Effects of drugs covalent binding on DNA: joint use of microRaman spectroscopy and HRTEM imaging

The detailed understanding of drugs interaction with cells biomolecules is fundamental to evaluate the most efficient drug dosage. In this work we provide details on the structural modification occurring to DNA upon cross-links formation with metal ions after the administration of chemotherapeutic compounds. We used nanometric filaments of suspended DNA on superhydrophobic-based devices (SHS) for an accurate analysis by microRaman spectroscopy and high-resolution transmission electron microscopy (HRTEM) to study the interaction of cisplatin with the double helix. Our data show a conformational transition of the nucleic acids upon drugs administration, relying on Raman shift and intensity variations to features such as backbone vibration (792, 834 cm^-1), guanine ring breathing (∼670 cm^-1), stretching modes of the adenine ring (∼1300 cm^-1, 1338 cm^-1), unpaired AT bases (1178 cm^-1 and 1204 cm^-1) and deoxyribosyl CH stretching vibrations (range 2800-3000 cm^-1). The conformational transitions towards a loosen DNA form and the integration of the drug into the double helix structures has been further confirmed by HRTEM, describing local helix denaturation. We demonstrated that the proposed methodology can be used to distinguish treated from pristine DNA by their Raman spectra, confirmed by the structural insights provided by direct imaging.