Targeting Sphingosine Kinase 1 in NK-LGL Leukemia

Abstract 1313 Natural killer cell large granular lymphocytic leukemia (NK-LGL) is a rare lymphoproliferative disorder of cytotoxic CD3-/CD56+ natural killer cells. Patients present with a malignant clinical course and a fatal outcome with median survival time of two months from diagnosis. Aggressive NK-LGL is refractory to conventional chemotherapy and pathogenetic mechanisms remain undefined. The sphingolipid metabolic pathway or ‘sphingolipid rheostat’ has been identified as a key player in determining cell fate. We hypothesize that this sphingolipid rheostat is dysregulated in NK-LGL leukemia. Ceramide and sphingosine are pro-apoptotic members of this pathway and sphingosine-1-phosphate (S1P) is pro-survival. Sphingosine kinase 1 (SphK1) is a cytosolic enzyme that converts sphingosine into S1P and has been implicated in oncogenesis. SphK1 is overexpressed in tumors of the breast, ovary, colon, brain, liver and esophagus and various leukemias and lymphomas. Here, we show that the sphingolipid rheostat is dysregulated in leukemic NK cells. Lipids were extracted from NK cells from nine NK-LGL patients and compared to nine, age and gender matched normal controls. Ceramide and S1P levels were quantified by tandem mass spectrometry. Ceramide levels were decreased 2-fold in NK-LGL patients compared to normal NK (p 4 times in NK-LGL patients compared to controls (p 4 fold increase, p L and survivin. Additionally, there was decreased phosphorylation of AKT and cleaved Poly ADP Ribose Polymerase (PARP). Treatment of NK cells with SKI-II (2.5u M), a pharmacologic inhibitor of SphK1, resulted in an increase in specific apoptosis in a dose-dependent manner by Annexin-V staining and flow cytometry in NK-LGL patients (n=4 patients, 20%, p Disclosures: Kester: Penn State Research Foundation: Licensed ceramide based nanotechnologies and siRNA based nanotechnologies, Keystonenano Inc. State College, PA, Co-founder and CMO Other.