Immunomodulatory drugs rewire mTORC1-dependent pathways in multiple myeloma to trigger cytotoxicity and immunogenic cell death

Abstract Immunomodulatory drugs (IMiDs), including lenalidomide and pomalidomide, are cornerstone therapies for multiple myeloma (MM). These agents exert antitumor effects by binding cereblon (CRBN), a substrate receptor of the CRL4CRBN E3 ubiquitin ligase and promoting the degradation of key transcription factors IKZF1 and IKZF3. However, this mechanism depends on intact proteasome activity and does not fully explain the broad therapeutic activity of IMiDs, particularly their synergy with proteasome inhibitors, suggesting the existence of additional antitumor mechanisms. To explore additional molecular pathways regulated by IMiDs, we performed RNA-seq in MM cells treated with IMiDs and identified significant downregulation of the mTORC1 signaling pathway, characterized by reduced phosphorylation of its downstream effector p70S6K, but not 4E-BP1. Clinical dataset analysis revealed that elevated mTOR/p70S6K expression correlates with high-risk disease and poor patient outcomes, highlighting its potential as a predictive biomarker. Mechanistically, IMiDs enhanced AMPK phosphorylation, leading to decreased phosphorylation of Raptor and suppression of mTORC1 activity. This process was CRBN-dependent, as CRBN knockout abolished AMPK activation and restored mTORC1 signaling. Importantly, MM patient samples treated with IMiDs also exhibited increased AMPK activity, confirming the clinical relevance of this finding. Functionally, mTORC1 inhibition by IMiDs induced autophagy and further upregulated CRBN expression, establishing a positive feedback loop that amplified IKZF1/3 degradation and direct cytotoxicity. In parallel, IMiDs downregulated DNA damage response pathways, especially CHEK1, a key regulator of cell cycle checkpoint control. CHEK1 suppression was also observed following treatment with selective mTORC1 inhibitors. Analysis of clinical cohorts demonstrated that low CHEK1 expression was associated with prolonged survival, and CHEK1 downregulation by IMiDs impaired DNA repair capacity and promoted accumulation of DNA damage. Notably, excessive DNA damage has been shown to activate the cGAS-STING pathway, leading to type I interferon responses. We found that IMiDs treatment significantly activated cGAS-STING signaling in MM cells, accompanied by increased expression of downstream cytokines such as IFN-β. Moreover, IMiDs triggered classical markers of immunogenic cell death (ICD), including calreticulin surface exposure, HMGB1 release, and upregulation of ICD gene signatures. These effects enhanced dendritic cell maturation and antigen presentation, ultimately promoting T cell–mediated cytotoxicity. In summary, our study reveals an unreported dual mechanism by which IMiDs exert potent antimyeloma activity: (1) CRBN-dependent AMPK activation suppresses mTORC1 signaling, inducing autophagy and reinforcing CRBN expression; (2) CHEK1 downregulation diminishes DNA repair, activates cGAS-STING signaling, and induces ICD, leading to robust immune responses. These findings not only deepen our understanding of IMiDs biology but also provide a strong rationale combining agents targeting mTORC1 or DNA damage response pathways to enhance their efficacy in relapsed or refractory MM.