Water-Soluble Mn(III)-Porphyrins with High Relaxivity\nand Photosensitization

Three water-soluble Mn(III)-porphyrin\ncomplexes with cationic pyridyl\nside groups bearing COOH- or OH-terminated carbon chains in the meta\nor para positions have been synthesized as probes for both magnetic\nresonance imaging (MRI) and photodynamic therapy (PDT). The complexes <b>Mn-1</b>, <b>Mn-2</b>, and <b>Mn-3</b> are highly\nwater-soluble, and their relaxivities range between 10 and 15 mM<sup>–1</sup> s<sup>–1</sup>, at 20–80 MHz and 298\nK, 2–3 times higher than that of commercial Gd(III)-based agents.\nThe complexes containing carboxylate (<b>Mn-2</b>) or alcoholic\n(<b>Mn-3</b>) side chains in the para position are endowed with\nhigher relaxivities and have also shown efficient photoinduced DNA\ncleavage and singlet oxygen (<sup>1</sup>O<sub>2</sub>) generation. <b>Mn-3</b> with stronger photoinduced DNA cleavage has also revealed\nstabilizing and binding activities for G4 DNA, at a similar level\nas the known G4 binder <b>Mn-TMPyP4</b>. Nevertheless, the G4-binding\nactivity of <b>Mn-3</b> was nonspecific. Preliminary tests evidenced\nphotocytotoxicity of <b>Mn-3</b> on HeLa cells without a significant\neffect in the absence of light. Altogether, these results underline\nthe potential of such water-soluble Mn(III)-porphyrins for the development\nof multimodal approaches combining MRI and PDT.