Malignant glioma experimental studies with an estrogen-linked cytostatic

Abstract: Malignant gliomas are the most common primary brain tumors in adults. Patients with these highly malignant tumors have an extremely poor prognosis. The situation with a highly proliferative tumor in a non-proliferating tissue should favor cytostatic treatment but so far the role of conventional chemotherapy has been adjunctive. The concentrations of three sex steroids, estradiol, progesterone and testosterone, were analyzed by radioimmunoassay after celite chromatography in brain tumor samples. Some malignant gliomas had high tissue concentrations of estradiol. Low progesterone levels may suggest steroid consumption. Estramustine (EM), a conjugate of estradiol-17ß and nornitrogen mustard had a dose-dependent antiproliferative effect on several human malignant glioma cell lines. At equimolar concentrations the inhibitory effects of the EM complex were clearly more pronounced than those of estradiol and nornitrogen mustard given alone or in combination. A specific binding protein (EMBP) is important for the cytotoxic action of EM. Using a mouse monoclonal antibody and an indirect antibodyperoxidase technique, EMBP was demonstrated in human glioma cells. Significant amounts of EMBP were also detected in human brain tumor tissue by radioimmunoassay. The mean concentrations (ng/mg protein) in 16 astrocytomas (2.6) and 7 meningiomas (5.1) were higher (p<0.001) than in 18 samples of normal brain (0.5). The presence of the specific binding protein may suggest a selective binding and effect of EM in human brain tumor tissue. Human glioma cells displayed significant uptake, retention and metabolism of estramustine phosphate (EMP). After incubation with ^H-EMP a progressive uptake of radioactivity was recorded during 24 hours. Metabolism of parent EMP into estramustine and estromustine, which is a well known part of the metabolic pathway in man, was also demonstrated. A dose- dependent increase in DNA strand breaks was recorded at EMP- concentrations ranging 10-40 yg/ml. The uptake of ®^Rb, used as a tracer for potassium to study ion transport and membrane permeability, was reduced after incubation with EMP. Scanning electron microscopy gave further evidence for membrane damage. According to flow cytometric analyses exponentially growing glioma cells were accumulated in the G2/M stage and the fraction of Gi/Gq was reduced. EM seems to attack malignant cells in a multifocal fashion on several vital functions including the microtubule, the nucleus, and the cell membrane. The intact EM complex may be important for effects related to microtubule function which add to the cytotoxic potential of its constituents. These experimental findings justify further investigations on the role of sex hormones in brain tumor growth and development and of hormone-linked cytostatics in clinical treatment.