The verotoxin receptor globotriaosyl ceramide (Gb3) is overexpressed in an ovarian tumour resistant to chemotherapy. An overlay of frozen tumour sections shows extensive staining of the tumour cells with verotoxin B subunit. In addition, blood vessels within the tumour mass are stained. The sensitivity of ovarian tumour cells in vitro to verotoxin can be modulated by culturing the cells in sodium butyrate to obtain an approximatly 5000-fold increase in susceptibility. This increased susceptibility is correlated with the intracellular targeting of verotoxin as monitored by using FITC-VT B subunit, in that prior to sodium butyrate treatment the toxin is internalized to a juxtanuclear (likely) Golgi location whereas, following butyrate treatment the intracellular toxin is distributed around the nucleus, consistent with endoplasmic reticulum and nuclear envelope location. This perinuclear location is similar to that found for drug-resistant variants of ovarian tumour cell lines. These results suggest that intracellular targeting of verotoxin to the perinuclear area results in increased cytotoxicity. Potentially such targeting may also occur in other human tumours.
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