Cytotoxicity of azadirachtin A in human glioblastoma cell lines.

The neem toxin azadirachtin A exhibits selective toxicity on insects. Despite its well-proven efficacy, the mode of action of this toxin remains obscure. The toxicity on vertebrate cells compared to insect cells is also not well characterized. We have cultivated six human glioblastoma cell lines G-28, G-112, G-60 (TP53 mutant) and G-44, G-62, G-120 (TP53 wild-type) in the presence of 28 microM of azadirachtin. This toxin concentration was chosen because it represents the 25 to 50% lethal dose in the glioma cells. Toxicity was measured in terms of cell proliferation (binucleation index), formation of micronuclei and cell survival. In the TP53 mutant cell lines, azadirachtin reduced the proportion of dividing cells and induced formation of micronuclei. Except for G-44 which showed a decrease in binucleation index, proliferation in the TP53 wild-type cell lines was unaffected by azadirachtin. In the TP53 wild-type cell lines, the decrease in micronuclei frequency is attributed to fewer cells entering mitosis to produce micronuclei. This is also apparent from the low surviving fractions. Cell survival was suppressed by 25-69% in all cell lines. The reduction of cell survival is a clear indication that azadirachtin affects reproductive integrity and cell division. The induction of micronuclei reflects DNA damage. Similar studies on damage induction in insect cell lines could elucidate the processes which precede the antifeedant and antimoulting effects of azadirachtin and other neem toxins in insects.