Electron microscopic localization of acridine orange binding to DNA within various human brain tumor cells.

The ultracytochemical acridine orange (AO) method has been employed to demonstrate DNA template activity within untreated human brain tumors. A total of 16 biopsies from brain tumors removed for frozen section examination were investigated. Ultrastructural examination revealed that AO binds to DNA exclusively within the extended euchromatin portion of the cell nucleus of brain tumors. The percentage of AO positive cells varied from 6.0 to 48.6% in various types of brain tumors. A few AO reaction products were visible in the nuclei of the endothelial cells and in the pericytes of the capillaries within neoplastic tissue. The present results suggested that untreated human brain tumors exhibit de-repression of DNA template normally repressed in the adult state. This altered DNA templates may be related to abnormal cell proliferation and differentiation diverted from the normal state.