Sphingosine Kinase Blockade Leads to Increased Natural Killer T Cell Responses to Mantle Cell Lymphoma

Abstract

Mantle cell lymphoma (MCL) is an aggressive subtype of non-Hodgkin's lymphoma. Despite being responsive to combination chemotherapy, median survival remains around 5 years due to high rates of relapse. Sphingolipid metabolism regulates MCL survival and proliferation and we found that sphingosine-1-phosphate (S1P) is upregulated in MCL cells. Therapeutic targeting of the S1P 1 receptor or knockdown of sphingosine kinase 1 (SK1), the enzyme responsible for generating S1P, in human MCL cells results in a significant increase in Natural Killer T (NKT) cell activation. NKT cells recognize glycolipid antigens presented on CD1d and can reduce MCL tumor burden in vivo. Lipidomic studies identified cardiolipin, which has been reported to bind to CD1d molecules, as being upregulated in SK1 knockdown cells. We found that the pretreatment of antigen presenting cells with cardiolipin leads to increased cytokine production by NKT cell hybridomas. Furthermore, the ability of cardiolipin to activate NKT cells was dependent on the structure of its acyl chains. Collectively, these studies delineate novel pathways important for immune recognition of malignant cells and could lead to the development of new treatments for lymphoma.as ischemia reperfusion injury [10]. NKT cells are characterized by a semi-invariant T cell receptor (TCR) (Vα14Jα18 in mice and Vα24Jα18 in humans). Unlike conventional CD4 and CD8 T cells, NKT cells are activated by glycolipid antigens presented in the context of the non-classical, class I major histocompatibility complex (MHC)-like molecule, CD1d [11,12]. α-Galactosylceramide (α-GalCer) is a potent activator of NKT cells [13,14], and following treatment with α-GalCer, NKT cells produce cytokines, undergo clonal expansion, and subsequently activate other immune cells [15][16][17][18][19]. After activation, human NKT cells can exhibit strong anti-tumor activity against many tumors [20,21]. Several groups have conducted clinical trials evaluating the effectiveness of α-GalCer as a potential therapeutic immunomodulator of NKT cells that yielded modest results, potentially due to a reduction in NKT cell number and function in cancer patients [22][23][24][25][26][27].Sphingosine-1-phosphate (S1P) regulates proliferation, survival, and migration of mammalian cells through both extracellular receptor-mediated and intracellular mechanisms [28][29][30]. S1P is generated from sphingolipids, essential serum membrane lipids which are concentrated in lipid rafts. There are several enzymes in this pathway, which culminates in sphingosine kinase (SK) conversion of sphingosine into S1P. S1P is involved in malignant transformation, cancer cell proliferation, inflammation, vasculogenesis, lymphocyte trafficking, and resistance to apoptosis. There are two forms of sphingosine kinase: SK1 and SK2. Over-expression of SK1 has been reported to induce malignant transformation and tumor formation in 3T3 fibroblasts [31], while SK2 has been shown to promote acute lymphoblastic leukemia by increasing MYC expression [32]. In additio...

Cell surface sphingomyelin: key role in cancer initiation, progression, and immune evasion

“…This is supported by multiple reports. Blocking SM synthesis was recently found to increase immune responses to hepatic cell carcinoma, mantle cell lymphoma, and glioblastoma [ 99 – 101 ]. Additionally, therapeutic treatments that increased SM hydrolysis via activating the surface membrane-associated nSMase allowed tumor cell apical membrane antigens exposure to the host immune effectors and prevention of an instrumental immune escape mechanism, together with accumulation of intracellular Cer [ 46 , 69 ].…”

The Role of Ceramide Metabolism and Signaling in the Regulation of Mitophagy and Cancer Therapy

“…When S1P secretion was inhibited in mice through knockdown of Spinster Homologue 2 (Spns2), an S1P transporter, pulmonary metastasis of melanoma cells was reduced compared to wild-type mice [184]. Additionally, when SphK1 or S1PR1 was therapeutically targeted or downregulated in mantle cell lymphoma, natural killer cell activation was increased [185]. Notably, ceramide was also found to affect the potency of immunotherapies and T cell responses.…”

Keep a Little Fire Burning—The Delicate Balance of Targeting Sphingosine-1-Phosphate in Cancer Immunity

“…Unconventional T cells were also activated upon SPHK1 ablation in Mantle cell lymphoma cells. An induction of natural killer T (NKT) cell activation was observed under these conditions accompanied by an increase in the NKT cell lipid antigen cardiolipin upon SPHK1 ablation [132]. Together, these studies suggest that targeting any SPHKs may remove immunosuppressive features in the TME.…”