The dichotomy of inflammation-induced cancer vs. cancer-induced inflammation is still enigmatic. Since sphingolipids are involved in both tumour cell survival and immune cell differentiation, migration and cytokine pattern we hypothesised their essential role in both mechanism of cancer development. We employed inducible S1P lyase (SGPL1) knockdown bone marrow-chimeric mice in a colitis associated colon cancer model leading to compartment-specific accumulation of sphingolipid levels. We found that, independent of the compartment of SGPL1 deficiency, haematopoietic or extra-haematopoietic, DSS/AOM-treated mice demonstrated tumours with s1pr1, stat3, and IL-6 elevation. However, compartment-specific actions of the SGPL1-S1P axis contributed both morphologically and genetically to a very distinct development of inflammation and carcinogenesis. Haematopoietic SGPL1 knockdown forced severe inflammatory colitis with delayed carcinogenesis characterised by pdcd4-down-regulation. In contrast, extra-haematopoietic SGPL1 knockdown triggered a much more rapid occurrence of epithelial-driven sphingosine kinase 1-positive tumours, exhibiting kras, egfr and IL23-p19 signatures and a weak but distinct Th2 driven immune microenvironment. Moreover, we found that SGPL1 derived from haematopoietic cells is sufficient for S1P-driven lymphocyte sequestration. In this study we demonstrate that compartment-specific sphingolipid modulation clarifies the dichotomy of inflammation-induced cancer vs. cancer-induced inflammation.

For the immune modulatory drug fingolimod (FTY720), lymphocyte sequestration has been extensively studied and accepted as mode of action. Further, direct effects on immune cell signalling are incompletely understood. Herein, we used the parent drug and newly synthesized analogues to investigate their effects on dendritic cell (DC) calcium signalling and on Th1, Th2 and Th17 responses. DC calcium signalling was determined with a single cell-based confocal assay and IL-33/ST2-TIR Th2-like response with ST2-transduced EL4-6.1 thymoma cells. The Th1/Th17 responses were examined with a LPS/TLR-enhanced antigen presentation assay with OVA-TCRtg CD4 and CD8 spleen cells. Our results revealed a comparable influence of fingolimod and S1P on intracellular calcium level in DC, while an oxy-derivative of fingolimod exhibited an EC50 of 3.3 nm, being 14 times more potent than FTY720-P. The IL-33/ST2-TIR Th2-like response in ST2-EL4 cells was inhibited by fingolimod and analogues at varying degrees. Using the OVA-TCRtg LPS/TLR-enhanced spleen cell assay, we found that fingolimod inhibited both IL-17 and IFN-γ production. In contrast, fingolimod phosphate failed to decrease Th1 cytokines. Interestingly, the effects of the parent compound fingolimod were modulated by the PP2A inhibitor okadaic acid, thus suggesting PP2A as relevant intracellular target. These studies describe detailed immune-modulating properties of fingolimod, including interference with a prototypical Th2 response via IL-33/ST2-TIR. Moreover, differential effects of fingolimod versus its phosphorylated derivative on TLR-activated and antigen-dependent Th1 activation suggest PP2A as an additional target of fingolimod immune therapy. Together with the analogues tested, these data may guide the development of more specific fingolimod derivatives.