Identification and characterization of G-quadruplex-interactive compounds as anticancer agents

G-quadruplexes are four-stranded DNA structures formed from stacking guanine-tetrads. It has been suggested that G-quadruplexes are potential targets for the design and development of novel anticancer drugs. Recently, several groups of small organic molecules which include the anthraquinones have been identified as G-quadruplex-interactive agents.; In order to identify G-quadruplex-interactive compounds in a simple and rapid way, a cell-free assay based upon a primer extension reaction by DNA polymerases was developed. The application of this assay resulted in the identification of several lead compounds including some perylene and porphyrin analogues. One of the perylene analogues, PIPER was further characterized for its interaction with G-quadruplexes. Gel mobility shift study revealed that PIPER was able to dramatically facilitate the dimerization of a DNA oligomer containing two repeats of human telomeric sequence. The formation of dimeric G-quadruplex was accelerated approximately 100-fold in the presence of 10 muM PIPER. Moreover, further studies showed that PIPER specifically prevented the unwinding of G-quadruplex DNA by yeast helicase Sgs1 via interaction with G-quadruplexes.; The differential interactions of three porphyrin analogues, TMPyP2, TMPyP3 and TMPyP4, with different types of G-quadruplexes were compared by using helicase and photocleavage assays. The results indicated that although these three porphyrins are closely related in chemical structures, they exhibited differences in their binding modes and ability to stabilize different G-quadruplexes.; The present study demonstrated that some G-quadruplex-interactive compounds were able not only to bind to and stabilize G-quadruplexes but also to facilitate the assembly of single-stranded DNA into G-quadruplexes. This result alongside the finding that G-quadruplex-interactive agents can prevent the unwinding of G-quadruplexes by helicase suggests a new way of targeting DNA: inducing and stabilizing G-quadruplex structures in the G-rich regions along the genome and consequently preventing them from being disassembled by cellular helicases. These stabilized G-quadruplex structures can then disrupt critical cellular functions such as telomere maintenance and transcription regulation and cause chromosomal anaphase bridges and slowing of tumor growth.