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Pozzo F, Forestieri G, Vit F, Ianna G, Tissino E, Bittolo T, Papotti R, Gaglio A, Terzi di Bergamo L, Steffan A, Polesel J, Bulian P, Laureana R, Tafuri A, Chiarenza A, Di Raimondo F, Olivieri J, Zaja F, Laurenti L, Del Principe MI, Postorino M, Del Poeta G, Bomben R, Zucchetto A, Rossi D, Gattei V. Early reappearance of intraclonal proliferative subpopulations in ibrutinib-resistant chronic lymphocytic leukemia. Leukemia 2024:10.1038/s41375-024-02301-y. [PMID: 38914716 DOI: 10.1038/s41375-024-02301-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Revised: 05/29/2024] [Accepted: 05/31/2024] [Indexed: 06/26/2024]
Abstract
The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib represents an effective strategy for treatment of chronic lymphocytic leukemia (CLL), nevertheless about 30% of patients eventually undergo disease progression. Here we investigated by flow cytometry the long-term modulation of the CLL CXCR4dim/CD5bright proliferative fraction (PF), its correlation with therapeutic outcome and emergence of ibrutinib resistance. By longitudinal tracking, the PF, initially suppressed by ibrutinib, reappeared upon early disease progression, without association with lymphocyte count or serum beta-2-microglobulin. Somatic mutations of BTK/PLCG2, detected in 57% of progressing cases, were significantly enriched in PF with a 3-fold greater allele frequency than the non-PF fraction, suggesting a BTK/PLCG2-mutated reservoir resident within the proliferative compartments. PF increase was also present in BTK/PLCG2-unmutated cases at progression, indicating that PF evaluation could represent a marker of CLL progression under ibrutinib. Furthermore, we evidence different transcriptomic profiles of PF at progression in cases with or without BTK/PLCG2 mutations, suggestive of a reactivation of B-cell receptor signaling or the emergence of bypass signaling through MYC and/or Toll-Like-Receptor-9. Clinically, longitudinal monitoring of the CXCR4dim/CD5bright PF by flow cytometry may provide a simple tool helping to intercept CLL progression under ibrutinib therapy.
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Affiliation(s)
- Federico Pozzo
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy.
| | - Gabriela Forestieri
- Experimental Hematology, Institute of Oncology Research, Bellinzona, 6500, Switzerland
| | - Filippo Vit
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Giulia Ianna
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Erika Tissino
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Tamara Bittolo
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Robel Papotti
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Annalisa Gaglio
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | | | - Agostino Steffan
- Immunopathology and Cancer Biomarkers, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Jerry Polesel
- Unit of Cancer Epidemiology, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, 33081, Italy
| | - Pietro Bulian
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Roberta Laureana
- Department of Biomedicine and Prevention, Hematology, University Tor Vergata, Rome, 00133, Italy
| | - Agostino Tafuri
- Hematology Unit, Azienda Ospedaliera-Universitaria Sant'Andrea, Rome, 00189, Italy
| | | | | | - Jacopo Olivieri
- Hematology Clinic, Azienda Sanitaria Universitaria Friuli Centrale (ASUFC), Udine, 33100, Italy
| | - Francesco Zaja
- Department of Medical, Surgical and Health Sciences, University of Trieste, Trieste, 34127, Italy
| | - Luca Laurenti
- Institute of Hematology, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, 00168, Italy
| | | | - Massimiliano Postorino
- Department of Biomedicine and Prevention, Hematology, University Tor Vergata, Rome, 00133, Italy
| | - Giovanni Del Poeta
- Department of Biomedicine and Prevention, Hematology, University Tor Vergata, Rome, 00133, Italy
| | - Riccardo Bomben
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Antonella Zucchetto
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy
| | - Davide Rossi
- Experimental Hematology, Institute of Oncology Research, Bellinzona, 6500, Switzerland
| | - Valter Gattei
- Clinical and Experimental Onco-Hematology Unit, Centro di Riferimento Oncologico di Aviano (CRO), IRCCS, Aviano, 33081, Italy.
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Hoferkova E, Seda V, Kadakova S, Verner J, Loja T, Matulova K, Skuhrova Francova H, Ondrouskova E, Filip D, Blavet N, Boudny M, Mladonicka Pavlasova G, Vecera J, Ondrisova L, Pavelkova P, Hlavac K, Kostalova L, Michaelou A, Pospisilova S, Dorazilova J, Chochola V, Jaros J, Doubek M, Jarosova M, Hampl A, Vojtova L, Kren L, Mayer J, Mraz M. Stromal cells engineered to express T cell factors induce robust CLL cell proliferation in vitro and in PDX co-transplantations allowing the identification of RAF inhibitors as anti-proliferative drugs. Leukemia 2024:10.1038/s41375-024-02284-w. [PMID: 38877102 DOI: 10.1038/s41375-024-02284-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 05/03/2024] [Accepted: 05/09/2024] [Indexed: 06/16/2024]
Abstract
Several in vitro models have been developed to mimic chronic lymphocytic leukemia (CLL) proliferation in immune niches; however, they typically do not induce robust proliferation. We prepared a novel model based on mimicking T-cell signals in vitro and in patient-derived xenografts (PDXs). Six supportive cell lines were prepared by engineering HS5 stromal cells with stable expression of human CD40L, IL4, IL21, and their combinations. Co-culture with HS5 expressing CD40L and IL4 in combination led to mild CLL cell proliferation (median 7% at day 7), while the HS5 expressing CD40L, IL4, and IL21 led to unprecedented proliferation rate (median 44%). The co-cultures mimicked the gene expression fingerprint of lymph node CLL cells (MYC, NFκB, and E2F signatures) and revealed novel vulnerabilities in CLL-T-cell-induced proliferation. Drug testing in co-cultures revealed for the first time that pan-RAF inhibitors fully block CLL proliferation. The co-culture model can be downscaled to five microliter volume for large drug screening purposes or upscaled to CLL PDXs by HS5-CD40L-IL4 ± IL21 co-transplantation. Co-transplanting NSG mice with purified CLL cells and HS5-CD40L-IL4 or HS5-CD40L-IL4-IL21 cells on collagen-based scaffold led to 47% or 82% engraftment efficacy, respectively, with ~20% of PDXs being clonally related to CLL, potentially overcoming the need to co-transplant autologous T-cells in PDXs.
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Affiliation(s)
- Eva Hoferkova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
- Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Vaclav Seda
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Sona Kadakova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Jan Verner
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Tomas Loja
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Kvetoslava Matulova
- Department of Pathology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Hana Skuhrova Francova
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Eva Ondrouskova
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Daniel Filip
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Nicolas Blavet
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Miroslav Boudny
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | | | - Josef Vecera
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Laura Ondrisova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Petra Pavelkova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Krystof Hlavac
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Lenka Kostalova
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Androniki Michaelou
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Sarka Pospisilova
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Jana Dorazilova
- Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic
| | - Vaclav Chochola
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Josef Jaros
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Michael Doubek
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Marie Jarosova
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Ales Hampl
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Lucy Vojtova
- Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic
| | - Leos Kren
- Department of Pathology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Jiri Mayer
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Marek Mraz
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
- Department of Internal Medicine, Hematology and Oncology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic.
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Xue X, Wen Z, Zhang X, Yang Y, Li Y, Liao R, Zheng Q, Fu Y, Liu Y, Liao H. CXCR4 overexpression in chronic lymphocytic leukemia associates with poorer prognosis: A prospective, single-center, observational study. Genes Immun 2024; 25:117-123. [PMID: 38366101 DOI: 10.1038/s41435-024-00258-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 01/28/2024] [Accepted: 02/02/2024] [Indexed: 02/18/2024]
Abstract
Controversial data have been reported on the prognostic value of C-X-C motif chemokine receptor 4 (CXCR4) in chronic lymphocytic leukemia (CLL). This prospective, single-center, observational study aimed to evaluate the role of CXCR4 in the pathophysiology of CLL and its prognostic role. A total of 158 patients of CLL were enrolled, and CXCR4 expression on CLL cells was detected by flow cytometry (FCM) at initial diagnosis. The patients were divided into 2 groups according to the CXCR4 mean fluorescence intensity (MFI) median. Also, four patient specimens from the CXCR4low and CXCR4high groups were selected for RNASeq analysis. The progression-free survival (PFS) of CLL patients in the CXCR4high group was significantly shorter than the CXCR4low group, with a median follow-up time of 27 months (log-rank P < 0.001). Moreover, CXCR4 overexpression (MFI > 3376) was an independent marker of poor PFS in CLL patients (P < 0.001). Analysis of RNASeq results revealed that CXCR4 plays an important role in the migration of CLL. Collectively, CXCR4 expression levels on leukemia cells can be detected rapidly by FCM. CXCR4 overexpression was significantly associated with poorer prognosis in CLL patients within a shorter follow-up time.
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MESH Headings
- Humans
- Leukemia, Lymphocytic, Chronic, B-Cell/diagnosis
- Leukemia, Lymphocytic, Chronic, B-Cell/genetics
- Leukemia, Lymphocytic, Chronic, B-Cell/metabolism
- Prospective Studies
- Receptors, CXCR4/genetics
- Receptors, CXCR4/metabolism
- Signal Transduction
- Prognosis
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Affiliation(s)
- Xinran Xue
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Zhihao Wen
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Xin Zhang
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Ying Yang
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Yifei Li
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Ruoxi Liao
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Qin Zheng
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Yang Fu
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Yu Liu
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Hongyan Liao
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China.
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Old and New Facts and Speculations on the Role of the B Cell Receptor in the Origin of Chronic Lymphocytic Leukemia. Int J Mol Sci 2022; 23:ijms232214249. [PMID: 36430731 PMCID: PMC9693457 DOI: 10.3390/ijms232214249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 11/09/2022] [Accepted: 11/11/2022] [Indexed: 11/19/2022] Open
Abstract
The engagement of the B cell receptor (BcR) on the surface of leukemic cells represents a key event in chronic lymphocytic leukemia (CLL) since it can lead to the maintenance and expansion of the neoplastic clone. This notion was initially suggested by observations of the CLL BcR repertoire and of correlations existing between certain BcR features and the clinical outcomes of single patients. Based on these observations, tyrosine kinase inhibitors (TKIs), which block BcR signaling, have been introduced in therapy with the aim of inhibiting CLL cell clonal expansion and of controlling the disease. Indeed, the impressive results obtained with these compounds provided further proof of the role of BcR in CLL. In this article, the key steps that led to the determination of the role of BcR are reviewed, including the features of the CLL cell repertoire and the fine mechanisms causing BcR engagement and cell signaling. Furthermore, we discuss the biological effects of the engagement, which can lead to cell survival/proliferation or apoptosis depending on certain intrinsic cell characteristics and on signals that the micro-environment can deliver to the leukemic cells. In addition, consideration is given to alternative mechanisms promoting cell proliferation in the absence of BcR signaling, which can explain in part the incomplete effectiveness of TKI therapies. The role of the BcR in determining clonal evolution and disease progression is also described. Finally, we discuss possible models to explain the selection of a special BcR set during leukemogenesis. The BcR may deliver activation signals to the cells, which lead to their uncontrolled growth, with the possible collaboration of other still-undefined events which are capable of deregulating the normal physiological response of B cells to BcR-delivered stimuli.
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Pacholewska A, Grimm C, Herling CD, Lienhard M, Königs A, Timmermann B, Altmüller J, Mücke O, Reinhardt HC, Plass C, Herwig R, Hallek M, Schweiger MR. Altered DNA Methylation Profiles in SF3B1 Mutated CLL Patients. Int J Mol Sci 2021; 22:ijms22179337. [PMID: 34502260 PMCID: PMC8431484 DOI: 10.3390/ijms22179337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 08/20/2021] [Accepted: 08/25/2021] [Indexed: 12/13/2022] Open
Abstract
Mutations in splicing factor genes have a severe impact on the survival of cancer patients. Splicing factor 3b subunit 1 (SF3B1) is one of the most frequently mutated genes in chronic lymphocytic leukemia (CLL); patients carrying these mutations have a poor prognosis. Since the splicing machinery and the epigenome are closely interconnected, we investigated whether these alterations may affect the epigenomes of CLL patients. While an overall hypomethylation during CLL carcinogenesis has been observed, the interplay between the epigenetic stage of the originating B cells and SF3B1 mutations, and the subsequent effect of the mutations on methylation alterations in CLL, have not been investigated. We profiled the genome-wide DNA methylation patterns of 27 CLL patients with and without SF3B1 mutations and identified local decreases in methylation levels in SF3B1mut CLL patients at 67 genomic regions, mostly in proximity to telomeric regions. These differentially methylated regions (DMRs) were enriched in gene bodies of cancer-related signaling genes, e.g., NOTCH1, HTRA3, and BCL9L. In our study, SF3B1 mutations exclusively emerged in two out of three epigenetic stages of the originating B cells. However, not all the DMRs could be associated with the methylation programming of B cells during development, suggesting that mutations in SF3B1 cause additional epigenetic aberrations during carcinogenesis.
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Affiliation(s)
- Alicja Pacholewska
- Institute for Translational Epigenetics, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (A.P.); (C.G.); (A.K.)
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
| | - Christina Grimm
- Institute for Translational Epigenetics, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (A.P.); (C.G.); (A.K.)
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
| | - Carmen D. Herling
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf, German CLL Study Group, Department I of Internal Medicine, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (C.D.H.); (H.C.R.); (M.H.)
| | - Matthias Lienhard
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany; (M.L.); (R.H.)
| | - Anja Königs
- Institute for Translational Epigenetics, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (A.P.); (C.G.); (A.K.)
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
| | - Bernd Timmermann
- Sequencing Core Facility, Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany;
| | - Janine Altmüller
- Cologne Center for Genomics, University of Cologne, 50931 Cologne, Germany;
| | - Oliver Mücke
- German Cancer Research Center, Cancer Epigenomics, 69120 Heidelberg, Germany; (O.M.); (C.P.)
| | - Hans Christian Reinhardt
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf, German CLL Study Group, Department I of Internal Medicine, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (C.D.H.); (H.C.R.); (M.H.)
- German Cancer Consortium (DKTK), 69120 Heidelberg, Germany
- West German Cancer Center Essen, Department of Hematology and Stem Cell Transplantation, University Hospital Essen, 45147 Essen, Germany
| | - Christoph Plass
- German Cancer Research Center, Cancer Epigenomics, 69120 Heidelberg, Germany; (O.M.); (C.P.)
- German Cancer Consortium (DKTK), 69120 Heidelberg, Germany
| | - Ralf Herwig
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany; (M.L.); (R.H.)
| | - Michael Hallek
- Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf, German CLL Study Group, Department I of Internal Medicine, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (C.D.H.); (H.C.R.); (M.H.)
| | - Michal R. Schweiger
- Institute for Translational Epigenetics, Faculty of Medicine, University Hospital Cologne, 50931 Cologne, Germany; (A.P.); (C.G.); (A.K.)
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany
- Correspondence:
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FoxO1-GAB1 axis regulates homing capacity and tonic AKT activity in chronic lymphocytic leukemia. Blood 2021; 138:758-772. [PMID: 33786575 DOI: 10.1182/blood.2020008101] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 03/21/2021] [Indexed: 12/18/2022] Open
Abstract
Recirculation of chronic lymphocytic leukemia (CLL) cells between the peripheral blood and lymphoid niches plays a critical role in disease pathophysiology, and inhibiting this process is one of the major mechanisms of action for B-cell receptor (BCR) inhibitors such as ibrutinib and idelalisib. Migration is a complex process guided by chemokine receptors and integrins. However, it remains largely unknown how CLL cells integrate multiple migratory signals while balancing survival in the peripheral blood and the decision to return to immune niches. Our study provided evidence that CXCR4/CD5 intraclonal subpopulations can be used to study the regulation of migration of CLL cells. We performed RNA profiling of CXCR4dimCD5bright vs CXCR4brightCD5dim CLL cells and identified differential expression of dozens of molecules with a putative function in cell migration. GRB2-associated binding protein 1 (GAB1) positively regulated CLL cell homing capacity of CXCR4brightCD5dim cells. Gradual GAB1 accumulation in CLL cells outside immune niches was mediated by FoxO1-induced transcriptional GAB1 activation. Upregulation of GAB1 also played an important role in maintaining basal phosphatidylinositol 3-kinase (PI3K) activity and the "tonic" AKT phosphorylation required to sustain the survival of resting CLL B cells. This finding is important during ibrutinib therapy, because CLL cells induce the FoxO1-GAB1-pAKT axis, which represents an adaptation mechanism to the inability to home to immune niches. We have demonstrated that GAB1 can be targeted therapeutically by novel GAB1 inhibitors, alone or in combination with BTK inhibition. GAB1 inhibitors induce CLL cell apoptosis, impair cell migration, inhibit tonic or BCR-induced AKT phosphorylation, and block compensatory AKT activity during ibrutinib therapy.
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