The G‐quadruplex‐stabilizing ligand RHPS4 enhances sensitivity of U251MG glioblastoma cells to clinical carbon ion beams

Abstract

The pentacyclic acridine RHPS4 is a highly potent and specific G-quadruplex (G4) ligand, which binds and stabilizes telomeric G4 leading to the block of the replication forks at telomeres and consequently to telomere dysfunctionalization. In turn, the cell recognizes unprotected telomeres as DNA double-strand breaks with consequent activation of DNA repair response at telomeres, cellular growth impairment, and death. Data from the literature showed the capability of this compound to sensitize U251MG glioblastoma radioresistant cell line to X-rays sparsely ionizing radiations. In the present paper, it was investigated whether RHPS4 is also able to increase the effect of clinical carbon ion beams (cells irradiated in the middle of a spread-out Bragg peak, in the energy range of 246-312 MeV·μm and a dose-averaged linear energy transfer of 46 keV·μm ). Interestingly, also for charged particles whose damage inflicted to DNA is more complex than that of sparsely ionizing radiations and results in higher Relative Biological Effectiveness (RBE), RHPS4 significantly potentiated the radiation effect in terms of cell killing, delayed rejoining of DNA double-strand breaks (γ-H2AX and 53BBP1 immunofluorescence staining), chromosome aberrations (pan-centromeric/telomeric FISH and multicolor FISH), and G /M-phase accumulation in GBM cells. Overall, the results provide the first evidence that the combined administration of the G4-ligand RHPS4 with charged particles interfere with cellular processes involved in cell survival leading to radiosensitization of highly radioresistant tumor cells.

Naphthalene diimide‐derivatives G‐quadruplex ligands induce cell proliferation inhibition, mild telomeric dysfunction and cell cycle perturbation in U251MG glioma cells

“…To investigate NDIs radiosensitizing effect on U251MG cells surviving fraction (SF) experiments were performed. In contrast to RHPS4, that shows a potent radiosensitizing effect on GBM cells [27,28] (Fig. 3A), NDIs did not increase cell killing up to 6 Gy of X-rays ( Fig.…”

“…Therefore, based on our previous results gained in radioresistant GBM cells [27,28], we decided to characterize in detail the cellular effects of three NDIs synthetized in our laboratory. Data from literature show that ligands able to stabilize telomeric G4, besides affecting cell proliferation when administered as single agent, might display also radiosensitizing properties when combined with IR treatment.…”

“…In contrast to RHPS4, that shows a potent radiosensitizing effect on GBM cells [27,28] (Fig. In contrast to RHPS4, that shows a potent radiosensitizing effect on GBM cells [27,28] (Fig.…”

Stilbene Compounds Inhibit Tumor Growth by the Induction of Cellular Senescence and the Inhibition of Telomerase Activity

“…In the past decade, many G-quadruplex ligands have been synthesized. BRACO-19, RHPS4, and porphyrin (TMPyP4) are some of the most attractive that have been developed to increase G-quadruplex stability [106,107,108,109]. Experimental data have proven that these ligands binds with high affinity to 3′ end of the telomere prompt the formation of G-quadruplexes in some malignant cancers.…”

G-quadruplex ligand RHPS4 radiosensitizes glioblastoma xenograft in vivo through a differential targeting of bulky differentiated- and stem-cancer cells

“…In particular, homologous recombination (HR), rather than non homologous end joining (NHEJ), is the preferential pathway involved in DNA double strand breaks (DSBs) repair in GSCs, pointing to the targeting of RAD51 as a possible strategy to overcome the intrinsic radioresistance of these cells [6, 11–13]. In addition to DNA repair proteins, telomeric targeting is a further attractive strategy to sensitize glioma radioresistant cells to conventional radiotherapy and to adrontherapy [14–17].…”