Early effect of cyclophosphamide on oncogene expression in vivo

Cyclophosphamide (CP) is a widely used chemotherapeutic drug, with proven carcinogenic effects. Secondary tumours induced by CP are kidney tumours in humans and haemopoietic malignancies in rodents. Previous experiments have shown its effect on H-ras, c-myc and p53 gene expression in long term in vivo experiments. Our model was developed to analyse the events in the first 24 hours after the administration of CP in short term experiments. The expression of Ha -ras, c-myc and p53 was investigated in the target organs during and up to 24 hours after the administration, at 0.25, 0.5, 1, 6, 12 and 24 h. Since the majority of CP-induced tumours are leukemias and lymphomas in the CBA/Ca mouse model, RNA was obtained from the thymus and the spleen. The results show that p53 is strongly expressed in the thymus during the focused period. On the other hand, the samples were subjected to in situ hybridisation and compared with the results of in situ hybridisation of lung and liver samples. Comparing the results of total RNA and in situ hybridisation should prove useful if the total RNA signal is too weak or not detectable at all. The in situ hybridisation picture showed many positive cells without high expression of oncogenes. Further flow-cytometric studies are necessary to provide a full explanation of the mechanism of CP induced changes.