Hepatocellular carcinoma cells, unlike adjacent normal liver cells, resist the accumulation of extra storage iron when confronted with parental iron overload. The cause and consequences of this biochemical pathology of iron storage in neoplastic cells is unknown; moreover, the relationship between this abnormal iron metabolism and the correlated presence of inappropriately increased amounts of the iron-storage protein, ferritin, is not understood. The hypothesis that neoplasia causes abnormal iron metabolism will be tested by the proposed experiments. Both in vivo approaches with human and murine hepatoma systems will be utilized. The relative amounts of different types of storage iron formed before and after experimental iron overload in transplantable hepatomas and host liver will be measured with light microscope histochemistry, immunochemistry, and analytical chemistry. Immunocytochemistry will be used to compare the relative levels of ferritin in these same samples with and without iron overload. The actual uptake of injected iron-dextran and its resultant subcellular processing into ferritin and hemosiderin will be measured in hepatoma and liver cells by electron microscopy. The major possibility that hepatoma cells have defective uptake of iron from the iron-transport protein, transferrin, will be tested by biochemical assays; analogous measurements will examine the subsequent movement of iron from transferrin into ferritin, and the ability of the tumor cells to release their internalized iron to extracellular transferrin. Corresponding experimental investigations also will be conducted with induced hepatocarcinogenesis, to evaluate the capacity for iron storage within the very earliest stages in the progression to hepatocellular neoplasia; the formation of increased ferritin and the coordinate presence of other normal or cancer-associated proteins (albumin, alpha-fetoprotein) will be examined in these very early tumor cells. The results obtained will provide important new information about the biochemical pathology of iron storage and iron proteins in liver cancer and hepatocarcinogenesis, and should be of value for new clinical approaches to its detection, diagnosis, and therapy. (W)
