Cytotoxic effects of mithramycin DIG-MSK can depend on the rise of autophagy

Abstract

a b s t r a c t 28 DIG-MSK (demycarosil-3D-b-D-digitoxosyl mithramycin SK; EC-8042), a novel analogue of mithramycin 29 A, induced autophagy in HCT116 human colon carcinoma and, to a lesser extent, in A2780 human ovarian 30 carcinoma cell lines, which was followed by apoptosis and/or necrotic cell death in a time-dependent 31 way. The effects of DIG-MSK included changes in the expression of a set of genes involved in autophagy, 32 the progression of cells through the different phases of cell cycle, and their halting at the checkpoints. 33 Cells treated with the glucose analogue 2-DG (2-deoxy-D-glucose), which induces autophagy because it 34 impairs cell metabolism, or co-treated with 2-DG plus DIG-MSK, also showed altered gene expression 35 and autophagy. In A2780 cells, some genes involved in autophagy were down-regulated by the different 36treatments, yet the levels of the proteins they encode could be enough to ensure autophagic flux. In 37 HCT116 cells, up-regulation of several pro-autophagic genes resulted in strong autophagic response. 38 Acidic cell organelles and autophagic flux were more evident in HCT116 than in A2780 cells. DIG-MSK 39 was still cytotoxic in cells that underwent autophagy induced by 2-DG. Therefore, we verified that autop-40 hagy resulting from a stress response did not protect cells against DIG-MSK, but, instead, autophagy pro-41 moted by either 2-DG or the novel mithralogue can enhance the antitumour activity, which depended on 42 the cell type. 43