NUCLEAR TARGETING OF CHLORIN E(6) ENHANCES ITS PHOTOSENSITIZING ACTIVITY

Although photosensitizers, molecules that produce active oxygen specie s upon activation by visible light, are being extensively used in phot odynamic therapy to treat cancer and other clinical conditions, proble ms include normal cell and tissue damage and associated side effects, which are attributable in part to the fact that cytotoxic effects are largely restricted to the plasma membrane, We have previously shown th at the photosensitizer chlorin e(6) has significantly higher photosens itizing activity when present in conjugates containing specific ligand s and thus able to be internalized by receptor-expressing cells. In th is study we use insulin-containing conjugates to which variants of the simian virus SV40 large tumor antigen nuclear localization signal (NL S) were linked to target chlorin e(6) to the nucleus, a hypersensitive site for active oxygen species-induced damage. NLSs were either inclu ded as peptides crosslinked to the carrier bovine serum albumin or enc oded within the sequence of a beta-galactosidase fusion protein carrie r. The results for photosensitization demonstrate clearly for the firs t time that NLSs increase the photosensitizing activity of chlorin e(6 ), maximally reducing the EC50 by a factor of over 2000-fold. This has wide-reaching implications for achieving efficient cell type-specific photodynamic therapy.