• Sinto Sebastian, Yuan X Zhu, Esteban Braggio, Chang-Xin Shi, Sonali C Panchabhai, Scott A Van Wier, Greg J Ahmann, Marta Chesi, P Leif Bergsagel, A Keith Stewart, and Rafael Fonseca.
• Division of Hematology and Medical Oncology, Mayo Clinic, Scottsdale, AZ.
• Blood. 2017 Feb 23; 129 (8): 991-1007.

AbstractLenalidomide is an immunomodulatory drug (IMiDs) with clinical efficacy in multiple myeloma (MM) and other late B-cell neoplasms. Although cereblon (CRBN) is an essential requirement for IMiD action, the complete molecular and biochemical mechanisms responsible for lenalidomide-mediated sensitivity or resistance remain unknown. Here, we report that IMiDs work primarily via inhibition of peroxidase-mediated intracellular H2O2 decomposition in MM cells. MM cells with lower H2O2-decomposition capacity were more vulnerable to lenalidomide-induced H2O2 accumulation and associated cytotoxicity. CRBN-dependent degradation of IKZF1 and IKZF3 was a consequence of H2O2-mediated oxidative stress. Lenalidomide increased intracellular H2O2 levels by inhibiting thioredoxin reductase (TrxR) in cells expressing CRBN, causing accumulation of immunoglobulin light-chain dimers, significantly increasing endoplasmic reticulum stress and inducing cytotoxicity by activation of BH3-only protein Bim in MM. Other direct inhibitors of TrxR and thioredoxin (Trx) caused similar cytotoxicity, but in a CRBN-independent fashion. Our findings could help identify patients most likely to benefit from IMiDs and suggest direct TrxR or Trx inhibitors for MM therapy.© 2017 by The American Society of Hematology.

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