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

[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.

Fatty acid synthase: association with insulin resistance, type 2 diabetes, and cancer

BACKGROUND

An emerging paradigm supports the notion that deregulation of fatty acid synthase (FASN)-catalyzed de novo FA biogenesis could play a central role in the pathogenesis of metabolic diseases sharing the hallmark of insulin-resistance.

CONTENT

We reviewed pharmacological and genetic alterations of FASN activity that have been shown to significantly influence energy expenditure rates, fat mass, insulin sensitivity, and cancer risk. This new paradigm proposes that insulin-resistant conditions such as obesity, type 2 diabetes, and cancer arise from a common FASN-driven "lipogenic state". An important question then is whether the development or the progression of insulin-related metabolic disorders can be prevented or reversed by the modulation of FASN status. If we accept the paradigm of FASN dysfunction as a previously unrecognized link between insulin resistance, type 2 diabetes, and cancer, the use of insulin sensitizers in parallel with forthcoming FASN inhibitors should be a valuable therapeutic approach that, in association with lifestyle interventions, would concurrently improve energy-flux status, ameliorate insulin sensitivity, and alleviate the risk of lipogenic carcinomas.

CONCLUSIONS

Although the picture is currently incomplete and researchers in the field have plenty of work ahead, the latest clinical and experimental evidence that we discuss illuminates a functional and drug-modifiable link that connects FASN-driven endogenous FA biosynthesis, insulin action, and glucose homeostasis in the natural history of insulin-resistant pathologies.

AMPK-sensed cellular energy state regulates the release of extracellular Fatty Acid Synthase

Fatty Acid Synthase (FASN), a 250-kDa cytosolic multi-enzyme catalyzing eukaryotic de novo FA biogenesis, unexpectedly localizes in cancer cell culture supernatants and in the blood of cancer patients. High levels of "extracellular FASN" have recently been found in supernatants from Hepatitis C Virus-infected liver cells. The ultimate mechanism regulating FASN release, however, remained completely undefined. When the AMPK-activating drug AICAR was used to simulate an elevated AMP/ATP ratio in breast cancer cells, ELISA-based analyses revealed that extracellular FASN dramatically augmented in a dose- and time-dependent manner. Immunoblotting procedures using a battery of anti-FASN antibodies further confirmed that, in response to AMPK activation, FASN protein is depleted from the cytosol to accumulate as different FASN isoforms in the extracellular milieu. siRNA-induced blockade of AMPK expression largely attenuated AICAR-promoted FASN release. FASN release might represent a previously unrecognized mechanism through which AMPK monitor and restores cellular energy state in response to increasing AMP/ATP ratios.

Fatty acid synthase is up-regulated during hepatitis C virus infection and regulates hepatitis C virus entry and production

Hepatitis C virus (HCV) is a major human pathogen that causes serious illness, including acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Using a mass spectrometry-based proteomics approach, we have identified 175 proteins from a cell culture supernatant fraction containing the HCV genotype 2a (JFH1) virus, among which fatty acid synthase (FASN), the multifunctional enzyme catalyzing the de novo synthesis of fatty acids, was confirmed to be highly enriched. Subsequent studies showed that FASN expression increased in the human hepatoma cell line, Huh7, or its derivative, upon HCV infection. Blocking FASN activity by C75, a pharmacological FASN inhibitor, led to decreased HCV production. Reduction of FASN by RNA interference suppressed viral replication in both replicon and infection systems. Remarkably, FASN appeared to be selectively required for the expression of claudin-1, a tight junction protein that was recently identified as an entry coreceptor for HCV, but not for the expression of another HCV coreceptor, CD81. The decrease in Claudin-1 expression resulting from FASN inhibition was accompanied by a decrease in transepithelial electric resistance of Huh7 cells, implying a reduction in the relative tightness of the cell monolayer. Consequently, the entry of human immunodeficiency virus-HCV pseudotypes was significantly inhibited in C75-treated Huh7 cells.

CONCLUSION

As far as we know, this is the first line of evidence that demonstrates that HCV infection directly induces FASN expression, and thus suggests a possible mechanism by which HCV infection alters the cellular lipid profile and causes diseases such as steatosis.

The extract of leaves ofAcer truncatum Bunge: A natural inhibitor of fatty acid synthase with antitumor activity

Fatty acid synthase (FAS) has been identified as a potential antitumor target. The extract from the leaves of Acer truncatum Bunge (Extr) was prepared to assay its inhibitory activity against FAS, which was isolated from duck liver, and the correlated antitumor bioactivity. Its inhibition of FAS is composed of reversible fast-binding inhibition, IC50 = 0.7 microg/ml, and irreversible slow-binding inhibition following saturation kinetics with a dissociation constant of 0.68 microg/ml and a limiting rate constant of 0.0288 min(-1). The Extr exhibited different type of inhibitions against the three substrates in the FAS overall reaction. Compared with EGCG in inhibition constant and IC50 value, the Extr appeared to be a more efficient inhibitor, and exhibited a considerable inhibition against the growth of four kinds of cancer cells (patent application number 200510068054.2). It was infered that the inhibitory activity is likely attributable to the co-operative effect of the components.

Creating a fatty acid methyl ester database for lipid profiling in a single drop of human blood using high resolution capillary gas chromatography and mass spectrometry

Capillary gas chromatography (CGC) in combination with mass spectrometry (MS) was optimized for the separation and detection of the fatty acids occurring in the lipid fraction of blood. A fingertip blood sample (ca. 50 microL) was transesterified into the methyl esters and analyzed on a 100 m x 0.25 mm ID column coated with a biscyanopropyl polysiloxane (HP-88) stationary phase. The method was retention time locked. Programmed temperature vaporization injection (PTV) in the solvent venting mode was applied to minimize the sample size, while maintaining high sensitivity. The total analysis time was ca. 60 min. Retention times and both electron impact (EI) and positive chemical ionization (PCI) mass spectrometry were combined to elucidate the fatty acids according to alkyl chain, degree of unsaturation and position of the double bonds. Using extracted ion chromatograms about 100 fatty acids and related compounds were detected in blood samples and most of them were identified. This work resulted in a very large fatty acid methyl esters database, containing retention time and mass spectral information that will be applied to metabolomic studies.

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.

Increased fatty acid synthase as a potential therapeutic target in multiple myeloma

OBJECTIVE

To determine fatty acid synthase (FAS) expression in human multiple myeloma and verify its potential as a therapeutic target in multiple myeloma.

METHODS

FAS expression was determined by immunohistochemistry, reverse-transcription polymerase chain reaction (RT-PCR) and immunoblot analysis in bone marrow samples obtained from 27 patients with multiple myeloma (MM patients) and peripheral blood mononuclear cells (PBMCs) obtained from 12 healthy donors. In parallel, additional analyses were performed on 2 human multiple myeloma cell lines, U266 and RPMI8226. U266 cells were treated with cerulenin at various concentrations (5 to 320 microg/ml) for 24 h, and metabolic activity was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Apoptosis was evaluated by dual Annexin V/PI (propidium iodide) labeling and flow cytometry (FCM) in U266 cells treated with 20 (g/ml cerulenin for 12 h or 24 h.

RESULTS

By immunohistochemistry, we found that 19 of 27 bone marrow samples obtained from MM patients expressed significantly high levels of FAS. Similarly, by RT-PCR, 22 of 27 bone marrow samples obtained from MM patients, U266 and RPMI8226 showed FAS expression, whereas PBMC samples from 12 healthy donors did not express detectable level of FAS. FAS protein expression was confirmed by immunoblot analysis in 16 of 27 bone marrow samples obtained from MM patients, U266 and RPMI8226 cell lines, and no FAS protein expression was detected in PBMC samples from 12 healthy donors. U266 cells were highly sensitive to cerulenin treatment, with a dosage-related effect on metabolic activity, as a measure for cell proliferation. U266 cells treated with 20 microg/ml cerulenin for 12 and 24 h also showed early sign of apoptosis with 56.9% and 69.3% Annexin V(+)/PI(-) cells, and late apoptotic and necrotic cells with 3.2% and 17.6% Annexin V(+)/PI(+) cells.

CONCLUSION

Increased FAS expression existed in multiple myeloma samples and human myeloma cell lines. Cerulenin greatly inhibited metabolic activity/cell proliferation of U266 cells and induced apoptosis, suggesting that FAS is an effective target for pharmacological therapy in human multiple myeloma.

Fatty acid synthase over expression is an indicator of tumor aggressiveness and poor prognosis in renal cell carcinoma

PURPOSE

Fatty acid synthase is a key enzyme in the de novo biosynthesis of fatty acids. Increased fatty acid synthase expression and its association with tumor aggressiveness and poor prognosis have been demonstrated in various human malignant tumors. We investigated fatty acid synthase expression in patients with renal cell carcinoma and its impact on clinicopathological parameters.

MATERIALS AND METHODS

Fatty acid synthase expression in 120 patients with renal cancer was examined by immunohistochemistry. The relationship between fatty acid synthase expression status and various clinicopathological parameters was analyzed. Survival analysis was performed using the log rank test and a Cox multivariate hazard model.

RESULTS

Of 120 tumors 18 (15%) showed positive fatty acid synthase expression, which was significantly associated with advanced pathological T stage (pT3-4, p = 0.0009), regional lymph node metastasis (p = 0.0429), distant metastasis (p = 0.0042), higher histological grade (G3, p = 0.0017) and microvascular invasion (p = 0.0357). Patients with positive fatty acid synthase expression had significantly shorter cancer specific survival than those with negative FAS expression (p <0.0001). Multivariate Cox proportional hazards model analysis demonstrated that positive fatty acid synthase expression was an independent predictor of shortened cancer specific survival (p = 0.0363, HR 3.736).

CONCLUSIONS

Increased FAS expression could be an indicator of tumor aggressiveness and poor prognosis of renal cell carcinoma. Patients with fatty acid synthase positive tumors should be followed closely and carefully, and adjuvant therapy should be considered.

Loss of heterozygosity of 17p13, with possible involvement of ACADVL and ALOX15B, in the pathogenesis of adrenocortical tumors

OBJECTIVE

To determine the minimal common region of loss on 17p13 in a cohort of adrenocortical carcinomas (ACCs) (defined by a Weiss score > or =3) and adrenocortical adenomas (ACAs) (defined by a Weiss score <3) and subsequently to assess 3 genes in this region that could be involved in adrenocortical tumorigenesis.

SUMMARY BACKGROUND DATA

Loss of heterozygosity (LOH) of 17p13 has been demonstrated to occur more frequently in ACCs compared with ACAs.

METHODS

Using 12 microsatellite markers across 17p13, LOH analysis was performed on 37 paired blood and adrenocortical tumor samples (23 ACC and 14 ACA samples) to determine the minimal common region of loss for ACCs and ACAs. From this minimal region of loss, 3 genes were selected for quantitative real time reverse transcription polymerase chain reaction analysis on 20 ACCs and 30 ACAs.

RESULTS

LOH at 17p13 was found in 74% of ACCs compared with 14% of ACAs. There was a 10.4-Mb common minimal region of loss in ACCs whereas no minimal region of loss in ACAs could be demonstrated. Expression of Acyl coenzyme-A dehydrogenase very long chain (ACADVL) and Arachidonate 15-lipoxygenase second type (ALOX15B) was significantly down-regulated in ACCs compared with ACAs whereas there was no difference in expression of Potassium channel tetramerization domain containing 11 (KCTD11) in ACCs and ACAs.

CONCLUSIONS

We demonstrated a minimal common region of loss of 10.4-Mb on 17p13 in ACCs and within this region, we found that ACADVL and ALOX15B expression are good discriminators between ACCs and ACAs.

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.

Evaluation of the inhibitory activities of aceraceous plants on fatty acid synthase

Fatty acid synthase (FAS) is a very significant lipogenic enzyme participating in energy metabolism in vivo and has been reported as a potential new therapeutic target for cancer treatment. The extracts from sixteen Aceraceae were prepared to assay their inhibitory activities against duck liver FAS and their correlated antitumor bioactivity. Their inhibition of FAS was composed of a reversible fast-binding inhibition, by which 0.41 microg/mL of the A. campestre extract inhibits 50% FAS activity, and an irreversible slow-binding inhibition with inactivation rate constants, k(obs), ranging between 1.5 x 10(-3) and 10.6 x 10(-3) min(-1). Three Aceraceae extracts were selected from their smaller IC50 values to study different type of inhibitions against the three substrates in the FAS overall reaction. As compared with other reported FAS inhibitors including EGCG with regard to inhibition constant and IC50 value, the extracts appeared to be more efficient inhibitors, and exhibited a considerable inhibition against the growth of five types of cancer cells (China patent application number 200610088901.6), which may be related to the inhibition of lipogenesis in these cells.

Delineation of molecular mechanisms of sensitivity to lapatinib in breast cancer cell lines using global gene expression profiles

Lapatinib (GW572016) is a small-molecule dual inhibitor of epidermal growth factor receptor (ErbB1) and ErbB2 receptor kinase activities currently in phase III clinical trials. We used phosphoprotein and microarray analyses to carry out targeted pathway studies of phosphorylation and gene expression changes in human breast cancer cell lines in the presence or absence of lapatinib. Studies were done in four breast cancer cell lines, two of which were responsive and two of which were nonresponsive to lapatinib. Responsive cell lines, BT474 and SKBr3, constitutively overexpress ErbB2 and show an IC(50) of 25 or 32 nmol/L for lapatinib, respectively. In contrast, nonresponsive MDA-MB-468 and T47D cells expressed a low basal level of ErbB2 and showed IC(50) values in the micromolar range. Cells responsive to lapatinib exhibited strong differential effects on multiple genes in the AKT pathway. After 12 h of exposure to 1.0 micromol/L of lapatinib, AKT1, MAPK9, HSPCA, IRAK1, and CCND1 transcripts were down-regulated 7- to 25-fold in responsive BT474 and SKBr3 cells. In contrast, lapatinib weakly down-regulated the AKT pathway in nonresponsive breast cancer cell lines (<5-fold down-regulation of most genes in the pathway). Furthermore, the proapoptotic gene FOXO3A, which is negatively regulated by AKT, was up-regulated 7- and 25-fold in lapatinib-responsive SKBr3 and BT474 cells, respectively. Phosphorylated Akt and Akt-mediated phosphorylation of FOXO3A also decreased in responsive breast cancer cell lines exposed to lapatinib. Gene expression profiling also revealed that lapatinib stimulated the expression of estrogen and progesterone receptors and modulated the expression of genes involved in cell cycle control, glycolysis, and fatty acid metabolism. In BT474 and T47D cells, which expressed moderate basal levels of the estrogen and progesterone receptors, 1.0 micromol/L of lapatinib induced expression by 7- to 11-fold. These data provide insight into the mechanism of action of lapatinib in breast cancer cells.

Inhibition of endothelial cell proliferation and angiogenesis by orlistat, a fatty acid synthase inhibitor

Orlistat, an antiobesity drug, is cytostatic and cytotoxic to tumor cells. The antitumor activity of orlistat can be attributed to its ability to inhibit the thioesterase domain of fatty acid synthase (FAS). The objective of the present study was to test the effect of orlistat on endothelial cell proliferation and angiogenesis. Orlistat inhibits endothelial cell FAS, blocks the synthesis of fatty acids, and prevents endothelial cell proliferation. More significantly, orlistat inhibits human neovascularization in an ex vivo assay, which suggests that it may be useful as an antiangiogenic drug. The mechanism of these effects can be traced to the fact that orlistat prevents the display of the vascular endothelial growth factor (VEGF) receptor (VEGFR2/KDR/Flk1) on the endothelial cell surface. Thus, orlistat is an antiangiogenic agent with a novel mechanism of action.

Fatty acid synthase: a novel target for antiglioma therapy

High levels of fatty acid synthase (FAS) expression have been observed in several cancers, including breast, prostate, colon and lung carcinoma, compared with their respective normal tissue. We present data that show high levels of FAS protein in human and rat glioma cell lines and human glioma tissue samples, as compared to normal rat astrocytes and normal human brain. Incubating glioma cells with the FAS inhibitor cerulenin decreased endogenous fatty acid synthesis by approximately 50%. Cell cycle analysis demonstrated a time- and dose-dependent increase in S-phase cell arrest following cerulenin treatment for 24 h. Further, treatment with cerulenin resulted in time- and dose-dependent decreases in glioma cell viability, as well as reduced clonogenic survival. Increased apoptotic cell death and PARP cleavage were observed in U251 and SNB-19 cells treated with cerulenin, which was independent of the death receptor pathway. Overexpressing Bcl-2 inhibited cerulenin-mediated cell death. In contrast, primary rat astrocytes appeared unaffected. Finally, RNAi-mediated knockdown of FAS leading to reduced FAS enzymatic activity was associated with decreased glioma cell viability. These findings suggest that FAS might be a novel target for antiglioma therapy.

Fatty acid synthase and cancer: new application of an old pathway

Fatty acid synthase (FAS), the sole mammalian enzyme capable of de novo fatty acid synthesis, is highly expressed in most human carcinomas. FAS is associated with poor prognosis in breast and prostate cancer, is elaborated into the blood of cancer patients, and its inhibition is selectively cytotoxic to human cancer cells. Thus, FAS and fatty acid metabolism in cancer has become a focus for the potential diagnosis and treatment of cancer.

Fatty acid synthase expression in Paget's disease of the vulva

We explored the immunohistochemical expression of fatty acid synthase (FAS) in Paget's disease of the vulva (PDV) and its association with clinico-pathological features. FAS is a recently discovered molecule involved in energy supply of normal cells. FAS is also overexpressed in neoplastic tissues because of their increased necessity of energy. Specimens from 20 patients with PDV were immunohistochemically evaluated; increased FAS expression was observed in 7 of 8 patients with invasive PDV (87%), in 3 of 4 patients with microinvasive PDV (75%), and in 1 of 8 patients with noninvasive PDV (12%). Statistical analysis revealed that increased FAS expression was associated with invasive PDV (p = 0.04). To our knowledge, this association of FAS in PDV is the first to be reported in literature. These observations reveal that FAS is a reliable marker of aggressiveness in PDV. The knowledge of FAS statistical association in invasive PDV is an important finding that may stratify these patients in different prognostic groups and determine therapeutic approaches for patient care.

KGF induces lipogenic genes through a PI3K and JNK/SREBP-1 pathway in H292 cells

Lipid synthesis is required for cell growth and is subject to pharmacologic regulation. Keratinocyte growth factor (KGF) stimulates proliferation and lipogenesis in H292 cells, a pulmonary epithelial cancer cell line, but the signaling pathways are not known. KGF stimulated the expression of the transcription factors sterol-regulatory element binding protein-1 (SREBP-1), CCAAT/enhancer binding protein alpha (C/EBPalpha), and C/EBPdelta and two key enzymes involved in lipogenesis, FAS and stearoyl coenzyme A desaturase-1 (SCD-1). We found that KGF induced rapid activation of Akt, p70 S6K, JNK, and extracellular signal-regulated (ERK). Induction of SREBP-1, SCD-1, and FAS by KGF was inhibited by the JNK inhibitor SP600125 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 but not by the ERK inhibitor PD98059. Using FAS and SCD-1-luciferase promoter constructs, we observed that KGF stimulated the transcription of these promoters and that exogenous cholesterol inhibited the induction. Mutation of the SREBP-1 binding site in the SCD-1 promoter abolished the effect of KGF on SCD-1 transcription. In addition, overexpression of active SREBP-1 directly stimulated SCD-1 and FAS. Conversely, adenovirus-mediated overexpression of a dominant negative form of SREBP-1 inhibited the KGF effect on FAS and SCD-1 expression. In summary, we conclude that KGF requires both PI3K and JNK signaling pathways to induce SREBP-1, which in turn induces SCD-1 and FAS expression in H292 cells.

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.

Molecular and prognostic distinction between serous ovarian carcinomas of varying grade and malignant potential

Profiles of gene transcription have begun to delineate the molecular basis of ovarian cancer, including distinctions between carcinomas of differing histology, tumor progression and patient outcome. However, the similarities and differences among the most commonly diagnosed noninvasive borderline (low malignant potential, LMP) lesions and invasive serous carcinomas of varying grade (G1, G2 and G3) have not yet been explored. Here, we used oligonucleotide arrays to profile the expression of 12,500 genes in a series of 57 predominantly stage III serous ovarian adenocarcinomas from 52 patients, eight with borderline tumors and 44 with adenocarcinomas of varying grade. Unsupervised and supervised analyses showed that LMP lesions were distinct from high-grade serous adenocarcinomas, as might be expected; however, well-differentiated (G1) invasive adenocarcinomas showed a strikingly similar profile to LMP tumors as compared to cancers with moderate (G2) or poor (G3) cellular differentiation, which were also highly similar. Comparative genomic hybridization of an independent cohort of five LMP and 63 invasive carcinomas of varying grade demonstrated LMP and G1 were again similar, exhibiting significantly less chromosomal aberration than G2/G3 carcinomas. A majority of LMP and G1 tumors were characterized by high levels of p21/WAF1, with concomitant expression of cell growth suppressors, gadd34 and BTG-2. In contrast, G2/G3 cancers were characterized by the expression of genes associated with the cell cycle and by STAT-1-, STAT-3/JAK-1/2-induced gene expression. The distinction between the LMP-G1 and G2-G3 groups of tumors was highly correlated to patient outcome (chi(2) for equivalence of death rates=7.681189; P=0.0056, log-rank test). Our results are consistent with the recent demonstration of a poor differentiation molecular 'meta-signature' in human cancer, and underscore a number of cell-cycle- and STAT-associated targets that may prove useful as points of therapeutic intervention for those patients with aggressive disease.

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.

The galloyl moiety of green tea catechins is the critical structural feature to inhibit fatty-acid synthase

It has been reported that inhibition of fatty-acid synthase (FAS) is selectively cytotoxic to human cancer cells. Considerable interest has developed in identifying novel inhibitors of this enzyme complex. Our previous work showed that green tea (-)-epigallocatechin gallate can inhibit FAS in vitro. To elucidate the structure-activity relationship of the inhibitory effects of tea polyphenols, we investigated the inhibition kinetics of the major catechins and analogues. Ungallated catechins from green tea do not show obvious inhibition compared with gallated catechins. Another gallated catechin, (-)-epicatechin gallate, was also found as a potent inhibitor of FAS and its inhibition characteristics are similar to (-)-epigallocatechin gallate. Furthermore, the analogues of galloyl moiety without the catechin skeleton such as propyl gallate also showed obvious slow-binding inhibition, whereas the green tea ungallated catechin not. Atomic orbital energy analyses suggest that the positive charge is more distinctly distributed on the carbon atom of ester bond of galloyl moiety of gallate catechins, and that gallated forms are more susceptible for a nucleophilic attack than other catechins. Here we identify the galloyl moiety of green tea catechins as critical in the inactivation of the ketoacyl reductase activity of FAS for the first time.

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.

Inhibitive effect of zinc ion on fatty acid synthase from chicken liver

Fatty acid synthase (FAS; acyl-CoA:malonyl-CoA C-acyltransferase [decarboxylating, oxoacyl- and enoyl-reducing and thioester-hydrolyzing], EC 2.3.1.85) is an important enzyme participating in energy metabolism in vivo which is related to adiposis and cancer [Cancer Lett. 167 (1) (2001) 99; Nat. Med. 8 (4) (2002) 335]. Tests of fast- and slow-binding inhibitions showed that fatty acid synthase of chicken liver is rapidly and irreversibly inactivated by low Zn(2+) concentrations. Electrophoresis and FPLC results showed that FAS cross-links occurred in the presence of high Zn(2+) concentrations (>4 microM) which may be another reason that FAS lost its activity. The modification velocity of FAS by DTNB decreased with increasing Zn(2+) concentration, which confirmed that Zn(2+) interacted with SH groups. Substrate protective experiments and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that all three substrates tested had some protective effects on FAS in the presence of Zn(2+), and malonyl-CoA was the most effective of the three substrates. In the presence of malonyl-CoA, the activity loss of FAS decreased sharply and almost no cross-link was observed in SDS-PAGE. This suggests that the phosphopantetheine SH group is the critical group in the cross-link and inhibition of FAS in the presence of Zn(2+).

Regulation of fatty acid synthase expression in breast cancer by sterol regulatory element binding protein-1c

Activation of fatty acid synthase (FAS) expression and fatty acid synthesis is a common event in human breast cancer. Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate genes involved in lipid metabolism, including FAS. SREBP-1c expression is induced in liver and adipose tissue by insulin and by fasting/refeeding and is critical for nutritional regulation of lipogenic gene expression. In contrast, upregulation of fatty acid metabolism during in vitro transformation of human mammary epithelial cells and in breast cancer cells was driven by increased MAP kinase and PI 3-kinase signaling, which increased SREBP-1 levels. SREBP-1a was more abundant than SREBP-1c in many proliferative tissues and cultured cells and was thus a candidate to regulate lipogenesis for support of membrane synthesis during cell growth. We now show that SREBP-1c and FAS mRNA were both increased by H-ras transformation of MCF-10a breast epithelial cells and were both reduced by exposure of MCF-7 breast cancer cells to the MAP kinase inhibitor, PD98059, or the PI 3-kinase inhibitor, wortmannin, while SREBP-1a and SREBP-2 showed less variation. Similarly, the mRNA levels for FAS and SREBP-1c in a panel of primary human breast cancer samples showed much greater increases than did those for SREBP-1a and SREBP-2 and were significantly correlated with each other, suggesting coordinate regulation of SREBP-1c and FAS in clinical breast cancer. We conclude that regulation of FAS expression in breast cancer is achieved through modulation of SREBP-1c, similar to the regulation in liver and adipose tissue, although the upstream regulation of liopgenesis differs in these tissues.