In human breast (MCF-7), bladder (MGH-U1), and colon (HT-29) cancer cell lines, 9-Aminocamptothecin cytotoxicity increases with both higher drug concentrations and longer exposure times. Minimal cell killing is also observed unless 9-Aminocamptothecin concentrations exceeds a threshold of 2.7 nm. 9-Aminocamptothecin inhibits PC-3, PC-3M, DU145, and LNCaP cells with IC50 values of 34.1, 10, 6.5, and 8.9 nM, respectively after 96 h of drug exposure.