unc569 and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

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.

Topics: Animals; Antimetabolites, Antineoplastic; Astrocytes; Blood Proteins; c-Mer Tyrosine Kinase; Case-Control Studies; Cell Survival; Central Nervous System; Child; Chromosomes, Human, Pair 1; Chromosomes, Human, Pair 19; Coculture Techniques; Female; Galectin 3; Galectins; Gene Expression Regulation, Leukemic; Glioma; Humans; Methotrexate; Mice; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Primary Cell Culture; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Pyrazoles; Pyrimidines; Receptor Protein-Tyrosine Kinases; RNA, Small Interfering; Signal Transduction; Translocation, Genetic; Tumor Cells, Cultured

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Although survival rates have improved, patients with certain biologic subtypes still have suboptimal outcomes. Current chemotherapeutic regimens are associated with short- and long-term toxicities and novel, less toxic therapeutic strategies are needed. Mer receptor tyrosine kinase is ectopically expressed in ALL patient samples and cell lines. Inhibition of Mer expression reduces prosurvival signaling, increases chemosensitivity, and delays development of leukemia in vivo, suggesting that Mer tyrosine kinase inhibitors are excellent candidates for targeted therapies. Brain and spinal tumors are the second most common malignancies in childhood. Multiple chemotherapy approaches and radiotherapies have been attempted, yet overall survival remains dismal. Mer is also abnormally expressed in atypical teratoid/rhabdoid tumors (AT/RT), providing a rationale for targeting Mer as a therapeutic strategy. We have previously described UNC569, the first small-molecule Mer inhibitor. This article describes the biochemical and biologic effects of UNC569 in ALL and AT/RT. UNC569 inhibited Mer activation and downstream signaling through ERK1/2 and AKT, determined by Western blot analysis. Treatment with UNC569 reduced proliferation/survival in liquid culture, decreased colony formation in methylcellulose/soft agar, and increased sensitivity to cytotoxic chemotherapies. MYC transgenic zebrafish with T-ALL were treated with UNC569 (4 μmol/L for two weeks). Fluorescence was quantified as indicator of the distribution of lymphoblasts, which express Mer and enhanced GFP. UNC569 induced more than 50% reduction in tumor burden compared with vehicle- and mock-treated fish. These data support further development of Mer inhibitors as effective therapies in ALL and AT/RT.

Topics: Animals; Animals, Genetically Modified; Antineoplastic Agents; c-Mer Tyrosine Kinase; Cell Line, Tumor; Gene Expression Regulation, Leukemic; Humans; Jurkat Cells; MAP Kinase Signaling System; Molecular Targeted Therapy; Neoplasms, Experimental; Phosphorylation; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Pyrazoles; Pyrimidines; Receptor Protein-Tyrosine Kinases; Rhabdoid Tumor; Teratoma; Zebrafish