Abstract 345: Characterizing and therapeutically targeting G-quadruplex DNA in ATRX-mutant glioma

Abstract Inactivating ATRX mutations are defining molecular alterations in several cancer variants, including large subsets of malignant glioma. ATRX encodes a chromatin binding protein widely implicated in epigenetic and transcriptional regulation. However, ATRX is also thought to guard against genomic instability, in part by mitigating the formation of deleterious G-quadruplex (G4) DNA secondary structures. G4s have been shown to stall DNA replication leading to single-strand breaks and, potentially, DNA damage and genomic instability. To study this biology in a glioma-relevant context, we generated an isogenic astrocyte model featuring intact or deficient ATRX. While ATRX deficiency had no effect on baseline proliferation, cell cycle progression, and apoptosis, it led to markedly increased G4 formation, DNA damage, and replication stress signaling. These effects were reversed by ATRX re-expression. Moreover, ATRX-deficient astrocytes acquired copy number alterations over time, unlike ATRX-intact counterparts. Given these findings, we hypothesized that therapeutically targeting G4s might serve to exploit the inherent genomic vulnerabilities of ATRX-deficient cancer. Remarkably, treatment with a G4 stabilizing compound (CX3543) selectively inhibited growth and colony formation in ATRX-deficient astrocytes at nanomolar concentrations, and synergistically potentiated the effects of ionizing radiation and hydroxyurea. Finally, CX3543 significantly inhibited the growth of patient-derived, ATRX-deficient glioma xenografts in mice, with only minimal effects on ATRX-intact glioma xenografts. These results confirm and characterize a novel functionality for ATRX in the mitigation of genomic instability and point towards a viable strategy for therapeutically targeting ATRX deficiency in cancer. Citation Format: Yuxiang Wang, Carla Danussi, Kasthuri Kannan, Timothy A. Chan, Jason T. Huse. Characterizing and therapeutically targeting G-quadruplex DNA in ATRX-mutant glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 345.