Mer tyrosine kinase promotes the survival of t(1;19)-positive acute lymphoblastic leukemia (ALL) in the central nervous system (CNS)

Abstract

Key Points• Mer mediates quiescence and chemotherapy resistance in a CNS coculture model and causes CNS infiltration in immunodeficient mice.• Mer expression correlates with CNS positivity upon initial diagnosis in t(1;19)-positive pediatric ALL patients.Patients with t(1;19)-positive acute lymphoblastic leukemia (ALL) are prone to central nervous system (CNS) relapses, and expression of the TAM (Tyro3, Axl, and Mer) receptor Mer is upregulated in these leukemias. We examined the functional role of Mer in the CNS in preclinical models and performed correlative studies in 64 t(1;19)-positive and 93 control pediatric ALL patients. ALL cells were analyzed in coculture with human glioma cells and normal rat astrocytes: CNS coculture caused quiescence and protection from methotrexate toxicity in Mer high ALL cell lines, which was antagonized by short hairpin RNA-mediated knockdown of Mer. Mer expression was upregulated, prosurvival Akt and mitogen-activated protein kinase signaling were activated, and secretion of the Mer ligand Galectin-3 was stimulated. Mer high t(1;19) primary cells caused CNS involvement to a larger extent in murine xenografts than in their Mer low counterparts.Leukemic cells from Mer high xenografts showed enhanced survival in coculture.Treatment of Mer high patient cells with the Mer-specific inhibitor UNC-569 in vivo delayed leukemia onset, reduced CNS infiltration, and prolonged survival of mice. Finally, a correlation between high Mer expression and CNS positivity upon initial diagnosis was observed in t(1;19) patients. Our data provide evidence that Mer is associated with survival in the CNS in t(1;19)-positive ALL, suggesting a role as a diagnostic marker and therapeutic target. (Blood. 2015;125(5):820-830) Introduction TAM (Tyro3, Axl, and Mer) receptors have been advocated as therapeutic targets in human cancers including leukemia. 1-3 The TAM receptor family consists of Tyro3, Axl, and Mer 4 which all have been found to have transforming properties. [5][6][7] Mer expression has been shown on macrophages, natural killer (NK) cells, dendritic cells, megakaryocytes, and platelets, 8 but it is not known to be present on normal T and B lymphocytes at any stage of differentiation. Aberrant Mer expression was detected in not only acute myeloid leukemia (AML), 9 but also lymphocytic malignancies as T-cell acute lymphoblastic leukemia (T-ALL).10 Studies overexpressing Mer in fibroblasts found that it can induce extracellular signalregulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p38, nuclear factor-kB (NF-kB) and enhance cell survival via phosphatidylinositol 3-kinase (PI3K)/AKT. 2,11 Linger et al 12 reported that Mer is overexpressed on pre-B-cell ALL (B-ALL) cells of pediatric patients with t(1;19)(q23;p13) translocation. Furthermore, inhibition of Mer by RNA interference (RNAi) reduced survival and chemoresistance of pre-B-ALL cell lines and prolonged survival of xenografts.12 Pediatric ALL with t(1;19)(q23;p13) translocation is found in about 3% to 5% of ALL patients and has ...

Central nervous system acute lymphoblastic leukemia: role of natural killer cells

“…Interestingly, these ALL cells carried the t(1;19)(q23 p13) chromosomal translocation that is known to be associated with increased risk for CNS involvement. 49,50 Increased NK cells (351 NK cells/10 5 splenic cells) were also observed in another t(1;19)(q23 p13) NOD/SCID xenograft with CNS leukemia (patient A in supplemental Figure 3). Thus, t(1;19)(q23 p13) may stimulate NK cells in an IL-15-independent manner.…”

The ability to cross the blood–cerebrospinal fluid barrier is a generic property of acute lymphoblastic leukemia blasts

“…We and others have reported on the potential role of the cytokine interleukin-15 in promoting leukemic cell survival in the hostile environment in the CSF. 13,36 A recent report has highlighted a critical role for MER tyrosine kinase in promoting survival of t(1:19)-positive ALL in the CNS, 37 and increased intercellular adhesion molecule 1, 38 stearoyl-CoA desaturase, and osteopontin 39 expression have also been associated with CNS disease. Additional mechanisms of CNS relapse may relate to evasion of chemotherapy 40 or immune surveillance 34,41 at this site.…”

The role of ZAP70 kinase in acute lymphoblastic leukemia infiltration into the central nervous system

“…697, REH and JURKAT cells were transduced with viruses and sorted for mCherry-positivity. 8,27 pMIG or pMIG-ZAP70 vectors, provided by Prof. Michael Reth (University of Freiburg, Germany), were used to transduce leukemic cells.…”

“…Eight to twelve week old female mice were injected intrafemorally with 1 × 10 6 ALL cells from patient BM (>90% blasts), or intravenously with 1 x 10 4 -1 x 10 5 ALL cells from cell lines. 8,27 Animals were sacrificed upon detection of >75% leukemic blasts or clinical leukemia (weight or activity loss, organomegaly, hind limb paralysis). CNS-leukemic cells were recovered from meninges and separated on 30% percoll.…”

“…CNS infiltration was scored negative (−), intermediate (+) and high (++) as described. 8 Quantitative real-time polymerase chain reaction (qRT-PCR) analyses were performed on an ABI7900HT using QuantiTect primer assays (Qiagen) and real-time quantitative PCR value (RQ) (2^-DCCT) was calculated.…”