gambogic-acid and Colonic-Neoplasms

Certain natural products such as gambogic acid (GA) exhibit potent antitumor effects. Unfortunately, administration of these natural products is limited by their poor solubility in conventional pharmaceutical solvents. In this study, a series of telodendrimers, composed of linear polyethylene glycol (PEG)-blocking-dendritic oligomer of cholic acid (CA) and vitamin E (VE), have been designed with architectures optimized for efficient delivery of GA and other natural anticancer compounds. Two of the telodendrimers with segregated CA and VE domains self-assembled into stable cylindrical and/or spherical nanoparticles (NPs) after being loaded with GA as observed under transmission electron microscopy (TEM), which correlated with the dynamic light scattering (DLS) analysis of sub-30 nm particle sizes. A very high GA loading capacity (3:10 drug/polymer w/w) and sustained drug release were achieved with the optimized telodendrimers. These novel nanoformulations of GA were found to exhibit similar in vitro cytotoxic activity against colon cancer cells as the free drug. Near-infrared fluorescence small animal imaging revealed preferential accumulation of GA-loaded NPs into tumor tissue. The optimized nanoformulation of GA achieved superior antitumor efficacy compared to GA-Cremophor EL formulation at equivalent doses in HT-29 human colon cancer xenograft mouse models. Given the mild adverse effects associated with this natural compound and the enhanced anticancer effects via tumor targeted telodendrimer delivery, the optimized GA nanoformulation is a promising alternative to the traditional chemotherapy in colon cancer treatment.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Colonic Neoplasms; Dendrimers; Drug Carriers; Drug Delivery Systems; Drug Design; Female; HCT116 Cells; Hemolysis; Humans; Light; MCF-7 Cells; Mice; Mice, Nude; Micelles; Microscopy, Confocal; Microscopy, Electron, Transmission; Nanoparticles; Neoplasm Transplantation; Polyethylene Glycols; Scattering, Radiation; Solubility; Vitamin E; Xanthones

To investigate the effects of gambognic acid (GA) on TRAIL-induced apoptosis of cancer cells, human colon HT-29 cancer cells were treated with GA to promote apoptosis. Inhibition of the cell proliferation was measured with MTT assay and cell apoptosis was detected with formation of DNA ladders in agarose gel electrophoresis, and activation of caspase activity. The content of cytosolic reactive oxygen species (ROS) was measured with flow cytometry. The activities of Caspase-3, -8, -9 were detected using spectrophotometric assay. The levels of c-FLIP, CHOP, DR4 and DR5 in cells were tested by Western blot. Combination of GA (1 µg · mL(-1)) and TRAIL (40 ng · mL(-1)) significantly reduced proliferation and increased apoptosis of HT-29 cells over those induced by each agent alone. Percentage of apoptotic cells was increased to 45.5%. GA markedly enhanced the intracellular ROS generation. Expression of CHOP, DR4 and DR5 was up-regulated to 7.38, 5.41, and 4.85 times of the control group, respectively. GA promoted activation of Caspase-3, -8, and -9 by TRAIL (P<0.05). Furthermore, the expression of anti-apoptotic protein c-FLIP was down-regulated to 0.22 ± 0.08 times of the control group. In conclusion, GA sensitizes HT-29 cells to TRAIL-induced apoptosis by promoting ROS-activated ERS pathways, up-regulating of DR4 and DR5, and inhibiting c-FLIP expression.

Topics: Apoptosis; Apoptosis Regulatory Proteins; Caspases; Cell Line, Tumor; Cell Proliferation; Colonic Neoplasms; Down-Regulation; HT29 Cells; Humans; Reactive Oxygen Species; TNF-Related Apoptosis-Inducing Ligand; Up-Regulation; Xanthones