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Bractoppin is a potent and selective drug-like inhibitor of phosphopeptide recognition by the human BRCA1 tandem(t) BRCT domain (binding IC50: 74 nM). Bractoppin diminishes BRCA1 recruitment to DNA breaks, in turn suppressing damage-induced G2 arrest and assembly of the recombinase, RAD51. Bractoppin preferentially inhibits BRCA1 tBRCT-dependent steps in the DNA damage response[1].

In a MST assay, Bractoppin exhibits nanomolar potency in displacing cognate BACH1 phosphopeptide substrate from the BRCA1 tBRCT, the binding IC50 value is 74 nM[1].In a selectivity profile by competitive MST assay, Bractoppin (0-100 μM) does not detectably bind to fluorescently labeled tBRCT domains from MCPH1, TOPBP1 7/8, ECT2, or TOPBP1 1/2[1].Bractoppin (100 μM) selectively inhibits damage-induced BRCA1 foci formation, but has little effect on the radiation-induced accumulation of MDC1 at sites of DNA damage. Similarly, Bractoppin has little effect on the radiation-induced recruitment of TOPBP1 (a protein containing multiple, structurally related tBRCT domains)[1].Bractoppin (10-100 μM; 0.5 hr before radiation (32 hours)) inhibits 4Gy radiation induced G2 arrest in a dose-dependent manner. The percentage of G2 arrest cell is 64%, 42% and 25% for 10 μM, 30 μM and 100 μM, respectively[1].

[1]. Jayaprakash Periasamy, et al. Targeting Phosphopeptide Recognition by the Human BRCA1 Tandem BRCT Domain to Interrupt BRCA1-Dependent Signaling. Cell Chem Biol. 2018 Jun 21;25(6):677-690.e12.

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