1 Scientific RepoRts | 6:28480 | DOI: 10.1038/srep28480 www.nature.com/scientificreports From non-covalent binding to irreversible DNA lesions: nile blue and nile red as photosensitizing agents Hugo Gattuso 1,2 , Vanessa Besancenot 3,4 , stéphanie Grandemange 3,4 , Marco Marazzi 1,2 & Antonio Monari 1,2 We report a molecular modeling study, coupled with spectroscopy experiments, on the behavior of two well known organic dyes, nile blue and nile red, when interacting with B-DNA. In particular, we evidence the presence of two competitive binding modes, for both drugs. However their subsequent photophysical behavior is diferent and only nile blue is able to induce DNA photosensitization via an electron transfer mechanism. Most notably, even in the case of nile blue, its sensitization capabilities strongly depend on the environment resulting in a single active binding mode: the minor groove. Fluorescence spectroscopy confrms the presence of competitive interaction modes for both sensitizers, while the sensitization via electron transfer, is possible only in the case of nile blue. DNA photosensitization 1,2 is a fundamental phenomenon with implication to public health, medicine and phar- macology. Indeed DNA is constantly exposed to diferent, endogenous and exogenous, sources of stress that may result in DNA bases or backbone damages 3–5 . Te sources of stress include free radical or reactive oxygen species, as well as radiation and exposure to UV-visible light. DNA lesions may be recognized and efciently repaired by the activation of specifcally tailored enzymes, however if the cycle of damages and repair is unbalanced one may assist to an accumulation of lesions. Tese facts could induce cellular apoptosis or, on the other hand, produce mismatches in the replication cycles that may ultimately result in mutations and carcinogenesis 6,7 . Concerning UV-visible induced damages one should divide between direct damages, resulting from UVB radiation absorp- tion by DNA bases, or indirect damages caused by external agents 3 . Te former have been the subject of intense theoretical and experimental studies and mostly result in bases dimerizations (such as cyclobutane pyrimidine dimers or the 6-4PP photodamage) 8–16 . On the other hand the interaction between DNA and external chromo- phores may lead to DNA damages subsequently to the exposure to UVA or even visible light 2,17 . Te former process is known under the name of photosensitization and requires the establishment of long-lived DNA/drug aggregates, the absorption of light by the drug and its subsequent photophysical or photochemical evolution leading to the lesion 18 . In many cases DNA photosensitization proceeds following an intersystem crossing that promotes the population of the sensitizer triplet manifold 19 . Tis can subsequently evolve via triplet-triplet energy transfer, usually toward thymine nucleobases 17,20 , or via the activation of singlet oxygen (type II photosensitiza- tion), the latter being known to selectively react with guanine 21,22 . Other photochemical channels leading both to bases and backbone lesions or strand breaks have been reported, such as hydrogen abstraction 23–25 . Finally one should recognize the possibility of photo-induced electron transfer from the DNA bases to the photosensitizer, happening both from triplet or singlet states, in the so-called type I photosensitization 4,26 . DNA photosensitization can be seen as an environmental threat since many common pollutants such as benzophenone and acetophenone are known to produce DNA photosensitization following complex and varied mechanisms 17,27,28 . As such, those molecules greatly enhance the dangerous spectral width capable of inducing potentially harmful DNA lesions. 1 Université de Lorraine – nancy, theory-Modeling-Simulation SRSMc, Vandoeuvre-lès-nancy, france. 2 cnRS, theory-Modeling-Simulation SRSMc, Vandoeuvre-lès-nancy, france. 3 Université de Lorraine – nancy Santé, Biologie, Signal - cRAn, Vandoeuvre-lès-nancy, france. 4 cnRS, Santé, Biologie, Signal, cRAn, Vandoeuvre-lès- nancy, france. correspondence and requests for materials should be addressed to M.M. (email: marco.marazzi@ univ-lorraine.fr) or A.M. (email: antonio.monari@univ-lorraine.fr) Received: 30 March 2016 Accepted: 03 June 2016 Published: 22 June 2016 opeN