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Michael E O'Dwyer

Publications and source records attributed to Michael E O'Dwyer.

11 recordsLinked to original sources
PubMed2004

Clonal evolution in chronic myelogenous leukemia.

Clonal evolution (CE) may be a marker of disease progression in chronic myelogenous leukemia (CML) and is thought to reflect the genetic instability of the highly proliferative CML progenitors. The frequency of CE increases with advancing stage, rising from 30%in accelerated phase and up to 80% in blast crisis. Given its association with disease progression, CE is considered a feature that defines accelerated-phase CML; however, not all studies have demonstrated a uniformly poor outcome for patients with CE. Chromosomal abnormalities in Ph chromosome negative metaphases increasingly have been recognized in patients treated with imatinib. The true incidence of this phenomenon is not clear but appears to occur in 2% to 17% of imatinib-treated patients. Regardless of the precise mechanism and the long-term clinical implications, the findings described in this article underscore the importance of routine cytogenetic analysis for patients treated with imatinib. The continued study of these phenomena will help us to understand better the pathogenesis of CML and improve the long-term treatment of patients with CML.

Antineoplastic Agents↗
PubMed2003

Clonal evolution and lack of cytogenetic response are adverse prognostic factors for hematologic relapse of chronic phase CML patients treated with imatinib mesylate.

We followed 141 patients treated with imatinib mesylate (> 300 mg) for chronicphase chronic myelogenous leukemia (CML) following failure of treatment with interferon. During 12 months from the start of imatinib mesylate treatment, 96.5% achieved a complete hematologic response, 47.0% achieved a major cytogenetic response, and 32.4% achieved a complete cytogenetic response. The proportion of patients with hematologic relapse was 10.9% at 12 months and 14.6% at 18 months. In a univariate Cox regression analysis, the only pretreatment characteristics that correlated with an increased risk of hematologic relapse were hemoglobin level less than 120 g/L (12 g/dL) (P =.02), increased bands in the peripheral blood (P =.01), and clonal evolution (P <.0001). In a multivariate analysis, an elevated platelet count (P =.03) and clonal evolution (P <.0001) were the only significant factors for hematologic relapse. During treatment, the absence of a major cytogenetic response within the first 6 months also significantly correlated with relapse (P =.03). Notably, patients failing to achieve a major cytogenetic response by 6 months had a significantly higher rate of hematologic relapse (27%) compared with those who achieved a major cytogenetic response by 6 months (3%), and patients with clonal evolution had a significantly higher risk of hematologic relapse (50%) than those without clonal evolution (9%).

Adult↗
PubMed2003

Acquired FANCA dysfunction and cytogenetic instability in adult acute myelogenous leukemia.

Myelodysplastic and leukemic stem cell clones that evolve in children and adults with Fanconi anemia universally bear complex cytogenetic abnormalities. The abnormalities are generally recurring deletions or chromosomal loss and involve precisely the same chromosomes with the same frequency as has been described in marrow cells from patients with secondary acute leukemia induced by alkylating agents. Reasoning that acquired Fanconi anemia protein dysfunction might contribute to cytogenetic instability in secondary acute myelogenous leukemia (AML) cells, we analyzed leukemic cells bearing characteristic complex cytogenetic defects obtained from a 68-year-old man whose lymphoblasts showed no evidence of Fanconi anemia. Unlike the lymphoblasts, this myeloid leukemia cell line (UoC-M1) was hypersensitive to mitomycin-C (MMC) and diepoxybutane (DEB) and exhibited a marked decrease in nuclear FANCA, FANCG, and FANCD2-L. Retroviral transduction of FANCA significantly reduced MMC sensitivity but FANCF, FANCG, and FANCC did not. Overexpression of FANCA restored levels of both FANCA and FANCG, whereas overexpression of FANCG or FANCC did not restore FANCA levels. The molecular mass of cytoplasmic FANCA, FANCG, FANCC, and nuclear FANCD2 were normal. All exons of FANCA and FANCG were sequenced, and no mutations were found. We conclude that perturbations of as yet unidentified factors that govern the binding activity or intracellular localization of FANCA may promote cytogenetic instability and clonal progression in patients with AML who do not have Fanconi anemia.

Aged↗
PubMed2003

STI571 as a targeted therapy for CML.

Chronic myelogenous leukemia (CML) is a clonal hematopoietic stem cell disorder that progresses through distinct phases as the malignant clone progressively loses the capacity for terminal differentiation. It is characterized by the (9;22) translocation and resultant production of the Bcr-Abl tyrosine kinase. Bcr-Abl functions as a constitutively activated tyrosine kinase, and this kinase activity is absolutely required for the transforming function of the Bcr-Abl protein. In preclinical studies, STI571 (Gleevec, imatinib mesylate), a Bcr-Abl tyrosine kinase inhibitor, specifically inhibited the proliferation of Bcr-Abl-expressing cells in vitro and in vivo. STI571 has shown remarkable results in all phases of CML. Although responses are seen in all phases of the disease, durable responses are most common in earlier stage patients. Thus, STI571 has emerged as a paradigm for gene product targeted therapy, offering expanded treatment options for patients with CML.

Antineoplastic Agents↗
PubMed2003

Chronic myelogenous leukemia.

Within the past few years, the introduction of imatinib mesylate (imatinib) has profoundly changed the management of patients with chronic myelogenous leukemia. This review article addresses the recent advances in the treatment of chronic myelogenous leukemia--in particular, maturing data on the use of imatinib in different phases of the disease; the optimal therapy of newly diagnosed patients; the emergence of resistance to imatinib and potential strategies to overcome this problem; and finally, the place of stem cell transplantation in current treatment algorithms.

Antineoplastic Agents↗
PubMed2002

The impact of clonal evolution on response to imatinib mesylate (STI571) in accelerated phase CML.

In chronic myelogenous leukemia (CML), the development of chromosomal abnormalities in addition to the Philadelphia chromosome (clonal evolution) is considered by many to be a feature of accelerated phase (AP). Imatinib mesylate (STI571), a selective inhibitor of the Bcr-Abl tyrosine kinase, has significant activity in AP CML. As clonal evolution could allow Bcr-Abl independent proliferation, we analyzed its impact on the outcome of 71 AP patients treated with 600 mg of imatinib mesylate. Fifteen patients had clonal evolution alone (AP-CE), 32 had AP features but no evidence of clonal evolution (HEM-AP), and 24 had AP features plus clonal evolution (HEM-AP + CE). Of the AP-CE patients, 73% had a major cytogenetic response, compared with 31% of the HEM-AP patients (P =.043) and 12.5% of the HEM-AP + CE patients (P =.007). Complete cytogenetic responses were seen in 60% of AP-CE patients, compared with 31% of HEM-AP patients (P =.19) and 8% of HEM-AP + CE patients (P <.001). With mean follow-up of 11.2 months, 35% of all patients failed treatment. The lowest estimated rate of treatment failure at 1 year, 0%, was seen in AP-CE patients, compared with rates of 31% for HEM-AP patients and 69% for HEM-AP + CE patients (P =.0004). After 1 year, 100% of AP-CE patients were still alive, compared with 85% of HEM-AP patients and 67.5% of HEM-AP + CE patients (P =.01). In conclusion, in patients with clonal evolution as the sole criterion of disease acceleration, good responses to imatinib are still possible. Once patients have other signs of acceleration, clonal evolution predicts lower response rates and a shorter time to treatment failure.

Adult↗
PubMed2002

Hematopathologic and cytogenetic findings in imatinib mesylate-treated chronic myelogenous leukemia patients: 14 months' experience.

Imatinib mesylate, an Abl kinase inhibitor, produces sustained complete hematologic responses (CHRs) in chronic myelogenous leukemia (CML) patients, but the sequence and timing of morphologic and cytogenetic changes in CML patients during prolonged imatinib mesylate treatment has not been described. In this report, we document sequential hematologic and bone marrow findings in 19 interferon-refractory/interferon-intolerant chronic phase CML patients on imatinib mesylate for at least 14 months. Patients treated at an effective oral dose (300 to 600 mg per day) were followed with peripheral blood (PB) counts, marrow examination, and cytogenetic studies at 0, 2, 5, 8, 11, and 14 months. By 2 months, 17 of 19 patients achieved CHR; 1 reached CHR by 5 months, and 1 at 11 months. Five of 19 patients developed cytopenias requiring treatment interruption and/or dose reduction, but all were able to continue in CHR on study. In contrast to interferon-alfa treatment, imatinib mesylate-treated CML patients achieved not only CHR but complete morphologic marrow response. Normalization of marrow lagged behind PB response; however, by 8 months, all marrows showed normal or reduced cellularity without morphologic evidence of CML. Eighteen of 19 patients continued in CHR and morphologic marrow remission at 14 months; 1 patient relapsed with chronic phase CML. Although hematologic and marrow responses were uniform, cytogenetic responses were variable. Complete cytogenetic responses occurred in 6 patients, with 4 also in remission by fluorescent in situ hybridization and/or reverse-transcription-polymerase chain reaction. Six of 19 had partial and 7 of 19 no cytogenetic response. Several patients acquired additional clonal cytogenetic abnormalities during therapy, a finding with significant implications for prognosis and laboratory monitoring in imatinib mesylate-treated CML patients.

Adult↗
PubMed2002

In vitro studies of the combination of imatinib mesylate (Gleevec) and arsenic trioxide (Trisenox) in chronic myelogenous leukemia.

OBJECTIVE: The aim of this study was the preclinical evaluation of imatinib mesylate (Gleevec, formerly STI571) in conjunction with arsenic trioxide (As2O3, Trisenox) for the treatment of chronic myelogenous leukemia (CML). MATERIALS AND METHODS: Tetrazolium-based cell line proliferation assays (MTT assays) were performed to determine the cytotoxicity of As2O3 alone and in combination with imatinib. Cell lines tested in this study were Bcr-Abl-expressing cells (K562, MO7p210, 32Dp210) and parental cells (MO7e, 32D). Isobologram analysis was performed manually and using the median effect method. In vitro cytotoxicity also was determined in colony-forming assays using CML patient cells. Western blot analysis was performed to detect Bcr-Abl protein levels in K562 cells exposed to As2O3 at graded concentrations. Bcr-Abl protein level kinetics were correlated with cell viability (trypan blue count) and activated caspase-3 detected by flow cytometry. RESULTS: We show additive to synergistic cytotoxicity in Bcr-Abl+ cell lines depending on inhibitory concentrations and cell type. Results obtained by colony-forming assays confirmed the findings in cell line proliferation assays. Flow cytometric detection of activated caspase-3 revealed synergistic activity in K562 cells. Treatment of K562 cells with As2O3 alone led to down-regulation of Bcr-Abl protein within 24 hours, even at low doses. The decline of Bcr-Abl preceded activation of caspase-3 and the loss of viable cells. CONCLUSIONS: Favorable cytotoxicity and proapoptotic activity of imatinib in conjunction with As2O3 and specific down-regulation of Bcr-Abl protein levels by As2O3 in K562 cells indicate that As2O3 in combination with imatinib might be useful for circumventing resistance to imatinib monotherapy.

Antineoplastic Agents↗
PubMed2002

Recent advances in Philadelphia chromosome-positive malignancies: the potential role of arsenic trioxide.

Chronic myelogenous leukemia (CML) is characterized by the presence of the Bcr-Abl fusion gene, which encodes a constitutively active tyrosine kinase that has been strongly implicated as the sole oncogenic abnormality in early-stage CML. Treatment with the specific tyrosine kinase inhibitor imatinib mesylate has achieved excellent results in CML, at all stages of the disease. However, limitations to the successful use of imatinib mesylate as a single agent include the problem of resistance, seen chiefly in patients with advanced-phase disease. This review summarizes the clinical results to date with imatinib mesylate and briefly discusses the problem of resistance before describing potential strategies, including the use of combination therapy. In particular, the rationale for combination therapy with arsenic trioxide will be examined.

Antineoplastic Agents↗
PubMed2002

Recent advancements in the treatment of chronic myelogenous leukemia.

Chronic myelogenous leukemia (CML) is a clonal hematopoetic stem cell disorder characterized by the Philadelphia chromosome and resultant production of the constitutively activated Bcr-Abl tyrosine kinase. Characterized clinically by marked myeloid proliferation, it invariably terminates in an acute leukemia. Conventional therapeutic options include interferon-based regimens and stem cell transplantation, with stem cell transplantation being the only curative therapy. Through rational drug development, STI571, a Bcr-Abl tyrosine kinase inhibitor, has emerged as a paradigm for gene product targeted therapy, offering new hope for expanded treatment options for patients with CML.

Antineoplastic Agents↗