LDC000067 (LDC067) is a highly specific and selective CDK9 inhibitor with an IC50 value of 44±10 nM.

CDK9:44±10 nM, CDK1-CyclinB1:5513 nM, CDK4-CyclinD1:9242 nM, ABL2/ARG:3640 nM, GSK-3α:1460 nM, HGK/MAP4K4:820 nM, CDK2-CyclinA:2441 nM

The fluorescence resonance energy transfer (FRET)-based LANCE Ultra KinaSelect Ser/Thr kit is used to determine IC50 values for various CDK inhibitors. Briefly, a specific ULight MBP peptide substrate (50 nM final concentration) is phosphorylated by a CDK-cyclin pair in buffer (50 mM HEPES-KOH pH 7.5, 10 mM MgCl2, 1 mM EGTA, 2 mM dithiothreitol) containing ATP at the concentration of the Km values of the individual kinases for 1 h at room temperature. Subsequently, phosphorylation is detected by addition of specific Eu-labelled anti-phospho-antibodies (2 nM), which upon binding to the phosphopeptide give rise to a FRET signal. FRET signals are then recorded[1].