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Abstract: Deep molecular response (DMR) is a prerequite for treatment-free remission (TFR) in chronic myeloid leukemia in chronic phase (CML-CP). The JALSG (Japan Adult Leukemia Study Group) conducted a prospective randomized phase 3 CML212 study for de novo CML-CP to compare the cumulative achievement of molecular response 4.5 (MR4.5; international scale BCR::ABL1 ≤0.0032%) by 18 months between nilotinib and dasatinib treatment as a primary end point. A total of 454 patients were randomly assigned to the 300 mg nilotinib twice daily arm or to the 100 mg dasatinib daily arm (both n = 227). BCR::ABL1 messenger RNA levels were monitored every 3 months. Study treatment was stopped if the patients were judged as failure according to the European LekemiaNet 2009 criteria or showed intolerance. The cumulative achievement rates of MR4.5 by 18 months were 32.6% (95% confidence interval [CI], 26.5-39.1) in the nilotinib arm and 30.8% (95% CI, 24.9-37.3) in the dasatinib arm with no significant difference (P = .66). The cumulative achievement rates of early molecular response, complete cytogenetic response, and major molecular response by 12, 18, 24, and 36 months were almost the same between the 2 arms. There was no significant difference in progression-free survival (PFS) or overall survival (OS) between the 2 arms by log-rank tests (PFS, P = .58; OS, P = .64). These results suggest that nilotinib and dasatinib would be equally effective for patients with de novo CML-CP. This trial was registered in the University Hospital Medical Information Network Clinical Trials Registry as #UMIN000007909., (© 2024 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Multiple myeloma (MM) is a uniformly fatal disorder of B cells characterized by the accumulation of abnormal plasma cells. Phosphoinositide 3-kinase (PI3K) signaling pathways play a critical regulatory role in MM pathology. Copanlisib, also known as BAY80-6946, is a potent PI3Kα and δ inhibitor. In this study, we investigated the efficacy of copanlisib and a proteasome inhibitor using MM cell lines and primary samples. The p110α and δ catalytic subunits of the class PI3K increased, and carfilzomib activity reduced in the presence of a supernatant from the feeder cell line, HS-5. Phosphorylation of Akt and activation of caspase 3 and poly (ADP-ribose) polymerase (PARP) partially reduced upon carfilzomib treatment in the presence of HS-5. Apoptosis also decreased. Copanlisib treatment for 72 h inhibited growth in MM cell lines and induced apoptosis. Combination treatment of MM cells with carfilzomib and copanlisib caused greater cytotoxicity than that caused by either drug alone and increased apoptosis. Caspase 3 activity increased while that of Akt decreased after combination treatment with copanlisib and carfilzomib. Further, copanlisib inhibited vascular endothelial growth factor (VEGF)-mediated angiogenesis in vitro and in vivo. It also inhibited C-X-C motif chemokine 12 (CXCL12)-mediated chemotaxis. The data suggest that administration of the PI3K inhibitor, copanlisib, may be a powerful strategy against stroma-associated drug resistance of MM cells and can enhance the cytotoxic effects of proteasome inhibitors in such residual MM cells.

ABL tyrosine kinase inhibitor (TKI) therapy has improved the survival of patients with Philadelphia (Ph) chromosome-positive leukemia. However, ABL TKIs cannot eradicate leukemia stem cells. Therefore, new therapeutic approaches for Ph-positive leukemia are needed. Aberrant activation of phosphoinositide 3-kinase (PI3K) signaling is important for the initiation and maintenance of human cancers. Copanlisib (BAY80-6946) is a potent inhibitor of PI3Kα and PI3K-δ. Here we investigated the efficacy of combination therapy of copanlisib with an ABL TKI (imatinib, nilotinib, or ponatinib) using BCR-ABL-positive cells. Although the effects of the ABL TKI treatment were reduced in the presence of the feeder cell line, HS-5, copanlisib inhibited cell growth. Upon combining ABL TKI and copanlisib, cell growth was reduced. Ponatinib and copanlisib combined therapy reduced tumor volume and increased survival in mouse allograft models, respectively. These results indicate that the PI3Kα and -δ inhibitors overcame the chemoprotective effects of the feeder cells and enhanced ABL TKI cytotoxicity. Thus, co-treatment with ABL TKI and copanlisib may be a powerful strategy against ABL TKI-resistant cells, including those harboring the related T315I mutation., Competing Interests: Kazuma Ohyashiki received research support from Novartis and Bristol-Myers Squibb Company.

Background: The ABL kinase inhibitor imatinib is highly effective in treating most, but not all, patients with chronic myeloid leukemia (CML). This is because residual CML cells are generally present in the bone marrow microenvironment and are refractory to imatinib. Hematopoietic cytokine receptor signaling is mediated by Janus kinases (JAKs) and their downstream transcription factor, signal transducer and activator of transcription (STAT). TG101348 (SAR302503) is an oral inhibitor of JAK2., Methods: We investigated the efficacy of imatinib and TG101348 using the break point cluster region-c-Abelson (BCR-ABL)-positive cell line and primary CML samples wherein leukemia cells were protected by a feeder cell line (HS-5)., Results: Imatinib treatment resulted in partial inhibition of cell growth in HS-5-conditioned medium. Furthermore, combined treatment with imatinib and TG101348 abrogated the protective effects of HS-5-conditioned medium on K562 cells. Phosphorylation of Crk-L, a BCR-ABL substrate, decreased considerably, while apoptosis increased. In addition, the combined treatment of CD34-positive primary samples resulted in considerably increased cytotoxicity, decreased Crk-L phosphorylation, and increased apoptosis. We also investigated TG101348 activity against feeder cells and observed that STAT5 phosphorylation, granulocyte macrophage colony-stimulating factor, and interleukin 6 levels decreased, indicating reduced cytokine production in HS-5 cells treated with TG101348., Conclusions: These results showed that JAK inhibitors may enhance the cytotoxic effect of imatinib against residual CML cells and that a combined approach may be a powerful strategy against the stroma-associated drug resistance of Philadelphia chromosome-positive cells.

Imatinib, an ABL tyrosine kinase inhibitor (TKI), has shown clinical efficacy against chronic myeloid leukemia (CML). However, a substantial number of patients develop resistance to imatinib treatment due to the emergence of clones carrying mutations in the protein BCR-ABL. The phosphoinositide 3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway regulates various processes, including cell proliferation, cell survival, and antiapoptosis activity. In this study, we investigated the efficacy of NVP-BEZ235, a dual PI3K and mTOR inhibitor, using BCR-ABL-positive cell lines. Treatment with NVP-BEZ235 for 48 h inhibited cell growth and induced apoptosis. The phosphorylation of the AKT kinase, eukaryotic initiation factor 4-binding protein 1 (4E-BP1), and p70 S6 kinase were decreased after NVP-BEZ235 treatment. The combination of NVP-BEZ235 with a BCR-ABL kinase inhibitor, imatinib, or nilotinib, induced a more pronounced colony growth inhibition, whereas the combination of NVP-BEZ235 and nilotinib was more effective in inducing apoptosis and reducing the phosphorylation of AKT, 4E-BP1, and S6 kinase. NVP-BEZ235 in combination with nilotinib also inhibited tumor growth in a xenograft model and inhibited the growth of primary T315I mutant cells and ponatinib-resistant cells. Taken together, these results suggest that administration of the dual PI3K and mTOR inhibitor NVP-BEZ235 may be an effective strategy against BCR-ABL mutant cells and may enhance the cytotoxic effects of nilotinib in ABL TKI-resistant BCR-ABL mutant cells.

A number of CML patients who achieve a sustained complete molecular response (CMR) for at least 2 years during imatinib (IM) therapy can discontinue IM without relapse. With the long-term goal of developing immunological criteria for managing IM therapy in CML patients, we compared the immunophenotypic profiles of three groups of CML patients: those who received IM and had a CMR for more than two consecutive years (CMR group); patients who received IM and did not have a sustained CMR but maintained a major molecular response for more than 2 years (fluctuating CMR group); and patients with a sustained CMR for more than 6 months after IM discontinuation (STOP-IM group), together with healthy controls. The percentages of effector populations of natural killer (NK) cells, such as interferon (IFN)-γ(+) CD3(-) CD56(+) cells, were significantly higher in the STOP-IM and CMR groups than in the fluctuating CMR and control groups. The elevated levels of these effector NK cells were sustained for more than 3 years after IM discontinuation. In contrast, the percentages of effector memory CD8(+) T cells, such as IFN-γ(+) CCR7(-) CD45RO(+) CD8(+) cells, were significantly higher in the STOP-IM and control groups than in the CMR and fluctuating CMR groups, possibly owing to IM intake. These results suggest that the immunological activation status of NK cells contributes to CMR maintenance. Higher activation levels of effector NK cells in CML patients being treated with IM might reflect minimization of BCR-ABL1 transcript levels and therefore could be additive information for determining whether to stop IM., (© 2013 Japanese Cancer Association.)

Hedgehog (Hh)-glioma-associated oncogene homolog (Gli) signaling is implicated in a large number of human cancers such as leukemia. In this study, we investigated the effects of the potent Hh antagonist GDC-0449 on the BCR-ABL-positive cell line OM9;22 and primary samples when leukemia cells were protected by a feeder cell line (S9 cells). The numbers of OM9;22 cells significantly increased with S9 cells. Treatment of OM9;22 cells with GDC-0449 caused cell growth inhibition and induced apoptosis. Moreover, GDC-0449 inhibited the colony growth of Philadelphia chromosome (Ph)-positive primary samples. We next investigated the effects of a combination of GDC-0449 and dasatinib on these cell lines. The growth inhibition typically promoted by dasatinib was significantly reduced in the presence of S9 cells. Treatment of Ph-positive leukemia cells with GDC-0449 and dasatinib in the presence of S9 caused significantly more cytotoxicity than that caused by each drug alone. Inhibition of Gli1 or Gli2 by siRNA transfection reduced the growth of the Ph-positive cell line K562 and increased cytotoxicity of dasatinib. Moreover, colony formations of Gli1 or Gli2 knockdown cells were also reduced. Data from this study suggest that administration of the Hh inhibitor GDC-0449 inhibits BCR-ABL-positive cell growth and enhances the cytotoxic effects of dasatinib in the presence of feeder cells.

A prospective multicenter Phase II study was performed to examine the efficacy and safety of imatinib therapy in newly diagnosed Japanese patients with chronic-phase CML. Patients were scheduled to receive imatinib 400 mg daily. Plasma imatinib concentrations were measured by liquid chromatography-tandem mass spectrometry. In 481 evaluable patients, estimated 7-year overall survival (OS) and event-free survival (EFS) at a median follow-up of 65 months were 93% and 87%, respectively. Because imatinib dosage was reduced in many patients due mainly to adverse events, subgroup analysis was performed according to the mean daily dose during the first 24 months of treatment: ≥360 mg (400-mg group; n = 294), 270-359 mg (300-mg group; n = 90) and <270 mg (200-mg group; n = 67). There were no significant differences in OS and EFS between the 300- and 400-mg groups; however, cumulative rates of complete cytogenetic and major molecular responses differed significantly between the two groups. There were no significant differences in mean imatinib trough levels between these two groups for the patients in whom trough levels had been measured. Survival and efficacy in the 200-mg group were markedly inferior to the former two groups. These results suggest that, although a daily dose of 400 mg imatinib is associated with better outcomes, 300 mg imatinib may be adequate for a considerable number of Japanese patients who are intolerant to 400 mg imatinib. Blood level monitoring would be useful to determine the optimal dose of imatinib., (© 2012 Japanese Cancer Association.)

Philadelphia-chromosome (Ph1)-positive leukemia cells frequently express death receptors DR4/DR5 for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and show high TRAIL-sensitivity. It has been reported that imatinib damaged cardiomyocytes by triggering endoplasmic reticulum (ER) stress and that ER stress inducers intensified TRAIL-sensitivity of some cancer cells by upregulating DR4/DR5 expression. In fact, ER stress inducers enhanced TRAIL-sensitivity of Ph1-positive leukemia cells by upregulating DR4/DR5 expression. In contrast, imatinib did not induce ER stress responses and unexpectedly downregulated DR4/DR5 expression, indicating that sensitization of Ph1-positive leukemia cells to TRAIL-mediated cellular immunity by imatinib through upregulation of DR4/DR5 expression is unlikely., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

To overcome imatinib resistance, more potent ABL tyrosine kinase inhibitors (TKIs), such as nilotinib and dasatinib have been developed, with demonstrable preclinical activity against most imatinib-resistant BCR-ABL kinase domain mutations, with the exception of T315I. However, imatinib-resistant patients already harboring mutations have a higher likelihood of developing further mutations under the selective pressure of potent ABL TKIs. NVP-AUY922 (Novartis) is a novel 4,5-diaryloxazole adenosine triphosphate-binding site heat shock protein 90 (HSP90) inhibitor, which has been shown to inhibit the chaperone function of HSP90 and deplete the levels of HSP90 client protein including BCR-ABL. In this study, we investigated the combined effects of AUY922 and nilotinib on random mutagenesis for BCR-ABL mutation (Blood, 109; 5011, 2007). Compared with single agents, combination with AUY922 and nilotinib was more effective at reducing the outgrowth of resistant cell clones. No outgrowth was observed in the presence of 2 μM of nilotinib and 20 nM of AUY922. The observed data from the isobologram indicated the synergistic effect of simultaneous exposure to AUY922 and nilotinib even in BaF3 cells expressing BCR-ABL mutants including T315I. In vivo studies also demonstrated that the combination of AUY922 and nilotinib prolonged the survival of mice transplanted with mixture of BaF3 cells expressing wild-type BCR-ABL and mutant forms. Taken together, this study shows that the combination of AUY922 and nilotinib exhibits a desirable therapeutic index that can reduce the in vivo growth of mutant forms of BCR-ABL-expressing cells.

The TARGET system is an online database that can be easily accessed by physicians. The registration of one's own chronic myeloid leukemia (CML) patients in the TARGET system makes it possible to share experiences among physicians, and, thus, may facilitate appropriate treatment for patients. Patients were registered in the TARGET system from October 2003 to March 2010 in Japan. A total of 1236 patients from 176 hospitals were registered in Japan. We analyzed data from 639 CML chronic phase patients not receiving prior therapy registered in this system. After 90 months follow-up, high survival rates were demonstrated for imatinib-treated newly diagnosed CML patients, with event-free survival (EFS), progression-free survival (PFS), and overall survival (OS) rates of 79.1, 94.8, and 95.1%, respectively. A landmark analysis of 296 patients who showed a complete cytogenetic response (CCyR) at 12 months after the initiation of imatinib treatment revealed that, at 90 months, 99% of patients (95% CI, 98-100) had not progressed to accelerated phase (AP) or blastic crisis (BC). The patients showing a CCyR and a reduction of at least 3log levels of BCR-ABL transcripts after 18 months of treatment had an estimated survival rate without CML progression of 100% at 84 months. The probability of achieving undetectable BCR-ABL in patients by 72 months with an major molecular response (MMR) at 12 months was 86.5%, compared with 64.7% for those without an MMR (p < 0.0001). There were no new safety issues. In summary, based on this 7-year TARGET analysis, imatinib showed a continual clinical benefit as first-line therapy for newly diagnosed CML. The TARGET system may represent a more practical and general feature compared with the IRIS study., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

We report a case of imatinib- and nilotinib-resistant Ph-positive chronic myeloid leukemia (CML) in blast crisis in which successful pretreatment with dasatinib with cord blood transplantation resulted in molecular remission. Before dasatinib therapy, the patient was found to have a F359V BCR-ABL mutation. He was treated with dasatinib for just 16, 19 days before allogeneic stem cell transplantation. This successful case indicates that reduction of tumor burden by second-generation tyrosine kinase inhibitors, in combination with stem cell transplantation, might be effective to treat CML, even in the advanced phase.

Although imatinib mesylate therapy is effective for chronic myeloid leukemia (CML) patients, there are still some unanswered questions. It is unclear whether imatinib can actually cure CML and whether this therapy can be safely discontinued in patients showing complete cytogenetic and molecular responses. This report describes the clinical outcome of a patient with chronic phase CML who discontinued imatinib therapy after achieving molecular remission. This patient has shown a relapse based on transcription-mediated amplification-hybridization protection assay (TMA-HPA) to monitor BCR-ABL transcripts, highlighting the uncertainty of discontinuing imatinib therapy for five months.

Imatinib at a daily dose of 400 mg is the standard treatment for chronic myelogenous leukemia in the chronic phase. However, the feasibility of this dose for small Japanese adults has not been clarified. We prospectively investigated the toxicity and efficacy of this dose in adult Japanese patients. Among the 89 evaluable patients with a median body weight of 62.8 kg, imatinib therapy was held in 40 subjects (45%), due to Grade 3-4 toxicities in 30 patients (75%) and Grade 2 toxicities at the discretion of the attending physician in 10 patients (25%). However, treatment was resumed and the dose was gradually increased until 62 of the 89 patients tolerated a maintenance dose of 400 mg. Older age and lower body weight were significant independent risk factors for discontinuation of imatinib. After a median follow-up period of 31 months, 84 patients were alive without progression. The complete cytogenetic response rate was 60 and 90% at 6 months and 1 year after starting imatinib, respectively. Older patients and those with a lower body weight were less likely to achieve a complete cytogenetic response. These findings suggest that the body weight has a significant influence on the toxicity and efficacy of imatinib in patients with a small body size, although dose reduction in proportion to weight may result in an inadequate response to imatinib., (Copyright 2008 Wiley-Liss, Inc.)

Since hematology is a highly specialized field, an individual physician may not have much direct treatment experience with a given disease. Therefore, the Japanese Society of Hematology (JSH) has discussed establishing a registry of hematologic disorders, in order to contribute to improving the quality of treatments and clinical outcomes in this field. As a first step, the Timely and Appropriate Registration System for GLIVEC Therapy (TARGET), a registration system for chronic myeloid leukemia (CML) patients treated with imatinib, was established in October 2003. We present the preliminary results of the first 4 years' experience with this system. CML patients treated with imatinib in Japan were registered through the website and the patient's clinical course, including parameters and events like imatinib dose, blood counts, adverse events, and efficacy were recorded in months 1, 3, 6, 9, and 12 and then every 6 months thereafter. By September 2007, 862 patients from 176 hospitals were registered. Follow-up period was 0-54 months, and 127 patients were followed-up for more than 36 months. Based on these cumulative data, present imatinib treatment trends were analyzed and safety and efficacy were compared with international trial data.

Purpose: Although dual src-family kinase/BCR/ABL inhibitor, dasatinib (BMS-354825), provides therapeutic advantages to imatinib-resistant cells, the mechanism of dasatinib resistance was not fully known., Experimental Design: We used TF-1 BCR/ABL cells, by introducing the BCR/ABL gene into a leukemia cell line, TF-1 and K562, and established dasatinib- (BMS-R) and imatinib-resistant (IM-R) cells. We characterized chronic myelogenous leukemia drug-resistant cells and examined intracellular signaling., Results: The IC(50) of dasatinib was 0.75 nmol/L (TF-1 BCR/ABL), 1 nmol/L (K562), 7.5 nmol/L (TF-1 BCR/ABL IM-R), 10 nmol/L (K562 IM-R), 15 micromol/L (TF-1 BCR/ABL BMS-R), and 25 micromol/L (K562 BMS-R). The number of BCR/ABL copies in resistant cell lines was the same as the parental cell line by fluorescence in situ hybridization analysis. There was no mutation in Abl kinase. We found that protein levels of BCR/ABL were reduced in dasatinib-resistant cell lines. BCR/ABL protein was increased by treatment of an ubiquitin inhibitor. The Src kinase, Lck, as well as mitogen-activated protein kinase and Akt were activated, but p21(WAF), phosphatase and tensin homologue was reduced in K562 BMS-R cells. Removal of dasatinib from the culture medium of K562 BMS-R cells led to apoptosis, and activated caspase 3 and poly (ADP-ribose) polymerase., Conclusion: These results suggest that the expression and protein activation signatures identified in this study provide insight into the mechanism of resistance to dasatinib and imatinib and may be of therapeutic chronic myelogenous leukemia value clinically.

Dasatinib is an ATP-competitive, multi-targeted SRC and ABL kinase inhibitor that can bind BCR-ABL in both the active and inactive conformations. From a clinical standpoint, dasatinib is particularly attractive because it has been shown to induce hematologic and cytogenetic responses in imatinib-resistant chronic myeloid leukemia patients. The fact because the combination of imatinib and dasatinib shows the additive/synergistic growth inhibition on wild-type p210 BCR-ABL-expressing cells, we reasoned that these ABL kinase inhibitors might induce the different molecular pathways. To address this question, we used DNA microarrays to identify genes whose transcription was altered by imatinib and dasatinib. K562 cells were cultured with imatinib or dasatinib for 16 h, and gene expression data were obtained from three independent microarray hybridizations. Almost all of the imatinib- and dasatinib-responsive genes appeared to be similarly increased or decreased in K562 cells; however, small subsets of genes were identified as selectively altered expression by either imatinib or dasatinib. The distinct genes that are selectively modulated by dasatinib are cyclin-dependent kinase 2 (CDK2) and CDK8, which had a maximal reduction of <5-fold in microarray screen. To assess the functional importance of dasatinib regulated genes, we used RNA interference to determine whether reduction of CDK2 and CDK8 affected the growth inhibition. K562 and TF-1BCR-ABL cells, pretreated with CDK2 or CDK8 small interfering RNA, showed additive growth inhibition with imatinib, but not with dasatinib. These findings demonstrate that the additive/synergistic growth inhibition by imatinib and dasatinib may be mediated in part by CDK2 and CDK8.

Imatinib mesylate is a relatively new drug that targets the BCR-ABL chimeric protein, the molecular basis of chronic myeloid leukemia (CML). A phase II clinical trial in 39 Japanese patients in the first chronic phase of CML was conducted with imatinib mesylate at a dose of 400 mg/day. Hematologic complete response was obtained in 92.3% of the patients, complete cytogenetic response (CR) was obtained in 43.6%, and major partial CR was obtained in 20.5% of the patients. Although 29 of 39 patients required an adjustment of dosing because of grade 3 or 4 adverse events, most of the events were reversible, and 25 of the 29 patients were able to resume therapy. Between day 15 and day 35, grade 3 or 4 neutropenia and/or leukocytopenia occurred in 13 patients, and grade 3 thrombocytopenia occurred in 5 patients. Overall, nonhematologic grade 3 adverse events occurred in 28.2% of the patients. These data support the use of imatinib mesylate as the treatment of choice for chronic-phase CML patients.

Imatinib therapy is an important contribution to the management of patients with chronic myelogenous leukemia (CML). Despite high rates of hematologic and cytogenetic responses to imatinib therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of CML. Experimental and clinical studies suggest that imatinib as a single drug may not be sufficient to eradicate BCR-ABL-positive stem cells. Therefore, whether combinations of imatinib with other agents can increase the length of molecular remission and whether such combinations can prolong survival should be determined by large-scale clinical studies. In this review, we discuss efficacious combinations for future clinical trials. These regimens combine imatinib with conventional chemotherapeutic agents or with inhibitors of other signal transduction molecules that may be preferentially activated in CML cells.

Despite high rates of hematologic and cytogenetic responses to imatinib therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of Ph-positive leukemia. The high frequency of BCR-ABL mutations and amplifications represents the high degree of heterogeneity in patients with advanced phase of CML, in whom multiple leukemic clones may exist. Therefore, a single inhibitor is unlikely to able to block all mutants.

Purpose: The near-universal emergence of imatinib resistance in patients with acute forms of Philadelphia chromosome-positive leukemia highlights the need for additional therapy to control this disease. G3139 (Genasense, oblimersen; Genta Inc.), a Bcl-2 antisense oligonucleotide, has been shown to down-regulate the Bcl-2 protein and induce apoptosis in myeloid leukemia cells from treated patients. We tested G3139 for its ability to inhibit BCR-ABL-mediated transformation in mice., Experimental Design: Nude mice (n = 5/group) were transplanted s.c. with imatinib-resistant BCR-ABL-transformed TF-1 cells (BCR-ABL-TF-1-R cells). Mice with established tumors (0.1 g) were treated for 14 days with G3139 (7 mg/kg/day i.p.), or with the reverse-sequence control oligonucleotide G3622 (7 mg/kg/day i.p.) or with imatinib (50 mg/kg/day i.p.)., Results: Mice treated with G3622 or imatinib died within 10-12 weeks. Nearly all of the mice treated with G3139 survived for >6 months and had reduced tumor volume. Three of the 5 mice showed complete tumor regression. A transient decrease in Bcl-2 protein was observed that correlated with histological evidence of apoptosis. In addition, we harvested BCR-ABL-TF-1-R tumor cells from mice treated with G3139 or control G3622 (7 mg/kg/day i.p., 7 days). Cells were then cultured with the antileukemic agents imatinib, daunorubicin, 1-beta-D-arabinofuranosylcytosine, or etoposide. G3139 pretreatment resulted in enhanced induction of apoptosis by all of the agents., Conclusion: These results suggest that G3139 is a promising candidate for treatment of patients with imatinib-resistant Ph-positive leukemia, and that combination of G3139 and imatinib may be useful to circumvent clinically acquired imatinib resistance.

Imatinib mesylate is a 2-phenylaminopyrimidine tyrosine kinase inhibitor with specific activity for ABL, platelet-derived growth factor receptor, and c-kit receptor. The pharmacological basis of this interaction has been elucidated by crystallographic studies. Imatinib mesylate binds to the amino acids of the BCR-ABL tyrosine kinase ATP binding site and stabilizes the inactive, non-ATP-binding form of BCR-ABL, thereby preventing tyrosine autophosphorylation, and in turn, phosphorylation of its substrates. This process ultimately results in a "switch-off" of the downstream signaling pathways that promote leukemogenesis. Despite high rates of hematologic and cytogenetic responses to imatinib therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of Ph-positive leukemia. Considerable progress has been made in developing therapeutic agents that are effective against molecular targets specifically expressed in CML cells. It is important to emphasize that BCR-ABL is the ideal target for therapy even at relapse; at least one general mechanism of resistance involves maintenance of an active BCR-ABL kinase inside leukemic cells. It is also notable that the high frequency of BCR-ABL mutations and amplifications represents the high degree of heterogeneity in patients with advanced CML, in whom multiple leukemic clones may exist. For these reasons, a single inhibitor is unlikely to be able to block all mutants described so far.

BCR-ABL fusion proteins exhibit elevated tyrosine kinase activity and transforming properties. Genetic and biochemical data suggest that Ras activation plays a central role in leukemogenic transformation by BCR-ABL. Imatinib (Novartis, Basel, Switzerland) is a potent and selective inhibitor of the tyrosine kinase activity of BCR-ABL. Although imatinib has shown promise against Ph-positive leukemia in human clinical trials, the emergence of imatinib resistance in patients with acute forms of Ph-positive leukemia has highlighted the need for combination chemotherapy to eradicate this disease. In the present study, combined use of a farnesyl transferase inhibitor, SCH66336 (lonafarnib), with the antileukemic agents imatinib, daunorubicin, cytosine arabinoside, or etoposide was investigated by cell proliferation assays. The effects of the combination of SCH66336 and imatinib were also investigated by apoptosis assay and colony-forming assay. In proliferation assays with BCR-ABL-expressing cells, combination of SCH66336 with imatinib or cytosine arabinoside showed enhanced antiproliferative activity, whereas combination of SCH66336 with daunorubicin or etoposide demonstrated an antagonistic effect. The combination of imatinib plus SCH66336 more effectively inhibited hematopoietic colony formation by primary human chronic myelogenous leukemia cells. SCH66336 combined with imatinib was shown to induce apoptosis in imatinib-resistant BCR-ABL cells by flow cytometric analysis with an APO2.7 monoclonal antibody. These results indicate that SCH66336 is a promising candidate for use in the treatment of patients with imatinib-resistant, Ph-positive leukemia and that the combination of SCH66336 plus imatinib may be useful to circumvent resistance.

A member of the Forkhead transcription factor family, FKHRL1, lies downstream of the phosphatidylinositol 3-kinase-Akt activation pathway in cytokine signaling. Because the phosphatidylinositol 3-kinase-Akt activation pathway is required for BCR-ABL-mediated transformation and survival signaling in chronic myelogenous leukemia (CML), in this study we examined the involvement of FKHRL1 in the BCR-ABL-mediated signaling pathway. FKHRL1 was constitutively phosphorylated in BCR-ABL-expressing cell lines KCL22 and KU812, and its phosphorylation was inhibited by treatment with STI571, a specific inhibitor of BCR-ABL tyrosine kinase. Concomitantly, STI571 induced cell cycle arrest at the G(0)/G(1) phase, accompanied by up-regulation of a cyclin-dependent kinase inhibitor p27/Kip1 in KCL22 cells. In addition, FKHRL1 was constitutively phosphorylated in the TF-1/bcr-abl cell line ectopically expressing BCR-ABL but not in the parent TF-1 cell line. Considering several lines of evidence that phosphorylated FKHRL1 has lost transcriptional activity and that p27/Kip1 expression is positively regulated by dephosphorylated "active" FKHRL1, BCR-ABL may down-regulate p27/Kip1 expression via the loss of FKHRL1 function as a transcription factor. To demonstrate this hypothesis, we generated a tamoxifen-inducible "active FKHRL1" FKHRL1-TM (a triple mutant of FKHRL1, in which all three Akt phosphorylation sites have been mutated), estrogen receptor system in the KCL22 cell line. The addition of tamoxifen inhibited the cell growth indicating that overexpression of FKHRL1 in the nucleus antagonized deregulated proliferation of CML cells. Collectively, FKHRL1 regulates the expression of p27/Kip1 as a downstream molecule of BCR-ABL signaling in CML cells. BCR-ABL-induced loss of FKHRL1 function may be involved in oncogenic transformation of CML partially via the down-regulation of p27/Kip1 proteins.

Purpose: Telomerase is a ribonucleoprotein enzyme that maintains protective structures at the ends of eukaryotic chromosomes. Earlier findings have supported an association between progressive telomere shortening in the chronic phase of chronic myelogenous leukemia and the up-regulation of telomerase activity occurring late in the evolution of the disease. We examined the impact of telomerase inhibition by dominant negative-human telomerase reverse transcriptase (DN-hTERT) on the biological features of BCR-ABL-transformed cells., Experimental Design: We introduced vectors encoding DN-hTERT, wild-type (WT)-hTERT, or a control vector expressing only a drug-resistant marker into Philadelphia chromosome-positive K562 cells and OM9;22 cells and assessed the biological effect of telomerase inhibition on cellular immortality., Results: Ectopic expression of DN-hTERT resulted in complete inhibition of telomerase activity and reduction of telomere length. The entire population of telomerase-inhibited K562 cells exhibited cytoplasmic blebbling and chromatin condensation, features of apoptosis. In contrast, K562 cells expressing WT-hTERT, which differ from the mutants by only two amino acids, exhibited normal morphology. The evidence of apoptosis in the telomerase-inhibited cells was determined by flow cytometric analysis with APO2.7 monoclonal antibody. We also observed enhanced induction of apoptosis by imatinib seen in DN-hTERT-expressing K562 cells, as compared with WT-hTERT-expressing cells., Conclusions: These results demonstrate that disruption of telomere maintenance limits the cellular life span of leukemia cells and show that the combined use of imatinib and telomere maintenance inhibition may be effective in the treatment of BCR-ABL-positive leukemia.

A 73-year-old woman with chronic myeloid leukemia was treated with interferon-alpha, hydroxyurea, and busulfan before imatinib mesylate treatment. The leukocyte count was 8,400/; hemoglobin concentration, 12.0 g/; and platelet count, 19.7 x 10(4)/. She received 400 mg of imatinib mesylate for 17 days before the agent was discontinued because of pancytopenia. A bone marrow biopsy on the 87th day after the last imatinib mesylate administration demonstrated severe hypocellularity. She needed many RBC and Plt transfusions and filgrastim administration. Grade 4 neutropenia continued for 35 days and Grade 3 thrombocytopenia continued for over 122 days. Imatinib mesylate, an agent targeting BCR-ABL, is expected to be useful as an effective therapeutic agent for chronic myeloid leukemia. However the present case suggests that its appropriate dose is individually variable and we should carefully consider the former treatment, and the clinical stage of the disease before initiating imatinib treatment.