Camptothecin Production and Biosynthesis in Plant Cell Cultures

Abstract

Camptothecin, a well-known monoterpenoid indole alkaloid originally identified in the extracts of the Chinese tree Camptotheca acuminata (Nyssaceae), exhibits antitumor activity due to its ability to kill cancer cells via topoisomerase I poisoning. Other plant species have since been shown to produce camptothecin and related compounds. In particular, Ophiorrhiza species (Rubiaceae) are important resources for the production of various alkaloids, including camptothecin. This chapter describes the production of camptothecin-related alkaloids and the elucidation of the mechanisms of camptothecin biosynthesis using plant cell and tissue cultures. In particular, aseptically grown plants, callus cultures, and hairy root cultures were established for several species, O. liukiuensis, O. kuroiwai, and O. pumila, which were then evaluated for production of camptothecin and related alkaloids. The metabolite profiles differed between the species, and between tissues of the same species; for example, profiles from hairy roots were not identical to those of aseptic plants. The complementary DNAs (cDNAs) for strictosidine synthase, tryptophan decarboxylase, and cytochrome P450 reductase were cloned from O. pumila and evaluated for involvement in production of camptothecin in this species. RNA interference (RNAi)-mediated knockdown of gene expression indicated that the production of camptothecin, strictosidine, and camptothecin-related alkaloids was suppressed in a TDC expression-dependent manner in RNAi hairy roots.