Binding of DNA Purine Sites to Dirhodium Compounds Probed by Mass Spectrometry

Abstract

The adducts formed between the antitumor active compounds [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2), Rh(2)(O(2)CCH(3))(4), and Rh(2)(O(2)CCF(3))(4) with DNA oligonucleotides have been assessed by matrix-assisted laser desorption ionization (MALDI) and nanoelectrospray (nanoESI) coupled to time-of-flight mass spectrometry (TOF MS). A series of MALDI studies performed on dipurine (AA, AG, GA, and GG)-containing single-stranded oligonucleotides of different lengths (tetra- to dodecamers) led to the establishment of the relative reactivity cis-[Pt(NH(3))(2)(OH(2))(2)](2+) (activated cisplatin) approximately Rh(2)(O(2)CCF(3))(4) > cis-[Pt(NH(3))(2)Cl(2)] (cisplatin) >> [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2) > Rh(2)(O(2)CCH(3))(4) approximately Pt(C(6)H(6)O(4))(NH(3))(2) (carboplatin). The relative reactivity of the complexes is associated with the lability of the leaving groups. The general trend is that an increase in the length of the oligonucleotide leads to enhanced reactivity for Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2) and Rh(2)(O(2)CCH(3))(4) (except for the case of [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+), which reacts faster with the GG octamers than with the dodecamers), whereas the reactivity of Rh(2)(O(2)CCF(3))(4) is independent of the oligonucleotide length. When monitored by ESI, the dodecamers containing GG react faster than the respectiveAA oligonucleotides in reactions with Rh(2)(O(2)CCF(3))(4) and Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2), whereas AA oligonucleotides react faster with Rh(2)(O(2)CCH(3))(4). The mixed (AG, GA) purine sequences exhibit comparable rates of reactivity with the homopurine (AA, GG) dodecamers in reactions with Rh(2)(O(2)CCH(3))(4). The observation of initial dirhodium-DNA adducts with weak axial (ax) interactions, followed by rearrangement to more stable equatorial (eq) adducts, was achieved by electrospray ionization; the Rh-Rh bond as well as coordinated acetate or acetonitrile ligands remain intact in these dirhodium-DNA adducts. MALDI in-source decay (ISD), collision-induced dissociation (CID) MS-MS, and enzymatic digestion studies followed by MALDI and ESI MS reveal that, in the dirhodium compounds studied, the purine sites of the DNA oligonucleotides interact with the dirhodium core. Ultimately, both MALDI and ESI MS proved to be complementary, valuable tools for probing the identity and stability of dinuclear metal-DNA adducts.

MALDI In-Source Decay, from Sequencing to Imaging

“…Alternatively, a pathway of electronic energy transfer was also proposed to occur in positive ion mode with 2-aminobenzoic acid and leads to the formation of supplementary ions (d-, b-, and y-ions) [77]. Concerning applications of ISD in the nucleic acids field, ISD was successfully applied by Wang et al to sequence covalently modified (phosphorothioate instead of phosphodiester bonds) oligonucleotides [78] but failed to allow locating covalent rhodium adducts on DNA [79].…”

Microwave-Assisted Synthesis and Characterization of [Rh2(OAc)4(L)2] Paddlewheel Complexes: A Joint Experimental and Computational Study

“…Finally, the NH 2 Ar ligand adopted a transoid geometry arrangement around the Rh-Rh core. [76][77][78][79][80]. The ESI-MS(+) spectrum of compound 1 shows the expected signal at / 713.0798, which was attributed to the protonated molecule; the same spectrum contains a fragment ion at / 577.9757, formed by the loss of one aniline group suggesting a formation of [Rh 2 (OAc) 4 (L)] + molecular ion.…”

Interactions of Metal—Metal‐Bonded Antitumor Active Complexes with DNA Fragments and DNA

“…13,14 In an attempt to address the issue of versatility and stability of dirhodium-DNA adducts, a comprehensive mass spectrometry study was undertaken. Dirhodium reactions with single-stranded oligonucleotides containing dipurine sites point to the following relative order of reactivity, which correlates with the lability of the leaving groups: 4 .…”

“…54 The study involved detecting the 14 10 ] 4+ 55 are an excellent indication that the dirhodium core remains intact, even in the absence of carboxylate bridging groups.…”

“…This observation supports the conclusion that purine rather than pyrimidine bases preferentially interact with the dirhodium core. 13,14 Detailed NMR spectroscopic studies of highperformance liquid chromatography (HPLC)-purified adducts are currently underway to determine the conformational changes and perturbations induced to the DNA structure upon metal binding.…”