Pristimerin demonstrates anticancer potential in colorectal cancer cells by inducing G1 phase arrest and apoptosis and suppressing various pro-survival signaling proteins

Analysis of signaling cascades from myeloma cells treated with pristimerin

Multiple myeloma (MM) is the 2nd most frequently diagnosed blood cancer after non-Hodgkin's lymphoma. The present study aimed to identify the differentially expressed genes (DEGs) between the control and pristimerin-treated MM cell lines. We examined the GSE14011 microarray dataset and screened DEGs with GEO2R statistical tool using the inbuilt limma package. We used a bioinformatics pipeline to identify the differential networks, signaling cascades, and the survival of the hub genes. We implemented two different enrichment analysis including ClueGO and Metacore™, to get accurate annotation for most significant DEGs. We screened the most significant 408 DEGs from the dataset based on p-values and logFC values. Using protein network analysis, we found the genes UBC, HSP90AB1, HSPH1, HSPA1B, HSPA1L, HSPA6, HSPD1, DNAJB1, HSPE1, DNAJC10, BAG3, and DNAJC7 had higher node degree distribution. In contrast, the functional annotation provided that the DEGs were predominantly enriched in B-cell receptor signaling, unfolded protein response, positive regulation of phagocytosis, HSP70, and HSP40-dependent folding, and ubiquitin-proteasomal proteolysis. Using network algorithms, and comparing enrichment analysis, we found the hub genes enriched were INHBE, UBC, HSPA1A, HSP90AB1, IKBKB, and BAG3. These DEGs were further validated with overall survival and gene expression analysis between the tumor and control groups. Finally, pristimerin effects were validated independently in a cell line model consisting of IM9 and U266 MM cells. Pristimerin induced in vitro cytotoxicity in MM cells in a dose-dependent manner. Pristimerin inhibited NF-κB, induced accumulation of ubiquitinated proteins and inhibited HSP60 in the validation of bioinformatics findings, while pristimerin-induced caspase-3 and PARP cleavage confirmed cell death. Taken together, we found that the identified DEGs were strongly associated with the apoptosis induced in MM cell lines due to pristimerin treatment, and combinatorial therapy derived from pristimerin could act as novel anti-myeloma multifunctional agents.

Inhibition and potential treatment of colorectal cancer by natural compounds via various signaling pathways

Colorectal cancer (CRC) is a common type of malignant digestive tract tumor with a high incidence rate worldwide. Currently, the clinical treatment of CRC predominantly include surgical resection, postoperative chemotherapy, and radiotherapy. However, these treatments contain severe limitations such as drug side effects, the risk of recurrence and drug resistance. Some natural compounds found in plants, fungi, marine animals, and bacteria have been shown to inhibit the occurrence and development of CRC. Although the explicit molecular mechanisms underlying the therapeutic effects of these compounds on CRC are not clear, classical signaling transduction pathways such as NF-kB and Wnt/β-catenin are extensively regulated. In this review, we have summarized the specific mechanisms regulating the inhibition and development of CRC by various types of natural compounds through nine signaling pathways, and explored the potential therapeutic values of these natural compounds in the clinical treatment of CRC.

The multifaceted mechanisms of pristimerin in the treatment of tumors state-of-the-art

As a globally complicated disease, malignant tumor has long been posing a threat to human health with increasingly high morbidity and mortality. Notably, existing treatments for tumors like chemotherapy generally carry intolerable toxicity, necessitating novel agents balancing safety and potency. Among them, the anti-tumor potency of herbs, featuring few adverse effects and promising efficacy, has attracted much attention recently. Pristimerin, a Quinone formamide triterpenoid compound extracted from Celastraceae and Portulacaceae, carries pronounced anti-tumor activity. It applies to various malignant tumors, including breast cancer, bile duct cancer, gastric cancer, pancreatic cancer, prostate cancer, glioblastoma, colorectal cancer, oral squamous cell carcinoma, cervical cancer, and lung cancer. In state-of-the-art understanding, pristimerin, alone or combined, can inhibit tumor cell proliferation, induce tumor cell apoptosis, inhibit tumor migration and invasion, inhibit angiogenesis, induce tumor cell autophagy, regulate the occurrence of inflammation related tumors, enhance chemosensitivity and regulate tumor microenvironment and immune cells. Despite the abundance of pristimerin-based research, systematic reviews on its anti-tumor mechanism remain needed. This study presented the anti-tumor mechanism of pristimerin by literature review, which might serve as a reference for further research and clinical practice.

Pristimerin induces apoptosis and tumor inhibition of oral squamous cell carcinoma through activating ROS-dependent ER stress/Noxa pathway

BACKGROUND

Pristimerin (Pri), a natural quinone methide triterpenoid isolated from Celastraceae and Hippocrateaceae, exhibits potent antitumor activity against various cancers. However, the mechanism of apoptosis induction by Pri in oral squamous cell carcinoma (OSCC) and its anti-OSCC effect in vivo has not been widely studied.

PURPOSE

This study aimed to investigate the anti-OSCC activities of Pri in vitro and in vivo and addressed the potential mechanisms of Pri-induced apoptosis.

METHODS

The effects of Pri on OSCC cells were analyzed by cell viability, colony formation and flow cytometry assays. Western blotting and qRT-PCR assays were chosen to detect the expression of proteins and genes. The anti-OSCC efficacy of Pri in vivo was evaluated by CAL-27 xenografts.

RESULTS

We showed that Pri inhibited the proliferation of human OSCC cell lines. Additionally, Pri induced apoptosis by upregulating Noxa expression. Furthermore, Pri treatment triggered excessive endoplasmic reticulum (ER) stress activation and subsequently induced c-Jun N-terminal kinase (JNK) signaling. ROS scavengers and ER stress inhibitors significantly attenuated Pri-induced OSCC cell apoptosis. Finally, Pri suppressed tumor growth in CAL-27 xenografts, accompanied ER stress activation and cell apoptosis.

CONCLUSION

These results reveal that Pri suppressed tumor growth and triggered cell apoptosis through ER stress activation in OSCC cells and xenografts, suggesting that Pri may serve as a therapeutic agent for OSCC.

Pristimerin synergistically sensitizes conditionally reprogrammed patient derived-primary hepatocellular carcinoma cells to sorafenib through endoplasmic reticulum stress and ROS generation by modulating Akt/FoxO1/p27kip1 signaling pathway

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-associated mortality worldwide. Sorafenib (SORA), as a first-line therapeutic drug, has been used to treat HCC, but resistance poses a major limitation on the efficacy of SORA chemotherapy. Pristimerin (PRIS), a natural bioactive component isolated from various plant species in the Celastraceae and Hippocrateaceae families, has been reported to exhibit outstanding antitumor effects in several types of cells in vitro.

PURPOSE

The aim of this study was to investigate whether PRIS can exert synergistic anti-tumor effects with the combination of SORA, and if so, through what mechanism.

METHODS

Conditionally reprogrammed patient derived-primary hepatocellular carcinoma cells (CRHCs) were isolated from human liver cancer tissues and treated with SORA and PRIS. Cell proliferation, apoptosis, migration and tube formation ability were detected by DNA content quantification, flow cytometry, transwell assay and Matrigel-based angiogenesis assay. Gene and protein expression were assessed by qRT-PCR and Western blot respectively.

RESULTS

Initially, we observed that the combination of the two drugs had a much stronger inhibitory effect on CRHCs growth than either drug alone. Moreover, the combination of 2 µM SORA and 1 µM PRIS exhibited a significant anti‑migrative and anti-invaded effect on CRHCs, and remarkably inhibited capillary structure formation of Human Umbilical Vein Endothelial Cells (HUVECs). Furthermore, the combined treatment with SORA and PRIS synergistically induced intrinsic apoptosis in CRHCs, involving a caspase-4-dependent mechanism paralleled by an increased Bax/Bcl-xL ratio. These activities were mediated through ROS generation and the induction of endoplasmic reticulum (ER) stress and mitochondrial dysfunction. GRP78 silencing or ER stress inhibitor 4-phenylbutyric acid administration was revealed to abolish the anticancer effects of PRIS, indicating the critical role of GRP78 in mediating the bioactivity of PRIS. The present study also provides mechanistic evidence that PRIS modulated the Akt/FoxO1/p27^kip1 signaling pathway, which is required for mitochondrial-mediated intrinsic apoptosis, activation of ER stress, and stimulation of caspase-4 induced by PRIS, and, consequently resulting in suppressed cell viability, migration and angiogenesis co-treated with SORA in CRHCs.

CONCLUSION

Our results suggest the use of PRIS as sensitizers of chemotherapy paving the way for innovative and promising targeted chemotherapy-based therapeutic strategies in human HCC.

Cellular and Molecular Mechanisms of Pristimerin in Cancer Therapy: Recent Advances

Seeking an efficient and safe approach to eliminate tumors is a common goal of medical fields. Over these years, traditional Chinese medicine has attracted growing attention in cancer treatment due to its long history. Pristimerin is a naturally occurring quinone methide triterpenoid used in traditional Chinese medicine to treat various cancers. Recent studies have identified alterations in cellular events and molecular signaling targets of cancer cells under pristimerin treatment. Pristimerin induces cell cycle arrest, apoptosis, and autophagy to exhibit anti-proliferation effects against tumors. Pristimerin also inhibits the invasion, migration, and metastasis of tumor cells via affecting cell adhesion, cytoskeleton, epithelial-mesenchymal transition, cancer stem cells, and angiogenesis. Molecular factors and pathways are associated with the anti-cancer activities of pristimerin. Furthermore, pristimerin reverses multidrug resistance of cancer cells and exerts synergizing effects with other chemotherapeutic drugs. This review aims to discuss the anti-cancer potentials of pristimerin, emphasizing multi-targeted biological and molecular regulations in cancers. Further investigations and clinical trials are warranted to understand the advantages and disadvantages of pristimerin treatment much better.

Effect of pristimerin on apoptosis through activation of ROS/ endoplasmic reticulum (ER) stress-mediated noxa in colorectal cancer

BACKGROUND

Pristimerin, a natural quinonemethid triterpenoid found in different spp. of Celastraceae and Hippocrateaceae families, has been reported to exhibit potent antitumor activities against colorectal cancer (CRC). However, the mechanisms underlying pristimerin-induced apoptosis in CRC is not clear.

PURPOSE

This study aimed to investigate the mechanisms of pristimerin-induced apoptosis against CRC in vitro and in vivo.

METHODS

Cell viability and cell apoptosis analyses were conducted to assess the effects of pristimerin on CRC. Western blotting was performed to detect the expression of proteins affected by pristimerin in vitro and in vivo. HCT116 colon cancer xenografts and APCmin/+ mouse models were used to evaluate the anti-CRC effect of pristimerin in vivo.

RESULTS

Our data showed that pristimerin induced apoptosis by regulating proapoptotic proteins of which Noxa showed higher expression. Pristimerin triggered reactive oxygen species (ROS)-mediated endoplasmic reticulum (ER) stress signaling activation. Pristimerin significantly elevated the expression of ER stress-related proteins, resulting in activation of the IRE1α and c-Jun N-terminal kinase (JNK) signal pathway through the formation of the IRE1α-TRAF2-ASK1 complex. Pristimerin exhibited apoptosis-inducing activities in HCT116 colon cancer xenografts and APCmin/+ mice.

CONCLUSION

Both in vitro and in vivo data demonstrated that pristimerin induced Noxa expression and apoptosis through activation of the ROS/ER stress/JNK axis in CRC. Thus, pristimerin may be a promising antitumor agent for CRC.

Pristimerin Exacerbates Cellular Injury in Conditionally Reprogrammed Patient-Derived Lung Adenocarcinoma Cells by Aggravating Mitochondrial Impairment and Endoplasmic Reticulum Stress through EphB4/CDC42/N-WASP Signaling

Lung cancer is the most common and lethal malignant disease for which the development of efficacious chemotherapeutic agents remains an urgent need. Pristimerin (PRIS), a natural bioactive component isolated from various plant species in the Celastraceae and Hippocrateaceae families, has been reported to exhibit outstanding antitumor effects in several types of cells. However, the underlying mechanisms involved remain poorly understood. Here, we reported the novel finding that PRIS significantly suppressed lung cancer growth in conditionally reprogrammed patient-derived lung adenocarcinoma cells (CRLCs). We demonstrated that PRIS inhibited the cell viabilities, migrative and invaded abilities, and capillary structure formation of CRLCs. Furthermore, our results clarified that PRIS induced mitochondrial dysfunction through reactive oxygen species (ROS) generation, activation of caspase-9, caspase-3, and caspase-4, and expression of endoplasmic reticulum (ER) stress-associated proteins. Inhibition of ER stress by 4-PBA (4-phenylbutyric acid, a specific ER stress inhibitor) or CHOP siRNA transfection ameliorated PRIS-induced loss of mitochondrial membrane potential and intrinsic apoptosis. The present study also provides mechanistic evidence that PRIS suppressed the EphB4/CDC42/N-WASP signaling pathway, which is required for mitochondrial-mediated intrinsic apoptosis, activation of ER stress, and stimulation of caspase-4 induced by PRIS, and consequently resulting in suppressed cell viability, migration, and angiogenesis in CRLCs. Taken together, by providing a mechanistic insight into the modulation of ER stress-induced cell death in CRLCs by PRIS, we suggest that PRIS has a strong potential of being a new antitumor therapeutic agent with applications in the fields of human lung adenocarcinoma.

Terpenoids, Cannabimimetic Ligands, beyond the Cannabis Plant

Medicinal use of Cannabis sativa L. has an extensive history and it was essential in the discovery of phytocannabinoids, including the Cannabis major psychoactive compound-Δ9-tetrahydrocannabinol (Δ9-THC)-as well as the G-protein-coupled cannabinoid receptors (CBR), named cannabinoid receptor type-1 (CB1R) and cannabinoid receptor type-2 (CB2R), both part of the now known endocannabinoid system (ECS). Cannabinoids is a vast term that defines several compounds that have been characterized in three categories: (i) endogenous, (ii) synthetic, and (iii) phytocannabinoids, and are able to modulate the CBR and ECS. Particularly, phytocannabinoids are natural terpenoids or phenolic compounds derived from Cannabis sativa. However, these terpenoids and phenolic compounds can also be derived from other plants (non-cannabinoids) and still induce cannabinoid-like properties. Cannabimimetic ligands, beyond the Cannabis plant, can act as CBR agonists or antagonists, or ECS enzyme inhibitors, besides being able of playing a role in immune-mediated inflammatory and infectious diseases, neuroinflammatory, neurological, and neurodegenerative diseases, as well as in cancer, and autoimmunity by itself. In this review, we summarize and critically highlight past, present, and future progress on the understanding of the role of cannabinoid-like molecules, mainly terpenes, as prospective therapeutics for different pathological conditions.

Pristimerin suppresses colorectal cancer through inhibiting inflammatory responses and Wnt/β-catenin signaling

Pristimerin, a triterpenoid, has exhibited potential anti-inflammatory and anti-tumor activities. Nevertheless, the role and mechanism of pristimerin in intestinal inflammation and colon cancer require further investigation. Here, we found that pristimerin protected mice from dextran sulfate sodium (DSS)-induced colitis, restoring epithelial damage and reducing tissue inflammation and inflammatory cell infiltration. In addition, pristimerin dramatically reduced the number and size of the tumors in a azoxymethane (AOM)/DSS-induced colitis-associated colorectal cancer (CAC) model. Furthermore, we found that pristimerin suppressed Wnt/β-catenin signaling by RNA-Seq. Pristimerin inhibited Wnt/β-catenin signaling via activation of GSK3β, thereby suppressing Wnt target gene expression in colon cancer HCT116 and HT-29 cells. In HCT116 colon cancer xenografts and APC^min/+ mice, which undergo spontaneous intestinal tumorigenesis, administration of pristimerin reduced the tumor progression and decreased the expression of phosphorylated GSK3β Ser 9, β-catenin, cyclin D1 and c-Myc. These results suggest that pristimerin is a potent agent for preventing colon inflammation and carcinogenesis.

Anti-Cancer Effects of Pristimerin and the Mechanisms: A Critical Review

As a quinonemethide triterpenoid extracted from species of the Celastraceae and Hippocrateaceae, pristimerin has been shown potent anti-cancer effects. Specifically, it was found that pristimerin can affect many tumor-related processes, such as apoptosis, autophagy, migration and invasion, vasculogenesis, and drug resistance. Various molecular targets or signaling pathways are also involved, such as cyclins, reactive oxygen species (ROS), microRNA, nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), and PI3K/AKT/mammalian target of rapamycin (mTOR) pathways. In this review, we will focus on the research about pristimerin-induced anti-cancer activities to achieve a deeper understanding of the targets and mechanisms, which offer evidences suggesting that pristimerin can be a potent anti-cancer drug.

Pristimerin enhances the effect of cisplatin by inhibiting the miR‑23a/Akt/GSK3β signaling pathway and suppressing autophagy in lung cancer cells

Lung cancer is a common type of cancer with a high mortality rate in China. Cisplatin (Cis) is one of the most effective broad‑spectrum chemotherapeutic drugs for the treatment of advanced lung cancer. However, Cis resistance remains an obstacle in the treatment of advanced lung cancer. Pristimerin (Pris), a naturally occurring triterpenoid quinone compound, not only possesses anticancer properties, but also enhances chemosensitivity. Therefore, the present study aimed to investigate whether Pris can enhance the chemosensitivity of lung cancer cells to Cis and identify the underlying mechanism. A Cell Counting kit‑8 and flow cytometry were used to determine cell viability, cell cycle progression and apoptosis in A549 and NCI‑H446 cells. Western blotting was used to determine cell apoptosis‑related, cell cycle‑related and autophagy‑related proteins. The results showed that Pris inhibited cell proliferation, and induced G0/G1 arrest and cell apoptosis in A549 and NCI‑H446 cells. The western blotting revealed that Pris effectively synergized with Cis to induce cell apoptosis by inhibiting the microRNA‑23a/Akt/glycogen synthase kinase 3β signaling pathway and suppressing autophagy. In vivo xenograft experiments confirmed that Pris effectively synergized with Cis to suppress tumor growth. Collectively, these results indicate that Pris synergized with Cis and that this may be a potential therapeutic strategy to overcome lung cancer.

Pristimerin induces apoptosis of oral squamous cell carcinoma cells via G1 phase arrest and MAPK/Erk1/2 and Akt signaling inhibition

Pristimerin is an active compound isolated from the traditional Chinese herbs Celastraceae and Hippocrateaceae. It has been reported to exert antitumor effects under experimental and clinical conditions; however, the antitumor effects and underlying mechanisms of pristimerin in oral cancer cells have not yet been identified. In the present study, the anticancer potential of pristimerin was investigated in two oral squamous cell carcinoma (OSCC) cell lines, CAL-27 and SCC-25. Results demonstrated that pristimerin was toxic against the two cell lines, and exhibited inhibitory effects against proliferation. Furthermore, pristimerin exhibited a more potent anti-proliferative activity in CAL-27 and SCC-25 cells than the common chemotherapy drugs cisplatin and 5-fluorouracil. In addition, cell cycle distribution analysis revealed that G₀/G₁ phase arrest was induced following pristimerin treatment in CAL-27 and SCC-25 cells, which was strongly associated with upregulation of p21 and p27, coupled with downregulation of cyclin D1 and cyclin E. Meanwhile, pristimerin induced significant apoptosis of CAL-27 and SCC-25 cells, alongside decreased levels of caspase-3 and specific cleavage of poly (ADP-ribose) polymerase. These effects were associated with inhibition of the mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 and protein kinase B signaling pathways. With regards to these results, pristimerin may be considered a potent novel active substance for the treatment of OSCC.

Combination of pristimerin and paclitaxel additively induces autophagy in human breast cancer cells via ERK1/2 regulation

Pristimerin, a quinonemethide triterpenoid, has demonstrated anticancer activity against a number of types of cancer, including breast cancer. However, its mechanism of action remains unclear. The present study investigated the autophagy-induced anticancer efficacy of pristimerin on MDA-MB-231 human breast cancer cells. Pristimerin inhibited the growth of these cells in a concentration-dependent manner. Treatment with pristimerin dose-dependently induced an increase of light chain 3B (LC3-II), whereas autophagy inhibitor 3-methyladenine (3-MA) inhibited pristimerin-induced LC3-II accumulation and cytotoxic effects. Autophagy was also activated by paclitaxel as observed by an elevated LC3-II level. Although 24 µM paclitaxel induced autophagy without cytotoxicity, combined with pristimerin it additively induced cell growth inhibition and autophagy induction. Autophagy induction was measured with an autophagy detection kit and LC3-II levels were monitored by western blot analysis. Treatment with 3-MA inhibited LC3-II accumulation and cell death induced by a combination of paclitaxel and pristimerin. Pristimerin and paclitaxel inhibited extracellular signal-regulated kinase (ERK)1/2/p90RSK signaling, consistent with autophagy indicators, namely p62 degradation and beclin 1 expression. In addition, ERK activator ceramide C6 treatment suppressed the LC3-II levels induced by a combination of paclitaxel and pristimerin. These results suggested that exposure to pristimerin induced autophagic cell death, whereas a combination treatment of pristimerin and paclitaxel resulted in an additive effect on ERK-dependent autophagic cell death.

Pristimerin, a naturally occurring triterpenoid, attenuates tumorigenesis in experimental colitis-associated colon cancer

BACKGROUND

Pristimerin is a quinonemethide triterpenoid with anti-cancer, anti-angiogenic, anti-inflammatory and anti-protozoal activity. However, the therapeutic role of pristimerin in colitis-associated colorectal carcinogenesis is unknown.

PURPOSE

We sought to examine the therapeutic effects of pristimerin on colitis-associated colon cancer induced in mice using azoxymethane (AOM)/dextran sulfate sodium (DSS). The goal was to identify the potential mechanism of action underlying the pharmacological activity of pristimerin.

METHODS

BALB/c mice were injected with AOM and administered 2% DSS in drinking water. The mice were fed with a diet supplemented with pristimerin (1 to 5 ppm), and colonic tissue was collected at 64 days. The inflammatory status of the colon was assessed by determining the levels of cyclooxygenase-2, inducible nitric oxide synthase and pro-inflammatory cytokines using Western blotting, immunohistochemistry and real-time RT-PCR analyses. Markers of proliferation (proliferating cell nuclear antigen) and apoptosis (TUNEL) were identified in the colon tissues immunohistochemically. The levels of cell cycle-, apoptosis-, and signaling-related proteins were detected by Western blot in colon tissues.

RESULTS

Administration of pristimerin significantly reduced the formation of colonic tumors. Western blot and immunohistological analyses revealed that dietary pristimerin markedly reduced NF-κB-positive cells and levels of inflammation-related proteins in colon tissue. Pristimerin also reduced cell proliferation, induced apoptosis, and decreased the phosphorylation of AKT and FOXO3a in colon tissue.

CONCLUSION

Pristimerin administration decreased inflammation and proliferation induced by AOM/DSS in colon tissue. It also induced apoptosis and regulated the AKT/FOXO3a signaling pathway. Overall, this study indicates the potential value of pristimerin in suppressing colon tumorigenesis.

Pristimerin exhibits in vitro and in vivo anticancer activities through inhibition of nuclear factor-кB signaling pathway in colorectal cancer cells

BACKGROUND

Colorectal cancer (CRC) is one of the most common malignancies associated with high mortality rate worldwide. We previously reported that pristimerin inhibits cell growth and induces apoptosis in CRC cells.

HYPOTHESIS/PURPOSE

To further understand the molecular mechanism by which pristimerin elicits its anticancer activities on colon cancer cells, we investigated its effect on nuclear factor-κB (NF-κB) signaling pathway.

STUDY DESIGN

This study consisted of both in vitro and in vivo experiments involving HCT-116 cell line and xenograft mouse model. Molecular techniques such as qRT-PCR, western blotting and immunofluorescence were used to demonstrate pristimerin in vitro effect on NF-κB signaling pathway; whereas it's in vivo activity was analyzed by western blot and immunohistochemistry on tumor tissues.

RESULTS

Our in vitro results on HCT-116 cells showed that pristimerin inhibited IKK phosphorylation, IкB-α degradations and IкB-α phosphorylation in both dose- and time- dependent manners, which caused suppression of NF-кB p65 phosphorylation, nuclear translocation and accumulation of NF-кB. Moreover, pristimerin was found to inhibit both constitutive activated-NF-кB and tumor necrosis factor-α (TNF-α)- and lipopolysaccharide (LPS)-induced activation of NF-кB signaling pathway. Furthermore, our in vivo results on xenograft animal model revealed that pristimerin inhibited tumor growth mainly through suppressing NF-кB activity in tumor tissues.

CONCLUSION

Pristimerin antitumor activities were mainly mediated through inhibition of NF-кB signaling pathway in colon tumor cells. These findings further explain that pristimerin has the therapeutic potential for targeting colon cancer.

Pristimerin Inhibits LPS-Triggered Neurotoxicity in BV-2 Microglia Cells Through Modulating IRAK1/TRAF6/TAK1-Mediated NF-κB and AP-1 Signaling Pathways In Vitro

Microglia plays a prominent role in the brain's inflammatory response to injury or infection by migrating to affected locations and secreting inflammatory molecules. However, hyperactivated microglial is neurotoxic and plays critical roles in the pathogenesis of neurodegenerative diseases. Pristimerin, a naturally occurring triterpenoid, possesses antitumor, antioxidant, and anti-inflammatory activities. However, the effect and the molecular mechanism of pristimerin against lipopolysaccharide (LPS)-induced neurotoxicity in microglia remain to be revealed. In the present study, using BV-2 microglial cultures, we investigated whether pristimerin modifies neurotoxicity after LPS stimulation and which intracellular pathways are involved in the effect of pristimerin. Here we show that pristimerin markedly suppressed the release of Regulated on Activation, Normal T Expressed and Secreted (RANTES), transforming growth factor-β1 (TGF-β1), IL-6, tumor necrosis factor-α (TNF-α), and nitric oxide (NO). Pristimerin also significantly inhibited migration of BV-2 microglia and alleviated the death of neuron-like PC12 cell induced by the conditioned medium from LPS-activated BV-2 microglial cells. Moreover, pristimerin reduced the expression and interaction of TNF Receptor-Associated Factor 6 (TRAF6) and Interleukin-1 Receptor-Associated Kinases (IRAK1), limiting TGF-beta activating kinase 1 (TAK1) activation, and resulting in an inhibition of IKKα/β/NF-κB and MKK7/JNK/AP-1 signaling pathway in LPS-activated BV-2 microglia. Taken together, the anti-neurotoxicity action of pristimerin is mediated through the inhibition of TRAF6/IRAK1/TAK1 interaction as well as the related pathways: IKKα/β/NF-κB and MKK7/JNK/AP-1 signaling pathways. These findings may suggest that pristimerin might serve as a new therapeutic agent for treating hyperactivated microglial induced neurodegenerative diseases.

Pristimerin effectively inhibits the malignant phenotypes of uveal melanoma cells by targeting NF‑κB pathway

Uveal melanoma (UM) is a highly aggressive intraocular malignancy that lacks any effective targeted-therapy. Neither survival nor prognosis has been improved for the past decades in patients with metastatic UM. NF‑κB pathway is reported to be abnormally activated in UM. However, the role of NF‑κB pathway as a potential therapeutical target in UM remains unclear. Here, the effect of pristimerin, a potent inhibitor of NF‑κB pathway, on UM cells in terms of growth, apoptosis, motility, invasion and cancer stem-like cells (CSCs) was evaluated in vitro. We showed that pristimerin suppressed tumor necrosis factor α (TNFα)-induced IκBα phosphorylation, translocation of p65, and expression of NF‑κB-dependent genes. Moreover, pristimerin decreased cell viability and clonogenic ability of UM cells. A synergistic effect was observed in the treatment of pristimerin combined with vinblastine, a frontline therapeutic agent, in UM. Pristimerin led to a significant increase in the Annexin V+ cell population as measured by flow cytometry. We also observed that pristimerin impaired the abilities of migration and invasion in UM cells. Furthermore, pristimerin eliminated the ALDH+ cells and weakened serial re-plating ability of melanosphere. Collectively, pristimerin shows remarkable anticancer activities in UM cells through inactivating NF‑κB pathway, revealing that pristimerin may be a promising therapeutic agent in UM.

Friedelin Synthase from Maytenus ilicifolia: Leucine 482 Plays an Essential Role in the Production of the Most Rearranged Pentacyclic Triterpene

Among the biologically active triterpenes, friedelin has the most-rearranged structure produced by the oxidosqualene cyclases and is the only one containing a cetonic group. In this study, we cloned and functionally characterized friedelin synthase and one cycloartenol synthase from Maytenus ilicifolia (Celastraceae). The complete coding sequences of these 2 genes were cloned from leaf mRNA, and their functions were characterized by heterologous expression in yeast. The cycloartenol synthase sequence is very similar to other known OSCs of this type (approximately 80% identity), although the M. ilicifolia friedelin synthase amino acid sequence is more related to β-amyrin synthases (65-74% identity), which is similar to the friedelin synthase cloned from Kalanchoe daigremontiana. Multiple sequence alignments demonstrated the presence of a leucine residue two positions upstream of the friedelin synthase Asp-Cys-Thr-Ala-Glu (DCTAE) active site motif, while the vast majority of OSCs identified so far have a valine or isoleucine residue at the same position. The substitution of the leucine residue with valine, threonine or isoleucine in M. ilicifolia friedelin synthase interfered with substrate recognition and lead to the production of different pentacyclic triterpenes. Hence, our data indicate a key role for the leucine residue in the structure and function of this oxidosqualene cyclase.

Rhein triggers apoptosis via induction of endoplasmic reticulum stress, caspase-4 and intracellular calcium in primary human hepatic HL-7702 cells

Rhein is an active component of rhubarb; a traditional Chinese medicine reported to induce apoptosis and cause liver toxicity. However, rhein's apoptotic-inducing effects, as well as its molecular mechanisms of action on hepatic cells need to be further explored. In the present study, rhein was found to trigger apoptosis in primary human hepatic HL-7702 cells as showed by annexin V/PI double staining assay and nuclear morphological changes demonstrated by Hoechst 33258 staining. Moreover, it was observed that the mechanism implicated in rhein-induced apoptosis was caspase-dependent, presumably via ER-stress associated pathways, as illustrated by up-regulation of glucose-regulated protein 78 (GRP 78), PKR-like ER kinase (PERK), C-Jun N-terminal kinase (JNK) and CCAAT/enhancer-binding protein homologous protein (CHOP). Meanwhile, caspase-4 as a hallmark of ER-stress, was also showed to be activated following by caspase-3 activation. Furthermore, rhein also promoted intracellular elevation of calcium that contributed in apoptosis induction. Interestingly, pre-treatment with calpain inhibitor I reduced the effects of rhein on apoptosis induction and JNK activation. These data suggested that rhein-induced apoptosis through ER-stress and elevated intracellular calcium level in HL-7702 cells.