ABSTRACT
From studies of the atomic bomb survivors, it is well known that ionizing radiation causes several forms of leukemia. However, since the specific mechanism behind this process remains largely unknown, it is difficult to extrapolate carcinogenic effects at acute high-dose exposures to risk estimates for the chronic low-dose exposures that are important for radiation protection purposes. Recently, it has become clear that the induction of acute myeloid leukemia (AML) in CBA/H mice takes place through two key steps, both involving the Sfpi1 gene. A similar mechanism may play a role in human radiation-induced AML. In the present paper, a two-mutation carcinogenesis model is applied to model AML in several data sets of X-ray- and neutron-exposed CBA/H mice. The models obtained provide good fits to the data. A comparison between the predictions for neutron-induced and X-ray-induced AML yields an RBE for neutrons of approximately 3. The model used is considered to be a first step toward a model for human radiation-induced AML, which could be used to estimate risks of exposure to low doses.
Subject(s)
Disease Models, Animal , Leukemia, Myeloid, Acute/genetics , Models, Biological , Mutation/radiation effects , Neoplasms, Radiation-Induced/genetics , Animals , Dose-Response Relationship, Radiation , Leukemia, Myeloid, Acute/etiology , Likelihood Functions , Male , Mice , Neutrons/adverse effects , Relative Biological Effectiveness , Stochastic ProcessesABSTRACT
BACKGROUND: Boron neutron capture therapy usually relies on soluble, rather than particulate, boron compounds. This study evaluated the use of a novel boron nanoparticle for boron neutron capture therapy. MATERIALS AND METHODS: Two hundred and fifty thousand B16-OVA tumour cells, pre-incubated with boron nanoparticles for 12 hours, were injected subcutaneously into C57BL/6J mice. The tumour sites were exposed to different doses of neutron radiation one, four, or eight days after tumour cell inoculation. RESULTS: When the tumour site was irradiated with thermal neutrons one day after injection, tumour growth was delayed and the treated mice survived longer than untreated controls (median survival time 20 days (N = 8) compared with 10 days (N = 7) for untreated mice). CONCLUSION: Boron nanoparticles significantly delay the growth of an aggressive B16-OVA tumour in vivo by boron neutron capture therapy.
Subject(s)
Boron Neutron Capture Therapy/methods , Melanoma, Experimental/prevention & control , Melanoma, Experimental/radiotherapy , Nanoparticles/therapeutic use , Neutrons/therapeutic use , Animals , Cell Line, Tumor , Female , Mice , Mice, Inbred C57BL , Xenograft Model Antitumor AssaysABSTRACT
The nucleotide sequence of the pMS1 clone was submitted to the GenBank Nucleotide Sequence Database under accession number AF288076. Changes in the expression of mucin genes in gastrointestinal cancers is thought to contribute to the development of the disease. In our laboratory we have shown previously that MUC5AC is aberrantly expressed in rectosigmoid villous adenomas. However, the regulatory mechanisms underlying that altered profile of expression is unknown. In order to study its regulation at the transcriptional level, we have isolated and characterized 5.5 kb of the 5'-flanking region of the mouse Muc5ac mucin gene. The promoter is flanked by a TATA box and a transcriptional start site is located 22 bp downstream of the TATA box. Analysis of the sequence showed a high density of binding sites for Smad4, an essential factor in the signalling cascade activated by TGF-beta (transforming growth factor-beta), and Sp1, an important factor in the regulation of MUC5AC. This led us to study Muc5ac regulation by TGF-beta. We show that exogenous addition of TGF-beta to the cells induces Muc5ac endogenous expression, promoter activity and Smad4 binding to the promoter. By co-transfection studies we show that Smad4 is essential for Muc5ac promoter activation and that it does not synergize with Smad2 or Smad3. By gel-retardation and co-transfection assays, we identified Sp1 and Sp3 as important regulators of Muc5ac expression and showed that Smad4 and Sp1 act in a co-operative manner to transactivate Muc5ac promoter activity. Altogether these results bring new insights into the molecular mechanisms of TGF-beta-mediated up-regulation of Muc5ac and enhance our understanding as to how Muc5ac is regulated in certain pathologies of the gastrointestinal tract.
