NanoAgents · Surface modified luminescent and magnetic gold nanoparticles as cellular targeting agents

Surface modified luminescent and magnetic gold nanoparticles as cellular targeting agents

Cisplatin and derivatives are widely used as anti-cancer drugs for chemotherapy. However, these drugs present some limitations and side effects. Because of that, currently there is a great interest for alternative drugs that can overcome these limitations. Among all the alternatives that are currently being tested Ruthenium has emerged as a promising next generation anti-cancer drugs.[1] Ruthenium also possess interesting photophysical and photochemical properties[2] which can be tuned via ligands and extend the range of applications as for example molecular recognition, photodynamic therapy, cellular signaling, drug delivery or biosensing among others.[3] One of the aspects of this project is the synthesis of Ruthenium polypyridyl complexes that contain extended aromatic rings. These extended rings are able to interact with DNA through intercalation[5] and because of their structure and positive charge they are expected to go into the nucleus and interact with nuclear DNA which is the primary target for cancer treatment. Some of this type of complexes we have synthesised are shown in Figure 1. We studied how these complexes interact with DNA and the results obtained so far indicate that these interactions are very strong. The strength of this interaction is quantified by the binding constants (Kb) which we have calculated using spectroscopic techniques. The values we found for them are bigger than 10^6M−1 which indicate that they from strong and stable aducts with DNA. For the case of complex 5 the Kb is remarkably high: 3x10^7M−1. We also observed that the nature of the other chelate ligands has a great influence in the overall behaviour. For complexes containing phenanthroline we observe that upon interaction with DNA the fluorescence in enhanced (see Figure 2) while for those containing tetraazaphenanthrene the fluorescence is quenched which means that these complexes act as a light switch. The fact that a compound interacts strongly with DNA is not enough to guarantee that these compounds will be active in the cells. We then carried out in vitro assays with HeLa cells (cervix cancer) and we have seen that these complexes have the ability to cross the cell membrane and go into the intracellular medium. Whether they can go into the nucleus or not is still unclear due to, in some cases, strong quenching of the luminiscence in the intracellular medium. However, it has been proved that some of the complexes can induce apoptosis in HeLa cells which is a key feature for cancer treatment (see Figure 3). Even more, this ability to induce apoptosis can be controlled with light irradiation which would provide an easy way to control the behaviour of these systems in the body. Unfortunately, we have no positive evidence that these complexes go into the nucleus. We also studied the toxicity effect of these complexes in HeLa cells both under visible light irradiation or in darkness to see whether they can be used for photodynamic therapy. In Figure 4 the cytotoxicity results are shown (blue for the results in darkness and red for the results under light irradiation). The difference between the red and the blue lines is called therapeutic window; the broader, the better. We can see that the complexes that contain the tetraazaphenanthroline ligand exhibit better therapeutic window and the ones containing phenanthroline don’t. This feature allows to switch the toxicity of the compounds on and off being this behaviour controlled by light. This particular feature could be of great interest for pharmaceutical industry. Gold nanoparticles (AuNPs) are a very interesting further step that can be done in order to keep the properties of Ruthenium complexes and at the same time improve some of their features like cellular uptake and luminescence. We previously demonstrated that these systems are attractive for cellular imaging and interact strongly with DNA.[5] We have explored the possibility of using these systems as gene delivery agents.We used plasmid DNA and measure the expression of green fluorescent protein on HeLa cells to see if transfection occurs in the presence of gold nanoparticles. Unfortunately the results were negative and no transfection was observed. The knowledge gained in this project We have also made major modifications on a trisphenanthroline ruthenium(II) core to study the possibility of making luminescent metallosurfactants. References: [1] Serenella Medici, Massimiliano Peana,Valeria Marina Nurchi, Joanna I. Lachowicz, Guido Crisponi, Maria Antonietta Zoroddu, Coord. Chem. Rev. 2015, 284, 329–350 [2] (a) N. L. Kilah and E. Meggers, Aust. J. Chem. 2012, 65, 1325–1332. (b) C. Mari, V. Pierroz, S. Ferrari and G. Gasser, Chem. Sci. 2015, Advance Article, doi: 10.1039/C4SC03759F [3](a) J. Massue, S. J. Quinn, and T. Gunnlaugsson, J. Am. Chem. Soc. 2008, 130, 6900–6901. (b) F. Marano, S. Hussain, F. Rodrigues-Lima, A. Baeza-Squiban, S. Boland, Arch. Toxicol. 2011, 85, 733–741. [4] J. P. Hall, D. Cook, S. Ruiz Morte, P. McIntyre, K. Buchner, H. Beer, D. J. Cardin, J. A. Brazier, G. Winter, J. M. Kelly and C. J. Cardin, J. Am. Chem. Soc. 2013, 135, 12652−12659. [5] Robert B. P. Elmes, Kim N. Orange, Suzanne M. Cloonan, D. Clive Williams and Thorfinnur Gunnlaugsson, J. Am. Chem. Soc. 2011, 133, 15862–15865

Data: CORDIS, © European Union