Abstract
Abstract Taking advantage of the‘heavy atom’effect, we have recently prepared a series of nine novel halogenated and sulfur‐substituted benzophenoxazines which have enhanced intersystem crossing to the triplet state as measured by singlet oxygen photobleaching of 1,3‐diphenylisobenzofuran. The dyes were evaluated for their dark and light‐induced toxicities towards several carcinomata and normal primary cell lines. One of these days, 5‐amino‐6‐iodo‐9‐diethylaminobenzol[a]phenoxazinium chloride, was found to be a potent photosensitizer for a murine sarcoma 180 and four human carcinomata cell lines (larynx Hep2, cervical HeLa, rectal tumor cell HRT, and transitional‐cell bladder BTC). Several dyes caused marked light dependent killing of two tumor cell lines (Hep2 and HRT) but were minimally toxic to a normal bovine fetal kidney (BFK) line. Sulfur substitutuion into the benzophenoxazine nucleus results, under the conditions studied, in the largest enhancement of phototoxicity both to normal and cancer cells. Comparisons between appropriate dyes show a correlation between the efficiency of singlet oxygen generation and phototoxicity. These results suggest that the photosensitizing efficacy of certain cationic benzophenoxazinium chromophores, such as Nile Blue A, can be greatly increased by appropriate structural modification. The demonstrated selectivity for carcinoma cells by some of these new photosensitizers may be useful therapeutically.
Published Version
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