UNC-2170 (1648707-58-7), identified by screening, was found to be a μM ligand for 53BP1 which also demonstrated at least 17-fold selectivity for 53BP1 over other methyl-lysine binding proteins. The DNA damage response protein 53BP1 utilizes its tandem tudor domain to recognize dimethylated lysine 20 on histone (H4K20me2), a modification associated with double-strand DNA breaks. UNC-2170 functions as a 53BP1 antagonist in cell lysates and suppresses class switch recombination in whole cells, a process requiring a functioning 53BP1 tudor domain.1
