Novel Agents In CML Therapy: Tyrosine Kinase Inhibitors and … · Novel Agents In CML Therapy:...

Article ID: WMC003540 ISSN 2046-1690

Novel Agents In CML Therapy: Tyrosine KinaseInhibitors and BeyondCorresponding Author:Dr. Sasmita Biswal,Assistant Professor, Pharmacology, S.C.B. Medical College and Hospital, Cuttack, 753001 - India

Submitting Author:Dr. Sasmita Biswal,Assistant Professor, Pharmacology, S.C.B. Medical College and Hospital, Cuttack, 753001 - India

Article ID: WMC003540

Article Type: Review articles

Submitted on:03-Jul-2012, 05:01:10 AM GMT Published on: 03-Jul-2012, 04:43:00 PM GMT

Article URL: http://www.webmedcentral.com/article_view/3540

Subject Categories:HAEMATO-ONCOLOGY

Keywords:BCR-ABL, Kinase Inhibitors, Cancer, Chronic Myelogenous Leukemia, Imatinib

How to cite the article:Biswal S. Novel Agents In CML Therapy: Tyrosine Kinase Inhibitors and Beyond .WebmedCentral HAEMATO-ONCOLOGY 2012;3(7):WMC003540

Copyright: This is an open-access article distributed under the terms of the Creative Commons AttributionLicense(CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided theoriginal author and source are credited.

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Novel Agents In CML Therapy: Tyrosine KinaseInhibitors and BeyondAuthor(s): Biswal S

Abstract

Treatment of Chronic myeloid leukemia representsone of cancer’s success stories. Deregulated tyrosinekinase activity of the BCR-ABL fusion protein hasbeen established as the causative molecular event inCML. The drug Imatinib has revolutionized thetreatment of CML and has become the gold standardof care in CML for it is a highly targeted BCR-ABLtyrosine kinase inhibitor (TKI) that induces completehematologic response and sustained completecytogenetic response in more than 80% of patients.Despite of such impressive response rates achievedwith imatinib, some patients in the advanced stage ofCML frequently obtain less modest responses. It maybe due to resistance to the wonder drug imatinib,which in turn results in failure of treatment, even afterlarge dose escalation. This has led to the developmentof novel treatment strategies which are currently beinginvestigated in newly diagnosed CML and includeupfront treatment with the next-generation tyrosinekinase inhibitors, such as dasatinib, nilotinib, orbosutinib, which also target the BCR-ABL but withincreased in vitro potency as compared to imatinib,and possibly with a reduced potential for resistance.Such newer agents and combination approaches canimprove treatment responses as compared withstandard imatinib treatment. In addition, many otherprotein kinases implicated in signaling transductiondownstream BCR-ABL also play critical roles in thepathogenesis of CML, thereby representing potentialtherapeutic targets as revealed from several clinicalstudies. While in many other cases, the CML cellsdevelop mutations, which is a change in the aminoacid sequence of the BCR-ABL oncogene, the mostdangerous amongst them is the T315I mutation, whichmakes them resistant to the current targeted therapies(imatinib, dasatinib, and nilotinib). Newer drugs thatwork against T315I mutant cells are now being tested.Ponatinib, is one such pan-BCR-ABL inhibitor, whichhas shown ongoing strong efficacy in its continuingPhase 1 trial in treatment of the T315I mutation CML,as well as all other known mutations. Still other noveldrugs in the pipeline, the farnesyl transferase inhibitors,such as lonafarnib and tipifarnib, seem to have someactivity against CML and patients may respond

favourably when such drugs are combined withimatinib. With many such novel drugs underdevelopment and many more in the pipe line, some ofsuch drugs which are in various phases of clinicaltrials are being discussed.

Introduction

Chronic myeloid leukemia (CML), also known aschronic granulocytic leukemia (CGL), is one of thecommonest hematological malignancies seen inclinical practice in Indian adults .1 It is a type of myeloproliferative disease linked togenetic abnormalities where there is a characteristicchromosomal translocation called the Philadelphiachromosome. The chromosomal defect is atranslocation, in which parts of two chromosomes, 9and 22, swap places.2The result is a fusion gene thatis created by juxta positioning the ABL 1 gene onchromosome 9 (region q34) to a part of the BCR("breakpoint cluster region") gene on chromosome 22(region q11). Thus a part of the BCR gene fromchromosome 22 is fused with the ABL gene onchromosome 9 .3 This BCR-ABL fusion gene productfunctions as a constitutively activated tyrosine kinase4 for it has a domain that can add phosphate groupsto its tyrosine residues but does not require activationby other cellular proteins. Thus it activates a numberof cell cycle controlling proteins and enzymes,accelerates cell division, inhibits DNA repair, causesgenomic instability and is responsible for the deadlyblast crisis in CML.5

TYROSINE KINASES: The tyrosine kinases are a subgroup of a larger classof protein kinases that has an ATP binding site, whichfunctions in several signaling pathways and can existin an active or inactive state.These kinases are broadly divided into two mainfamilies:1. The transmembrane receptor-linked tyrosinekinases family 2. And the cytoplasmic tyrosine kinases familyThe receptor tyrosine kinases functions intransmembrane signaling, whereas the cytoplasmictyrosine kinases is responsible for signal transductionto the nucleus.6 The fused oncogene bcr-abl encoded Bcr-Abl is a



transmembrane receptor-linked tyrosine kinase whichis expressed in the leukemic clonal cells, activatesmany pro-growth and cell survival mechanisms, whichconfers resistance of such clonal cells to apoptosis. 7Two of the major pathways activated by BCR-ABL arethe class I PI3K and the Ras pathways, which arederegulated in most human cancers. 8 Since tyrosinekinase activity is essential for this transformingfunction of BCR-ABL, an inhibitor of this kinase couldserve as an ef fect ive t reatment for CML.ATP-competitive inhibitors like tyrosine kinaseinhibitors (TKI) can prevent the binding of ATP, inhibitthe phosphorylation of Bcr-Abl and can cause deathof an apoptotic cell.9,10

1. 1st GENERATION BCR ABL KINASE INHIBITOR-IMATINIB MESYLATE:Imatinib binds to the amino acids of the BCR/ABLtyrosine kinase ATP binding site and stabilizes theinactive form of the receptor thereby preventingtyrosine auto phosphorylation. This process ultimatelyresults in “switching-off” the downstream signaling pathways that promote leukemogenesis. .11However, approximately 20-25% of patients initiallytreated with imatinib will need alternative therapy, dueto drug resistance.12 This resistance is usually due totwo mechanisms, the Bcr-Abl dependent mechanismslike over expression or amplification of the Bcr-Ablgene, point mutations within the Bcr-Abl kinasedomain that interfere with drug binding and Bcr-Ablindependent mechanisms, l ike decreasedintracellular concentration of imatinib, alterations indrug influx and efflux and activation of otherindependent pathways, like the Src kinase pathway.13Within the Bcr-Abl kinase domain, around 40 pointmutations have been described which have beenlinked to imatinib resistance in CML. These mutationsare of two broad categories, those that directlyinterfere with the ability of imatinib to bind to thekinase domain (e.g., T315I), and those that impair theability of Bcr-Abl to achieve inactive conformationrequired for binding to the drug. Imatinib binds only tothe inactive or closed conformation of ABL. This factexplains why many BCR-ABL mutations can causeresistance to imatinib by shifting its equilibrium towardthe open or active conformation. 14Some of theseresistant mutatants are the M351T, E255V, F317L,Y253F, D276G and the highly resistant T3151 mutant.There is hence an urgent need for the development ofnovel compounds to prevent or overcome imatinibresistance.

2. 2nd GENERATION ABL KINASE INHIBITORS These include nilotinib, bosutinib, dasatinib and INNO406. Both nilotinib and bosutinib are approved as

second-line treatments in all phases of CML and arehighly effective in patients resistant to or intolerant toimatinib for these drugs target all the resistantBCR-ABL mutants, with the exception of the T3151mutant.15

Nilotinib:Substitution of the N-methylpiperazine moiety ofimatinib by an amide moiety resulted in a more potentcompound, Nilotinib which in addition to inhibition oftyrosine kinases also inhibited the activity of the Arg,Kit, and platelet-derived growth factor receptor(PDGFR), but not the Src-family kinases (SFK).16Nilotinib is 10 to 50 times more selective and morepotent than imatinib17in inhibiting the proliferation andauto phosphorylation of the wild-type Bcr-Abl cell lines,most of the Bcr-Abl mutants, except the T315Imutant.18 Studies have shown it to be superior toimatinib in reducing the leukemic burden andprolonging the survival of mice transplanted with thew i l d - t y p e B c r - A b l , t h e M 3 5 1 T a n dE255Vmutants.19Also nilotinib does not require atransporter mediated transport into cells, is welltolerated but the common adverse events includes myelosuppression, elevated bilirubin and lipaselevels.

Dasatinib:Dasatinib is a multi-target kinase inhibitor as it binds toother tyrosine and serine/threonine kinases, like theTEC family kinases, the mitogen activated proteinkinases in addition to the receptor tyrosine kinase.20Imatinib binds only the closed conformation of ABLwhere as dasa t i n i b b i nds t o t he open(active)conformation.21 Dasatinib once dailyadministration induces significantly higher and fasterrates of complete cytogenetic and molecular response,better long term progression-free survival in patientsas compared to imatinib. 22 It is well tolerated withadverse effects like grade 3–4 myelosuppression inadvanced phases, diarrhea, nausea, headache,peripheral edema but with a higher incidence ofpleural and pericardial effusions as compared toimatinib and nilotinib. However dasatinib is resistant inpatients who harbor the T315I mutant and the novelF317L mutant .23

3. 3RD GENERATION TKI’S-HIGHLY ACTIVEAGAINST T315I MUTANT-PONATINIBHowever, there still remains a small subset of patientswho do not respond to TKIs because they harbor theBCR-ABL T315I mutant gene which confers themresistant to the first and second generation tyrosinekinase inhibitors. T315I represents about 15-20



percent of all clinically observed BCR-ABL mutationsand is completely resistant to all currently approvedpharmaceutical therapies.24, 25 This was the firstmutation to be detected in imatinib-resistant patientsand is due to the substitution of threonine withisoleucine at position 315 of the Abl protein .26 Theprevalence of the T315I mutant is likely to increasewith the increase in the use of the currentsecond-generation BCR-ABL inhibitors. Therefore,development of a T315I inhibitor represents asignificant unmet medical need in CML.A substrate-competitive inhibitor of Bcr-Abl, Ponatinib,was recently reported to have potent in vitro inhibitoryactivity in cell lines expressing wild-type Bcr-Abl andall the Bcr-Abl mutants, including the T315I mutant. Itwas also active in vivo in mice expressing the T315Imutant and caused decrease in leukemic cells.27Ponatinib is currently in Phase II clinical trials inpatients with resistant or intolerant CML and Ph+ ALL.Ponatinib was designed using ARIAD’s computationaland structure-based drug design platform to inhibit notonly the native BCR-ABL, but also its isoforms withvery high potency and specificity. A Phase I study ofponatinib in patients with resistant and refractorychronic myeloid leukemia and Philadelphia-positiveacute lymphoblastic leukemia (Ph+ ALL) haddemonstrated that about 66 % of patients in the trialhad achieved a major cytogenetic response.28 Otherthird-generation TKIs which are under developmentinclude XL-228, a multi-kinase inhibitor with activityagainst the mutant type of BCR-ABL. DCC-2036 isanother multi-kinase inhibitor in Phase I studies thatimpaires proliferation and induced apoptosis of cellstransfected with unmutated or mutated BCR-ABL,including T315I.

4. DUAL SRC-FAMILY KINASE/ABL KINASEINHIBITORS:The Src family kinases includes the nine structurallyrelated, cytoplasmic non-receptor tyrosine kinases(Src, Fyn, Yes, Blk,Yrk, Fgr, Hck, Lck and Lyn), whichare ubiquitous and display a tissue-specificexpression pattern. Members of this family of kinasesare important mediators of downstream signalling byABL from cell-surface receptors. So inhibitors of theseenzymes can therefore act synergistically with Bcr-Ablinhibitors and hence can potentially counteract theavailability of alternative survival pathways which theCML cells uti l ise during Bcr-Abl inhibit ion.Consequently the combined inhibition of the tyrosinekinase activity of both Abl and Src-family kinasesmight have an added advantage over purely Ablinhibition by counteracting the drug-resistant mutantforms of Bcr Abl in the treatment of CML. Interestingly,

much lower concentrations of the dual src/abl inhibitorare required to ablate the Bcr-Abl phosphorylationwhen compared to the first-generation tyrosine kinaseinhibitor imatinib (IM).29

Bafetinib or INNO-406: Is a dual Abl/Lyn kinaseinhibitor that is up to 55times more potent thanimatinib as it inhibits the clonal proliferation of cells aswell as of most of the Bcr-Abl mutants, except theT315Imutant.30 Unlike the other second-generationtyrosine kinase inhibitors, bafetinib inhibits Lyn kinaseonly with little or action against the other SFK.30 Sinceover expression of Lyn kinase has been implicated inBcr-Abl independent resistance, this drug may havesignificant importance in imatinib-resistant CMLpatients. 31The drug is well tolerated with someelevation of serum transaminases.

Bosutinib: Bosutinib (SKI-606) is 7-alkoxy-3-quinolinecarbonitrile, which functions as a dual inhibitor of bothSrc and Abl kinases has a 10- to 20-fold higher potentantiproliferative activity against imatinib-sensitive aswell as the resistant Bcr-Abl–positive cell lines, like theY253F, E255K and D276G mutants, but not the T315Imutant.22 It can bind to both inactive and intermediateconformations of Bcr-Abl tyrosine kinase receptor andis currently in phase II studies.22 Bosutinib inhibits theproliferation of the CML progenitors but is moderatelyeffective in inducing apoptosis.32Unlike dasatinib,bosutinib does not significantly inhibit Kit or PDGFRbut has a more favorable toxicity profi le incomparision.22

5. AURORA KINASE INHIBITORS:Apart from TKIs, the next promising group ofmolecules are the inhibitors of the Aurora family ofserine/threonine kinases that are essential for cellproliferation. Aurora kinases play a crucial role incellular division by controlling the segregation of thechromatids . Defects in this segregation can causegenetic instability, which is associated withtumorigenesis. They are hence found over expressedin various cancers 34 like leukemia, colon cancer,prostate cancer and carcinoma of the breast. Thereare three mammalian aurora kinase , A, B and C out ofwhich the first two play an important role inoncogenesis33 Aurora A kinase has a crucial role inmitotic spindle formation and centrosome maturation,so its inhibition can disrupt the progression of acell-cycle. On the other hand Aurora B is achromosomal passenger protein essential forchromosomal congression and cytokinesis associatedwith centromeres during prometaphase and with thespindle mid zone during anaphase and telophase. On



the contrary the expression of Aurora C kinase ispredominantly restricted to the germ cells, whosefunction is unclear.35TOZASERTIB: Is a potent inhibitor of all the threeAurora kinases in a nanomolar range, a moderate tostrong inhibitor of other kinases, like the ABL andJAK2, which are also the targets for a range ofmyeloproliferative disorders.36 It also inhibits theautophosphorylation of T315I mutant BCR-ABL intransformed cells.36 Dasatinib with tozasertib incombination resulted in higher attenuation ofphosphorylation and increased apoptosis andprolonged survival in athymic nude mice as comparedto treatment with either agent alone.37 These resultsprovide the rationale for combination trials oftozasertib and dasatinib in patients with BCR-ABLT315I-positive CML. 37DANUSERTIB: PHA-739358 - which is currently in phase II clinical trial in patients who have relapsedafter imatinib therapy is an orally bioavailable inhibitorof all the types of Aurora kinases with additionalactivity against the T315 BCR-ABL kinase. 38Treatment with danusertib in T315I mutants revealedsignificantly decreased phosphorylation of histone H3Ser10, a marker of Aurora B activity, indicating thatthis compound simultaneously inhibits Aurora B andthe mutants of BCR-ABL. It also has potentanti-proliferative activity on a wide range of othercancer cell lines, where it significantly inhibits tumourgrowth in different animal tumour models and atwell-tolerated doses.38BARASERTIB: Is yet another selective Aurora-Bi n h i b i t o r w h i c h i s a h i g h l y s o l u b l eacetanilide-substituted pyrazole aminoquinazolonepro-drug that is cleaved completely in the humanplasma to yield the active drug substance .39

6. NON-ATP-COMPETITIVE INHIBITORS OFBCR-ABL -ALLOSTERIC INHIBITORS:A potential alternative approach to ATP-competitiveBCR-ABL inhibition is to use molecules that inhibit thekinase activity either by a non-ATP competitiveallosteric mechanism potentially involving binding tothe myristate pocket in the C-lobe of the Bcr-Ablkinase domain 40 or by preventing the binding ofsubstrates to the kinase through covalent interactions.Th is s t ra tegy has the advan tage tha t imatinib-resistant mutants are unlikely to be resistantto such inhibitors, owing to the different binding sitesand hence can provide an important pharmacologicaltool to overcome mutations that cause resistance tothe conventional ATP-competitive inhibitors. Theability of these compounds to synergize withATP-competitive inhibitors to inhibit the growth of

transformed cells in Bcr-Abl mutants is also likely toprevent or delay the emergence of resistancemutations. A major advantage of such non competitivekinase inhibitors is that they can be highly selective fora particular kinase.GNF-2(3-[6-[[4-(trifluoromethoxy)phenyl]amino]-4-pyrimidinyl]benzamide) is the lead compound in this classwhich has no activity against most kinases but inhibitthe activity of imatinib-resistant BCR-ABLkinase-domain mutants. 41

Heat Shock Protein 90 InhibitorsThe BCR-ABL tyrosine kinase is a client protein of theheat shock protein (hsp) 90.HSP90 proteins play important roles in the regulationof the cell cycle, cell growth, cell survival, apoptosis,angiogenesis and oncogenesis. They function as molecular chaperone that interacts with proteins likeRaf, Akt, FLT-3 and Bcr-Abl and keeps these proteinsin a stable and functional conformation inside the cell.HSP90 inhibitors can inhibit the ability of the protein tofunction as a chaperone, thereby leading to the downregulation of Bcr-Abl mutants including the E255K andT315I mutants and can also induce apoptosis in CMLcell lines preferentially over their normal cellularcounterparts. 42

Geldanamycin: Is a naturally existing HSP90 inhibitorthat belongs to the class of benzoquinone ansamycinantibiotic. Hepatotoxicity is a dreadful adverse effectfor which GA has not moved forward in clinical trialsbut development of its analogues show higher affinityto HSP90 in tumor cells as compared to normaltissues and constitute a class of potential antitumord r u g s ( 2 - 3 ) . T h e s e i n c l u d e17-allylamino-demethoxygeldamycin (17-AAG) and17-dimethylamino- geldanamycin (17-DMAG) thathave completed phase I and are currently enteringphase II clinical trials. In addition,the analogue17-AAG targets and inhibits the P-glycoproteinmultidrug resistance pump and thereby can inhibitdrug efflux, one of the common cause of imatinibresistance.43

7. INDEPENDENT OF TYROSINE KINASEINHIBITION -Homoharringtonine:Homoharringtonine (HHT) is a plant alkaloid derivedfrom an evergreen tree of the genus Cephalotaxus. Itinhibits multiple pathways, which includes theup-regulation of genes associated with apoptosis,angiogenesis in CML. HHT in combination withimatinib, is synergistic in CML cell lines as it results ina reduction in BCR-ABL transcript levels in 50% ofpatients 44 and a reduction or disappearance of the



T315Imutant in patients who had developed thismutation while on imatinib therapy.44 For thetreatment of CML, homoharringtonine is administeredsubcutaneously twice-daily for 14 days in a 28 daycycle (induction phase of 1 to 2 cycles), followed bytwice-daily for 7 days in a 28 cycle for up to 24 cycles.45 Its semisynthetic derivative Omacetaxine iscurrently being tested in Phase II trials in TKI-resistantpatients. 46 So it may provide a treatment option fora population of patients, who do not have anyavailable approved drug therapy.

8. HISTONE DEACETYLASE INHIBITORS –VORINOSTAT:For gene expression the control of the coiling anduncoiling of DNA in a cell is accomplished with thehelp of histone acetylases (HAT), which acetylate thelysine residues in the core histone moiety leading to aless compact and more transcriptionally activechromatin. On the other hand, the actions of histonedeacetylases (HDAC), is to remove these acetylgroups from the lysine residues leading to theformation of a condensed and transcriptionallysilenced chromatin, thereby affecting geneexpression.47It also causes transcriptionalupregulation of cyclin-dependent kinase inhibitor,cell-cycle arrest and apoptosis in tumorcells.48 It alsoinduces expression of p27, a key cell-cycle regulator,and is associated with downregulation of Bcr-Ablprotein. In CML cells the activity of the Bcr-Abl tyrosinekinase (TK) in the cytosol activates several molecularmechanisms which inhibits apoptosis.49 Thesemechanisms include increased expression of theantiapoptotic Bcl-xL protein and increased activity ofAKT kinase that confers resistance to apoptosisthrough several known mechanisms. Vorinostat orSAHA is a HDAC inhibitor, treatment with which leadsto increased levels of p21 and p27 which are genesinvolved in cell cycle regulation, generation of reactiveoxygen species (ROS), upregulation of the levels ofthe pro-death proteins, e.g., Bax, Bak and Bim.Collectively, these effects inhibit cell-cycle growth,lower the threshold to apoptotic stimuli and induceapoptosis of CML cells. By inducing acetylation ofhsp90 it also inhibits the ATP-binding and chaperonefunction of hsp90. This leads to poly ubiquitylation,proteasomal degradation and depletion of hsp90 clientproteins, including Bcr-Abl itself and its downstreameffectors c-Raf and AKT. 50 Combination treatment with imatinib resulted in a greater level of apoptosisthan that was achieved with either agent alone50whereas co-treatment with nilotinib was synergistic ininducing apoptosis in imatinib-resistant cell linesexpressing the T315I and E255K mutants leading to

the depletion of the Bcr-Abl levels.51 Collectively,these ?ndings generate the rationale to investigate theclinical ef?cacy of the combined treatment with SAHAand imatinib against the advanced phases of CML aswell as test the antileukemia effects of SAHA againstimatinib-refractory CML .

Arsenic Trioxide (ATO):Arsenic trioxide (As2O3, Trisenox) induces apoptosisin Bcr-Abl–positive cell lines and reduces theproliferation of CML blasts.52 It causes downregulation and auto phosphorylation of the Bcr-Ablprotein in imatinib-resistant cell lines that arecharacterized by Bcr-Abl dependent resistance.53Combination with imatinib induces synergisticinhibition of the growth of Bcr-Abl–expressing celllines,50 cell death in imatinib-resistant cell lines thatover expressed Bcr-Abl or had the M351T or Y253F,but not theT315I mutants.53 A recent report showedthat As2O3, via the degradation of the promyelocyticleukemia protein, was able to sensitize quiescent CMLl e u k e m i a - i n i t i a t i n g c e l l s t o c y t o s i n earabinoside–mediated induction of apoptosis.54 makeimatinib resistant cell lines and primary cellssusceptible to imatinib-induced growth inhibition andapoptosis.

Proteasome Inhibitors:The ubiquitin-proteasome system (UPS) is theprinciple pathway for diverse intracellular proteindegradation so it is critical for normal cell survival andfunction 55. Proteasome is a large proteolyticcomplex that consists of a 20S catalytic complex andtwo 19S regulatory subunits. Proteins that are to bedegraded are tagged with ubiquitin chains and bind toa receptor on the 19S complex and the protein isdenatured and presented to the 20S proteasome fordegradation 55. Proteasome inhibitors target thecatalytic 20S core of the proteasome and suppress thep ro teasoma l deg rada t ion o f numerouscellularproteins.56 Inhibition of transcription activatedby nuclearfactor B (NF- B) has been implicated as themechanism responsible for the antitumor effect ofproteasome inhibitors. The proteasome inhibitor,bortezomib inhibits proliferation, induces G2/Mphase cell cycle arrest and promotes apoptosis ofimatinib-sensitive and resistant CML cell lines.57 Synergism between bortezomib and the HDI vorinostatand between bortezomib and flavopiridol has beenreported in in vitro studies of growth inhibition of CMLcell lines.56 They also exert synergic effects withhistone deacetylase inhibitors and cyclin-dependentkinase inhibitor flavopiridol 58. Thus it offers apotential therapeutic option in CML by targeting both



TKI-insensitive stem cells and TKI-resistant BCR-ABLmutations. Hence combined use of tyrosine kinaseinhibitor and proteasome inhibitor might be helpful foroptimizing CML treatment CYCLIN-DEPENDENT KINASE INHIBITORS- FLAVOPIRIDOL:They are a family of protein kinases that regulatesthe cell cycle and whose aberrant upregulation canlead to oncogenic effects. Consequent ly,cyclin-dependent kinase inhibitors (CDKNI) are thenegative cell regulatory proteins that can block thiskinase activity in response to signals from theenvironment or from a damaged DNA, and can causeselective interruption of the cell cycle usually duringthe G1 phase which eventually results in death ofthese cells. The CDKNI family contains three members which areCDKNIA (also known as p21CIP), CDKNIB (alsoknown as p27KIP1) and CDKNIC (also known asp57KIP2) .59 A number of oncogenes like c-myc andras target these pathways causing inappropriateactivation of CDKs.60 The BcrAbl tyrosime kinase activates the mitogenic signaling pathways byactivation of the RAS, Erk, and JNK pathways whichstimulates the G1-to-S phase transit ion inhematopoietic cells. The chronic myelogenousleukemic cell proliferation also depends on thenucleo-cytoplasmic ratio of the cyclin-dependentkinase inhibitor p27. There is also an associatedBcr-Abl driven activation of cyclin dependent kinase 2(CDK2) in cells. 61 Thus there is a defectivecheckpoint combined with increased survival whichcauses clonal evolution of the disease in CML.Flavopiridol a semi-synthetic flavone, is the first CDKinhibitor to be tested in clinical trials after beingidentified in an anti-cancer agent screen in 1992.Studies report that reatment with imatinib andflavopiridol leads to an increased mitochondrialdamage, activation of caspases and enhancedapoptosis in imatinib-resistant CML cell line.62

DNA-METHYLTRANSFERASE INHIBITORS:The methylation of DNA a process occurring both ineukaryotic and prokaryotic cells, carried out by DNAmethyl transferases (DNMT) plays an important role inthe normal embryological development, genomicstability and also in carcinogenesis, and hence is anovel target for the treatment of malignancy .63Cancers are usually hypomethylated due to inhibition of the inhibitory effects of homologousrecombination and transcription of the normallyrepressed genes. DNA methyl transferase hence cantheoretically serve as a reasonable target for

antineoplastic drugs by preventing methylation theycan limit the damaging recombination and alsoprevent transposon transcription and can silence thesuppressor genes, ultimately inhibiting tumor growthand possibly inducing involution. Such novel agents inclinical trials which prevent methylation are5-azacytidine (azacitidine), 5-aza-2′-deoxycytidine(decitabine), 1-β-Darabinofuranosyl-5-azacytosine(fazarabine) and dihydro-5- azacytidine (DHAC). Afterphosphorylation, they are incorporated into the DNA orRNA and are covalently linked with DNMT wherethey induce cell death by structural instability at thesite of incorporation and by inhibition of DNAsynthesis.64 The may be useful in CML. An in vitrostudy revealed that a combination of combination ofdecitabine with imatinib had additive to synergisticgrowth inhibitory effects upon cells containing Bcr-Ablwith the M351T and Y253Fmutants.

TUMOR SUPPRESSOR PP2A:Increased expression of Bcr-Abl protein leads toinactivation of tumor suppression gene proteinphosphatase 2A (PP2A) tumor suppressor byenhancing the expression of one inhibitor. Themolecular or pharmacologic reactivation of PP2Aactivity suppresses Bcr-Abl expression and function,resulting in growth inhibition, increased apoptosis,impaired clonogenicity and decreased in vivoleukemogenesis in CML cell lines and primary CMLcells. Some PP2A activators like FTY720 is now inthe phase of clinical trials in the management ofpatients with multiple sclerosis or undergoing renaltransplantation. This agent also suppresses the growth,abolishes Bcr-Abl phosphorylation and inducedBcr-Abl down-regulation via the activation of PP2Ainimatinib-sensitive and T315I-expressing cell lines.

Conclusion

Without doubt, imatinib represents a majorachievement for the treatment of CML but resistanceto this drug has become and will continue to be atherapeutic challenge. Single agent therapy withimatinib may not be the best long-term option in CML,at least for a proportion of patients and otherstrategies need to be explored. Many novelcompounds are currently being investigatedpreclinically and clinically, and therapeutic approachesto circumvent the problem of imatinib resistance arenow possible. Dasatinib and nilotinib represent the firstof the newer generation TKIs which are effective andsafe in patients with imatinib resistant and intolerantCML. It is likely, however, that sub clones with novel



Bcr-Abl mutants will again develop in response tothese new small-molecule inhibitors. Although it isnowadays emphasized as a clinical emergency, theproblem of resistance driven by the T315I mutant islikely to be resolved soon. Therefore, alternativetherapeutic approaches are required and these mayinvolve the combination of Bcr-Abl TKIs with inhibitorsof non-Bcr-Abl targets or targets downstream ofBcr-Abl to achieve a synergistic effect and possiblyprevent or overcome resistance.

References

1. Parikh PM, Chakra BS, Banvali SD et al Aretrospective analysis of 224 cases of chronic myeloidleukemia. Ind. J.Hemat.1988; 6: 85-87.2. Skorski T. BCR/ABL, DNA damage and DNA repair:implications for new treatment concepts. LeukLymphoma 2008; 49:610–4.3. Faderl S, Talpaz M, Estrov Z, Kantarjian HM. Chronic myelogenous leukemia: biology and therapy.Annals of Internal Medicine 1999; 131 (3): 207–219.4. Tefferi A. Classification, diagnosis and managementof myeloproliferative disorders in the JAK2V617F era.Hematology Am Soc Hematol Educ Program 2006:240–5.5. Hare T, Eide C & Deininger M. BCR-ABL kinasemutations, drug resistance and the road to a cure ofchronic myeloid leukaemia. Blood First Edition Paper,pre published online, 11th May 2007.6. Carlesso N, Griffin JD, Druker BJ. Use of atemperature-sensitive mutant to define the biologicaleffects of the p210BCR-ABL tyrosine kinase onproliferation of a factor-dependent murine myeloid cellline. Oncogene. 1994 Jan; 9(1):149–156.7. Clarkson B, Strife A. Linkage of proliferative andmaturational abnormalities in chronic myelogenousleukemia and relevance to treatment. Leukemia. 1993Nov; 7(11):1683–1721.8. Eck.M, Manley,P. The interplay of structuralinformation and functional studies in kinase drugdesign: insights from BCR-ABL. Current opinion in cellbiology 2009,21(2):288-295.9. Shawver, L. K., Slamon, D. and Ullrich, A. Smartdrugs: Tyrosine kinase inhibitors in cancer therapy.Cancer Cell: 2002:117-123.10. Druker, B. J. and Lydon, N. B. (2000). Lessonslearned from the development of an Abl tyrosinekinase inhibitor for chronic myelogenous leukemia.The journal of Clinical Investigation: 2000: 3-7.11. Takimoto CH, Calvo E. Principles of OncologicPharmacotherapy" in Pazdur R, Wagman LD,Camphausen KA, Hoskins WJ (Eds) Cancer

Management: A Multidisciplinary Approach. 11 ed.2008.12. Graham SM, Jorgensen HG, Allan E, et al.Primitive, quiescent, Philadelphia-positive stem cellsfrom patients with chronic myeloid leukemia areinsensitive to STI571 in vitro. Blood. 2002 ;99:319–325.13. An, X.; Tiwari, A.; Sun, Y.; Ding, P.; Ashby Jr, C.;Chen, Z. BCR-ABL tyrosine kinase inhibitors in thetreatment of Philadelphia chromosome positivechronic myeloid leukemia: a review. Leukemiaresearch 2010; 34 (10): 1255–1268. 14. Gambacorti-Passerini CB, Gunby RH, Piazza R,Galietta A, Rostagno R, Scapozza L . Molecularmechanisms of res is tance to imat in ib inPhiladelphia-chromosome-positive leukaemias .Lancet Oncol. 2003; 4 (2): 75–85.15. Shah NP, Tran C, Lee FY, et al. Overridingimatinib resistance with a novel ABL kinase inhibitor.Science. 2004; 305:399–401.16. Weisberg E, Manley PW, Breitenstein W, et al.Characterization of AMN107, a selective inhibitor ofnative and mutant Bcr-Abl. Cancer Cell. 2005; 7:129–141.17. Kelly K, Swords R, Mahalingam D, et al. Serosalinflammation related to tyrosine kinase inhibitors.Targ Oncol. 2009; 4(2):99-105.18. Weisberg E, Manley PW, Breitenstein W, et al.Characterization of AMN107, a selective inhibitor ofnative and mutant Bcr-Abl. Cancer Cell. 2005;7:129–141. 19. Weisberg E, Manley PW, Breitenstein W, et al.Characterization of AMN107, a selective inhibitor ofnative and mutant Bcr-Abl. Cancer Cell. 2005; 7:129–141.20. Rix U, Hantschel O, Durnberger G, et al. Chemicalproteomic profiles of the BCR-ABL inhibitors imatinib,nilotinib, and dasatinib reveal novel kinase and nonkinase targets. Blood. 2007; 110: 4055–4063.21. Vajpai N, Strauss A, Fendrich G, et al. Solutionconformations and dynamics of ABL kinase-inhibitorcomplexes determined by NMR substantiate thedifferent binding modes of imatinib/nilotinib anddasatinib. J Biol Chem 2008; 283:18292–302.22. Puttini M, Coluccia AM, Boschelli F, et al. In vitroand in vivo activity of SKI-606, a novel Src-Abl inhibitor,against imatinib-resistant Bcr-Abl+ neoplastic cells.Cancer Res. 2006; 66:11314–11322.23. Soverini S, Martinelli G, Colarossi S, et al.Presence or the emergence of a F317L BCR-ABLmutation may be associated with resistance todasatinib in Philadelphia chromosome-positiveleukemia. J Clin Oncol. 2006; 24. e51–e5224. Soverini S, Colarossi S, Gnani A, et al.



Contribution of ABL kinase domain mutations toimatinib resistance in dif ferent subsets ofPhiladelphia-positive patients: by the GIMEMAWorking Party on Chronic Myeloid Leukemia. ClinCancer Res. 2006; 12: 7374–7379.25. Nicolini FE, Corm S, Le QH, et al. Mutation statusand clinical outcome of 89 imatinib mesylate-resistantchronic myelogenous leukemia patients: aretrospective analysis from the French intergroup ofCML (Fi(phi)-LMC GROUP). Leukemia. 2006;20:1061–1066.26. Gorre ME, Mohammed M, Ellwood K, et al. Clinicalresistance to STI-571 cancer therapy caused byBCR-ABL gene mutation or amplification. Science.2001; 293:876–880.27. Gumireddy K, Baker SJ, Cosenza SC, et al. Anon-ATP-competitive inhibitor of BCR-ABL overridesimatinib resistance. Proc Natl Acad Sci U S A.2005;102:1992–199728. http://journals.lww.com/oncology-times.29. Gambacorti-Passerini C, Kantarjian HM, BaccaraniM, et al. Activity and tolerance of bosutinib in patientswith AP and BP CML and Ph+ ALL [abstract]. J ClinOncol. 2008; 26:7049.30. Kimura S, Naito H, Segawa H, et al. NS-187, apotent and selective dual Bcr-Abl/Lyn tyrosine kinaseinhibitor, is a novel agent for imatinib-resistantleukemia. Blood. 2005; 106: 3948–3954.31. Kantarjian HM, Cortes J, le Coutre P, et al. Aphase I study of INNO-406 in patients with advancedPhiladelphia (Ph+) chromosome-positive leukemiaswho are resistant or intolerant to imatinib and secondgeneration tyrosine kinase inhibitors [abstract]. Blood.2007; 110.32. Konig H, Holyoake TL, Bhatia R. Effective andselective inhibition of chronic myeloid leukemiaprimitive hematopoietic progenitors by the dual Src/Ablkinase inhibitor SKI-606. Blood. 2008; 111: 2329–2338.33. Giet R, Prigent C. Aurora/Ipl1p-related kinases, anew oncogenic family of mitotic serine-threoninekinases. Journal of Cell Science 1999 ; 112:3591–3601.34. Jingyan Fu, Minglei Bian, Qing Jiang, andChuanmao Zhang Roles of Aurora Kinases in Mitosisand Tumorigenesis Mol. Cancer Res., 2007; 5: 1-10.35. Katayama H., Brinkley WR, Sen S. The Aurorakinases: Role in cell transformation and tumorigenesis.Cancer and Metastasis Reviews 2003; 22(4): 451-64.36. Samanta AK, Lin H, Sun T, Kantarjian H,Arlinghaus RB. Janus kinase 2: a critical target inchronic myelogenous leukemia. Cancer Res 2006;66:6468–6472.37. Paquette RL, Shah NP, Sawyers CL, et al.PHA-739358, an aurora kinase inhibitor, induces

clinical responses in chronic myeloid leukemiaharboring T315I mutations of BCR-ABL [abstract].Blood. 2007; 110.38. Gontarewicz A, Balabanov S, Keller G, et al.Simultaneous targeting of Aurora kinases and Bcr-Ablkinase by the small molecule inhibitor PHA-739358 iseffective against imatinib-resistant BCR-ABLmutations including T315I. Blood. 2008; 111:4355–4364.39. Foote, KM., ASC National Meeting and Exposition2008, 235th, (Medi-198).40. Adrian FJ, Ding Q, Sim T, et al. Allosteric inhibitorsof Bcr-abl-dependent cell proliferation. Nat Chem Biol.2006;2:95–102.41. Zhang J.; Adrian F. J.; Jahnke W.; Cowan-Jacob S.W.; Li A. G.; Iacob R. E.; Sim T.; Powers J.; Dierks C.;Sun F.; Guo G. R.; Ding Q.; Okram B.; Choi Y.;Wojciechowski A.; Deng X.; Liu G.; Fendrich G.;Strauss A.; Vajpai N.; Grzesiek S.; Tuntland T.; Liu Y.;Bursulaya B.; Azam M.; Manley P. W.; Engen J. R.;Daley G. Q.; Warmuth M.; Gray N. S. TargetingBcr-Abl by combining allosteric with ATP-binding-siteinhibitors. Nature 2010; 463, 501–506 42. Gorre ME, Ellwood-Yen K, Chiosis G, Rosen N,Sawyers CL. BCR-ABL point mutants isolated frompatients with imatinib mesylate- resistant chronicmyeloid leukemia remain sensitive to inhibitors of theBCR-ABL chaperone heat shock protein 90. Blood.2002; 100:3041–3044.43. Nimmanapall i R, O’Bryan E, Bhalla K.G e l d a n a m y c i n a n d i t s a n a l o g u e17-allylamino-17-demethoxygeldanamycin lowersBcr-Abl levels and induces apoptosis anddifferentiation of Bcr- Abl-positive human leukemicblasts. Cancer Res. 2001; 61: 1799–1804.44. Marin D, Kaeda JS, Andreasson C, et al. Phase I/IItrial of adding semisynthetic homoharringtonine inchronic myeloid leukemia patients who have achievedpartial or complete cytogenetic response on imatinib.Cancer. 2005; 103:1850–1855 .45. Lavallade H, Khorashad JS, Davis HP, et al.Interferon-alpha or homoharringtonine as salvagetreatment for chronic myeloid leukemia patients whoacquire the T315I BCR-ABL mutation. Blood. 2007;110: 2779–2780.46. Quintas-Cardama A, Kantarjian H, Garcia-ManeroG, et al. Phase I/I I study of subcutaneoushomoharringtonine in patients with chronic myeloidleukemia who have failed prior therapy. Cancer. 2007;109: 248–255.47. Thiagalingam S, Cheng KH, Lee HJ, Mineva N,Thiagalingam A, Ponte JF (March 2003). Histonedeacetylases: unique players in shaping the epigenetichistone code . Ann. N. Y. Acad. Sci. 983: 84–100.



48. Yu C, Rahmani M, Almenara J, et al. Histonedeacetylase inhibitors promote STI571-mediatedapoptosis in STI571-sensitive and -resistant Bcr/Abl+human myeloid leukemia cells. Cancer Res. 2003;63:2118–2126.49. Deininger M, Goldman J, Melo J. The molecularbiology of chronic myeloid leukemia. Blood.2000;96:3343-3356.50. Nimmanapalli R, Fuino L, Stobaugh C, Richon V,Bhalla K. Cotreatment with the histone deacetylaseinhibitor suberoylanilide hydroxamic acid (SAHA)enhances imat in ib- induced apoptos is ofBcr-Abl-positive human acute leukemia cells. Blood.2003; 101: 3236 –3239.51. Fiskus W, Pranpat M, Bali P, et al. Combinedeffects of novel tyrosine kinase inhibitor AMN107 andhistone deacetylase inhibitor LBH589 against Bcr-Ablexpressing human leukemia cells. Blood. 2006; 108:645–652.52. Perkins C, Kim CN, Fang G, Bhalla KN. Arsenicinduces apoptosis of multidrug-resistant humanmyeloid leukemia cells that express Bcr-Abl oroverexpress MDR, MRP, Bcl-2, or Bcl-x(L). Blood.2000; 95:1014–1022.53. La Rosée P, Johnson K, Corbin AS, Stoffregen EP,Moseson EM, Willis S, et al. In vitro efficacy ofcombined treatment depends on the underlyingmechanism of resistance in imatinib-resistantBcr-Abl-positive cell lines. Blood 2004; 103 :208-15.54. Ito K, Bernardi R, Morotti A, et al. PML targetingeradicates quiescent leukaemia-initiating cells. Nature.2008; 453: 1072–1078.55. Ciechanover A (2005) Proteolysis: from thelysosome to ubiquitin and the proteasome. Nat RevMol Cell Biol 6: 79–87.56. Yu C, Rahmani M, Conrad D, et al. Theproteasome inhibitor bortezomib interactssynergistically with histone deacetylase inhibitors toinduce apoptosis in Bcr/Abl+ cells sensitive andresistant to STI571. Blood. 2003; 102:3765–3774.57. Gatto S, Scappini B, Pham L, et al. Theproteasome inhibitor PS-341 inhibits growth andinduces apoptosis in Bcr/Abl-positive cell linessensitive and resistant to imatinib mesylate.Haematologica. 2003; 88:853–863.58. Soligo D, Servida F, Delia D, Fontanella E,Lamorte G, et al. The apoptogenic response ofhuman myeloid leukaemia cell lines and of normal andmalignant haematopoietic progenitor cells to theproteasome inhibitor PSI. Br J Haematol. 2001; 113:126–135.59. Sausville, Edward A. Complexities in thedevelopment of cyclin-dependent kinase inhibitordrugs Trends in Molecular Medicine 2002 ; 8:S32-S37.

60. Steiner P, Philipp A, Lukas J, et al. Identi?cation ofa Myc-dependent step during the formation of activeG1 cyclin-cdk complexes. EMBO J. 1995; 14:4814-4826.61. Cortez D, Reuther G, Pendergast AM. The BcrAbltyrosime kinase activates mitogenic signalingpathways and stimulates G1-to-S phase transition inhematopoietic cells. Oncogene. 1997;15: 2333-2342.62. Yu C, Krystal G, Dent P, Grant S. Flavopiridolpotentiates STI571-induced mitochondrial damageand apoptosis in BCR-ABL-positive human leukemiacells. Clin Cancer Res. 2002; 8: 2976–2984.63. Colot V, Rossignol JL. Eukaryotic DNA methylationas an evolutionary device. Bioessays 1999; 21:402–411.64. Lubbert M. DNA methylation inhibitors in thetreatment of leukemias, myelodysplastic syndromesand hemoglobinopathies: clinical results and possiblemechanisms of action. Curr Top Microbiol Immunol2000; 249: 135–164.



Illustrations

Illustration 1

Signalling Pathway In CML



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