p185(BCR/ABL) has a lower sensitivity than p210(BCR/ABL) to the allosteric inhibitor GNF-2 in Philadelphia chromosome-positive acute lymphatic leukemia

Background: The t(9;22) translocation leads to the formation of the chimeric breakpoint cluster region/c-abl oncogene 1 (BCR/ABL) fusion gene on der22, the Philadelphia chromosome. The p185(BCR/ABL) or the p210(BCR/ABL) fusion proteins are encoded as a result of the translocation, depending on whether a "minor" or "major" breakpoint occurs, respectively. Both p185(BCR/ABL) and p210(BCR/ABL) exhibit constitutively activated ABL kinase activity. Through fusion to BCR the ABL kinase in p185(BCR/ABL) and p210(BCR/ABL) "escapes" the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. A novel class of compounds including GNF-2 restores allosteric inhibition of the kinase activity and the transformation potential of BCR/ABL. Here we investigated whether there are differences between p185(BCR/ABL) and p210(BCR/ABL) regarding their sensitivity towards allosteric inhibition by GNF-2 in models of Philadelphia chromosome-positive acute lymphatic leukemia. Design and methods: We investigated the anti-proliferative activity of GNF-2 in different Philadelphia chromosome-positive acute lymphatic leukemia models, such as cell lines, patient-derived long-term cultures and factor-dependent lymphatic Ba/F3 cells expressing either p185(BCR/ABL) or p210(BCR/ABL) and their resistance mutants. Results: The inhibitory effects of GNF-2 differed constantly between p185(BCR/ABL) and p210(BCR/ABL) expressing cells. In all three Philadelphia chromosome-positive acute lymphatic leukemia models, p210(BCR/ABL)-transformed cells were more sensitive to GNF-2 than were p185BCR/ABL-positive cells. Similar results were obtained for p185(BCR/ABL) and the p210(BCR/ABL) harboring resistance mutations. Conclusions: Our data provide the first evidence of a differential response of p185(BCR/ABL)- and p210(BCR/ABL)- transformed cells to allosteric inhibition by GNF-2, which is of importance for the treatment of patients with Philadelphia chromosome-positive acute lymphatic leukemia

Allosteric inhibition enhances the efficacy of ABL kinase inhibitors to target unmutated BCR-ABL and BCR-ABL-T315I

Background: Chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphatic leukemia (Ph + ALL) are caused by the t(9;22), which fuses BCR to ABL resulting in deregulated ABL-tyrosine kinase activity. The constitutively activated BCR/ABL-kinase "escapes" the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. The ABL-kinase inhibitors (AKIs) Imatinib, Nilotinib or Dasatinib, which target the ATP-binding site, are effective in Ph + leukemia. Another molecular therapy approach targeting BCR/ABL restores allosteric inhibition. Given the fact that all AKIs fail to inhibit BCR/ABL harboring the 'gatekeeper' mutation T315I, we investigated the effects of AKIs in combination with the allosteric inhibitor GNF2 in Ph + leukemia. Methods: The efficacy of this approach on the leukemogenic potential of BCR/ABL was studied in Ba/F3 cells, primary murine bone marrow cells, and untransformed Rat-1 fibroblasts expressing BCR/ABL or BCR/ABL-T315I as well as in patient-derived long-term cultures (PDLTC) from Ph + ALL-patients. Results: Here, we show that GNF-2 increased the effects of AKIs on unmutated BCR/ABL. Interestingly, the combination of Dasatinib and GNF-2 overcame resistance of BCR/ABL-T315I in all models used in a synergistic manner. Conclusions: Our observations establish a new approach for the molecular targeting of BCR/ABL and its resistant mutants using a combination of AKIs and allosteric inhibitors

Targeting the oligomerization of BCR/ABL by membrane permeable competitive peptides inhibits the proliferation of Philadelphia Chromosome positive leukemic cells

The BCR/ABL fusion protein is the hallmark of Philadelphia Chromosome positive (Ph+) leukemia. The constitutive activation of the ABL-kinase in BCR/ABL cells induces the leukemic phenotype. Targeted inhibition of BCR/ABL by small molecule inhibitors reverses the transformation potential of BCR/ABL. Recently, we definitively proved that targeting the tetramerization of BCR/ABL mediated by the N-terminal coiled-coil domain (CC) using competitive peptides, representing the helix-2 of the CC, represents a valid therapeutic approach for treating Ph+ leukemia. To further develop competitive peptides for targeting BCR/ABL, we created a membrane permeable helix-2 peptide (MPH-2) by fusing the helix-2 peptide with a peptide transduction tag. In this study, we report that the MPH-2: (i) interacted with BCR/ABL in vivo; (ii) efficiently inhibited the autophosphorylation of BCR/ABL; (iii) suppressed the growth and viability of Ph+ leukemic cells; and (iv) was efficiently transduced into mononuclear cells (MNC) in an in vivo mouse model. This study provides the first evidence that an efficient peptide transduction system facilitates the employment of competitive peptides to target the oligomerization interface of BCR/ABL in vivo

Differential effects of selective inhibitors targeting the PI3K/AKT/mTOR pathway in acute lymphoblastic leukemia

Purpose: Aberrant PI3K/AKT/mTOR signaling has been linked to oncogenesis and therapy resistance in various malignancies including leukemias. In Philadelphia chromosome (Ph) positive leukemias, activation of PI3K by dysregulated BCR-ABL tyrosine kinase (TK) contributes to the pathogenesis and development of resistance to ABL-TK inhibitors (TKI). The PI3K pathway thus is an attractive therapeutic target in BCR-ABL positive leukemias, but its role in BCR-ABL negative ALL is conjectural. Moreover, the functional contribution of individual components of the PI3K pathway in ALL has not been established. Experimental design: We compared the activity of the ATP-competitive pan-PI3K inhibitor NVP-BKM120, the allosteric mTORC1 inhibitor RAD001, the ATP-competitive dual PI3K/mTORC1/C2 inhibitors NVP-BEZ235 and NVP-BGT226 and the combined mTORC1 and mTORC2 inhibitors Torin 1, PP242 and KU-0063794 using long-term cultures of ALL cells (ALL-LTC) from patients with B-precursor ALL that expressed the BCR-ABL or TEL-ABL oncoproteins or were BCR-ABL negative. Results: Dual PI3K/mTOR inhibitors profoundly inhibited growth and survival of ALL cells irrespective of their genetic subtype and their responsiveness to ABL-TKI. Combined suppression of PI3K, mTORC1 and mTORC2 displayed greater antileukemic activity than selective inhibitors of PI3K, mTORC1 or mTORC1 and mTORC2. Conclusions: Inhibition of the PI3K/mTOR pathway is a promising therapeutic approach in patients with ALL. Greater antileukemic activity of dual PI3K/mTORC1/C2 inhibitors appears to be due to the redundant function of PI3K and mTOR. Clinical trials examining dual PI3K/mTORC1/C2 inhibitors in patients with B-precursor ALL are warranted, and should not be restricted to particular genetic subtypes

Understanding a high-risk acute myeloid leukemia by analyzing the interactome of its major driver mutation

The WHO classifies t(6;9)-positive acute myeloid leukemia (AML) as a subgroup of high-risk AML because of its clinical and biological peculiarities, such as young age and therapy resistance. t(6;9) encodes the DEK/NUP214 fusion oncoprotein that targets only a small subpopulation of bone marrow progenitors for leukemic transformation. This distinguishes DEK/NUP214 from other fusion oncoproteins, such as PML/RARα, RUNX1/ETO, or MLL/AF9, which have a broad target population they block differentiation and increase stem cell capacity. A common theme among most leukemogenic fusion proteins is their aberrant localization compared to their wild-type counterparts. Although the actual consequences are widely unknown, it seems to contribute to leukemogenesis most likely by a sequester of interaction partners. Thus, we applied a global approach to studying the consequences of the aberrant localization of t(6;9)-DEK/NUP214 for its interactome. This study aimed to disclose the role of localization of DEK/NUP214 and the related sequester of proteins interacting with DEK/NUP214 for the determination of the biology of t(6;9)-AML. Here we show the complexity of the biological consequences of the expression of DEK/NUP214 by an in-depth bioinformatic analysis of the interactome of DEK/NUP214 and its biologically dead mutants. DEK/NUP214’s interactome points to an essential role for aberrant RNA-regulation and aberrant regulation of apoptosis and leukocyte activation as a significant determinant of the phenotype of t(6;9)-AML. Taken together, we provide evidence that the interactome contributes to the aberrant biology of an oncoprotein, providing opportunities for developing novel targeted therapy approaches

Activation of signaling pathways in models of t(6;9)-acute myeloid leukemia

Patients within the WHO-subgroup of t(6;9)-positive acute myeloid leukemia (AML) differ from other AML subgroups as they are characterised by younger age and a grim prognosis. Leukemic transformation can often be attributed to single chromosomal aberrations encoding oncogenes, in the case of t(6;9)-AML to the fusion protein DEK-CAN (also called DEK-NUP214). As being a rare disease there is the urgent need for models of t(6;9)-AML. The only cell line derived from a t(6;9)-AML patient currently available is FKH1. By using phospho-proteomics on FKH1 cells, we found a strongly activated ABL1 kinase. Further investigation revealed the presence of ETV6-ABL1. This finding renders necessary to determine DEK-CAN- and ETV6-ABL1-related features when using FKH1. This can be done as ETV6-ABL1 activity in FKH1 is responsive to imatinib. Nevertheless, we provided evidence that both SFK and mTOR activation in FKH1 are DEK-CAN-related features as they were activated also in other t(6;9) and DEK-CAN-positive models. The activation of STAT5 previously shown to be strong in t(6;9)-AML and activated by DEK-CAN is regulated in FKH1 by both DEK-CAN and ETV6-ABL1. In conclusion, FKH1 cells still represent a model for t(6;9)-AML and could serve as model for ETV6-ABL1-positive AML if the presence of these leukemia-inducing oncogenes is adequately considered. Taken together, all our results provide clear evidence of novel and specific interdependencies between leukemia-inducing oncogenes and cancer signaling pathways which will influence the design of therapeutic strategies to better address the complexity of cancer signaling

Dasatinib and Azacitidine followed by Haploidentical stem cell transplant for chronic Myeloid leukemia with evolving Myelodysplasia : a case report and review of treatment options

Background: CML presenting with a variant Philadelphia translocation, atypical BCR-ABL transcript, additional chromosomal aberrations, and evolving MDS is uncommon and therapeutically challenging. The prognostic significance of these genetic findings is uncertain, even as singular aberrations, with nearly no data on management and outcome when they coexist. MDS evolving during the course of CML may be either treatment-associated or an independently coexisting disease, and is generally considered to have an inferior prognosis. Tyrosine kinase inhibitors (TKI) directed against BCR-ABL are the mainstay of treatment for CML, whereas treatment modalities that may be utilized for MDS and CML include allogeneic stem cell transplant and – at least conceptually – hypomethylating agents. Case report: Here, we describe the clinical course of such a patient, demonstrating that long-term combined treatment with dasatinib and azacitidine for coexisting CML and MDS is feasible and well tolerated, and may be capable of slowing disease progression. This combination therapy had no deleterious effect on subsequent potentially curative haploidentical bone marrow transplantation. Conclusions: The different prognostic implications of this unusual case and new therapeutic options in CML are discussed, together with a review of the current literature on CML presenting with different types of genomic aberrations and the coincident development of MDS. Additionally, this case gives an example of long-term combined treatment of tyrosine kinase inhibitors and hypomethylating agents, which could be pioneering in CML treatment

BCR-ABL mediates arsenic trioxide-induced apoptosis independently of its aberrant kinase activity

In the prechemotherapy era arsenic derivatives were used for treatment of chronic myelogenous leukemia, a myeloproliferative disorder characterized by the t(9;22) translocation, the Philadelphia chromosome (Ph+). In acute promyelocytic leukemia response to arsenic trioxide (As2O3) has been shown to be genetically determined by the acute promyelocytic leukemia-specific t(15;17) translocation product PML/RARalpha. Hence, we reasoned that As2O3 might have a selective inhibitory effect on proliferation of BCR-ABL-expressing cells. Here, we report that: (a) As2O3 induced apoptosis in Ph+ but not in Ph- lymphoblasts; (b) enforced expression of BCR-ABL in U937 cells dramatically increased the sensitivity to As2O3; (c) the effect of As2O3 was independent of BCR-ABL kinase activity; and (d) As2O3 reduced proliferation of chronic myelogenous leukemia blasts but not of peripheral CD34+ progenitors. In summary, these data establish As2O3 as a tumor cell-specific agent, making its clinical application in Ph+ leukemia feasible

PIC-1/SUMO-1-modified PML-retinoic acid receptor alpha mediates arsenic trioxide-induced apoptosis in acute promyelocytic leukemia.

Fusion proteins involving the retinoic acid receptor alpha (RARalpha) and PML or PLZF nuclear protein are the genetic markers of acute promyelocytic leukemia (APL). APLs with PML-RARalpha or PLZF-RARalpha fusion protein differ only in their response to retinoic acid (RA) treatment: the t(15;17) (PML-RARalpha-positive) APL blasts are sensitive to RA in vitro, and patients enter disease remission after RA treatment, while those with t(11;17) (PLZF-RARalpha-positive) APLs do not. Recently it has been shown that complete remission can be achieved upon treatment with arsenic trioxide (As2O3) in PML-RARalpha-positive APL, even when the patient has relapsed and the disease is RA resistant. This appears to be due to apoptosis induced by As2O3 in the APL blasts by poorly defined mechanisms. Here we report that (i) As2O3 induces apoptosis only in cells expressing the PML-RARalpha, not the PLZF-RARalpha, fusion protein; (ii) PML-RARalpha is partially modified by covalent linkage with a PIC-1/SUMO-1-like protein prior to As2O3 treatment, whereas PLZF-RARalpha is not; (iii) As2O3 treatment induces a change in the modification pattern of PML-RARalpha toward highly modified forms; (iv) redistribution of PML nuclear bodies (PML-NBs) upon As2O3 treatment is accompanied by recruitment of PIC-1/SUMO-1 into PML-NBs, probably due to hypermodification of both PML and PML-RARalpha; (v) As2O3-induced apoptosis is independent of the DNA binding activity located in the RARalpha portion of the PML-RARalpha fusion protein; and (vi) the apoptotic process is bcl-2 and caspase 3 independent and is blocked only partially by a global caspase inhibitor. Taken together, these data provide novel insights into the mechanisms involved in As2O3-induced apoptosis in APL and predict that treatment of t(11;17) (PLZF-RARalpha-positive) APLs with As2O3 will not be successful