Abstract: Molecularly targeted kinase inhibitor cancer therapies are currently administered sequentially rather than simultaneously. We addressed the potential long-term impact of this strategy in patients with chronic myelogenous leukemia (CML), which is driven by the fusion oncogene BCR-ABL. Analysis of BCR-ABL genotypes in CML patients who relapsed after sequential treatment with the ABL inhibitors imatinib and dasatinib revealed evolving resistant BCR-ABL kinase domain mutations in all cases. Twelve patients relapsed with the pan-resistant T315I mutation, whereas 6 patients developed novel BCR-ABL mutations predicted to retain sensitivity to imatinib based on in vitro studies. Three of these patients were retreated with imatinib (or the chemically related compound nilotinib) and responded; however, selection for compound mutants (2 or 3 BCR-ABL mutations in the same molecule) can substantially limit the potential effectiveness of retreating patients with inhibitors that have previously failed. Furthermore, drug-resistant mutations, when compounded, can increase oncogenic potency relative to the component mutants in transformation assays. The Aurora kinase inhibitor VX-680, currently under clinical evaluation based on its activity against the T315I mutation, is also effective against the other commonly detected dasatinib-resistant mutation in our analysis, V299L. Our findings demonstrate the potential hazards of sequential kinase inhibitor therapy and suggest a role for a combination of ABL kinase inhibitors, perhaps including VX-680, to prevent the outgrowth of cells harboring drug-resistant BCR-ABL mutations.

Abstract: Blast crisis chronic myelogenous leukemia (CML-BC) and Philadelphia chromosome–positive (Ph1-positive) acute lymphocytic leukemia (ALL) are 2 fatal BCR/ABL-driven leukemias against which Abl kinase inhibitors fail to induce a long-term response. We recently reported that functional loss of protein phosphatase 2A (PP2A) activity is important for CML blastic transformation. We assessed the therapeutic potential of the PP2A activator FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol hydrochloride), an immunomodulator in Phase III trials for patients with multiple sclerosis or undergoing organ transplantation, in CML-BC and Ph1 ALL patient cells and in in vitro and in vivo models of these BCR/ABL+ leukemias. Our data indicate that FTY720 induces apoptosis and impairs clonogenicity of imatinib/dasatinib-sensitive and -resistant p210/p190BCR/ABL myeloid and lymphoid cell lines and CML-BCCD34+ and Ph1 ALLCD34+/CD19+ progenitors but not of normal CD34+ and CD34+/CD19+ bone marrow cells. Furthermore, pharmacologic doses of FTY720 remarkably suppress in vivo p210/p190BCR/ABL-driven [including p210/p190BCR/ABL (T315I)] leukemogenesis without exerting any toxicity. Altogether, these results highlight the therapeutic relevance of rescuing PP2A tumor suppressor activity in Ph1 leukemias and strongly support the introduction of the PP2A activator FTY720 in the treatment of CML-BC and Ph1 ALL patients.

Abstract: Dasatinib is a small-molecule kinase inhibitor used for the treatment of imatinib-resistant chronic myelogenous leukemia (CML). We have analyzed the kinases targeted by dasatinib by using an unbiased chemical proteomics approach to detect binding proteins directly from lysates of CML cells. Besides Abl and Src kinases, we have identified the Tec kinases Btk and Tec, but not Itk, as major binders of dasatinib. The kinase activity of Btk and Tec, but not of Itk, was inhibited by nanomolar concentrations of dasatinib in vitro and in cultured cells. We identified the gatekeeper residue as the critical determinant of dasatinib susceptibility. Mutation of Thr-474 in Btk to Ile and Thr-442 in Tec to Ile conferred resistance to dasatinib, whereas mutation of the corresponding residue in Itk (Phe-435) to Thr sensitized the otherwise insensitive Itk to dasatinib. The configuration of this residue may be a predictor for dasatinib sensitivity across the kinome. Analysis of mast cells derived from Btk-deficient mice suggested that inhibition of Btk by dasatinib may be responsible for the observed reduction in histamine release upon dasatinib treatment. Furthermore, dasatinib inhibited histamine release in primary human basophils and secretion of proinflammatory cytokines in immune cells. The observed inhibition of Tec kinases by dasatinib predicts immunosuppressive (side) effects of this drug and may offer therapeutic opportunities for inflammatory and immunological disorders.

Abstract: The tyrosine kinase inhibitor imatinib (Gleevec, Novartis Pharmaceuticals Corporation; Basel, Switzerland) is a powerful drug for treatment of chronic myelogenous leukemia (CML) and other malignancies. It selectively targets various tyrosine kinases, thereby leading to growth arrest of respective cancer cells. Given its wide application, it is of high importance to know all related underlying molecular mechanisms. We had previously found that imatinib increases the cellular clearance of intracellular protein aggregates by targeting the abl pathway and thereby upregulating lysosomal activity. Here, we describe that imatinib dose dependently activates the cellular autophagy machinery in mammalian cells, independently of tissue type, species origin or immortalization status of cells. Autophagy is an archetypical cellular degradation mechanism implicated in many physiological and pathophysiological conditions. Our data link for the first time the process of autophagy with the mode of action of imatinib. Induction of autophagy might represent an additional mechanism of imatinib to induce growth arrest, promote apoptosis in cancer cells and eventually even promote tumour regression.

Abstract: Background Imatinib mesylate treatment causes remissions in a majority of patients with chronic myeloid leukemia (CML), but relapses are an increasing problem. We hypothesized that imatinib-resistant leukemic cells emerge from CML stem cells that acquire BCR-ABL gene mutations even before exposure to BCR-ABL-targeted agents such as imatinib. Methods Lineage-negative (i.e., immature) CD34+ CD38- CML stem cell-enriched populations were isolated from five patients with chronic phase CML samples by fluorescence-activated cell sorting. To identify BCR-ABL gene mutations, complementary DNAs (cDNAs) prepared from purified CML stem cells were subjected to allele-specific amplification using primers corresponding to 16 kinase domain mutations, with normal bone marrow cells serving as negative controls. We also cloned and directly sequenced BCR-ABL cDNAs prepared from freshly isolated CML stem cells and from their progeny generated after 3-5 weeks of culture. Results In 20%-33% of cDNA preparations from freshly isolated CML stem cell-enriched populations, both allele-specific amplification and direct sequencing methods revealed mutations in sequences corresponding to the BCR-ABL kinase domain. Mutations were not observed in cDNA sequences encoding the c-ABL kinase domain that were obtained from similar types of primitive normal cells. More than 70 different BCR-ABL mutations (including frameshift mutations and premature stop codons) were identified in the progeny of cultured CML stem cells. Analysis of individual clones derived from the cultured cells demonstrated that new BCR-ABL mutations were produced. Conclusions Primary CML stem cells display instability of the BCR-ABL fusion gene both in vivo and in vitro. Thus, patients may possess leukemic stem cells with BCR-ABL kinase mutations before initiation of BCR-ABL-targeted therapies and would likely be predisposed to develop resistance to these agents.

Abstract: The Aurora kinases play an important role in chromosome alignment, segregation, and cytokinesis during mitosis. Aberrant expression of these kinases occurs in solid tumors and is associated with aneuploidy and carcinogenesis. We found in this study that Aurora kinase A and B were aberrantly expressed in a variety of types of human leukemia cell lines (n = 15, e.g., PALL-1, PALL-2, HL-60, NB4, MV4-11, etc.), as well as freshly isolated leukemia cells from individuals with acute myelogenous leukemia (n = 44) compared with bone marrow mononuclear cells from healthy volunteers (n = 11), as measured by real-time PCR. ZM447439 is a novel selective Aurora kinase inhibitor. The compound induced growth inhibition, caused accumulation of cells with 4N/8N DNA content, and mediated apoptosis of human leukemia cells as measured by thymidine uptake, cell cycle analysis, and annexin V staining, respectively. Especially profound growth inhibition occurred with the PALL-1 and PALL-2 cells, which possess wild-type p53 gene. In contrast, ZM447439 did not inhibit clonogenic growth of myeloid committed stem cells harvested from healthy normal volunteers. Taken together, inhibition of Aurora kinases may be a promising treatment strategy for individuals with leukemia.

Abstract: Mutations in the kinase domain of Bcr-Abl are the most common cause of resistance to therapy with imatinib in patients with chronic myelogenous leukemia (CML). Second-generation Bcr-Abl inhibitors are able to overcome most imatinib-resistant mutants, with the exception of the frequent T315I substitution, which is emerging as a major cause of resistance to these drugs in CML patients. Structural studies could be used to support the drug design process for the development of inhibitors able to target the T315I substitution, but until now no crystal structure of the T315I Abl mutant has been solved. We show here the first crystal structure of the kinase domain of Abl T315I in complex with PHA-739358, an Aurora kinase inhibitor currently in clinical development for solid and hematologic malignancies. This compound inhibits in vitro the kinase activity of wild-type Abl and of several mutants, including T315I. The cocrystal structure of T315I Abl kinase domain provides the structural basis for this activity: the inhibitor associates with an active conformation of the kinase domain in the ATP-binding pocket and lacks the steric hindrance imposed by the substitution of threonine by isoleucine.

Abstract: The identification of the Philadelphia chromosome in cells from individuals with chronic myelogenous leukemia (CML) led to the recognition that the BCR-ABL tyrosine kinase causes CML. This in turn led to the development of imatinib mesylate, a clinically successful inhibitor of the BCR-ABL kinase. Incorporating the use of markers of BCR-ABL kinase inhibition into clinical trials led to the realization that imatinib-resistant kinase domain mutations are the major cause of relapse during imatinib therapy and the subsequent development of new inhibitors to treat CML patients. The development of imatinib validates an emerging paradigm in cancer, in which a tumor is defined by genetic abnormalities and effective therapies are developed that target events critical to the growth and survival of a specific tumor.

Abstract: Acute lymphoblastic leukemia (ALL) is the most common hematological malignancy affecting children. Despite significant progress and success in the treatment of ALL, a significant number of children continue to relapse and for them, outcome remains poor. Therefore, the search for novel therapeutic approaches is warranted. The aim of this study was to investigate the AMP activated protein kinase (AMPK) as a potential target in childhood acute lymphoblastic leukemia (ALL) subtypes characterized by non-random translocation signature profiles. We evaluated the effects of the AMPK activator AICAR on cell growth, cell cycle regulators and apoptosis of various childhood ALL cells. We found that treatment with AICAR inhibited cell proliferation, induced cell cycle arrest in G1-phase, and apoptosis in CCRF-CEM (T-ALL), NALM6 (Bp-ALL), REH (Bp-ALL, TEL/AML1) and SupB15 (Bp-ALL, BCR/ABL) cells. These effects were abolished by treatment with the adenosine kinase inhibitor 5'-iodotubericidin prior to addition of AICAR indicating that AICAR's cytotoxicity is mediated through AMPK activation. Moreover, we determined that growth inhibition exerted by AICAR was associated with activation of p38-MAPK and increased expression of the cell cycle regulators p27 and p53. We also demonstrated that AICAR mediated apoptosis through the mitochondrial pathway as revealed by the release of cytochrome C and cleavage of caspase 9. Additionally, AICAR treatment resulted in phosphorylation of Akt suggesting that activation of the PI3K/Akt pathway may represent a compensatory survival mechanism in response to apoptosis and/or cell cycle arrest. Combined treatment with AICAR and the mTOR inhibitor rapamycin resulted in additive anti-proliferative activity ALL cells. AICAR-mediated AMPK activation was found to be a proficient cytotoxic agent in ALL cells and the mechanism of its anti-proliferative and apoptotic effect appear to be mediated via activation of p38-MAPK pathway, increased expression of cell cycle inhibitory proteins p27 and p53, and downstream effects on the mTOR pathway, hence exhibiting therapeutic potential as a molecular target for the treatment of childhood ALL. Therefore, activation of AMPK by AICAR represents a novel approach to targeted therapy, and suggests a role for AICAR in combination therapy with inhibitors of the PI3K/Akt/mTOR pathways for the treatment of childhood in ALL.

Abstract: Purpose: Review the state-of-art knowledge of the biology and therapy of chronic myelogenous leukemia (CML). Experimental Design: A review of the literature was undertaken to summarize current information on the pathophysiology of CML and to update data of imatinib mesylate therapy, mechanisms of resistance, and in vitro and clinical data with the new tyrosine kinase inhibitors. Results: Imatinib, which targets the ABL kinase activity of BCR-ABL, has prolonged survival in CML. Despite the efficacy of imatinib, some patients in chronic phase and more in advanced phases of CML develop resistance, frequently as a result of BCR-ABL tyrosine kinase domain mutants that impair imatinib binding but retain enzymatic activity. New tyrosine kinase inhibitors inhibit BCR-ABL more potently than imatinib and maintain activity against an array of imatinib-resistant BCR-ABL mutants. The IC 50 values of nilotinib and dasatinib are at least 10- to 100-fold lower for BCR-ABL compared with imatinib. Phase I-II trials of nilotinib and dasatinib showed high activity in imatinib-resistant CML and Philadelphia chromosome–positive ALL. Dasatinib also inhibits members of the Src family of kinases (SFKs); nilotinib does not. Whether SFKs have a critical role in imatinib resistance or BCR-ABL–mediated oncogenesis is unresolved. Agents that target signals downstream of BCR-ABL (e.g. Ras/Raf and phosphatidylinositol 3-kinase) are under investigation. Conclusions: Understanding the pathophysiology of CML and mechanisms of resistance has produced effective targeted strategies for imatinib-resistant CML.

Abstract: Ph-positive leukemias are caused by the aberrant fusion of the BCR and ABL genes. Nilotinib is a selective Bcr/Abl tyrosine kinase inhibitor related to imatinib, which is widely used to treat chronic myelogenous leukemia. Because Ph-positive acute lymphoblastic leukemia only responds transiently to imatinib therapy, we have used mouse models to test the efficacy of nilotinib against lymphoblastic leukemia caused by the P190 form of Bcr/Abl. After transplant of 10,000 highly malignant leukemic cells into compatible recipients, untreated mice succumbed to leukemia within 21 days, whereas mice treated with 75 mg/kg nilotinib survived significantly longer. We examined cells from mice that developed leukemia while under treatment for Bcr/Abl kinase domain point mutations but these were not detected. In addition, culture of such cells ex vivo showed that they were as sensitive as the parental cell line to nilotinib but that the presence of stromal support allowed resistant cells to grow out. Nilotinib also exhibited impressive anti-leukemia activity in P190 Bcr/Abl transgenic mice that had developed overt leukemia/lymphoma masses and that otherwise would have been expected to die within 7 days. Visible lymphoma masses disappeared within six days of treatment and leukemic cell numbers in peripheral blood were significantly reduced. Treated mice survived more than 30 days. These results show that nilotinib has very impressive anti-leukemia activity but that lymphoblastic leukemia cells can become unresponsive to it both in vitro and in vivo through mechanisms that appear to be Bcr/Abl independent.

Abstract: An acquired autoactivating mutation with a V617F amino-acid substitution in the JAK2 tyrosine kinase is frequently found in BCR/ABL-negative myeloproliferative disorders (MPD). Hypermethylation of CpG islands within gene promoter regions is associated with transcriptional inactivation and represents an important mechanism of gene silencing in the pathogenesis of hematopoietic malignancies. In this study, we determined the DNA methylation status of 13 cancer-related genes in the context of JAK2 mutations in 39 patients with MPD. Genes analyzed for hypermethylation were SOCS-1, SHP-1, E-cadherin, MGMT, TIMP-2, TIMP-3, p15, p16, p73, DAPK1, RASSF1A, RARβ2 and hMLH1. We found at least one hypermethylated gene in 15/39 MPD patient specimens, and in 6/39 samples aberrant methylation of the negative cytokine regulator SOCS-1 was present. The JAK2V617F mutation was found in 21/39 patients as determined by allele-specific polymerase chain reaction. Hypermethylation of SOCS-1 was observed in 3/21 patients with an autoactivating JAK2 mutation and in 3/18 patients with wild-type JAK2. Our results suggest that epigenetic inactivation of SOCS-1 may be a complementary mechanism to the JAK2V617F mutation in the pathogenesis of MPD that leads to dysregulation of JAK-STAT signal transduction and thus contributes to growth factor hypersensitivity.

Abstract: The effect of ABT-737, a BH3-mimicking inhibitor for anti-apoptotic Bcl-2 and Bcl-X(L), but not Mcl-1, against Bcr-Abl-positive (Bcr-Abl(+)) leukaemic cells was examined. ABT-737 potently induced apoptosis in Bcr-Abl(+) chronic myeloid leukaemia (CML) cell lines and primary CML samples in vitro and prolonged the survival of mice xenografted with BV173 cells, a CML cell line. Higher expression of anti-apoptotic Bcl-2 proteins reduced cell killing by ABT-737 in each cell line, but there was no correlation between the sensitivities to ABT-737 and the specific expression patterns of Bcl-2 family proteins among cell lines. Thus, the cell killing effect of ABT-737 must be determined not only by the expression patterns of Bcl-2 family proteins but also by other mechanisms, such as high expression of Bcr-Abl, or a drug-efflux pump, in CML cells. ABT-737 augmented the cell killing effect of imatinib in Bcr-Abl(+) cells with diverse drug-resistance mechanisms unless leukaemic cells harboured imatinib-insensitive Abl kinase domain mutations, such as T315I. The combination of homoharringtonine that reduces Mcl-1 enhanced the killing by ABT-737 strongly in Bcr-Abl(+) cells even with T315I mutation. These results suggest that ABT-737 is a useful component of chemotherapies for CML with diverse drug-resistance mechanisms.

Abstract: In lung cancer, frequent loss of one allele of chromosome 3p is seen in both small cell lung cancer and non-small cell lung cancer (NSCLC), providing evidence of tumor suppressor genes (TSGs) in this chromosomal region. The mechanism of Fus1 tumor suppressor activity is unknown. We have found that a Fus1 peptide inhibits the Abl tyrosine kinase in vitro (IC50 35 μ M). The inhibitory Fus1 sequence was derived from a region that was deleted in a mutant FUS1 gene (FUS1 (1–80)) detected in some lung cancer cell lines. Importantly, a stearic acid-modified form of this peptide was required for the inhibition, but stearic acid alone was not inhibitory. Two NSCLC cell lines, which lack expression of wild-type Fus1, contain activated c-Abl. Forced expression of an inducible FUS1 cDNA in H1299 NSCLC cells decreased levels of activated c-Abl and inhibited its tyrosine kinase activity. Similarly, treatment of c-Abl immune complexes with the inhibitory Fus1 peptide also reduced the level of c-Abl in these immune complexes. The size and number of colonies of the NSCLC cell line, H1299, in soft agar was strongly inhibited by the Abl kinase inhibitor imatinib mesylate. Co-expression of FUS1 and c-ABL in COS1 cells blocked activation of c-Abl tyrosine kinase. In contrast, co-expression of mutant FUS1 (1–80) with c-ABL had little inhibitory activity against c-Abl. These findings provide strong evidence that c-Abl is a possible target in NSCLC patients that have reduced expression of Fus1 in their tumor cells.

Abstract: Many cancers and leukemias are associated with strong dominant oncogenic mutations that activate tyrosine kinases and other classes of molecules, including transcription factors and antiapoptotic mechanisms. Some of these events can be targeted with small molecules or antibody-based therapeutics, but many remain intractable. In addition, cancer-related enzyme targets can often mutate, and drug-resistant variants are selected. Therapies directed at the mRNA encoding dominant oncogenes could provide a more global set of technologies for cancer treatment. To test this concept, we have used the model of transformation of hematopoietic cells by the chimeric Bcr-Abl oncogene, a highly activated tyrosine kinase. Our results show that tandem arrays of miRNA mimics, but not single miRNA mimics, directed against the Abl portion of the mRNA and introduced by lentiviral vectors can effectively alter the leukemogenic potency when the degree of suppression of expression of Bcr-Abl is reduced >200-fold from control levels. Only methods capable of such dramatic sustained reduction in the level of expression of highly activated kinase oncogenes are likely to be effective in controlling malignant cell populations.

Abstract: Chronic myelogenous leukemia (CML) results from the transformation of a primitive hematopoietic cell by the BCR/ABL gene. BCR/ABL signaling has been studied in cell lines and murine models, but the transforming effects of BCR/ABL are highly dependent on cellular context, and mechanisms responsible for the transformation of primitive human hematopoietic cells remain poorly understood. Current targeted therapies fail to eliminate malignant CML progenitors, and improved understanding of crucial molecular mechanisms of progenitor transformation may facilitate the development of improved therapeutic approaches. We investigated the role of BCR/ABL tyrosine 177 (BCR/ABL-Y177) in CML progenitor transformation by comparing the effects of expression of Y177-mutated BCR/ABL, wild-type BCR/ABL, or green fluorescent protein alone on normal CD34+ cells. We show that BCR/ABL-Y177 plays a critical role in CML progenitor expansion, proliferation, and survival. BCR/ABL expression results in enhanced Ras and Akt activity but reduced mitogen-activated protein kinase activity in human hematopoietic cells, which is reversed by BCR/ABL-Y177 mutation. Blocking BCR/ABL-Y177–mediated signaling enhances targeting of CML progenitors by imatinib mesylate. Our studies indicate that BCR/ABL-Y177 plays an essential role in Ras and Akt activation and in human hematopoietic progenitor transformation in CML. [Cancer Res 2007;67(14):7045–53]

Abstract: The effects of the multikinase inhibitor sorafenib (BAY 43-9006), an agent shown previously to induce apoptosis in human leukemia cells through inhibition of myeloid cell leukemia-1 (Mcl-1) translation, have been examined in Bcr/Abl+ leukemia cells resistant to imatinib mesylate (IM). When administered at pharmacologically relevant concentrations (10–15 μM), sorafenib potently induced apoptosis in imatinib mesylate-resistant cells expressing high levels of Bcr/Abl, cells exhibiting a Bcr/Abl-independent, Lyn-dependent form of resistance, and CD34+ cells obtained from imatinib-resistant patients. In addition, Ba/F3 cells expressing mutations rendering them resistant to IM (e.g., E255K, M351T) or to IM, dasatinib, and nilotinib (T315I) remained fully sensitive to sorafenib. Induction of apoptosis by sorafenib was associated with rapid and pronounced down-regulation of Mcl-1 and diminished signal transducer and activator of transcription (STAT) 5 phosphorylation and reporter activity but only very modest and delayed inactivation of the Bcr/Abl downstream target Crkl. Moreover, transfection with a constitutively active STAT5 construct partially but significantly protected cells from sorafenib lethality. Ba/F3 cells expressing Bcr/Abl mutations were as sensitive to sorafenib-induced Mcl-1 down-regulation and dephosphorylation of STAT5 and eukaryotic initiation factor 4E as wild-type cells. Finally, stable knockdown of Bcl-2-interacting mediator of cell death (Bim) with short hairpin RNA in K562 cells significantly diminished sorafenib lethality, arguing strongly for a functional role of this proapoptotic Bcl-2 family member in the lethality of this agent. Together, these findings suggest that sorafenib effectively induces apoptosis in highly imatinib-resistant chronic myelogenous leukemia cells, most likely by inhibiting or down-regulating targets (i.e., STAT5 and Mcl-1) downstream or independent of Bcr/Abl.

Abstract: Chronic myeloid leukemia (CML) was the first human malignant disease to be linked to a single, acquired genetic abnormality. Identification of the Bcr-Abl kinase fusion protein and its pivotal role in the pathogenesis of CML provided new opportunities to develop molecular-targeted therapies. Imatinib mesylate (IM, Gleevec, Novartis Pharmaceuticals, Basel, Switzerland), which specifically inhibits the autophosphorylation of the Abl TK, has improved the treatment of CML. However, resistance is often reported in patients with advanced-stage disease. Several novel TK inhibitors have been developed that override IM resistance mechanisms caused by point mutations within the Abl kinase domain. Inhibitors of Abl TK are divided into two main groups, namely, ATP-competitive and ATP noncompetitive inhibitors. The ATP-competitive inhibitors fall into two subclasses, the Src/Abl inhibitors, and the 2-phenylaminopyrimidine-based compounds. Dasatinib (formerly BMS-354825), AP23464, SKI-606, and PD166326 are classified as Src/Abl inhibitors, while nilotinib (AMN107) and INNO-406 (NS-187) belong to the latter subclass of inhibitors. Of these agents, dasatinib and nilotinib underwent clinical trials earlier than the others and favorable results are now accumulating. Clinical studies of the other compounds, including SKI-606 and INNO-406, have been performed in rapid succession. Because of their strong affinities for the ATP-binding site compared to IM, most ATP-competitive inhibitors may be effective in IM-resistant patients. However, an ATP-competitive inhibitor that can inhibit the phosphorylation of T315I Bcr-Abl has not yet been developed. Instead, ATP noncompetitive inhibitors, such as ON012380, Aurora kinase inhibitor MK0457 (VX-680), and p38 MAP kinase inhibitor BIRB-796, have been developed to address this problem. This review provides an update on the underlying pathophysiologies of disease progression and IM resistance, and discusses the development of new targeted TK inhibitors for managing CML and the importance of future strategies targeting CML stem cells.

Abstract: The cytoplasmic tyrosine kinase Src has been implicated in signal transduction induced by growth factors and integrins. Src also shows oncogenic activity when deregulated. Accumulating evidence indicates that the tyrosine kinase Abl is an important substrate for Src signalling in normal cells. Here we show that Abl is also required for Src-induced transformation of mouse fibroblasts. Abl does not mediate tyrosine phosphorylation of Stat3 and Shc, two important regulators of Src oncogenic activity. In contrast, Abl controls the activation of the small GTPase Rac for oncogenic signalling and active Rac partly rescued Src transformation in cells with inactive Abl. Moreover, Abl mediates Src-induced extracellular regulated kinase 5 (ERK5) activation to drive cell transformation. Finally, we find that Abl/Rac and Abl/ERK5 pathways also operate in human MCF7 and BT549 breast cancer cells, where neoplastic transformation depends on Src-like activities. Therefore, Abl is an important regulator of Src oncogenic activity both in mouse fibroblasts and in human cancer cells. Targeting these Abl-dependent signalling cascades may be of therapeutic value in breast cancers where Src-like function is important.

Abstract: Altered mRNA metabolism is a feature of many cancers including blast crisis chronic myelogenous leukemia. Indeed, loss of function of many tumor suppressors regulating cell proliferation, survival, and differentiation results from aberrant mRNA processing, nuclear export, and/or translation. Here, we summarize the effects of increased BCR/ABL oncogenic activity on the expression and function of RNA binding proteins (e.g., FUS, hnRNP A1, hnRNP E2, hnRNP K, and La/SSB) with posttranscriptional and translational regulatory activities and their importance for the phenotype of BCR/ABL-transformed hematopoietic progenitors. We also provide evidence that these studies not only advance our understanding on the molecular mechanisms contributing to tumor/leukemia emergence, maintenance, and/or progression but they also serve for the identification of novel molecular targets useful for the development of alternative therapies for imatinib-resistant and blast crisis chronic myelogenous leukemia and, perhaps, for other cancers characterized by similar alterations in the mRNA metabolism.