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Gambogic acid is a xanthone that is derived from the brownish or orange resin from Garcinia hanburyi. This natural chemical has shown promising antitumor activity in clinical trials with mice. Garcinia hanburyi is a small to medium sized evergreen tree (up to approximately 15 m in height) with smooth grey bark. It is native to Cambodia, southern Vietnam, and Thailand and has been successfully introduced in Singapore.

Original uses
Gambogic acid is the principal pigment of gamboge resin which, in addition to early medicinal uses in Southeast Asia, is also a sought after dye due to the bright orange color it imparts to cloth. According to traditional Chinese medical documentation, gamboge was described as poisonous and acidic and possessed the ability to detoxify, kill parasites, and stop bleeding as a hemostatic agent. Gambogic acid has also been used in various food preparations in Asian cultures.

Medical uses
Gambogic acid shows promising results as a treatment cancerous tumors and as an anti-inflammatory agent.

Effects on tumor growth
In studies conducted with mice and transplanted tumors (from human lung carcinoma SPC-A1 cells), tumor growth remained suppressed for up to 21 days during treatment with gambogic acid. The ratio of relative tumor volume (RTV) for the treated group of mice to the control group indicates the gambogic acid was having an impact on tumor size while having no adverse effects on body weight or mortality. Tumor volume was measured twice each week during the study, and the ratio of treated to control group tumor volume ranged from 45.0% to 72.7% for the 8 mg/kg dose and from 55.6% to 78.8% for the 4mg/kg dose. Tumor growth rate shows a dependence on the dose of gambogic acid, with the 8 mg/kg dose providing improved results at suppressing tumor growth in these trials.

Effects on cell growth
The effect of gambogic acid on the growth of SPC-A1 cells was also investigated. Cells were cultured with various concentrations of gambogic acid, and then living cells were counted. The results indicate that both the concentration of gambogic acid used to treat the cells as well as the length of treatment affected the growth inhibiting factor. For the same length of exposure, the higher the concentration of gambogic acid that was administered, the greater the effect on inhibiting cell growth. When comparing cultures at the same dose, the longer the cells were exposed to gambogic acid, the higher the growth inhibition. Results indicate that cell growth is dependent on both the magnitude of the dose administered as well as the length of time exposed to gambogic acid.

Effects on telomerase activity
Enhanced telomerase activity can be an indicator of abnormal cells. Most normal tissues have inactivated or repressed telomerase activity, but it becomes activated in germ cells and most malignant tumors. Treatment of SPC-A1 cells with gambogic acid resulted in a significant decline in telomerase activity when treated for 48 or 72 hours (detecting 80.7% and 84.9% reduction in activity, respectively). When treated with gambogic acid for only 24 hours, the decrease was only 25.9% which led researchers to believe there are at least two mechanisms responsible for slowing cell growth.

Current research
Current research is focusing on the mechanisms involved with gambogic acid's antitumor activity. Results are supporting the hypothesis that gambogic acid works to suppress nuclear factor-κΒ (NF-κΒ) activation that is induced by various inflammatory agents and carcinogens. Gambogic acid has also been found to bind to transferrin receptor1 (TfR) and rapidly induce cell apoptosis without competing with the transferrin (Tf) binding site. A brief exposure to this compound resulted in a rapid start to apoptosis, including membrane blebbing within 15 minutes.

Toxicity
Gambogic acid has proven to be minimally toxic in trials so far. Analyzing the mice that received the 4 mg/kg and 8 mg/kg doses, there was no substantial weight loss, no gastrointestinal reactions to medication, no obvious changes in any vital organs, and no fatalities. Previous toxicity experiments at the 30 mg/kg and 60 mg/kg level also concluded that there were no significant changes to vital organs (such as the liver, heart, spleen, kidneys, lungs, testicles, and uterus) as well as no changes in body weight or white blood cells in peripheral blood. At the highest level of 120 mg/kg the primary toxic target organs were the liver and kidneys.