Mechanisms of Resistance and Implications for Treatment Strategies in Chronic Myeloid Leukaemia

Simple Summary

Chronic myeloid leukaemia (CML) is a type of blood cancer that is currently well-managed with drugs that target cancer-causing proteins. However, a significant proportion of CML patients do not respond to those drug treatments or relapse when they stop those drugs because the cancer cells in those patients stop relying on that protein and instead develop a new way to survive. Therefore, new treatment strategies may be necessary for those patients. In this review, we discuss those additional survival pathways and outline combination treatment strategies to increase responses and clinical outcomes, improving the lives of CML patients.

Abstract

Tyrosine kinase inhibitors (TKIs) have revolutionised the management of chronic myeloid leukaemia (CML), with the disease now having a five-year survival rate over 80%. The primary focus in the treatment of CML has been on improving the specificity and potency of TKIs to inhibit the activation of the BCR::ABL1 kinase and/or overcoming resistance driven by mutations in the BCR::ABL1 oncogene. However, this approach may be limited in a significant proportion of patients who develop TKI resistance despite the effective inhibition of BCR::ABL1. These patients may require novel therapeutic strategies that target both BCR::ABL1-dependent and BCR::ABL1-independent mechanisms of resistance. The combination treatment strategies that target alternative survival signalling, which may contribute towards BCR::ABL1-independent resistance, could be a successful strategy for eradicating residual leukaemic cells and consequently increasing the response rate in CML patients.

Integrated Genomic Analysis Identifies ANKRD36 Gene as a Novel and Common Biomarker of Disease Progression in Chronic Myeloid Leukemia

Simple Summary

Chronic myeloid leukemia is a type of blood cancer that is regarded as a success story in determining the exact biological origin, pathogenesis and development of a molecularly targeted (mutation-specific) therapy that has led to successful treatment of this fatal cancer. It is caused by the BCR-ABL fusion gene, which is formed from the translocation between chromosomes 9 and 22. Anti-BCR-ABL drugs, known as tyrosine kinase inhibitors (TKIs), have led to long-term remissions in more than 80% of CML patients and even cure in about one-third of patients. Nevertheless, many patients face drug resistance, and disease progression occurs in about 30% of CML patients, leading to morbidities and mortality. Unfortunately, no biomarkers of CML progression are available due to a poor understanding of the mechanism of progression. Therefore, finding reliable molecular biomarkers of CML progression is one of the most attractive research areas in 21st-century cancer research. In this study, we report novel genomic variants exclusively found in all our advanced-phase CML patients. This study will help in identifying CML patients at risk of disease progression and timely therapeutic interventions to avoid or at least delay fatal disease progression in this cancer.

Abstract

Background: Chronic myeloid leukemia (CML) is initiated in bone marrow due to chromosomal translocation t(9;22) leading to fusion oncogene BCR-ABL. Targeting BCR-ABL by tyrosine kinase inhibitors (TKIs) has changed fatal CML into an almost curable disease. Despite that, TKIs lose their effectiveness due to disease progression. Unfortunately, the mechanism of CML progression is poorly understood and common biomarkers for CML progression are unavailable. This study was conducted to find novel biomarkers of CML progression by employing whole-exome sequencing (WES). Materials and Methods: WES of accelerated phase (AP) and blast crisis (BC) CML patients was carried out, with chronic-phase CML (CP-CML) patients as control. After DNA library preparation and exome enrichment, clustering and sequencing were carried out using Illumina platforms. Statistical analysis was carried out using SAS/STAT software version 9.4, and R package was employed to find mutations shared exclusively by all AP-/BC-CML patients. Confirmation of mutations was carried out using Sanger sequencing and protein structure modeling using I-TASSER followed by mutant generation and visualization using PyMOL. Results: Three novel genes (ANKRD36, ANKRD36B and PRSS3) were mutated exclusively in all AP-/BC-CML patients. Only ANKRD36 gene mutations (c.1183_1184 delGC and c.1187_1185 dupTT) were confirmed by Sanger sequencing. Protein modeling studies showed that mutations induce structural changes in ANKRD36 protein. Conclusions: Our studies show that ANKRD36 is a potential common biomarker and drug target of early CML progression. ANKRD36 is yet uncharacterized in humans. It has the highest expression in bone marrow, specifically myeloid cells. We recommend carrying out further studies to explore the role of ANKRD36 in the biology and progression of CML.

[The basophil: From control of immunity to control of leukemias]

The basophils, first described by Paul Ehlrich in 1879, are rare circulating cells, representing approximately 0.01 to 0.3% of the blood leukocytes. Until recently, these cells have been neglected because of their minority status among immune cells and because they show some similarities to mast cells residing in tissues. However, basophils and mast cells are now recognized as distinct cell lines and it appears that basophils have important and non-redundant functions, distinct from those of mast cells. On the one hand, basophils have beneficial contribution to protective immunity, in particular against parasitic infections. On the other hand, basophils are involved in the development of various benign and malignant pathologies, ranging from allergy to certain leukemias. Basophils interact with other immune cells or neoplastic cells through direct contacts or soluble mediators, such as cytokines and proteases, thus contributing to the regulation of the immune system but also to allergic responses, and probably to the process of neoplastic transformation. In this review, we will develop recent knowledge on the involvement of basophils in the modulation of innate and adaptive immunity. We will then describe the benign or malignant circumstances in which an elevation of circulating basophils can be observed. Finally, we will discuss the role played by these cells in the pathophysiology of certain leukemias, particularly during chronic myeloid leukemia.

Identification of Phosphate-Containing Compounds as New Inhibitors of 14-3-3/c-Abl Protein-Protein Interaction

The 14-3-3/c-Abl protein-protein interaction (PPI) is related to carcinogenesis and in particular to pathogenesis of chronic myeloid leukemia (CML). Previous studies have demonstrated that molecules able to disrupt this interaction improve the nuclear translocation of c-Abl, inducing apoptosis in leukemia cells. Through an X-ray crystallography screening program, we have identified two phosphate-containing compounds, inosine monophosphate (IMP) and pyridoxal phosphate (PLP), as binders of human 14-3-3σ, by targeting the protein amphipathic groove. Interestingly, they also act as weak inhibitors of the 14-3-3/c-Abl PPI, demonstrated by NMR, SPR, and FP data. A 37-compound library of PLP and IMP analogues was investigated using a FP assay, leading to the identification of three further molecules acting as weak inhibitors of the 14-3-3/c-Abl complex formation. The antiproliferative activity of IMP, PLP, and the three derivatives was tested against K-562 cells, showing that the parent compounds had the most pronounced effect on tumor cells. PLP and IMP were also effective in promoting the c-Abl nuclear translocation in c-Abl overexpressing cells. Further, these compounds demonstrated low cytotoxicity on human Hs27 fibroblasts. In conclusion, our data suggest that 14-3-3σ targeting compounds represent promising hits for further development of drugs against c-Abl-dependent cancers.

The growth of K562 human leukemia cells was inhibited by therapeutic neural stem cells in cellular and xenograft mouse models

To confirm the anti-tumor effect of engineered neural stem cells (NSCs) expressing cytosine deaminase (CD) and interferon-β (IFN-β) with prodrug 5-fluorocytosine (FC), K562 chronic myeloid leukemia (CML) cells were co-cultured with the neural stem cell lines HB1.F3.CD and HB1.F3.CD.IFN-β in 5-FC containing media. A significant decrease in the viability of K562 cells was observed by the treatment of the NSC lines, HB1.F3.CD and HB1.F3.CD.IFN-β, compared with the control. A modified trans-well assay showed that engineered human NSCs significantly migrated toward K562 CML cells more than human normal lung cells. In addition, the important chemoattractant factors involved in the specific migration ability of stem cells were found to be expressed in K562 CML cells. In a xenograft mouse model, NSC treatments via subcutaneous and intravenous injections resulted in significant inhibitions of tumor mass growth and extended survival dates of the mice. Taken together, these results suggest that gene therapy using genetically engineered stem cells expressing CD and IFN-β may be effective for treating CML in these mouse models.

Biophysical differences between chronic myelogenous leukemic quiescent and proliferating stem/progenitor cells

The treatment of chronic myeloid leukemia (CML), a clonal myeloproliferative disorder has improved recently, but most patients have not yet been cured. Some patients develop resistance to the available tyrosine kinase treatments. Persistence of residual quiescent CML stem cells (LSCs) that later resume proliferation is another common cause of recurrence or relapse of CML. Eradication of quiescent LSCs is a promising approach to prevent recurrence of CML. Here we report on new biophysical differences between quiescent and proliferating CD34+ LSCs, and speculate how this information could be of use to eradicate quiescent LSCs. Using AFM measurements on cells collected from four untreated CML patients, substantial differences are observed between quiescent and proliferating cells in the elastic modulus, pericellular brush length and its grafting density at the single cell level. The higher pericellular brush densities of quiescent LSCs are common for all samples. The significance of these observations is discussed.

Reconsideration of BCR-ABL protein flow cytometric immunobead assay: how potent to diagnose and monitor chronic myeloid leukemia?

INTRODUCTION

Chronic myeloid leukemia (CML) is typically associated with the Philadelphia chromosome, resulting in the production of BCR-ABL fusion oncoprotein with upregulated tyrosine kinase activity. We aimed to evaluate a new flow cytometric immunobead assay to detect BCR-ABL protein in a group of patients with CML.

METHODS

We enrolled 49 patients with CML, whose qRT-PCR and/or cytogenetic analysis of Philadelphia chromosome aberration was available, including tyrosine kinase inhibitors (TKIs)-naïve and (TKIs)-treated patients with various levels of response. Twenty Philadelphia-negative healthy individuals were also enrolled to obtain analytical negative controls. Peripheral blood samples were analyzed for BCR-ABL fusion protein by flow cytometry.

RESULTS

The BCR-ABL fusion protein flow cytometric assay seemed efficacious to both diagnose the presence (P-value <0.0001) and distinguish the levels (P-value = 0) of the Philadelphia chromosome aberration. Groups of TKI-naïve and TKI-treated patients as well as levels of molecular/cytogenetic response to TKI-therapy were effectively discriminated (P-value <0.01). The receiver operating characteristic (ROC) curve analysis indicated the diagnostic value of the assay as excellent (AUC = 0.95, P-value = 0).

CONCLUSIONS

The evaluated BCR-ABL fusion protein assay might be useful for diagnosing and monitoring Philadelphia chromosome aberration.

Sphingomyelin synthase 1 activity is regulated by the BCR-ABL oncogene

Sphingomyelin synthase (SMS) produces sphingomyelin while consuming ceramide (a negative regulator of cell proliferation) and forming diacylglycerol (DAG) (a mitogenic factor). Therefore, enhanced SMS activity could favor cell proliferation. To examine if dysregulated SMS contributes to leukemogenesis, we measured SMS activity in several leukemic cell lines and found that it is highly elevated in K562 chronic myelogenous leukemia (CML) cells. The increased SMS in K562 cells was caused by the presence of Bcr-abl, a hallmark of CML; stable expression of Bcr-abl elevated SMS activity in HL-60 cells while inhibition of the tyrosine kinase activity of Bcr-abl with Imatinib mesylate decreased SMS activity in K562 cells. The increased SMS activity was the result of up-regulation of the Sms1 isoform. Inhibition of SMS activity with D609 (a pharmacological SMS inhibitor) or down-regulation of SMS1 expression by siRNA selectively inhibited the proliferation of Bcr-abl-positive cells. The inhibition was associated with an increased production of ceramide and a decreased production of DAG, conditions that antagonize cell proliferation. A similar change in lipid profile was also observed upon pharmacological inhibition of Bcr-abl (K526 cells) and siRNA-mediated down-regulation of BCR-ABL (HL-60/Bcr-abl cells). These findings indicate that Sms1 is a downstream target of Bcr-abl, involved in sustaining cell proliferation of Bcr-abl-positive cells.

Association of HLA antigens and BCR-ABL transcripts in leukemia patients with the Philadelphia chromosome

Objective

This study aimed to verify the association between human leukocyte antigens and the bcr-abl fusion protein resulting from t(9;22)(q34;q11) in chronic leukemia myeloid and acute lymphoblastic leukemia patients.

Methods

Forty-seven bcr-abl positive individuals were evaluated. Typing was performed bymicrolymphocytotoxicity and molecular biological methods (human leukocyte antigens Class I and Class II). A control group was obtained from the data of potential bone marrow donors registered in the Brazilian Bone Marrow Donor Registry (REDOME).

Results

Positive associations with HLA-A25 and HLA-B18 were found for the b2a2 transcript, as well as a tendency towards a positive association with HLA-B40 and a negative association with HLA-A68. The b3a2 transcript showed positive associations with HLA-B40 and HLA-DRB1*3.

Conclusion

The negative association between human leukocyte antigens and the BCR-ABL transcript suggests that binding and presentation of peptides derived from the chimeric protein are effective to increase a cytotoxic T lymphocyte response appropriate for the destruction of leukemic cells.

Case-matched comparison with standard versus reduced intensity conditioning regimen in chronic myeloid leukemia patients

This retrospective case-matched study evaluated the efficacy of reduced intensity conditioning (RIC) regimen on early and late allogeneic transplant outcome in chronic myeloid leukemia (CML) patients. Twenty-eight patients conditioned with RIC regimen were matched to 56 patients who received a myeloablative conditioning (MAC) regimen. The main criteria for case matching among our CML allotransplant cohort were the Gratwohl scoring system. The median score was 2 (1-4) in each group. The pretransplant disease status was first chronic phase (CP1, n = 20), CP2 (n = 2), and advanced phase (n = 6) in RIC, and CP1 (n = 46), CP2 (n = 3), and advanced phase (n = 7) in MAC. The duration of neutropenia and thrombocytopenia was shorter in RIC than MAC. The grade and duration of mucositis were less in RIC. The need for total parenteral nutrition (21% vs. 77%, p < 0.0001) and febrile neutropenic episodes (50% vs. 95%, p < 0.0001) were observed less frequently in RIC compared with MAC-given patients. Acute or chronic graft versus host diseases (GvHD) were not affected by the intensity of conditioning regimen. The incidence of transplant-related mortality was higher in MAC (7% vs. 14%, p = 0.01). Although more relapse/progression was observed in the RIC group, the probability of 5- and 10-year leukemia-free- and overall survival were similar regardless of conditioning regimen intensity (p > 0.05). In early first CP, the pair of female donor-male recipient and the development of chronic GvHD prolonged both leukemia-free survival and overall survival in multivariate analysis. According to our single-center matched-pair analysis, the use of RIC regimens in patients with low-risk CML results with toxicities less, responses later, and relapses more frequent than the MAC regimens.

Role of peroxisome proliferator-activated receptor gamma and its ligands in the treatment of hematological malignancies

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a multifunctional transcription factor with important regulatory roles in inflammation, cellular growth, differentiation, and apoptosis. PPARgamma is expressed in a variety of immune cells as well as in numerous leukemias and lymphomas. Here, we review recent studies that provide new insights into the mechanisms by which PPARgamma ligands influence hematological malignant cell growth, differentiation, and survival. Understanding the diverse properties of PPARgamma ligands is crucial for the development of new therapeutic approaches for hematological malignancies.

Monitoring response and resistance to treatment in chronic myeloid leukemia

Chronic myeloid leukemia (cml) results from expression of the constitutive tyrosine kinase activity of the Bcr-Abl oncoprotein. Imatinib, a tyrosine kinase inhibitor (tki), is highly effective in the treatment of cml. However, some patients treated with imatinib will fail to respond, will respond suboptimally, or will relapse because of primary or acquired resistance or intolerance. Research activities focusing on the mechanisms that underlie imatinib resistance have identified mutations in the BCR-ABL gene, clonal evolution, and amplification of the BCR-ABL gene as common causes. Cytogenetic and molecular techniques are currently used to monitor cml therapy for both response and relapse. With multiple and more potent therapeutic options now available, monitoring techniques can permit treatment to be tailored to the individual patient based on disease characteristics-for example, according to BCR-ABL mutation profile or to patient characteristics such as certain comorbid conditions. This approach should benefit patients by increasing the potential for better long-term outcomes.

Detection of DNA fusion junctions for BCR-ABL translocations by Anchored ChromPET

Anchored ChromPET, a technique to capture and interrogate targeted sequences in the genome, has been developed to identify chromosomal aberrations and define breakpoints. Using this method, we could define the BCR-ABL1 translocation DNA breakpoint to a base-pair resolution in Philadelphia chromosome-positive samples. This DNA-based method is highly sensitive and can detect the fusion junction using samples from which it is hard to obtain RNA or cells where the RNA expression has been silenced.

A rare case of Philadelphia chromosome-positive chronic myelogenous leukemia with inversion in chromosome 9 and t(10;17)

The reciprocal translocation t(9;22)(q34;q11), leading to the formation of two fusion genes, BCR/ABL and ABL/BCR, is found in 90-95% of cases with chronic myeloid leukemia (CML). ABL-BCR expression does not correlate with prognosis, as assessed by cytogenetic response, since the ABL/BCR gene is expressed in only a proportion of CML patients. This study examined an exceptional BCR/ABL-positive CML case with inversion in 9q22q34 leading to the absence of ABL/BCR. Moreover, an unbalanced translocation between chromosomes 10 and 17 which caused deletion of the TP53 gene was identified. The TP53 gene plays a potential role in CML progression, and loss of TP53 may be regarded as a poor prognostic factor.

Novel complex translocation involving 5 different chromosomes in a chronic myeloid leukemia with Philadelphia chromosome: a case report

BACKGROUND

The well-known typical fusion gene BCR/ABL can be observed in connection with a complex translocation event in only 2-10% of cases with chronic myeloid leukemia (CML). As currently most CML cases are treated with Imatinib, variant rearrangements have in general no specific prognostic significance, though the emergence of therapy resistance remains to be studied.

RESULTS

Here we report an exceptional CML case with complex chromosomal aberrations not observed before, involving a 5 chromosome translocation implying chromosomal regions such as 1q42, 4p14 and 5q31 besides 9q34 and 22q11.2.

CONCLUSION

The reported rearrangement developed most probably in one initial step and had no influence on a good response during Imatinib treatment.