Novel Corrector for Variants of SLC6A8: A Therapeutic Opportunity for Creatine Transporter Deficiency

Abstract: Mutations in creatine transporter SLC6A8 cause creatine transporter deficiency (CTD), which is responsible for 2% of all cases of X-linked intellectual disability. CTD has no current treatments and has a high unmet medical need. Inspired by the transformational therapeutic impact of small molecule “correctors” for the treatment of cystic fibrosis, which bind to mutated versions of the CFTR ion channel to promote its trafficking to the cell surface, we sought to identify small molecules that could stabilize SLC6A8 as a potential treatment for CTD. We leveraged a novel chemoproteomic technology for ligand discovery, reactive affinity probe interaction discovery, to identify small-molecule fragments with photoaffinity handles that bind to SLC6A8 in a cellular environment. We synthesized a library of irreversible covalent analogs of these molecules to characterize in functional assays, which revealed molecules that could promote the trafficking of mutant SLC6A8 variants to the cell surface. Further medicinal chemistry was able to identify reversible drug-like small molecules that both promoted trafficking of the transporter and also rescued creatine uptake. When profiled across the 27 most prevalent SLC6A8 missense variants, we found that 10–20% of patient mutations were amenable to correction by our molecules. These results were verified in an endogenous setting using the CRISPR knock-in of selected missense alleles. We established in vivo proof-of-mechanism for correctors in a novel CTD mouse model with the P544L patient-defined variant knocked in to the SLC6A8 locus, where treatment with our orally bioavailable and brain penetrant tool corrector increased brain creatine levels in heterozygous female mice, validating correctors as a potential therapeutic approach for CTD.

Parent Summary: This study focuses on developing a new treatment for creatine transporter deficiency (CTD), which currently has no therapies. Inspired by drugs that correct faulty proteins in cystic fibrosis, researchers found small molecules that bind and stabilize the creatine transporter protein (SLC6A8), helping to fix the problems caused by mutations. They created and tested molecules that help mutant transporters reach the cell surface and restore creatine uptake. Testing on common patient mutations showed that 10 to 20 percent of mutations responded to these corrector molecules. Using gene-edited cells and a new mouse model with a patient-specific mutation, they demonstrated that a brain-penetrating corrector taken by mouth increased brain creatine levels in mice. This work supports small-molecule correctors as a promising treatment strategy for CTD.

Link to article: https://pubs.acs.org/doi/10.1021/acschembio.4c00571

PubMed: https://pubmed.ncbi.nlm.nih.gov/39418577/

Authors:Lara N. Gechijian, Giovanni Muncipinto, T. Justin Rettenmaier, Matthew T. Labenski, Victor Rusu, Lea Rosskamp, Leslie Conway, Daniel van Kalken, Liam Gross, Gianna Iantosca, William Crotty, Robert Mathis, Hyejin Park, Benjamin Rabin, Christina Westgate, Matthew Lyons, Chloe Deshusses, Nicholas Brandon, Dean G. Brown, Heather S. Blanchette, Nicholas Pullen, Lyn H. Jones, Joel C. Barrish

Key Terms: CTD, Mutation Study, Animal Study, In vitro, Small Molecule Therapy, Basic Science, Therapeutics