UNC-669 is a small molecule nicotinamide derivative that acts asan antagonist of the MBT(Malignant Brain Tumor) domain, a family of methyl-lysine binding reader proteins. UNC669 displays selectivity for L3MBTL3 (IC₅₀ = 3.1 µM) and L3MBTL1(IC₅₀ = 4.2 µM) over L3MBTL4 (IC₅₀ = >10 µM).