Uptake and phototoxicity of the methyl-, ethyl-, n-propyl, and 2-propyl esters of 13²- hydroxy bacteriopheophorbide a were studied in OAT 75 SCLC cells and 3 different amelanotic melanoma cell lines. (A 375, Melur SP 18, SkAMel 25). Specific phototoxicity did not substantially differ for the different esters. Most surprisingly, these photosensitizers did not show any significant threshold behavior: even at 25 (mu) W/cm² (775 nm, diode laser) cancer cell suspensions were killed in a time-dependent logarithmic fashion. Furthermore, phototoxicity is enhanced at low power densities if compared with the effects at 1 - 10 mW/cm². This can be related only in part to a lack of oxygen at higher power densities. Complementary experiments confirmed that threshold is power but not dose dependent. Thus, threshold power density should be included into a prospective list of criteria characterizing photosensitizers suitable for photodynamic cancer therapy. The obvious lack of a limiting power density in bacteriopheophobide a esters make these sensitizers a prospective tool for tumor therapy in considerable tissue depth.

Date Published: 1 March 1994
PDF: 12 pages
Proc. SPIE 2078, Photodynamic Therapy of Cancer, (1 March 1994);

Published in SPIE Proceedings Vol. 2078:
Photodynamic Therapy of Cancer
Giulio Jori; Johan Moan; Willem M. Star, Editor(s)