e14615 Background: Sphingolipid-metabolizing enzymes control the dynamic balance of important bioactive lipids, including apoptotic ceramide and proliferative sphingosine 1-phosphate (S1P). Several growth factors and inflammatory cytokines promote the cleavage of sphingomyelin and ceramide leading to rapid elevation of S1P levels through the action of sphingosine kinases (SKs). SK1 is oncogenic and is markedly overexpressed in a variety of human cancers, making this enzyme a potential molecular target for cancer therapy. Methods: SK inhibitors were synthesized and evaluated in a variety of cellular and in vivo models. Antitumor activity was assessed in an allogeneic model utilizing murine JC mammary adenocarcinoma cells growing in Balb/c mice, and a xenograft model of human Bxpc pancreatic adenocarcinoma cells growing in scid-mice. Results: The lead SK inhibitors, called ABC294640 and ABC294735, inhibit SK1 and SK2 at low micromolar concentrations, and are nontoxic to rodents at acute doses up to at least 1000 mg/kg (po). ABC294640 is orally-available, and has excellent pharmacokinetics, with serum levels exceeding the effective SK inhibitory concentration for at least 8 hours. Acute- and chronic- toxicology studies indicate that ABC294640 induces a transient minor decrease in the hemotocrit of rats and mice receiving 100 and 250 mg/kg/day; however, this normalizes by 28 days of treatment. No other changes in hematology parameters, or gross or microscopic tissue pathology result from treatment with ABC294640. Oral administration of ABC294640 to mice bearing JC adenocarcinomas results in dose-dependent antitumor activity associated with depletion of S1P levels in the tumors and progressive tumor cell apoptosis. ABC294735 is also orally-active in both JC and Bxpc tumor models, and demonstrates synergistic antitumor activity when combined with cisplatin or gemcitabine. Conclusions: These newly developed SK inhibitors provide orally-available drug candidates for the treatment of pancreatic cancer and other diseases. IND-enabling CMC and toxicology work is currently underway, and an SK inhibitor is expected to enter clinical trials in early 2010. [Table: see text]