number of toxicities, and other baseline hematologic parameters were not. After adjusting for variations in baseline %HbF, the baseline reticulocyte count (P =.05) and baseline WBC count (P =.05) were also significantly associated with a higher %HbF at MTD. Hydroxyurea-induced increases in the hemoglobin concentration and mean corpuscular volume (both higher absolute values at MTD and larger positive changes from baseline values), as well as hydroxyurea-induced decreases in reticulocytes and WBC count, were significantly associated with a higher %HbF at MTD. These data suggest that selected baseline laboratory parameters, a higher MTD dose with attention to compliance, and greater therapy-related changes in blood counts may predict the HbF response to hydroxyurea therapy for children with sickle cell anemia. The HbF response to hydroxyurea is variable and complex, however, and even children with low baseline %HbF values can develop substantial increases in %HbF at MTD.

Anemia, Sickle Cell↗

PubMed1989

Hydroxyurea, fluorouracil, and concomitant radiotherapy in poor-prognosis head and neck cancer: a phase I-II study.

Hydroxyurea and fluorouracil (5-FU) are active cytotoxic drugs in head and neck cancer and have shown synergistic activity in vitro. Both drugs also act as radiosensitizers. Therefore, we administered radiotherapy at daily fractions of 180 to 200 cGy with simultaneous continuous infusion 5-FU at 800 mg/m2/d and escalating daily doses of hydroxyurea for five days. Cycles were repeated every other week until completion of radiotherapy. Thirty-nine inoperable patients were treated at six dose levels of hydroxyurea ranging from 500 mg to 3,000 mg orally daily. Little effect of hydroxyurea on the WBC or platelet count was noted in patients receiving less than 2,000 mg daily, whereas both parameters decreased progressively in patients receiving 2,000 mg daily or more. Mucositis occurred at all dose levels, requiring frequent dose reduction of 5-FU; however, in patients receiving a daily hydroxyurea dose of 2,000 mg or less, the median weekly 5-FU dose administered was 1,725 mg/m2 (86% of the intended 5-FU dose), whereas at daily hydroxyurea doses exceeding 2,000 mg, the median weekly 5-FU dose decreased to 1,133 mg/m2 (57%) (P = .001). Of 15 evaluable patients with recurrent disease after prior local therapy only one failed to respond; six had a complete response (CR), and eight a partial response (PR). Of 17 evaluable patients without prior local therapy, 12 had a CR, with no patient developing recurrence in the irradiated field to date; five patients had a PR. We conclude that the recommended dose of hydroxyurea in this regimen is 2,000 mg daily. That dose will cause mild to moderate myelosuppression and will allow for delivery of greater than 80% of the intended 5-FU dose. The activity of this regimen in poor-prognosis head and neck cancer exceeds 90%; its further investigation in previously untreated patients is warranted.

Adult↗

PubMed2003

Effect of hydroxyurea on G gamma chain fetal hemoglobin synthesis by sickle-cell disease patients.

Hydroxyurea is used for sickle-cell disease patients in order to increase fetal hemoglobin synthesis and consequently decrease the severity of pain episodes. Fetal hemoglobin, which is formed by gamma-globin chains A and G, is present in a constant composition throughout fetal development: about 75% of Ggamma and 25% of Agamma. In contrast, adult red cells contain about 40% of Ggamma and 60% of Agamma. In the present study, we analyzed the effect of hydroxyurea induction on the gamma chain composition of fetal hemoglobin in 31 sickle-cell disease patients treated with hydroxyurea. The control group was composed of 30 sickle-cell disease patients not treated with hydroxyurea in clinical steady state. The patients were older than 13 years and were not matched for age. All patients were seen at Hemocentro/UNICAMP and Boldrini Infantile Center, Campinas, SP, Brazil. The levels of total hemoglobin were significantly higher in patients treated with hydroxyurea (mean +/- SD, 9.6+/-2.16 g/dl) than in untreated patients (8.07+/-0.91 g/dl). Fetal hemoglobin levels were also higher in treated patients (14.16+/-8.31%) than in untreated patients (8.8+/-4.09%), as was the Ggamma/Agamma ratio (1.45+/-0.78 vs 0.98+/-0.4, P < 0.005). The increase in the Ggamma/Agamma ratio in patients treated with hydroxyurea suggests the prevalence of a pattern of fetal hemoglobin synthesis, whereas patients not treated with hydroxyurea maintain the adult pattern of fetal hemoglobin synthesis. Because no correlation was observed between the Ggamma/Agamma ratio and total hemoglobin or fetal hemoglobin levels, the increase in Ggamma chain synthesis may not imply a higher production of hemoglobin.

Anemia, Sickle Cell↗

PubMed2001

Involvement of p38 kinase in hydroxyurea-induced differentiation of K562 cells.

Hydroxyurea is a differentiation-inducing agent of human erythroleukemia K562 cells. However, the cellular mechanisms by which hydroxyurea exerts its effects on tumor cells, leading to the inhibition of cell growth and the induction of differentiation markers, are largely unknown. This study examined the role of different mitogen-activated protein kinase signal transduction pathways in hydroxyurea-induced erythroid differentiation of K562 cells. Using a panel of anti-extracellular signal-related kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38 phosphospecific antibodies, we demonstrated that phosphorylation of ERK and JNK is decreased after the treatment of cells with hydroxyurea, whereas phosphorylation of p38 is increased. Moreover, inhibition of ERK activity by PD98059 induced erythroid differentiation, and it acted synergistically with hydroxyurea on hemoglobin synthesis, whereas inhibition of p38 activity by SB203580 inhibited induction of hemoglobin production by hydroxyurea. These findings suggest that the activation of p38 kinase may play important roles in the signal transduction mechanisms of hydroxyurea leading to erythroid differentiation.

Cell Differentiation↗

PubMed1992

Spectrum of fetal hemoglobin responses in sickle cell patients treated with hydroxyurea: the National Institutes of Health experience.

Hydroxyurea is one of several cytostatic agents that increase fetal hemoglobin (HbF) production in some patients with sickle-cell disease, although their mechanisms of action remain to be defined. We have studied the effects of hydroxyurea in several hospitalized patients with sickle-cell disease treated for 3 months, who were then maintained on outpatient therapy. Among hydroxyurea-treated patients, we found that about 75% respond with at least a twofold increase in the percentages of F reticulocytes and HbF. Among the responders, HbF levels increased twofold to 10-fold, with three patients achieving levels of 10% to 15%. Statistical analysis of the three cellular variables that determine HbF levels in patients with sickle-cell disease--namely, increased F-cell production, F-cell survival, and HbF/F cells--disclosed that HbF production, as measured by an increase in F reticulocytes, accounted for about 70% of the HbF elevation, with smaller contributions coming from augmentation of HbF/F cells and preferential survival of F cells. Four responders were re-treated with their optimal weekly hydroxyurea dose, given either in daily fractions or over 4 consecutive days, after a 1- to 3-month washout period. Greater HbF responses were attained with the optimal hydroxyurea dose than with the dose-regimen escalation, and usually occurred after a lag period. Furthermore, increases in HbF and F-cell levels were more rapid in patients receiving therapy on 4 out of 7 days rather than on a daily schedule. Our calculations show that the increases in HbF/F and F cells and the decrease in the fraction of dense cells during limited hydroxyurea administration should cause a significant improvement in intracellular sickle hemoglobin polymerization tendency. Controlled prospective trials are necessary to establish whether these effects lead to clinical benefit. Alternate schedules of hydroxyurea administration, or its use in conjunction with other means to elevate HbF or reduce mean cell hemoglobin concentration, may achieve greater inhibition of polymerization and thus be more likely to result in unequivocal amelioration of disease manifestations.

Anemia, Sickle Cell↗

PubMed2004

[Effect of celecoxib on enhancing the chemotherapic sensitivity of hydroxyurea to K562 cells and its mechanism].

OBJECTIVE: To determine whether celecoxib can enhance the anti-proliferative effect of hydroxyurea on K562 cells and to reveal its molecular mechanism. METHODS: K562 cells were treated with low dose celecoxib (40 micromol/L) or hydroxyurea (10 mmol/L) and celecoxib (40 micromol/L) combined with hydroxyurea (10 mmol/L) for 36 h. The effects of the drugs on K562 cell growth inhibitation, apoptosis inducement and its molecular mechanism were analyzed by MTT assay, DNA fragment analysis, Western blotting, and RT-PCR. RESULTS: The treatment of celecoxib (40 micromol/L) combined with hydroxyurea (10 mmol/L) could significantly inhibit the K562 cell viability and induce the K562 cell apoptosis than those treatments of celecoxib or hydroxyurea alone. The combination of celecoxib and hydroxyurea could evidently inhibit the expression of COX-2 protein or COX-2 mRNA of K562 cells. CONCLUSION: Celecoxib can enhance the anti-proliferative effect of hydroxyurea on K562 cells, which is associated with the down-regulation of both COX-2 protein and COX-2 mRNA on K562 cells.

Antineoplastic Agents↗

PubMed1992

Enhancement of the loss of multiple drug resistance by hydroxyurea.

Gene amplification is one mechanism whereby tumor cells can become resistant to antineoplastic agents. Unstably amplified genes occur either on submicroscopic circular pieces of extrachromosomal DNA called episomes or on small acentric chromosomes called double minutes. Double minutes are frequently associated with cells containing amplified drug-resistance genes. Human epidermoid carcinoma KBV1 cells contain unstably amplified mdr1 genes and overexpress P glycoprotein, resulting in decreased intracellular drug accumulation. In this cell line, a nonlethal concentration of hydroxyurea accelerated the rate of loss of vinblastine resistance once vinblastine had been removed from the culture medium. After removal of vinblastine, KBV1 cells exposed to hydroxyurea for the time required to complete 12 cell doublings accumulated more vinblastine than control cells grown in the absence of hydroxyurea. In contrast, hydroxyurea had no effect on vinblastine sensitivity and accumulation in parental drug-sensitive KB-3-1 cells. Hydroxyurea also had no effect on sensitivity to cisplatin in cisplatin-resistant human ovarian carcinoma 2008/C13* cells, indicating that hydroxyurea's effect on drug sensitivity was specific for a drug-resistance phenotype associated with unstably amplified drug-resistance genes. These results indicate that, after removing selective pressure, hydroxyurea accelerates loss of resistance to vinblastine and increases accumulation of vinblastine in KBV1 cells, presumably by accelerating loss of amplified mdr1 genes and thus P glycoprotein.

Carcinoma, Squamous Cell↗

PubMed1987

Influence of hydroxyurea on fetal hemoglobin production in vitro.

Cytotoxic drugs increase circulating fetal hemoglobin levels. We examined the mechanism by measuring the fetal hemoglobin produced per BFU-E-derived erythroblast following hydroxyurea treatment in vivo and in vitro. Treatment of four sickle cell patients increased the percentage of circulating F reticulocytes. The frequencies of bone marrow or peripheral blood BFU-E or CFU-E-derived colonies and their fetal hemoglobin content were unaffected. In all cases, the number of erythroid cells/progenitor-derived colony increased. To explore further the effect of hydroxyurea on fetal hemoglobin production, we added 50 mumol/L hydroxyurea to cultures of peripheral blood BFU-E-derived erythroblasts on 1 of 9 days (day 5 through 13) to nine samples. These BFU-E were derived from the peripheral blood of normal donors, sickle trait donors, and sickle cell anemia patients and from the bone marrows of monkeys. This concentration of hydroxyurea was selected so that the frequency of BFU-E and their size was moderately decreased. Addition of hydroxyurea to these progenitor-derived erythroid cells had no effect on fetal hemoglobin content per cell. Neither did transient exposure of progenitors to hydroxyurea prior to culture in nontoxic concentrations (0 to 500 mumol/L) result in a significant increase in fetal hemoglobin content in progenitor-derived erythroblasts. These data suggest that hydroxyurea does not directly alter the HbF program expressed by progenitor-derived erythroid cells. Instead, it enhances hemoglobin F content secondarily, possibly by inducing alterations in erythropoiesis.

Anemia, Sickle Cell↗