Here, we show that TC11 does not induce degradation of CRBN's substrates, IKZF1/3 and CK1α, and induces apoptosis of CRBN-silenced MM; this effect was independent of the cereblon (CRBN) pathway, which is involved in the mechanism of action of IMiDs used for the treatment of MM.
It is suggested that selected germline CRBN allelic variants (rs1714327G > C and rs1705814T > C) affect lenalidomide efficacy in patients with relapsed/refractory MM.
Taken together, our results, in conjunction with recently published findings, provide a rationale for investigating the efficacy of ARV 825 for MM, use of cereblon as a biomarker for therapy of MM patients, and the combination of ARV 825 with small molecule inhibitors to improve the outcome of MM patients.
We also demonstrated that treatment with a pan-PIM kinase inhibitor resulted in increased expression of cereblon, and that knockdown of cereblon via a shRNA lentivirus abolished the effects of PIM kinase inhibition on the degradation of IKZF1 and IKZF3 and myeloma cell apoptosis, demonstrating a central role of cereblon in pan-PIM kinase inhibitor-mediated down-regulation of IKZF1 and IKZF3 and myeloma cell killing.
Emerging evidence suggests that IMiDs can block MEIS2 from binding to CRBN facilitating the subsequent activation of a <sup>CRL4</sup>CRBN<sup>IMiD</sup>-E3-ubiquitin ligase activity and proteasome-mediated degradation of critical substrates regulators of Multiple Myeloma (MM) cell survival and proliferation.
Immunomodulatory drugs (IMiDs) including lenalidomide and pomalidomide bind cereblon (CRBN) and activate the CRL4<sup>CRBN</sup> ubiquitin ligase to trigger proteasomal degradation of the essential transcription factors IKZF1 and IKZF3 and multiple myeloma (MM) cytotoxicity.
Selected CRBN SNPs may be useful in assessing the probability of AEs in the form of peripheral polyneuropathy and gastrointestinal motility disorders associated with the use of thalidomide in patients with MM.
We herein report our new generation of multifunctional HDAC6 degraders by tethering selective HDAC6 inhibitor Nexturastat A with CRBN ligand that can synergize with HDAC6 degradation for the antiproliferation of multiple myeloma (MM).
Notably, targeting CRL4 has recently emerged as a noval anti-cancer strategy, including thalidomide and its derivatives that bind to the substrate recognition receptor cereblon (CRBN), and anticancer sulfonamides that target DCAF15 to suppress the neoplastic proliferation of multiple myeloma and colorectal cancers, respectively.
This strategy also appeared to be more broadly applicable as SGC-CBP30 could re-sensitize two resistant HMCLs with low but detectable CRBN expression to lenalidomide, suggesting that targeting CBP/E300 is a promising approach to restore IMiD sensitivity in MM with detectable CRBN expression.
Thus, our data argue against the use of CRBN and its downstream targets as predictive biomarkers of IMiD response in MM and confirm clonal evolution patterns during lenalidomide resistance.
These results indicate that the Cereblon-mediated immunomodulatory properties of lenalidomide are maintained in lenalidomide-refractory MM patients and may contribute to immune-mediated killing of MM cells.
Recently, high expression levels of cereblon (CRBN) and MUM1 have been associated with better response rates in multiple myeloma treated with lenalidomide.
More broadly, these findings establish key proteins required for lenalidomide-dependent CRL4<sup>CRBN</sup> function in myeloma and inform potential mechanisms of drug resistance.
Lenalidomide increased intracellular H<sub>2</sub>O<sub>2</sub> 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.
Lenalidomide (LEN) acts directly on multiple myeloma (MM) cells by inducing cereblon-mediated degradation of interferon regulatory factor 4, Ikaros (IKZF)1 and IKZF3, transcription factors that are essential for MM cell survival.
To determine whether the traditional Chinese medicine arsenic trioxide, could potentiate sensitivity of multiple myeloma (MM) cells to lenalidomide and identify the mechanism by which this happens, the present study investigated how arsenic trioxide affected CRBN on MM cell lines and examined the anti-myeloma effect and mechanism in the combination of arsenic trioxide and lenalidomide.
In addition, their epitopes have been precisely determined and the peptides covering their epitopes completely blocked the antibody binding to cereblon in western blot analysis or in immunohistochemistry staining of MM patients' specimens.
This dual assay demonstrated superior Cereblon IHC measurement in MM samples compared with the single IHC assay using a published commercial rabbit polyclonal Cereblon antibody and could be used to explore the potential utility of Cereblon as a biomarker in the clinic.
Cereblon binding partners were identified from a MM cell line expressing histidine-tagged cereblon by pulling down cereblon and its binding partners and verified by co-immunoprecipitation.
CRBN was expressed in all the myeloma cell lines tested, independently of their sensitivity to IMIDs, and the CRBN-DDB1-CUL4 complex was efficiently formed.