Animal models of malignant mesothelioma.

Animal models of diffuse malignant mesothelioma have historically been used to assess carcinogenicity of various fiber types and to study the pathogenesis of this unusual neoplasm. Pleural and peritoneal mesotheliomas have been induced in rodents following exposure to erionite or asbestos fibers, radionuclides, particulate nickel compounds, and chemicals such as 3-methylcholanthrene. The role of SV40 virus as a cofactor with asbestos fibers in the development of diffuse malignant mesotheliomas in humans has been explored in animal models. SV40 virus alone induces mesotheliomas in hamsters. Generation of new transgenic mouse strains with targeted expression of SV40 large T and small t antigens in the mesothelium would be very useful for mechanistic studies. Human malignant mesotheliomas frequently show hypermethylation or deletions at the Cdkn2a/Arf and Cdkn2b gene loci and deletions or mutations at the NF2 gene locus. Heterozygous Nf2 (+/-) mice exposed to crocidolite asbestos fibers exhibited accelerated development of malignant mesotheliomas compared to wild-type littermates. Loss of the wild-type Nf2 allele, leading to biallelic inactivation, was observed in nine mesothelioma cell lines derived from Nf2 (+/-) mice. Similar to human malignant mesotheliomas, tumors from Nf2 (+/-) mice showed frequent homozygous deletions of the Cdkn2a/Arf locus and adjacent Cdkn2b tumor suppressor gene. As in the human disease, murine mesotheliomas also showed constitutive activation of Akt. This murine model of asbestos carcinogenesis recapitulates the molecular and histopathological features of the human disease and has significant implications for preclinical testing of novel preventive or therapeutic modalities.