Biochem/physiol Actions

LDC000067 (LDC067) is an ATP-competitive, potent and selective cyclin-dependent kinase 9 (CDK9) inhibitor (IC50 = 44 nM/CDK9-CycT1 vs. 5.51 µM/CDK1-CycB1, 2.44 µM/CDK2-CycA, 9.24 µM/CDK4-CycD1, >10 µM/CDK6-CycD3 & CDK7-CycH-MAT1; Kd = 32.7 nM/CDK9-CycT1 vs. 1.01 µM/CDK2-CycA, 16.0 µM/CDK7-CycH-MAT1) with much reduced or little potency against a panel of 28 non-CDK kinases. LDC067 selectively inhibits cellular RNA polymerase II CTD Ser2 phosphorylation (by 40% in HeLa; 60-min, 10 µM LDC067), but not CDK9-independent pSer5 or pSer7, causing apoptosis induction (by 239% and 200% of untreated control in A549 and MCF7 cultures) as a result of blocking RNAPII-mediated mRNA synthesis.