Page 114 - Haematologica June

1016
L. Trentin et al.
Interestingly, ROSlow cells possessed an engraftment advantage with the transplanted mice having a shorter leukemia-free survival. Therefore, as already reported for HSC,30,33 our data suggest that increased ROS levels are associated with reduced repopulating stem cell activity in BCP-ALL. Along this line, it is interesting to note that higher endogenous ROS levels were detected in TTLlong/good prognosis samples. While an increased ROS level in HSC was directly linked to MAP kinase activation, we could not detect differential expression of p38α/β in the TTLlong/TTLshort subgroups characterized by different engraftment properties and ROS levels. In T-ALL, a differ- ent pathway for modulating the ROS status involving PKC-θ was described. However, we could not detect PKC expression at all in our leukemia cells. Thus, the molecular mechanism and/or association of specific pathways with different ROS states is unclear, but may be linked to dif- ferent activation of survival pathways, as indicated by the gene profile.
In addition to cell intrinsic mechanisms, neighboring cells in the bone marrow environment interact with resid- ing hematopoietic or leukemia cells and contribute to reg- ulation of cellular programs including proliferation and cell cycle,47 and homing and interaction of leukemia cells with the environment are modulated by the expression of adhesion molecules.48 Topographically, in ALL a rare sub- fraction of cells was described to preferentially reside close to the endosteum,40 the assumed site of the hematopoietic niche in the bone marrow.49 Similar to our findings, these cells were characterized by low prolifera- tion and insensitivity to chemotherapy, but did not show higher LIC activity compared to the corresponding non- dormant bulk leukemia cells.40 It appears very likely, that the ability of a cell to initiate leukemia is determined by different factors including niche interactions contributing to the phenotype of early cycling cells with low metabol- ic activity identified in our study. Interestingly, recently presented data showed that HSC are able to transfer mitochondria into adjacent stromal cells, thereby lower-
ing their intracellular ROS levels.50 High mTOR expres- sion,15 lower cellular propensity to undergo apoptosis,16 and the higher cycling capacity are cell intrinsic character- istics leading to the high proliferative potential of leukemia cells in poor prognosis patients, independently of the capacity of all leukemia cells to engraft in mice as described in this work, and the even higher LIC potential distinguishing G1blow leukemia cells.
Our work adds new information in the search for LIC in BCP-ALL, at least in experimental models of human BCP-ALL. The ability to initiate leukemia seems not to be associated with particular subtypes of the heterogeneous leukemia subfractions and also appears to be independent of the cell cycle compartment from which the leuke- mogenic cells are transplanted. This argues strongly against the concept that leukemogenesis is restricted to quiescent clones and absent or reduced in cycling cells or vice versa. Thus, this finding has consequences for thera- peutic strategies, which aim to target exclusively quies- cent or dividing cells. Interestingly however, cells in qui- escence or the early phase of the cell cycle appear to be more resistant to cell death induction than cells in other compartments of the cell cycle. The high LIC potential and low metabolic activity associated with cell death resistance may also indicate that strategies to activate these cells to exit quiescence or the early phase compart- ment may decrease intrinsic cell death resistance with resulting consequences for treatment sensitivity.
Acknowledgments
The authors would like to thank Sandra Lutz and Manuel Herrmann for excellent technical assistance and the Sorting and Chip Core Facilities, Ulm University. This work was supported by the German Research Foundation (KFO 167, K-MD and MQ; SFB1074 B6, LHM and K-MD), the Helmholtz Association/Preclinical Comprehensive Cancer Center (K-MD), the International Graduate School in Molecular Medicine Ulm (MNH, VM and EB), and the “Förderkreis für Tumor- und Leukämiekranke Kinder Ulm”.
References
1. Bryder D, Rossi DJ, Weissman IL. Hematopoietic stem cells: the paradigmatic tissue-specific stem cell. Am J Pathol. 2006;169(2):338-346.
2. Lapidot T, Sirard C, Vormoor J, et al. A cell initiating human acute myeloid leukaemia after transplantation into SCID mice. Nature. 1994;367(6464):645-648.
3. Bonnet D, Dick JE. Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat Med. 1997;3(7):730-737.
4. Sarry JE, Murphy K, Perry R, et al. Human acute myelogenous leukemia stem cells are rare and heterogeneous when assayed in NOD/SCID/IL2Rgammac-deficient mice. J Clin Invest. 2011;121(1):384-395.
5. Taussig DC, Miraki-Moud F, Anjos-Afonso F, et al. Anti-CD38 antibody-mediated clear- ance of human repopulating cells masks the heterogeneity of leukemia-initiating cells. Blood. 2008;112(3):568-575.
6. Taussig DC, Vargaftig J, Miraki-Moud F, et
al. Leukemia-initiating cells from some acute myeloid leukemia patients with mutated nucleophosmin reside in the CD34(-) frac- tion. Blood. 2010;115(10):1976-1984.
7. Jin L, Lee EM, Ramshaw HS, et al. Monoclonal antibody-mediated targeting of CD123, IL-3 receptor alpha chain, eliminates human acute myeloid leukemic stem cells. Cell Stem Cell. 2009;5(1):31-42.
8. Eppert K, Takenaka K, Lechman ER, et al. Stem cell gene expression programs influ- ence clinical outcome in human leukemia. Nat Med. 2011;17(9):1086-1093.
9. Rehe K, Wilson K, Bomken S, et al. Acute B lymphoblastic leukaemia-propagating cells are present at high frequency in diverse lym- phoblast populations. EMBO Mol Med. 2012;5(1):38-51.
10. Cobaleda C, Gutierrez-Cianca N, Perez- Losada J, et al. A primitive hematopoietic cell is the target for the leukemic transforma- tion in human Philadelphia-positive acute lymphoblastic leukemia. Blood. 2000;95(3): 1007-1013.
11. Hong D, Gupta R, Ancliff P, et al. Initiating and cancer-propagating cells in TEL-AML1-
associated childhood leukemia. Science.
2008;319(5861):336-339.
12. le Viseur C, Hotfilder M, Bomken S, et al. In
childhood acute lymphoblastic leukemia, blasts at different stages of immunopheno- typic maturation have stem cell properties. Cancer Cell. 2008;14(1):47-58.
13. Cox CV, Diamanti P, Evely RS, Kearns PR, Blair A. Expression of CD133 on leukemia- initiating cells in childhood ALL. Blood. 2009;113(14):3287-3296.
14. Meyer LH, Eckhoff SM, Queudeville M, et al. Early relapse in ALL is identified by time to leukemia in NOD/SCID mice and is char- acterized by a gene signature involving sur- vival pathways. Cancer Cell. 2011;19(2): 206-217.
15. Hasan MN, Queudeville M, Trentin L, et al. Targeting of hyperactivated mTOR signal- ing in high-risk acute lymphoblastic leukemia in a pre-clinical model. Oncotarget. 2015;6(3):1382-1395.
16. Queudeville M, Seyfried F, Eckhoff SM, et al. Rapid engraftment of human ALL in NOD/SCID mice involves deficient apopto- sis signaling. Cell Death Dis. 2012;3(e364.
haematologica | 2018; 103(6)