IKZF1/3 and CRL4CRBN E3 ubiquitin ligase mutations and resistance to immunomodulatory drugs in multiple myeloma

Cereblon (CRBN), a target of immunomodulatory drugs (IMiD), forms the CRL4 CRBN E3 ubiquitin ligase (CRL4) complex with DDB1, CUL4B and ROC1. Under the influence of IMiD, CRL4 polyubiquitinates and thus depletes the transcription factors IKZF1 and IKZF3, resulting in cytotoxicity to multiple myeloma (MM) cells. 4] In order to select the most promising patient-derived candidate mutations for functional validation, we first generated a comprehensive overview of point mutations affecting IKZF1, IKZF3 or CRL4 genes in patients with advanced MM. Next, we contextualized all described mutations at the protein level, to investigate their structural impact on complex formation and stability. Based on these analyses, we then selected a subset for functional validation by expressing mutant IKZF1, CRBN or CUL4B in MM cell lines and analyzed their effects on resistance to IMiD, thus probing the relevance of such alterations for complex integrity and the transmission of IMiD activity.