Water-soluble gadolinium porphyrin as a multifunctional theranostic agent: Phosphorescence-based oxygen sensing and photosensitivity

Photodynamic therapy (PDT) is the most advanced treatment method for cancer. Challenges including quantification of the photosensitizer (PS) and oxygen necessitate the development of multifunctional PS that can function as oxygen indicators and magnetic resonance imaging (MRI) contrast agents (CA). A water-soluble gadolinium-containing porphyrin, gadolinium-containing sinoporphyrin sodium (Gd-DVDMS), was developed as a multifunctional theranostic agent: a PS for PDT, an MRI CA, and a phosphorescence-based oxygen indicator. The MRI enhancing effect of the PS can be used to measure its concentration. The luminescence and photosensitivity of Gd-DVDMS were studied and compared to those of Gd-hematoporphyrin monomethyl ether (Gd-HMME). The molar absorption coefficient of Gd-DVDMS was greater than that of Gd-HMME because it has two porphyrin rings. The emission of Gd-DVDMS at 712 nm was confirmed to be phosphorescence with a lifetime of 49 μs and quantum yield of 0.015. The phosphorescence was effectively quenched by oxygen: the phosphorescence intensity in air-saturated methanol was 33% of that in deoxygenated methanol. The phosphorescence quenching highlights the potential utility of Gd-DVDMS in the quantification of oxygen in PDT. The singlet oxygen quantum yield of Gd-DVDMS was 0.46, which was slightly higher than that of Gd-HMME. Overall, Gd-DVDMS is a promising multifunctional PS with many advantages over existing PS. In particular, DVDMS with double porphyrin rings can coordinate to two different metal ions in order to design agents with more functions.