Mitocans induce lipid flip-flop and permeabilize the membrane to signal apoptosis.

Pancratistatin (PST) and narciclasine (NRC) are natural therapeutic agents that exhibit specificity toward the mitochondria of cancerous cells and initiate apoptosis. Unlike traditional cancer therapeutic agents, PST and NRC are effective, targeted, and have limited adverse effects on neighboring healthy, noncancerous cells. Currently, the mechanistic pathway of action for PST and NRC remains elusive, which in part inhibits PST and NRC from becoming efficacious therapeutic alternatives. Herein, we use neutron and x-ray scattering in combination with calcein leakage assays to characterize the effects of PST, NRC, and tamoxifen (TAM) on a biomimetic model membrane. We report an increase in lipid flip-flop half-times (t) (≈12.0%, ≈35.1%, and a decrease of ≈45.7%) with 2 mol percent PST, NRC, and TAM respectively. An increase in bilayer thickness (≈6.3%, ≈7.8%, and ≈7.8%) with 2 mol percent PST, NRC, and TAM, respectively, was also observed. Lastly, increases in membrane leakage (≈31.7%, ≈37.0%, and ≈34.4%) with 2 mol percent PST, NRC, and TAM, respectively, were seen. Considering the maintenance of an asymmetric lipid composition across the outer mitochondrial membrane (OMM) is crucial to eukaryotic cellular homeostasis and survival, our results suggest PST and NRC may play a role in disrupting the native distribution of lipids within the OMM. A possible mechanism of action for PST- and NRC-induced mitochondrial apoptosis is proposed via the redistribution of the native OMM lipid organization and through OMM permeabilization.