A novel approach for analysis of oligonucleotide-cisplatin interactions by continuous elution gel electrophoresis coupled to isotope dilution inductively coupled plasma mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry

In this work we present a novel approach for in vitro studies of cisplatin interactions with 8‐mer oligonucleotides. The approach is based on the recently developed coupling of continuous elution gel electrophoresis (GE) to an inductively coupled plasma‐sector field mass spectrometer (ICP‐SFMS) with the aim of monitoring the interaction process between this cytostatic drug and the nucleotides. In contrast to existing methods, the electrophoretic separation conditions used here allow both the determination of the reaction kinetics in more detail as well as the observation of dominant intermediates. Two different nucleotides sequences have been investigated for comparison purposes, one containing two adjacent guanines (5′‐TCCGGTCC‐3′) and one with a combination of thymine and guanine (5′‐TCCTGTCC‐3′), respectively. In order to gain further structural information, MALDI‐TOF MS measurements have been performed after fraction collection. This allows for identification of the intermediates and the final products and confirms the stepwise coordination of cisplatin via monoadduct to bisadduct formation. Furthermore, the ICP‐MS results were quantitatively evaluated in order to calculate the kinetics of the entire process.