Biochemische Untersuchungen �ber den Einflu� von Umwandlungsprodukten des Endoxans auf isolierte Ascitestumorzellen

Detection of induced tumour-resistance to cyclophosphamide by the in vitro short term test

Treatment of the solid Walker carcinosarcoma of the rat for a period of one year with cyclophosphamide (40 mg/kg at each passage; tumours were transplanted weekly) resulted in the formation of a cyclophosphamide-resistant tumour cell line. Without further treatment, animals injected with non-treated or cyclophosphamide pre-treated cells survived for 10 days on an average. After therapy with cyclophosphamide (2 x 38 mg/kg), rats with non-treated tumour cells survived 22 days whereas those with pre-treated tumours survived only for 17 days. Tumour cells which were shown to be sensitive in vivo also exhibited a larger reduction in 3H-thymidine and 3H-uridine incorporation in the in vitro short term test after incubation with urine from cyclophosphamide-treated rats or with 4-hydroperoxy-cyclophosphamide. The resistance to cyclophosphamide which was detected in animal experiments with Walker carcinosarcoma can therefore also be observed using the in vitro short term test.

[The evaluation of the cyclophosphamide sensitivity of human tumours by determining the incorporation of tritiated uridine and thymidine into the nucleic acids of human tumor cells in vitro in presence of 4-hydroxycyclophosphamide (author's transl)]

A new in vitro assay for screening the sensitivity of human tumour cells against Cyclophosphamide has been developed. While biologically activated Cyclophosphamide was unsuitable because of unpurities in the material, synthetic 4-Hydroxycyclophosphamide was shown to inhibit the incorporation of tritiated uridine and thymidine into the nucleic acids of human tumour cells in vitro. 29 tumours including 14 mammarial carcinomas, 8 ovarial carcinomas and 7 other malignant tumours were tested. While 12 tumours showed a significant and 5 only a slight inhibition of the 3H-uridine incorporation in vitro. 12 tumours showed no effect. Histologically none-differentiated tumours were more sensitive against 4-Hydroxycyclophosphamide as compared with the more differentiated ones. First observations point to 4-Hydroperoxycyclophosphamide instead of 4-Hydroxycyclophosphamide as a more suitable form of activated Cyclophosphamid for the in vitro assay of Cyclophosphamide sensitiveness because of the higher stability and better availability of this compound.

[The effect of cyclophosphamide on tumors in the sensitivity-test (author's transl)]

The sensitivity of tumors to cyclophosphamide was tested in vitro. For this purpose, the urine of cyclophosphamide-treated rats (90 min., 500 mg/kg) was used. This method of activating cyclophosphamid proved more advantageous than other methods; all cytostatically effective metabolites can be used in the test and the production of metabolites can easily be standardized. Consequently results with good reproducibility can be obtained. In various long-term and short-term test models with animal transplantation-tumors in vitro, the effects of the cyclophosphamide metabolites depended on the dose used. This test results in the various test models are comparable. In the tissue-culture of tumors (long-term test) sensitivity was evaluated by using morphological criteria as well as by counting cell numbers. In the short-term test the sensitivity of tumors was found out by influencing the nucleic acid syntheses (3-H-thymidine-, 3-H-uridine-incorporation). As the tissue-culture meets with difficulties as a routine clinical examination, the use of the short-term test is recommended. Using as model the fast proliferating WALKER-256-carcinosarcoma and a slowly proliferating rat adenocarcinoma, the results of the sensitivity-test in vitro were compared with the effects of therapy in animal tests. Tumor remissions corresponding with the results reached in vitro, which depended on dosis, could also be achieved in both transplantation-tumors. Human tumors, tested in in vitro studies (short-term-test), show a different sensitivity to cyclophosphamide.