By Vince Giuliano
This is the third post in a three-part series concerned with new, emerging and potential future treatments for cancers. This Part 3 post relates to a vast and largely unknown area from the viewpoint of Western medicine. The area is that of traditional Chinese herbal substances that have also been extensively researched only in China, but using the latest tools and intellectual frameworks of Western science and shown to have anti-cancer properties. In previous blog entries I have discussed a number of traditional Chinese herbal medicines such as curcumin, ginger, danshen root and epimedium. On this blog entry, emphasis will on an additional substances with anti-cancer properties, ones derived from gamboge resin. Again, you will note that the area of interest is “hot” with many of the publications published in 2012 and a few just last week.
The Part 1 post in this series is concerned principally with anti-cancer interventions that address the mTOR pathway, a growth pathway also of great interest from the viewpoint of longevity. That post also at least partially explains why certain familiar substances like aspirin, coffee, curcumin, resveratrol and green tea may convey both protection against cancers and a longevity benefit.
The Part 2 post in this series is concerned with mainline anti-cancer drug interventions that simultaneously address multiple growth pathways, ones that are entering clinical practice.
The Part 1 and Part 2 posts are about hot areas of intensive research as well as practical clinical experimentation. This Part 3 blog entry is concerned with a selected less-known phytochemicals that have long been used in traditional Chinese medicine and that in recent years have been subjected to research scrutiny in China. They are not well-known in Western circles and have not been subjected to clinical trials.
Background on traditional Chinese medicines
Many traditional Chinese medicines have been extensively studied in China during the last 10-20 years using the current tools and intellectual frameworks of modern Western science. These medicines have been looked at in terms of their detailed chemical structures, their proteomic properties, the molecular biological pathways through which they work, their gene activation and epigenetic properties, their pharmacological properties, etc, This work has generally been of high quality and has resulted in thousands or tens of thousands of research reports, many of them published in highly respected Western journals. Abstracts to these publications can be found in the definitive US National Library of Medicine database pubmed.org.
However, availability of this information does not necessarily mean it is read or paid attention to be non-Asian researchers or practitioners. In general, those medicines that have been studied are ones known to be efficacious in traditional Chinese practices but are not used in Western medical clinical practices. Also, the Chinese research appears to be heavily oriented to molecular biology and in-vitro studies, infrequently involves animal experiments, and generally stops short of clinical trials.
A good place to start is with the July 2011 e-publication Anti-cancer natural products isolated from chinese medicinal herbs, as to be expected written by a team of Chinese researchers. “In recent years, a number of natural products isolated from Chinese herbs have been found to inhibit proliferation, induce apoptosis, suppress angiogenesis, retard metastasis and enhance chemotherapy, exhibiting anti-cancer potential both in vitro and in vivo. This article summarizes recent advances in in vitro and in vivo research on the anti-cancer effects and related mechanisms of some promising natural products. These natural products are also reviewed for their therapeutic potentials, including flavonoids (gambogic acid, curcumin, wogonin and silibinin), alkaloids (berberine), terpenes (artemisinin, β-elemene, oridonin, triptolide, and ursolic acid), quinones (shikonin and emodin) and saponins (ginsenoside Rg3), which are isolated from Chinese medicinal herbs. In particular, the discovery of the new use of artemisinin derivatives as excellent anti-cancer drugs is also reviewed. — Surgery, chemotherapy and radiotherapy are the main conventional cancer treatment often supplemented by other complementary and alternative therapies in China . While chemotherapy is one of the most extensively studied methods in anti-cancer therapies, its efficacy and safety remain a primary concern as toxicity and other side effects of chemotherapy are severe. Moreover, multi-drug resistant cancer is even a bigger challenge. Medicinal herbs are main sources of new drugs. Newman et al. reported that more than half of the new chemicals approved between 1982 and 2002 were derived directly or indirectly from natural products . Some active compounds have been isolated from Chinese medicinal herbs and tested for anti-cancer effects. For example, β-elemene, a compound isolated from Curcuma wenyujin Y. H. Chen et C. Ling (Wenyujin), is used as an anti-cancer drug in China. For this study, we searched three databases, namely PubMed, Scopus and Web of Science, using keywords “cancer”, “tumor”, “neoplastic” and “Chinese herbs” or “Chinese medicine”. Publications including research and review papers covered in this review were dated between 1987 and 2011, the majority of which were published between 2007 and 2011. Chinese herb-derived ingredients, including flavonoids, alkaloids, terpenes, quinones and saponins, were found.”
The March 2012 review article Fighting fire with fire: poisonous Chinese herbal medicine for cancer therapy reports: “Ethnopharmacological Relevance: Following the known principle of “fighting fire with fire”, poisonous Chinese herbal medicine (PCHM) has been historically used in cancer therapies by skilled Chinese practitioners for thousands of years. In fact, most of the marketed natural anti-cancer compounds (e.g., camptothecin derivatives, vinca alkaloids, etc.) are often known in traditional Chinese medicine (TCM) and recorded as poisonous herbs as well. Inspired by the encouraging precedents, significant researches into the potential of novel anticancer drugs from other PCHM-derived natural products have been ongoing for several years and PCHM is increasingly being recognized as a gathering place for promising anti-cancer drugs. The present review aimed at giving a rational understanding of the toxicity of PCHM and, especially, providing the most recent developments on PCHM-derived anti-cancer compounds. Materials and Methods: Information on the toxicity and safety control of PCHM, as well as PCHM-derived anti-cancer compounds, was gathered from the articles, books and monographs published in the past 20 years. Results: Based on an objective introduction to the CHM toxicity, we clarified the general misconceptions about the safety of CHM and summarized the traditional experiences in dealing with the toxicity. Several PCHM-derived compounds, namely gambogic acid, triptolide, arsenic trioxide, and cantharidin, were selected as representatives, and their traditional usage and mechanism of anti-cancer actions were discussed. Conclusions: Natural products derived from PCHM are of extreme importance in devising new drugs and providing unique ideas for the war against cancer. To fully exploit the potential of PCHM in cancer therapy, more attentions are advocated to be focused on their safety evaluation and mechanism exploration.”
Traditional Chinese medicines tend to fall into three categories when looked at from a US perspective:
a) The substances have been researched almost exclusively in China or Asia, that are little or not known to either our Western research or clinical practice establishments. And, in the US and Europe, the benefits of these substances are at best known to only a handful of alternative health practitioners. One example I have discussed in this blog is danshen root. See the blog entry Focus on phytosubstances – Danshen root – amazing properties of salvia miltiorrhiza Bunge. Almost all of the 1684 publications are written by researchers in China, complemented by a few written by researchers in Korea.
b) Substances like in category a) and studied only by Chinese but somewhat widely used as supplements in the US and Western countries, basically purchased only for a single benefit. A good example is epimedium, discussed in the blog entry Focus on phytosubstances – amazing properties of epimedium and icariin. Though epimedium appears to offer a broad spectrum of health benefits and may have many medical applications, in the US it is purchased mainly as an aphrodisiac and is sold as Horny Goat Weed.
c) Substances that have also been widely studied in Western research laboratories as well as Chinese ones and that are more-generally acknowledged to have significant curative powers though they are not part of mainline Western medical practice. These may be widely used as dietary supplements. A good example that I have written about frequently in this blog is curcumin. For example, see Cancer, epigenetics and dietary substances and Dietary factors and dementia – Part 3: plant-derived substances that can make a difference. In some cases these substances or drug analogs of them have been the subject of clinical trials. The clinicaltrials.gov database lists 68 clinical trials related to curcumin. Another good example is ginger. See the blog entry Focus on ginger. The clinicaltrials.gov database lists 43 clinical trials related to ginger.
The substance I selected specifically for discussion in this blog entry, gambogic and gambogenic acids, appear to be quite firmly in category a). Pubmed.org lists 126 research publications related to gamboic acid and 15 related to gambogenic acid, the vast majority of which being published within the last five years. And clinicaltrials.gov lists no clinical trials for either substance.
|About gambogic and gambogenic acidGambogic and gambogenic acids are Cytotoxicxanthonoids, two of many substances present in the resin from gamboge trees of the species Garcinia hanburyi. Gamboge is a traditional medicine based in a bark extract from the tree. Gambogenic acid and gamboic acid are two of the seventeen or more substances that can be isolated from the latex of the tree.
Garcinia hanburyi Image source: livejournal
The January 2012 publication Prenylated caged xanthones: chemistry and biologyis written by researchers in Thailand. “Context: Prenylated caged xanthones are “privileged structure” characterized by the presence of the unusual 4-oxo-tricyclo[184.108.40.206(3,7)]dec-8-en-2-one scaffold. The natural sources of these compounds confines mainly in the Garcinia genus in the family of Guttiferae. Gambogic acid is the most abundant substance and most of the studies have been done on this compound, particularly as a new potential antitumor agent. The history, sources, structural diversity, and biological activities of these compounds are covered. Objective: This review is written with the intention to provide additional aspects from what have been published of prenylated caged xanthones, including history, sources, structural diversity, and biological activities. Methods: This review has been compiled using information from a number of reliable references mainly from major databases including SciFinder, ScienceDirect, and PubMed. Results: More than 120 prenylated caged xanthones have been found in the plant genera Garcinia, Cratoxylum, and Dascymaschalon. These compounds exhibited various potentially useful biological activities such as anticancer, anti-HIV-1, antibacterial, anti-inflammatory, and neurotrophic activities. Conclusions: Prenylated caged xanthones, both naturally occurring and synthetic analogues, have been identified as promising bioactive compounds, especially for anticancer agents. Gambogic acid has been demonstrated to be a highly valuable lead compound for antitumor chemotherapy. The structure activity relationship (SAR) study of its analogues is still the subject of intensive research. Apoptosis cytotoxic mechanism has been identified as the major pathway. Research on the delineation of the in-depth mechanism of action is still on-going. Analogues of gambogic acid had been identified to be effective against a rare and special form of liver cancer, cholangiocarcinoma for which currently there is no chemotherapeutic treatment available.”
Biological anti-cancer activities activity of gambogic acid
A February 2012review article Gambogic Acid Is A Novel Anti-Cancer Agent That Inhibits Cell Proliferation, Angiogenesis And Metastasis sums the situation up: “Gambogic acid (GA) is a caged xanthone that is derived from Garcinia hanburyi and functions as a strong apoptotic inducer in many types of cancer cells. The distinct effectiveness of GA has led to its characterization as a novel anti-cancer agent. There is an increasing number of research studies focused on elucidating the molecular mechanisms of GA-induced anti-cancer effects, and several critical signaling pathways have been reported to be influenced by GA treatment. In this review, we summarize the multiple functional effects of GA administration in cancer cells including the induction of apoptosis, the inhibition of proliferation
From Anti-cancer natural products isolated from chinese medicinal herbs: GA (Figure (Figure1A)1A) is the principal active ingredient of gamboges which is the resin from various Garcinia species including Garcinia hanburyi Hook.f. (Tenghuang) . GA has various biological effects, such as anti-inflammatory, analgesic and anti-pyretic  as well as anti-cancer activities [4,5]. In vitro and in vivo studies have demonstrated its potential as an excellent cytotoxicity against a variety of malignant tumors, including glioblastoma, as well as cancers of the breast, lung and liver. GA is currently investigated in clinical trials in China [6–8].”
Continuing (ref), “GA induces apoptosis in various cancer cell types and the action mechanisms of GA remain unclear. Transferrin receptor (TfR) significantly over-expressed in a variety of cancers cells may be the primary target of GA . The binding of GA to TfR in a manner independent of the transferrin binding site, leading to the rapid apoptosis of tumor cells . Proteomics analysis suggests that stathmin may be another molecular target of GA . The importance of the role of p53 in GA-induced apoptosis remains controversial [5,10]. Furthermore, GA antagonizes the anti-apoptotic B-cell lymphoma 2 (Bcl-2) family of proteins and inhibits all six human Bcl-2 proteins to various extents, most potently inhibiting myeloid cell leukemia sequence 1 (Mcl-1) and Bcl-B, as evidenced by a half maximal inhibitory concentration (IC50) lower than 1 μM . Moreover, GA also influences other anti-cancer targets, such as nuclear factor-kappa B (NF-κB)  and topoisomerase IIα . — GA causes a dose-dependent suppression of cell invasion and inhibits lung metastases of MDA-MB-435 cells in vivo through protein kinase C (PKC)-mediated matrix metalloproteinase-2 (MMP-2) and matrix metallopeptidase-9 (MMP-9) inhibition . GA also exhibits significant anti-metastatic activities on B16-F10 melanoma cancer cells partially through the inhibition of the cell surface expression of integrin α4 in C57BL/6 mice . — Notably, the combination of GA with other compounds enhances their anti-cancer activities [15–17]. For example, He et al.  reports that proliferative inhibition and apoptosis induction are much more visibly increased when Tca8113 cells are treated with combined GA and celastrol, indicating that the combination of GA and celastrol can be a promising modality for treating oral squamous cell carcinoma. Another study showed that GA in combined use with 5-fluorouracil (5-FU) induced considerably higher apoptosis rates in BGC-823 human gastric cells and inhibited tumor growth in human xenografts . Furthermore, low concentrations of GA were found to cause a dramatic increase in docetaxel-induced cytotoxicity in docetaxel-resistant BGC-823/Doc cells . Magnetic nanoparticles of Fe3O4 (MNPs-Fe3O4) were reported to enhance GA-induced cytotoxicity and apoptosis in K562 human leukemia cells .”
The publications cited below are mostly recent, subsequent to those cited in the quote above.
Gambogic acid is a HSP90 inhibitor.
“Hsp90 (heat shock protein 90) is a molecular chaperone and is one of the most abundant proteins expressed in cells. It is a member of the heat shock protein family, which is upregulated in response to stress(ref).” Targeting HSP90 in cancer cells could reduce their resistance to chemotherapy agents. The 2011 publication Gambogic acid, a natural product inhibitor of Hsp90is a bit unique in that it was written by researchers at Oklahoma State University. “A high-throughput screening of natural product libraries identified (-)-gambogic acid (1), a component of the exudate of Garcinia harburyi, as a potential Hsp90 inhibitor, in addition to the known Hsp90 inhibitor celastrol (2). Subsequent testing established that 1 inhibited cell proliferation, brought about the degradation of Hsp90 client proteins in cultured cells, and induced the expression of Hsp70 and Hsp90, which are hallmarks of Hsp90 inhibition. Gambogic acid also disrupted the interaction of Hsp90, Hsp70, and Cdc37 with the heme-regulated eIF2α kinase (HRI, an Hsp90-dependent client) and blocked the maturation of HRI in vitro. Surface plasmon resonance spectroscopy indicated that 1 bound to the N-terminal domain of Hsp90 with a low micromolar Kd, in a manner that was not competitive with the Hsp90 inhibitor geldanamycin (3). Molecular docking experiments supported the posit that 1 binds Hsp90 at a site distinct from Hsp90s ATP binding pocket. The data obtained have firmly established 1 as a novel Hsp90 inhibitor and have provided evidence of a new site that can be targeted for the development of improved Hsp90 inhibitors.”
Gambogic acid can enhance the efficacy of chemotherapy agents for the treatment of gastric cancers.
The March 2012 publicationEnhancement of Anticancer Efficacy of Chemotherapeutics by Gambogic Acid Against Gastric Cancer Cells reports: “Gambogic acid (GA), the main active component of gamboge, is well known for its marked antitumor effect in vitro and in vivo. The aim of this study was to assess the natural interaction between GA and chemotherapeutic agents, 5-fluorouracil (5-FU), oxaliplatin (Oxa), and docetaxel (Doc), which are widely used in gastric cancer treatment. This study also investigated the effect of GA on cell apoptosis and drug-associated gene expression for further mechanism research. Synergistic interaction on human gastric cancer BGC-823 cells and MKN-28 cells was evaluated using the combination index (CI) method. The double staining method with Annexin-V-FITC and PI was employed to distinguish the apoptotic cells from others. Expression of drug-associated genes, that is, thymidylate synthase (TS), excision repair cross-complementing (ERCC1), BRCA1, tau, and β-tubulin III, was measured by real-time quantitative RT-PCR. This study found that GA had a synergistic effect on the cytotoxity of chemotherapeutic agents against both cell lines. The combination of GA and chemotherapeutic agents could also induce apoptosis in a synergistic manner. The mRNA levels of TS, ERCC1, BRCA1, tau, and β-tubulin III were suppressed at 0.009, 0.075, 0.140, 0.267, and 0.624-fold, respectively, when cells were exposed to GA at the concentration of 0.25 μM. These data suggest that GA has a promising role in enhancing the efficacy of 5-FU, Oxa, and Doc in the treatment of gastric cancer. The potential mechanism would be their synergistic effects on apoptosis induction and the downregulation of chemotherapeutic agent-associated genes.”
Gamboic acud may help prevent metastasis in human breast cancers.
The 2008 publication Involvement of matrix metalloproteinase 2 and 9 in gambogic acid induced suppression of MDA-MB-435 human breast carcinoma cell lung metastasisreported:.”Cancer cell invasion is one of the crucial events in local spreading, growth, and metastasis of tumors. The present study investigated the antiinvasive and antimetastatic action of gambogic acid (GA) in MDA-MB-435 human breast carcinoma cells. GA caused a concentration-dependent suppression of cell invasion through Matrigel and significantly inhibited lung metastases of the cells transplanted in vivo. The potent effects of GA have been attributed to its ability to reduce the expression of matrix metalloproteinases (MMP) 2 and 9 in vitro and in vivo both at the protein and mRNA levels, which were associated with protein kinase C (PKC) signaling pathway as supported by the diminished antiinvasive effect of GA in the presence of specific activator of the pathway. Collectively, our data demonstrated that GA exhibited antiinvasion properties on highly invasive cancer cells via PKC mediated MMP-2/9 expression inhibition. This indicated that GA can be served as a potential novel therapeutic candidate for the treatment of cancer metastasis.”
Gamboic acid may help prevent tumor metastasis in cholangiocarcinoma.
The 2011 publication Anti-migrative effect of gambogic acid in human cholangiocarcinoma KKU-M213 cellsreports: “Tumor metastasis is the most common cause of death in cancer patients. Cholangiocarcinoma (CCA) is a malignant tumor of bile duct epithelium with a slow growing but rapid and high metastasis. Recently, the antiinvasive effect of gambogic acid (GA) in human breast carcinoma cells was reported. In the present study, we investigated the anti-migrative effect of GA in CCA KKU-M213 cells by wound migration assay. We found that the KKU-M213 cells of the control group migrated into the wound area by 12 hours, whereas in the GA treated cells showed a delay in cell moving into the wound area in a dose-dependent manner. At the 0.6 and 1.2 μM of GA treatments, the migration area of treated cells was significantly decreased compared to the control cells. These results indicated that GA had a potential anti-migrative effect on KKU-M213 cells in vitro. Therefore, GA may deserve further exploration as an anti-metastatic agent against CCA.”
In prostate cancer cells in vitro, gambogenic acid inhibits activation in the of the PI3K/Akt and NF-κB signaling pathways, expression of TNF-α and invasion of PC3 cells
Another brand-new publication is the March 2012 item Gambogic acid inhibits TNF-α-induced invasion of human prostate cancer PC3 cells in vitro through PI3K/Akt and NF-κB signaling pathways. “Aim:To investigate the mechanisms underlying the inhibitory effect of gambogic acid (GA) on TNF-α-induced metastasis of human prostate cancer PC3 cells in vitro. Methods:TNF-α-mediated migration and invasion of PC3 cells was examined using migration and invasion assays, respectively. NF-κB transcriptional activity and nuclear translocation were analyzed with luciferase reporter gene assays, immunofluorescence assays and Western blots. The ability of p65 to bind the promoter of Snail, an important mesenchymal molecular marker, was detected using a chromatin immunoprecipitation (ChIP) assay. After treatment with Snail-specific siRNA, the expression of invasiveness-associated genes was measured using quantitative real-time PCR and Western blot. Results:GA significantly inhibited the viability of PC3 cells at 1-5 μmol/L, but did not produce cytotoxic effect at the concentrations below 0.5 μmol/L. GA (0.125-0.5 μmol/L) dose-dependently inhibited the migration and invasion of PC3 cells induced by TNF-α (10 ng/mL). Moreover, the TNF-α-mediated activation of phosphatidylinositol-3-OH kinase/protein kinase B (PI3K/Akt) and NF-κB pathways was suppressed by GA (0.5 μmol/L). Furthermore, this anti-invasion effect of GA was associated with regulation of Snail. Snail expression was significantly down-regulated by treatment with GA (0.5 μmol/L) in the TNF-α-stimulated PC3 cells. Conclusion:GA inhibits TNF-α-induced invasion of PC3 cells via inactivation of the PI3K/Akt and NF-κB signaling pathways, which may offer a novel approach for the treatment of human prostate cancer.”
Various cell-level studies have been directed at discovering the pathways through which gamboic and gambogenic acids leads to apoptosis of cancer cells.
One of the actions of gambonic acid in cancer cells is generation of mitochondrial stress leading to apoptosis, at least in HepG2 cells.
Another new March 2012 publication Gambogenic acid induced mitochondrial-dependent apoptosis and referred to Phospho-Erk1/2 and Phospho-p38 MAPK in human hepatoma HepG2 cells reports: “Gambogenic acid, identified from Gamboge, is responsible for anti-tumor effects, and has been shown to be a potential molecule against human cancers. In this study, the molecular mechanism of gambogenic acid-induced apoptosis in HepG2 cells was investigated. Gambogenic acid significantly inhibited cell proliferation and induced apoptosis. Acridine orange/ethidium bromide (AO/EB) staining was used to observe apoptosis, and then confirmed by transmission electron microscopy. Gambogenic acid induced apoptosis and morphological changes in mitochondria, and intracellular reactive oxygen species (ROS) and mitochondrial membrane permeabilization (MMP) in mitochondrial apoptosis pathway were also examined. Results showed that the levels of Phospho-p38 and its downstream Phospho-Erk1/2 of HepG2 cells increased in time- and concentration-dependent manners after gambogenic acid treatments. Additionally, gambogenic acid increased expression ratio of Bcl-2/Bax in mRNA levels, Western blotting analysis also further confirmed the reduced level of Bcl-2 and increase the expression level of Bax in HepG2 cells. These results indicated that gambogenic acid induced mitochondrial oxidative stress and activated caspases through a caspase-3 and caspase-9-dependent apoptosis pathway. Moreover, gambogenic acid mediated apoptosis and was involved in the Phospho-Erk1/2 and Phospho-p38 MAPK proteins expression changes in HepG2 cells.”
In MCF-7 breast cancer cells at least, the anti-cancer effect of neogamboic acid is due to the G(0)/G(1) arrest, increased apoptosis and activation of Fas/FasL and cytochrome C pathway.
The September 2011 publication The mechanism of neogambogic acid-induced apoptosis in human MCF-7 cells reports: “Neogambogic acid (NGA), an active ingredient in garcinia, can inhibit the growth of some solid tumors and result in an anticancer effect. We hypothesize that NGA may be responsible for the inhibition of proliferation of human breast cancer cell line MCF-7 cells. To investigate its anticancer mechanism in vitro, MCF-7 cells were treated with various concentrations of NGA. Results of MTT (methyl thiazolyl tetrazolum) assay showed that treatment with NGA significantly reduced the proliferation of MCF-7 cells in a dose-dependent manner. NGA could increase the expression of the apoptosis-related proteins FasL, caspase-3, caspase-8, caspase-9, and Bax and decrease the expression of anti-apoptotic protein Bcl-2 accompanied by the mitochondrial transmembrane damage. The antiproliferative effect of NGA on MCF-7 cells is due to the G(0)/G(1) arrest, increased apoptosis and activation of Fas/FasL and cytochrome C pathway. These results provide an important insight into the cellular and molecular mechanisms through which NGA impairs the proliferation of breast cancer cells.”
Another mechanism through which gambogenic acid leads to cancer apoptosis is inactivation of the Akt signaling pathway due to mitochondrial stress.
The February 2011 publication Gambogenic acid mediated apoptosis through the mitochondrial oxidative stress and inactivation of Akt signaling pathway in human nasopharyngeal carcinoma CNE-1 cells reports: “In the present study, Gambogenic acid exhibits potential anti-tumor activity in several cancer cell lines. However, Gambogenic acid-induced apoptosis mechanism is not well understood. Here, we report that Gambogenic acid was capable to induce CNE-1 cells apoptosis and caused mitochondrial and endoplasmic reticulum injury, analyzed via transmission electron microscopy and acridine orange/ethidium bromide (AO/EB) double staining. To quantitatively analyze apoptosis, through the propidium iodide (PI)/Annexin V-FITC double staining to detect cell apoptosis, PI staining of the cell cycle distribution. To further explore the potential mechanism of Gambogenic acid mediated apoptosis in CNE-1 cells, we also examined mitochondrial oxidative stress in the levels of reactive oxygen species, the release of cytochrome c, intracellular Ca(2+) concentration and mitochondrial membrane potential by flow cytometry. Moreover, Gambogenic acid could result in a time and concentration-dependent decrease in Phospho-Akt expression, basal expression levels of Akt change was not obvious, In addition, we detected Bcl-2 family including Bcl-2, Bax and Bad expression in mRNA level. This resulted in a decrease of Bcl-2 and Bad increased in CNE-1 cells after Gambogenic acid treatment. Overall, our results indicated that Gambogenic acid mediated apoptosis through inactivation of Akt, accompanied with mitochondrial oxidative stress and cross-talk with Bcl-2 family in the process of apoptosis.”
Gamboic acid derivatives may be useful for developing liver and osteosarcoma cancer treatments.
The January 2012 publication Synthesis and biological evaluation of novel derivatives of gambogic acid as anti-hepatocellular carcinoma agents reports: “A series of novel derivatives of gambogic acid (GA) were synthesized and evaluated for their in vitro cytotoxicity against human hepatocellular carcinoma (HCC) cells. All derivatives showed better aqueous solubility than GA, and compounds 3a, 3e, and 3f displayed potent inhibition of HCC cell proliferation (IC(50): 0.045-0.59 μM on Bel-7402 cells and 0.067-0.94 μM on HepG2 cells) superior to GA and taxol. Additionally, the most potent compound 3e did not affect significantly the proliferation of non-tumor liver cells, suggesting that it might selectively inhibit HCC proliferation. Furthermore, 3e induced high frequency of Bel-7402 cell apoptosis. Our findings suggest that these novel GA derivatives may hold a great promise as therapeutic agents for the intervention of human HCC.”
The 2011 publication Gambogic acid inhibits the growth of osteosarcoma cells in vitro by inducing apoptosis and cell cycle arrest reports: “The natural product gambogic acid (GA) has been demonstrated to be a promising chemotherapeutic drug for some cancers because of its ability to induce apoptosis and cell cycle arrest. Until now, no studies have looked at the role of GA in osteosarcoma. In this study, we observed the effects of GA on the growth and apoptosis of osteosarcoma cells in vitro. We found that GA treatment inhibits the proliferation of osteosarcoma cells by inducing cell cycle arrest. Moreover, we found that GA induces apoptosis in MG63, HOS and U2OS cells. Furthermore, we showed that GA treatment elevates the Bax/Bcl-2 ratio. GA mediated the G0/G1 phase arrest in U2OS cells; this arrest was associated with a decrease in phospho-GSK3-β (Ser9) and the expression of cyclin D1. Similarly, in MG63 cells, GA mediated G2/M cell cycle arrest, which was associated with a decrease in phospho-cdc2 (Thr 161) and cdc25B. Overall, our findings suggest that GA may be an effective anti-osteosarcoma drug because of its capability to inhibit proliferation and induce apoptosis of osteosarcoma cells.”
One of the ways gamboic acid works against cancers is by limiting cancer cell adhesion to fibronectin via suppressing integrin β1 abundance and cholesterol content.
The December 2011 publication Gambogic acid inhibits tumor cell adhesion by suppressing integrin β1 and membrane lipid rafts-associated integrin signaling pathway reports: “Cell adhesion plays an important role in the steps of cancer metastasis. Regulation of cell-cell (intercellular) and cell-matrix adhesion is a promising strategy for cancer progression. Gambogic acid is a xanthone derived from the resin of the Chinese plant Garciania hanburyi, with potent anti-metastasis activity on highly metastatic cells. The aim of this study was to investigate the function and mechanism of gambogic acid on tumor adhesion. We found that gambogic acid strongly inhibited the adhesion of human cancer cells to fibronectin. This inhibition was associated with the deformation of focal adhesion complex, which was mediated by suppressing the expression of integrin β1 and integrin signaling pathway. In vitro, cell lipid rafts clustering was inhibited following treatment of gambogic acid, which induced the suppression of integrin β1 and focal adhesion complex proteins colocalization within rafts. Moreover, gambogic acid significantly decreased cellular cholesterol content, whereas cholesterol replenishment lessened the inhibitory effect of gambogic acid on cell adhesion. Real-time PCR analysis showed that gambogic acid reduced mRNA levels of hydroxymethylglutaryl-CoA reductase and sterol regulatory element binding protein-2, while increased acetyl-CoA acetyltransferase-1/2. Taken together, these results demonstrate that gambogic acid inhibits cell adhesion via suppressing integrin β1 abundance and cholesterol content as well as the membrane lipid raft-associated integrin function, which provide new evidence for the anti-cancer activity of gambogic acid.”
It appears that gambogenic acid inhibits cyclin D1 inhibitor and activates GSK3β activator and can result on apoptosis and and repressed colony-forming activity of lung cancer cells.
Another new (March 2012publication is Gambogenic acid induces G1 arrest via GSK3β-dependent Cyclin D1 degradation and triggers autophagy in lung cancer cells. “Cyclin D1, an oncogenic G1 cyclin which can be induced by environmental carcinogens and whose over-expression may cause dysplasia and carcinoma, has been shown to be a target for cancer chemoprevention and therapy. In this study, we investigated the effects and underlying mechanisms of action of a polyprenylated xanthone, gambogenic acid (GEA) on gefitinib-sensitive and -resistant lung cancer cells. We found that GEA inhibited proliferation, caused G1 arrest and repressed colony-forming activity of lung cancer cells. GEA induced degradation of cyclin D1 via the proteasome pathway, and triggered dephosphorylation of GSK3β which was required for cyclin D1 turnover, because GSK3β inactivation by its inhibitor or specific siRNA markedly attenuated GEA-caused cyclin D1 catabolism. GEA induced autophagy of lung cancer cells, possibly due to activation of GSK3β and inactivation of AKT/mTOR signal pathway. These results indicate that GEA is a cyclin D1 inhibitor and a GSK3β activator which may have chemopreventive and therapeutic potential for lung cancer.”
Gambogic or gambogenic acid might be useful for treating glioblastoma.
The 2008 publication Inhibition of glioblastoma growth and angiogenesis by gambogic acid: an in vitro and in vivo study reports: “Gambogic acid (GA) is the major active ingredient of gamboge, a brownish to orange resin exuded from Garcinia hanburryi tree in Southeast Asia. The present study aims to demonstrate that gambogic acid (GA) has potent anticancer activity for glioblastoma by in vitro and in vivo study. Rat brain microvascular endothelial cells (rBMEC) were used as an in vitro model of the blood-brain barrier (BBB). To reveal an involvement of the intrinsic mitochondrial pathway of apoptosis, the mitochondrial membrane potential and the western blot evaluation of Bax, Bcl-2, Caspase-3, caspase-9 and cytochrome c released from mitochondria were performed. Angiogenesis was detected by CD31 immunochemical study. The results showed that the uptake of GA by rBMEC was time-dependent, which indicated that it could pass BBB and represent a possible new target in glioma therapy. GA could cause apoptosis of rat C6 glioma cells in vitro in a concentration-dependent manner by triggering the intrinsic mitochondrial pathway of apoptosis. In vivo study also revealed that i.v. injection of GA once a day for two weeks could significantly reduce tumor volumes by antiangiogenesis and apoptotic induction of glioma cells. Collectively, the current data indicated that GA may be of potential use in treatment of glioblastoma by apoptotic induction and antiangiogenic effects.”
The 2012 publication Gambogenic acid-induced time- and dose-dependent growth inhibition and apoptosis involving Akt pathway inactivation in U251 glioblastoma cells reports: “Glioblastoma multiforme is the most common and aggressive type of primary brain tumor. Uncontrolled activation of the PI3K/Akt signaling pathway resulting from genetic alterations in phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and epidermal growth factor receptor (EGFR) correlates with poor prognosis and resistance to chemotherapy and radiotherapy of glioblastomas. In this study, we found that gambogenic acid (GNA), a polyprenylated xanthone isolated from the traditional medicine gamboge, efficiently arrested the cell cycle at the G(0)/G(1) phase by specifically repressing the expression of cyclin D1 and cyclin E, suppressed cell proliferation, colony formation and cell migration, and induced caspase-dependent apoptosis in U251 glioblastoma cells in a time- and dose-dependent manner. The pro-apoptotic effect of GNA on U251 cells was shown to be mediated through inactivation of the Akt pathway, because GNA efficiently suppressed the expression level of EGFR and reduced the phosphorylation of Akt (T308) and GSK3β (S9). Furthermore, the combined treatment with LY294002, a specific inhibitor of the PI3K/Akt kinase pathway, and GNA showed a synergistic or additive effect on the growth of U251 cells. Our results showed that GNA is a promising therapeutic agent for glioblastomas.”
Besides speaking to the ability of gamboic acid to promote apoptosis in cancer cells, some publications relate to the mechanisms by which gambogenic acid do the same.
For example, the 2010 publication Gambogenic acid inhibits proliferation of A549 cells through apoptosis-inducing and cell cycle arresting reports: “Although anticancer effect of gambogic acid (GA) and its potential mechanisms were well documented in past decades, limited information is available on the anticancer effect of gambogenic acid (GNA), another major active component of Gamboge. Here we performed a study to determine whether GNA possesses anticancer effect and find its potential mechanisms. The results suggested that GNA significantly inhibited the proliferation of several tumor cell lines in vitro and in vivo. Treatment with GNA dose and time dependently induced A549 cells apoptosis, arrested the cells to G0/G1 phase in vitro and down-regulated the expression of cyclin D1 and cyclooxygenase (COX)-2 in mRNA level. In addition, anticancer effect was further demonstrated by applying xenografts in nude mice coupled with the characteristic of apoptosis in the GNA treated group. Taken together, these observations might suggest that GNA inhibits tumor cell proliferation via apoptosis-induction and cell cycle arrest.”
Another publication related to gambogenic acid and A549 cells is the October 2011 report Gambogenic acid inhibits proliferation of A549 cells through apoptosis inducing through up-regulation of the p38 MAPK cascade. “Gamboge is a dry resin secreted from Garcinia hanburryi, and gambogenic acid (GNA) is one of the main active compounds of gamboge. We have previously demonstrated the anticancer activity of GNA in A549 cells and pointed out its potential effects in anticancer therapies. Previous studies reported that GNA induced apoptosis in many cancer cell lines and inhibited A549 tumor growth in xenograft of nude mice in vivo. However, the anticancer mechanism of GNA has still not been well studied. In this paper, we have investigated whether GNA-induced apoptosis is critically mediated by the p38 mitogen-activated protein kinase (MAPK) pathway. Our findings revealed that GNA could induce apoptosis, inhibit proliferation, down-regulate the expression of p38 and MAPK, increase the activations of caspase-9, caspase-3, and cytochrome c release. Furthermore, using SB203580, an adenosine triphosphate-competitive inhibitor of p38 MAPK, inhibit the expression of p-p38 and the experimental results show that it may promote the occurrence of apoptosis induced by GNA. Taken together, these results suggested that up-regulation of the p38 MAPK cascade may account for the activation of GNA-induced apoptosis.”
Wrapping it up
- A great many other publications report on the anti-cancer effects of gambogenic and gambogic acids, all by Asian authors, the great preponderance by Chinese authors.
- The parent substance gamboges has long been used in traditional Chinese medical practice. And, as far as I can discern, is still being used today.
- On a molecular biology level, the two substances gambogic and gambogenic acids seem to have remarkable anti-cancer properties. Tested against a variety of cancer cell types they are pro-apoptic and anti-proliferative. I could find little on small-animal experiments and nothing on human trials.
- The substances appear to be quite unknown in the Western world. As reported in the literature they are not used in clinical practice, are not being researched for their anti-cancer properties, and are not being considered for clinical trials.
- Many other cancer treatments beyond those covered in these three blog entries are being researched or tried. Some have been discussed in past blog entries; I expect to cover others in the future.
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