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EXCITED STATES AS PROBES TO INVESTIGATE DRUG-DNA AND DRUG-PROTEIN INTERACTIONS. PHOTOSENSITIZED PROCESSES LEADING TO DAMAGE TO BIOMOLECULES

Final Report Summary - PHOTOBIODRUG (EXCITED STATES AS PROBES TO INVESTIGATE DRUG-DNA AND DRUG-PROTEIN INTERACTIONS. PHOTOSENSITIZED PROCESSES LEADING TO DAMAGE TO BIOMOLECULES)

The objective of the project was to investigate the photoreactivity of drugs with biomolecules by means of spectroscopic techniques. These interactions are of great importance because the investigated drugs are known to absorb UV light and generate photosensitising side effects directly related to phototoxicity, photomutagenicity and photoallergy.
Model systems that aim to simulate the real drug/biomolecule interactions were first synthesized; their photoreactivity were investigated and compared to the real drug/protein complexes. Compounds containing drugs such as naproxen (NPX), flurbiprofen (FBP) and fenofibric acid (FA) covalently linked to tyrosine, histidine or tryptophan were synthesized, among others. In some cases, spacers of different length were used to separate the chromophores and evaluate the possible changes in their photoreactivity. The mechanism of photoproduct formation varied depending on the drug coupled to an amino acid; thus, for NPX a type II photooxygenation mechanism triggered by the generation of 1O2 was observed, while for FA a type I mechanism was predominant. In general, the photoreactivity was highly modified by the spacer. In all cases stereoselective dynamic fluorescence quenching was observed. In the drug/protein complexes, fluorescence experiments clearly showed that the protein microenvironment plays a significant role in the conformational relaxation of the drug. This stereo-selectivity was possibly related to the modes of drug binding to the protein, a process of pharmacological relevance. Laser flash photolysis experiments evidenced that the reaction mechanism of the drug within the protein was clearly different than in the bulk solution. The yield of photoproduct formation varied between two proteins and was also different to that of the bulk solution. The reaction mechanism in the presence of protein was again supported by the results obtained in model FA-amino acid dyads. This reinforces the value of linked systems as models for non-covalent drug/protein complexes. In addition, a series of dyads where the chromophores are separated by a rigid spacer evidenced a rapid triplet-triplet energy transfer process via through-bond mechanism followed by a through-bond triplet exciplex formation; this was the first time that this process has been observed in related systems. Finally, the photoreactivity of alternating adenine-thymine and guanine-cytosine duplexes have been evaluated. The experimental results combined with theoretical calculations evidenced the existence of stabilized high energy mixed states.
Dr. Vayá has consolidated close collaborations with the groups of Dr. Markovitsi and Dr. Improta, and he has also established new collaborations with other research groups. A number of articles have been published during this project and others that are in preparation will be submitted in the early future. He has also participated in national and international conferences as speaker. Dr. Vayá is following the natural steps to finally get a permanent position at the Host Institution. The level of independence the researcher has reached is in accordance with the possibilities that the Host Institution offers to researchers at this stage. Thus, he was the principal investigator of two additional projects, one funded by the Technical University of Valencia and other funded by the autonomic government (Consellería d’Educació).