Abstract
Background: DNA G-quadruplex (G4) structures represent potential anti-cancer targets. In this study, we compared the effect of two G4-targeting compounds, C066-3108 and the gold standard BRACO-19. Methods: In breast and prostate cancer cells, cytotoxicity induced by both molecules was measured by a sulforhodamine B assay. In breast cancer cells, cycle, apoptosis, the formation of G4 structures, calreticulin and high mobility group box 1 (HMGB1), as well as T cell activation, were analyzed by flow cytometry and adenosine triphosphate (ATP) by luminescence. Results: Both ligands inhibited cell survival and induced DNA damage. In MCF-7 cells, G4 ligands increased the subG0/G1 phase of the cell cycle inducing apoptosis and reduced intracellular ATP. In untreated MCF-7 cells, we observed a slight presence of G4 structures associated with the G2/M phase. In MDA-MB231 cells, G4 ligands decreased the G1 and enhanced the G2/M phase. We observed a decrease of intracellular ATP, calreticulin cell surface exposure and an increase of HMGB1, accompanied by T cell activation. Both compounds induced G4 structure formation in the subG0/G1 phase. Conclusions: Our data report similar effects for both compounds and the first evidence that G4 ligands induce the release of danger signals associated with immunogenic cell death and induction of T cell activation.
Highlights
In the human genome, polymorphic guanine (G)-rich sequences can fold into G-quadruplex (G4)secondary structures, characterized by the formation of the so-called G-tetrads, planar cyclic arrays of four guanine bases linked by Hoogsteen hydrogen bonds [1]
In order to compare the anti-proliferative effects of C066-3108 and BRACO-19 in several cancer cell lines, we selected prostate and breast cancer cells
Cells were cultured for 72 h in the presence and in the absence of G4 ligands, and we observed cytotoxicity in PC3, MCF-7 and MDA-MB231 cells at the highest ligand concentration, whereas no effect was detected in LNCaP (Figure 2A)
Summary
Polymorphic guanine (G)-rich sequences can fold into G-quadruplex (G4)secondary structures, characterized by the formation of the so-called G-tetrads, planar cyclic arrays of four guanine bases linked by Hoogsteen hydrogen bonds [1]. Stabilization of G4 structures with specific ligands induced DNA damage at telomeres along with the induction of cancer cell senescence and apoptosis [6]. Targeting G4 structures by means of selective small molecules is a key challenge to elicit a therapeutic response and the focus of clinical investigation. To this aim, several classes of ligands able to bind and stabilize G4 structures have been described so far [7,8,9]. DNA G-quadruplex (G4) structures represent potential anti-cancer targets. Cycle, apoptosis, the formation of G4 structures, calreticulin and high mobility group box 1 (HMGB1), as well as T cell activation, were analyzed by flow cytometry and adenosine triphosphate (ATP) by luminescence
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