LIGHTSWITCHES · Multifunctional DNA light-switches: sensors and devices

Periodic Report Summary 1 - LIGHTSWITCHES (Multifunctional DNA light-switches: sensors and devices)

Briefly, the aims of this project were: 1. to target the synthesis of mononuclear complexes with tuneable luminescent and/or photo-redox properties 2. to synthesise 'light-switch' systems designed to display selectivity on binding with deoxyribonucleic acid (DNA) 3. to investigate strategies designed to enhance the overall binding affinity of mixed bis-intercalators. Such systems would be synthesised as tools to study DNA mediated energy transfer processes. 4. to investigate the synthesis of multifunctional DNA probes. The main project results could be summarised as follows: 1. regarding tuning photophysical properties of DNA binding complexes, by using a variety of different intercalating ligands and non-intercalating ancillary ligands the physical properties of our intercalative systems were tuned. For example, although we previously reported that dppz-complex 1 was a simple 'light-switch' complex that possessed an excited state incapable of cleaving DNA, work during this project revealed that the photoexcited state of the related dppn-based complex 2 was a highly efficient singlet oxygen sensitiser. Singlet oxygen was capable of damaging and cleaving DNA. By changing the donor or acceptor capability of the ancillary ligands in complex 1 we tuned the emission wavelength from approximately 600 nm to almost 680 nm. 2. in terms of tuning the binding selectivity of the complexes, studies on our prototypical quadruplex DNA binding agent 3 revealed that the complex bound to specific quadruplexes with specific structural features. It bound with highest affinity to quadruplexes with diagonal external loops. The binding intensity was also reflected in the emission response, with the highest luminescence enhancements observed for the structures that were bound with the highest affinity. Approaches to sequence selectivity were also developed. For example, by adding hydrogen-bonding units to the pyridyl ancillary ligand of complex 1 we were able to create systems that demonstrated binding preferences for A-rich or G-rich DNA sequences. We were even able to switch off intercalation. 3. as far as bis-intercalators were concerned, we found that we could enhance binding of our dinuclear complexes by a consideration of the employed linkers. For example, by using linkers that contained amines, such as complex 4, we were able to enhance the overall binding affinity of the systems by one to two orders of magnitude. 4. in addition, regarding multifunctional probes, our key result was probably the fact that we began to study the interaction of such systems in cellulo. In these studies we found that while complex 3 was a live/dead stain, the closely related complex 5 was a multifunctional probe for cellular imaging. Confocal microscopy (CFM) could be used to image duplex DNA-based heterochromatin, e.g. individual chromosomes could be imaged during mitosis. However, at a different emission wavelength, the same complex was a marker for higher order DNA structures within cells. Finally, since the complex incorporated heavy ruthenium nuclei, it was also a novel contrast stain for transmission electron microscope (TEM) which could be used to image nuclear DNA. Furthermore, we also recently found that the related mononuclear complex 6 was not only an imaging agent for cells through CFM and TEM, but also displayed a cytotoxicity that was comparable to cisplatin. This cyctotoxicity was even retained in cisplatin-resistant cell lines. Several publications in high impact journals and a patent application resulted from this project. A second patent application was being drafted by the time of this report. The potential impact of this work was high, including the identification of therapeutic leads for cancer treatment and the development of a new paradigm for cell imaging.

Data: CORDIS, © European Union