DIFFERENTIAL sensitivity of normal and neoplastic rodent fibroblasts growing in vitro to the toxic action of carcinogenic polycyclic hydrocarbons, suggested long ago by Haddow (1938), has been demonstrated by a number of investigators (Starikova and Vasiliev, 1962;Berwald and Sachs, 1963; Alfred and collaborators, 1964;Diamond, 1966). Neoplastic cells were found to be much more resistant to these compounds than their normal counterparts. Resistance to the toxic effects of carcinogenic hydrocarbons was shown to be characteristic for the cells of sarcomas induced by various types of agents: carcinogenic chemicals, plastic films, SV40 and polyoma viruses. Thus, decrease of the sensitivity to carcinogens regularly accompanied neoplastic transformation of these cells (see review and discussion in Vasiliev and Guelstein, 1963Guelstein, , 1966.The causes of the differential sensitivity of normal and neoplastic cells to carcinogenic hydrocarbons remain obscure. These compounds undergo various metabolic transformations in vivo (see review in Boyland and Weigert, 1947; Miller and Miller, 1965). In vitro they are rapidly accumulated by normal and neoplastic cells (Marimura, Kotin and Falk, 1964;Alfred et al., 1964;Diamond, 1966). It was not known, however, whether these substances might be metabolized by cells growing in vitro.The experiments described in this paper were performed in order to study the rate of metabolism of a carcinogenic hydrocarbon, 3,4-benzopyrene (BP), in cultures of normal and neoplastic fibroblasts of mice and hamsters.Similar experiments were made with cultures of fibroblasts from normal human embryos. As shown by Diamond (1966) and confirmed in this laboratory, normal human fibroblasts, in contrast to normal rodent cells, are resistant to the toxic effects of carcinogenic hydrocarbons.
MATERIALS AND METHODS
Cell culturesFirst subcultures of trypsinized cells of mouse, hamster and human embryos were used; the age of human embryos taken for trypsinization was about 2-3 months, that of rodent embryos about 17-19 days of pregnancy.Trypsinized embryonic cells were first grown in large vessels and then transferred into stoppered Carrel flasks 5 cm. in diameter. Continuous lines of neoplastic cells were also grown in Carrel flasks. Some information on the origin
