Light scattering of human skin: a comparison between zinc (II)-phthalocyanine and photofrin II.

Zinc(II)-phthalocyanine is the active component of the liposomal formulation CGP 55847 which showed a highly activity in photodynamic therapy studies on a variety of animal tumours (K. Schieweck et al., SPIE Conf. Proc., 2078 (1994) 107-118). The photophysical properties of zinc(II)-phthalocyanine have been studied in detail and compared with those of Photofrin II(R), the only sensitizing agent approved so far for Phase III and IV clinical trials (M. Ochsner-Bruderer, Inaugural Dissertation, University of Basle, 1994). As will be shown in a series of papers, the main photophysical properties of zinc(II)-phthalocyanine are significantly better than those of Photofrin II(R) (M. Ochsner-Bruderer, Inaugural Dissertation, University of Basle, 1994). In this paper we especially consider the effect of the absorption wavelength on the penetration of light into the human skin. The results clearly show that the longer absorption wavelength of zinc(II)-phthalocyanine causes a deeper penetration of light into the human skin as compared with Photofrin II(R). In addition to this, the higher extinction coefficient (epsilon S) lowers the zinc(II)-phthalocyanine dose required to induce a tumour necrosis.