DRB

DRB is a nucleoside analog that inhibits several carboxyl-terminal domain (CTD) kinases including casein kinase II (IC50 range of 4-10 µM){15211}, Cdk7 (IC50 = ~20 µM){15209,15207}, Cdk8 (IC50 = ~20 µM){15207}, and Cdk9 (IC50 = 3 µM).{15214} Through inhibition of certain CTD kinases, DRB inhibits an elongation step during RNA polymerase II transcription{15210,15208}, which can trigger p53-dependent apoptosis of human colon adenocarcinoma cells without inducing genotoxic stress to healthy cells.{15213} DRB can also inhibit HIV transcription (IC50 = ~4 µM) by targeting elongation enhanced by the HIV-encoded transactivator Tat.{15212}