Production of the antitumor compound deoxyharringtonine by suspension-culturedcells of Cephalotaxus hainanensis

Plant cell fermentation can be a sustainable biotechnological alternative to the wild collection of medicinal plants. As aparadigm, we explored the potential of using the highly endangered endemic tree Cephalotaxus hainanensis, which accumulatescephalotaxine esters—potent anticancer compounds. We successfully established a suspension cell line able to convert cephalotaxineinto its esters, including deoxyharringtonine, harringtonine, isoharringtonine and homoharringtonine at a remarkable maximalconversion rate of up to 86%, when supplemented with L-homoleucine, a precursor for the side chains of these esters. Furthermore, byadding elicitors, we were able to enhance the yield significantly beyond the values expected from the complete conversion of the addedcephalotaxine. In particular, the addition of silver nitrate allowed the production of up to 19 mg/L of deoxyharringtonine and 3.3 mg/L ofcephalotaxine, more than doubling the expected yield from the complete conversion of the fed precursor (10 mg/L cephalotaxine). Thus,these treatments not only promoted the bioconversion of exogenous cephalotaxine but also stimulated the biosynthesis of endogenouscephalotaxine. This stimulation required more than 5 days to become manifest. This is the first case where deoxyharringtonine couldbe produced by plant cell culture, paving the way for the commercial production of this valuable pharmaceutical compound whilesafeguarding the highly endangered and endemic population of the tree itself.