Effect of DNA topoisomerase I inhibitor, 10-hydroxycamptothecin, on the structure and function of nuclei and nuclear matrix in bladder carcinoma MBT-2 cells

The effects of 10-hydroxycamptothecin (HCPT), a DNA topoisomerase I inhibitor, on the structure of nuclei and nuclear matrix and new DNA replication was investigated in murine bladder carcinoma MBT-2 cells. Following 10-30 min exposure of exponentially growing cells to 10-50 μM HCPT, the rate of 2 min pulse-labeling with [³H]thymidine in whole nuclei, nonmatrix, and matrix fractions was markedly decreased in a concentration- and time-dependent manner. Reduction was highest in the nuclear matrix. After treatment of cultures with 50 μM HCPT for 10 min, inhibition of DNA synthesis was 60% in the nuclear matrix and 27% in the low-salt extract fraction tended to be stimulated after drug treatment. SDS-PAGE analysis of [³⁵S]methionine labeled proteins indicated that 50 μM HCPT decreased protein synthesis in the matrix and other nuclear subfractions. HCPT-induced ultrastructural changes in nuclei and nuclear matrix were similar to those typically associated with lesions of DNA replication or RNA transcription.