Total Synthesis and Chemoproteomics Connect Curcusone Diterpenes with Oncogenic Protein BRAT1

Natural products are an indispensable source of lifesaving medicine, but natural product-based drug discovery often suffers from scarce natural supply and unknown mode of action. The study and development of anticancer curcusone diterpenes fall into such a dilemma. Meanwhile, many biologically-validated disease targets are considered “undruggable” due to the lack of enzymatic activity and/or predicted small molecule binding sites. The oncogenic BRCA1-associated ATM activator 1 (BRAT1) belongs to such an “undruggable” category. Here, we report our synthetic and chemoproteomics studies of the curcusone diterpenes that culminate in an efficient total synthesis and the identification of BRAT1 as a cellular target. We demonstrate for the first time that BRAT1 can be inhibited by a small molecule (curcusone D), resulting in impaired DNA damage response, reduced cancer cell migration, potentiated activity of the DNA damaging drug etoposide, and other phenotypes similar to BRAT1 knockdown.