SLC7A11 is the transporter component of the membrane bound cystine-glutamate antiporter system xc- and is essential for the production of glutathione, a major anti-oxidant that is crucial for preventing accumulation of toxic ROS. We recently demonstrated that mutant p53 cancer cells are selectively killed by inhibition of SLC7A11. Furthermore, SLC7A11 inhibition potently synergises with the mutant p53 reactivating drug, APR-246, which is currently in early phase clinical trials. However, current SLC7A11 small molecule inhibitors lack potency and/or specificity. This prompted us to undertake a high-throughput screen to identify novel compounds to target SLC7A11.
A phenotypic screen (inhibition of glutamate export) of ~25,000 novel compounds at a single dose (10μM) identified 32 compounds of high interest (Category 1, z score <-6 and inhibition of glutamate release >45%), which were validated in 11-point dose titration curves (20μM-17nM). A further 160 Category 2 compounds (z score -6 to -3 and % inhibition 30-45%) were also repeated in a 4-point dose titration curve (40-5uM). From the secondary screen 20 compounds with an IC50 <10uM were selected for further investigation, with the most prominent structural group being trifluoromethyl thiadazoles.
A counter screen identified 5 compounds that inhibited enzymes involved in the detection of glutamate in the screening assay, and were excluded from subsequent analysis. Fourteen of these compounds were freshly synthesised and have been further characterised in a secondary assay of SLC7A11 function (C14-labelled cystine uptake) and cell death assays in mutant p53 cancer cell lines and isogenic cell line models with different p53 status and SLC7A11 expression levels, with or without inhibitors of ferroptosis, a caspase-independent form of regulated cell death.
Aberrant SLC7A11 function has been implicated in a number of cancers and neurological disorders, which has provoked interest in this transporter system as a therapeutic target. Our screen has identified potential novel inhibitors of SLC7A11 function and work is ongoing to characterize these compounds further, including potential therapeutic index in the oncological setting.