Anti-cancer activities of cytokinin ribosides

Cytokinins are plant hormones and play essential roles in regulating plant growth and development. They also have diverse pharmacological effects in animals and humans. Whereas cytokinin bases have been studied mainly for their cytoprotective activities, cytokinin ribosides have been explored as anti-cancer agents. Cytokinin ribosides inhibit growth or cause apoptosis in various cell lines derived from diverse malignancies including those with a mutant p53 gene. Activity against cancer stem cells, anti-angiogenic activity, and the ability to stimulate an immune response to malignant cells have been reported as well. There are also positive results from in vivo studies and reports of activity in patients with hematological malignancies and solid tumors. Here, we review studies of the anti-cancer activity of cytokinin ribosides since the 1960s and comment on the issues that need to be addressed for the further development of cytokinin ribosides into anti-cancer drugs.