The Myeloma Drug Lenalidomide Promotes the Cereblon-Dependent Destruction of Ikaros Proteins

Drug With a (Re)Purpose

Thalidomide, once infamous for its deleterious effects on fetal development, has re-emerged as a drug of great interest because of its beneficial immunomodulatory effects. A derivative drug called lenalidomide significantly extends the survival of patients with multiple myeloma, but the molecular mechanisms underlying its efficacy remain unclear (see the Perspective by Stewart ). Building on a previous observation that thalidomide binds to cereblon, a ubiquitin ligase, Lu et al. (p. 305 , published online 28 November) and Krönke et al. (p. 301 , published online 28 November) show that in the presence of lenalidomide, cereblon selectively targets two B cell transcription factors (Ikaros family members, IKZF1 and IKZF3) for degradation. In myeloma cell lines and patient cells, down-regulation of IKZF1 and IKZF3 was necessary and sufficient for the drug's anticancer activity. Thus, lenalidomide may act, at least in part, by “grepurposing” a ubiquitin ligase.