Interferon-α or homoharringtonine as salvage treatment for chronic myeloid leukemia patients who acquire the T315I BCR-ABL mutation

CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML

Purpose

Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1^T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1^T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1^T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro.

Methods

Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and ³H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting.

Findings

HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1^T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1^T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1^T315I-associated TKI resistance.

Interpretation

HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1^T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML.

Funding

This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Cephalotaxus Alkaloids

Cephalotaxus alkaloids represent a family of plant secondary metabolites known for 60 years. Significant activity against leukemia in mice was demonstrated for extracts of Cephalotaxus. Cephalotaxine (CET) (1), the major alkaloid of this series was isolated from Cephalotaxus drupacea species by Paudler in 1963. The subsequent discovery of promising antitumor activity among new Cephalotaxus derivatives reported by Chinese, Japanese, and American teams triggered extensive structure elucidation and biological studies in this family. The structural feature of this cephalotaxane family relies mainly on its tetracyclic alkaloid backbone, which comprises an azaspiranic 1-azaspiro[4.4]nonane unit (rings C and D) and a benzazepine ring system (rings A and B), which is linked by its C3 alcohol function to a chiral oxygenated side chain by a carboxylic function alpha to a tetrasubstituted carbon center. The botanical distribution of these alkaloids is limited to the Cephalotaxus genus (Cephalotaxaceae). The scope of biological activities of the Cephalotaxus alkaloids is mainly centered on the antileukemic activity of homoharringtonine (HHT) (2), which in particular demonstrated marked benefits in the treatment of orphan myeloid leukemia and was approved as soon as 2009 by European Medicine Agency and by US Food and Drug Administration in 2012. Its exact mechanism of action was partly elucidated and it was early recognized that HHT (2) inhibited protein synthesis at the level of the ribosome machinery. Interestingly, after a latency period of two decades, the topic of Cephalotaxus alkaloids reemerged as a prolific source of new natural structures. To date, more than 70 compounds have been identified and characterized. Synthetic studies also regained attention during the past two decades, and numerous methodologies were developed to access the first semisynthetic HHT (2) of high purity suitable for clinical studies, and then high grade enantiomerically pure CET (1), HHT (2), and analogs.

Deep molecular response by IFN-α and dasatinib combination in a patient with T315I-mutated chronic myeloid leukemia

The T315I mutation is especially challenging as it confers resistance to all first- and second-generation tyrosine kinase inhibitors. We present here a chronic myeloid leukemia patient harboring the T315I and E255V BCR-ABL1 mutation successfully achieved deep molecular response with a combined treatment of dasatinib and IFN-α. To our knowledge, this is the second case of a T315I-bearing chronic myeloid leukemia patient displaying satisfactory response to the combination therapy of dasatinib and IFN-α.

Incidence of Bcr-Abl kinase domain mutations in imatinib refractory chronic myeloid leukemia patients from South India

Mutations in the Bcr-Abl kinase domain (KD) are a major cause for acquired resistance to imatinib (IM) treatment and have been associated with progression and poor prognosis in chronic myeloid leukemia patients. The present study includes 63 patients resistant to standard imatinib dose of 400 mg according to ELN guidelines. Direct sequencing method is used for mutational analysis. The present study revealed 15 exonic mutations in 46.03 % of patients; among them, seven cases (24.13 %) had multiple mutations. Mutations were found to be higher in sokal high- (45.0 %) and intermediate- (68.42 %) compared to low-risk (29.16 %) group. Mutations were observed in 38.09 % of patients with EUTOS (European Treatment and Outcome Study) high risk and in 50.0 % with low risk. The frequency of mutations was 50.0 % in advanced phase, 47.36 % in late chronic-phase, and 43.33 % in chronic-phase patients. 42.10 % of patients with primary resistance and 52.0 % with secondary resistance had mutations. P-loop and T315I mutations were associated with poor survival in advanced phase patients (85.71 %) (P = 0.03). No significant variation was observed with Bcr-Abl transcript levels between the patients with the presence or absence of mutations (P = 0.73). Bcr-Abl levels were found to be significantly elevated in P-loop and T315I mutation carriers (P = 0.001) and also in T315I mutation-positive patients (P = 0.01). P-loop mutations and T315I are frequent in advanced phases and strongly associated with poor prognosis and survival. Hence, the identification of mutations in IM-resistant CML patients will help in treatment optimization with 2nd- or 3rd-generation tyrosine kinase inhibitors (TKIs).

Homoharringtonine/omacetaxine mepesuccinate: the long and winding road to food and drug administration approval

Homoharringtonine/omacetaxine is a unique agent with a long history of research development. It has been recently approved by the Food and Drug Administration for the treatment of chronic myeloid leukemia after failure of 2 or more tyrosine kinase inhibitors. Research with this agent has spanned over 40 years, with many instructive lessons to cancer research, which are summarized in this review.

Subcutaneous omacetaxine mepesuccinate in patients with chronic-phase chronic myeloid leukemia previously treated with 2 or more tyrosine kinase inhibitors including imatinib

INTRODUCTION

Omacetaxine mepesuccinate (omacetaxine) is a first-in-class cephalotaxine that has demonstrated efficacy in CML. In this analysis we evaluated omacetaxine in CML patients with resistance or intolerance to 2 or more tyrosine kinase inhibitors (TKIs).

PATIENTS AND METHODS

Data were pooled from 2 phase II trials of subcutaneous omacetaxine, administered at 1.25 mg/m(2) twice daily for 14 consecutive days every 28 days until response, then for 7 days every 28 days as maintenance. Patients with resistance or intolerance to imatinib and at least 1 other approved TKI (dasatinib and/or nilotinib) were included; results for patients in chronic phase (CP) are reported here. Major cytogenetic response (MCyR) was the primary end point.

RESULTS

Eighty-one patients with CML-CP (median age, 59 years; range, 26-83 years) were included in the analysis. All patients previously received imatinib, 69 (85%) previously received dasatinib, and 48 (59%) previously received nilotinib. Median omacetaxine exposure was 7.5 months (range, 0.03-38.6 months), with 13 patients ongoing. MCyR was reported in 16 patients (20%; one-sided 95% lower confidence limit, 12.8%), including 8 complete responses; median duration was 17.7 months (95% confidence interval, 4.1 months - not reached). Fifty-six patients (69%) achieved and/or maintained hematologic response for at least 8 weeks; median duration was 12.2 months (range, 8.4-26.2 months). Median failure-free and overall survival were 9.6 months and 34 months, respectively. Toxicity was mainly hematologic: the most common grade 3/4 adverse events were thrombocytopenia (67%), neutropenia (47%), and anemia (37%).

CONCLUSION

Omacetaxine produced clinically meaningful responses with acceptable tolerability in patients with CML-CP previously treated with 2 or more TKIs.

The BCR-ABLT315I mutation compromises survival in chronic phase chronic myelogenous leukemia patients resistant to tyrosine kinase inhibitors, in a matched pair analysis

The BCR-ABL T315I mutation confers resistance to currently licensed tyrosine kinase inhibitors in chronic myelogenous leukemia. However, the impact of this mutation on survival in early stages of disease, in chronic phase, has never been detailed. Using matched pair analysis, a cohort of 64 patients with chronic phase chronic myelogenous leukemia harboring a T315I mutation and resistant to imatinib mesylate was compared to a similar cohort of 53 chronic phase patients resistant to imatinib, but with no detectable T315I mutation, in the pre-ponatinib era. These patients were matched according to age at diagnosis, interval between disease diagnosis and start of imatinib treatment, and duration of imatinib therapy. Kaplan-Meier survival analyses demonstrated the significant negative impact of the presence of the T315I mutation on overall survival (since imatinib-resistance: 48.4 months for T315I(+) patients versus not reached for T315I(-) ones; P=0.006) and failure-free survival (since imatinib-resistance: 34.7 months for T315I(+) patients versus not reached for T315I(-) patients; P=0.003). In addition, Cox proportional hazard models adjusted on overall survival demonstrated the negative influence of the T315I mutation (P=0.02, HR=2.54). These results confirm early assumptions concerning the poor prognosis of chronic phase chronic myelogenous leukemia patients with the T315I mutation who are not eligible for allogeneic transplantation, and demonstrate the need for more therapeutic options.

Selection of therapy: rational decisions based on molecular events

This article reviews to what extent molecular data can be used to rationalize therapeutic choices in the treatment of chronic myeloid leukemia. Two categories of data are discussed: markers that globally measure risk but do not provide a molecular rationale for therapy selection; and biomarkers with a causal link to a clinical phenotype, such as certain mutations of the BCR-ABL kinase domain. As therapy selection is still mainly based on clinical criteria, molecular biomarkers are discussed in the context of available clinical prognostication tools, focusing on biomarkers that do not reflect disease burden as a surrogate of responsiveness to treatment.

Omacetaxine mepesuccinate for the treatment of leukemia

INTRODUCTION

Omacetaxine mepesuccinate, formerly known as homoharringtonine, is a first-in-class cephalotaxine that has experienced phases of increasing and waning interest since its first use in traditional Chinese medicine. With activity being reported in patients with chronic myeloid leukemia (CML) resistant to currently available tyrosine kinase inhibitors, renewed interest has recently been generated.

AREAS COVERED

The development of omacetaxine mepesuccinate, with emphasis on synthesis and mode of administration, is addressed. An overview on current clinical results as a single agent or within combination regimens in patients with acute myeloid leukemia (AML) and CML is given.

EXPERT OPINION

Omacetaxine mepesuccinate has a unique mode of action and appreciable activity in AML and CML with generally mild nonhematologic toxicity. In patients with AML, results indicate a role within combination regimens in selected, possibly elderly patient populations. In CML, patients with resistance to tyrosine kinase inhibitors, especially due to the T315I mutation, are the most intensively studied. Despite successful results in some patients, single-agent therapy with omacetaxine mepesuccinate has resulted in modest results. However, upfront combination with tyrosine kinase inhibitor represents an attractive option due their differing mechanisms of action.

Successful treatment of a chronic-phase T-315I-mutated chronic myelogenous leukemia patient with a combination of imatinib and interferon-alfa

The T315I BCR-ABL mutation in chronic myelogenous leukemia (CML) patients is responsible for up to 20% of all clinically observed resistance. This mutation confers resistance not only to imatinib, but also to second-generation BCR-ABL tyrosine kinases, such as nilotinib and dasatinib. A number of strategies have been implemented to overcome this resistance, but allogeneic stem cell transplantation remains the only established therapeutic option for a cure. A 61-year-old male was diagnosed with Philadelphia chromosome-positive chronic-phase CML in 2002. He was initially treated with imatinib and complete cytogenetic response (CCyR) was achieved 12 months later. However, after 18 months, a loss of CCyR was observed and a molecular study at 24 months revealed a T315I mutation of the BCR-ABL gene. At 30 months, imatinib/interferon-alfa (IFNα) combination therapy was initiated in an effort to overcome the resistance. Thirty months later, he re-achieved CCyR, and the T315I BCR-ABL mutation disappeared at 51 months. To our knowledge, this is the first case report showing the effectiveness of imatinib/IFNα combination therapy for CML patients bearing the T315I BCR-ABL mutation.

Allogeneic stem cell transplantation for patients harboring T315I BCR-ABL mutated leukemias

T315I(+) Philadelphia chromosome-positive leukemias are inherently resistant to all licensed tyrosine kinase inhibitors, and therapeutic options remain limited. We report the outcome of allogeneic stem cell transplantation in 64 patients with documented BCR-ABL(T315I) mutations. Median follow-up was 52 months from mutation detection and 26 months from transplantation. At transplantation, 51.5% of patients with chronic myeloid leukemia were in the chronic phase and 4.5% were in advanced phases. Median overall survival after transplantation was 10.3 months (range 5.7 months to not reached [ie, still alive]) for those with chronic myeloid leukemia in the blast phase and 7.4 months (range 1.4 months to not reached [ie, still alive]) for those with Philadelphia chromosome-positive acute lymphoblastic leukemia but has not yet been reached for those in the chronic and accelerated phases of chronic myeloid leukemia. The occurrence of chronic GVHD had a positive impact on overall survival (P = .047). Transplant-related mortality rates were low. Multivariate analysis identified only blast phase at transplantation (hazard ratio 3.68, P = .0011) and unrelated stem cell donor (hazard ratio 2.98, P = .011) as unfavorable factors. We conclude that allogeneic stem cell transplantation represents a valuable therapeutic tool for eligible patients with BCR-ABL(T315I) mutation, a tool that may or may not be replaced by third-generation tyrosine kinase inhibitors.

Omacetaxine may have a role in chronic myeloid leukaemia eradication through downregulation of Mcl-1 and induction of apoptosis in stem/progenitor cells

Chronic myeloid leukaemia (CML) is maintained by a rare population of tyrosine kinase inhibitor (TKI)-insensitive malignant stem cells. Our long-term aim is to find a BcrAbl-independent drug that can be combined with a TKI to improve overall disease response in chronic-phase CML. Omacetaxine mepesuccinate, a first in class cetaxine, has been evaluated by clinical trials in TKI-insensitive/resistant CML. Omacetaxine inhibits synthesis of anti-apoptotic proteins of the Bcl-2 family, including (myeloid cell leukaemia) Mcl-1, leading to cell death. Omacetaxine effectively induced apoptosis in primary CML stem cells (CD34(+)38(lo)) by downregulation of Mcl-1 protein. In contrast to our previous findings with TKIs, omacetaxine did not accumulate undivided cells in vitro. Furthermore, the functionality of surviving stem cells following omacetaxine exposure was significantly reduced in a dose-dependant manner, as determined by colony forming cell and the more stringent long-term culture initiating cell colony assays. This stem cell-directed activity was not limited to CML stem cells as both normal and non-CML CD34(+) cells were sensitive to inhibition. Thus, although omacetaxine is not leukaemia stem cell specific, its ability to induce apoptosis of leukaemic stem cells distinguishes it from TKIs and creates the potential for a curative strategy for persistent disease.

Bcl-xL is a dominant antiapoptotic protein that inhibits homoharringtonine-induced apoptosis in leukemia cells

Homoharringtonine (HHT) has been reported to be effective in a portion of patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). To investigate its mechanism of action, cell growth inhibition and cytotoxicity of HHT were investigated in three AML cell lines, HL-60, NB4, and U937, and in three CML cell lines, K562, KU812, and KCL22. AML cells were more sensitive than CML cells to HHT-induced cytotoxicity. Using HL-60 cells, it was revealed that HHT decreased the levels of myeloid cell leukemia 1 (Mcl-1), X-linked inhibitor of apoptosis protein (XIAP), survivin, and B-cell lymphoma 2 (Bcl-2)-homology domain 3 (BH3)-only proteins as well as the mitochondrial membrane potential. The levels of Bcl-2, Bcl-2-associated X protein (Bax), and Bcl-2 homologous antagonist/killer (Bak) proteins in HL-60 cells were not changed after HHT treatment. U937, K562, KU812, and KCL22 cells expressed B-cell lymphoma-extra large (Bcl-xL) and were less responsive to HHT-induced apoptosis than HL-60 cells. Silencing Mcl-1 or Bcl-xL, but not XIAP or survivin, enhanced HHT-induced apoptosis in U937 cells. The levels of HHT-induced apoptosis in K562, KCL22, and KU812 cells were inversely correlated with the levels of Bcl-xL but not those of Bcl-2 or Mcl-1. K562 cells expressing high levels of Bcl-xL but no Bcl-2 were less responsive to HHT-induced apoptosis than KCL22 cells that expressed lower levels of Bcl-xL and higher levels of Bcl-2 protein. In K562 cells, knockdown of Bcl-xL, but not of Mcl-1, enhanced HHT-induced apoptosis. Transfection of Bcl-xL into KCL22 cells attenuated HHT-induced apoptosis. These data suggest that Bcl-xL plays a more important role than Bcl-2 and Mcl-1 in protecting against HHT-induced apoptosis.

Rapid clonal shifts in response to kinase inhibitor therapy in chronic myelogenous leukemia are identified by quantitation mutation assays

Treatment of CML with the tyrosine kinase inhibitor (TKI) imatinib mesylate results in the emergence of point mutations within the kinase domain (KD) of the BCR-ABL1 fusion transcript. The introduction of next-generation TKIs that can overcome the effects of some BCR-ABL1 KD mutations requires quantitative mutation profiling methods to assess responses. We report the design and validation of such quantitative assays, using pyrosequencing and mutation-specific RT-PCR techniques, to allow sequential monitoring and illustrate their use in tracking specific KD mutations (e.g. G250E, T315I, and M351T) following changes in therapy. Pyrosequencing and mutation-specific RT-PCR allows sequential monitoring of specific mutations and identification of rapid clonal shifts in response to kinase inhibitor therapy in CML. Rapid reselection of TKI-resistant clones occurs following therapy switch in CML.

Nilotinib: evaluation and analysis of its role in chronic myeloid leukemia

Nilotinib, formally known as AMN107, is a second-generation tyrosine kinase inhibitor, rationally designed from its revolutionary parent compound imatinib, to produce a 30–40-fold enhancement in the inhibition of the BCR–ABL1-derived oncoprotein associated with chronic myeloid leukemia. In clinical trials, nilotinib has proven to be a useful agent in the treatment of imatinib-refractory disease and was initially approved by both the US FDA and EMA in 2007 for use in adults as a second-line therapy. More recently, data from the first randomized controlled trials of the front-line use of nilotinib in newly diagnosed patients with chronic phase chronic myeloid leukemia have demonstrated superiority in the rates of major molecular responses at 12 months over the gold standard–imatinib 400 mg. As such, in June 2010, the FDA granted accelerated approval for its use in newly diagnosed Philadelphia chromosome-positive chronic myeloid leukemia. Nilotinib is well tolerated, with a favorable side-effect profile. With the emergence of supportive trial data, it is likely to have a leading role both in the front-line management of newly presenting patients and in the second-line treatment of patients resistant to or intolerant of imatinib and other second-line agents.

Mutation-specific control of BCR-ABL T315I positive leukemia with a recombinant yeast-based therapeutic vaccine in a murine model

Chromosomal translocations generating the BCR-ABL oncogene cause chronic myeloid leukemia (CML) and a subset of acute lymphoblastic leukemia. The BCR-ABL(T315I) mutation confers drug resistance to FDA-approved targeted therapeutics imatinib mesylate, dasatinib, and nilotinib. We tested the ability of a recombinant yeast-based vaccine expressing the T315I-mutated BCR-ABL antigen to stimulate an anti-BCR-ABL(T315I) immune response. The yeast-based immunotherapy significantly reduced or eliminated BCR-ABL(T315I) leukemia cells from the peripheral blood of immunized animals and extended leukemia-free survival in a murine model of BCR-ABL(+) leukemia compared to animals receiving sham injection or yeast expressing ovalbumin. With immunization, leukemic cells harboring BCR-ABL(T315I) were selectively eliminated after challenge with a mixed population of BCR-ABL and BCR-ABL(T315I) leukemias. In summary, yeast-based immunotherapy represents a novel approach against the emergence of cancer drug resistance by the pre-emptive targeted ablation of tumor escape mutants.

Mechanisms of Resistance to Imatinib and Second-Generation Tyrosine Inhibitors in Chronic Myeloid Leukemia

Targeted therapy in the form of selective tyrosine kinase inhibitors (TKI) has transformed the approach to management of chronic myeloid leukemia (CML) and dramatically improved patient outcome to the extent that imatinib is currently accepted as the first-line agent for nearly all patients presenting with CML, regardless of the phase of the disease. Impressive clinical responses are obtained in the majority of patients in chronic phase; however, not all patients experience an optimal response to imatinib, and furthermore, the clinical response in a number of patients will not be sustained. The process by which the leukemic cells prove resistant to TKIs and the restoration of BCR-ABL1 signal transduction from previous inhibition has initiated the pursuit for the causal mechanisms of resistance and strategies by which to surmount resistance to therapeutic intervention. ABL kinase domain mutations have been extensively implicated in the pathogenesis of TKI resistance, however, it is increasingly evident that the presence of mutations does not explain all cases of resistance and does not account for the failure of TKIs to eliminate minimal residual disease in patients who respond optimally. The focus of exploring TKI resistance has expanded to include the mechanism by which the drug is delivered to its target and the impact of drug influx and efflux proteins on TKI bioavailability. The limitations of imatinib have inspired the development of second generation TKIs in order to overcome the effect of resistance to this primary therapy. (Clin Cancer Res 2009;15(24):7519-27).

Homoharringtonine, omacetaxine mepesuccinate, and chronic myeloid leukemia circa 2009

Homoharringtonine (HHT) is a natural alkaloid that is obtained from various Cephalotaxus species. The mechanism of action by which HHT exerts its antitumor activity is through inhibition of protein synthesis and promotion of apoptosis. In the 1990s, HHT proved to be significantly active as salvage therapy for patients with chronic myeloid leukemia (CML) after failure on interferon-alpha therapy. However, the remarkable success of imatinib mesylate in the treatment of CML relegated HHT to oblivion. The development of omacetaxine mepesuccinate, a subcutaneously bioavailable semisynthetic form of HHT, and its activity in imatinib-resistant CML has established this agent for the second time as a valuable option in the management of this disease. Preliminary results appear to support the use of this agent for patients who have imatinib-resistant CML, including those who carry the tyrosine kinase inhibitor-insensitive mutation that exchanges the amino acids threonine and isoleucine at position 315 (the T315I mutation). In this article, the authors discuss the current data on omacetaxine and the prospects of this agent to be integrated into the state-of-the-art treatment algorithms for CML.

The antiproliferation effect of berbamine on k562 resistant cells by inhibiting NF-kappaB pathway

Imatinib mesylate is effective against Ph chromosome-positive leukemia; however, resistance has been reported. High expression of bcr-abl in mRNA and protein levels, and other alterations were found in patients who experienced imatinib treatment failures and thus it is important to design alternative treatment strategies. The aim of this study was to evaluate the in vitro effect of berbamine, on imatinib-resistant chronic myelogenous leukemia (CML) K562 (K562-r) cells, and explore the mechanisms. The growth of K562-r cells was examined using the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Morphological analysis and DNA agarose electrophoresis were used to detect apoptosis in K562-r cells, and the extent of the cells in the sub-G1 cell cycle phase was measured using flow cytometry. The expression levels of BCR-ABL, phospho-BCR-ABL, and nuclear factor kappaB (NF-kappaB), IkappaBalpha, phospho-IkappaBalpha, IkappaB kinases alpha(IKKalpha), and Survivin were determined by Western blot. bcr-abl mRNA expression was determined by RT-PCR. MTT assays indicated that berbamine significantly inhibited the proliferation of K562-r cells. Cells with characteristics of apoptosis were confirmed by morphology examination and DNA agarose electrophoresis and percentage of apoptosis were increased after treatment with berbamine. The results also showed that berbamine was able to down-regulate BCR-ABL and phospho-BCR-ABL proteins by affecting bcr-abl mRNA expression and decrease expression of nuclear NF-kappaB, phospho-IkappaBalpha, IKKalpha, and Survivin. Collectively, berbamine could inhibit the proliferation of K562-r cells and induce apoptosis. The mechanisms may be related at least in part, to inhibit BCR-ABL and its downstream NF-kappaB signaling. Berbamine may provide an alternative candidate for the treatment of patients with CML resistant to imatinib therapy.

Second-line therapy and beyond resistance for the treatment of patients with chronic myeloid leukemia post imatinib failure

Chronic myeloid leukemia (CML) is characterized at the molecular level by the presence of the Philadelphia chromosome (Ph) and the resultant oncogenic signaling by the BCR-ABL fusion protein. The treatment and outlook for CML were revolutionized by the introduction of imatinib, but resistance is a substantial barrier to successful treatment in many patients. Introduction of the second-generation tyrosine kinase inhibitors (TKI) dasatinib and nilotinib has provided effective therapeutic options for many patients with resistance to front-line imatinib. However, the T315I mutation remains a significant clinical issue because it is insensitive to all currently available agents. A number of new agents are in development and many hold the promise of activity in T315I-mutated disease. Successful treatment of patients with disease harboring T315I might lie in the effective combination or sequencing of these new agents with existing TKI therapies.

Suppression of interferon (IFN)-inducible genes and IFN-mediated functional responses in BCR-ABL-expressing cells

The interferons (IFNs) are cytokines that play key roles in host defense against viral infections and immune surveillance against cancer. We report that BCR-ABL transformation of hematopoietic cells results in suppression of IFN-dependent responses, including transcription of IFN-inducible genes and generation of IFN-mediated antiviral effects. BCR-ABL transformation suppresses expression of several IFN-regulated genes containing IFN-sensitive response element (ISRE) or GAS elements in their promoters, including Isg15, Irf1, Irf9, and Ifit2 (interferon-induced protein with tetratricopeptide repeats 2). Suppression of transcription of ISRE-containing genes is also seen in cells expressing various BCR-ABL kinase domain mutants, including T315I, H396P, Y253F, and E255K, but not kinase-defective BCR-ABL. Such effects are associated with impaired IFN-dependent phosphorylation of Stat1 on Tyr(701) and Stat3 on Tyr(705) and defective binding of Stat complexes to ISRE or GAS elements. Beyond suppression of Stat activities, BCR-ABL inhibits IFN-inducible phosphorylation/activation of the p38 MAPK, suggesting a dual mechanism by which this abnormal fusion protein blocks IFN transcriptional responses. The inhibitory activities of BCR-ABL ultimately result in impaired IFNalpha-mediated protection against encephalomyocarditis virus infection and reversal of IFN-dependent growth suppression. Altogether, our data provide evidence for a novel mechanism by which BCR-ABL impairs host defenses and promotes malignant transformation, involving dual suppression of IFN-activated signaling pathways.

SGX393 inhibits the CML mutant Bcr-AblT315I and preempts in vitro resistance when combined with nilotinib or dasatinib

Imatinib inhibits Bcr-Abl, the oncogenic tyrosine kinase that causes chronic myeloid leukemia. The second-line inhibitors nilotinib and dasatinib are effective in patients with imatinib resistance resulting from Bcr-Abl kinase domain mutations. Bcr-Abl(T315I), however, is resistant to all Abl kinase inhibitors in clinical use and is emerging as the most frequent cause of salvage therapy failure. SGX393 is a potent inhibitor of native and T315I-mutant Bcr-Abl kinase that blocks the growth of leukemia cell lines and primary hematopoietic cells expressing Bcr-Abl(T315I), with minimal toxicity against Bcr-Abl-negative cell lines or normal bone marrow. A screen for Bcr-Abl mutants emerging in the presence of SGX393 revealed concentration-dependent reduction in the number and range of mutations. Combining SGX393 with nilotinib or dasatinib preempted emergence of resistant subclones, including Bcr-Abl(T315I). These findings suggest that combination of a T315I inhibitor with the current clinically used inhibitors may be useful for reduction of Bcr-Abl mutants in Philadelphia chromosome-positive leukemia.

Novel agents in CML therapy: tyrosine kinase inhibitors and beyond

The emergence of resistance to imatinib has become a significant problem despite the remarkable clinical results achieved with this tyrosine kinase inhibitor in the treatment of chronic myeloid leukaemia. The most common cause of imatinib resistance is the selection of leukemic clones with point mutations in the Abl kinase domain. These mutations lead to amino acid substitutions and prevent the appropriate binding of imatinib. Genomic amplification of BCR-ABL, modulation of drug efflux or influx transporters, and Bcr-Abl-independent mechanisms also play important roles in the development of resistance. Persistent disease is another therapeutic challenge and may in part, be due to the inability of imatinib to eradicate primitive stem cell progenitors. A multitude of novel agents have been developed and have shown in vitro and in vivo efficacy in overcoming imatinib resistance. In this review, we will discuss the current status of the ATP-competitive and non-ATP-competitive Bcr-Abl tyrosine kinase inhibitors. We will also describe inhibitors acting on targets found in signaling pathways downstream of Bcr-Abl, such as the Ras-Raf-mitogen-activated protein kinase and phosphatidylinositol-3 kinase-Akt-mammalian target of rapamycin pathways, and targets without established links with Bcr-Abl.