Combination therapy with imatinib mesylate (STI571): synopsis of in vitro studies

Treatment and monitoring of Philadelphia chromosome-positive leukemia patients: recent advances and remaining challenges

The Philadelphia (Ph) chromosome, resulting from the t(9;22)(q34;q11) translocation, can be found in chronic myeloid leukemia (CML) as well as in a subset of acute lymphoblastic leukemias (ALL). The deregulated BCR-ABL1 tyrosine kinase encoded by the fusion gene resulting from the translocation is considered the pathogenetic driver and can be therapeutically targeted. In both CML and Ph-positive (Ph+) ALL, tyrosine kinase inhibitors (TKIs) have significantly improved outcomes. In the TKI era, testing for BCR-ABL1 transcript levels by real-time quantitative polymerase chain reaction (RQ-PCR) has become the gold standard to monitor patient response, anticipate relapse, and guide therapeutic decisions. In CML, key molecular response milestones have been defined that draw the ideal trajectory towards optimal long-term outcomes. Treatment discontinuation (treatment-free remission, TFR) has proven feasible in a proportion of patients, and clinical efforts are now focused on how to increase this proportion and how to best select TFR candidates. In Ph+ ALL, results of trials with second- and third-generation TKIs are challenging the role of intensive chemotherapy and even that of allogeneic stem cell transplantation. Additional weapons are offered by the recently introduced monoclonal antibodies. In patients harboring mutations in the BCR-ABL1 kinase domain, prompt therapeutic reassessment and individualization based on mutation status are important to regain response and prevent disease progression. Next-generation sequencing is likely to become a precious tool for mutation testing because of the greater sensitivity and the possibility to discriminate between compound and polyclonal mutations. In this review, we discuss the latest advances in treatment and monitoring of CML and Ph+ ALL and the issues that still need to be addressed to make the best use of the therapeutic armamentarium and molecular testing technologies currently at our disposal.

Combined cyto/genotoxic activity of a selected antineoplastic drug mixture in human circulating blood cells

Antineoplastic drugs are highly cytotoxic chemotherapeutic agents that can often interfere directly or indirectly with the cell's genome. In an environmental or medical setting simultaneous exposure may occur. Such multiple exposures may pose a higher risk than it could be assumed from the studies evaluating the effect of a single substance. Therefore, in the present study we tested the combined cyto/genotoxicity of a mixture of selected antineoplastic drugs with different mechanisms of action (5-fluorouracil, etoposide, and imatinib mesylate) towards human lymphocytes in vitro. The results suggest that the selected antineoplastic drug mixture is potentially cyto/genotoxic and that it can induce cell and genome damage even at low concentrations. Moreover, the changes in the measured oxidative stress parameters suggest the participation of reactive oxygen species in the cyto/genotoxicity of the selected mixture. The obtained results indicate not only that such mixtures may pose a risk to cell and genome integrity, but also that single compound toxicity data are not sufficient for the predicting toxicity in a complex environment. Altogether, the results emphasise the need for further toxicological screening of antineoplastic drug mixtures, especially at low environmentally relevant concentrations, as to avoid any possible adverse effects on the environment and human health.

Prediction and assessment of ecogenotoxicity of antineoplastic drugs in binary mixtures

The combined genotoxic effects of four anticancer drugs (5-fluorouracil [5-FU], cisplatin [CDDP], etoposide [ET], and imatinib mesylate [IM]) were studied testing their binary mixtures in two crustaceans that are part of the freshwater food chain, namely Daphnia magna and Ceriodaphnia dubia. Genotoxicity was assessed using the in vivo comet assay. Assessment was based on two distinct effect sizes determined from dose-response experiments. Doses for single and combined exposures expected to result in these effect sizes were computed based on Bliss independence as reference model. Statistical comparison by analysis of variance of single and combined toxicities allowed accepting or rejecting the independency hypothesis. The results obtained for D. magna showed independent action for all mixtures except for IM+5-FU that showed an antagonistic interaction. In C. dubia, most mixtures had antagonist interactions except IM+5-FU and IM+CDDP that showed Bliss independence. Despite the antagonistic interactions, our results demonstrated that combinations of anticancer drugs could be of environmental concern because effects occur at very low concentrations that are in the range of concentrations encountered in aquatic systems.

Low serum vitamin D levels are associated with shorter survival after first-line azacitidine treatment in patients with myelodysplastic syndrome and secondary oligoblastic acute myeloid leukemia

BACKGROUND & AIMS

Azacitidine (AZA) therapy has become the recommended first-line treatment for patients with high-risk myelodysplastic syndromes (MDS) and oligoblastic (<30% bone marrow blasts) acute myeloid leukemia (AML). However, improvement of the efficacy of AZA treatment remains a challenge. We retrospectively tested the hypothesis that VitD levels (25-hydroxyvitamin D3) prior to start of first-line AZA therapy are predictive of overall survival (OS) in patients diagnosed with MDS and secondary oligoblastic AML. Furthermore, the antiproliferative effects of AZA in combination with 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3 were investigated in vitro.

METHODS

A total of 58 patients treated at our center between 2006 and 2014 were analyzed. Serum levels of VitD were quantified using a standard, commercially available 25-hydroxyvitamin D3 chemiluminescent immunoassay. Effects on cell proliferation were assessed using tetrazolium-based MTT assays.

RESULTS

Median serum VitD level prior to AZA treatment was 32.8 nM (range 11.0-101.5 nM). Patient, disease and treatment characteristics did not differ significantly between the low (≤32.8 nM; n = 29) and high (>32.8 nM; n = 29) VitD group. Estimated probability of 2-year OS in the low versus high VitD group was 14% versus 40% (P < 0.05). In multivariable analysis with OS as endpoint, adverse cytogenetics (HR 2.66, P = 0.03) and VitD (per 10 nM decrease, HR 1.68, P = 0.02) were independent predictors of worse survival. In-vitro treatment of myeloid cell lines with AZA in combination with VitD produced synergistic and additive antiproliferative effects. Addition of nanomolar VitD concentrations to AZA resulted in potentiation of AZA activity. Conversely, combination with the VitD antagonist TEI-9647 resulted in inhibition of AZA activity.

CONCLUSIONS

Our study suggests that higher VitD levels were associated with a survival advantage following first-line AZA therapy. Enhanced cytotoxic effects upon combination treatment may contribute to the observed clinical effects. VitD repletion/supplementation during AZA treatment should be explored.

In vitro testing of drug combinations employing nilotinib and alkylating agents with regard to pretransplant conditioning treatment of advanced-phase chronic myeloid leukemia

PURPOSE

The prognosis of patients with advanced-phase chronic myeloid leukemia (CML) remains dismal despite the availability of targeted therapies and allogeneic stem cell transplantation (allo-SCT). Increasing the antileukemic efficacy of the pretransplant conditioning regimen may be a strategy to increase remission rates and duration. We therefore investigated the antiproliferative effects of nilotinib in combination with drugs that are usually used for conditioning: the alkylating agents mafosfamide, treosulfan, and busulfan.

METHODS

Drug combinations were tested in vitro in different imatinib-sensitive and imatinib-resistant BCR-ABL-positive cell lines. A tetrazolium-based MTT assay was used for the assessment and quantification of growth inhibition after exposure to alkylating agents alone or to combinations with nilotinib. Drug interaction was analyzed using the median-effect method of Chou and Talalay, and combination index (CI) values were calculated according to the classic isobologram equation.

RESULTS

Treatment of imatinib-sensitive, BCR-ABL-positive K562 and LAMA84 cells with nilotinib in combination with mafosfamide, treosulfan, or busulfan resulted in synergistic (CI < 1), additive (CI ~ 1), and predominantly antagonistic (CI > 1) effects, respectively. In imatinib-resistant K562-R and LAMA84-R cells, all applied drug combinations were synergistic (CI < 1) at higher growth inhibition levels.

CONCLUSIONS

Our in vitro data warrant further investigation and may provide the basis for nilotinib-supplemented conditioning regimens for allo-SCT in advanced-phase CML.

Cryptotanshinone acts synergistically with imatinib to induce apoptosis of human chronic myeloid leukemia cells

Imatinib resistance has emerged as a significant clinical problem in chronic myeloid leukemia (CML) treatment. In this study, we investigated the effect and mechanism of combination treatment with imatinib and cryptotanshinone (CPT) in CML cells. Cotreatment with imatinib and CPT showed a significant synergistic killing effect in both imatinib sensitive and resistant CML cell lines, as well as primary CML cells. Furthermore, combination treatment induced apoptosis significantly, as indicated by increases in apoptotic cell fraction and activities of proapoptotic proteins. Subsequent studies revealed that CPT significantly inhibited Bcr/Abl protein expression, as well as phosphorylation expression levels of signal transducer and activator of transcription 3 (STAT3), mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E (eIF4E), which are critical mediators of Bcr/Abl transformation. Furthermore, CPT in combination with imatinib dramatically decreased the activity of the Bcr/Abl pathway in both K562 and K562-R cells. Our results demonstrated that CPT increased imatinib-induced apoptosis in a Bcr/Abl dependent manner, suggesting a novel strategy for the treatment of CML.

Current and future management of Ph/BCR-ABL positive ALL

Following the introduction of targeted therapy with tyrosine kinase inhibitors (TKI) at the beginning of the past decade, the outcome of patients with Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) has dramatically improved. Presently, the use of refined programs with first/second generation TKI's and chemotherapy together with allogeneic stem cell transplantation allow up to 50% of all patients to be cured. Further progress is expected with the new TKI ponatinib, overcoming resistance caused by T315I point mutation, other targeted therapies, autologous transplantation in molecularly negative patients, therapeutic monoclonal antibodies like inotuzumab ozogamicin and blinatumomab, and chimeric antigen receptor-modified T cells. Ph+ ALL could become curable in the near future even without allogeneic stem cell transplantation, minimizing the risk of therapy-related death and improving greatly the quality of patients' life.

Chemotherapy-phased imatinib pulses improve long-term outcome of adult patients with Philadelphia chromosome-positive acute lymphoblastic leukemia: Northern Italy Leukemia Group protocol 09/00

PURPOSE

Short imatinib pulses were added to chemotherapy to improve the long-term survival of adult patients with Philadelphia chromosome (Ph) -positive acute lymphoblastic leukemia (ALL), to optimize complete remission (CR) and stem-cell transplantation (SCT) rates.

PATIENTS AND METHODS

Of 94 total patients (age range, 19 to 66 years), 35 represented the control cohort (ie, imatinib-negative [IM-negative] group), and 59 received imatinib 600 mg/d orally for 7 consecutive days (ie, imatinib-positive [IM-positive] group), starting from day 15 of chemotherapy course 1 and from 3 days before chemotherapy during courses 2 to 8. Patients in CR were eligible for allogeneic SCT or, alternatively, for high-dose therapy with autologous SCT followed by long-term maintenance with intermittent imatinib.

RESULTS

CR and SCT rates were greater in the IM-positive group (CR: 92% v 80.5%; P = .08; allogeneic SCT: 63% v 39%; P = .041). At a median observation time of 5 years (range, 0.6 to 9.2 years), 22 patients in the IM-positive group versus five patients in the IM-negative group were alive in first CR (P = .037). Patients in the IM-positive group had significantly greater overall and disease-free survival probabilities (overall: 0.38 v 0.23; P = .009; disease free: 0.39 v 0.25; P = .044) and a lower incidence of relapse (P = .005). SCT-related mortality was 28% (ie, 15 of 54 patients), and postgraft survival probability was 0.46 overall.

CONCLUSION

This imatinib-based protocol improved long-term outcome of adult patients with Ph-positive ALL. With SCT, post-transplantation mortality and relapse remain the major hindrance to additional therapeutic improvement. Additional intensification of imatinib therapy should warrant a better molecular response and clinical outcome, both in patients selected for SCT and in those unable to undergo this procedure.

The Influence of Imatinib Mesylate (STI571) used alone or in Combination with Purine Nucleoside Analogues on the Normal and Chronic Myelogenous Leukaemia Progenitor CellsIn Vitro

Imatinib mesylate (STI571, Glivec), a signal transduction inhibitor used as a single agent demonstrates significant activity in patients with chronic myelogenous leukaemia (CML). Nevertheless, the interaction between STI571 and other antileukaemic drugs such as hydroxyurea, interferon alpha or cytarabine have also been investigated in order to further improve its effectiveness. In this study we have tried to answer the question if the combination of STI571 with purine nucleoside analogues (PNAs)- cladribine (2-CdA) and fludarabine (F-ara-A) intensifies the antiproliferative effect on granulocyte-macrophage progenitor cells (CFU-GM) from patients with CML as well as from normal persons. Our studies were based on the method of semisolid CFU-GM cultures in vitro. We added STI571 or PNAs singly to the culture, each of the drugs at three concentrations, as well as in combinations of the concentrations used. We showed that STI571 (0.5, 1.0 and 2.0 microM) used alone inhibited the colony growth of CML CFU-GM, as compared to CFU-GM derived from normal donors (p = 0.03; p = 0.0004; p = 0.0001). We also observed that STI571 used together with 2-CdA (5,10 and 20 microM) or F-ara-A (0.2, 0.4 and 0.8 microM) at all the combinations significantly inhibited the colony growth of CML CFU-GM, as compared either to the control or to STI571 used alone (p < 0.05). In addition, the differences between CML and normal CFU-GM colony growth inhibition after the use of the combination of the highest concentrations of STI571 either with 2-CdA or F-ara-A were statistically significant (p = 0.03 and p = 0.01, respectively). In conclusion, STI571 used together with both the PNAs had an additive effect on CML CFU-GM cells. However, further experimental and clinical studies concerning the usefulness of these combinations in the treatment of CML patients seem warranted.

Plerixafor inhibits chemotaxis toward SDF-1 and CXCR4-mediated stroma contact in a dose-dependent manner resulting in increased susceptibility of BCR-ABL+ cell to Imatinib and Nilotinib

Despite Imatinib's remarkable success in chronic myelogenous leukemia treatment, monotherapy frequently causes resistance, underlining the rationale for combination chemotherapy. A potential approach would be interrupting the SDF-1/CXCR4 axis using the selective CXCR4 antagonist Plerixafor (previously AMD3100), as this axis has been reported to provide survival-enhancing effects to myeloid progenitor cells. By efficient CXCR4 blocking in the CXCR4(+)/BCR-ABL(+) cell line BV-173, plerixafor (1-100 muM) significantly inhibits SDF-1alpha-mediated chemotaxis and cell migration toward the murine stroma cell line FBMD-1. Furthermore, plerixafor also significantly (10-100 muM) increased the detachment rate of SDF-1-mediated/VCAM-1-associated cell adherence under shear stress. Using a stroma-dependent coculture assay, plerixafor sensitized BCR-ABL(+) cells toward tyrosine kinase inhibitor therapy. Because the level of cell killing nearly reached that of samples cultured without stroma, a cell-cell interaction disruption seems to improve the efficacy of BCR-ABL-targeting drugs. In addition, we could show that exposure of BCR-ABL(+) cells to Imatinib or Nilotinib induced an increase in surface CXCR4 expression. Our data suggest that for BCR-ABL(+) leukemia, the selective blocking of the SDF-1/CXCR4 axis by plerixafor is a potential mechanism to overcome the protective effect of the bone marrow environment, thereby increasing the therapeutic potency of anti-BCR-ABL drugs and the therapeutic window.

Synergistic activity of nilotinib and established chemotherapeutic drugs in imatinib-sensitive and -resistant BCR-ABL-positive cells

We investigated various combination treatment regimens employing nilotinib with established chemotherapeutic agents (daunorubicin, mitoxantrone, etoposide and cytarabine) in imatinib-sensitive and -resistant BCR-ABL-positive cells. Mitoxantrone or cytarabine showed synergism (CI < 1) in combination with nilotinib in imatinib-sensitive LAMA84 cells, whereas in imatinib-resistant LAMA84-R cells synergistic effects could be assessed for daunorubicin, mitoxantrone and etoposide when combined with nilotinib. In both imatinib-sensitive and -resistant K562 cells daunorubicin, mitoxantrone and etoposide demonstrated synergism in combination with nilotinib. Moreover, both daunorubicin and mitoxantrone led to synergistic antiproliferative effects when combined with nilotinib in imatinib-resistant Ba/F3 cells carrying point mutations in the ABL TK domain (E255K, E255V and T315I). Annexin V/propidium iodide staining revealed a significant enhancement of nilotinib-induced apoptosis in imatinib-resistant Ba/F3T315I and LAMA84-R cells upon combination with daunorubicin and mitoxantrone, respectively. Our results demonstrate the efficacy of combination treatment regimens employing nilotinib and established chemotherapeutic agents in improving antileukemic effects in imatinib-sensitive and imatinib-resistant cells. This may be the foundation for further study on the potential of the applied combinations in a clinical setting.

Imatinib: a review of its use in chronic myeloid leukaemia

Imatinib (Gleevec, Glivec) is a synthetic tyrosine kinase inhibitor used in the treatment of chronic myeloid leukaemia (CML). It is specifically designed to inhibit the breakpoint cluster region (BCR)-Abelson (ABL) fusion protein that results from the chromosomal abnormality known as the Philadelphia chromosome. CML is characterised by this abnormality, which leads to abnormalities of the peripheral blood and bone marrow including an increase in the number of granular leukocytes. Imatinib is approved in numerous countries worldwide for the treatment of newly diagnosed Philadelphia chromosome-positive (Ph+) chronic-phase CML, Ph+ accelerated-phase or blast-crisis CML, and in patients with Ph+ chronic-phase CML who have failed to respond to interferon-alpha therapy. It is also indicated in paediatric patients with newly diagnosed Ph+ chronic-phase CML, in accelerated-phase or blast-crisis CML, or in chronic-phase CML after failure of interferon-alpha therapy or when the disease has recurred after haematopoietic stem cell transplantation (HSCT). Approved indications, however, may vary by country. Imatinib is effective and generally well tolerated in patients with Ph+ CML. In patients with newly diagnosed chronic-phase CML, imatinib was more effective than interferon-alpha plus cytarabine in preventing progression of the disease and in achieving haematological and cytogenetic responses. Overall survival rates remain high after 5 years of follow-up, and historical comparisons with other treatments demonstrate improved overall survival with imatinib in the long term. Patients with accelerated-phase or blast-crisis CML, or those who have not responded to prior interferon-alpha therapy also benefit from imatinib treatment. Some patients become resistant or intolerant to imatinib therapy; management strategies to overcome these problems include dosage adjustment, other treatments, or combination therapy with imatinib and other agents. Allogeneic HSCT is currently the only potentially curative treatment, but it is associated with high rates of morbidity and mortality and is not suitable for all patients. The introduction of imatinib has had a marked impact on outcomes in patients with CML. It remains a valuable treatment for all stages of the disease, especially initial treatment of newly diagnosed Ph+ chronic-phase CML, and is endorsed by European and US treatment guidelines as a first-line option.

Imatinib combined with mitoxantrone/etoposide and cytarabine is an effective induction therapy for patients with chronic myeloid leukemia in myeloid blast crisis

BACKGROUND

Despite advances in drug therapy and allogeneic stem cell transplantation (allo-SCT), the prognosis of patients with chronic myeloid leukemia (CML) in blast crisis remains poor. Imatinib has demonstrated synergistic effects in vitro with mitoxantrone, etoposide, and cytarabine.

METHODS

A Phase I/II trial was performed in patients with CML myeloid blast crisis. Patients were treated with imatinib + mitoxantrone/etoposide in four cohorts: mitoxantrone 10 mg/m(2)/day and etoposide 100 mg/m(2)/day for 2 or 3 consecutive days and imatinib 600 mg/day from Day 15 (cohorts 1 and 2) or from Day 1 (cohorts 3 and 4). After hematologic reconstitution after the cytopenic phase, cytarabine was given at a dose of 10 mg/m(2)/day in addition to imatinib as maintenance treatment.

RESULTS

A total of 16 patients were available for analysis, median age 59 years (range, 37-74). All patients who received more intensive induction treatment (cohorts 3 and 4, n = 7) achieved a hematologic response (HR). In contrast, HR was achieved in only 6 of 9 patients treated in cohorts 1 and 2. The induction treatment was well tolerated. Six patients who achieved HR received an allo-SCT with myeloablative conditioning. The median survival in the transplant group was 16.2 months vs 4.7 months in the group with conventional treatment only (P = .067).

CONCLUSIONS

The combination of mitoxantrone/etoposide and imatinib is well tolerated, with mild nonhematologic toxicity even in older patients. Eligible patients benefit from allo-SCT after response to the induction treatment.

Hypusination of eukaryotic initiation factor 5A (eIF5A): a novel therapeutic target in BCR-ABL-positive leukemias identified by a proteomics approach

Inhibition of BCR-ABL tyrosine kinase with imatinib represents a major breakthrough in the treatment of patients with chronic myeloid leukemia (CML). However, resistance to imatinib develops frequently, particularly in late-stage disease. To identify new cellular BCR-ABL downstream targets, we analyzed differences in global protein expression in BCR-ABL-positive K562 cells treated with or without imatinib in vitro. Among the 19 proteins found to be differentially expressed, we detected the down-regulation of eukaryotic initiation factor 5A (eIF5A), a protein essential for cell proliferation. eIF5A represents the only known eukaryotic protein activated by posttranslational hypusination. Hypusination inhibitors (HIs) alone exerted an antiproliferative effect on BCR-ABL-positive and -negative leukemia cell lines in vitro. However, the synergistic dose-response relationship found for the combination of imatinib and HI was restricted to Bcr-Abl-positive cells. Furthermore, this synergistic effect was confirmed by cytotoxicity assays, cell-cycle analysis, and CFSE labeling of primary CD34+ CML cells. Specificity of this effect could be demonstrated by cotreatment of K562 cells with imatinib and siRNA against eIF5. In conclusion, through a comparative proteomics approach and further functional analysis, we identified the inhibition of eIF5A hypusination as a promising new approach for combination therapy in BCR-ABL-positive leukemias.

Evolving molecular therapy for chronic myeloid leukaemia--are we on target?

Chronic myeloid leukaemia (CML) is a clonal disease of stem cell origin that develops when a single pluripotent haemopoietic stem cell acquires the Philadelphia (Ph) chromosome. The unique fusion gene product translated, p210 (Bcr-Abl), is a constitutively active tyrosine kinase that is specific to, and has a central role in the pathogenesis of, CML, making it an atractive target for drug therapy. Imatinib mesylate (IM) is one such therapy that also targets Abl, c-kit and PDGF-R tyrosine kinases. Although IM induces a much higher rate of complete cytogenetic remission (CCR), with improved tolerability and better progression free survival compared to other licensed therapies, resistance is a significant clinical problem. The most common mechanism of IM resistance is mutation of the Bcr-Abl kinase catalytic domain. In addition, molecular persistence in patients in CCR is most likely attributable to persisting Ph(+) stem cells that are insensitive to IM by unknown mechanisms and this is a major focus of current research interest. Current results from pre-clinical in vitro work on novel agents and combination strategies as well as clinical trials including immunotherapy approaches are reviewed. Despite the widespread use of molecularly targeted therapies and the development of new therapeutic drugs and strategies, it is our belief that there is a requirement for further research into and development of stem cell-directed therapies to overcome molecular persistence. It is likely that a combination of molecularly targeted therapies or treatment modalities will finally eliminate the quiescent stem cell population, leading to a "molecular cure" of CML.

CML clonal evolution with resistance to single agent imatinib therapy

We describe a 58-year-old male diagnosed with chronic myeloid leukaemia (CML) who failed to have a cytogenetic response to interferon-alpha and hydroxyurea. On subsequent therapy with imatinib mesylate he failed to have any cytogenetic response but also developed a complex clonal evolution with an additional Philadelphia (Ph) chromosome and trisomy 8 respectively in two Ph-positive subclones. The addition of cytosine arabinoside to imatinib resulted in reversion to single Ph-chromosome positivity with the disappearance of the previous additional clonal abnormalities. The case demonstrates the efficacy of combined treatment with imatinib and cytarabine in the management of CML resistant to single agent imatinib.

Synergistic activity of imatinib and 17-AAG in imatinib-resistant CML cells overexpressing BCR-ABL – Inhibition of P-glycoprotein function by 17-AAG

Overexpression of BCR-ABL and P-glycoprotein (Pgp) are two of the known mechanisms of imatinib resistance. As combination therapy may allow to overcome drug resistance, we investigated the effect of combination treatment with imatinib and 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heat-shock protein 90 (Hsp90) inhibitor, on different imatinib-sensitive and imatinib-resistant CML cell lines. In imatinib-sensitive cells, combination index (CI) values obtained using the method of Chou and Talalay indicated additive (CI=1) or marginally antagonistic (CI>1) effects following simultaneous treatment with imatinib and 17-AAG. In imatinib-resistant cells both drugs acted synergistically (CI<1). In primary chronic-phase CML cells additive or synergistic effects of the combination of imatinib plus 17-AAG were discernible. Annexin V/propidium iodide staining showed that the activity of imatinib plus 17-AAG is mediated by apoptosis. Combination treatment with imatinib plus 17-AAG was more effective in reducing the BCR-ABL protein level than 17-AAG alone. Monotherapy with 17-AAG decreased P-glycoprotein activity, which may increase intracellular imatinib levels and contribute to the sensitization of CML cells to imatinib. The results suggest that combination of imatinib and 17-AAG may be useful to overcome imatinib resistance in a clinical setting.

Targeting the silent minority: emerging immunotherapeutic strategies for eradication of malignant stem cells in chronic myeloid leukaemia

Standard allogeneic stem cell transplantation (alloSCT) has provided a cure for chronic myeloid leukaemia (CML) over the last 25 years, but is only an option for a minority of patients. It was hoped that the introduction of imatinib mesylate (IM), a specific tyrosine kinase inhibitor that targets the Bcr-Abl oncogene product, would provide long-term remission or even cure for those patients without a donor, but studies have shown that IM does not eliminate leukaemic stem cells in CML patients. To overcome this problem of molecular persistence, research is underway to combine reduced intensity stem cell transplant or non-donor-dependent immunotherapies with IM with the aim of increasing cure rate, reducing toxicity and improving quality of life. The alternative approach is to combine IM or second-generation agents with other novel drugs that interrupt key signalling pathways activated by Bcr-Abl. This article will focus on the latest immunotherapy and molecularly targeted therapeutic options in CML and how they may be combined to improve the outcome for CML patients in the future.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

Patupilone (epothilone B, EPO906) and imatinib (STI571, Glivec) in combination display enhanced antitumour activity in vivo against experimental rat C6 glioma

PURPOSE

The microtubule-stabilizing agent patupilone (epothilone B, EPO906) and the tyrosine kinase inhibitor imatinib (STI571, Glivec) which primarily inhibits Bcr-Abl, PDGF and c-Kit tyrosine kinase receptors, were combined in vivo to determine if any interaction would occur with respect to antitumour effect and tolerability using rat C6 glioma xenografted into nude mice.

METHODS

Patupilone and imatinib were administered alone or in combination at suboptimal doses. Imatinib treatment (orally once daily) was initiated 4 days after s.c. injection of rat C6 glioma cells into athymic nude mice and patupilone administration (i.v. once per week) was started 3 or 4 days after imatinib treatment.

RESULTS

As a single agent, imatinib was inactive in the regimens selected (100 mg/kg: T/C 86% and 116%; 200 mg/kg: T/C 68% and 84%; two independent experiments), but well tolerated (gain in body weight and no mortalities). Patupilone weekly monotherapy demonstrated dose-dependent antitumour effects (1 mg/kg: T/C 67% and 70%; 2 mg/kg: T/C 32% and 63%; 4 mg/kg: T/C 3% and 46%). As expected, dose-dependent body weight losses occurred (final body weight changes at 1 mg/kg were -7% and -3%; at 2 mg/kg were -23% and -13%; and at 4 mg/kg were -33% and -15%). Combining 2 mg/kg patupilone and 200 mg/kg per day imatinib in one experiment produced a non-statistically significant trend for an improved antitumour effect over patupilone alone (combination, T/C 9%), while in the second experiment, enhancement was seen with the combination and reached statistical significance versus patupilone alone (combination, T/C 22%; P=0.008). Reduction of the imatinib dose to 100 mg/kg per day resulted in no enhancement of antitumour activity in combination with 2 mg/kg patupilone. Reduction of the patupilone dose to 1 mg/kg resulted in a reduced antitumour effect, and only a trend for synergy with either imatinib dose (combination, T/C 46% and 40%). Pooling the data from the two experiments confirmed a significant synergy for the combination of 2 mg/kg patupilone and 200 mg/kg per day imatinib (P=0.032), and a trend for synergy at the 1 mg/kg patupilone dose. Reduction in the imatinib dose to 100 mg/kg per day resulted only in additivity with either dose of patupilone. Body weight losses were dominated by the effect of patupilone, since no greater body weight loss was observed in the combination groups.

CONCLUSION

Combining patupilone with high-dose imatinib produced an increased antitumour effect without affecting the tolerability of treatment in a relatively chemoresistant rat C6 glioma model. Such results indicate that further evaluation is warranted, in particular to elucidate possible mechanisms of combined action.

Imatinib mesylate (STI571) for myeloid malignancies other than CML

Imatinib mesylate, a small molecule tyrosine kinase inhibitor, has had a major impact on the treatment of Philadelphia chromosome positive chronic myelogenous leukemia. This review will explore its potential in the treatment of other myeloid neoplasms, based on its ability to inhibit Kit and PDGFR kinases in addition to Bcr-Abl. Imatinib's potential role in the treatment of Philadelphia chromosome negative chronic myelogenous leukemia, systemic mastocytosis with associated hematologic neoplasms, chronic myelomonocytic leukemia, specific subtypes of acute myelogenous leukemia, myelofibrosis/myeloid metaplasia, and polycythemia vera is discussed.

IFN-α promotes the rapid differentiation of monocytes from patients with chronic myeloid leukemia into activated dendritic cells tuned to undergo full maturation after LPS treatment

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease arising from the clonal expansion of a stem cell expressing the bcr/abl oncogene. CML patients frequently respond to treatment with interferon-α (IFN-α), even though the mechanisms of the response remain unclear. In the present study, we evaluated the role of IFN-α in differentiation and activity of monocyte-derived dendritic cells (DCs) from CML patients as well as in modulation of the cell response to lipopolysaccharide (LPS). Treatment of CML monocytes with IFN-α and granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in the rapid generation of activated DCs (CML-IFN-DCs) expressing interleukin-15 (IL-15) and the antiapoptotic bcl-2 gene. These cells were fully competent to induce IFN-γ production by cocultured autologous T lymphocytes and expansion of CD8+ T cells. LPS treatment of CML-IFN-DCs, but not of immature DCs generated in the presence of IL-4/GM-CSF, induced the generation of CD8+ T cells reactive against autologous leukemic CD34+ cells. Altogether, these results suggest that (1) the generation of highly active monocyte-derived DCs could be important for the induction of an antitumor response in IFN-treated CML patients and (2) IFN-α can represent a valuable cytokine for the rapid generation of active monocyte-derived DCs to be utilized for vaccination strategies of CML patients. (Blood. 2004;103:980-987)

Chronic myeloid leukemia: pathophysiology, diagnostic parameters, and current treatment concepts

Chronic myeloid leukemia (CML) is a stem cell disease characterized by excessive accumulation of clonal myeloid (precursor) cells in hematopoietic tissues. CML cells display the translocation t(9; 22) that creates the bcr/abl oncogene. The respective oncoprotein (= BCR/ABL) exhibits constitutive tyrosine kinase activity and promotes growth and survival in CML cells. Clinically, CML can be divided into three phases: the chronic phase (CP), the accelerated phase (AP), and the blast phase (BP) that resembles acute leukemia. Progression to AP and BP is associated with occurrence of additional genetic defects that cooperate with bcr/abl in leukemogenesis and lead to resistance against antileukemic drugs. The prognosis in CML is variable depending on the phase of disease, age, and response to therapy. The only curative approach available to date is stem cell transplantation. For those who cannot be transplanted, the BCR/ABL tyrosine kinase inhibitor STI571 (Glivec, Imatinib), interferon-alpha (with or without ARAC), or other cytoreductive drugs are prescribed. Currently available data show that STI571 is a superior compound compared to other drugs in producing complete cytogenetic and molecular responses. However, despite superior initial data and high expectations for an effect on survival, long term results are not available so far, and resistance against STI571 has been reported. Forthcoming strategies are therefore attempting to prevent or counteract STI571 resistance by co-administration of other antileukemic drugs. Whether these strategies will lead to curative drug therapy in CML in the future remains at present unknown.