NEOPLASTIC TRANSFORMATION BY CRYSTALLINE SILICA AND OTHER MINERALS

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Two new cell lines were established from young adult rat lung alveolar type II epithelium, in order to investigate quartz-induced transformation mechanisms. Primary cultures were transfected with plasmids containing immortalizing genes (either SV40 T antigen or adenovirus 2 E1A) and a selective marker. Transfected colonies, selected for morphological characteristics of epithelial polygonal cells, maintained normal morphology and near diploid karyotype for 40 passages. The new cell lines were cryopreserved at several passage levels. In the AE6 line (E1A- immortalized), treatment with quartz particles induced dose dependent toxicity and morphological changes with elongated cells showing a crisscross growth pattern, which became manifested after 4-5 weeks in culture. The transformed morphology was maintained over several passages. The transformed cells showed limited karyotypic alterations. When injected in nude mice, several transformed lines grew as anaplastic carcinomas. Two independent experiments confirmed this quartz-induced malignant transformation. When tested for anchorage independent growth in soft agar, the untreated AE6 cells were negative, whereas the transformed cell lines formed large spheroids with high frequency. Current work is aimed at standardizing this assay for transformation of alveolar cells. The AE5 cell line (SV40-Tag-immortalized) showed a much higher sensitivity to quartz-induced toxicity than the AE6 (E1A- transfected) cell line, and is being studied as a specially sensitive model for transformation by silica.