Isotype-specific inhibitors of the glycolytic key regulator pyruvate kinase subtype M2 moderately decelerate tumor cell proliferation

The PKM2 inhibitor shikonin enhances piceatannol-induced apoptosis of glyoxalase I-dependent cancer cells

Glyoxalase I (GLO I), a major enzyme involved in the detoxification of the anaerobic glycolytic byproduct methylglyoxal, is highly expressed in various tumors, and is regarded as a promising target for cancer therapy. We recently reported that piceatannol potently inhibits human GLO I and induces the death of GLO I-dependent cancer cells. Pyruvate kinase M2 (PKM2) is also a potential therapeutic target for cancer treatment, so we evaluated the combined anticancer efficacy of piceatannol plus low-dose shikonin, a potent and specific plant-derived PKM2 inhibitor, in two GLO I-dependent cancer cell lines, HL-60 human myeloid leukemia cells and NCI-H522 human non-small-cell lung cancer cells. Combined treatment with piceatannol and low-dose shikonin for 48 h synergistically reduced cell viability, enhanced apoptosis rate, and increased extracellular methylglyoxal accumulation compared to single-agent treatment, but did not alter PKM1, PKM2, or GLO I protein expression. Taken together, these results indicate that concomitant use of low-dose shikonin potentiates piceatannol-induced apoptosis of GLO I-dependent cancer cells by augmenting methylglyoxal accumulation.

TRAF6 promotes chemoresistance to paclitaxel of triple negative breast cancer via regulating PKM2-mediated glycolysis

Ample evidence reveals that glycolysis is crucial to tumor progression; however, the underlying mechanism of its drug resistance is still worth being further explored. TRAF6, an E3 ubiquitin ligase, is well recognized to overexpress in various types of cancer, which predicts a poor prognosis. In our study, we discovered that TRAF6 was expressed more significantly in the case of triple-negative breast cancer (TNBC) than in other of breast cancers, promoting chemoresistance to paclitaxel; that inhibited TRAF6 expression in the chemoresistant TNBC (TNBC-CR) cells enhanced the sensitivity by decreasing glucose uptake and lactate production; that TRAF6 regulated glycolysis and facilitated chemoresistance via binding directly to PKM2; and that overexpressing PKM2 in the TNBC-CR cells with TRAF6 knocked down regained significantly TRAF6-dependent drug resistance and glycolysis. Additionally, we verified that TRAF6 could facilitate PKM2-mediated glycolysis and chemoresistance in animal models and clinical tumor tissues. Thus, we identified the novel function of TRAF6 to promote glycolysis and drug resistance in TNBC with the regulation of PKM2, which could provide a potential molecular target for TNBC treatment.

The Role of RNA m6A Modification in Cancer Glycolytic Reprogramming

As one of the main characteristics of neoplasia, metabolic reprogramming provides nutrition and energy to enhance cell proliferation and maintain environment homeostasis. Glycolysis is one of the most important components of cancer metabolism and the Warburg effect contributes to the competitive advantages of cancer cells in the threatened microenvironment. Studies show strong links between N⁶-methyladenosine (m⁶A) modification and metabolic recombination of cancer cells. As the most abundant modification in eukaryotic RNA, m⁶A methylation plays important roles in regulating RNA processing, including splicing, stability, transportation, translation and degradation. The aberration of m⁶A modification can be observed in a variety of diseases such as diabetes, neurological diseases and cancers. This review describes the mechanisms of m⁶A on cancer glycolysis and their applications in cancer therapy and prognosis evaluation, aiming to emphasize the importance of targeting m⁶A in modulating cancer metabolism.

The roles of glycolysis in osteosarcoma

Metabolic reprogramming is of great significance in the progression of various cancers and is critical for cancer progression, diagnosis, and treatment. Cellular metabolic pathways mainly include glycolysis, fat metabolism, glutamine decomposition, and oxidative phosphorylation. In cancer cells, reprogramming metabolic pathways is used to meet the massive energy requirement for tumorigenesis and development. Metabolisms are also altered in malignant osteosarcoma (OS) cells. Among reprogrammed metabolisms, alterations in aerobic glycolysis are key to the massive biosynthesis and energy demands of OS cells to sustain their growth and metastasis. Numerous studies have demonstrated that compared to normal cells, glycolysis in OS cells under aerobic conditions is substantially enhanced to promote malignant behaviors such as proliferation, invasion, metastasis, and drug resistance of OS. Glycolysis in OS is closely related to various oncogenes and tumor suppressor genes, and numerous signaling pathways have been reported to be involved in the regulation of glycolysis. In recent years, a vast number of inhibitors and natural products have been discovered to inhibit OS progression by targeting glycolysis-related proteins. These potential inhibitors and natural products may be ideal candidates for the treatment of osteosarcoma following hundreds of preclinical and clinical trials. In this article, we explore key pathways, glycolysis enzymes, non-coding RNAs, inhibitors, and natural products regulating aerobic glycolysis in OS cells to gain a deeper understanding of the relationship between glycolysis and the progression of OS and discover novel therapeutic approaches targeting glycolytic metabolism in OS.

Research progress on the role of PKM2 in the immune response

Pyruvate kinase (PK) is a key enzyme that catalyzes the dephosphorylation of phosphoenolpyruvate (PEP) into pyruvate, and is responsible for the production of ATP during glycolysis. As another important isozyme of PK, pyruvate kinase M2 (PKM2) exists in cells with high levels of nucleic acid synthesis, such as normal proliferating cells (e.g., lymphocytes and intestinal epithelial cells), embryonic cells, adult stem cells, and tumor cells. With further research, PKM2, as an important regulator of cellular pathophysiological activity, has attracted increasing attention in the process of autoimmune response and inflammatory. In this re]view, we examine the contribution of PKM2 to the human immune response. Further studies on the immune mechanisms of PKM2 are expected to provide more new ideas and drug targets for immunotherapy of inflammatory and autoimmune diseases, guiding drug development and disease treatment.

Development and validation of a novel epigenetic-related prognostic signature and candidate drugs for patients with lung adenocarcinoma

Background: Epigenetic dysregulation has been increasingly proposed as a hallmark of cancer. Here, the aim of this study is to establish an epigenetic-related signature for predicting the prognosis of lung adenocarcinoma (LUAD) patients.

Results: Five epigenetic-related genes (ERGs) (ARRB1, PARP1, PKM, TFDP1, and YWHAZ) were identified as prognostic hub genes and used to establish a prognostic signature. According our risk score system, LUAD patients were stratified into high and low risk groups, and patients in the high risk group had a worse prognosis. ROC analysis indicated that the signature was precise in predicting the prognosis. A new nomogram was constructed based on the five hub genes, which can predict the OS of every LUAD patients. The calibration curves showed that the nomogram had better accuracy in prediction. Finally, candidate drugs that aimed at hub ERGs were identified, which included 47 compounds.

Conclusions: Our epigenetic-related signature nomogram can effectively and reliably predict OS of LUAD patients, also we provide precise targeted chemotherapeutic drugs.

Methods: The genomic data and clinical data of LUAD cohort were downloaded from the TCGA database and ERGs were obtained from the EpiFactors database. GSE31210 and GSE50081 microarray datasets were included as independent external datasets. Univariate Cox, LASSO regression, and multivariate Cox analyses were applied to construct the epigenetic-related signature.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

Specific Pyruvate Kinase M2 Inhibitor, Compound 3K, Induces Autophagic Cell Death through Disruption of the Glycolysis Pathway in Ovarian Cancer Cells

Ovarian cancer is a common cause of death among gynecological cancers. Although ovarian cancer initially responds to chemotherapy, frequent recurrence in patients remains a therapeutic challenge. Pyruvate kinase M2 (PKM2) plays a pivotal role in regulating cancer cell survival. However, its therapeutic role remains unclear. Here, we investigated the anticancer effects of compound 3K, a specific PKM2 inhibitor, on the regulation of autophagic and apoptotic pathways in SK-OV-3 (PKM2-overexpressing human ovarian adenocarcinoma cell line). The anticancer effect of compound 3K was examined using MTT and colony formation assays in SK-OV-3 cells. PKM2 expression was positively correlated with the severity of the tumor, and expression of pro-apoptotic proteins increased in SK-OV-3 cells following compound 3K treatment. Compound 3K induced AMPK activation, which was accompanied by mTOR inhibition. Additionally, this compound inhibited glycolysis, resulting in reduced proliferation of SK-OV-3 cells. Compound 3K treatment suppressed tumor progression in an in vivo xenograft model. Our findings suggest that the inhibition of PKM2 by compound 3K affected the Warburg effect and induced autophagic cell death. Therefore, use of specific PKM2 inhibitors to block the glycolytic pathway and target cancer cell metabolism represents a promising therapeutic approach for treating PKM2-overexpressing ovarian cancer.

Mechanism of PKM2 affecting cancer immunity and metabolism in Tumor Microenvironment

PKM2 is the enzyme that regulates the final rate-limiting step of glycolysis. PKM2 expression can reinforce the utilization of oxygen and synthesis of growth substances in cancer cells by enhancing OXPHOS and the Warburg effect. In cancer immunity, PKM2 can modulate the expression of PD-L1 in M2 macrophage and decrease the amount and activity of CD8⁺ T cells. This affects cancer cell killing and immune escape sequentially. How PKM2 regulates PD-L1 expression through immunometabolism is summarized. PKM2 builds a bridge between energy metabolism and cancer immunity. The activator and inhibitor of PKM2 both promote the anti-cancer immune response and inhibit cancer growth and metastasis by regulating the metabolism of cancer cells and immune cells in the tumor microenvironment through HIF-1α/PKM2 pathway. This review focuses on the precise role of PKM2 modulating immunometabolism, providing valuable suggestions for further study in this field.

Tumor suppressor SMAR1 regulates PKM alternative splicing by HDAC6-mediated deacetylation of PTBP1

BACKGROUND

Highly proliferating cancer cells exhibit the Warburg effect by regulation of PKM alternative splicing and promoting the expression of PKM2. Majority of the alternative splicing events are known to occur in the nuclear matrix where various MARBPs actively participate in the alternative splicing events. SMAR1, being a MARBP and an important tumor suppressor, is known to regulate the splicing of various cancer-associated genes. This study focuses on the regulation of PKM alternative splicing and inhibition of the Warburg effect by SMAR1.

METHODS

Immunohistochemistry was performed in breast cancer patient samples to establish the correlation between SMAR1 and PKM isoform expression. Further, expression of PKM isoforms upon modulation in SMAR1 expression in breast cancer cell lines was quantified by qRT-PCR and western blot. The acetylation status of PTBP1 was estimated by immunoprecipitation along with its enrichment on PKM pre-mRNA by CLIP in SMAR1 knockdown conditions. The role of SMAR1 in tumor metabolism and tumorigenesis was explored by in vitro enzymatic assays and functional assays upon SMAR1 knockdown. Besides, in vivo tumor formation by injecting adeno-SMAR1-transduced MDA-MB-231 cells in NOD/SCID mice was performed.

RESULTS

The expression profile of SMAR1 and PKM isoforms in breast cancer patients revealed that SMAR1 has an inverse correlation with PKM2 and a positive correlation with PKM1. Further quantitative PKM isoform expression upon modulation in SMAR1 expression also reflects that SMAR1 promotes the expression of PKM1 over tumorigenic isoform PKM2. SMAR1 deacetylates PTBP1 via recruitment of HDAC6 resulting in reduced enrichment of PTBP1 on PKM pre-mRNA. SMAR1 inhibits the Warburg effect, tumorigenic potential of cancer cells, and in vivo tumor generation in a PKM2-dependent manner.

CONCLUSIONS

SMAR1 regulates PKM alternative splicing by causing HDAC6-dependent deacetylation of PTBP1, resulting in reduced enrichment of PTBP1 on PKM pre-mRNA. Additionally, SMAR1 suppresses glucose utilization and lactate production via repression of PKM2 expression. This suggests that tumor suppressor SMAR1 inhibits tumor cell metabolism and tumorigenic properties of cancer cells via regulation of PKM alternative splicing.

Structural basis for allosteric regulation of pyruvate kinase M2 by phosphorylation and acetylation

Pyruvate kinase muscle isoform 2 (PKM2) is a key glycolytic enzyme and transcriptional coactivator and is critical for tumor metabolism. In cancer cells, native tetrameric PKM2 is phosphorylated or acetylated, which initiates a switch to a dimeric/monomeric form that translocates into the nucleus, causing oncogene transcription. However, it is not known how these post-translational modifications (PTMs) disrupt the oligomeric state of PKM2. We explored this question via crystallographic and biophysical analyses of PKM2 mutants containing residues that mimic phosphorylation and acetylation. We find that the PTMs elicit major structural reorganization of the fructose 1,6-bisphosphate (FBP), an allosteric activator, binding site, impacting the interaction with FBP and causing a disruption in oligomerization. To gain insight into how these modifications might cause unique outcomes in cancer cells, we examined the impact of increasing the intracellular pH (pH_i) from ∼7.1 (in normal cells) to ∼7.5 (in cancer cells). Biochemical studies of WT PKM2 (wtPKM2) and the two mimetic variants demonstrated that the activity decreases as the pH is increased from 7.0 to 8.0, and wtPKM2 is optimally active and amenable to FBP-mediated allosteric regulation at pH_i 7.5. However, the PTM mimetics exist as a mixture of tetramer and dimer, indicating that physiologically dimeric fraction is important and might be necessary for the modified PKM2 to translocate into the nucleus. Thus, our findings provide insight into how PTMs and pH regulate PKM2 and offer a broader understanding of its intricate allosteric regulation mechanism by phosphorylation or acetylation.

HMGCR inhibition stabilizes the glycolytic enzyme PKM2 to support the growth of renal cell carcinoma

Renal cell carcinoma (RCC) is responsible for most cases of the kidney cancer. Previous research showed that low serum levels of cholesterol level positively correlate with poorer RCC-specific survival outcomes. However, the underlying mechanisms and functional significance of the role of cholesterol in the development of RCC remain obscure. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) plays a pivotal role in RCC development as it is the key rate-limiting enzyme of the cholesterol biosynthetic pathway. In this study, we demonstrated that the inhibition of HMGCR could accelerate the development of RCC tumors by lactate accumulation and angiogenesis in animal models. We identified that the inhibition of HMGCR led to an increase in glycolysis via the regulated HSP90 expression levels, thus maintaining the levels of a glycolysis rate-limiting enzyme, pyruvate kinase M2 (PKM2). Based on these findings, we reversed the HMGCR inhibition-induced tumor growth acceleration in RCC xenograft mice by suppressing glycolysis. Furthermore, the coadministration of Shikonin, a potent PKM2 inhibitor, reverted the tumor development induced by the HMGCR signaling pathway.

Protein kinase function of pyruvate kinase M2 and cancer

Pyruvate kinase is a terminal enzyme in the glycolytic pathway, where it catalyzes the conversion of phosphoenolpyruvate to pyruvate and production of ATP via substrate level phosphorylation. PKM2 is one of four isoforms of pyruvate kinase and is widely expressed in many types of tumors and associated with tumorigenesis. In addition to pyruvate kinase activity involving the metabolic pathway, increasing evidence demonstrates that PKM2 exerts a non-metabolic function in cancers. PKM2 has been shown to be translocated into nucleus, where it serves as a protein kinase to phosphorylate various protein targets and contribute to multiple physiopathological processes. We discuss the nuclear localization of PKM2, its protein kinase function and association with cancers, and regulation of PKM2 activity.

Biochemical and structural insights into how amino acids regulate pyruvate kinase muscle isoform 2

Pyruvate kinase muscle isoform 2 (PKM2) is a key glycolytic enzyme involved in ATP generation and critical for cancer metabolism. PKM2 is expressed in many human cancers and is regulated by complex mechanisms that promote tumor growth and proliferation. Therefore, it is considered an attractive therapeutic target for modulating tumor metabolism. Various stimuli allosterically regulate PKM2 by cycling it between highly active and less active states. Several small molecules activate PKM2 by binding to its intersubunit interface. Serine and cysteine serve as an activator and inhibitor of PKM2, respectively, by binding to its amino acid (AA)-binding pocket, which therefore represents a potential druggable site. Despite binding similarly to PKM2, how cysteine and serine differentially regulate this enzyme remains elusive. Using kinetic analyses, fluorescence binding, X-ray crystallography, and gel filtration experiments with asparagine, aspartate, and valine as PKM2 ligands, we examined whether the differences in the side-chain polarity of these AAs trigger distinct allosteric responses in PKM2. We found that Asn (polar) and Asp (charged) activate PKM2 and that Val (hydrophobic) inhibits it. The results also indicate that both Asn and Asp can restore the activity of Val-inhibited PKM2. AA-bound crystal structures of PKM2 displayed distinctive interactions within the binding pocket, causing unique allosteric effects in the enzyme. These structure-function analyses of AA-mediated PKM2 regulation shed light on the chemical requirements in the development of mechanism-based small-molecule modulators targeting the AA-binding pocket of PKM2 and provide broader insights into the regulatory mechanisms of complex allosteric enzymes.

Pyruvate kinase M2 represses thermogenic gene expression in brown adipocytes

Utilizing the thermogenic capacity of brown adipose tissue is a potential anti-obesity strategy; therefore, the mechanisms controlling expression of thermogenesis-related genes are of interest. Pyruvate kinase (PK) catalyzes the last step of glycolysis and exists as four isoenzymes: PK, liver, PK, red blood cell, PK, muscle (PKM1 and PKM2). PKM2 has both glycolytic and nuclear functions. Here, we report that PKM2 is enriched in brown adipose compared with white adipose tissue. Specific knockdown of PKM2 in mature brown adipocytes demonstrates that silencing of PKM2 does not lead to a decrease in PK activity, but causes a robust upregulation of thermogenic uncoupling protein 1 (Ucp1) and fibroblast growth factor 21 (Fgf21) gene expression. This increase is not mediated by any of the known mechanisms for PKM2-regulated gene expression, thus implying the existence of a novel mechanism for PKM2-dependent effects on gene expression.

Activation of AMPK promotes thyroid cancer cell migration through its interaction with PKM2 and β-catenin

AMP-activated protein kinase (AMPK) is induced by the exhaustion of cellular energy and activates adaptive alterations in cellular metabolism, which is the basis for cell survival during different environmental stresses. We aimed to investigate the biological functions of AMPK and its molecular mechanism in regulating thyroid cancer (TC) progression. In current study, we found that activation of AMPK by multiple agonists suppresses TC cell proliferation. However, AMPK activation also led to TC cell migration at the same time. Depletion of AMPK abolished the effect of its agonist on cell multiplication and migration. Mechanistic investigations revealed that the impact of AMPK in terms of cell migration is dependent on its nuclear translocation, since site mutation of AMPK in its nuclear translocation domain (K244A) abolished TC cell migration but did not affect the inhibition of cell proliferation by AMPK agonist. Moreover, the nuclear AMPK recruits PKM2 and β-catenin by their interaction, which promotes the transcription of cell migration related genes, including MMP7 and c-Myc. Furthermore, depletion of PKM2/β-catenin abolished the migration effect of AMPK agonists, but did not affect their effects on suppression of cell proliferation. Our results provided a novel function of AMPK in cancer migration, and suggested that a combination of AMPK activation and PKM2 depletion or inhibition can be a new strategy to achieve better therapeutic effects for TC patients.

The role of pyruvate kinase M2 in anticancer therapeutic treatments

Cancer cells are characterized by a high glycolytic rate, which leads to energy regeneration and anabolic metabolism; a consequence of this is the abnormal expression of pyruvate kinase isoenzyme M2 (PKM2). Multiple studies have demonstrated that the expression levels of PKM2 are upregulated in numerous cancer types. Consequently, the mechanism of action of certain anticancer drugs is to downregulate PKM2 expression, indicating the significance of PKM2 in a chemotherapeutic setting. Furthermore, it has previously been highlighted that the downregulation of PKM2 expression, using either inhibitors or short interfering RNA, enhances the anticancer effect exerted by THP treatment on bladder cancer cells, both in vitro and in vivo. The present review summarizes the detailed mechanisms and therapeutic relevance of anticancer drugs that inhibit PKM2 expression. In addition, the relationship between PKM2 expression levels and drug resistance were explored. Finally, future directions, such as the targeting of PKM2 as a strategy to explore novel anticancer agents, were suggested. The current review explored and highlighted the important role of PKM2 in anticancer treatments.

A critical review of the role of M2PYK in the Warburg effect

It is becoming generally accepted in recent literature that the Warburg effect in cancer depends on inhibition of M₂PYK, the pyruvate kinase isozyme most commonly expressed in tumors. We remain skeptical. There continues to be a general lack of solid experimental evidence for the underlying idea that a bottle neck in aerobic glycolysis at the level of M₂PYK results in an expanded pool of glycolytic intermediates (which are thought to serve as building blocks necessary for proliferation and growth of cancer cells). If a bottle neck at M₂PYK exists, then the remarkable increase in lactate production by cancer cells is a paradox, particularly since a high percentage of the carbons of lactate originate from glucose. The finding that pyruvate kinase activity is invariantly increased rather than decreased in cancer undermines the logic of the M₂PYK bottle neck, but is consistent with high lactate production. The "inactive" state of M₂PYK in cancer is often described as a dimer (with reduced substrate affinity) that has dissociated from an active tetramer of M₂PYK. Although M₂PYK clearly dissociates easier than other isozymes of pyruvate kinase, it is not clear that dissociation of the tetramer occurs in vivo when ligands are present that promote tetramer formation. Furthermore, it is also not clear whether the dissociated dimer retains any activity at all. A number of non-canonical functions for M₂PYK have been proposed, all of which can be challenged by the finding that not all cancer cell types are dependent on M₂PYK expression. Additional in-depth studies of the Warburg effect and specifically of the possible regulatory role of M₂PYK in the Warburg effect are needed.

Virtual high-throughput screens identifying hPK-M2 inhibitors: Exploration of model extrapolation

Glycolysis with PK-M2 occurs typically in anaerobic conditions and atypically in aerobic conditions, which is known as the Warburg effect. The Warburg effect is found in many oncogenic situations and is believed to provide energy and biomass for oncogenesis to persist. The work presented targets human PK-M2 (hPK-M2) in a virtual high-throughput screen to identify new inhibitors and leads for further study. In the initial screen, one of the 12 candidates selected for experimental validation showed biological activity (hit-rate = 8.13%). In the second screen with retrained models, six of 11 candidates selected for experimental validation showed biological activity (hit-rate: 54.5%). Additionally, four different scaffolds were identified for further analysis when examining the tested candidates and compounds in the training data. Finally, extrapolation was necessary to identify a sufficient number of candidates to test in the second screen. Examination of the results suggested stepwise extrapolation to maximize efficiency.

Activation of AMPK by metformin promotes renal cancer cell proliferation under glucose deprivation through its interaction with PKM2

Metformin, a common therapeutics for type 2 diabetics, was recently demonstrated to possess antitumor activity in various cancer types. However, its therapy effect in renal cell carcinoma (RCC) still remains controversial. In this study, we found that metformin treatment in RCC cells lead to activation of AMPK, which suppressed the cell proliferation under normal condition, but enhanced cell proliferation under glucose deprivation (GD) condition. Depletion of AMPK by siRNA abolished the proliferation effect of MF under GD condition. Mechanistic investigations revealed that the effect of AMPK on cell proliferation under GD condition is dependent on its nuclear translocation. Moreover, the nuclear AMPK recruits PKM2 and β-Catenin to form a complex, which promotes the transcription of cell proliferation related genes, including CCND1 and c-Myc. Furthermore, depletion of PKM2 or β-Catenin abrogated the proliferative effects of metformin under GD condition. And inhibition of PKM2 also re-sensitized the A498 xenograft in response to metformin treatment. Together, our results suggested that combined of AMPK activation and PKM2 depletion or inhibition can achieve better therapeutic effect for RCC patients.

PKM2 Inhibitor Shikonin Overcomes the Cisplatin Resistance in Bladder Cancer by Inducing Necroptosis

Cisplatin-based chemotherapy often results in the development of chemo-resistance when used to treat bladder cancer (BC), which is difficult to overcome. Recent data indicate that pyruvate kinase M2 (PKM2), a glycolytic enzyme for Warburg effect, is strongly upregulated in BC, and contributes to the cisplatin resistance in BC. However, the underlying mechanisms remain unclear. In this study, we also found that the expression level of PKM2 is also higher in cisplatin resistant BC cells and tumors. Down-regulation of PKM2 by siRNA or inhibition of PKM2 by shikonin re-sensitized the cisplatin resistant T24 cells. Shikonin and cisplatin together exhibit significantly greater killing effects than when used alone. Interestingly, we found shikonin kills the T24 cisplatin resistant cells by inducing necroptosis, as the cell death could not inhibited by apoptosis inhibitor, z-VAD, but compromised by RIP3 inhibitor, GSK872, or RIP3 siRNA. In contrast, shikonin induced apoptosis in T24 parental cells. We further investigate the underlying mechanism, and found that the dysregulation of Bcl-2 family proteins, including Bcl-2, PUMA, Bax, play an important role in deciding that shikonin kills the BC cells by necroptosis or apoptosis. Collectively, our results suggested that inducing necroptosis is an alternative way to overcome the apoptosis resistant in BC therapy, and orchestrating the regulation of Bcl-2, PUMA, and Bax in BC cisplatin resistant cells may improve the therapy effect of cisplatin in BC tumor.

Dysregulation of Glucose Metabolism by Oncogenes and Tumor Suppressors in Cancer Cells

Cancers are complex diseases having several unique features, commonly described as ‘hallmarks of cancer’. Among them, altered signaling pathways are the common characteristic features that drive cancer progression; this is achieved due to mutations that lead to the activation of growth promoting(s) oncogenes and inactivation of tumor suppressors. As a result of which, cancer cells increase their glycolytic rate by consuming a large amount of glucose, and convert a majority of glucose to lactate even in the presence of oxygen known as the “Warburg effect”. Tumor cells like other cells are strictly dependent on energy for growth and survival; therefore, understanding energy metabolism will give us an idea to develop new effective anti-cancer therapies that target cancer energy production pathways. This review summarizes the roles of tumor suppressors and oncogenes and their products that provide metabolic advantages to cancer cells which in turn leads to the establishment of the “Warburg effect” and ultimately leads to cancer progression. Understanding cancer cell’s vulnerability will provide potential targets for its control.

Identification of a new pyruvate kinase M2 isoform (PKM2) activator for the treatment of non-small-cell lung cancer (NSCLC)

Lung cancer is the number one cancer in terms of both mortality and incidence. Cancer cells differ from normal cells in that they can reprogram their metabolism to support a rapid proliferation rate and alter oxidative phosphorylation processes toward lactic acid fermentation, even under aerobic conditions. Therefore, we aimed to identify new compounds that might act as pyruvate kinase M2 isoform (PKM2) activators and to investigate their anti-cancer efficacy in non-small-cell lung cancer (NSCLC) cells. The molecular docking method was applied to screen PKM2 activators from our virtual natural products library. Then, compounds with promising docking scores were examined for cytotoxic effects in a panel of NSCLC cells using the MTT assay. Functional effects and therapeutic mechanisms were investigated by in vitro enzyme assays, western blotting (WB), and flow cytometry. Molecular docking showed that 0089-0022 acts as a potential PKM2 activator by binding to the kinase pocket. An in vitro enzyme activity assay showed that 0089-0022 is a direct PKM2 activator and that it effectively induces apoptosis in A549 and H1975 cells through inhibition of AKT phosphorylation. Our results suggest that 0089-0022 activates PKM2 and thus is a promising anti-cancer therapeutic candidate in NSCLC.

Plasma TuM2-PK correlates with tumor size, CRP and CA 15-3 in metastatic breast carcinomas; short versus long term follow up study of the Egyptian breast cancer patients

BACKGROUND

The key regulator of tumor metabolome is the glycolytic isoenzyme M2-PK which favors the generation of nucleic acid via glutaminolysis as hypoxic adaptive mechanism in the tumor cells.

AIM

The study aimed to evaluate the prognostic role of M2-PK, CRP, and CA 15-3 in preoperative and metastatic breast carcinomas.

PATIENTS AND METHODS

The study included 70 females; 15 controls, 33 preoperative primary breast carcinomas clinically metastasis free, and 22 clinically diagnosed metastatic breast carcinomas. M2-PK and CA 15-3 were detected by ELISA. CRP was quantified using the CRP LATEX kit.

RESULTS

TuM2-PK significantly increased in metastatic and preoperative groups when compared to controls (p= 0.049, p= 0.001); respectively. Both CRP and CA 15-3 were significantly increased in metastatic than the preoperative group (p= 0.002). CA 15-3 was significantly increased in both groups when compared to controls (p= 0.016; p< 0.001; respectively). TuM2-PK level significantly related to tumor size in metastatic group (p= 0.006) and with menstruation status (p= 0.039), and liver metastasis (p= 0.036) in preoperative group. TuM2-PK significantly correlated with CRP (r= 0.793, p= 0.004), and CA 15-3 (r= 0.568, p= 0.006) in the metastatic group.Metastatic group with TuM2-PK ⩽ 15 U/ml had significantly higher survival rate than those with > 15 U/ml (χ2= 13.841, p< 0.001) within 3.3-4.2 but not after 10-20 years follow up period. Metastasis to bone and lymph nodes significantly increased in the metastatic than the preoperative group (p= 0.002, p= 0.013; respectively). Within 3.3-4.2 years, CA15.3 has the highest prognostic performance in metastatic group while both TuM2-PK and CRP have same specificity. On the other hand, TuM2-PK has the highest prognostic performance in preoperative group. After 20 years follow up period, there was neither significant difference in the performance of the three markers in predicting mortality in metastatic and preoperative groups nor in predicting metastasis in preoperative group.

CONCLUSION

Current results document for the first time, a cross-talk between TuM2-PK and each of CRP and CA 15-3 in metastatic breast cancer.

Pyruvate kinase M2 fuels multiple aspects of cancer cells: from cellular metabolism, transcriptional regulation to extracellular signaling

Originally identified as a metabolic enzyme that catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP in the glycolytic pathway, pyruvate kinase M2-type (PKM2) has been shown to exhibit novel biological activities in the nucleus and outside the cells. Although cell-based studies reveal new non-canonical functions of PKM2 in gene transcription, epigenetic modulation and cell cycle progression, the importance of these non-canonical functions in PKM2-mediated tumorigenesis is still under debate because studies in genetically modified mice do not consistently echo the findings observed in cultured cancer cells. In addition to regulation of gene expression, the existence of PKM2 in exosomes opens a new venue to study the potential role of this glycolytic enzyme in cell-cell communication and extracellular signal initiation. In this review, we briefly summarize current understanding of PKM2 in metabolic switch and gene regulation. We will then emphasize recent progress of PKM2 in extracellular signaling and tumor microenvironment reprogramming. Finally, the discrepancy of some PKM2’s functions in vitro and in vivo, and the application of PKM2 in cancer detection and treatment will be discussed.

The sweet trap in tumors: aerobic glycolysis and potential targets for therapy

Metabolic change is one of the hallmarks of tumor, which has recently attracted a great of attention. One of main metabolic characteristics of tumor cells is the high level of glycolysis even in the presence of oxygen, known as aerobic glycolysis or the Warburg effect. The energy production is much less in glycolysis pathway than that in tricarboxylic acid cycle. The molecular mechanism of a high glycolytic flux in tumor cells remains unclear. A large amount of intermediates derived from glycolytic pathway could meet the biosynthetic requirements of the proliferating cells. Hypoxia-induced HIF-1&alpha;, PI3K-Akt-mTOR signaling pathway, and many other factors, such as oncogene activation and tumor suppressor inactivation, drive cancer cells to favor glycolysis over mitochondrial oxidation. Several small molecules targeting glycolytic pathway exhibit promising anticancer activity both in vitro and in vivo. In this review, we will focus on the latest progress in the regulation of aerobic glycolysis and discuss the potential targets for the tumor therapy.

Immunogenicity of mammary tumor cells can be induced by shikonin via direct binding-interference with hnRNPA1

Immunogenic cell death (ICD) of tumor cells occurs via various pathways that activate immune cell systems against cancer. Previous studies have demonstrated that shikonin (SK), a plant secondary metabolite, can confer strong pharmacological activities that activate ICD and strong immunogenicity of tumor cells. However, the exact hierarchical regulatory mechanisms including the molecular targets of SK-activated immunogenicity are still unknown. Here, the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) was revealed to serve as a specific protein target for SK. This binding plays a key role in SK-stimulated ICD activity and the suppression of post-transcriptional mRNA processing, including nuclear export activity of newly synthesized mRNAs in mammary carcinoma cells in vitro. Moreover, it also mechanistically mediates the anti-metastatic effect of a tumor cell lysate (TCL) vaccine, which can be readily generated from SK-treated 4T1 tumor cells (SK-TCL), and the derived tumor-immunogenicity of SK-TCL-treated dendritic cells in vivo. Together, the identification of hnRNPA1 as the intracellular molecular target provides compelling pharmacology-based knowledge for the potential clinical use of SK-induced immunogenicity. In addition, SK may also serve as a potent suppressor that interferes with specific post-transcriptional activities, a mechanism which may be useful for exploitation in cancer therapeutics.

Modulation of GLO1 Expression Affects Malignant Properties of Cells

The energy metabolism of most tumor cells relies on aerobic glycolysis (Warburg effect) characterized by an increased glycolytic flux that is accompanied by the increased formation of the cytotoxic metabolite methylglyoxal (MGO). Consequently, the rate of detoxification of this reactive glycolytic byproduct needs to be increased in order to prevent deleterious effects to the cells. This is brought about by an increased expression of glyoxalase 1 (GLO1) that is the rate-limiting enzyme of the MGO-detoxifying glyoxalase system. Here, we overexpressed GLO1 in HEK 293 cells and silenced it in MCF-7 cells using shRNA. Tumor-related properties of wild type and transformed cells were compared and key glycolytic enzyme activities assessed. Furthermore, the cells were subjected to hypoxic conditions to analyze the impact on cell proliferation and enzyme activities. Our results demonstrate that knockdown of GLO1 in the cancer cells significantly reduced tumor-associated properties such as migration and proliferation, whereas no functional alterations where found by overexpression of GLO1 in HEK 293 cells. In contrast, hypoxia caused inhibition of cell growth of all cells except of those overexpressing GLO1. Altogether, we conclude that GLO1 on one hand is crucial to maintaining tumor characteristics of malignant cells, and, on the other hand, supports malignant transformation of cells in a hypoxic environment when overexpressed.

Tissue metabolic profiling of human gastric cancer assessed by (1)H NMR

Background

Gastric cancer is the fourth most common cancer and the second most deadly cancer worldwide. Study on molecular mechanisms of carcinogenesis will play a significant role in diagnosing and treating gastric cancer. Metabolic profiling may offer the opportunity to understand the molecular mechanism of carcinogenesis and help to identify the potential biomarkers for the early diagnosis of gastric cancer.

Methods

In this study, we reported the metabolic profiling of tissue samples on a large cohort of human gastric cancer subjects (n = 125) and normal controls (n = 54) based on ¹H nuclear magnetic resonance (¹H NMR) together with multivariate statistical analyses (PCA, PLS-DA, OPLS-DA and ROC curve).

Results

The OPLS-DA model showed adequate discrimination between cancer tissues and normal controls, and meanwhile, the model excellently discriminated the stage-related of tissue samples (stage I, 30; stage II, 46; stage III, 37; stage IV, 12) and normal controls. A total of 48 endogenous distinguishing metabolites (VIP > 1 and p < 0.05) were identified, 13 of which were changed with the progression of gastric cancer. These modified metabolites revealed disturbance of glycolysis, glutaminolysis, TCA, amino acids and choline metabolism, which were correlated with the occurrence and development of human gastric cancer. The receiver operating characteristic diagnostic AUC of OPLS-DA model between cancer tissues and normal controls was 0.945. And the ROC curves among different stages cancer subjects and normal controls were gradually improved, the corresponding AUC values were 0.952, 0.994, 0.998 and 0.999, demonstrating the robust diagnostic power of this metabolic profiling approach.

Conclusion

As far as we know, the present study firstly identified the differential metabolites in various stages of gastric cancer tissues. And the AUC values were relatively high. So these results suggest that the metabolic profiling of gastric cancer tissues has great potential in detecting this disease and helping to understand its underlying metabolic mechanisms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2356-4) contains supplementary material, which is available to authorized users.

Glucose metabolic phenotype of pancreatic cancer

AIM: To construct a global “metabolic phenotype” of pancreatic ductal adenocarcinoma (PDAC) reflecting tumour-related metabolic enzyme expression.

METHODS: A systematic review of the literature was performed using OvidSP and PubMed databases using keywords “pancreatic cancer” and individual glycolytic and mitochondrial oxidative phosphorylation (MOP) enzymes. Both human and animal studies investigating the oncological effect of enzyme expression changes and inhibitors in both an in vitro and in vivo setting were included in the review. Data reporting changes in enzyme expression and the effects on PDAC cells, such as survival and metastatic potential, were extracted to construct a metabolic phenotype.

RESULTS: Seven hundred and ten papers were initially retrieved, and were screened to meet the review inclusion criteria. 107 unique articles were identified as reporting data involving glycolytic enzymes, and 28 articles involving MOP enzymes in PDAC. Data extraction followed a pre-defined protocol. There is consistent over-expression of glycolytic enzymes and lactate dehydrogenase in keeping with the Warburg effect to facilitate rapid adenosine-triphosphate production from glycolysis. Certain isoforms of these enzymes were over-expressed specifically in PDAC. Altering expression levels of HK, PGI, FBA, enolase, PK-M2 and LDA-A with metabolic inhibitors have shown a favourable effect on PDAC, thus identifying these as potential therapeutic targets. However, the Warburg effect on MOP enzymes is less clear, with different expression levels at different points in the Krebs cycle resulting in a fundamental change of metabolite levels, suggesting that other essential anabolic pathways are being stimulated.

CONCLUSION: Further characterisation of the PDAC metabolic phenotype is necessary as currently there are few clinical studies and no successful clinical trials targeting metabolic enzymes.

Pantoprazole inhibits human gastric adenocarcinoma SGC-7901 cells by downregulating the expression of pyruvate kinase M2

The Warburg effect is important in tumor growth. The human M2 isoform of pyruvate kinase (PKM2) is a key enzyme that regulates aerobic glycolysis in tumor cells. Recent studies have demonstrated that PKM2 is a potential target for cancer therapy. The present study investigated the effects of pantoprazole (PPZ) treatment and PKM2 transfection on human gastric adenocarcinoma SGC-7901 cells in vitro. The present study revealed that PPZ inhibited the proliferation of tumor cells, induced apoptosis and downregulated the expression of PKM2, which contributes to the current understanding of the functional association between PPZ and PKM2. In summary, PPZ may suppress tumor growth as a PKM2 protein inhibitor.

Pyruvate kinase M2 at a glance

Reprogrammed metabolism is a key feature of cancer cells. The pyruvate kinase M2 (PKM2) isoform, which is commonly upregulated in many human cancers, has been recently shown to play a crucial role in metabolism reprogramming, gene transcription and cell cycle progression. In this Cell Science at a glance article and accompanying poster, we provide a brief overview of recent advances in understanding the mechanisms underlying the regulation of PKM2 expression, enzymatic activity, metabolic functions and subcellular location. We highlight the instrumental role of the non-metabolic functions of PKM2 in tumorigenesis and evaluate the potential to target PKM2 for cancer treatment.

The multifaceted regulation and functions of PKM2 in tumor progression

Tumor cells undergo metabolic rewiring from oxidative phosphorylation towards aerobic glycolysis to maintain the increased anabolic requirements for cell proliferation. It is widely accepted that specific expression of the M2 type pyruvate kinase (PKM2) in tumor cells contributes to this aerobic glycolysis phenotype. To date, researchers have uncovered myriad forms of functional regulation for PKM2, which confers a growth advantage on the tumor cells to enable them to adapt to various microenvironmental signals. Here the richness of our understanding on the modulations and functions of PKM2 in tumor progression is reviewed, and some new insights into the paradoxical expression and functional differences of PKM2 in distinct cancer types are offered.

Targeting pyruvate kinase M2 contributes to radiosensitivity of non-small cell lung cancer cells in vitro and in vivo

Aerobic glycolysis, a metabolic hallmark of cancer, is associated with radioresistance in non-small cell lung cancer (NSCLC). Pyruvate kinase M2 isoform (PKM2), a key regulator of glycolysis, is expressed exclusively in cancers. However, the impact of PKM2 silencing on the radiosensitivity of NSCLC has not been explored. Here, we show a plasmid of shRNA-PKM2 for expressing a short hairpin RNA targeting PKM2 (pshRNA-PKM2) and demonstrate that treatment with pshRNA-PKM2 effectively inhibits PKM2 expression in NSCLC cell lines and xenografts. Silencing of PKM2 expression enhanced ionizing radiation (IR)-induced apoptosis and autophagy in vitro and in vivo, accompanied by inhibiting AKT and PDK1 phosphorylation, but enhanced ERK and GSK3β phosphorylation. These results demonstrated that knockdown of PKM2 expression enhances the radiosensitivity of NSCLC cell lines and xenografts as well as may aid in the design of new therapies for the treatment of NSCLC.

PKM2 and ACVR 1C are prognostic markers for poor prognosis of gallbladder cancer

PURPOSE

To identify biological markers related to the progression and prognosis of GBC.

METHODS

The expressions of pyruvate kinase isoenzyme type M2 (PKM2) and activin A receptor type IC (ACVR 1C) in 46 squamous cell/adenosquamous carcinomas (SC/ASC) and 80 adenocarcinomas (AC) were examined using immunohistochemistry.

RESULTS

Positive PKM2 and negative ACVR 1C expressions were significantly associated with lymph node metastasis, invasion and TNM stage of SC/ASCs and ACs. Univariate Kaplan-Meier analysis showed that either elevated PKM2 or loss of ACVR 1C expression significantly correlated with shorter average survival times in both SC/ASC and AC patients. Multivariate Cox regression analysis showed that positive PKM2 expression and loss of ACVR 1C expression were poor prognosis biomarkers in both SC/ASC and AC patients.

CONCLUSIONS

Our study suggested that PKM2 overexpression is a marker of metastasis, invasion and poor prognosis of GBC. ACVR 1C is a tumor suppressor, and lowered ACVR 1C expression is an important marker for the metastasis, invasion, and prognosis of GBC.

Tumor glycolysis as a target for cancer therapy: progress and prospects

Altered energy metabolism is a biochemical fingerprint of cancer cells that represents one of the “hallmarks of cancer”. This metabolic phenotype is characterized by preferential dependence on glycolysis (the process of conversion of glucose into pyruvate followed by lactate production) for energy production in an oxygen-independent manner. Although glycolysis is less efficient than oxidative phosphorylation in the net yield of adenosine triphosphate (ATP), cancer cells adapt to this mathematical disadvantage by increased glucose up-take, which in turn facilitates a higher rate of glycolysis. Apart from providing cellular energy, the metabolic intermediates of glycolysis also play a pivotal role in macromolecular biosynthesis, thus conferring selective advantage to cancer cells under diminished nutrient supply. Accumulating data also indicate that intracellular ATP is a critical determinant of chemoresistance. Under hypoxic conditions where glycolysis remains the predominant energy producing pathway sensitizing cancer cells would require intracellular depletion of ATP by inhibition of glycolysis. Together, the oncogenic regulation of glycolysis and multifaceted roles of glycolytic components underscore the biological significance of tumor glycolysis. Thus targeting glycolysis remains attractive for therapeutic intervention. Several preclinical investigations have indeed demonstrated the effectiveness of this therapeutic approach thereby supporting its scientific rationale. Recent reviews have provided a wealth of information on the biochemical targets of glycolysis and their inhibitors. The objective of this review is to present the most recent research on the cancer-specific role of glycolytic enzymes including their non-glycolytic functions in order to explore the potential for therapeutic opportunities. Further, we discuss the translational potential of emerging drug candidates in light of technical advances in treatment modalities such as image-guided targeted delivery of cancer therapeutics.

Nuclear PKM2 expression predicts poor prognosis in patients with esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common tumors worldwide, with a high malignant degree and poor prognosis. The present study aims to investigate the relationship between pyruvate kinase M2 (PKM2) expression and the prognosis of patients with ESCC. The expression of PKM2 in 86 cases of esophageal carcinoma tissues was tested using immunohistochemistry. The relationship between PKM2 expression and clinical pathological parameters, and their effects on the prognosis of patients with ESCC were analyzed. The expression levels of PKM2 in both cytoplasm and nucleus of ESCC tissues were significantly higher than those in paracancerous tissues (P=6.73×10(-9) and 4.32×10(-6), respectively). The Kaplan-Meier analysis showed that nuclear PKM2 expression was closely related to the survival of patients with ESCC (P=0.005). Patients with high PKM2 expression in the nucleus had significantly shorter survival times than those with low PKM2 expression in the nucleus (hazard ratio for death, 2.358; 95% confidence interval, 1.156-4.812; P=0.018). No other significant difference was found between PMK2 expression and clinico-pathological features of ESCC patients (all P>0.05). In conclusion, high PKM2 expression in the nucleus is essential in the pathogenic process of ESCC and may be used to predict the prognosis of patients with ESCC.

Protein tyrosine phosphatase 1B regulates pyruvate kinase M2 tyrosine phosphorylation

Protein-tyrosine phosphatase 1B (PTP1B) is a physiological regulator of glucose homeostasis and adiposity and is a drug target for the treatment of obesity and diabetes. Here we identify pyruvate kinase M2 (PKM2) as a novel PTP1B substrate in adipocytes. PTP1B deficiency leads to increased PKM2 total tyrosine and Tyr(105) phosphorylation in cultured adipocytes and in vivo. Substrate trapping and mutagenesis studies identify PKM2 Tyr-105 and Tyr-148 as key sites that mediate PTP1B-PKM2 interaction. In addition, in vitro analyses illustrate a direct effect of Tyr-105 phosphorylation on PKM2 activity in adipocytes. Importantly, PTP1B pharmacological inhibition increased PKM2 Tyr-105 phosphorylation and decreased PKM2 activity. Moreover, PKM2 Tyr-105 phosphorylation is regulated nutritionally, decreasing in adipose tissue depots after high-fat feeding. Further, decreased PKM2 Tyr-105 phosphorylation correlates with the development of glucose intolerance and insulin resistance in rodents, non-human primates, and humans. Together, these findings identify PKM2 as a novel substrate of PTP1B and provide new insights into the regulation of adipose PKM2 activity.

Pyruvate kinase M2: multiple faces for conferring benefits on cancer cells

The M2 splice isoform of pyruvate kinase (PKM2), an enzyme that catalyzes the later step of glycolysis, is a key regulator of aerobic glycolysis (known as the Warburg effect) in cancer cells. Expression and low enzymatic activity of PKM2 confer on cancer cells the glycolytic phenotype, which promotes rapid energy production and flow of glycolytic intermediates into collateral pathways to synthesize nucleic acids, amino acids, and lipids without the accumulation of reactive oxygen species. PKM2 enzymatic activity has also been shown to be negatively regulated by the interaction with CD44 adhesion molecule, which is a cell surface marker for cancer stem cells. In addition to the glycolytic functions, nonglycolytic functions of PKM2 in cancer cells are of particular interest. PKM2 is induced translocation into the nucleus, where it activates transcription of various genes by interacting with and phosphorylating specific nuclear proteins, endowing cancer cells with a survival and growth advantage. Therefore, inhibitors and activators of PKM2 are well underway to evaluate their anticancer effects and suitability for use as novel therapeutic strategies.

Comparative proteomic and phosphoproteomic profiling of pancreatic adenocarcinoma cells treated with CB1 or CB2 agonists

The pancreatic adenocarcinoma cell line Panc1 was treated with cannabinoid receptor ligands (arachidonylcyclopropylamide or GW405833) in order to elucidate the molecular mechanism of their anticancer effect. A proteomic approach was used to analyze the protein and phosphoprotein profiles. Western blot and functional data mining were also employed in order to validate results, classify proteins, and explore their potential relationships. We demonstrated that the two cannabinoids act through a widely common mechanism involving up- and down-regulation of proteins related to energetic metabolism and cell growth regulation. Overall, the results reported might contribute to the development of a therapy based on cannabinoids for pancreatic adenocarcinoma.

Anticancer agent shikonin is an incompetent inducer of cancer drug resistance

PURPOSE

Cancer drug resistance is a major obstacle for the success of chemotherapy. Since most clinical anticancer drugs could induce drug resistance, it is desired to develop candidate drugs that are highly efficacious but incompetent to induce drug resistance. Numerous previous studies have proven that shikonin and its analogs not only are highly tumoricidal but also can bypass drug-transporter and apoptotic defect mediated drug resistance. The purpose of this study is to investigate if or not shikonin is a weak inducer of cancer drug resistance.

EXPERIMENTAL DESIGN

Different cell lines (K562, MCF-7, and a MDR cell line K562/Adr), after repeatedly treated with shikonin for 18 months, were assayed for drug resistance and gene expression profiling.

RESULTS

After 18-month treatment, cells only developed a mere 2-fold resistance to shikonin and a marginal resistance to cisplatin and paclitaxel, without cross resistance to shikonin analogs and other anticancer agents. Gene expression profiles demonstrated that cancer cells did strongly respond to shikonin treatment but failed to effectively mobilize drug resistant machineries. Shikonin-induced weak resistance was associated with the up-regulation of βII-tubulin, which physically interacted with shikonin.

CONCLUSION

Taken together, apart from potent anticancer activity, shikonin and its analogs are weak inducers of cancer drug resistance and can circumvent cancer drug resistance. These merits make shikonin and its analogs potential candidates for cancer therapy with advantages of avoiding induction of drug resistance and bypassing existing drug resistance.

Orlistat, a novel potent antitumor agent for ovarian cancer: proteomic analysis of ovarian cancer cells treated with Orlistat

Orlistat is an orally administered anti-obesity drug that has shown significant antitumor activity in a variety of tumor cells. To identify the proteins involved in its antitumor activity, we employed a proteomic approach to reveal protein expression changes in the human ovarian cancer cell line SKOV3, following Orlistat treatment. Protein expression profiles were analyzed by 2-dimensional polyacrylamide gel electrophoresis (2-DE) and protein identification was performed on a MALDI-Q-TOF MS/MS instrument. More than 110 differentially expressed proteins were visualized by 2-DE and Coomassie brilliant blue staining. Furthermore, 71 proteins differentially expressed proteins were positively identified via mass spectrometry (MS)/MS analysis. In particular, PKM1/2, a key enzyme involved in tumorigenesis, was found to be significantly downregulated in SKOV3 cells following treatment with Orlistat. Moreover, PKM1/2 was proved to be downregulated in SKOV3 cells by western blot analysis after treatment with Orlistat. Taken together, using proteomic tools, we identified several differentially expressed proteins that underwent Orlistat-induced apoptosis, particularly PKM2. These changes confirmed our hypothesis that Orlistat is a potential inhibitor of ovarian cancer and can be used as a novel adjuvant antitumor agent.

Rocking cell metabolism: revised functions of the key glycolytic regulator PKM2 in cancer

Cancer cell metabolism is exemplified by high glucose consumption and lactate production. Pyruvate kinase (PK), which catalyzes the final step of glycolysis, has emerged as a potential regulator of this metabolic phenotype. The M2 isoform of PK (PKM2) is highly expressed in cancer cells. However, the mechanisms by which PKM2 coordinates high energy requirements with high anabolic activities to support cancer cell proliferation are still not completely understood. Current research has elucidated novel regulatory mechanisms for PKM2, contributing to its important role in cancer. This review summarizes the current understanding and explores future directions in the field, highlighting controversies regarding the activity and specificity of PKM2 in cancer. In light of this knowledge, the potential therapeutic implications and strategies are critically discussed.

Anticancer agents that counteract tumor glycolysis

Can we consider cancer to be a "metabolic disease"? Tumors are the result of a metabolic selection, forming tissues composed of heterogeneous cells that generally express an overactive metabolism as a common feature. In fact, cancer cells have increased needs for both energy and biosynthetic intermediates to support their growth and invasiveness. However, their high proliferation rate often generates regions that are insufficiently oxygenated. Therefore, their carbohydrate metabolism must rely mostly on a glycolytic process that is uncoupled from oxidative phosphorylation. This metabolic switch, also known as the Warburg effect, constitutes a fundamental adaptation of tumor cells to a relatively hostile environment, and supports the evolution of aggressive and metastatic phenotypes. As a result, tumor glycolysis may constitute an attractive target for cancer therapy. This approach has often raised concerns that antiglycolytic agents may cause serious side effects toward normal cells. The key to selective action against cancer cells can be found in their hyperbolic addiction to glycolysis, which may be exploited to generate new anticancer drugs with minimal toxicity. There is growing evidence to support many glycolytic enzymes and transporters as suitable candidate targets for cancer therapy. Herein we review some of the most relevant antiglycolytic agents that have been investigated thus far for the treatment of cancer.

Vitamin K(3) and K(5) are inhibitors of tumor pyruvate kinase M2

Pyruvate kinase M2 (PKM2) is a rate-limiting enzyme of aerobic glycolysis in cancer cells and plays important roles in cancer metabolism and growth. Here we show that vitamin K(3) and K(5) (VK(3) and VK(5)) are relatively specific PKM2 inhibitors. VK(3) and VK(5) showed a significantly stronger potency to inhibit PKM2 than to inhibit PKM1 and PKL, 2 other isoforms of PK dominantly expressed in most adult tissues and liver. This study combined with previous reports supports that VK(3) and VK(5) have potential as adjuvant for cancer chemotherapy.