BCR-ABL mutations in chronic myeloid leukemia

The advent of imatinib has been a major breakthrough in chronic myeloid leukemia (CML) treatment. A few patients treated with imatinib are either refractory to imatinib or eventually relapse. Resistance is frequently associated with mutations in the kinase domain of BCR-ABL. Over 100 point mutations coding for single amino acid substitutions in the BCR-ABL kinase domain have been isolated from CML patients resistant to imatinib treatment. Most reported mutants are rare, whereas 7 mutated residues comprise two-thirds of all mutations detected. BCR-ABL mutations affect amino acids involved in imatinib binding or in regulatory regions of the BCR-ABL kinase domain, resulting in decreased sensitivity to imatinib while retaining aberrant kinase activity. The early detection of BCR-ABL mutants during therapy may aid in risk stratification as well as molecularly based treatment decisions.     

A phase 2 study of MK-0457 in patients with BCR-ABL T315I mutant chronic myelogenous leukemia and philadelphia chromosome-positive acute lymphoblastic leukemia

Aurora kinase overexpression has been observed in patients with hematologic malignancies. MK-0457, a pan-aurora kinase inhibitor that also inhibits the ABL T315I mutant, was evaluated to treat patients with chronic myelogenous leukemia (CML) or Philadelphia chromosome (Ph+) acute lymphoblastic leukemia (ALL) with the T315I mutation. Adults with Ph+ chronic phase (CP)-, accelerated phase (AP)- or blast phase (BP)-CML, or ALL and documented BCR-ABL T315I mutation were treated with a 5-day continuous infusion of MK-0457 administered every 14 days at 40 mg/m²/h, 32 mg/m²/h or 24 mg/m²/h. Fifty-two patients (CP, n=15; AP, n=14; BP, n=11; Ph+ ALL, n=12) were treated. Overall, 8% of patients achieved major cytogenetic response; 6% achieved unconfirmed complete or partial response; 39% had no response. Two patients (CP CML) achieved complete hematologic response. No patients with advanced CML or Ph+ ALL achieved major hematologic response. The most common adverse event (AE) was neutropenia (50%). The most common grade 3/4 AEs were neutropenia (46%) and febrile neutropenia (35%). MK-0457 demonstrated minimal efficacy and only at higher, intolerable doses; lower doses were tolerated and no unexpected toxicities were observed. These data will assist in the development of future aurora kinase inhibitors and in the selection of appropriate target patient populations.     

Treatment of philadelphia chromosome-positive, accelerated-phase chronic myelogenous leukemia with imatinib mesylate.

PURPOSE: Imatinib mesylate, a specific Bcr-Abl tyrosine kinase inhibitor, has shown encouraging activity in chronic myelogenous leukemia (CML). EXPERIMENTAL DESIGN: We treated 237 patients (median age, 50 years; age range, 18-82 years) with Philadelphia chromosome (Ph)-positive accelerated-phase CML with oral imatinib mesylate at daily doses of 400 mg (26 patients) or 600 mg (211 patients) and evaluated response and survival characteristics in univariate and multivariate analyses. RESULTS: Among the 200 patients with accelerated-phase CML for whom follow-up was 3 months or more, rates of complete and partial hematological response were 80% and 10%. Cytogenetic responses were evident in 90 patients [45%; complete response in 47 patients (24%) and partial response (Ph 1-34%) in 21 patients (11%)]. The estimated 18-month survival rate was 73%. The estimated complete hematological response rate at 18 months was 68%; that for cytogenetic response was 82%. In multivariate analyses, a diagnosis-to-treatment interval of 3 years or more, splenomegaly, and peripheral blasts predicted poor major cytogenetic response; age >60 years, marrow basophilia, and clonal evolution predicted poor survival. The 600-mg drug dose was associated with better cytogenetic response and survival in univariate analysis (P < 0.01) but not in multivariate analysis. Landmark analysis showed that achieving a cytogenetic response at 3 months or a major cytogenetic response (Ph < 35%) at 6 months was associated with better long-term survival. Seven of 15 patients who were in a second chronic phase achieved major cytogenetic response. The incidence of severe nonhematological toxic effects was 23%; drug discontinuation for severe toxicity was needed in 3% of patients. CONCLUSIONS: Imatinib mesylate was active against Ph-positive, accelerated-phase CML, and the prognostic factors identified in this study could aid in tailoring treatment strategies to specific risk groups.     

Chronic myeloid leukemia: clinical impact of BCR-ABL1 mutations and other lesions associated with disease progression

The introduction of the tyrosine kinase inhibitors (TKIs) imatinib, dasatinib, and nilotinib has dramatically improved the treatment of chronic myeloid leukemia (CML). However, a minority of CML patients in chronic phase (CP) and a substantial proportion of patients in advanced phase are either initially refractory to TKIs or eventually develop resistance. Rates of resistance and relapse directly correlate with disease progression. The most frequently identified mechanism of acquired TKI resistance is BCR-ABL1 kinase domain (KD) mutations that impair TKI binding by disrupting the drug contact sites or causing conformational changes that make the contact sites inaccessible. The underlying mechanisms of disease progression are heterogeneous and only poorly understood. So far the most frequent and best characterized include genomic instability, loss of tumor-suppressor functions, and differentiation arrest. Clinical data indicate that both development of a BCR-ABL1 KD mutation during TKI treatment and/or disease progression are associated with a poorer outcome. Thus, therapeutic strategies are needed for the treatment or prevention of resistance and disease progression. They include, for example, TKI dose escalation, treatment interruption to stop selection of resistant cells, and allogeneic stem cell transplantation in eligible patients, as well as the use of novel TKIs with activity against resistant mutations and/or inhibition of alternative pathways.     

Measuring response to BCR-ABL inhibitors in chronic myeloid leukemia

In patients with chronic myeloid leukemia (CML), the hallmark Philadelphia chromosome is the marker of disease that can be detected by conventional metaphase cytogenetics, fluorescence in situ hybridization, or polymerase chain reaction. The current "gold standard" of treatment response is cytogenetic response. Cytogenetic response to imatinib is strongly associated with disease progression and survival. Various strategies aimed at improving cytogenetic response have been explored, such as escalation of imatinib and switching to the newer breakpoint cluster region/v-abl Abelson murine leukemia viral oncogene (BCR-ABL) inhibitors dasatinib and nilotinib. Data from recent randomized trials of dasatinib and nilotinib as first-line therapy of newly diagnosed chronic-phase CML suggest that these agents are more effective than imatinib in achieving 6-month and 12-month complete cytogenetic responses. However, it is still too early to know whether or not this early response will translate into a long-term survival advantage. In addition, more sensitive assays to detect residual disease also may be associated with improved long-term outcomes. The deepest measure of response-a complete molecular response-may help identify patients who can stop taking imatinib for the short term, although the long-term consequences of this strategy remain unknown.     

Approval summary: imatinib mesylate capsules for treatment of adult patients with newly diagnosed philadelphia chromosome-positive chronic myelogenous leukemia in chronic phase.

PURPOSE: The purpose is to describe the Food and Drug Administration (FDA) review and approval of imatinib (Gleevec; Novartis Pharmaceuticals, East Hanover, NJ) for treatment of adult patients with newly diagnosed Philadelphia chromosome-positive chronic myelogenous leukemia (CML) in chronic phase. EXPERIMENTAL DESIGN: The FDA reviewed data in electronic format from a randomized controlled clinical trial of 1106 adult patients with newly diagnosed Philadelphia chromosome-positive CML in chronic phase, comparing imatinib with the combination of IFN-alpha and cytarabine. RESULTS: Imatinib showed clinically and statistically significantly better results for time-to-progression to accelerated phase or blast crisis, progression-free survival, complete hematological response rate, and cytogenetic response rate. With a median follow-up of 14 months, a maximum follow-up of 19.5 months, and an expected median survival of 5-6 years on the IFN-alpha/cytarabine control arm, few of the expected progressions to accelerated or blast phase or deaths have occurred. Imatinib was also better tolerated. Edema, nausea, rigors, neutropenia, and headache were more frequent in women. Only 57% of the IFN-alpha target dose was administered, and only 68% of patients received any cytarabine. However, this does not appear to adequately explain the superiority of imatinib observed in this trial. Results of a population pharmacokinetic study in a subgroup of 371 patients and a separate rifampin-imatinib drug-drug interaction study in healthy volunteers are presented. CONCLUSIONS: On December 20, 2002, imatinib was granted accelerated approval under subpart H, rather than regular approval. Follow-up is short compared with the natural history of chronic phase CML or more mature results with established therapies such as IFN-alpha or transplantation. If imatinib should stop working after 1.5-2 years, the results could be importantly different from the present analysis. As a Phase IV postmarketing commitment, the applicant has agreed to provide follow-up reports on this imatinib study annually for the next 6 years.     

Interphase FISH for follow-up of Philadelphia chromosome-positive chronic myeloid leukemia treatment

BACKGROUND: Several attempts have been made to determine whether interphase fluorescence in situ hybridization (I-FISH) on bone marrow or peripheral blood specimens is a good alternative to conventional cytogenetics (CC) in calculating the residual proportion of Philadelphia (Ph) chromosome-positive cells during treatment follow-up of patients with chronic myeloid leukemia. MATERIALS AND METHODS: Nineteen patients were selected for I-FISH follow-up compared to CC. All samples were also classified into 4 groups according to the percentage of residual Ph chromosome-positive metaphases analyzed in CC. I-FISH was performed using the LSI bcr/abl dual ES color probe (Vysis). RESULTS: A high correlation was observed between the frequency of Ph chromosome-positive cells, assessed by CC and I-FISH (p<0.001). A high correlation was found between CC and I-FISH for 12 patients, but not for the remaining 7. Applying the same classification for I-FISH did not show a good relationship between the two techniques (p<0.001). CONCLUSION: Dual color I-FISH is a reliable method to monitor the size of the Ph chromosome-positive clone in bone marrow of treated CML patients. However, it has to be complementary to conventional cytogenetics because it cannot detect the emergence of other chromosomal abnormalities in Ph chromosome-positive or -negative cells.     

Conventional and fluorescence in situ hybridization analysis of three-way complex BCR-ABL rearrangement in a chronic myeloid leukemia patient

Chromosomal analysis was carried out in bone marrow sample of an 11-year-old girl suspected of myeloproliferative disorder. Conventional G-banding study detected a complex three-way translocation involving 7, 9 and 22, which has resulted in the formation of a variant Philadelphia chromosome causing rearrangement of abl and bcr genes in 87% cells. Fluorescence in situ hybridization (FISH) confirmed the fusion of bcr-abl oncogene. Thus the bone marrow karyotype was observed as 46,XX (13%)/46,XX,t(7;9;22)(q11;q34;q11) (87%). Hyperdiploidy was present in two cells. In this study, both conventional cytogenetic and FISH diagnosis proved to be significant to identify the variant nature of the Philadelphia chromosome and hyperdiploid condition for introduction of a suitable treatment regimen and estimation of life expectancy of the young girl.     

Essential role for telomerase in chronic myeloid leukemia induced by BCR-ABL in mice

The telomerase protein is constitutively activated in malignant cells from many patients with cancer, including the chronic myeloid leukemia (CML), but whether telomerase is essential for the pathogenesis of this disease is not known. Here, we used telomerase deficient mice to determine the requirement for telomerase in CML induced by BCR-ABL in mouse models of CML. Loss of one telomerase allele or complete deletion of telomerase prevented the development of leukemia induced by BCR-ABL. However, BCR-ABL was expressed and active in telomerase heterozygous and null leukemic hematopoietic stem cells. These results demonstrate that telomerase is essential for oncogene-induced reprogramming of hematopoietic stem cells in CML development and validate telomerase and the genes it regulates as targets for therapy in CML.     

The prognosis for patients with chronic myeloid leukemia who have clonal cytogenetic abnormalities in philadelphia chromosome-negative cells

BACKGROUND: Clonal cytogenetic abnormalities (CCA) were detected in Philadelphia chromosome (Ph)-negative cells in some patients with chronic myeloid leukemia (CML) who attained a cytogenetic response to imatinib mesylate. In some patients, CCA/Ph-negative status was associated with myelodysplasia or acute myeloid leukemia. The objective of the current study was to determine the prognostic impact of CCA/Ph-negative cells. METHODS: The authors compared the pretherapeutic risk factors (Kruskall-Wallis test), exposure to cytotoxic drugs (chi-square test), and overall and progression-free survival (Kaplan-Meyer and logistic regression analysis, respectively) of 515 patients with mostly chronic-phase CML who were treated with imatinib mesylate after failure of interferon-alpha according to whether they attained a major cytogenetic response (MCR) (n = 324 patients), an MCR with CCA/Ph-negative status (n = 30 patients), or no MCR (n = 161 patients). RESULTS: CCA/Ph-negative status most frequently involved chromosomes Y, 8, and 7. No significant differences in pretherapeutic risk factors were detected between patients who attained an MCR with and without CCA/Ph-negative cells, except that exposure to alkylating agents was more frequent in patients with CCA/Ph-negative cells, and overall and progression-free survival were identical. With a median follow-up of 51 months, only 2 patients developed myelodysplastic syndromes (MDS). CONCLUSIONS: The overall prognosis for patients who had CML with CCA/Ph-negative status was good and was driven by the CML response to imatinib mesylate. Isolated CCA/Ph-negative cells in the absence of morphologic evidence of MDS do not justify a change in therapy.