New Diterpenoids from <i>Mesona procumbens</i> with Antiproliferative Activities Modulate Cell Cycle Arrest and Apoptosis in Human Leukemia Cancer Cells

Mesona procumbens is a popular material used in foods and herbal medicines in Asia for clearing heat and resolving toxins. However, phytochemical research on this plant is very rare. In this study, eleven new diterpenoids, mesonols A-K (1–11), comprising seven ent-kauranes, three ent-atisanes, and one sarcopetalane, were isolated from its methanolic extract. Structural elucidation of compounds 1–11 was performed by spectroscopic methods, especially 2D NMR, HRESIMS, and X-ray crystallographic analysis. All isolates were assessed for their antiproliferative activity, and compounds 1–4 showed potential antiproliferative activities against A549, Hep-3B, PC-3, HT29, and U937 cancer cells, with IC50 values ranging from 1.97 to 19.86 µM. The most active compounds, 1 and 2, were selected for further investigation of their effects on cell cycle progression, apoptosis, and ROS generation in U937 human leukemia cancer cells. Interestingly, it was found that compounds 1 and 2 induced antiproliferative effects in U937 cells through different mechanisms. Compound 1 caused cell cycle arrest at the G2/M phase and subsequent cell death in a dose- and time-dependent manner. However, 2-mediated antiproliferation of U937 cells triggered ROS-mediated mitochondrial-dependent apoptosis. These results provide insight into the molecular mechanism involved in the antiproliferative activities of compounds 1 and 2 in U937 cells. Altogether, the study showed that new diterpenoid compounds 1 and 2 from M. procumbens are potent and promising anticancer agents