Invasiveness, proliferative activity and ultrastructural phenotypes of hepatocytes from diethylnitrosamine‐induced neoplastic nodules and hepacarcinomas in vitro

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Abstract
The invasive behavior of hepatocytes from diethylnitrosamine (DENA) induced neoplastic nodules and hepatocarcinomas was studied in a confronting culture system in vitro. These observations confirm our previous report, demonstrating that hepatocytes from hepatocarcinomas and from neoplastic nodules invaded into embryonic chick precultured heart fragments (PHF), a property associated with malignancy (Mareel, 1979). We now further demonstrate that: (1) Invasiveness was expressed by the hepatocytes in 10 out of 12 samples from hepatocarcinomas, and in 13 out of 36 confronted nodular samples. The hepatocytes from the other two‐thirds of nodule samples died off in the confrontation as did all normal hepatocytes. (2) Invasive hepatocytes from tumors and from nodules showed the same arrangement of invasive liver cells in relation to the heart tissue, and the same ultrastructural phenotypes. The latter did not differ from those in the non‐invading subpopulations, with the exception perhaps of a higher proportion of cells with an indented nucleus. (3) None of the scored ultrastructural alterations was present in all the invasive cells, thus excluding any specific requisite in this respect. (4) When 3H‐TdR was made continuously available to the cultures, starting at the time of confrontation between heart and liver tissues, unlabelled as well as labelled invasive hepatocytes were found inside the PHF in about equal proportions. It is concluded that nodular hepatocytes deviate from normality by at least 2 different properties that may or may not be related to each other and are revealed under in vitro conditions, namely the ability to survive and to proceed through S‐phase and mitosis under such conditions and to actively invade precultured chick heart fragments. The latter property indicates that at least some of the nodules contain hepatocytes that have performed one step in malignant progression.