Platination of telomeric sequences and nuclease hypersensitive elements of human c‐myc and PDGF‐A promoters and their ability to form G‐quadruplexes

Abstract

G-rich regions appear in several locations in the human genome, including at the ends of linear chromomes, the immunoglobin switch region, centromeres, fragile X syndrome repeats, and promoters of some genes [1]. The sequences repeated in tandem, with three or four adjacent guanines, have been known to form polymorphic quadruplexes containing G-quartets stabilized by cyclic Hoogsteen hydrogen bondings. Quadruplex structures are highly stable DNA or RNA structures formed on G-rich sequences [2]. The Na + and K + ions stabilize the stacking through their interactions with carbonyl oxygens of the eight guanines of two adjacent quartets [3]. Direct evidence for the presence of G-quadruplex structures in vivo has been reported both at the telomeres of the ciliate Stylonychia [4] and those of humans [5], and at the promoter of c-myc [6,7]. Moreover, other genomic regions were shown to be able to adopt quadruplex structures, such as the promoters of c-kit oncogene [6], HIF-1a [9], Bcl2 [10] and vascular endothelial growth factor [11].The stabilization of the G-quadruplex structure by small molecules is currently emerging as a very promising anti-cancer strategy. Therefore, molecules that stabilize G-quadruplex structures can be used as potential anti-cancer agents [12]. Indeed, recent studies strongly suggest that molecules able to stabilize the quadruplex structure of DNA can lead to an arrest of the proliferation of cancer cells [5,[12][13][14]. At each division of somatic cells, telomeres are shortened, a process leading to senescence and death. It has been shown in vitro that G-quadruplex structures of the human sequence (G 3 T 2 A) 3 G 3 formed in the presence of molecules stabilizing the G-quartet stacks, similar to anthraquinones or porphyrins, inhibit the activity of telomerase [13][14][15][16][17].The anti-tumor drug cisplatin (cis-[PtCl2(NH3)2]), known for its high affinity for G-rich sequences, was Naturally occurring G-rich DNA sequences that are able to form G-quadruplex structures appear as potential targets for anti-cancer chemotherapy, and therefore play an important role in cellular processes, such as cell aging, death and carcinogenesis. The telomeric regions of DNA and nuclease hypersensitive elements of human c-myc and PDGF-A promoters represent a very appealing target for cisplatin and may interfere with normal DNA function. Platinum complexes bind covalently to nucleobases, and especially to the N7 atom of guanines, and the four guanines of a G-quartet have their N7 atoms involved in hydrogen bonding. Therefore, within a G-quadruplex structure, only the guanines out of the stack of G-quartets should react with electrophilic species such as platinum (II) complexes. Platinum complexes have significant influence on the formation of G-quadruplexes. Results obtained by CD spectroscopy and temperature gradientgel electrophoresis clearly demonstrate that DNA platination significantly affects G-quadruplex folding for telomeric sequences; the abundance of un ⁄ misfolded DNAs compared to the G-quadruplex is...

Evidence for G-quadruplex in the promoter of vegfr-2 and its targeting to inhibit tumor angiogenesis

“…Using the same technique, the folding patterns of several G4 promoters have been proposed, including those of molecules involved in angiogenic process such as VEGF (45–47), HIF1α (48,49), platelet-derived growth factor α polypeptide (50,51) and PDGF receptor β polypeptide (52,53). However, there are several novel aspects in our study, which include not only the discovery of a new G4-containg gene but also the functional relevance of this finding through intervention with small molecules, both in cell cultures and in animal model.…”

Wechselwirkung von Metallkomplexen mit G‐Quadruplex‐DNA

“…Während die Platinierung zuvor gebildeter Quadruplex‐DNA gut dokumentiert ist, sind Berichte über eine Platinierung unter Quadruplex‐Destabilisierung vergleichsweise neu. Auf der Grundlage von CD‐spektroskopischen Untersuchungen wurde die Auffaltung der telomeren Quadruplexe Tel‐1 und Tel‐2 durch Einwirkung von Cis‐ und Transplatin beobachtet 51. Dagegen wurden die DNA‐Quadruplexe von c‐myc und PDGF‐A nicht angegriffen.…”

G-quadruplex compounds and cis-platin act synergistically to inhibit cancer cell growth in vitro and in vivo

“…Since human telomeric DNA comprises tandem repeats of G-rich DNA sequences (TTAGGG) n , it has been suggested it is especially susceptible to interaction with cis-platin [26,27,35], and may explain why the action of quadruplex-binding compounds is potentiated by cisplatin. A low ratio of cis-platin to a quadruplex compound may allow G-rich telomeric quadruplex formation to preferentially occur, aided by compound binding, without the telomeric DNA residues being already bound to cis-platin.…”