A Cyclometallated Iridium(III) Complex As a c-myc G-Quadruplex Stabilizer and Down-Regulator of c-myc Oncogene Expression

Discovery of a New Four-Leaf Clover-Like Ligand as a Potent c-MYC Transcription Inhibitor Specifically Targeting the Promoter G-Quadruplex

Downregulating transcription of the oncogene c-MYC is a feasible strategy for cancer therapy. Stabilization of the G-quadruplex structure present in the c-MYC promoter can suppress c-MYC transcription. Thus, far, several ligands targeting this structure have been developed. However, most have shown no selectivity for the c-MYC G-quadruplex over other G-quadruplexes, leading to uncertain side effects. In this study, through structural modification of aryl-substituted imidazole/carbazole conjugates, a brand-new, four-leaf clover-like ligand called IZCZ-3 was found to preferentially bind and stabilize the c-MYC G-quadruplex. Further intracellular studies indicated that IZCZ-3 provoked cell cycle arrest and apoptosis and thus inhibited cell growth, primarily by blocking c-MYC transcription through specific targeting of the promoter G-quadruplex structure. Notably, IZCZ-3 effectively suppressed tumor growth in a mouse xenograft model. Accordingly, this work provides an encouraging example of a selective small molecule that can target one particular G-quadruplex structure, and the selective ligand might serve as an excellent anticancer agent.

G-quadruplexes as potential therapeutic targets for embryonal tumors

Embryonal tumors include a heterogeneous group of highly malignant neoplasms that primarily affect infants and children and are characterized by a high rate of mortality and treatment-related morbidity, hence improved therapies are clearly needed. G-quadruplexes are special secondary structures adopted in guanine (G)-rich DNA sequences that are often present in biologically important regions, e.g. at the end of telomeres and in the regulatory regions of oncogenes such as MYC. Owing to the significant roles that both telomeres and MYC play in cancer cell biology, G-quadruplexes have been viewed as emerging therapeutic targets in oncology and as tools for novel anticancer drug design. Several compounds that target these structures have shown promising anticancer activity in tumor xenograft models and some of them have entered Phase II clinical trials. In this review we examine approaches to DNA targeted cancer therapy, summarize the recent developments of G-quadruplex ligands as anticancer drugs and speculate on the future direction of such structures as a potential novel therapeutic strategy for embryonal tumors of the nervous system.