Part II: Management of resistance to imatinib in chronic myeloid leukaemia

Review

Part II: Management of resistance to imatinib in chronic myeloid leukaemia Jane F Apperley Lancet Oncol 2007; 8: 1116–28 Department of Haematology, Imperial College, Hammersmith Hospital, London, UK (Prof J F Apperley MD) Correspondence to: Prof Jane F Apperley [email protected] For Part I: Mechanisms of resistance to imatinib in chronic myeloid leukaemia see Lancet Oncol 2007; 8: 1018–29.

Updated findings from a randomised comparison of imatinib versus previous standard treatment in the treatment of newly diagnosed chronic myeloid leukaemia suggest that this first-generation tyrosine-kinase inhibitor can induce excellent long-term responses in most patients. However, a small proportion of patients will not respond or will lose previous responses, and, for these patients, alternative treatments are needed. This review is the second of two parts: the first part provided a review of the mechanisms underlying resistance to imatinib and this second part will discuss the management of patients who are resistant to imatinib by reviewing the many new drugs being introduced into clinical practice and suggesting strategies for decision making.

Introduction The introduction of tyrosine-kinase inhibitors (TKIs) for the treatment of chronic myeloid leukaemia (CML; figure 1) has had a profound and beneficial effect on this disease, which previously had a median survival of 5–7 years.1 The first of these TKIs to be introduced into clinical practice was imatinib, introduced in 1998. This drug moved rapidly from phase I and II trials to a phase III randomised controlled trial (International Randomised Study of Interferon versus ST1571 [IRIS]) in which it was compared with interferon alfa plus cytosine arabinoside (IFN-ara-C).2 Complete haematological responses and complete cytogenetic remissions were 95% and 94%, respectively, for imatinib, compared with 55% and 8·5% for IFN-ara-C. Progression-free survival at 18 months was 96·7% for imatinib compared with 91·5% for IFN-ara-C.2 These early findings led to accelerated regulatory approval of imatinib for all phases of CML and the drug became first-line treatment for most patients. The findings of the IRIS trial have been updated3 and show that the cumulative incidences of complete haematological response and complete cytogenetic

remission at 5 years are 98% and 87%, respectively, for imatinib. However, a complete cytogenetic remission of 87% does not mean that this percentage of patients will achieve a durable complete cytogenetic remission, because about 30% of patients in the study were no longer taking imatinib at 5 years for various reasons (eg, disease progression, drug toxicity, referral for allogeneic stem-cell transplantation, or death from other causes) and were censored from the analysis at the time of drug cessation. Nevertheless, for those who achieved complete cytogenetic remission at 18 months, and for patients who had a three-log reduction in tumour load (major molecular response), 5-year progression-free survival was excellent at 97% and 99%, respectively. Perhaps of more importance was the realisation that the risk of progression for these responders became less each successive year from diagnosis and reached zero for patients with a major molecular response after the third year. However, despite these encouraging findings, 20–25% of patients who do not achieve complete cytogenetic remission or whose disease continues to progress on imatinib, will need alternative drugs. Several of these new drugs have been, or will shortly be, introduced into routine clinical practice and will compete with established strategies, such as allogeneic stem-cell transplantation, as a second-line treatment, with imatinib continued as first-line treatment.

New drugs for CML

Professor Aaron Polliack/Science Photo Library

Over the past few years, second-generation TKIs have been rapidly assessed and introduced into clinical practice. The first of these drugs to gain a license in Europe and the USA was dasatinib, which will be followed closely by nilotinib (having completed phase I and II trials), bosutinib (currently in phase II trials), and Inno 406 (currently in phase I trials). Additionally, several other new drugs with alternative mechanisms of action are entering clinical development (figure 2).

Second-generation TKIs Dasatinib Figure 1: White blood cells from a patient with chronic myeloid leukaemia

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Dasatinib was identified by screening a series of substituted 2-(aminopyridyl) and 2-(aminopyrimidinyl) http://oncology.thelancet.com Vol 8 December 2007

Review

CI HN

H N

CF₃

Inno 406

F N

N

N

N N

N H

N

O

N

N CI

R

OMe CN

MeO

Bosutinib

PD180970

CI

N

O

CI

Me₂N

N NH

CH₃

N

O

Imatinib (STl571) O

AP23464

H

P

N

HN

N

H

N

N

N

N

N O

CGP76030

N

N N

N

O

CH₃

N

NH₂

N N

OH

N

Nilotinib (AMN107) N

O CH₃

Dasatinib (BMS345825) CH₃

N

N H N

CI

S

N H

H N

N N

N

CF₃

HC₃ O

N

O

N H

N

OH

N

NH

O

Figure 2: Chemical structures for new second-generation tyrosine-kinase inhibitors

thiazole-5-carboxamides.4 This drug is a dual SRC-ABLkinase inhibitor that is thought to bind to both the active and inactive conformations of ABL kinase and inhibit most of the clinically relevant kinase-domain mutations, except T315I. Dasatinib is a more powerful inhibitor of CRKL phosphorylation (a downstream target of BCR-ABL) than imatinib in primitive CD34+CD38- CML cells, but does not induce death of the quiescent stem-cell population.5 It has an oral bioavailability in mammals that varies from 14% to 34%, probably as a result of a combination of incomplete absorption and high first-pass metabolism. Pharmacokinetic data suggest that dasatinib is mainly cleared by oxidative metabolism, which involves CYP3A4.6 Dasatinib is probably a substrate for an intestinal efflux transporter, although this transporter is unlikely to be the ATP-binding competitor B1 (ABCB1; also known as ATPase permeability glycoprotein, the product of the multidrug resistance gene).6 A phase I dose-escalation study of dasatinib in 84 patients with imatinib failure showed complete haematological responses and complete cytogenetic remissions in chronic phase, accelerated phase, myeloid blast crisis, and lymphoid blast crisis/acute lymphoblastic leukaemia of 92%, 45%, 45%, and 27%, and 35%, 35%, 70%, and 80%, respectively.7 Responses in the chronic and acceleration phases were durable during the follow-up period of 2–19 months, but were generally http://oncology.thelancet.com Vol 8 December 2007

transient in more advanced disease (myeloid and blast crises). Responses were similar in patients with mutations (60 of 84 [71%]) compared with those without mutations, but no responses were noted in those with the T315I mutation. A maximum tolerated dose was not reached, leading to the adoption of a schedule of 70 mg of dasatinib twice a day in phase II studies. In a phase II study (CA-180013 START-C), 387 patients with chronic-phase CML and imatinib resistance (n=288) or intolerance (n=99) were enrolled.8,9 At a median follow-up of 15 months, 52% and 40% of patients who were resistant to imatinib had achieved a major cytogenetic response and complete cytogenetic remission, respectively, compared with 80% and 75% of patients who were intolerant of imatinib. The occurrence of a major cytogenetic response was similar in patients with and without mutations, and in the 72% of patients who had received imatinib at doses of 600 mg or higher before starting dasatinib compared with those who had received lower doses. A trend towards better cytogenetic responses in those who had shown similar responses to previous imatinib was also noted. These cytogenetic responses were durable in most patients. Progression-free survival was about 90% for the entire study group. 201 patients were assessable for mutation analysis with 27 different mutations noted in 84 patients (42%).10 Clinical responses were related to the cellular half maximum-inhibitory concentration (IC50) of the mutants, 1117

Review

Amino acid with ABLkinase domain mutation

Chronic phase*

Accelerated phase†

Patients, n

Patients, n

Complete Major haematological cytogenetic response, n response, n

Major cytogenetic response, n

M244

16

7

5

5

2

L248

2

2

1

3

1

G250

20

19

11

9

1

Q252

3

2

1

NA

NA

Y253

5

4

3

6

2

E255

5

5

1

8

1

T315

6

1

1

5

0 0

F317

4

4

1

4

M351

6

6

2

6

1

F359

6

6

3

9

3

E355

NA

NA

NA

4

2

V379

NA

NA

NA

4

2

H396

13

10

5

NA

NA

E459

NA

NA

NA

3

P-loop mutant

45

42

22

30

7

A-loop mutant

24

19

11

7

4

Others

48

42

23

24

8

3

*Data from references 10 and 11. †Data from reference 12. NA=not available.

Table 1: Haematological and cytogenetic responses to dasatinib in chronic and accelerated phases by kinase-domain mutation

with fewer cytogenetic responses noted in patients expressing Q252H, T315I, and F317L mutations (table 1).10,12 174 patients in accelerated phase, with imatinib resistance or intolerance, were enrolled in the CA-180005 START-A study.11,13 Complete haematological responses and major cytogenetic responses were noted in 49% and 39% of patients, respectively. No differences in outcome were noted between patients who were intolerant of imatinib and those who were resistant. Progression-free survival was 66% at 12 months. The START-B and START-L studies recruited 157 patients in myeloid blast crisis (n=109) and lymphoid blast crisis (n=48).14,15 Complete cytogenetic remission was noted in 26% of patients with myeloid blast transformation and in 46% of patients with lymphoid blast transformation. However, responses were not durable and the median progression-free survival was 6·7 months and 3·0 months for patients with myeloid blast crisis and lymphoid blast crisis, respectively. Dose interruptions and dose reductions of dasatinib were common and alternative dosing schedules are being explored in further phase II trials. In one such study16 four dosing schedules were adopted—ie, 70 mg daily, 50 mg twice a day, 100 mg daily, and 70 mg twice a day. Similar cytogenetic and haematological responses were seen in all groups, but the 100-mg-daily dose was associated with a reduced incidence of cytopenia and pleural effusions and fewer dose interruptions and 1118

reductions. If these findings are confirmed with longer follow up, this dose might become the favoured dose, irrespective of licensing recommendations. Fluid retention seems to be the most troublesome non-haematogical toxic effect of dasatinib. 48 (35%) of 138 patients treated at the M D Anderson Cancer Center (Houston, TX, USA) developed pleural effusions17 that were usually exudative. 23 episodes reached grade 3 or 4 toxicity, and were mainly in participants who received daily doses of 140 mg of dasatinib or greater. Most patients were given diuretics and a few received short courses of corticosteroids, although these did not reduce the duration of time off dasatinib. Patients who report the onset or worsening of respiratory or cardiac symptoms should be investigated with imaging and echocardiography.

Nilotinib Nilotinib was designed by maintaining the concept of binding to the inactive conformation of the ABL kinase, but by changing the groups bound to the N-methyl piperazine moiety while retaining the hydrogen bonds with E286 and A381. Furthermore, nilotinib makes two additional hydrogen bonds with M318 and T315.18 Unfortunately, the T315I mutation remains resistant to this new drug. Nilotinib is about 30-times more potent than imatinib with less interpatient variability, measured by CRKL phosphorylation. No correlation between the IC50 of nilotinib and imatinib exists in vivo, which suggests different mechanisms of cellular uptake of these two drugs. Furthermore, unlike imatinib, nilotinib is not a substrate for either ABCB1 (drug efflux) or organic cation transporter 1 (drug influx).19 Like imatinib, nilotinib seems to have an antiproliferative effect rather than a destructive effect in primitive CML stem cells. In the presence of nilotinib, CRKL phosphorylation was not inhibited and apoptosis was not induced in the CD34+CD38- cell population.20 Findings reported by Wang and colleagues21 suggest an autocrine mechanism of protection from the effects of both imatinib and nilotinib by the production of granulocyte-macrophage colony-stimulating factor and subsequent BCR-ABL-independent activation of the JAK-2/STAT-5 signalling pathway. However, Jorgensen and co-workers20 were unable to overcome nilotinib resistance of primary CD34+ cells by adding growth factors. 106 patients with CML (chronic phase [n=17]; accelerated phase [n=56]; and blast crisis [n=33]) and 13 patients with Philadelphia-chromosome-positive acute lymphoblastic leukaemia, all of whom were resistant to imatinib, were treated in a dose-escalating phase I study.22 Haematological responses were noted in 39%, 74%, and 92% of those in blast crisis, accelerated phase, and chronic phase, respectively. A major cytogenetic response was noted in five patients with myeloid or lymphoid blast crisis, 15 patients in http://oncology.thelancet.com Vol 8 December 2007

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acceleration phase, and six patients in chronic phase. Nilotinib-induced responses in patients with or without mutations were similar, but no response was recorded in two patients with T315I mutations. A few sudden and unexpected deaths occurred, although subsequent investigations have failed to establish any clear causal association with nilotinib. Preliminary data from phase II studies of nilotinib have been reported23,24 for the 10-month follow-up of 132 patients with chronic-phase CML (70% were resistant to imatinib and 30% were intolerant of imatinib). Major cytogenetic responses and complete cytogenetic remissions were 49% and 32%, respectively, in both the resistant and intolerant groups. 44 of 101 assessable patients were known to have mutations in the ABL-kinase domain. Responses were more likely to occur in patients without mutations (51% had major cytogenetic response and 33% had complete cytogenetic remission) than in those with mutations (25% and 16%, respectively). 316 patients treated with nilotinib in various phases of CML were assessable for adverse events, which showed a similar spectrum to those seen with imatinib and other second-generation TKIs (table 2).8,9,11,23,25 No cross sensitivity with imatinib seemed to exist. Increases in the QT interval of more than 60 ms from baseline were noted in six (2%) patients. Fluid retention did not seem to be an issue. Neutropenia and thrombocytopenia occurred in more than 50% of patients and were of grade 3–4 toxicity in 28% and 29% of patients respectively. Metabolic changes that involved various abnormalities in liver function, or concentrations of calcium, phosphate, and magnesium were also common, although usually transient. By contrast to imatinib, for which several case reports have suggested better control of glucose concentrations in patients with pre-existing type-2 diabetes mellitus than without imatinib,26,27 nilotinib induced increases in the concentrations of fasting glucose in two-thirds of patients. Similar findings have been reported by Breccia and colleagues.28 A small number of patients worldwide have received all three of the TKIs imatinib, dasatinib, and nilotinib. Quintas-Cardama and co-workers29 described responses, including major cytogenetic response, in 13 of 23 patients treated with dasatinib after failing both imatinib and nilotinib. Responses were durable and occurred in 13 of 16 patients with known ABL-kinase domain mutations except T315I.29

growth factor (the inhibition of which is thought to account for the fluid retention noted with other TKIs), fibroblast growth factor, or insulin-like growth factor-1.31 Bosutinib is known to reduce vascular endothelial growth factor-mediated vascular permeability and tumour-cell extravasation, and its effect on cell-to-cell interactions between tumour cells and host cells might be crucial for its in-vivo efficacy. Data for 19 assessable patients with chronic-phase CML, who were resistant to or intolerant of imatinib, showed that 16 achieved complete haematological remission and about a third had a major cytogenetic response on bosutinib.32 These preliminary findings are comparable to those obtained at similar time points with both dasatinib and nilotinib.

INNO-406 INNO-406, also known as CNS-9 or NS-187, is 25–55-times more potent than imatinib against the ABL kinase and also inhibits LYN, a protein that has been implicated in progression to blastic phase.33 However, this drug is also not active against the T315I mutation. INNO-406 is orally bioavailable in a murine model and seems to be a competitive inhibitor of ATP.34,35 It is currently being trialled in phase I studies in patients known to be resistant to at least two other TKIs. Up to now, both haematological and cytogenetic responses have been shown. This drug is likely to be a competitor for first-line or second-line treatment of CML, rather than third-line treatment. Imatinib (N=532)*

Dasatinib (N=655)†

Nilotinib (N=316)‡

All grades, Grades 3–4, % %

All grades, Grades 3–4, % %

All grades, Grades 3–4, % %

Nausea

55

2

25

1

31

1

Vomiting

28

0·9

10

0

21

<1

Diarrhoea

33

0·9

31

2

22

3

Arthalgia or myalgia

27

1

7

<1

18

2

Rash

27

1

23

<1

34

2

Headache

28

0·2

31

2

30

3

Fatigue

25

0·2

25

2

28

1

Cough

9

0

8

0

17

<1

5

0·2

11

3

NA

NA

1

16

0

11

0·6

··

Dyspnoea Peripheral oedema

51

Other oedema§

2

··

··

0 ··

Pleural effusion

··

··

23

4

<1

<1

Pericardial effusion

··

··

1

<1

NA

NA

Congestive cardiac failure

NA

NA

3

2

NA

NA

Anaemia

NA

4

NA

17

50

9

Bosutinib

Neutropenia

NA

33

NA

48

50

28

Bosutinib, previously known as SKI-606, is a 4-anilino-3-quinoline carbonitrile dual inhibitor of SRC and ABL, which is orally active and has anti-tumour activity in murine models of colorectal tumours and K562-induced CML.30 However, this drug has no activity against the tyrosine-kinase receptors for platelet-derived

Thrombocytopenia

NA

16

NA

46

58

29

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Duration of treatment at time of reporting varies for each drug. All data derived from patients treated in phase II studies in chronic phase. *Data from reference 23. †Data from references 8, 9, and 11. ‡Data from reference 25. §Includes pleural and pericardial effusions, pulmonary oedema, and anasarca. NA=not available.

Table 2: Most frequent toxic effects of imatinib, dasatinib, and nilotinib

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PD compounds Several members of the pyrido [2,3-d] pyrimidine family were originally developed as SRC inhibitors, but were subsequently noted to have potent anti-ABL activity.36,37 The crystal structure of PD173955 (which is closely related to other members, such as PD180970 and PD166326) suggests that these inhibitors bind to both the active and inactive conformations of BCR-ABL.38 When six of these PD compounds were compared, PD166326 was recorded as the most potent inhibitor of leukaemic CD34+ cells derived from patients with CML,39 and PD166324 was noted to be more effective than imatinib in a murine model of CML.40 Furthermore, PD166326 inhibits LYN. Imatinib is known to interact with 21 amino-acid residues, whereas the pyridopyrimidines have fewer contact points with only 11 amino acids, which might explain their activity against many of the clinically relevant ABL-kinase-domain mutations, with the exception of T315I and F317V.41 Up to now, these compounds have not reached clinical trials. Studies in mice showed these compounds to be safe, although PD166326 caused tubular interstitial nephritis at high dose concentrations.40 Furthermore, concerns exist regarding their oral bioavailability because of their limited solubility.

AP23464 A library of trisubstituted purine analogues was used to identify AP23464 as a potent dual SRC-ABL-kinase inhibitor, which prevented proliferation, blocked cell-cycle progression, and promoted apoptosis in a series of CML cell lines that represented known ABL-kinase-domain mutations.42 AP23464 conferred sensitivity to all mutations in the cell lines, except T315I, and might be less susceptible to resistance than imatinib.42 However, this drug has not yet been entered in clinical trials. Guided by mutagenesis studies and molecular modelling, Azam and colleagues43 designed a series of AP23464 analogues to target T315I. AP23846 inhibited both native and T315I variants of BCR-ABL with submicromolar potency, but showed non-specific cellular toxic effects.43

Other SRC-ABL-kinase inhibitors 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d] pyrimidine (PPI) and CGP 76030 are also SCR-kinase inhibitors that have been shown to block BCR-ABL-tyrosine phosphorylation, albeit at high concentrations.44 Neither of these drugs inhibited phosphorylation of the T315I-mutated kinase, but both were able to decrease tumour-cell growth and survival.44

Developing resistance to second-generation TKIs Although both nilotinib and dasatinib show encouraging preliminary findings, the concern exists that their use will result in the identification of new mutations in the ABL-kinase domain. Several investigators have explored 1120

the use of in-vitro mutagenesis screening to try to predict mutations that might be selected with second-generation TKIs.45–48 Ray and colleagues47 identified 17 mutations in the kinase domain that were 2·5–800-times more resistant to nilotinib than the wild-type protein, including six mutations already known to have resistance to imatinib (L248V, Q252H, Y253H/C, E255K, and T315I) and 11 additional changes (K247N, E282K, K285N, V289L, L273F, E292K, N297T, H375P, T406I, W430L, and E431G). Further follow-up of patients treated with nilotinib will show whether these mutations prove to be clinically relevant. At low concentrations of nilotinib in vitro, Bradeen and co-workers48 identified ten mutations, of which only one, E292V, was new. At intermediate nilotinib concentrations Y253H, E255V, and T315I were selected and at higher concentrations only cells expressing the T315I mutant survived. These findings predicted the efficacy of nilotinib in phase II studies. 13 patients with mutations (T315I, Y253H, E255K, and F359L) and an IC50 in excess of 100 nM had major cytogenetic responses compared with ten of 18 patients with mutations who had an IC50 of less than 100 nM.24 Several groups have now reported clinical resistance to dasatinib in association with persisting or emerging mutations. The START studies identified F317L/I and T315I as the most frequent mutations, but Y232H, G250E, V299L, Y320C, l342Q, A344V, M351T, F486S, and E507G were also noted.10 Furthermore, Soverini and co-workers49 described the emergence of mutations involving residues 315 and 317 (ie, T315I, T315A, F317L, and F317I) in 20 of 21 patients who were resistant to dasatinib. However, as for imatinib, the role of the mutation in the cause of the resistance has recently been questioned.50 In many patients, mechanisms other than kinase-domain mutations are obviously responsible for disease resistance.

Other compounds in development MK0457 The aurora family of serine-threonine kinases is essential for mitotic progression. All members of this family have identifiable ATP-binding sites and have been linked to tumour genesis via induction of genetic instability. MK0457, previously known as VX680, is an example of an aurora-kinase inhibitor and exerts antiproliferative and proapoptotic activity in several tumour-cell lines.51 For example, cells treated with MK0457 enter mitosis and proceed through the S-phase, but do not divide. Furthermore, MK0457 binds to the active conformation of BCR-ABL52 and has activity against the T315I mutation.53 This inhibitor has entered clinical studies of imatinib-resistant CML and Philadelphia-chromosomepositive acute lymphoblastic leukaemia. Initial reports show that three patients with resistant disease associated with the T315I mutation had haematological responses, and in two of these patients, the concentration of the mutant clone decreased.54 http://oncology.thelancet.com Vol 8 December 2007

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ON012380 ON012380 was identified by the screening of a library of small-molecule inhibitors, which are unrelated to ATP or other purine or pyrimidine nucleosides, for agents that would decrease autophosphorylation of BCR-ABL and phosphorylation of downstream substrates. ON012380 is not affected by the presence of ATP, suggesting that it does not compete with the triphosphate. Instead, it is likely to bind with the substrate at the ABL binding site, because natural substrates, such as CRKL, compete with it. In general, this agent does not inhibit other tyrosine kinases, although at higher concentrations it does have some activity against LYN-B and FYN. A particular advantage of this compound is that it is 10 000-times more active against the T315I mutation than imatinib, both in vivo and in vitro. ON012380 might be able to enter clinical trials soon in view of its satisfactory safety profile in mice.55

GNF-2 GNF-2 was identified by screening a combinatorial kinase-directed heterocyclic library for agents that decrease proliferation of BCR-ABL-transformed cells. GNF-2 probably inhibits the ABL-kinase by an allosteric non-ATP competitive mechanism.56

BIRB-796 Carter and colleagues53 screened several drugs that were already approved by the US Food and Drug Administration or were in development for other diseases, against kinases with mutations that conferred resistance in various conditions. BIRB-796, a P38 inhibitor, was noted to bind to T315I, but was relatively ineffective against other mutant BCR-ABL proteins.

Adaphostin Adaphostin (also known as NSC680410) is a tyrophostin inhibitor that was designed to compete for the ATP substrate with BCR-ABL. Adaphostin has the ability to select CML cells over healthy cells in clonogenic assays and induces apoptosis in other leukaemic cells, which suggests that its effect might not be entirely BCR-ABL specific. This might relate to an increase in reactive oxygen species, which amplifies the effect of adaphostin.57 Adaphostin also down-regulates the BCR-ABL protein. This effect is not prevented by antioxidants, thereby implying that the downregulation of BCR-ABL precedes or parallels the production of reactive oxygen species.

Drug combinations Emerging data in vitro and in vivo suggest an additive or synergistic effect of drug combinations. However, with the limited data currently available, combination treatment seems unlikely to be beneficial in resistant disease and might be better as first-line management instead.58 http://oncology.thelancet.com Vol 8 December 2007

O’Hare and colleagues59 investigated the synergistic effects of imatinib plus dasatinib or AP23848 in vitro, using Ba/F3 cells engineered to express wild-type BCR-ABL or some of the more common mutants of BCR-ABL. They showed that the effects of imatinib on wild-type BCR-ABL and on an example of a weakly imatinib-resistant mutation, namely M351T, were enhanced when imatinib was combined with a second drug.59 By contrast, Weisberg and co-workers60 showed additive to synergistic effects of combining imatinib with nilotinib in CML-derived cell lines, with the exception of a line carrying the Y253H mutation.60 Similar additive effects of this combination were noted in a murine model of CML.60 Crystallographic studies suggest that BCR-ABL is capable of binding only one molecule of a tyrosine-kinase inhibitor at a time; therefore, these combined-treatment effects might be due to a useful interaction with drug-transporter molecules.60 By use of assays involving cell lines, BCR-ABL-expressing murine cells, and primary cells from patients with CML, first-generation and second-generation TKIs have been effectively combined with the histone deacetylase inhibitor, LBH589,61 12-0-tetradecanoylphorbol-13acetate (TPA),62 and the farnesyl-transferase inhibitors, L744832 and LB42918.63 Although these combinations are encouraging, whether they can be reproduced clinically or whether two drugs will be tolerated is still unclear. In particular, the use of the farnesyl-transferase inhibitor zoledronic acid, at a dose of 8 mg once a month, together with imatinib, did not improve responses in ten patients who had a complete haematological response, but who were not in compete cytogenetic remission.64

Management of patients with resistance to imatinib Several possible strategies exist for the management of patients with imatinib-resistant disease, which include increasing the dose of imatinib; changing to a second-generation TKI; adding or switching to a more traditional treatment, such as hydroxycarbamide, interferon-alfa, or busulphan; investigating the use of new agents; or proceeding to autologous or allogeneic stem-cell transplantation. Decision-making needs to include: consideration of the disease course up to that point; investigation of any possible causes of failure or suboptimum responses; and an assessment of the patient’s current situation, in terms of disease status, rate of development of failure, comorbid conditions, eligibility for further treatment, and donor availability. In the first part of this review, several potential mechanisms of resistance were discussed, including variations in drug absorption; metabolism; drug influx and drug efflux; and the presence of point mutations in the ABL-kinase domain. For practical purposes, the only mechanisms that can be investigated at the time that 1121

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resistance develops are those associated with plasma drug concentrations, point mutations, clonal evolution, and gene amplification. Poor compliance is a problem that is well known within the pharmaceutical industry, especially with long-term medication for chronic disorders. Newly described methods for the measurement of plasma drug concentrations might help to identify non-compliant patients. Several studies have identified substantial variations in drug concentrations in seemingly compliant patients. Picard and colleagues65 showed that mean trough-plasma imatinib concentrations at least 12 months after the start of treatment were higher in patients with complete cytogenetic remission or major molecular response than in patients with worse responses.65 Larson and co-workers66 used trough drug concentrations on day 29 of treatment to divide patients into four quartiles. At 4 years, complete cytogenetic remissions and major molecular responses were 89% and 86%, respectively, for patients in the highest quartile compared with 81% and 63% for those in the lower quartile. In this case, consideration of an increase in imatinib dose rather than a switch to a new TKI for patients with subtherapeutic plasma-imatinib concentrations would be reasonable. Additionally, high concentrations might explain any especially severe side-effects and could, therefore, merit a dose reduction in responding patients. The sensitivity of most techniques used for the detection of mutations is poor, so the likelihood of identifying a mutation will be low. Although these techniques will undoubtedly identify a mutated clone that is responsible for disease progression (ie, when the mutated clone forms a considerable proportion of the total tumour load), in any situation in which a mutation occurs without being responsible for lack or loss of response, the incidence of mutations will be underestimated. Until recently, an option for patients who had failing or suboptimum responses to imatinib was simply to increase the dose. Reports from the MD Anderson Cancer Center (Houston, TX, USA) suggested that increasing the dose to 600 mg or 800 mg daily could improve or reinstate previous responses.67 Although this finding was not universal, most investigators agreed that the strategy was likely to be successful in patients who had previously achieved some degree of cytogenetic response on a lower dose. However, the durability of these responses was less certain.68,69 In the START-R study, patients who were resistant to imatinib at a dose of 400 or 600 mg daily, and who did not have mutations, were randomly assigned to either dasatinib (70 mg twice a day [n=101]) or imatinib (800 mg daily [n=49]).11 Two-thirds of the patients had previously had 600 mg of imatinib daily. At 15 months follow up, 72% of patients treated with dasatinib and 18% of patients treated with high-dose imatinib were still continuing treatment. 1122

The median time to treatment failure was 3·5 months for high-dose imatinib, and had not been reached for dasatinib. Major cytogenetic responses, complete cytogenetic remissions, and major molecular responses were 52%, 40%, and 16%, respectively, for patients assigned dasatinib, and 33%, 16%, and 4% for those assigned high-dose imatinib. Responses for imatinib were especially poor in patients who did not have previous cytogenetic responses. In a study of 374 patients who had imatinib failure,70 3-year overall survival was better for those whose disease proved resistant or progressed, but who remained in chronic phase, compared with those in whom failure was identified in the accelerated phase or blastic phase (72% vs 30% vs 7%, respectively). In chronic–phase disease, overall survival was 100% at 2 years for those who subsequently received dasatinib or nilotinib (n=40) compared with 65–70% for those who were subsequently assigned alternative treatments (eg, allogeneic stem-cell transplantion [n=10] and other treatments [n=68]). For patients who failed in the accelerated phase, 2-year overall survival was about 80% for those who received either allogeneic stem-cell transplantation (n=5) or dastinib or nilotinib (n=20) compared with less than 30% for those assigned other treatments (n=64). For patients who failed in blast crisis, 2-year survivals were 50%, 25%, and 10% for allogeneic stem-cell transplantation, dasatinib or nilotinib, and other treatments, respectively. Factors predictive of survival after imatinib failure were splenomegaly and loss of complete haematological response. The use of dasatinib and nilotinib was not an independent predictive factor. Patients with one or two adverse factors had 2-year probabilities of survival of 75% and 0%, respectively. Those who had no adverse factors had a predicted 2-year survival of 91%.

Clinical management of imatinib resistance Primary or acquired imatinib resistance in chronic phase Responses to imatinib have been defined not only by morphological, cytogenetic, and molecular parameters, but also by the time taken to achieve these responses.71 The times are somewhat arbitrary and based on the current body of experience, but decisions taken at these time points must be tempered by the progress of the patient up to that particular time point.

Failure to achieve complete haematological response by 3 months Patients in this category mainly fall into two groups. The first group consists of those who tolerate imatinib without the development of side-effects, but continue to have abnormal blood counts. Patients in this group, a small percentage of the total, should be offered alternative treatment as soon as possible. Mutation analysis can be done, but rarely provides an explanation for their lack of response. Those of a suitable age should be considered http://oncology.thelancet.com Vol 8 December 2007

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for allogeneic stem-cell transplantation. Others can be offered a trial of an alternative TKI, but a durable response would not be likely. Conventional treatments, such as hydroxyurea, interferon alfa with or without ara-C, and autologous transplantation might be reasonable alternatives. The second group are those whose failure to normalise their blood counts might be attributable to their inability to tolerate the recommended dose of imatinib. If this intolerability is related to non-haematological toxic effects, tolerance of imatinib can sometimes be established by supportive measures, such as reintroduction of the drug together with a low-dose steroid for hepatic or skin toxic effects or diuretics for fluid retention; however, with the availability of a second-generation TKI, these strategies might become redundant. Individual judgements need to be reached for patients whose imatinib dosing has been sporadic or subtherapeutic because of the development of troublesome cytopenias. Support should be offered in terms of granulocyte colony-stimulating factor, erythropoietin, and platelet transfusions. Changing to an alterative TKI is unlikely to be useful because both nilotinib and dasatinib induce more haematological toxic effects than imatinib. A failure to normalise the blood count might be consistent with a lack of, or inactivity of, normal haemopoietic progenitors. Replacement by a normal haemopoietic system (ie, allogeneic stem-cell transplantation) might be the only successful strategy for these patients (figure 3).

Absence of cytogenetic and molecular responses and loss of haematological, cytogenetic, and molecular remissions (figure 4) The recommendations of a consensus group, established under the auspices of the European Leukemia Network (ELN), currently distinguish patients who have failed imatinib from those who have suboptimum responses.71 These recommendations acknowledge the likelihood of a poor response to imatinib, but balance this risk against the known morbidity and mortality of the most effective therapeutic alternatives that were readily available at the time these recommendations were made—ie, allogeneic stem-cell transplantation. If the efficacy and durability of responses to a second-generation TKI are substantiated, these recommendations might soon be revised. The choice of 12 and 18 months as therapeutic decision points for the achievement of major cytogenetic responses and complete cytogenetic remissions, respectively, is consistent with the fact that very few patients who do not have cytogenetic responses at these times will achieve Philadelphia-chromosome negativity. However by 12 or 18 months, a clear pattern of cytogenetic or molecular responses should exist, antedating the decision point. If evidence exists of a gradual decline in Philadelphia chromosome-positivity, continuation of imatinib at 400 mg daily or consideration of a dose increase to 600 mg or 800 mg daily might be appropriate, depending on the rate of decline. If a poor cytogenetic response with no evidence of a decline is

Haematological toxic effects

Support with blood products and growth factors

Imatinib not tolerated at 400 mg daily

If successful stay on imatinib Non-haematological toxic effects

Failure to achieve complete haematological response

Stop until symptoms settle: reintroduce imatinib with support Failure

Imatinib well tolerated at 400 mg daily Allogeneic stem-cell transplantation for suitable patients; consider RICT

Failure to achieve major cytogenetic response or complete cytogenetic remission

Plasma concentration mutation analysis, FISH, cytogenetics

Lack of decline in Ph-chromosome positivity or RT-PCR levels

Second generation TKI

Conventional chemotherapy

Gradual decline in Ph-chromosome positivity or RT-PCR levels

Continue imatinib: consider increased dose

Ph-chromosome or RT-PCR positivity persists

Continued response: stay on imatinib

Figure 3: Algorithm for management of lack of complete haematological response or complete cytogenetic remission in chronic phase RICT=reduced-conditioning-intensity transplantation. FISH=fluorescence in-situ hybridisation. Ph=Philadelphia chromosome.

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Trial of T315 inhibitor T315I mutation Loss of complete haematological response

Plasma concentration mutation analysis, FISH, cytogenics

Allogeneic stem-cell transplantation for suitable patients Other or no mutation Second generation TKI: allogeneic stem-cell transplantation when remission re-established P-loop mutation

Loss of complete cytogenetic remission

Partially resistant mutation

Increased dose of imatinib

Resistant or absent mutation

Trial of second-generation TKI

T315I mutation

Trial of T315 inhibitor

Plasma concentration mutation analysis, FISH, cytogenetics Loss of major molecular response

Allogeneic stem-cell transplantation for suitable patients

Figure 4: Algorithm for management of loss of haematological, cytogenetic, or molecular response in chronic phase FISH=fluorescence in-situ hybridisation.

noted, mutation analysis is indicated, although this is more likely to yield a positive result at the time of loss of cytogenetic and haematological responses. However, interpretation of the results of such an analysis is an issue. The presence of a T315I mutation would be an indication for allogeneic stem-cell transplantation whenever possible. For patients who are not candidates for a transplant, entry into a study of new agents would be appropriate. Furthermore, two groups have shown that a P-loop mutation is associated with a worse survival than a non P-loop mutation.72,73 If this finding can be substantiated, the most useful treatment for patients in chronic phase with a P-loop mutation would be allogeneic stem-cell transplantation. In the absence of a P-loop mutation, or indeed any mutation, a trial of a second-generation TKI would be reasonable. If no early response is noted, all patients suitable for allogeneic stem-cell transplantation should be offered this definitive procedure. An early analysis of the findings of the IRIS study74 seemed to show a difference in overall progression-free survival according to whether or not patients obtained a major molecular response. A more recent update suggests very little difference in 5-year survival between patients in complete cytogenetic remission with or without a major molecular response.3 This finding makes the current management of patients in complete cytogenetic remission but with no molecular reponse more difficult. Continuation of imatinib at its current 1124

dosage would not be unreasonable in this setting, and trials of a new TKI in this clinical situation are currently underway. A similarly controversial subject is the definition of, and subsequent management of, loss of molecular response. Branford and colleagues75 suggested screening for mutations when a two-times increase in a reverse-transcriptase polymerase chain reaction (RT-PCR) level is recorded.75 This suggestion seems like a reasonable trigger for further investigation, but becomes more difficult to support when the RT-PCR level is very low. For example, the question arises as to how frequently an increase in level (eg, from 0·002% to 0·004%) will represent loss of response, especially when such findings are compatible with long-term durable remissions after allogeneic stem-cell transplantation.76 In this setting, global harmonisation of RT-PCR assays will help to direct patient management.77 In the case of loss of molecular response, the use of a second-generation TKI would be reasonable, or, in the presence of mutations with only partial resistance to imatinib, an increase in the imatinib dose (table 3).42,43,48,78–85 Either strategy could be tried in the absence of a mutation. A logical assumption would be that patients who lose previously established responses to imatinib have a more unstable disease than those who simply fail to obtain complete cytogenetic remission and a major molecular response. However, initial results from phase II studies of both dasatinib and nilotinib suggest that responses are http://oncology.thelancet.com Vol 8 December 2007

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more likely to be obtained in patients who had good, previous responses to imatinib (eg, major cytogenetic remission). The durability of such responses will only be assessable with longer follow up. If patients with cytogenetic responses to imatinib can consistently be returned to Philadelphia-chromosome negativity by second-generation TKIs, they will become less of a concern than those who do not show such negativity with these TKIs. A good case might be made for changing patients without early cytogenetic responses to imatinib by about 3–6 months to a second-generation TKI as early as possible, to establish whether earlier intervention with a more potent drug might change the natural course of the disease. All these situations refer to patients in chronic phase. If transplant is under consideration then a reduced intensity conditioning procedure might be appropriate for patients over the age of 45 years or for those with comorbidities. Ideally, such patients should be entered into clinical studies of reduced-intensity-conditioning transplantation versus myeloablative conditioning transplantation. However, the numbers of patients eligible for transplant and the inability to randomly assign older patients to conventional transplant, render such studies almost impossible.

Progression to advanced phase Progression to accelerated phase or blast crisis while on imatinib is indicative of a clinical situation that is incurable without allogeneic stem-cell transplantation. For patients of a suitable age and with a suitable donor, every effort should be made to achieve a second chronic phase. Once obtained, allogeneic stem-cell transplantation should be done as soon as possible. Alternative strategies include a second-generation TKI or conventional chemotherapy, such as that used for acute myeloid leukaemia (AML). Identification of an ABL-kinase domain mutation could help direct treatment, especially if a T315I or P-loop mutation is identified. For patients who are unsuitable for allogeneic stem-cell transplantation, the aim of treatment is to extend survival. Several useful treatments exist that could be used sequentially, such as a second-generation TKIs, AML-like chemotherapy, and autologous transplantation.

Mutation

IC50 (biochemical) Median (range)

IC50 (biological) Number of published reports for mutation

Median (range)

Number of published reports for mutation

M237I

1·9 (1·8–2·2)

3

3·0 (2·3–2·6)

M244V

1·2 (0·8–4·2)

4

3·0 (3·0–5·1)

3

L248V

4·7 (1·8–17)

4

7·0 (3·1≥30)

3

G250A

1·45 (1·4–1·5)

2

2·5 (1·9–3·0)

2

G250E

5·9 (3·3–26)

5

G250V

2·3 (2·2–2·2)

2

Q252H

5·2 (3·7–10)

5

Y253F

15·3 (15–72)

3

12 (10–15)

2

Y253H

>18 (17–150)

3

26·4 (18·6≥33)

4

13 (4·8≥30) 1·2 (0·9–1·5) 4·8 (1·3–9·0)

2

5 2 5

E255D

3·5 (3·4–3·6)

2

2 (1·6–2·5)

E255K

18 (>8·3–200)

9

2 (10·6–33)

2 5

E255R

8·75(8·5–9·5)

2

3·0 (2·3–3·6)

2

E255V

>17 (13·2≥200)

2

4

27·9 (22·8–33)

E275K

4·85 (4·7–5·0)

2

1·3 (1·3,1·3)

2

D276G

5·8 (5·4–6·2)

3

5·8 (5·8, 5·8)

2

E281K

2·7 (2·6–2·8)

2

4·1 (2·4–5·7)

2

E285N

4·3 (4·2–4·4)

2

3·2 (1·9–4·5)

2

E292K

1·2

1

2·3

1

F311V

2·7 (1·0–7·1)

6

2·1 (1·4–8·2)

5

T315I

>18 (>8·3≥200)

8

F317C

5·2 (4·9–8·3)

3

1·6 (1·0–13)

3

>23 (>10–33)

5

F317L

3·0 (1·4–11·3)

5

3·8 (2·25≥15)

3

F317V

2·55 (2·5–2·6)

2

1·0 (0·8–1·3)

2

G321E

3·5

1

D325N

2·7 (2·6–2·8)

2

1·7 (1·3–2·1)

2

S348L

2·6 (2·5–2·7)

2

2·6 (2·0–3·2)

2

M351T

3·0 (1·6–3·8)

5

3·7 (2·4–9·2)

5

Y353H

1·8

1

··

··

E355A

3·15 (3·1–3·2)

2

2·7 (2·1–3·3)

2

E355G

2·75 (2·7–2·8)

2

4·5 (3·5–5·5)

2

E355K

4·6 (0·8–10)

3

F359C

5·25 (5·1–5·4)

2

4·7 (3·5–5·5)

2

F359V

6·9 (1·8–15·6)

3

2·8 (0·9–6·5)

3

E373G

6·5

1

V379I A380S

2·7 (1·1–3·4) 12·15 (11·8–12·5)

4 2

··

·· 3·8 (2·0–5·8)

2

··

L387A

2·6 (2·0–9·6)

6

7·1 (5·5–8·7)

M388H

2·4 (2·3–2·5)

2

1·2 (0·3–3·6)

2 4

H396P

6·7 (5·4–11)

4

1·0 (0·8–1·2)

2

H396R

5·9 (2·7–22·3)

4

··

Table 3: IC50 of imatinib for ABL-kinase domain mutations measured by biochemical and biological assays and expressed as fold difference from wild-type ABL-kinase domains42,43,48,78–85

Conclusion The management of CML has been effectively and profoundly changed by the introduction of TKIs. Although methods of management continue to develop rapidly, definitive statements regarding management are impossible. In patients who respond to imatinib, their disease is likely to remain under control on oral treatment for many years. In those whose responses are less good, their disease reverts to its original chronic, but fatal, course and alternative strategies should be used. The http://oncology.thelancet.com Vol 8 December 2007

significance of ABL-kinase mutations will become apparent with time, as will the efficacy of chemotherapeutic drugs designed to target these new oncoprotein isoforms. In the immediate future, physicians must continue to monitor their patients carefully by sensitive RT-PCR assays, check for mutations when appropriate, and enter their patients in well-designed studies of alternative treatments as indicated. 1125

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Search strategy and selection criteria Data for this review were identified by searches of PubMed and the ISI Web of Science using the search terms “chronic myeloid leukaemia”, “chronic granulocytic leukaemia”, “resistance”, “imatinib (Glivec, Gleevec)”, “dasatinib”, “nilotinib (AMN107)”, “BCR-ABL inhibition”, “kinase-domain mutations”, and “tyrosine-kinase inhibitors”. Only papers published in English from 1996 onwards were included. Acknowledgments I would like to thank John Goldman, Junia Melo, and David Marin for their review of the draft manuscript and helpful suggestions. Conflicts of interest The author declared no conflicts of interest. References 1 Silver RT, Woolf SH, Hehlmann R, et al. An evidence-based analysis of the effect of busulfan, hydroxyurea, interferon, and allogenic bone marrow transplantation in treating the chronic phase of chronic myeloid leukaemia: developed for the American Society of Hematology. Blood 1999; 94: 1517–36. 2 O’Brien SG, Guilhot F, Larson RA, et al. Imatinib compared with interferon and low-dose cytarabine for newly diagnosed chronic-phase chronic myeloid leukemia. N Engl J Med 2003; 348: 994–1004. 3 Druker BJ, Guilhot F, O’Brien SG, et al. Five-year follow-up of patients receiving imatinib for chronic myeloid leukemia. N Engl J Med 2006; 355: 2408–17. 4 Lombardo LJ, Lee FY, Chen P, et al. Discovery of N-(2-chloro-6-methyl- phenyl)-2-(6-(4-(2-hydroxyethyl)piperazin-1-yl)-2-methylpyrimidin-4- ylamino)thiazole-5-carboxamide (BMS-354825), a dual Src/Abl kinase inhibitor with potent antitumor activity in preclinical assays. J Med Chem 2004; 47: 6658–61. 5 Copland M, Hamilton A, Eirick LJ, et al. Dasatinib (BMS-354825) targets an earlier progenitor population than imatinib in primary CML but does not eliminate the quiescent fraction. Blood 2006; 107: 4532–39. 6 Kamath AV, Wang J, Lee FY, Marathe PH. Preclinical pharmacokinetics and in vitro metabolism of dasatinib (BMS-354825): a potent oral multi-targeted kinase inhibitor against SRC and BCR-ABL. Cancer Chemother Pharmacol 2007; published online April 11. DOI: 10.1007/s00280-007-0478-8 7 Talpaz M, Shah NP, Kantarjian H, et al. Dasatinib in imatinib-resistant Philadelphia chromosome-positive leukemias. N Engl J Med 2006; 354: 2531–41. 8 Hochhaus A, Kantarjian HM, Baccarani M, et al. Dasatinib induces notable hematologic and cytogenetic responses in chronic-phase chronic myeloid leukemia after failure of imatinib therapy. Blood 2007; 109: 2303–09. 9 Baccarani M, Kantarjian HM, Apperley JF, et al. Efficacy of dasatinib (SPRYCEL ®) in patients (pts) with chronic phase chronic myelogenous leukemia (CP-CML) resistant to or intolerant of imatinib: updated results of the CA180013 ‘START C’ study. Blood 2006; 108: 53A (abstr 164). 10 Muller MC, Erben P, Schenk T, et al. Response to dasatinib after imatinib failure according to type of preexisting BCR-ABL mutations. Blood 2006; 108: 225A. 11 Kantarjian H, Pasquini R, Hamerschlak N, et al. Dasatinib or highdose imatinib for chronic-phase chronic myeloid leukemia after failure of first-line imatinib: a randomized phase 2 trial. Blood 2007; 109: 5143–50. 12 Guilhot F, Apperley J, Kim DW, et al. Dasatinib induces significant hematologic and cytogenetic responses in patients with imatinib-resistant or -intolerant chronic myeloid leukemia in accelerated phase. Blood 2007; 109: 4143–50. 13 Cortes J, Kim DW, Guilhot F, et al. Dasatinib (SPRYCEL®) in patients (pts) with chronic myelogenous leukemia in accelerated phase (AP-CML) that is imatinib-resistant (im-r) or -intolerant (im-i): updated results of the CA180-005 ‘START-A’ phase II study. Blood 2006; 108: 613A (abstr 2160).

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Cortes J, Rousselot P, Kim DW, et al. Dasatinib induces complete hematologic and cytogenetic responses in patients with imatinibresistant or -intolerant chronic myeloid leukemia in blast crisis. Blood 2007; 109: 3207–13. Martinelli G, Hochhaus A, Coutre S, et al. Dasatinib (SPRYCEL®) efficacy and safety in patients (pts) with chronic myelogenous leukemia in lymphoid (CML-LB) or myeloid blast (CML-MB) phase who are imatinib-resistant (Im-r) or -intolerant (Im-i). Blood 2006; 108: 224A (abstr 745). Hochhaus A, Kim DW, Rousselot P, et al. Dasatinib (SPRYCEL®) 50mg or 70mg BID versus 100mg or 140mg QD in patients with chronic myeloid leukemia in chronic phase (CML-CP) resistant or intolerant to imatinib: results of the CA180-034 study. Blood 2006; 108: 53A (abstr 166). Quintas-Cardama A, Kantarjian HM, Munden R, et al. Pleural effusion in patients (pts) with chronic myelogenous leukemia (CML) treated with dasatinib after imatinib failure. Blood 2006; 108: 614A (abstr 2164). Golemovic M, Verstovsek S, Giles F, et al. AMN107, a novel aminopyrimidine inhibitor of Bcr-Abl, has in vitro activity against imatinib-resistant chronic myeloid leukemia. Clin Cancer Res 2005; 11: 4941–47. White DL, Saunders VA, Dang P, et al. OCT-1 mediated influx is a key determinant of the intracellular uptake of imatinib but not nilotinib (AMN107): reduced OCT-1 activity is the cause of low in vitro sensitivity to imatinib. Blood 2006; 108: 697–704 Jorgensen HG, Allan EK, Jordanides NE, Mountford JC, Holyoake TL. Nilotinib exerts equipotent antiproliferative effects to imatinib and does not induce apoptosis in CD34+ CML cells. Blood 2007; 109: 4016–19. Wang Y, Cai D, Brendel C, et al. Adaptive secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates imatinib and nilotinib resistance in BCR/ABL+ progenitors via JAK-2/STAT-5 pathway activation. Blood 2007; 109: 2147–55. Kantarjian H, Giles F, Wunderle L, et al. Nilotinib in imatinib-resistant CML and Philadelphia chromosome-positive ALL. N Engl J Med 2006; 354: 2542–51. le Coutre P, Bhalla K, Giles F, et al. A phase II study of nilotinib, a novel tyrosine kinase inhibitor administered to imatinib-resistant and -intolerant patients with chronic myelogenous leukemia (CML) in chronic phase (CP). Blood 2006; 108: 53A (abstr 165). Hochhaus A, Erben P, Branford S, et al. Hematologic and cytogenetic response dynamics to nilotinib (AMN107) depend on the type of BCR-ABL mutations in patients with chronic myelogeneous leukemia (CML) after imatinib failure. Blood 2006; 108: 225A (abstr 749). Cohen MH, Williams G, Johnson JR, et al. Approval summary for imatinib mesylate capsules in the treatment of chronic myelogenous leukemia. Clin Cancer Res 2002; 8: 935–42. Breccia M, Muscaritoli M, Aversa Z, Mandelli F, Alimena G. Imatinib mesylate may improve fasting blood glucose in diabetic Ph+ chronic myelogenous leukemia patients responsive to treatment. J Clin Oncol 2004; 22: 4653–55. Veneri D, Franchini M, Bonora E. Imatinib and regression of type 2 diabetes. N Engl J Med 2005; 352: 1049–50. Breccia M, Muscaritoli M, Gentilini F, et al. Impaired fasting glucose level as metabolic side effect of nilotinib in non-diabetic chronic myeloid leukemia patients resistant to imatinib. Leuk.Res 2007; published online March 26. DOI:10.1016/j.leukres.2007.01.024 Quintas-Cardama A, Kantarjian H, Jones D, et al. Dasatinib (BMS-354825) is active in Philadelphia chromosome-positive chronic myelogenous leukemia after imatinib and nilotinib (AMN107) therapy failure. Blood 2007; 109: 497–99. Golas JM, Arndt K, Etienne C, et al. SKI-606, a 4-anilino-3-quinolinecarbonitrile dual inhibitor of Src and Abl kinases, is a potent antiproliferative agent against chronic myelogenous leukemia cells in culture and causes regression of K562 xenografts in nude mice. Cancer Res 2003; 63: 375–81. Puttini M, Coluccia AM, Boschelli F, et al. In vitro and in vivo activity of SKI-606, a novel Src-Abl inhibitor, against imatinib-resistant Bcr-Abl+ neoplastic cells. Cancer Res 2006; 66: 11314–22.

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Cortes J, Kantarjian HM, Baccarani M, et al. A phase 1/2 study of SKI-606, a dual inhibitor of src and abl kinases, in adult patients with Philadelphia chromosome positive (Ph+) chronic myelogenous leukemia (CML) or acute lymphocytic leukemia (ALL) relapsed, refractory or intolerant of imatinib. Blood 2006; 108: 54A (abstr 168). Donato NJ, Wu JY, Stapley J, et al. BCR-ABL independence and LYN kinase overexpression in chronic myelogenous leukemia cells selected for resistance to STI571. Blood 2003; 101: 690–98. Kimura S, Naito H, Segawa H, et al. NS-187, a potent and selective dual Bcr-Abl/Lyn tyrosine kinase inhibitor, is a novel agent for imatinib-resistant leukemia. Blood 2005; 106: 3948–54. Naito H, Kimura S, Nakaya Y, et al. In vivo antiproliferative effect of NS-187, a dual Bcr-Abl/Lyn tyrosine kinase inhibitor, on leukemic cells harbouring Abl kinase domain mutations. Leuk Res 2006; published online March 20. DOI: 10.1016/j.leukres.2006.01.006. Dorsey JF, Jove R, Kraker AJ, Wu J. The pyrido[2,3-d]pyrimidine derivative PD180970 inhibits p210Bcr-Abl tyrosine kinase and induces apoptosis of K562 leukemic cells. Cancer Res 2000; 60: 3127–31. Huang M, Dorsey JF, Epling-Burnette PK, et al. Inhibition of Bcr-Abl kinase activity by PD180970 blocks constitutive activation of Stat5 and growth of CML cells. Oncogene 2002; 21: 8804–16. Nagar B, Bornmann WG, Pellicena P, et al. Crystal structures of the kinase domain of c-Abl in complex with the small molecule inhibitors PD173955 and imatinib (STI-571). Cancer Res 2002; 62: 4236–43. Wisniewski D, Lambek CL, Liu C, et al. Characterization of potent inhibitors of the Bcr-Abl and the c-kit receptor tyrosine kinases. Cancer Res 2002; 62: 4244–55. Wolff NC, Veach DR, Tong WP, Bornmann WG, Clarkson B, Ilaria RL Jr. PD166326, a novel tyrosine kinase inhibitor, has greater antileukemic activity than imatinib mesylate in a murine model of chronic myeloid leukemia. Blood 2005; 105: 3995–4003. Tipping AJ, Baluch S, Barnes DJ, et al. Efficacy of dual-specific Bcr-Abl and Src-family kinase inhibitors in cells sensitive and resistant to imatinib mesylate. Leukemia 2004; 18: 1352–56. O’Hare T, Pollock R, Stoffregen EP, et al. Inhibition of wild-type and mutant Bcr-Abl by AP23464, a potent ATP-based oncogenic protein kinase inhibitor: implications for CML. Blood 2004; 104: 2532–39. Azam M, Nardi V, Shakespeare WC, et al. Activity of dual SRC-ABL inhibitors highlights the role of BCR/ABL kinase dynamics in drug resistance. Proc Natl Acad Sci USA 2006; 103: 9244–49. Warmuth M, Simon N, Mitina O, et al. Dual-specific Src and Abl kinase inhibitors, PP1 and CGP76030, inhibit growth and survival of cells expressing imatinib mesylate-resistant Bcr-Abl kinases. Blood 2003; 101: 664–72. Burgess MR, Skaggs BJ, Shah NP, Lee FY, Sawyers CL. Comparative analysis of two clinically active BCR-ABL kinase inhibitors reveals the role of conformation-specific binding in resistance. Proc Natl Acad Sci USA 2005; 102: 3395–400. von Bubnoff N, Manley PW, Mestan J, Sanger J, Peschel C, Duyster J. Bcr-Abl resistance screening predicts a limited spectrum of point mutations to be associated with clinical resistance to the Abl kinase inhibitor nilotinib (AMN107). Blood 2006; 108: 1328–33. Ray A, Cowan-Jacob SW, Manley PW, Mestan J, Griffin JD. Identification of BCR-ABL point mutations conferring resistance to the Abl kinase inhibitor AMN107 (nilotinib) by a random mutagenesis study. Blood 2007; 109: 5011–15. Bradeen HA, Eide CA, O’Hare T, et al. Comparison of imatinib mesylate, dasatinib (BMS-354825), and nilotinib (AMN107) in an N-ethyl-N-nitrosourea (ENU)-based mutagenesis screen: high efficacy of drug combinations. Blood 2006; 108: 2332–38. Soverini S, Colarossi S, Gnani A, et al. Resistance to dasatinib in Philadelphia-positive leukemia patients and the presence or the selection of mutations at residues 315 and 317 in the BCR-ABL kinase domain. Haematologica 2007; 92: 401–04. Nicolini FE, Chabane K, Tigaud I, Michallet M, Magaud JP, Hayette S. BCR-ABL mutant kinetics in CML patients treated with dasatinib. Leuk Res 2007; 31: 865–68. Harrington EA, Bebbington D, Moore J, et al. VX-680, a potent and selective small-molecule inhibitor of the Aurora kinases, suppresses tumor growth in vivo. Nat Med 2004; 10: 262–67.

http://oncology.thelancet.com Vol 8 December 2007

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

Young MA, Shah NP, Chao LH, et al. Structure of the kinase domain of an imatinib-resistant Abl mutant in complex with the Aurora kinase inhibitor VX-680. Cancer Res 2006; 66: 1007–14. Carter TA, Wodicka LM, Shah NP, et al. Inhibition of drug-resistant mutants of ABL, KIT, and EGF receptor kinases. Proc Natl Acad Sci USA 2005; 102: 11011–16. Giles FJ, Cortes J, Jones D, Bergstrom D, Kantarjian H, Freedman SJ. MK-0457, a novel kinase inhibitor, is active in patients with chronic myeloid leukemia or acute lymphocytic leukemia with the T315I BCR-ABL mutation. Blood 2007; 109: 500–02. Gumireddy K, Baker SJ, Cosenza SC, et al. A non-ATP-competitive inhibitor of BCR-ABL overrides imatinib resistance. Proc Natl Acad Sci USA 2005; 102: 1992–97. Adrian FJ, Ding Q, Sim T, et al. Allosteric inhibitors of Bcr-abl-dependent cell proliferation. Nat Chem Biol 2006; 2: 95–102. Chandra J, Tracy J, Loegering D, et al. Adaphostin-induced oxidative stress overcomes BCR/ABL mutation-dependent and -independent imatinib resistance. Blood 2006; 107: 2501–06. Komarova NL, Wodarz D. Drug resistance in cancer: principles of emergence and prevention. Proc Natl Acad Sci USA 2005; 102: 9714–19. O’Hare T, Walters DK, Stoffregen EP, et al. Combined AN inhibitor therapy for minimizing drug resistance in chronic myeloid leukemia: Src/Abl inhibitors are compatible with imatinib. Clin Cancer Res 2005; 11: 6987–93. Weisberg E, Catley L, Wright RD, et al. Beneficial effects of combining nilotinib and imatinib in preclinical models of BCR-ABL+ leukemias. Blood 2007; 109: 2112–20. Fiskus W, Pranpat M, Bali P, et al. Combined effects of novel tyrosine kinase inhibitor AMN107 and histone deacetylase inhibitor LBH589 against Bcr-Abl-expressing human leukemia cells. Blood 2006; 108: 645–52. Fang B, Song Y, Han Z, et al. Synergistic interactions between 12-0-tetradecanoylphorbol-13-acetate (TPA) and imatinib in patients with chronic myeloid leukemia in blastic phase that is resistant to standard-dose imatinib. Leuk Res 2007; 31: 1441–14. Radujkovic A, Topaly J, Fruehauf S, Zeller WJ. Combination treatment of imatinib-sensitive and -resistant BCR-ABL-positive CML cells with imatinib and farnesyltransferase inhibitors. Anticancer Res 2006; 26: 2169–77. Pavlu J, Andreasson C, Chuah C, et al. Dual inhibition of ras and bcr-abl signalling pathways in chronic myeloid leukaemia: a phase I/II study in patients in complete haematological remission. Br J Haematol 2007; 137: 423–28. Picard S, Titier K, Etienne G, et al. Trough imatinib plasma levels are associated with both cytogenetic and molecular responses to standard-dose imatinib in chronic myeloid leukemia. Blood 2007; 109: 3496–99. Larson RA, Druker BJ, Guilhot F, et al. Correlation of pharmacokinetic data with cytogenetic and molecular response in newly diagnosed patients with chronic myeloid leukemia in chronic phase (CML-CP) treated with imatinib—an analysis of IRIS study data. Blood 2006; 108: 131A. Kantarjian HM, Talpaz M, O’Brien S, et al. Dose escalation of imatinib mesylate can overcome resistance to standard-dose therapy in patients with chronic myelogenous leukemia. Blood 2003; 101: 473–75. Zonder JA, Pemberton P, Brandt H, Mohamed AN, Schiffer CA. The effect of dose increase of imatinib mesylate in patients with chronic or accelerated phase chronic myelogenous leukemia with inadequate hematologic or cytogenetic response to initial treatment. Clin Cancer Res 2003; 9: 2092–97. Marin D, Goldman JM, Olavarria E, Apperley JF. Transient benefit only from increasing the imatinib dose in CML patients who do not achieve complete cytogenetic remissions on conventional doses. Blood 2003; 102: 2702–03. Kantarjian H, O’Brien S, Talpaz M, et al. Outcome of patients with Philadelphia chromosome-positive chronic myelogenous leukemia post-imatinib mesylate failure. Cancer 2007; 109: 1556–60. Baccarani M, Saglio G, Goldman J, et al. Evolving concepts in the management of chronic myeloid leukemia: recommendations from an expert panel on behalf of the European LeukemiaNet. Blood 2006; 108: 1809–20.

1127

Review

72

73

74

75

76

77

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Branford S, Rudzki Z, Walsh S, et al. Detection of BCR-ABL mutations in patients with CML treated with imatinib is virtually always accompanied by clinical resistance, and mutations in the ATP phosphate-binding loop (P-loop) are associated with a poor prognosis. Blood 2003; 102: 276–83. Soverini S, Martinelli G, Rosti G, et al. ABL mutations in late chronic phase chronic myeloid leukemia patients with up-front cytogenetic resistance to imatinib are associated with a greater likelihood of progression to blast crisis and shorter survival: a study by the GIMEMA working party on chronic myeloid leukemia. J Clin Oncol 2005; 23: 4100–09. Hughes TP, Kaeda J, Branford S, et al. Frequency of major molecular responses to imatinib or interferon alfa plus cytarabine in newly diagnosed chronic myeloid leukemia. N Engl J Med 2003; 349: 1423–32. Branford S, Rudzki Z, Parkinson I, et al. Real-time quantitative PCR analysis can be used as a primary screen to identify patients with CML treated with imatinib who have BCR-ABL kinase domain mutations. Blood 2004; 104: 2926–32. Kaeda J, O’Shea D, Szydlo RM, et al. Serial measurement of BCR-ABL transcripts in the peripheral blood after allogeneic stem cell transplant for chronic myeloid leukemia: an attempt to define patients who may not require further therapy. Blood 2006; 107: 4171–76. Hughes T, Deininger M, Hochhaus A, et al. Monitoring CML patients responding to treatment with tyrosine kinase inhibitors: review and recommendations for harmonizing current methodology for detecting BCR-ABL transcripts and kinase domain mutations and for expressing results. Blood 2006; 108: 28–37.

78

79

80

81

82

83

84

85

Shah NP, Nicoll JM, Nagar B, et al. Multiple BCR-ABL kinase domain mutations confer polyclonal resistance to the tyrosine kinase inhibitor imatinib (STI571) in chronic phase and blast crisis chronic myeloid leukemia. Cancer Cell 2002; 2: 117–25. Weisberg E, Manley P, Mestan J, Cowan-Jacob S, Ray A, Griffin JD. AMN107 (nilotinib): a novel and selective inhibitor of BCR-ABL. Br J Cancer 2006; 94: 1765–69. Roumiantsev S, Shah NP, Gorre ME, et al. Clinical resistance to the kinase inhibitor STI-571 in chronic myeloid leukemia by mutation of Tyr-253 in the Abl kinase domain P-loop. Proc Natl Acad Sci USA 2002; 99: 10700–05. Corbin AS, Rosee PL, Stoffregen EP, Druker BJ, Deininger MW. Several Bcr-Abl kinase domain mutants associated with imatinib mesylate resistance remain sensitive to imatinib. Blood 2003; 101: 4611–14. Chu S, Xu H, Shah NP, et al. Detection of BCR-ABL kinase mutations in CD34+ cells from chronic myelogenous leukemia patients in complete cytogenetic remission on imatinib mesylate treatment. Blood 2005; 105: 2093–98. Deininger M, Buchdunger E, Druker BJ. The development of imatinib as a therapeutic agent for chronic myeloid leukemia. Blood 2005; 105: 2640–53. O’Hare T, Walters DK, Stoffregen EP, et al. In vitro activity of Bcr-Abl inhibitors AMN107 and BMS-354825 against clinically relevant imatinib-resistant Abl kinase domain mutants. Cancer Res 2005; 65: 4500–05. Azam M, Latek RR, Daley GQ. Mechanisms of autoinhibition and STI-571/imatinib resistance revealed by mutagenesis of BCR-ABL. Cell 2003; 112: 831–43.

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