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This final analysis from the phase 4 BYOND trial reports outcomes with bosutinib in patients with previously treated chronic myeloid leukemia (CML); 163 patients with CML resistant/intolerant to previous tyrosine kinase inhibitors received bosutinib (starting dose: 500 mg QD). At study completion (median follow-up, 47.8 months), 48.1% (n = 75/156) of patients with Philadelphia chromosome-positive chronic phase CML were still receiving treatment. Among evaluable patients, 71.8% (95% CI, 63.9-78.9) and 59.7% (95% CI, 51.4-67.7) attained or maintained major molecular response (MMR) and molecular response (MR) 4 , respectively, at any time on treatment. The majority of patients achieved a deeper molecular response relative to baseline while on bosutinib. Kaplan-Meier probabilities (95% CI) of maintaining MMR and MR 4 at 36 months were 87.2% (78.0-92.7) and 80.7% (69.4-88.1), respectively. At 48 months, the Kaplan-Meier overall survival rate was 88.3% (95% CI, 81.8-92.6); there were 17 deaths, including 2 that were considered CML related. Long-term adverse events (AEs) were consistent with the known safety profile of bosutinib, and no new safety issues were identified. The management of AEs through dose reduction maintained efficacy while improving tolerability. These results support the use of bosutinib in patients with previously treated CML.ClinicalTrials.gov, NCT02228382., (© 2024. The Author(s).)

Bosutinib is a second-generation tyrosine kinase inhibitor indicated for the treatment of patients with newly diagnosed Philadelphia chromosome-positive chronic phase chronic myeloid leukemia (CML), and for patients with Ph + chronic phase, accelerated phase, or blast phase CML resistant or intolerant to prior therapy. As is the case for all TKIs approved for treatment of CML, bosutinib is associated with adverse events (AEs) that require appropriate management to ensure adherence to treatment and optimized outcomes. The aim of this review is to provide physicians with updated practical information for the prevention and management of AEs occurring during treatment with bosutinib, including dosing strategies, based on the latest published evidence and clinical experience. Clinical studies and real-world evidence have shown bosutinib has a generally favorable safety profile, which has remained consistent across lines of therapy and in long-term reports. Adjusting the starting dose and/or modifying the dose during treatment with bosutinib are important strategies to manage AEs and improve tolerability, which are recognized within the label and in treatment guidelines. Dosing adjustment strategies to manage AEs are a recognized management approach for other TKIs in the treatment of CML and are not exclusive to bosutinib. In summary, long-term results from clinical trials and emerging real-world evidence demonstrate bosutinib has a safety profile that can largely be managed with treatment modifications and/or supportive care. Increased experience in managing toxicities and by using a personalized dosing approach may further improve adherence and outcomes with bosutinib., (© 2024. The Author(s).)

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported. The European Stop Kinase Inhibitors (EURO-SKI) study is the largest clinical trial for investigating the cessation of tyrosine kinase inhibitors (TKIs) in patients with chronic myeloid leukemia in stable deep molecular remission (DMR). Among 728 patients, 434 patients (61%; 95% CI, 57 to 64) remained in major molecular response (MMR) at 6 months and 309 patients of 678 (46%; 95% CI, 42 to 49) at 36 months. Duration of TKI treatment and DMR before TKI stop were confirmed as significant factors for the prediction of MMR loss at 6 months. In addition, the type of BCR::ABL1 transcript was identified as a prognostic factor. For late MMR losses after 6 months, TKI treatment duration, percentage of blasts in peripheral blood, and platelet count at diagnosis were significant factors in multivariate analysis. For the entire study period of 36 months, multiple logistic regression models confirmed duration of treatment, blasts, and transcript type as independent factors for MMR maintenance. In addition to the duration of treatment, transcript type as well as blasts in peripheral blood at diagnosis should be considered as important factors to predict treatment-free remission.

The development of the BCR::ABL1 tyrosine kinase inhibitors (TKIs) has transformed Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML) from a fatal disease to an often-indolent illness that, when managed effectively, can restore a life expectancy close to that of the normal population. Bosutinib is a second-generation TKI approved for adults with Ph-positive CML in chronic phase, accelerated phase, or blast phase that is resistant or intolerant to prior therapy, and for newly diagnosed Ph-positive chronic phase CML. This review details the efficacy of bosutinib for the treatment of CML in the first- and second-line settings, as well as in third- and later-line settings for high-risk patients resistant or intolerant to at least 2 TKIs. It also outlines bosutinib studies that provide evidence for dose-optimization strategies that can be used to improve efficacy and effectively manage adverse events. The studies that provide evidence for specific patient populations benefiting particularly from bosutinib dose-optimization strategies are also discussed. The well-established, long-term side-effect profile and the potential to make dose adjustments with bosutinib make it an appropriate treatment option for patients with CML. Bosutinib has demonstrated a positive impact on health-related quality of life and an important role in the long-term treatment of patients with CML., Competing Interests: Disclosure HMK served as a consultant for AbbVie, Amgen, Amphista, Ascentage, Astellas, Biologix, Curis, Ipsen Biopharmaceuticals, KAHR Medical, Labcorp, Novartis, Pfizer, Shenzhen Target Rx, Stemline, Takeda, and has received research funding from AbbVie, Amgen, Ascentage, BMS, Daiichi-Sankyo, Immunogen, Jazz, Novartis. EJJ has received research grants and consultancy fees from Bristol Myers Squibb, Incyte, Novartis, Pfizer, and Takeda. JHL has served as a consultant for and has received research funding from Bristol Myers Squibb, Novartis, Pfizer, and Takeda, and has received honoraria from Bristol Myers Squibb, Incyte, Novartis, Pfizer, and Takeda. FC has received honoraria from Bristol Myers Squibb, Incyte, Novartis, and Pfizer. THB has been a consultant for Gilead, Janssen, Merck, Novartis, and Pfizer, and has received research support from Novartis and Pfizer., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The introduction of orally available tyrosine kinase inhibitors (TKI) into the treatment of chronic myeloid leukemia (CML) 25 years ago has substantially improved the clinical outcome of affected patients and resulted in a near-normal life expectancy in chronic phase (CP). Despite of a significant fraction of currently about one third of newly diagnosed CP patients eventually reaching treatment-free remission, the majority of patients still remain on life-long treatment with TKIs. Therefore, a profound knowledge of TKI-related side effects including an increased sensitivity for organ systems predominantly involved, grading, kinetics, duration and reversibility, class-effects versus compound-relatedness as well as a better understanding of how particularly long-lasting, chronic, sometimes formally low-grade toxicities can actually significantly impair patient's self-assessed quality of life is of utmost importance for an adequate patient/doctor relationship. Given that nowadays, severity and degree of preexisting comorbidities might predict long-term survival of individual patients more significantly than the underlying CML itself, it becomes most important to properly and thoroughly select the TKI of choice on this basis as well as on the individually required co-medications. Given the variety of 2nd, 3rd and now allosteric TKIs available for the molecular targeting of the disease-driving BCR-ABL oncogene in addition to the "class-defining" Imatinib, personalization of CML therapy should now be further extended towards a better appreciation of comorbidities and co-medications before selection of an individual's TKI treatment complemented by a long-term oriented, patient-centered management and prevention of (sometimes irreversible) TKI side effects., Competing Interests: TB erhielt Honorare von Janssen, Novartis, Pfizer, Merck, Takepart Media; er hielt Vorträge und/oder war als Berater tätig für Pfizer, Novartis und Merck. Er erhielt Forschungsunterstützung von Novartis, Pfizer, Repeat Diagnostics. MC erhielt Honorare im Rahmen von Vorträgen und Beratertätigkeiten von Incyte, Pfizer und Novartis, sowie Unterstützung von Dienstreisen von Pfizer und Jazz Pharmaceuticals., (Thieme. All rights reserved.)

Bosutinib is approved in the United States, Europe, Japan, and other countries for treatment of newly diagnosed chronic phase (CP) chronic myeloid leukemia (CML), and CML resistant/intolerant to prior therapy. In the phase 3 BFORE trial (Clinicaltrials.gov, NCT02130557), patients were randomized 1:1 to first-line bosutinib or imatinib 400 mg once daily. We examined efficacy, safety, and patient-reported outcomes of bosutinib vs imatinib and pharmacokinetics of bosutinib in the Asian (n = 33 vs 34) and non-Asian (n = 235 vs 234) subpopulations of BFORE followed for at least 24 months. At the data cutoff date, 72.7 vs 66.7% of Asian and 70.6 vs 66.4% of non-Asian patients remained on treatment. The major molecular response rate at 24 months favored bosutinib vs imatinib among Asian (63.6 vs 38.2%) and non-Asian (60.9 vs 52.6%) patients, as did the complete cytogenetic response rate by 24 months (86.7 vs 76.7%, 81.5 vs 76.3%). Treatment-emergent adverse events in both subpopulations were consistent with the primary BFORE results. Trough bosutinib concentration levels tended to be higher in Asian patients. Health-related quality of life was maintained after 12 months of bosutinib in both subpopulations. These results support bosutinib as a first-line treatment option in Asian patients with CP CML.

Despite the successes achieved with molecular targeted inhibition of the oncogenic driver Bcr-Abl in chronic myeloid leukemia (CML), the majority of patients still require lifelong tyrosine kinase inhibitor (TKI) therapy. This is primarily caused by resisting leukemic stem cells (LSCs), which prevent achievement of treatment-free remission in all patients. Here we describe the ITIM (immunoreceptor tyrosine-based inhibition motif)-containing Fc gamma receptor IIb (FcγRIIb, CD32b) for being critical in LSC resistance and show that targeting FcγRIIb downstream signaling, by using a Food and Drug Administration-approved BTK inhibitor, provides a successful therapeutic approach. First, we identified FcγRIIb upregulation in primary CML stem cells. FcγRIIb depletion caused reduced serial re-plaiting efficiency and cell proliferation in malignant cells. FcγRIIb targeting in both a transgenic and retroviral CML mouse model provided in vivo evidence for successful LSC reduction. Subsequently, we identified BTK as a main downstream mediator and targeting the Bcr-Abl-FcγRIIb-BTK axis in primary CML CD34 + cells using ibrutinib, in combination with standard TKI therapy, significantly increased apoptosis in quiescent CML stem cells thereby contributing to the eradication of LSCs.. As a potential curative therapeutic approach, we therefore suggest combining Bcr-Abl TKI therapy along with BTK inhibition.

Hypereosinophilia (HE) is caused by a variety of disorders, ranging from parasite infections to autoimmune diseases and cancer. Only a small proportion of HE cases are clonal malignancies, and one of these, the group of eosinophilia-associated tyrosine kinase fusion-driven neoplasms, is sensitive to tyrosine kinase inhibitors, while most subtypes lack specific treatment. Eosinophil functions are highly dependent on actin polymerization, promoting priming, shape change, and infiltration of inflamed tissues. Therefore, we investigated the role of the actin-binding protein lymphocyte cytosolic protein 1 (LCP1) in malignant and nonmalignant eosinophil differentiation. We use the protein kinase C-β (PKCβ) selective inhibitor enzastaurin (Enza) to dephosphorylate and inactivate LCP1 in FIP1L1-platelet-derived growth factor receptor α (PDGFRA)-positive Eol-1 cells, and this was associated with reduced proliferation, metabolic activity, and colony formation as well as enhanced apoptosis and impaired migration. While Enza did not alter FIP1L1-PDGFRA-induced signal transducer and activator of transcription 3 (STAT3), STAT5, and ERK1/2 phosphorylation, it inhibited STAT1 Tyr701 and AKT Ser473 (but not AKT Thr308 ) phosphorylation, and short hairpin RNA knockdown experiments confirmed that this process was mediated by LCP1 and associated mammalian target of rapamycin complex 2 (mTORC2) activity loss. Homeobox protein HoxB8 immortalized murine bone marrow cells showed impaired eosinophilic differentiation upon Enza treatment or LCP1 knockdown. Furthermore, Enza treatment of primary HE samples reduced eosinophil differentiation and survival. In conclusion, our data show that HE involves active LCP1, which interacts with mTOR and triggers mTORC2 activity, and that the PKCβ inhibitor Enza as well as targeting of LCP1 may provide a novel treatment approach to hypereosinophilic disorders., (© 2019 The Authors. Molecular Carcinogenesis published by Wiley Periodicals, Inc.)

Background: Expression of Bcr-Abl in hematopoietic stem cells is sufficient to cause chronic myeloid leukemia (CML) and tyrosine kinase inhibitors (TKI) induce molecular remission in the majority of CML patients. However, the disease driving stem cell population is not fully targeted by TKI therapy, and leukemic stem cells (LSC) capable of re-inducing the disease can persist. Single-cell RNA-sequencing technology recently identified an enriched inflammatory gene signature with TNFα and TGFβ being activated in TKI persisting quiescent LSC. Here, we studied the effects of human TNFα antibody infliximab (IFX), which has been shown to induce anti-inflammatory effects in mice, combined with TKI treatment on LSC function., Methods: We first performed GSEA-pathway analysis using our microarray data of murine LSK cells (lin - ; Sca-1 + ; c-kit + ) from the SCLtTA/Bcr-Abl CML transgenic mouse model. Bcr-Abl positive cell lines were generated by retroviral transduction. Clonogenic potential was assessed by CFU (colony forming unit). CML mice were treated with nilotinib or nilotinib plus infliximab, and serial transplantation experiments were performed., Results: Likewise to human CML, TNFα signaling was specifically active in murine CML stem cells, and ectopic expression of Bcr-Abl in murine and human progenitor cell lines induced TNFα expression. In vitro exposure to human (IFX) or murine (MP6-XT22) TNFα antibody reduced clonogenic growth of CML cells. Interestingly, TNFα antibody treatment enhanced TKI-induced effects on immature cells in vitro. Additionally, in transplant and serial transplant experiments, using our transgenic CML mouse model, we could subsequently show that IFX therapy boosted TKI-induced effects and further reduced the proportion of malignant stem cells in vivo., Conclusion: TNFα signaling is induced in CML stem cells, and anti-inflammatory therapy enhances TKI-induced decline of LSC, confirming that successful targeting of persisting CML stem cells can be enhanced by addressing their malignant microenvironment simultaneously.

We evaluated pazopanib (800 mg orally QD) in patients not eligible for intensive treatment with relapsed/refractory AML or at initial diagnosis. Patients receiving pazopanib for > 14 days were analyzed for safety, tolerability, and efficacy. Co-primary endpoints were cumulative response rate and reduction of bone marrow microvessel density. Twenty patients (median age 76 years, range 52-86) were treated. Fifteen had relapsed/refractory and five had newly diagnosed AML. Median ECOG performance status was 1 (range 1-3). Four patients had adverse, 15 intermediate, and 1 patient favorable cytogenetic/molecular risk (ELN 2010 criteria). The safety profile of pazopanib was as reported. The most common adverse events of any grade were gastrointestinal. Two patients achieved PR (blast reduction > 50%), 14 stable disease (SD), and 4 progressive disease. Median PFS was 65 days (95% CI 29-105). After the end of the study, 1 CRi and 1 CRp occurred on demethylating agents, and 1 CR upon alloSCT. In these patients, SD and improved general condition on pazopanib allowed therapy escalation. Median OS for the overall study population was 191 days (95% CI 87-435) and 1-year survival was 35%. There was no significant change in microvessel density. Clinical trial information: NCT01361334.

Purpose Bosutinib is a potent dual SRC/ABL kinase inhibitor approved for adults with Philadelphia chromosome-positive chronic myeloid leukemia (CML) resistant and /or intolerant to prior therapy. We assessed the efficacy and safety of bosutinib versus imatinib for first-line treatment of chronic-phase CML. Methods In this ongoing, multinational, phase III study, 536 patients with newly diagnosed chronic-phase CML were randomly assigned 1:1 to receive 400 mg of bosutinib once daily (n = 268) or imatinib (n = 268). Per protocol, efficacy was assessed in patients who were Philadelphia chromosome-positive with typical (e13a2/e14a2) transcripts (bosutinib, n = 246; imatinib, n = 241). Patients with Philadelphia chromosome-negative-/ BCR-ABL1-positive status and those with unknown Philadelphia chromosome status and/or atypical BCR-ABL1 transcript type were excluded from this population. Results The major molecular response (MMR) rate at 12 months (primary end point) was significantly higher with bosutinib versus imatinib (47.2% v 36.9%, respectively; P = .02), as was complete cytogenetic response (CCyR) rate by 12 months (77.2% v 66.4%, respectively; P = .0075). Cumulative incidence was favorable with bosutinib (MMR: hazard ratio, 1.34; P = .0173; CCyR: hazard ratio, 1.38; P < .001), with earlier response times. Four patients (1.6%) receiving bosutinib and six patients (2.5%) receiving imatinib experienced disease progression to accelerated/blast phase. Among treated patients, 22.0% of patients receiving bosutinib and 26.8% of patients receiving imatinib discontinued treatment, most commonly for drug-related toxicity (12.7% and 8.7%, respectively). Grade ≥ 3 diarrhea (7.8% v 0.8%) and increased ALT (19.0% v 1.5%) and AST (9.7% v 1.9%) levels were more common with bosutinib. Cardiac and vascular toxicities were uncommon. Conclusion Patients who received bosutinib had significantly higher rates of MMR and CCyR and achieved responses faster than those who received imatinib. Consistent with the known safety profile, GI events and transaminase elevations were more common with bosutinib. Results indicate bosutinib may be an effective first-line treatment for chronic-phase CML.

Bosutinib is one of the five tyrosine kinase inhibitors which are currently approved for the treatment of chronic myeloid leukemia. By its dual inhibition of Src and ABL kinase and also targeting further kinases, it creates a unique target portfolio which also explains its unique side effect profile. The approval of bosutinib in 2013 made the drug available for patients previously treated with one or more tyrosine kinase inhibitor(s) and for whom imatinib, nilotinib, and dasatinib are not considered appropriate treatment options. As initially the first-line clinical trial comparing bosutinib with imatinib in CML patients in chronic phase did not reach its primary endpoint and therefore the product was not licensed for first-line therapy, a second first-line trial, the so-called BFORE study, was performed and just recently the promising results have been published predicting a quick expansion of the existing label. In comparison with the other approved TKIs, bosutinib harbors a distinct side effect profile with only very few cardiovascular and thromboembolic events and minimal long-term safety issues with most adverse events happening during the first months of treatment. On the other hand, gastrointestinal side effects are very common (e.g., diarrhea rates in more than 80% of the patients) with bosutinib surprising some of the investigators during the early clinical trials evaluating bosutinib. Until then, several approaches have been used to face this problem resulting in extensive supportive efforts (such as early loperamid treatment) as well as new trials testing alternative dosing strategies with early dose adjustment schedules. This article reports preclinical and clinical data available for bosutinib both in hematologic diseases such as CML or ALL and solid tumours as well as other diseases and envisions future perspectives including additional patient groups in which bosutinib might be of clinical benefit.

Background: The purpose of the study was to assess renal function in patients with Philadelphia chromosome-positive leukemias receiving bosutinib or imatinib., Patients and Methods: Patients received first-line bosutinib (n = 248) or imatinib (n = 251; phase III trial), or second-line or later bosutinib (phase I/II trial; n = 570). Adverse events (AEs) and changes from baseline in estimated glomerular filtration rate (eGFR) and serum creatinine were assessed., Results: Time from the last patient's first dose to data cutoff was ≥ 48 months. Renal AEs were reported in 73/570 patients (13%) receiving second-line or later bosutinib, and in 22/248 (9%) and 16/251 (6%) receiving first-line bosutinib and imatinib, respectively. eGFR in patients receiving bosutinib declined over time with more patients developing Grade ≥ 3b eGFR (< 45 mL/min/1.73 m 2 according to the Modification of Diet in Renal Disease method) with second-line or later bosutinib (139/570, 24%) compared with first-line bosutinib (26/248, 10%) and imatinib (25/251, 10%); time to Grade ≥ 3b eGFR was shortest with second-line or later bosutinib. Similar proportions of patients receiving second-line or later bosutinib (74/139, 53%), first-line bosutinib (15/26, 58%), and first-line imatinib (15/25, 60%) improved to ≥ 45 mL/min/1.73 m 2 eGFR as of the last follow-up. In a regression analysis, first-line treatment with bosutinib versus imatinib was not a significant predictor of Grade ≥ 3b eGFR., Conclusion: Long-term bosutinib treatment is associated with an apparently reversible decline in renal function with frequency and characteristics similar to renal decline observed with long-term imatinib treatment. Patients with risk factors for Grade ≥ 3b eGFR should be monitored closely., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Purpose: Tyrosine kinase inhibitors (TKIs) have well-characterized immunomodulatory effects on T and NK cells, but the effects on the humoral immunity are less well known. In this project, we studied TKI-induced changes in B cell-mediated immunity., Methods: We collected peripheral blood (PB) and bone marrow (BM) samples from chronic myeloid leukemia (CML) patients before and during first-line imatinib (n = 20), dasatinib (n = 16), nilotinib (n = 8), and bosutinib (n = 12) treatment. Plasma immunoglobulin levels were measured, and different B cell populations in PB and BM were analyzed with flow cytometry., Results: Imatinib treatment decreased plasma IgA and IgG levels, while dasatinib reduced IgM levels. At diagnosis, the proportion of patients with IgA, IgG, and IgM levels below the lower limit of normal (LLN) was 0, 11, and 6% of all CML patients, respectively, whereas at 12 months timepoint the proportions were 6% (p = 0.13), 31% (p = 0.042) and 28% (p = 0.0078). Lower initial Ig levels predisposed to the development of hypogammaglobulinemia during TKI therapy. Decreased Ig levels in imatinib-treated patients were associated with higher percentages of immature BM B cells. The patients, who had low Ig levels during the TKI therapy, had significantly more frequent minor infections during the follow-up compared with the patients with normal Ig values (33% vs. 3%, p = 0.0016). No severe infections were reported, except recurrent upper respiratory tract infections in one imatinib-treated patient, who developed severe hypogammaglobulinemia., Conclusions: TKI treatment decreases plasma Ig levels, which should be measured in patients with recurrent infections.

Purpose: Achievement of deep molecular response with a tyrosine kinase inhibitor in patients with chronic myeloid leukemia (CML) is required to attempt discontinuation of therapy in these patients. The current subanalysis from the Evaluating Nilotinib Efficacy and Safety in Clinical Trials as First-Line Treatment (ENEST1st) study evaluated whether age has an impact on the achievement of deeper molecular responses or safety with frontline nilotinib in patients with CML., Methods: ENEST1st is an open-label, multicenter, single-arm, prospective study of nilotinib 300 mg twice daily in patients with newly diagnosed CML in chronic phase. The patients were stratified into the following 4 groups based on age: young (18-39 years), middle age (40-59 years), elderly (60-74 years), and old (≥75 years). The primary end point was the rate of molecular response 4 ([MR 4 ] BCR-ABL1 ≤0.01% on the international scale) at 18 months from the initiation of nilotinib., Results: Of the 1091 patients enrolled, 1089 were considered in the analysis, of whom, 23% (n = 243), 45% (n = 494), 27% (n = 300), and 5% (n = 52) were categorized as young, middle age, elderly, and old, respectively. At 18 months, the rates of MR 4 were 33.9% (95% confidence interval [CI], 27.8-40.0%) in the young, 39.6% (95% CI, 35.3-44.0%) in the middle-aged, 40.5% (95% CI, 34.8-46.1%) in the elderly, and 35.4% (95% CI, 21.9-48.9%) in the old patients. Although the incidence of adverse events was slightly different, no new specific safety signals were observed across the 4 age groups., Conclusions: This subanalysis of the ENEST1st study showed that age did not have a relevant impact on the deep molecular response rates associated with nilotinib therapy in newly diagnosed patients with CML and eventually on the eligibility of the patients to attempt treatment discontinuation.

The second generation tyrosine kinase inhibitor (TKI) dasatinib is a clinically approved drug for chronic myeloid leukemia (CML) as well as Ph+ acute lymphoblastic leukemia. In addition to its antileukemic effects, dasatinib was shown to impact on normal hematopoiesis and cells of the immune system.Due to the fact that the murine in vivo studies so far have not been performed in a chronic-phase CML model under steady-state conditions, our aim was to study the hematopoietic effects of dasatinib (20 mg/kg p.o.) in BCR-ABL expressing SCLtTAxBCR-ABL double transgenic (dtg) mice. Dasatinib robustly antagonized the CML phenotype in vivo in our transgenic mouse model, and this effect included both mature and immature cell populations. However, similar to patients with CML, the fraction of LinnegSca-1+KIT+CD48negCD150+ hematopoietic stem cells was not reduced by dasatinib treatment, suggesting that these cells are not oncogene-addicted. Moreover, we observed differential effects of dasatinib in these animals as compared to wild-type (wt) animals: while granulocytes were significantly reduced in dtg animals, they were increased in wt mice. And Ter119+ erythrocytic and B220+ B cells were increased in dtg mice but decreased in wt mice. Finally, while dasatinib induced a shift from CD49b/NK1.1 positive NK cells from the bone marrow to the spleen in wt animals, there was no change in dtg mice. In conclusion, the present mouse model provides a useful tool to study mechanisms of TKI resistance and dasatinib-associated beneficial effects and adverse events.

Treatment of chronic myeloid leukemia (CML) has been profoundly improved by the introduction of tyrosine kinase inhibitors (TKIs). Long-term survival with imatinib is excellent with a 8-year survival rate of ∼88%. Long-term toxicity of TKI treatment, especially carcinogenicity, has become a concern. We analyzed data of the CML study IV for the development of secondary malignancies. In total, 67 secondary malignancies were found in 64 of 1525 CML patients in chronic phase treated with TKI (n=61) and interferon-α only (n=3). The most common malignancies (n⩾4) were prostate, colorectal and lung cancer, non-Hodgkin's lymphoma (NHL), malignant melanoma, non-melanoma skin tumors and breast cancer. The standardized incidence ratio (SIR) for all malignancies excluding non-melanoma skin tumors was 0.88 (95% confidence interval (0.63-1.20)) for men and 1.06 (95% CI 0.69-1.55) for women. SIRs were between 0.49 (95% CI 0.13-1.34) for colorectal cancer in men and 4.29 (95% CI 1.09-11.66) for NHL in women. The SIR for NHL was significantly increased for men and women. An increase in the incidence of secondary malignancies could not be ascertained. The increased SIR for NHL has to be considered and long-term follow-up of CML patients is warranted, as the rate of secondary malignancies may increase over time.

The Evaluating Nilotinib Efficacy and Safety in Clinical Trials as First-Line Treatment (ENEST1st) study included 1089 patients with newly diagnosed chronic myeloid leukemia in chronic phase. The rate of deep molecular response (MR(4) (BCR-ABL1⩽0.01% on the International Scale or undetectable BCR-ABL1 with ⩾10,000 ABL1 transcripts)) at 18 months was evaluated as the primary end point, with molecular responses monitored by the European Treatment and Outcome Study network of standardized laboratories. This analysis was conducted after all patients had completed 24 months of study treatment (80.9% of patients) or discontinued early. In patients with typical BCR-ABL1 transcripts and ⩽3 months of prior imatinib therapy, 38.4% (404/1052) achieved MR(4) at 18 months. Six patients (0.6%) developed accelerated or blastic phase, and 13 (1.2%) died. The safety profile of nilotinib was consistent with that of previous studies, although the frequencies of some nilotinib-associated adverse events were lower (for example, rash, 21.4%). Ischemic cardiovascular events occurred in 6.0% of patients. Routine monitoring of lipid and glucose levels was not mandated in the protocol. These results support the use of frontline nilotinib, particularly when achievement of a deep molecular response (a prerequisite for attempting treatment-free remission in clinical trials) is a treatment goal.

Long-term efficacy and safety of bosutinib (≥4 years follow-up from last enrolled patient) were evaluated in an ongoing phase 1/2 study in the advanced leukemia cohort with prior treatment failure (accelerated-phase [AP, n = 79] chronic myeloid leukemia [CML], blast-phase [BP, n = 64] CML, acute lymphoblastic leukemia [ALL, n = 24]). Fourteen AP, 2 BP, and 1 ALL patient remained on bosutinib at 4 years (vs. 38, 8, 1 at 1 year); median (range) treatment durations: 10.2 (0.1-88.6), 2.8 (0.03-55.9), 0.97 (0.3-89.2) months. Among AP and BP patients, 57% and 28% newly attained or maintained baseline overall hematologic response (OHR); 40% and 37% attained/maintained major cytogenetic response (MCyR) by 4 years (most by 12 months). In responders at 1 versus 4 years, Kaplan-Meier (KM) probabilities of maintaining OHR were 78% versus 49% (AP) and 28% versus 19% (BP); KM probabilities of maintaining MCyR were 65% versus 49% (AP) and 21% versus 21% (BP). Most common AEs (AP, BP) were gastrointestinal (96%; 83%), primarily diarrhea (85%; 64%), which was typically low grade (maximum grade 1/2: 81%; 59%) and transient; no patient discontinued due to diarrhea. Serious AEs occurred in 44 (56%) AP and 37 (58%) BP patients, most commonly pneumonia (n = 9) for AP and pyrexia (n = 6) for BP; 11 and 13 died within 30 days of last dose (2 considered bosutinib-related [AP] per investigator). Responses were durable in ∼50% AP responders at 4 years (∼25% BP patients responded at year 1, suggesting possible bridge-to-transplant role in BP patients); toxicity was manageable., (© 2015 Wiley Periodicals, Inc.)

Bosutinib is an oral, dual SRC/ABL1 tyrosine kinase inhibitor for resistant/intolerant chronic myeloid leukaemia (CML). We assessed the efficacy and safety of bosutinib 500 mg/d (n = 250) versus imatinib 400 mg/d (n = 252) after >24 months from accrual completion in newly diagnosed chronic phase (CP)-CML (Bosutinib Efficacy and Safety in Newly Diagnosed CML trial [BELA]). Cumulative complete cytogenetic response (CCyR) rates by 24 months were similar (bosutinib, 79%; imatinib, 80%); cumulative major molecular response (MMR) rates were 59% for bosutinib and 49% for imatinib. Responses were durable; 151/197 vs. 172/204 and 125/153 vs. 117/131 responders remained on treatment and maintained CCyR and MMR, respectively. Since the 12-month primary analysis, no new accelerated-/blast-phase transformations occurred with bosutinib; four occurred with imatinib. Early response (BCR-ABL1/ABL1 ≤ 10%, 3 months) was associated with better CCyR and MMR rates by 12 and 24 months (both arms). Gastrointestinal events and liver function test elevations were more common, and neutropenia, musculoskeletal events and oedema were less common with bosutinib. Discontinuations due to adverse events were more common with bosutinib versus imatinib (most commonly alanine aminotransferase elevation: 4% vs. <1%); most occurred within the first 12 months. Cardiovascular adverse events were similar in both arms. Bosutinib continues to demonstrate good efficacy and manageable tolerability in newly diagnosed CP-CML patients., (© 2014 The Authors. British Journal of Haematology published by John Wiley & Sons Ltd.)

Resistance against tyrosine kinase inhibitors (TKIs) represents a relevant clinical problem in treatment of chronic myelogenous leukemia (CML). On the basis of their activity against the spectrum of BCR-ABL mutations that have shown to be the most prominent mechanism of resistance to imatinib, new TKIs have been classified as second generation (such as nilotinib, dasatinib and bosutinib) or third generation (also cover- ing T315I such as ponatinib) TKIs. However, mutations in BCR-ABL only account for about half of the cases of treatment failure under TKI and other mechanisms either rendering the leukemic cells still dependent of BCR-ABL activity or supporting oncogenic properties of the leukemic cells independent of BCR-ABL signaling have been identified. A detailed understanding of the different underlying resistance mechanisms will be the prerequisite to eventually overcome clinical resistance and for the successful use of tailored combinations of targeted inhibitors in the future.

Bosutinib is an oral, dual SRC/ABL tyrosine kinase inhibitor (TKI) with clinical activity in Philadelphia chromosome-positive (Ph(+)) leukemia. We assessed the safety and tolerability of bosutinib 500 mg per day in a phase 1/2 study in chronic-phase (CP) chronic myeloid leukemia (CML) or advanced Ph(+) leukemia following resistance/intolerance to imatinib and possibly other TKIs. Patient cohorts included second-line CP CML (n = 286), third-/fourth-line CP CML (n = 118), and advanced leukemia (n = 166). Median bosutinib duration was 11.1 (range, 0.03-83.4) months. Treatment-emergent adverse events (TEAEs) in each cohort were primarily gastrointestinal (diarrhea [86%/83%/74%], nausea [46%/48%/48%], and vomiting [37%/38%/43%]). Diarrhea presented early, with few (8%) patients experiencing grade 3/4 events; dose reduction due to diarrhea occurred in 6% of affected patients. Grade 3/4 myelosuppression TEAEs were reported in 41% of patients; among affected patients, 46% were managed with bosutinib interruption and 32% with dose reduction. Alanine aminotransferase elevation TEAEs occurred in 17% of patients (grade 3/4, 7%); among patients managed with dose interruption, bosutinib rechallenge was successful in 74%. Bosutinib demonstrated acceptable safety with manageable toxicities in Ph(+) leukemia. This trial (NCT00261846) was registered at www.ClinicalTrials.gov (this manuscript is based on a different data snapshot from that in ClinicalTrials.gov).

In drug discovery, the characterisation of the precise modes of action (MoA) and of unwanted off-target effects of novel molecularly targeted compounds is of highest relevance. Recent approaches for identification of MoA have employed various techniques for modeling of well defined signaling pathways including structural information, changes in phenotypic behavior of cells and gene expression patterns after drug treatment. However, efficient approaches focusing on proteome wide data for the identification of MoA including interference with mutations are underrepresented. As mutations are key drivers of drug resistance in molecularly targeted tumor therapies, efficient analysis and modeling of downstream effects of mutations on drug MoA is a key to efficient development of improved targeted anti-cancer drugs. Here we present a combination of a global proteome analysis, reengineering of network models and integration of apoptosis data used to infer the mode-of-action of various tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) cell lines expressing wild type as well as TKI resistance conferring mutants of BCR-ABL. The inferred network models provide a tool to predict the main MoA of drugs as well as to grouping of drugs with known similar kinase inhibitory activity patterns in comparison to drugs with an additional MoA. We believe that our direct network reconstruction approach, demonstrated on proteomics data, can provide a complementary method to the established network reconstruction approaches for the preclinical modeling of the MoA of various types of targeted drugs in cancer treatment. Hence it may contribute to the more precise prediction of clinically relevant on- and off-target effects of TKIs.

The success of Imatinib (IM) therapy in chronic myeloid leukemia (CML) is compromised by the development of IM resistance and by a limited IM effect on hematopoietic stem cells. Danusertib (formerly PHA-739358) is a potent pan-aurora and ABL kinase inhibitor with activity against known BCR-ABL mutations, including T315I. Here, the individual contribution of both signaling pathways to the therapeutic effect of Danusertib as well as mechanisms underlying the development of resistance and, as a consequence, strategies to overcome resistance to Danusertib were investigated. Starting at low concentrations, a dose-dependent inhibition of BCR-ABL activity was observed, whereas inhibition of aurora kinase activity required higher concentrations, pointing to a therapeutic window between the two effects. Interestingly, the emergence of resistant clones during Danusertib exposure in vitro occurred considerably less frequently than with comparable concentrations of IM. In addition, Danusertib-resistant clones had no mutations in BCR-ABL or aurora kinase domains and remained IM-sensitive. Overexpression of Abcg2 efflux transporter was identified and functionally validated as the predominant mechanism of acquired Danusertib resistance in vitro. Finally, the combined treatment with IM and Danusertib significantly reduced the emergence of drug resistance in vitro, raising hope that this drug combination may also achieve more durable disease control in vivo.

Bosutinib (SKI-606) is a 7-alkoxy-3-quinolinecarbonitrile, which functions as a dual inhibitor of Src and Abl kinases. In biochemical and proliferation assays, the compound was shown to be active against src family kinases and Bcr-Abl at IC50s of 100 and 90 nM, respectively. The bcr-abl fusion gene product, a consecutively activated tyrosine kinase, which is crucial for the development of chronic myeloid leukaemia (CML), is highly sensitive to bosutinib. Interestingly, distinctly lower concentrations of the dual src/abl inhibitor are required to ablate Bcr-Abl phosphorylation when compared to first-generation tyrosine kinase inhibitor imatinib (IM). Bosutinib is a potent inhibitor of CML cell proliferation in vitro and in vivo experiments and has demonstrated promising harbouring results in CML patients resistance or intolerance to IM in ongoing phase I/II clinical trials. Remarkably, bosutinib has been found to be capable of overcoming the majority of IM-resistant bcr-abl mutations. A randomised open label phase III clinical study to compare the efficacy of bosutinib and IM in first-line therapy of Ph+ chronic phase (CP) CML has recently been initiated. In a phase I/II clinical study with subjects suffering from advanced stages of solid tumours, long-term responses have also been reported. In conclusion, Bosutinib is a promising novel small molecule inhibitor for targeted therapy of CML and solid tumours.

Dasatinib is an inhibitor of BCR-ABL and SRC-family kinases for patients with imatinib-resistant or -intolerant chronic myelogenous leukemia (CML). In this international phase II trial, dasatinib was administered orally (70 mg twice daily) to patients with myeloid blast phase (MBP, n=109) or lymphoid blast phase (LBP, n=48) CML. After a minimum follow-up of 12 months (range 0.03-20.7 months), major hematologic responses were induced in 34% (MBP-CML) and 35% (LBP-CML) of patients. Major cytogenetic responses were attained in 33% (MBP-CML) and 52% (LBP-CML) of patients and complete cytogenetic responses were attained in 26 and 46%, respectively. Median progression-free survival was 6.7 (MBP-CML) and 3.0 (LBP-CML) months. Median overall survival was 11.8 (MBP-CML) and 5.3 (LBP-CML) months. Overall, dasatinib had acceptable tolerability. Fluid retention events were more frequent in the MBP-CML than the LBP-CML cohort: pleural effusion occurred in 36 and 13% (all grades) and 15 and 6% (grades 3/4), respectively. Other non-hematologic side effects were primarily grade 1/2; grade 3/4 events were recorded in