[{"from": "human", "value": "Describe this molecule. [C][C][C@@][Branch2][Ring2][=Branch1][C][=C][Branch1][#Branch1][C][O][C][Ring1][=Branch1][=O][C][=Branch1][C][=O][N][C][C][=C][C][=C][C][=C][C][=C][Ring1][=Branch1][N][=C][Ring1][#Branch2][C][Ring1][=N][=C][Ring2][Ring1][=Branch1][O]"}, {"from": "gpt", "value": "The molecule is an alkaloid isolated from the Chinese tree Camptotheca acuminata, with antineoplastic activity.  During the S phase of the cell cycle, camptothecin selectively stabilizes topoisomerase I-DNA covalent complexes, thereby inhibiting religation of topoisomerase I-mediated single-strand DNA breaks and producing potentially lethal double-strand DNA breaks when encountered by the DNA replication machinery. (NCI)"}]