Notch2 Increases the Resistance to Venetoclax-Induced Apoptosis in Chronic Lymphocytic Leukemia B Cells by Inducing Mcl-1.

Stefania Fiorcari,Silvia Martinelli,Claudio Giacinto Atene,Ambra Paolini,Roberto Marasca,Giulia Debbia,Mario Luppi,Vincenzo Nasillo,Nicolò Mesini,Leonardo Potenza,Giovanna Leonardi,Monica Maccaferri,Rossana Maffei

doi:10.3389/fonc.2021.777587

Stefania Fiorcari, Silvia Martinelli + Show 11 more

Open Access

https://doi.org/10.3389/fonc.2021.777587

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Abstract

Chronic lymphocytic leukemia (CLL) has experienced a clinical revolution—thanks to the discovery of crucial pathogenic mechanisms. CLL is still an incurable disease due to intrinsic or acquired resistance of the leukemic clone. Venetoclax is a Bcl-2 inhibitor with a marked activity in CLL, but emerging patterns of resistance are being described. We hypothesize that intrinsic features of CLL cells may contribute to drive mechanisms of resistance to venetoclax. We analyzed the expression of Interferon Regulatory Factor 4 (IRF4), Notch2, and Mcl-1 in a cohort of CLL patients. We evaluated CLL cell viability after genetic and pharmaceutical modulation of Notch2 expression in patients harboring trisomy 12. We tested venetoclax in trisomy 12 CLL cells either silenced or not for Notch2 expression or in combination with an inhibitor of Mcl-1, AMG-176. Trisomy 12 CLL cells were characterized by low expression of IRF4 associated with high levels of Notch2 and Mcl-1. Notch2 and Mcl-1 expression determined protection of CLL cells from spontaneous and drug-induced apoptosis. Considering the involvement of Mcl-1 in venetoclax resistance, our data demonstrated a contribution of high levels of Notch2 and Mcl-1 in a reduced response to venetoclax in CLL cells carrying trisomy 12. Furthermore, reduction of Mcl-1 expression by silencing Notch2 or by treatment with AMG-176 was able to restore the response of CLL cells to venetoclax. The expression of Notch2 identifies a subset of CLL patients, mainly harboring trisomy 12, characterized by high levels of Mcl-1. This biological mechanism may compromise an effective response to venetoclax.

Highlights

Chronic lymphocytic leukemia (CLL) represents the most common leukemia in western countries
We analyzed the level of Interferon Regulatory Factor 4 (IRF4) protein, confirming a lower expression of IRF4 in +12 CLL cells compared to no +12
We determined the differential expression of IRF4 in Notch1 unmutated and mutated samples and showed no significant difference between the two groups (Supplementary Figure S1, p = ns)

Summary

Introduction

Chronic lymphocytic leukemia (CLL) represents the most common leukemia in western countries. CLL is characterized by a wide clinical heterogeneity ranging from patients with a highly stable disease for many years to patients with an aggressive disease [1]. The deep reason of such clinical heterogeneity is not fully elucidated, it is mainly determined by genetic factors and by the complex relationship that leukemic cells entertain with the surrounding microenvironment. Trisomy 12 (+12) arises in about 15%–18% of CLL cases. Patients who harbor +12 are characterized by more rapid disease progression, huge lymph node involvement, and increased prevalence of Notch mutations [2]. Acquisition of trisomy 12 occurs in one-third of CLL patients who develop Richter syndrome [3]. Progresses in understanding CLL pathogenesis have been achieved, the molecular events underlying the complex biology of trisomy 12 CLL are still under investigation

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