Characterization of gastrin-induced cytostatic effect on cell proliferation in experimental malignant gliomas

OBJECTIVE: Growth patterns of astrocytic tumors can be modulated in vitro by gastrin. In this study, the influence of gastrin on the in vitro cell cycle kinetics and the in vivo growth features of three experimental malignant gliomas was investigated. METHODS: Gastrin-induced influence on overall growth was assayed in vitro by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium colorimetric assay for human U373 and rat C6 gliomas and for rat 9L gliosarcoma. Although cell cycle analyses were performed by means of computer-assisted microscope analyses of Feulgen-stained nuclei, the gastrin-induced effects of the levels of expression of cyclins D3 and E, CDK2, CDK4, CDK5, CDK7, p15, p16, E2F1, and E2F2 were assayed by means of quantitative Western blot test. The presence of ribonucleic acids for the CCKB and CCKC gastrin receptors in the U373, C6, and 9L models was assayed by means of quantitative reverse transcriptase-polymerase chain reaction, and the presence or absence of ribonucleic acids for CCKA receptor was checked by means of conventional polymerase chain reaction. The influence of gastrin was also characterized in vivo in terms of the survival periods of conventional rats orthotopically grafted with the C6 and 9L models and nude rats with the U373 model. RESULTS: Gastrin significantly decreased the overall growth rate in the rat C6 and the human U373 high-grade astrocytic tumor models with either CCKB or CCKC gastrin receptor but not in the 9L rat gliosarcoma, which had no CCKB gastrin receptor (but had CCKA receptor) and only weak amounts of CCKC receptor. This effect seems to occur via a cytostatic effect; that is, an accumulation of tumor astrocytes occurs in the G(1) cell cycle phase. The cytostatic effect could relate to a gastrin-induced decrease in the amounts of the cyclin D3-CDK4 complex in both CIS and U373 glioma cells. In vivo, gastrin significantly increased the survival periods of C6 and U373 glioma-bearing rats, but not of 9L gliosarcoma-bearing rats. CONCLUSION: Gastrin is able to significantly modify the growth levels of a number of experimental gliomas.