Applicability of new degradable hypericin-polymer-conjugates as photosensitizers: principal mode of action demonstrated by in vitro models.

Two series of water soluble novel conjugates of the photosensitizer hypericin were prepared and evaluated for their use as agents for photodynamic therapy, with covalently and non-covalently loaded hypericin on functionalised, hydrolytically degradable inorganic-organic hybrid polyphosphazenes. The conjugates showed excellent aqueous solubility and similar fluorescence spectra to pristine hypericin. Detailed in vitro investigations revealed that the substances were non-toxic in the dark over a wide concentration range, but displayed phototoxicity upon irradiation.