A selective ATP-competitive sphingosine kinase inhibitor demonstrates anti-cancer properties

Abstract

The dynamic balance of cellular sphingolipids, the sphingolipid rheostat, is an important determinant of cell fate, and is commonly deregulated in cancer. Sphingosine 1-phosphate is a signaling molecule with anti-apoptotic, pro-proliferative and pro-angiogenic effects, while conversely, ceramide and sphingosine are pro-apoptotic. The sphingosine kinases (SKs) are key regulators of this sphingolipid rheostat, and are attractive targets for anti-cancer therapy. Here we report a first-in-class ATP-binding site-directed small molecule SK inhibitor, MP-A08, discovered using an approach of structural homology modelling of the ATP-binding site of SK1 and in silico docking with small molecule libraries. MP-A08 is a highly selective ATP competitive SK inhibitor that targets both SK1 and SK2. MP-A08 blocks pro-proliferative signalling pathways, induces mitochondrial-associated apoptosis in a SK-dependent manner, and reduces the growth of human lung adenocarcinoma tumours in a mouse xenograft model by both inducing tumour cell apoptosis and inhibiting tumour angiogenesis. Thus, this selective ATP competitive SK inhibitor provides a promising candidate for potential development as an anti-cancer therapy, and also, due to its different mode of inhibition to other known SK inhibitors, both validates the SKs as targets for anti-cancer therapy, and represents an important experimental tool to study these enzymes.

Targeting sphingosine kinase 1 induces MCL1-dependent cell death in acute myeloid leukemia

“…30 Briefly, mice were sublethally irradiated (275 cGy) 24 hours prior to IV injection of 5-10 3 10 6 primary human AML cells via tail vein. Engraftment levels were quantified by flow cytometry and expressed as the percentage of human CD45 Immunohistochemistry on mouse bone marrow was performed as previously described 33 with human mitochondrial antibodies (Abcam). An event was defined to occur when the mice exhibited signs of leukemia related morbidity and the bone marrow exhibited .25% hCD45 staining.…”

“…[18][19][20][21] Indeed, MP-A08 treatment of mice engrafted with primary human AML cells significantly reduced leukemic burden and prolonged mouse survival without impacting on normal mouse hematopoiesis or blood, kidney, liver, heart, and spleen pathology. 33 Notably, MP-A08 is known to be equally effective at inhibiting human and mouse sphingosine kinases. 33 This therapeutic response occurred in 2 independent AML samples, both with normal karyotype, carrying the FLT3-ITD mutation and either IDH1 or IDH2 mutations, a common occurrence in AML, 54 suggesting SPHK1-directed therapies may have utility across this spectrum of AML.…”

“…33 Notably, MP-A08 is known to be equally effective at inhibiting human and mouse sphingosine kinases. 33 This therapeutic response occurred in 2 independent AML samples, both with normal karyotype, carrying the FLT3-ITD mutation and either IDH1 or IDH2 mutations, a common occurrence in AML, 54 suggesting SPHK1-directed therapies may have utility across this spectrum of AML. Notably, cells from patient AML8, harboring the 11q23 MLL translocation, were nonresponsive to MP-A08 in vivo, consistent with our subsequent findings that SPHK1 inhibition in these cells did not result in loss of MCL1, a protein known to be critical for AML cell survival.…”

Combination therapy approaches to target insulin-like growth factor receptor signaling in breast cancer

“…Specifically in relation to cancer, a number of different SphK inhibitors have been developed and shown to elicit anticancer effects including SKI-II, ABC294640 and MP-A08 (Pitman & Pitson 2010, Pitman et al 2015, McNaughton et al 2016. Currently, SphK1 inhibitors are not clinically in testing for breast cancer, but the preclinical and prognostic findings of a relationship between IGF1R and SphK1 expression provide evidence that there is a need to learn more about the potential clinical benefits of IGF1R and SphK1 as novel dual therapeutic targets (Fig.…”

Recent advances in the development of sphingosine kinase inhibitors

“…In particular, the crystal structure of SK1, and its sequence similarity to SK2, has provided molecular insights into the differences between these two enzymes. As recently reviewed by Adams et al [43], SK1 and SK2 show differences in four key residues in their sphingosinebinding pockets and three in their ATP-binding pockets [41][42][43][44], enabling exploitation for the development of isoform-selective inhibitors. Indeed, the recent identification of potent isoform selective inhibitors has also delivered important insights into some of the roles of SK1 and SK2 in the regulation of key oncogenes and involvement in inflammatory signalling.…”