Microfluorometric comparisons of heat-induced nuclear acridine orange metachromasia between normal cells and neoplastic cells from primary tumors of diverse origin.

Nuclear fluorescence metachromasia of heated fixed cells subsequently stained with acridine orange was compared in smears and isolated nuclei of various types of primary tumors and normal cells from the tissues that gave rise to the tumors. The ratios of fluorescence emission at 590 and 530 nm reflect the thermal stability of chromatin in situ. The results show that the mean thermal stability of the chromatin in neoplastic cells was lower than the stability of their normal counterparts in all cases. This was found in both spontaneous and chemically induced tumors as divergent in type as a dog vaginal tumor and murine lymphocytic leukemia. These data, together with our previous observations in other neoplastic systems, indicate that reduced chromatin thermal stability may be a general characteristic of cells that have undergone neoplastic transformation and is not confined to rapidly growing tumors. The present investigation identifies the sources of variability encountered in measuring fluorescence metachromasia in slide preparations, and methods of minimizing this variability for potential cytodiagnostic application are discussed.