Pectinesterase Inhibitor from Jelly Fig (Ficus awkeotsang Makino) Achene Induces Apoptosis of Human Leukemic U937 Cells

: The antitumor activity of pectinesterase inhibitor (PEI), a group of cationic polypeptides, from jelly fig (Ficus awkeotsang Makino) achene was first examined as a treatment for leukemia in this study. PEI displayed strong growth inhibition against human leukemic U937 cells via induction of apoptosis in a dose‐ and time‐dependent manner. At a level of 50 μg/mL, PEI inhibited 90% of cell growth, and the concentration of PEI required to induce 50% of cell viability (LC50) was about 180 μg/mL. Meanwhile, cell cycle arrest at G2/M phase was observed when cells were incubated with 100 μg PEI/mL for 24 h. PEI displayed a dose‐dependent influence on mitochondria transmembrane potential (MTP, ΔΨm) of cells when detected by a flow cytometry. MTP of more than 50% cells was reduced when cells were incubated with PEI at levels higher than 50 μg PEI/mL for 24 h. In addition, PEI upregulated caspase‐3 activity. Taken together, PEI potently inhibited the proliferation of human leukemic U937 cells via cell cycle arrest and apoptosis in association with MTP reduction and caspase‐3 activation, respectively, and showed therapy potential for U937 cells.