Tandem mass spectrometry of platinated quadruplex DNA

Abstract

Quadruplexes are higher-order structures formed by G-rich DNA strands that are involved in various processes of cell cycle regulation, such as control of telomere length and participation in gene regulation. Because of these central biological functions, quadruplex DNA represents a promising target for cancer therapy, e.g. by applying organometallic drugs, such as cisplatin. High-resolution electrospray tandem mass spectrometry is evaluated as a technique for exploring structural features of unplatinated and platinated quadruplexes. Results of experiments on tetramolecular, bimolecular and monomolecular quadruplexes provide information about the extent of platination and the binding sites of the drug. The dissociation behavior of the different types of quadruplexes is compared. Tetramolecular quadruplexes were found to weave out a strand end in order to provide a platination site, and their fragmentation is characterized by the release of an unplatinated strand and the formation of a platinated triplex. Partial opening of the structure in combination with the loss of small fragments leads to truncated quadruplex ions. For the bimolecular quadruplexes studied, strand separation is the predominant dissociation pathway. Depending on the loop sequence, cross-linking of the loops by cisplatin is demonstrated. Distinct differences in the product ion spectra of unannealed and annealed monomolecular sequences provide proof of quadruplex formation and show that platination preferentially occurs at the terminal regions.

Elucidation of Nucleic Acid–Drug Interactions by Tandem Mass Spectrometry

“…Electrospray mass spectrometry was demonstrated by several research groups to be a suitable tool for exploring the in vitro formation of tetra-, bi-, and monomolecular quadruplexes [25][26][27][28] and even mechanistic data were provided about the gas-phase dissociation of these intriguing higher-order structures. [15,26,29] In a recent study, we reported on the investigation of the dissociation behavior of quadruplex DNA and cisplatin adducts thereof by high-resolution electrospray tandem mass spectrometry. [29] The (unplatinated) tetramolecular assembly [d(TG 6 T) 4 + 5 NH 4 + ] (see inset in Fig.…”

“…[15,26,29] In a recent study, we reported on the investigation of the dissociation behavior of quadruplex DNA and cisplatin adducts thereof by high-resolution electrospray tandem mass spectrometry. [29] The (unplatinated) tetramolecular assembly [d(TG 6 T) 4 + 5 NH 4 + ] (see inset in Fig. 4) served as a first model compound laying the basis for the detailed characterization of the interaction of transition metal-based anti-cancer drugs with quadruplex DNA.…”

Mass spectrometry as a powerful tool to study therapeutic metallodrugs speciation mechanisms: Current frontiers and perspectives

“…[276] Tandem mass spectrometry using CID fragmentation experiments were reported by Schürch et al to explore structural modification of mono-, bi-and tetra-molecular quadruplexes exposed to cisplatin. [277] By comparison with CD experiments, it was concluded that peaks of un-annealed single strands could not be attributed to decomposition of the structures upon ionization but rather to incomplete quadruplex formation prior to the measurements. For each of the three types of quadruplexes, exhibiting different structural features, the platination stoichiometry and rate of binding were found to be very different.…”

“…Identification of the platination sites on the monomolecular structure was possible, and the terminal G-repeats sequences were determined to be the favourable metallation sites. [277] Interestingly …”

Differentiation and Distributions of DNA/Cisplatin Crosslinks by Liquid Chromatography-Electrospray Ionization-Infrared Multiphoton Dissociation Mass Spectrometry

“…demonstrated that the enhanced cleavage of the 3’-C-O bond next to a GG site in oligodeoxyribonucleotides was catalyzed by the adjacent cisplatin adduction site, as revealed by the formation of a highly characteristic w ion [42]. This same group also elucidated the fragmentation pathways of platinated quadruplex DNA [43] and RNA [44]. More recently, our group reported a comparison of MS/MS methods, including CID, IRMPD (10.6 μm), ETD, NETD and UVPD (193 nm) as well as hybrid MS/MS processes [45], termed ETcaD, ET-IRMPD and ET-UVPD, for characterization of DNA/cisplatin adducts [46].…”