Camptothecins

Camptothecins act through DNA topoisomerase I (Top1), an enzyme essential for DNA replication and transcription[1][2]. Mechanistically, camptothecin, topotecan, and irinotecan stabilize Top1-DNA cleavable complexes, block DNA resealing, and generate replication-associated DNA double-strand breaks[3][4]. This Top1-focused mechanism distinguishes camptothecins from Top2 inhibitors, which can induce DNA damage in both replicating and non-replicating cells[3]. In intact cells, topotecan-induced Top1-DNA covalent complexes can be detected by immunoblotting, immunofluorescence, or flow cytometry, supporting mechanism-based pharmacodynamic analysis[5]. In cancer models, ATR inhibition sensitizes cells to camptothecin-class Top1 inhibitors by disabling DNA replication initiation and fork elongation responses[6]. Camptothecin derivatives also poison Leishmania DNA topoisomerase IB and reduce parasitic burden in infected splenocytes[7]. For colorectal cancer research, SN-38 suppresses Nrf2 transcriptional activity and can enhance sensitivity to Nrf2-sensitive anticancer drugs[8].
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