Photochemical property of two Ru(II) compounds based on 5-(2-pyrazinyl)tetrazole for cancer phototherapy by changing auxiliary ligand.

Ru(II) compounds are potential candidates for photodynamic therapy (PDT) and auxiliary ligands may have an impact on the property of the resulting coordination compounds. In the present study, two Ru(II) compounds based on 5-(2-pyrazinyl)tetrazole (Hpztz) and two classic auxiliary ligands, 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) have been prepared and characterized, namely [Ru(pztz)(bipy)2][PF6] (1) and [Ru(pztz)(phen)2][PF6] (2). The nanoparticles (NPs) of the two compounds have been prepared by self-assembly in aqueous solution. In vitro MTT assay on HeLa cells show that [Ru(pztz)(phen)2][PF6] with a lower IC50 (half-maximal inhibitory concentration) of only 7.4 µg/mL is superior to that of [Ru(pztz)(bipy)2][PF6] (17.8 µg/mL) under irradiation. Meanwhile, negligible dark toxicity have been also observed for the two compounds. In addition, in vivo fluorescence imaging suggests that [Ru(pztz)(phen)2][PF6] NPs are able to target to the tumor by enhanced permeability and retention effect (EPR). Furthermore, in vivo phototherapy on nude mice demonstrate that such NPs can effectively inhibit the growth of the tumor. After treatment for 10 cycles, an obvious decrease in the tumor volume can be observed while the normal tissues, including heart, liver, spleen, lung and kidney, suffer from no damage, indicating the high phototoxicity, low dark toxicity and excellent biocompatibility of [Ru(pztz)(phen)2][PF6] NPs.