Suppression of colitis-driven colon cancer in mice by a novel small molecule inhibitor of sphingosine kinase

Abstract

Sphingolipid metabolism is driven by inflammatory cytokines. These cascade of events include the activation of sphingosine kinase (SK), and subsequent production of the mitogenic and proinflammatory lipid sphingosine 1-phosphate (S1P). Overall, S1P is one of the crucial components in inflammation, making SK an excellent target for the development of new anti-inflammatory drugs. We have recently shown that SK inhibitors suppress colitis and hypothesize here that the novel SK inhibitor, ABC294640, prevents the development of colon cancer. In an azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model, there was a dose-dependent decrease in tumor incidence with SK inhibitor treatment. The tumor incidence (number of animals with tumors per group) in the vehicle, ABC294640 (20 mg/kg) and ABC294640 (50 mg/kg) groups were 80, 40 and 30%, respectively. Tumor multiplicity (number of tumors per animal) also decreased from 2.1 ± 0.23 tumors per animal in the AOM + DSS + vehicle group to 1.2 ± 0 tumors per animal in the AOM + DSS + ABC294640 (20 mg/kg) and to 0.8 ± 0.4 tumors per animal in the AOM + DSS + ABC294640 (50 mg/kg) group. Importantly, with ABC294640, there were no observed toxic side effects. To explore mechanisms, we isolated cells from the colon (CD45-, representing primarily colon epithelial cells) and (CD45+, representing primarily colon inflammatory cells) then measured known targets of SK that control cell survival. Results are consistent with the hypothesis that the inhibition of SK activity by our novel SK inhibitor modulates key pathways involved in cell survival and may be a viable treatment strategy for the chemoprevention colitis-driven colon cancer.

Fig. 1.

Effects of the SK inhibitor ABC294640 (50 mg/kg dose) on the colon histology score (A), colon length (B), weight difference (C) and complete white blood cells count (D) in the acute stage (Day 15) in the AOM + DSS mouse model of colitis. Values represent the individual scores of each mouse (n = 5 per group). The line represents the mean score for the group. Asterisk represents significant difference from the control group.

Fig. 2.

Effects of the SK inhibitor ABC294640 (50 mg/kg dose) on Sph levels in colons of animals in the AOM + DSS mouse model of colitis. Colon samples from mice described in Table I were extracted and assayed for levels of Sph by liquid chromatography-tandem mass spectroscopy as described in the ‘Materials and Methods’ section. Values represent the mean ± standard error for five samples per group.

Fig. 3.

Protective effect of SK inhibitor ABC294640 on AOM/DSS colitis-induced epithelial damage. Representative microphotographs for AOM + Vehicle (A), AOM + DSS (B) and AOM + DSS + ABC294640 (50 mg/kg) (C) groups at Days 15 (left panels) and 70 (right panels).

Fig. 4.

Effects of the SK inhibitor ABC294640 (50 mg/kg dose) on cell survival pathways in CD45− cells (non-inflammatory cells, assuming mostly colon epithelial cells) and CD45+ (mostly inflammatory cells). Beclin-1 is a putative tumor suppressor, which plays a key role in autophagy. AKT phosphorylation and ERK1/2 phosphorylation are associated with cell survival. The finding that ABC294640 can increase Beclin-1 and suppress the phosphorylation of AKT and ERK1/2, especially in epithelial cells, gives us insight into the unpinning mechanisms associated with the suppression of colitis-driven colon cancer by ABC294640.