GSK1379725A is a selective BPTF ligand (Kd = 2.8 μM).

BPTF:2.8 μM(Kd)

Although GSK1379725A has been demonstrated to be selective over Brd4, a full selectivity panel against other bromodomains will be needed. A database search using ChEMBL only showed GSK1379725A to be active in five cellular assays (EC50: 500 nM) carried out. Additionally, no kinase activity has been reported for GSK1379725A despite the growing screening use of the PKIS library[1]. From the NMR titration of GSK1379725A, the bound and unbound resonances are separated by 171 Hz, providing an upper bound for the chemical exchange rate. Assuming an association rate of 1×108 M-1 s-1 as a high end for a range of protein-small molecule interactions, (e.g., chymotrypsin: proflavin k1=1.2×108 M-1 s-1), an upper Kd of 8 μM is estimated from this experiment. For a more accurate determination with a non-fluorinated protein, ITC is used as a complementary direct binding assay using unlabeled BPTF. A Kd of 2.8 μM is obtained, consistent with our intermediate exchange resonance broadening by PrOF NMR.