Role of damage-sensing/processing genes in the radiation response of haemopoietic in vitro colony-forming cells.

PURPOSE: To characterize the role of various cellular damagesensing, processing and survival genes in the in-vitro radiosensitivity of haemopoietic colony-forming cells. MATERIALS AND METHODS: Bone marrow cells from a range of different gene-knockout mice were irradiated in vitro with graded radiation doses and assayed for colony-forming efficiency. RESULTS: Colony-forming efficiency in the nulls was often lower by up to threefold compared with the wild-types. This was noticeable in particular for the atm, bax and p21 nulls. Radiosensitivity was markedly increased in the scid mouse (about 2.3-fold), more than in the atm null mouse (about 1.7-fold). There was resistance in the p53 nulls compared with the wild-types, using two different background strains, that gave similar results. There was slight sensitization in the p21 nulls. In the bcl-2 nulls, there was sensitization at low dose, but not at high dose. In contrast, in the bax nulls, there was protection at low dose, but again not at high dose. The heterozygotes for p53, bcl-2 and bax responded similarly to the wild types, so that no gene dosage effects were identified. CONCLUSIONS: These studies are the first to elucidate the role of as many as six relevant genes in the radiosensitivity of a single cell type. They show the greater importance of 'survival' genes at lower cytotoxic doses of radiation compared with the greater importance of 'damage-sensing' genes at higher doses.

Bone marrow toxicity in mice treated with indium-114m-labelled blood cells.

Clinical trials with autologous indium-114m-labelled lymphocytes have revealed significant anti-tumour effects in chronic lymphocytic leukaemia patients with highly resistant disease. Substitution of the lymphocyte vector with heat-damaged red blood cells (HDRBC) may make this treatment more universally applicable and reduce the dose-limiting myelosuppression encountered with labelled lymphocytes. Therefore, the bone marrow localization and toxicities of indium-labelled lymphocytes or HDRBC have been investigated in BDFI mice. At 24 hours approximately 4% and 1.2% of 114In(m) administered as labelled lymphocytes or HDRBC respectively was localized within the bone marrow and remained constant for 57 days thereafter. Toxicity towards bone marrow stem cells, measured as CFU-S, was equivalent for both cellular vectors. However, at clinically relevant activities, 114In(m) HDRBC were less toxic than labelled lymphocytes towards committed progenitors, assayed as in vitro-CFC and CFU-Meg. These data suggest that substitution of HDRBC for lymphocytes as the 114In(m) vector may be beneficial in reducing the myelosuppression associated with this technique.

Mutation studies in lacI transgenic mice after exposure to radiation or cyclophosphamide.

We have used the Big Blue lacI transgenic mouse reporter system to investigate mutation induction in the testes, spleen and liver after exposure to an internally incorporated radionuclide, 114mIn, whole body irradiation with 60Co gamma-rays and systemically administered cyclophosphamide. Spontaneous mutation frequencies were 6-17x10(-6). No statistically significant mutation induction was observed in testes or spleen at 35 days after exposure to any test agent, although mutation frequencies tended to be increased (by approximately 1.5-fold) after exposure to 1 Gy gamma-rays. However, liver mutation frequencies were doubled after treatment with 100 mg/kg cyclophosphamide and were elevated by approximately 2.5-fold after systemic administration of 114mIn and 4.5-fold after 1 Gy 60Co gamma-rays. When data from all organs were pooled, mutation frequency was doubled after exposure to 1 Gy gamma-rays, but no other significant increases were observed. These findings support the hypothesis that the lacI transgenic mouse may be relatively inefficient at detecting mutations induced by exposure to ionizing radiation or other agents which produce a spectrum of deletion sizes, including those which are larger than the lacI transgene.