以往在迅速增殖的啮齿动物细胞中的研究表明，DNA 拓扑异构酶 I 抑制剂喜树碱（CPT）的致死效应取决于 DNA 复制的积极参与（Holm 等人，Cancer Res. 49:6365-6368; 1989）。本研究的目的是确定这种关系是否适用于生长缓慢的人类细胞。在我们目前的研究中，我们使用人类结肠癌细胞株 HT-29（45 小时的倍增时间）。通过 S 相合适模型或矩形合适模型分析，流式细胞仪确定 S 相细胞的百分比，预测指数增长 HT-29 细胞中有 21% 正在进行 DNA 复制。这些结果由溴脱氧尿嘧啶标记细胞的免疫荧光显微镜证实。根据这些发现，我们预计只有 20-30% 的细胞会对 CPT 的短暂处理（30 分钟）敏感。然而，90-95% 的 HT-29 细胞却被杀死了，这个表面上的不一致不是由于处理后细胞保留药物时间过长所致，因为药物移除后蛋白质连接的 DNA 链断裂在 15 分钟内就发生了逆转。此外，DNA 复制抑制剂蚜脲霉素完全保护 HT-29 细胞免受 CPT 引起的杀伤，但不影响 CPT 引起的蛋白质联结 DNA 链断裂。使用 CPT 类似物 10,11-二氧杂喜树碱也取得了类似的结果，其比喜树碱更强 5-10 倍（O'Connor 等人，Cancer Commun. 2:395-400; 1990）。

Previous studies in rapidly proliferating rodent cells have suggested that the lethal effect of the DNA topoisomerase I inhibitor, camptothecin (CPT) is dependent upon the active participation of DNA replication (Holm et al. Cancer Res. 49:6365-6368; 1989). The purpose of the current study was to determine if this relationship applies to more slowly growing human cells. In our present study, we employed the human colon carcinoma cell line, HT-29 (45 hr doubling time). Flow cytometric determination of S-phase cells either by S-phase fit model or rectangle fit model analysis predicted that 21% of exponentially growing HT-29 cells were undergoing DNA replication. These findings were confirmed by immunofluorescence microscopy of bromodeoxyuridine labeled cells. Based on these findings, we would have expected only 20-30% of the cells to be susceptible to brief treatment (30 min) with CPT. Instead, 90-95% of HT-29 cells were killed. This apparent disparity was not due to prolonged cellular retention of drug after treatment because protein-linked DNA strand breaks reversed within 15 min of drug removal. Moreover, the DNA replication inhibitor, aphidicolin, fully protected HT-29 cells against CPT-induced killing but did not affect the production of CPT-induced protein-linked DNA strand breaks. Similar results were also obtained using the CPT-analog, 10,11-methylenedioxy-camptothecin, which was 5- to 10-fold more potent than camptothecin (O'Connor et al. Cancer Commun. 2:395-400; 1990).(ABSTRACT TRUNCATED AT 250 WORDS)