epz-6438 and Multiple-Myeloma

Thalidomide and its derivatives, lenalidomide and pomalidomide (also known as IMiDs), have significantly changed the treatment landscape of multiple myeloma, and the recent discovery of cereblon (CRBN) as their direct biological target has led to a deeper understanding of their complex mechanism of action. In an effort to comprehend the precise mechanisms behind the development of IMiD resistance and examine whether it is potentially reversible, we established lenalidomide-resistant (-LR) and pomalidomide-resistant (-PR) human myeloma cell lines from two IMiD-sensitive cell lines, OPM2 and NCI-H929, by continuous culture in the presence of lenalidomide or pomalidomide for 4-6 months, until acquirement of stable resistance. By assessing genome-wide DNA methylation and chromatin accessibility in these cell lines, we found that acquired IMiD resistance is associated with an increase in genome-wide DNA methylation and an even greater reduction in chromatin accessibility. Transcriptome analysis confirmed that resistant cell lines are mainly characterized by a reduction in gene expression, identifying SMAD3 as a commonly downregulated gene in IMiD-resistant cell lines. Moreover, we show that these changes are potentially reversible, as combination of 5-azacytidine and EPZ-6438 not only restored the observed accessibility changes and the expression of SMAD3, but also resensitized the resistant cells to both lenalidomide and pomalidomide. Interestingly, the resensitization process was independent of CRBN. Our data suggest that simultaneous inhibition of DNA methyl transferases and EZH2 leads to an extensive epigenetic reprogramming which allows myeloma cells to (re)gain sensitivity to IMiDs.

Topics: Adaptor Proteins, Signal Transducing; Azacitidine; Benzamides; Biphenyl Compounds; Cell Line, Tumor; Chromatin; DNA Methylation; Drug Resistance, Neoplasm; Enhancer of Zeste Homolog 2 Protein; Gene Expression; Gene Expression Profiling; Humans; Lenalidomide; Morpholines; Multiple Myeloma; Peptide Hydrolases; Pyridones; Thalidomide; Ubiquitin-Protein Ligases

Multiple myeloma (MM) is a malignant plasma cell disease with a poor survival, characterized by the accumulation of myeloma cells (MMCs) within the bone marrow. Epigenetic modifications in MM are associated not only with cancer development and progression, but also with drug resistance.. We identified a significant upregulation of the polycomb repressive complex 2 (PRC2) core genes in MM cells in association with proliferation. We used EPZ-6438, a specific small molecule inhibitor of EZH2 methyltransferase activity, to evaluate its effects on MM cells phenotype and gene expression prolile.. PRC2 targeting results in growth inhibition due to cell cycle arrest and apoptosis together with polycomb, DNA methylation, TP53, and RB1 target genes induction. Resistance to EZH2 inhibitor is mediated by DNA methylation of PRC2 target genes. We also demonstrate a synergistic effect of EPZ-6438 and lenalidomide, a conventional drug used for MM treatment, activating B cell transcription factors and tumor suppressor gene expression in concert with MYC repression. We establish a gene expression-based EZ score allowing to identify poor prognosis patients that could benefit from EZH2 inhibitor treatment.. These data suggest that PRC2 targeting in association with IMiDs could have a therapeutic interest in MM patients characterized by high EZ score values, reactivating B cell transcription factors, and tumor suppressor genes.

Topics: Benzamides; Biphenyl Compounds; Cell Line, Tumor; Cell Proliferation; DNA Methylation; Drug Resistance, Neoplasm; Drug Synergism; Epigenesis, Genetic; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Lenalidomide; Morpholines; Multiple Myeloma; Polycomb Repressive Complex 2; Pyridones; Sequence Analysis, RNA