Pharmacology and Antitumor Activity of ABC294640, a Selective Inhibitor of Sphingosine Kinase-2

Abstract

Sphingolipid-metabolizing enzymes control the dynamic balance of the cellular levels of important bioactive lipids, including the apoptotic compound ceramide and the proliferative compound sphingosine 1-phosphate (S1P). Many 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 (SK1 and SK2). SK1 and SK2 are overexpressed in a variety of human cancers, making these enzymes potential molecular targets for cancer therapy. We have identified an aryladamantane compound, termed ABC294640 [3-(4-chlorophenyl)-adamantane-1-carboxylic acid (pyridin-4-ylmethyl)amide], that selectively inhibits SK2 activity in vitro, acting as a competitive inhibitor with respect to sphingosine with a K i of 9.8 M, and attenuates S1P formation in intact cells. In tissue culture, ABC294640 suppresses the proliferation of a broad panel of tumor cell lines, and inhibits tumor cell migration concomitant with loss of microfilaments. In vivo, ABC294640 has excellent oral bioavailability, and demonstrates a plasma clearance half-time of 4.5 h in mice. Acute and chronic toxicology studies indicate that ABC294640 induces a transient minor decrease in the hematocrit of rats and mice; 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 mammary adenocarcinoma xenografts results in dose-dependent antitumor activity associated with depletion of S1P levels in the tumors and progressive tumor cell apoptosis. Therefore, this newly developed SK2 inhibitor provides an orally available drug candidate for the treatment of cancer and other diseases.Sphingolipids have become a focal point in biological research, with excellent rationale for their manipulation for the treatment of diseases, including cancer (reviewed in Ogretmen, 2006;Cuvillier, 2007; and Huwiler and ZangemeisterWittke, 2007). The parent lipid sphingomyelin is a structural component of cellular membranes, but also serves as the precursor for potent second messengers that have profound cellular effects. Stimulus-induced metabolism of these lipids is critically involved in cancer cell biology and inflammatory diseases; hence, this metabolic pathway offers exciting new molecular targets for drug development.In response to stimuli, including growth factors and inflammatory cytokines, sphingomyelin is enzymatically hydrolyzed to ceramide, which can be further hydrolyzed by the action of ceramidase to produce sphingosine. Ceramide and sphingosine induce apoptosis in cancer cells by mechanisms that remain to be elucidated. Sphingosine is rapidly phosphorylated by sphingosine kinase (SK) to produce sphingosine 1-phosphate (S1P), which is mitogenic and antiapoptotic. Through these conversions, a critical balance, i.e., a ceramide/S1P rheostat, has been hypothesized to determine the fate of the cell (Cuvillier e...

A Novel Sphingosine Kinase Inhibitor Induces Autophagy in Tumor Cells

“…A current lead SK2 inhibitor, ABC294640, was developed to improve the oral bioavailability and enzyme specificity that hampered the development of other lipidmimetic SK inhibitors (French et al, 2010). We have shown previously that ABC294640 has anti-inflammatory activity in vivo (Maines et al, 2006(Maines et al, , 2008Smith et al, 2008) and in this work that it also has antitumor activity (Fig.…”

“…6). Pharmacokinetic studies of ABC294640 indicate that the compound reaches a peak plasma concentration of approximately 20 M after an oral dose of 50 mg/kg and is eliminated with a half-time of clearance of approximately 4.5 h (French et al, 2010), suggesting that even more pronounced antitumor effects can be obtained with higher doses and/or more frequent administration. ABC294640 is currently in certified Good Laboratory Practice toxicology studies and is expected to enter clinical trials in 2010.…”

“…1A), as a first orally available, SK2-selective inhibitor. ABC294640 acts as a competitive inhibitor with respect to sphingosine with a K i of 10 M for recombinant human SK2 (French et al, 2010) and has therapeutic efficacy in models of diabetic retinopathy (Maines et al, 2006) and inflammatory bowel disease (Maines et al, 2008). Importantly, we have recently demonstrated that ABC294640 has favorable pharmacologic properties and can reach therapeutic levels in mouse plasma and tumors without overt toxicity (French et al, 2010).…”

Sphingosine Kinase 2 Promotes Acute Lymphoblastic Leukemia by Enhancing MYC Expression

“…Furthermore, exogenous expression of MYC resulted in a degree of resistance to SK2 inhibition by ABC294640. SK2 inhibition has been associated with both caspasedependent (45) and -independent cell death (46), with autophagy being involved in the latter. Autophagy also has cell survival roles (47) and although SK2 inhibition induced autophagy in ALL cells, this was not the cause of cell death, a situation similar to that following FTY720 exposure (48).…”

Targeting NFĸB mediated breast cancer chemoresistance through selective inhibition of sphingosine kinase-2

“…However, some have suggested that overexpressing Sphk isoforms may change their subcellular localization and alter endogenous function. 21,22 Despite increased understanding of the importance of sphingolipid signaling in anticancer drug resistance, pharmacologically targeting this pathway as a therapeutic has been inhibited by a lack of small molecule inhibitors. In this study we use the recently discovered selective sphingosine kinase-2 inhibitor, ABC294640, to elucidate the role of Sphk2 in breast cancer biology.…”