Proscillaridin A effects on histone acetylation and C-MYC degradation in acute lymphoblastic leukemia
Acute lymphoblastic leukemia (ALL) represents approximately 25% of all pediatric cancers diagnosed every year. In about 80% of cases, pediatric patients will attain a 5-year event-free survival. Unfortunately, patients who are resistant to treatment or who relapse have a poor prognosis. Hence, novel therapeutic approaches are necessary to increase survival rates. Epigenetic alterations, such as DNA methylation and histone modifications, are involved in disease development, progression, and in particular, resistance to treatment. These reversible alterations represent novel targets in ALL. We recently discovered candidate epigenetic drugs in FDA-approved drug libraries. We performed a secondary screen to test the activity of these drugs in a panel of cancer cell lines. We found that a cardiac glycoside, called proscillaridin A, had anticancer specificity against pediatric leukemia cell lines. Thus, we hypothesize that proscillaridin A has some drug repositioning potential in pediatric ALL. To characterize its epigenetic mechanism of action, we treated two ALL cell lines Nalm-6 (pre-B ALL) and Molt-4 (T-ALL) in vitro for different time points (2-96h) with clinically relevant concentrations of proscillaridin A and analyzed cell growth, cell cycle, gene expression and chromatin modifications. We observed dose-dependent growth inhibition in both cell lines, where 50% of growth inhibition (IC50) was obtained at 3.0 and 2.3 nM in Nalm-6 and Molt-4, respectively. Our results using BrdU staining indicate a cell cycle block in the G2/M phase. By western blot, we detected significant decreases in histone 3 acetylation levels (H3K14ac, H3K9ac, and H3K27ac). Decreases in histone acetylation were associated with a significant reduction in histone acetyltransferase expression (CBP, P300 and TIP60) as well as the CMYC oncogene. By RNA sequencing and gene set enrichment analysis, we observed an upregulation of apoptosis and cell differentiation genes, as well as a decrease in cell proliferation and C-MYC target genes. These promising results illustrate the potential of using the cardiac glycoside proscillaridin A as a novel drug in treatment of relapsed or refractory ALL.
Acetylation Oncogene Leukemia