Periodic Reporting for period 1 - CylcoRu4PACT (Cyclometallated ruthenium complexes for photo-activated chemotherapy)
Reporting period: 2018-04-01 to 2020-03-31
The main problem of the complexes studied in this project is their low thermal stability in the dark and their insolubility in water. Follow-up research is now taking place to introduce ligands that improve the dark stability and water solubility of these complexes. With these improvements, new complexes will be at hand that will show much higher light-induced toxicity in vitro and can be further tested in animal models. Overall, the present project has opened new prospects for the design of light-activated anticancer drugs.
The potential of new compounds to be used in photodynamic therapy (PDT) was further investigated using singlet oxygen measurements. Obtained results suggest that the PDT properties of the new complexes are low, which is expected for PACT complexes.
The antiproliferative activity of the ruthenium complexes on commercially available human cancer cell lines has been tested first in the dark and then upon visible light irradiation using a colorimetric SRB assay. The cytotoxicity was tested on A431 (skin) and A549 (lung) cancer cells for the organoruthenium complexes, and on A431 (skin) for cyclometallated compounds, in both normoxic (95% air and 5% CO2) and hypoxic (1% O2 and 5% CO2) conditions. The biological experiments showed that the organoruthenium compounds have a low dark cytotoxicity, with EC50-values above 100 µM, and a low phototoxicity. This indicates that either there was not enough photo-activation of these complexes in the irradiation conditions of the biological experiment (blue light λ = 455 nm), or that the photoactivated products were not cytotoxic.
The cytotoxicity of the cyclometallated compounds was overall very high, with effective concentrations (EC50) values around 0.5 µM and photoindexes around 2 in normoxic conditions, and around 1 for hypoxic condition. The low photo index comes from the toxicity in the dark, which is already quite high, because these compounds are highly hydrophobic. Overall the cyclometallated complexes have shown more potential for PACT than the organoruthenium complexes, but their phototoxicity index was still low. Their toxicity in the dark needs to be reduced. A possible way to do this would be to attach a hydrophilic group to the ligand that undergoes light-mediated photosubstitution. This would decrease the lipophilicity and hence cellular uptake and therefore decrease the toxicity before irradiation, without jeopardizing the light toxicity, for which the hydrophilic ligand would be detached. This strategy could not be investigated due to the early termination of the contract.
During the project various trainings were followed by the researcher. In May 2018 a course on lab safety and fire extinguishing were offered by the Faculty of Science. Trainings on physical and health hazards in the work area, along with applicable exposure control measures were provided. Within the research group the researcher followed 1 day training related to using a glove box for handling air sensitive compounds or reactions. Also, training on photosubstitution quantum yield and singlet oxygen measurement by members of the Prof. Bonnet group has been provided. Training on cancer cell cytotoxicity measurements and cell irradiation, using their specific training protocols, were organised in November and December 2018, also by members of the Bonnet group.
The results of this research will be disseminated via 2 scientific publications in peer-reviewed international journals such as Angewandte Chemie and Dalton Transaction. Some of results were presented in national conference CHAINS Dutch Chemistry meeting and HRSMC annual symposium. The supervisor Bonnet will also show the results of this work in international scientific conferences planned in 2020.
By combining cyclometallation to statically hindered bidentate ligands, we re-installed photoreactivity, and obtained green-colored, ie red light-absorbing, photosubstitutionally active ruthenium(II) complexes, which is going beyond the state of the art in ruthenium photochemistry.
This project has been stopped on request of the researcher, 6 months before the end (31 March 2020). Further research in the host group focuses on introducing a ligand which improves thermal stability and water solubility of these cyclometallated complexes.