Evolving treatment strategies for patients newly diagnosed with chronic myeloid leukemia: the role of second-generation BCR-ABL inhibitors as first-line therapy

Simultaneous Inhibition of BCR-ABL1 Tyrosine Kinase and PAK1/2 Serine/Threonine Kinase Exerts Synergistic Effect against Chronic Myeloid Leukemia Cells

Tyrosine kinase inhibitors (TKIs) revolutionized the treatment of chronic myeloid leukemia in the chronic phase (CML-CP). However, it is unlikely that they can completely “cure” the disease. This might be because some subpopulations of CML-CP cells such as stem and progenitor cells are resistant to chemotherapy, even to the new generation of TKIs. Therefore, it is important to look for new methods of treatment to improve therapeutic outcomes. Previously, we have shown that class I p21-activated serine/threonine kinases (PAKs) remained active in TKI-naive and TKI-treated CML-CP leukemia stem and early progenitor cells. In this study, we aimed to determine if simultaneous inhibition of BCR-ABL1 oncogenic tyrosine kinase and PAK1/2 serine/threonine kinase exert better anti-CML effect than that of individual treatments. PAK1 was inhibited by small-molecule inhibitor IPA-3 (p21-activated kinase inhibitor III), PAK2 was downregulated by specific short hairpin RNA (shRNA), and BCR-ABL1 tyrosine kinase was inhibited by imatinib (IM). The studies were conducted by using (i) primary CML-CP stem/early progenitor cells and normal hematopoietic counterparts isolated from the bone marrow of newly diagnosed patients with CML-CP and from healthy donors, respectively, (ii) CML-blast phase cell lines (K562 and KCL-22), and (iii) from BCR-ABL1-transformed 32Dcl3 cell line. Herein, we show that inhibition of the activity of PAK1 and/or PAK2 enhanced the effect of IM against CML cells without affecting the normal cells. We observed that the combined use of IM with IPA-3 increased the inhibition of growth and apoptosis of leukemia cells. To evaluate the type of interaction between the two drugs, we performed median effect analysis. According to our results, the type and strength of drug interaction depend on the concentration of the drugs tested. Generally, combination of IM with IPA-3 at the 50% of the cell kill level (EC50) generated synergistic effect. Based on our results, we hypothesize that IM, a BCR-ABL1 tyrosine kinase inhibitor, combined with a PAK1/2 inhibitor facilitates eradication of CML-CP cells.

The Bone Phenotype and Pain Response to Pamidronate in Tyrosine Kinase Inhibitor-Treated Chronic Myelogenous Leukemia

Tyrosine kinase inhibitors (TKIs) have been linked to bone pain and linear growth attenuation in children with TKI-treated chronic myelogenous leukemia (CML). We describe the skeletal phenotype in an 11-year-old boy with chronic bone pain due to TKI-treated CML, including his response to intravenous (IV) pamidronate. This boy was diagnosed with Philadelphia chromosome-positive CML at 4 years of age. He was treated with imatinib for 3 years, followed by dasatinib for 4 years. At age 11 years, he was seen in a bone health clinic with a 4-year history of leg pains that necessitated regular nonsteroidal anti-inflammatory drugs (NSAIDS) and downward crossing of height percentiles (from the 25th to fifth). The bone volume/tissue volume Z-score was +1.6 for a trans-iliac bone biopsy specimen, with an increase in trabecular number (Z-score, +3.1). Bone formation and resorption parameters on trabecular surfaces were within normal limits. Tibia volumetric bone mineral density (BMD) and bone geometry were normal by peripheral quantitative computed tomography, areal BMD Z-scores were average or above average at multiple skeletal sites by dual-energy x-ray absorptiometry, and tibia length Z-score was reduced (−2.3). Growth- and bone-related biochemical studies were unremarkable except a low serum alkaline phosphatase level. His bone pain resolved completely after 9 months of low-dose IV pamidronate. An increase in trans-iliac trabecular number and shortened tibia were the main skeletal features in this patient. Short-term IV pamidronate was effective for mitigating bone pain, allowing this boy to continue receiving dasatinib without the need for chronic NSAID therapy.

Can therapeutic drug monitoring increase the safety of Imatinib in GIST patients?

Imatinib at 400 mg daily is the standard treatment for patients affected with CML and GIST. The intervariability in plasma concentration is very significant. In many reports, a good therapeutic effect is attributed to an adequate concentration of Imatinib. However, few studies have been conducted to investigate the association between plasma concentration and side effects. Besides, no upper concentration limit of Imatinib plasma concentration detection has been established. The correlation of Imatinib trough concentrations (Cmin ) with adverse effects (AEs) was described here. Plasma samples were obtained from patients after 3 months treatment with Imatinib (steady state, n = 122). Liquid chromatography/ tandem mass spectrometry was used to determine the concentration of Imatinib and its metabolite NDI. The incidence of myelosuppression was increased significantly with the increased Imatinib trough plasma concentration. The plasma level of Imatinib and NDI in patients who developed myelosuppression are 1698.3 ± 598.6 ng/mL and 242.1 ng/mL, respectively, which were significantly higher than those in patients who did not (1327.2 ± 623.4 ng/mL, P = 1.75 × 10-4 ; 206.3 ng/mL, P = 0.006). Estimated exposure thresholds of Imatinib and NDI were 1451.6 ng/mL with ROCAUC (95%CI) of 0.693 (0.597-0.789) and 207.1 ng/mL with ROCAUC (95%CI) of 0.646 (0.546-0.745), respectively. Multivariate regression confirmed the correlation of Imatinib Cmin with myelosuppression. Other side effects such as fluid retention and rash were not found to be correlated with Imatinib concentrations. These results suggest that trough concentration of Imatinib should be taken into consideration to increase the safety of Imatinib therapy in GIST patients.

Early BCR-ABL1 Transcript Decline after 1 Month of Tyrosine Kinase Inhibitor Therapy as an Indicator for Treatment Response in Chronic Myeloid Leukemia

In chronic myeloid leukemia (CML), early treatment prediction is important to identify patients with inferior overall outcomes. We examined the feasibility of using reductions in BCR-ABL1 transcript levels after 1 month of tyrosine kinase inhibitor (TKI) treatment to predict therapy response. Fifty-two first-line TKI-treated CML patients were included (imatinib n = 26, dasatinib n = 21, nilotinib n = 5), and BCR-ABL1 transcript levels were measured at diagnosis (dg) and 1, 3, 6, 12, 18, 24, and 36 months. The fold change of the BCR-ABL1 transcripts at 1 month compared to initial BCR-ABL1 transcript levels was used to indicate early therapy response. In our cohort, 21% of patients had no decrease in BCR-ABL1 transcript levels after 1 month and were classified as poor responders. Surprisingly, these patients had lower BCR-ABL1 transcript levels at dg compared to responders (31% vs. 48%, p = 0.0083). Poor responders also significantly more often had enlarged spleen (55% vs. 15%; p<0.01) and a higher percentage of Ph+ CD34+CD38- cells in the bone marrow (91% vs. 75%, p<0.05). The major molecular response rates were inferior in the poor responders (at 12m 18% vs. 64%, p<0.01; 18m 27% vs. 75%, p<0.01; 24m 55% vs. 87%, p<0.01). In conclusion, early treatment response analysis defines a biologically distinct patient subgroup with inferior long-term outcomes.

Rotation of nilotinib and imatinib for first-line treatment of chronic phase chronic myeloid leukemia

The introduction of second-generation tyrosine-kinase inhibitors (TKIs) has generated a lively debate on the choice of first-line TKI in chronic phase, chronic myeloid leukemia (CML). Despite the TKIs have different efficacy and toxicity profiles, the planned use of two TKIs has never been investigated. We report on a phase 2 study that was designed to evaluate efficacy and safety of a treatment alternating nilotinib and imatinib, in newly diagnosed BCR-ABL1 positive, chronic phase, CML patients. One hundred twenty-three patients were enrolled. Median age was 56 years. The probabilities of achieving a complete cytogenetic response, a major molecular response, and a deep molecular response (MR 4.0) by 2 years were 93%, 87%, and 61%, respectively. The 5-year overall survival and progression-free survival were 89%. Response rates and survival are in the range of those reported with nilotinib alone. Moreover, we observed a relatively low rate of cardiovascular adverse events (5%). These data show that the different efficacy and toxicity profiles of TKIs could be favorably exploited by alternating their use. Am. J. Hematol. 91:617-622, 2016. © 2016 Wiley Periodicals, Inc.

Simplifying procedure for prediction of resistance risk in CML patients - Test of sensitivity to TKI ex vivo

Tyrosine kinase inhibitors (TKIs) targeting BCR-ABL have dramatically improved chronic myeloid leukemia therapy. While imatinib remains to be the first line therapy, about 30% of patients develop resistance or intolerance to this drug and are recommended to switch to other TKIs. Nilotinib and dasatinib are currently implemented into the first line therapy and other inhibitors have already entered the clinical practice. This opens further questions on how to select the best TKI for each patient not only during the therapy but also at diagnosis. The individualized therapy concept requires a reliable establishment of prognosis and prediction of response to the available TKIs. We tested the ex vivo sensitivity of patient primary leukocytes to imatinib, nilotinib and dasatinib - two concentrations of each inhibitor for 48h incubation - and we evaluated the usefulness of such tests for the clinical practice. Besides reflecting the actual sensitivity to the therapy, our optimized simple tests were able to predict the outcome in 90/87% of patients, for the next 12/24months, respectively. According to these results, the presented ex vivo testing could help clinicians to select the appropriate drug for each patient at diagnosis and also at any time of the therapy.

CR-LAAO antileukemic effect against Bcr-Abl(+) cells is mediated by apoptosis and hydrogen peroxide

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of the Bcr-Abl tyrosine kinase protein, which confers resistance to apoptosis in leukemic cells. Tyrosine kinase inhibitors (TKIs) are effectively used to treat CML; however, CML patients in the advanced (CML-AP) and chronic (CML-CP) phases of the disease are usually resistant to TKI therapy. Thus, it is necessary to seek for novel agents to treat CML, such as the enzyme l-amino acid oxidase from Calloselasma rhodostoma (CR-LAAO) snake venom. We examined the antitumor effect of CR-LAAO in Bcr-Abl(+) cell lines and peripheral blood mononuclear cells (PBMC) from healthy subjects and CML patients. CR-LAAO was more cytotoxic towards Bcr-Abl(+) cell lines than towards healthy subjects' PBMC. The H2O2 produced during the enzymatic action of CR-LAAO mediated its cytotoxic effect. The CR-LAAO induced apoptosis in Bcr-Abl(+) cells, as detected by caspases 3, 8, and 9 activation, loss of mitochondrial membrane potential, and DNA damage. CR-LAAO elicited apoptosis in PBMC from CML-CP patients without TKI treatment more strongly than in PBMC from healthy subjects and TKI-treated CML-CP and CML-AP patients. The antitumor effect of CR-LAAO against Bcr-Abl(+) cells makes this toxin a promising candidate to CML therapy.

Assessment of bone marrow lymphocytic status during tyrosine kinase inhibitor therapy and its relation to therapy response in chronic myeloid leukaemia

PURPOSE

Tyrosine kinase inhibitors (TKIs) used in the treatment of chronic myeloid leukaemia have been reported to induce immunomodulatory effects. We aimed to assess peripheral blood (PB) and bone marrow (BM) lymphocyte status at the diagnosis and during different TKI therapies and correlate it with treatment responses.

METHODS

BM and PB samples were acquired from 105 first-line TKI-treated patients. Relative number of BM lymphocytes was evaluated from MGG-stained BM aspirates, and immunophenotypic analyses were performed with multicolour flow cytometry.

RESULTS

Early 3-month expansion of BM lymphocytes was found during all different TKIs (imatinib n = 71, 20 %; dasatinib n = 25, 21 %; nilotinib n = 9, 22 %; healthy controls n = 14, 12 %, p < 0.0001). Increased PB lymphocyte count was only observed during dasatinib therapy. The BM lymphocyte expansion was associated with early molecular response; patients with 3-month BCR-ABL1 <10 % showed higher lymphocyte counts than patients with BCR-ABL1 >10 % (23 vs. 17 %, p < 0.05). Detailed phenotypic analysis showed that BM lymphocyte expansion consisted of various lymphocyte subclasses, but especially the proportion of CD19+ B cells and CD3negCD16/56+ NK cells increased from diagnostic values. During dasatinib treatment, the lymphocyte balance in both BM and PB was shifted more to cytotoxic direction (increased CD8+CD57+ and CD8+HLA-DR+ cells, and low T regulatory cells), whereas no major immunophenotypic differences were observed between imatinib and nilotinib patients.

CONCLUSIONS

Early BM lymphocytosis occurs with all current first-line TKIs and is associated with better treatment responses. PB and BM immunoprofile during dasatinib treatment markedly differs from both imatinib- and nilotinib-treated patients.

Managing chronic myeloid leukaemia in the elderly with intermittent imatinib treatment

The aim of this study was to investigate the effects of a non-standard, intermittent imatinib treatment in elderly patients with Philadelphia-positive chronic myeloid leukaemia and to answer the question on which dose should be used once a stable optimal response has been achieved. Seventy-six patients aged ⩾65 years in optimal and stable response with ⩾2 years of standard imatinib treatment were enrolled in a study testing a regimen of intermittent imatinib (INTERIM; 1-month on and 1-month off). With a minimum follow-up of 6 years, 16/76 patients (21%) have lost complete cytogenetic response (CCyR) and major molecular response (MMR), and 16 patients (21%) have lost MMR only. All these patients were given imatinib again, the same dose, on the standard schedule and achieved again CCyR and MMR or an even deeper molecular response. The probability of remaining on INTERIM at 6 years was 48% (95% confidence interval 35-59%). Nine patients died in remission. No progressions were recorded. Side effects of continuous treatment were reduced by 50%. In optimal and stable responders, a policy of intermittent imatinib treatment is feasible, is successful in about 50% of patients and is safe, as all the patients who relapsed could be brought back to optimal response.

Long-term outcome of chronic myeloid leukemia patients treated frontline with imatinib

For almost 10 years imatinib has been the therapeutic standard of chronic myeloid leukemia. The introduction of other tyrosine kinase inhibitors (TKIs) raised a debate on treatment optimization. The debate is still heated: some studies have protocol restrictions or limited follow-up; in other studies, some relevant data are missing. The aim of this report is to provide a comprehensive, long-term, intention-to-treat, analysis of 559 newly diagnosed, chronic-phase, patients treated frontline with imatinib. With a minimum follow-up of 66 months, 65% of patients were still on imatinib, 19% were on alternative treatment, 12% died and 4% were lost to follow-up. The prognostic value of BCR-ABL1 ratio at 3 months (⩽10% in 81% of patients) was confirmed. The prognostic value of complete cytogenetic response and major molecular response at 1 year was confirmed. The 6-year overall survival was 89%, but as 50% of deaths occurred in remission, the 6-year cumulative incidence of leukemia-related death was 5%. The long-term outcome of first-line imatinib was excellent, also because of second-line treatment with other TKIs, but all responses and outcomes were inferior in high-risk patients, suggesting that to optimize treatment results, a specific risk-adapted treatment is needed for such patients.

A review of the European LeukemiaNet recommendations for the management of CML

Several guidelines and recommendations on the management of chronic myeloid leukemia (CML) have been prepared by several scientific societies. The European LeukemiaNet (ELN) appointed a panel of experts who submitted their recommendations to peer-reviewed scientific journals in 2006, 2009, and 2013. Here, we make a critical review of the last, 2013, ELN recommendations, concerning the use of the five available tyrosine kinase inhibitors (TKIs), the evaluation of cytogenetic and molecular response, and the strategy of treatment. Three TKIs (imatinib, nilotinib, dasatinib) are recommended first-line. Bosutinib and ponatinib are available second-line; ponatinib is particularly indicated in case of the T315I mutation. Achieving an optimal response, not only for survival but also for a deeper, stable, treatment-free remission, requires a BCR-ABL transcripts level ≤ 10 % at 3 months, ≤ 1 % at 6 months, ≤ 0.1 % at 1 year, and ≤ 0.01 % later on. Molecular monitoring must include mutational analysis in every case of failure. A successful treatment of accelerated and blastic phase requires TKIs, and in many cases also allogeneic stem cell transplantation.

Chronic myeloid leukemia in children: clinical findings, management, and unanswered questions

Chronic myelogenous leukemia (CML) is a rare disease in children. There is little evidence of biological differences between CML in children and adults, although host factors are different. Children develop distinct morbidities related to the off-target effects of tyrosine kinase inhibitors. The goal of treatment in children should be cure rather than suppression of disease, which can be the treatment goal for many older adults. This article reviews data from the literature on the treatment of CML, discusses the issues that are unique to CML in children, and recommends management that takes these issues into consideration.

Resistant mutations in CML and Ph(+)ALL - role of ponatinib

In 2012, ponatinib (Iclusig^®), an orally available pan-BCR-ABL tyrosine kinase inhibitor (TKI) developed by ARIAD Pharmaceuticals, Inc., was approved by the US Food and Drug Administration for use in resistant or intolerant chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ALL). Ponatinib is the only approved TKI capable of inhibiting BCR-ABL with the gatekeeper T315I kinase domain mutation, known to be the cause for 20% of resistant or relapsed CML cases. In 2013, ponatinib sales were temporarily suspended due to serious side effects seen in nearly 12% of the patient population. These side effects are thought to stem from the potent nature and pan-activity of this TKI. ARIAD Pharmaceuticals, Inc. has since been permitted to resume sales and marketing of ponatinib to a limited patient population with an expanded black box warning. In the following review, the use of ponatinib in CML and Ph⁺ALL will be discussed. Mechanisms of resistance in CML are discussed, which provide insight and background into the need for this third generation TKI, followed by the molecular design and pharmacology of ponatinib, which lead to its success as a therapeutic. Finally, the efficacy, safety, and tolerability of ponatinib will be highlighted, including summaries of the important clinical trials involving ponatinib as well as its current place in therapy.

Clinical usefulness of therapeutic concentration monitoring for imatinib dosage individualization: results from a randomized controlled trial

PURPOSE

This study assessed whether a cycle of "routine" therapeutic drug monitoring (TDM) for imatinib dosage individualization, targeting an imatinib trough plasma concentration (C min) of 1,000 ng/ml (tolerance: 750-1,500 ng/ml), could improve clinical outcomes in chronic myelogenous leukemia (CML) patients, compared with TDM use only in case of problems ("rescue" TDM).

METHODS

Imatinib concentration monitoring evaluation was a multicenter randomized controlled trial including adult patients in chronic or accelerated phase CML receiving imatinib since less than 5 years. Patients were allocated 1:1 to "routine TDM" or "rescue TDM." The primary endpoint was a combined outcome (failure- and toxicity-free survival with continuation on imatinib) over 1-year follow-up, analyzed in intention-to-treat (ISRCTN31181395).

RESULTS

Among 56 patients (55 evaluable), 14/27 (52 %) receiving "routine TDM" remained event-free versus 16/28 (57 %) "rescue TDM" controls (P = 0.69). In the "routine TDM" arm, dosage recommendations were correctly adopted in 14 patients (median C min: 895 ng/ml), who had fewer unfavorable events (28 %) than the 13 not receiving the advised dosage (77 %; P = 0.03; median C min: 648 ng/ml).

CONCLUSIONS

This first target concentration intervention trial could not formally demonstrate a benefit of "routine TDM" because of small patient number and surprisingly limited prescriber's adherence to dosage recommendations. Favorable outcomes were, however, found in patients actually elected for target dosing. This study thus shows first prospective indication for TDM being a useful tool to guide drug dosage and shift decisions. The study design and analysis provide an interesting paradigm for future randomized TDM trials on targeted anticancer agents.

Autophagy contributes to dasatinib-induced myeloid differentiation of human acute myeloid leukemia cells

A breakthrough in clinical oncology was achieved as All-trans-retinoic acid (ATRA) sparked intensive differentiation therapy research. However, differentiation therapy is limited because ATRA is the sole efficient agent. Dasatinib is reported to induce myeloid differentiation of acute myeloid leukemia (AML) cells in vitro, but its mechanism remains unclear. Furthermore, the ability of dasatinib to cause differentiation of AML cells has not yet been proven. We assessed the contribution of autophagy to dasatinib-induced differentiation of AML cells. We found that dasatinib induces myeloid differentiation of AML cells accompanied with autophagy induction. Pharmacological inhibition of autophagy by 3-MA, Wortmannin, LY294002 and chloroquine block dasatinib-induced AML cell differentiation, whereas the induction of autophagy by rapamycin enhances AML cell differentiation. Our results suggest that retinoic acid receptors alpha (RARα) may not be involved in dasatinib-induced differentiation. In addition, we further illustrated that even low concentration of dasatinib can enhance ATRA-induced differentiation capability through initiation of autophagy. Taken together, we conclude that autophagy enhances the dasatinib-induced differentiation, which may provide theoretical support for developing dasatinib as a promising strategy for future differentiation therapy in AML patients.

Proliferation and survival signaling from both Jak2-V617F and Lyn involving GSK3 and mTOR/p70S6K/4EBP1 in PVTL-1 cell line newly established from acute myeloid leukemia transformed from polycythemia vera

The gain of function mutation JAK2-V617F is very frequently found in myeloproliferative neoplasms (MPNs) and is strongly implicated in pathogenesis of these and other hematological malignancies. Here we report establishment of a new leukemia cell line, PVTL-1, homozygous for JAK2-V617F from a 73-year-old female patient with acute myeloid leukemia (AML) transformed from MPN. PVTL-1 is positive for CD7, CD13, CD33, CD34, CD117, HLA-DR, and MPO, and has complex karyotypic abnormalities, 44,XX,-5q,-7,-8,add(11)(p11.2),add(11)(q23),−16,+21,−22,+mar1. Sequence analysis of JAK2 revealed only the mutated allele coding for Jak2-V617F. Proliferation of PVTL-1 was inhibited and apoptosis was induced by the pan-Jak inhibitor Jak inhibitor-1 (JakI-1) or dasatinib, which inhibits the Src family kinases as well as BCR/ABL. Consistently, the Src family kinase Lyn was constitutively activated with phosphorylation of Y396 in the activation loop, which was inhibited by dasatinib but not by JakI-1. Further analyses with JakI-1 and dasatinib indicated that Jak2-V617F phosphorylated STAT5 and SHP2 while Lyn phosphorylated SHP1, SHP2, Gab-2, c-Cbl, and CrkL to induce the SHP2/Gab2 and c-Cbl/CrkL complex formation. In addition, JakI-1 and dasatinib inactivated the mTOR/p70S6K/4EBP1 pathway and reduced the inhibitory phosphorylation of GSK3 in PVTL-1 cells, which correlated with their effects on proliferation and survival of these cells. Furthermore, inhibition of GSK3 by its inhibitor SB216763 mitigated apoptosis induced by dasatinib but not by JakI-1. Together, these data suggest that apoptosis may be suppressed in PVTL-1 cells through inactivation of GSK3 by Lyn as well as Jak2-V617F and additionally through activation of STAT5 by Jak2-V617F. It is also speculated that activation of the mTOR/p70S6K/4EBP1 pathway may mediate proliferation signaling from Jak2-V617F and Lyn. PVTL-1 cells may provide a valuable model system to elucidate the molecular mechanisms involved in evolution of Jak2-V617F-expressing MPN to AML and to develop novel therapies against this intractable condition.

Treatment recommendations for chronic myeloid leukemia

The first treatment of chronic myeloid leukemia (CML) included spleen x-radiation and conventional drugs, mainly Busulfan and Hydroxyurea. This therapy improved the quality of life during the chronic phase of the disease, without preventing nor significantly delaying the progression towards advanced phases. The introduction of allogeneic stem cell transplantation (alloSCT) marked the first important breakthrough in the evolution of CML treatment, because about 50% of the eligible patients were cured. The second breakthrough was the introduction of human recombinant interferon-alfa, able to achieve a complete cytogenetic remission in 15% to 30% of patients, with a significant survival advantage over conventional chemotherapy. At the end of the last century, about 15 years ago, all these treatments were quickly replaced by a class of small molecules targeting the tyrosine kinases (TK), which were able to induce a major molecular remission in most of the patients, without remarkable side effects, and a very prolonged life-span. The first approved TK inhibitor (TKI) was Imatinib Mesylate (Glivec or Gleevec, Novartis). Rapidly, other TKIs were developed tested and commercialized, namely Dasatinib (Sprycel, Bristol-Myers Squibb), Nilotinib (Tasigna, Novartis), Bosutinib (Busulif, Pfizer) and Ponatinib (Iclusig, Ariad). Not all these compounds are available worldwide; some of them are approved only for second line treatment, and the high prices are a problem that can limit their use. A frequent update of treatment recommendations is necessary. The current treatment goals include not only the prevention of the transformation to the advanced phases and the prolongation of survival, but also a length of survival and of a quality of life comparable to that of non-leukemic individuals. In some patient the next ambitious step is to move towards a treatment-free remission. The CML therapy, the role of alloSCT and the promising experimental strategies are reviewed in the context of the new therapeutic goals.

A critical history of chromic myeloid leukemia

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Excellent therapeutic results achieved in chronic myeloid leukemia patients with front-line imatinib and early treatment modifications in suboptimal responders: a retrospective study on 91 unselected patients

Second generation tyrosine kinase-inhibitors (TKI) have been claimed to represent now the first-choice therapy for chronic myeloid leukemia (CML). Indeed, they generally induce faster and deeper molecular responses compared to imatinib that, however, is equally effective in at least 50% of patients. Moreover, some recent reports have questioned the long term safety of dasatinib and nilotinib. Therefore, upfront imatinib with early shift to second generation TKI for patients with slow/incomplete response might be as effective as front-line second generation TKI, with a possibly better safety profile. We retrospectively evaluated 91 chronic phase CML patients (median follow-up 57 months, median age 61 years), treated front-line with standard-dose imatinib and early therapy modifications (at 3-12 months) in case of unsatisfactory response or intolerance. Thirty-three patients (24 with unsatisfactory response, 9 intolerant) changed therapy, either by increasing imatinib dose (11/91) or by switching to second generation TKI (22 directly, 4 after high-dose imatinib). Globally, our strategy led to complete cytogenetic response (CCyR) in 98% of the patients, major molecular response (MMR) in 88% and molecular response 4 logs (MR(4.0) ) in 62%. Three patients in CCyR (3%), 2 of them in MMR too, suddenly progressed to blastic phase. At the last follow-up nine patients had died, seven of CML-unrelated causes and two only of CML progression. These results suggest that our strategy could be as effective as front line second generation TKI, with most of patients still receiving imatinib, a drug of better known long-term side effects and lower cost.

Multidomain targeting of Bcr-Abl by disruption of oligomerization and tyrosine kinase inhibition: toward eradication of CML

The oncoprotein Bcr-Abl, the causative agent of chronic myeloid leukemia (CML), requires homo-oligomerization via a coiled-coil domain to function [Bartram, C. R.; et al. Nature 1983, 306 (5940), 277-280; and Zhao, X.; et al. Nat. Struct. Biol. 2002, 9(2), 117-120]. While tyrosine kinase inhibitors (TKIs) have shown great efficacy as treatment options for CML, their use may cause an acquisition of mutations in the tyrosine kinase domain, which prevent TKI binding and lead to a loss in activity [Woessner, D. W.; et al. Cancer J. 2011, 17(6), 477-486]. Previously, we have shown that a rationally modified coiled-coil domain (CC(mut3)) can disrupt this oligomerization, inhibit proliferation, and induce apoptosis in CML cells [Dixon, A. S.; et al. Mol. Pharmaceutics 2012, 9(1), 187-195]. Here, we show that using the most recently approved TKI, ponatinib (Iclusig), in combination with CC(mut3) allows a dose reduction of ponatinib and increased therapeutic efficacy in vitro measured by reduction in kinase activity, induction of apoptosis via caspase-3/7 and 7-AAD/Annexin V assays, and reduced transformative ability measured by a colony forming assay. The combination was effective not only in cells containing wild-type Bcr-Abl (K562, Ba/F3-p210) but also cells with Bcr-Abl containing the T315I mutation (Ba/F3-p210-T315I). In addition, we report for the first time the ability of CC(mut3) alone to inhibit the T315I mutant form of Bcr-Abl. This novel combination may prove to be more potent than single agent therapies and should be further explored for clinical use.

European LeukemiaNet recommendations for the management of chronic myeloid leukemia: 2013

Advances in chronic myeloid leukemia treatment, particularly regarding tyrosine kinase inhibitors, mandate regular updating of concepts and management. A European LeukemiaNet expert panel reviewed prior and new studies to update recommendations made in 2009. We recommend as initial treatment imatinib, nilotinib, or dasatinib. Response is assessed with standardized real quantitative polymerase chain reaction and/or cytogenetics at 3, 6, and 12 months. BCR-ABL1 transcript levels ≤10% at 3 months, <1% at 6 months, and ≤0.1% from 12 months onward define optimal response, whereas >10% at 6 months and >1% from 12 months onward define failure, mandating a change in treatment. Similarly, partial cytogenetic response (PCyR) at 3 months and complete cytogenetic response (CCyR) from 6 months onward define optimal response, whereas no CyR (Philadelphia chromosome-positive [Ph+] >95%) at 3 months, less than PCyR at 6 months, and less than CCyR from 12 months onward define failure. Between optimal and failure, there is an intermediate warning zone requiring more frequent monitoring. Similar definitions are provided for response to second-line therapy. Specific recommendations are made for patients in the accelerated and blastic phases, and for allogeneic stem cell transplantation. Optimal responders should continue therapy indefinitely, with careful surveillance, or they can be enrolled in controlled studies of treatment discontinuation once a deeper molecular response is achieved.

NUP214-ABL1-mediated cell proliferation in T-cell acute lymphoblastic leukemia is dependent on the LCK kinase and various interacting proteins

The NUP214-ABL1 fusion protein is a constitutively active protein tyrosine kinase that is found in 6% of patients with T-cell acute lymphoblastic leukemia and that promotes proliferation and survival of T-lymphoblasts. Although NUP214-ABL1 is sensitive to ABL1 kinase inhibitors, development of resistance to these compounds is a major clinical problem, underlining the need for additional drug targets in the sparsely studied NUP214-ABL1 signaling network. In this work, we identify and validate the SRC family kinase LCK as a protein whose activity is absolutely required for the proliferation and survival of T-cell acute lymphoblastic leukemia cells that depend on NUP214-ABL1 activity. These findings underscore the potential of SRC kinase inhibitors and of the dual ABL1/SRC kinase inhibitors dasatinib and bosutinib for the treatment of NUP214-ABL1-positive T-cell acute lymphoblastic leukemia. In addition, we used mass spectrometry to identify protein interaction partners of NUP214-ABL1. Our results strongly support that the signaling network of NUP214-ABL1 is distinct from that previously reported for BCR-ABL1. Moreover, we found that three NUP214-ABL1-interacting proteins, MAD2L1, NUP155, and SMC4, are strictly required for the proliferation and survival of NUP214-ABL1-positive T-cell acute lymphoblastic leukemia cells. In conclusion, this work identifies LCK, MAD2L1, NUP155 and SMC4 as four new potential drug targets in NUP214-ABL1-positive T-cell acute lymphoblastic leukemia.

MEK/ERK dependent activation of STAT1 mediates dasatinib-induced differentiation of acute myeloid leukemia

Dasatinib (BMS-354825) is a FDA-approved multitargeted kinase inhibitor of BCR/ABL and Src kinases. It is now used in the treatment of chronic myelogenous leukemia (CML) with resistance or intolerance to prior therapies, including imatinib. Here we report a novel effect of dasatinib on inducing the differentiation of acute myeloid leukemia (AML) cells through MEK/ERK-dependent activation of signal transducer and activator of transcription 1 (STAT1). We found that dasatinib could induce the differentiation of AML cells as demonstrated by the expression of differentiation marker CD11b, G0/G1 phase arrest and decreased ratio of nucleus to cytoplasm. Of note, dasatinib induced robust phosphorylation of STAT1 both at Tyr701 and Ser727 as well as the redistribution of STAT1 from the cytoplasm to the nucleus, thus leading to the transcription of STAT1-targeted genes. Knocking down STAT1 expression by shRNA significantly attenuated dasatinib-induced differentiation, indicating an important role of STAT1 in myeloid maturation. We further found that dasatinib-induced activation of STAT1 was regulated by the MEK/ERK kinases. The phosporylation of MEK and ERK occurred rapidly upon dasatinib treatment and increased progressively as differentiation was induced. MEK inhibitors PD98059 and U0216 not only inhibited the phosphorylation of STAT1, but also abrogated dasatinib-induced myeloid differentiation, suggesting that MEK/ERK dependent phosphorylation of STAT1 might be indispensable for the differentiating effect of dasatinib in AML cells. Taken together, our study suggests that STAT1 is an important mediator in dasatinib-induced differentiation of AML cells, whose activation requires the activation of MEK/ERK cascades.

Impact of malignant stem cell burden on therapy outcome in newly diagnosed chronic myeloid leukemia patients

Chronic myeloid leukemia (CML) stem cells appear resistant to tyrosine kinase inhibitors (TKIs) in vitro, but their impact and drug sensitivity in vivo has not been systematically assessed. We prospectively analyzed the proportion of Philadelphia chromosome-positive leukemic stem cells (LSCs, Ph+CD34+CD38-) and progenitor cells (LPCs, Ph+CD34+CD38+) from 46 newly diagnosed CML patients both at the diagnosis and during imatinib or dasatinib therapy (ClinicalTrials.gov NCT00852566). At diagnosis, the proportion of LSCs varied markedly (1-100%) between individual patients with a significantly lower median value as compared with LPCs (79% vs 96%, respectively, P=0.0001). The LSC burden correlated with leukocyte count, spleen size, hemoglobin and blast percentage. A low initial LSC percentage was associated with less therapy-related hematological toxicity and superior cytogenetic and molecular responses. After initiation of TKI therapy, the LPCs and LSCs rapidly decreased in both therapy groups, but at 3 months time point the median LPC level was significantly lower in dasatinib group compared with imatinib patients (0.05% vs 0.68%, P=0.032). These data detail for the first time the prognostic significance of the LSC burden at diagnosis and show that in contrast to in vitro data, TKI therapy rapidly eradicates the majority of LSCs in patients.

Rapid mobilization of cytotoxic lymphocytes induced by dasatinib therapy

Tyrosine kinase inhibitors (TKIs) have potent effects on malignant cells, and they also target kinases in normal cells, which may have therapeutic implications. Using a collection of 55 leukemia patients treated with TKI therapy (chronic myeloid leukemia, n=47; acute lymphoblastic leukemia, n=8), we found that dasatinib, a second-generation broad-spectrum TKI, induced a rapid, dose-dependent and substantial mobilization of non-leukemic lymphocytes and monocytes in blood peaking 1-2 h after an oral intake and the blood counts closely mirrored drug plasma concentration. A preferential mobilization was observed for natural killer (NK), NK T, B and γδ+ T cells. Mobilization was coupled with a more effective transmigration of leukocytes through an endothelial cell layer and improved cytotoxicity of NK cells. Platelet numbers decreased markedly after the drug intake in a proportion of patients. Similar effects on blood cell dynamics and function were not observed with any other TKI (imatinib, nilotinib and bosutinib). Thus, dasatinib induces a unique, rapid mobilization and activation of cytotoxic, extravasation-competent lymphocytes, which may not only enhance antileukemia immune responses but can also be causally related to the side-effect profile of the drug (pleural effusions, thrombocytopenia).

Stem cell persistence in chronic myeloid leukemia

Tyrosine kinase inhibitors (TKIs) of BCR-ABL have turned chronic myeloid leukemia (CML) from a deadly disease into a chronic ailment. Unfortunately, evidence is accumulating that TKIs are not curative, since CML stem cells are not addicted to BCR-ABL, and persist despite TKI therapy. On closer view this is not surprising, as it reflects fundamental principles of CML pathogenesis. Strategies to eradicate CML stem cells will most likely be based on synthetic lethality though parallel inhibition of BCR-ABL and other critical pathways.

Natural killer cell mediated missing-self recognition can protect mice from primary chronic myeloid leukemia in vivo

Background

Natural Killer (NK) cells are thought to protect from residual leukemic cells in patients receiving stem cell transplantation. However, multiple retrospective analyses of patient data have yielded conflicting conclusions regarding a putative role of NK cells and the essential NK cell recognition events mediating a protective effect against leukemia. Further, a NK cell mediated protective effect against primary leukemia in vivo has not been shown directly.

Methodology/Principal Findings

Here we addressed whether NK cells have the potential to control chronic myeloid leukemia (CML) arising based on the transplantation of BCR-ABL1 oncogene expressing primary bone marrow precursor cells into lethally irradiated recipient mice. These analyses identified missing-self recognition as the only NK cell-mediated recognition strategy, which is able to significantly protect from the development of CML disease in vivo.

Conclusion

Our data provide a proof of principle that NK cells can control primary leukemic cells in vivo. Since the presence of NK cells reduced the abundance of leukemia propagating cancer stem cells, the data raise the possibility that NK cell recognition has the potential to cure CML, which may be difficult using small molecule BCR-ABL1 inhibitors. Finally, our findings validate approaches to treat leukemia using antibody-based blockade of self-specific inhibitory MHC class I receptors.