Abstract 3253: Targeting G-quadruplex nucleic acids: a series of β-carboline alkaloids with new skeletons from the seeds of Peganum harmala

Abstract

Abstract G-quadruplexes are DNA secondary structures implicated in essential physiological and pathological processes, such as tumorgenesis. Small molecules which can stabilize or induce G-quadruplex formation have potential as antitumor agents through the alteration of oncogene expression levels or the disruption of telomere maintenance. Targeting G-quadruplex nucleic acids, we screened 17 medicinal plants for binding activity to a model G-quadruplex d(TTGGGTT)4 system by 1H NMR experiment. We found that the crude extract of Peganum harmala L. seeds showed the most potential binding activity and specific cytotoxicity against the PC-3 cancer cell line with an IC50 value of 13.65 μg/mL. Subsequently, 1H NMR and bioassay co-guided isolation of the extract of P. harmala L. was performed and obtained 21 new alkaloids, including 10 novel β-carboline alkaloids with unprecedented carbon skeletons, and 12 known analogues. Their structures including the absolute configurations were determined by extensive analysis of spectroscopic data, X-ray crystallography, ECD calculations, and ECD exciton chirality approaches. The antiproliferative activities and G-quadruplex binding activities were evaluated for these newly discovered and previously reported alkaloids. Some of the isolates showed pronounced cytotoxic effects with IC50 values below 10 µM and significant G-quadruplex binding activities. More interestingly, pegaharmine D (4), which showed the strongest G-quadruplex interaction, exhibited significant cytotoxic activity against HL-60, PC-3 and SGC-7901 cell lines, with IC50 values of 3.81 ± 0.32, 11.52 ± 0.62, and 15.16 ± 0.42 µM, respectively. The G-quadruplex interactions positively correlated with antiproliferative activities suggesting these β-carboline alkaloids may exert their anti-cancer effects through G-quadruplex interactions. This work contributed a practical strategy at first time for the discovery of novel G-quadruplex ligands from natural products and provided potential insights for using β-carboline alkaloids as anticancer lead compounds specifically targeting G-quadruplexes. Citation Format: Kaibo wang, Huiming Hua, Danzhou Yang. Targeting G-quadruplex nucleic acids: a series of β-carboline alkaloids with new skeletons from the seeds of Peganum harmala [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3253. doi:10.1158/1538-7445.AM2017-3253