Targeting sphingosine kinase 1 induces MCL1-dependent cell death in acute myeloid leukemia

Abstract

Key Points• Inhibition of SPHK1 in human AML cells induces MCL1 degradation and caspasedependent cell death.• SPHK1 inhibitors reduce leukemic burden and prolong survival in orthotopic patientderived xenografts of AML.Acute myeloid leukemia (AML) is an aggressive malignancy where despite improvements in conventional chemotherapy and bone marrow transplantation, overall survival remains poor. Sphingosine kinase 1 (SPHK1) generates the bioactive lipid sphingosine 1-phosphate (S1P) and has established roles in tumor initiation, progression, and chemotherapy resistance in a wide range of cancers. The role and targeting of SPHK1 in primary AML, however, has not been previously investigated. Here we show that SPHK1 is overexpressed and constitutively activated in primary AML patient blasts but not in normal mononuclear cells. Subsequent targeting of SPHK1 induced caspase-dependent cell death in AML cell lines, primary AML patient blasts, and isolated AML patient leukemic progenitor/stem cells, with negligible effects on normal bone marrow CD34 1 progenitors from healthy donors. Furthermore, administration of SPHK1 inhibitors to orthotopic AML patient-derived xenografts reduced tumor burden and prolonged overall survival without affecting murine hematopoiesis. SPHK1 inhibition was associated with reduced survival signaling from S1P receptor 2, resulting in selective downregulation of the prosurvival protein MCL1. Subsequent analysis showed that the combination of BH3 mimetics with either SPHK1 inhibition or S1P receptor 2 antagonism triggered synergistic AML cell death. These results support the notion that SPHK1 is a bona fide therapeutic target for the treatment of AML. (Blood. 2017;129(6):771-782)

Sphingolipid metabolism in cancer signalling and therapy

“…In tumour cells, S1PR2 signalling induced AML growth and/or proliferation 113 and was shown to activate ezrin–radixin–moesin (ERM) proteins to induce motility and invasion of HeLa cells in culture 114 , consistent with S1PR2-mediated tumour metastasis of bladder cancer and melanoma cells in mouse models 107 . By contrast, systemic S1PR2 signalling, mainly in endothelial cells and bone-marrow-derived cells (BMDCs), was reported to inhibit tumour angiogenesis in mouse models 115 .…”

“…However, the mechanism of how S1PR4 regulates nuclear translocation of S1PR2, and the nuclear signalling roles of S1PR2 in ER-negative breast cancer cell growth suppression, remain unknown. Nevertheless, this mechanism appears to be cell type and/or context-dependent, as there are multiple reports suggesting that S1PR2 signalling promotes tumour growth and/or metastasis in various other cancer types, such as AML, melanoma and bladder or cervical cancers 107,113–115 …”

Investigation of sphingosine kinase 1 in interferon responses during dengue virus infection

“…Cells were treated in culture for 15–20 min with recombinant mouse IFN‐β (Biolegend, San Diego, CA, USA) or pretreated for 90 min with 5 μ m SK1‐I (Enzo Life Sciences, Farmingdale, NY, USA) prior to stimulation with IFN‐β. HEK293 cells expressing control or SK1 shRNA were generated following lentivirus transduction and selection as previously described 44 . Cells were passaged in tetracycline‐free media (Dulbecco's modified Eagles medium (DMEM) with 10% (v/v) fetal calf serum) to minimise basal shRNA expression.…”

Fat for fuel: lipid metabolism in haematopoiesis

“…S1P fosters leukaemic cell growth and survival by preventing apoptosis by inhibiting cytochrome c and Smac/DIABLO release from the mitochondria, ultimately preventing the terminal activation of caspase 3 (Figure ) . Accordingly, altering the metabolism by inducing ceramide synthesis or inhibiting S1P synthesis sensitises HL‐60 and U937 cells and in primary myeloblasts to irradiation and apoptosis . This does not appear to be limited to S1P metabolism, but rather to ceramide availability as chemotherapy‐resistant tumors have increased sphingomyelin and glucosylceramide synthesis compared to chemotherapy‐sensitive ones, concomitant with a decrease in ceramide‐induced apoptosis…”

“…95 Accordingly, altering the metabolism by inducing ceramide synthesis or inhibiting S1P synthesis sensitises HL-60 and U937 cells and in primary myeloblasts to irradiation and apoptosis. [96][97][98] This does not appear to be limited to S1P metabolism, but rather to ceramide availability as chemotherapy-resistant tumors have increased sphingomyelin and glucosylceramide synthesis compared to chemotherapy-sensitive ones, concomitant with a decrease in ceramideinduced apoptosis. 99 Haematopoietic stem and progenitor cells with defective cholesterol efflux in a hypercholesterolaemic environment are noted to phenocopy myeloproliferative neoplasms (MPN), and, as such, cholesterol transport and synthesis are upregulated in certain leukaemias and lymphomas.…”