α-Solanine inhibits human melanoma cell migration and invasion by reducing matrix metalloproteinase-2/9 activities

Solanine-induced reactive oxygen species inhibit the growth of human hepatocellular carcinoma HepG2 cells

The aim of the present study was to investigate the effect of solanine on promoting human hepatocellular carcinoma HepG2 cells to produce reactive oxygen species (ROS), and the molecular mechanisms leading to tumor cell apoptosis. Solanine was administered to HepG2 cells in vitro. A selection of probes targeting various cellular localizations of ROS were used to detect ROS expression using flow cytometry. The expression levels of apoptosis-associated proteins, including apoptosis signal-regulating kinase 1 (ASK1) and thioredoxin binding protein 2 (TBP-2), and proliferation-associated proteins, including histone deacetylase 1 (HDAC1), were detected using western blotting. The percentage of cells undergoing apoptosis was measured using an Annexin V-fluorescein isothiocyanate/propidium iodide assay, and cell morphology was examined using Wright's stain followed by inverted microscopy analysis. ROS detection probes 2',7'-dichlorofluorescin diacetate and dihydrorhodamine 123 identified that abundant ROS, including hydroxyl radical (OH^-) and hydrogen peroxide (H₂O₂), were produced in the cytoplasm and mitochondria of the solanine-treated HepG2 cells compared with the control cells (P<0.05). Superoxide anion specific probes dihydroethidium and MitoSOX™ demonstrated that there were no significant alterations in the HepG2 cells following solanine treatment compared with the control cells (P>0.05). Western blotting results revealed that solanine upregulated the expression levels of ASK1 and TBP-2 and enhanced their kinase activities, whereas solanine decreased the expression level of the proliferation-associated protein, HDAC1. The cell apoptotic rate was significantly increased (P<0.0001) in the solanine-treated HepG2 cells compared with the control cells. (P<0.05). Overall, the study indicated that solanine induces HepG2 cells to produce ROS, mainly OH^- and H₂O₂, in a mitochondria-dependent and -independent manner. In addition, solanine stimulates the expression of ASK1 and TBP-2, and their kinase activities, but inhibits the expression of proliferation-associated proteins, such as HDAC1, thus contributing to HepG2 cell apoptosis.

α-Solanine inhibits vascular endothelial growth factor expression by down-regulating the ERK1/2-HIF-1α and STAT3 signaling pathways

In tumors, vascular endothelial growth factor (VEGF) contributes to angiogenesis, vascular permeability, and tumorigenesis. In our previous study, we found that α-solanine, which is widespread in solanaceae, has a strong anti-cancer effect under normoxia. However, it is unknown whether α-solanine has a similar effect under hypoxia. We used cobalt chloride (CoCl2) to mimic hypoxia in vitro. HIF-1α, which is almost undetectable under normoxia, was significantly increased. Simultaneously, another regulator of VEGF, STAT3, was also significantly activated by CoCl2. We utilized α-solanine in co-culture with CoCl2. α-solanine decreased the expression of VEGF and loss of E-cadherin. α-solanine also suppressed the activation of phospho-ERK1/2 (p-ERK1/2), HIF-1α, and STAT3 signaling. The results provide new evidence that α-solanine has a strong anti-cancer effect via the ERK1/2-HIF-1α and STAT3 signaling pathways and suggest that it may be a potential new drug.

Anticancer function of α-solanine in lung adenocarcinoma cells by inducing microRNA-138 expression

Currently, lung cancer is still a main cause of malignancy-associated death worldwide. Even though various methods for prevention and treatment of lung cancer have been improved in recent decades, the 5-year survival rate has remained very low. Insights into the anticancer function of small-molecule anticancer compounds have opened our visual field about cancer therapy. α-Solanine has been well studied for its antitumor properties, but its effect in lung cancer and associated molecular mechanisms have not yet been evaluated. To explore the anticancer function of α-solanine, we performed an MTT assay, Transwell arrays, colony-forming survival assay, quantitative reverse transcription PCR (qRT-PCR), Western blotting, and dual luciferase reporter assays in A549 and H1299 cells. We found that α-solanine not only inhibited cell migration and invasion ability but also enhanced the chemosensitivity and radiosensitivity of A549 and H1299 cells. Moreover, we discovered that α-solanine could affect the expression of miR-138 and focal adhesion kinase (FAK), both of which were also found to affect the chemosensitivity and radiosensitivity of A549 and H1299 cells. In conclusion, α-solanine could affect miR-138 and FAK expression to restrict cell migration and invasion and enhance the chemosensitivity and radiosensitivity of A549 and H1299 cells. The α-solanine/miR-138/FAK cascade can probably be a potential therapy target against lung adenocarcinoma.

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.

α-Solanine induces ROS-mediated autophagy through activation of endoplasmic reticulum stress and inhibition of Akt/mTOR pathway

α-Solanine is a glycoalkaloid found in species of the nightshade family including potato. It was primarily reported to have toxic effects in humans. However, there is a growing body of literature demonstrating in vitro and in vivo anticancer activity of α-solanine. Most of these studies have shown activation of apoptosis as the underlying mechanism in antitumor activity of α-solanine. In this study, we report α-solanine as a potential inducer of autophagy, which may act synergistically or in parallel with apoptosis to exert its cytotoxic effect. Induction of autophagy was demonstrated by several assays including electron microscopy, immunoblotting of autophagy markers and immunofluorescence for LC3 (microtubule-associated protein 1 (MAP1) light chain-3) puncta. α-Solanine-induced autophagic flux was demonstrated by additionally enhanced – turnover of LC3-II and – accumulation of LC3-specific puncta after co-incubation of cells with either of the autophagolysosome inhibitors – chloroquine and – bafilomycin A1. We also demonstrated α-solanine-induced oxidative damage in regulating autophagy where pre-incubation of cells with reactive oxygen species (ROS) scavenger resulted in suppression of CM-H₂DCFDA (5 (and 6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate acetyl ester) fluorescence as well as decrease in LC3-II turnover. α-Solanine treatment caused an increase in the expression of endoplasmic reticulum (ER) stress proteins (BiP, activating transcription factor 6 (ATF6), X-box-binding protein 1, PERK, inositol-requiring transmembrane kinase/endonuclease 1, ATF4 and CCAAT-enhancer-binding protein (C/EBP)-homologous protein) suggesting activation of unfolded protein response pathway. Moreover, we found downregulation of phosphorylated Akt (Thr³⁰⁸ and Ser⁴⁷³), mammalian target of rapamycin (mTOR; Ser²⁴⁴⁸ and Ser²⁴⁸¹) and 4E-BP1 (Thr^37/46) by α-solanine implying suppression of the Akt/mTOR pathway. Collectively, our results signify that α-solanine induces autophagy to exert anti-proliferative activity by triggering ER stress and inhibiting Akt/mTOR signaling pathway.

Chemistry and anticarcinogenic mechanisms of glycoalkaloids produced by eggplants, potatoes, and tomatoes

Inhibition of cancer can occur via apoptosis, a genetically directed process of cell self-destruction that involves numerous biomarkers and signaling pathways. Glycoalkaloids are nitrogen-containing secondary plant metabolites found in numerous Solanaceous plants including eggplants, potatoes, and tomatoes. Exposure of cancer cells to glycoalkaloids produced by eggplants (α-solamargine and α-solasonine), potatoes (α-chaconine and α-solanine), and tomatoes (α-tomatine) or their hydrolysis products (mono-, di-, and trisaccharide derivatives and the aglycones solasodine, solanidine, and tomatidine) inhibits the growth of the cells in culture (in vitro) as well as tumor growth in vivo. This overview comprehensively surveys and consolidates worldwide efforts to define the following aspects of these natural compounds: (a) their prevalence in the three foods; (b) their chemistry and structure-activity relationships; (c) the reported factors (biomarkers, signaling pathways) associated with apoptosis of bone, breast, cervical, colon, gastric, glioblastoma, leukemia, liver, lung, lymphoma, melanoma, pancreas, prostate, and squamous cell carcinoma cell lines in vitro and the in vivo inhibition of tumor formation and growth in fish and mice and in human skin cancers; and (d) future research needs. The described results may make it possible to better relate the structures of the active compounds to their health-promoting function, individually, in combination, and in food, and allow the consumer to select glycoalkaloid-containing food with the optimal content of nontoxic beneficial compounds. The described findings are expected to be a valuable record and resource for further investigation of the health benefits of food-related natural compounds.

Therapeutic Potential of Steroidal Alkaloids in Cancer and Other Diseases

Steroidal alkaloids are a class of secondary metabolites isolated from plants, amphibians, and marine invertebrates. Evidence accumulated in the recent two decades demonstrates that steroidal alkaloids have a wide range of bioactivities including anticancer, antimicrobial, anti-inflammatory, antinociceptive, etc., suggesting their great potential for application. It is therefore necessary to comprehensively summarize the bioactivities, especially anticancer activities and mechanisms of steroidal alkaloids. Here we systematically highlight the anticancer profiles both in vitro and in vivo of steroidal alkaloids such as dendrogenin, solanidine, solasodine, tomatidine, cyclopamine, and their derivatives. Furthermore, other bioactivities of steroidal alkaloids are also discussed. The integrated molecular mechanisms in this review can increase our understanding on the utilization of steroidal alkaloids and contribute to the development of new drug candidates. Although the therapeutic potentials of steroidal alkaloids look promising in the preclinical and clinical studies, further pharmacokinetic and clinical studies are mandated to define their efficacy and safety in cancer and other diseases.

α-Solanine inhibits invasion of human prostate cancer cell by suppressing epithelial-mesenchymal transition and MMPs expression

α-Solanine, a naturally occurring steroidal glycoalkaloid found in nightshade (Solanum nigrum Linn.), was found to inhibit proliferation and induce apoptosis of tumor cells. However, the mechanism involved in suppression of cancer cell metastasis by α-solanine remains unclear. This study investigates the suppression mechanism of α-solanine on motility of the human prostate cancer cell PC-3. Results show that α-solanine reduces the viability of PC-3 cells. When treated with non-toxic doses of α-solanine, cell invasion is markedly suppressed by α-solanine. α-Solanine also significantly elevates epithelial marker E-cadherin expression, while it concomitantly decreases mesenchymal marker vimentin expression, suggesting it suppresses epithelial-mesenchymal transition (EMT). α-Solanine reduces the mRNA level of matrix metalloproteinase-2 (MMP-2), MMP-9 and extracellular inducer of matrix metalloproteinase (EMMPRIN), but increases the expression of reversion-inducing cysteine-rich protein with kazal motifs (RECK), and tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2. Immunoblotting assays indicate α-solanine is effective in suppressing the phosphorylation of phosphatidylinositide-3 kinase (PI3K), Akt and ERK. Moreover, α-solanine downregulates oncogenic microRNA-21 (miR-21) and upregulates tumor suppressor miR-138 expression. Taken together, the results suggest that inhibition of PC-3 cell invasion by α-solanine may be, at least in part, through blocking EMT and MMPs expression. α-Solanine also reduces ERK and PI3K/Akt signaling pathways and regulates expression of miR-21 and miR-138. These findings suggest an attractive therapeutic potential of α-solanine for suppressing invasion of prostate cancer cell.

Solanine induces mitochondria-mediated apoptosis in human pancreatic cancer cells

Steroid alkaloids have been suggested as potential anticancer compounds. However, the underlying mechanisms of how steroid alkaloids inhibit the tumor growth are largely unknown. Here, we reported that solanine, a substance of steroid alkaloids, has a positive effect on the inhibition of pancreatic cancer cell growth in vitro and in vivo. In pancreatic cancer cells and nu/nu nude mice model, we found that solanine inhibited cancer cells growth through caspase-3 dependent mitochondrial apoptosis. Mechanically, solanine promotes the opening of mitochondrial membrane permeability transition pore (MPTP) by downregulating the Bcl-2/Bax ratio; thereafter, Cytochrome c and Smac are released from mitochondria into cytosol to process the caspase-3 zymogen into an activated form. Moreover, we found that the expression of tumor metastasis related proteins, MMP-2 and MMP-9, was also decreased in the cells treated with solanine. Therefore, our results suggested that solanine was an effective compound for the treatment of pancreatic cancer.

The protective and therapeutic effects of alpha-solanine on mice breast cancer

Alpha-solanine, a naturally steroidal glycoalkaloid, is found in leaves and fruits of plants as a defensive agent against fungi, bacteria and insects. Herein, we investigated solanine toxicity in vitro and in vivo, and assessed its protective and the therapeutic effects on a typical animal model of breast cancer. The study conducted in three series of experiments to obtain (i) solanine effects on cell viability of mammary carcinoma cells, (ii) in vivo toxicity of solanine, and (iv) the protective and therapeutic effects of solanine on animal model of breast cancer. Alpha-solanine significantly suppressed proliferation of mouse mammary carcinoma cells both in vitro and in vivo (P<0.05). Under the dosing procedure, 5 mg/kg solanine has been chosen for assessing its protective and therapeutic effects in mice breast cancer. Tumor take rate in the solanine-treated group was zero compared with a 75% rate in its respective control group (P<0.05). The average tumor size and weight were significantly lower in solanine-treated animals than its respective control ones (P<0.05). Proapoptotic Bax protein expression increased in breast tumor by solanine compared with its respective control group (P<0.05). Antiapoptotic Bcl-2 protein expression found to be lower in solanine-treated animals (P<0.05). Proliferative and angiogenic parameters greatly decreased in solanine-treated mice (P<0.05). Data provide evidence that solanine exerts a significant chemoprotective and chemotherapeutic effects on an animal model of breast cancer through apoptosis induction, cell proliferation and angiogenesis inhibition. These findings reveal a new therapeutic potential for solanine in cancer.

Tomatidine inhibits invasion of human lung adenocarcinoma cell A549 by reducing matrix metalloproteinases expression

Tomatidine is an aglycone of glycoalkaloid tomatine in tomato. Tomatidine is found to possess anti-inflammatory properties and may serve as a chemosensitizer in multidrug-resistant tumor cells. However, the effect of tomatidine on cancer cell metastasis remains unclear. This study examines the effect of tomatidine on the migration and invasion of human lung adenocarcinoma A549 cell in vitro. The data demonstrates that tomatidine does not effectively inhibit the viability of A549 cells. When treated with non-toxic doses of tomatidine, cell invasion is markedly suppressed by Boyden chamber invasion assay, while cell migration is not affected. Tomatidine reduces the mRNA level of matrix metalloproteinase-2 (MMP-2), MMP-9 and increases the expression of reversion-inducing cysteine-rich protein with kazal motifs (RECK), as well as tissue inhibitor of metalloproteinase-1 (TIMP-1). The immunoblotting assays indicate that tomatidine is very effective in suppressing the phosphorylation of Akt and extracellular signal regulating kinase (ERK). In addition, tomatidine significantly decreases the nuclear level of nuclear factor kappa B (NF-κB), which suggests that tomatidine inhibits NF-κB activity. Furthermore, the treatment of inhibitors specific for PI3K/Akt (LY294002), ERK (U0126), or NF-κB (pyrrolidine dithiocarbamate) to A549 cells reduced cell invasion and MMP-2/9 expression. The results suggest that tomatidine inhibits the invasion of A549 cells by reducing the expression of MMPs. It also inhibits ERK and Akt signaling pathways and NF-κB activity. These findings demonstrate a new therapeutic potential for tomatidine in anti-metastatic therapy.

Evaluation of heparanase and matrix metalloproteinase-9 in patients with cutaneous malignant melanoma

Elevated heparanase and matrix metalloproteinase (MMP)-9, frequently found in human cancer, is a major cause of degradation of the extracellular matrix (ECM) and basement membrane (BM), thus facilitating tumor cell migration and invasion. Although a lot of work has been done, the role of heparanase and MMP-9 has not been delineated in skin cancer progression. The purpose of this study was to do such an exploration. To investigate the role of heparanase and MMP-9 in cutaneous malignant melanoma (CMM) development, we performed immunohistochemical analysis to detect the alternation of these two factors in paraffin-embedded biopsy specimens of normal skin, junctional nevi and CMM. It is interesting to note that the expression profile of heparanase and MMP-9 was similar. Contrary to negative staining in normal skin, overexpression of heparanase and cytoplasmic MMP-9 was observed in as many as 70% of CMM, whereas only 10% of the junctional nevi exhibited faint staining (P = 0.0005, P = 0.0000). Considering the lymph node (LN) metastasis, the expression of the two factors is significantly higher in LN-positive lesions than that in LN-negative lesions (P = 0.0295, P = 0.0013). Meanwhile, there was positive correlation between the expression of MMP-9 and heparanase (r = 0.689, P = 0.003). The first expression of MMP-9 and heparanase occurs at benign lesions. However, the significantly increased expression in advanced CMM stages, particularly in LN-positive metastasis lesions, might synergistically contribute to degradation of ECM and BM, therefore promoting carcinogenesis and metastasis.

Low molecular weight heparin inhibits melanoma cell adhesion and migration through a PKCa/JNK signaling pathway inducing actin cytoskeleton changes

Low molecular weight heparin (LMWH) has significant antimetastatic capabilities and affects cancer progression in humans through, not fully defined mechanisms. Here we evaluated its activity at the intracellular level and how it is correlated with melanoma cell adhesion and migration. LMWH inhibited M5 and A375 melanoma cell adhesion and migration in a dose-dependent manner (p⩽0.01). Treatment of M5 melanoma cells with LMWH caused a marked down regulation of constitutive as well as the FN-induced phosphorylation (p⩽0.01) of protein kinase C alpha (PKCa). This was associated with a profound decrease in the cytoplasmic pPKCa (p⩽0.05) and a simultaneous enhancement of nuclear pPKCa localization (p⩽0.01). A significant decrease in the levels of pJNK (p⩽0.01), which is a downstream effector of PKCa, was also demonstrated in the LMWH-treated cells. Furthermore, LMWH-treated cells had disorganized actin stress fibers correlated to a strong decrease in cell-substratum interface area (p⩽0.05) and altered morphology. The decrease in the activation of PKCa, which is an important regulator of cell motility, was directly correlated to the reduced ability of the LMWH-treated melanoma cells to adhere onto and migrate towards the fibronectin (FN) substrate (p⩽0.01). The lineage activation of PKCa-JNK/p38 and their correlation to M5 cell adhesion was confirmed with the utilization of specific inhibitors. In conclusion, LMWH through the downregulation of pPKCa and redistribution to nuclear region attenuates JNK activation, which in turn induces cytoskeleton changes correlated to M5 cell decreased adhesion/migration. This may provide clues for the pharmacological targeting of melanoma.

Diosgenin, a steroidal saponin, inhibits migration and invasion of human prostate cancer PC-3 cells by reducing matrix metalloproteinases expression

Background

Diosgenin, a steroidal saponin obtained from fenugreek (Trigonella foenum graecum), was found to exert anti-carcinogenic properties, such as inhibiting proliferation and inducing apoptosis in a variety of tumor cells. However, the effect of diosgenin on cancer metastasis remains unclear. The aim of the study is to examine the effect of diosgenin on migration and invasion in human prostate cancer PC-3 cells.

Methods and Principal Findings

Diosgenin inhibited proliferation of PC-3 cells in a dose-dependent manner. When treated with non-toxic doses of diosgenin, cell migration and invasion were markedly suppressed by in vitro wound healing assay and Boyden chamber invasion assay, respectively. Furthermore, diosgenin reduced the activities of matrix metalloproteinase-2 (MMP-2) and MMP-9 by gelatin zymography assay. The mRNA level of MMP-2, -9, -7 and extracellular inducer of matrix metalloproteinase (EMMPRIN) were also suppressed while tissue inhibitor of metalloproteinase-2 (TIMP-2) was increased by diosgenin. In addition, diosgenin abolished the expression of vascular endothelial growth factor (VEGF) in PC-3 cells and tube formation of endothelial cells. Our immunoblotting assays indicated that diosgenin potently suppressed the phosphorylation of phosphatidylinositide-3 kinase (PI3K), Akt, extracellular signal regulating kinase (ERK) and c-Jun N-terminal kinase (JNK). In addition, diosgenin significantly decreased the nuclear level of nuclear factor kappa B (NF-κB), suggesting that diosgenin inhibited NF-κB activity.

Conclusion/Significance

The results suggested that diosgenin inhibited migration and invasion of PC-3 cells by reducing MMPs expression. It also inhibited ERK, JNK and PI3K/Akt signaling pathways as well as NF-κB activity. These findings reveal new therapeutic potential for diosgenin in anti-metastatic therapy.

Interleukin-8 is associated with adhesion, migration and invasion in human gastric cancer SCG-7901 cells

Interleukin-8 is known as an important chemokine involved in tumor angiogenesis and progression. Overexpression of interleukin-8 has been detected in a variety of human tumors, including gastric cancer, and is negatively correlated with prognosis. The aim of our study is to determine the effects of interleukin-8 on proliferation, adhesion, migration and invasion abilities and correlated molecular mechanisms in gastric cancer. We made recombinant interleukin-8 ranged from 0 ng/ml to 100 ng/ml interferes in human gastric cancer SCG-7901 cells in vitro. The results shown that interleukin-8 did not change cell proliferation, but promoted cell adhesion to endothelial cell and extracellular matrix components (collagen, laminin and fibronectin) as detected by Cell Counting Kit-8. And it induced migration and invasion ability based on scratch and transwell-chamber assays. Also, interleukin-8 regulated the protein and mRNA expression of matrix metalloproteinase-9, intercellular adhesion molecule-1 and E-cad and there was obviously a dose-dependent relationship, but the protein or mRNA expression of matrix metalloproteinase-2 was not obviously changed under the tested conditions. Our findings indicate that interleukin-8 is associated with adhesion, migration and invasion in gastric cancer and the regulation of matrix metalloproteinase-9, intercellular adhesion molecule-1 and E-cad expression is one of the potential molecule mechanisms. The studies imply interleukin-8 may be an alternative treatment strategy against gastric cancer.