Comparison of the photoactivation efficacy of two chlorin derivative

We investigated the in vitro photoactivation properties of two chlorin derivatives, 8-cis-heptylchlorin dicarboxylic acid and 3-trans-heptylchlorin bisamidoglucose derivative, that exhibit a very strong absorbance peak in the red region of the spectrum and a value of the extinction coefficient (at the wavelength of the maximum absorbance) higher by one order of magnitude than the corresponding value for the porphyrins. The experiments of photoactivation were performed on a normal epithelial cell line (FRTL-5), using as an irradiation source an array of diodes emitting red light (lambda equals 675 nm). We found that, in the concentration range of 1 to 3000 ng/ml, photoactivation of chlorins greatly enhanced mortality of drug exposed irradiated cells (density of energy equals 0.25 mJ/cm2) with respect to the ones exposed to the drug but kept in the dark. This response is immediate and it looks line an 'all or none' effect. The comparison between the extinction coefficient and the efficacy of photoactivation of the two chlorin derivatives seems to indicate that they have similar values of the photophysical and photochemical quantities characterizing the processes responsible of the generation of singlet oxygen, the reactive species to whom the photoinduced toxicity of chlorins was generally imputed.