Acquired resistance to DZNep-mediated apoptosis is associated with copy number gains of AHCY in a B-cell lymphoma model
Chidimma Agatha Akpa,
Karsten Kleo,
Elisabeth Oker,
Nancy Tomaszewski,
Clemens Messerschmidt,
Cristina López,
Rabea Wagener,
Kathrin Oehl-Huber,
Katja Dettmer,
Anne Schoeler,
Dido Lenze,
Peter J. Oefner,
Dieter Beule,
Reiner Siebert,
David Capper,
Lora Dimitrova,
Michael Hummel
Affiliations
Chidimma Agatha Akpa
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Karsten Kleo
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Elisabeth Oker
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Nancy Tomaszewski
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Clemens Messerschmidt
Berlin Institute of Health, Charité Core Unit Bioinformatics
Cristina López
Institute of Human Genetics, Ulm University and Ulm University Medical Center
Rabea Wagener
Institute of Human Genetics, Ulm University and Ulm University Medical Center
Kathrin Oehl-Huber
Institute of Human Genetics, Ulm University and Ulm University Medical Center
Katja Dettmer
Institute of Functional Genomics, University of Regensburg
Anne Schoeler
Department of Neuropathology, Charité, Medical University of Berlin, corporate member of Free University Berlin, Humboldt-University Berlin, and Berlin Institute of Health
Dido Lenze
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Peter J. Oefner
Berlin School of Integrative Oncology, Charité - Medical University of Berlin
Dieter Beule
Berlin Institute of Health, Charité Core Unit Bioinformatics
Reiner Siebert
Institute of Human Genetics, Ulm University and Ulm University Medical Center
David Capper
Berlin School of Integrative Oncology, Charité - Medical University of Berlin
Lora Dimitrova
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Michael Hummel
Department of Experimental Hematopathology, Institute of Pathology, Charité Medical University, Berlin
Abstract Background Enhancer of zeste homolog 2 (EZH2) is considered an important driver of tumor development and progression by its histone modifying capabilities. Inhibition of EZH2 activity is thought to be a potent treatment option for eligible cancer patients with an aberrant EZH2 expression profile, thus the indirect EZH2 inhibitor 3-Deazaneplanocin A (DZNep) is currently under evaluation for its clinical utility. Although DZNep blocks proliferation and induces apoptosis in different tumor types including lymphomas, acquired resistance to DZNep may limit its clinical application. Methods To investigate possible mechanisms of acquired DZNep resistance in B-cell lymphomas, we generated a DZNep-resistant clone from a previously DZNep-sensitive B-cell lymphoma cell line by long-term treatment with increasing concentrations of DZNep (ranging from 200 to 2000 nM) and compared the molecular profiles of resistant and wild-type clones. This comparison was done using molecular techniques such as flow cytometry, copy number variation assay (OncoScan and TaqMan assays), fluorescence in situ hybridization, Western blot, immunohistochemistry and metabolomics analysis. Results Whole exome sequencing did not indicate the acquisition of biologically meaningful single nucleotide variants. Analysis of copy number alterations, however, demonstrated among other acquired imbalances an amplification (about 30 times) of the S-adenosyl-L-homocysteine hydrolase (AHCY) gene in the resistant clone. AHCY is a direct target of DZNep and is critically involved in the biological methylation process, where it catalyzes the reversible hydrolysis of S-adenosyl-L-homocysteine to L-homocysteine and adenosine. The amplification of the AHCY gene is paralleled by strong overexpression of AHCY at both the transcriptional and protein level, and persists upon culturing the resistant clone in a DZNep-free medium. Conclusions This study reveals one possible molecular mechanism how B-cell lymphomas can acquire resistance to DZNep, and proposes AHCY as a potential biomarker for investigation during the administration of EZH2-targeted therapy with DZNep.
