A Tale of Two Mechanisms: The p53 Modulator COTI-2 Is a Zn Metallochaperone.

Mutations in, or misregulation of, Tp53 are found in approximately 50% of all cancers. p53 functions by ensuring that cells with irretrievably damaged DNA undergo apoptosis. Tp53 mutations often induce conformational changes that inhibit activity; however, small-molecule chaperones could theoretically restore conformation and activity. COTI-2, a thiosemicarbazone with orphan-drug status for ovarian cancer, has proven an effective cytotoxic agent against various cancer cell lines in vitro, exhibited efficacy in vivo, and has demonstrated a good safety profile in Phase 1b human clinical trials. The proposed mechanism, direct engagement and refolding of mutant p53, has been supported by a combination of cell-based assays and transcriptomics data. Through a combination of experimental and computational approaches, we demonstrate that this is an unlikely mechanism of action, and that COTI-2 instead likely acts as a selective, well-tolerated, zinc chaperone to replace zinc ions lost to p53 mutants' deficient zinc-binding.