Resumen de hAGT inhibitors as chemotherapy enhancers
María Tintoré Gazulla
The O6-alkylguanine DNA alkyltransferase (hAGT or MGMT) is a DNA repair protein in charge of removing alkyl adducts from the O6 position of guanines, blocking their cytotoxic effects and playing an important role as a resistance mechanism to chemotherapy in cancer patients. For these reasons, it is considered relevant as a prognosis marker of cancer and represents a potential therapeutic target. Intense research efforts have been devoted to the identification of small molecules capable of inhibiting hAGT activity and enhancing the cytotoxic effect of the alkylating agents in tumour cells. In this doctoral thesis, we have explored 10 compounds with potential inhibitory activity against hAGT. The analysis by mass spectrometry (ESI-MS) confirmed the complex formation of hAGT with 5 of them (compounds 5, 6, 7, 8 and 9). MTT cytotoxicity studies in cell culture showed that 2 compounds (5 and 8) were non-toxic and showed enhancement of carmustine toxicity. This compounds were further analysed by colony formation assays, which confirmed that compound 8 was non-toxic at long-term experiments and exhibited a stimulation effect of carmustine. Compound 8 seem to be the best candidates for hAGT inhibition, as it forms a complex with hAGT and it enhances BCNU without being toxic in MTT and colony formation assays. Due to the lack of a consistent in vitro assay for the activity of hAGT, we have devoted part of this doctoral thesis to the search of bio and nanotechnologies to detect hAGT activity which enable the evaluation of potential inhibitors of the protein. Chapter 2 describes the development of a new fluorescence method using the conformational change of a DNA Gquadruplex, the thrombin binding aptamer (TBA), as a molecular beacon for the detection of hAGT activity and the development of new inhibitor compounds. The conformational change of TBA is further explored to develop a detection platform on DNA origami which allows de quantification of the repair activity of hAGT on a single molecules basis, through the direct visualization by AFM of the interaction of TBA with its target protein ¿-thrombin when its G-quadruplex structure is restored. In addition, this work reports the synthesis of guanine derivatives modified at position 6 and properly functionalized for their incorporation into double stranded oligonucleotides that are used for the development of another novel fluorescence methodology to evaluate hAGT activity and to assess potential inhibitors as enhancers of chemotherapy. Finally, during a short stay in the University of Milan, we have developed a new sensor to detect a methylation in TBA using three types of nanoparticles: AuNPs, SPIONs and AuSPIONs. AuSPIONs combine the features of the gold coating and the magnetic core, and exhibit similar performance as AuNPs and SPIONs in UV, DLS and MRI assays to detect thrombin and a single methylation in TBA. Ths results provide the basis for the development of a new straightforward method to study hAGT activity and to evaluate potential inhibitors.
