DNA FRAGMENTATION INDUCED BY THE ANTIMITOTIC DRUG ESTRAMUSTINE IN MALIGNANT RAT GLIOMA BUT NOT IN NORMAL BRAIN - SUGGESTING AN APOPTOTIC CELL-DEATH

Estramustine, a combination of 17 beta-oestradiol and nor-nitrogen mus tard, has been shown to be metabolised and to induce specific antiprol iferative effects in malignant glioma, including arrest of glioma cell s in the G(2)/M phase of the cell cycle, damage to cell membranes and DNA and induction of free oxygen radicals. To evaluate further the eff ects of estramustine, an in vivo rat glioma model using inbred BD-IX r ats and the BT4C cell line was set up. In order to detect cells with f ragmented DNA, tumour and brain specimens were, following fixation for histological examination, processed for in situ end labelling (ISEL) with biotin-labelled nucleotides. Fresh tissue fragments were also use d for DNA integrity analysis on agarose gels. It was demonstrated that estramustine induced clusters of ISEL-positive cells and a pronounced typical fragmentation of DNA 0.5-8 h after treatment. In tumours exam ined 24 or 94 h after estramustine treatment, and in untreated tumours , only occasional single ISEL-positive cells were scattered in the tum our. DNA from normal brain tissue did not display any visible sign of fragmentation. These changes are indicative of programmed cell death i nduced by estramustine in glioma cells but not in normal brain tissue. Further studies are, however, needed to establish in detail the mecha nisms of cell death following treatment with the antimitotic drug estr amustine.