Fatty acid synthase inhibition engages a novel caspase-2 regulatory mechanism to induce ovarian cancer cell death

Identification of genes predicting chemoresistance and short survival in ovarian cancer

Background

Ovarian cancer (OC) is a kind of lethiferous cancer in gynecology, and the development of chemoresistance is the brief reason for treatment failure. The genes which contribute to chemoresistance are often leading to short survival. Thus, this study aims to identify predictive markers for chemoresistance and survival from chemoresistant-related genes.

Methods

Coremine was used to retrieve of genes linked to OC chemoresistance. The relationship of genes with patient survival was analyzed in 489 OC patients of The Cancer Genome Atlas (TCGA) cohort, which the subgroup of 90 resistant and 197 sensitive samples was used to determine gene expression. Kaplan-Meier (KM) plotter of 1,816 OC patients with survival data was retrieved for survival analysis. Survival analysis was carried out by the R survival package in R (version 3.3.1). KM and receiver operating characteristic (ROC) curve were respectively used to access the ability of a gene to predict survival and chemoresistance.

Results

In this study, a group of genes potentially linked to OC chemoresistance was identified, which dysregulated in 90 chemoresistant tissues compared with 197 sensitive tissues. Of them, thirteen genes could predict chemoresistance in 1,347 patients, especially SOS1, MSH6, STAT5A were excellent for predicting chemoresistance to any drugs, platin and taxane, CASP2 and PARD6B for any drugs and platin, and HSP90AA1 and HSP90B1 for taxane. Meanwhile, 44 genes linked to OC chemoresistance could predict short overall survival (OS) and/or disease-free survival (DFS) in 489 OC patients, and 10 of them could predict short OS in large cohort of up to 1,657 patients. Finally, it is noteworthy that CASP2 was down-regulated in 90 chemoresistant samples, and low expression of the gene predicted chemoresistance in 1,347 patients, short OS and DFS in 489 patients, and short OS and progression-free survival (PFS) in 1,657 patients.

Conclusions

The identified genes specifically the CASP2 might be potentially used as predictive marker, prognostic marker and therapeutic target in management of OC.

Targeting endogenous fatty acid synthesis stimulates the migration of ovarian cancer cells to adipocytes and promotes the transport of fatty acids from adipocytes to cancer cells

Despite significant advances in oncology, 1 of 108 female patients succumb to ovarian cancer (OC) each year. Improved novel treatments against this aggressive disease would be a major improvement. The growth of OC cells has been demonstrated to be highly dependent on lipids. OC cells are abundantly present in the abdominal cavity and omentum, the main sites of OC expansion. Accordingly, it has been attempted not only to block the hyperactive synthesis of fatty acids (FAs) in cancer cells, but also to disrupt lipid supply. While either strategy has yielded promising results as monotherapy, the induction of resistance pathways diminishing the anticancer effects is yet conceivable. The endogenous regulation of lipid biosynthesis in OC has been extensively studied. However, the role of stromal cells in the modulation of the effects of anti‑lipogenic drugs has not yet been well documented. The present study thus examined the interaction between OC cells and associated stromal cells, when de novo FA synthesis was blocked. It has recently been revealed by the authors that when FA are provided to OC cells in monoculture, the lipid deficiency induced by pharmacological inhibition of FA synthase (FASN), the key enzyme of endogenous FA synthesis, cannot be compensated through an increased FA uptake by OC cells. In the present study, OC cells were co‑cultured with adipocytes preloaded with fluorescent FA and the effects of FASN‑inhibition on OC homing to adipocytes and the transcellular delivery of fluorescent FA from adipocytes to OC cells were examined. The FASN inhibitors, G28UCM and Fasnall, stimulated the spontaneous migration of A2780 OC cells in a concentration‑dependent manner and stimulated the transfer of FA from adipocytes to OC cells. Similar effects were observed with all types of adipocytes tested. The models applied in the present study demonstrated that co‑cultured cancer‑associated adipocytes may attenuate the anticancer effects of FASN inhibitors by attracting tumor cells and by supplying the cells with FA. This lipid‑mediated dependency may provide a rationale for the design of new treatment approaches for the treatment of OC.

MK8722 initiates early-stage autophagy while inhibiting late-stage autophagy via FASN-dependent reprogramming of lipid metabolism

Background and objective: Epithelial ovarian cancer (EOC) is associated with latent onset and poor prognosis, with drug resistance being a main concern in improving the prognosis of these patients. The resistance of cancer cells to most chemotherapeutic agents can be related to autophagy mechanisms. This study aimed to assess the therapeutic effect of MK8722, a small-molecule compound that activates AMP-activated protein kinase (AMPK), on EOC cells and to propose a novel strategy for the treatment of EOC. Purpose: To explore the therapeutic effects of MK8722 on EOC cells, and to elucidate the underlying mechanism. Methods and results: It was found that MK8722 effectively inhibited the malignant biological behaviors of EOC cells. In vitro experiments showed that MK8722 targeted and decreased the lipid metabolic pathway-related fatty acid synthase (FASN) expression levels, causing the accumulation of lipid droplets. In addition, transmission electron microscopy revealed the presence of autophagosome-affected mitochondria. Western blotting confirmed that MK8722 plays a role in activating autophagy upstream (PI3K/AKT/mTOR) and inhibiting autophagy downstream via FASN-dependent reprogramming of lipid metabolism. Plasmid transient transfection demonstrated that MK8722 suppressed late-stage autophagy by blocking autophagosome-lysosome fusion. Immunofluorescence and gene silencing revealed that this effect was achieved by inhibiting the interaction of FASN with the SNARE complexes STX17-SNP29-VAMP8. Furthermore, the antitumor effect of MK8722 was verified using a subcutaneous xenograft mouse model. Conclusion: The findings suggest that using MK8722 may be a new strategy for treating EOC, as it has the potential to be a new autophagy/mitophagy inhibitor. Its target of action, FASN, is a molecular crosstalk between lipid metabolism and autophagy, and exploration of the underlying mechanism of FASN may provide a new research direction.

Machine Learning Developed a Programmed Cell Death Signature for Predicting Prognosis, Ecosystem, and Drug Sensitivity in Ovarian Cancer

Background

Ovarian cancer (OC) is the leading cause of gynecological cancer death and the fifth most common cause of cancer-related death in women in America. Programmed cell death played a vital role in tumor progression and immunotherapy response in cancer.

Methods

The prognostic cell death signature (CDS) was constructed with an integrative machine learning procedure, including 10 methods, using TCGA, GSE14764, GSE26193, GSE26712, GSE63885, and GSE140082 datasets. Several methods and single-cell analysis were used to explore the correlation between CDS and the ecosystem and therapy response of OC patients.

Results

The prognostic CDS constructed by the combination of StepCox (n = both) + Enet (alpha = 0.2) acted as an independent risk factor for the overall survival (OS) of OC patients and showed stable and powerful performance in predicting the OS rate of OC patients. Compared with tumor grade, clinical stage, and many developed signatures, the CDS had a higher C-index. OC patients with low CDS score had a higher level of CD8+ cytotoxic T, B cell, and M1-like macrophage, representing a related immunoactivated ecosystem. A low CDS score indicated a higher PD1 and CTLA4 immunophenoscore, higher tumor mutation burden score, lower tumor immune dysfunction and exclusion score, and lower tumor escape score in OC, demonstrating a better immunotherapy response. OC patients with high CDS score had a higher gene set score of cancer-related hallmarks, including angiogenesis, epithelial-mesenchymal transition, hypoxia, glycolysis, and notch signaling.

Conclusion

The current study constructed a novel CDS for OC, which could serve as an indicator for predicting the prognosis, ecosystem, and immunotherapy benefits of OC patients.

Tumor metabolism rewiring in epithelial ovarian cancer

The mortality rate of epithelial ovarian cancer (EOC) remains the first in malignant tumors of the female reproductive system. The characteristics of rapid proliferation, extensive implanted metastasis, and treatment resistance of cancer cells require an extensive metabolism rewiring during the progression of cancer development. EOC cells satisfy their rapid proliferation through the rewiring of perception, uptake, utilization, and regulation of glucose, lipids, and amino acids. Further, complete implanted metastasis by acquiring a superior advantage in microenvironment nutrients competing. Lastly, success evolves under the treatment stress of chemotherapy and targets therapy. Understanding the above metabolic characteristics of EOCs helps to find new methods of its treatment.

Glycolysis and de novo fatty acid synthesis cooperatively regulate pathological vascular smooth muscle cell phenotypic switching and neointimal hyperplasia

Switching of vascular smooth muscle cells (VSMCs) from a contractile phenotype to a dedifferentiated (proliferative) phenotype contributes to neointima formation, which has been demonstrated to possess a tumor-like nature. Dysregulated glucose and lipid metabolism is recognized as a hallmark of tumors but has not thoroughly been elucidated in neointima formation. Here, we investigated the cooperative role of glycolysis and fatty acid synthesis in vascular injury-induced VSMC dedifferentiation and neointima formation. We found that the expression of hypoxia-inducible factor-1α (HIF-1α) and its target 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3), a critical glycolytic enzyme, were induced in the neointimal VSMCs of human stenotic carotid arteries and wire-injured mouse carotid arteries. HIF-1α overexpression led to elevated glycolysis and resulted in a decreased contractile phenotype while promoting VSMC proliferation and activation of the mechanistic target of rapamycin complex 1 (mTORC1). Conversely, silencing Pfkfb3 had the opposite effects. Mechanistic studies demonstrated that glycolysis generates acetyl coenzyme A to fuel de novo fatty acid synthesis and mTORC1 activation. Whole-transcriptome sequencing analysis confirmed the increased expression of PFKFB3 and fatty acid synthetase (FASN) in dedifferentiated VSMCs. More importantly, FASN upregulation was observed in neointimal VSMCs of human stenotic carotid arteries. Finally, interfering with PFKFB3 or FASN suppressed vascular injury-induced mTORC1 activation, VSMC dedifferentiation, and neointima formation. Together, this study demonstrated that PFKFB3-mediated glycolytic reprogramming and FASN-mediated lipid metabolic reprogramming are distinctive features of VSMC phenotypic switching and could be potential therapeutic targets for treating vascular diseases with neointima formation. © 2023 The Pathological Society of Great Britain and Ireland.

Bisphenol A and bisphenol S both disrupt ovine granulosa cell steroidogenesis but through different molecular pathways

BACKGROUND

Ovarian granulosa cells (GC) are essential for the development and maturation of a proper oocyte. GC are sensitive to endocrine disruptors, including bisphenol A (BPA) and its analogue bisphenol S (BPS), plasticisers present in everyday consumer products. BPA exhibits greater binding affinity for the membrane oestrogen receptor (GPER) than for the nuclear oestrogen receptors (ERα and ERβ). Here, we analysed the effects of BPA and BPS on the steroidogenesis of ovine GC in vitro, as well as their early mechanisms of action, the ovine being a relevant model to study human reproductive impairment. Disruption of GC steroidogenesis might alter oocyte quality and consequently fertility rate. In addition, we compared the effects of a specific GPER agonist (G-1) and antagonist (G-15) to those of BPA and BPS. Ewe GC were cultured with BPA or BPS (10 or 50 µM) or G-1 (1 µM) and/or G-15 (10 µM) for 48 h to study steroidogenesis.

RESULTS

Both BPA and BPS (10 µM) altered the secretion of progesterone, however, only BPS (10 µM) affected oestradiol secretion. RNA-seq was performed on GC after 1 h of culture with BPA or BPS (50 µM) or G-1 (10 µM), followed by real-time PCR analyses of differentially expressed genes after 12, 24 and 48 h of culture. The absence of induced GPER target genes showed that BPA and BPS did not activate GPER in GC after 1 h of treatment. These molecules exhibited mainly independent early mechanisms of action. Gene ontology analysis showed that after 1 h of treatment, BPA mainly disrupted the expression of the genes involved in metabolism and transcription, while BPS had a smaller effect and impaired cellular communications. BPA had a transient effect on the expression of CHAC1 (NOTCH signalling and oxidative balance), JUN (linked to MAPK pathway), NR4A1 (oestradiol secretion inhibition), ARRDC4 (endocytose of GPCR) and KLF10 (cell growth, differentiation and apoptosis), while expression changes were maintained over time for the genes LSMEM1 (linked to MAPK pathway), TXNIP (oxidative stress) and LIF (cell cycle regulation) after 12 and 48 h, respectively.

CONCLUSION

In conclusion, although they exhibited similar effects, BPA and BPS impaired different molecular pathways in GC in vitro. New investigations will be necessary to follow the temporal changes of these genes over time, as well as the biological processes involved.

Fatty acid synthase (FASN) inhibits the cervical squamous cell carcinoma (CESC) progression through the Akt/mTOR signaling pathway

BACKGROUND

Cervical cancer is a malignant tumor that affects females and remains the cause of the highest morbidity and mortality among women worldwide. Currently, gene-targeted therapy is a novel treatment option for clinicians. Furthermore, fatty acid synthase (FASN) plays a therapeutic role in various cancers. Nonetheless, the mechanism of action of this enzyme in cervical squamous cell carcinoma and cervical duct adenocarcinoma (CESC) has not yet been reported.

METHODS

RNA (ribonucleic acid) sequencing data and clinical information were obtained from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx). The expression levels of FASN were obtained from Gene Expression Profiling Interactive Analysis 2 (GEPIA2) and Human Protein Atlas (HPA). Univariate and multivariate Cox regression analyses were utilized to assess independent prognostic factors associated with survival. A nomogram and receiver operating characteristic curve (ROC) were employed to evaluate survival and predictive power. In vitro experiments and real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) were conducted to identify cell interference efficiency. MTS, monoclonal formation, and EDU assays were used to determine cell viability. Wound healing and invasion assays (transwell assay) were used to evaluate cell migration and invasion. Finally, Hoechst 33342, propidium iodide (PI) staining and Annexin V-FITC staining were used to assess apoptosis and the cell cycle, while western blotting was utilized to determine the protein expression levels.

RESULTS

FASN was aberrantly expressed in various cancers, including CESC, where it was highly expressed. Kaplan-Meier, univariate, multivariate Cox regression analyses and ROC curve indicated that FASN is a potential key indicator of survival prognosis among CESC patients and demonstrated good predictive ability and efficacy. Complementary in vitro experiments confirmed that FASN is an important target for CESC therapy.

CONCLUSION

The current study validated the biological and clinical significance of FASN in CESC prognosis, suggesting that FASN knockdown may exert antitumor activity against cervical cancer through the Akt/mTOR signaling pathway.

REDD1 gene knockout alleviates vascular smooth muscle cell remodeling in pulmonary hypertension

OBJECTIVES

Regulated in development and DNA damage responses 1 (REDD1) is an important transcription factor regulating mitochondria homeostasis, which is the important pathological alteration of pulmonary hypertension (PH). However, it is unclear whether REDD1 regulates the PASMCs mitochondria homeostasis by the similar mechanism in pulmonary arterial remodeling induced by hypoxia.

METHODS

The global REDD1-knockout rats (REDD1-KO) on Sprague-Dawley background were used to generate a chronic hypoxia model of PH. Right ventricular hypertrophy and vascular remodeling were detected after exposure to hypoxia. Additionally, proliferation, apoptosis, migration, mitochondria homeostasis, and autophagy were performed in vivo and in vitro.

RESULTS

The current research found that in human and experimental rats of PH, REDD1 expression is upregulated in the PASMCs. REDD1 gene knockout alleviated hypoxia PH and hemodynamic changes effectively and reversed hypoxic pulmonary vascular remodeling. In addition, REDD1 knockdown reduces the impairment of mitochondrial function caused by hypoxia in HPASMCs via autophagy inhibition, and this process may be regulated through the Parkin gene. Moreover, REDD1 knockdown can effectively inhibit the proliferation and migration of hypoxic PASMCs, and induce their apoptosis in vivo and in vitro.

CONCLUSIONS

Our results suggested that REDD1 might be a potential target for improved pulmonary vascular remodeling in PH.

Her-2 directed systemic delivery of fatty acid synthase (FASN) siRNA with novel liposomal carrier systems in the breast cancer mouse model

Despite the current advancements in the gene silencing therapy in vitro, the systemic delivery of siRNA still remains a challenging task for its transition into clinics. We have previously developed the Her2-targeted fatty acid synthase (FASN) siRNA-encapsulating immunoliposomes (ILs) with a great stability in the presence of serum. We report here the therapeutic potential of the lipid-based novel formulations in the breast cancer mouse model. The growth inhibitory and gene silencing effects of various formulations were determined by measuring the size of the tumor, cell proliferation, apoptotic index and immunoassays against Her2-over expressed tumor xenografts in nude mice. The pegylated DSPC/Chol and DOPE/CHEMS immunoliposomes containing FASN-siRNA significantly decreased the tumor growth relative to non-targeted liposomes. They induced the 1.5-fold increase in cellular apoptosis and several fold decrease in proliferation as compared to non-targeted liposomal formulations of FASN-siRNA. Moreover, FASN-siRNA-ILs produced several fold increase in the ratios of p53/p21 and Bax/Bcl-2. The gene silencing effects of targeted FASN-liposomes were found significantly superior, resulting in 30%-40% downregulation in FASN as compared to non-targeted similar formulations. Both types of FASN immunoliposomes provided a highly efficient approach for targeted delivery in Her-2-expressed breast cancer and thus offered a promising anticancer strategy in the clinical therapy.

The role of metabolic ecosystem in cancer progression — metabolic plasticity and mTOR hyperactivity in tumor tissues

Despite advancements in cancer management, tumor relapse and metastasis are associated with poor outcomes in many cancers. Over the past decade, oncogene-driven carcinogenesis, dysregulated cellular signaling networks, dynamic changes in the tissue microenvironment, epithelial-mesenchymal transitions, protein expression within regulatory pathways, and their part in tumor progression are described in several studies. However, the complexity of metabolic enzyme expression is considerably under evaluated. Alterations in cellular metabolism determine the individual phenotype and behavior of cells, which is a well-recognized hallmark of cancer progression, especially in the adaptation mechanisms underlying therapy resistance. In metabolic symbiosis, cells compete, communicate, and even feed each other, supervised by tumor cells. Metabolic reprogramming forms a unique fingerprint for each tumor tissue, depending on the cellular content and genetic, epigenetic, and microenvironmental alterations of the developing cancer. Based on its sensing and effector functions, the mechanistic target of rapamycin (mTOR) kinase is considered the master regulator of metabolic adaptation. Moreover, mTOR kinase hyperactivity is associated with poor prognosis in various tumor types. In situ metabolic phenotyping in recent studies highlights the importance of metabolic plasticity, mTOR hyperactivity, and their role in tumor progression. In this review, we update recent developments in metabolic phenotyping of the cancer ecosystem, metabolic symbiosis, and plasticity which could provide new research directions in tumor biology. In addition, we suggest pathomorphological and analytical studies relating to metabolic alterations, mTOR activity, and their associations which are necessary to improve understanding of tumor heterogeneity and expand the therapeutic management of cancer.

Landscape of the oncogenic role of fatty acid synthase in human tumors

Background: Identifying a unique and common regulatory pathway that drives tumorigenesis in cancers is crucial to foster the development of effective treatments. However, a systematic analysis of fatty acid synthase across pan-cancers has not been carried out.

Methods: We investigated the oncogenic roles of fatty acid synthase in 33 cancers based on the cancer genome atlas and gene expression omnibus.

Results: Fatty acid synthase is profoundly expressed in most cancers and is an important factor in predicting the outcome of cancer patients. Further, the level of S207 phosphorylation was found to be improved in several neoplasms (e.g., colon cancer). Fatty acid synthase expression is related to tumor-infiltrating immune cells in tumors (e.g., CD8+ T-cell infiltration level in cervical squamous cell carcinoma). Moreover, hormone receptor binding- and fatty acid metabolic process-associated pathways are involved in the functional mechanisms of fatty acid synthase.

Conclusions: This study provides a complete understanding of the oncogenic role of fatty acid synthase in human tumors.

Metformin alleviates inflammation through suppressing FASN-dependent palmitoylation of Akt

Metformin, traditionally regarded as a hypoglycemic drug, has been studied in other various fields including inflammation. The specific mechanism of metformin’s effect on immune cells remains unclear. Herein, it is verified that LPS-induced macrophages are characterized by enhanced endogenous fatty acid synthesis and the inhibition of fatty acid synthase (FASN) downregulates proinflammatory responses. We further show that metformin could suppress such elevation of FASN as well as proinflammatory activation in macrophages. In vivo, metformin treatment ameliorates dextran sulfate sodium (DSS)-induced colitis through impairing proinflammatory activation of colonic lamina propria mononuclear cells (LPMCs). The reduction of FASN by metformin hinders Akt palmitoylation, which further disturbs Akt membrane attachment and its phosphorylation. Metformin-mediated suppression of FASN/Akt pathway and its downstream MAPK signaling contributes to its anti-inflammatory role in macrophages. From the perspective of immunometabolism, our work points towards metformin utilization as an effective and potential intervention against macrophages-involved inflammatory diseases.

A review of the mechanism of DDIT4 serve as a mitochondrial related protein in tumor regulation

DDIT4 is a mitochondrial and tumor-related protein involved in anti-tumor therapy resistance, proliferation, and invasion, etc. Its expression level increases under the stress such as chemotherapy, hypoxia, and DNA damage. A number of clinical studies have confirmed that DDIT4 can change the behavior of tumor cells and the prognosis of patients with cancer. However, the role of DDIT4 in promoting or suppressing cancer is still inconclusive. This article summarized the four characteristics of DDIT4 including a mitochondria-related protein, interactions with various protein molecules, immune and metabolic cell related proteins and participator in the oxygen sensing pathway, which may be related to the progress of cancer.

Redox tolerance and metabolic reprogramming in solid tumors

Tumor cells need to cope with the host environment for survival and keep growing in hard conditions. This suggests that tumors must acquire characteristics more potent than what is seen for normal tissue cells, without which they are condemned to disruption.  For example, cancer cells have more potent redox tolerance compared with normal cells, which is due to their high adaptation to an oxidative crisis. In addition, increased demand for bioenergetics and biosynthesis can cause a rise in nutrient uptake in tumors. Utilizing nutrients in low nutrient conditions suggests that tumors are also equipped with adaptive metabolic processes. Switching the metabolic demands toward glucose consumption upon exposure to the hypoxic tumor microenvironment, or changing toward using other sources when there is an overconsumption of glucose in the tumor area are examples of fitness metabolic systems in tumors. In fact, cancer cells in cooperation with their nearby stroma (in a process called metabolic coupling) can reprogram their metabolic systems in their favor. This suggests the high importance of stroma for meeting the metabolic demands of a growing tumor, an example in this context is the metabolic symbiosis between cancer-associated fibroblasts with cancer cells. The point is that redox tolerance and metabolic reprogramming are interrelated, and that, without a doubt, disruption of redox tolerance systems by transient exposure to either oxidative or antioxidative loading, or targeting metabolic rewiring by modulation of tumor glucose availability, controlling tumor/stroma interactions, etc. can be effective from a therapeutic standpoint.

Occurrence of differing metabolic dysregulations, a glucose driven and another fatty acid centric in gastric cancer subtypes

Gastric cancer is one of the most common cancers and ranks third in cancer-related deaths across globe. Cancer cells are known to take advantage of the altered metabolic processes to sustain their survival, proliferation, and cancer progression. In this investigation, we explored the available genome-wide expression profiles of few hundreds of gastric tumors and non-cancerous gastric tissues and analyzed in the context of metabolic pathways. Gastric tumors were investigated for the metabolic processes related to glucose metabolism, glucose transport, glutamine metabolism, and fatty acid metabolism, by metabolic pathway-focused gene set enrichment analysis. Notably, all glucose metabolism and glutamine metabolism-related gene sets were found enriched in intestinal subtype gastric tumors. On the other hand, the gene sets related to glucose transport and glucan (glycan) metabolisms are enriched in diffuse subtype gastric tumors. Strikingly, fatty acid metabolisms, fatty acid transport, and fat differentiation-related signatures are also highly activated in diffuse subtype gastric tumors. Exploration of the recently established metabolome profile of the massive panel of cell lines also revealed the metabolites of glucose and fatty acid metabolic pathways to show the differing abundance across gastric cancer subtypes. The subtype-specific metabolic rewiring and the existence of two distinct metabolic dysregulations involving glucose and fatty acid metabolism in gastric cancer subtypes have been identified. The identified differing metabolic dysregulations would pave way for the development of targeted therapeutic strategies for the gastric cancer subtypes.

Targeting mTOR and Metabolism in Cancer: Lessons and Innovations

Cancer cells support their growth and proliferation by reprogramming their metabolism in order to gain access to nutrients. Despite the heterogeneity in genetic mutations that lead to tumorigenesis, a common alteration in tumors occurs in pathways that upregulate nutrient acquisition. A central signaling pathway that controls metabolic processes is the mTOR pathway. The elucidation of the regulation and functions of mTOR can be traced to the discovery of the natural compound, rapamycin. Studies using rapamycin have unraveled the role of mTOR in the control of cell growth and metabolism. By sensing the intracellular nutrient status, mTOR orchestrates metabolic reprogramming by controlling nutrient uptake and flux through various metabolic pathways. The central role of mTOR in metabolic rewiring makes it a promising target for cancer therapy. Numerous clinical trials are ongoing to evaluate the efficacy of mTOR inhibition for cancer treatment. Rapamycin analogs have been approved to treat specific types of cancer. Since rapamycin does not fully inhibit mTOR activity, new compounds have been engineered to inhibit the catalytic activity of mTOR to more potently block its functions. Despite highly promising pre-clinical studies, early clinical trial results of these second generation mTOR inhibitors revealed increased toxicity and modest antitumor activity. The plasticity of metabolic processes and seemingly enormous capacity of malignant cells to salvage nutrients through various mechanisms make cancer therapy extremely challenging. Therefore, identifying metabolic vulnerabilities in different types of tumors would present opportunities for rational therapeutic strategies. Understanding how the different sources of nutrients are metabolized not just by the growing tumor but also by other cells from the microenvironment, in particular, immune cells, will also facilitate the design of more sophisticated and effective therapeutic regimen. In this review, we discuss the functions of mTOR in cancer metabolism that have been illuminated from pre-clinical studies. We then review key findings from clinical trials that target mTOR and the lessons we have learned from both pre-clinical and clinical studies that could provide insights on innovative therapeutic strategies, including immunotherapy to target mTOR signaling and the metabolic network in cancer.

Hallmarks of Endothelial Cell Metabolism in Health and Disease

In 2009, it was postulated that endothelial cells (ECs) would only be able to execute the orders of growth factors if these cells would accordingly adapt their metabolism. Ten years later, it has become clear that ECs, often differently from other cell types, rely on distinct metabolic pathways to survive and form new blood vessels; that manipulation of EC metabolic pathways alone (even without changing angiogenic signaling) suffices to alter vessel sprouting; and that perturbations of these metabolic pathways can underlie excess formation of new blood vessels (angiogenesis) in cancer and ocular diseases. Initial proof of evidence has been provided that targeting (normalizing) these metabolic perturbations in diseased ECs and delivery of metabolites deserve increasing attention as novel therapeutic approaches for inhibiting or stimulating vessel growth in multiple disorders.

The peculiarities of cancer cell metabolism: A route to metastasization and a target for therapy

The last decade has witnessed the peculiarities of metabolic reprogramming in tumour onset and progression, and their relevance in cancer therapy. Also, it has been indicated that the metastatic process may depend on the metabolic rewiring and adaptation of cancer cells to the pressure of tumour microenvironment and limiting nutrient availability. The present review gatherers the existent knowledge on the influence of tumour microenvironment and metabolic routes driving metastasis. A focus will be given to glycolysis, fatty acid metabolism, glutaminolysis, and amino acid handling. In addition, the role of metabolic waste driving metastasization will be explored. Finally, we discuss the status of cancer treatment approaches targeting metabolism. This knowledge revision will highlight the critical metabolic targets in metastasis and the chemicals already used in preclinical studies and clinical trials, providing clues that would be further exploited in medicinal chemistry research.

Impairment of Angiogenesis by Fatty Acid Synthase Inhibition Involves mTOR Malonylation

The role of fatty acid synthesis in endothelial cells (ECs) remains incompletely characterized. We report that fatty acid synthase knockdown (FASN^KD) in ECs impedes vessel sprouting by reducing proliferation. Endothelial loss of FASN impaired angiogenesis in vivo, while FASN blockade reduced pathological ocular neovascularization, at >10-fold lower doses than used for anti-cancer treatment. Impaired angiogenesis was not due to energy stress, redox imbalance, or palmitate depletion. Rather, FASN^KD elevated malonyl-CoA levels, causing malonylation (a post-translational modification) of mTOR at lysine 1218 (K1218). mTOR K-1218 malonylation impaired mTOR complex 1 (mTORC1) kinase activity, thereby reducing phosphorylation of downstream targets (p70S6K/4EBP1). Silencing acetyl-CoA carboxylase 1 (an enzyme producing malonyl-CoA) normalized malonyl-CoA levels and reactivated mTOR in FASN^KD ECs. Mutagenesis unveiled the importance of mTOR K1218 malonylation for angiogenesis. This study unveils a novel role of FASN in metabolite signaling that contributes to explaining the anti-angiogenic effect of FASN blockade.

The effect of FASN inhibition on the growth and metabolism of a cisplatin-resistant ovarian carcinoma model

Overexpression of fatty acid synthase (FASN), a key regulator of the de novo synthesis of fatty acids, has been demonstrated in a variety of cancers and is associated with poor prognosis and increased multidrug resistance. Inhibition of FASN with the anti-obesity drug orlistat has been shown to have significant anti-tumourigenic effects in many cancers, notably breast and prostate. In our study, we investigated whether FASN inhibition using orlistat is an effective adjunctive treatment for ovarian cancers that have become platinum resistant using a cisplatin-resistant ovarian tumour xenograft model in mice. Mice were treated with orlistat or cisplatin or a combination and metabolite analysis and histopathology were performed on the tumours ex vivo. Orlistat decreased tumour fatty acid metabolism by inhibiting FASN, cisplatin reduced fatty acid β-oxidation, and combination treatment delayed tumour growth and induced apoptotic and necrotic cell death in cisplatin-resistant ovarian cancer cells over and above that with either treatment alone. Combination treatment also decreased glutamine metabolism, nucleotide and glutathione biosynthesis and fatty acid β-oxidation. Our data suggest that orlistat chemosensitised platinum-resistant ovarian cancer to treatment with platinum and resulted in enhanced efficacy.

Dimer-specific immunoprecipitation of active caspase-2 identifies TRAF proteins as novel activators

Caspase-2 has been shown to initiate apoptotic cell death in response to specific intracellular stressors such as DNA damage. However, the molecular mechanisms immediately upstream of its activation are still poorly understood. We combined a caspase-2 bimolecular fluorescence complementation (BiFC) system with fluorophore-specific immunoprecipitation to isolate and study the active caspase-2 dimer and its interactome. Using this technique, we found that tumor necrosis factor receptor-associated factor 2 (TRAF2), as well as TRAF1 and 3, directly binds to the active caspase-2 dimer. TRAF2 in particular is necessary for caspase-2 activation in response to apoptotic cell death stimuli. Furthermore, we found that dimerized caspase-2 is ubiquitylated in a TRAF2-dependent manner at K15, K152, and K153, which in turn stabilizes the active caspase-2 dimer complex, promotes its association with an insoluble cellular fraction, and enhances its activity to fully commit the cell to apoptosis. Together, these data indicate that TRAF2 positively regulates caspase-2 activation and consequent cell death by driving its activation through dimer-stabilizing ubiquitylation.

Fatty acid synthase is required for profibrotic TGF-β signaling

Evidence is provided that the fibroproliferative actions of TGF-β are dependent on a metabolic adaptation that sustains pathologic growth. Specifically, profibrotic TGF-β signaling is shown to require fatty acid synthase (FASN), an essential anabolic enzyme responsible for the de novo synthesis of fatty acids. With the use of pharmacologic and genetic approaches, we show that TGF-β-stimulated FASN expression is independent of Smad2/3 and is mediated via mammalian target of rapamycin complex 1. In the absence of FASN activity or protein, TGF-β-driven fibrogenic processes are reduced with no apparent toxicity. Furthermore, as increased FASN expression was also observed to correlate with the degree of lung fibrosis in bleomycin-treated mice, inhibition of FASN was examined in a murine-treatment model of pulmonary fibrosis. Remarkably, inhibition of FASN not only decreased expression of profibrotic targets, but lung function was also stabilized/improved, as assessed by peripheral blood oxygenation.-Jung, M.-Y., Kang, J.-H., Hernandez, D. M., Yin, X., Andrianifahanana, M., Wang, Y., Gonzalez-Guerrico, A., Limper, A. H., Lupu, R., Leof, E. B. Fatty acid synthase is required for profibrotic TGF-β signaling.

Orlistat as a FASN inhibitor and multitargeted agent for cancer therapy

INTRODUCTION

Cancer cells have increased glycolysis and glutaminolysis. Their third feature is increased de novo lipogenesis. As such, fatty acid (FA) synthesis enzymes are over-expressed in cancer and their depletion causes antitumor effects. As fatty acid synthase (FASN) plays a pivotal role in this process, it is an attractive target for cancer therapy.

AREAS COVERED

This is a review of the lipogenic phenotype of cancer and how this phenomenon can be exploited for cancer therapy using inhibitors of FASN, with particular emphasis on orlistat as a repurposing drug.

EXPERT OPINION

Disease stabilization only has been observed with a highly selective FASN inhibitor used as a single agent in clinical trials. It is too early to say whether the absence of tumor responses other than stabilization results because even full inhibition of FASN is not enough to elicit antitumor responses. The FASN inhibitor orlistat is a 'dirty' drug with target-off actions upon at least seven targets with a proven role in tumor biology. The development of orlistat formulations suited for its intravenous administration is a step ahead to shed light on the concept that drug promiscuity can or not be a virtue.

Glutamine-utilizing transaminases are a metabolic vulnerability of TAZ/YAP-activated cancer cells

The transcriptional regulators TAZ and YAP (TAZ/YAP) have emerged as pro-tumorigenic factors that drive many oncogenic traits, including induction of cell growth, resistance to cell death, and activation of processes that promote migration and invasion. Here, we report that TAZ/YAP reprogram cellular energetics to promote the dependence of breast cancer cell growth on exogenous glutamine. Rescue experiments with glutamine-derived metabolites suggest an essential role for glutamate and α-ketoglutarate (AKG) in TAZ/YAP-driven cell growth in the absence of glutamine. Analysis of enzymes that mediate the conversion of glutamate to AKG shows that TAZ/YAP induce glutamic-oxaloacetic transaminase (GOT1) and phosphoserine aminotransferase (PSAT1) expression and that TAZ/YAP activity positively correlates with transaminase expression in breast cancer patients. Notably, we find that the transaminase inhibitor aminooxyacetate (AOA) represses cell growth in a TAZ/YAP-dependent manner, identifying transamination as a potential vulnerable metabolic requirement for TAZ/YAP-driven breast cancer.

Effects of Fatty Acid Synthase Inhibition by Orlistat on Proliferation of Endometrial Cancer Cell Lines

OBJECTIVE

Fatty acid synthase (FAS) is a key lipogenic enzyme that is highly expressed in endometrial cancer. Orlistat is a weight loss medication that has been shown to be a potent inhibitor of FAS. The goal of this study was to evaluate the anti-tumorigenic potential of orlistat in endometrial cancer cell lines.

METHODS

The endometrial cancer cell lines ECC-1 and KLE were used. Cell proliferation was assessed by MTT assay after treatment with orlistat. Cell cycle progression was evaluated by Cellometer and apoptosis was assessed using the Annexin V assay. Reactive oxygen species (ROS) was measured using the DCFH-DA assay. Western immunoblotting was performed to determine changes in FAS, cellular stress, cell cycle progression, and the AMPK/mTOR pathways.

RESULTS

Orlistat inhibited cell proliferation by 61 % in ECC-1 cells and 57 % in KLE cells at a dose of 500 μM. Treatment with orlistat at this concentration resulted in G1 arrest (p < 0.05) but did not affect apoptosis. Orlistat increased ROS and induced the expression of BIP (1.28-fold in ECC-1 compared to control, p < 0.05; 1.92-fold in KLE, p < 0.05) and PERK (2.25-fold in ECC-1, 1.4-fold in KLE, p < 0.05). Western immunoblot analysis demonstrated that orlistat decreased expression of important proteins in fatty acid metabolism including FAS (67 % in ECC-1, 15 % in KLE), acetyl-CoA carboxylase (40 % in ECC-1, 35 % in KLE), and carnitine palmitoyltransferase 1A (CPT1A) (65 % in ECC-1, 25 % in KLE) in a dose-dependent manner. In addition, orlistat at a dose of 500 μM increased expression of phosphorylated-AMPK (1.9-fold in ECC-1, p < 0.01; 1.5-fold in KLE, p < 0.05) and decreased expression of phosphorylated-Akt (25 % in ECC-1, p < 0.05; 37 % in KLE, p < 0.05) and phosphorylated-S6 (68 % in ECC-1, 56 % in KLE).

CONCLUSIONS

Orlistat inhibits cell growth in endometrial cancer cell lines through inhibition of fatty acid metabolism, induction of cell cycle G1 arrest, activation of AMPK and inhibition of the mTOR pathway. Given that patients with endometrial cancer have high rates of obesity, orlistat should be further investigated as a novel strategy for endometrial cancer treatment.

Fatty acid synthase as a potential therapeutic target in feline oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is an aggressive and treatment-resistant malignancy in both feline and human patients. Recent work has demonstrated aberrant expression of fatty acid synthase (FASN) and an increased capacity for lipogenesis in human OSCC and other cancers. In human OSCC, inhibition of FASN decreased cell viability and growth in vitro, and diminished tumour growth and metastasis in murine preclinical models. This study aimed to characterize FASN as a therapeutic target in feline OSCC. Immunohistochemistry revealed high FASN expression in primary feline OSCC tumours, and FASN expression was detected in OSCC cell lines (3 feline and 3 human) by immunoblotting and quantitative real-time-polymerase chain reaction (qRT-PCR). Orlistat, a FASN inhibitor, substantially reduced cell viability in both feline and human OSCC lines, although feline cell lines consistently displayed higher sensitivity to the drug. FASN mRNA expression among cell lines mirrored sensitivity to orlistat, with feline cell lines expressing higher levels of FASN. Consistent with this observation, diminished sensitivity to orlistat treatment and decreased FASN mRNA expression were observed in feline OSCC cells following incubation under hypoxic conditions. Treatment with orlistat did not potentiate sensitivity to carboplatin in the cell lines investigated; instead, combinations of the 2 drugs resulted in additive to antagonistic effects. Our results suggest that FASN inhibition is a viable therapeutic target for feline OSCC. Furthermore, cats may serve as a spontaneous large animal model for human oral cancer, although differences in the regulation of lipogenesis between these 2 species require further investigation.

Dynamic Protein Acylation: New Substrates, Mechanisms, and Drug Targets

Post-translational attachment of lipids to proteins is found in all organisms, and is important for many biological processes. Acylation with myristic and palmitic acids are among the most common lipid modifications, and understanding reversible protein palmitoylation dynamics has become a particularly important goal. Linking acyltransferase enzymes to disease states can be challenging due to a paucity of robust models, compounded by functional redundancy between many palmitoyl transferases; however, in cases such as Wnt or Hedgehog signalling, small molecule inhibitors have been identified, with some progressing to clinical trials. In this review, we present recent developments in our understanding of protein acylation in human health and disease through use of chemical tools, global profiling of acylated proteomes, and functional studies of specific protein targets.

(-)-UB006: A new fatty acid synthase inhibitor and cytotoxic agent without anorexic side effects

C75 is a synthetic anticancer drug that inhibits fatty acid synthase (FAS) and shows a potent anorexigenic side effect. In order to find new cytotoxic compounds that do not impact food intake, we synthesized a new family of C75 derivatives. The most promising anticancer compound among them was UB006 ((4SR,5SR)-4-(hydroxymethyl)-3-methylene-5-octyldihydrofuran-2(3H)-one). The effects of this compound on cytotoxicity, food intake and body weight were studied in UB006 racemic mixture and in both its enantiomers separately. The results showed that both enantiomers inhibit FAS activity and have potent cytotoxic effects in several tumour cell lines, such as the ovarian cell cancer line OVCAR-3. The (-)-UB006 enantiomer's cytotoxic effect on OVCAR-3 was 40-fold higher than that of racemic C75, and 2- and 38-fold higher than that of the racemic mixture and its opposite enantiomer, respectively. This cytotoxic effect on the OVCAR-3 cell line involves mechanisms that reduce mitochondrial respiratory capacity and ATP production, DDIT4/REDD1 upregulation, mTOR activity inhibition, and caspase-3 activation, resulting in apoptosis. In addition, central and peripheral administration of (+)-UB006 or (-)-UB006 into rats and mice did not affect food intake or body weight. Altogether, our data support the discovery of a new potential anticancer compound (-)-UB006 that has no anorexigenic side effects.

Metabolic Regulation of Apoptosis in Cancer

Apoptosis is a cellular suicide program that plays a critical role in development and human diseases, including cancer. Cancer cells evade apoptosis, thereby enabling excessive proliferation, survival under hypoxic conditions, and acquired resistance to therapeutic agents. Among various mechanisms that contribute to the evasion of apoptosis in cancer, metabolism is emerging as one of the key factors. Cellular metabolites can regulate functions of pro- and antiapoptotic proteins. In turn, p53, a regulator of apoptosis, also controls metabolism by limiting glycolysis and facilitating mitochondrial respiration. Consequently, with dysregulated metabolism and p53 inactivation, cancer cells are well-equipped to disable the apoptotic machinery. In this article, we review how cellular apoptosis is regulated and how metabolism can influence the signaling pathways leading to apoptosis, especially focusing on how glucose and lipid metabolism are altered in cancer cells and how these alterations can impact the apoptotic pathways.

Acetate functions as an epigenetic metabolite to promote lipid synthesis under hypoxia

Besides the conventional carbon sources, acetyl-CoA has recently been shown to be generated from acetate in various types of cancers, where it promotes lipid synthesis and tumour growth. The underlying mechanism, however, remains largely unknown. We find that acetate induces a hyperacetylated state of histone H3 in hypoxic cells. Acetate predominately activates lipogenic genes ACACA and FASN expression by increasing H3K9, H3K27 and H3K56 acetylation levels at their promoter regions, thus enhancing de novo lipid synthesis, which combines with its function as the metabolic precursor for fatty acid synthesis. Acetyl-CoA synthetases (ACSS1, ACSS2) are involved in this acetate-mediated epigenetic regulation. More importantly, human hepatocellular carcinoma with high ACSS1/2 expression exhibit increased histone H3 acetylation and FASN expression. Taken together, this study demonstrates that acetate, in addition to its ability to induce fatty acid synthesis as an immediate metabolic precursor, also functions as an epigenetic metabolite to promote cancer cell survival under hypoxic stress.

Cancer cells under stress use acetate to maintain the acetyl-CoA pool and fuel lipid biosynthesis. Here, the authors show that acetate also promotes de novo lipid synthesis by increasing histone acetylation at the promoters of lipogenic enzymes ACACA and FASN, thus inducing their expression.

Overexpression of fatty acid synthase predicts a poor prognosis for human gastric cancer

Fatty acid synthase (FASN), a lipogenic multi-enzyme complex, is reported to be overexpressed in various types of of tumor tissues and serves an important role in tumor development and progression. However, the expression of FASN and its possible role in gastric cancer (GC) remains to be defined. In the present study, FASN expression in a group sample of 167 GC tissues was detected by immunohistochemistry and its correlation with clinicopathological features was analyzed. By clinical analysis, it was identified that FASN overexpression was positively correlated with the overall survival [P=0.008; hazard ratio (HR), 4.412; 95% confidence interval (CI), 1.463‑13.305] and recurrence rate (P=0.014; HR, 1.705; 95% CI, 1.116‑2.606) in patients with GC. In addition, expression of the FASN protein in GC tissues was correlated with age (P=0.032), clinical stage (P<0.001), gastric wall invasion (P=0.014), lymph node metastasis (P<0.001) and distant metastasis (P<0.001), however not with gender (P>0.05). In addition, FASN was observed to be overexpressed in GC tissues at an mRNA and protein level, compared with the adjacent non-cancerous tissues (P<0.05). Taken together, it was suggested that FASN was closely associated with GC metastasis and survival, which further provided evidence that FASN may be a promising prognostic biomarker for patients with GC.

Metabolic reprogramming in glioblastoma: the influence of cancer metabolism on epigenetics and unanswered questions

A defining hallmark of glioblastoma is altered tumor metabolism. The metabolic shift towards aerobic glycolysis with reprogramming of mitochondrial oxidative phosphorylation, regardless of oxygen availability, is a phenomenon known as the Warburg effect. In addition to the Warburg effect, glioblastoma tumor cells also utilize the tricarboxylic acid cycle/oxidative phosphorylation in a different capacity than normal tissue. Altered metabolic enzymes and their metabolites are oncogenic and not simply a product of tumor proliferation. Here we highlight the advantages of why tumor cells, including glioblastoma cells, require metabolic reprogramming and how tumor metabolism can converge on tumor epigenetics and unanswered questions in the field.

Antitumor effects of a drug combination targeting glycolysis, glutaminolysis and de novo synthesis of fatty acids

There is a strong rationale for targeting the metabolic alterations of cancer cells. The most studied of these are the higher rates of glycolysis, glutaminolysis and de novo synthesis of fatty acids (FAs). Despite the availability of pharmacological inhibitors of these pathways, no preclinical studies targeting them simultaneously have been performed. In the present study it was determined whether three key enzymes for glycolysis, glutaminolysis and de novo synthesis of FAs, hexokinase-2, glutaminase and fatty acid synthase, respectively, were overexpressed as compared to primary fibroblasts. In addition, we showed that at clinically relevant concentrations lonidamine, 6-diazo-5-oxo-L-norleucine and orlistat, known inhibitors of the mentioned enzymes, exerted a cell viability inhibitory effect. Genetic downregulation of the three enzymes also reduced cell viability. The three drugs were highly synergistic when administered as a triple combination. Of note, the cytotoxicity of the triple combination was low in primary fibroblasts and was well tolerated when administered into healthy BALB/c mice. The results suggest the feasibility and potential clinical utility of the triple metabolic targeting which merits to be further studied by using either repositioned old drugs or newer, more selective inhibitors.

Targeting glycogen metabolism in bladder cancer

Metabolism has been a heavily investigated topic in cancer research for the past decade. Although the role of aerobic glycolysis (the Warburg effect) in cancer has been extensively studied, abnormalities in other metabolic pathways are only just being understood in cancer. One such pathway is glycogen metabolism; its involvement in cancer development, particularly in urothelial malignancies, and possible ways of exploiting aberrations in this process for treatment are currently being studied. New research shows that the glycogen debranching enzyme amylo-α-1,6-glucosidase, 4-α-glucanotransferase (AGL) is a novel tumour suppressor in bladder cancer. Loss of AGL leads to rapid proliferation of bladder cancer cells. Another enzyme involved in glycogen debranching, glycogen phosphorylase, has been shown to be a tumour promoter in cancer, including in prostate cancer. Studies demonstrate that bladder cancer cells in which AGL expression is lost are more metabolically active than cells with intact AGL expression, and these cells are more sensitive to inhibition of both glycolysis and glycine synthesis--two targetable pathways. As a tumour promoter and enzyme, glycogen phosphorylase can be directly targeted, and preclinical inhibitor studies are promising. However, few of these glycogen phosphorylase inhibitors have been tested for cancer treatment in the clinical setting. Several possible limitations to the targeting of AGL and glycogen phosphorylase might also exist.