Chromosome numbers and DNA-content in intracerebrally transplanted experimental gliomas

Serially transplanted experimental tumors of the central and peripheral nervous system can be used as models to investigate open questions in human neurooncology. Altered susceptibility of higher passages to chemotherapy might be correlated with chromosome number and DNA-content variations which would be partly expressed as changes in proliferation behaviour. Karyotypes therefore were analysed in the 73rd to 90th generations of transplanted experimental gliomas. Wide variation of chromosome number was observed; 2 major types of distribution occurred, the one presenting with, the other without stemlines. Large chromosomes # 1 and # 4 were often monosomic, while small chromosomes of ## 8 to 20 were increased up to the fivefold. Lines with prominent and few markers were observed. On the whole, cells of the proliferating pool of the tumor had to be considered as hypotetraploid. Comparison of chromosome numbers and DNA content gave good correlation; differences between the 2 were explained by the fact that only the number of chromosomes was taken into account, regardless of whether small or large chromosomes were lacking or in excess. When intracerebrally transplanted tumors had been previously treated by administration of BCNU, the DNA content was altered, indicating an increased share of diploid cells in the proliferation pool. Results are at variance with earlier findings in tissue cultures of directly induced malignant gliomas and neurinomas in rats. The findings in transplanted tumors can be interpreted as a result of increased malignancy in transplantation tumors, documented by rapid growth in the animal and dedifferentiated histologic morphology.