Imatinib induces hematologic and cytogenetic responses in patients with chronic myelogenous leukemia in myeloid blast crisis: results of a phase II study

Imatinib: the first 3 years

Imatinib (Glivec, formerly STI571, Novartis Pharma AG, Basel, Switzerland) potently inhibits several protein tyrosine kinases, including Bcr-Abl, Kit, and the platelet-derived growth factor receptor. Phase I and II studies demonstrated that orally administered imatinib is highly effective and well tolerated in all phases of chronic myeloid leukemia (CML) at doses ranging from 400 to 600 mg. Importantly, preliminary evidence suggests that patients with advanced CML achieving hematologic or major cytogenetic responses to imatinib may have longer survival than those without such responses, whereas chronic phase patients who respond to treatment may have longer times to disease progression. Ongoing and planned studies are focused on optimizing CML treatment with imatinib, evaluating imatinib-based combination therapy, defining additional therapeutic targets and exploring the use of imatinib in children. In particular, results from several combination phase I studies are expected shortly, including an evaluation of combination imatinib-interferon-alpha therapy and imatinib-cytarabine in chronic phase CML, and a phase I study of single-agent imatinib in children with Philadelphia chromosome-positive leukemia is ongoing. A large phase III trial comparing imatinib with standard inferferon alfa plus cytarabine in first-line CML treatment is also ongoing.

Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia

Through sequencing analysis of blood or bone marrow samples from patients with chronic myeloid leukemia, we identified BCR-ABL kinase domain mutations in 29 of 32 patients whose disease relapsed after an initial response to the tyrosine kinase inhibitor imatinib. Fifteen different amino acid substitutions affecting 13 residues in the kinase domain were found. Mutations fell into two groups-those that alter amino acids that directly contact imatinib and those postulated to prevent BCR-ABL from achieving the inactive conformational state required for imatinib binding. Distinct mutations conferred varying degrees of imatinib resistance. Mutations detected in a subset of patients with stable chronic phase disease correlated with subsequent disease progression. Multiple independent mutant clones were detected in a subset of relapsed cases. Our data support a clonal selection model of preexisting BCR-ABL mutations that confer imatinib resistance.

Chronic myelogenous leukemia

The treatment recommendations for chronic myelogenous leukemia (CML) are evolving rapidly. In the past year, pegylated interferon and STI571 (Gleevec, imatinib mesylate), a Bcr-Abl tyrosine kinase inhibitor, have become commercially available and non-myeloablative stem cell transplants continue to be refined. Clinicians and patients face a bewildering array of treatment options for CML. In this article Dr. Sawyer reviews the clinical results with STI571 and ongoing investigations into mechanisms of resistance to STI571. Given the newness of STI571, a practical overview on the administration of STI571 is presented by Drs. Druker and Ford, focusing on aspects such as optimal dose, management of common side effects, and potential drug interactions. The most recent data on interferon-based regimens are reviewed by Dr. Baccarani in the third section. In the last section Dr. Goldman presents recent results of allogeneic stem cell transplants, including the reduced intensity conditioning regimens. Lastly, the proposed place of each of these treatments in the management of CML patients is addressed to assist in deciding amongst treatment options for CML patients.

Insights from pre-clinical studies for new combination treatment regimens with the Bcr-Abl kinase inhibitor imatinib mesylate (Gleevec/Glivec) in chronic myelogenous leukemia: a translational perspective

Clinical phase I/II studies with the Abl kinase inhibitor imatinib mesylate (Gleevec/Glivec, formerly STI571) for the treatment for chronic myelogenous leukemia (CML) demonstrated the safety and the remarkable efficacy of this molecularly targeted agent. However, a significant proportion of patients treated in the chronic phase of the disease after having failed interferon alpha (IFN) remain predominantly Philadelphia chromosome positive (Ph(+)), suggesting a risk of later relapses. Furthermore, results in blast crisis patients revealed a high frequency of relapses or resistance to imatinib. To circumvent resistance, improve response rates, or prolong survival, pre-clinical evaluations of combinations of imatinib with other agents have been pursued. Some of these have already been translated into clinical studies. Here, we first summarize evidence from pre-clinical studies on new combination regimens with imatinib in the treatment of CML. Second, we analyze preliminary clinical data of ongoing combination studies. Finally, we provide a summary of approaches that use novel antileukemic agents with molecularly characterized modes of action.

Safety and efficacy of STI-571 (imatinib mesylate) in patients with bcr/abl-positive chronic myelogenous leukemia (CML) after autologous peripheral blood stem cell transplantation (PBSCT)

We examined safety and efficacy of STI-571 in 24 bcr/abl-positive patients with CML post PBSCT. At start of STI-571 therapy, nine patients presented in blast crisis (BC) or in accelerated phase (AP), and 15 in chronic phase (CP). Patients were evaluated for hematologic, cytogenetic and molecular response, survival and toxicity. In general, STI-571 was well tolerated in this heavily pretreated group of patients with a non-hematologic and hematologic toxicity profile similar to that observed in a previous phase I trial at comparable doses. Five of nine patients with CML in transformation (AP, BC) were evaluable for hematologic response. Two of five patients had transient reductions in WBC and blasts, and three patients achieved a sustained hematologic response (>4 weeks). Cytogenetic analysis in these patients revealed numerical and/or structural responses. In CML chronic phase, STI-571 induced complete hematologic responses in all patients and major cytogenetic responses in 61% of patients with a complete cytogenetic response rate of 46%. This report indicates that STI-571 is a safe and effective drug in heavily pretreated patients. No apparent additional side-effects were noted in this patient cohort. The high rate of complete hematologic and complete cytogenetic responses in CP patients is remarkable, as intensive treatment approaches plus IFN-alpha failed to be efficient in achieving long-term stabilization of CML in this patient cohort.

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.

Glivec (STI571, imatinib), a rationally developed, targeted anticancer drug

In the early 1980s, it became apparent that the work of pioneers such as Robert Weinberg, Mariano Barbacid and many others in identifying cancer-causing genes in humans was opening the door to a new era in anticancer research. Motivated by this, and by dissatisfaction with the limited efficacy and tolerability of available anticancer modalities, a drug discovery programme was initiated with the aim of rationally developing targeted anticancer therapies. Here, we describe how this programme led to the discovery and continuing development of Glivec (Gleevec in the United States), the first selective tyrosine-kinase inhibitor to be approved for the treatment of a cancer.

Finding the next Gleevec: FLT3 targeted kinase inhibitor therapy for acute myeloid leukemia

Activating mutations in the FLT3 receptor tyrosine kinase occur in 30% of patients with acute myeloid leukemia. Small molecule FLT3 kinase inhibitors show selective antitumor activity in preclinical models. Clinical studies are underway.