Parameters affecting photodynamic activity of Foscan® or meta-tetra(hydroxyphenyl)chlorin (mTHPC) in vitro and in vivo

In vitro photodynamic activity of Foscan(R) or meta-tetra(hydroxyphenyl)chlorin (mTHPC) was approximately five times lower in the presence of protein in comparison with serum-free medium. Photocytotoxicity does not depend on the incubation time of the dye with cells. The in vitro results are discussed from the point of view of photodynamically active aggregated species. The photodynamic activity of mTHPC was elevated in vivo by macroscopic measurement of the necrosis depth after tumoral resection using an in vivo staining procedure with Evans blue dye. Only tumours from treated animals presented measurable necrosis areas, mostly localised in the surface around the irradiated site with a mean depth of 3.0 +/- 0.3 mm. The photodynamic activity was found to be significantly higher when using low irradiance (32 mW/cm(2)) than when using a higher one (160 mW/cm(2)). These results were not related, to intratumoral mTHPC photodestruction analysed by in vivo fluorescence spectral analysis.