Pestones Aand B from a Fungus <i>Pestalotiopsis</i> sp. Bound to Mutantp53 and Changed Its Conformation

Oncogenic mutant p53 is one of the targets for cancer therapy, and the development of anticancer drugs that reactivate mutant p53 is a promising strategy. The extract of fungus <i>Pestalotiopsis</i> sp. changed mutant p53 to wild-type-like p53 in Saos-2 (p53^R175H) cells, as shown by fluorescent immunostaining, and bioassay-guided purification of the extract afforded new dimeric epoxyquinoids, pestones A and B (<b>1</b> and <b>2</b>), and a known compound, rosnecatrone (<b>3</b>). The relative and absolute configurations of <b>1</b> and <b>2</b> were determined based on the spectroscopic data and semisynthesis from <b>3</b>. Compounds <b>1</b> and <b>2</b> altered the conformation of mutant p53 in Saos-2 (p53^R175H) cells, as shown by immunofluorescence staining. The cellular thermal shift assay analysis showed that <b>1</b> increased the thermostability of mutant p53 in Saos-2 (p53^R175H) cells, suggesting the direct binding of <b>1</b> to mutant p53. Compounds <b>1</b> and <b>2</b> exhibited cytotoxic activities against Saos-2 (p53^R175H) cells with IC₅₀ values of 1.0 and 1.1 μM, respectively. Compound <b>1</b> was found to induce apoptosis in Saos-2 (p53^R175H) cells by flow cytometry analysis and decreased tumor growth <i>in vivo</i> using a mouse model with HuCCT1 (p53^R175H) cells.