Inhibition of alpha(4) integrin mediated adhesion was involved in the reduction of B16-F10 melanoma cells lung colonization in C57BL/6 mice treated with gambogic acid

Autophagy regulates tumor growth and metastasis

The role of autophagy in tumorigenesis and tumor metastasis remains poorly understood. Here we show that inhibition of autophagy stabilizes the transcription factor Twist1 through Sequestosome-1 (SQSTM1, also known as p62) and thus increases cell proliferation, migration, and epithelial-mesenchymal transition (EMT) in tumor development and metastasis. Inhibition of autophagy or p62 overexpression blocks Twist1 protein degradation in the proteasomes, while p62 inhibition enhances it. SQSTM1/p62 interacts with Twist1 via the UBA domain of p62, in a Twist1-ubiquitination-dependent manner. Lysine 175 in Twist1 is critical for Twist1 ubiquitination, degradation, and SQSTM1/p62 interaction. For squamous skin cancer and melanoma cells that express Twist1, SQSTM1/p62 increases tumor growth and metastasis in mice. Together, our results identified Twist1 as a key downstream protein for autophagy and suggest a critical role of the autophagy/p62/Twist1 axis in cancer development and metastasis.

Comparative Dynamic Features of Apo and Bound MDM2 Protein Reveal the Mechanism of Inhibitor Recognition for Anti-Cancer Activity

BACKGROUND

Mouse Double Minute 2 Homolog (MDM2) oncogenic protein is the principal cellular antagonist of the p53 tumor suppressor gene. Restoration of p53 activity by inhibiting the MDM2-P53 interactions at the molecular level has become the cornerstone of cancer research due to its promising anticancer effects. Natural medicinal products possess various chemical structures and represent an essential source for drug discovery. α-Mangostin (AM) and gambogic acid (G250) are plant-derived compounds that showed inhibitory effects on MDM2-P53 interactions in vitro and in vivo.

METHODS

Despite the many clinical studies which performed deeper insight about the molecular understanding of the structural mechanisms exhibited by α-Mangostin and Gambogic acid-binding to MDM2 remains critical. In this study, comparative molecular dynamics simulations were performed for each Apo and bound p53 and MDM2 proteins to shed light on the MDM2-p53 interactions and get a better understanding of the inhibition mechanisms.

RESULTS

Results revealed atomistic interaction of AM and G250 within the MDM2-p53 interaction cleft. Both compounds mediate the interaction between the α-helix motifs of the p53 amino-terminal domain, which caused a significant separation between orthogonally opposed residues, specifically Lys8 and Gly47 residues of the p53 and MDM2, respectively. Contrasting changes in magnitudes were observed in per-residue fluctuation on AM and G250 (~0.04 nm and ~2.3 nm, respectively). The Radius of gyration (~0.03 nm and 0.04 nm, respectively), C-alpha deviations (~0.06 nm and 0.1 nm, respectively). The phenolic group of AM was found to establish hydrogen interactions with Glu28 and His96 residues of MDM2. The trioxahexacyclo-ring of G250 also forms hydrogen bond interactions with Lys51 and Leu26 residues of MDM2.

CONCLUSION

Utilizing the information provided on the inhibitory binding mode adopted by each compound in this study may further assist in the tailored designs for cancer therapeutics.

Identification of Therapeutic Targets and Prognostic Biomarkers Among Integrin Subunits in the Skin Cutaneous Melanoma Microenvironment

The roles of different integrin alpha/beta (ITGA/ITGB) subunits in skin cutaneous melanoma (SKCM) and their underlying mechanisms of action remain unclear. Oncomine, UALCAN, GEPIA, STRING, GeneMANIA, cBioPortal, TIMER, TRRUST, and Webgestalt analysis tools were used. The expression levels of ITGA3, ITGA4, ITGA6, ITGA10, ITGB1, ITGB2, ITGB3, ITGB4, and ITGB7 were significantly increased in SKCM tissues. The expression levels of ITGA1, ITGA4, ITGA5, ITGA8, ITGA9, ITGA10, ITGB1, ITGB2, ITGB3, ITGB5, ITGB6 and ITGB7 were closely associated with SKCM metastasis. The expression levels of ITGA1, ITGA4, ITGB1, ITGB2, ITGB6, and ITGB7 were closely associated with the pathological stage of SKCM. The expression levels of ITGA6 and ITGB7 were closely associated with disease-free survival time in SKCM, and the expression levels of ITGA6, ITGA10, ITGB2, ITGB3, ITGB6, ITGB7, and ITGB8 were markedly associated with overall survival in SKCM. We also found significant correlations between the expression of integrin subunits and the infiltration of six types of immune cells (B cells, CD8+ T cells, CD4+T cells, macrophages, neutrophils, and dendritic cells). Finally, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed, and protein-protein interaction (PPI) networks were constructed. We have identified abnormally-expressed genes and gene regulatory networks associated with SKCM, improving understanding of the underlying pathogenesis of SKCM.

New Delivery Route of Gambogic Acid Via Skin for Topical Targeted Therapy of Cutaneous Melanoma and Reduction of Systemic Toxicity

Cutaneous melanoma is the deadliest form of skin cancer, and gambogic acid (GA) exhibits potent anti-melanoma activity. However, clinical application of GA via intravenous injection and oral administration is limited by systemic toxicity and rapid metabolism in the blood. Here, we developed a new, topical route of GA delivery for anti-melanoma activity and reduction of systemic toxicity. The results indicated that the barrier of the stratum corneum (SC) and low diffusion of GA in the hydrophilic viable skin (epidermis and dermis) limited the GA penetration through intact skin. The combination of azone (AZ) and propylene glycol (PG) showed obvious synergistic effects on skin penetration by GA via improving the permeability of the SC and greatly increasing the skin accumulation of GA, thereby forming a high drug concentration in the skin and achieving a topical targeted treatment of melanoma. In addition, GA (AZ-PG) achieved the same anti-melanoma effect via topical delivery as via intravenous injection. Intravenous injection and oral administration of GA induced remarkable pathological changes in various organs in mice, whereas GA was not toxic to various organs or to the skin via topical delivery. These findings indicated that topical administration of GA is an alternative route for melanoma treatment.

Gambogic Acid as a Candidate for Cancer Therapy: A Review

Gambogic acid (GA), a kind of dry resin secreted by the Garcinia hanburyi tree, is a natural active ingredient with various biological activities, such as anti-cancer, anti-inflammatory, antioxidant, anti-bacterial effects, etc. An increasing amount of evidence indicates that GA has obvious anti-cancer effects via various molecular mechanisms, including the induction of apoptosis, autophagy, cell cycle arrest and the inhibition of invasion, metastasis, angiogenesis. In order to improve the efficacy in cancer treatment, nanometer drug delivery systems have been employed to load GA and form micelles, nanoparticles, nanofibers, and so on. In this review, we aim to offer a summary of chemical structure and properties, anti-cancer activities, drug delivery systems and combination therapy of GA, which might provide a reference to promote the development and clinical application of GA.

Natural Xanthones and Skin Inflammatory Diseases: Multitargeting Mechanisms of Action and Potential Application

The pathogenesis of skin inflammatory diseases such as atopic dermatitis, acne, psoriasis, and skin cancers generally involve the generation of oxidative stress and chronic inflammation. Exposure of the skin to external aggressors such as ultraviolet (UV) radiation and xenobiotics induces the generation of reactive oxygen species (ROS) which subsequently activates immune responses and causes immunological aberrations. Hence, antioxidant and anti-inflammatory agents were considered to be potential compounds to treat skin inflammatory diseases. A prime example of such compounds is xanthone (xanthene-9-one), a class of natural compounds that possess a wide range of biological activities including antioxidant, anti-inflammatory, antimicrobial, cytotoxic, and chemotherapeutic effects. Many studies reported various mechanisms of action by xanthones for the treatment of skin inflammatory diseases. These mechanisms of action commonly involve the modulation of various pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor α (TNF-α), as well as anti-inflammatory cytokines such as IL-10. Other mechanisms of action include the regulation of NF-κB and MAPK signaling pathways, besides immune cell recruitment via modulation of chemokines, activation, and infiltration. Moreover, disease-specific activity contributed by xanthones, such as antibacterial action against Propionibacterium acnes and Staphylococcus epidermidis for acne treatment, and numerous cytotoxic mechanisms involving pro-apoptotic and anti-metastatic effects for skin cancer treatment have been extensively elucidated. Furthermore, xanthones have been reported to modulate pathways responsible for mediating oxidative stress and inflammation such as PPAR, nuclear factor erythroid 2-related factor and prostaglandin cascades. These pathways were also implicated in skin inflammatory diseases. Xanthones including the prenylated α-mangostin (2) and γ-mangostin (3), glucosylated mangiferin (4) and the caged xanthone gambogic acid (8) are potential lead compounds to be further developed into pharmaceutical agents for the treatment of skin inflammatory diseases. Future studies on the structure-activity relationships, molecular mechanisms, and applications of xanthones for the treatment of skin inflammatory diseases are thus highly recommended.

Gambogic acid exhibits anti-metastatic activity on malignant melanoma mainly through inhibition of PI3K/Akt and ERK signaling pathways

Gambogic acid (GA) is a potential anti-cancer compound that is extracted from the resin of Garciania hanburyi. The present study was designed to evaluate the anti-metastatic effect of GA on melanoma cell lines in vitro and to explore the underlying mechanism. The anti-proliferative activity of GA on melanoma cells was assessed by CCK-8 assay. The Wound-healing, transwell, adhesion, and tube formation assays were performed to examine the inhibition of GA on the cell's migration, invasion, adhesion, and angiogenesis capacities, respectively. Enzymatic activity of MMP-2 and MMP-9 were detected by gelatin zymography assay. Protein expressions regulated by GA treatment were tested by Western blot assay. The present results showed that GA significantly inhibited the proliferation of highly metastatic melanoma A375, B16-F10 cells and human umbilical vein endothelial cells (HUVECs) in time- and doses-dependent manners. Furthermore, GA significantly inhibited the migratory, invasive and adhesive properties of A375 and B16-F10 cells, and tube-forming potential of HUVECs at sub-IC50 concentrations, where no significant cytotoxicity was observed. Mechanistically, GA treatment suppressed the EMT and angiogenesis processes and reduced the enzymatic activity of MMP-2 and MMP-9. Moreover, abnormal PI3K/Akt and ERK signaling pathways in A375 and B16-F10 cells and HUVECs were notably suppressed by GA treatment. Collectively, our results suggest that GA exerts anti-metastasis activity in melanoma cells by suppressing the EMT and angiogenesis through the PI3K/Akt and ERK signaling pathways, and might be used as a phytomedicine against metastatic melanoma.

Improved druggability of gambogic acid using core–shell nanoparticles

A core-shell hybrid nanoparticle has been developed to improve the druggability of Gambogic acid (GA), a natural antitumor drug candidate.

The role of p53 in cancer drug resistance and targeted chemotherapy

Cancer has long been a grievous disease complicated by innumerable players aggravating its cure. Many clinical studies demonstrated the prognostic relevance of the tumor suppressor protein p53 for many human tumor types. Overexpression of mutated p53 with reduced or abolished function is often connected to resistance to standard medications, including cisplatin, alkylating agents (temozolomide), anthracyclines, (doxorubicin), antimetabolites (gemcitabine), antiestrogenes (tamoxifen) and EGFR-inhibitors (cetuximab). Such mutations in the TP53 gene are often accompanied by changes in the conformation of the p53 protein. Small molecules that restore the wild-type conformation of p53 and, consequently, rebuild its proper function have been identified. These promising agents include PRIMA-1, MIRA-1, and several derivatives of the thiosemicarbazone family. In addition to mutations in p53 itself, p53 activity may be also be impaired due to alterations in p53s regulating proteins such as MDM2. MDM2 functions as primary cellular p53 inhibitor and deregulation of the MDM2/p53-balance has serious consequences. MDM2 alterations often result in its overexpression and therefore promote inhibition of p53 activity. To deal with this problem, a judicious approach is to employ MDM2 inhibitors. Several promising MDM2 inhibitors have been described such as nutlins, benzodiazepinediones or spiro-oxindoles as well as novel compound classes such as xanthone derivatives and trisubstituted aminothiophenes. Furthermore, even naturally derived inhibitor compounds such as a-mangostin, gambogic acid and siladenoserinols have been discovered. In this review, we discuss in detail such small molecules that play a pertinent role in affecting the p53-MDM2 signaling axis and analyze their potential as cancer chemotherapeutics.

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.

Intracellular targeting of annexin A2 inhibits tumor cell adhesion, migration, and in vivo grafting

Cytoskeletal-associated proteins play an active role in coordinating the adhesion and migration machinery in cancer progression. To identify functional protein networks and potential inhibitors, we screened an internalizing phage (iPhage) display library in tumor cells, and selected LGRFYAASG as a cytosol-targeting peptide. By affinity purification and mass spectrometry, intracellular annexin A2 was identified as the corresponding binding protein. Consistently, annexin A2 and a cell-internalizing, penetratin-fused version of the selected peptide (LGRFYAASG-pen) co-localized and specifically accumulated in the cytoplasm at the cell edges and cell-cell contacts. Functionally, tumor cells incubated with LGRFYAASG-pen showed disruption of filamentous actin, focal adhesions and caveolae-mediated membrane trafficking, resulting in impaired cell adhesion and migration in vitro. These effects were paralleled by a decrease in the phosphorylation of both focal adhesion kinase (Fak) and protein kinase B (Akt). Likewise, tumor cells pretreated with LGRFYAASG-pen exhibited an impaired capacity to colonize the lungs in vivo in several mouse models. Together, our findings demonstrate an unrecognized functional link between intracellular annexin A2 and tumor cell adhesion, migration and in vivo grafting. Moreover, this work uncovers a new peptide motif that binds to and inhibits intracellular annexin A2 as a candidate therapeutic lead for potential translation into clinical applications.

DYT-40, a novel synthetic 2-styryl-5-nitroimidazole derivative, blocks malignant glioblastoma growth and invasion by inhibiting AEG-1 and NF-κB signaling pathways

Astrocyte elevated gene-1 (AEG-1) has been explored as a novel target for human glioma therapy, thus reflecting its potential contribution to gliomagenesis. In the present study, we investigated the effect of DYT-40, a novel synthetic 2-styryl-5-nitroimidazole derivative, on cell growth and invasion in glioblastoma (GBM) and uncovered the underlying mechanisms of this molecule. DYT-40 induces the intrinsic mitochondrial pathway of apoptosis and inhibits the epithelial-mesenchymal transition (EMT) and invasion of GBM cell lines. Furthermore, DYT-40 deactivates PI3K/Akt and MAPK pathways, suppresses AEG-1 expression, and inhibits NF-κB nuclear translocation. DYT-40 reduced the tumor volumes in a rat C6 glioma model by apoptotic induction. Moreover, HE staining demonstrated that the glioma rat model treated with DYT-40 exhibited better defined tumor margins and fewer invasive cells to the contralateral striatum compared with the vehicle control and temozolomide-treated rats. Microscopic examination showed a decrease in AEG-1-positive cells in DYT-40-treated rats compared with the untreated controls. DYT-40-treatment increases the in vivo apoptotic response of glioma cells to DYT-40 treatment by TUNEL staining. In conclusion, the inhibitory effects of DYT-40 on growth and invasion in GBM suggest that DYT-40 might be a potential AEG-1 inhibitor to prevent the growth and motility of malignant glioma.

Natural Product Inhibitors of Ubiquitin Conjugation and Deconjugation

The ubiquitin–proteasome system has been recognized as fundamental toward protein turnover in eukaryotic cells. The system comprises the ubiquitin conjugation machinery consisting of an enzyme cascade of E1, E2, and E3 enzymes, the deubiquitinases (DUBs) and the proteasome, a multisubunit protease complex acting through an N-terminal threonine protease mechanism. A number of natural product inhibitors of the proteasome have been studied in detail and these inhibitors and their derivatives have been highly valuable in developing our understanding of this system. These efforts culminated in the successful development of bortezomib as a pharmacological agent used clinically as a cancer therapeutic in the treatment of multiple myeloma.

This review is focused on natural product inhibitors of the enzymes involved in intracellular ubiquitin conjugation (ubiquitin-activating enzyme E1, ubiquitin-conjugating enzyme E2, ubiquitin ligase E3) and ubiquitin deconjugation (DUBs). Members of both of these enzyme systems have been proposed as pharmacological targets for cancer therapy and several other diseases. Furthermore compounds with activities toward enzymes from the analogous ubiquitin-like (Ubl) protein families have been identified for SUMO and NEDD8. To date natural product inhibitors have been described for members of each of these protein families and were isolated from plant, fungal, animal, and microbial sources. Insights into the mechanism of action of natural products and their derivatives will enhance our understanding of this complex system and will improve our ability to rationally design novel inhibitors. The increased availability of assays and research tools for the study of protein ubiquitination, deubiquitination, and Ubl proteins will contribute to the discovery of more potent and selective compounds. We expect that these studies will stimulate development of further potential pharmacological agents in this area.

Natural products with therapeutic potential in melanoma metastasis

Malignant melanoma is the most aggressive form of skin cancer and accounts for about 3% of all cases of malignant tumour. Its incidence is increasing worldwide and it is becoming resistant to current therapeutic agents. Natural products continue to provide lead cytotoxic compounds for cancer treatment but less attention has been given to antimigratory compounds. This paper systematically and critically surveys all natural products with direct in vitro and in vivo pharmacological effects on migration and/or metastasis of melanoma cells and maps the mechanisms of action for these underexploited properties. As a result, over 30 natural active principles are described acting mainly through their antagonistic effects upon the TNF-α and EP2 receptors or the suppression of several protein kinases involved in metastatic pathways such as RAS, PI3K, ERK and FAK. Also, some were able to reduce the level of mesenchymal biomarkers such as N-cadherin and/or elevate the expression of other molecules such as E-cadherin. Consequently, downstream transcription factors namely NF-kB, AP-1, ATF-2, CREB, and HIF were inactivated leading to diminished production of MMPs, IL-1, IL-6, COX-2, VEGF and GM-CSF. This review also discusses the opportunity of combination therapies based on natural products and approved drugs, such as the combination of EGCG and dacarbazine, or the combination of two natural compounds such as quercetin and sulforaphane.

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.

Gambogic acid induces apoptosis and inhibits colorectal tumor growth via mitochondrial pathways

AIM: To investigate the effect of gambogic acid (GA) on apoptosis in the HT-29 human colon cancer cell line.

METHODS: H-29 cells were used for in vitro experiments in this study. Relative cell viability was assessed using MTT assays. Cell apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling and Hoechst 33342 staining, and quantified by flow cytometry. Cellular ultrastructure was observed by transmission electron microscopy. Real-time PCR and Western blot analyses were used to evaluate gene and protein expression levels. For in vivo experiments, BALB/c nude mice received subcutaneous injections of HT-29 cells in the right armpit. When well-established xenografts were palpable with a tumor size of 75 mm³, mice were randomly assigned to a vehicle (negative) control, positive control or GA treatment group (n = 6 each). The animals in the treatment group received one of three dosages of GA (in saline; 5, 10 or 20 mg/kg) via the caudal vein twice weekly, whereas animals in the negative and positive control groups were given equal volumes of 0.9% saline or 10 mg/kg docetaxel, respectively, via the caudal vein once weekly.

RESULTS: The cell viability assay showed that GA inhibited proliferation of HT-29 cells in a dose- and time-dependent manner after treatment with GA (0.00, 0.31, 0.62, 1.25, 2.50, 5.00 or 10.00 μmol/L) for 24, 48 or 72 h. After 48 h, the percentage of apoptotic cells in cells treated with 0.00, 1.25, 2.50 and 5.00 μmol/L GA was 1.4% ± 0.3%, 9.8% ± 1.2%, 25.7% ± 3.3% and 49.3% ± 5.8%, respectively. Ultrastructural analysis of HT-29 cells treated for 48 h with 2.5μmol/L GA revealed apoptotic bodies and condensed and fragmented nuclei. Levels of caspase-8, -9 and -3 mRNAs were significantly increased after treatment with GA (1.25, 2.50 or 5.00 μmol/L) for 48 h (P < 0.05 for all). Protein levels of apoptosis-related factors Fas, FasL, FADD, cytochrome c, and Apaf-1 were increased in GA-treated cells, whereas levels of pro-caspase-8, -9 and -3 were significantly decreased (P < 0.05 for all). Furthermore, GA significantly and dose-dependently inhibited the growth of HT-29 tumors in a mouse xenograft model (P < 0.05).

CONCLUSION: GA inhibits HT-29 proliferation via induction of apoptosis. The anti-cancer effects are likely mediated by death receptor (extrinsic) and mitochondrial (intrinsic) pathways.

A pentacyclic triterpene natural product, ursolic acid and its prodrug US597 inhibit targets within cell adhesion pathway and prevent cancer metastasis

Here we showed that ursolic acid (UA), a pentacyclic triterpene natural product, and its novel prodrug derivative US597 suppressed cancer cells adhesion, invasion and migration. This effect was accompanied by inhibition of focal adhesion signaling pathway including alterations in ICAM-1, VCAM-1, E-selectin, P-selectin, integrin α6β1, FAK, Src, paxillin and PTEN. While oral administration of UA or US597 increases survival rate of melanoma lung metastasis in C57BL/6 mice, US597 treatment extend the survival rate above that of UA. Immunohistochemical analysis revealed that US597 treatment regulates ICAM-1, a biomarker of metastasis. We did not detect side effects with US597 in mice such as weight loss, viscera tissues toxicity and blood cell abnormalities. Thus, UA and US597 are potential drug candidates for preventing cancer metastasis. Molecular and cellular study data suggest that UA and US597 modulate expression of cell adhesion molecules within focal adhesion signaling pathway leading to cancer cell motility.

Inhibitory effects of kaempferol on the invasion of human breast carcinoma cells by downregulating the expression and activity of matrix metalloproteinase-9

Matrix metalloproteinases (MMPs) have been regarded as major critical molecules assisting tumor cells during metastasis, for excessive ECM (ECM) degradation, and cancer cell invasion. In the present study, in vitro and in vivo assays were employed to examine the inhibitory effects of kaempferol, a natural polyphenol of flavonoid family, on tumor metastasis. Data showed that kaempferol could inhibit adhesion, migration, and invasion of MDA-MB-231 human breast carcinoma cells. Moreover, kaempferol led to the reduced activity and expression of MMP-2 and MMP-9, which were detected by gelatin zymography, real-time PCR, and western blot analysis, respectively. Further elucidation of the mechanism revealed that kaempferol treatment inhibited the activation of transcription factor activator protein-1 (AP-1) and MAPK signaling pathway. Moreover, kaempferol repressed phorbol-12-myristate-13-acetate (PMA)-induced MMP-9 expression and activity through suppressing the translocation of protein kinase Cδ (PKCδ) and MAPK signaling pathway. Our results also indicated that kaempferol could block the lung metastasis of B16F10 murine melanoma cells as well as the expression of MMP-9 in vivo. Taken together, these results demonstrated that kaempferol could inhibit cancer cell invasion through blocking the PKCδ/MAPK/AP-1 cascade and subsequent MMP-9 expression and its activity. Therefore, kaempferol might act as a therapeutic potential candidate for cancer metastasis.

LFG-500 inhibits the invasion of cancer cells via down-regulation of PI3K/AKT/NF-κB signaling pathway

Cancer cell invasion, one of the crucial events in local growth and metastatic spread of tumors, possess a broad spectrum of mechanisms, especially altered expression of matrix metalloproteinases. LFG-500 is a novel synthesized flavonoid with strong anti-cancer activity, whose exact molecular mechanism remains incompletely understood. This current study was designed to examine the effects of LFG-500 on tumor metastasis using in vitro and in vivo assays. LFG-500 could inhibit adhesion, migration and invasion of MDA-MB-231 human breast carcinoma cells. Meanwhile, it reduced the activities and expression of MMP-2 and MMP-9 via suppressing the transcriptional activation of NF-κB rather than AP-1 or STAT3. Moreover, LFG-500 repressed TNF-α induced cell invasion through inhibiting NF-κB and subsequent MMP-9 activity. Further elucidation of the mechanism revealed that PI3K/AKT but not MAPK signaling pathway was involved in the inhibitory effect of LFG-500 on NF-κB activation. LFG-500 could also suppress lung metastasis of B16F10 murine melanoma cells in vivo. Taken together, these results demonstrated that LFG-500 could block cancer cell invasion via down-regulation of PI3K/AKT/NF-κB signaling pathway, which provides new evidence for the anti-cancer activity of LFG-500.

Melanoma stem cells and metastasis: mimicking hematopoietic cell trafficking?

Malignant melanoma is a highly metastatic cancer that bears responsibility for the majority of skin cancer-related deaths. Amidst the research efforts to better understand melanoma progression, there has been increasing evidence that hints at a role for a subpopulation of virulent cancer cells, termed malignant melanoma stem or initiating cells (MMICs), in metastasis formation. MMICs are characterized by their preferential ability to initiate and propagate tumor growth and their selective capacity for self-renewal and differentiation into less tumorigenic melanoma cells. The frequency of MMICs has been shown to correlate with poor clinical prognosis in melanoma. In addition, MMICs are enriched among circulating tumor cells in the peripheral blood of cancer patients, suggesting that MMICs may be a critical factor in the metastatic cascade. Although these links exist between MMICs and metastatic disease, the mechanisms by which MMICs may advance metastatic progression are only beginning to be elucidated. Recent studies have shown that MMICs express molecules critical for hematopoietic cell maintenance and trafficking, providing a possible explanation for how circulating MMICs could drive melanoma dissemination. We therefore propose that MMICs might fuel melanoma metastasis by exploiting homing mechanisms commonly utilized by hematopoietic cells. Here we review the biological properties of MMICs and the existing literature on their metastatic potential. We will discuss possible mechanisms by which MMICs might initiate metastases in the context of established knowledge of cancer stem cells in other cancers and of hematopoietic homing molecules, with a particular focus on selectins, integrins, chemokines and chemokine receptors known to be expressed by melanoma cells. Biological understanding of how these molecules might be utilized by MMICs to propel the metastatic cascade could critically impact the development of more effective therapies for advanced disease.

Α-mangostin and gambogic acid as potential inhibitors of the p53-MDM2 interaction revealed by a yeast approach

α-Mangostin (1) and gambogic acid (2) are natural products with potent cytotoxic activity against several human tumor cells. However, their molecular mechanisms of action remain controversial. In this work, using yeast-based assays, it was shown that both xanthones are potential inhibitors of the p53-MDM2 interaction. This activity on p53-MDM2 interaction was confirmed by a gene reporter assay in a human tumor cell. Additionally, computational docking studies supported the potential of these xanthones to bind to MDM2 and therefore act as putative MDM2 inhibitors. Altogether, this work provides a new insight concerning the molecular basis of activity for these compounds.

Gambogic acid promotes apoptosis and resistance to metastatic potential in MDA-MB-231 human breast carcinoma cells

Gambogic acid (GA) is considered a potent anti-tumor agent for its multiple effects on cancer cells in vitro and in vivo. Low concentrations of GA (0.3-1.2 µmol/L) can suppress invasion of human breast carcinoma cells without affecting cell viability. To get a whole profile of the inhibition on breast cancers, higher concentrations of GA and spontaneous metastatic animal models were employed. Treatment with GA (3 and 6 µmol/L) induced apoptosis in MDA-MB-231 cells and the accumulation of reactive oxygen species (ROS). Furthermore, GA induced PARP cleavage, activation of caspase-3, caspase-8, and caspase-9, as well as an increased ratio of Bax/Bcl-2. Moreover, the translocation of apoptotic inducing factor (AIF) and the release of cytochrome c (Cyt c) from mitochondria were observed, indicating that GA induced apoptosis through accumulation of ROS and mitochondrial apoptotic pathway. GA also inhibited cell survival via blocking Akt/mTOR signaling. In vivo, GA significantly inhibited the xenograft tumor growth and lung metastases in athymic BALB/c nude mice bearing MDA-MB-231 cells. Collectively, these data provide further support for the multiple effects of GA on human breast cancer cells, as well as for its potential application to inhibit tumor growth and prevent metastasis in human cancers.

Molecular pathways: VCAM-1 as a potential therapeutic target in metastasis

Interactions between disseminated tumor cells (DTC) and stromal cells in the microenvironment are critical for tumor colonization of distal organs. Recent studies have shown that vascular cell adhesion molecule-1 (VCAM-1) is aberrantly expressed in breast cancer cells and mediates prometastatic tumor-stromal interactions. Moreover, the usefulness of VCAM-1 to DTCs in 2 different organs--lung and bone--is based on distinct mechanisms. In the lungs, VCAM-1 on the surface of cancer cells binds to its counterreceptor, the α4β1 integrin (also known as very-late antigen, VLA-4), on metastasis-associated macrophages, triggering VCAM-1-mediated activation of the phosphoinositide 3-kinase growth and survival pathway in the cancer cells. In the bone marrow, cancer cell VCAM-1 attracts and tethers α4 integrin-expressing osteoclast progenitors to facilitate their maturation into multinucleated osteoclasts that mediate osteolytic metastasis. These findings highlight the importance of direct interactions between DTCs and stromal cells during tumor dissemination and draw attention to the possibility of targeting the α4 integrin-VCAM-1 interactions in metastatic breast cancer. Anti-α4 integrin inhibitors have been developed to treat various diseases driven by massive leukocyte infiltrates and have gained U.S. Food and Drug Administration approval or are undergoing clinical trials. Testing these drugs against tumor-stromal leukocyte interactions may provide a new strategy to suppress lung and bone relapse of breast cancer.

Knockdown of von Hippel-Lindau protein decreases lung cancer cell proliferation and colonization

Although von Hippel-Lindau protein (pVHL) is known as a tumor suppressor in kidney and other organs, it remains unclear whether pVHL plays a role in lung cancer development. We investigated the role of pVHL in lung cancer cell proliferation, migration, and colonization using stable A549 cells with knockdown of pVHL. We found that knockdown of pVHL promotes epithelial-mesenchymal transition (EMT) in lung cancer cells. Knockdown of pVHL decreased tumor colonization in a tail-vein injection model and decreased cell proliferation, whereas overexpression of constitutive active HIF increased tumor colonization, suggesting a HIF-independent function of pVHL in lung. Knockdown of pVHL decreased phosphorylation of FAK and expression of integrin, suggesting that pVHL regulates lung cancer development via integrin/FAK signaling pathway.

Anticancer drugs from traditional toxic Chinese medicines

Many anticancer drugs are obtained from natural sources. Nature produces a variety of toxic compounds, which are often used as anticancer drugs. Up to now, there are at least 120 species of poisonous botanicals, animals and minerals, of which more than half have been found to possess significant anticancer properties. In spite of their clinical toxicity, they exhibit pharmacological effects and have been used as important traditional Chinese medicines for the different stages of cancer. The article reviews many structures such as alkaloids of Camptotheca acuminata, Catharanthus roseus and Cephalotaxus fortunei, lignans of Dysosma versipellis and Podophyllum emodi, ketones of Garcinia hanburyi, terpenoids of Mylabris and Ginkgo biloba, diterpenoids of Tripterygium wilfordii, Euphorbia fischeriana, Euphorbia lathyris, Euphorbia kansui, Daphne genkwa, Pseudolarix kaempferi and Brucea javanica, triterpenoids of Melia toosendan, steroids of Periploca sepium, Paris polyphylla and Venenum Bufonis, and arsenic compounds including Arsenicum and Realgar. By comparing their related phytochemistry, toxic effects and the recent advances in understanding the mechanisms of action, this review puts forward some ideals and examples about how to increase antitumour activity and/or reduce the side effects experienced with Chinese medicine.

Prenylated caged xanthones: chemistry and biology

CONTEXT

Prenylated caged xanthones are "privileged structure" characterized by the presence of the unusual 4-oxo-tricyclo[4.3.1.0(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.

Gambogic acid inhibits tumor cell adhesion by suppressing integrin β1 and membrane lipid rafts-associated integrin signaling pathway

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.

Anti-cancer natural products isolated from chinese medicinal herbs

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.

Anti-cancer natural products isolated from chinese medicinal herbs

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.

Absolute configuration of (-)-gambogic acid, an antitumor agent

(-)-Gambogic acid (1), a biologically active "caged xanthone" from gamboge, the dried resin of Garcinia hanburyi, is of interest as a potential anticancer agent. The planar structure of (-)-gambogic acid has been determined previously by analysis of its detailed NMR data and confirmed by single-crystal X-ray diffraction, with the absolute configuration at C-13 deduced as R through a series of chemical degradations. Using (-)-morellic acid (2), an analogue of (-)-gambogic acid, as a model compound, the 5R, 7S, 10aS, 13R, 27S absolute configuration of (-)-gambogic acid was determined for the first time by comparison of physical and spectroscopic data, especially experimental and calculated electronic circular dichroism.

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.

Biomarkers: the useful and the not so useful--an assessment of molecular prognostic markers for cutaneous melanoma

Among individuals with localized (Stage I-II) melanoma, stratifying patients by a number of phenotypic variables (e.g., depth of invasion, ulceration) yields a wide range of 10-year melanoma-specific survival rates. With the possible exception of Ki-67, no molecular assessment is routinely used. However, there have been a tremendous number of studies assessing protein expression by immunohistochemistry toward the goal of better prediction of recurrence. In a previous systematic review, which required publication of multivariable prognostic models as a strict inclusion criterion, we identified 37 manuscripts that collectively reported on 62 proteins. Data for 324 proteins extracted from 418 manuscripts did not meet our inclusion criteria for that study, but are revisited here, emphasizing trends of protein expression across either melanocytic lesion progression or gradations of tumor thickness. These identified 101 additional proteins that stratify melanoma, organized according to the Hanahan and Weinberg functional capabilities of cancer.

Vitamin A enhances antitumor effect of a green tea polyphenol on melanoma by upregulating the polyphenol sensing molecule 67-kDa laminin receptor

Background

Green tea consumption has been shown to have cancer preventive qualities. Among the constituents of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG) is the most effective at inhibiting carcinogenesis. However, the concentrations of EGCG that are required to elicit the anticancer effects in a variety of cancer cell types are much higher than the peak plasma concentration that occurs after drinking an equivalent of 2–3 cups of green tea. To obtain the anticancer effects of EGCG when consumed at a reasonable concentration in daily life, we investigated the combination effect of EGCG and food ingredient that may enhance the anticancer activity of EGCG on subcutaneous tumor growth in C57BL/6N mice challenged with B16 melanoma cells.

Methodology/Principal Findings

All-trans-retinoic acid (ATRA) enhanced the expression of the 67-kDa laminin receptor (67LR) and increased EGCG-induced cell growth inhibition in B16 melanoma cells. The cell growth inhibition seen with the combined EGCG and ATRA treatment was abolished by treatment with an anti-67LR antibody. In addition, the combined EGCG and ATRA treatment significantly suppressed the melanoma tumor growth in mice. Expression of 67LR in the tumor increased upon oral administration of ATRA or a combined treatment of EGCG and ATRA treatment. Furthermore, RNAi-mediated silencing of the retinoic acid receptor (RAR) α attenuated the ATRA-induced enhancement of 67LR expression in the melanoma cells. An RAR agonist enhanced the expression levels of 67LR and increased EGCG-induced cell growth inhibition.

Conclusions/Significance

Our findings provide a molecular basis for the combination effect seen with dietary components, and indicate that ATRA may be a beneficial food component for cancer prevention when combined with EGCG.

In vivo tumor cell adhesion in the pulmonary microvasculature is exclusively mediated by tumor cell--endothelial cell interaction

BACKGROUND

Metastasis formation is the leading cause of death among colon cancer patients. We established a new in-situ model of in vivo microscopy of the lung to analyse initiating events of metastatic tumor cell adhesion within this typical metastatic target of colon cancer.

METHODS

Anaesthetized CD rats were mechanically ventilated and 106 human HT-29LMM and T84 colon cancer cells were injected intracardially as single cell suspensions. Quantitative in vivo microscopy of the lung was performed in 10 minute intervals for a total of 40 minutes beginning with the time of injection.

RESULTS

After vehicle treatment of HT-29LMM controls 15.2 +/- 5.3; 14.2 +/- 7.5; 11.4 +/- 5.5; and 15.4 +/- 6.5 cells/20 microscopic fields were found adherent within the pulmonary microvasculature in each 10 minute interval. Similar numbers were found after injection of the lung metastasis derived T84 cell line and after treatment of HT-29LMM with unspecific mouse control-IgG. Subsequently, HT-29LMM cells were treated with function blocking antibodies against beta1-, beta4-, and alphav-integrins wich also did not impair tumor cell adhesion in the lung. In contrast, after hydrolization of sialylated glycoproteins on the cells' surface by neuraminidase, we observed impairment of tumor cell adhesion by more than 50% (p < 0.05). The same degree of impairment was achieved by inhibition of P- and L-selectins via animal treatment with fucoidan (p < 0.05) and also by inhibition of the Thomson-Friedenreich (TF)-antigen (p < 0.05).

CONCLUSIONS

These results demonstrate that the initial colon cancer cell adhesion in the capillaries of the lung is predominantly mediated by tumor cell - endothelial cell interactions, possibly supported by platelets. In contrast to reports of earlier studies that metastatic tumor cell adhesion occurs through integrin mediated binding of extracellular matrix proteins in liver, in the lung, the continuously lined endothelium appears to be specifically targeted by circulating tumor cells.

Involvement of matrix metalloproteinase 2 and 9 in gambogic acid induced suppression of MDA-MB-435 human breast carcinoma cell lung metastasis

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.