In vitro photo-activation of newlysynthesizedchlorinderivatives with red-light-emitting diodes

We investigated the in vitro photo-activation properties of two chlorinderivatives, i.e. 8-cis-heptylchlorin dicarboxylic acid and 3-trans-heptylchlorin bisamidoglucose derivative, which exhibit lipophilic properties similar to those of the active fractions of Photofrin II, on a normal epithelial cell line (FRTL-5). We used as an irradiation source an array of diodesemittingredlight (λ = 675 nm), which produced a fluence of 7 MW cm−2 on the cells. We found that photo-activation with chlorinderivatives in the concentration range 1–100 ng ml−1 greatly enhanced the mortality of the irradiated cells (energy density, 0.25 J cm−2) with respect to the control cells kept in the dark. This response is immediate and appears to be an ‘all or none’ effect. Taking into account that compounds exhibit a strong absorbance peak in the long wavelength region of visible light where tissues are relatively transparent, our results suggest that chlorins can be considered to be good candidates for application in photodynamic therapy.