The long-term culture of a diploid rat hepatocyte cell strain.

We have developed a cell culture system of cloned rat hepatocytes which is named RL-PR-C. This culture has been grown in culture for over 150 passages (560 p.d.). It remains diploid by modal number count for over 50 passages (183 p.d.) after which there is a variation in the modal number between 41 and 42. The culture becomes intrinsically (spontaneously) malignantly transformed at about this time whereas cells treated with aflatoxin B1, at subacute and subtoxic doses, from Passage 12(65 p.d.) were malignantly transformed at Passage 35(135 p.d.). Evidence indicates that not all cells in the population are malignantly transformed. Back injection of mixed population of malignantly transformed cells into isogenic rat pups, yield tumors which are histologically classified as mixed. That is, areas of the same tissue slice exhibit both carcinomas and sarcoma characteristics. Data obtained by injection of clones derived from malignantly transformed cells suggest that the cells injected are multipotent with respect to the type of tumor formed. Further investigations are continuing in this regard. This cultural system will be used to study the evolution and maintenance of the transformed state and to develop a test system for putative carcinogens and mutagens.