DNA topoisomerases relax supercoiled DNA during replication, transcription, recombination, repair, and chromosome condensation. The relaxation of DNA supercoiling by topoisomerase I at single-strand breaks represents a target for anticancer agents to intercalate between DNA base pairs, leading to the activation of apoptotic and cell cycle arrest pathways. 9-amino Camptothecin is a topoisomerase I inhibitor that was developed as a more water-soluble analog of camptothecin . It is cytotoxic to HT-29 cells at an IC50 value of 19 nM, induces DNA damage in whole cells at a concentration of 85 nM, and demonstrates significant anti-tumor activity in clinical studies.
