Fluorescence imaging and phototoxicity effects of new formulation of chlorin e6–polyvinylpyrrolidone

Evaluations of the efficiency of a new formulation of chlorin consisting of a complex of trisodium salt chlorin e6 (Ce6) and polyvinylpyrrolidone (PVP) in photodynamic therapy (PDT) and fluorescence diagnosis was performed on poorly differentiated human bladder carcinoma murine model with the following specific aims: (i) to qualitatively evaluate the fluorescence accumulation in human bladder tumor, (ii) to determine fluorescence distribution of Ce6–PVP using the tissue extraction technique and fluorescence imaging technique, (iii) to compare the fluorescence distribution of Ce6, Ce6–PVP and Photofrin in skin of nude mice, and (iv) to investigate phototoxicity caused by different parameters (drug-light interval, drug dose, irradiation fluence rate and total light fluence) in PDT. The fluorescence of the Ce6–PVP formulation was determined either by fluorescence imaging measurements or by chemical extraction from the tissues displaying similar trends of distribution. Our results demonstrated that the Ce6–PVP formulation possesses less in vivo phototoxic effect compared to Ce6 alone. The phototoxicity revealed a strong dependence on the drug and light dosimetry as well as on the drug-light interval. In PDT, the Ce6–PVP compound was most toxic at the 1 h drug-light interval at 200 J/cm2, while Ce6 alone was most toxic at a light dose of more that 50 J/cm2 at the 1 and 3 h drug-light interval. We also confirmed that Ce6–PVP has a faster clearance compared to Ce6 alone or Photofrin. This eliminates the need for long-term photosensitivity precautions. In conclusion, the Ce6–PVP formulation seems to be a promising photosensitizer for fluorescence imaging as well as for photodynamic treatment.