Kohji Maruo

Studies on beige–nude mice with low natural killer cell activity 1. Introduction of the bg gene into nude mice and the characteristics of beige–nude mice

To improve the take-rate of human tumours in nude mice, a nude mouse strain with the bg gene was established. The introduction of the bg gene was confirmed by examination of giant granules of blood neutrophils. The genetic profile of beige–nude mice was the same as that of the C57BL/6 strain according to genetic screening. The natural killer cell activity in the beige–nude mice was much lower than that in ordinary nude mice but slightly higher than that in beige mice. The reproductivity of beige–nude mice was as high as that of ordinary nude mice.

Strain-Dependent Growth of a Human Carcinoma in Nude Mice with Different Genetic Backgrounds

Human gastric carcinoma showed different growth in nude mice depending on their genetic backgrounds which included BALB/cA-nu (nude mice with a BALB/cA genetic background), CBA/N-nu, NFS/N-nu, NIH(s)-nu, C3H/HeN+-nu, C57BL/6N-nu and lasat mice (BALB/cA-nu, Dh). Rapid growth of human carcinoma was observed in CBA/N-nu, NFS/N-nu and NIH(s)-nu. The human carcinoma in NIH(s)-nu showed the widest deviation in tumor weight. These data suggest that NFS/N-nu and CBA/N-nu are strains which are more recommended for anticancer agent screening systems than BALB/cA-nu, NIH(s)-nu, C3H/HeN+-nu, C57BL/6N-nu and lasat mice, although many other factors including productivity of the mice, strain differences in drug metabolism and drug toxicity must be considered.

Role of x-linked immunodeficiency (xid) and NK activity in rejection of human tumor xenotransplants in nude mice.

In order to elucidate the factors influencing the takes of human tumor xenografts in nude mice, we compared the transplantability of human tumors in nude mice with additional genetic defects in the immune system. The nude mice strains tested were classified as follows by expression of the beige gene and the x‐linked immunodeficiency (xid) gene: 1) high NK nude (C57BL/6N, nu/nu), 2) low NK nude (C57BL/6 bg/bg nu/nu), 3) high NK nude with B‐cell defect (CBA/N nu/nu), and 4) low NK nude with B‐cell defect (NIH(S)III). Takes of human tumor xenografts including gastric carcinoma, T‐cell lymphoma and B‐cell lymphoma were better in nude mice with xid (CBA/N and NIH(S) III nude mice) than in nude mice without xid (B6 and beige nude mice). In addition, among the nude mice with xid expression, the takes were slightly better in nude mice with a CBA/N background than in those with a NIH(S) background. Moreover, the xenotransplantation rate in (CBA/N × C57BL/6N)F1 male nude mice with xid expression was higher than in (C57BL/6N × CBA/N)F1 males without xid expression, but did not react the same level as that in CBA/N nude. On the other hand, introduction of the beige gene into nude mice minimally improved the takes of human tumor xenografts under limited experimental conditions (inoculation of 100 times 105 T‐cell lymphoma and 1 times 105 gastric carcinoma cells) despite the reduction of NK activity. In xenotransplantation of human tumors directly from patients, the take rates of the tumors were also better in CBA/N nude mice than in BALB/cA nude mice. The results in the present report confirmed the effect of xid and CBA/N genetic background on human tumor xenografts in nude mice, suggesting the existence of serum factors, possibly present in serum IgM, mediating rejection of the xenografts.

Toxicity of anticancer agents, growth and chemosensitivity of human tumour xenografts in a segregating stock of AF nude mice

An investigation of the usefulness of a segregating stock of nude mice [AF nude mice (AF-nu)] for screening anticancer agents was undertaken. The toxicity of anticancer agents, takes and growth rates of human tumour xenografts and chemosensitivities of xenografts in AF-nu were studied and compared with those in BALB/cA nude mice (BALB/cA-nu). The results showed differences in the pattern of mortalities of AF-nu and BALB/cA-nu administered a range of anticancer agents. Body weight changes in the two nude mouse strains differed in the case of 5-fluorouracil, but not for nimustine, adriamycin and vincristine. All tumours transplanted in AF-nu grew as in BALB/cA-nu. Growth rates of 2 xenografts (gastric cancer and glioblastoma) were not significantly different between the 2 nude mouse strains, but those of 2 lung tumour xenografts were significantly greater in AF-nu than those in BALB/cA-nu. There were no significant differences in chemosensitivities of human tumours in AF-nu and BALB/cA-nu (consistency rate as evaluated by our criteria was 88%). From these results, it is suggested that AF-nu are more suitable for anticancer agent screening and experimental chemotherapy of human tumour xenografts than BALB/cA-nu because of lower costs and high reproductive rate. Although they are genetically heterogeneous, sets of experimental animals sharing the same gene pool can be produced routinely.

Alterations of Mouse Proto‐oncogenes in Sarcomas Induced after Transplantation of Human Tumors in Athymic Nude Mice

During serial subcutaneous transplantation of several types of human tumors into nude mice, the local development of malignant mouse‐specific sarcomas has been observed. Although the frequency of sarcoma induction is low, this phenomenon is very important because the mouse‐specific sarcomas completely replaced the human tumors during serial transplantation. The DNA of five independently induced mouse‐specific sarcomas was transfected into NIH/3T3 cells in order to detect oncogenes associated with mouse‐specific sarcoma induction. Two of these DNAs were found to carry activated mouse c‐N‐ras and c‐Ki‐ras genes. The sequence analysis of the molecularly cloned mouse c‐N‐ras oncogene showed a single nucleotide transition from G to A at the 12th codon. This results in substitution of aspartic acid for glycine at this position. The mouse c‐myc gene was also found to be amplified in a sarcoma. In these mouse sarcoma DNAs, human Alu sequences were not detected. These data strongly suggest that the mouse‐specific sarcomas were not induced by the transfer of human transforming sequences but by the alterations of mouse proto‐oncogenes.