Piperlongumine induces autophagy by targeting p38 signaling

Fibroin nanodisruptor with Ferroptosis-Autophagy synergism is potent for lung cancer treatment

Chemotherapy agents for lung cancer often cause apoptotic resistance in cells, leading to suboptimal therapeutic outcomes. FIN56 can be a potential treatment for lung cancer as it induces non-apoptotic cell death, namely ferroptosis. However, a bottleneck exists in FIN56-induced ferroptosis treatment; specifically, FIN56 fails to induce sufficient oxidative stress and may even trigger the defense system against ferroptosis, resulting in poor therapeutic efficacy. To overcome this, this study proposed a strategy of co-delivering FIN56 and piperlongumine to enhance the ferroptosis treatment effect by increasing oxidative stress and connecting with the autophagy pathway. FIN56 and piperlongumine were encapsulated into silk fibroin-based nano-disruptors, named FP@SFN. Characterization results showed that the particle size of FP@SFN was in the nanometer range and the distribution was uniform. Both in vivo and in vitro studies demonstrated that FP@SFN could effectively eliminate A549 cells and inhibit subcutaneous lung cancer tumors. Notably, ferroptosis and autophagy were identified as the main cell death pathways through which the nano-disruptors increased oxidative stress and facilitated cell membrane rupture. In conclusion, nano-disruptors can effectively enhance the therapeutic effect of ferroptosis treatment for lung cancer through the ferroptosis-autophagy synergy mechanism, providing a reference for the development of related therapeutics.

Saikosaponin D Inhibits Lung Metastasis of Colorectal Cancer Cells by Inducing Autophagy and Apoptosis

Saikosaponin D (SSD), derived from Bupleurum falcatum L., has various pharmacological properties, including immunoregulatory, anti-inflammatory, and anti-allergic effects. Several studies have investigated the anti-tumor effects of SSD on cancer in multiple organs. However, its role in colorectal cancer (CRC) remains unclear. Therefore, this study aimed to elucidate the suppressive effects of SSD on CRC cell survival and metastasis. SSD reduced the survival and colony formation ability of CRC cells. SSD-induced autophagy and apoptosis in CRC cells were measured using flow cytometry. SSD treatment increased LC3B and p62 autophagic factor levels in CRC cells. Moreover, SSD-induced apoptosis occurred through the cleavage of caspase-9, caspase-3, and PARP, along with the downregulation of the Bcl-2 family. In the in vivo experiment, a reduction in the number of metastatic tumor nodules in the lungs was observed after the oral administration of SSD. Based on these results, SSD inhibits the metastasis of CRC cells to the lungs by inducing autophagy and apoptosis. In conclusion, SSD suppressed the proliferation and metastasis of CRC cells, suggesting its potential as a novel substance for the metastatic CRC treatment.

Inhibition of the thioredoxin system for radiosensitization therapy of cancer

Radiotherapy (RT) stands as a cornerstone in the clinical armamentarium against various cancers due to its proven efficacy. However, the intrinsic radiation resistance exhibited by cancer cells, coupled with the adverse effects of RT on normal tissues, often compromises its therapeutic potential and leads to unwanted side effects. This comprehensive review aims to consolidate our understanding of how radiosensitizers inhibit the thioredoxin (Trx) system in cellular contexts. Notable radiosensitizers, including gold nanoparticles (GNPs), gold triethylphosphine cyanide ([Au(SCN) (PEt3)]), auranofin, ceria nanoparticles (CONPs), curcumin and its derivatives, piperlongamide, indolequinone derivatives, micheliolide, motexafin gadolinium, and ethane selenide selenidazole derivatives (SeDs), are meticulously elucidated in terms of their applications in radiotherapy. In this review, the sensitization mechanisms and the current research progress of these radiosensitizers are discussed in detail, with the overall aim of providing valuable insights for the judicious application of Trx system inhibitors in the field of cancer radiosensitization therapy.

Ferroptosis-modulating small molecules for targeting drug-resistant cancer: Challenges and opportunities in manipulating redox signaling

Ferroptosis is an iron-dependent cell death program that is characterized by excessive lipid peroxidation. Triggering ferroptosis has been proposed as a promising strategy to fight cancer and overcome drug resistance in antitumor therapy. Understanding the molecular interactions and structural features of ferroptosis-inducing compounds might therefore open the door to efficient pharmacological strategies against aggressive, metastatic, and therapy-resistant cancer. We here summarize the molecular mechanisms and structural requirements of ferroptosis-inducing small molecules that target central players in ferroptosis. Focus is placed on (i) glutathione peroxidase (GPX) 4, the only GPX isoenzyme that detoxifies complex membrane-bound lipid hydroperoxides, (ii) the cystine/glutamate antiporter system Xc - that is central for glutathione regeneration, (iii) the redox-protective transcription factor nuclear factor erythroid 2-related factor (NRF2), and (iv) GPX4 repression in combination with induced heme degradation via heme oxygenase-1. We deduce common features for efficient ferroptotic activity and highlight challenges in drug development. Moreover, we critically discuss the potential of natural products as ferroptosis-inducing lead structures and provide a comprehensive overview of structurally diverse biogenic and bioinspired small molecules that trigger ferroptosis via iron oxidation, inhibition of the thioredoxin/thioredoxin reductase system or less defined modes of action.

USP5-Beclin 1 axis overrides p53-dependent senescence and drives Kras-induced tumorigenicity

Non-small cell lung cancers (NSCLC) frequently contain KRAS mutation but retain wild-type TP53. Abundant senescent cells are observed in premalignant but not in malignant tumors derived from the Kras-driven mouse model, suggesting that KRAS oncogenic signaling would have to overcome the intrinsic senescence burden for cancer progression. Here, we show that the nuclear Beclin 1-mediated inhibition of p53-dependent senescence drives Kras-mediated tumorigenesis. KRAS activates USP5 to stabilize nuclear Beclin 1, leading to MDM2-mediated p53 protein instability. KrasG12D mice lacking Beclin 1 display retarded lung tumor growth. Knockdown of USP5 or knockout of Becn1 leads to increased senescence and reduced autophagy. Mechanistically, KRAS elevates ROS to induce USP5 homodimer formation by forming the C195 disulfide bond, resulting in stabilization and activation of USP5. Together, these results demonstrate that activation of the USP5-Beclin 1 axis is pivotal in overriding intrinsic p53-dependent senescence in Kras-driven lung cancer development.

The Impact of Oxidative Stress and AKT Pathway on Cancer Cell Functions and Its Application to Natural Products

Oxidative stress and AKT serine-threonine kinase (AKT) are responsible for regulating several cell functions of cancer cells. Several natural products modulate both oxidative stress and AKT for anticancer effects. However, the impact of natural product-modulating oxidative stress and AKT on cell functions lacks systemic understanding. Notably, the contribution of regulating cell functions by AKT downstream effectors is not yet well integrated. This review explores the role of oxidative stress and AKT pathway (AKT/AKT effectors) on ten cell functions, including apoptosis, autophagy, endoplasmic reticulum stress, mitochondrial morphogenesis, ferroptosis, necroptosis, DNA damage response, senescence, migration, and cell-cycle progression. The impact of oxidative stress and AKT are connected to these cell functions through cell function mediators. Moreover, the AKT effectors related to cell functions are integrated. Based on this rationale, natural products with the modulating abilities for oxidative stress and AKT pathway exhibit the potential to regulate these cell functions, but some were rarely reported, particularly for AKT effectors. This review sheds light on understanding the roles of oxidative stress and AKT pathway in regulating cell functions, providing future directions for natural products in cancer treatment.

A Derivative of Piperlongumine and Ligustrazine as a Potential Thioredoxin Reductase Inhibitor in Drug-Resistant Hepatocellular Carcinoma

The natural products piperlongumine (1) and ligustrazine (2) have been reported to exert antiproliferative effects against various types of cancer cells by up-regulating the level of reactive oxidative species (ROS). However, the moderate activities of 1 and 2 limit their application. To improve their potential antitumor activity, novel piperlongumine/ligustrazine derivatives were designed and prepared, and their potential pharmacological effects were determined in vitro and in vivo. Among the derivatives obtained, 11 exerted more prominent inhibitory activities against proliferation of drug-sensitive/-resistant cancer cells with lower IC50 values than 1. Particularly, the IC50 value of 11 against drug-resistant Bel-7402/5-FU cells was 0.9 μM, which was about 9-fold better than that of 1 (IC50 value of 8.4 μM). Mechanistic studies showed that 11 demonstrated thioredoxin reductase (TrxR) inhibitory activity, increase of ROS levels, decrease of mitochondrial transmembrane potential levels, and occurrence of DNA damage and autophagy, in a dose-dependent manner, via regulation of DNA damage protein H2AX and autophagy-associated proteins LC3, beclin-1, and p62 in drug-resistant Bel-7402/5-FU cells. Finally, compound 11 at 5 mg/kg displayed potent antitumor activity in vivo with tumor suppression of 76% (w/w). Taken together, compound 11 may represent a promising candidate drug for the chemotherapy of drug-resistant hepatocellular carcinoma and warrant more intensive study.

Identification of Novel Drug Candidate for Epithelial Ovarian Cancer via In Silico Investigation and In Vitro Validation

Epithelial ovarian cancer (EOC) has a poor prognosis and high mortality rate; patients are easy to relapse with standard therapies. So, there is an urgent need to develop novel drugs. In this study, differentially expressed genes (DEGs) of EOC were identified in The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Enrichment and protein–protein interaction (PPI) analyses were performed. The drug candidate which has the possibility to treat EOC was predicted by Connectivity Map (CMAP) databases. Moreover, molecular docking was selected to calculate the binding affinity between drug candidate and hub genes. The cytotoxicity of drug candidates was assessed by MTT and colony formation analysis, the proteins coded by hub genes were detected by Western blots, and apoptosis analysis was evaluated by flow cytometry. Finally, 296 overlapping DEGs (|log 2 fold change|>1; q-value <0.05), which were principally involved in the cell cycle (p < 0.05), and cyclin-dependent kinase 1 (CDK1) were screened as the significant hub gene from the PPI network. Furthermore, the 21 drugs were extracted from CMAPs; among them, piperlongumine (PL) showed a lower CMAP score (-0.80, -62.92) and was regarded as the drug candidate. Furthermore, molecular docking results between PL and CDK1 with a docking score of –8.121 kcal/mol were close to the known CDK1 inhibitor (–8.24 kcal/mol). Additionally, in vitro experiments showed that PL inhibited proliferation and induced apoptosis via targeting CDK1 in EOC SKOV3 cells. Our results reveal that PL may be a novel drug candidate for EOC by inhibiting cell cycle.

Synergistic effects of piperlongumine and gemcitabine against KRAS mutant lung cancer

OBJECTIVE

To determine the combined efficacy of piperlongumine and gemcitabine for treatment of KRAS mutant lung cancer.

METHODS

The cell growth inhibition of piperlongumine, gemcitabine, and piperlongumine plus gemcitabine was measured by Cell Counting Kit‑8 assay and the combination index was calculated. In addition, the combined effects of piperlongumine and gemcitabine on cell apoptosis, reactive oxygen species (ROS) contents, and microtubule-associated protein 1 light chain 3B (LC3B) expression were examined.

RESULTS

Piperlongumine increased ROS contents and LC3B-II expression. Following the combined treatment with piperlongumine and 10 mM N-acetyl-L-cysteine (NAC), intracellular ROS and cell viability returned to normal levels, and the expression of LC3B-II decreased to the predose level. Gemcitabine also induced cell apoptosis, increased ROS contents, and LC3B-II expression. The combination of piperlongumine with gemcitabine exhibited a synergetic anticancer activity with the combination index <1. The combined application of gemcitabine and piperlongumine yielded synergistic effects on cell apoptosis, but failed to synergistically increase ROS levels and LC3B-II expression.

CONCLUSION

Combination therapy with piperlongumine and gemcitabine is a promising treatment option for KRAS mutant lung cancer.

Challenges and Therapeutic Opportunities of Autophagy in Cancer Therapy

Simple Summary

Autophagy is a physiological process characterized by the degradation of the cell components through lysosomes due to stimuli/stress. In this study, we review the challenges and therapeutic opportunities that autophagy presents in the treatment of cancer. We discussed the results of several studies that evaluated autophagy as a therapeutic strategy in cancer, both through the modulation of therapeutic resistance and the death of cancer cells. Moreover, we discussed the role of autophagy in the biology of cancer stem cells and the inhibition of this process as a strategy to overcome resistance and progression of cancer stem cells.

Abstract

Autophagy is a physiological cellular process that is crucial for development and can occurs in response to nutrient deprivation or metabolic disorders. Interestingly, autophagy plays a dual role in cancer cells—while in some situations, it has a cytoprotective effect that causes chemotherapy resistance, in others, it has a cytotoxic effect in which some compounds induce autophagy-mediated cell death. In this review, we summarize strategies aimed at autophagy for the treatment of cancer, including studies of drugs that can modulate autophagy-mediated resistance, and/or drugs that cause autophagy-mediated cancer cell death. In addition, the role of autophagy in the biology of cancer stem cells has also been discussed.

Piperlonguminine and Piperine Analogues as TrxR Inhibitors that Promote ROS and Autophagy and Regulate p38 and Akt/mTOR Signaling

The natural products piperlongumine and piperine have been shown to inhibit cancer cell proliferation through elevation of reactive oxidative species (ROS) and eventually cell death, but only have modest cytotoxic potencies. A series of 14 novel phenylallylidenecyclohexenone analogues based on piperlongumine and piperine therefore were designed and synthesized, and their pharmacological properties were evaluated. Most of the compounds produced antiproliferative activities against five human cancer cells with IC50 values lower than those of piperlongumine and piperine. Among these, compound 9m exerted the most potent antiproliferative activity against drug-resistant Bel-7402/5-FU human liver cancer 5-FU resistant cells (IC50 = 0.8 μM), which was approximately 10-fold lower than piperlongumine (IC50 = 8.4 μM). Further, 9m showed considerably lower cytotoxicity against LO2 human normal liver epithelial cells compared to Bel-7402/5-FU. Mechanistically, compound 9m inhibited thioredoxin reductase (TrxR) activity, increased ROS levels, reduced mitochondrial transmembrane potential (MTP), and induced autophagy in Bel-7402/5-FU cells via regulation of autophagy-related proteins LC3, p62, and beclin-1. Finally, 9m activated significantly the p38 signaling pathways and suppressed the Akt/mTOR signaling pathways. In conclusion, 9m could be a promising candidate for the treatment of drug-resistant cancer cells and, as such, warrants further investigation.

Recent Advances in Characterizing Natural Products that Regulate Autophagy

Autophagy, an intricate response to nutrient deprivation, pathogen infection, Endoplasmic Reticulum (ER)-stress and drugs, is crucial for the homeostatic maintenance in living cells. This highly regulated, multistep process has been involved in several diseases including cardiovascular and neurodegenerative diseases, especially in cancer. It can function as either a promoter or a suppressor in cancer, which underlines the potential utility as a therapeutic target. In recent years, increasing evidence has suggested that many natural products could modulate autophagy through diverse signaling pathways, either inducing or inhibiting. In this review, we briefly introduce autophagy and systematically describe several classes of natural products that implicated autophagy modulation. These compounds are of great interest for their potential activity against many types of cancer, such as ovarian, breast, cervical, pancreatic, and so on, hoping to provide valuable information for the development of cancer treatments based on autophagy.

Nanocomposites for X-Ray Photodynamic Therapy

Photodynamic therapy (PDT) has long been known as an effective method for treating surface cancer tissues. Although this technique is widely used in modern medicine, some novel approaches for deep lying tumors have to be developed. Recently, deeper penetration of X-rays into tissues has been implemented, which is now known as X-ray photodynamic therapy (XPDT). The two methods differ in the photon energy used, thus requiring the use of different types of scintillating nanoparticles. These nanoparticles are known to convert the incident energy into the activation energy of a photosensitizer, which leads to the generation of reactive oxygen species. Since not all photosensitizers are found to be suitable for the currently used scintillating nanoparticles, it is necessary to find the most effective biocompatible combination of these two agents. The most successful combinations of nanoparticles for XPDT are presented. Nanomaterials such as metal-organic frameworks having properties of photosensitizers and scintillation nanoparticles are reported to have been used as XPDT agents. The role of metal-organic frameworks for applying XPDT as well as the mechanism underlying the generation of reactive oxygen species are discussed.

Piperlongumine, a potent anticancer phytotherapeutic: Perspectives on contemporary status and future possibilities as an anticancer agent

Piperlongumine, a white to beige biologically active alkaloid/amide phytochemical, has high pharmacological relevance as an anticancer agent. Piperlongumine has several biological activities, including selective cytotoxicity against multiple cancer cells of different origins at a preclinical level. Several preclinical studies have documented the anticancer potential of piperlongumine through its targeting of multiple molecular mechanisms, such as cell cycle arrest, anti-angiogenesis, anti- invasive and anti-metastasis pathways, autophagy pathways, and intrinsic apoptotic pathways in vitro and in vivo. Mechanistically, piperlongumine inhibits cancer growth by resulting in the accumulation of intracellular reactive oxygen species, decreasing glutathione and chromosomal damage, or modulating key regulatory proteins, including PI3K, AKT, mTOR, NF-kβ, STATs, and cyclin D1. Furthermore, combined treatment with piperlongumine potentiates the anticancer activity of conventional chemotherapeutics and overcomes resistance to chemo- and radio- therapy. Nanoformulation of piperlongumine has been associated with increased aqueous solubility and bioavailability and lower toxicity, thus enhancing therapeutic efficacy in both preclinical and clinical settings. The current review highlights anticancer studies on the occurrence, chemical properties, chemopreventive mechanisms, toxicity, bioavailability, and pharmaceutical relevance of piperlongumine in vitro and in vivo.

Targeting Autophagic Pathways by Plant Natural Compounds in Cancer Treatment

Nowadays, natural compounds of plant origin with anticancer effects have gained more attention because of their clinical safety and broad efficacy profiles. Autophagy is a multistep lysosomal degradation pathway that may have a unique potential for clinical benefit in the setting of cancer treatment. To retrieve articles related to the study, the databases of Google Scholar, Web of sciences, Medline and Scopus, using the following keywords: Autophagic pathways; herbal medicine, oncogenic autophagic pathways, tumor-suppressive autophagic pathways, and cancer were searched. Although natural plant compounds such as resveratrol, curcumin, oridonin, gossypol, and paclitaxel have proven anticancer potential via autophagic signaling pathways, there is still a great need to find new natural compounds and investigate the underlying mechanisms, to facilitate their clinical use as potential anticancer agents through autophagic induction.

Naringin Induces Lysosomal Permeabilization and Autophagy Cell Death in AGS Gastric Cancer Cells

Autophagy is a process of active programmed cell death, where a dying cell induces autophagosomes and subsequently regulated by degradative machinery. The aim of this study was to investigate the mechanism behind induction of autophagic cell death by Naringin flavonoid in AGS cancer cells. Growth inhibition of AGS cells showed downregulation of PI3K/Akt/mTOR signaling by Naringin treatment. Transmission electron microscopy observation showed swollen mitochondria and lysosome near peri-nuclear zone fused with autophagic vacuoles. Rapamycin pre-treatment with Naringin showed significant decrease in mTOR phosphorylation and increase in LC3B activation in AGS cells. Decrease in mTOR phosphorylation is associated with lysosomal function activation was observed by time-dependent treatment of Naringin. Induction of lysosomal membrane permeabilization (LMP) was observed by LAMP1 activation leading lysosomal cell death by releasing Cathepsin D from lysosomal lumen to cytosol. Naringin treated AGS cells showed up-regulating BH3 domain Bad, down-regulating Bcl-xL, and Bad phosphorylation and significant mitochondrial fluorescence intensity expression. Significant localization of mitochondria and LC3B activation was examined by person coefficient correlation. Activation of ERK1/2-p38 MAPKs and production of intracellular ROS has been observed over Naringin treatment. It has also been elucidated that pre-treatment with NAC inhibited mitochondria-LC3B colocalization, where ROS acted as upstream of ERK1/2-p38 MAPKs activation. Lysosomal cell death involvement has been evaluated by BAF A1 pre-treatment, inhibiting LAMP1, Cathepsin D, ROS, and blocking autophagolysosome in AGS cell death. Taken together, these findings show that, Naringin induced autophagy cell death involves LMP mediated lysosomal damage and BH3 protein Bad activation in AGS cancer cells.

Piperlongumine Inhibits Akt Phosphorylation to Reverse Resistance to Cisplatin in Human Non-Small Cell Lung Cancer Cells via ROS Regulation

Resistance is a major concern when administering chemotherapy to patients with non-small cell lung cancer (NSCLC). Chemosensitizer are agents that can reverse resistance to chemotherapeutic drugs, thereby enhancing the chemosensitivity of tumor cells. Thus, their development will improve therapeutic efficacy in cancer. However, few effective chemosensitizer have been identified to date. Piperlongumine (PL) has been shown to effectively reverse resistance to chemotherapeutic drugs in several types of cancers. However, the mechanisms associated with the chemotherapy resistance reversal effect of PL and its regulation of target factors in chemotherapy resistance cells are still unclear. This study investigated the reversal effect of PL both in vitro and in vivo, and provided evidence that PL inhibited the phosphorylation of Akt via the accumulation of reactive oxygen species in chemotherapy resistance cells. Consequently, various Akt activation-dependent genes caused a reduction of drug efflux and induction of apoptosis in cisplatin-resistant A549 NSCLC cells. Our results indicate that Akt phosphorylation may play a functional role in the reversal effect of PL and contribute, at least in part, to the treatment outcomes of patients with chemotherapy resistance.

Piplartine suppresses proliferation and invasion of hepatocellular carcinoma by LINC01391-modulated Wnt/β-catenin pathway inactivation through ICAT

Although piplartine is regarded as an anticancer agent, the relationship between long noncoding RNAs (lncRNAs), which are involved in various diseases (e.g., tumors) and piplartine in hepatocellular carcinoma (HCC) remains unclear. We identified LINC01391 using microarray analysis and validated its expression by qRT-PCR. Functional assays were applied to evaluate the biological effects of LINC01391 and inhibitory of β-catenin and T-cell factor (ICAT) on HepG2 and SMMC-7721 cells. The binding relationship between LINC01391 and ICAT was determined by RNA pull-down and RNA immunoprecipitation (RIP). Results showed that piplartine attenuated cell proliferation and invasion but promoted cell apoptosis. Upregulation of LINC01391 induced by piplartine inhibited HCC cell proliferation, invasion in vitro, and tumor growth in vivo. LINC01391 interacted with ICAT and promoted its inhibitory effect on the Wnt/β-catenin pathway, as enhanced interaction between β-catenin and ICAT, and dampened interaction of β-catenin and TCF/LEF were induced by overexpression of LINC01391. Knockdown of ICAT also promoted cell proliferation in vitro and tumor growth in vivo. Our study supported a role for piplartine and LINC01391 in HCC treatment. We found that LINC01391 inhibited the Wnt/β-catenin pathway and suppressed tumor growth via ICAT.

Ruthenium Complexes With Piplartine Cause Apoptosis Through MAPK Signaling by a p53-Dependent Pathway in Human Colon Carcinoma Cells and Inhibit Tumor Development in a Xenograft Model

Ruthenium complexes with piplartine, [Ru(piplartine)(dppf)(bipy)](PF₆)₂ (1) and [Ru(piplartine)(dppb)(bipy)](PF₆)₂ (2) (dppf = 1,1-bis(diphenylphosphino) ferrocene; dppb = 1,4-bis(diphenylphosphino)butane and bipy = 2,2′-bipyridine), were recently synthesized and displayed more potent cytotoxicity than piplartine in different cancer cells, regulated RNA transcripts of several apoptosis-related genes, and induced reactive oxygen species (ROS)-mediated apoptosis in human colon carcinoma HCT116 cells. The present work aimed to explore the underlying mechanisms through which these ruthenium complexes induce cell death in HCT116 cells in vitro, as well as their in vivo action in a xenograft model. Both complexes significantly increased the percentage of apoptotic HCT116 cells, and co-treatment with inhibitors of JNK/SAPK, p38 MAPK, and MEK, which inhibits the activation of ERK1/2, significantly reduced the apoptosis rate induced by these complexes. Moreover, significant increase in phospho-JNK2 (T183/Y185), phospho-p38α (T180/Y182), and phospho-ERK1 (T202/Y204) expressions were observed in cells treated with these complexes, indicating MAPK-mediated apoptosis. In addition, co-treatment with a p53 inhibitor (cyclic pifithrin-α) and the ruthenium complexes significantly reduced the apoptosis rate in HCT116 cells, and increased phospho-p53 (S15) and phospho-histone H2AX (S139) expressions, indicating induction of DNA damage and p53-dependent apoptosis. Both complexes also reduced HCT116 cell growth in a xenograft model. Tumor mass inhibition rates were 35.06, 29.71, and 32.03% for the complex 1 (15 μmol/kg/day), complex 2 (15 μmol/kg/day), and piplartine (60 μmol/kg/day), respectively. These data indicate these ruthenium complexes as new anti-colon cancer drugs candidates.

Piperlongumine increases sensitivity of colorectal cancer cells to radiation: Involvement of ROS production via dual inhibition of glutathione and thioredoxin systems

Piperlongumine (PL), naturally synthesized in long pepper, is known to selectively kill tumor cells via perturbation of reactive oxygen species (ROS) homeostasis. ROS are the primary effector molecules of radiation, and increase of ROS production by pharmacological modulation is known to enhance radioresponse. We therefore investigated the radiosensitizing effect of PL in colorectal cancer cells (CT26 and DLD-1) and CT26 tumor-bearing mice. Firstly, we found that PL induced excessive production of ROS due to depletion of glutathione and inhibition of thioredoxin reductase. Secondly, PL enhanced both the intrinsic and hypoxic radiosensitivity of tumor cells, linked to ROS-mediated increase of DNA damage, G2/M cell cycle arrest, and inhibition of cellular respiration. Finally, the radiosensitizing effect of PL was verified in vivo. PL improved the tumor response to both single and fractionated radiation, resulting in a significant increase of survival rate of tumor-bearing mice, while it was ineffective on its own. In line with in vitro findings, enhanced radioresponse is associated with inhibition of antioxidant systems. In conclusion, our results suggest that PL could be a potential radiosensitizer in colorectal cancer.

Piperlongumine, a piper alkaloid targets Ras/PI3K/Akt/mTOR signaling axis to inhibit tumor cell growth and proliferation in DMH/DSS induced experimental colon cancer

Colorectal cancer (CRC) is the most common carcinoma of the digestive tract. The slow growing nature of CRC offers a great opportunity for prevention strategies. The concept of chemoprevention of colorectal cancer using plant derived natural products is gaining substantial attention because it is an inherently safe and cost-effective alternative to conventional cancer therapies. Piperlongumine (PL), a natural alkaloid present in Piper longum Linn has been reported to exhibit notable anticancer effects in various in vitro studies. Nonetheless, the chemopreventive potential of PL has not been studied in experimentally induced colon cancer yet. Ras/PI3K/Akt/mTOR signaling axis plays a central role in promoting tumor cell growth, proliferation and survival by inhibiting apoptosis. In the present study, we demonstrated, for the first time, the chemopreventive effects of PL in DMH + DSS induced colon carcinogenesis animal model. We showed that PL displayed potent antineoplastic activity against colon cancer cell growth by targeting Ras proteins and PI3K/Akt signaling cascade. PL mediated inhibition of tumor cell growth was associated with inhibition of Ras protein levels and its preferred companion protein PI3K levels that led to suppressed activity of Akt/NF-κB, c-Myc and cyclin D1. It was also found that PL arrested the cell cycle progression at G2/M phase and induced mitochondrial apoptotic pathway by downregulating Bcl-2 levels. Furthermore, the results of liver and kidney toxicity suggested that PL exhibit no toxicity in animals. Our results suggest that PL may be an effective chemopreventive agent for colon cancer.

Piperlongumine and p53-reactivator APR-246 selectively induce cell death in HNSCC by targeting GSTP1

TP53 mutations frequently occur in head and neck squamous cell carcinoma (HNSCC) patients without human papillomavirus infection. The recurrence rate for these patients is distinctly high. It has been actively explored to identify agents that target TP53 mutations and restore wild-type (WT) TP53 activities in HNSCC. PRIMA-1 (p53-reactivation and induction of massive apoptosis-1) and its methylated analogue PRIMA-1Met (also called APR-246) were found to be able to reestablish the DNA-binding activity of p53 mutants and reinstate the functions of WT p53. Herein we report that piperlongumine (PL), an alkaloid isolated from Piper longum L., synergizes with APR-246 to selectively induce apoptosis and autophagic cell death in HNSCC cells, whereas primary and immortalized mouse embryonic fibroblasts and spontaneously immortalized non-tumorigenic human skin keratinocytes (HaCat) are spared from the damage by the co-treatment. Interestingly, PL-sensitized HNSCC cells to APR-246 are TP53 mutation-independent. Instead, we demonstrated that glutathione S-transferase pi 1 (GSTP1), a GST family member that catalyzes the conjugation of GSH with electrophilic compounds to fulfill its detoxification function, is highly expressed in HNSCC tissues. Administration of PL and APR-246 significantly suppresses GSTP1 activity, resulting in the accumulation of ROS, depletion of GSH, elevation of GSSG, and DNA damage. Ectopic expression of GSTP1 or pre-treatment with antioxidant N-acetyl-L-cysteine (NAC) abrogates the ROS elevation and decreases DNA damage, apoptosis, and autophagic cell death prompted by PL/APR-246. In addition, administration of PL and APR-246 impedes UMSCC10A xenograft tumor growth in SCID mice. Taken together, our data suggest that HNSCC cells are selectively sensitive to the combination of PL and APR-246 due to a remarkably synergistic effect of the co-treatment in the induction of ROS by suppression of GSTP1.

Natural products as modulator of autophagy with potential clinical prospects

Natural compounds derived from living organisms are well defined for their remarkable biological and pharmacological properties likely to be translated into clinical use. Therefore, delving into the mechanisms by which natural compounds protect against diverse diseases may be of great therapeutic benefits for medical practice. Autophagy, an intricate lysosome-dependent digestion process, with implications in a wide variety of pathophysiological settings, has attracted extensive attention over the past few decades. Hitherto, accumulating evidence has revealed that a large number of natural products are involved in autophagy modulation, either inducing or inhibiting autophagy, through multiple signaling pathways and transcriptional regulators. In this review, we summarize natural compounds regulating autophagy in multifarious diseases including cancer, neurodegenerative diseases, cardiovascular diseases, metabolic diseases, and immune diseases, hoping to inspire further investigation of the underlying mechanisms of natural compounds and to facilitate their clinical use for multiple human diseases.

Piperlongumine rapidly induces the death of human pancreatic cancer cells mainly through the induction of ferroptosis

Pancreatic cancer is one of the most lethal types of cancer with a mortality rate of almost 95%. Treatment with current chemotherapeutic drugs has limited success due to poor responses. Therefore, the development of novel drugs or effective combination therapies is urgently required. Piperlongumine (PL) is a natural product with cytotoxic properties restricted to cancer cells by significantly increasing intracellular reactive oxygen species (ROS) levels. In the present study, we demonstrated that PL induced cancer cell death through, at least in part, the induction of ferroptosis, as the cancer cell-killing activity was inhibited by the antioxidant, N‑acetylcysteine, ferroptosis inhibitors (ferrostatin‑1 and liproxstatin‑1) and the iron chelator, deferoxamine (DFO), but not by the apoptosis inhibitor, Z-VAD-FMK, or the necrosis inhibitor, necrostatin‑1. Cotylenin A (CN‑A; a plant growth regulator) exhibits potent antitumor activities in several cancer cell lines, including pancreatic cancer cell lines. We found that CN‑A and PL synergistically induced the death of pancreatic cancer MIAPaCa‑2 and PANC‑1 cells for 16 h. CN‑A enhanced the induction of ROS by PL for 4 h. The synergistic induction of cell death was also abrogated by the ferroptosis inhibitors and DFO. The present results revealed that clinically approved sulfasalazine (SSZ), a ferroptosis inducer, enhanced the death of pancreatic cancer cells induced by PL and the combined effects were abrogated by the ferroptosis inhibitors and DFO. SSZ further enhanced the cancer cell-killing activities induced by combined treatment with PL plus CN‑A. On the other hand, the synergistic induction of cell death by PL and CN‑A was not observed in mouse embryonic fibroblasts (MEFs), and SSZ did not enhance the death of MEFs induced by PL plus CN‑A. These results suggest that the triple combined treatment with PL, CN‑A and SSZ is highly effective against pancreatic cancer.

Piperlongumine restores the balance of autophagy and apoptosis by increasing BCL2 phosphorylation in rotenone-induced Parkinson disease models

Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease and is caused by genetics, environmental factors and aging, with few treatments currently available. Apoptosis and macroautophagy/autophagy play critical roles in PD pathogenesis; as such, modulating their balance is a potential treatment strategy. BCL2 (B cell leukemia/lymphoma 2) is a key molecule regulating this balance. Piperlongumine (PLG) is an alkaloid extracted from Piper longum L. that has antiinflammatory and anticancer effects. The present study investigated the protective effects of PLG in rotenone-induced PD cell and mouse models. We found that PLG administration (2 and 4 mg/kg) for 4 wk attenuated motor deficits in mice and prevented the loss of dopaminergic neurons in the substantia nigra induced by oral administration of rotenone (10 mg/kg) for 6 wk. PLG improved cell viability and enhanced mitochondrial function in primary neurons and SK-N-SH cells. These protective effects were exerted via inhibition of apoptosis and induction of autophagy through enhancement of BCL2 phosphorylation at Ser70. These results demonstrate that PLG exerts therapeutic effects in a rotenone-induced PD models by restoring the balance between apoptosis and autophagy.

ABBREVIATIONS

6-OHDA, 6-hydroxydopamine; ACTB, actin, beta; BafA1, bafilomycin A1; BAK1, BCL2-antagonist/killer 1; BAX, BCL2-associated X protein; BCL2, B cell leukemia/lymphoma2; BECN1, Beclin 1, autophagy related; CoQ10, coenzyme Q10; COX4I1/COX IV, cytochrome c oxidase subunit 4I1; CsA, cyclosporine A; ED50, 50% effective dose; FITC, fluorescein isothiocyanate; GFP, green fluorescent protein; HPLC, high-performance liquid chromatography; JC-1, tetraethylbenz-imidazolylcarbocyanine iodide; LC3, microtubule-associated protein 1 light chain3; LC-MS/MS, liquid chromatography-tandem mass spectrometry; LDH, lactate dehydrogenase; l-dopa, 3, 4-dihydroxyphenyl-l-alanine; MAPK8/JNK1, mitogen-activated protein kinase 8; MMP, mitochondrial membrane potential; mPTP, mitochondrial permeability transition pore; mRFP, monomeric red fluorescent protein; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NFE2L2/NRF2, nuclear factor, erythroid derived 2, like 2; PD, Parkinson disease; PLG, piperlongumine; pNA, p-nitroanilide; PI, propidium iodide; PtdIns3K, phosphatidylinositol 3-kinase; PtdIns3P, phosphatidylinositol-3-phosphate; PTX, paclitaxel; Rap, rapamycin; SQSTM1/p62, sequestosome 1; TH, tyrosine hydroxylase; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling; WIPI2, WD repeat domain, phosphoinositide interacting 2; ZFYVE1/DFCP1, zinc finger, FYVE domain containing 1.

Piperlongumine induces apoptosis and autophagy in leukemic cells through targeting the PI3K/Akt/mTOR and p38 signaling pathways

Piperlongumine is an alkaloid compound extracted from Piper longum L. It is a chemical substance with various pharmacological effects and medicinal value, including anti-tumor, lipid metabolism regulatory, antiplatelet aggregation and analgesic properties. The present study aimed to understand whether piperlongumine induces the apoptosis and autophagy of leukemic cells, and to identify the mechanism involved. Cell viability and autophagy were detected using MTT, phenazine methyl sulfate and trypan blue exclusion assays. The apoptosis rate was calculated using flow cytometry. The protein expression levels of microtubule-associated protein 1A/1B-light chain 3, Akt and mechanistic target of rapamycin (mTOR) were measured using western blotting. The cell growth of leukemic cells was completely inhibited following treatment with piperlongumine, and marked apoptosis was also induced. Dead cells as a result of autophagy were stained using immunofluorescence and observed under a light microscope. Phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling was suppressed by treatment with piperlongumine, while p38 signaling and caspase-3 activity were induced by treatment with piperlongumine. It was concluded that piperlongumine induces apoptosis and autophagy in leukemic cells through targeting the PI3K/Akt/mTOR and p38 signaling pathways.

Natural agents mediated autophagic signal networks in cancer

Recent studies suggested that natural compounds are important in finding targets for cancer treatments. Autophagy (“self-eating”) plays important roles in multiple diseases and acts as a tumor suppressor in cancer. Here, we examined the molecular mechanism by which natural agents regulate autophagic signals. Understanding the relationship between natural agents and cellular autophagy may provide more information for cancer diagnosis and chemoprevention.

Escin induces caspase-dependent apoptosis and autophagy through the ROS/p38 MAPK signalling pathway in human osteosarcoma cells in vitro and in vivo

Osteosarcoma is one of the most malignant neoplasms in adolescents, and it generally develops multidrug resistance. Escin, a natural mixture of triterpene saponins isolated from Aesculus hippocastanum (horse chestnut), has demonstrated potent anti-tumour potential in vitro and in vivo. In the present study, we found that escin inhibited osteosarcoma proliferation in a dose- and time-dependent manner. Additionally, escin-induced apoptosis was evidenced by the increased expression of caspase-related proteins and the formation of apoptotic bodies. Escin also induced autophagy, with elevated LC3, ATG5, ATG12 and Beclin expression as well as autophagosome formation. Inhibition of escin-induced autophagy promoted apoptosis. Moreover, p38 mitogen-activated protein kinases (MAPKs) and reactive oxygen species (ROS) were activated by escin. A p38 MAPK inhibitor partially attenuated the autophagy and apoptosis triggered by escin, but a ROS scavenger showed a greater inhibitory effect. Finally, the therapeutic efficacy of escin against osteosarcoma was demonstrated in an orthotopic model. Overall, escin counteracted osteosarcoma by inducing autophagy and apoptosis via the activation of the ROS/p38 MAPK signalling pathway; these findings provide evidence for escin as a novel and potent therapeutic for the treatment of osteosarcoma.

Blocking autophagy enhances the apoptotic effect of 18β-glycyrrhetinic acid on human sarcoma cells via endoplasmic reticulum stress and JNK activation

Sarcoma, a rare form of cancer, is unlike the much more common carcinomas as it occurs in a distinct type of tissue. The potent antitumor effects of 18β-glycyrrhetinic acid (GA), a novel naturally derived agent, have been demonstrated in various cancers. However, the effect of GA on human sarcoma, and the underlying mechanisms, remain to be elucidated. In the current study, we show that GA inhibits sarcoma cell proliferation by inducing G0/G1-phase arrest. Exposure to GA resulted in the activation of caspase-3, -8, and -9, indicating that GA induced apoptosis through both extrinsic and intrinsic pathways. In addition, the autophagy pathway, characterized by the conversion of LC3-I to LC3- II, was activated, resulting in increased Beclin-1 protein levels, decreased p62 expression, and stimulation of autophagic flux. The present findings showed that GA stimulated autophagy by inducing endoplasmic reticulum (ER) stress via the IRE1–JNK pathway. Our data supported the prosurvival role of GA-induced autophagy when the autophagy pathway was blocked with specific chemical inhibitors. Finally, GA markedly reduced sarcoma growth, with little organ-related toxicity, in vivo. The present results suggest that the combination of GA with a specific autophagy inhibitor represents a promising therapeutic approach for the treatment of sarcoma.

A diphenyldiselenide derivative induces autophagy via JNK in HTB-54 lung cancer cells

Symmetric aromatic diselenides are potential anticancer agents with strong cytotoxic activity. In this study, the in vitro anticancer activities of a novel series of diarylseleno derivatives from the diphenyldiselenide (DPDS) scaffold were evaluated. Most of the compounds exhibited high efficacy for inducing cytotoxicity against different human cancer cell lines. DPDS 2, the compound with the lowest mean GI₅₀ value, induced both caspase-dependent apoptosis and arrest at the G₀ /G₁ phase in acute lymphoblastic leucemia CCRF-CEM cells. Consistent with this, PARP cleavage; enhanced caspase-2, -3, -8 and -9 activity; reduced CDK4 expression and increased levels of p53 were detected in these cells upon DPDS 2 treatment. Mutated p53 expressed in CCRF-CEM cells retains its transactivating activity. Therefore, increased levels of p21^CIP1 and BAX proteins were also detected. On the other hand, DPDS 6, the compound with the highest selectivity index for cancer cells, resulted in G₂ /M cell cycle arrest and caspase-independent cell death in p53 deficient HTB-54 lung cancer cells. Autophagy inhibitors 3-methyladenine, wortmannin and chloroquine inhibited DPDS 6-induced cell death. Consistent with autophagy, increased LC3-II and decreased SQSTM1/p62 levels were detected in HTB-54 cells in response to DPDS 6. Induction of JNK phosphorylation and a reduction in phospho-p38 MAPK were also detected. Moreover, the JNK inhibitor SP600125-protected HTB-54 cells from DPDS 6-induced cell death indicating that JNK activation is involved in DPDS 6-induced autophagy. These results highlight the anticancer effects of these derivatives and warrant future studies examining their clinical potential.

Sinomenine Hydrochloride Inhibits Human Glioblastoma Cell Growth through Reactive Oxygen Species Generation and Autophagy-Lysosome Pathway Activation: An In Vitro and In Vivo Study

Glioblastoma is the most common malignant primary brain tumor, and it is one of the causes of cancer fatality in both adult and pediatric populations. Patients with glioblastoma require chemotherapy after surgical resection and radiotherapy. Therefore, chemotherapy constitutes a viable approach for the eradication of glioblastoma cells. In this study, the anti-tumor activity of sinomenine hydrochloride (SH) was evaluated in U87 and SF767 cells in vitro and in vivo. The results showed that SH potently inhibited U87 and SF767 cell viability and did not cause caspase-dependent cell death, as demonstrated by the absence of significant early apoptosis and caspase-3 cleavage. Instead, SH activated an autophagy-mediated cell death pathway, as indicated by the accumulated microtubule-associated protein light chain 3B (LC3B)-II, triggered autophagic flux and enhanced cell viability after pretreatment with autophagy inhibitors. SH-mediated autophagy in the two cell lines was implicated in reactive oxygen species (ROS) generation, protein kinase B (Akt)-mammalian target of rapamycin (mTOR) pathway suppression and c-Jun NH2-terminal kinase (JNK) pathway activation. The ROS antioxidant N-acetylcysteine (NAC), the Akt-specific activator insulin-like growth factor-1 (IGF-1) and the JNK-specific inhibitor SP600125 attenuated SH-induced autophagy. Moreover, ROS activated autophagy via the Akt-mTOR and JNK pathways. Additionally, SH treatment may promote lysosome biogenesis through activating transcription factor EB (TFEB). The in vivo study found that SH effectively suppressed glioblastoma growth without exhibiting significant toxicity. In conclusion, our findings reveal a novel mechanism of action of SH in cancer cells via the induction of autophagy through ROS generation and autophagy-lysosome pathway activation; these findings also supply a new potential therapeutic agent for the treatment of human glioblastoma.

Piperlongumine Induces Reactive Oxygen Species (ROS)-Dependent Downregulation of Specificity Protein Transcription Factors

Piperlongumine is a natural product found in the plant species Piper longum, and this compound exhibits potent anticancer activity in multiple tumor types and has been characterized as an inducer of reactive oxygen species (ROS). Treatment of Panc1 and L3.6pL pancreatic, A549 lung, 786-O kidney, and SKBR3 breast cancer cell lines with 5 to 15 μmol/L piperlongumine inhibited cell proliferation and induced apoptosis and ROS, and these responses were attenuated after cotreatment with the antioxidant glutathione. Piperlongumine also downregulated expression of Sp1, Sp3, Sp4, and several pro-oncogenic Sp-regulated genes, including cyclin D1, survivin, cMyc, EGFR and hepatocyte growth factor receptor (cMet), and these responses were also attenuated after cotreatment with glutathione. Mechanistic studies in Panc1 cells showed that piperlongumine-induced ROS decreased expression of cMyc via an epigenetic pathway, and this resulted in downregulation of cMyc-regulated miRNAs miR-27a, miR-20a, and miR-17 and induction of the transcriptional repressors ZBTB10 and ZBTB4. These repressors target GC-rich Sp-binding sites to decrease transactivation. This pathway observed for piperlongumine in Panc1 cells has previously been reported for other ROS-inducing anticancer agents and shows that an important underlying mechanism of action of piperlongumine is due to downregulation of Sp1, Sp3, Sp4, and pro-oncogenic Sp-regulated genes. Cancer Prev Res; 10(8); 467-77. ©2017 AACR.

Piperlongumine downregulates the expression of HER family in breast cancer cells

HER family receptors are frequently deregulated in breast cancer and the deregulation of these receptors is associated with poor prognosis. Thus, these receptors are considered therapeutic targets. In the present study, we found that piperlongumine (PL) downregulates the expression of HER family receptors HER1, HER2, and HER3 in breast cancer cells. Downregulation of these receptors by PL is mediated through the generation of reactive oxygen species (ROS), as N-acetyl-cysteine blocks it. Interestingly, the HER2-overexpressing cell lines BT474 and SkBr3 are somewhat more sensitive to PL than the low HER2-expressing cell line MCF7. In addition, the overexpression of HER2 increases the sensitivity of MCF7 cells to PL. Collectively, our data indicate the therapeutic potential of PL in the treatment of breast cancer.

Structural and Biochemical Analyses Reveal the Mechanism of Glutathione S-Transferase Pi 1 Inhibition by the Anti-cancer Compound Piperlongumine

Glutathione S-transferase pi 1 (GSTP1) is frequently overexpressed in cancerous tumors and is a putative target of the plant compound piperlongumine (PL), which contains two reactive olefins and inhibits proliferation in cancer cells but not normal cells. PL exposure of cancer cells results in increased reactive oxygen species and decreased GSH. These data in tandem with other information led to the conclusion that PL inhibits GSTP1, which forms covalent bonds between GSH and various electrophilic compounds, through covalent adduct formation at the C7-C8 olefin of PL, whereas the C2-C3 olefin of PL was postulated to react with GSH. However, direct evidence for this mechanism has been lacking. To investigate, we solved the X-ray crystal structure of GSTP1 bound to PL and GSH at 1.1 Å resolution to rationalize previously reported structure activity relationship studies. Surprisingly, the structure showed that a hydrolysis product of PL (hPL) was conjugated to glutathione at the C7-C8 olefin, and this complex was bound to the active site of GSTP1; no covalent bond formation between hPL and GSTP1 was observed. Mass spectrometry (MS) analysis of the reactions between PL and GSTP1 confirmed that PL does not label GSTP1. Moreover, MS data also indicated that nucleophilic attack on PL at the C2-C3 olefin led to PL hydrolysis. Although hPL inhibits GSTP1 enzymatic activity in vitro, treatment of cells susceptible to PL with hPL did not have significant anti-proliferative effects, suggesting that hPL is not membrane-permeable. Altogether, our data suggest a model wherein PL is a prodrug whose intracellular hydrolysis initiates the formation of the hPL-GSH conjugate, which blocks the active site of and inhibits GSTP1 and thereby cancer cell proliferation.

Isomahanine induces endoplasmic reticulum stress and simultaneously triggers p38 MAPK-mediated apoptosis and autophagy in multidrug-resistant human oral squamous cell carcinoma cells

Advanced oral squamous cell carcinoma (OSCC) is typically aggressive and closely correlated with disease recurrence and poor survival. Multidrug resistance (MDR) is the most critical problem leading to therapeutic failure. Investigation of novel anticancer candidates targeting multidrug-resistant OSCC cells may provide a basis for developing effective strategies for OSCC treatment. In the present study, we investigated the cytotoxic mechanism of a carbazole alkaloid, namely isomahanine, in a multidrug‑resistant OSCC cell line CLS-354/DX. We demonstrated that CLS-354/DX cells overexpressing multidrug resistance-associated protein 1 (MRP1) were resistant to anticancer drugs cisplatin and camptothecin. Isomahanine effectively induced cytotoxicity against CLS-354/DX cells regardless of resistance. Apoptosis as determined by FITC‑Annexin V/PI staining and western blot analysis of cleaved caspase-3 and cleaved poly(ADP‑ribose) polymerase (PARP) was significantly induced in a time-dependent manner upon isomahanine treatment. Isomahanine-induced caspase‑dependent apoptosis was determined using z-VAD‑fmk. The effects on autophagy in isomahanine-treated cells were investigated via conversion of LC3B and degradation of p62/SQSTM1 (p62). Isomahanine obviously induced autophagic flux as shown by an increase in punctate GFP-LC3B and the LC3B-II/LC3B-I ratio with a concomitant decrease in p62 levels. Autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ) protected isomahanine-induced cell death, indicating the activation of autophagic cell death. Endoplasmic reticulum (ER) stress and MAPK activation were examined to elucidate the mechanism underlying cell death. The expression levels of PERK, CHOP and phosphorylated MAPK (p38, ERK1/2 and JNK1/2) were upregulated following isomahanine treatment. We found that p38 MAPK inhibitor (SB203580) significantly attenuated isomahanine-induced apoptosis and autophagic flux and this prevented cell death. Collectively, the present study demonstrated that isomahanine was able to induce ER stress and trigger p38 MAPK-mediated apoptosis and autophagic cell death in multidrug-resistant OSCC cells. The potential cytotoxic action of isomahanine may provide the development of anticancer candidates for treating multidrug-resistant cancer.

Discovery of piperlongumine as a potential novel lead for the development of senolytic agents

Accumulating evidence indicates that senescent cells play an important role in many age-associated diseases. The pharmacological depletion of senescent cells (SCs) with a "senolytic agent", a small molecule that selectively kills SCs, is a potential novel therapeutic approach for these diseases. Recently, we discovered ABT-263, a potent and highly selective senolytic agent, by screening a library of rationally-selected compounds. With this screening approach, we also identified a second senolytic agent called piperlongumine (PL). PL is a natural product that is reported to have many pharmacological effects, including anti-tumor activity. We show here that PL preferentially killed senescent human WI-38 fibroblasts when senescence was induced by ionizing radiation, replicative exhaustion, or ectopic expression of the oncogene Ras. PL killed SCs by inducing apoptosis, and this process did not require the induction of reactive oxygen species. In addition, we found that PL synergistically killed SCs in combination with ABT-263, and initial structural modifications to PL identified analogs with improved potency and/or selectivity in inducing SC death. Overall, our studies demonstrate that PL is a novel lead for developing senolytic agents.

A Central Role for Phosphorylated p38α in Linking Proteasome Inhibition-Induced Apoptosis and Autophagy

Autophagy and the ubiquitin proteasome system (UPS), as two major protein degradation pathways, coordinate with each other in regulating programmed cell death. Autophagy can compensate for the UPS impairment-induced cell dysfunction and apoptosis. However, it is not clear how cells maintain the delicate balance between UPS-related apoptosis and autophagy. Here, we showed that proteasome inhibition-mediated UPS impairment can activate the phosphorylated p38α (p-p38α)-dependent apoptotic pathway and autophagy pathway in both neuroblastoma cell line N2a and primary cortical neuronal cells. Multiple indices were utilized for the autophagy detection including LC3II transition, acidic vesicle formation, lysosomal accumulation, and p62 reduction. Blockade of autophagy flux with autophagy inhibitor 3-methyladenine or bafilomycin A1 resulted in further phosphorylation of p38α, polyubiquitinated protein aggregation, and greater apoptotic cell death. On the contrary, enhancement of autophagy by rapamycin attenuated the cell loss by lowering p-p38α level and degrading protein aggregates, indicating a protective role of autophagy in cell stress and apoptosis. Moreover, de-activation of p38α with pharmaceutical p38α inhibitor BIRB796 greatly increased autophagy activation, reduced protein aggregates, and attenuated cell loss, suggesting a bidirectional regulation between p-p38α and autophagy. In addition, manipulation of p-p38α by BIRB796 or p38α knockdown decreased the phosphorylation of key components of the mammalian target of rapamycin (mTOR)-dependent pathway, indicating that the mTOR pathway mediates the p-p38α regulation on autophagy. Overall, our data emphasize p-p38α as a key mediator in the antagonistic interaction between apoptosis and autophagy in response to UPS impairment. Centering p-p38α as a potential regulatory target may provide a dual advantage of proteostasis maintenance and cell survival for simultaneous inhibition of apoptosis and activation of autophagy.

Piperlongumine induces apoptosis and reduces bortezomib resistance by inhibiting STAT3 in multiple myeloma cells

Effective new therapies are urgently needed for the treatment of multiple myeloma (MM), an incurable hematological malignancy. In this study, we evaluated the effects of piperlongumine on MM cell proliferation both in vivo and in vitro. Piperlongumine inhibited the proliferation of MM cells by inducing cell apoptosis and blocking osteoclastogenesis. Notably, piperlongumine also reduced bortezomib resistance in MM cells. In a disseminated MM mouse model, piperlongumine prolonged the survival of tumor-bearing mice without causing any obvious toxicity. Mechanistically, piperlongumine inhibited the STAT3 signal pathway in MM cells by binding directly to the STAT3 Cys712 residue. These findings suggest that the clinical use of piperlongumine to overcome bortezomib resistance in MM should be evaluated.

Glycyrrhetinic acid induces cytoprotective autophagy via the inositol-requiring enzyme 1α-c-Jun N-terminal kinase cascade in non-small cell lung cancer cells

Glycerrhetinic acid (GA), one of the main bioactive constituents of Glycyrrhiza uralensis Fisch, exerts anti-cancer effects on various cancer cells. We confirmed that GA inhibited cell proliferation and induced apoptosis in non-small cell lung cancer A549 and NCI-H1299 cells. GA also induced expression of autophagy marker phosphatidylethanolamine-modified microtubule-associated protein light-chain 3 (LC3-II) and punta formation of green fluorescent protein microtubule-associated protein light-chain 3. We further proved that expression of GA-increased autophagy marker was attributed to activation instead of suppression of autophagic flux. The c-jun N-terminal kinase (JNK) pathway was activated after incubation with GA. Pretreatment with the JNK inhibitor SP600125 or silencing of the JNK pathway by siRNA of JNK or c-jun decreased GA-induced autophagy. The endoplasmic reticulum (ER) stress responses were also apparently stimulated by GA by triggering the inositol-requiring enzyme 1α (IRE1α) pathway. The GA-induced JNK pathway activation and autophagy were decreased by IRE1α knockdown, and inhibition of autophagy or the JNK cascade increased GA-stimulated IRE1α expression. In addition, GA-induced cell proliferative inhibition and apoptosis were increased by inhibition of autophagy or the JNK pathway. Our study was the first to demonstrate that GA induces cytoprotective autophagy in non-small cell lung cancer cells by activating the IRE1α-JNK/c-jun pathway. The combined treatment of autophagy inhibitors markedly enhances the anti-neoplasmic activity of GA. Such combination shows potential as a strategy for GA or GA-contained prescriptions in cancer therapy.

A Survey of the Chemical Compounds of Piper spp. (Piperaceae) and Their Biological Activities

The genus Piper is one of the largest genera in the Piperaceae, with most species widely distributed globally, covering all continents. To date, many Piper species have been scientifically investigated for their chemical diversities and interesting broad spectrum of bioactivities, including central nervous system (CNS), pesticidal, antifungal and antibacterial effects. This review systematically summarizes the scaffolds of the alkaloids reported, the major chemicals isolated from Piper spp., and their biological activities. Besides the alkaloids, some neolignans with rearranged skeletons show structural diversities, while the chalcones, flavonoids and kava-pyrones have some potential activities. Herein, the sesquiterpenes and phenolic compounds from Piper species and their bioactivities are also surveyed.

Targeted Inhibition of Glutamine-Dependent Glutathione Metabolism Overcomes Death Resistance Induced by Chronic Cycling Hypoxia

AIMS

Tumor hypoxia is a major biological factor causing poor patient outcome. Evidence is increasing that improved protection against reactive oxygen species (ROS) participates in therapy resistance of chronically hypoxic cancer cells. We aimed at characterizing the relevance of improved ROS defense for radiation resistance of cancer cells with tolerance to cycling anoxia/re-oxygenation stress ("anoxia-tolerant") and at designing rational treatment strategies for overcoming the resulting therapy resistance by targeting the underlying mechanisms identified in an in vitro model.

RESULTS

We demonstrate that chronic exposure of NCH-H460 lung adenocarcinoma, DU145 prostate cancer, and T98G glioblastoma cells to cycling anoxia/re-oxygenation stress induced upregulation of the aspartate-aminotransferase glutamic-oxaloacetic transaminase (GOT1), particularly in RAS-driven anoxia-tolerant NCI-H460 cells. Altered glutamine utilization of the anoxia-tolerant cancer cells contributed to the observed decrease in cellular ROS levels, the increase in cellular glutathione levels, and improved cell survival on ROS-inducing treatments, including exposure to ionizing radiation. Importantly, targeting glutamine-dependent antioxidant capacity or glutathione metabolism allowed us to hit anoxia-tolerant cancer cells and to overcome their increased resistance to radiation-induced cell death. Targeting glutathione metabolism by Piperlongumine also improved the radiation response of anoxia-tolerant NCI-H460 cells in vivo.

INNOVATION

Improved antioxidant capacity downstream of up-regulated GOT1-expression is a characteristic of anoxia-tolerant cancer cells and is predictive for a specific vulnerability to inhibition of glutamine utilization or glutathione metabolism, respectively.

CONCLUSION

Unraveling the molecular alterations underlying improved ROS defense of anoxia-tolerant cancer cells allows the design of rational strategies for overcoming radiation resistance caused by tumor cell heterogeneity in hypoxic tumors. Antioxid. Redox Signal. 25, 89-107.

Hypoxia potentiates the cytotoxic effect of piperlongumine in pheochromocytoma models

Hypoxia is a common feature of solid tumors that activates a plethora of pathways, resulting in proliferation and resistance of cancer cells to radio- and chemotherapy. Pheochromocytomas/paragangliomas (PHEOs/PGLs) with mutations in the gene coding for the subunit B of succinate dehydrogenase (SDHB) are the most aggressive forms of the disease, which is partially due to their pseudohypoxic character, metabolic abnormalities, and elevated reactive oxygen species (ROS) levels. We investigated the effect of piperlongumine (PL), a natural product with cytotoxic properties restricted to cancer cells by significantly increasing intracellular ROS levels, on PHEO cells. Here we report for the first time that PL mediates PHEO cell death by activating both apoptosis and necroptosis in vitro and in vivo. This effect is magnified in hypoxic conditions, making PL a promising potential candidate for use as a therapeutic option for patients with PHEO/PGL, including those with SDHB mutations.

Transcriptome Analysis of Piperlongumine-Treated Human Pancreatic Cancer Cells Reveals Involvement of Oxidative Stress and Endoplasmic Reticulum Stress Pathways

Piperlongumine (PL), an alkaloid obtained from long peppers, displays antitumorigenic properties for a variety of human cell- and animal-based models. The aim of this study was to identify the underlying molecular mechanisms for PL anticancer effects on human pancreatic cancer cells. RNA sequencing (RNA-seq) was used to identify the effects of PL on the transcriptome of MIA PaCa-2 human pancreatic cancer cells. PL treatment of pancreatic cancer cells resulted in differential expression of 683 mRNA transcripts with known protein functions, 351 of which were upregulated and 332 of which were downregulated compared to control-treated cells. Transcripts associated with oxidative stress, endoplasmic reticulum (ER) stress, and unfolded protein response pathways were significantly overexpressed with PL treatment. Reverse transcription-quantitative polymerase chain reaction and western blotting were used to validate the RNA-seq results, which included upregulation of HO-1, IRE1α, cytochrome c, and ASNS. The results provide key insight into the mechanisms by which PL alters cancer cell physiology and identify that activation of oxidative stress and ER stress pathways is a critical avenue for PL anticancer effects.

A Fucus vesiculosus extract inhibits estrogen receptor activation and induces cell death in female cancer cell lines

BACKGROUND

We previously reported the anti-estrogenic activity of the brown seaweed, Fucus vesiculosus. The present study aimed to further investigate its anti-estrogenic modes of action and to assess other potentially biologically relevant anti-tumorigenic effects in estrogen receptor (ER)-dependent and -independent female cancer cell lines.

METHODS

The CALUX® assay was used to determine the effect of a F. vesiculosus extract (FVE) on activation of the ER. Aromatase enzymatic activity was measured to determine the potential effect of FVE on estradiol (E2) biosynthesis. Transcriptional activity profiling of 248 genes involved in cancer, immunity, hormonal regulation, protein phosphorylation, transcription, metabolism, and cellular structure was conducted using the NanoString nCounter® analysis system in FVE-treated breast, ovarian and endometrial cancer cell lines. The effects of FVE on cell viability, morphology, membrane integrity, mitochondrial toxicity, induction of apoptotic and autophagic markers, and cell signaling were also analyzed.

RESULTS

In co-treatments with 12.5 pM (EC50) E2, FVE (2 %) reduced ER activation by 50 %, exhibiting potent ER antagonistic effects. FVE inhibited aromatase activity in an in vitro assay (IC50 2.0 %). ER-dependent and -independent cancer cell lines showed significantly decreased viability that correlated with increasing FVE concentrations and altered morphological features suggestive of apoptosis and autophagy. Expression of genes that were significantly altered by FVE (p < 0.05) revealed predominantly apoptotic, autophagic and kinase signaling pathways. FVE also effectively inhibited the phosphorylation of Akt, resulting in reduced mTORC1 activities to stimulate autophagy in cells. Concentration-dependent cleavage of PARP and induction of caspase-3 and -7 activities were observed in MDA-MB-231 cells supporting a role for FVE in the promotion of apoptosis.

CONCLUSIONS

Our study provides new insights into the anti-estrogenic activity of F. vesiculosus. Moreover, the induction of autophagy and apoptosis on breast, endometrial and ovarian cancer cell lines suggests additional anti-tumorigenic actions of FVE that are independent of ER status in female cancers.

Piperlongumine Suppresses Proliferation of Human Oral Squamous Cell Carcinoma through Cell Cycle Arrest, Apoptosis and Senescence

Oral squamous cell carcinoma (OSCC), an aggressive cancer originating in the oral cavity, is one of the leading causes of cancer deaths in males worldwide. This study investigated the antitumor activity and mechanisms of piperlongumine (PL), a natural compound isolated from Piper longum L., in human OSCC cells. The effects of PL on cell proliferation, the cell cycle, apoptosis, senescence and reactive oxygen species (ROS) levels in human OSCC cells were investigated. PL effectively inhibited cell growth, caused cell cycle arrest and induced apoptosis and senescence in OSCC cells. Moreover, PL-mediated anti-human OSCC behavior was inhibited by an ROS scavenger N-acetyl-l-cysteine (NAC) treatment, suggesting that regulation of ROS was involved in the mechanism of the anticancer activity of PL. These findings suggest that PL suppresses tumor growth by regulating the cell cycle and inducing apoptosis and senescence and is a potential chemotherapy agent for human OSCC cells.

New Potential Pharmacological Functions of Chinese Herbal Medicines via Regulation of Autophagy

Autophagy is a universal catabolic cellular process for quality control of cytoplasm and maintenance of cellular homeostasis upon nutrient deprivation and environmental stimulus. It involves the lysosomal degradation of cellular components such as misfolded proteins or damaged organelles. Defects in autophagy are implicated in the pathogenesis of diseases including cancers, myopathy, neurodegenerations, infections and cardiovascular diseases. In the recent decade, traditional drugs with new clinical applications are not only commonly found in Western medicines, but also highlighted in Chinese herbal medicines (CHM). For instance, pharmacological studies have revealed that active components or fractions from Chaihu (Radix bupleuri), Hu Zhang (Rhizoma polygoni cuspidati), Donglingcao (Rabdosia rubesens), Hou po (Cortex magnoliae officinalis) and Chuan xiong (Rhizoma chuanxiong) modulate cancers, neurodegeneration and cardiovascular disease via autophagy. These findings shed light on the potential new applications and formulation of CHM decoctions via regulation of autophagy. This article reviews the roles of autophagy in the pharmacological actions of CHM and discusses their new potential clinical applications in various human diseases.

Piperlongumine Suppresses Growth and Sensitizes Pancreatic Tumors to Gemcitabine in a Xenograft Mouse Model by Modulating the NF-kappa B Pathway

Pancreatic cancer is an aggressive malignancy, which generally respond poorly to chemotherapy. Hence, novel agents that are safe and effective are highly needed. The aim of this study was to investigate whether piperlongumine, a natural product isolated from the fruit of the pepper Piper longum, has any efficacy against human pancreatic cancer when used either alone or in combination with gemcitabine in vitro and in a xenograft mouse model. In vitro, piperlongumine inhibited the proliferation of pancreatic cancer cell lines, potentiated the apoptotic effects of gemcitabine, inhibited the constitutive and inducible activation of NF-κB, and suppressed the NF-κB-regulated expression of c-Myc, cyclin D1, Bcl-2, Bcl-xL, Survivin, XIAP, VEGF, and matrix metalloproteinase-9 (MMP-9). Furthermore, in an in vivo xenograft model, we found piperlongumine alone significantly suppressed tumor growth and enhanced the antitumor properties of gemcitabine. These results were consistent with the downregulation of NF-κB activity and its target genes, decreased proliferation (PCNA and Ki-67), decreased microvessel density (CD31), and increased apoptosis (TUNEL) in tumor remnants. Collectively, our results suggest that piperlongumine alone exhibits significant antitumor effects against human pancreatic cancer and it further enhances the therapeutic effects of gemcitabine, possibly through the modulation of NF-κB- and NF-κB-regulated gene products.