Chelidonine is a cholinesterase or acetylcholinesterase (AChE) inhibitor. A cholinesterase inhibitor (or 'anticholinesterase') suppresses the action of acetylcholinesterase. Because of its essential function, chemicals that interfere with the action of acetylcholinesterase are potent neurotoxins, causing excessive salivation and eye-watering in low doses, followed by muscle spasms and ultimately death.  Nerve gases and many substances used in insecticides have been shown to act by binding a serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. Acetylcholine esterase breaks down the neurotransmitter acetylcholine, which is released at nerve and muscle junctions, in order to allow the muscle or organ to relax. The result of acetylcholine esterase inhibition is that acetylcholine builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop. Among the most common acetylcholinesterase inhibitors are phosphorus-based compounds, which are designed to bind to the active site of the enzyme. The structural requirements are a phosphorus atom bearing two lipophilic groups, a leaving group (such as a halide or thiocyanate), and a terminal oxygen.
Chelidonine has an acetylcholinesterase and butyrylcholinesterase inhibitory activity. (Wikipedia)
Generally, some of the alkaloid extract from Chelidonium majus, which contains protoberberine and benzo[c]phenanthridine alkaloids such as chelidonine, intercalate DNA, and in consequence inhibit DNA and RNA polymerase, topoisomerase, telomerase, and even ribosomal protein biosynthesis or bind to tubulin/microtubules, thus acting as spindle poisons. Chelidonine has the ability to overcome multidrug resistance (MDR) of different cancer cell lines through interaction with ABC-transporters, CYP3A4 and GST, by induction of apoptosis, and cytotoxic effects. It induced apoptosis in MDR cells which was accompanied by an activation of caspase-3, -8,-6/9, and phosphatidyl serine (PS) exposure. (A15442) Chelidonine is known to cause mitotic arrest and to interact weakly with tubulin. Chelidonine has proven to be a weak inhibitor of cell growth in two normal (monkey kidney and Hs27), two transformed (Vero and Graham 293) and two malignant (WHCO5 and HeLa) cell lines. (A15443)