1802251-00-8

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 1×10 ⁸ M ^-1 s ^-1 as a high end for a range of protein-small molecule interactions, (e.g., chymotrypsin: proflavin k ₁ =1.2×10 ⁸ M ^-1 s ^-1 ), an upper K _d 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 K _d of 2.8 μM is obtained, consistent with our intermediate exchange resonance broadening by PrOF NMR. 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 with an EC ₅₀ of 500 nM carried out. Additionally, no kinase activity has been reported for GSK1379725A despite the growing screening use of the PKIS library.