Betulinic acid induces a novel cell death pathway that depends on cardiolipin modification

Death and the desaturase: implication of Stearoyl-CoA desaturase-1 in the mechanisms of cell stress, apoptosis, and ferroptosis

Growth and proliferation of normal and cancerous cells necessitate a finely-tuned regulation of lipid metabolic pathways to ensure the timely supply of structural, energetic, and signaling lipid molecules. The synthesis and remodeling of lipids containing fatty acids with an appropriate carbon length and insaturation level are required for supporting each phase of the mechanisms of cell replication and survival. Mammalian Stearoyl-CoA desaturases (SCD), particularly SCD1, play a crucial role in modulating the fatty acid composition of cellular lipids, converting saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA) in the endoplasmic reticulum (ER). Extensive research has elucidated in great detail the participation of SCD1 in the molecular mechanisms that govern cell replication in normal and cancer cells. More recently, investigations have shed new light on the functional and regulatory role of the Δ9-desaturase in the processes of cell stress and cell death. This review will examine the latest findings on the involvement of SCD1 in the molecular pathways of cell survival, particularly on the mechanisms of ER stress and autophagy, as well in apoptotic and non-apoptotic cell death.

The role of cardiolipin and cytochrome c in mitochondrial metabolism of cancer cells determined by Raman imaging: in vitro study on the brain glioblastoma U-87 MG cell line

In this paper, we present Raman imaging as a non-invasive approach for studying changes in mitochondrial metabolism caused by cardiolipin-cytochrome c interactions. We investigated the effect of mitochondrial dysregulation on cardiolipin (CL) and cytochrome c (Cyt c) interactions for a brain cancer cell line (U-87 MG). Mitochondrial metabolism was monitored by checking the intensities of the Raman bands at 750 cm-1, 1126 cm-1, 1310 cm-1, 1337 cm-1, 1444 cm-1 and 1584 cm-1. The presented results indicate that under pathological conditions, the content and redox status of Cyt c in mitochondria can be used as a Raman marker to characterize changes in cellular metabolism. This work provides evidence that cardiolipin-cytochrome c interactions are crucial for mitochondrial energy homeostasis by controlling the redox status of Cyt c in the electron transport chain, switching from disabling Cyt c reduction and enabling peroxidase activity. This paper provides experimental support for the hypothesis of how cardiolipin-cytochrome c interactions regulate electron transfer in the respiratory chain, apoptosis and mROS production in mitochondria.

Antiproliferative and Cytotoxic Properties of Propynoyl Betulin Derivatives against Human Ovarian Cancer Cells: In Vitro Studies

Due to the incidence of ovarian cancer (OC) and the limitations of available therapeutic strategies, it is necessary to search for novel therapeutic solutions. The aim of this study was to evaluate the cytotoxic effect of betulin 1 and its propynoyl derivatives 2-6 against ovarian cancer cells (SK-OV-3, OVCAR-3) and normal myofibroblasts (18Co). Paclitaxel was used as the reference compound. The propynoyl derivatives 2-6 exhibited stronger antiproliferative and cytotoxic activities compared to betulin 1. In both ovarian cancer cell lines, the most potent compound was 28-propynoylbetulin 2. In the case of compound 2, the calculated IC50 values were 0.2 µM for the SK-OV-3 cells and 0.19 µM for the OVCAR-3 cells. Under the same culture conditions, the calculated IC50 values for compound 6 were 0.26 µM and 0.59 µM, respectively. It was observed that cells treated with compounds 2 and 6 caused a decrease in the potential of the mitochondrial membrane and a significant change in cell morphology. Betulin 1, a diol from the group of pentacyclic triterpenes, has a confirmed wide spectrum of biological effects, including a significant anticancer effect. It is characterized by low bioavailability, which can be improved by introducing changes to its structure. The results showed that chemical modifications of betulin 1 only at position C-28 with the propynoyl group (compound 2) and additionally at position C-3 with the phosphate group (compound 3) or at C-29 with the phosphonate group (compound 6) allowed us to obtain compounds with greater cytotoxic activity than their parent compounds, which could be used to develop novel therapeutic systems effective in the treatment of ovarian cancer.

Stearoyl-CoA Desaturase 1 as a Therapeutic Biomarker: Focusing on Cancer Stem Cells

The dysregulation of lipid metabolism and alterations in the ratio of monounsaturated fatty acids (MUFAs) to saturated fatty acids (SFAs) have been implicated in cancer progression and stemness. Stearoyl-CoA desaturase 1 (SCD1), an enzyme involved in lipid desaturation, is crucial in regulating this ratio and has been identified as an important regulator of cancer cell survival and progression. SCD1 converts SFAs into MUFAs and is important for maintaining membrane fluidity, cellular signaling, and gene expression. Many malignancies, including cancer stem cells, have been reported to exhibit high expression of SCD1. Therefore, targeting SCD1 may provide a novel therapeutic strategy for cancer treatment. In addition, the involvement of SCD1 in cancer stem cells has been observed in various types of cancer. Some natural products have the potential to inhibit SCD1 expression/activity, thereby suppressing cancer cell survival and self-renewal activity.

Lipid Metabolic Reprogramming in Embryonal Neoplasms with MYCN Amplification

Tumor cells reprogram their metabolism, including glucose, glutamine, nucleotide, lipid, and amino acids to meet their enhanced energy demands, redox balance, and requirement of biosynthetic substrates for uncontrolled cell proliferation. Altered lipid metabolism in cancer provides lipids for rapid membrane biogenesis, generates the energy required for unrestricted cell proliferation, and some of the lipids act as signaling pathway mediators. In this review, we focus on the role of lipid metabolism in embryonal neoplasms with MYCN dysregulation. We specifically review lipid metabolic reactions in neuroblastoma, retinoblastoma, medulloblastoma, Wilms tumor, and rhabdomyosarcoma and the possibility of targeting lipid metabolism. Additionally, the regulation of lipid metabolism by the MYCN oncogene is discussed.

Development of Spectral Nano-Flow Cytometry for High-Throughput Multiparameter Analysis of Individual Biological Nanoparticles

Correlated analysis of multiple biochemical parameters at the single-particle level and in a high-throughput manner is essential for insights into the diversity and functions of biological nanoparticles (BNPs), such as bacteria and subcellular organelles. To meet this challenge, we developed a highly sensitive spectral nano-flow cytometer (S-nFCM) by integrating a spectral recording module to a laboratory-built nFCM that is 4-6 orders of magnitude more sensitive in side scattering detection and 1-2 orders of magnitude more sensitive in fluorescence detection than conventional flow cytometers. An electron-multiplying charge-coupled device (EMCCD) was used to acquire the full fluorescence spectra of single BNPs upon holographic grating dispersion. Up to 10,000 spectra can be collected in 1 min with 2.1 nm resolution. The precision, linearity, and sensitivity were examined. Complete discernment of single influenza viruses against the background signal, discrimination of different strains of marine cyanobacteria in a mixed sample based on their spectral properties of natural fluorescence, classification of bacterial categories exhibiting different patterns of antigen expression, and multiparameter analysis of single mitochondria for drug discovery were successfully demonstrated.

Cardiolipin-Targeted NIR-II Fluorophore Causes "Avalanche Effects" for Re-Engaging Cancer Apoptosis and Inhibiting Metastasis

Restoring innate apoptosis and simultaneously inhibiting metastasis by a molecular drug is an effective cancer therapeutic approach. Herein, a large rigid and V-shaped NIR-II dye, DUT850, is rationally designed for potential cardiolipin (CL)-targeted chemo-phototheranostic application. DUT850 displays moderate NIR-II fluorescence, excellent photodynamic therapy (PDT) and photothermal therapy (PTT) performance, and ultra-high photostability. More importantly, the unique rigid V-shaped backbone, positive charge, and lipophilicity of DUT850 afford its specific recognition and efficient binding to CL; such an interaction of DUT850-CL induced a spectrum of physiological disruptions, including translocation of cytochrome c, Ca²⁺ overload, reactive oxygen species burst, and ATP depletion, which not only activated cancer cell apoptosis but also inhibited tumor metastasis both in vitro and in vivo. Furthermore, the tight binding of DUT850-CL improves the phototoxicity of DUT850 toward cancer cells (IC₅₀ as low as 90 nM) under safe 808 nm laser irradiation (330 mW cm^-2). Upon encapsulation into bovine serum albumin (BSA), DUT850@BSA exerted a synergetic chemo-PDT-PTT effect on the 4T1 tumor mouse model, eventually leading to solid tumor annihilation and metastasis inhibition, which could be followed in real time with the NIR-II fluorescence of DUT850. This work contributed a promising approach for simultaneously re-engaging cancer cell apoptotic networks and activating the anti-metastasis pathway by targeting a pivotal upstream effector, which will bring a medical boon for inhibition of tumor proliferation and metastasis.

New dawn for cancer cell death: Emerging role of lipid metabolism

BACKGROUND

Resistance to cell death, a protective mechanism for removing damaged cells, is a "Hallmark of Cancer" that is essential for cancer progression. Increasing attention to cancer lipid metabolism has revealed a number of pathways that induce cancer cell death.

SCOPE OF REVIEW

We summarize emerging concepts regarding lipid metabolic reprogramming in cancer that is mainly involved in lipid uptake and trafficking, de novo synthesis and esterification, fatty acid synthesis and oxidation, lipogenesis, and lipolysis. During carcinogenesis and progression, continuous metabolic adaptations are co-opted by cancer cells, to maximize their fitness to the ever-changing environmental. Lipid metabolism and the epigenetic modifying enzymes interact in a bidirectional manner which involves regulating cancer cell death. Moreover, lipids in the tumor microenvironment play unique roles beyond metabolic requirements that promote cancer progression. Finally, we posit potential therapeutic strategies targeting lipid metabolism to improve treatment efficacy and survival of cancer patient.

MAJOR CONCLUSIONS

The profound comprehension of past findings, current trends, and future research directions on resistance to cancer cell death will facilitate the development of novel therapeutic strategies targeting the lipid metabolism.

Integration of glucose and cardiolipin anabolism confers radiation resistance of HCC

BACKGROUND AND AIMS

Poor response to ionizing radiation (IR) due to resistance remains a clinical challenge. Altered metabolism represents a defining characteristic of nearly all types of cancers. However, how radioresistance is linked to metabolic reprogramming remains elusive in hepatocellular carcinoma (HCC).

APPROACH AND RESULTS

Baseline radiation responsiveness of different HCC cells were identified and cells with acquired radio-resistance were generated. By performing proteomics, metabolomics, metabolic flux, and other functional studies, we depicted a metabolic phenotype that mediates radiation resistance in HCC, whereby increased glucose flux leads to glucose addiction in radioresistant HCC cells and a corresponding increase in glycerophospholipids biosynthesis to enhance the levels of cardiolipin. Accumulation of cardiolipin dampens the effectiveness of IR by inhibiting cytochrome c release to initiate apoptosis. Mechanistically, mammalian target of rapamycin complex 1 (mTORC1) signaling-mediated translational control of hypoxia inducible factor-1α (HIF-1α) and sterol regulatory element-binding protein-1 (SREBP1) remodels such metabolic cascade. Targeting mTORC1 or glucose to cardiolipin synthesis, in combination with IR, strongly diminishes tumor burden. Finally, activation of glucose metabolism predicts poor response to radiotherapy in cancer patients.

CONCLUSIONS

We demonstrate a link between radiation resistance and metabolic integration and suggest that metabolically dismantling the radioresistant features of tumors may provide potential combination approaches for radiotherapy in HCC.

Identification of icaritin derivative IC2 as an SCD-1 inhibitor with anti-breast cancer properties through induction of cell apoptosis

Background

Breast cancer is the most common malignancy affecting women, yet effective targets and related candidate compounds for breast cancer treatment are still lacking. The lipogenic enzyme, stearoyl-CoA desaturase-1 (SCD1), has been considered a potential target for breast cancer treatment. Icaritin (ICT), a prenylflavonoid derivative from the Traditional Chinese Medicine Epimedii Herba, has been reported to exert anticancer effects in various types of cancer. The purpose of the present study was to explore the effect of the new ICT derivative, IC2, targeting SCD1 on breast cancer cells and to explore the specific mechanism.

Methods

Immunohistochemistry and semiquantitative evaluation were performed to detect the expression level of SCD1 in normal and tumor samples. Computer-aided drug design (CADD) technology was used to target SCD1 by molecular docking simulation, and several new ICT derivatives were prepared by conventional chemical synthesis. Cell viability was evaluated by an MTT assay and dead cell staining. SCD1 expression in cancer cells was determined by Western blot and qRT-PCR analyses. The enzymatic activity of SCD1 was evaluated by detecting the conversion rate of [d31] palmitic acid (PA) using Gas chromatography-mass spectrometry (GC–MS). DAPI staining, flow cytometry and Western blot were used to detect cell apoptosis. Mitochondrial membrane potential and reactive oxygen species (ROS) assays were used to determine cell mitochondrial function. Lentiviral transduction was utilized to generate SCD1-overexpressing cell lines.

Results

We found that SCD1 was overexpressed and correlated with poor prognosis in breast cancer patients. Among a series of ICT derivatives, in vitro data showed that IC2 potentially inhibited the viability of breast cancer cells, and the mechanistic study revealed that IC2 treatment resulted in ROS activation and cellular apoptosis. We demonstrated that IC2 inhibited SCD1 activity and expression in breast cancer cells in a dose-dependent manner. Moreover, SCD1 overexpression alleviated IC2-induced cytotoxicity and apoptosis in breast cancer cells.

Conclusions

The new ICT derivative, IC2, was developed to induce breast cancer cell apoptosis by inhibiting SCD1, which provides a basis for the development of IC2 as a potential clinical compound for breast cancer treatment.

A Review on Preparation of Betulinic Acid and Its Biological Activities

Betulinic acid, a pentacyclic triterpene, is distributed in a variety of plants, such as birch, eucalyptus and plane trees. It shows a wide spectrum of biological and pharmacological properties, such as anti-inflammatory, antibacterial, antiviral, antidiabetic, antimalarial, anti-HIV and antitumor effects. Among them, the antitumor activity of betulinic acid has been extensively studied. However, obtaining betulinic acid from natural resources can no longer meet the needs of medicine and nutrition, so methods such as chemical synthesis and microbial biotransformation have also been used to prepare betulinic acid. At the same time, with the development of synthetic biology and genetic engineering, and the elucidation of the biosynthetic pathways of terpenoid, the biosynthesis of betulinic acid has also been extensively researched. This article reviews the preparation of betulinic acid and its pharmacological activities, in order to provide a reference for the research and utilization of betulinic acid.

Lipid metabolism and cancer

Dysregulation in lipid metabolism is among the most prominent metabolic alterations in cancer. Cancer cells harness lipid metabolism to obtain energy, components for biological membranes, and signaling molecules needed for proliferation, survival, invasion, metastasis, and response to the tumor microenvironment impact and cancer therapy. Here, we summarize and discuss current knowledge about the advances made in understanding the regulation of lipid metabolism in cancer cells and introduce different approaches that have been clinically used to disrupt lipid metabolism in cancer therapy.

Betulinic acid in the treatment of tumour diseases: Application and research progress

Betulinic acid (BA) is a pentacyclic triterpene compound that can be obtained by separation, chemical synthesis and biotransformation from birch. BA has antitumour activity, and its mechanisms of action mainly include the induction of mitochondrial oxidative stress; the regulation of specificity protein transcription factors, and the inhibition of signal transducer and activator of transcription 3 and nuclear factor-κB signalling pathways. In addition, BA can increase the sensitivity of cancer cells to other chemotherapy drugs. Recent studies have shown that BA plays an anticancer role in several kinds of tumour diseases. In this article, the anticancer mechanism of BA and its application in the treatment of tumour diseases are reviewed.

Messing Up the Cancer Stem Cell Chemoresistance Mechanisms Supported by Tumor Microenvironment

Despite the recent advances in cancer patient management and in the development of targeted therapies, systemic chemotherapy is currently used as a first-line treatment for many cancer types. After an initial partial response, patients become refractory to standard therapy fostering rapid tumor progression. Compelling evidence highlights that the resistance to chemotherapeutic regimens is a peculiarity of a subpopulation of cancer cells within tumor mass, known as cancer stem cells (CSCs). This cellular compartment is endowed with tumor-initiating and metastasis formation capabilities. CSC chemoresistance is sustained by a plethora of grow factors and cytokines released by neighboring tumor microenvironment (TME), which is mainly composed by adipocytes, cancer-associated fibroblasts (CAFs), immune and endothelial cells. TME strengthens CSC refractoriness to standard and targeted therapies by enhancing survival signaling pathways, DNA repair machinery, expression of drug efflux transporters and anti-apoptotic proteins. In the last years many efforts have been made to understand CSC-TME crosstalk and develop therapeutic strategy halting this interplay. Here, we report the combinatorial approaches, which perturb the interaction network between CSCs and the different component of TME.

Ziziphus jujuba Mill. leaf extract restrains adipogenesis by targeting PI3K/AKT signaling pathway

The escalation in the global prevalence of obesity has focused attention on finding novel approaches for its management. Ziziphus jujuba Mill. (ZJL) leaf extract is reported as a traditional remedy for diverse pathological conditions, including obesity. The present study investigated whether ZJL affects adipogenic differentiation in human adipocytes. Additionally, following metabolite profiling of the extract, apigenin (APG), betulinic acid (BA) and maslinic acid (MA) were selected for biological activity evaluation. The possible interactions between APG, BA, MA and target proteins with a central role in adipogenesis were assessed through molecular docking. The potential mechanisms of ZJL, APG, BA and MA were identified using transcriptional analysis through real-time quantitative PCR and protein abundance evaluation by Western blotting. The obtained results revealed a concentration-dependent reduction of accumulated lipids after ZJL, BA and MA application. The key adipogenic transcription factors peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT-enhancer-binding protein alpha (C/EBPα) were strongly decreased at a protein level by all treatments. Moreover, the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway was found to be involved in the anti-adipogenic effect of ZJL, APG and BA. Collectively, our findings indicate that ZJL and its pure compounds hampered adipocyte differentiation through PI3K/AKT inhibition. Among the selected compounds, BA exhibits the most promising anti-adipogenic activity. Furthermore, being a complex mixture of phytochemicals, the ZJL extract could be utilized as source of yet unknown bioactive leads with potential implementation in obesity management.

Metabolic rerouting via SCD1 induction impacts X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (ALD) is a progressive neurodegenerative disease caused by mutations in ABCD1, the peroxisomal very long-chain fatty acid (VLCFA) transporter. ABCD1 deficiency results in accumulation of saturated VLCFAs. A drug screen using a phenotypic motor assay in a zebrafish ALD model identified chloroquine as the top hit. Chloroquine increased expression of stearoyl-CoA desaturase-1 (scd1), the enzyme mediating fatty acid saturation status, suggesting that a shift toward monounsaturated fatty acids relieved toxicity. In human ALD fibroblasts, chloroquine also increased SCD1 levels and reduced saturated VLCFAs. Conversely, pharmacological inhibition of SCD1 expression led to an increase in saturated VLCFAs, and CRISPR knockout of scd1 in zebrafish mimicked the motor phenotype of ALD zebrafish. Importantly, saturated VLCFAs caused ER stress in ALD fibroblasts, whereas monounsaturated VLCFA did not. In parallel, we used liver X receptor (LXR) agonists to increase SCD1 expression, causing a shift from saturated toward monounsaturated VLCFA and normalizing phospholipid profiles. Finally, Abcd1-/y mice receiving LXR agonist in their diet had VLCFA reductions in ALD-relevant tissues. These results suggest that metabolic rerouting of saturated to monounsaturated VLCFAs may alleviate lipid toxicity, a strategy that may be beneficial in ALD and other peroxisomal diseases in which VLCFAs play a key role.

Natural Products Targeting the Mitochondria in Cancers

There are abundant sources of anticancer drugs in nature that have a broad prospect in anticancer drug discovery. Natural compounds, with biological activities extracted from plants and marine and microbial metabolites, have significant antitumor effects, but their mechanisms are various. In addition to providing energy to cells, mitochondria are involved in processes, such as cell differentiation, cell signaling, and cell apoptosis, and they have the ability to regulate cell growth and cell cycle. Summing up recent data on how natural products regulate mitochondria is valuable for the development of anticancer drugs. This review focuses on natural products that have shown antitumor effects via regulating mitochondria. The search was done in PubMed, Web of Science, and Google Scholar databases, over a 5-year period, between 2015 and 2020, with a keyword search that focused on natural products, natural compounds, phytomedicine, Chinese medicine, antitumor, and mitochondria. Many natural products have been studied to have antitumor effects on different cells and can be further processed into useful drugs to treat cancer. In the process of searching for valuable new drugs, natural products such as terpenoids, flavonoids, saponins, alkaloids, coumarins, and quinones cover the broad space.

Alterations of Lipid Metabolism in Cancer: Implications in Prognosis and Treatment

Cancer remains the second leading cause of mortality worldwide. In the course of this multistage and multifactorial disease, a set of alterations takes place, with genetic and environmental factors modulating tumorigenesis and disease progression. Metabolic alterations of tumors are well-recognized and are considered as one of the hallmarks of cancer. Cancer cells adapt their metabolic competences in order to efficiently supply their novel demands of energy to sustain cell proliferation and metastasis. At present, there is a growing interest in understanding the metabolic switch that occurs during tumorigenesis. Together with the Warburg effect and the increased glutaminolysis, lipid metabolism has emerged as essential for tumor development and progression. Indeed, several investigations have demonstrated the consequences of lipid metabolism alterations in cell migration, invasion, and angiogenesis, three basic steps occurring during metastasis. In addition, obesity and associated metabolic alterations have been shown to augment the risk of cancer and to worsen its prognosis. Consequently, an extensive collection of tumorigenic steps has been shown to be modulated by lipid metabolism, not only affecting the growth of primary tumors, but also mediating progression and metastasis. Besides, key enzymes involved in lipid-metabolic pathways have been associated with cancer survival and have been proposed as prognosis biomarkers of cancer. In this review, we will analyze the impact of obesity and related tumor microenviroment alterations as modifiable risk factors in cancer, focusing on the lipid alterations co-occurring during tumorigenesis. The value of precision technologies and its application to target lipid metabolism in cancer will also be discussed. The degree to which lipid alterations, together with current therapies and intake of specific dietary components, affect risk of cancer is now under investigation, and innovative therapeutic or preventive applications must be explored.

Triple Negative Breast Cancer and Breast Epithelial Cells Differentially Reprogram Glucose and Lipid Metabolism upon Treatment with Triterpenic Acids

Plant-derived pentacyclic triterpenic acids (TAs) have gained increasing attention due to their multiple biological activities. Betulinic acid (BA) and ursolic acid (UA) modulate diverse pathways in carcinogenesis, offering increased changes of success in refractory cancers, such as triple negative breast cancer (TNBC). The present work aimed to assess the metabolic effects of BA and UA in MDA-MB-231 breast cancer cells (TNBC model), as well as in MCF-10A non-cancer breast epithelial cells, with a view to unveiling the involvement of metabolic reprogramming in cellular responses to these TAs. Cell viability and cell cycle analyses were followed by assessment of changes in the cells exo- and endometabolome through 1H NMR analysis of cell culture medium supernatants, aqueous and organic cell extracts. In MDA-MB-231 cells, BA was suggested to induce a transient upregulation of glucose consumption and glycolytic conversion, tricarboxylic acid (TCA) cycle intensification, and hydrolysis of neutral lipids, while UA effects were much less pronounced. In MCF-10A cells, boosting of glucose metabolism by the two TAs was accompanied by diversion of glycolytic intermediates to the hexosamine biosynthetic pathway (HBP) and the synthesis of neutral lipids, possibly stored in detoxifying lipid droplets. Additionally, breast epithelial cells intensified pyruvate consumption and TCA cycle activity, possibly to compensate for oxidative impairment of pyruvate glycolytic production. This study provided novel insights into the metabolic effects of BA and UA in cancer and non-cancer breast cells, thus improving current understanding of the action of these compounds at the molecular level.

Metabolic Escape Routes of Cancer Stem Cells and Therapeutic Opportunities

Although improvement in early diagnosis and treatment ameliorated life expectancy of cancer patients, metastatic disease still lacks effective therapeutic approaches. Resistance to anticancer therapies stems from the refractoriness of a subpopulation of cancer cells-termed cancer stem cells (CSCs)-which is endowed with tumor initiation and metastasis formation potential. CSCs are heterogeneous and diverge by phenotypic, functional and metabolic perspectives. Intrinsic as well as extrinsic stimuli dictated by the tumor microenvironment (TME)have critical roles in determining cell metabolic reprogramming from glycolytic toward an oxidative phenotype and vice versa, allowing cancer cells to thrive in adverse milieus. Crosstalk between cancer cells and the surrounding microenvironment occurs through the interchange of metabolites, miRNAs and exosomes that drive cancer cells metabolic adaptation. Herein, we identify the metabolic nodes of CSCs and discuss the latest advances in targeting metabolic demands of both CSCs and stromal cells with the scope of improving current therapies and preventing cancer progression.

Betulinic Acid-Nitrogen Heterocyclic Derivatives: Design, Synthesis, and Antitumor Evaluation in Vitro

Betulinic acid (BA) is a star member of the pentacyclic triterpenoid family, which exhibits great prospects for antitumor drug development. In an attempt to develop novel antitumor candidates, 21 BA-nitrogen heterocyclic derivatives were synthetized, in addition to four intermediates, 23 of which were first reported. Moreover, they were screened for in-vitro cytotoxicity against four tumor cell lines (Hela, HepG-2, BGC-823 and SK-SY5Y) by a standard methylthiazol tetrazolium (MTT) assay. The majority of these derivatives showed much stronger cytotoxic activity than BA. Remarkably, the most potent compound 7e (the half maximal inhibitory concentration (IC₅₀) of which was 2.05 ± 0.66 μM) was 12-fold more toxic in vitro than BA-treated Hela. Furthermore, multiple fluorescent staining techniques and flow cytometry collectively revealed that compound 7e could induce the early apoptosis of Hela cells. Structure–activity relationships were also briefly discussed. The present study highlighted the importance of introducing nitrogen heterocyclic rings into betulinic acid in the discovery and development of novel antitumor agents.

Modulation of dysregulated cancer metabolism by plant secondary metabolites: A mechanistic review

Several signaling pathways and basic metabolites are responsible for the control of metabolism in both normal and cancer cells. As emerging hallmarks of cancer metabolism, the abnormal activities of these pathways are of the most noticeable events in cancer. This altered metabolism expedites the survival and proliferation of cancer cells, which have attracted a substantial amount of interest in cancer metabolism. Nowadays, targeting metabolism and cross-linked signaling pathways in cancer has been a hot topic to investigate novel drugs against cancer. Despite the efficiency of conventional drugs in cancer therapy, their associated toxicity, resistance, and high-cost cause limitations in their application. Besides, considering the numerous signaling pathways cross-linked with cancer metabolism, discovery, and development of multi-targeted and safe natural compounds has been a high priority. Natural secondary metabolites have exhibited promising anticancer effects by targeting dysregulated signaling pathways linked to cancer metabolism. The present review reveals the metabolism and cross-linked dysregulated signaling pathways in cancer. The promising therapeutic targets in cancer, as well as the critical role of natural secondary metabolites for significant anticancer enhancements, have also been highlighted to find novel/potential therapeutic agents for cancer treatment.

Betulinic acid shows anticancer activity against equine melanoma cells and permeates isolated equine skin in vitro

BACKGROUND

Equine malignant melanoma (EMM) is a frequently occurring dermoepidermal tumor in grey horses. Currently available therapies are either challenging or inefficient. Betulinic acid (BA), a naturally occurring triterpenoid, is a promising compound for cancer treatment. To evaluate the potential of BA as a topical therapy for EMM, its anticancer effects on primary equine melanoma cells and dermal fibroblasts and its percutaneous permeation through isolated equine skin were assessed in vitro.

RESULTS

BA showed antiproliferative and cytotoxic effects on both primary equine melanoma cells and fibroblasts in a time- and dose-dependent manner. The lowest half-maximal inhibitory concentrations were obtained 96 h after the beginning of drug exposure (12.7 μmol/L and 23.6 μmol/L for melanoma cells eRGO1 and MelDuWi, respectively, in cytotoxicity assay). High concentrations of the compound were reached in the required skin layers in vitro.

CONCLUSION

BA is a promising substance for topical EMM treatment. Further clinical studies in horses are necessary to assess safety and antitumoral effects in vivo.

Betulinic acid induces apoptosis of gallbladder cancer cells via repressing SCD1

Gallbladder cancer (GBC) is the most common and aggressive malignancy of the biliary tract. Betulinic acid (BetA) has been reported to have anti-inflammatory and antitumor effects; however, the effect of BetA on GBC is still unknown. In this study, we investigated the effect of BetA on five GBC cell lines and found that BetA significantly inhibited the proliferation of NOZ cells but had little inhibitory effect on other GBC cells. BetA disturbed mitochondrial membrane potential and induced apoptosis in NOZ cells. Real-time polymerase chain reaction analysis revealed that stearoyl-coenzyme A desaturase 1 (SCD1) was highly expressed in NOZ cells but low expressed in other GBC cells. BetA inhibited SCD1 expression in a concentration-dependent manner in NOZ cells. Downregulation of SCD1 expression by RNA interference inhibited the proliferation of NOZ cells and induced cell apoptosis. Moreover, BetA inhibited the growth of xenografted tumors and suppressed SCD1 expression in nude mice. Thus, our results showed that BetA induced apoptosis through repressing SCD1 expression in GBC, suggesting that BetA might be an effective agent for the treatment of patients with GBC that highly expresses SCD1.

Greasing the Wheels of the Cancer Machine: The Role of Lipid Metabolism in Cancer

Altered lipid metabolism is among the most prominent metabolic alterations in cancer. Enhanced synthesis or uptake of lipids contributes to rapid cancer cell growth and tumor formation. Lipids are a highly complex group of biomolecules that not only constitute the structural basis of biological membranes but also function as signaling molecules and an energy source. Here, we summarize recent evidence implicating altered lipid metabolism in different aspects of the cancer phenotype and discuss potential strategies by which targeting lipid metabolism could provide a therapeutic window for cancer treatment.

X anthium Orientale subsp. Italicum (Moretti) Greuter: bioassay-guided isolation and its chemical basis of antitumor cytotoxicity

Inspired by the allelopathetic effects of Xanthium orientale subsp. italicum (Moretti) Greuter, bioassay-guided isolation was employed to identify its antitumor constituents and clarify the chemical basis of its multitarget activity. Among four fractions of X.orientale extraction, TCM-fr and PE-fr were discovered to exhibit significant cytotoxicity aganist HepG two and A549 cells, which were further isolated by chromatographic methods to yield 16 compounds, including six active ones: xanthatin (1), xanthinosin (2), lupeol (6), oleanolic acid (9), betulinic acid (10) and emodin (12) with IC₅₀ of 10 ∼ 120μM. The systematically study of antitumor constituents has firstly provided a chemical basis for the multitarget and synergistic anticancer activity of the genus Xanthium. The method presented could be utilized to guide the exploitation and promising utilization of X. orientale on cancer therapy.

The expanded role of fatty acid metabolism in cancer: new aspects and targets

Cancer cells undergo metabolic reprogramming to support cell proliferation, growth, and dissemination. Alterations in lipid metabolism, and specifically the uptake and synthesis of fatty acids (FAs), comprise one well-documented aspect of this reprogramming. Recent studies have revealed an expanded range of roles played by FA in promoting the aggressiveness of cancer while simultaneously identifying new potential targets for cancer therapy. This article provides a brief review of these advances in our understanding of FA metabolism in cancer, highlighting both recent discoveries and the inherent challenges caused by the metabolic plasticity of cancer cells in targeting lipid metabolism for cancer therapy.

DHRS2 mediates cell growth inhibition induced by Trichothecin in nasopharyngeal carcinoma

BACKGROUND

Cancer is fundamentally a deregulation of cell growth and proliferation. Cancer cells often have perturbed metabolism that leads to the alteration of metabolic intermediates. Dehydrogenase/reductase member 2 (DHRS2) belongs to short-chain alcohol dehydrogenase/reductase (SDR) superfamily, which is functionally involved in a number of intermediary metabolic processes and in the metabolism of lipid signaling molecules. DHRS2 displays closely association with the inhibition of cell proliferation, migration and quiescence in cancers.

METHODS

3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4- sulfophenyl)-2H-tetrazolium (MTS), 5-ethynyl-2'-deoxyuridine (EdU) and colony formation assays were applied to evaluate the proliferative ability of nasopharyngeal carcinoma (NPC) cells. We performed lipid metabolite profiling using gas chromatography coupled with mass spectrometry (GC/MS) to identify the proximal metabolite changes linked to DHRS2 overexpression. RNA sequencing technique combined with differentially expressed genes analysis was applied to identify the expression of genes responsible for the anti-tumor effect of trichothecin (TCN), a natural sesquiterpenoid compound isolated from an endophytic fungus.

RESULTS

Our current findings reveal that DHRS2 affects lipid metabolite profiling to induce cell cycle arrest and growth inhibition in NPC cells. Furthermore, we demonstrate that TCN is able to induce growth inhibition of NPC in vitro and in vivo by up-regulating DHRS2.

CONCLUSIONS

Our report suggests that activating DHRS2 to reprogram lipid homeostasis may be a target for the development of targeted therapies against NPC. Moreover, TCN could be exploited for therapeutic gain against NPC by targeting DHRS2 and it may also be developed as a tool to enhance understanding the biological function of DHRS2.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Sorafenib kills liver cancer cells by disrupting SCD1-mediated synthesis of monounsaturated fatty acids via the ATP-AMPK-mTOR-SREBP1 signaling pathway

Sorafenib is a multikinase inhibitor that is effective in treating advanced liver cancer. Although its mechanism of action through several established cancer-related protein kinase targets is well-characterized, sorafenib induces variable responses among human tumors, and the cause for this variation is yet unknown. To investigate the underlying mechanisms, we applied mass spectrometry-based proteomic analysis to Huh7.5 human liver cancer cells and found that sorafenib significantly affected the expression of the key lipogenic enzymes, especially stearoyl coenzyme A desaturase 1 (SCD1), in these cells. Given that SCD1 catalyzes the most crucial and rate-limiting step in the synthesis of monounsaturated fatty acids (FAs), we performed a lipidomic analysis, which showed a dramatically altered lipid profile in sorafenib-treated cells. Detection and analysis of free FAs showed that the levels of monounsaturated FAs, including oleate, were significantly decreased in those cells treated by sorafenib. Addition of oleate protected liver cancer cells from sorafenib-induced death and alleviated the abnormalities of mitochondrial morphology and function caused by the drug. Treatment with sorafenib suppressed ATP production, resulting in AMPK activation via phosphorylation. Further secondary effects included reduction of the levels of sterol regulatory element-binding protein 1 (SREBP1) and the phosphorylation of mammalian target of rapamycin (mTOR) in liver cancer cells. These effects were partly abolished in the presence of compound C (an AMPK inhibitor) and ATP and adenosine, and SREBP1c overexpression also could be resistant to the effects of sorafenib, suggesting that the sorafenib-induced reduction in cell viability was mediated by the ATP-AMPK-mTOR-SREBP1 signaling pathway. Taken together, our results suggest that sorafenib's anticancer activity in liver cancer cells is based on the inhibition of ATP production, SCD1 expression, and monounsaturated FA synthesis. In addition, the decreased monounsaturated FA synthesis further triggered the more serious reduction of ATP production in sorafenib-treated cells. To our knowledge, this is the first evidence that sorafenib disrupts lipogenesis and triggers liver cancer cell death by targeting SCD1 through the ATP-AMPK-mTOR-SREBP1 pathway.-Liu, G., Kuang, S., Cao, R., Wang, J., Peng, Q., Sun, C. Sorafenib kills liver cancer cells by disrupting SCD1-mediated synthesis of monounsaturated fatty acids via the ATP-AMPK-mTOR- SREBP1 signaling pathway.

Mitochondria in cancer: in the aspects of tumorigenesis and targeted therapy

Mitochondria play pivotal roles in most eukaryotic cells, ranging from energy production to regulation of apoptosis. As sites of cellular respiration, mitochondria experience accumulation of reactive oxygen species (ROS) due to damage in electron transport chain carriers. Mutations in mitochondrial DNA (mtDNA) as well as nuclear DNA are reported in various cancers. Mitochondria have a dual role in cancer: the development of tumors due to mutations in mitochondrial genome and the generation of ROS. Impairment in the mitochondria-regulated apoptosis pathway accelerates tumorigenesis. Numerous strategies targeting mitochondria have been developed to induce the mitochondrial (i.e. intrinsic) apoptosis pathway in cancer cells. This review elaborates the roles of mitochondria in cancer with respect to mutations and apoptosis and discusses mitochondria-targeting strategies as cancer therapies to enhance the killing of cancer cells.

Treatment implications of natural compounds targeting lipid metabolism in nonalcoholic fatty liver disease, obesity and cancer

Metabolic disorders can lead to a scarcity or excess of certain metabolites such as glucose, lipids, proteins, purines, and metal ions, which provide the biochemical foundation and directly contribute to the etiology of metabolic diseases. Nonalcoholic fatty liver disease, obesity, and cancer are common metabolic disorders closely associated with abnormal lipid metabolism. In this review, we first describe the regulatory machinery of lipid metabolism and its deregulation in metabolic diseases. Next, we enumerate and integrate the mechanism of action of some natural compounds, including terpenoids and flavonoids, to ameliorate the development of metabolic diseases by targeting lipid metabolism. Medicinal natural products have an established history of use in health care and therapy. Natural compounds might provide a good source of potential therapeutic agents for treating or preventing metabolic diseases with lipid metabolic abnormalities.

Genetic variants in ELOVL2 and HSD17B12 predict melanoma-specific survival

Fatty acids play a key role in cellular bioenergetics, membrane biosynthesis and intracellular signaling processes and thus may be involved in cancer development and progression. In the present study, we comprehensively assessed associations of 14,522 common single-nucleotide polymorphisms (SNPs) in 149 genes of the fatty-acid synthesis pathway with cutaneous melanoma disease-specific survival (CMSS). The dataset of 858 cutaneous melanoma (CM) patients from a published genome-wide association study (GWAS) by The University of Texas M.D. Anderson Cancer Center was used as the discovery dataset, and the identified significant SNPs were validated by a dataset of 409 CM patients from another GWAS from the Nurses' Health and Health Professionals Follow-up Studies. We found 40 noteworthy SNPs to be associated with CMSS in both discovery and validation datasets after multiple comparison correction by the false positive report probability method, because more than 85% of the SNPs were imputed. By performing functional prediction, linkage disequilibrium analysis, and stepwise Cox regression selection, we identified two independent SNPs of ELOVL2 rs3734398 T>C and HSD17B12 rs11037684 A>G that predicted CMSS, with an allelic hazards ratio of 0.66 (95% confidence interval = 0.51-0.84 and p = 8.34 × 10^-4 ) and 2.29 (1.55-3.39 and p = 3.61 × 10^-5 ), respectively. Finally, the ELOVL2 rs3734398 variant CC genotype was found to be associated with a significantly increased mRNA expression level. These SNPs may be potential markers for CM prognosis, if validated by additional larger and mechanistic studies.

Pharmacological modulation of mitochondrial ion channels

The field of mitochondrial ion channels has undergone a rapid development during the last three decades, due to the molecular identification of some of the channels residing in the outer and inner membranes. Relevant information about the function of these channels in physiological and pathological settings was gained thanks to genetic models for a few, mitochondria-specific channels. However, many ion channels have multiple localizations within the cell, hampering a clear-cut determination of their function by pharmacological means. The present review summarizes our current knowledge about the ins and outs of mitochondrial ion channels, with special focus on the channels that have received much attention in recent years, namely, the voltage-dependent anion channels, the permeability transition pore (also called mitochondrial megachannel), the mitochondrial calcium uniporter and some of the inner membrane-located potassium channels. In addition, possible strategies to overcome the difficulties of specifically targeting mitochondrial channels versus their counterparts active in other membranes are discussed, as well as the possibilities of modulating channel function by small peptides that compete for binding with protein interacting partners. Altogether, these promising tools along with large-scale chemical screenings set up to identify new, specific channel modulators will hopefully allow us to pinpoint the actual function of most mitochondrial ion channels in the near future and to pharmacologically affect important pathologies in which they are involved, such as neurodegeneration, ischaemic damage and cancer. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Targeting Tumor Metabolism with Plant-Derived Natural Products: Emerging Trends in Cancer Therapy

Recognition of neoplastic metabolic reprogramming as one of cancer's hallmarks has paved the way for developing novel metabolism-targeted therapeutic approaches. The use of plant-derived natural bioactive compounds for this endeavor is especially promising, due to their diverse structures and multiple targets. Hence, over the past decade, a growing number of studies have assessed the impact of phytochemicals on tumor cell metabolism, aiming at improving current knowledge on their mechanisms of action and, at the same time, evaluating their potential as anti-cancer metabolic modulators. In this Review, we focus on three classes of plant-derived compounds with promising anti-cancer activity-phenolic compounds, isoprenoids, and alkaloids-to describe their effects on major energetic and biosynthetic pathways of human tumor cells. Such a comprehensive and integrated account of the ability of these compounds to hit different metabolic targets is expected to contribute to the rational design and critical assessment of novel anti-cancer therapies based on natural-product-mediated metabolic reprogramming.

The natural compound GL22, isolated from Ganoderma mushrooms, suppresses tumor growth by altering lipid metabolism and triggering cell death

Cancer cells rewire their metabolism to satisfy the demands of uncontrolled proliferation and survival. The reprogramming of lipid metabolism supports tumor growth, metastasis, and therapy-resistance. Therefore, targeting lipid metabolic reprogramming is a potential cancer treatment strategy. We recently isolated the novel natural triterpene GL22 from Ganoderma leucocontextum, a traditional Chinese medicine. Here, we show that GL22 significantly inhibits the growth of the liver cancer cell line Huh7.5 in vitro and of Huh7.5-derived tumor xenografts in vivo. We further find that GL22 induces mitochondrial dysfunction and cell death in Huh7.5 cells, in part due to fatty acid immobilization and loss of the mitochondrial lipid cardiolipin, which has vital structural and metabolic functions. Importantly, we demonstrate that GL22 treatment decreases the expression of fatty acid-binding proteins (FABPs), which likely underlies the loss of cardiolipin, mitochondrial dysfunction, and cell death. The over-expressions of FABPs prevented the GL22-induced cell death, loss of cardiolipin, decrease of ATP production, and reduction of oxygen consumption rate in Huh7.5 cells. Our results support targeting lipid metabolism via manipulating FABPs as a cancer treatment strategy, and promote Chinese medicine as an important source of novel anticancer drugs.

Proteasome-associated deubiquitinases and cancer

Maintenance of protein homeostasis is a crucial process for the normal functioning of the cell. The regulated degradation of proteins is primarily facilitated by the ubiquitin proteasome system (UPS), a system of selective tagging of proteins with ubiquitin followed by proteasome-mediated proteolysis. The UPS is highly dynamic consisting of both ubiquitination and deubiquitination steps that modulate protein stabilization and degradation. Deregulation of protein stability is a common feature in the development and progression of numerous cancer types. Simultaneously, the elevated protein synthesis rate of cancer cells and consequential accumulation of misfolded proteins drives UPS addiction, thus sensitizing them to UPS inhibitors. This sensitivity along with the potential of stabilizing pro-apoptotic signaling pathways makes the proteasome an attractive clinical target for the development of novel therapies. Targeting of the catalytic 20S subunit of the proteasome is already a clinically validated strategy in multiple myeloma and other cancers. Spurred on by this success, promising novel inhibitors of the UPS have entered development, targeting the 20S as well as regulatory 19S subunit and inhibitors of deubiquitinating and ubiquitin ligase enzymes. In this review, we outline the manner in which deregulation of the UPS can cause cancer to develop, current clinical application of proteasome inhibitors, and the (pre-)clinical development of novel inhibitors of the UPS.

Plant Secondary Metabolites as Anticancer Agents: Successes in Clinical Trials and Therapeutic Application

Cancer is a multistage process resulting in an uncontrolled and abrupt division of cells and is one of the leading causes of mortality. The cases reported and the predictions for the near future are unthinkable. Food and Drug Administration data showed that 40% of the approved molecules are natural compounds or inspired by them, from which, 74% are used in anticancer therapy. In fact, natural products are viewed as more biologically friendly, that is less toxic to normal cells. In this review, the most recent and successful cases of secondary metabolites, including alkaloid, diterpene, triterpene and polyphenolic type compounds, with great anticancer potential are discussed. Focusing on the ones that are in clinical trial development or already used in anticancer therapy, therefore successful cases such as paclitaxel and homoharringtonine (in clinical use), curcumin and ingenol mebutate (in clinical trials) will be addressed. Each compound’s natural source, the most important steps in their discovery, their therapeutic targets, as well as the main structural modifications that can improve anticancer properties will be discussed in order to show the role of plants as a source of effective and safe anticancer drugs.

Synergistic activity of sorafenib and betulinic acid against clonogenic activity of non-small cell lung cancer cells

The highly selective multi‐targeted agent sorafenib is an inhibitor of a number of intracellular signaling kinases with anti‐proliferative, anti‐angiogenic and pro‐apoptotic effects in various types of tumors, including human non‐small cell lung cancer (NSCLC). Betulin displays a broad spectrum of biological and pharmacological properties, including anticancer and chemopreventive activity. Combination of drugs with different targets is a logical approach to overcome multilevel cross‐stimulation among key signaling pathways in NSCLC progression. NSCLC cell lines, A549, H358 and A427, with different KRAS mutations, and normal human peripheral blood lymphocyte cells, were treated with sorafenib and betulinic acid alone and in combination. We examined the effect of different combined treatments on viability (MTS test), proliferation and apoptotic susceptibility based on flow cytometry, alterations in signaling pathways by western blotting and colony‐forming ability. The combination of sorafenib with betulinic acid had a strong effect on the induction of apoptosis of different NSCLC cell lines. In addition, this combination was not toxic for human peripheral blood lymphocytes. Combination treatment changed the expression of proteins involved in the mitochondrial apoptosis pathway and induced apoptotic death by caspase activation. Importantly, combination treatment with low drug concentrations tremendously reduced the colony‐forming ability of A549, H358 and A427 cells, as compared to both compounds alone. In this study, we showed that combination therapy with low concentrations of sorafenib and betulinic acid had the capacity to induce high levels of cell death and abolish clonogenic activity in some NSCLC cell lines regardless of KRAS mutations.

PP2A mediates apoptosis or autophagic cell death in multiple myeloma cell lines

The crosstalk between apoptosis and autophagy contributes to tumorigenesis and cancer therapy. The process by which BetA (betulinic acid), a naturally occurring triterpenoid, regulates apoptosis and autophagy as a cancer therapy is unclear. In this study, we show for the first time that protein phosphatase 2A (PP2A) acts as a switch to regulate apoptosis and autophagic cell death mediated by BetA. Under normal conditions, caspase-3 is activated by the mitochondrial pathway upon BetA treatment. Activated caspase-3 cleaves the A subunit of PP2A (PP2A/A), resulting in the association of PP2A and Akt. This association inactivates Akt to initiate apoptosis. Overexpression of Bcl-2 attenuates the mitochondrial apoptosis pathway, resulting in caspase-3 inactivation and the dissociation of PP2A and Akt. PP2A isolated from Akt binds with DAPK to induce autophagic cell death. Meanwhile, in vivo tumor experiments have demonstrated that BetA initiates different types of cell death in a myeloma xenograft model. Thus, PP2A can shift myeloma cells from apoptosis to autophagic cell death. These findings have important implications for the therapeutic application of BetA, particularly against apoptosis-resistant cancers.

Stearoyl-CoA-desaturase 1 regulates lung cancer stemness via stabilization and nuclear localization of YAP/TAZ

Recent evidences suggest that stearoyl-CoA-desaturase 1 (SCD1), the enzyme involved in monounsaturated fatty acids synthesis, has a role in several cancers. We previously demonstrated that SCD1 is important in lung cancer stem cells survival and propagation. In this article, we first show, using primary cell cultures from human lung adenocarcinoma, that the effectors of the Hippo pathway, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), are required for the generation of lung cancer three-dimensional cultures and that SCD1 knock down and pharmacological inhibition both decrease expression, nuclear localization and transcriptional activity of YAP and TAZ. Regulation of YAP/TAZ by SCD1 is at least in part dependent upon β-catenin pathway activity, as YAP/TAZ downregulation induced by SCD1 blockade can be rescued by the addition of exogenous wnt3a ligand. In addition, SCD1 activation of nuclear YAP/TAZ requires inactivation of the β-catenin destruction complex. In line with the in vitro findings, immunohistochemistry analysis of lung adenocarcinoma samples showed that expression levels of SCD1 co-vary with those of β-catenin and YAP/TAZ. Mining available gene expression data sets allowed to observe that high co-expression levels of SCD1, β-catenin, YAP/TAZ and downstream targets have a strong negative prognostic value in lung adenocarcinoma. Finally, bioinformatics analyses directed to identify which gene combinations had synergistic effects on clinical outcome in lung cancer showed that poor survival is associated with high co-expression of SCD1, β-catenin and the YAP/TAZ downstream target birc5. In summary, our data demonstrate for the first time the involvement of SCD1 in the regulation of the Hippo pathway in lung cancer, and point to fatty acids metabolism as a key regulator of lung cancer stem cells.

A piperazidine derivative of 23-hydroxy betulinic acid induces a mitochondria-derived ROS burst to trigger apoptotic cell death in hepatocellular carcinoma cells

BACKGROUND

Elevated production of reactive oxygen species (ROS) and an altered redox state have frequently been observed in hepatocellular carcinoma (HCC); therefore, selective killing of HCC cells by chemotherapeutic agents that stimulate ROS generation or impair antioxidant systems may be a feasible approach in HCC chemotherapy. Recently, betulinic acid and its derivatives have attracted attention because they showed anti-cancer effects via a ROS- and mitochondria-related mechanism. However, the source of ROS overproduction and the role of mitochondria were poorly identified, and the weak in vivo antitumour activity of these compounds limits their development as drugs.

METHODS

Cytotoxicity was detected using MTT assays. In vivo anti-HCC effects were assessed using nude mice bearing HepG2 tumour xenografts. Cell cycle analysis, apoptosis rate and mitochondrial membrane potential were measured by flow cytometry. ROS production was detected using a microplate reader or a fluorescence microscope. Changes in gene and protein levels were measured by RT-PCR and western blotting, respectively. Other assays were performed using related detection kits.

RESULTS

B5G9, a piperazidine derivative of 23-hydroxy betulinic acid (23-HBA), showed excellent in vivo anti-HCC effects, with a tumour growth inhibitory rate of greater than 80%, and no significant side effects. B5G9 stimulated the production of ROS, which were derived from the mitochondria, but it had no effect on various other antioxidant systems. Moreover, B5G9 induced mitochondrial dysfunction, which was characterized by morphological changes, membrane potential collapse, membrane permeabilization, and decreases in the O2 consumption rate and ATP production. Furthermore, mtDNA-depleted ρ0 HepG2 cells were less sensitive to B5G9 treatment than wt HepG2 cells, indicating the importance of mitochondria in B5G9-induced cell death.

CONCLUSION

We discovered a piperazidine derivative of 23-HBA, B5G9, with excellent anti-HCC effects both in vivo and in vitro and no obvious toxic effects. The underlying mechanism was associated with mitochondria-derived ROS overproduction, and mitochondria played essential roles in B5G9-induced cell death. This study identified a potential agent for anti-HCC therapy and elucidated the mitochondria-related mechanism of BA and its derivatives.

The multifaceted roles of fatty acid synthesis in cancer

Lipid metabolism, in particular the synthesis of fatty acids (FAs), is an essential cellular process that converts nutrients into metabolic intermediates for membrane biosynthesis, energy storage and the generation of signalling molecules. This Review explores how different aspects of FA synthesis promote tumorigenesis and tumour progression. FA synthesis has received substantial attention as a potential target for cancer therapy, but strategies to target this process have not yet translated into clinical practice. Furthermore, efforts to target this pathway must consider the influence of the tumour microenvironment.

Cancer metabolism at a glance

A defining hallmark of cancer is uncontrolled cell proliferation. This is initiated once cells have accumulated alterations in signaling pathways that control metabolism and proliferation, wherein the metabolic alterations provide the energetic and anabolic demands of enhanced cell proliferation. How these metabolic requirements are satisfied depends, in part, on the tumor microenvironment, which determines the availability of nutrients and oxygen. In this Cell Science at a Glance paper and the accompanying poster, we summarize our current understanding of cancer metabolism, emphasizing pathways of nutrient utilization and metabolism that either appear or have been proven essential for cancer cells. We also review how this knowledge has contributed to the development of anticancer therapies that target cancer metabolism.

Stearoyl CoA desaturase-1: New insights into a central regulator of cancer metabolism

The processes of cell proliferation, cell death and differentiation involve an intricate array of biochemical and morphological changes that require a finely tuned modulation of metabolic pathways, chiefly among them is fatty acid metabolism. The critical participation of stearoyl CoA desaturase-1 (SCD1), the fatty acyl Δ9-desaturing enzyme that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), in the mechanisms of replication and survival of mammalian cells, as well as their implication in the biological alterations of cancer have been actively investigated in recent years. This review examines the growing body of evidence that argues for a role of SCD1 as a central regulator of the complex synchronization of metabolic and signaling events that control cellular metabolism, cell cycle progression, survival, differentiation and transformation to cancer.

Inhibition of fatty acid desaturation is detrimental to cancer cell survival in metabolically compromised environments

BACKGROUND

Enhanced macromolecule biosynthesis is integral to growth and proliferation of cancer cells. Lipid biosynthesis has been predicted to be an essential process in cancer cells. However, it is unclear which enzymes within this pathway offer the best selectivity for cancer cells and could be suitable therapeutic targets.

RESULTS

Using functional genomics, we identified stearoyl-CoA desaturase (SCD), an enzyme that controls synthesis of unsaturated fatty acids, as essential in breast and prostate cancer cells. SCD inhibition altered cellular lipid composition and impeded cell viability in the absence of exogenous lipids. SCD inhibition also altered cardiolipin composition, leading to the release of cytochrome C and induction of apoptosis. Furthermore, SCD was required for the generation of poly-unsaturated lipids in cancer cells grown in spheroid cultures, which resemble those found in tumour tissue. We also found that SCD mRNA and protein expression is elevated in human breast cancers and predicts poor survival in high-grade tumours. Finally, silencing of SCD in prostate orthografts efficiently blocked tumour growth and significantly increased animal survival.

CONCLUSIONS

Our data implicate lipid desaturation as an essential process for cancer cell survival and suggest that targeting SCD could efficiently limit tumour expansion, especially under the metabolically compromised conditions of the tumour microenvironment.