Areas of hyperplastic livers that acquire hyperbasophilic properties at advanced stages of carcinogenesis apparently represent the sites of neoplastic transformation, and hyperstaining of cytoplasmic RNA with basic dyes also characterizes the cancer cells. Estimations of the RNA content of cell fractions from normal rat liver and solid Novikoff hepatoma provided no evidence that the intense staining of cancer cells could be explained on the basis of an increase in cytoplasmic RNA content.

The possibility that cytoplasmic fractions of Novikoff hepatoma show greater affinity for basic dyes than corresponding normal fractions has been examined by means of a test-tube toluidine blue-binding assay. The results revealed that the dye-binding capacity of total cytoplasmic fractions from tumors is 75% higher than normal after Carnoy fixation which retains mostly ribosomal RNA. Assays on fresh ribosomes indicated that tumor ribosomes bind 71% more toluidine blue per mg of RNA than the ribosomal preparation from normal liver.

This study thus demonstrates a greater affinity of tumor RNA for basic dyes, and a comparison of biochemical and cytophotometric analyses suggests that an increase in basophilia by a factor of about 2 would be due to a qualitative alteration in ribosomal RNA molecules and/or ribosome structure in cancer cells.

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This work was supported by grants from the National Cancer Institute of Canada, Le Ministére des Affaires sociales du Québec, La Fondation J. H. Biermans and Les Fondations J. Rhéaume.

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