The bark and stems of C. acuminata contain the alkaloid camptothecin. This alkaloid compound is used as an anti-cancer agent. It is a topoisomerase I inhibitor in DNA synthesis. Camptothecin has been shown to bind and stabilize a topoisomerase I-DNA complex in vitro, preventing the enzyme from reannealing DNA strands. This inhibition specifically effects the S-phase of cell development and ultimately results in apoptosis due to damaged DNA. Camptothecin is produced by endosymbiotic fungi, from the division Ascomycota (Phycomycete), that are present in the tree Camptotheca acuminata which is native to southern China.