Sphingosine is phosphorylated via the action of the enzymes sphingosine kinase 1 (SK1) and sphingosine kinase 2 (SK2) to produce the bioactive signalling molecule sphingosine 1-phosphate (S1P). S1P drives cancer cell proliferation and migration whilst also promoting cell survival. Many studies have demonstrated that SK is a promising target for the treatment of cancer and the development of novel isoform-selective SK inhibitors to treat human cancers is of major interest. To date, inhibitors for this enzyme have either been selective for SK1 or non-selective for both isoforms. However, most SK inhibitors have only weak potency. This project involves the design and synthesis of small molecule inhibitors of SK as potential anti-cancer compounds. In this drug discovery project, a series of potent and selective inhibitors of SK (SK1 or SK2 or SK1/SK2) were developed based on the structure of PF-543, a known potent SK1 selective inhibitor. Analogues of PF-543 were prepared that were potent selective inhibitors of SK1 over SK2 and nM potent SK2 inhibitors with selectivity over SK1. These compounds represent some of the first nM potent SK2 inhibitors with selectivity over SK1. Indeed, the studies identified a structural determinant in the catalytic site of SK1 and SK2 that confers selectivity, with the heel and toe regions of the so-called J-channel in either enzyme providing a means toward selectivity. Exemplars from the series were shown to have potent cellular activity but poor in vitro microsomal stability. Effective target engagement and selectivity for SK1 in prostate cancer cell lines (LNCaP and LNCaP-AI) and proliferating human pulmonary artery smooth muscle cells (hPSMAC) were also established. A variety of biological assays associated with SK inhibition were used to evaluate their ability to induce cancer cell death, which was shown to involve a caspase-3/7-independent mechanism. Our SK1 and SK1/SK2 inhibitors, but not SK2 inhibitors, also reduced expression of dihydroceramide desaturase 1 (Des1) in a dose dependent manner, causing growth arrest and caspase-independent cell death. This project highlighted the importance for combining SK1 with Des1 inhibition in terms of endowing compounds with cytotoxicity against cancer cells.
|Date of Award||25 May 2018|
- University Of Strathclyde
|Supervisor||Simon MacKay (Supervisor) & Nigel Pyne (Supervisor)|