STEREOCHEMICAL FACTORS IN THE TRANSPORT AND BINDING OF PHOTOSENSITIZERS IN BIOLOGICAL-SYSTEMS AND IN PHOTODYNAMIC THERAPY

The uptake and biological activity of porphyrins and phthalocyanines i n tumours were correlated with the geometrical features of the photose nsitizer molecules. The data suggest that a critical distance of appro ximately 1.2 nm between oxygen atoms (originating in SO3-, COO- or OH substituents) characterizes a biologically active photosensitizer for photodynamic therapy. We propose that tubulin, which is available in l arge amounts during mitosis, is the main receptor molecule which binds these photosensitizers. Basic amino acid residues or tightly bound ca tions in tubulin or homologous proteins may act as binding sites on th e receptor molecule.