Therapy options in imatinib failures

Protein kinase inhibitor-based cancer therapies: Considering the potential of nitric oxide (NO) to improve cancer treatment

The deregulation of a wide variety of protein kinases is associated with cancer cell initiation and tumor progression. Owing to their indispensable function in signaling pathways driving malignant cell features, protein kinases constitute major therapeutic targets in cancer. Over the past two decades, intense efforts in drug development have been dedicated to this field. The development of protein kinase inhibitors (PKIs) have been a real breakthrough in targeted cancer therapy. Despite obvious successes across patients with different types of cancer, the development of PKI resistance still prevails. Combination therapies are part of a comprehensive approach to address the problem of drug resistance. The therapeutic use of nitric oxide (NO) donors to bypass PKI resistance in cancer has never been tested in clinic yet but several arguments suggest that the combination of PKIs and NO donors may exert a potential anticancer effect. The present review summarized the current state of knowledge on common targets to both PKIs and NO. Herein, we attempt to provide the rationale underlying a potential combination of PKIs and NO donors for future directions and design of new combination therapies in cancer.

Cytotoxic Effects of Some Flavonoids and Imatinib on the K562 Chronic Myeloid Leukemia Cell Line: Data Analysis Using the Combination Index Method

Background:

Flavonoids are natural compounds with antioxidant, anticarcinogenic, and anti-inflammatory effects.

Aims:

To determine the cytotoxic effects of flavonoids and drug resistance related to P-gp on K562 human chronic myeloid leukemia cells. We also aimed to evaluate the therapeutic potential of imatinib and flavonoid combinations.

Study Design:

Cell culture study.

Methods:

In this study, K562 cells were treated with apigenin, luteolin, 5-desmethyl sinensetin and the anticancer drug imatinib mesylate. The effect of flavonoids on K562 cell proliferation was detected using the 3-(4,5-dimethylthiazolyl)2,5‑diphenyl‑tetrazolium bromide assay. Concentrations of apigenin, luteolin, and 5-desmethyl sinensetin ranging from 25 to 200 μM and of imatinib from 5 to 50 μM administered for 72 h were studied. Apoptosis/necrosis and P-gp activity were measured using flow cytometry. The combined effects of different concentrations of flavonoids with imatinib were evaluated according to combination index values calculated using CompuSyn software.

Results:

In our study, the IC₅₀ values for apigenin, luteolin, and 5-desmethyl sinensetin were found to be 140 μM, 100 μM, and >200 μM, respectively. Luteolin (100 μM) had the highest cytotoxic activity of these flavonoids. These results were statistically significant (p<0.05). Among the flavonoids studied, the combination of luteolin and imatinib was the most effective and is therefore recommended for its cytotoxic activity in the K562 cell line. After 72 h of incubation at their respective IC₅₀ concentrations, all flavonoids were associated with an apoptosis rate of approximately 50%. P-glycoprotein activity was increased in all groups. Combination treatment may provide better outcomes in terms of cytotoxicity and thus reduce the dosages of imatinib used.

Conclusion:

The combination of some flavonoids and imatinib mesylate may increase the cytotoxic effect; However, the antagonistic effect should be considered in combined use on k562 cells.

Comparison of Frequency and Sensitivity of BCR-ABL1 Kinase Domain Mutations in Asian and White Patients With Imatinib-resistant Chronic-Phase Chronic Myeloid Leukemia

INTRODUCTION

BCR-ABL1 mutations require consideration during second-line tyrosine kinase inhibitor selection for patients with chronic myeloid leukemia (CML). The present retrospective analysis compared the frequency of BCR-ABL1 mutations in Asian and white patients in whom imatinib therapy had failed.

PATIENTS AND METHODS

A nonstudy cohort (76 Asian patients from community clinical practices) and 2 study cohorts (29 Asian and 352 white patients from dasatinib phase II and III clinical trials) were identified.

RESULTS

In the nonstudy cohort, 80 mutations were identified; the most frequent was T315I (15%), followed by phosphate-binding loop mutations E255K (11%), G250E (10%), and Y253H (10%). Asian patients had a greater proportion of T315I and phosphate-binding loop mutations compared with the white patients. The nonstudy cohort was less likely to have multiple mutations compared with either study cohort. Single mutations highly resistant to dasatinib, nilotinib, and bosutinib were more frequent in the Asian than in the white cohorts.

CONCLUSION

These results suggest that mutational analysis findings will be invaluable for choosing an appropriate second-line tyrosine kinase inhibitor in Asia.

Safety and efficacy of second-line bosutinib for chronic phase chronic myeloid leukemia over a five-year period: final results of a phase I/II study

Bosutinib is a Src/Abl tyrosine kinase inhibitor indicated for adults with newly-diagnosed Philadelphia positive chronic myeloid leukemia or with resistant/intolerant disease. We report the final results of a phase I/II study of second-line bosutinib in chronic phase chronic myeloid leukemia patients after imatinib failure (n=284). Median follow up and treatment durations were 54.8 (range 0.6–96.3) and 25.6 (0.2–96.3) months, respectively. At years 2 and 5, 54% and 40% of patients, respectively, remained on bosutinib. Cumulative major cytogenetic response and complete cytogenetic response rates (newly-attained or maintained from baseline) were 58% and 46%, respectively, by year 2 and 60% and 50% by year 5. Kaplan-Meier probability of maintaining major and complete cytogenetic response was 76% and 78%, respectively, at year 2 and 71% and 69% at year 5. Cumulative incidence of on-treatment disease progression/death was similar at years 5 (19%) and 2 (15%); Kaplan-Meier overall survival was 91% at year 2 and 84% at year 5. Of 169 patients who had discontinued bosutinib by year 5, 38 did so after year 2, most commonly for disease progression (n=11). Most adverse events initially occurred within two years. Overall, gastrointestinal events were the most common (diarrhea 86%, nausea 46%, vomiting 37%); the most common grade 3/4 toxicity was thrombocytopenia (25%). None of the 4 on-treatment deaths in years 3–5 were related to bosutinib. Bosutinib demonstrated durable efficacy and manageable toxicity through year 5 confirming its importance in the treatment of chronic phase chronic myeloid leukemia patients resistant/intolerant to prior imatinib. This trial was registered at clinicaltrials.gov identifier: 00261846.

Outcome of Chronic Myeloid Leukemia-Chronic Phase Patients Treated With Imatinib: A Local Experience

BACKGROUND

Imatinib was the first tyrosine kinase inhibitor that has revolutionized the therapy of chronic myeloid leukemia. It binds breakpoint cluster region-Abelson kinase domain inducing apoptosis of the leukemic cells. In this study, we assessed the efficacy and toxicity of imatinib therapy in patients with chronic myeloid leukemia in chronic phase (CML-CP) in our hospital.

PATIENTS AND METHODS

We retrospectively analyzed the outcome of 17 patients with CML-CP treated with imatinib.

RESULTS

The median age at the time of presentation was 35 years with male preponderance. The most common presenting clinical features were fatigue, abdominal distention, and discomfort. Forty-seven percent of patients had fever at presentation whereas 35.29% were referred to our hospital because of incidental findings of high blood cell counts. With a median follow-up of 8 years (range, 2-16 years) the overall survival is 100% and progression-free survival 85%. Two patients had acceptable adverse effects.

CONCLUSION

After a median follow-up of 8 years, imatinib was found to induce long survival with manageable side effect in adult Saudi patients with CML-CP.

Clinical Pharmacokinetics and Pharmacodynamics of Bosutinib

Chronic myeloid leukemia (CML) is a clonal myeloproliferative stem cell disorder. Bosutinib is an oral, once-daily SRC/ABL tyrosine kinase inhibitor with very potent inhibitory activity. Bosutinib is effective against all phases of intolerant or resistant Philadelphia chromosome-positive CML that do not harbor the T315I or V299LABL kinase domain mutations. Peak plasma concentrations of bosutinib occur at 4-6 h following oral administration, and dose-proportional increases in exposure are observed at doses ranging from 200 to 800 mg. Absorption of bosutinib increases with food. Bosutinib is distributed extensively into the tissues. It is highly plasma protein bound (94 %) and is primarily metabolized in the liver by cytochrome P450 3A4. Bosutinib is well tolerated overall and has a unique but manageable toxicity profile. This article provides a review of the available clinical pharmacokinetic, pharmacodynamic, and drug-drug interaction data on bosutinib in healthy subjects, patients with CML, and special populations.

Long-term bosutinib for chronic phase chronic myeloid leukemia after failure of imatinib plus dasatinib and/or nilotinib

Bosutinib is an Src/Abl tyrosine kinase inhibitor (TKI) indicated for adults with Ph+ chronic myeloid leukemia (CML) resistant/intolerant to prior TKIs. This long-term update of an ongoing phase 1/2 study evaluated the efficacy and safety of third-/fourth-line bosutinib in adults with chronic phase (CP) CML. Median durations of treatment and follow-up were 8.6 (range, 0.2-87.7) months and 32.7 (0.3-93.3) months, respectively. Cumulative confirmed complete hematologic response (cCHR) and major cytogenetic response (MCyR) rates were 74% (95% CI, 65-81%) and 40% (31-50%), respectively; Kaplan-Meier (K-M) probability of maintaining cCHR or MCyR at 4 years was 63% (95% CI, 50-73%) and 69% (52-81%). Cumulative incidence of on-treatment disease progression (PD)/death at 4 years was 24% (95% CI, 17-33%); K-M 4-year overall survival was 78% (68-85%). Baseline Ph+ cells ≤35 vs. ≥95% was prognostic of MCyR and CCyR by 3 and 6 months, increased baseline basophils was prognostic of PD/death, and no prior response to second-line TKI was prognostic of death. Common adverse events included diarrhea (83%), nausea (48%), vomiting (38%), and thrombocytopenia (39%). Bosutinib demonstrates durable efficacy and a toxicity profile similar to previous bosutinib studies in CP CML patients resistant/intolerant to multiple TKIs, representing an important treatment option for patients in this setting. This trial is registered at www.clinicaltrials.gov (NCT00261846). Am. J. Hematol. 91:1206-1214, 2016. © 2016 Wiley Periodicals, Inc.

PBA2, a novel inhibitor of imatinib-resistant BCR-ABL T315I mutation in chronic myeloid leukemia

Chronic Myeloid Leukemia (CML) is largely caused by the Philadelphia (Ph) chromosome carrying the Break point Cluster Region-Abelson (BCR-ABL) oncogene. Imatinib is a BCR-ABL-targeted therapy and considered the standard of care in CML management. Resistance to imatinib therapy often develops because of mutations in the BCR-ABL kinase domain. In this study, we evaluated PBA2, a novel BCR-ABL inhibitor, for its anti-cancer activity against BCR-ABL expressing BaF3 cells. PBA2 shows potent activity against wild-type and T315I mutated BaF3 cells as compared with imatinib. PBA2 inhibited the phosphorylation of BCR-ABL and its downstream signaling in BaF3/WT and BaF3/T315I cells. PBA2 inhibited the mRNA expression of BCR-ABL in BaF3/WT and BaF3/T315I cells. Mechanistically, PBA2 increased the cell population in sub G1 phase of the cell cycle, induced apoptosis and elevated ROS production in both BaF3/WT and BaF3/T315I cells. Taken together, our results indicate that PBA2 exhibits anti-proliferative effects and inhibits the imatinib-resistant T315I BCR-ABL mutation. PBA2 may be a novel drug candidate for overcoming the resistance to imatinib in CML patients.

A NOX2/Egr-1/Fyn pathway delineates new targets for TKI-resistant malignancies

Tyrosine kinase inhibitors (TKI) have improved CML response rates, and some are effective against resistance-promoting point mutations in BCR-ABL1. However, in the absence of point mutations, resistance still occurs. Here, we identify a novel pathway mediating resistance which connects p47phox, the organizer subunit of NADPH oxidase-2 (NOX2), with early growth response-1 (Egr-1) and the Src family kinase Fyn. We found up-regulation of p47phox, Egr-1, and Fyn mRNA and protein using paired isogenic CML cell lines and mined data. Isolation of CD34⁺ cells and tissue microarray staining from blast crisis CML patients confirmed in vivo over-expression of components of this pathway. Knockdown studies revealed that p47phox modulated reactive oxygen species and Egr-1 expression, which, in turn, controlled Fyn expression. Interestingly, Fyn knockdown sensitized TKI-resistant cells to dasatinib, a dual BCR-ABL1/Src inhibitor. Egr-1 knockdown had similar effects, indicating the utility of targeting Fyn expression over activation. Pointedly, p47phox knockdown also restored TKI-sensitivity, indicating that targeting the NOX2 complex can overcome resistance. The NOX2/Egr-1/Fyn pathway was also conserved within TKI-resistant EGFRΔIII-expressing glioblastoma and patient-derived glioblastoma stem cells. Thus, our findings suggest that targeting the NOX2/Egr-1/Fyn pathway may have clinical implications within multiple cancer types; particularly where efficacy of TKI is compromised.

Health-related quality of life during bosutinib (SKI-606) therapy in patients with advanced chronic myeloid leukemia after imatinib failure

OBJECTIVES

The tyrosine kinase inhibitor (TKI) bosutinib has demonstrated activity in patients with advanced phase chronic myeloid leukemia (CML), but effects on health-related quality of life (HRQoL) remain unexplored. This study evaluated HRQoL in advanced CML patients receiving bosutinib in an ongoing phase 2 study following resistance or intolerance to prior imatinib therapy.

METHODS

This analysis included data from 76 accelerated-phase (AP) and 64 blast-phase (BP) patients resistant/intolerant to prior imatinib with or without prior exposure to other TKIs. Patient-reported HRQoL assessments completed at baseline; weeks 4, 8, and 12; every 12 weeks thereafter; and at treatment completion included the Functional Assessment of Cancer Therapy-Leukemia (FACT-Leu); general health status was assessed using the 5-item EuroQol (EQ-5D) instrument and a visual analog scale (VAS).

RESULTS

HRQoL at baseline was somewhat worse in BP versus AP CML patients. There was a significant improvement in the mean FACT-Leu Total scale at weeks 24, 36, and 48 in AP CML patients and at weeks 4, 8, 12, 24, 36, 48, and 96 in BP CML patients compared with baseline. EQ-5D Utility scores were stable throughout treatment in AP CML patients but significantly improved versus baseline in BP CML patients at weeks 4, 8, 12, and 36. Mean VAS scores were significantly improved at weeks 8, 36, and 48 in AP CML patients and at weeks 4, 8, 12, 24, 36, and 96 in BP CML patients. The lack of a comparison group limits attribution of improvements in HRQoL specifically to bosutinib treatment; potential bias due to non-ignorable dropout may limit the ability to generalize these findings to situations where durations of therapy exceed the 96-week follow-up duration of the present study.

CONCLUSION

These findings suggest that bosutinib therapy is associated with improved HRQoL in advanced phase CML patients.

CLINICAL TRIAL REGISTRATION

NCT00261846.

Lymphocytosis after treatment with dasatinib in chronic myeloid leukemia: Effects on response and toxicity

BACKGROUND

The proliferation of clonal cytotoxic T‐cells or natural killer cells has been observed after dasatinib treatment in small studies of patients with chronic myeloid leukemia (CML).

METHODS

The incidence of lymphocytosis and its association with response, survival, and side effects were assessed in patients from 3 large clinical trials. Overall, 1402 dasatinib‐treated patients with newly diagnosed CML in chronic phase (CML‐CP), CML‐CP refractory/intolerant to imatinib, or with CML in accelerated or myeloid‐blast phase were analyzed.

RESULTS

Lymphocytosis developed in 32% to 35% of patients and persisted for >12 months. This was not observed in the patients who received treatment with imatinib. Dasatinib‐treated patients in all stages of CML who developed lymphocytosis were more likely to achieve a complete cytogenetic response, and patients who had CML‐CP with lymphocytosis were more likely to achieve major and deep molecular responses. Progression‐free and overall survival rates were significantly longer in patients with CML‐CP who were refractory to or intolerant of imatinib and had lymphocytosis. Pleural effusions developed more commonly in patients with lymphocytosis.

CONCLUSIONS

Overall, lymphocytosis occurred and persisted in many dasatinib‐treated patients in all phases of CML. Its presence was associated with higher response rates, significantly longer response durations, and increased overall survival, suggesting an immunomodulatory effect. Prospective studies are warranted to characterize the functional activity of these cells and to assess whether an immunologic effect against CML is detectable. Cancer 2016;122:1398–1407. © 2016 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.

Lymphocytosis develops frequently after treatment of chronic myeloid leukemia with dasatinib and is associated with higher response rates, significantly longer response durations, and increased overall survival. Prospective studies are warranted to assess whether dasatinib produces an immunomodulatory effect against chronic myeloid leukemia.

Induction of Apoptosis and Antitumor Activity of Eel Skin Mucus, Containing Lactose-Binding Molecules, on Human Leukemic K562 Cells

For innate immune defense, lower animals such as fish and amphibian are covered with skin mucus, which acts as both a mechanical and biochemical barrier. Although several mucus sources have been isolated and studied for their biochemical and immunological functions, the precise mechanism(s) of action remains unknown. In the present study, we additionally found the eel skin mucus (ESM) to be a promising candidate for use in anti-tumor therapy. Our results showed that the viability of K562 cells was decreased in a dose-dependent manner by treatment with the isolated ESM. The cleaved forms of caspase-9, caspase-3 and poly adenosine diphosphate-ribose polymerase were increased by ESM. The levels of Bax expression and released cytochrome C were also increased after treatment with ESM. Furthermore, during the ESM mediated-apoptosis, phosphorylation levels of ERK1/2 and p38 but not JNK were increased and cell viabilities of the co-treated cells with ESM and inhibitors of ERK 1/2 or p38 were also increased. In addition, treatment with lactose rescued the ESM-mediated decrease in cell viability, indicating lactose-containing glycans in the leukemia cells acted as a counterpart of the ESM for interaction. Taken together, these results suggest that ESM could induce mitochondria-mediated apoptosis through membrane interaction of the K562 human leukemia cells. To the best of our knowledge, this is the first observation that ESM has anti-tumor activity in human cells.

Incidence and clinical importance of BCR-ABL1 mutations in Iranian patients with chronic myeloid leukemia on imatinib

Mutations of the BCR-ABL1 kinase domain seem to be the most common cause of imatinib mesylate resistance in chronic myeloid leukemia (CML). We screened BCR-ABL1 kinase domain mutations using nested reverse transcriptase polymerase chain reaction and direct sequencing in 30 CML patients including 22 resistant patients and 8 patients with optimal response to imatinib. Three mutations of two different types were identified in 3 of 22 (13.6%) resistant patients. Two patients had p.E355G mutation in the catalytic domain, and the third patient had p.G398R in the activation loop that is reported here for the first time. No mutation was found in patients with optimal response to imatinib. The frequency of mutations was similar in patients with primary resistance compared with patients with secondary resistance (25 vs 11%; P=1). Mutation status had no impact on the overall survival and progression-free survival. p.E355G mutation was correlated with shorter survival (P=0.047) in resistant patients. We conclude that BCR- ABL1 mutations are associated with the clinical resistance, but may not be considered the only cause of resistance to imatinib. Mutational analysis may identify resistant patients at risk of disease progression.

Bosutinib versus imatinib in newly diagnosed chronic-phase chronic myeloid leukaemia: results from the 24-month follow-up of the BELA trial

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.

Dasatinib

Dasatinib (Sprycel®), a second-generation TKI, has been shown to be effective as an anticancer drug in the treatment of patients with chronic myeloid leukemia or Philadelphia chromosome-positive acute lymphoblastic leukemia who are resistant or intolerant to imatinib. Several methods of gefitinib synthesis are included in this review. UV spectroscopy of dasatinib showed a λmax of approximately 320-330nm, and IR spectroscopy principal peaks were observed at 3418 (NH), 3200 (OH), 1620 (CO), 1582 (CC and CN), 1513 (CHCH) cm(-1). Characteristic NH peaks were observed in nuclear magnetic resonance (NMR) spectroscopy at 11.47 and 9.88ppm. The molecular mass was observed at m/z=487.3((35)Cl) and 488.9((37)Cl) (molecular weight=487.15) and the fragmentation pattern was studied using ion trap mass spectrometry. In addition, different analytical methods for determination of dasatinib are also described in this review. Pharmacokinetically, dasatinib is rapidly absorbed after oral administration where the solubility is dependent on pH. Dasatinib extensively binds to human plasma proteins by approximately 96%. In leukemic patient, the calculated apparent volume of distribution for dasatinib was 2502L and the estimated elimination half-life was approximately 3-5h. Dasatinib is metabolized in humans markedly by CYP3A4 to active metabolites and by phase II drug-metabolizing enzymes, such as UDP glucuronosyltransferase. Dasatinib is mainly eliminated via the feces (85%), of which relatively small amount of dasatinib is excreted unchanged as intact drug (19%). Most of the adverse effects associated with dasatinib therapy are mild to moderate in severity and are usually reversible and manageable with appropriate intervention, such as cardiac failure, hypertension, and coronary artery disease.

Bortezomib induces apoptosis by interacting with JAK/STAT pathway in K562 leukemic cells

In the current study, we aimed to identify the cytotoxic and apoptotic effects of bortezomib (BOR) on human K562 chronic myelogenous leukemia cells and to evaluate the potential roles of Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway members STAT3, STAT5, and JAK2 on BOR-induced cell death of leukemic cells. Cell viability was assessed via trypan blue dye exclusion test, and cytotoxicity of the BOR-treated cells was conducted by 2,3-bis(2-methoxy-4-nitro-5-sulphophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT) assay. The relative messenger RNA (mRNA) expression levels of STAT3, STAT5A, STAT5B, and JAK2 were analyzed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). On the other hand, their protein expression levels were detected by western blot method. The obtained results indicated that BOR treatment reduced cell viability and induced leukemic cell apoptosis in a dose- and time-dependent manner as compared to untreated control cells. While mRNA expression levels of STAT5A, STAT5B, and STAT3 were significantly reduced following BOR treatment when compared to untreated controls, it had no effect upon JAK2 mRNA expression. As for protein levels, STAT expressions were downregulated after BOR treatment especially at 72nd and 96th hours. Our results pointed out that BOR treatment had a significant potential of being an anticancer agent for chronic myelogenous leukemia therapy, and this effect could be due to the expressional downregulations of JAK/STAT pathway members.

Therapy of chronic myeloid leukemia: twilight of the imatinib era?

Chronic myeloid leukemia (CML) results from the clonal expansion of pluripotent hematopoietic stem cells containing the active BCR/ABL fusion gene produced by a reciprocal translocation of the ABL1 gene to the BCR gene. The BCR/ABL protein displays a constitutive tyrosine kinase activity and confers on leukemic cells growth and proliferation advantage and resistance to apoptosis. Introduction of imatinib (IM) and other tyrosine kinase inhibitors (TKIs) has radically improved the outcome of patients with CML and some other diseases with BCR/ABL expression. However, a fraction of CML patients presents with resistance to this drug. Regardless of clinical profits of IM, there are several drawbacks associated with its use, including lack of eradication of the malignant clone and increasing relapse rate resulting from long-term therapy, resistance, and intolerance. Second and third generations of TKIs have been developed to break IM resistance. Clinical studies revealed that the introduction of second-generation TKIs has improved the overall survival of CML patients; however, some with specific mutations such as T315I remain resistant. Second-generation TKIs may completely replace imatinib in perspective CML therapy, and addition of third-generation inhibitors may overcome resistance induced by every form of point mutations.

Bosutinib safety and management of toxicity in leukemia patients with resistance or intolerance to imatinib and other tyrosine kinase inhibitors

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).

Effective targeting of chronic myeloid leukemia initiating activity with the combination of arsenic trioxide and interferon alpha

Imatinib is the standard of care in chronic meloid leukemia (CML) therapy. However, imatinib is not curative since most patients who discontinue therapy relapse indicating that leukemia initiating cells (LIC) are resistant. Interferon alpha (IFN) induces hematologic and cytogenetic remissions and interestingly, improved outcome was reported with the combination of interferon and imatinib. Arsenic trioxide was suggested to decrease CML LIC. We investigated the effects of arsenic and IFN on human CML cell lines or primary cells and the bone marrow retroviral transduction/transplantation murine CML model. In vitro, the combination of arsenic and IFN inhibited proliferation and activated apoptosis. Importantly, arsenic and IFN synergistically reduced the clonogenic activity of primary bone marrow cells derived from CML patients. Finally, in vivo, combined interferon and arsenic treatment, but not single agents, prolonged the survival of primary CML mice. Importantly, the combination severely impaired engraftment into untreated secondary recipients, with some recipients never developing the disease, demonstrating a dramatic decrease in CML LIC activity. Arsenic/IFN effect on CML LIC activity was significantly superior to that of imatinib. These results support further exploration of this combination, alone or with imatinib aiming at achieving CML eradication rather than long-term disease control.

Organopalladium compound 7b targets mitochondrial thiols and induces caspase-dependent apoptosis in human myeloid leukemia cells

The advances in the treatment of chronic myeloid leukemia (CML) during the last years were also accompanied by the development of evading strategies by tumor cells, resulting in chemotherapy resistance in some patients. Patented organopalladium compounds derived from the reaction of N,N-dimethyl-1-phenethylamine (dmpa) with [1,2-ethanebis(diphenylphosphine)] (dppe) exhibited a potent antitumor activity in vivo and in vitro in melanoma cells. We showed here that the cyclopalladated derivative [Pd2(R(+))C(2), N-dmpa)2(μ-dppe)Cl2], named compound 7b, was highly effective to promote cell death in the K562 human leukemia cells and its mechanisms of action were investigated. It was shown that compound 7b was able to promote exclusively apoptotic cell death in K562 cells associated to cytochrome c release and caspase 3 activation. This cytotoxic effect was not observed in normal peripheral mononuclear blood cells. The compound 7b-induced intrinsic apoptotic pathway was triggered by the protein thiol oxidation that resulted in the dissipation of the mitochondrial transmembrane potential. The preventive effect of the dithiothreitol on the compound 7b-induced cell death and all downstream events associated to apoptosis confirmed that death signal was elicited by the thiol oxidation. These findings contribute to the elucidation of the palladacycle 7b-induced cell death mechanism and present this compound as a promising drug in the CML antitumor chemotherapy.

Managing inadequate responses to frontline treatment of chronic myeloid leukemia: a case-based review

The tyrosine kinase inhibitors (TKIs) imatinib, nilotinib, and dasatinib are the standard of care for treating patients with newly diagnosed chronic-phase chronic myeloid leukemia (CML). Compared with interferon-based treatment, the previous standard of care, imatinib is associated with significantly higher cytogenetic response rates and prolonged overall survival. Nilotinib and dasatinib, both newer and more potent TKIs, significantly improve cytogenetic and molecular response rates compared with imatinib. Despite significant advances in CML treatment enabled by the TKIs, a fraction of patients who receive frontline treatment with a TKI demonstrate inadequate response. The reasons for this vary, but in many cases, inadequate response can be attributed to non-adherence to the treatment regimen, intolerance to the drug, intrinsic or acquired resistance to the drug, or a combination of reasons. More often than not, strategies to improve response necessitate a change in treatment plan, either a dose adjustment or a switch to an alternate drug, particularly in the case of drug intolerance or drug resistance. Improved physician-patient communication and patient education are effective strategies to address issues relating to adherence and intolerance. Because inadequate response to TKI treatment correlates with poor long-term outcomes, it is imperative that patients who experience intolerance or who fail to achieve appropriate responses are carefully evaluated so that appropriate treatment modifications can be made to maximize the likelihood of positive long-term outcome.

DNA damage response in imatinib resistant chronic myeloid leukemia K562 cells

Resistance to imatinib in patients with chronic myeloid leukemia can lead to advanced disease and blast crisis. Conventional chemotherapy with DNA damaging agents is then used, alone or in combination with other tyrosine kinase inhibitors (TKIs). Our aim was to assess whether imatinib resistant K562 cells were also resistant to DNA damaging agents. After treatment with H(2)O(2) and doxorubicin, but not camptothecin, cell survival was higher in imatinib resistant cells compared to parental cells. DNA damage, measured by comet and γ-H2AX assays, was lower in imatinib resistant cells. mRNA expression levels of 50 genes of the DNA damage response pathway showed increased expression of the base excision repair (BER) genes MBD4 and NTHL1. Knockdown of MBD4 and NTHL1 expression in resistant cells using siRNA decreased cell survival after treatment with H(2)O(2) and doxorubicin. Our results indicate that imatinib resistant cells display cross-resistance to oxidative agents, partly through up-regulation of BER genes. Expression of these genes in imatinib resistant patients was not significantly different compared to sensitive patients. However, the strategy followed in this study could help identify chemotherapeutic agents that are more effective as alternative agents in cases of resistance to TKIs.

Bosutinib is active in chronic phase chronic myeloid leukemia after imatinib and dasatinib and/or nilotinib therapy failure

Bosutinib, a dual Src/Abl tyrosine kinase inhibitor (TKI), has shown potent activity against chronic myeloid leukemia (CML). This phase 1/2 study evaluated the efficacy and safety of once-daily bosutinib 500 mg in leukemia patients after resistance/intolerance to imatinib. The current analysis included 118 patients with chronic-phase CML who had been pretreated with imatinib followed by dasatinib and/or nilotinib, with a median follow-up of 28.5 months. In this subpopulation, major cytogenetic response was attained by 32% of patients; complete cytogenetic response was attained by 24%, including in one of 3 patients treated with 3 prior TKIs. Complete hematologic response was achieved/maintained in 73% of patients. On-treatment transformation to accelerated/blast phase occurred in 5 patients. At 2 years, Kaplan-Meier-estimated progression-free survival was 73% and estimated overall survival was 83%. Responses were seen across Bcr-Abl mutations, including those associated with dasatinib and nilotinib resistance, except T315I. Bosutinib had an acceptable safety profile; treatment-emergent adverse events were primarily manageable grade 1/2 gastrointestinal events and rash. Grade 3/4 nonhematologic adverse events (> 2% of patients) included diarrhea (8%) and rash (4%). Bosutinib may offer a new treatment option for patients with chronic-phase CML after treatment with multiple TKIs. This trial was registered at www.clinicaltrials.gov as NCT00261846.

Hydroxychavicol, a Piper betle leaf component, induces apoptosis of CML cells through mitochondrial reactive oxygen species-dependent JNK and endothelial nitric oxide synthase activation and overrides imatinib resistance

Alcoholic extract of Piper betle (Piper betle L.) leaves was recently found to induce apoptosis of CML cells expressing wild type and mutated Bcr-Abl with imatinib resistance phenotype. Hydroxy-chavicol (HCH), a constituent of the alcoholic extract of Piper betle leaves, was evaluated for anti-CML activity. Here, we report that HCH and its analogues induce killing of primary cells in CML patients and leukemic cell lines expressing wild type and mutated Bcr-Abl, including the T315I mutation, with minimal toxicity to normal human peripheral blood mononuclear cells. HCH causes early but transient increase of mitochondria-derived reactive oxygen species. Reactive oxygen species-dependent persistent activation of JNK leads to an increase in endothelial nitric oxide synthase-mediated nitric oxide generation. This causes loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, cleavage of caspase 9, 3 and poly-adenosine diphosphate-ribose polymerase leading to apoptosis. One HCH analogue was also effective in vivo in SCID mice against grafts expressing the T315I mutation, although to a lesser extent than grafts expressing wild type Bcr-Abl, without showing significant bodyweight loss. Our data describe the role of JNK-dependent endothelial nitric oxide synthase-mediated nitric oxide for anti-CML activity of HCH and this molecule merits further testing in pre-clinical and clinical settings.

p185(BCR/ABL) has a lower sensitivity than p210(BCR/ABL) to the allosteric inhibitor GNF-2 in Philadelphia chromosome-positive acute lymphatic leukemia

BACKGROUND

The t(9;22) translocation leads to the formation of the chimeric breakpoint cluster region/c-abl oncogene 1 (BCR/ABL) fusion gene on der22, the Philadelphia chromosome. The p185(BCR/ABL) or the p210(BCR/ABL) fusion proteins are encoded as a result of the translocation, depending on whether a "minor" or "major" breakpoint occurs, respectively. Both p185(BCR/ABL) and p210(BCR/ABL) exhibit constitutively activated ABL kinase activity. Through fusion to BCR the ABL kinase in p185(BCR/ABL) and p210(BCR/ABL) "escapes" the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. A novel class of compounds including GNF-2 restores allosteric inhibition of the kinase activity and the transformation potential of BCR/ABL. Here we investigated whether there are differences between p185(BCR/ABL) and p210(BCR/ABL) regarding their sensitivity towards allosteric inhibition by GNF-2 in models of Philadelphia chromosome-positive acute lymphatic leukemia.

DESIGN AND METHODS

We investigated the anti-proliferative activity of GNF-2 in different Philadelphia chromosome-positive acute lymphatic leukemia models, such as cell lines, patient-derived long-term cultures and factor-dependent lymphatic Ba/F3 cells expressing either p185(BCR/ABL) or p210(BCR/ABL) and their resistance mutants.

RESULTS

The inhibitory effects of GNF-2 differed constantly between p185(BCR/ABL) and p210(BCR/ABL) expressing cells. In all three Philadelphia chromosome-positive acute lymphatic leukemia models, p210(BCR/ABL)-transformed cells were more sensitive to GNF-2 than were p185BCR/ABL-positive cells. Similar results were obtained for p185(BCR/ABL) and the p210(BCR/ABL) harboring resistance mutations.

CONCLUSIONS

Our data provide the first evidence of a differential response of p185(BCR/ABL)- and p210(BCR/ABL)- transformed cells to allosteric inhibition by GNF-2, which is of importance for the treatment of patients with Philadelphia chromosome-positive acute lymphatic leukemia.

Safety and efficacy of bosutinib (SKI-606) in chronic phase Philadelphia chromosome-positive chronic myeloid leukemia patients with resistance or intolerance to imatinib

Bosutinib, a dual Src/Abl kinase inhibitor, has shown potent activity against chronic myeloid leukemia (CML). In this phase 1/2 study we evaluated bosutinib in patients with chronic phase imatinib-resistant or imatinib-intolerant CML. Part 1 was a dose-escalation study to determine the recommended starting dose for part 2; part 2 evaluated the efficacy and safety of bosutinib 500 mg once-daily dosing. The study enrolled 288 patients with imatinib-resistant (n = 200) or imatinib-intolerant (n = 88) CML and no other previous kinase inhibitor exposure. At 24 weeks, 31% of patients achieved major cytogenetic response (primary end point). After a median follow-up of 24.2 months, 86% of patients achieved complete hematologic remission, 53% had a major cytogenetic response (41% had a complete cytogenetic response), and 64% of those achieving complete cytogenetic response had a major molecular response. At 2 years, progression-free survival was 79%; overall survival at 2 years was 92%. Responses were seen across Bcr-Abl mutants, except T315I. Bosutinib exhibited an acceptable safety profile; the most common treatment-emergent adverse event was mild/moderate, typically self-limiting diarrhea. Grade 3/4 nonhematologic adverse events (> 2% of patients) included diarrhea (9%), rash (9%), and vomiting (3%). These data suggest bosutinib is effective and tolerable in patients with chronic phase imatinib-resistant or imatinib-intolerant CML. This trial was registered at http://www.clinicaltrials.gov as NCT00261846.

Release of intracellular calcium primes chronic myeloid leukaemia cells for tyrosine kinase inhibitor-induced apoptosis

Imatinib is a substrate for hOCT1 (SLC22A1) and inhibitors of this influx transporter, such as amantadine and prazosin, have previously been shown to decrease cellular imatinib uptake. However, here we report that in longer term experiments, both drugs paradoxically increase the cytotoxicity of all three currently licensed tyrosine kinase inhibitors (TKIs), imatinib, nilotinib and dasatinib. This effect is due to release of intracellular calcium from the endoplasmic reticulum (ER), with changes in mitochondrial calcium and alterations in mitochondrial membrane permeability, resulting in caspase-mediated apoptosis. The effect is confined to BCR-ABL-positive cells, and is greater in primary cells than in cell lines. Furthermore, in primary cells at original diagnosis, the effect is only seen in samples from patients destined to become complete cytogenetic responders to imatinib. These results indicate that calcium release from the ER, here induced by amantadine or prazosin, may prime BCR-ABL-positive cells to TKI-induced apoptosis. Amantadine/prazosin primed TKI cytotoxicity in vitro may be a useful test for the level of ER-releasable calcium, and may be of prognostic value.

Targeted inhibition of kinases in cancer therapy

With an understanding of the molecular changes that accompany cell transformation, cancer drug discovery has undergone a dramatic change in the past few years. Whereas most of the emphasis in the past has been placed on developing drugs that induce cell death based on mechanisms that do not discriminate between normal and tumor cells, recent strategies have emphasized targeting specific mechanisms that have gone awry in tumor cells. However, the identification of cancer-associated mutations in oncogenes and their amplification in tumors has suggested that inhibitors against such proteins might represent attractive substrates for targeted therapy. In the clinic, the success of imatinib (Gleevec®, STI571) and trastuzumab (Herceptin®), both firsts of their kind, spurred further development of new, second-generation drugs that target kinases in cancer. This review highlights a few important examples each of these types of therapies, along with some newer agents that are in various stages of development. Second-generation kinase inhibitors aimed at overriding emerging resistance to these therapies are also discussed.

Global phosphoproteomics reveals crosstalk between Bcr-Abl and negative feedback mechanisms controlling Src signaling

In subtypes and late stages of leukemias driven by the tyrosine kinase fusion protein Bcr-Abl, signaling by the Src family kinases (SFKs) critically contributes to the leukemic phenotype. We performed global tyrosine phosphoprofiling by quantitative mass spectrometry of Bcr-Abl-transformed cells in which the activities of the SFKs were perturbed to build a detailed context-dependent network of cancer signaling. Perturbation of the SFKs Lyn and Hck with genetics or inhibitors revealed Bcr-Abl downstream phosphorylation events either mediated by or independent of SFKs. We identified multiple negative feedback mechanisms within the network of signaling events affected by Bcr-Abl and SFKs and found that Bcr-Abl attenuated these inhibitory mechanisms. The C-terminal Src kinase (Csk)-binding protein Pag1 (also known as Cbp) and the tyrosine phosphatase Ptpn18 both mediated negative feedback to SFKs. We observed Bcr-Abl-mediated phosphorylation of the phosphatase Shp2 (Ptpn11), and this may contribute to the suppression of these negative feedback mechanisms to promote Bcr-Abl-activated SFK signaling. Csk and a kinase-deficient Csk mutant both produced similar globally repressive signaling consequences, suggesting a critical role for the adaptor protein function of Csk in its inhibition of Bcr-Abl and SFK signaling. The identified Bcr-Abl-activated SFK regulatory mechanisms are candidates for dysregulation during leukemia progression and acquisition of SFK-mediated drug resistance.

Carboxyamidotriazole inhibits cell growth of imatinib-resistant chronic myeloid leukaemia cells including T315I Bcr-Abl mutant by a redox-mediated mechanism

Mutation of the Bcr-Abl oncoprotein is one of most frequent mechanisms by which chronic myelogenous leukemia (CML) cells become resistant to imatinib. Here, we show that treatment of cell lines harbouring wild type or mutant BCR-ABL with carboxyamidotriazole (CAI), a calcium influx and signal transduction inhibitor, inhibits cell growth, the expression of Bcr-Abl and its downstream signalling, and induces apoptosis. Moreover, we show that CAI acts by increasing intracellular ROS. Clinically significant, CAI has also inhibitory effects on T315I Bcr-Abl mutant, a mutation that causes CML cells to become insensitive to imatinib and second generation abl kinase inhibitors.

Long-term outcomes in the second-line treatment of chronic myeloid leukemia: a review of tyrosine kinase inhibitors

Chronic myeloid leukemia (CML) is a progressive and often fatal myeloproliferative neoplasm. The hallmark of CML is an acquired chromosomal translocation known as the Philadelphia chromosome (Ph), which results in the synthesis of the breakpoint cluster region-Abelson murine leukemia (BCR-ABL) fusion oncoprotein, a constitutively active tyrosine kinase. The introduction of imatinib, a tyrosine kinase inhibitor (TKI) that is specific for BCR-ABL, was a major breakthrough in CML therapy. Although most patients respond to first-line imatinib therapy, some experience loss of response (resistance) or require treatment discontinuation because of toxicity (intolerance). For patients with CML, failure on standard-dose imatinib therapy (400 mg daily), imatinib dose escalation (600-800 mg daily) is a second-line option. However, high-dose imatinib is not an appropriate approach for patients who experience drug toxicity, and there remain questions over the durability of responses achieved with this strategy. Alternative second-line options include the TKIs dasatinib and nilotinib. A substantial amount of long-term data for these agents is available. Although both are potent and specific BCR-ABL TKIs, dasatinib and nilotinib exhibit unique pharmacologic profiles and response patterns relative to different patient characteristics, such as disease stage and BCR-ABL mutation status. To optimize therapeutic benefit, clinicians should select treatment based on each patient's historic response, adverse-event tolerance, and risk factors.

ABL tyrosine kinases: evolution of function, regulation, and specificity

ABL-family proteins comprise one of the best conserved branches of the tyrosine kinases. Each ABL protein contains an SH3-SH2-TK (Src homology 3-Src homology 2-tyrosine kinase) domain cassette, which confers autoregulated kinase activity and is common among nonreceptor tyrosine kinases. This cassette is coupled to an actin-binding and -bundling domain, which makes ABL proteins capable of connecting phosphoregulation with actin-filament reorganization. Two vertebrate paralogs, ABL1 and ABL2, have evolved to perform specialized functions. ABL1 includes nuclear localization signals and a DNA binding domain through which it mediates DNA damage-repair functions, whereas ABL2 has additional binding capacity for actin and for microtubules to enhance its cytoskeletal remodeling functions. Several types of posttranslational modifications control ABL catalytic activity, subcellular localization, and stability, with consequences for both cytoplasmic and nuclear ABL functions. Binding partners provide additional regulation of ABL catalytic activity, substrate specificity, and downstream signaling. Information on ABL regulatory mechanisms is being mined to provide new therapeutic strategies against hematopoietic malignancies caused by BCR-ABL1 and related leukemogenic proteins.

Integrated microfluidic and imaging platform for a kinase activity radioassay to analyze minute patient cancer samples

Oncogenic kinase activity and the resulting aberrant growth and survival signaling are a common driving force of cancer. Accordingly, many successful molecularly targeted anticancer therapeutics are directed at inhibiting kinase activity. To assess kinase activity in minute patient samples, we have developed an immunocapture-based in vitro kinase assay on an integrated polydimethylsiloxane microfluidics platform that can reproducibly measure kinase activity from as few as 3,000 cells. For this platform, we adopted the standard radiometric (32)P-ATP-labeled phosphate transfer assay. Implementation on a microfluidic device required us to develop methods for repeated trapping and mixing of solid-phase affinity microbeads. We also developed a solid-state beta-particle camera imbedded directly below the microfluidic device for real-time quantitative detection of the signal from this and other microfluidic radiobioassays. We show that the resulting integrated device can measure ABL kinase activity from BCR-ABL-positive leukemia patient samples. The low sample input requirement of the device creates new potential for direct kinase activity experimentation and diagnostics on patient blood, bone marrow, and needle biopsy samples.

New effective inhibitors of the Abelson kinase

The effects of substituents on the aryl ring were studied by the preparation and testing of several PD173955 analogs. Inserting a single carbon atom into the C-N bond in the aniline subunit (PDC) reduced the kinase inhibition by a factor of 200. Despite its decreased affinity for Abl compared with PD173955, PDC exhibits a Ki very similar to that reported for Imatinib. Increased water solubility is also gained by replacing the thiomethyl group with an amino or glycyl moiety. For both PD173955 and PDC, the analogs with amino groups in place of the methylthio group are 10 times more inhibitory than the parent molecules. Two molecules were identified with Kis about three orders of magnitude lower than reported for Imatinib.

On the stem cell origin of cancer

In each major theory of the origin of cancer-field theory, chemical carcinogenesis, infection, mutation, or epigenetic change-the tissue stem cell is involved in the generation of cancer. Although the cancer type is identified by the more highly differentiated cells in the cancer cell lineage or hierarchy (transit-amplifying cells), the property of malignancy and the molecular lesion of the cancer exist in the cancer stem cell. In the case of teratocarcinomas, normal germinal stem cells have the potential to become cancers if placed in an environment that allows expression of the cancer phenotype (field theory). In cancers due to chemically induced mutations, viral infections, somatic and inherited mutations, or epigenetic changes, the molecular lesion or infection usually first occurs in the tissue stem cells. Cancer stem cells then give rise to transit-amplifying cells and terminally differentiated cells, similar to what happens in normal tissue renewal. However, the major difference between cancer growth and normal tissue renewal is that whereas normal transit amplifying cells usually differentiate and die, at various levels of differentiation, the cancer transit-amplifying cells fail to differentiate normally and instead accumulate (ie, they undergo maturation arrest), resulting in cancer growth.

Bortezomib decreases Rb phosphorylation and induces caspase-dependent apoptosis in Imatinib-sensitive and -resistant Bcr-Abl1-expressing cells

The use of c-abl-specific inhibitors such as Imatinib (IM) or Dasatinib has revolutionized the treatment of chronic myeloid leukemia (CML). However, a significant percentage of patients become resistant to IM. In this report, we have analyzed the possibility of using the proteasome as a molecular target in CML. Our results show that cells that express Bcr-Abl1 are more sensitive to the inhibition of the proteasome with Bortezomib (Btz) than control cells. This treatment reduces the proliferation of Bcr-Abl1-expressing cells, by inactivating NF-kappaB2 and decreasing the phosphorylation of Rb, eventually leading to an increase in caspase-dependent apoptosis. Furthermore, we show that Btz also induces cell-cycle arrest and apoptosis in cells expressing Bcr-Abl1 mutants that are resistant to IM. These results unravel a new molecular target of Btz, that is the Rb pathway, and open new possibilities in the treatment of CML especially for patients that become resistant to IM because of the presence of the T315I mutation.