Phototoxicity of Tridentate Ru(II) Polypyridyl Complex with Expanded Bite Angles toward Mammalian Cells and Multicellular Tumor Spheroids

Parentand peptide conjugates of bistridentate Ru(II) complexeswith expanded bite angles show high phototoxicity toward cancerousand non-cancerous cell monolayers, and pancreatic multicellular tumorspheroids upon irradiation at 470 nm. Tridentate ligand-coordinated ruthenium (II) polypyridylcomplexeswith large N-Ru-N bite angles have been shown to promoteligand field splitting and reduce singlet-triplet state mixingleading to dramatically extended emission quantum yields and lifetimesunder ambient conditions. These effects are anticipated to enhancetheir photoinduced singlet oxygen production, promoting prospectsfor such complexes as type II phototherapeutics. In this contribution,we examined this putative effect for [Ru(bqp)(bqpCOOEt)](2+), Ru-bqp-ester, a heteroleptic complex containing bqp = [2,6-bi(quinolin-8-yl)pyridine],a well-established large bite angle tridentate ligand, as well asits peptide conjugates [Ru(bqp)(bqpCONH-ahx-FrFKFrFK(Ac)-CONH2)](5+) (Ru-bqp-MPP) and [Ru(bqp) (bqp)(CONH-ahx-RRRRRRRR-CONH2)](10+) (Ru-bqp-R8) that were prepared in an effortto promote live cell/tissue permeability and targeting of the parent.Membrane permeability of both parent and peptide conjugates were comparedacross 2D cell monolayers; A549, Chinese hamster ovary, human pancreaticcancer (HPAC), and 3D HPAC multicellular tumor spheroids (MCTS) usingconfocal microscopy. Both the parent complex and peptide conjugatesshowed exceptional permeability with rapid uptake in both 2D and 3Dcell models but with little distinction in permeability or distributionin cells between the parent or peptide conjugates. Unexpectedly, theuptake was temperature independent and so attributed to passive permeation.Both dark and photo-toxicity of the Ru(II) complexes were assessedacross cell types, and the parent showed notably low dark toxicity.In contrast, the parent and conjugates were found to be highly phototoxic,with impressive phototoxic indices (PIs) toward HPAC cell monolayersin particular, with PI values ranging from & SIM;580 to 760. Overall,our data indicate that the Ru(II) parent complex and its peptide conjugatesshow promise at both cell monolayers and 3D MCTS as photosensitizersfor photodynamic therapy.

Automated summary

Parent and peptide conjugates of bistridentate Ru(II) complexes with expanded bite angles demonstrate high phototoxicity and exceptional permeability in both 2D and 3D cell models for potential use in photodynamic therapy. The Ru(II) complexes show enhanced emission quantum yields and lifetimes, promoting their photoinduced singlet oxygen production. The complexes exhibit significant phototoxicity toward pancreatic cancer cell monolayers, with phototoxic indices ranging from 580 to 760.