Selective binding of an organoruthenium complex to G‐rich human telomeric sequence by tandem mass spectrometry

Abstract

Rationale Human telomeric DNA is reported to be a potential target for anticancer organometallic ruthenium(II) complexes, however, the interaction sites were not clearly discriminated and identified. Methods In the current study, tandem mass spectrometry (MS/MS) using collision‐induced dissociation (CID) was firstly introduced to identify the interaction sites of an organometallic ruthenium(II) complex [(η6‐biphenyl)Ru(en)Cl][PF6] (1; en = ethylenediamine) with 5′‐T1T2A3G4G5G6‐3′ (I), the repeating unit of human telomeric DNA, in both positive‐ and negative‐ion mode at a low reaction molar ratio (1/I = 0.2) which was applied to preserve the site selectivity. Results Mass spectrometric results showed that mono‐ruthenated I was the main product under the conditions. In positive‐ion mode, MS/MS results indicated that ruthenium complex 1 binds to T2 or G6 in strand I. However, in negative‐ion mode, no efficient information was obtained for exact identification of ruthenation sites which may be attributed to losses of fragment ions due to charge neutralization by the coordination of the positively charged ruthenium complex to the short MS/MS fragments. Conclusions This is the first report of using top‐down MS to characterize the interactions of organometallic ruthenium(II) complexes and human telomeric DNA. Thymine can be thermodynamically competitive with guanine for binding to ruthenium complexes even at low reaction molar ratio, which inspired us to explore in greater depth the significance of thymine binding.

Tandem Mass Spectrometry Reveals Preferential Ruthenation of Thymines in Human Telomeric G-Quadruplex DNA by an Organometallic Ruthenium Anticancer Complex

“…For the bound Ru moiety, only the chloride ligand and no en or biphenyl was lost from the ruthenium complex in the primary mass spectrum. This is similar to the reaction between complex 1 and the 6-mer human telomeric sequence TTAGGG by ESI-MS . Interestingly, the free G4- I containing two NH 4 + ions ([G4- I + 2NH 4 + ] 5– and [G4- I + 2NH 4 + ] 4– ; Figure S2) were also clearly observed, which further verified the successful folding of strand I into the G-quadruplex structure in the presence of NH 4 + ions and its high stability under the current ESI-MS conditions.…”

“…During top-down MS analysis, the metalated products, for example, ruthenated DNA identified by the primary mass spectrometry analysis, can be exclusively selected and directly introduced into a dissociation cell for fragmentation followed by a secondary mass spectrometry detection. The binding site information can be obtained by the metalated or unmetalated sequential fragments generated from either the 3′- or 5′-terminal. , Recently, we demonstrated by tandem mass spectrometry analysis that the ruthenium arene complex [(η 6 -biphenyl)­Ru­(en)­(Cl)]­PF 6 ( 1 ) binds at T 2 or G 6 of a 6-mer human telomeric DNA model sequence, 5′-T 1 T 2 A 3 G 4 G 5 G 6 -3′ . This again confirmed the thermodynamic competition of thymine with guanine in a linear oligonucleotide for ruthenation.…”

Investigation of the binding site of ruthenium complexes to short single‐stranded oligodeoxynucleotides using electrospray ionization tandem mass spectrometry

“…The fragmentation behavior in negative ion mode may also be attributed to the formation of exclusive stable ruthenated adducts together with the attachment of two or one positively charged triethyl ammonium ions. As previously reported, MS/MS spectra in negative ion mode do not provide sufficient informative fragments required for accurate localization of the interaction site 36,46–53 . Therefore, MS/MS using the positive ion mode is more suited for identifying the interaction sites between positively charged metal complexes and negatively charged short single‐stranded ODNs.…”

“…Generally the N7 nitrogen of guanine (G) and the N3 of thymine (T) are the most affinitive binding sites for ruthenium complexes in nucleosides, nucleotides, single‐ and double‐stranded DNA 10,28,29,32–35 . Recently, it was demonstrated by tandem mass spectrometric analysis that the ruthenium arene complex [(η 6 ‐biphenyl)Ru(en)(Cl)][PF 6 ] binds at T 2 or G 6 of a 6‐mer human telomeric DNA model sequence, 5′‐T 1 T 2 A 3 G 4 G 5 G 6 ‐3′ 36 …”

Investigating the exceptional adducts of alkoxides with Ru(II)–arene cations in alkyl alcohol solution using electrospray ionization mass spectrometry

“…Ru(II)–arene complexes are a class of potential metal anticancer drug molecules with high antitumor activity in vitro and low cytotoxicity 1–4 . Meanwhile, Ru(II)–arene complexes are widely used as catalysts due to their ease of preparation, 5 unique reactivity and selectivity, such as in arylation reactions, 6 catalytic reduction of esters, 7 catalytic oxidation of alcohols 8 and carbon–hydrogen bond functionalization 9 .…”