In the present study, we investigated whether the clinical efficacy of thalidomide in multiple myeloma is associated with CRBN expression in myeloma cells.
One of the downstream targets of CRBN identified is interferon regulatory factor 4 (IRF4), which is critical for myeloma cell survival and is down-regulated by IMiD treatment.
Responsiveness of cytogenetically discrete human myeloma cell lines to lenalidomide: lack of correlation with cereblon and interferon regulatory factor 4 expression levels.
The aim of the study was to evaluate CRBN and IL-6R expressions and their impact on clinical efficacy of dexamethasone-thalidomide therapy in multiple myeloma (MM) patients, in addition to their association with other clinical and prognostic parameters.
These results suggest that, similar to the treatment of MM, high levels of full-length CRBN mRNA in lower risk 5q- patients are necessary for the efficacy of lenalidomide.
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.
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.
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.
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.