Early reports using mouse models indicated that Nile Blue A (NBA) is taken
up more efficiently by tumor cells than normal tissue and retards tumor gro
wth. NBA also shows both dark toxicity and phototoxicity of human tumor cel
ls in vitro. However, studies on the dark toxicity of NBA and the effects o
f NBA-mediated photodynamic treatment in normal human cells are lacking. In
the current study we have examined the cytotoxicity of NBA in normal human
fibroblasts, spontaneously immortalized Li-Fraumeni Syndrome (LFS) cells a
nd three different human tumor cell lines. The normal human fibroblasts sho
wed extreme sensitivity to NBA compared with LFS cells and the human tumor
cell lines. Treatment with 0.1 mug/mL of NBA for 1 h reduced the colony for
mation of normal human fibroblasts by greater than 95%, but had no signific
ant effect on the colony formation of LFS cells. No significant numbers of
apoptotic cells were detected in either normal human fibroblasts or LFS cel
ls following this drug concentration. Thus, unlike photodynamic therapy wit
h some other photosensitizers, the dark toxicity of NBA was not caused by a
poptosis. Although the drug uptake was higher in normal human fibroblasts c
ompared with LFS cells, the difference in sensitivity between normal human
fibroblasts and LFS cells could not be accounted for by the difference in d
rug uptake alone. In addition, we could not detect any significant photocyt
otoxic effect of NBA in either normal human fibroblasts or LFS cells for a
drug concentration of 0.05 mug/mL at light exposures of up to 6.7 J/cm(2).
These data indicate an extreme sensitivity of normal human fibroblasts to N
BA and an inability to produce a significant photocytotoxic effect on human
cells using NBA concentrations that have relatively low toxicity for norma
l human fibroblasts.