Photosensitization by the near-IR-absorbing photosensitizer lutetium texaphyrin: Spectroscopic, in vitro and in vivo studies

The spectroscopic and biological properties of the new photosensitizer lute tium texaphyrin (Lu-Tex) were assessed in vitro and in vivo on a C26 colon carcinoma model, in comparison with hematopotphyrin (Hp), photofrin II (PII ) and chlorin e(6) (Chl). Strong binding of Lu-Tex to lipid bilayer membran es was observed. The results of confocal fluorescence microscopy on C26 cel ls showed that Lu-Tex was localized in small vesicles in the cytoplasm, pos sibly in the lysosomes, while Chi and Hp were distributed in larger cytopla smic vesicles attributed to mitochondria. Scanning electron microscopy and X-ray microanalysis revealed that photodynamic therapy with Lu-Tex induced only slight damage to the cell membrane, leading to a delayed cell response . Chi and Hp caused significant structural damage to the outer cell membran e, resulting in ionic imbalance and fast cell death. The in vitro quantitat ive assessment of the relative efficiency per absorbed photon of the sensit izers revealed that Lu-Tex was less effective than Chi and Hp. However, the results of our in vivo study showed that at the same light and drug doses the anti-tumor efficiency of the agents was in the following order: Lu-Tex > Chl > PII. The strong in vivo anti-tumor effect of Lu-Tex can be explaine d by its higher integrated absorption in the long-wavelength range. (C) 199 8 John Wiley & Sons, Ltd.