5,6-Dichlorobenzimidazole riboside (DRB) is a nucleoside analog that inhibits several carboxyl-terminal domain kinases, including casein kinase II and cell cycle-dependent kinases ( CDK ) . 5, 6-dichlorobenzimidazole riboside has antitumor activity. 5, 6-dichlorobenzimidazole riboside can induce apoptosis.