BIOLOGICAL POTENTIAL OF SILICON 2,3-NAPHTHALOCYANINE DERIVATIVES AS SENSITIZERS FOR PHOTODYNAMIC THERAPY OF CANCER

Photodynamic therapy (PDT) of cancer relies upon the activation by red light of systemically administered photosensitisers which have been selectively retained in malignant tissues. Over the past years, several classes of dyes have been proposed as new photosensitisers. Among them, naphthalocyanines offer a high absorption around 780 nm, where light transmission into tissues is optimal. We therefore prepared four silicon 2,3-naphthalocyanine derivatives substituted with two axial alkylsiloxy chains of increasing lengths. Their photobiological activity was determined in vitro in V-79 Chinese Hamster fibroblasts and in vivo in BALB/c mice bearing the EMT-6 tumour. In spite of the limited phototoxicity observed at the cellular level, in vivo, all dyes injected at 0.1 mu mol/kg, 24 h prior to PDT induced a complete tumour regression in at least 50% of mice. These data demonstrate the potential of silicon naphthalocyanines for the PDT of cancer.