targeting the bcr-abl signaling pathway in therapy ...targeting the bcr-abl signaling pathway in...

Molecular Pathways

Targeting the BCR-ABL Signaling Pathway in Therapy-ResistantPhiladelphia Chromosome-Positive Leukemia

Thomas O’Hare1,2, Michael W.N. Deininger3, Christopher A. Eide1,2, Tim Clackson4, and Brian J. Druker1,2

AbstractBeginning with imatinib a decade ago, therapy based on targeted inhibition of the BCR-ABL kinase

has greatly improved the prognosis for chronic myeloid leukemia (CML) patients. The recognition that

some patients experience relapse due to resistance-conferring point mutations within BCR-ABL sparked

the development of the second-generation ABL kinase inhibitors nilotinib and dasatinib. Collectively,

these drugs target most resistant BCR-ABL mutants, with the exception of BCR-ABLT315I. A third wave of

advances is now cresting in the form of ABL kinase inhibitors whose target profile encompasses BCR-

ABLT315I. The leading third-generation clinical candidate for treatment-refractory CML, including

patients with the T315I mutation, is ponatinib (AP24534), a pan-BCR-ABL inhibitor that has entered

pivotal phase 2 testing. A second inhibitor with activity against the BCR-ABLT315I mutant, DCC-2036, is

in phase 1 clinical evaluation. We provide an up-to-date synopsis of BCR-ABL signaling pathways,

highlight new findings on mechanisms underlying BCR-ABL mutation acquisition and disease progres-

sion, discuss the use of nilotinib and dasatinib in a first-line capacity, and evaluate ponatinib, DCC-

2036, and other ABL kinase inhibitors with activity against BCR-ABLT315I in the development pipeline.

Clin Cancer Res; 17(2); 1–21. �2010 AACR.

Background

Chronic myeloid leukemia and the BCR-ABL signalingpathwayChronic myeloid leukemia (CML) is characterized by the

(9;22)(q34;q11) translocation, which is cytogeneticallyvisible as the Philadelphia chromosome (Ph) that givesrise to the BCR-ABL fusion protein (1, 2). BCR-ABL is aconstitutively active tyrosine kinase that drives survival andproliferation through multiple downstream pathways(Fig. 1A; reviewed in refs. 3–5). CML typically begins witha chronic phase characterized by expansion of functionallynormal myeloid cells; left untreated, the disease progressesto a fatal acute leukemia (blastic phase) of myeloid orlymphoid phenotype. The hallmark of blastic phase is lossof terminal differentiation capacity (6). A subset of patientswith B-cell acute lymphoblastic leukemia (Phþ ALL) also

harbors the Philadelphia chromosome (7, 8). The indis-pensable role of BCR-ABL in CML was established with theuse of a murine model in which recipients of BCR-ABLretrovirus-transduced bone marrow developed an aggres-sive CML-like myeloproliferative disorder (9). Mice expres-sing kinase-inactive BCR-ABL failed to develop leukemia,confirming a requirement for BCR-ABL kinase activity inleukemogenesis in vivo and suggesting BCR-ABL kinase as atherapeutic target (10).

TheN-terminal coiled coil domain of BCR-ABL facilitatesdimerization and trans-autophosphorylation (11, 12)(Fig. 1A). Autophosphorylation of tyrosine-177 of BCR-ABL promotes formation of a GRB2 complex with GAB2and son-of-sevenless (SOS), triggering activation of RASand recruitment of phosphatidylinositol 3-kinase (PI3K)and the tyrosine phosphatase SHP2 (13, 14). Signalingfrom RAS activates mitogen-activated protein kinase(MAPK) and enhances proliferation. PI3K activates theserine-threonine kinase AKT, which functions in: (1) pro-moting survival by suppressing the activity of forkhead O(FOXO) transcription factors (15); (2) enhancing cellproliferation by proteasomal degradation of p27 throughupregulation of SKP2, the F-Box recognition protein of theSCFSKP2 E3 ubiquitin ligase (16); and (3) activation ofmTOR, which leads to enhanced protein translation andcell proliferation (17, 18). An additional critical outlet ofBCR-ABL is STAT5 activation through direct phosphoryla-tion or indirectly through phosphorylation by HCK orJAK2 (19, 20); lack of STAT5 abrogates both myeloidand lymphoid leukemogenesis (21). Collectively, these

Authors' Affiliations: 1Division of Hematology and Medical Oncology,Oregon Health & Science University Knight Cancer Institute, Portland,Oregon; 2Howard Hughes Medical Institute, Portland, Oregon; 3Division ofHematology and Hematologic Malignancies, Huntsman Cancer Institute,University of Utah, Salt Lake City, Utah; 4ARIAD Pharmaceuticals, Inc.,Cambridge, Massachusetts

T. O’Hare and M. Deininger contributed equally to this work.

Corresponding Author: ThomasO’Hare, 3181 SWSam Jackson Park Rd,Mailcode L592, Portland, OR 97239. Phone: 503-494-1916; Fax: 503-494-3688; E-mail: [email protected]

doi: 10.1158/1078-0432.CCR-09-3314

�2010 American Association for Cancer Research.

ClinicalCancer

Research

www.aacrjournals.org OF1

Research. on July 16, 2017. © 2010 American Association for Cancerclincancerres.aacrjournals.org Downloaded from

Published OnlineFirst November 22, 2010; DOI: 10.1158/1078-0432.CCR-09-3314

http://clincancerres.aacrjournals.org/

pathways modulate gene transcription (Fig. 1A). Addi-tional signaling abnormalities characterize the transforma-tion to blastic phase (6, 22).

BCR-ABL inhibition in the treatment of CMLThe success of imatinib treatment for CML established

that BCR-ABL is an excellent therapeutic target (23–26).Newly diagnosed chronic-phase patients with CML treatedwith imatinib exhibited 5-year rates of overall and progres-sion-free survival of 93% and 89%, respectively (26). Thecumulative failure rate was 17% at 60 months, peaking inyear 2 at 7.5% and declining to <1% by year 5. During the6th year of study treatment, there were no reports of diseaseprogression (27). Imatinib therapy is much less effective inblastic-phase CML, and themore potent second-generation

inhibitors dasatinib and nilotinib have not changed this.Thus, a more profound understanding of BCR-ABL signal-ing in blastic-phase CML is a prerequisite for developingbetter treatments. Three recent advances have revealedimportant new mechanistic details pertaining to diseaseprogression in CML (28–31), as described below.

BCR-ABL signaling and disease progression in CMLThe B-cell mutator activation-induced deaminase promotes

disease progression and drug resistance in CML. Activa-tion-induced deaminase (AID) is a B-cell–restricted anti-body diversification enzyme that is involved in somatichypermutation in mature, antigen-exposed B cells. AID isalso present and active in a subset of patients with lym-phoid blastic-phase CML or Phþ ALL (28). The DNA

Figure 1. The BCR-ABL signaling network and ABL kinase inhibition. A, BCR-ABL signaling pathways activated in CML. Dimerization of BCR-ABL triggersautophosphorylation events that activate the kinase and generate docking sites for intermediary adapter proteins (purple) such as GRB2. BCR-ABL–dependent signaling facilitates activation of multiple downstream pathways that enforce enhanced survival, inhibition of apoptosis, and perturbation of celladhesion andmigration. A subset of these pathways and their constituent transcription factors (blue), serine/threonine-specific kinases (green), and apoptosis-related proteins (red) are shown. A few pathways that were more recently implicated in CML stem cell maintenance and BCR-ABL–mediated diseasetransformation are shown (orange). Of note, this is a simplified diagram and many more associations between BCR-ABL and signaling proteins have beenreported. BCR-ABL is unstable upon disruption of primary CML cells; therefore, pharmacodynamic evaluation of BCR-ABL activity is performed bymonitoringthe tyrosine phosphorylation status of either CRKL or STAT5, with CRKL phosphorylation considered the most specific readout. B, Predicted effectiveness ofABL kinase inhibitors in three therapeutic scenarios: to inhibit native BCR-ABL (top), to inhibit mutated BCR-ABL (middle), and as a component in the control ofCML involving a BCR-ABL–independent alternate lesion (bottom).

O’Hare et al.

Clin Cancer Res; 17(2) January 15, 2011 Clinical Cancer ResearchOF2




mutator activity of AID in this context is unchecked byprotective mechanisms inherent in normal activated Bcells, and is correlated with a dramatic increase in geneticinstability. For example, copy number alterations and theintroduction of point mutations bearing the AID finger-print were detected in genes controlling cell cycle, DNArepair, and other critical cellular functions. Klemm andcolleagues (28) established that abnormal expression ofAID promotes disease progression through genomicinstability and also plays a major role in generation ofBCR-ABL point mutations, implicating AID in drug resis-tance. Because BCR-ABL kinase domain mutations are notlimited to lymphoid disease, the authors investigated thepossibility of lineage conversion and suggested that PAX5, atranscription factor that is important for B cell develop-ment and AID expression, may orchestrate interconversionof lymphoid and myeloid lineages. Alternatively, an as yetunknown mechanism could drive mutation acquisition inmyeloid lineage cells.miR-328 plays multiple roles in controlling myeloid dif-

ferentiation in CML. The myeloid-specific transcriptionfactor C/EBPa is a master regulator of target genes that arerequired for differentiation of CML progenitors into gran-ulocytes. BCR-ABL influences C/EBPa levels by stabilizingheterogeneousnuclear ribonucleoproteinE2 (hnRNPE2), aposttranscriptional gene regulator that binds to the 50-UTRof C/EPBamRNA and blocks translation. In chronic-phaseCML cells, C/EBPa expression is not substantially impairedby hnRNP E2, which is tightly regulated and kept at lowlevels. Conversely, C/EBPa is downregulated in blastic-phase CML through a BCR-ABL/MAPK/hnRNP E2 pathway(22), resulting in accumulation of blasts (32).Eiring and colleagues (29) now reveal further complexity

in the regulation of C/EBPa expression. Working from theobservation that the microRNA miR-328 is subject to BCR-ABL–dependentdownregulation inblastic-phaseCML, theyestablished multiple functions for miR-328 in a regulatorynetwork that is central to the differentiation of myeloidprogenitors. PIM1, a cell cycle and apoptosis regulator thatis important for the survival of CML blasts, was identified asa direct target for canonical silencing bymiR-328 in associa-tion with the RISC complex. More surprisingly, they foundthat miR-328 binds directly to hnRNP E2, acting as an RNAdecoy that interfereswithhnRNPE2-mediated repressionofC/EBPa mRNA translation. The RNA decoy function isindependent of proteins associated with the RISC genesilencingmachinery. In total, restorationofmiR-328 expres-sion rescues differentiation by sequestering hnRNP E2, andimpairs survival of leukemic blasts by interacting with themRNA encoding the survival factor PIM1. C/EPBa furtherinfluences its own fate by binding to themiR-328 promoterand inducing its expression in myeloid progenitors. Thisstudy reveals a previously unrecognized function for micro-RNAs as RNA decoy molecules.Musashi2-Numb signaling in CML disease progression.

Recent studies disclosed that primary blast-phase cellsexpress high levels of the RNA-binding protein Musashi2in comparison with chronic-phase cells, whereas the Musa-

shi2-repressed differentiation factor Numb shows the oppo-site expression profile (30, 31). Follow-on mechanisticstudies in mouse model systems provided compelling evi-dence that loss or reduction in expressionofNumb results inarrested differentiation and contributes to disease progres-sion (30). NUP98-HOXA9, a chimeric transcription factorpreviously linked to blastic-phase CML, was shown to facil-itate upregulation of Musashi2, leading to repression ofNumb. Experimental attenuation of Musashi2 expressionrestored Numb expression and reinstated the chronic phase(30). Conversely, overexpression of Musashi2 in a mousemodel led to increased cell cycle progression and, in coop-eration with BCR-ABL, induction of an aggressive diseasecourse (31). Given that it was detected in a majority ofpatients who went on to experience disease progression,Musashi2 upregulation also appears to be a reliable earlyindicator of poor prognosis (30, 31). Pharmacologicalmanipulations that activate Numb and/or repress Musashi2could open therapeutic avenues for preventing or control-ling disease progression in CML and may also provide newapproaches for the treatment of acute myeloid leukemia(31).

Mechanisms of resistance to ABL kinase inhibitors inCML

Imatinib is an effective first-line therapy for chronic-phase CML (33). However, some patients experience treat-ment failure after an initial response. Studies of relapsedpatients revealed that BCR-ABL signaling is often reacti-vated at the time of resistance (34). Crystallographic ana-lysis of the ABL kinase domain in complex with imatinibrevealed that the drug binds exclusively to a catalyticallyinactive conformation of the ABL kinase (35, 36). Pointmutations at residues that make direct contacts with ima-tinib or are critical for ABL to adopt an inactive conforma-tion interfere with drug binding. Kinase domain mutationsat >55 residues that confer varying levels of imatinibresistance have been identified (reviewed in ref. 37). Thesefindings guided the design of the second-generation ABLinhibitors nilotinib, an imatinib derivative with �30-foldhigher potency (38), and dasatinib, a SRC/ABL inhibitorthat is �300-fold more potent than imatinib (39, 40).These inhibitors are effective against most BCR-ABLmutants, although the T315I "gatekeeper" mutation withinthe ATP-binding domain is completely resistant to all threeapproved therapies, exposing a critical gap in coverage(38). As a pan-BCR-ABL inhibitor, ponatinib (Table 1) isactive against this mutant, and is in phase 2 clinicalevaluation for refractory CML. Other new inhibitors,including DCC-2036 (41, 42) (Table 1), have also enteredclinical testing for refractory CML.

Clinical-Translational Advances

New first-line therapies for chronic-phase CMLImatinib remains the first-line CML therapy on the basis

of its efficacy, side-effect profile, and safety record. None-theless, it is possible that another ABL inhibitor or combi-

Targeting the BCR-ABL Signaling in Ph+ Leukemia

www.aacrjournals.org Clin Cancer Res; 17(2) January 15, 2011 OF3




nation of ABL inhibitors might represent a better first-lineoption for some or all patients. Possible benefits include: 1)reaching response milestones sooner, potentially resultingin a reduced risk of relapse (43); 2) being able to suppress awider range of mutant clones, leading to a reduced risk ofBCR-ABL mutation-based treatment failure; 3) improvingside-effect and tolerability profiles; and 4) profoundlyreducing and perhaps eradicating residual disease.

Recently, 14-month reports were issued from rando-mized phase 3 trials comparing either nilotinib (44)[300 or 400 mg twice daily; Evaluating Nilotinib Efficacy

and Safety in Clinical Trials of Newly Diagnosed Philadel-phia-Positive CML Patients (ENESTnd)] or dasatinib (45)[100 mg once daily; Dasatinib versus Imatinib Study inTreatment na€�ve CML Patients (DASISION)] with standarddose imatinib (400 mg once daily) as initial treatment.Both studies found the investigational treatment to besuperior in terms of complete cytogenetic response(CCR) and major molecular response (MMR; defined asa BCR-ABL transcript level of�0.1% in peripheral blood onRQ-PCR assay as expressed on the International Scale) at 12months, meeting the primary endpoints of the trials

Table 1. Examples of New Targeted Agents with Potential Activity Against BCR-ABLT315I in Clinical andPreclinical Development

O’Hare et al.





(Fig. 2). These are important benchmarks because patientswith newly diagnosed chronic-phase CML who achieveboth CCR and MMR within the first 12 months of therapyhave a low risk of long-term progression (26, 27, 46, 47).Ofmore importance from a clinical point of view, there wasalso early evidence of reduced progression to accelerated orblastic phase: 4% of patients treated with imatinib com-pared with <1% treated with nilotinib (ENESTnd), and3.5%of patients treatedwith imatinib compared with 1.9%treated with dasatinib (DASISION). Although this evidencemust be regarded as preliminary, the improved time toprogression is arguably the most impressive result fromthese studies.The availability of new and potentially more effective

ABL kinase inhibitors ensures that imatinib will havecompetition as the first-line therapy for CML, and raisesdifficult questions about balancing costs against treatment

with the "latest and greatest" medications. In fact, nilotinibwas approved for first-line treatment of newly diagnosed,chronic-phase CML in June 2010, and dasatinib followedin short order in October 2010. The second-generationinhibitor bosutinib is also being tested in this setting(phase 3: NCT00574873; http://www.clinicaltrials.gov)(48, 49). Imatinib is an excellent therapy for the majorityof patients with chronic-phase CML. Thus, it is impressivethat potentially better options are positioned to take centerstage within the first decade of the recognition that ABLkinase inhibitors could completely change the treatment ofCML. The issue of whether administration of two or moreABL inhibitors as a cocktail or in a sequential rotationwould equate with better disease control as compared withsingle-agent therapy for certain patients is certainly ofinterest, but it presents formidable difficulties in termsof clinical trial design.

© 2011 American Association for Cancer Research

Imatinib(400 mg qd)

0

20

40

60

80

100

% r

esp

onse

CCR (1 yr)

DASISION Study

Dasatinib(100 mg qd)

Imatinib(400 mg qd)

Dasatinib(100 mg qd)

MMR (1 yr)

Imatinib(400 mg qd)

0

20

40

60

80

100

% r

esp

onse

CCR (1 yr)

ENESTnd Study

Nilotinib(300 mg bid)


Imatinib(400 mg qd)

MMR (1 yr)



Figure 2. Results from two independent clinical trials evaluating potential first-line use of nilotinib or dasatinib as compared with imatinib for newly diagnosedCML: A, ENESTnd; B, DASISION. Both studies demonstrated that the comparator drug was superior to imatinib with respect to the number of patientsreaching a CCR andMMR at 12 months. Nilotinib and dasatinib were also superior to imatinib with respect to lowered incidence of progression to acceleratedphase or blastic phase. Results from the two trials cannot be compared directly.






Targeting the BCR-ABLT315I mutant: clinicalcandidates

Despite the approval of three therapeutic options, thecross-resistant BCR-ABLT315I mutant and compoundmutants selected on sequential ABL inhibitor therapy(50) present clinical challenges. In response to the needfor a clinically useful BCR-ABLT315I inhibitor, a variety ofapproaches are being pursued (51, 52).

Ponatinib (AP24534), a pan-BCR-ABL inhibitor. Werecently reported the design and preclinical evaluation ofponatinib (Table 1), a potent inhibitor of native BCR-ABL, BCR-ABLT315I, and other resistant mutants (IC50:0.5–36 nM) (53–55). Ponatinib inhibited all testedBCR-ABL mutants in cellular and biochemical assays,suppressed BCR-ABLT315I-driven tumor growth in mice,and completely abrogated resistance in cell-based muta-genesis screens, confirming its profile as a pan-BCR-ABLinhibitor. Interim data from a phase 1 trial in patientswith refractory CML and hematologic malignancies havebeen reported (56). Pancreatitis was the dose-limitingtoxicity at 60 mg daily, and 45 mg daily was selected asthe recommended dose for further testing (phase 1:NCT00660920; http://www.clinicaltrials.gov). Therewas clear evidence of antileukemia activity, with majorcytogenetic responses in 46% of chronic-phase patientsresistant to second-line tyrosine kinase inhibitors, includ-ing 67% of those with the T315I mutation, as well asMMRs (56). A pivotal phase 2 trial of ponatinib is nowunder way (NCT01207440; http://www.clinicaltrials.gov). In a sense, ponatinib is positioned where nilotiniband dasatinib were a few years ago: under evaluation inthe demanding setting of treatment failure. Farther on thehorizon, if ponatinib can provide pan-BCR-ABL coverageand is proven to be safe and effective, it may have a futureas a first-line CML therapeutic.

DCC-2036, an ABL switch control inhibitor. DCC-2036is an ABL inhibitor that accesses a distinctive switch controlpocket that is transiently formed in the course of conforma-tional regulation of the kinase (42). In Ba/F3 cellular pro-liferation assays, DCC-2036 was shown to be effectiveagainst cells expressing native BCR-ABL as well as severalimatinib-resistant mutants (Y253F, T315I, and M351T)with IC50 values of 45–74 nM (41). In a mouse bonemarrow transduction/transplantationmodel of CML invol-ving BCR-ABLT315I, daily oral dosing of DCC-2036 resultedin significant prolongation of survival compared with vehi-cle-treated mice (42). DCC-2036 and related compoundsare reported to be orally bioavailable, to exhibit a limitedoff-target profile, and to perform well in safety studies.DCC-2036 is undergoing phase 1 evaluation for use inimatinib-refractory CML (NCT00827138; http://www.clin-icaltrials.gov), including patients with a T315I mutation.

Preclinical BCR-ABLT315I inhibitors: recentapproaches

Whereas ponatinib and DCC-2036 have advanced toclinical evaluation, additional inhibitors are in preclinicaldevelopment. These include HG-7-85-01 (Table 1), which

uses a modified nilotinib-dasatinib hybrid structure toavoid gatekeeper mutations (57), and GNF-2, an allostericABL inhibitor that has been shown to be effective incombination with ATP-competitive ABL inhibitors(Table 1) (58, 59).

HG-7-85-01 combines elements of nilotinib and dasatinibto inhibit the T315I mutant. An effort to design ATP-competitive inhibitors with activity against BCR-ABLT315I

and other clinically important gatekeeper mutants, such asc-KITT670I (gastrointestinal stromal tumors) andPDGFRaT674I (hypereosinophilic syndrome), led to thediscovery of HG-7-85-01 (Table 1). This compound incor-porates design features of nilotinib and dasatinib but alsohas an unprecedented tolerance for a range of gatekeeperside chains. Despite this feature, however, HG-7-85-01remains a relatively selective kinase inhibitor (IC50: 59nM for Ba/F3 native BCR-ABL cells, and 140 nM for Ba/F3 BCR-ABLT315I cells). HG-7-85-01 was less effectiveagainst Ba/F3 cells expressing several clinically importantBCR-ABL mutants (IC50: 500–1000 nM for Ba/F3 BCR-ABLF317L cells), but was effective when combined withnilotinib. HG-7-85-01 (57) is among the first kinase inhi-bitors that can target numerous gatekeeper mutant kinasesand still exhibit a restricted kinase selectivity profile. Itwill be of interest to monitor the therapeutic potential ofHG-7-85-01-type inhibitors.

Allosteric inhibition by GNF-2. The regulatory controlmechanisms governing ABL kinase activity include an inter-action between a myristoyl-modified glycine residue nearthe N-terminus and its cognate myristate-binding pocket(60, 61). Because the ABLN-terminal region is absent fromBCR-ABL, the vestigialmyristate pocket is unoccupied in thefusion protein. GNF-2 and the analogGNF-5 (Table 1) bindin the myristate-binding pocket, with surprising conse-quences. As a single agent, GNF-2 is a selective non-ATPcompetitive inhibitor of BCR-ABL activity [IC50: 138 nM forBa/F3 BCR-ABL cells (62)] with a potency comparable tothat of imatinib. Although neither GNF-2 nor GNF-5 is aninhibitor of BCR-ABLT315I, a combination of high concen-trations of GNF-5 and nilotinib showed inhibitory activityagainst this gatekeeper mutant in biochemical and cellularassays.Onepuzzling aspect of the cellular data (see Fig. 4a inRef. 58) is the single-agent effectiveness of nilotinib againstBa/F3 BCR-ABLT315I cells (IC50 � 4 mM). We have notobserved nilotinib to be a T315I inhibitor in cellular orbiochemical assays (39, 53). The ability of an allostericinhibitor to influence the conformation of the ABL kinasedomain represents an exciting advance, and this process isbeing studied inmore detail, particularly through the use ofnuclear magnetic resonance spectroscopy (58, 63).The combination of GNF-5withHG-7-85-01 exhibits coop-erative inhibitory effects against the T315I mutant (59).

Targeting CML stem cellsIn the majority of patients on imatinib, residual disease

is detectable and only a few achieve a complete molecularresponse (defined as no detectable BCR-ABL by RT-PCR);even fewer maintain these responses upon discontinuation

O’Hare et al.





of therapy (64). The inability of imatinib to eliminate allleukemia cells is referred to as disease persistence, andit remains to be seen whether the results will be funda-mentally different with second- and third-generation ABLinhibitors. At present, we have to assume that the preva-lence of CML patients requiring continuous therapy andmonitoring will continue to increase, with significanthealth-economic implications. The characteristics of leu-kemic stem cell populations that allow them topersist in theface of successful ABL kinase inhibitor treatment are underintense scrutiny (65, 66). Conceptually, persistence may bedue to BCR-ABL–dependent or –independent mechanisms.Increasing evidence is in favor of the latter, implying thatCML stem cells are not yet fully addicted to BCR-ABL kinaseactivity. This natural limitation of BCR-ABL kinase inhibi-tors implies that eliminating the leukemic stem cell clonewill require the targeting of additional pathways such asHedgehog/Smoothened andb-catenin (reviewed in ref. 67).Given the role of these pathways in normal stem cellphysiology, the question is whether a sufficient therapeuticwindow exists to distinguish between normal and CMLstem cells. Our bias is that such a window may only openwith the use of drug combinations, when simultaneousinhibition of BCR-ABL and a yet to be determined addi-tional pathway may generate a synthetic lethality that dis-criminates between CML and normal cells. There is thealternative, empirical approach, exemplified by the combi-nation of histone deacetylase inhibitors and imatinib thatwas recently reported to induce apoptosis in quiescent CMLprogenitors that were not eliminated by imatinib alone(66), or the mechanistically unexplained ability of BMS-214662, a farnesyl transferase inhibitor, to induce apoptosisin primitive CML cells (68). A completely differentapproach is immunotherapy, which may anatomically tar-get CML stem cells. The promising data reported for ima-tinib/interferon-a combinations are testimony to thepotential of this approach (reviewed in ref. 69).

Future Developments and Considerations

There is reason for optimism in the realm of CMLtherapy. Nilotinib and dasatinib may reduce the rate ofprogression compared with imatinib, and for thosepatients who fail these inhibitors, third-generation drugsare in development that show activity against the T315Imutant, which has emerged as a common pathway ofresistance. Thus, clinicians may soon have at their disposala complete set of tools needed to curtail the emergence ofBCR-ABL mutation-based resistance.However, this is unlikely to be the end of tyrosine kinase

inhibitor resistance in CML. BCR-ABL kinase domainmutations have attracted the most attention withrespect to treatment failure, yet they are present inonly 60% of patients with imatinib resistance. In theremainder of patients, poorly understood BCR-ABL–-

independent mechanisms of growth and survival are acti-vated (Fig. 1B). In patients who are resistant to imatiniband have no detectable kinase domain mutation, kinasedomain mutations are rarely detected if resistance to nilo-tinib also develops (70). Further, these patients respondpoorly to third-line dasatinib (71). BCR-ABL–independentactivation of LYN has been observed in some mutation-negative, imatinib-resistant patients who responded todasatinib, consistent with dasatinib’s activity against bothABL and SRC family kinases (72–74).

We previously argued that BCR-ABLT315I-driven escapefrom treatment with nilotinib or dasatinib suggests that thedisease is still BCR-ABL–dependent (75). This appears to beconsistent with emerging data from the ponatinib phase 1study, wherein both cytogenetic and molecular responseswere observed in patients with the T315I mutation whopreviously failed second-line therapy with nilotinib ordasatinib or both (56). Although establishing responserates for patients with the T315I mutation will be onefocus of the ponatinib phase 2 trial, these preliminaryfindings suggest that the long-awaited goal of clinicalcontainment of resistance due to single BCR-ABL kinasedomain mutations may be soon be attained. Of note,T315I-inclusive compound kinase domain mutations(defined as two mutations in the same BCR-ABL molecule)can confer high-level resistance even to ponatinib, andremain an area of concern (53, 76). Although some muta-tions, most notably BCR-ABLT315I and compound muta-tions, have proven difficult to address therapeutically withcurrently approved inhibitors, mutation-based relapses arebetter understood than those involving a partially BCR-ABL–independent resistance phenotype. Fortunately, the>10-year experience with ABL kinase inhibitors suggeststhat the proportion of newly diagnosed chronic-phase CMLpatients who have acquired BCR-ABL–independent clonesis small, and that primary resistance may become a trulyrare occurrence.

On the other hand, we do not expect advances in ABLinhibitor-based therapies as single agents to have a directpositive impact on disease eradication, given that the fountof disease appears to be largely insensitive to ABL kinaseinhibitors (reviewed in ref. 77). More likely, approachesthat create a situation of synthetic lethality or that targetCML stem cells anatomically rather than biochemically willbe required to translate profound responses into diseaseelimination. In the interim, clinical efforts should focus onkeeping patients in the chronic phase and rapidly max-imizing the depth of response.

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Received October 28, 2010; accepted November 17, 2010; publishedOnlineFirst November 22, 2010.






References1. Kurzrock R, Gutterman JU, Talpaz M. The molecular genetics of

Philadelphia chromosome-positive leukemias. N Engl J Med1988;319 :990–8. PubMed doi:10.1056/NEJM198810133191506

2. Deininger MW, Goldman JM, Melo JV. The molecular biology ofchronic myeloid leukemia. Blood 2000;96 :3343–56. PubMed

3. Ren R. Mechanisms of BCR-ABL in the pathogenesis of chronicmyelogenous leukaemia. Nat Rev Cancer 2005;5:172–83. PubMeddoi:10.1038/nrc1567

4. Cowan-Jacob SW, Guez V, Fendrich G, Griffin JD, Fabbro D, Furet P,et al. Imatinib (STI571) resistance in chronic myelogenous leukemia:molecular basis of the underlyingmechanisms and potential strategiesfor treatment. Mini Rev Med Chem 2004;4 :285–99. PubMeddoi:10.2174/1389557043487321

5. Quintas-Cardama A, Cortes J. Molecular biology of bcr-abl1-positivechronic myeloid leukemia. Blood 2009;113:1619–30. PubMeddoi:10.1182/blood-2008-03-144790

6. Calabretta B, Perrotti D. The biology of CML blast crisis. Blood2004;103:4010–22. PubMed doi:10.1182/blood-2003-12-4111

7. Fielding AK. How I treat Philadelphia chromosome positive acutelymphoblastic leukaemia. Blood 2010;16:3409–17.

8. Fei F, Stoddart S, Muschen M, Kim YM, Groffen J, Heisterkamp N.Development of resistance to dasatinib in Bcr/Abl-positive acutelymphoblastic leukemia. Leukemia 2010;24:813–20. PubMeddoi:10.1038/leu.2009.302

9. Daley GQ, Van Etten RA, Baltimore D. Induction of chronic myelo-genous leukemia in mice by the P210bcr/abl gene of the Philadelphiachromosome. Science 1990;247:824–30. PubMed doi:10.1126/science.2406902

10. Zhang X, Ren R. Bcr-Abl efficiently induces a myeloproliferativedisease and production of excess interleukin-3 and granulocyte-macrophage colony-stimulating factor in mice: a novel model forchronic myelogenous leukemia. Blood 1998;92:3829–40. PubMed

11. McWhirter JR, Galasso DL, Wang JY. A coiled-coil oligomerizationdomain of Bcr is essential for the transforming function of Bcr-Abloncoproteins. Mol Cell Biol 1993;13 :7587–95. PubMed

12. Zhao X, Ghaffari S, Lodish HF, Malashkevich VN, Kim PS. Structureof the Bcr-Abl oncoprotein oligomerization domain. Nat Struct Biol2002;9 :117–20. PubMed

13. Chu S, Li L, Singh H, Bhatia R. BCR-tyrosine 177 plays an essentialrole in Ras and Akt activation and in human hematopoietic progenitortransformation in chronic myelogenous leukemia. Cancer Res2007;67:7045–53. PubMed doi:10.1158/0008-5472.CAN-06-4312

14. Sattler M, Mohi MG, Pride YB, Quinnan LR, Malouf NA, Podar K, et al.Critical role for Gab2 in transformation by BCR/ABL. Cancer Cell2002;1:479–92. PubMed doi:10.1016/S1535-6108(02)00074-0

15. Naka K, Hoshii T, Muraguchi T, Tadokoro Y, Ooshio T, Kondo Y, et al.TGF-beta-FOXO signalling maintains leukaemia-initiating cells inchronic myeloid leukaemia. Nature 2010;463:676–80. PubMeddoi:10.1038/nature08734

16. Agarwal A, Bumm TG, Corbin AS, O'Hare T, Loriaux M, VanDyke J,et al. Absence of SKP2 expression attenuates BCR-ABL-inducedmyeloproliferative disease. Blood 2008;112 :1960–70. PubMeddoi:10.1182/blood-2007-09-113860

17. Markova B, Albers C, Breitenbuecher F, Melo JV, Brummendorf TH,Heidel F, et al. Novel pathway in Bcr-Abl signal transduction involvesAkt-independent, PLC-gamma1-driven activation of mTOR/p70S6-kinase pathway. Oncogene 2010;29:739–51. PubMed doi:10.1038/onc.2009.374

18. Ly C, Arechiga AF, Melo JV, Walsh CM, Ong ST. Bcr-Abl kinasemodulates the translation regulators ribosomal protein S6 and 4E-BP1in chronic myelogenous leukemia cells via the mammalian target ofrapamycin. Cancer Res 2003;63:5716–22. PubMed

19. Ilaria RL Jr, Van Etten RA. P210 and P190(BCR/ABL) induce thetyrosine phosphorylation and DNA binding activity of multiple specificSTAT family members. J Biol Chem 1996;271:31704–10. PubMeddoi:10.1074/jbc.271.49.31704

20. Klejman A, Schreiner SJ, Nieborowska-Skorska M, Slupianek A, Wil-sonM, Smithgall TE, et al. The Src family kinaseHck couplesBCR/ABL

to STAT5 activation in myeloid leukemia cells. EMBO J 2002;21:5766–74. PubMed doi:10.1093/emboj/cdf562

21. Hoelbl A, Schuster C, Kovacic B, Zhu B, Wickre M, Hoelzl MA, et al.Stat5 is indispensable for the maintenance of bcr/abl-positive leu-kaemia. EMBO Mol Med 2010;2:98–110. PubMed doi:10.1002/emmm.201000062

22. Chang JS, Santhanam R, Trotta R, Neviani P, Eiring AM, Briercheck E,et al. High levels of the BCR/ABL oncoprotein are required for theMAPK-hnRNP-E2 dependent suppression of C/EBPalpha-drivenmyeloid differentiation. Blood 2007;110:994–1003. PubMeddoi:10.1182/blood-2007-03-078303

23. Druker BJ, Tamura S, Buchdunger E, Ohno S, Segal GM, Fanning S,et al. Effects of a selective inhibitor of the Abl tyrosine kinase on thegrowth of Bcr-Abl positive cells. Nat Med 1996;2:561–6. PubMeddoi:10.1038/nm0596-561

24. Druker BJ, Talpaz M, Resta DJ, Peng B, Buchdunger E, Ford JM, et al.Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosinekinase in chronic myeloid leukemia. N Engl J Med 2001;344:1031–7.PubMed doi:10.1056/NEJM200104053441401

25. O’Brien SG, Guilhot F, Larson RA, Gathmann I, Baccarani M, CervantesF, et al. Imatinib compared with interferon and low-dose cytarabine fornewlydiagnosedchronic-phasechronicmyeloid leukemia.NEngl JMed2003;348:994–1004. PubMed doi:10.1056/NEJMoa022457

26. Druker BJ, Guilhot F, O’Brien SG, Gathmann I, Kantarjian H, Gatter-mann N, et al. Five-year follow-up of patients receiving imatinib forchronic myeloid leukemia. N Engl J Med 2006;355:2408–17. PubMeddoi:10.1056/NEJMoa062867

27. Hochhaus A, O’Brien SG, Guilhot F, Druker BJ, Branford S, Foroni L,et al. Six-year follow-up of patients receiving imatinib for the first-linetreatment of chronic myeloid leukemia. Leukemia 2009;23:1054–61.PubMed doi:10.1038/leu.2009.38

28. Klemm L, Duy C, Iacobucci I, Kuchen S, von Levetzow G, Feldhahn N,et al. The B cell mutator AID promotes B lymphoid blast crisis and drugresistance in chronic myeloid leukemia. Cancer Cell 2009;16:232–45.PubMed doi:10.1016/j.ccr.2009.07.030

29. Eiring AM, Harb JG, Neviani P, Garton C, Oaks JJ, Spizzo R, et al. miR-328 functions as an RNA decoy to modulate hnRNP E2 regulation ofmRNA translation in leukemic blasts. Cell 2010;140:652–65. PubMeddoi:10.1016/j.cell.2010.01.007

30. Ito T, Kwon HY, Zimdahl B, Congdon KL, Blum J, Lento WE, et al.Regulation of myeloid leukaemia by the cell-fate determinant Musa-shi. Nature 2010;466:765–8. PubMed doi:10.1038/nature09171

31. Kharas MG, Lengner CJ, Al-Shahrour F, Bullinger L, Ball B, Zaidi S,et al. Musashi-2 regulates normal hematopoiesis and promotesaggressive myeloid leukemia. Nat Med 2010;16:903–8. PubMeddoi:10.1038/nm.2187

32. Perrotti D, Cesi V, Trotta R, Guerzoni C, Santilli G, Campbell K, et al.BCR-ABL suppresses C/EBPalpha expression through inhibitoryaction of hnRNP E2. Nat Genet 2002;30:48–58. PubMeddoi:10.1038/ng791

33. Druker BJ. Perspectives on the development of imatinib and the futureof cancer research. Nat Med 2009;15:1149–52. PubMed doi:10.1038/nm1009-1149

34. Gorre ME, Mohammed M, Ellwood K, Hsu N, Paquette R, Rao PN,et al. Clinical resistance to STI-571 cancer therapy caused by BCR-ABL gene mutation or amplification. Science 2001;293:876–80.PubMed doi:10.1126/science.1062538

35. Nagar B, Bornmann WG, Pellicena P, Schindler T, Veach DR, MillerWT, et al. Crystal structures of the kinase domain of c-Abl in complexwith the small molecule inhibitors PD173955 and imatinib (STI-571).Cancer Res 2002;62:4236–43. PubMed

36. Schindler T, Bornmann W, Pellicena P, Miller WT, Clarkson B, KuriyanJ. Structural mechanism for STI-571 inhibition of abelson tyrosinekinase. Science 2000;289:1938–42. PubMed doi:10.1126/science.289.5486.1938

37. Apperley JF. Part I: mechanisms of resistance to imatinib in chronicmyeloid leukaemia. Lancet Oncol 2007;8:1018–29. PubMeddoi:10.1016/S1470-2045(07)70342-X

O’Hare et al.





38. Weisberg E, Manley PW, Breitenstein W, Brüggen J, Ray A, Cowan-Jacob SW, et al. Characterization of AMN107, a selective inhibitor ofwild-type and mutant Bcr-Abl. Cancer Cell 2005;7:129–41. PubMeddoi:10.1016/j.ccr.2005.01.007

39. O’Hare T, Walters DK, Stoffregen EP, Jia T, Manley PW, Mestan J,et al. In vitro activity of Bcr-Abl inhibitors AMN107 and BMS-354825against clinically relevant imatinib-resistant Abl kinase domainmutants. Cancer Res 2005;65:4500–5. PubMed doi:10.1158/0008-5472.CAN-05-0259

40. Shah NP, Tran C, Lee FY, Chen P, Norris D, Sawyers CL. Overridingimatinib resistance with a novel ABL kinase inhibitor. Science2004;305:399–401. PubMed doi:10.1126/science.1099480

41. O’Hare T, Eide CA,Wise S, Smith B, Petillo P, Flynn D, et al. Activationswitch pocket inhibitors target the T315I mutant of BCR-ABL. ProcAm Assoc Cancer Res 2008;[Abstract 4867].

42. Van Etten RA, Chan WW, Zaleskas VM, Evangelista P, Lazarides K,Peng C, et al. DCC-2036: A novel switch pocket inhibitor of ABLtyrosine kinase with therapeutic efficacy against BCR-ABL T315I invitro and in a CMLmouse model. [abstract 463] Blood 2007;110:142a.doi:10.1182/blood-2006-02-002931

43. Hughes TP, Hochhaus A, Branford S, Muller MC, Kaeda JS, Foroni L,et al. Long-term prognostic significance of early molecular responseto imatinib in newly diagnosed chronic myeloid leukemia: an analysisfrom the international randomized study of interferon versus STI571(IRIS). Blood 2010;116:3758–65.

44. Saglio G, Kim DW, Issaragrisil S, le Coutre P, Etienne G, Lobo C, et al.Nilotinib versus imatinib for newly diagnosed chronic myeloid leuke-mia. N Engl J Med 2010;362 :2251–9. PubMed doi:10.1056/NEJ-Moa0912614

45. Kantarjian H, Shah NP, Hochhaus A, Cortes J, Shah S, Ayala M, et al.Dasatinib versus imatinib in newly diagnosed chronic-phase chronicmyeloid leukemia. N Engl J Med 2010;362:2260–70. PubMeddoi:10.1056/NEJMoa1002315

46. de Lavallade H, Apperley JF, Khorashad JS, Milojkovic D, Reid AG,Bua M, et al. Imatinib for newly diagnosed patients with chronicmyeloid leukemia: incidence of sustained responses in an inten-tion-to-treat analysis. J Clin Oncol 2008;26:3358–63. PubMeddoi:10.1200/JCO.2007.15.8154

47. Quintas-Cardama A, Kantarjian H, Jones D, Shan J, Borthakur G,Thomas D, et al. Delayed achievement of cytogenetic and molecularresponse is associated with increased risk of progression amongpatients with chronic myeloid leukemia in early chronic phase receiv-ing high-dose or standard-dose imatinib therapy. Blood2009;113:6315–21. PubMed doi:10.1182/blood-2008-07-166694

48. Boschelli F, Arndt K, Gambacorti-Passerini C. Bosutinib: a review ofpreclinical studies in chronic myelogenous leukaemia. Eur J Cancer2010;46:1781–9. PubMed doi:10.1016/j.ejca.2010.02.032

49. Puttini M, Coluccia AM, Boschelli F, Cleris L, Marchesi E, Donella-Deana A, et al. In vitro and in vivo activity of SKI-606, a novel Src-Ablinhibitor, against imatinib-resistant Bcr-Ablþ neoplastic cells. CancerRes 2006;66:11314–22. PubMed doi:10.1158/0008-5472.CAN-06-1199

50. Shah NP, Skaggs BJ, Branford S, Hughes T, Nicoll J, Paquette R, et al.Sequential kinase inhibitor therapy in CML patients can select for cellsharboring compound BCR-ABL kinase domain mutations withincreased oncogenic potency: rationale for early combination therapyof ABL kinase inhibitors. Blood 2006;108:225a[Abstr.].

51. Quintas-Cardama A, Cortes J. Therapeutic options against BCR-ABL1 T315I-positive chronic myelogenous leukemia. Clin CancerRes 2008;14:4392–9. PubMed doi:10.1158/1078-0432.CCR-08-0117

52. Schenone S, Brullo C, Botta M. New opportunities to treat theT315I-Bcr-Abl mutant in chronic myeloid leukaemia: tyrosinekinase inhibitors and molecules that act by alternative mechanisms.Curr Med Chem 2010;17:1220–45. PubMed doi:10.2174/092986710790936310

53. O’Hare T, ShakespeareWC, Zhu X, Eide CA, Rivera VM,Wang F, et al.AP24534, a pan-BCR-ABL inhibitor for chronic myeloid leukemia,potently inhibits the T315I mutant and overcomes mutation-basedresistance. Cancer Cell 2009;16:401–12. PubMed doi:10.1016/j.ccr.2009.09.028

54. Huang WS, Metcalf CA, Sundaramoorthi R, Wang Y, Zou D, ThomasRM, et al. Discovery of 3-[2-(imidazo[1,2-b]pyridazin-3-yl)ethynyl]-4-methyl-N-{4-[(4-methylpipera zin-1-yl)methyl]-3-(trifluoromethyl)phe-nyl}benzamide (AP24534), a potent, orally active pan-inhibitor ofbreakpoint cluster region-abelson (BCR-ABL) kinase including theT315I gatekeeper mutant. J Med Chem 2010;53:4701–19. PubMeddoi:10.1021/jm100395q

55. Zhou T, Commodore L, Huang W-S, Wang Y, Thomas M, Keats J,et al. Structural mechanism of the pan-BCR-ABL inhibitor ponatinib(AP24534): lessons for overcoming kinase inhibitor resistance. ChemBiol Drug Des 2010; (in press). PubMed

56. Talpaz M, Cortes JE, Deininger MW, Shah NP, Flinn IW, Mauro MJ,et al. Phase I trial of AP24534 in patients with refractory chronicmyeloid leukemia (CML) and hematologic malignancies. J Clin Oncol2010;28:490S. doi:10.1200/JCO.2010.29.6293

57. Weisberg E, Choi HG, Ray A, Barrett R, Zhang J, Sim T, et al.Discovery of a small-molecule type II inhibitor of wild-type and gate-keeper mutants of BCR-ABL, PDGFRalpha, Kit, and Src kinases:novel type II inhibitor of gatekeeper mutants. Blood2010;115:4206–16. PubMed doi:10.1182/blood-2009-11-251751

58. Zhang J, Adrian FJ, Jahnke W, Cowan-Jacob SW, Li AG, Iacob RE,et al. Targeting Bcr-Abl by combining allosteric with ATP-binding-siteinhibitors. Nature 2010;463:501–6. PubMed doi:10.1038/nature08675

59. Weisberg E, Deng X, Choi HG, Barrett R, Adamia S, Ray A, et al.Beneficial effects of combining a type II ATP competitive inhibitor withan allosteric competitive inhibitor of BCR-ABL for the treatment ofimatinib-sensitive and imatinib-resistant CML. Leukemia 2010;24:1375–8.

60. Nagar B, Hantschel O, Young MA, Scheffzek K, Veach D, BornmannW, et al. Structural basis for the autoinhibition of c-Abl tyrosine kinase.Cell 2003;112:859–71. PubMed doi:10.1016/S0092-8674(03)00194-6

61. Hantschel O, Nagar B, Guettler S, Kretzschmar J, Dorey K, Kuriyan J,et al. A myristoyl/phosphotyrosine switch regulates c-Abl. Cell2003;112:845–57. PubMed doi:10.1016/S0092-8674(03)00191-0

62. Adrian FJ, Ding Q, Sim T, Velentza A, Sloan C, Liu Y, et al. Allostericinhibitors of Bcr-abl-dependent cell proliferation. Nat Chem Biol2006;2:95–102. PubMed doi:10.1038/nchembio760

63. Jahnke W, Grotzfeld RM, Pelle X, Strauss A, Fendrich G, Cowan-Jacob SW, et al. Binding or bending: distinction of allosteric Abl kinaseagonists from antagonists by an NMR-based conformational assay. JAm Chem Soc 2010;132:7043–8. PubMed doi:10.1021/ja101837n

64. Rousselot P, Huguet F, Rea D, Legros L, Cayuela JM, Maarek O, et al.Imatinib mesylate discontinuation in patients with chronic myelogen-ous leukemia in complete molecular remission for more than 2 years.Blood 2007;109:58–60. PubMed doi:10.1182/blood-2006-03-011239

65. Sengupta A, Arnett J, Dunn S, Williams DA, Cancelas JA. Rac2GTPase deficiency depletes BCR-ABLþ leukemic stem cells andprogenitors in vivo. Blood 2010;116:81–4. PubMed doi:10.1182/blood-2009-10-247437

66. Zhang B, Strauss AC, Chu S, Li M, Ho Y, Shiang KD, et al. Effectivetargeting of quiescent chronic myelogenous leukemia stem cells byhistone deacetylase inhibitors in combination with imatinib mesylate.Cancer Cell 2010;17:427–42. PubMed doi:10.1016/j.ccr.2010.03.011

67. Helgason GV, Young GA, Holyoake TL. Targeting chronic myeloidleukemia stem cells. Curr Hematol Malig Rep 2010;5:81–7. PubMeddoi:10.1007/s11899-010-0043-0

68. Copland M, Pellicano F, Richmond L, Allan EK, Hamilton A, Lee FY,et al. BMS-214662 potently induces apoptosis of chronic myeloidleukemia stem and progenitor cells and synergizes with tyrosinekinase inhibitors. Blood 2008;111:2843–53. PubMed doi:10.1182/blood-2007-09-112573

69. Guilhot F, Roy L, Saulnier PJ, Guilhot J. Interferon in chronic myeloidleukaemia: past and future. Best Pract Res Clin Haematol2009;22:315–29. PubMed doi:10.1016/j.beha.2009.10.005

70. Hughes T, Saglio G, Branford S, Soverini S, Kim DW, Muller MC, et al.Impact of baseline BCR-ABL mutations on response to nilotinib inpatients with chronic myeloid leukemia in chronic phase. J Clin Oncol2009;27:4204–10. PubMed doi:10.1200/JCO.2009.21.8230

71. Garg RJ, Kantarjian H, O’Brien S, Quintas-Cardama A, Faderl S,Estrov Z, et al. The use of nilotinib or dasatinib after failure to 2 prior






tyrosine kinase inhibitors: long-term follow-up. Blood 2009;114:4361–8. PubMed doi:10.1182/blood-2009-05-221531

72. Donato NJ, Wu JY, Stapley J, Lin H, Arlinghaus R, Aggarwal B, et al.Imatinib mesylate resistance through BCR-ABL independence inchronic myelogenous leukemia. Cancer Res 2004;64:672–7. PubMeddoi:10.1158/0008-5472.CAN-03-1484

73. Donato NJ, Wu JY, Stapley J, Gallick G, Lin H, Arlinghaus R, et al.BCR-ABL independence and LYN kinase overexpression in chronicmyelogenous leukemia cells selected for resistance to STI571. Blood2003;101:690–8. PubMed doi:10.1182/blood.V101.2.690

74. O’Hare T, Eide CA, Deininger MW. Persistent LYN signaling inimatinib-resistant, BCR-ABL-independent chronic myelogenous leu-

kemia. J Natl Cancer Inst 2008;100:908–9. PubMed doi:10.1093/jnci/djn204

75. O’Hare T, Eide CA, Deininger MW. Bcr-Abl kinase domain mutations,drug resistance, and the road to a cure for chronic myeloid leukemia.Blood 2007;110:2242–9. PubMed doi:10.1182/blood-2007-03-066936

76. Shah NP, Skaggs BJ, Branford S, Hughes TP, Nicoll JM, Paquette RL,et al. Sequential ABL kinase inhibitor therapy selects for compounddrug-resistant BCR-ABL mutations with altered oncogenic potency. JClin Invest 2007;117:2562–9. PubMed doi:10.1172/JCI30890

77. Nicholson E, Holyoake T. The chronic myeloid leukemia stem cell.Clin Lymphoma Myeloma 2009;9[Suppl 4]:S376–81. PubMeddoi:10.3816/CLM.2009.s.037

O’Hare et al.





Published OnlineFirst November 22, 2010.Clin Cancer Res Thomas O'Hare, Michael W.N. Deininger, Christopher A. Eide, et al. LeukemiaTherapy-Resistant Philadelphia Chromosome-Positive Targeting the BCR-ABL Signaling Pathway in

Updated version

10.1158/1078-0432.CCR-09-3314doi:

Access the most recent version of this article at:

E-mail alerts related to this article or journal.Sign up to receive free email-alerts

Subscriptions

Reprints and

[email protected] at

To order reprints of this article or to subscribe to the journal, contact the AACR Publications

Permissions

[email protected] at

To request permission to re-use all or part of this article, contact the AACR Publications



http://clincancerres.aacrjournals.org/lookup/doi/10.1158/1078-0432.CCR-09-3314

http://clincancerres.aacrjournals.org/cgi/alerts

mailto:[email protected]

mailto:[email protected]


targeting the bcr-abl signaling pathway in therapy ...targeting the bcr-abl signaling pathway in...

Documents