General pharmacological properties, developmental toxicity, and analgesic activity of gambogic acid, a novel natural anticancer agent

Naturally Occurring Xanthones; Biological Activities, Chemical Profiles and In Silico Drug Discovery

Xanthones are widely distributed polyphenols, present commonly in higher plants; Garcinia, Calophyllum, Hypericum, Platonia, Mangifera, Gentiana and Swertia. Xanthone tricyclic scaffold is able to interact with different biological targets, showing antibacterial and cytotoxic effects, as well as potent effects against osteoarthritis, malaria, and cardiovascular diseases. Thus, in this article we focused on pharmacological effects, applications and preclinical studies with the recent updates of xanthon´s isolated compounds from 2017-2020. We found that only α-mangostin, gambogic acid, and mangiferin, have been subjected to preclinical studies with particular emphasis on the development of anticancer, diabetes, antimicrobial and hepatoprotective therapeutics. Molecular docking calculations were performed to predict the binding affinities of xanthone-derived compounds against SARS-CoV-2 M^pro. According to the results, cratoxanthone E and morellic acid demonstrated promising binding affinities towards SARS-CoV-2 M^pro with docking scores of -11.2 and -11.0 kcal/mol, respectively. Binding features manifested the capability of cratoxanthone E and morellic acid to exhibit nine and five hydrogen bonds, respectively, with the key amino acids of the M^pro active site. In conclusion, cratoxanthone E and morellic acid are promising anti-COVID-19 drug candidates that warrant further detailed in vivo experimental estimation and clinical assessment.

Recent Advances (2015-2020) in Drug Discovery for Attenuation of Pulmonary Fibrosis and COPD

A condition of scarring of lung tissue due to a wide range of causes (such as environmental pollution, cigarette smoking (CS), lung diseases, some medications, etc.) has been reported as pulmonary fibrosis (PF). This has become a serious problem all over the world due to the lack of efficient drugs for treatment or cure. To date, no drug has been designed that could inhibit fibrosis. However, few medications have been reported to reduce the rate of fibrosis. Meanwhile, ongoing research indicates pulmonary fibrosis can be treated in its initial stages when symptoms are mild. Here, an attempt is made to summarize the recent studies on the effects of various chemical drugs that attenuate PF and increase patients' quality of life. The review is classified based on the nature of the drug molecules, e.g., natural/biomolecule-based, synthetic-molecule-based PF inhibitors, etc. Here, the mechanisms through which the drug molecules attenuate PF are discussed. It is shown that inhibitory molecules can significantly decrease the TGF-β1, profibrotic factors, proteins responsible for inflammation, pro-fibrogenic cytokines, etc., thereby ameliorating the progress of PF. This review may be useful in designing better drugs that could reduce the fibrosis process drastically or even cure the disease to some extent.

Investigations into the antibacterial effects and potential mechanism of gambogic acid and neogambogic acid

The growing threat of antibiotic-resistant bacterial infections to public health necessitates the development of novel antibacterial agents. Inhibiting bacterial cell wall synthesis has remained a key focus for antibiotic development. Our search for inhibitors of undecaprenyl diphosphate synthase (UPPS), an essential enzyme required for bacterial cell wall formation, revealed that two primary components of gamboge, gambogic acid (GA) and neogambogic acid (NGA), significantly inhibited the activity of Enterococcus faecalis UPPS (EfaUPPS) with the half maximal inhibitory concentrations (IC₅₀) of 3.08 μM and 3.07 μM, respectively. In the in vitro antibacterial assay, both GA and NGA also exhibited inhibitory activities against E. faecalis with the minimal inhibitory concentrations (MICs) of 2 μg/mL. Using microscale thermophoresis, molecular docking, and enzymatic assays, we further confirmed that GA and NGA occupy the substrate binding pocket of EfaUPPS with micro-molar binding affinity, preventing the natural substrates farnesyl diphosphate (FPP) from entering. Mutagenesis analysis revealed that L91 and L146 are two key residues in the binding between GA/NGA and UPPS. Furthermore, we also demonstrated that GA and NGA can improve E. faecalis-induced undesirable inflammation in a mouse infection model. Taken together, our findings provide a basis for structural optimization of GA/NGA to develop improved antibiotic leads and enhance treatment success rates in clinical practice.

In Situ Nanoparticle Self-Assembly for Combination Delivery of Therapeutics to Non-Small Cell Lung Cancer

Chemotherapy often experiences several challenges including severe systemic toxicity and adverse effects. The combination chemotherapy arose as an effective clinical practice aimed at reducing doses of drugs to achieve synergistic actions with low toxicity. Our recent efforts demonstrated a synergistic therapeutic benefit of gambogic acid (GA) and gemcitabine (Gem) against lung cancer. However, simultaneous delivery of these two drugs at the tumor site is highly challenging. Therefore, the development of an injectable formulation that can effectively deliver both hydrophobic (GA) and hydrophilic (Gem) drugs in one formulation is a clinically unmet need. Herein, this study reports an in situ human serum albumin (HSA)- and tannic acid (TA)-mediated complexed GA and Gem nanoparticles (G-G@HTA NPs). G-G@HTA NP formation was confirmed by the particle size, Fourier transform infrared spectroscopy, and ¹H NMR spectroscopy. The superior therapeutic activity of G-G@HTA NPs was demonstrated by multiple in vitro functional assays. Additionally, G-G@HTA NPs revealed an obvious and precise targeting of tumors in vivo. The promoted and more synergistic anti-tumor efficacy of G-G@HTA NPs was attained than that of combined treatments and single drug treatments. These events have resulted in no apparent systemic and organ toxicities. Together, this study suggests that in situ HSA-TA-based combinatorial treatment strategy is a suitable approach for application in lung cancer treatment.

Structural Optimization and Improving Antitumor Potential of Moreollic Acid from Gamboge

Moreollic acid, a caged-tetraprenylated xanthone from Gamboge, has been indicated as a potent antitumor molecule. In the present study, a series of moreollic acid derivatives with novel structures were designed and synthesized, and their antitumor activities were determined in multifarious cell lines. The preliminary screening results showed that all synthesized compounds selectively inhibited human colon cancer cell proliferation. TH12-10, with an IC50 of 0.83, 1.10, and 0.79 μM against HCT116, DLD1, and SW620, respectively, was selected for further antitumor mechanism studies. Results revealed that TH12-10 effectively inhibited cell proliferation by blocking cell-cycle progression from G1 to S. Besides, the apparent structure-activity relationships of target compounds were discussed. To summarize, a series of moreollic acid derivatives were discovered to possess satisfactory antitumor potentials. Among them, TH12-10 displays the highest antitumor activities against human colon cancer cells, in which the IC50 values in DLD1 and SW620 are lower than that of 5-fluorouracil.

Gambogic acid: Multi-gram scale isolation, stereochemical erosion toward epi-gambogic acid and biological profile

Introduction

Extracted from gamboge resin, gambogic acid (GBA) is a natural product that displays a complex caged xanthone structure and exhibits promising antitumor properties. However, efforts to advance this compound to clinical applications have been thwarted by its limited availability that in turn, restricts its pharmacological optimization.

Methods

We report here an efficient method that allows multigram scale isolation of GBA in greater than 97% diastereomeric purity from various sources of commercially available gamboge. The overall process includes: (a) isolation of organic components from the resin; (b) separation of GBA from the organic components via crystallization as its pyridinium salt; and (c) acidification of the salt to isolate the free GBA.

Results and Discussion

We found that GBA is susceptible to epimerization at the C2 center that produces epi-gambogic acid ( epi-GBA), a common contaminant of all commercial sources of this compound. Mechanistic studies indicate that this epimerization proceeds via an ortho-quinone methide intermediate. Although the observed stereochemical erosion accounts for the chemical fragility of GBA, it does not significantly affect its biological activity especially as it relates to cancer cell cytotoxicity. Specifically, we measured similar levels of cytotoxicity for either pure GBA or an equilibrated mixture of GBA/ epi-GBA in MBA-MB-231 cells with IC50 values at submicromolar concentration and induction of apoptosis after 12 hours of incubation. The results validate the pharmacological promise of gambogic acid and, combined with the multigram-scale isolation, should enable drug design and development studies.

Gambogic acid protects LPS-induced apoptosis and inflammation in a cell model of neonatal pneumonia through the regulation of TrkA/Akt signaling pathway

Objective

In this work, we investigated the effects of gambogic acid (GA) on lipopolysaccharide (LPS)-induced apoptosis and inflammation in a cell model of neonatal pneumonia.

Method

Human WI-38 cells were maintained in vitro and incubated with various concentrations of GA to examine WI-38 survival. GA-preincubated WI-38 cells were then treated with LPS to investigate the protective effects of GA on LPS-induced death, apoptosis and inflammation. Western blot assay was utilized to analyze the effect of GA on tropomyosin receptor kinase A (TrkA) signaling pathway in LPS-treated WI-38 cells. In addition, human AKT serine/threonine kinase 1 (Akt) gene was knocked down in WI-38 cells to further investigate the associated genetic mechanisms of GA in protecting LPS-induced inflammation and apoptosis.

Results

Pre-incubating WI-38 cells with low and medium concentrations GA protected LPS-induced cell death, apoptosis and inflammatory protein productions of IL-6 and MCP-1. Using western blot assay, it was demonstrated that GA promoted TrkA phosphorylation and Akt activation in LPS-treated WI-38 cells. Knocking down Akt gene in WI-38 cells showed that GA-associated protections against LPS-induced apoptosis and inflammation were significantly reduced.

Conclusions

GA protected LPS-induced apoptosis and inflammation, possibly through the activations of TrkA and Akt signaling pathway. This work may broaden our understanding on the molecular mechanisms of human neonatal pneumonia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-021-00496-9.

Ag NPs on chitosan-alginate coated magnetite for synthesis of indazolo[2,1-b]phthalazines and human lung protective effects against α-Guttiferin

Biocomposite nanomaterials have been evolved as the new generation catalysts and therapeutic supplement in these days. Magnetically isolation has added new features to this category. This has encouraged us to synthesize a novel Ag NP adorned chitosan-alginate dual bio-polysaccharide (two of the more versatile polysaccharides) modified core-shell magnetic nanocomposite (Fe₃O₄/CS-Alg/Ag NPs). The material was meticulously characterized following different physicochemical techniques, such as, FT-IR, ICP-OES, FESEM, EDX, atomic mapping, TEM, VSM, XRD and XPS studies. The as synthesized material was catalytically explored in the one-pot multicomponent synthesis of biologically potent 2H-indazolo[2,1-b]phthalazine-trione derivatives involving a wide range of substrates. The reactions were ended up with excellent yields under solvent-free heating conditions. The catalyst recyclability, heterogeneity and leaching tests were performed to ensure its high stability and robustness. It could be reused as much as 10 times in succession with almost unchanged catalytic performances. In the lung protective part of the present research, the human lung toxicity was induced by α-Guttiferin. The cell viability of lung MRC-5, CCD19Lu, WI-38, and BEAS-2B cell lines was measured by trypan blue assay. Caspase-3 activity was assessed by the caspase activity colorimetric assay kit and mitochondrial membrane potential of lung cells was studied by Rhodamine123 fluorescence dye. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) test was used to show DNA fragmentation and apoptosis of lung cells. Also, the Rat inflammatory cytokine assay kit was used to measure the concentrations of inflammatory cytokines. The catalyst-treated cell cutlers significantly (p ≤ 0.01) reduced the DNA fragmentation, caspase-3 activity, and inflammatory cytokines concentrations, and raised the mitochondrial membrane potential and cell viability in the high concentration of α-Guttiferin-treated lung MRC-5, CCD19Lu, WI-38, and BEAS-2B cells. The best result of lung protective properties of catalyst against α-Guttiferin was seen in the high dose of catalyst i.e., 4 μg. DPPH test revealed similar antioxidant potentials for catalyst and butylated hydroxytoluene. The catalyst inhibited half of the DPPH molecules in the concentration of 171 μg/mL. According to the above results, catalyst can be administrated as a lung protective drug for the treatment of lung diseases after approving in the clinical trial studies in humans.

Gambogic acid potentiates gemcitabine induced anticancer activity in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the most frequent type of lung cancer accounting up to 80-85% of all lung cancer (LC) cases. Gemcitabine (Gem), a pyrimidine nucleoside antimetabolite, is widely used chemotherapy offering several months survival benefit in patients with NSCLC. The emergence of Gem resistance is a main clinical concern in cancer treatment and thus a continuous demand for development of new therapeutic strategies to improve its antitumor activity. Hence, we report an adjuvant therapeutic regimen based on natural compound, gambogic acid (GA) which has been shown to enhanced Gem induced inhibition of cancer cell growth, arrest cell cycle, and induce apoptosis by enhanced accumulation of Gem. The in vitro cell viability, clonogenicity, invasion, and migration assays demonstrated a significant higher therapeutic effect of Gem when it was combined with GA in A549 and H1299 cells. A better access of internalization of drug molecules achieved in rhodamine 123 assay when GA was used as adjuvant treatment. Further, GA and Gem combination significantly reduced tubular formation of HUVEC cells indicates lowering angiogenesis potential. Microarray and Western blot studies confirm that GA + Gem co-treatment strategy promotes cancer cell death by downregulating anti-apoptotic proteins, chemoresistance-associated proteins, and upregulation of apoptosis proteins. More importantly, a significant higher therapeutic benefit was noticed for GA and Gem combination in A549 xenograft mice model. Together, these results offer a rationale to evaluate the clinical translational possibility of GA as adjuvant therapy to overcome Gem resistance. This combination regimen can be a new therapeutic concept to eradicate this devastating disease.

Gambogic acid: A shining natural compound to nanomedicine for cancer therapeutics

The United States Food and Drug Administration has permitted number of therapeutic agents for cancer treatment. Most of them are expensive and have some degree of systemic toxicity which makes overbearing in clinical settings. Although advanced research continuously applied in cancer therapeutics, but drug resistance, metastasis, and recurrence remain unanswerable. These accounts to an urgent clinical need to discover natural compounds with precisely safe and highly efficient for the cancer prevention and cancer therapy. Gambogic acid (GA) is the principle bioactive and caged xanthone component, a brownish gamboge resin secreted from the of Garcinia hanburyi tree. This molecule showed a spectrum of biological and clinical benefits against various cancers. In this review, we document distinct biological characteristics of GA as a novel anti-cancer agent. This review also delineates specific molecular mechanism(s) of GA that are involved in anti-cancer, anti-metastasis, anti-angiogenesis, and chemo-/radiation sensitizer activities. Furthermore, recent evidence, development, and implementation of various nanoformulations of gambogic acid (nanomedicine) have been described.

Repurposing old drugs as new inhibitors of the ubiquitin-proteasome pathway for cancer treatment

The ubiquitin-proteasome system (UPS) plays a central role in the degradation of cellular proteins. Targeting protein degradation has been validated as an effective strategy for cancer therapy since 2003. Several components of the UPS have been validated as potential anticancer targets, including 20S proteasomes, 19S proteasome-associated deubiquitinases (DUBs) and ubiquitin ligases (E3s). 20S proteasome inhibitors (such as bortezomib/BTZ and carfilzomib/CFZ) have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of multiple myeloma (MM) and some other liquid tumors. Although survival of MM patients has been improved by the introduction of BTZ-based therapies, these clinical 20S proteasome inhibitors have several limitations, including emergence of resistance in MM patients, neuro-toxicities, and little efficacy in solid tumors. One of strategies to improve the current status of cancer treatment is to repurpose old drugs with UPS-inhibitory properties as new anticancer agents. Old drug reposition represents an attractive drug discovery approach compared to the traditional de novo drug discovery process which is time-consuming and costly. In this review, we summarize status of repurposed inhibitors of various UPS components, including 20S proteasomes, 19S-associated DUBs, and ubiquitin ligase E3s. The original and new mechanisms of action, molecular targets, and potential anticancer activities of these repurposed UPS inhibitors are reviewed, and their new uses including combinational therapies for cancer treatment are discussed.

Transcriptional Analysis of the Effects of Gambogic Acid and Neogambogic Acid on Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infection is a major threat to human health, as this bacterium has developed resistance to a variety of conventional antibiotics. This is especially true of MRSA biofilms, which not only exhibit enhanced pathogenicity but also are resistant to most antibiotics. In this work, we demonstrated that two natural products with antitumor activity, namely, gambogic acid (GA) and neogambogic acid (NGA), have significant inhibitory activity toward MRSA. GA and NGA can not only effectively inhibit planktonic MRSA strains in vivo and in vitro, but also have strong inhibitory effects on MRSA biofilms formation. By transcriptome sequencing, Q-RT-PCR and PRM, we found that GA and NGA could reduce the expression of S. aureus virulence factors by inhibiting the saeRS two-component, thus achieving inhibition of MRSA. We found that GA and NGA had anti-MRSA activity in vivo and in vitro and identified saeRS to be the target, indicating that saeRS inhibitors may be used to treat biofilm-related infections.

Gambogic acid triggers vacuolization-associated cell death in cancer cells via disruption of thiol proteostasis

Gambogic acid (GA), a xanthonoid extracted from the resin of the tree, Garcinia hanburyi, was recently shown to exert anticancer activity in multiple studies, but the underlying action mechanism remains unclear. Here, we show that GA induces cancer cell death accompanied by vacuolation in vitro and in vivo. This GA-induced vacuolation in various cancer cells was derived from dilation of the endoplasmic reticulum (ER) and mitochondria, and was blocked by cycloheximide. These findings suggest that GA kills cancer cells by inducing paraptosis, a vacuolization-associated cell death. We found that megamitochondria formation, which arose from the fusion of swollen mitochondria, preceded the fusion of ER-derived vacuoles. GA-induced proteasomal inhibition was found to contribute to the ER dilation and ER stress seen in treated cancer cells, and megamitochondria formation was followed by mitochondrial membrane depolarization. Interestingly, GA-induced paraptosis was effectively blocked by various thiol-containing antioxidants, and this effect was independent of ROS generation. We observed that GA can react with cysteinyl thiol to form Michael adducts, suggesting that the ability of GA to covalently modify the nucleophilic cysteinyl groups of proteins may cause protein misfolding and subsequent accumulation of misfolded proteins within the ER and mitochondria. Collectively, our findings show that disruption of thiol proteostasis and subsequent paraptosis may critically contribute to the anti-cancer effects of GA.

Negative allosteric modulators of cannabinoid receptor 2: protein modeling, binding site identification and molecular dynamics simulations in the presence of an orthosteric agonist

Selective activation of the cannabinoid receptor subtype 2 (CB2) shows promise for treating pain, inflammation, multiple sclerosis, cancer, ischemic/reperfusion injury and osteoporosis. Target selectivity and off-target side effects are two major limiting factors for orthosteric ligands, and therefore, the search for allosteric modulators (AMs) is a widely used drug discovery approach. To date, only a limited number of negative CB2 AMs have been identified, possessing only micromolar activity at best, and the CB2 receptor's allosteric site(s) are not well characterized. Herein, we used computational approaches including receptor modeling, site mapping, docking, molecular dynamics (MD) simulations and binding free energy calculations to predict, characterize and validate allosteric sites within the complex of the CB2 receptor with bound orthosteric agonist CP55,940. After docking of known negative CB2 allosteric modulators (NAMs), dihydro-gambogic acid (DHGA) and trans-β-caryophyllene (TBC) (note that TBC also shows agonist activity), at the predicted allosteric sites, the best total complex with CB2, CP55,940 and NAM was embedded into a hydrated lipid bilayer and subjected to a 200 ns MD simulation. The presence of an AM affected the CB2-CP55,940 complex, altering the relative positioning of the toggle switch residues and promoting a strong π-π interaction between Phe117^3.36 and Trp258^6.48. Binding of either TBC or DHGA to a putative allosteric pocket directly adjacent to the orthosteric ligand reduced the binding free energy of CP55,940, which is consistent with the expected effect of a negative AM. The identified allosteric sites present immense scope for the discovery of novel classes of CB2 AMs.

Adaptation of the Systematic Review Framework to the Assessment of Toxicological Test Methods: Challenges and Lessons Learned with the Zebrafish Embryotoxicity Test

Systematic review methodology is a means of addressing specific questions through structured, consistent, and transparent examinations of the relevant scientific evidence. This methodology has been used to advantage in clinical medicine, and is being adapted for use in other disciplines. Although some applications to toxicology have been explored, especially for hazard identification, the present preparatory study is, to our knowledge, the first attempt to adapt it to the assessment of toxicological test methods. As our test case, we chose the zebrafish embryotoxicity test (ZET) for developmental toxicity and its mammalian counterpart, the standard mammalian prenatal development toxicity study, focusing the review on how well the ZET predicts the presence or absence of chemical-induced prenatal developmental toxicity observed in mammalian studies. An interdisciplinary team prepared a systematic review protocol and adjusted it throughout this piloting phase, where needed. The final protocol was registered and will guide the main study (systematic review), which will execute the protocol to comprehensively answer the review question. The goal of this preparatory study was to translate systematic review methodology to the assessment of toxicological test method performance. Consequently, it focused on the methodological issues encountered, whereas the main study will report substantive findings. These relate to numerous systematic review steps, but primarily to searching and selecting the evidence. Applying the lessons learned to these challenges can improve not only our main study, but may also be helpful to others seeking to use systematic review methodology to compare toxicological test methods. We conclude with a series of recommendations that, if adopted, would help improve the quality of the published literature, and make conducting systematic reviews of toxicological studies faster and easier over time.

Therapeutic potential of gambogic acid, a caged xanthone, to target cancer

Natural compounds have enormous biological and clinical activity against dreadful diseases such as cancer, as well as cardiovascular and neurodegenerative disorders. In spite of the widespread research carried out in the field of cancer therapeutics, cancer is one of the most prevalent diseases with no perfect treatment till date. Adverse side effects and the development of chemoresistance are the imperative limiting factors associated with conventional chemotherapeutics. For this reason, there is an urgent need to find compounds that are highly safe and efficacious for the prevention and treatment of cancer. Gambogic acid (GA) is a xanthone structure extracted from the dry, brownish gamboge resin secreted from the Garcinia hanburyi tree in Southeast Asia and has inherent anti-cancer properties. In this review, the molecular mechanisms underlying the targets of GA that are liable for its effective anti-cancer activity are discussed that reveal the potential of GA as a pertinent candidate that can be appropriately developed and designed into a capable anti-cancer drug.

'Click Chemistry' Synthesis of Novel Natural Product-Like Caged Xanthones Bearing a 1,2,3-Triazole Moiety with Improved Druglike Properties as Orally Active Antitumor Agents

DDO-6101, a natural-product-like caged xanthone discovered previously in our laboratory based on the pharmacophoric scaffold of the Garcinia natural product gambogic acid (GA), shows potent cytotoxicity in vitro, but poor efficacy in vivo due to its poor druglike properties. In order to improve the druglike properties and in vivo antitumor potency, a novel series of ten triazole-bearing caged xanthone derivatives of DDO-6101 has been efficiently synthesized by 'click chemistry' and evaluated for their in vitro antitumor activity and druglike properties. Most of the target compounds have sustained cytotoxicity against A549, HepG2, HCT116, and U2OS cancer cells and possess improved aqueous solubility, as well as permeability. Notably, these caged xanthones are also active towards taxol-resistant or cisplatin-resistant A549 cancer cells. Taking both the in vitro activities and druglike properties into consideration, compound 8g has been advanced into in vivo efficacy experiments. The results reveal that 8g (named as DDO-6318), both by intravenous or per os administration, are much more potent than the lead DDO-6101 in A549-transplanted mice models and it could be a promising antitumor candidate for further evaluation.

Caged Garcinia Xanthones, a Novel Chemical Scaffold with Potent Antimalarial Activity

Caged Garcinia xanthones (CGXs) constitute a family of natural products that are produced by tropical/subtropical trees of the genus Garcinia CGXs have a unique chemical architecture, defined by the presence of a caged scaffold at the C ring of a xanthone moiety, and exhibit a broad range of biological activities. Here we show that synthetic CGXs exhibit antimalarial activity against Plasmodium falciparum, the causative parasite of human malaria, at the intraerythrocytic stages. Their activity can be substantially improved by attaching a triphenylphosphonium group at the A ring of the caged xanthone. Specifically, CR135 and CR142 were found to be highly effective antimalarial inhibitors, with 50% effective concentrations as low as ∼10 nM. CGXs affect malaria parasites at multiple intraerythrocytic stages, with mature stages (trophozoites and schizonts) being more vulnerable than immature rings. Within hours of CGX treatment, malaria parasites display distinct morphological changes, significant reduction of parasitemia (the percentage of infected red blood cells), and aberrant mitochondrial fragmentation. CGXs do not, however, target the mitochondrial electron transport chain, the target of the drug atovaquone and several preclinical candidates. CGXs are cytotoxic to human HEK293 cells at the low micromolar level, which results in a therapeutic window of around 150-fold for the lead compounds. In summary, we show that CGXs are potent antimalarial compounds with structures distinct from those of previously reported antimalarial inhibitors. Our results highlight the potential to further develop Garcinia natural product derivatives as novel antimalarial agents.

Novel Natural Product-like Caged Xanthones Bearing a Carbamate Moiety Exhibit Antitumor Potency and Anti-Angiogenesis Activity In vivo

DDO-6101, a simplified structure obtained from the Garcinia natural product (NP) gambogic acid (GA), has been previously shown to possess high cytotoxicity to a variety of human tumour cell lines. To improve its physicochemical properties and in vivo cytotoxic potency, a series of novel carbamate-bearing derivatives based on DDO-6101 was synthesized and characterized. The structural modifications revealed that the presence of a carbamate moiety was useful for obtaining comparable cytotoxicity and improved aqueous solubility and permeability. 8n, which contains a bipiperidine carbamate moiety, displayed better drug properties and potential in in vivo antitumor activity. In addition, an antitumor mechanistic study suggested that 8n (DDO-6337) inhibited the ATPase activity of Hsp90 (Heat shock protein 90), leading to the inhibition of HIF-1a and ultimately contributing to its anti-angiogenesis and antitumor properties.

Protective role of gambogic acid in experimental pulmonary fibrosis in vitro and in vivo

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive disorder with poor prognosis. The treatment options for IPF are very limited. Gambogic acid (GA) has anticancer effect and anti-proliferative activity which is extracted from a dried yellow resin of the Garcinia hanburyi Hook.f. [Clusiaceae (Guttiferae)] in Southeast Asia. However, the anti-fibrotic activities of GA have not been previously investigated.

METHODS

In this study, the effects of GA on TGF-β1-mediated epithelial-mesenchymal transition (EMT) in A549 cells and endothelial-mesenchymal transition (EndoMT) in human pulmonary microvascular endothelial cells (HPMECs), on the proliferation of human lung fibroblasts (HLF-1) were investigated in vitro, and on bleomycin (BLM)-induced pulmonary fibrosis was investigated in vivo.

RESULTS

In TGF-β1 stimulated A549 cells, treatment with GA resulted in a reduction of EMT with a decrease in vimentin and p-Smad3 and an increase in E-cadherin instead. In TGF-β1 stimulated HPMECs, treatment with GA resulted in a reduction of EndoMT with a decrease in vimentin, and an increase in VE-cadherin instead. In the hypoxic HPMECs, treatment with GA reduced Vasohibin-2 (VASH-2), whereas increased VASH-1. In TGF-β1 stimulated HLF-1, treatment with GA reduced HLF-1 proliferation with a decrease in platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF-2) expressions. In vivo, treatment with GA for 2 weeks resulted in an amelioration of the BLM-induced pulmonary fibrosis in rats with a lower VASH-2. Instead, it was observed a higher VASH-1 expression at early stage of fibrosis at 1 mg/kg, with reductions of the pathological score, collagen deposition, α-SMA, PDGF and FGF-2 expressions at fibrotic stage at 0.5 mg/kg and 1 mg/kg.

CONCLUSION

In summary, GA reversed EMT and EndoMT, as well as HLF-1 proliferation in vitro and prevented pulmonary fibrosis in vivo by modulating VASH-2/VASH-1 and suppressing the TGF-β1/Smad3 pathway.

Global profiling of cellular targets of gambogic acid by quantitative chemical proteomics

Gambogic acid has shown significant potential as an anti-cancer and anti-inflammatory compound, here we report that the target profiling of gambogic acid in human cancer cells via quantitative chemical proteomics.

Synergistic Anticancer Activities of Natural Substances in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is highly resistant to currently available chemotherapeutic agents. The clinical outcome of HCC treatment remains unsatisfactory. Therefore, new effective and well-tolerated therapy strategies are needed. Natural products are excellent sources for the development of new medications for disease treatment. Recently, we and other researchers have suggested that the combined effect of natural products may improve the effect of chemotherapy treatments against the proliferation of cancer cells. In addition, many combination treatments with natural products augmented intracellular reactive oxygen species (ROS). In this review we will demonstrate the synergistic anticancer effects of a combination of natural products with chemotherapeutic agents or natural products against human HCC and provide new insight into the development of novel combination therapies against HCC.

Recent research on bioactive xanthones from natural medicine: Garcinia hanburyi

Garcinia hanburyi, a tropical plant found in south Asia, has a special long history in the development of both medicine and art. This review mainly focuses on the pharmacy research of the bioactive compounds from the plant in recent years. Preparative and analysis separation methods were introduced. Moreover, the chemical structure of the isolated compounds was included. The studies of biological activities of the caged xanthones from the plant, including antitumor, anti-HIV-1, antibacterial, and neurotrophic activities, were reviewed in detail. Furthermore, the mechanisms of its antitumor activity were also reviewed. As mentioned above, some of the xanthones from G. hanburyi can be promising drug candidates, which is worth studying. However, we still need much evidence to prove their efficacy and safety. So, further research is critical for the future application of xanthones from G. hanburyi.

A-ring oxygenation modulates the chemistry and bioactivity of caged Garcinia xanthones

Natural products of the caged Garcinia xanthones (CGX) family are characterized by a unique chemical structure, potent bioactivities and promising pharmacological profiles. We have developed a Claisen/Diels-Alder reaction cascade that, in combination with a Pd(0)-catalyzed reverse prenylation, provides rapid and efficient access to the CGX pharmacophore, represented by the structure of cluvenone. To further explore this pharmacophore, we have synthesized various A-ring oxygenated analogues of cluvenone and have evaluated their bioactivities in terms of growth inhibition, mitochondrial fragmentation, induction of mitochondrial-dependent cell death and Hsp90 client inhibition. We found that installation of an oxygen functionality at various positions of the A-ring influences significantly both the site-selectivity of the Claisen/Diels-Alder reaction and the bioactivity of these compounds, due to remote electronic effects.

Studies on chemical-structure modification and structure-activity relationship of gambogic acid derivatives at carbon(34)

Gambogic acid (GA), a natural product, was identified as a promising antitumor agent. To further explore the structure-activity relationship of GA and discover novel GA derivatives as antitumor agents, 19 novel GA derivatives modified at C(34) were synthesized and evaluated against A549, BGC-823, U251, HepG2, and MB-231 cancer cell lines by cellular assays. Among them, 15 compounds were found to be more potent than GA against some cancer cell lines. Notably, compound 3 possessed potent inhibitory activities against five cell lines with IC(50) values ranging between 0.24 and 1.09 μM. Compounds 9 and 18 were seven to eightfold more active than GA against A549 cell line. Chemical modification at C(34) of GA by introducing of hydrophilic aliphatic amines resulted in increased activity and improved drug-like properties. These findings will enhance our understanding of the SAR of GA and can lead to the discovery of novel GA derivatives as potential antitumor agents.

Garcinia xanthones as orally active antitumor agents

Using a newly developed strategy whose key step is the regioselective propargylation of hydroxyxanthone substrates, 99 structurally diverse Garcinia natural-product-like xanthones based on gambogic acid were designed and synthesized and their in vitro antitumor activity was evaluated. A set of 40 related compounds was chosen for determination of their physicochemical properties including polar surface area, log D₇.₄, aqueous solubility, and permeability at pH 7.4. In the light of the in vitro antitumor activity and the physicochemical properties, two compounds were advanced into in vivo efficacy experiments. The antitumor activity of compound 112, administered po, showed more potent in vivo oral antitumor activity than gambogic acid.

Subcellular localization and activity of gambogic acid

The natural product gambogic acid (GA) has shown significant potential as an anticancer agent as it is able to induce apoptosis in multiple tumor cell lines, including multidrug-resistant cell lines, as well as displaying antitumor activity in animal models. Despite the fact that GA has entered phase I clinical trials, the primary cellular target and mode of action of this compound remain unclear, although many proteins have been shown to be affected by it. By thorough analysis of several cellular organelles, at both the morphological and functional levels, we demonstrate that the primary effect of GA is at the mitochondria. We found that GA induces mitochondrial damage within minutes of incubation at low-micromolar concentrations. Moreover, a fluorescent derivative of GA was able to localize specifically to the mitochondria and was displaced from these organelles after competition with unlabeled GA. These findings indicate that GA directly targets the mitochondria to induce the intrinsic pathway of apoptosis, and thus represents a new member of the mitocans.

Fighting fire with fire: poisonous Chinese herbal medicine for cancer therapy

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.

Gambogic acid inhibits Hsp90 and deregulates TNF-α/NF-κB in HeLa cells

Gambogic acid (GB) is an important anti-cancer drug candidate, but the target protein by which it exerts its anti-cancer effects has not been identified. This study is the first to show that GB inhibits heat shock protein 90 (Hsp90) and down-regulates TNF-α/NF-κB in HeLa cells. The effects of GB on Hsp90 were studied by characterizing its physical interactions with Hsp90 upon binding, the noncompetitive inhibition of Hsp90 ATPase activity, and the degradation of Hsp90 client proteins (i.e., Akt, IKK) in HeLa cells. GB seems to bind to the N-terminal ATP-binding domain of Hsp90. Additionally, GB suppresses the activation of TNF-α/NF-κB and decreases XIAP expression levels and the ratio of Bcl-2/Bax, which in turn induces HeLa cell apoptosis. Thus, GB represents a promising therapeutic agent for cancer; it may also be useful as a probe to increase understanding of the biological functions of Hsp90.

Chemistry and biology of the caged Garcinia xanthones

Natural products have been a great source of many small molecule drugs for various diseases. In spite of recent advances in biochemical engineering and fermentation technologies that allow us to explore microorganisms and the marine environment as alternative sources of drugs, more than 70 % of the current small molecule therapeutics derive their structures from plants used in traditional medicine. Natural-product-based drug discovery relies heavily on advances made in the sciences of biology and chemistry. Whereas biology aims to investigate the mode of action of a natural product, chemistry aims to overcome challenges related to its supply, bioactivity, and target selectivity. This review summarizes the explorations of the caged Garcinia xanthones, a family of plant metabolites that possess a unique chemical structure, potent bioactivities, and a promising pharmacology for drug design and development.