Pifithrin-alpha is a small molecule p53 functional inhibitor reported to behave like an antiapoptotic agent in neurodegenerative models. Pifithrin-alpha is a prodrug that under physiological conditions spontaneously undergoes ring closure to yield pifithrin-beta. Pifithrin-beta demonstrated antiproliferative and neuroprotective effects in vitro. Pifithrin-beta is able to activate the aryl hydrocarbon receptor (AhR) in a complete independent way of the p53 inhibition.

Calactin and calotropin were the major cardenolides in Danaus plexippus reared on A. fruticosa or A. curassavica. It was discovered, that calactin could be potential anticancer compound that was supported for human leukemia cells. It was shown, that calactin decreased the expression of cell cycle regulatory proteins Cyclin B1, Cdk1, and Cdc25C was consistent with a G2/M phase arrest. Furthermore, calactin induced extracellular signal-regulated kinase (ERK) phosphorylation, activation of caspase-3, caspase-8, and caspase-9, and PARP cleavage.