Abstract
Photoactivatable chemotherapy (PACT) based on ruthenium drugs is gaining importance as a new way for targeting cancer. This therapy relies on the administration of a sterically strained ruthenium drug that can be activated by light to induce cell death. The present study evaluates the effect of a photoactivatable Ru (II) complex 1 [Ru(bipy)2(dpphen)]Cl2 (where bipy = 2,2’-bipyridine and dpphen = 2,9-diphenyl-1,10-phenanthroline) as a potential photoactivatable chemotherapeutic drug along with its plausible mechanism of action. A non-photoactivatable Ru (II) complex 2 [Ru(bipy)2(phen)]Cl2 (where phen = 1,10-phenanthroline) was used as a control. Synthesis, purification and identification were reported using 1H and 13C NMR, HR-MS/MS, ESI-MS/MS, MALDI-TOF/MS and elemental analysis. The UV-vis spectroscopy for both complexes, showed a λmax=450 nm corresponding to the maximum absorption in the visible spectrum. Consequently, all experiments requiring photoactivation were carried out using blue LED light operating at 460 nm. The photochemistry studies using NMR and ESI-MS/MS showed that, upon light activation, complex 1 undergoes a complete dissociation into an aquated photoproduct [Ru(bipy)(dpphen)(H2O)]2+ and bipy, while complex 2 exhibits no dissociation and, therefore, confirmed to be non-photoactivatable. Uptake of complex 1 by LC-MS/MS started within the first hour, reached the maximum after 12 hours incubation and was shown to be mediated by endocytosis. It was also shown that complex 1 possesses a promising anticancer activity, only upon photoactivation, against A549, B16-F10, Caco-2, MDA-MB-231 and HT29 cancer cell lines when compared to cisplatin. The phototoxicity index (PI) values ranged between 39.2 and >100 after 72 reflecting the potency of complex 1 photoactivation. Importantly, complex 1 showed a relatively low toxicity against non-cancer cells when compared to cancer cells. The dissociating ligand bipy showed no significant cytotoxicity proposing that the aquated photoproduct is the one behind the cytotoxicity. Complex 1 also showed a significant increase in cell rounding and detachment, loss of membrane integrity, ROS accumulation and DNA damage. Flow cytometry and a fluorescent assay showed an induction of cell apoptosis. Western blot analysis revealed the involvement of both intrinsic and extrinsic pathways, in addition to an inhibition of the MAPK and PI3K pathways. In conclusion, the present study revealed that complex 1 is a potent multi-mechanistic photoactivatable chemotherapeutic drug that may serve as a potential lead molecule for cancer chemotherapy.