Interactome of Aiolos/Ikaros Reveals Combination Rationale of Cereblon Modulators with HDAC Inhibitors in DLBCL.

PURPOSE: Cereblon (CRBN), a substrate receptor of the E3 ubiquitin ligase complex CRL4CRBN, is the target of the small molecules lenalidomide (Len) and avadomide (Ava). Upon binding of the drugs, Aiolos and Ikaros are recruited to the E3 ligase, ubiquitylated and subsequently degraded. In DLBCL cells, Aiolos and Ikaros are direct transcriptional repressors of interferon stimulated genes (ISG) and degradation of these substrates results in increased ISG protein levels resulting in decreased proliferation and apoptosis. Herein, we aimed to uncover the mechanism(s) Aiolos and Ikaros use to repress ISG transcription and provide a mechanistic rationale for a combination strategy enhance cell autonomous activites of CELMoDs Experimental design: We conducted paired RNAseq with histone modification and Aiolos/Ikaros ChIP-seq to identify genes regulated by these transcription factors and to elucidate correlations to drug sensitivity. We confirmed Aiolos/Ikaros mediated transcriptional complex formation in DLBCL patient samples including those treated with avadomide.

RESULTS: In DLBCL, the repression of ISG transcription is accomplished in part through recruitment of large transcriptional complexes such as the nucleosome remodeling and deacetylase (NuRD) which modify the chromatin landscape of these promoters. A rational combination approach of Ava with a specific HDAC inhibitor leads to a significant increase in ISG transcription compared to either single agent, and synergistic antiproliferative activity in DLBCL cell lines.

CONCLUSION: Our results provide a novel role for lineage factors Aiolos and Ikaros in DLBCL as well as further insight into the mechanism(s) of Aiolos and Ikaros mediated transcriptional repression and unique therapeutic combination strategies.