Abstract
BackgroundCardiac 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.MethodsProscillaridin 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.ResultsAt 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.ConclusionOverall, these results strongly support the repurposing of proscillaridin A in MYC overexpressing leukemia.
Highlights
Cardiac glycosides are approved for the treatment of heart failure as Na+/K+ pump inhibitors
Cardiac glycoside Proscillaridin A targets MYC-driven leukemic cells To identify cancer types with high sensitivity to proscillaridin A in order to obtain concentrations within their therapeutic window, we screened a panel of 14 human cancer cell lines and measured cancer cell proliferation after a 24 h treatment
We found that proscillaridin A produced a significant time-dependent reduction of lysine acetylation at H3K9, H3K14, H3K18, H3K27 residues and global loss of Histone 3 (H3) acetylation in MOLT-4 cells (Fig. 3a; Additional file 4: Figure S3A)
Summary
Cardiac glycosides are approved for the treatment of heart failure as Na+/K+ pump inhibitors. MYC (c-MYC) transcription factor is a driver of oncogenic programs It contributes to gene deregulation in cancer by promoting expression of genes involved in cell proliferation [1]. Indirect MYC inhibition demonstrated therapeutic efficacy with bromodomain inhibitors (such as JQ1 or THZ1), by blocking MYC transcriptional effects [7,8,9]. Cancer cells, such as leukemia, breast and ovarian cancers, develop resistance to these inhibitors by compensatory mechanisms using other bromodomain containing proteins or kinome reprogramming [10, 11]. These studies highlight the need to develop new strategies to abrogate MYC addiction in cancer
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