Background Cardiac glycosides are approved for the treatment of heart failure as Na + /K + pump inhibitors. Their repurposing in oncology is currently investigated in preclinical and clinical studies. However, the identification of a specific cancer type defined by a molecular signature to design targeted clinical trials with cardiac glycosides remains to be characterized. Here, we demonstrate that cardiac glycoside proscillaridin A specifically targets MYC overexpressing leukemia cells and leukemia stem cells by causing MYC degradation, epigenetic reprogramming and leukemia differentiation through loss of lysine acetylation. Methods Proscillaridin A anticancer activity was investigated against a panel of human leukemia and solid tumor cell lines with different MYC expression levels, overexpression in vitro systems and leukemia stem cells. RNA-sequencing and differentiation studies were used to characterize transcriptional and phenotypic changes. Drug-induced epigenetic changes were studied by chromatin post-translational modification analysis, expression of chromatin regulators, chromatin immunoprecipitation, and mass-spectrometry. Results At a clinically relevant dose, proscillaridin A rapidly altered MYC protein half-life causing MYC degradation and growth inhibition. Transcriptomic profile of leukemic cells after treatment showed a downregulation of genes involved in MYC pathways, cell replication and an upregulation of hematopoietic differentiation genes. Functional studies confirmed cell cycle inhibition and the onset of leukemia differentiation even after drug removal. Proscillaridin A induced a significant loss of lysine acetylation in histone H3 (at lysine 9, 14, 18 and 27) and in non-histone proteins such as MYC itself, MYC target proteins, and a series of histone acetylation regulators. Global loss of acetylation correlated with the rapid downregulation of histone acetyltransferases. Importantly, proscillaridin A demonstrated anticancer activity against lymphoid and myeloid stem cell populations characterized by MYC overexpression. Conclusion Overall, these results strongly support the repurposing of proscillaridin A in MYC overexpressing leukemia. Electronic supplementary material The online version of this article (10.1186/s13046-019-1242-8) contains supplementary material, which is available to authorized users.
Targeting MYC oncogene remains a major therapeutic goal in cancer chemotherapy. Here, we demonstrate that proscillaridin, a cardiac glycoside approved for heart failure treatment exhibit anticancer selectivity towards high MYC expressing leukemic cell lines and leukemia stem cells. At a clinically relevant concentration, proscillaridin induced a rapid downregulation of MYC protein level, due to a significant decrease in MYC protein half-life. Proscillaridin treatment induced a downregulation of gene sets involved in MYC pathway, and a concomitant upregulation of genes involved in hematopoietic differentiation. Proscillaridin induced a significant loss of lysine acetylation in histone H3 (K9, K14, K18 and K27) and in non-histone proteins such as MYC, MYC target proteins, and a series of histone acetylation regulators. Loss of lysine acetylation correlated with a rapid downregulation of histone acetyltransferase protein levels, involved in histone and MYC acetylation (CBP, P300, GCN5, TIP60, and MOZ), preferentially in MYC overexpressing leukemia as compared to other cancer cells.These results support the repurposing of proscillaridin in MYC overexpressing leukemia and propose a novel strategy to target MYC in cancer.
In cancer, epigenetic modifications are strongly altered and are responsible for gene expression aberrations. In a drug screening initiative, we recently reported that proscillaridin, a cardiac glycoside (CG), exhibits unsuspected epigenetic and anticancer activities. To understand CG's epigenetic mechanisms of action, we performed RNA sequencing analysis, which showed proscillaridin effects on global gene expressions in acute lymphoblastic leukemia cells (MOLT-4). Genes associated with apoptosis and cell differentiation were upregulated whereas master transcription factors and oncogenic pathway genes were downregulated. Mechanistic studies revealed that proscillaridin decreased histone 3 acetylation, which correlated with histone acetyltransferase (KATs) downregulation (CBP, P300, TIP60, GCN5 and MOZ). Acetylome studies by mass spectrometry showed an acetylation loss in chromatin regulators, the oncogene C-MYC and its associated proteins. Proscillaridin induced C-MYC transcript and protein degradation. Moreover, in a panel of cancer cell lines, we measured that cancer cells sensitivity to proscillaridin treatment was positively correlated with C-MYC protein levels. Conversely, proscillaridin did not affect C-MYC protein level in low C-MYC expressing cancer cell lines. For the first time, we showed that CGs target histone acetyltransferases and C-MYC oncogene in high C-MYC expressing cancers. We propose that CGs can be repurposed as new epigenetic drugs in high C-MYC expressing cancers. Citation Format: Elodie M. Da Costa, Gregory Armaos, Annie Beaudry, Chantal Richer, Maxime Caron, Pascal St-Onge, Jeffrey Johnson, Nevan Krogan, Yuka Sai, Michael Downey, Daniel Sinnett, Serge McGraw, Noël J. Raynal. Targeting histone acetyltransferases to reprogram high C-MYC expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1381.
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