Nucleolar Fragmentation in L Cells Exposed to Quinacrine in Vitro¹ Free

Quinacrine (15 µg/ml) has been demonstrated by phase contrast and electron microscopy to produce nuclear changes in L strain fibroblasts in vitro. Within 30 minutes after exposure to quinacrine, apparent fragmentation of nucleoli is visible under phase microscopy. Early ultrastructural changes in nuclei after quinacrine exposure show segregation of the fibrillar components in the nucleolus and margination of chromatin around the nuclear membrane. Two hours after drug exposure there is fragmentation of the nucleolus; masses of fibrillar components and increased numbers of interchromatinic granules are prominent. When cells are exposed to 15 µg/ml of quinacrine for two hours and then washed and incubated in drug-free medium, they survive, but 24 hours later structural nucleolar abnormalities persist in some cells. The structural changes in L cell nuclei are presumably related to the known binding of quinacrine to DNA.