Stimulation of topoisomerase II-mediated DNA cleavage by three DNA-intercalating plant alkaloids: Cryptolepine, matadine, and serpentine

Cryptolepine, matadine, and serpentine are three indoloquinoline alkaloids isolated from the roots of African plants: Cryptolepis sanguinolenta, Stryc hnos gossweileri, and Rauwolfia serpentina respectively. For a long time, t hese alkaloids have been used in African folk medicine in the form of plant extracts for the treatment of multiple diseases, in particular as antimala rial drugs. To date, the molecular basis for their diverse biological effec ts remains poorly understood. To elucidate their mechanism of action, we st udied their interaction with DNA and their effects on topoisomerase II. The strength and mode of binding to DNA of the three alkaloids were investigat ed by spectroscopy. The alkaloids bind tightly to DNA and behave as typical intercalating agents, All three compounds stabilize the topoisomerase II-D NA covalent complex and stimulate the cutting of DNA by topoisomerase Il. T he poisoning effect is more pronounced with cryptolepine than with matadine and serpentine, but none of the drugs exhibit a preference for cutting at a specific base. Cryptolepine which binds 10-fold more tightly to DNA than the two related alkaloids proves to be much more cytotoxic toward B16 melan oma cells than matadine and serpentine. The cellular consequences of the in hibition of topoisomerase II by cryptolepine were investigated using the HL 60 leukemia cell line. The flow cytometry analysis shows that the drug alte rs the cell cycle distribution, but no sign of drug-induced apoptosis was d etected when evaluating the internucleosomal fragmentation of DNA in cells. Cryptolepine-treated cells probably die via necrosis rather than via apopt osis, The results provide evidence that DNA and topoisomerase II are the pr imary targets of cryptolepine, matadine, and serpentine.