Fatty Acid Synthase (Fas) Predictive Strength in Poorly Differentiated Early Breast Carcinomas

Fatty acid synthase is over-expressed in large aberrant crypt foci in rats treated with azoxymethane

Fatty acid synthase (FAS) is over-expressed in many human cancers including colon. High levels of FAS expression have also been observed in a number of lesions that are precursors to invasive colorectal cancer. However, FAS expression in aberrant crypt foci (ACF), the earliest identifiable lesions in colon cancer development, has not been investigated. In this study, we treated Fisher rats with a single dose of the colon carcinogen azoxymethane then evaluated ACF 100 days later. We showed that large ACF (>or=4 crypts/focus) have a significantly higher level of immunohistochemical staining for FAS than either small ACF (<or=3 crypts/focus) or normal crypts. Furthermore, the severity of nuclear atypia in ACF was positively associated with increased expression of FAS. These findings suggest that the genes associated with FAS over-expression are activated early in the stepwise development of colon cancer, though not until the ACF have reached a critical size with a level of nuclear atypia indicative of dysplasia.

[Fatty acid synthase: a new anti-tumor target]

Fatty acid synthase (FASN), an enzyme capable of de novo fatty acid synthesis, is highly expressed and activated in most human carcinomas. FASN is associated with poor prognosis in prostate and breast cancer and its inhibition is selectively cytotoxic to human cancer cells. Thus, FASN and fatty acid metabolism have become an important focus for the diagnostic and treatment of cancer. In this sense, there is an increasing interest in identifying and developing new antitumor compounds that inhibit FASN.

Novel fatty acid synthase (FAS) inhibitors: design, synthesis, biological evaluation, and molecular docking studies

Several novel series of C75 derivatives were synthesized and evaluated for their FAS inhibitory activities. The results showed compound 4-methylene-2-octyl-5-oxo-tetrahydro-thiophene-3-carboxylic acid (1c) had more effective FAS inhibitory (IC(50) was 2.56 microM and T.I. was 9.26) and potent anti-tumor activities on HL60 and Hela cells in vitro (IC(50) were 5.38 microM and 46.10 microM, respectively).

Erythrocyte fatty acids and risk of proliferative and nonproliferative fibrocystic disease in women in Shanghai, China

BACKGROUND

Although benign breast changes are more common than breast cancer, little evidence regarding risk factors for benign breast conditions is available. Omega-3 (n-3) fatty acids have antiinflammatory and antiproliferative actions and may be important in reducing the risk of benign conditions. There is a lack of research on the association of n-3 fatty acids with risk of benign fibrocystic breast changes.

OBJECTIVES

The objectives of the study were to evaluate the role of n-3 and other fatty acids in the development of benign proliferative fibrocystic conditions (PFCs) and nonproliferative fibrocystic conditions (NPFCs) in the breast and to evaluate the progression of fibrocystic changes in breast cancer.

DESIGN

We conducted a case-control study to determine erythrocyte fatty acid concentrations in 155 women with NPFCs, 185 women with PFCs, 241 women with breast cancer (127 with nonproliferative and 114 with proliferative changes in the noncancerous extratumoral mammary epithelium), and 1,030 control subjects. We estimated the relative risk of NPFCs, PFCs, and breast cancer with proliferative and nonproliferative changes in extratumoral tissue compared with the risk of these changes alone.

RESULTS

Women in the highest quartile of eicosapentaenoic acid concentrations were 67% less likely to have an NPFC alone or with breast cancer and 49% less likely to have breast cancer than were women with PFCs. gamma-Linolenic acid (18:3n-6) was positively associated with all fibrocystic and cancerous conditions. Palmitic:palmitoleic acid (n-7 saturation index) was inversely associated with risk in all comparisons.

CONCLUSION

Our results support a protective effects of n-3 fatty acid intake and the n-7 saturation index against benign fibrocystic breast changes and the progression of proliferative changes to breast cancer.

Characterization of a novel anti-fatty acid synthase (FASN) antiserum in breast tissue

Fatty acid synthase (FASN) expression has been reported in many different tumors, including breast cancer. In gene microarray studies, the fatty acid synthase gene co-clustered with cytokeratins 5 and 17 and other genes that defined the basal-like subset of breast cancers. To define the use of this marker in breast pathology, a rabbit polyclonal antiserum (S143) to a peptide fragment of this gene was produced and compared with a commercially available monoclonal antibody by immunohistochemistry on various tissue microarrays and whole tissue sections. The tissue microarrays included 1090 breast cancers and 244 normal breast tissues. Whole tissue sections consisted of benign and malignant tissues from breast resection specimens. In contrast to other 'basal' markers identified by gene expression profiling data, the fatty acid synthase (FASN) expression pattern in normal breast was notable for its expression in only a small subset of basal and suprabasal cells. Dual staining experiments revealed that the subpopulation of cells labeling with FASN did not coexpress myoepithelial markers CK5/6 or p63, but did coexpress e-cadherin. In addition to staining a subset of basal and suprabasal cells, the antiserum highlighted apocrine differentiation, and stained 106/144 (74%) cases of columnar cell lesions and five of five cases of flat epithelial atypia. Despite its association with basal keratins in gene array studies, FASN expression did not correlate significantly with the outcome in breast cancer. We describe an expression pattern that highlights only a subset of basal and suprabasal cells in normal breast ducts and we show by dual expression studies that this subset of cells is different from myoepithelial and basal cytokeratin-positive cells. In addition, FASN expression is described in apocrine metaplasia, columnar cell lesions, and flat epithelial atypia.

ErbB2 and fatty acid synthase (FAS) expression in 102 squamous cell carcinomas of the tongue: Correlation with clinical outcomes

The oncoprotein ErbB2 (HER-2/neu) is a tyrosine kinase cell surface receptor overexpressed in several human malignancies, including oral squamous cell carcinoma (OSCC). ErbB2 was recently shown to regulate the expression of fatty acid synthase (FAS), a multifunctional enzyme complex responsible for the de novo biosynthesis of saturated fatty acids. Here we evaluated the relationship between the immunohistochemical expression of ErbB2, FAS, and Ki-67 with the clinicopathologic characteristics of tongue squamous cell carcinoma (SCC). One hundred and two patients with tongue SCC treated from 1990 to 1995 were studied. Clinical and treatment data were obtained from the medical records and histopathological features revised. Paraffin-embedded tissues were submitted to standard immunohistochemical reactions for ErbB2, FAS and Ki-67. A strong positive correlation between ErbB2 labeling at the cell membrane and FAS expression was found in the tongue SCC samples (p<0.0001). The intracytoplasmatic expression of ErbB2 as well as Ki-67 nuclear staining were significantly associated with a high risk of recurrence by predicting both disease free survival (log-rank test, p=0.0096 and p=0.0047, respectively) and overall survival (log-rank test, p=0.0029 and p=0.0001, respectively). Taken together, our results suggest that the immunolocalization of ErbB2 at the cell surface of malignant oral keratinocytes is linked to FAS expression whereas the intracytoplasmatic ErbB2 or Ki-67 staining predict high risk of recurrence of tongue SCC.

Examining the relationship between Cu-ATSM hypoxia selectivity and fatty acid synthase expression in human prostate cancer cell lines

INTRODUCTION

Positron emission tomography (PET) imaging with copper (II)-diacetyl-bis(N4-Methylthiosemicarbazone)(Cu-ATSM) for delineating hypoxia has provided valuable clinical information, but investigations in animal models of prostate cancer have shown some inconsistencies. As a defense mechanism in prostate cancer cells, the fatty acid synthesis pathway harnesses its oxidizing power for improving the redox balance despite conditions of extreme hypoxia, potentially altering Cu-ATSM hypoxia selectivity.

METHODS

Human prostate tumor-cultured cell lines (PC-3, 22Rv1, LNCaP and LAPC-4), were treated with a fatty acid synthase (FAS) inhibitor (C75, 100 microM) under anoxia. The 64Cu-ATSM uptake in these treated cells and nontreated anoxic cells was then examined. Fatty acid synthase expression level in each cell line was subsequently quantified by ELISA. An additional study was performed in PC-3 cells to examine the relationship between the restoration of 64Cu-ATSM hypoxia selectivity and the concentration of C75 (100, 20, 4 or 0.8 microM) administered to the cells.

RESULTS

Inhibition of fatty acid synthesis with C75 resulted in a significant increase in 64Cu-ATSM retention in prostate tumor cells in vitro under anoxia over 60 min. Inhibition studies demonstrated higher uptake values of 20.9+/-3.27%, 103.0+/-32.6%, 144.2+/-32.3% and 200.1+/-79.3% at 15 min over control values for LAPC-4, PC-3, LNCaP and 22Rv1 cells, respectively. A correlation was seen (R2=.911) with FAS expression plotted against percentage change in 64Cu-ATSM uptake with C75 treatment.

CONCLUSIONS

Although Cu-ATSM has clinical relevance in the PET imaging of hypoxia in many tumor types, its translation to the imaging of prostate cancer may be limited by the overexpression of FAS associated with prostatic malignancies.

Fatty acid synthase inhibitors: new directions for oncology

Fatty acid synthase (FASN) is the enzyme that catalyzes the de novo synthesis of fatty acids in cells. Because of the strong expression in many cancers, FASN is an attractive and tractable target for therapeutic intervention. The discovery and development of pharmacologic agents that block FASN activity highlight the promise of these anticancer compounds. FASN inhibitors have also proven to be invaluable in developing a better understanding of the contribution of FASN and fatty acid synthesis to tumor cells. Recent advances in the development of crystal structures of FASN have provided promise towards the development of novel FASN inhibitors. This review outlines the preclinical development of FASN inhibitors, their antitumor effects and the strategies underway to develop novel inhibitors.

A new targeting approach for breast cancer gene therapy using the human fatty acid synthase promoter

Gene therapy with adenoviral vectors is a promising new approach for the treatment of refractory advanced breast cancer. Strategies to restrict adenoviral-mediated therapeutic gene expression are important to avoid harming normal cells. Fatty acid synthase (FAS) is overexpressed in several human cancers. FAS is highly expressed in infiltrating breast cancer tissue, and always associated with malignant phenotypes and poor prognosis. In this study, expression of the FAS was evaluated in three breast cancer cell lines. A 680 bp-FAS promoter was cloned and its transcriptional activity was analyzed in breast cancer cell lines. We made a recombinant adenovirus construct carrying herpes simplex virus thymidine kinase (HSV-TK) driven by human FAS promoter (Ad-FAS-TK) and analyzed its target cytotoxicity in vitro and in vivo against human breast cancer cells combined with prodrug ganciclovir (GCV). The results show that the expression of FAS varies in the three breast cancer cell lines examined (respectively, SK-Br3>MCF-7>MDA-MB-231), but FAS promoter can initiate relative high transcriptional activities in all three kinds of cancer cells while little in normal fibroblast cells. Furthermore, FAS promoter can drive the therapeutic gene in a wider range of human breast cancers than cerbB2 promoter and exhibit a stronger activity than midkine (MK) promoter. Combination of Ad-FAS-TK and GCV treatment exhibited strong-targeted cytotoxic effect on breast cancer cells but showed little activity in normal fibroblast cells. The tumorigenic capability of breast cancer cells treated with Ad-FAS-TK/GCV was completely inhibited in vitro and in vivo assays. In conclusion, adenoviral-mediated suicide gene therapy controlled by tumor associated-FAS promoter can induce specific cytotoxic effect on human breast cancer cells in vitro and in vivo. So it is a promising target for the development of gene therapy against breast cancers.

Fatty acid synthase and the lipogenic phenotype in cancer pathogenesis

There is a renewed interest in the ultimate role of fatty acid synthase (FASN)--a key lipogenic enzyme catalysing the terminal steps in the de novo biogenesis of fatty acids--in cancer pathogenesis. Tumour-associated FASN, by conferring growth and survival advantages rather than functioning as an anabolic energy-storage pathway, appears to necessarily accompany the natural history of most human cancers. A recent identification of cross-talk between FASN and well-established cancer-controlling networks begins to delineate the oncogenic nature of FASN-driven lipogenesis. FASN, a nearly-universal druggable target in many human carcinomas and their precursor lesions, offers new therapeutic opportunities for metabolically treating and preventing cancer.

Erythrocyte fatty acids and breast cancer risk: a case-control study in Shanghai, China

BACKGROUND

The role of individual fatty acids in the development and progression of breast cancer is unclear. Although in vitro and animal experiments have supported an inverse association between intake of long chain n-3 fatty acids [primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid] and breast cancer risk, findings from population studies are inconsistent. Recent studies have also shown associations between the ratio of saturated to monounsaturated fatty acids (SI) and breast cancer risk. The SI reflects the activity of several genes involved in lipid metabolism, including fatty acid synthase and steroyl coenzyme-A desaturase, that have been shown to be overexpressed in breast cancer.

OBJECTIVE

The purpose of this analysis was to determine the association between erythrocyte fatty acid concentrations and breast cancer risk among women participating in a randomized trial of breast self-examination in Shanghai, China.

DESIGN

We conducted a case-control study. Erythrocyte fatty acid concentrations were determined in specimens from 322 women with histologically confirmed breast cancer and 1030 frequency age-matched control women.

RESULTS

We report a significant direct association among palmitic, gamma-linolenic, palmitoleic, and vaccenic acids and risk of breast cancer. Total n-3 fatty acids, EPA, and the SI for palmitic to palmitoleic acid were associated with significantly lower risk of breast cancer.

CONCLUSION

Our results support a protective effect of n-3 fatty acids on breast cancer risk and provide additional evidence for the importance of evaluating the ratio of fatty acids when evaluating diet and breast cancer risk.

Targeting fatty acid synthase in breast and endometrial cancer: An alternative to selective estrogen receptor modulators?

There is an urgent need to identify and develop a new generation of therapeutic agents and systemic therapies targeting the estradiol (E2)/estrogen receptor (ER) signaling in breast cancer. In this regard, new information on the mechanisms of E2/ER function and/or cross talk with other prosurvival cascades should provide the basis for the development of other ideal anti-E2 therapies with the intent to enhance clinical efficacy, reduce side effects or both. Our very recent assessment of the mechanisms by which cancer-associated increased lipogenesis and its inhibition alters the E2/ER signaling discovered that fatty acid synthase (FASN), the enzyme catalyzing the terminal steps in the de novo biosynthesis of long-chain fatty acids, differentially modulates the state of sensitivity of breast and endometrial cancer cells to E2-stimulated ER transcriptional activation and E2-dependent cell growth and survival: 1) pharmacological inhibition of FASN activity induced a dramatic augmentation of E2-stimulated ER-driven gene transcription, whereas interference (RNAi)-mediated silencing of FAS gene expression drastically lowered E2 requirements for optimal activation of ER transcriptional activation in breast cancer cells; conversely, pharmacological and RNAi-induced inhibition of FASN worked as an antagonist of E2- and tamoxifen-dependent ER transcriptional activity in endometrial adenocarcinoma cells; 2) pharmacological and RNAi-induced inhibition of FASN synergistically enhanced E2-mediated down-regulation of ER protein and mRNA expression in breast cancer cells, whereas specific FASN blockade resulted in a marked down-regulation of E2-stimulated ER expression in endometrial cancer cells; and 3) FASN inhibition decreased cell proliferation and cell viability by promoting apoptosis in hormone-dependent breast and endometrial cancer cells. In this review we propose that, through a complex mechanism involving the regulation of MAPK/ER cross talk as well as critical E2-related proteins including the Her-2/neu (erbB-2) oncogene and the cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(Kip1), a previously unrevealed connection exists between FASN and the genomic and nongenomic ER activities in breast and endometrial cancer cells. From a clinical perspective, we suggest that if chemically stable FASN inhibitors or cell-selective systems able to deliver RNAi targeting FASN gene demonstrate systemic anticancer effects of FASN inhibition in vivo, additional preclinical studies to characterize their anti-breast cancer actions should be of great interest as the specific blockade of FASN activity may also provide a protective means against endometrial carcinoma associated with tamoxifen-based breast cancer therapy.

Mechanism of apoptosis induced by the inhibition of fatty acid synthase in breast cancer cells

Fatty acid synthase (FAS) has been found to be overexpressed in a wide range of epithelial tumors, including breast cancer. Pharmacologic inhibitors of FAS cause apoptosis of breast cancer cells and result in decreased tumor size in vivo. However, how the inhibition of FAS induces apoptosis in tumor cells remains largely unknown. To understand the apoptotic pathway resulting from direct inhibition of FAS, we treated breast tumor cells with or without FAS small interfering RNA (siRNA) followed by a microarray analysis. Our results indicated that the proapoptotic genes BNIP3, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and death-associated protein kinase 2 (DAPK2) were significantly up-regulated on direct inhibition of the FAS gene. We also found that the knockdown of FAS expression significantly increased ceramide level in the tumor cells, and this increase was abrogated by acetyl-CoA carboxylase inhibitor. In addition, carnitine palmitoyltransferase-1 (CPT-1) inhibitor up-regulated the ceramide and BNIP3 levels in these cells, whereas treatment of tumor cells with FAS siRNA in the presence of a ceramide synthase inhibitor abrogated the up-regulation of BNIP3 and inhibited apoptosis. Furthermore, we found that treatment of cells with BNIP3 siRNA significantly counteracted the effect of FAS siRNA-mediated apoptosis. Consistent with these results, a significant inverse correlation was observed in the expression of FAS and BNIP3 in clinical samples of human breast cancer. Collectively, our results indicate that inhibition of FAS in breast cancer cells causes accumulation of malonyl-CoA, which leads to inhibition of CPT-1 and up-regulation of ceramide and induction of the proapoptotic genes BNIP3, TRAIL, and DAPK2, resulting in apoptosis.

Acetyl-CoA carboxylase alpha is essential to breast cancer cell survival

Activation of de novo fatty acid synthesis is a characteristic feature of cancer cells. We have recently described an interaction between acetyl-CoA carboxylase alpha (ACCalpha), a key enzyme in fatty acid synthesis, and BRCA1, which indicates a possible connection between lipid synthesis and genetic factors involved in susceptibility to breast and ovarian cancers. For this reason, we explored the role of ACCalpha in breast cancer cell survival using an RNA interference (RNAi) approach. We show that specific silencing of either the ACCalpha or the fatty acid synthase (FAS) genes in cancer cells results in a major decrease in palmitic acid synthesis. Depletion of the cellular pool of palmitic acid is associated with induction of apoptosis concomitant with the formation of reactive oxygen species (ROS) and mitochondrial impairment. Expression of a small interfering RNA (siRNA)-resistant form of ACCalpha mRNA prevented the effect of ACCalpha-RNAi but failed to prevent the effect of FAS gene silencing. Furthermore, supplementation of the culture medium with palmitate or with the antioxidant vitamin E resulted in the complete rescue of cells from both ACCalpha and FAS siRNA-induced apoptosis. Finally, human mammary epithelial cells are resistant to RNAi against either ACCalpha or FAS. These data confirm the importance of lipogenesis in cancer cell survival and indicate that this pathway represents a key target for antineoplastic therapy that, however, might require specific dietary recommendation for full efficacy.

A functional variant in the transcriptional regulatory region of gene LOC344967 cosegregates with disease phenotype in familial nasopharyngeal carcinoma

Nasopharyngeal carcinoma is a common malignancy in Southeast Asian countries, and genetic background is a well-known component of the complexity underlying its tumorigenic process. We have mapped a nasopharyngeal carcinoma susceptibility locus to chromosome 4p15.1-q12 in a previous linkage study on nasopharyngeal carcinoma pedigrees. In this study provided in this communication, we screened all the genes in this region, with a focus on exons, promoters, and the exon-intron boundary to identify nasopharyngeal carcinoma-associated mutations or functional variants. Importantly, we found a novel gene (LOC344967) with a single nucleotide polymorphism -32G/A in the promoter region. This gene is a member of the acyl CoA thioesterase family that plays an important role in fatty acid metabolism and is involved in the progression of various types of tumors. The -32A variant was found cosegregated with the disease phenotype in the nasopharyngeal carcinoma pedigrees that we previously used for the linkage study. Moreover, this -32A variant creates an activator protein (AP-1)-binding site in the transcriptional regulatory region of LOC344967, which significantly enhanced the binding of AP-1 to the promoter region and the transcription activity of the promoter in vivo. Furthermore, the expression of LOC344967 was significantly up-regulated at both mRNA and protein levels in nasopharyngeal carcinoma cells sharing the -32G/A genotype compared with nasopharyngeal carcinoma cells with the -32G/G genotype. Collectively, these results provide evidence that the -32A variant is a functional sequence change and may be related to nasopharyngeal carcinoma susceptibility in the families studied.

Co-ordinate activation of lipogenic enzymes in hepatocellular carcinoma

Hepatocellular carcinoma is a very common neoplastic disease in countries where hepatitis viruses B and/or C are prevalent. Small hepatocellular carcinoma lesions detected by ultrasonography at an early stage are often hyperechoic because they are composed of well-differentiated cancer cells that are rich in triglyceride droplets. The triglyceride content of hepatocytes depends in part on the rate of lipogenesis. Key lipogenic enzymes, such as fatty acid synthase, are co-ordinately regulated at the transcriptional level. We therefore examined the mRNA expression of lipogenic enzymes in human hepatocellular carcinoma samples from 10 patients who had undergone surgical resection. All of the samples exhibited marked elevation of expression of mRNA for lipogenic enzymes, such as fatty acid synthase, acetyl-CoA carboxylase and ATP citrate lyase, compared with surrounding non-cancerous liver tissue. In contrast, the changes in mRNA expression of SREBP-1, a transcription factor that regulates a battery of lipogenic enzymes, did not show a consistent trend. In some cases where SREBP-1 was elevated, the main contributing isoform was SREBP-1c rather than SREBP-1a. Thus, lipogenic enzymes are markedly induced in hepatocellular carcinomas, and in some cases SREBP-1c is involved in this activation.

Fatty acid synthase expression in cutaneous melanocytic neoplasms

Mammalian fatty acid synthase is a multifunctional enzyme complex involved in de novo synthesis of saturated fatty acids, and inhibitors of fatty acid synthase are being evaluated as potential therapeutic agents. Increased fatty acid synthase expression has been demonstrated in subsets of malignancies, including colon, breast, endometrium, prostate and ovarian carcinomas, and recently malignant melanomas. We evaluated the immunohistochemical expression of fatty acid synthase in 155 cutaneous melanocytic lesions. They included 30 congenital nevi, 19 compound nevi, 40 Spitz nevi, 48 primary melanomas, and 18 metastatic melanomas. Fatty acid synthase expression was stronger in malignant melanomas in comparison to conventional nevi and Spitz nevi, and was the highest for metastatic melanoma. Of the primary malignant melanomas, mean fatty acid synthase scores were significantly greater for Clark levels IV and V compared to Clark levels I and II (P<0.001). In addition, melanomas with Breslow thickness 0.75-1.50 mm and >1.50 mm showed significantly higher mean fatty acid synthase scores compared with those with Breslow thickness <0.75 mm (P=0.013 and <0.001, respectively). Of interest, congenital melanocytic nevi also showed strong fatty acid synthase expression, similar to that seen in metastatic melanoma. This may represent persistence of or regression to a fetal phenotype since normal fetal tissues are known to express high levels of fatty acid synthase.

Pharmacological and small interference RNA-mediated inhibition of breast cancer-associated fatty acid synthase (oncogenic antigen-519) synergistically enhances Taxol (paclitaxel)-induced cytotoxicity

The relationship between breast cancer-associated fatty acid synthase (FAS; oncogenic antigen-519) and chemotherapy-induced cell damage has not been studied. We examined the ability of C75, a synthetic slow-binding inhibitor of FAS activity, to modulate the cytotoxic activity of the microtubule-interfering agent Taxol (paclitaxel) in SK-Br3, MDA-MB-231, MCF-7 and multidrug-resistant MDR-1 (P-Glycoprotein)-overexpressing MCF-7/AdrR breast cancer cells. When the combination of C75 with Taxol in either concurrent (C75 + Taxol 24 hr) or sequential (C75 24 hr --> Taxol 24 hr) schedules were tested for synergism, addition or antagonism using the isobologram and the median-effect plot analyses, co-exposure of C75 and Taxol mostly demonstrated synergistic effects, whereas sequential exposure to C75 followed by Taxol mainly showed additive or antagonistic interactions. Because the nature of the cytotoxic interactions was definitely schedule-dependent in MCF-7 cells, we next evaluated the effects of C75 on Taxol-induced apoptosis as well as Taxol-activated cell death and cell survival-signaling pathways in this breast cancer cell model. An ELISA for histone-associated DNA fragments demonstrated that C75 and Taxol co-exposure caused a synergistic enhancement of apoptotic cell death, whereas C75 pre-treatment did not enhance the apoptosis-inducing activity of Taxol. Co-exposure to C75 and Taxol induced a remarkable nuclear accumulation of activated p38 mitogen-activated protein kinase (p38 MAPK), which was accompanied by a synergistic nuclear accumulation of the p53 tumor-suppressor protein that was phosphorylated at Ser46, a p38 MAPK-regulated pro-apoptotic modification of p53. As single agents, FAS blocker C75 and Taxol induced a significant stimulation of the proliferation and cell survival mitogen-activated protein kinase extracellular signal-regulated kinase (ERK1/ERK2 MAPK) activity, whereas, in combination, they interfered with ERK1/ERK2 activation. Moreover, the combined treatment of C75 and Taxol inactivated the anti-apoptotic AKT (protein kinase B) kinase more than either agent alone, as evidenced by a synergistic down-regulation of AKT phosphorylation at its activating site Ser(473) without affecting AKT protein levels. To rule out a role for non-FAS C75-mediated effects, we finally used the potent and highly sequence-specific mechanism of RNA interference (RNAi) to block FAS-dependent signaling. Importantly, SK-Br3 and multi-drug resistant MCF-7/AdrR cells transiently transfected with sequence-specific double-stranded RNA oligonucleotides targeting FAS gene demonstrated hypersensitivity to Taxol-induced apoptotic cell death. Our findings establish for the first time that FAS blockade augments the cytotoxicity of anti-mitotic drug Taxol against breast cancer cells and that this chemosensitizing effect is schedule-dependent. We suggest that the alternate activation of both the pro-apoptotic p38 MAPK-p53 signaling and the cytoprotective MEK1/2 --> ERK1/2 cascade, as well as the inactivation of the anti-apoptotic AKT activity may explain, at least in part, the sequence-dependent enhancement of Taxol-induced cytotoxicity and apoptosis that follows inhibition of FAS activity in breast cancer cells. If chemically stable FAS inhibitors demonstrate systemic anticancer effects of FAS inhibition in vivo, these findings may render FAS as a valuable molecular target to enhance the efficacy of taxanes-based chemotherapy in human breast cancer.

Antitumoral actions of the anti-obesity drug orlistat (XenicalTM) in breast cancer cells: blockade of cell cycle progression, promotion of apoptotic cell death and PEA3-mediated transcriptional repression of Her2/neu (erbB-2) oncogene

BACKGROUND

Orlistat (Xenicaltrade mark), a US Food and Drug Administration (FDA)-approved drug for bodyweight loss, has recently been demonstrated to exhibit antitumor properties towards prostate cancer cells by virtue of its ability to block the lipogenic activity of fatty acid synthase (FAS). FAS (oncogenic antigen-519) is up-regulated in about 50% of breast cancers, is an indicator of poor prognosis, and has recently been functionally associated with the Her2/neu (erbB-2) oncogene.

MATERIALS AND METHODS

We assessed the antitumoral effects of orlistat against the human breast cancer cell line SK-Br3, an in vitro paradigm of FAS and Her2/neu overexpression in breast cancer.

RESULTS

Cell cycle analyses revealed that micromolar concentrations of orlistat induced, in a time- and dose-dependent manner, significant changes in the distribution of cell populations including a complete loss of G2-M phase, S-phase accumulation and a concomitant increase in the emerging sub-G1 (apoptotic) cells. Poly (ADP-ribose) polymerase (PARP) cleavage, an early event required for cells committed to apoptosis, was more predominant in orlistat-treated G1 phase cells. When we characterized signaling molecules participating in the cellular events following orlistat-induced inhibition of FAS activity and preceded inhibition of breast cancer cell proliferation, a dramatic down-regulation of Her2/neu-coded p185(Her2/neu) oncoprotein was found in orlistat-treated SK-Br3 cells (>90% reduction). Interestingly, a significant accumulation of the DNA-binding protein PEA3, a member of the Ets transcription factor family that specifically targets a PEA3-binding motif present on the Her2/neu gene promoter and down-regulates its activity, was observed in orlistat-treated SK-Br3 cells. When a Luciferase reporter gene driven by the Her2/neu promoter was transiently transfected in SK-Br3 cells, orlistat exposure was found to dramatically repress the promoter activity of Her2/neu gene, whereas a Her2/neu promoter bearing a mutated binding DNA sequence was not subject to negative regulation by orlistat, thus demonstrating that the intact PEA3 binding site on the Her2/neu promoter is required for the orlistat-induced transcriptional repression of Her2/neu overexpression. RNA interference (RNAi)-mediated silencing of FAS gene expression similarly repressed Her2/neu gene expression in a PEA3-dependent manner, thus ruling out a role for non-FAS orlistat-mediated effects. When the combination of orlistat and the anti-Her2/neu antibody trastuzumab (Herceptintrade mark) in either concurrent (orlistat + trastuzumab) or sequential (orlistat --> trastuzumab; trastuzumab --> orlistat) schedules was tested for synergism, addition or antagonism using the combination index (CI) method of Chou-Talalay, co-exposure of orlistat and trastuzumab demonstrated strong synergistic effects (CI10-90 = 0.110-0.847), whereas sequential exposure to orlistat followed by trastuzumab (CI10-90 = 0.380-1.210) and trastuzumab followed by orlistat (CI10-90 = 0.605-1.278) mainly showed additive or antagonistic interactions. Indeed, orlistat-induced FAS inhibition synergistically promoted apoptotic cell death when concurrently combined with trastuzumab as determined by an ELISA for histone-associated DNA fragments. Importantly, the degree of FAS expression in a panel of human breast cancer cell lines was predictive of sensitivity to orlistat-induced anti-proliferative effects as determined by a MTT-based characterization of metabolically viable breast cancer cells. Moreover, hypersensitivity to orlistat-induced cytotoxicity was observed in MCF-7 breast cancer cells engineered to overexpress Her2/neu (MCF-7/Her2-18 cells), which exhibit a significant up-regulation of FAS expression and activity.

CONCLUSIONS

These findings reveal that the development of more potent and/or bioavailable orlistat's variants targeting the lipogenic activity of FAS may open a novel therapeutic avenue for treating Her2/neu-overexpressing breast carcinomas.

Why does tumor-associated fatty acid synthase (oncogenic antigen-519) ignore dietary fatty acids?

The hyperactivation of fatty acid synthase (FAS)-catalyzed de novo biosynthesis of fatty acids is a molecular marker linked to tumor virulence in population studies of human malignancies. This activation appears to be linked to neoplastic transformation, since high levels of FAS have also been identified in pre-malignant lesions. This dependence of cancer upon accelerated lipogenesis differs from normal human tissues, in which FAS is suppressed by the presence of small amounts of fatty acids in the diet. The molecular mechanisms by which cancer cells constitutively exhibit FAS overexpression and hyperactivity have begun to emerge. The active involvement of the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (MAPK ERK1/2) and phosphatidylinositol-3'-kinase (PI-3'K)/protein kinase B (AKT) transduction cascades in the overexpression of FAS has been recently demonstrated in several cancer cell models. Strikingly, insulin-regulated stimulation of FAS expression in adipose cells is also mediated by the PI-3'K pathway with AKT being involved as a downstream effector. Moreover, FAS overexpression in tumor cells has been demonstrated to occur through a modification of the transcription factor sterol regulatory element-binding protein-1c (SREBP-1c), the major regulatory factor of FAS in liver and adipose tissues, which, in turn, is known to be regulated by MAPK ERK1/2 and PI-3'K/AKT pathways. Therefore, the signal transduction pathways regulating FAS expression in normal and cancer cells seem to share several downstream elements. However, the upstream mechanisms controlling FAS expression in cancer cells must be different from those in normal tissues, since tumor-associated FAS expression seems to be insensitive to nutritional signals. In pre-neoplastic lesions, we hypothesize that the early activation of FAS in pre-malignant cells represents a survival strategy which occurs to compensate for an insufficiency of both oxygen and dietary fatty acids due to, e.g., lack of angiogenesis. Thus, FAS activation reflects an epigenetic dysregulation of the lipogenic pathway in response to the microenvironment of tumors containing regions of poor oxygenation. Upon this unusual metabolic situation, FAS up-regulation also represent a metabolic strategy to maintain high proliferation rates of surviving cells in the absence of exogenous dietary fatty acids. Concomitantly, a variety of oncogenic changes (H-ras, erb B-2, etc.) may result in the constitutive activation of MAPK and PI-3'K/AKT signaling cascades, which, in turn, can activate SREBP-1c and, subsequently, tumor-associated FAS-catalyzed endogenous lipogenesis. Thereafter, high levels of FAS are maintained in coordination with increased demand for fatty acid metabolism and/or membrane synthesis in response to cancer-related overexpression of growth factors (e.g., EGF, heregulin) and/or growth factor receptors (e.g., EGFR, Her-2/neu). The aberrant MAPK and PI-3'K/AKT cascades driven by these oncogenic changes subvert the downregulatory effects of physiological concentrations of dietary fatty acids, resulting in a cancer-associated FAS insensitivity to nutritional signals. This model does not exclude that fundamental differences in the ability of FAS gene to respond to normal fatty acid's downregulatory actions may also synergistically interact with oncogenic signals to constitutively maintain an elevated FAS-dependent de novo endogenous fatty acid biogenesis in cancer cells in spite of high levels of circulating dietary fatty acids.

Human fatty acid synthase: structure and substrate selectivity of the thioesterase domain

Human fatty acid synthase is a large homodimeric multifunctional enzyme that synthesizes palmitic acid. The unique carboxyl terminal thioesterase domain of fatty acid synthase hydrolyzes the growing fatty acid chain and plays a critical role in regulating the chain length of fatty acid released. Also, the up-regulation of human fatty acid synthase in a variety of cancer makes the thioesterase a candidate target for therapeutic treatment. The 2.6-A resolution structure of human fatty acid synthase thioesterase domain reported here is comprised of two dissimilar subdomains, A and B. The smaller subdomain B is composed entirely of alpha-helices arranged in an atypical fold, whereas the A subdomain is a variation of the alpha/beta hydrolase fold. The structure revealed the presence of a hydrophobic groove with a distal pocket at the interface of the two subdomains, which constitutes the candidate substrate binding site. The length and largely hydrophobic nature of the groove and pocket are consistent with the high selectivity of the thioesterase for palmitoyl acyl substrate. The structure also set the identity of the Asp residue of the catalytic triad of Ser, His, and Asp located in subdomain A at the proximal end of the groove.

Inhibition of fatty acid synthase (FAS) suppresses HER2/neu (erbB-2) oncogene overexpression in cancer cells

Fatty acid synthase (FAS) activity is a potential therapeutic target to treat cancer and obesity. Here, we have identified a molecular link between FAS and HER2 (erbB-2) oncogene, a marker for poor prognosis that is overexpressed in 30% of breast and ovarian cancers. Pharmacological FAS inhibitors cerulenin and C75 were found to suppress p185(HER2) oncoprotein expression and tyrosine-kinase activity in breast and ovarian HER2 overexpressors. Similarly, p185(HER2) expression was dramatically down-regulated when FAS gene expression was silenced by using the highly sequence-specific mechanism of RNA interference (RNAi). Pharmacological and RNAi-mediated silencing of FAS specifically down-regulated HER2 mRNA and, concomitantly, caused a prominent up-regulation of PEA3, a transcriptional repressor of HER2. A cytoplasmic redistribution of p185(HER2) was associated with marked morphological changes of FAS RNAi-transfected cells, whereas chemical inhibitors of FAS promoted a striking nuclear accumulation of p185(HER2). The simultaneous targeting of FAS and HER2 by chemical FAS inhibitors and the humanized antibody directed against p185(HER2) trastuzumab, respectively, was synergistically cytotoxic toward HER2 overexpressors. Similarly, concurrent RNAi-mediated silencing of FAS and HER2 genes synergistically stimulated apoptotic cell death in HER2 overexpressors. p185(HER2) was synergistically down-regulated after simultaneous inhibition of FAS and HER2 by either pharmacological inhibitors or small interfering RNA. These findings provide evidence of an active role of FAS in cancer evolution by specifically regulating oncogenic proteins closely related to malignant transformation, strongly suggesting that HER2 oncogene may act as the key molecular sensor of energy imbalance after the perturbation of tumor-associated FAS hyperactivity in cancer cells.

Inhibition of tumor-associated fatty acid synthase activity antagonizes estradiol- and tamoxifen-induced agonist transactivation of estrogen receptor (ER) in human endometrial adenocarcinoma cells

Overexpression of the lipogenic enzyme fatty acid synthase (FAS) is a common molecular feature in subsets of sex-steroid-related tumors including endometrium and breast carcinomas that are associated with poor prognosis. Pharmacological inhibition of tumor-associated FAS hyperactivity is under investigation as a chemotherapeutic target. We examined the effects of the mycotoxin cerulenin (a covalent FAS inactivator), and the novel small compound C75 (a slow-binding FAS inhibitor) on estradiol (E2)- and tamoxifen (TAM)-stimulated ER-driven molecular responses in Ishikawa cells, an in vitro model of well-differentiated human endometrial carcinoma. We evaluated the effects of FAS inhibition on E2- and TAM-induced estrogen receptor (ER) transcriptional activity by using transient cotransfection assays with an estrogen-response element reporter construct (ERE-Luciferase). Antiestrogenic effects of cerulenin and C75 were observed by dose-dependent inhibition of E2-stimulated ERE-dependent transcription, whereas FAS inhibitors did not significantly increase the levels of ERE transcriptional activity in the absence of E2. Moreover, pharmacological blockade of FAS activity completely abolished TAM-stimulated ERE activity. To address the reliability of transient transfection assays, the effects of FAS inhibitors on E2-inducible gene products were evaluated. FAS blockade induced a dose-dependent decrease in E2-inducible alkaline phosphatase activity. E2-stimulated accumulation of progesterone receptor (PR) and HER-2/neu oncogene was abolished in the presence of FAS blockers. FAS inhibition also resulted in a marked downregulation of E2-stimulated ERalpha expression, and noticeably impaired E2-induced ERalpha nuclear accumulation. A dose-dependent decrease in cell proliferation and cell viability was observed after FAS blockade. A Cell Death ELISA, detecting DNA fragmentation, demonstrated that FAS inhibitors stimulated apoptosis of Ishikawa cells. The analysis of critical E2- and TAM-related cell cycle proteins revealed an increase of both the expression and the nuclear accumulation of cyclin-dependent kinase inhibitors p21WAF1/CIP1 and p27Kip1 following FAS inhibition. To rule out non-FAS cerulenin- and C75-related effects, we finally monitored ER signaling after silencing of FAS gene expression using the highly sequence-specific mechanism of RNA interference (RNAi). The concentrations of E2 and TAM inducing half-maximal ERE activity (EC50) dramatically increased (>100 times) in FAS RNAi-transfected Ishikawa cells. Moreover, depletion of FAS by RNAi also caused loss of ERalpha expression, downregulation of PR, and accumulation of p21WAF1/CIP1 and p27Kip1 in E2-stimulated Ishikawa cells. If chemically stable FAS inhibitors or cell-selective vector systems able to deliver RNAi targeting FAS gene demonstrate systemic anticancer effects in vivo, our results render FAS as a novel target for the prevention and treatment of endometrial carcinoma.

Fatty acid synthase expression and clinicopathological findings in endometrial cancer

BACKGROUND

Over-expression of fatty acid synthase (FAS), the enzyme involved in the anabolic conversion of dietary carbohydrates to fatty acid, has been reported in many human malignancies. This study investigated whether clinicopathological findings [histological grade, myometrial invasion, vessel permeation, lymphatic permeation, nodal metastasis, and Federation of International Gynecologic Obstetrics (FIGO) stage] and body fat distribution differ with the level of FAS expression in endometrial cancer.

METHODS

Subjects were 73 postmenopausal women (mean age, 62.2 +/- 7.4 years; range, 49-75 years) with endometrioid adenocarcinoma. Baseline characteristics included age, height, body weight (BW), body mass index (BMI), and years since menopause (YSM). Percentage of body fat and the trunk-leg fat mass ratio were measured by dual-energy X-ray absorptiometry. FAS expression was determined using immunohistochemical methods in formalin-fixed and paraffin-embedded cancer specimens. FAS expression was defined as none, low, and high.

RESULTS

Sixty-six (90.4%) cases showed positive FAS status. Sixty-nine percent of cases showed myometrial invasion > or =1/2, 50% of cases showed myometrial invasion <1/2, and 23% of cases without myometrial invasion demonstrated a positive FAS status. Lymphatic permeation, vessel permeation, nodal metastasis, and advancing FigO stage were associated with FAS status. The trunk-leg fat ratio and BMI in high and low FAS status groups were significantly greater than that in those not expressing FAS (p < 0.05). However, age, height, weight, YSM, and percentage of body fat did not differ with FAS status.

CONCLUSION

FAS expression in endometrial cancer is associated with cancer progression and upper body fat distribution.

Inhibition of tumor-associated fatty acid synthase hyperactivity induces synergistic chemosensitization of HER -2/ neu -overexpressing human breast cancer cells to docetaxel (taxotere)

The lipogenic enzyme fatty acid synthase (FAS) is differentially overexpressed and hyperactivated in a biologically aggressive subset of breast carcinomas and minimally in most normal adult tissues, rendering it an interesting target for antineoplastic therapy development. Recently, a molecular connection between the HER -2/ neu (c- erb B-2) oncogene and FAS has been described in human breast cancer cells. Here, we examined the relationship between breast cancer-associated FAS hyperactivity and HER -2/ neu -induced breast cancer chemoresistance to taxanes. Co-administration of docetaxel (Taxotere) and the mycotoxin cerulenin, a potent and non-competitive inhibitor of FAS activity, demonstrated strong synergism in HER -2/ neu -overexpressing and docetaxel-resistant SK-Br3 cells, modest synergism in moderately HER -2/ neu -expressing MCF-7 cells, and it showed additive effects in low HER -2/ neu -expressing and docetaxel-sensitive MDA-MB-231 cells. Sequential exposure to cerulenin followed by docetaxel again yielded strong synergism in SK-Br3 cells, whereas antagonistic and moderate synergistic interactions were observed in MCF-7 and MDA-MB-231 cells, respectively. Importantly, inhibition of FAS activity dramatically decreased the expression of HER -2/ neu oncogene in SK-Br3 breast cancer cells. To the best of our knowledge this is the first study demonstrating that FAS is playing an active role in HER -2/ neu -induced breast cancer chemotherapy resistance.

A fatty acid synthase blockade induces tumor cell-cycle arrest by down-regulating Skp2

In eukaryotes, fatty acid synthase (FAS) is the enzyme responsible for synthesis of palmitate, the precursor of long-chain nonessential fatty acids. FAS is up-regulated in a wide range of cancers and has been suggested as a relevant drug target. Here, two independent approaches are taken toward knocking down FAS and then probing its connection to tumor cell proliferation. In one approach, Orlistat, a drug approved for treating obesity, is used as a potent inhibitor of the thioesterase function of FAS. In a separate strategy, the expression of FAS is suppressed by targeted knock-down with small interfering RNA. In both circumstances, the ablation of FAS activity causes a dramatic down-regulation of Skp2, a component of the E3 ubiquitin ligase that controls the turnover of p27Kip1. These effects ultimately tie into the retinoblastoma protein pathway and lead to a cell-cycle arrest at the G1/S boundary. Altogether, the findings of the study reveal unappreciated links between fatty acid synthase and ubiquitin-dependent proteolysis of cell-cycle regulatory proteins.

Orlistat is a novel inhibitor of fatty acid synthase with antitumor activity

One of the fundamental principles of pharmacology is that most drugs have side effects. Although considerable attention is paid to detrimental side effects, drugs can also have beneficial side effects. Given the time and expense of drug development, it would be particularly exciting if a systematic method could be applied to reveal all of the activities, including the unappreciated actions, of a potential drug. The present study takes the first step along this path. An activity-based proteomics strategy was used to simultaneously identify targets and screen for their inhibitors in prostate cancer. Orlistat, a Food and Drug Administration-approved drug used for treating obesity, was included in this screen. Surprisingly, we find a new molecular target and a potential new application for Orlistat. Orlistat is a novel inhibitor of the thioesterase domain of fatty acid synthase, an enzyme strongly linked to tumor progression. By virtue of its ability to inhibit fatty acid synthase, Orlistat halts tumor cell proliferation, induces tumor cell apoptosis, and inhibits the growth of PC-3 tumors in nude mice.

A new model ELISA, based on two monoclonal antibodies, for quantification of fatty acid synthase

A new model ELISA, based on two monoclonal antibodies, was developed for the quantification of fatty acid synthase (FAS). In this sandwich assay, a monoclonal antibody M6 was used as a capture on Nunc MaxiSorp ELISA/EIA Modules and another monoclonal antibody M3, labeled with biotin, was used as a detection antibody. More than 10 molecules of biotin were labeled on the anti-FAS monoclonal antibody using modified biotinylation conditions. The within- and between-run CVs were less than 10%, and the detection limit was 3.22 ng/mL. Recoveries were 98.54-121.95%, averaging 106.05%. The average FAS concentration obtained from the total 55 healthy volunteers blood was 4.07 +/- 1.81 ng/mL, 4.25 +/- 2.14 ng/mL in women (n = 37) and 3.70 +/- 0.74 ng/mL in men (n = 18). When compared with the previously developed polyclonal-monoclonal ELISA, a different pattern of FAS levels was observed in the supernatant of two cultured breast cancer cell lines in a time course study and there was no linear correlation between the two assays using 215 human blood samples. Thus, this new model FAS-ELISA could be used as an independent assay in measuring clinical samples. In summary, this monoclonal-monoclonal FAS-ELISA is sensitive, accurate, and precise in quantification of fatty acid synthase and has potential as a complementary tool in testing clinical samples.

Expression of the lipogenic enzyme fatty acid synthase (FAS) as a predictor of poor outcome in nephroblastoma: an interinstitutional study

BACKGROUND

Treatment of nephroblastoma (Wilms tumor) has presently achieved a greater than 80% cure rate. Pathologic stage and grade are considered the most reliable prognostic parameters, but other biologic factors are under study in order to improve patient stratification into risk groups. Correlation of elevated levels of the lipogenic enzyme fatty acid synthase (FAS) with aggressiveness of some cancers has drawn attention to this enzyme as a possible marker of poor prognosis.

PROCEDURE

To determine the predictive strength of FAS expression in Wilms tumor (with particular emphasis on intermediate risk, i.e., non anaplastic tumors, the vast majority of nephroblastomas), we evaluated immunostaining expression in archival specimens from 94 neoplasms. The degree of expression was correlated with stage, grade, clinical course and administration of prenephrectomy chemotherapy.

RESULTS

Expression of FAS increased in anaplastic tumors (P = 0.043) and higher stages (P = 0.029). FAS expression correlated with OS and DFS at both univariate and multivariate analysis. Comparable results were obtained when analyzing the intermediate risk population separately. Pretreatment resulted in an increased FAS expression, without reaching significance level (P = 0.059).

CONCLUSIONS

Expression of FAS might be an independent prognostic factor, particularly for intermediate-risk patients. The blockade of fatty acid synthesis by inhibition of FAS enzymatic function by means of metabolic analogues might prove a novel target pathway for the treatment of nephroblastoma.

Fatty acid synthase is highly expressed in carcinoma, adenoma and in regenerative epithelium and intestinal metaplasia of the stomach

AIMS

To investigate the relation of fatty acid synthase (FAS) expression to the clinicopathological characteristics of gastric cancers and gastric tumorigenesis.

METHODS AND RESULTS

FAS expression was examined immunohistochemically in 626 gastric cancers, 51 gastric adenomas, and non-neoplastic epithelium contiguous with cancer tissue including normal foveolae, intestinal metaplasia, regenerative epithelium, and gastric glands. FAS expression was found in more than 70% of gastric cancers. Interestingly, it occurred preferentially in differentiated carcinomas, male cases, and in patients over 51 years old. Although previous reports showed that FAS expression is closely related to cancer progression, in gastric cancers FAS expression had no relationship with prognosis, cancer progression as indicated by depth of invasion, venous and lymphatic permeation, and distant metastasis. Gastric tubular adenoma and intestinal metaplasia, which are thought to be associated with well-differentiated gastric carcinomas, showed a frequency of FAS expression similar to that of differentiated carcinomas; however, normal foveolae and gastric glands showed no or less FAS expression.

CONCLUSIONS

FAS expression occurs at the early stage of tumorigenesis and plays important roles in the formation of precancerous foci rather than in the progression of carcinoma of the stomach.

Androgens stimulate lipogenic gene expression in prostate cancer cells by activation of the sterol regulatory element-binding protein cleavage activating protein/sterol regulatory element-binding protein pathway

Using two independent prostate cancer cell lines (LNCaP and MDA-PCa-2a), we demonstrate that coordinated stimulation of lipogenic gene expression by androgens is a common phenomenon in androgen-responsive prostate tumor lines and involves activation of the sterol regulatory element-binding protein (SREBP) pathway. We show 1) that in both cell lines, androgens stimulate the expression of fatty acid synthase and hydroxymethylglutaryl-coenzyme A synthase, two key lipogenic genes representative for the fatty acid and the cholesterol synthesis pathway, respectively; 2) that treatment with androgens results in increased nuclear levels of active SREBP; 3) that the effects of androgens on promoter-reporter constructs derived from both lipogenic genes (fatty acid synthase and hydroxymethylglutaryl-coenzyme A synthase) depend on the presence of intact SREBP-binding sites; and 4) that cotransfection with dominant-negative forms of SREBPs abolishes the effects of androgens. Related to the mechanism underlying androgen activation of the SREBP pathway, we show that in addition to minor effects on SREBP precursor levels, androgens induce a major increase in the expression of sterol regulatory element-binding protein cleavage-activating protein (SCAP), an escort protein that transports SREBPs from their site of synthesis in the endoplasmic reticulum to their site of proteolytical activation in the Golgi. Both time course studies and overexpression experiments showing that increasing levels of SCAP enhance the production of mature SREBP and stimulate lipogenic gene expression support the contention that SCAP plays a pivotal role in the lipogenic effects of androgens in tumor cells.

Fatty acid synthase (FAS) expression in human breast cancer cell culture supernatants and in breast cancer patients

Fatty acid synthase (FAS) is selectively expressed in certain human cancers, including carcinoma of the breast, prostate, colon, ovary, and endometrium, compared to normal human tissues and therefore is a putative tumor marker. In this study, we found FAS concentrations were elevated in cell culture supernatants during cell growth in two human breast cancer cell lines but not other cancer cell lines. A quantitative enzyme-linked immunosorbent assay and Western blot analysis were employed in this study. In addition, serum FAS levels were significantly higher in breast cancer patients with different clinical stages (Stage II: 0.59+/-0.09 units/l, Stage III: 0.79+/-0.13 units/l, and Stage IV: 1.39+/-0.35 units/l) compared with healthy subjects (0.27+/-0.02 units/l, P<0.05). Taken together, our data suggest that FAS expression may be a useful tumor marker for breast cancer and play a role in assessing cancer virulence.

Two-site ELISA for the quantitative determination of fatty acid synthase

Fatty acid synthase (FAS) is an enzyme which plays a central role in the de novo biosynthesis of fatty acids. FAS is selectively expressed in certain human cancers and therefore is a putative tumor marker. We developed an enzyme-linked immunosorbent assay (ELISA) for measuring FAS, and investigated its expression and clinical features. In this two-site sandwich ELISA, a polyclonal antibody was used as a capture on Nunc MaxiSorp ELISA/EIA modules and a monoclonal antibody labeled with biotin was used as a signal antibody. The assay was linear with no cross-reactivity with other tumor markers. The within- and between-run CVs were <10%, and the detection limit was 0.15 arbitrary Units/l. Recoveries were 92.4-105.1%. FAS was stable in buffer at 4 degrees C for more than 10 days and stable at 37 degrees C for 2 days. In human serum, FAS levels were significantly higher in patients with breast (1.01+/-0.71 Units/l, mean+/-S.D.), prostate (0.79+/-0.76 Units/l), colon (0.89+/-0.49 Units/l), and ovarian (0.84+/-0.9 Units/l) cancers compared to normal subjects (0.27+/-0.09 Units/l, P<0.01). This assay is sensitive, accurate, and precise and can distinguish between patients with various types of cancer and normal subjects.

Stimulation of tumor-associated fatty acid synthase expression by growth factor activation of the sterol regulatory element-binding protein pathway

Increased expression of fatty acid synthase (FAS) is observed in a clinically aggressive subset of various common cancers and interference with FAS offers promising opportunities for selective chemotherapeutic intervention. The mechanisms by which FAS expression is (up)-regulated in these tumors remain, however, largely unknown. Recently we demonstrated that in LNCaP prostate cancer cells FAS expression is markedly elevated by androgens via an indirect pathway involving sterol regulatory element-binding proteins (SREBPs). Here, we also show that growth factors such as EGF are able to stimulate FAS mRNA, protein and activity. Several observations also indicate that the effects of EGF on FAS expression are ultimately mediated by SREBPs. EGF stimulates SREBP-1c mRNA expression and induces an increase in mature nuclear SREBP-1. Moreover, in transient transfection studies EGF stimulates the transcriptional activity of a 178 bp FAS promoter fragment harboring a complex SREBP-binding site. Deletion or mutation of this binding site abolishes these effects and ectopic expression of dominant negative SREBP-1 inhibits FAS expression and induction in intact LNCaP cells. Given the frequent dysregulation of growth factor signaling in cancer and the key role of SREBP-1 in lipid homeostasis, growth factor-induced activation of the SREBP pathway is proposed as one of the mechanisms responsible for up-regulation of lipogenic gene expression in a subset of cancer cells.

Identification of a novel FAS/ER-alpha fusion transcript expressed in human cancer cells

A semi-nested reverse transcriptase-polymerase chain reaction (RT-PCR) was applied to evaluate the presence of estrogen receptor-alpha (ER-alpha) in human prostate cancer cells. Unexpectedly, a novel fatty acid synthase (FAS)/ER-alpha fusion transcript was identified, in which the N-terminus of FAS was fused in-frame with the C-terminus of ER-alpha. The existence of the FAS/ER-alpha transcript was further confirmed by RT-PCR analysis using various sets of amplification primers and different reverse-transcribed primers in the presence of dimethyl sulfoxide to eliminate the secondary structure of RNA. The predicted FAS/ER-alpha protein would contain largely domain I of FAS and the entire ligand binding domain of ER-alpha. The FAS/ER-alpha was expressed in a variety of human cancer cell lines including prostate, breast, cervical and bladder cancer cell lines. Our data suggest that the presence of FAS/ER-alpha may complicate the FAS and the ER-alpha signalling pathway.

Synthesis and antitumor activity of an inhibitor of fatty acid synthase

Compared to normal human tissues, many common human cancers, including carcinoma of the colon, prostate, ovary, breast, and endometrium, express high levels of fatty acid synthase (FAS, EC ), the primary enzyme responsible for the synthesis of fatty acids. This differential expression of FAS between normal tissues and cancer has led to the notion that FAS is a target for anticancer drug development. Recent studies with C75, an inhibitor of fatty acid synthesis, have shown significant antitumor activity with concomitant inhibition of fatty acid synthesis in tumor tissue and normal liver. Importantly, histopathological analysis of normal tissues after C75 treatment showed no adverse effects on proliferating cellular compartments, such as bone marrow, gastrointestinal tract, skin, or lymphoid tissues. In this study, we describe the de novo synthesis of C75 based on the known mechanism of action of cerulenin and the theoretical reaction intermediates of the beta-ketoacyl synthase moiety of FAS. In addition, we demonstrate that C75 is a synthetic, chemically stable inhibitor of FAS. C75 inhibits purified mammalian FAS with characteristics of a slow-binding inhibitor and also inhibits fatty acid synthesis in human cancer cells. Treatment of human breast cancer cells with [5-(3)H]C75 demonstrates that C75 reacts preferentially with FAS in whole cells. Therefore, we have shown that the primary mechanism of the antitumor activity of C75 is likely mediated through its interaction with, and inhibition of, FAS. This development will enable the in vivo study of FAS inhibition in human cancer and other metabolic diseases.

Progestins and androgens increase expression of Spot 14 in T47-D breast tumor cells

Enhanced expression of fatty acid synthase and other lipogenic enzymes has been observed in a subset of breast cancers with poor prognosis. This phenomenon has been related to amplification of a gene on chromosome region 11q13 encoding Spot 14, a putative regulator of lipogenic enzyme expression. In this paper we demonstrate that the induction of lipogenesis by progestins and androgens in the breast cancer cell line T47-D is accompanied by a marked increase in the expression of Spot 14. These data corroborate the correlation between Spot 14 expression and increased lipogenesis. Moreover they show that apart from gene amplification there is another steroid-regulated pathway that may enhance Spot 14 expression and lipogenesis in tumor cells.

Fatty-acid synthase and human cancer: new perspectives on its role in tumor biology

This review documents the changing perspectives on the function of fatty-acid synthase and fatty-acid synthesis in human tumor biology. With the recent discovery that human cancer cells express high levels of fatty-acid synthase and undergo significant endogenous fatty-acid synthesis, our understanding of the role of fatty acids in tumor biology is expanding. Once considered largely an anabolic-energy-storage pathway, fatty-acid synthesis is now associated with clinically aggressive tumor behavior and tumor-cell growth and survival and has become a novel target pathway for chemotherapy development. These findings will ultimately enhance our understanding of fatty acids in tumor biology and may provide new diagnostic and therapeutic moieties for patient care.