Characterization of metallocene-oligonucleotide adducts with different activation techniques

Eberle, Rahel Patricia; Schürch, Stefan (6 June 2017). Characterization of metallocene-oligonucleotide adducts with different activation techniques. In: 65th Conference on Mass Spectrometry and Allied Topics. American Society for Mass Spectrometry

Introduction: Bent metallocenes [Cp2M]2+ (with Cp = cyclopentadienyl and derivatives) based on the transition metals Ti, V, Nb, and Mo are a promising class of antitumor compounds that are active against cisplatin sensitive or resistant cancer cell lines. The anticancer activity of these metallodrugs is mainly based on the interaction with nuclear DNA. Building on previous experiments on dinucleoside monophosphates, we investigated the suitability of the Pearson concept to predict the preferred binding sites in DNA and RNA oligonucleotides. Furthermore, we aim at the elucidation of the dissociation mechanisms of oligonucleotide-metallocene adducts.

Methods: Unmodified and modified oligonucleotides were incubated with solutions of metallocene dichlorides in an equimolar ratio. The adducts were investigated in the positive ion mode and subsequently fragmented by collision-induced dissociation (CID) and electron transfer dissociation (ETD) on a LTQ Orbitrap Velos instrument.

Preliminary Data: The incubation of the metallocenes with DNA hexamers resulted in the formation of adducts with titanium, molybdenum, and vanadium, whereas no adducts were obtained with niobium. ESI-MS experiments in the positive ion mode revealed the formation of adducts that either retained both cyclopentadienyl ligands (titanocene and molybdenocene) or underwent ligand exchange (vanadocene). Reaction of DNA with vanadocene resulted in the release of both cyclopentadienyl ligands and retention of a single hydroxo ligand. Collision induced dissociation of metallocene-DNA hexamer adducts revealed a significantly altered dissiciation behavior compared to their unadducted counterparts, resulting in an increased number of fragment ions. Our data on adducts with molybdenum give proof for binding to the nucleobases, yielding product ions of the type (B+Cp2Mo). On the other hand, the metal centers titanium and vanadium were found to preferably bind to the deprotonated phosphate oxygen atoms. Even for metallocenes that primarily target the deprotonated phosphate groups, a steering effect of the nucleobase sequence was detected. This was reflected by the data on titanocene adducts, which revealed interaction of the metal center with the phosphate linkers in proximity to thymine nucleobases. Oligonucleotides with modified backbone served as targets to further investigate the detailed binding patterns. Furthermore, alternative activation methods, such as electron transfer, were evaluated for the characterization of the metallodrug adducts.

Novel Aspect: Data demonstrate the unique binding patterns of metallocenes to oligonucleotides and reveal the specific fragmentation pathways of the metallodrug adducts.

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