Towards Covalent Approaches to Stabilise 14-3-3σ Protein-Protein Interactions as a Therapeutic Modality for Cancer

14-3-3 proteins are a ubiquitous family of proteins that play an essential role in cellular homeostasis^1,2. They interact with over 200 proteins to modulate their activity, protein folding, subcellular localisation and their interaction with other protein partners^3,4. Among 14-3-3 interacting partners are important pharmaceutical targets such as CFTR⁵, p53⁶, ERα⁷, Tau⁸, and LRRK2⁹ that are involved in various diseases such as cystic fibrosis⁵, cancer^10–13 and neurodegenerative diseases^14–18. Moreover, 14-3-3 proteins were reported as one of nine key host proteins during SARS CoV-2 infection¹⁹. For these reasons, 14-3-3 Protein-Protein Interactions (PPIs) have great potential as novel drug targets and selective stabilisation of 14-3-3 PPIs by using ‘molecular glues’ would therefore have a significant impact in terms of therapeutic development in many fields of medicine.

This work shows that WR-1065 (3), the active species of the approved drug amifostine (AM; 2)²⁰, covalently modifies 14-3-3σ at an isoform-unique residue, Cys38 (Figure 1). This modification leads to isoform specific stabilisation of two 14-3-3σ PPIs (with p53 and the oestrogen receptor α (ERα)) in a manner that is cooperative with a well characterised molecular glue, fusicoccin A²¹ (FC-A, 1; Figure 1). A novel stabilisation mechanism for 14-3-3σ, an isoform strongly implicated in cancer, was revealed, and this is likely to contribute to the in vivo pharmacodynamics of amifostine. Here, the cellular relevance of the two ligands has been demonstrated in two cancer cell lines where the cooperative behaviour of 1 and 3 leads to enhanced efficacy for inducing cell death and attenuating cell growth. New WR-1065 analogues bearing different electrophilic ‘warheads’ have been also synthesised and some of them exhibit a ERα/14-3-3σ stabilisation effect. This represents the starting point for the development of new selective and efficacious 14-3-3σ PPIs stabilisers that can be potentially use in anticancer therapies.