Going malignant: the hypoxia-cancer connection in the prostate

Broadband coherent anti-Stokes Raman scattering (BCARS) microscopy for rapid, label-free biological imaging

Broadband coherent anti-Stokes Raman scattering (BCARS) microscopy is a label-free imaging approach that provides detailed chemical information at high spatial resolution in a sample through nonlinear, coherent excitation of molecular vibrations and detection of Raman spectra. While its utility for biological imaging has been demonstrated, many aspects of this technique must mature before it can be widely adopted. One of the areas of required improvement is imaging speed-most BCARS implementations involve sample rastering, which limits imaging speed. Beam scanning can provide faster BCARS imaging but presents some unique challenges. Here, we describe a beam-scanning BCARS microscopy system that improves spatial resolution twofold and imaging speed by fivefold over a previous beam-scanning implementation. These enhancements were enabled by an improvement in supercontinuum power and the use of a sCMOS camera for its high data transfer rate and low read noise. Implementation of the sCMOS camera required correction for the significant pixel-to-pixel background and photon response nonuniformity. We report on the method that we implemented for calibrating and correcting the pixel-to-pixel differences in sCMOS camera noise.

The dual role of citrate in cancer

Citrate is a key metabolite of the Krebs cycle that can also be exported in the cytosol, where it performs several functions. In normal cells, citrate sustains protein acetylation, lipid synthesis, gluconeogenesis, insulin secretion, bone tissues formation, spermatozoid mobility, and immune response. Dysregulation of citrate metabolism is implicated in several pathologies, including cancer. Here we discuss how cancer cells use citrate to sustain their proliferation, survival, and metastatic progression. Also, we propose two paradoxically opposite strategies to reduce tumour growth by targeting citrate metabolism in preclinical models. In the first strategy, we propose to administer in the tumor microenvironment a high amount of citrate, which can then act as a glycolysis inhibitor and apoptosis inducer, whereas the other strategy targets citrate transporters to starve cancer cells from citrate. These strategies, effective in several preclinical in vitro and in vivo cancer models, could be exploited in clinics, particularly to increase sensibility to current anti-cancer agents.

The sialyl-Tn antigen synthase genes regulates migration-proliferation dichotomy in prostate cancer cells under hypoxia

A low-oxygen (hypoxia) tumor microenvironment can facilitate chemotherapy and radiation therapy resistance in tumors and is associated with a poor prognosis. Hypoxia also affects PCa (prostate cancer) phenotype transformation and causes therapeutic resistance. Although O-glycans are known to be involved in the malignancy of various cancers under hypoxia, the expression and function of O-glycans in PCa are not well understood. In this study, the saccharide primer method was employed to analyze O-glycan expression in PCa cells. Results showed that the expression of sTn antigens was increased in PCa cells under hypoxia. Furthermore, it was found that ST6GalNAc1, the sTn antigen synthase gene, was involved in the migration-proliferation dichotomy and drug resistance in PCa cells under hypoxia. The results of this study will contribute to the development of novel diagnostic markers and drug targets for PCa under hypoxia.

Extracellular citrate and metabolic adaptations of cancer cells

It is well established that cancer cells acquire energy via the Warburg effect and oxidative phosphorylation. Citrate is considered to play a crucial role in cancer metabolism by virtue of its production in the reverse Krebs cycle from glutamine. Here, we review the evidence that extracellular citrate is one of the key metabolites of the metabolic pathways present in cancer cells. We review the different mechanisms by which pathways involved in keeping redox balance respond to the need of intracellular citrate synthesis under different extracellular metabolic conditions. In this context, we further discuss the hypothesis that extracellular citrate plays a role in switching between oxidative phosphorylation and the Warburg effect while citrate uptake enhances metastatic activities and therapy resistance. We also present the possibility that organs rich in citrate such as the liver, brain and bones might form a perfect niche for the secondary tumour growth and improve survival of colonising cancer cells. Consistently, metabolic support provided by cancer-associated and senescent cells is also discussed. Finally, we highlight evidence on the role of citrate on immune cells and its potential to modulate the biological functions of pro- and anti-tumour immune cells in the tumour microenvironment. Collectively, we review intriguing evidence supporting the potential role of extracellular citrate in the regulation of the overall cancer metabolism and metastatic activity.

Evaluation of 18F-EF5 for detection of hypoxia in localized adenocarcinoma of the prostate

BACKGROUND

A common feature of solid tumours that are resistant to therapy is the presence of regions with low oxygen content (i.e., hypoxia). Oxygen electrode studies suggest that localized prostate adenocarcinoma is commonly hypoxic, although conflicting data have been reported between immunohistochemical detection of hypoxia-induced proteins in biopsy specimens and positron emission tomography (PET) imaging of ¹⁸F-labeled hypoxia reporters. Although the 2-nitroimidazole ¹⁸F-EF5 is well-established to label hypoxic tumour cells in pre-clinical tumour models and clinical trials of multiple primary tumour sites, it has yet to be tested in prostate cancer. The purpose of this study was to evaluate the feasibility of using ¹⁸F-EF5 to detect hypoxia in clinical prostate tumours.

MATERIAL AND METHODS

Patients with localized adenocarcinoma of the prostate were recruited for pre-treatment ¹⁸F-EF5 PET scans. Immunohistochemistry was conducted on diagnostic biopsies to assess the expression of glucose transporter 1 (GLUT1), osteopontin (OPN), and carbonic anhydrase IX (CAIX). Immunoreactivity scores of staining intensity and frequency were used to indicate the presence of tumour hypoxia.

RESULTS

We found low tumour-to-muscle ratios of ¹⁸F-EF5 uptake that were not consistent with tumour hypoxia, causing early termination of the study. However, we observed GLUT1 and OPN expression in all prostate tumour biopsies, indicating the presence of hypoxia in all tumours.

CONCLUSION

Our data do not support the use of ¹⁸F-EF5 PET to detect hypoxia in prostate adenocarcinoma, and suggest the use of immunohistochemistry to quantify expression of the hypoxia-inducible proteins GLUT1 and OPN as indications of prostate tumour hypoxia.

The Role of MicroRNAs in Lung Cancer Metabolism

MicroRNAs (miRNAs) are short-strand non-coding RNAs that are responsible for post-transcriptional regulation of many biological processes. Their differential expression is important in supporting tumorigenesis by causing dysregulation in normal biological functions including cell proliferation, apoptosis, metastasis and invasion and cellular metabolism. Cellular metabolic processes are a tightly regulated mechanism. However, cancer cells have adapted features to circumvent these regulations, recognizing metabolic reprogramming as an important hallmark of cancer. The miRNA expression profile may differ between localized lung cancers, advanced lung cancers and solid tumors, which lead to a varying extent of metabolic deregulation. Emerging evidence has shown the relationship between the differential expression of miRNAs with lung cancer metabolic reprogramming in perpetuating tumorigenesis. This review provides an insight into the role of different miRNAs in lung cancer metabolic reprogramming by targeting key enzymes, transporter proteins or regulatory components alongside metabolic signaling pathways. These discussions would allow a deeper understanding of the importance of miRNAs in tumor progression therefore providing new avenues for diagnostic, therapeutic and disease management applications.

Androgen receptor (AR) antagonism triggers acute succinate-mediated adaptive responses to reactivate AR signaling

Treatment-induced adaptive pathways converge to support androgen receptor (AR) reactivation and emergence of castration-resistant prostate cancer (PCa) after AR pathway inhibition (ARPI). We set out to explore poorly defined acute adaptive responses that orchestrate shifts in energy metabolism after ARPI and identified rapid changes in succinate dehydrogenase (SDH), a TCA cycle enzyme with well-known tumor suppressor activity. We show that AR directly regulates transcription of its catalytic subunits (SDHA, SDHB) via androgen response elements (AREs). ARPI acutely suppresses SDH activity, leading to accumulation of the oncometabolite, succinate. Succinate triggers calcium ions release from intracellular stores, which in turn phospho-activates the AR-cochaperone, Hsp27 via p-CaMKK2/p-AMPK/p-p38 axis to enhance AR protein stabilization and activity. Activation of this pathway was seen in tissue microarray analysis on prostatectomy tissues and patient-derived xenografts. This adaptive response is blocked by co-targeting AR with Hsp27 under both in vitro and in vivo studies, sensitizing PCa cells to ARPI treatments.

Lipid Metabolism in Cancer Cells

Metabolic reprogramming is one of the most critical hallmarks in cancer cells. In the past decades, mounting evidence has demonstrated that, besides the Warburg Effect, lipid metabolism dysregulation is also one of the essential characteristics of cancer cell metabolism. Lipids are water-insoluble molecules with diverse categories of phosphoglycerides, triacylglycerides, sphingolipids, sterols, etc. As the major utilization for energy storage, fatty acids are the primary building blocks for synthesizing triacylglycerides. And phosphoglycerides, sphingolipids, and sterols are the main components constructing biological membranes. More importantly, lipids play essential roles in signal transduction by functioning as second messengers or hormones. Much evidence has shown specific alterations of lipid metabolism in cancer cells. Consequently, the structural configuration of biological membranes, the energy homeostasis under nutrient stress, and the abundance of lipids in the intracellular signal transduction are affected by these alterations. Furthermore, lipid droplets accumulate in cancer cells and function adaptively to different types of harmful stress. This chapter reviews the regulation, functions, and therapeutic benefits of targeting lipid metabolism in cancer cells. Overall, this chapter highlights the significance of exploring more potential therapeutic strategies for malignant diseases by unscrambling lipid metabolism regulation in cancer cells.

Extracellular Citrate Fuels Cancer Cell Metabolism and Growth

Cancer cells need excess energy and essential nutrients/metabolites not only to divide and proliferate but also to migrate and invade distant organs for metastasis. Fatty acid and cholesterol synthesis, considered a hallmark of cancer for anabolism and membrane biogenesis, requires citrate. We review here potential pathways in which citrate is synthesized and/or supplied to cancer cells and the impact of extracellular citrate on cancer cell metabolism and growth. Cancer cells employ different mechanisms to support mitochondrial activity and citrate synthesis when some of the necessary substrates are missing in the extracellular space. We also discuss the different transport mechanisms available for the entry of extracellular citrate into cancer cells and how citrate as a master metabolite enhances ATP production and fuels anabolic pathways. The available literature suggests that cancer cells show an increased metabolic flexibility with which they tackle changing environmental conditions, a phenomenon crucial for cancer cell proliferation and metastasis.

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

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

Metabolic regulation of cell growth and proliferation

Cellular metabolism is at the foundation of all biological activities. The catabolic processes that support cellular bioenergetics and survival have been well studied. By contrast, how cells alter their metabolism to support anabolic biomass accumulation is less well understood. During the commitment to cell proliferation, extensive metabolic rewiring must occur in order for cells to acquire sufficient nutrients such as glucose, amino acids, lipids and nucleotides, which are necessary to support cell growth and to deal with the redox challenges that arise from the increased metabolic activity associated with anabolic processes. Defining the mechanisms of this metabolic adaptation for cell growth and proliferation is now a major focus of research. Understanding the principles that guide anabolic metabolism may ultimately enhance ways to treat diseases that involve deregulated cell growth and proliferation, such as cancer.

Fatty Acid Inhibition Sensitizes Androgen-Dependent and -Independent Prostate Cancer to Radiotherapy via FASN/NF-κB Pathway

Elevated fatty acid synthase (FASN) has been reported in both androgen-dependent and -independent prostate cancers. Conventional treatment for prostate cancer is radiotherapy (RT); however, the following radiation-induced radioresistance often causes treatment failure. Upstream proteins of FASN such as Akt and NF-κB are found increased in the radioresistant prostate cancer cells. Nevertheless, whether inhibition of FASN could improve RT outcomes and reverse radiosensitivity of prostate cancer cells is still unknown. Here, we hypothesised that orlistat, a FASN inhibitor, could improve RT outcomes in prostate cancer. Orlistat treatment significantly reduced the S phase population in both androgen-dependent and -independent prostate cancer cells. Combination of orlistat and RT significantly decreased NF-κB activity and related downstream proteins in both prostate cancer cells. Combination effect of orlistat and RT was further investigated in both LNCaP and PC3 tumour-bearing mice. Combination treatment showed the best tumour inhibition compared to that of orlistat alone or RT alone. These results suggest that prostate cancer treated by conventional RT could be improved by orlistat via inhibition of FASN.

Fatty Acid Synthase and Acetyl-CoA Carboxylase Are Expressed in Nodal Metastatic Melanoma But Not in Benign Intracapsular Nodal Nevi

BACKGROUND

Melanoma is a potentially lethal form of skin cancer for which the current standard therapy is complete surgical removal of the primary tumor followed by sentinel lymph node biopsy when indicated. Histologic identification of metastatic melanoma in a sentinel node has significant prognostic and therapeutic implications, routinely guiding further surgical management with regional lymphadenectomy. While melanocytes in a lymph node can be identified by routine histopathologic and immunohistochemical examination, the distinction between nodal nevus cells and melanoma can be morphologically problematic. Previous studies have shown that malignant melanoma can over-express metabolic genes such as fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC). This immunohistochemical study aims to compare the utility of FASN and ACC in differentiating sentinel lymph nodes with metastatic melanomas from those with benign nodal nevi in patients with cutaneous melanoma.

MATERIALS AND METHODS

Using antibodies against FASN and ACC, 13 sentinel lymph nodes from 13 patients with metastatic melanoma and 14 lymph nodes harboring benign intracapsular nevi from 14 patients with cutaneous malignant melanoma were examined. A diagnosis of nodal melanoma was based on cytologic atypia and histologic comparison with the primary melanoma. All nodal nevi were intracapsular and not trabecular. Immunohistochemistry for Melan-A, S100, human melanoma black 45 (HMB45), FASN, and ACC were performed. The percentage of melanocytes staining with HMB45, FASN, and ACC was determined and graded in 25% increments; staining intensity was graded as weak, moderate, or strong.

RESULTS

All metastatic melanomas tested had at least 25% tumor cell staining for both FASN and ACC. Greater than 75% of the tumor cells stained with FAS in 7/13 cases and for ACC in 5/12 cases. Intensity of staining was variable; strong staining for FASN and ACC was observed in 69% and 50% of metastatic melanoma, respectively. HMB45 was negative in 40% of nodal melanoma cases all of which stained with FASN and ACC. Capsular nevi were uniformly negative for FASN, ACC, and HMB45 immunoreactivity.

CONCLUSIONS

All metastatic melanoma cases involving sentinel lymph nodes were positive for FASN and ACC while no staining was observed in intracapsular nevi. These findings suggest that FASN and ACC could be used as valuable ancillary stains in the distinction between nodal nevi and metastatic melanoma.

50 years of comparative biochemistry: The legacy of Peter Hochachka

Peter Hochachka was an early pioneer in the field of comparative biochemistry. He passed away in 2002 after 4 decades of research in the discipline. To celebrate his contributions and to coincide with what would have been his 80th birthday, a group of his former students organized a symposium that ran as a satellite to the 2017 Canadian Society of Zoologists annual meeting in Winnipeg, Manitoba (Canada). This Special Issue of CBP brings together manuscripts from symposium attendees and other authors who recognize the role Peter played in the evolution of the discipline. In this article, the symposium organizers and guest editors look back on his career, celebrating his many contributions to research, acknowledging his role in training of generations of graduate students and post-doctoral fellows in comparative biochemistry and physiology.

Comparative biochemistry of cytochrome c oxidase in animals

Cytochrome c oxidase (COX), the terminal enzyme of the electron transport system, is central to aerobic metabolism of animals. Many aspects of its structure and function are highly conserved, yet, paradoxically, it is also an important model for studying the evolution of the metabolic phenotype. In this review, part of a special issue honouring Peter Hochachka, we consider the biology of COX from the perspective of comparative and evolutionary biochemistry. The approach is to consider what is known about the enzyme in the context of conventional biochemistry, but focus on how evolutionary researchers have used this background to explore the role of the enzyme in biochemical adaptation of animals. In synthesizing the conventional and evolutionary biochemistry, we hope to identify synergies and future research opportunities. COX represents a rare opportunity for researchers to design studies that span the breadth of biology: molecular genetics, protein biochemistry, enzymology, metabolic physiology, organismal performance, evolutionary biology, and phylogeography.

New and Emerging Diagnostic and Prognostic Immunohistochemical Biomarkers in Prostate Pathology

The diagnosis of minimal prostatic adenocarcinoma can be challenging on prostate needle biopsy, and immunohistochemistry may be used to support the diagnosis of cancer. The International Society of Urologic Pathology currently recommends the use of the basal cell markers high-molecular-weight cytokeraratin and p63, and α-methylacyl-coenzyme-A racemase. However, there are caveats associated with the interpretation of these markers, particularly with benign mimickers. Another issue is that of early detection of presence and progression of disease and prediction of recurrence after clinical intervention. There remains a lack of reliable biomarkers to accurately predict low-risk cancer and avoid over treatment. As such, aggressive forms of prostate cancer may be missed and indolent disease may be subjected to unnecessary radical therapy. New biomarker discovery promises to improve early detection and prognosis and to provide targets for therapeutic interventions. In this review, we present the emerging immunohistochemical biomarkers of prostate cancer PTEN, ERG, FASN, MAGI-2, and SPINK1, and address their diagnostic and prognostic advantages and limitations.

Inhibition of fatty acid synthase suppresses neovascularization via regulating the expression of VEGF-A in glioma

PURPOSE

Fatty acids (FAs) are essential for membrane lipids biosynthesis and energy consumption in cancer cells. De novo FAs synthesis is catalyzed by fatty acid synthase (FASN), which is overexpressed and correlates with histological grade in glioma. Herein, we focused on the role of FASN in glioma neovascularization.

METHODS

The expression levels of FASN, Ki67 and CD34 were determined using immunohistochemistry (IHC). FASN specific-targeted shRNA and C75 were applied to evaluate the influence of FASN on glioma stem cell proliferation, migration and tube formation ability in vitro. An intracranial glioma model was established to study the effects of FASN on tumor growth and neovascularization in vivo.

RESULTS

IHC staining showed that the expression level of FASN correlated with tumor grade, Ki67 levels and microvessels density (MVD) in human gliomas. Inhibition of FASN using shRNAs or C75 decreased tumor growth, prolonged the overall survival of xenograft mice and decreased MVD in brain tumor sections. Moreover, inhibition of FASN blocked hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor A (VEGF-A) signaling and upregulated the anti-angiogenic isoform-VEGF165b.

CONCLUSION

Our results suggest that FASN plays a pivotal role in glioma neovascularization, and inhibition of FASN may be a potential target for anti-angiogenic therapy for glioma.

Effects of ω-3 Fatty Acids and Catechins on Fatty Acid Synthase in the Prostate: A Randomized Controlled Trial

Animal and human studies suggest fish oil and green tea may have protective effect on prostate cancer. Fatty acid synthase (FAS) has been hypothesized to be linked to chemoprotective effects of both compounds. This study evaluated the independent and joint effects of fish oil (FO) and green tea supplement (epigallocatechin-3-gallate, EGCG) on FAS and Ki-67 levels in prostate tissue. Through a double-blinded, randomized controlled trial with 2 × 2 factorial design, 89 men scheduled for repeat prostate biopsy following an initial negative prostate biopsy were randomized into either FO alone (1.9 g DHA + EPA/day), EGCG alone (600 mg/day), a combination of FO and EGCG, or placebo. We used linear mixed-effects models to test the differences of prostate tissue FAS and Ki-67 by immunohistochemistry between pre- and post-intervention within each group, as well as between treatment groups. Results did not show significant difference among treatment groups in pre-to-post-intervention changes of FAS (P = 0.69) or Ki-67 (P = 0.26). Comparing placebo group with any of the treatment groups, we did not find significant difference in FAS or Ki-67 changes (all P > 0.05). Results indicate FO or EGCG supplementation for a short duration may not be sufficient to produce biologically meaningful changes in FAS or Ki-67 levels in prostate tissue.

Lipid desaturation - the next step in targeting lipogenesis in cancer?

Metabolic reprogramming is a central feature of transformed cells. Cancer metabolism is now fully back in the focus of cancer research, as the interactions between oncogenic signalling and cellular metabolic processes are uncovered. One aspect of metabolic reprogramming in cancer is alterations in lipid metabolism. In contrast to most untransformed tissues, which satisfy their demand from dietary lipids, cancer cells frequently re-activate de novo lipogenesis. However, compounds targeting fatty acid synthase (FASN), a multiprotein complex integral to lipogenesis, have so far shown limited efficacy in pre-clinical cancer models and to date only one FASN inhibitor has entered clinical trials. Recently, a number of studies have suggested that enhanced production of fatty acids in cancer cells could also increases their dependence on the activity of desaturases, a class of enzymes that insert double bonds into acyl-CoA chains. Targeting desaturase activity could provide a window of opportunity to selectively interfere with the metabolic activity of cancer cells. This review will summarise some key findings that implicate altered lipid metabolism in cancer and investigate the molecular interactions between lipid desaturation and cancer cell survival.

Bruton's tyrosine kinase is a potential therapeutic target in prostate cancer

Bruton's tyrosine kinase (BTK) is a non-receptor tyrosine kinase that has mainly been studied in haematopoietic cells. We have investigated whether BTK is a potential therapeutic target in prostate cancer. We find that BTK is expressed in prostate cells, with the alternate BTK-C isoform predominantly expressed in prostate cancer cells and tumors. This isoform is transcribed from an alternative promoter and results in a protein with an amino-terminal extension. Prostate cancer cell lines and prostate tumors express more BTK-C transcript than the malignant NAMALWA B-cell line or human lymphomas. BTK protein expression is also observed in tumor tissue from prostate cancer patients. Down regulation of this protein with RNAi or inhibition with BTK-specific inhibitors, Ibrutinib, AVL-292 or CGI-1746 decrease cell survival and induce apoptosis in prostate cancer cells. Microarray results show that inhibiting BTK under these conditions increases expression of apoptosis related genes, while overexpression of BTK-C is associated with elevated expression of genes with functions related to cell adhesion, cytoskeletal structure and the extracellular matrix. These results are consistent with studies that show that BTK signaling is important for adhesion and migration of B cells and suggest that BTK-C may confer similar properties to prostate cancer cells. Since BTK-C is a survival factor for these cells, it represents both a potential biomarker and novel therapeutic target for prostate cancer.

KRAS NF-κB is involved in the development of zinc resistance and reduced curability in prostate cancer

Zinc(II) ions are important components of many proteins and are involved in numerous cellular processes such as apoptosis or drug resistance. Prostate cancer has a unique relationship with zinc(II) ions. However, the relationship was examined only in short-term zinc(II) treatments. Therefore, the aim of this study was to create zinc-resistant prostatic cell lines at various stages of the disease (22Rv1 and PC-3) and a normal prostate epithelium (PNT1A) using a long-term zinc exposure. Consequently, the expression profile of the following genes was analyzed: BAX, Bcl-2, Beclin-1, CFLAR, HIF1α, KRAS, mTOR, MT1A, MT2A, NF-κB1, p53, survivin, ZIP1, ZnT-1. The resistance was verified using the MTT test; on average a 1.35-fold lower zinc(II) toxicity (higher IC50) was determined in zinc(II)-resistant cells. The associated resistance to cisplatin was also determined; IC50 for cisplatin was 1.52-fold higher. With regard to the gene expression profiles, our results indicate that differential mechanisms participate in the short-term zinc toxicity regulation and long-term resistance; the short-term treatment was associated with MT2A (p < 0.001), ZnT-1 (p < 0.001), and MT1A (p < 0.03) and the long-term resistance was associated particularly with NF-κB1 (p < 0.001), CFLAR (p < 0.001), KRAS (p < 0.001), p53 (p < 0.002), survivin (p = 0.02), ZIP1 (p = 0.002), BAX (p = 0.005), and HIF1α (p = 0.05). Therefore, the KRAS-PI3K-NF-κB pathway is expected to play a crucial role in the regulation of zinc resistance. In summary, compared to previous studies, identical mechanisms of resistance were demonstrated on multiple cell lines, both non-tumor and tumorous, derived both from primary and advanced secondary sites.

The Warburg effect revisited--lesson from the Sertoli cell

Otto Warburg observed that cancerous cells prefer fermentative instead of oxidative metabolism of glucose, although the former is in theory less efficient. Since Warburg's pioneering works, special attention has been given to this difference in cell metabolism. The Warburg effect has been implicated in cell transformation, immortalization, and proliferation during tumorigenesis. Cancer cells display enhanced glycolytic activity, which is correlated with high proliferation, and thus, glycolysis appears to be an excellent candidate to target cancer cells. Nevertheless, little attention has been given to noncancerous cells that exhibit a "Warburg-like" metabolism with slight, but perhaps crucial, alterations that may provide new directions to develop new and effective anticancer therapies. Within the testis, the somatic Sertoli cell (SC) presents several common metabolic features analogous to cancer cells, and a clear "Warburg-like" metabolism. Nevertheless, SCs actively proliferate only during a specific time period, ceasing to divide in most species after puberty, when they become terminally differentiated. The special metabolic features of SC, as well as progression from the immature but proliferative state, to the mature nonproliferative state, where a high glycolytic activity is maintained, make these cells unique and a good model to discuss new perspectives on the Warburg effect. Herein we provide new insight on how the somatic SC may be a source of new and exciting information concerning the Warburg effect and cell proliferation.

Dietary-suppression of hepatic lipogenic enzyme expression in intact male transgenic mice

AIM: To study, in intact male transgenic mice, the effects of three diets based on olive oil and olive oil diet supplemented with lovastatin and orlistat on hepatic lipogenic enzymes expression, considered markers of cell proliferation.

METHODS: Forty Apc^Min/+ mice were randomly divided into 4 groups and fed for 10 wk: olive oil (OO) group, n = 10 animals received a diet with olive oil 12%; olive oil plus lovastatin (LOVA) group, n = 10 animals received the same diet with olive oil supplemented with lovastatin 5 mg/kg; olive oil plus orlistat (OR) group, n = 10 animals fed the diet with olive oil supplemented with orlistat 50 mg/kg and SD group, n = 10 animals fed a standard diet. The activity of lipogenic enzymes and their gene expression were evaluated by radiometric and real-time reverse transcription-polymerase chain reaction assay, respectively.

RESULTS: After 10 wk of dietary treatment, the body weight was no different among animal groups (21.3 ± 3.1 g for standard group, 22.1 ± 3.6 g for OO group, 22.0 ± 3.2 g for LOVA group and 20.7 ± 3.4 g for OR group, data expressed as mean ± SD), observing a generalized well-being in all animals. All the dietary managed treated groups presented significantly reduced hepatic levels of fatty acid synthase, farnesyl pyrophosphate synthase and 3-hydroxyl-3-methyl-glutaryl CoA reductase activity and gene expression when compared with the mice fed the standard diet. To evaluate cell proliferation in the liver of treated mice, the levels of cyclin E mRNA have been measured, demonstrating a significant reduction of cyclin E gene expression in all treated groups. Evidence of reduced hepatic cell proliferation was present overall in OO group mice.

CONCLUSION: We confirm the role of lipogenic enzymes as markers of cell proliferation, suggesting that appropriate dietary management alone or with drugs can be a feasible approach to counteract hepatic cell proliferation in mice.

Non-invasive in-cell determination of free cytosolic [NAD+]/[NADH] ratios using hyperpolarized glucose show large variations in metabolic phenotypes

Accumulating evidence suggest that the pyridine nucleotide NAD has far wider biological functions than its classical role in energy metabolism. NAD is used by hundreds of enzymes that catalyze substrate oxidation and, as such, it plays a key role in various biological processes such as aging, cell death, and oxidative stress. It has been suggested that changes in the ratio of free cytosolic [NAD(+)]/[NADH] reflects metabolic alterations leading to, or correlating with, pathological states. We have designed an isotopically labeled metabolic bioprobe of free cytosolic [NAD(+)]/[NADH] by combining a magnetic enhancement technique (hyperpolarization) with cellular glycolytic activity. The bioprobe reports free cytosolic [NAD(+)]/[NADH] ratios based on dynamically measured in-cell [pyruvate]/[lactate] ratios. We demonstrate its utility in breast and prostate cancer cells. The free cytosolic [NAD(+)]/[NADH] ratio determined in prostate cancer cells was 4 times higher than in breast cancer cells. This higher ratio reflects a distinct metabolic phenotype of prostate cancer cells consistent with previously reported alterations in the energy metabolism of these cells. As a reporter on free cytosolic [NAD(+)]/[NADH] ratio, the bioprobe will enable better understanding of the origin of diverse pathological states of the cell as well as monitor cellular consequences of diseases and/or treatments.

Tumor necrosis factor alpha increases aerobic glycolysis and reduces oxidative metabolism in prostate epithelial cells

BACKGROUND

Chronic inflammation promotes prostate cancer formation and progression. Furthermore, alterations in energy metabolism are a hallmark of prostate cancer cells. However, the actions of inflammatory factors on the energy metabolism of prostate epithelial cells have not been previously investigated. This is the first study to report on the effect of the inflammatory cytokine tumor necrosis factor alpha (TNFα) on the glycolytic and oxidative metabolism, and the mitochondrial function of widely used prostate epithelial cells.

METHODS

Pre-malignant RWPE-1 and cancerous LNCaP and PC-3 cells were treated with low-dose TNFα. Glycolytic and oxidative metabolism was quantified by measuring extracellular acidification and oxygen consumption rates, respectively. ATP content and lactate export were measured by luminescence and fluorescence, respectively. Mitochondrial content and the expression of glucose transporter 1 (GLUT1), peroxisome proliferator-activated receptor co-activator 1 alpha (PGC-1α), and Cytochrome C were measured by flow cytometry.

RESULTS

Our data suggest that TNFα increases glycolysis, ATP production, and lactate export, while it reduces oxidative metabolism and mitochondrial function in prostate epithelial cells. The highly aggressive PC-3 cells tend to be less responsive to the actions of TNFα than the pre-malignant RWPE-1 and the non-aggressive LNCaP cells.

CONCLUSIONS

Cellular energetics, that is, glycolytic and oxidative metabolism is significantly influenced by low-level inflammation in prostate epithelial cells. In widely used prostate epithelial cell models, the micro-environmental inflammatory cytokine TNFα induces aerobic glycolysis while inhibiting oxidative metabolism. This supports the hypothesis that low-level inflammation can induce Warburg metabolism in prostate epithelial cells, which may promote cancer formation and progression.

Bioenergetic and antiapoptotic properties of mitochondria from cultured human prostate cancer cell lines PC-3, DU145 and LNCaP

The purpose of this work was to reveal the metabolic features of mitochondria that might be essential for inhibition of apoptotic potential in prostate cancer cells. We studied mitochondria isolated from normal prostate epithelial cells (PrEC), metastatic prostate cancer cell lines LNCaP, PC-3, DU145; and non-prostate cancer cells - human fibrosarcoma HT1080 cells; and normal human lymphoblastoid cells. PrEC cells contained 2 to 4 times less mitochondria per gram of cells than the three PC cell lines. Respiratory activities of PrEC cell mitochondria were 5-20-fold lower than PC mitochondria, depending on substrates and the metabolic state, due to lower content and lower activity of the respiratory enzyme complexes. Mitochondria from the three metastatic prostate cancer cell lines revealed several features that are distinctive only to these cells: low affinity of Complex I for NADH, 20-30 mV higher electrical membrane potential (ΔΨ). Unprotected with cyclosporine A (CsA) the PC-3 mitochondria required 4 times more Ca²⁺ to open the permeability transition pore (mPTP) when compared with the PrEC mitochondria, and they did not undergo swelling even in the presence of alamethicin, a large pore forming antibiotic. In the presence of CsA, the PC-3 mitochondria did not open spontaneously the mPTP. We conclude that the low apoptotic potential of the metastatic PC cells may arise from inhibition of the Ca²⁺-dependent permeability transition due to a very high ΔΨ and higher capacity to sequester Ca²⁺. We suggest that due to the high ΔΨ, mitochondrial metabolism of the metastatic prostate cancer cells is predominantly based on utilization of glutamate and glutamine, which may promote development of cachexia.

Cholesterol accumulation in prostate cancer: a classic observation from a modern perspective

Prostate cancer (PCa) is the most common cancer in men in developed countries. Epidemiological studies have associated high blood-cholesterol levels with an increased risk of PCa, whilst cholesterol-lowering drugs (statins) reduce the risk of advanced PCa. Furthermore, normal prostate epithelial cells have an abnormally high cholesterol content, with cholesterol levels increasing further during progression to PCa. In this review, we explore why and how this occurs. Concurrent to this observation, intense efforts have been expended in cardiovascular research to better understand the regulators of cholesterol homeostasis. Here, we apply this knowledge to elucidate the molecular mechanisms driving the accumulation of cholesterol in PCa. For instance, recent evidence from our group and others shows that major signalling players in prostate growth and differentiation, such as androgens and Akt, modulate the key transcriptional regulators of cholesterol homeostasis to enhance cholesterol levels. This includes adjusting central carbon metabolism to sustain greater lipid synthesis. Perturbations in cholesterol homeostasis appear to be maintained even when PCa approaches the advanced, 'castration-resistant' state. Overall, this provides a link between cholesterol accumulation and PCa cell growth. Given there is currently no cure for castration-resistant PCa, could cholesterol metabolism be a novel target for PCa therapy? Overall, this review presents a picture that cholesterol metabolism is important for PCa development: growth-promoting factors stimulate cholesterol accumulation, which in turn presents a possible target for chemotherapy. Consequently, we recommend future investigations, both to better elucidate the mechanisms driving this accumulation and applying it in novel chemotherapeutic strategies.

Hypoxia upregulates the gene expression of mitochondrial aconitase in prostate carcinoma cells

Hypoxia induces metabolic alteration in cancer cells by stabilizing hypoxia-inducible factor 1α (HIF-1α (HIF1A)), which regulates the bioenergetic genes of glycolysis and lipid metabolic pathways. However, the target genes of hypoxia-induced metabolic alterations in the prostate remain uncertain. Mitochondrial aconitase (mACON) (ACONM) is an enzyme that is central to carbohydrate and energy metabolism and is responsible for the interconversion of citrate to isocitrate as part of the citric acid cycle in the human prostate. We evaluated the effects of the molecular mechanisms of hypoxia on mACON gene expression in PC-3 and LNCaP human prostate carcinoma cells. Immunoblotting assays revealed that hypoxia modulated mACON and lactate dehydrogenase A (LDHA) protein expression, while these effects were attenuated when HIF-1α was knocked down. Hypoxia induced fatty acid synthase (FASN) in PC-3 cells while hypoxia blocked FASN gene expression in LNCaP cells after 24-h incubation. Results of real-time RT-qPCR, immunoblotting, and transient gene expression assays revealed that hypoxia treatment or co-transfection with HIF-1α expression vector enhanced gene expression of mACON, implying that hypoxia modulated mACON at the transcriptional level. Hypoxia-induced mACON promoter activity is dependent on the DNA fragment located at -1013 to -842 upstream of the translation initiation site. l-mimosine, an iron chelator, stabilized HIF-1α but downregulated mACON gene expression, suggesting that iron chelation blocked the hypoxia-induced mACON gene expression. These results suggest that hypoxia dysregulates the expressions of LDHA, FASN, and mACON genes, and the hypoxia-induced mACON gene expression is via the HIF-1α-dependent and iron-dependent pathways in prostate carcinoma cells.

Targeted therapy with fatty acid synthase inhibitors in a human prostate carcinoma LNCaP/tk-luc-bearing animal model

BACKGROUND

Fatty acid synthase (FASN) is highly upregulated in human prostate carcinomas. Inhibition of FASN could arrest cell cycle and trigger apoptosis rapidly, implying the reliance of cancer cell survival on FASN. However, little is known about the effect of C75, a FASN inhibitor, and siFASN (that is, small interfering RNA targeted at FASN) on prostate cancer in living subjects.

METHODS

We used C75 and siFASN to mediate the endogenous fatty acid metabolism in LNCaP human prostate cancer cells stably expressing herpes simplex virus type 1 thymidine kinase (HSV1-tk) and luciferase (luc) reporter genes, and assessed the effect of FASN blockade with different schedules of administration on tumor growth using noninvasive molecular imaging.

RESULTS

FASN blockade exhibited the proliferative inhibition and induced G1-phase cell cycle arrest of LNCaP cells. For in vivo studies, the tumor growth inhibition by C75 (total 120 mgkg(-1); 30 mgkg(-1) once a week or 15 mgkg(-1) twice a week for 4 weeks) and siFASN (1.4 mgkg(-1) every alternate day up to 16 days) treatments were 80% and 70%, respectively, compared with that of the control.

CONCLUSION

The results suggest that C75 may be superior to siFASN in anticancer effect on prostate cancer.

Downregulation and prognostic performance of microRNA 224 expression in prostate cancer

INTRODUCTION

The extensive use of prostate-specific antigen as a general prostate cancer biomarker has introduced the hazards of overdiagnosis and overtreatment. Recent studies have revealed the immense biomarker capacity of microRNAs (miRNAs) in prostate cancer. The aim of this study was to analyze the expression pattern of miR-224, a cancer-related miRNA, in prostate tumors and investigate its clinical utility.

METHODS

Total RNA was isolated from 139 prostate tissue samples. After the polyadenylation of total RNA by poly(A) polymerase, cDNA was synthesized with a suitable poly(T) adapter. miR-224 expression was assessed by quantitative real-time PCR and analyzed with the comparative quantification cycle method, C(q)(2(-ΔΔCq)). We performed comprehensive biostatistical analyses to explore the clinical value of miR-224 in prostate cancer.

RESULTS

miR-224 expression was significantly downregulated in malignant samples compared with benign samples (P < 0.001). Higher miR-224 expression levels were found in prostate tumors that were less aggressive (P = 0.017) and in an earlier disease stage (P = 0.018). Patients with prostate cancer who were positive for miR-224 had significantly enhanced progression-free survival intervals compared with miR-224-negative patients (P = 0.021). Univariate bootstrap Cox regression confirmed that miR-224 was associated with favorable prognosis (hazard ratio 0.314, P = 0.013); nonetheless, multivariate analysis, adjusted for conventional markers, did not identify miR-224 as an independent prognostic indicator.

CONCLUSIONS

miR-224 is aberrantly expressed in prostate cancer. Its assessment by cost-effective quantitative molecular methodologies could provide a useful biomarker for prostate cancer.

Spectrum of somatic mitochondrial mutations in five cancers

Somatic mtDNA mutations have been reported in some human tumors, but their spectrum in different malignancies and their role in cancer development remain incompletely understood. Here, we describe the breadth of somatic and inherited mutations across the mitochondrial genome by sequence analyses of paired tumor and normal tissue samples from 226 individuals with five types of cancer using whole-genome data generated by The Cancer Genome Atlas Research Network. The frequencies of deleterious tumor-specific somatic mutations found in mtDNA varied across tumor types, ranging from 13% of glioblastomas to 63% of rectal adenocarcinomas. Compared with inherited mtDNA variants, somatic mtDNA mutations were enriched for nonsynonymous vs. synonymous changes (93 vs. 15; P < 2.2E-16) and were predicted to functionally impact the encoded protein. Somatic missense mutations in tumors were distributed uniformly among the mitochondrial protein genes, but 65% of somatic truncating mutations occurred in NADH dehydrogenase 5. Analysis of staging data in colon and rectal cancers revealed that the frequency of damaging mitochondrial mutations is the same in stages I and IV tumors. In summary, these data suggest that damaging somatic mtDNA mutations occur frequently (13-63%) in these five tumor types and likely confer a selective advantage in oncogenesis.

Lipid metabolism in cancer

Lipids form a diverse group of water-insoluble molecules that include triacylglycerides, phosphoglycerides, sterols and sphingolipids. They play several important roles at cellular and organismal levels. Fatty acids are the major building blocks for the synthesis of triacylglycerides, which are mainly used for energy storage. Phosphoglycerides, together with sterols and sphingolipids, represent the major structural components of biological membranes. Lipids can also have important roles in signalling, functioning as second messengers and as hormones. There is increasing evidence that cancer cells show specific alterations in different aspects of lipid metabolism. These alterations can affect the availability of structural lipids for the synthesis of membranes, the synthesis and degradation of lipids that contribute to energy homeostasis and the abundance of lipids with signalling functions. Changes in lipid metabolism can affect numerous cellular processes, including cell growth, proliferation, differentiation and motility. This review will examine some of the alterations in lipid metabolism that have been reported in cancer, at both cellular and organismal levels, and discuss how they contribute to different aspects of tumourigenesis.

Chronic hypoxia induces androgen-independent and invasive behavior in LNCaP human prostate cancer cells

PURPOSE

Tumor hypoxia is a common feature of any cancer, including prostate cancer (CaP), and associated with tumor cell aggressiveness. Although some reports are available on acute hypoxia-response in CaP cells aggressiveness, little is known about chronic hypoxia-response. We investigated the effects of chronic hypoxia on human CaP cells.

MATERIALS AND METHODS

The human androgen-dependent CaP cell line LNCaP was cultured under normoxia (21% O2), acute hypoxia (1% O2), or chronic hypoxia (1% O2 for over 6 months). The cell growth, cell cycle and cell behavior of these cells were analyzed by cell count, flow cytometric analysis and in vitro cell migration and invasion assay, respectively. The expression of matrix metalloproteinases and intracellular signaling pathways were tested by real time reverse transcriptase-polymerase chain reaction and Western blotting.

RESULTS

Chronic hypoxia-conditioned LNCaP cells grew in an androgen-independent manner with acceleration of G1 to S phase cell cycle progression. Chronic hypoxia, but not acute hypoxia, accelerated cell migration and invasion. The expressions of matrix metalloproteinase-7, -9, -14, and -15 were significantly up-regulated in LNCaP cells under chronic hypoxia, but not under acute hypoxia. In addition, PI3K/Akt, JAK/STAT, and HIF-1 pathways were activated in chronic hypoxia-conditioned LNCaP cells.

CONCLUSIONS

These results suggested that chronic hypoxia plays an important role in enhancement of malignant potential during androgen-independent CaP progression.

Metabolite detection of pancreatic carcinoma by in vivo proton MR spectroscopy at 3T: initial results

PURPOSE

The authors sought to identify metabolic features of pancreatic carcinoma by in vivo proton magnetic resonance (MR) spectroscopy at 3 Tesla.

MATERIALS AND METHODS

Forty healthy volunteers and 40 patients with pancreatic carcinoma confirmed by histopathology underwent T2-weighted imaging for localisation of the single voxel. Respiration-triggered (1)H MR spectroscopy was used to detect metabolites in normal pancreas and cancerous tissue. All spectral data were processed with SAGE software. Unsuppressed water at 4.7 ppm was used as an internal reference to determine metabolite concentrations. Each ratio among the different peak areas was statistically evaluated between normal pancreas and pancreatic carcinoma.

RESULTS

The following five groups of spectra were detected: unsaturated fatty acids (-CH = CH-) at 5.4 ppm; residual water at 4.7 ppm; choline metabolites at 3.2 ppm; unsaturated fatty acids (-CH2-CH = CH-) or a combination of N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), glutamine, glutamate, macromolecules and unsaturated fatty acids (-CH2-CH = CH-) at 2.0 ppm and lipids at 1.3 ppm. Ratio of lipids to unsuppressed water in normal pancreas was statistically greater than that in pancreatic cancer (p=0.004). Ratio of choline to unsuppressed water in normal pancreas was statistically greater than that in pancreatic cancer (p=0.0001). Ratio of fatty acids (-CH = CH-) to lipids in normal pancreas was statistically lower than that in pancreatic cancer (p=0.006).

CONCLUSIONS

Compared with normal pancreas, pancreatic carcinoma has a higher ratio of fatty acids (-CH = CH-) to lipids and lower ratios of lipids to unsuppressed water and choline to unsuppressed water at 3T.

Antitumor effect of orlistat, a fatty acid synthase inhibitor, is via activation of caspase-3 on human colorectal carcinoma-bearing animal

We established a HT-29/tk-luc human colorectal carcinoma-bearing animal model for the study of the inhibition effect and mechanism of orlistat, a fatty acid synthase (FASN) inhibitor. The results showed that orlistat caused cell cycle arrest at G1 phase, and triggered apoptosis through caspase-3 activation. The tumor inhibition effect of orlistat may also due to the inhibition of fatty acid synthesis without altering FASN activity. The tumor size of orlistat-treated mice in vivo was significantly smaller than that of the controls with 55% inhibition. The therapeutic efficacy was further confirmed with the bioluminescent imaging and nuclear molecular imaging with ¹³¹I-FIAU/gamma scintigraphy and ¹¹C-acetate/microPET. We suggest that FASN is a potential target for the treatment of human colorectal carcinoma.

Molecular characterization and mRNA expression of two key enzymes of hypoxia-sensing pathways in eastern oysters Crassostrea virginica (Gmelin): hypoxia-inducible factor α (HIF-α) and HIF-prolyl hydroxylase (PHD)

Oxygen homeostasis is crucial for development, survival and normal function of all metazoans. A family of transcription factors called hypoxia-inducible factors (HIF) is critical in mediating the adaptive responses to reduced oxygen availability. The HIF transcription factor consists of a constitutively expressed β subunit and an oxygen-dependent α subunit; the abundance of the latter determines the activity of HIF and is regulated by a family of O(2)- and Fe(2+)-dependent enzymes prolyl hydroxylases (PHDs). Currently very little is known about the function of this important pathway and the molecular structure of its key players in hypoxia-tolerant intertidal mollusks including oysters, which are among the animal champions of anoxic and hypoxic tolerance and thus can serve as excellent models to study the role of HIF cascade in adaptations to oxygen deficiency. We have isolated transcripts of two key components of the oxygen sensing pathway - the oxygen-regulated HIF-α subunit and PHD - from an intertidal mollusk, the eastern oyster Crassostrea virginica, and determined the transcriptional responses of these two genes to anoxia, hypoxia and cadmium (Cd) stress. HIF-α and PHD homologs from eastern oysters C. virginica show significant sequence similarity and share key functional domains with the earlier described isoforms from vertebrates and invertebrates. Phylogenetic analysis shows that genetic diversification of HIF and PHD isoforms occurred within the vertebrate lineage indicating functional diversification and specialization of the oxygen-sensing pathways in this group, which parallels situation observed for many other important genes. HIF-α and PHD homologs are broadly expressed at the mRNA level in different oyster tissues and show transcriptional responses to prolonged hypoxia in the gills consistent with their putative role in oxygen sensing and the adaptive response to hypoxia. Similarity in amino acid sequence, domain structure and transcriptional responses between HIF-α and PHD homologs from oysters and other invertebrate and vertebrate species implies the highly conserved functions of these genes throughout the evolutionary history of animals, in accordance with their critical role in oxygen sensing and homeostasis.

Repositioning chloroquine and metformin to eliminate cancer stem cell traits in pre-malignant lesions

Ideal oncology drugs would be curative after a short treatment course if they could eliminate epithelium-originated carcinomas at their non-invasive, pre-malignant stages. Such ideal molecules, which are expected to molecularly abrogate all the instrumental mechanisms acquired by migrating cancer stem cells (CSCs) to by-pass tumour suppressor barriers, might already exist. We here illustrate how system biology strategies for repositioning existing FDA-approved drugs may accelerate our therapeutic capacity to eliminate CSC traits in pre-invasive intraepithelial neoplasias. First, we describe a signalling network signature that overrides bioenergetics stress- and oncogene-induced senescence (OIS) phenomena in CSCs residing at pre-invasive lesions. Second, we functionally map the anti-malarial chloroquine and the anti-diabetic metformin ("old drugs") to their recently recognized CSC targets ("new uses") within the network. By discussing the preclinical efficacy of chloroquine and metformin to inhibiting the genesis and self-renewal of CSCs we finally underscore the expected translational impact of the "old drugs-new uses" repurposing strategy to open a new CSC-targeted chemoprevention era.

p53 downregulates the gene expression of mitochondrial aconitase in human prostate carcinoma cells

BACKGROUND

Mitochondrial aconitase (mACON) is regarded as the key enzyme in citrate oxidation in human prostate epithelial cells, and its abnormal expression has been implicated in tumorigenesis of the prostate. Evidence also supports a broad role for the p53 gene in suppressing prostatic tumorigenesis. We investigated whether p53 regulates mACON expression and explore the potential mechanisms responsible for its effect on prostate cancer cells.

METHODS

Camptothecin (CPT) treatments and transient overexpression of p53 were used to investigate p53 regulation of mACON and may effects were assessed using immunoblotting and transient gene expression assays.

RESULTS

In vitro enzymatic activity assays and immunoblot assays showed that CPT treatment induced p53 expression while reducing mACON protein biosynthesis in wild-type p53 expressing LNCaP cells. Immunoblot assays and reporter assays revealed that transient transfection of a p53 expression vector into p53-null PC-3 cells decreased mACON expression. Cyclic pifithrin-α, an inhibitor of p53 transcriptional activity, blocked the decrease in mACON gene expression resulting from CPT treatment in LNCaP cells. Two putative p53 response elements were identified within the mACON promoter; however, mutation of these putative p53 response elements did not abolish the effect of CPT whereby it decreased mACON expression. A similar result was obtained for the effect of these mutants on the promoter activity of the mACON gene after transient overexpression of p53.

CONCLUSIONS

Together these results suggest that p53 downregulation of mACON gene expression in human prostate carcinoma cells may not occur through the putative consensus p53 response elements found within the mACON promoter.

Hypoxia-induced metabolic shifts in cancer cells: moving beyond the Warburg effect

Hypoxia has been recognized to play a role in promoting the invasive and metastatic behaviour of cancer cells. Largely via the transcription factor, hypoxia-induced factor 1, hypoxia exerts significant effects on cellular metabolism, with numerous downstream consequences. Energetically there is a significant shift away from oxidative phosphorylation in mitochondria towards glycolysis, a state also involved in the 'Warburg effect'. The proteins involved in mediating the altered metabolic pathways seen in tumour cells thus represent new targets for potential therapeutic intervention. Hypoxia has been associated with the development of aggressive phenotypes in cancer cells, and can be accompanied by changes in carbohydrate and lipid metabolism that impact tumour cell proliferation, adhesion, and angiogenesis. Herein, we examine glycolytic and other less investigated metabolic pathways in relation to cancer and hypoxia, with a focus on emerging tools for large-scale metabolite profiling ('metabolomics'). Metabolomic technologies permit the measurement of a wide range of metabolites in an untargeted manner, however, to date, this technology has been relatively under utilized for studying cellular responses to hypoxia. We detail some of the common experimental approaches employed in metabolomics experiments, including nuclear magnetic resonance and new mass spectrometry-based methods of analysis. Selected examples of the application of these technologies to the study of metabolic alterations brought about by hypoxia are provided, particularly as they relate to energy, carbohydrate, and lipid metabolism. Finally, the potential for therapeutic targeting of metabolic processes activated by hypoxia is presented.

The Akt-SREBP nexus: cell signaling meets lipid metabolism

Phosphatidylinositol 3'-kinase (PI3K) and Akt are signaling kinases involved in cell survival and proliferation. Recent evidence suggests that PI3K/Akt activates the sterol-regulatory element-binding proteins (SREBPs), master transcriptional regulators of lipid metabolism. The precise molecular mechanisms are controversial and differ between SREBP isoforms; proposed mechanisms include increased trafficking and processing of SREBP, reduced degradation, and involvement of the downstream signaling hub, mammalian target of rapamycin complex 1 (mTORC1). In this report, we explore the various mechanistic links between Akt and SREBP. We consider this relationship in diseases where Akt and lipids play crucial roles, including diabetes, viral infections and cancer, suggesting that this Akt-SREBP link provides fresh insights into human health and disease.

Metabolic function in Drosophila melanogaster in response to hypoxia and pure oxygen

This study examined the metabolic response of Drosophila melanogaster exposed to O(2) concentrations ranging from 0 to 21% and at 100%. The metabolic rate of flies exposed to graded hypoxia remained nearly constant as O(2) tensions were reduced from normoxia to approximately 3 kPa. There was a rapid, approximately linear reduction in fly metabolic rate at P(O(2))s between 3 and 0.5 kPa. The reduction in metabolic rate was especially pronounced at P(O(2)) levels <0.5 kPa, and at a P(O(2)) of 0.1 kPa fly metabolic rate was reduced approximately 10-fold relative to normoxic levels. The metabolic rate of flies exposed to anoxia and then returned to normoxia recovered to pre-anoxic levels within 30 min with no apparent payment of a hypoxia-induced oxygen debt. Flies tolerated exposure to hypoxia and/or anoxia for 40 min with nearly 100% survival. Fly mortality increased rapidly after 2 h of anoxia and >16 h exposure was uniformly lethal. Flies exposed to pure O(2) for 24 h showed no apparent alteration of metabolic rate, even though such O(2) tensions should damage respiratory enzymes critical to mitochondria function. Within a few hours the metabolic rate of flies recovering from exposure to repeated short bouts of anoxia was the same as flies exposed to a single anoxia exposure.

Fluorescence lifetime imaging of endogenous fluorophores in histopathology sections reveals differences between normal and tumor epithelium in carcinoma in situ of the breast

The classical examination of histology slides from a mouse model of breast cancer has been extended in this study to incorporate modern multiphoton excitation and photon-counting techniques. The advantage of such approaches is quantification of potential diagnostic parameters from the fluorescence emission signal, whereby the traditional descriptive staging process is complemented by measurements of fluorescence intensity, lifetime, and spectra. We explored whether the clinical "gold standard" of eosin and hematoxylin stained histology slides would provide optical biomarker signatures of diagnostic value. Alternatively, we examined unstained slides for changes in intensity and/or fluorescence lifetime of relevant endogenous fluorophores. Although eosin provided a strong emission signal and had distinct spectra and lifetime, we found that it was not useful as a fluorescent biological marker, particularly when combined with hematoxylin. Instead, we found that the properties of the fluorescence from the endogenous fluorophores NADH and FAD were indicative of the pathological state of the tissue. Comparing regions of carcinoma in situ to adjacent histologically normal regions, we found that tumor cells produced higher intensity and had a longer fluorescence lifetime. By imaging at 780 nm and 890 nm excitation, we were able to differentiate the fluorescence of FAD from NADH by separating the emission spectra. The shift to a longer lifetime in tumor cells was independent of the free or bound state of FAD and NADH, and of the excitation wavelength. Most forms of cancer have altered metabolism and redox ratios; here we present a method that has potential for early detection of these changes, which are preserved in fixed tissue samples such as classic histopathology slides.

Two-photon autofluorescence dynamics imaging reveals sensitivity of intracellular NADH concentration and conformation to cell physiology at the single-cell level

Reduced nicotinamide adenine dinucleotide, NADH, is a major electron donor in the oxidative phosphorylation and glycolytic pathways in cells. As a result, there has been recent resurgence in employing intrinsic NADH fluorescence as a natural probe for a range of cellular processes that include apoptosis, cancer pathology, and enzyme kinetics. Here, we report on two-photon fluorescence lifetime and polarization imaging of intrinsic NADH in breast cancer (Hs578T) and normal (Hs578Bst) cells for quantitative analysis of the concentration and conformation (i.e., free-to-enzyme-bound ratios) of this coenzyme. Two-photon fluorescence lifetime imaging of intracellular NADH indicates sensitivity to both cell pathology and inhibition of the respiratory chain activities using potassium cyanide (KCN). Using a newly developed non-invasive assay, we estimate the average NADH concentration in cancer cells (168+/-49 microM) to be approximately 1.8-fold higher than in breast normal cells (99+/-37 microM). Such analyses indicate changes in energy metabolism and redox reactions in normal breast cells upon inhibition of the respiratory chain activity using KCN. In addition, time-resolved associated anisotropy of cellular autofluorescence indicates population fractions of free (0.18+/-0.08) and enzyme-bound (0.82+/-0.08) conformations of intracellular NADH in normal breast cells. These fractions are statistically different from those in breast cancer cells (free: 0.25+/-0.08; bound: 0.75+/-0.08). Comparative studies on the binding kinetics of NADH with mitochondrial malate dehydrogenase and lactate dehydrogenase in solution mimic our findings in living cells. These quantitative studies demonstrate the potential of intracellular NADH dynamics (rather than intensity) imaging for probing mitochondrial anomalies associated with neurodegenerative diseases, cancer, diabetes, and aging. Our approach is also applicable to other metabolic and signaling pathways in living cells, without the need for cell destruction as in conventional biochemical assays.

Recent advances in the chemistry and biology of naturally occurring antibiotics

Ever since the world-shaping discovery of penicillin, nature's molecular diversity has been extensively screened for new medications and lead compounds in drug discovery. The search for agents intended to combat infectious diseases has been of particular interest and has enjoyed a high degree of success. Indeed, the history of antibiotics is marked with impressive discoveries and drug-development stories, the overwhelming majority of which have their origin in natural products. Chemistry, and in particular chemical synthesis, has played a major role in bringing naturally occurring antibiotics and their derivatives to the clinic, and no doubt these disciplines will continue to be key enabling technologies. In this review article, we highlight a number of recent discoveries and advances in the chemistry, biology, and medicine of naturally occurring antibiotics, with particular emphasis on total synthesis, analogue design, and biological evaluation of molecules with novel mechanisms of action.