Preliminary anti-cancer photodynamic therapeutic in vitro studies with mixed-metal binuclear ruthenium(ii)–vanadium(iv) complexes

Abstract

We report the synthesis and characterisation of mixed-metal binuclear ruthenium(II)–vanadium(IV) complexes, which were used as potential photodynamic therapeutic agents for melanoma cell growth inhibition. The novel complexes, [Ru(pbt)₂(phen₂DTT)](PF₆)₂·1.5H₂O 1 (where phen₂DTT = 1,4-bis(1,10-phenanthrolin-5-ylsulfanyl)butane-2,3-diol and pbt = 2-(2′-pyridyl)benzothiazole) and [Ru(pbt)₂(tpphz)](PF₆)₂·3H₂O 2 (where tpphz = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine) were synthesised and characterised. Compound 1 was reacted with [VO(sal-L-tryp)(H₂O)] (where sal-L-tryp = N-salicylidene-L-tryptophanate) to produce [Ru(pbt)₂(phen₂DTT)VO(sal-L-tryp)](PF₆)₂·5H₂O 4; while [VO(sal-L-tryp)(H₂O)] was reacted with compound 2 to produce [Ru(pbt)₂(tpphz)VO(sal-L-tryp)](PF₆)₂·6H₂O 3. All complexes were characterised by elemental analysis, HRMS, ESI MS, UV-visible absorption, ESR spectroscopy, and cyclic voltammetry, where appropriate. In vitro cell toxicity studies (with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay) via dark and light reaction conditions were carried out with sodium diaqua-4,4′,4′′,4′′′ tetrasulfophthalocyaninecobaltate(II) (Na₄[Co(tspc)(H₂O)₂]), [VO(sal-L-tryp)(phen)]·H₂O, and the chloride salts of complexes 3 and 4. Such studies involved A431, human epidermoid carcinoma cells; human amelanotic malignant melanoma cells; and HFF, non-cancerous human skin fibroblast cells. Both chloride salts of complexes 3 and 4 were found to be more toxic to melanoma cells than to non-cancerous fibroblast cells, and preferentially led to apoptosis of the melanoma cells over non-cancerous skin cells. The anti-cancer property of the chloride salts of complexes 3 and 4 was further enhanced when treated cells were exposed to light, while no such effect was observed on non-cancerous skin fibroblast cells. ESR and ⁵¹V NMR spectroscopic studies were also used to assess the stability of the chloride salts of complexes 3 and 4 in aqueous media at pH 7.19. This research illustrates the potential for using mixed-metal binuclear ruthenium(II)–vanadium(IV) complexes to fight skin cancer.