Differentiation status of primary chronic myeloid leukemia cells affects sensitivity to BCR-ABL1 inhibitors.

Paavo O Pietarinen,Olli Kallioniemi,John P Mpindi,Satu Mustjoki,Swapnil Potdar,Pilar Ayuda-Durán,Mika Kontro,Heikki Kuusanmäki,Henrik Hjorth-Hansen,Jorrit M Enserink,Krister Wennerberg,Kimmo Porkka,Brian J Druker,Caroline A Heckman,Jeffrey W Tyner,Emma I Andersson,Christopher A Eide,Tea Pemovska

doi:10.18632/oncotarget.15146

Abstract

Tyrosine kinase inhibitors (TKI) are the mainstay treatment of BCR-ABL1-positive leukemia and virtually all patients with chronic myeloid leukemia in chronic phase (CP CML) respond to TKI therapy. However, there is limited information on the cellular mechanisms of response and particularly on the effect of cell differentiation state to TKI sensitivity in vivo and ex vivo/in vitro. We used multiple, independent high-throughput drug sensitivity and resistance testing platforms that collectively evaluated 295 oncology compounds to characterize ex vivo drug response profiles of primary cells freshly collected from newly-diagnosed patients with BCR-ABL1-positive leukemia (n = 40) and healthy controls (n = 12). In contrast to the highly TKI-sensitive cells from blast phase CML and Philadelphia chromosome-positive acute lymphoblastic leukemia, primary CP CML cells were insensitive to TKI therapy ex vivo. Despite maintaining potent BCR-ABL1 inhibitory activity, ex vivo viability of cells was unaffected by TKIs. These findings were validated in two independent patient cohorts and analysis platforms. All CP CML patients under study responded to TKI therapy in vivo. When CP CML cells were sorted based on CD34 expression, the CD34-positive progenitor cells showed good sensitivity to TKIs, whereas the more mature CD34-negative cells were markedly less sensitive. Thus in CP CML, TKIs predominantly target the progenitor cell population while the differentiated leukemic cells (mostly cells from granulocytic series) are insensitive to BCR-ABL1 inhibition. These findings have implications for drug discovery in CP CML and indicate a fundamental biological difference between CP CML and advanced forms of BCR-ABL1-positive leukemia.

Highlights

All patients with chronic myeloid leukemia in chronic phase (CP CML) and other forms of BCRABL1-positive leukemia are currently treated with BCR-ABL1 tyrosine kinase inhibitors (TKIs)
Primary CP CML mononuclear cells are insensitive to TKI therapy ex vivo We first assessed the ex vivo drug sensitivity of fresh primary bone marrow (BM) and peripheral blood (PB) mononuclear cells (MNCs) from 25 CP CML patients using a panel of 295 approved and investigational drugs
The ex vivo drug sensitivity was assessed with a sensitivity score taking into account the area under the dose-response curve and normalizing the value to drug responses observed in healthy controls

Summary

Introduction

All patients with chronic myeloid leukemia in chronic phase (CP CML) and other forms of BCRABL1-positive leukemia are currently treated with BCR-ABL1 tyrosine kinase inhibitors (TKIs). Not all patients respond optimally to TKIs and some develop intolerance or secondary resistance. Most cases of TKI resistance are caused by mutations in the kinase domain of the BCRABL1 gene, but some patients develop resistance due to other mechanisms [3, 4]. Third generation TKIs targeting key gatekeeper mutations have been developed (e.g. ponatinib), there still is a need for novel treatment modalities for suboptimal responders. Several biological and genetic factors are known to differentiate the BCR-ABL1positive leukemias but the basic mechanisms governing the evolution from chronic to blast phase are still mostly unknown [5]. CP CML cells consist mostly of differentiated, mature myeloid cells (predominantly neutrophils) with a short half-life, while in BC CML and Ph+ ALL the predominant population consists of undifferentiated, primitive blast cells

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