A novel in vitro-in vivo approach to carcinogenesis studies designed for use with human cells and tissues

A novel in vitro-in vivo approach for the study of initiation and neoplastic transformation was tested. The approach is based on two in vivo observations: (1) hepatocytes are most sensitive to initiating effects of chemicals during cell proliferation and (2) one population of initiated hepatocytes shows resistance to the mitoinhibitory effects of 2-acetylaminofluorene (AAF). We found that (1) normal rat hepatocytes exposed to 1 mM 14C-methylnitrosourea (MNU) for one hour show alkylation of their DNA, as measured by the accumulation of N-7- and O6-methylguanine; (2) hepatocytes isolated for 18 hours following partial hepatectomy (PH) continue the S-phase in vitro, as evidenced by a 400-fold increase in tritiated thymidine incorporation as compared to non-PH (normal) hepatocytes; (3) hepatocytes survive the conditions of isolation, three hours in culture and exposure to MNU and grow following transfer to the livers and spleens of recipient animals; and (4) nodular and hepatoma hepatocytes retained their property of AAF-resistance and grew faster than did normal hepatocytes following transfer to recipients selected with AAF plus PH. We are applying this in vitro-in vivo approach to the study of human cells and tissues.