Photosensitizing dyes for the selection of nontumorigenic revertants from human lung cancer cell lines

Certain positively charged, lipophilic dyes have been noted by various authors to localize selectively in the mitochondria of carcinoma cells. Oseroff et al. (Proc. Natl. Acad. Sci. USA, 83:9729-9733, 1986) studied 10 carcinoma-specific mitochondrial photosensitizers and judged N,N'-bis(2-ethyl-1,3-dioxolane)kryptocyanine (EDKC) to be the most effective in selective carcinoma cell photolysis, a system where light-absorbing molecules accumulate only in carcinoma cells and on illumination initiate a reaction that kills or damages those cells. The present study duplicated the published EDKC retention result for the normal monkey kidney epithelial cell line CV-1. A series of nontumorigenic and tumorigenic human bronchial epithelial and human pleural mesothelial cells were assayed for EDKC uptake and retention, with the intent of using selective carcinoma cell photolysis to isolate nontumorigenic revertants of the tumorigenic lung cell lines. In addition, the uptake and retention of the fluorescent, mitochondria- and carcinoma-specific dye rhodamine-123 were surveyed in a series of hybrids between tumorigenic and nontumorigenic human bronchial epithelial cells. The half-life of dye retention ranged from 6 to 12 h in all the bronchial epithelial and mesothelial cells studied, with little or no dye selectivity for tumorigenic cells. When EDKC-retaining bronchial epithelial cells were illuminated with red light, significant reductions in short term viability and colony-forming efficiency were seen, which became more pronounced as light and dye doses were increased. However, these effects did not correlate with tumorigenicity within the cell series. The method, therefore, does not appear generally useful for the selection of nontumorigenic variants of human bronchial epithelial or pleural mesothelial cancers of the lung.