Disrupting the leukemia niche in the central nervous system attenuates leukemia chemoresistance

Abstract

word count: 200 Text word count: 3955 Abstract 1Protection from acute lymphoblastic leukemia (ALL) relapse in the central nervous system (CNS) is 2 crucial to survival and quality of life for ALL patients. Current CNS-directed therapies cause significant 3 toxicities and are only partially effective. Moreover, the impact of the CNS microenvironment on 4 leukemia biology is poorly understood. Herein, we showed that leukemia cells associated with the 5 meninges of xenotransplanted mice, or co-cultured with meningeal cells, exhibit enhanced 6 chemoresistance due to effects on both apoptosis balance and quiescence. From a mechanistic 7 standpoint, we identified that leukemia chemoresistance is primarily mediated by direct leukemia-8 meningeal cell interactions and overcome by detaching the leukemia cells from the meninges. Next, 9 we used a co-culture adhesion assay to identify drugs that disrupted leukemia-meningeal adhesion. In 1 0 addition to identifying several drugs that inhibit canonical cell adhesion targets we found that 1 1Me6TREN, a novel hematopoietic stem cell (HSC) mobilizing compound, also disrupts leukemia-1 2 meningeal adhesion in vitro and in vivo. Finally, Me6TREN enhanced the efficacy of cytarabine in 1 3 treating CNS leukemia in xenotransplanted mice. This work demonstrates that the meninges exert a 1 4 critical influence on leukemia chemoresistance, elucidates mechanisms of CNS relapse beyond the 1 5well-described role of the blood-brain barrier, and identifies novel therapeutic approaches for 1 6 overcoming chemoresistance. 1 7 Introduction 1 8 Central nervous system (CNS) relapse is a common cause of treatment failure among patients with 1 9 acute lymphoblastic leukemia (ALL) 1-3 . Relapses occur despite CNS-directed therapies which include 2 0 high-dose systemic chemotherapy, intrathecal chemotherapy, and cranial irradiation in some high-risk 2 1 patients. These current CNS-directed therapies are also associated with significant acute and long-2 2 3 1 mice demonstrated that all, or most, B-cell ALL clones are capable of disseminating to the CNS 14,15 . 3 2 Third, CNS leukemia relapses occur despite high dose systemic and intrathecal chemotherapy. These 3 3therapies either overcome or bypass the blood-brain barrier. Fourth, it was shown that high Mer 3 4 kinase expressing, t(1;19) leukemia cells co-cultured with CNS-derived cells exhibit G0/G1 cell cycle 3 5 arrest, suggestive of dormancy or quiescence, as well as methotrexate resistance 16 . Similarly, Akers 3 6 et al. showed that co-culture of leukemia cells with astrocytes, choroid plexus epithelial cells, or 3 7meningeal cells enhanced leukemia chemoresistance 17 . Together these observations suggest that the 3 8 pathophysiology of CNS leukemia extends beyond the role of the blood-brain barrier. We hypothesize 3 9 that the ability of leukemia cells to persist in the unique CNS niche and escape the effects of 4 0 chemotherapy and immune surveillance likely also play critical roles in CNS leukemia and relapse. 4 1 4 2 However, while extensive...

When the bond breaks – targeting adhesion of leukemia cells to the meninges

“…In this issue of Haematologica, Jonart et al describe how ALL cells seek shelter by adhering to meningeal cells, resulting in quiescence and chemoresistance. The authors propose interference with adhesion mechanisms as a novel therapeutic strategy in CNS leukemia 5 (Figure 1).…”

“…CNS metastasis of solid cancers mostly affects the brain parenchyma, but ALL cells predominantly reside in the leptomeninges, a conjunctive tissue surrounding the parenchyma and the ventricular choroid plexus. [5][6][7] Hence, the mech-anisms of CNS infiltration in solid tumors and hematologic malignancies likely differ fundamentally. To enter the CNS environment, ALL cells need to pass protective physiological barriers such as the blood-brain barrier, the blood-leptomeningeal barrier and the blood-cerebrospinal fluid barrier, which in physiological conditions ensure the controlled flux of molecules and passage of cells into the organ.…”

“…To investigate the behavior of ALL cells in the CNS, Jonart et al co-cultured B-cell precursor ALL and T-ALL cell lines as well as primary B-cell precursor ALL cells with primary human meningeal cells, modeling the leptomeningeal microenvironment. 5 The authors found that ALL cells efficiently adhered to the primary human meningeal cells, rendering them less vulnerable to chemotherapy. Therapy sensitivity was markedly reduced when ALL cells were grown in direct contact with the meningeal cells and treated with methotrexate and cytarabine, two major compounds of CNS-directed chemotherapy in ALL.…”

“…Me6TREN was first described as a compound mobilizing hematopoietic progenitor cells from the bone marrow by upregulating matrix metalloprotease-9 and disrupting the CCL12/CXCR4 axis, thereby outperforming AMD3100. 17 Accordingly, compared to AMD3100, Me6TREN showed enhanced efficacy in disturbing the adhesion of ALL cells to meningeal cells in the work by Jonart et al 5 Me6TREN has proven to be well tolerated in mice. 17 If Me6TREN is demonstrated to penetrate the CNS in pharmacokinetic and pharmacodynamics studies, this compound could indeed be considered as a drug the for prevention and therapy of CNS disease.…”

“…Therefore, to survive the transformation process, tumor cells become more dependent on their anti-apoptotic BCL2 proteins (e.g., BCL2, BCLXL, and MCL1) than their normal counterparts. [5][6][7] This dependency is the result of binding and neutralizing the pro-apoptotic family members (e.g., BIM, BAK, and BAX) and is often referred to as mitochondrial priming, as increased Are meningeal cells also involved in specific homing of ALL cells into the CNS? Is adhesion-mediated chemoresistance of ALL cells in contact with meningeal cells simply a cause of decreased proliferation and therefore diminished vulnerability to chemotherapeutic agents or is an active process involved (e.g., regulation of drug transporters)?…”