What is the impact, present and future, of novel targeted agents in acute lymphoblastic leukemia?

Best Practice & Research Clinical Haematology 25 (2012) 453–464

Contents lists available at SciVerse ScienceDirect

Best Practice & Research Clinical Haematology journal homepage: www.elsevier.com/locate/beha

8

What is the impact, present and future, of novel targeted agents in acute lymphoblastic leukemia? Dan Douer, MD, Attending Physician * Leukemia Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, Weill Cornell Medical College, 1275 York Ave, New York, NY 10065, USA

Keywords: acute lymphoblastic leukemia ALL antibody asparaginase Berlin-Frankfurt-Munster (BFM) blinatumomab chimeric antigen receptor (CAR) hyperCVAD imatinib intrathecal methotrexate minimal residual disease (MRD) tyrosine kinase inhibitor nonmyelosuppresive pediatric inspired rituximab steroids targeted agents vincristine

The absence of a standard of care for adults with acute lymphoblastic leukemia (ALL), the inadequate outcome of all adult regimens, and the lack of improvement in treatment outcomes over the past decades suggest a critical need for new approaches to treating adults with this disease. Several new strategies are now being considered, including the use of novel targeted agents alone and in combination with other chemotherapeutic drugs. This paper discusses several of these approaches and their impact on overall outcome. Ó 2012 Elsevier Ltd. All rights reserved.

Introduction There is no universally accepted standard of care for adults with acute lymphoblastic leukemia (ALL). First, multiple different chemotherapy regimens have been studied all resulting in similar outcomes, with only few comparable trials [1,2]. Therefore the choice of a specific treatment is arbitrary, based on prior experience, training, practice preference and convenience. Second, children with ALL are treated differently from adults, with better outcome. Furthermore, it is becoming clear that * Tel.: þ1 212 639 2471; Fax: þ1 212 772 4881. E-mail address: [email protected]. 1521-6926/$ – see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.beha.2012.10.008

454

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

adults with ALL at different ages should not be treated uniformly. Three age groups may be considered separately: adolescents and young adults (AYA) aged 15–39 years, adults aged 40–60/65 years, and adults older than 60/64þ years [3]. Finally, the role of allogeneic hematopoietic stem cell transplantation (HSCT) in front-line ALL is uncertain. Thus, the absence of a standard regimen, the inadequate outcome of all adult regimens, and the lack of improvement over the past decades imply a critical need for new approaches. Several new strategies are now being considered; one of them is the introduction of novel targeted drugs. This review will discuss several concepts of applying targeted agents as single drugs and in combination with chemotherapy in adult ALL, and their current and potential future impact on overall outcome.

Current treatment approaches In adult acute lymphoblastic leukemia (ALL), the cure rate has not improved over the past 2-1/2 decades, as shown in epidemiological surveys in all age groups [4] and in multiple large clinical trials [1]. Table 1 presents several of the more recent large trials. They vary by upper age limit, selection of specific chemotherapy agents, and indication for allogeneic HSCT yet have an almost identical long-term survival of 35%–40% [5–12]. If Phþ ALL is excluded, the overall survival (OS) is approximately 45% [9]. In general, the treatment of ALL is complex, consisting of several different chemotherapy cycles with a variety of agents. The regimens can be roughly grouped into several treatment models. The first are multidrug combinations based on the treatment model developed by Dr. Bayard Clarkson from Memorial Sloan-Kettering Cancer Center (MSKCC), called L-20, with daunorubicin, prednisone, vincristine and cyclophosphamide [13]. This concept was modified in children to the Berlin-FrankfurtMunster (BFM) ALL model that consists of two-phase inductions: the first with four drugs (daunorubicin, prednisone, vincristine and asparaginase) and the second phase with cyclophosphamide, cytarabine, and 6-mercaptopurine. Post remission cycles vary, but all include asparaginase and a cycle of delayed reinduction (a modified repetition of the induction), which in high-risk children has proven to be advantageous [14]. Hoelzer et al. applied the principals of the BFM treatment model to adult ALL [15,16]. Several other regimens listed in Table 1 [5,6] and others [16–19] are variants of the BFM model principles. The largest ever front-line adult ALL study (UKALL XII/ECOG 2993) was conducted by a joint effort of the US Eastern Cooperative Oncology Group (ECOG) and the British Medical Research Council (MRC), which used a variant BFM model [8,9]. The second treatment model, hyperCVAD, consists of fractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone, alternating with high-dose methotrexate and cytarabine [12]. It is probably the most commonly used regimen in adult ALL in the United States despite having no proven advantage, greater marrow toxicity, requires longer hospitalization, does not include asparaginase, but has a simpler structure. The third treatment model is an aggressive “AML-style” induction that was studied in the hope that more rapid complete response (CR) would lead to more cures. The MSKCC ALL-2 regimen combined Table 1 Newly diagnosed adult ALL: recent large clinical trials. Study

Years

N

Age

Treatment

CR (%)

DFS (%)

GMALL 05/93 [5] CALGB 8811 [6] CALGB 19802 [7] MRC/ECOG-UKALLXII/E2993a [8,9] UCSF 8707 [10] b L-2 [11] HyperCVAD [12] b

’93–’99 ’88–’91 ’99–’01 ’93–’06 ’87–’98 00–06 ’92–’00

1163 198 163 1913 84 78 288

35 35 41 15–64 27 33 40

Variants of a BFM model

87 85 78 90 93 85 92

35 36 35 OS 39 52 34 38

BFM model  SCT VPDA þ intensified HD-MITOX þ HD-ARA-C A) Cyclophosphamide, DEX, ADR, V B) HD-MTX þ HD-ARA-C

Abbreviations: A, asparaginase; ADR, adriamycin; BFM, Berlin-Frankfurt-Munster ALL treatment model; D, daunorubicin; DEX, dexamethasone; DFS, disease-free survival; HD-ARA-C, high-dose cytarabine; HD-MITOX, high-dose mitoxantrone; HD-MTX, high-dose methotrexate; OS, overall survival; P, prednisone; V, vincristine. a Randomized. b Single institution.

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

455

high-dose cytarabine and a very high-dose mitoxantrone for induction, without vincristine or steroids. In a randomized trial of 164 patients, the CR rate was 83% with the ALL-2 regimen compared to 71% in the L-20 standard 4-drug induction (L-20) ([11]; Lamanna et al. submitted for publication). However, despite the substantial intensification of myelosuppression, the overall survival (OS) using the ALL-2 regimen was 33%, not different from all other protocols. In the absence of a standard regimen for adult ALL, the recently published NCCN guidelines for the treatment of newly diagnosed adults with ALL (http://www.nccn.org/professionals/physician_gls/pdf/all.pdf) recommend a clinical trial as the first treatment in these patients [3]. The outcome of ALL patients who have relapsed, regardless of age or treatment, is extremely dismal [20]. All treatment approaches are based on small studies with complete remission rates of 25%–60% that are very short [2]. In relapsed ALL, the goal is to achieve a short time-window of second CR for prompt allogeneic HSCT with any available suitable donor. Summary of new directions Promising new strategies are emerging for adult ALL. One approach is adopting pediatric protocolsdthe so called “pediatric inspired” regimens [21]. These regimens have common features, including (1) adopting a general pediatric structure, usually following a BFM model, (2) significantly increasing the non-myelosuppressive agents such as vincristine and steroids, (3) using much higher cumulative doses of asparaginase for prolonged asparagine depletion, and (4) administering very early and extended intrathecal methotrexate together with very high-dose systemic methotrexate. Several studies from Europe and the USA [22–26] reported that pediatric inspired approaches are feasible in adults, at least for patients younger than 45–55 years, and improved the event-free survival (EFS) rate of newly diagnosed Ph-negative ALL to 60% or higher. This compared to 35%–40% for historical controls and without additional benefit of HSCT. These studies have also shown that prolonged administration of asparaginase is feasible. While the unique side effects of asparaginase do occur, they can be safely managed. An ongoing national US trial (CALGB 10304) is studying a pediatric regimen in AYA patients aged 15–39 years [21,27]. Another strategy is to measure the depth of CR and minimal residual disease (MRD) early during remission with sensitive immunophenotyping by flow cytometry or polymerase chain reaction (PCR) techniques to better discriminate between risk groups and apply risk adaptive approaches. In pediatric ALL the degree of MRD negativity and the optimal time to achieve this status is well defined [28]. In adults, initial MRD studies were successful in defining prognostic groups [29–31], but the degree of MRD and its timing have yet to be better standardized. More recently, gene profiling and expression are reclassifying prognostic groups both for prognosis and to serve as targets for novel treatments [32–34]. General concepts in developing targeted agents in ALL In general, targeted agents can be of various forms, with a single target or a range of targets. They can be monoclonal antibodies that specifically bind to a membranous target, or inhibitors of an enzymatic activity (e.g., kinase inhibitors) or a molecular pathway. The target(s) should be of biological significance and the agent should preferably have less off–target activity on normal cells. An example of a promising target in ALL cells is the recently described rearranged CRLF2 (Cytokine Receptor-Like Factor 2) gene that normally partners with IL-7R and forms the receptor for thymic stromal lymphopoietin receptor (TSLPR); when activated, it effects the survival and maturation of B and T lymphocytes and enhances cytokine production [35,36]. The CRLF2 gene is located on the short arm of the sex chromosome. In ALL cells it can translocate to the long arm of chromosome 14 and fuse with the immunoglobulin heavy chain (IgH) gene forming the IgH/CRLF2 fusion gene. An alternative translocation of CRLF2 results from an internal deletion on the short arm of the sex chromosome fusing the CRLF2 with P2RYS genes on the same X or Y chromosome. These translocations result in high expression of CRLF2 on the leukemia cell membrane that promotes B-cell leukemogenesis and could be an excellent membranous target for novel treatment. Rearrangement and high expression of CRLF2 was found in 14% of high-risk pediatric ALL, is associated with mutations in JAK1, JAK2, and deletions or mutations in IZKF1, has poor outcome, and interestingly is more common in Latinos [35,36].

456

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

Although targeted agents may inhibit normal blood cell production, they are often considered less myelosuppressive than standard cytotoxic chemotherapy. Their low myelotoxicity is consistent with a concept that optimal ALL treatment is likely to be less dependent on intensive myelosuppression. This concept is supported by several well-known facts:  Low-dose long-term maintenance is mandatory in adult ALL for successful outcome [37]  Steroids and vincristine have major activity in ALL, probably more than in any other cancer  Effective pediatric regimens include more non-myelosuppressive drugs and prolonged asparaginase enzymatic activity [38–43]  A worse outcome after autologous HSCT, i.e., a single myeloablative cytotoxic therapy, than after much longer and less intense consolidation and maintenance [9]  Several studies have shown no improvement in adult ALL by anthracycline intensification [7,11,44] Several general factors should be considered when developing new targeted agents in addition to defining their specific target: Should the agent be studied in clinical overt or molecular disease (MRD positive)? In newly diagnosed or relapsed patients? An important question is whether the new agent is highly effective as a single-agent or is better when combined with chemotherapy; if so, what chemotherapy “backbone.” It is unknown if ALL chemotherapy regimens that are currently used are optimal backbones when combined with a very active targeted agent, and perhaps less intense or cytotoxic drugs could be employed without losing efficacy. For example, avoiding the use of genotoxic chemotherapy drugs may prevent new mutations in the target, inducing resistance to the targeted agent [2]. Further, a very active targeted agent may be able to minimize or eliminate cytotoxic chemotherapy, which has special appeal in older ALL adults for whom current approaches are often too toxic. When allogeneic transplantation is part of the overall treatment strategy, optimal timing of the targeted agents during the transplant process should be defined. For example, is a targeted agent sufficiently efficacious in reducing tumor burden prior to HSCT with less toxic chemotherapy, and healthier HSCT candidates, or does it improve the outcome as post-transplantation maintenance? Clinical trials will be more challenging to design with targeted agents when taking into account such factors, in particular when they are combined with chemotherapy. Currently available targeted agents Several targeted agents are commercially available for other indications and have been studied in ALL, also. Preliminary results have been reported in adult ALL using monoclonal anti-CD20 antibodies (i.e., rituximab) for precursor B-cell ALL and tyrosine kinase inhibitors (TKI), such as imatinib and dasatinib, for Ph-positive ALL. Although CD52 is expressed on almost all ALL cells, the data on alemtuzumab in pediatric and adult ALL is limited [45,46].

Targeting CD20 (rituximab) The effect of rituximab in precursor B-cell ALL is limited by the expression of CD20 in only half the patients, as opposed to being expressed in almost all of mature B-cell lymphoproliferative disorders. Though CD20 expression could be increased with steroids [47], rituximab has little single-agent activity in CD20-positive precursor ALL cells. The studies on the impact of CD20 on outcome of ALL reported conflicting results. Thomas et al reported a lower survival rate in adult ALL expressing CD20 than in CD20-negative patients [48]. Maury et al. showed a negative impact of CD20 expression on relapse rate limited only to those with high white blood cell count and not on OS [49]. A study from St Jude’s Children’s Research Hospital has reported that CD20 expression in children may even be associated with better outcome [50]. Two studies, with different chemotherapy backbones, have shown better survival rates in adults younger than 60 years with CD20-positive ALL when chemotherapy is combined with rituximab, compared to chemotherapy alone (Table 2) [51,52]. In the German GMALL 7/03 study, adding rituximab

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

457

Table 2 CD20-positive ALL: chemotherapy with or without rituximab. Rituximab

GMALL 7/03a [51] Standard risk High-risk HyperCVADb [52] a b

CR (%)

CD20þ

CD20þ

Overall survival (%)

Yes

No

94

91

95

93

Yes

No

P value

71 55 75

57 36 47

0.03

Study included only ages 15–55 years. Subset of patients younger than 60 years.

improved the OS in both standard- and high-risk CD20-positive patients [51]. In the MD Anderson study [52], rituximab was combined with hyperCVAD and the OS was 61%, higher than 45% in their historical control, but the difference was not statistically significant. However, in a subset of patients younger than 60 years, the OS was significantly better with the combination of chemotherapy plus rituximab than with chemotherapy alone (Table 2). Interestingly, the outcome with combined immunochemotherapy was similar to that of CD20-negative patients on chemotherapy alone [52]. However, the question of routinely including rituximab as part of the treatment regimen in CD20positive adult ALL is not definitively answered. Both studies were nonrandomized, and the comparisons were in sequential groups of patients, where rituximab may not have been the only variable. In the second study [52], the conclusion was based on a retrospective analysis of patients younger than 60 years; the regimen was without benefit in older patients. It is also not clear whether rituximab adds to the benefit of using pediatric approaches. Targeting BCR/ABL, tyrosine kinase inhibitors in Ph-positive ALL In contrast to rituximab, TKIs as single agents induce a very high CR rate in Ph-positive ALL, although the response is not sustained. Several studies have convincingly demonstrated that concomitant TKI with multi-agent chemotherapy markedly improved OS rates to 50% of patients compared to chemotherapy alone [53–58]. In adults allogeneic HSCT appears to further improve the outcome, but it is unclear to what extent [58], and in pediatric Ph-positive ALL treated with chemotherapy plus imatinib, allogeneic transplantation may not be necessary [59]. As a result, the overall outlook of patients with Ph-positive ALL has changed and is no longer considered the least favorable subtype of ALL. Although the addition of a TKI in treatment of Ph-positive ALL improved the outcome in all age groups, the optimal chemotherapy regimen accompanying it is not clearly defined. In most studies, TKIs were added, both in children and adults, to the same aggressive, multi-agent regimens administered to Ph-negative ALL. However, it is unknown if the same or any cytotoxic chemotherapy should be used when patients are treated with a very active TKI, especially if followed by an allogeneic HSCT. This question was partially studied in adult Ph-positive ALL by the GIMEMA Group in their LAL 1205 trial [60]. Fifty-three patients, aged 24–76 (median 54) years were induced without chemotherapy but with dasatinib 70 mg twice daily for 84 days and prednisone 60 mg/m2 daily for 32 days plus two doses of intrathecal methotrexate. This combination of dasatinib plus steroids induced 100% complete hematological remission, 92.5% by day 22. Also, 52% of the patients had minimal residual disease (MRD) measured by PCR using the BCR/ABL fusion transcripts lower than 103; 8 patients achieved a complete molecular remission. The degree of molecular response correlated favorably with diseasefree survival. The question of eliminating chemotherapy was not answered in this study since the treatment after day 85 was not defined and left to the discretion of the individual investigators. Therefore, despite these promising induction data, post-induction therapy is still a critical unmet clinical need. Another example of using TKIs in Ph-positive ALL is as maintenance therapy after HSCT. In a recent study, patients treated with imatinib prophylactically after transplantation had a longer duration of molecular remission than those who were treated preemptively with imatinib [61], implying a role for post-transplantation TKIs in all patients (Table 3). More studies are needed because of the short followup and the lack of survival difference between the two approaches.

458

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

Table 3 Ph-positive ALL and post allogeneic HSCT imatinib (IM): prophylaxis versus preemptive [61].

HSCT to imatinib, days Median sustained PCR negative, Mo Conversion to PCR positive OS at 5 yrs

IM prophylaxisa N ¼ 26

IM preemptiveb N ¼ 29

P value

48 27 40% 80%

70 7 69% 75%

0.065 0.046 NS

Abbreviations: HSCT, hematopoietic stem cell transplant; Mo, month(s); OS, overall survival; PCR, polymerase chain reaction. Median F/U 30 Mo. a IM prophylaxis, imatinib after HSCT. b IM preemptive, imatinib after conversion to PCR positive for BCR-ABL.

Experimental ex vivo modified monoclonal antibodies Although “naked” monoclonal anti B-cell antibodies target the leukemia cells, their clinical activity, especially as single agents, is often limited. A more promising approach is by bioengineering fusing antibodies with conjugates, in which the antibody mostly targets the malignant cells and the conjugate harnesses other mechanism of antitumor activity. The technologies and some preliminary clinical data can be exemplified with CD19 and CD22 as targets expressed on most precursor B-cell ALL patients. Targeting CD19 – blinatumomab Blinatumomab is a bispecific T-cell engager (BiTE) single chain antibody that targets CD19 and CD3, enabling targeting of cytotoxic normal CD3 T cells and CD19-expressing malignant B-lineage ALL cells and bringing cytotoxic T cells and malignant B cells in close proximity. Conventional monoclonal antibodies are unable to promote this degree of proximity, due to cytotoxic T cells lacking Fcg receptors. Thus, blinatumomab provides superior and potent tumor killing at low concentrations. Cell death is mediated by apoptosis [62]. Two-phase 2 trials of single-agent blinatumomab in adult ALL have been reported by Topp et al. (Table 4) [63,64]. The first trial evaluated 20 patients with precursor B-ALL with molecularly persistent or relapsed disease (MRD positive) after chemotherapy. Each blinatumomab cycle was administered as a 4-week continuous intravenous infusion followed by a 14-day treatment-free interval. MRD negativity (complete molecular remission) was achieved in 16 patients (80%). After a median follow-up of 405 days and with 8 of the 16 CR patients subsequently undergoing HSCT, the relapse-free survival was 78% [63]. In the second trial, 25 patients with hematologic overt relapsed or refractory adult ALL were treated with blinatumomab [64]. A complete hematologic response (CR) or CR with partial hematological response (CRh) was seen within 2 cycles in 17 of 25 (68%) patients with MRD < 104. For the first 18 patients the response duration was 7.1 months. The most common side effect was fever, and the most serious toxicity was neurological seen in 5 patients with confusion and seizures. Steroids were used to treat the side effects. These results represent an exceptionally high CR rate and profound reduction in tumor burden with a single-agent in relapsed disease that had not been seen with single-agent chemotherapy. Blinatumomab may become the most effective new single targeted agent so far developed for B-lineage ALL. Blinatumomab administration has logistical challenges, namely a continuous intravenous infusion for 28 days mostly in the outpatient setting, mandatory drug bag changes at intervals of 48 h or less, and the availability of a sterile room on-site for drug preparation. Table 4 Single-agent blinatumomab in relapsed/refractory precursor B-ALL. Relapse

Patients

End point

Outcome

Molecular (MRD positive) [63] Clinical [64]

20 (5 Phþ) 25

MRD negative CR/CRh

16 (80%) 17 (68%)a

Abbreviations: CR, complete hematologic response; CRh, complete response with partial hematologic recovery; MRD, minimal residual disease. a All 17 CR patients had MRD response of <104 after 2 cycles.

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

459

The next step in developing blinatumomab is in front-line ALL. As with other targeted agents, the choice of a chemotherapy backbone is unclear, particularly without a standard treatment regimen. This is further compounded by the promising preliminary, but short-term, results of pediatric inspired studies. Other factors to consider are the timing of blinatumomab within the structure of any chemotherapy, stratification between MRD-negative or -positive patients, its role in Ph-positive ALL, and flexible strategies among the wide age range of adult ALL. Targeting CD19 (chimeric antigen receptor-modified T cells – CAR) A different concept is to use targeted cell therapy rather than targeted agents. The patient’s own T cells are genetically modified in the laboratory to target antigens expressed on tumor cells [65]. By genetic engineering, autologous normal T cells are virally transduced with a chimeric antigen receptor (CAR) DNA that encodes a protein product composed of a tumor-targeted monoclonal antibody (usually a single chain fragment of the variable region of the monoclonal antibody – scFvs) fused with a T cell-derived costimulatory signaling domain. For B-lineage malignancies, CARs were developed to encode a single chain of the variable region of the anti-CD19 antibody connected to the z chain of CD3 (a signal-transduction component of the T-cell antigen receptor) and a T-cell-derived signaling domain, for example CD28 [66] or CD137 [67]. Autologous T cells are collected from the patients by leukapheresis, transduced with CAR, cryopreserved, and later re-infused. The anti-CD19 region of the CAR redirects the modified T cells toward the CD19-positive ALL cells, the costimulatory signaling domain in CAR, and enhance the proliferation, survival, and persistence of memory cells with cytotoxic antileukemic effect. Recent clinical trials reported early preliminary results in a few patients with chronic lymphocytic leukemia and B-lineage ALL with some impressive clinical response [66,67]. Both blinatumomab antibody and CAR cells redirected autologous normal T cells towards CD19expressing ALL cells and have effective cytotoxicity against the tumor cells in an HLA-independent manner. In both, clinical activity can be associated with serious tumor lysis or cytokine release side effects and suppression of normal B cells. Such side effects can be reduced if both technologies are used in minimal residual disease status. However in both cases, clinical application will require meticulous institutional planning, strict supportive care guidelines, and a staff well trained beyond the expertise required for standard chemotherapy administration. Blinatumomab and CAR cell technologies also have important differences. Blinatumomab is a protein with a very short half life, has time-limited Tcell cytotoxicity, and hence the very long infusion. On the other hand, CAR cell therapy technology requires pre-conditioning of the patient with immunosuppressive chemotherapy to enhance the in vivo replication of the genetically modified T cells, with long-term persistence and possible sustained tumor control [66,67]. This persistence of memory T-cell activity can also potentially have longterm toxicity on normal cells carrying the same target. Targeting CD22 Another important target for B-lineage ALL is CD22. An advantage over CD20 is that it is more commonly expressed on almost all B-lineage ALL patients. In contrast to CD20, which binds rituximab but stays on the cell surface, CD22 rapidly internalizes after binding to the antibody, making it more amiable for conjugation with intracellular toxins [68]. Epratuzumab, the “naked” humanized monoclonal against CD22, was studied in children showing minimal single-agent activity [69]. Inotuzumab ozogamicin [70] and moxetumomab pasudotox (HA22) [71], each linked to a different potent toxin, have shown single-agent activity in refractory and relapsed disease (Table 5). Recently inotuzumab ozogamicin was delivered to B-lineage ALL patients at smaller doses and a more frequent schedule than previously studied [70], reducing toxicity with similar activity. Given the heavily pretreated patients, the response rate in relapsed ALL is promising, with a median OS of 7þ months (Table 5). A potential problem of the drug is that calicheamicin, the toxin linked to CD22, when linked to an anti-CD33 such as gemtuzumab ozogamicin, was associated with veno-occlusive disease (VOD) in AML patients, especially after HSCT [72]. With the new schedule of inotuzumab ozogamicin, only 2 patients had severe liver function abnormalities, none had VOD, and 4 patients proceeded to HSCT [70].

460

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

Table 5 Monoclonal anti-CD22 antibodies and their conjugates. Drug

Conjugate

Development

Results

Epratuzumab [69]

None

Moxetumomab Pasudotox (HA22) [71] Inotuzumab ozogamicin [70] Epratuzumab-SN-38 [73]

Truncated pseudomonas exotoxin A Calicheamicin Topoisomerase I inhibitor

Phase I/II children refractory ALL Phase I children refractory ALL Phase II/III Relapse refractory Pre-clinical

Minimal single-agent activity CR 24%

Fused CD19-CD22

Single fusion protein fused with diphtheria toxin

CR þ CRp ¼ 8/20(40%)a Higher activity with un-conjugated anti-CD20?

Pre-clinical

Abbreviations: CR, complete response; CRp, pathologic complete response; MRD, minimal residual disease. a 7 of the 8 responders became MRD negative.

The active agents mentioned above are conjugates with sub nanomolar activity (called ultra-toxics). Recently the differences between the rapid internalizing of the anti-CD22 epratuzumab and the slower internalizing of the anti-CD20 veltuzumab were explored using the conjugate drug SN-33, which is a topoisomerase I inhibitor with low nanomolar potency. Using a linker that allows the conjugate to slowly dissociate from the antibody into the serum, a new antibody-drug conjugate called epratuzumabSN-38 was developed. Pre-clinical in vivo and in vitro experiments showed that the conjugated epratuzumab-SN-38 could be combined with the unconjugated veltuzumab for more activity against Bcell tumors without additional toxicity and without competing for the same target [73]. Novel small molecule agents Table 6 provides a partial list of other novel targeted agents directed to different targets; some are already in clinical trials. Two agents will be discussed in more detail. Targeting mutated Notch1 Notch1 is a transmembrane glycoprotein receptor that regulates cellular differentiation, proliferation, self-renewal, and survival. Ligand binding to the Notch receptor induces cleavage by gammasecretase of its intracellular domain Notch (ICD) that then translocates to the nucleus and activates several transcription factors. Notch1 pathway is involved in the development of normal lymphocytes. More than 50% of patients with T-ALL have mutations in NOTCH1, increasing the rate of its activation by action of gamma-secretase. Therefore agents that inhibit gamma-secretase (GSI) block the final step in NOTCH1 activation and prevent formation of the ICD. Several GSIs targeting NOTCH1 are now in phase 1 clinical trials in T-ALL and T-cell lymphoblastic lymphoma. Since the major dose-limiting activity of GSIs is diarrhea, the search is for an agent that would have a high therapeutic index. Interestingly, even in the absence of NOTCH1 mutation, T-ALL cells may be dependent on Notch pathway activation [74,75]. Table 6 Potential novel targeted agents. Target

Drug

Comments

Notch1 MLL (q11.34) PP2A PNP NUP214-ABL1 mTOR JAK IL-7R and RCLF2

g secretase inhibitors (GSI)

Mutated in >50% of T-ALL GI toxicity

DOT1L inhibitor [84], FLT3 inhibitors FTY720 [85] Forodesine (Bcx-1777) [86] Tyrosine kinase inhibitors [87] Everolimus, temsirolimus [88] JAK inhibitors

Fingolimod used in multiple sclerosis; Phþ ALL? T-ALL 5% of T-ALL

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

461

Targeting mutated MLL The mixed lineage leukemia (MLL) gene located on chromosome 11q23 normally encodes for a histone methyltransferase (HMT) protein that is responsible for methylation of histone H3 associated with active transcription. Rearrangements of the MLL gene occur by chromosomal translocation of the MLL gene on chromosome 11q23 in approximately 5%–10% of adult ALL [76–78], 5% of adult acute myeloid leukemia [76–81], and 70% of infant leukemia, all associated with a poor prognosis [76]. Patients with acute leukemia related to previous exposure to cytotoxic chemotherapy also often have translocations of 11q23 [82]. The chromosomal translocation partners in MLL leukemia are varied, but the acute leukemia phenotype produced with the translocation is conserved between translocation partners. In adult ALL, 9% of patients enrolled on the UK MRC E2993 study had a translocation involving 11q23, most of them as t(4:11), which has a very dismal outcome [77]. The translocation partner of MLL t(4:11) is the AF4 gene on chromosome 4 forming the fusion MLL-AF4 protein; other common partners of translocated MLL are AF9 and ENL genes. These partners normally recruit another histone methyltransferase named DOT1L. With translocations of MLL, the catalytic domain of this protein is lost, but by the fusion of the partial MLL gene to its translocation partner, MLL gains the ability to recruit DOT1L. The aberrantly recruited DOT1L to the MLL fusion target genes results in ectopic H3K79 methylation and increased expression of genes involved in leukemogenesis of the MLL rearranged leukemias [83]. Therefore the mis-targeted DOT1L enzymatic activity could be required for the development and maintenance of MLL rearranged leukemia. Recently, small molecules that inhibit DOT1L have been developed that result in reducing histone H3K79 methylation, decreasing expression of MLL fusion target genes, and inducting apoptosis selectively in leukemia cell lines derived from MLL rearranged leukemia patients. In addition, they demonstrated in vivo efficacy of a DOT1L inhibitor in a xenografted mouse model of MLL leukemia [84]. Summary Several new strategies are evolving that promise to improve outcomes in various clinical settings; among them are the targeted agents. The molecules with very high activity as single agents may be those that most impact outcomes, for example TKIs for Ph-positive ALL and blinatumomab for precursor B-ALL, which induce high rates of complete response in both overt and molecular relapses. Highly active single agents may be identified in the future, although they may be active only against limited specific molecular subsets of ALL. This progress is likely to accelerate with parallel efforts in search of genetic abnormalities that drive the growth of ALL cells and serve as new targets for novel agents. The safety of targeted agents in development will need to take into consideration toxicity on normal cells, both on target and off target. Important questions arise about combinations with chemotherapy for potential added activity, and redefining optimal chemotherapy backbones aimed at reducing their cytotoxicity. Other clinical settings for targeted agents are in maintenance therapy when the leukemia burden is minimal or in concert with a bone marrow transplantation approach. From an immunological standpoint, new technologies can further bioengineer antibodies into complex structures that can better recruit normal T cells or conjugate them with a variety of drugs. After decades of minimal progress, the new focus and surge of novel concepts are likely to revolutionize the approach to adult ALL and narrow the outcome gap that currently exists between adults and children. In the late 1990s, two drugs with good single-agent activity were introduced: the monoclonal antibody against CD20 (rituximab) for B-cell lymphomas and the small molecule, all-trans retinoic acid, targeting its mutated receptor in acute promyelocytic leukemia. A decade later, in both cases, when combined with chemotherapy, the agents dramatically improved the cure rate of their respective diseases. These examples provide a genuine, realistic optimism that it is possible to improve the outcome in certain subtypes of ALL, and within a similar time frame. Conflict of interest statement Fees for non-CME services: Sigma Tau.

462

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

References [1] Bassan R, Hoelzer D. Modern therapy of acute lymphoblastic leukemia. J Clin Oncol 2011;29:532–43. [2] Douer D. Is asparaginase a critical component in the treatment of acute lymphoblastic leukemia? Best Pract Res Clin Haematol 2008;21:647–58. [3] Alvarnas JC, Brown PA, Aoun P, et al. Acute lymphoblastic leukemia. J Natl Compr Canc Netw 2012;10:858–914. [4] Pulte D, Gondos A, Brenner H. Improvement in survival in younger patients with acute lymphoblastic leukemia from the 1980s to the early 21st century. Blood 2009;113:1408–11. [5] Gökbuget N, Arnold R, Buechner T, et al. Intensification of induction and consolidation improves only subgroups of adult ALL: analysis of 1200 patients in GMALL study 05/93. Blood 2001;98. 802a–802b [abstr 3337]. [6] Larson RA, Dodge RK, Burns CP, et al. A five-drug remission induction regimen with intensive consolidation for adults with acute lymphoblastic leukemia: cancer and leukemia group B study 8811. Blood 1995;85:2025–37. [7] Stock W, Johnson J, Yu D, et al. Daunorubicin dose intensification during treatment of adult acute lymphoblastic leukemia (ALL): final results from cancer and leukemia Group B study 19802. Blood 2005;106:521a [abstr 833]. [8] Rowe JM, Buck G, Burnett AK, et al. Induction therapy for adults with acute lymphoblastic leukemia: results of more than 1500 patients from the international ALL trial: MRC UKALL XII/ECOG E2993. Blood 2005;106:3760–7. [9] Goldstone AH, Richards SM, Lazarus HM, et al. In adults with standard-risk acute lymphoblastic leukemia, the greatest benefit is achieved from a matched sibling allogeneic transplantation in first complete remission, and an autologous transplantation is less effective than conventional consolidation/maintenance chemotherapy in all patients: final results of the International ALL Trial (MRC UKALL XII/ECOG E2993). Blood 2008;111:1827–33. [10] Linker C, Damon L, Ries C, et al. Intensified and shortened cyclical chemotherapy for adult acute lymphoblastic leukemia. J Clin Oncol 2002;20:2464–71. [11] Weiss MA, Heffner L, Kalaycio M, et al. A randomized trial demonstrating the superiority of cytarabine with high-dose mitoxantrone compared to a standard vincristine/prednisone-based regimen as induction therapy for adult patients with ALL. J Clin Oncol 2005;23 [abstr 6516]. [12] Kantarjian H, Thomas D, O’Brien S, et al. Long-term follow-up results of hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (hyper-CVAD), a dose-intensive regimen, in adult acute lymphocytic leukemia. Cancer 2004;101:2788–801. [13] Clarkson BD, Fried J. Changing concepts of treatment in acute leukemia. Med Clin North Am 1971;55:561–600. [14] Reiter A, Schrappe M, Ludwig WD, et al. Chemotherapy in 998 unselected childhood acute lymphoblastic leukemia patients. Results and conclusions of the multicenter trial ALL-BFM 86. Blood 1994;84:3122–33. [15] Hoelzer D, Thiel E, Loffler H, et al. Intensified therapy in acute lymphoblastic and acute undifferentiated leukemia in adults. Blood 1984;64:38–47. [16] Hoelzer D, Thiel E, Loffler H, et al. Prognostic factors in a multicenter study for treatment of acute lymphoblastic leukemia in adults. Blood 1988;71:123–31. [17] Larson RA. The U.S. trials in adult acute lymphoblastic leukemia. Ann Hematol 2004;83(Suppl. 1):S127–8. [18] Larson RA, Dodge RK, Linker CA, et al. A randomized controlled trial of filgrastim during remission induction and consolidation chemotherapy for adults with acute lymphoblastic leukemia: CALGB study 9111. Blood 1998;92:1556–64. [19] Wetzler M, Sanford BL, Kurtzberg J, et al. Effective asparagine depletion with pegylated asparaginase results in improved outcomes in adult acute lymphoblastic leukemia: cancer and leukemia Group B Study 9511. Blood 2007;109:4164–7. [20] Fielding AK, Richards SM, Chopra R, et al. Outcome of 609 adults after relapse of acute lymphoblastic leukemia (ALL); an MRC UKALL12/ECOG 2993 study. Blood 2007;109:944–50. [21] Wood WA, Lee SJ. Malignant hematologic diseases in adolescents and young adults. Blood 2011;117:5803–15. [22] Ribera JM, Oriol A, Sanz MA, et al. Comparison of the results of the treatment of adolescents and young adults with standard-risk acute lymphoblastic leukemia with the Programa Espanol de Tratamiento en Hematologia pediatric-based protocol ALL-96. J Clin Oncol 2008;26:1843–9. [23] Huguet F, Leguay T, Raffoux E, et al. Pediatric-inspired therapy in adults with Philadelphia chromosome-negative acute lymphoblastic leukemia: the GRAALL-2003 study. J Clin Oncol 2009;27:911–8. [24] Goekbuget N, Baumann A, Beck J, et al. PEG-asparaginase in adult acute lymphoblastic leukemia (ALL): efficacy and feasibility analysis with increasing dose levels. Blood 2008;112 [abstr 302]. [25] DeAngelo DJ, Dahlberg S, Silverman LB, et al. A multicenter phase II study using a dose intensified pediatric regimen in adults with untreated acute lymphoblastic leukemia. Blood 2007;110:181a [abstr 587]. [26] Douer D, Watkins K, Mark L, et al. Sustained and prolonged asparagine depletion by multiple doses of intravenous pegylated asparaginase in the treatment of adults with newly diagnosed acute lymphoblastic leukemia. Blood 2008;112 [abstr 1928]. [27] No authors listed. An intergroup phase 2 clinical trial for adolescents and young adults with untreated acute lymphoblstic leukemia (ALL). Available at: http://www.clinicaltrials.gov/ct2/show/NCT00558519 [Accessed 14.8.12]. [28] Pui CH, Evans WE. Treatment of acute lymphoblastic leukemia. N Engl J Med 2006;354:166–78. [29] Bruggemann M, Gokbuget N, Kneba M. Acute lymphoblastic leukemia: monitoring minimal residual disease as a therapeutic principle. Semin Oncol 2012;39:47–57. [30] Bruggemann M, Raff T, Flohr T, et al. Clinical significance of minimal residual disease quantification in adult patients with standard-risk acute lymphoblastic leukemia. Blood 2006;107:1116–23. [31] Bassan R, Spinelli O, Oldani E, et al. Improved risk classification for risk-specific therapy based on the molecular study of minimal residual disease (MRD) in adult acute lymphoblastic leukemia (ALL). Blood 2009;113:4153–62. [32] Armstrong SA, Look AT. Molecular genetics of acute lymphoblastic leukemia. J Clin Oncol 2005;23:6306–15. [33] Mullighan CG, Downing JR. Genome-wide profiling of genetic alterations in acute lymphoblastic leukemia: recent insights and future directions. Leukemia 2009;23:1209–18. [34] Mullighan CG, Su X, Zhang J, et al. Deletion of IKZF1 and prognosis in acute lymphoblastic leukemia. N Engl J Med 2009; 360:470–80.

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

463

[35] Harvey RC, Mullighan CG, Chen IM, et al. Rearrangement of CRLF2 is associated with mutation of JAK kinases, alteration of IKZF1, hispanic/latino ethnicity, and a poor outcome in pediatric B-progenitor acute lymphoblastic leukemia. Blood 2010; 115:5312–21. [36] Mullighan CG. New strategies in acute lymphoblastic leukemia: translating advances in genomics into clinical practice. Clin Cancer Res 2011;17:396–400. [37] Dekker AW, van’t Veer MB, Sizoo W, et al. Intensive postremission chemotherapy without maintenance therapy in adults with acute lymphoblastic leukemia. Dutch Hemato-Oncology Research Group. J Clin Oncol 1997;15:476–82. [38] Sallan SE, Hitchcock-Bryan S, Gelber R, et al. Influence of intensive asparaginase in the treatment of childhood non-T-cell acute lymphoblastic leukemia. Cancer Res 1983;43:5601–7. [39] Nachman JB, Sather HN, Sensel MG, et al. Augmented post-induction therapy for children with high-risk acute lymphoblastic leukemia and a slow response to initial therapy. N Engl J Med 1998;338:1663–71. [40] Silverman LB, Gelber RD, Dalton VK, et al. Improved outcome for children with acute lymphoblastic leukemia: results of Dana-Farber Consortium Protocol 91-01. Blood 2001;97:1211–8. [41] Pession A, Valsecchi MG, Masera G, et al. Long-term results of a randomized trial on extended use of high dose L-asparaginase for standard risk childhood acute lymphoblastic leukemia. J Clin Oncol 2005;23:7161–7. [42] Moghrabi A, Levy DE, Asselin B, et al. Results of the Dana-Farber Cancer Institute ALL Consortium Protocol 95-01 for children with acute lymphoblastic leukemia. Blood 2007;109:896–904. [43] Seibel NL, Steinherz PG, Sather HN, et al. Early postinduction intensification therapy improves survival for children and adolescents with high-risk acute lymphoblastic leukemia: a report from the Children’s Oncology Group. Blood 2008;111: 2548–55. [44] Thomas D, O’Brien S, Faderl S, et al. Anthracycline dose intensification in adult acute lymphoblastic leukemia: lack of benefit in the context of the fractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone regimen. Cancer 2010;116:4580–9. [45] Angiolillo AL, Yu AL, Reaman G, et al. A phase II study of Campath-1H in children with relapsed or refractory acute lymphoblastic leukemia: a Children’s Oncology Group report. Pediatr Blood Cancer 2009;53:978–83. [46] Stock W, Yu D, Sanford B, et al. Incorporation of alemtuzumab into front-line therapy of adult acute lymphoblastic leukemia (ALL) is feasible: a phase I/II study from the cancer and leukemia Group B (CALGB 10102). Blood 2005;106 [abstr 145]. [47] Dworzak MN, Schumich A, Printz D, et al. CD20 up-regulation in pediatric B-cell precursor acute lymphoblastic leukemia during induction treatment: setting the stage for anti-CD20 directed immunotherapy. Blood 2008;112:3982–8. [48] Thomas DA, O’Brien S, Jorgensen JL, et al. Prognostic significance of CD20 expression in adults with de novo precursor B-lineage acute lymphoblastic leukemia. Blood 2009;113:6330–7. [49] Maury S, Huguet F, Leguay T, et al. Adverse prognostic significance of CD20 expression in adults with Philadelphia chromosome-negative B-cell precursor acute lymphoblastic leukemia. Haematologica 2010;95:324–8. [50] Jeha S, Behm F, Pei D, et al. Prognostic significance of CD20 expression in childhood B-cell precursor acute lymphoblastic leukemia. Blood 2006;108:3302–4. [51] Hoelzer D, Huettmann A, Kaul F, et al. Immunochemotherapy with rituximab improves molecular CR rate and outcome in CD20þ B-lineage standard and high risk patients; results of 263 CD20þ patients studied prospectively in GMALL study 07/ 2003. Blood 2010;116 [abstr 170]. [52] Thomas DA, O’Brien S, Faderl S, et al. Chemoimmunotherapy with a modified hyper-CVAD and rituximab regimen improves outcome in de novo Philadelphia chromosome-negative precursor B-lineage acute lymphoblastic leukemia. J Clin Oncol 2010;28:3880–9. [53] Lee S, Kim YJ, Min CK, et al. The effect of first-line imatinib interim therapy on the outcome of allogeneic stem cell transplantation in adults with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia. Blood 2005;105:3449–57. [54] Thomas DA, Faderl S, Cortes J, et al. Treatment of Philadelphia chromosome-positive acute lymphocytic leukemia with hyper-CVAD and imatinib mesylate. Blood 2004;103:4396–407. [55] Yanada M, Takeuchi J, Sugiura I, et al. High complete remission rate and promising outcome by combination of imatinib and chemotherapy for newly diagnosed BCR-ABL-positive acute lymphoblastic leukemia: a phase II study by the Japan Adult Leukemia Study Group. J Clin Oncol 2006;24:460–6. [56] Ravandi F, O’Brien S, Thomas D, et al. First report of phase 2 study of dasatinib with hyper-CVAD for the frontline treatment of patients with Philadelphia chromosome-positive (Phþ) acute lymphoblastic leukemia. Blood 2010;116: 2070–7. [57] Wassmann B, Pfeifer H, Goekbuget N, et al. Alternating versus concurrent schedules of imatinib and chemotherapy as front-line therapy for Philadelphia-positive acute lymphoblastic leukemia (Phþ ALL). Blood 2006;108:1469–77. [58] Ravandi F, Kebriaei P. Philadelphia chromosome-positive acute lymphoblastic leukemia. Hematol Oncol Clin North Am 2009;23:1043–63 [vi]. [59] Schultz KR, Bowman WP, Aledo A, et al. Improved early event-free survival with imatinib in Philadelphia chromosomepositive acute lymphoblastic leukemia: a children’s oncology group study. J Clin Oncol 2009;27:5175–81. [60] Foa R, Vitale A, Vignetti M, et al. Dasatinib as first-line treatment for adult patients with Philadelphia chromosomepositive acute lymphoblastic leukemia. Blood 2011;118:6521–8. [61] Pfeifer H, Wassmann B, Bethge WA, et al. Updated long-term results of a randomized comparison of prophylactic and preemptive imatinib following allogeneic stem cell transplantation for Philadelphia chromosome positive acute lymphoblastic leukemia (Phþ ALL). Blood 2011;118 [abstr 247]. [62] Nagorsen D, Baeuerle PA. Immunomodulatory therapy of cancer with T cell-engaging BiTE antibody blinatumomab. Exp Cell Res 2011;317:1255–60. [63] Topp MS, Kufer P, Gokbuget N, et al. Targeted therapy with the T-cell-engaging antibody blinatumomab of chemotherapyrefractory minimal residual disease in B-lineage acute lymphoblastic leukemia patients results in high response rate and prolonged leukemia-free survival. J Clin Oncol 2011;29:2493–8. [64] Topp M, Goekbuget N, Zugmaier G, et al. Effect of anti-CD19 BiTE blinatumomab on complete remission rate and overall survival in adult patients with relapsed/refractory B-precursor ALL. J Clin Oncol 2012;30 [abstr 6500].

464

D. Douer / Best Practice & Research Clinical Haematology 25 (2012) 453–464

[65] Brentjens RJ. CARs and cancers: questions and answers. Blood 2012;119:3872–3. [66] Brentjens RJ, Riviere I, Park JH, et al. Safety and persistence of adoptively transferred autologous CD19-targeted T cells in patients with relapsed or chemotherapy refractory B-cell leukemias. Blood 2011;118:4817–28. [67] Porter DL, Levine BL, Kalos M, et al. Chimeric antigen receptor-modified T cells in chronic lymphoid leukemia. N Engl J Med 2011;365:725–33. [68] Poe JC, Fujimoto Y, Hasegawa M, et al. CD22 regulates B lymphocyte function in vivo through both ligand-dependent and ligand-independent mechanisms. Nat Immunol 2004;5:1078–87. [69] Raetz EA, Cairo MS, Borowitz MJ, et al. Chemoimmunotherapy reinduction with epratuzumab in children with acute lymphoblastic leukemia in marrow relapse: a Children’s Oncology Group Pilot Study. J Clin Oncol 2008;26:3756–62. [70] Jabbour E, O’Brien SM, Thomas DA, et al. Inotuzumab ozogamycin (IO), a CD22 monoclonal antibody conjugated to calecheamicin, given weekly, for refractory-relapse acute lymphocytic leukemia (R-R ALL). J Clin Oncol 2012;30 [abstr 6501]. [71] Wayne AS, Bhojwani D, Silverman LB, et al. A novel anti-CD22 immunotoxin, moxetumomab pasudotox: phase I study in pediatric acute lymphoblastic leukemia (ALL). Blood 2011;118 [abstr 248]. [72] Cohen AD, Luger SM, Sickles C, et al. Gemtuzumab ozogamicin (Mylotarg) monotherapy for relapsed AML after hematopoietic stem cell transplant: efficacy and incidence of hepatic veno-occlusive disease. Bone Marrow Transplant 2002;30:23–8. [73] Sharkey RM, Govindan SV, Cardillo TM, et al. Epratuzumab-SN-38: a new antibody-drug conjugate for the therapy of hematologic malignancies. Mol Cancer Ther 2012;11:224–34. [74] Clappier E, Collette S, Grardel N, et al. NOTCH1 and FBXW7 mutations have a favorable impact on early response to treatment, but not on outcome, in children with T-cell acute lymphoblastic leukemia (T-ALL) treated on EORTC trials 58881 and 58951. Leukemia 2010;24:2023–31. [75] Mansour MR, Sulis ML, Duke V, et al. Prognostic implications of NOTCH1 and FBXW7 mutations in adults with T-cell acute lymphoblastic leukemia treated on the MRC UKALLXII/ECOG E2993 protocol. J Clin Oncol 2009;27:4352–6. [76] Wetzler M, Dodge RK, Mrozek K, et al. Prospective karyotype analysis in adult acute lymphoblastic leukemia: the cancer and leukemia Group B experience. Blood 1999;93:3983–93. [77] Moorman AV, Harrison CJ, Buck GA, et al. Karyotype is an independent prognostic factor in adult acute lymphoblastic leukemia (ALL): analysis of cytogenetic data from patients treated on the Medical Research Council (MRC) UKALLXII/ Eastern Cooperative Oncology Group (ECOG) 2993 trial. Blood 2007;109:3189–97. [78] Tamai H, Inokuchi K. 11q23/MLL acute leukemia: update of clinical aspects. J Clin Exp Hematop 2010;50:91–8. [79] Mrozek K, Heinonen K, Lawrence D, et al. Adult patients with de novo acute myeloid leukemia and t(9; 11)(p22; q23) have a superior outcome to patients with other translocations involving band 11q23: a cancer and leukemia group B study. Blood 1997;90:4532–8. [80] Schoch C, Schnittger S, Klaus M, et al. AML with 11q23/MLL abnormalities as defined by the WHO classification: incidence, partner chromosomes, FAB subtype, age distribution, and prognostic impact in an unselected series of 1897 cytogenetically analyzed AML cases. Blood 2003;102:2395–402. [81] Grimwade D, Hills RK, Moorman AV, et al. Refinement of cytogenetic classification in acute myeloid leukemia: determination of prognostic significance of rare recurring chromosomal abnormalities among 5876 younger adult patients treated in the United Kingdom Medical Research Council trials. Blood 2010;116:354–65. [82] Kayser S, Dohner K, Krauter J, et al. The impact of therapy-related acute myeloid leukemia (AML) on outcome in 2853 adult patients with newly diagnosed AML. Blood 2011;117:2137–45. [83] Nguyen AT, Taranova O, He J, et al. DOT1L, the H3K79 methyltransferase, is required for MLL-AF9-mediated leukemogenesis. Blood 2011;117:6912–22. [84] Daigle SR, Olhava EJ, Therkelsen CA, et al. Selective killing of mixed lineage leukemia cells by a potent small-molecule DOT1L inhibitor. Cancer Cell 2011;20:53–65. [85] Neviani P, Santhanam R, Oaks JJ, et al. FTY720, a new alternative for treating blast crisis chronic myelogenous leukemia and Philadelphia chromosome-positive acute lymphocytic leukemia. J Clin Invest 2007;117:2408–21. [86] Gandhi V, Kilpatrick JM, Plunkett W, et al. A proof-of-principle pharmacokinetic, pharmacodynamic, and clinical study with purine nucleoside phosphorylase inhibitor immucillin-H (BCX-1777, forodesine). Blood 2005;106:4253–60. [87] Deenik W, Beverloo HB, van der Poel-van de Luytgaarde SC, et al. Rapid complete cytogenetic remission after upfront dasatinib monotherapy in a patient with a NUP214-ABL1-positive T-cell acute lymphoblastic leukemia. Leukemia 2009; 23:627–9. [88] Saunders P, Cisterne A, Weiss J, et al. The mammalian target of rapamycin inhibitor RAD001 (everolimus) synergizes with chemotherapeutic agents, ionizing radiation and proteasome inhibitors in pre-B acute lymphocytic leukemia. Haematologica 2011;96:69–77.