Luotonin A is an alkaloid originally isolated from a plant used in traditional Chinese medicine. It inhibits the growth of mouse leukemia P388 cells (IC = 1.8 μg/ml). Luotonin A is structurally similar to the alkaloid camptothecin and, like camptothecin, it binds to and stabilizes the topoisomerase I-DNA binary complex, leading to DNA breakage and cell death (IC = 5.07-12.6 μM). Also like camptothecin, luotonin A forms non-covalent complexes with double-stranded DNA in the minor groove and this association can be followed by native fluorescence associated with the aromatic and heterocyclic ring structure. Luotonin A also selectively inhibits the cytochrome P450 (CYP) isoforms CYP1A1 and CYP1A2 (IC = ~6 μM for each) in human liver microsomes.