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Isozyme pattern of pyruvate kinase in the liver of nude mice bearing Ehrlich ascites tumor changed markedly during tumor growth. The change in isozyme pattern of pyruvate kinase was not due to infiltration or metastasis of tumor cells in the liver. Such a change in isozyme pattern of pyruvate kinase was also found in the liver of nude mice bearing canine gastric leiomyosarcoma induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), but not in the liver of nude mice bearing MNNG-induced canine gastric adenocarcinoma or human gastric adenocarcinoma.

The subrenal capsule (SRC) assay for cancer chemotherapy was tested according to Bogden's methodology. Of 37 patients providing tumor tissue for assay, 29 cases were considered suitable for evaluable assays. Fourteen patients had clinically evaluable diseases and 10 cases were evaluable for SRC assays. Correspondence between sensitive assay and clinical sensitivity was seen in 2 cases, and that between resistant assay and clinical resistance was seen in 4 cases. Discordance between sensitive assay and clinical resistance was seen in 4 cases. In histological studies, cancer tissues implanted in the subrenal space in immunocompetent mice did not show marked proliferation and were replaced by prominent leukocyte infiltration and fibrosis on day 6 after inoculation. The degree of leukocyte infiltration in the xenografts in the mice administered some anti-cancer drugs was slight in comparison with that in untreated control mice, which showed a remarkable trend in xenografts treated with 5-fluorouracil and cyclophosphamide, respectively. Our study suggests that there are many problems involved in the SRC assay methodology of Bogden, and that careful examination of this aspect will be required.

We carried out fundamental subrenal capsule assay methodology, using tumor specimens of human cancer xenografts (breast cancer and colon cancer) serially transplanted into nude mice. With regard to sequential changes in the tumor grafts implanted under the renal space of immunocompetent mice, tumor size was largest macroscopically around day 6 after inoculation, and later involuted gradually. Histological findings showed that implanted tumor tissues were preserved to a moderate extent until day 4 after inoculation, but leukocyte infiltration by host reaction had begun by day 4, and tumor tissues were almost replaced by host reactive tissues on day 6. Labeling index scoring did not indicate growth of implanted tumor cells. We found that macroscopic tumor size was largest around day 6 because we measured tumor size with involved leukocyte infiltration, and the macroscopic tumor did not represent the true extent of the tumor tissue.

Since 1974, approximately 200 fresh cancer tissues obtained from various types of cancer patients were inoculated into athymic BALB/c nude mice, of which 30 percent were taken and grown in the subcutaneous space of mice. Among them 15 lines of gastrointestinal and breast cancer xenografts were selected for experimental single agent chemotherapy. The response rates of 14 drugs examined in this xenograft system were compared with the cumulative clinical response rate of each drug in the same type of cancer. Drugs which were clinically effective against one type of tumor were found to be also effective against the corresponding xenograft in nude mice. Thus the human cancer-nude mouse system was considered useful as a predictive secondary screening method for new drugs. This evidence suggested to us the feasibility of utilizing the system as a chemosensitivity test for determining the drugs effective for an individual human malignancy. In our present study, the responses to 15 experimental chemotherapies with single agent or drug combination of 11 lines of cancer xenografts in nude mice were directly compared with the clinical response in each donor patient to the corresponding chemotherapy. Good correlation was obtained between these respective results, the overall predictive accuracy of the experimental results being 93%. Therefore, if the rate of transplantability to nude mice were to be improved, this nude mouse system would become a promising tool for the individual chemosensitivity test. The subrenal capsule (SRC) assay recently introduced by Bogden and his colleagues has excited much attention among Japanese clinical oncologists. In our study, cancer tissues implanted under the renal capsule 6 days after inoculation, did not show marked proliferation and a high percentage of implants was almost replaced by host reactive tissue. It therefore seems necessary to solve some fundamental problems before we can apply this assay method to clinical chemosensitivity trial.