PULMONARY FIBROSIS CAUSED BY N-METHYL-N-NITROSOURETHANE INHIBITS LUNGTUMORIGENESIS BY URETHANE IN TRANSGENIC MICE CARRYING THE HUMAN PROTOTYPE C-HA-RAS GENE

Male and female transgenic mice carrying the human prototype c-Ha-ras gene (rasH2 mice) and their wild littermates (non-Tg mice) received th ree subcutaneous injections of 0.3 mg N-methyl-N-nitrosourethane (MNUR ) once every 2 weeks for the first 4 weeks followed by a single intrap eritoneal injection of 1000 or 0 mg/kg urethane (UR) 2 weeks later. Th ey were then maintained without any other treatment for a further 13 w eeks and sacrificed for assessment of pulmonary pathology. Inflammator y lesions, such as macrophage infiltration, alveolar bronchiolization and/or fibrosis, were induced in both rasH2 and non-Tg mice treated wi th MNUR or MNUR + UR. Lung proliferative lesions were induced in 100% of the UP-treated rasH2 mice but to a significantly lesser extent in t he MNUR + UR case. The incidences of lung tumors in non-Tg mice treate d with UR or MNUR + UR were relatively low. Point mutations of the tra nsgene were detected in approximately 80% of lung tumors in rasH2 mice treated with UR and MNUR + UR, but murine Ki-ras mutations were rare. No marked difference in the mutation pattern was found between the UP -treated and the MNUR + UP-treated rasH2 mice. In non-Tg mice treated with UR or MNUR + UR, point mutations of the murine c-Ki-rns gene were observed in about 50% of the lung tumors examined. The present study confirmed that rasH2 mice are very sensitive to lung tumor induction b y UR and suggested that alveolar epithelial cells in the reparative st age during pulmonary fibrosis are resistant to DNA damage by this carc inogen. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.