Preferential metabolism of N-nitrosodiethylamine by two cell lines derived from human pulmonary adenocarcinomas

Diethylnitrosamine (DEN), in common with other nitrosamines, is a carcinogenic agent which produces tumors in a wide variety of tissues in experimental animals. The pulmonary Clara cell is a major target of N-nitrosamine-induced carcinogenesis in hamsters and rats. DEN is believed to require metabolic activation to elicit its carcinogenic effects. The metabolism of [¹⁴C]DEN was studied in two cell lines derived from human lung adenocarcinomas and two cell lines derived from human small cell lung cancers by monitoring ¹⁴CO₂ production and covalent binding of radiolabel from [¹⁴C]DEN to the cell protein and DNA fractions. [¹⁴C]DEN was metabolized by adenocarcinoma-derived NCI-H322 (with Clara cell features) and NCI-H358 (with features of alveolar type II cells) but not by NCI-H69 and NCI-H128 (derived from small cell carcinoma). Metabolism was markedly inhibited by heat denaturation of the cell protein. [¹⁴C]DEN metabolism by NCI-H322 was greatly decreased when the incubation was carried out under (i) anaerobic conditions and (II) in the presence of a carbon monoxide enriched atmosphere. These results suggested the involvement of the cytochrome P-450-dependent monooxygenase enzyme system. Metabolism by NCI-H358 was also decreased in the absence of oxygen or presence of carbon monoxide although the effects were relatively small compared with the results with NCI-H322. On the other hand, aspirin or indomethacin, which are inhibitors of the fatty acid cyclooxygenase component of prostaglandin endoperoxide synthetase, preferentially inhibited [¹⁴C]DEN metabolism by NIC-H358. There were little or no effects of these inhibitors on the metabolism of DEN in NCI-H322. The data suggest that DEN metabolism in different lung cell types may be carried out by different enzyme systems which in turn may contribute to the selective effect of DEN in the lung.