Cell experiment:

The colorectal cancer (CRC) cells are seeded into 96-well culture plates at 5000 cells/well. The cells are treated with 0, 2.5, 5, and 7.5 μM Cucurbitacin E for 1-3 days. MTT dye (1 mg/mL) is added to each well for at least 4 h of treatment. The reaction is stopped by the addition of DMSO, and optical density is measured at 540 nm on a multi-well plate reader. Background absorbance of the medium in the absence of cells is subtracted. All samples are assayed in triplicate, and the mean for each experiment is calculated. Results are expressed as a percentage of control, which is considered as 100%. Each assay is carried out in triplicate, and the results are expressed as the mean[1].

Animal experiment:

Mice[2]C57BL/6 male mice are used. The mice are designated as metabolic syndrome mice (HFD-MetS-mice). Briefly, the mice are randomly assigned into two groups according to their diet for 8 weeks (n = 10-12): high fat diet group (HFD) (60% fat, 20% carbohydrate, 20% protein) or the matched low fat, standard diet group (SD) (10% fat, 70% carbohydrate, 20% protein). After eight weeks on high fat diet, the mice with significant obese phenotype and fasting blood glucose levels ≥126 mg/dL are considered MetS mice. The MetS mice are continued on the HFD throughout the study. The MetS mice are then randomly divided into three additional groups, according to the treatment administered by oral gavage for 10 weeks (n=10-12): a low dose 0.25 mg/kg/day of Cucurbitacin E designated as HFD+Cucurbitacin E (L) or high dose 0.5 mg/kg/day of Cucurbitacin E, designated as HFD+Cucurbitacin E (H) or 50 mg/kg/day Orlistat (HFD+Orlistat). Animals on SD are administered 0.5% CMC by oral gavage[2].

Cucurbitacin E, a widely available plant-derived natural product, is a useful tool to study actin dynamics in cells and actin-based processes such as cytokinesis [1].

In vitro: In assays using pure fluorescently labeled actin, Cucurbitacin E affected depolymerization without affecting the polymerization. It inhibited actin depolymerization at substoichiometric concentrations up to 1:6 cucurbitacin E:actin. Cucurbitacin E specifically bound to F-actin to form a covalent bond at residue Cys257, but not to monomeric actin (G-actin) [1]. In human leukemia HL-60 cells, Cucurbitacin E (3-50 nmol/l) inhibited the growth of HL-60 cells. At high concentrations (1-10 mol/l), Cucurbitacin E induced apoptosis of HL-60 cells and activation of caspase-3, 8 and 9. Jurkat leukemia cells with or without caspase-8 expression were nearly equally sensitive to cucurbitacin E-induced apoptosis[2]. Cucurbitacin E disrupted the actin cytoskeleton. In a series of cucurbitacin analogues, the anti-proliferative activity was correlated with the disruption of the F-actin cytoskeleton directly [3].

References:
[1]. Sorensen P M, Iacob R E, Fritzsche M, et al. The natural product cucurbitacin E inhibits depolymerization of actin filaments[J]. ACS chemical biology, 2012, 7(9): 1502-1508.
[2]. Li Y, Wang R, Ma E, et al. The induction of G2/M cell-cycle arrest and apoptosis by cucurbitacin E is associated with increased phosphorylation of eIF2α in leukemia cells[J]. Anti-cancer drugs, 2010, 21(4): 389-400.
[3]. Duncan K L K, Duncan M D, Alley M C, et al. Cucurbitacin E-induced disruption of the actin and vimentin cytoskeleton in prostate carcinoma cells[J]. Biochemical pharmacology, 1996, 52(10): 1553-1560.