Synthesis and antitumor activity of novel 2, 3-didithiocarbamate substituted naphthoquinones as inhibitors of pyruvate kinase M2 isoform

Identification of a novel cuproptosis inducer that induces ER stress and oxidative stress to trigger immunogenic cell death in tumors

Cuproptosis, a copper-dependent form of regulated cell death, has been implicated in the progression and treatment of various tumors. The copper ionophores, such as Disulfiram (DSF), an FDA-approved drug previously used to treat alcohol dependence, have been found to induce cuproptosis. However, the limited solubility and effectiveness of the combination of DSF and copper ion restrict its widespread application. In this study, through a random screening of our in-house compound library, we identified a novel cuproptosis inducer, YL21, comprising a naphthoquinone core substituted by two dithiocarbamate groups. The combination of YL21 with copper ion induces cuproptosis by disrupting mitochondrial function and promoting the oligomerization of lipoylated protein DLAT. Further, this combination induces endoplasmic reticulum (ER) stress and oxidative stress, triggering immunogenic cell death (ICD) and subsequently promoting the activation of antitumor immune responses to suppress tumor growth in the mice breast cancer model. Notably, the combination of YL21 and copper ion demonstrated improved solubility and increased antitumor activity compared to the combination of DSF and copper ion. Thus, YL21 functions as a novel cuproptosis inducer and may serve as a promising candidate for antitumor immunotherapy.

Mannich Base Derived from Lawsone Inhibits PKM2 and Induces Neoplastic Cell Death

Background/Objectives: Pyruvate kinase M2, a central regulator of cancer cell metabolism, has garnered significant attention as a promising target for disrupting the metabolic adaptability of tumor cells. This study explores the potential of the Mannich base derived from lawsone (MB-6a) to interfere with PKM2 enzymatic activity both in vitro and in silico. Methods: The antiproliferative potential of MB-6a was tested using MTT assay in various cell lines, including SCC-9, Hep-G2, HT-29, B16-F10, and normal human gingival fibroblast (HGF). The inhibition of PKM2 mediated by MB-6a was assessed using an LDH-coupled assay and by measuring ATP production. Docking studies and molecular dynamics calculations were performed using Autodock 4 and GROMACS, respectively, on the tetrameric PKM2 crystallographic structure. Results: The Mannich base 6a demonstrated selective cytotoxicity against all cancer cell lines tested without affecting cell migration, with the highest selectivity index (SI) of 4.63 in SCC-9, followed by B16-F10 (SI = 3.9), Hep-G2 (SI = 3.4), and HT-29 (SI = 2.03). The compound effectively inhibited PKM2 glycolytic activity, leading to a reduction of ATP production both in the enzymatic reaction and in cells treated with this naphthoquinone derivative. MB-6a showed favorable binding to PKM2 in the ATP-bound monomers through docking studies (PDB ID: 4FXF; binding affinity scores ranging from -6.94 to -9.79 kcal/mol) and MD simulations, revealing binding affinities stabilized by key interactions including hydrogen bonds, halogen bonds, and hydrophobic contacts. Conclusions: The findings suggest that MB-6a exerts its antiproliferative activity by disrupting cell glucose metabolism, consequently reducing ATP production and triggering energetic collapse in cancer cells. This study highlights the potential of MB-6a as a lead compound targeting PKM2 and warrants further investigation into its mechanism of action and potential clinical applications.

Babesia duncani Pyruvate Kinase Inhibitor Screening and Identification of Key Active Amino Acid Residues

Babesia duncani (B. duncani), a protozoan parasite prevalent in North America, is a significant threat for human health. Given the regulatory role of pyruvate kinase I (PyK I) in glycolytic metabolism flux and ATP generation, PyK I has been considered the target for drug intervention for a long time. In this study, B. duncani PyK I (BdPyK I) was successfully cloned, expressed, and purified. Polyclonal antibodies were confirmed to recognize the native BdPyK I protein (56 kDa) using Western blotting. AlphaFold software predicted the three-dimensional structure of BdPyK I, and molecular docking with small molecules was conducted to identify potential binding sites of inhibitor on BdPyK I. Moreover, inhibitory effects of six inhibitors (tannic acid, apigenin, shikonin, PKM2 inhibitor, rosiglitazone, and pioglitazone) on BdPyK I were examined under the optimal enzymatic conditions of 3 mM PEP and 3 mM ADP, and significant activity reduction was found. Enzyme kinetics and growth inhibition assays further confirmed the reliability of these inhibitors, with PKM2 inhibitor, tannic acid, and apigenin exhibiting the highest selectivity index as specific inhibitors for B. duncani. Subsequently, key amino acid residues were mutated in both BdPyK I and Homo sapiens pyruvate kinase I (HPyK I), and two differential amino acid residues (isoleucine and phenylalanine) were identified between HPyK I and BdPyK I through PyK activity detection experiments. These findings lay foundation for understanding the role of PyK I in the growth and development of B. duncani, providing insights for babesiosis prevention and drug development.

The PI3K/Akt Pathway and Glucose Metabolism: A Dangerous Liaison in Cancer

Aberrant activation of the PI3K/Akt pathway commonly occurs in cancers and correlates with multiple aspects of malignant progression. In particular, recent evidence suggests that the PI3K/Akt signaling plays a fundamental role in promoting the so-called aerobic glycolysis or Warburg effect, by phosphorylating different nutrient transporters and metabolic enzymes, such as GLUT1, HK2, PFKB3/4 and PKM2, and by regulating various molecular networks and proteins, including mTORC1, GSK3, FOXO transcription factors, MYC and HIF-1α. This leads to a profound reprogramming of cancer metabolism, also impacting on pentose phosphate pathway, mitochondrial oxidative phosphorylation, de novo lipid synthesis and redox homeostasis and thereby allowing the fulfillment of both the catabolic and anabolic demands of tumor cells. The present review discusses the interactions between the PI3K/Akt cascade and its metabolic targets, focusing on their possible therapeutic implications.

Unlocking the potential of 1,4-naphthoquinones: A comprehensive review of their anticancer properties

Cancer encompasses a group of pathologies with common characteristics, high incidence, and prevalence in all countries. Although there are treatments available for this disease, they are not always effective or safe, often failing to achieve the desired results. This is why it is necessary to continue the search for new therapies. One of the strategies for obtaining new antitumor drugs is the use of 1,4-naphthoquinone as a scaffold in synthetic or natural products with antitumor activity. This review focuses on compiling studies related to the antitumor activity of 1,4-naphthoquinone and its natural and synthetic derivatives over the last 10 years. The work describes the main natural naphthoquinones with antitumor activity and classifies the synthetic naphthoquinones based on the structural modifications made to the scaffold. Additionally, the formation of metal complexes using naphthoquinones as a ligand is considered. After a thorough review, 197 synthetic compounds with potent biological activity against cancer have been classified according to their chemical structures and their mechanisms of action have been described.

Targeting the Warburg effect: A revisited perspective from molecular mechanisms to traditional and innovative therapeutic strategies in cancer

Cancer reprogramming is an important facilitator of cancer development and survival, with tumor cells exhibiting a preference for aerobic glycolysis beyond oxidative phosphorylation, even under sufficient oxygen supply condition. This metabolic alteration, known as the Warburg effect, serves as a significant indicator of malignant tumor transformation. The Warburg effect primarily impacts cancer occurrence by influencing the aerobic glycolysis pathway in cancer cells. Key enzymes involved in this process include glucose transporters (GLUTs), HKs, PFKs, LDHs, and PKM2. Moreover, the expression of transcriptional regulatory factors and proteins, such as FOXM1, p53, NF-κB, HIF1α, and c-Myc, can also influence cancer progression. Furthermore, lncRNAs, miRNAs, and circular RNAs play a vital role in directly regulating the Warburg effect. Additionally, gene mutations, tumor microenvironment remodeling, and immune system interactions are closely associated with the Warburg effect. Notably, the development of drugs targeting the Warburg effect has exhibited promising potential in tumor treatment. This comprehensive review presents novel directions and approaches for the early diagnosis and treatment of cancer patients by conducting in-depth research and summarizing the bright prospects of targeting the Warburg effect in cancer.

Recent Advances on PKM2 Inhibitors and Activators in Cancer Applications

Metabolic reprogramming of cells, from the normal mode of glucose metabolism named glycolysis, is a pivotal characteristic of impending cancerous cells. Pyruvate kinase M2 (PKM2), an important enzyme that catalyzes the final rate-limiting stage during glycolysis, is highly expressed in numerous types of tumors and aids in development of favorable conditions for the survival of tumor cells. Increasing evidence has suggested that PKM2 is one of promising targets for innovative drug discovery, especially for the developments of antitumor therapeutics. Herein, we systematically summarize the recent advancement on PKM2 modulators including inhibitors and activators in cancer applications. We also discussed the classifications of pyruvate kinases in mammals and the biological functions of PKM2 in this review. We do hope that this review would provide a comprehensive understanding of the current research on PKM2 modulators, which may benefit the development of more potent PKM2-related drug candidates to treat PKM2-associated diseases including cancers in future.

Shikonin-Loaded Hollow Fe-MOF Nanoparticles for Enhanced Microwave Thermal Therapy

Microwave (MW) thermal therapy has been widely used for the treatment of cancer in clinics, but it still shows limited efficacy and a high recurrence rate owing to non-selective heat delivery and thermo-resistance. Regulating glycolysis shows great promise to improve MW thermal therapy since glycolysis plays an important role in thermo-resistance, progression, metabolism, and recurrence. Herein, we developed a delivery nanosystem of shikonin (SK)-loaded and hyaluronic acid (HA)-modified hollow Fe-MOF (HFM), HFM@SK@HA, as an efficient glycolysis-meditated agent to improve the efficacy of MW thermal therapy. The HFM@SK@HA nanosystem shows a high SK loading capacity of 31.7 wt %. The loaded SK can be effectively released from the HFM@SK@HA under the stimulation of an acidic tumor microenvironment and MW irradiation, overcoming the intrinsically low solubility and severe toxicity of SK. We also find that the HFM@SK@HA can not only greatly improve the heating effect of MW in the tumor site but also mediate MW-enhancing dynamic therapy efficiency by catalyzing the endogenous H2O2 to generate reactive oxygen species (ROS). As such, the MW irradiation treatment in the presence of HFM@SK@HA in vitro enables a highly improved anti-tumor efficacy due to the combined effect of released SK and generated ROS on inhibiting glycolysis in cancer cells. Our in vivo experiments show that the tumor inhibition rate is up to 94.75% ± 3.63% with no obvious recurrence during the 2 weeks after treatment. This work provides a new strategy for improving the efficacy of MW thermal therapy.

Development of isoselenazolium chlorides as selective pyruvate kinase isoform M2 inhibitors

Alterations in cancer metabolic pathways open up an opportunity for targeted and effective elimination of tumor cells. Pyruvate kinase M2 (PKM2) is predominantly expressed in proliferating cells and plays an essential role in directing glucose metabolism in cancer. Here, we report the design of novel class of selective PKM2 inhibitors as anti-cancer agents and their mechanism of action. Compound 5c being the most active with IC₅₀ = 0.35 ± 0.07 μM, also downregulates PKM2 mRNA expression, modulates mitochondrial functionality, induces oxidative burst and is cytotoxic for various cancer types. Isoselenazolium chlorides have an unusual mechanism of PKM2 inhibition, inducing a functionally deficient tetrameric assembly, while exhibiting a competitive inhibitor character. The discovery of robust PKM2 inhibitors not only offers candidates for anticancer therapy but is also crucial for studying the role of PKM2 in cancer.

Targeting hPKM2 in cancer: A bio isosteric approach for ligand design

The term cancer refers to a plethora of diseases characterized by the development of abnormal cells that divide uncontrollably and can infiltrate further proximal or distal body tissues. Each type of cancer can be defined by aggressiveness, localization, metabolism, and response to available treatments. Among the most common hallmarks of cancer is a more acidic intracellular microenvironment. Offset pH values are due to an excess of lactate and an increased hypoxia-inducible factor (HIF) expression, which leads to a hypoxic state and a metabolic shift towards glycolysis to produce adenosine-5'-triphosphate (ATP) necessary for cellular metabolism. Warburg's hypothesis underpins this concept, making glycolysis and its central enzyme pyruvate kinase (hPKM2), an ideal target for drug development. Using molecular docking and extensive molecular dynamics (MD) simulations we investigated the binding mode of phosphoenolpyruvate (PEP) inside the hPKM2 active site, and then evaluated a set of known bio-isosteric inhibitors to understand the differences caused by their substitutions on their binding mode. Ultimately, we propose a new molecular entity to hamper hPKM2, unbalance cellular energy, and possibly trigger autophagic mechanisms.

Novel Specific Pyruvate Kinase M2 Inhibitor, Compound 3h, Induces Apoptosis and Autophagy through Suppressing Akt/mTOR Signaling Pathway in LNCaP Cells

Pyruvate kinase M2 (PKM2) is a key enzyme involved in the regulation of glycolysis. Although PKM2 is overexpressed in various tumor tissues, its functional role in cancer chemotherapy remains unexplored. In this study, we investigated the anticancer activity of a new PKM2 inhibitor, compound 3h, through the cell metabolism and associated signaling pathways in prostate cancer cells. To evaluate the molecular basis of specific PKM2 inhibitors, the interactions of compounds 3h and 3K with the PKM2 protein were assessed via molecular docking. We found that, compared to compound 3K, compound 3h exhibited a higher binding affinity for PKM2. Moreover, compound 3h significantly inhibited the pyruvate kinase activity and PKM2 expression. Cytotoxicity and colony formation assays revealed the potent anticancer activity of compound 3h against LNCaP cells. Compound 3h significantly increased the apoptotic and autophagic cell death in LNCaP cells. In addition, compound 3h induced AMPK activation along with the inhibition of the mTOR/p70S6K pathway. Furthermore, compound 3h significantly inhibited glycolysis and mitochondrial respiration, as determined by analyzing the extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) production. Our results revealed that compound 3h caused apoptotic and autophagic cell death in LNCaP cells by inhibiting cancer cell metabolism. Therefore, blocking glycolytic pathways using specific PKM2 inhibitors can target cancer cell metabolism in PKM2-overexpressed prostate cancer cells.

Down-regulation of NOTCH1 and PKM2 can inhibit the growth and metastasis of colorectal cancer cells

BACKGROUND

Previous studies have revealed the overexpression of Notch receptor 1 (NOTCH1) and pyruvate kinase M2 (PKM2) in colorectal cancer (CRC) tissue and their relationship to disease development. However, whether there is synergy between PKM2 and NOTCH1 needs to be verified. This study aims to analyze the mechanism and relationship between NOTCH1 and PKM2 in CRC.

METHODS

Immunohistochemistry was used to measure the expression of NOTCH1 and PKM2 in colorectal cancer, and the correlation between them was analyzed by Pearson test. The protein and mRNA expressions in CRC cell lines were determined by western blot (WB) and real-time quantitative reverse transcription PCR (qRT-PCR). Compound 3K and tangeretin (TGN) were used to inhibit the expressions of PKM2 and NOTCH1, respectively. The wound healing assay and CCK-8 assay were applied to measure the migration and proliferation of cancer cells.

RESULTS

Immunohistochemical analysis showed that NOTCH1 and PKM2 were overexpressed in patients with colorectal cancer, and patients with overexpression showed a higher number of lymph node metastases and high tumor stage (III+IV) (P<0.05). In addition, Pearson test showed that the level of NOTCH1 was positively correlated with the level of PKM2 (P<0.05). WB and qRT-PCR showed that the protein and mRNA levels of NOTCH1 and PKM2 in colorectal cancer cells were significantly up-regulated (P<0.05). The inhibition of PKM2 and NOTCH1 had a synergistic effect on reducing the invasion and proliferation of CRC cells.

CONCLUSION

NOTCH1 and PKM2 are highly expressed in CRC patients. Inhibiting the expression of NOTCH1 and PKM2 can inhibit the growth and metastasis of CRC cells, providing therapeutic targets for the treatment of CRC.

PKM2 Is Overexpressed in Glioma Tissues, and Its Inhibition Highly Increases Late Apoptosis in U87MG Cells With Low-density Specificity

BACKGROUND/AIM

Pyruvate kinase M2 (PKM2) functions as an important rate-limiting enzyme in aerobic glycolysis and is involved in tumor initiation and progression. However, there are few studies on the correlation between PKM2 expression and its role in glioma.

MATERIALS AND METHODS

PKM2 expression was immunohistochemically examined in human brain tumor samples. Furthermore, we studied the effects of two PKM2 inhibitors (shikonin and compound 3K) on the U87MG glioma cell line.

RESULTS

PKM2 was overexpressed in most glioma tissues when compared to controls. Interestingly, glioma-adjacent tissues from showed slight PKM2 overexpression. This suggests that PKM2 overexpression maybe an important trigger factor for glioma tumorigenesis. We found that the PKM2 inhibitor shikonin was effective against U87MG cells at a relatively low dose and was largely dependent on low cellular density compared to the effects of the anticancer drug vincristine. Shikonin highly increased late-apoptosis of U87MG cells. We also demonstrated that autophagy was involved in the increase in late-apoptosis levels caused by shikonin. Although vincristine treatment led to a high level of G2-phase arrest in U87MG cells, shikonin did not increase G2 arrest. Co-treatment with two PKM2 inhibitors, shikonin and compound 3K, increased the inhibitory effects.

CONCLUSION

Combination therapy with PKM2 inhibitors together might be more effective than combination therapy with anticancer drugs. Our findings encourage the application of PKM2-targeting in gliomas, and lay the foundation for the development of PKM2 inhibitors as promising antitumor agents for glioma.

A Perspective on Medicinal Chemistry Approaches for Targeting Pyruvate Kinase M2

The allosteric regulation of pyruvate kinase M2 (PKM2) affects the switching of the PKM2 protein between the high-activity and low-activity states that allow ATP and lactate production, respectively. PKM2, in its low catalytic state (dimeric form), is chiefly active in metabolically energetic cells, including cancer cells. More recently, PKM2 has emerged as an attractive target due to its role in metabolic dysfunction and other interrelated conditions. PKM2 (dimer) activity can be inhibited by modulating PKM2 dimer-tetramer dynamics using either PKM2 inhibitors that bind at the ATP binding active site of PKM2 (dimer) or PKM2 activators that bind at the allosteric site of PKM2, thus activating PKM2 from the dimer formation to the tetrameric formation. The present perspective focuses on medicinal chemistry approaches to design and discover PKM2 inhibitors and activators and further provides a scope for the future design of compounds targeting PKM2 with better efficacy and selectivity.

Discovery and development of tumor glycolysis rate-limiting enzyme inhibitors

Tumor cells mainly provide necessary energy and substances for rapid cell growth through aerobic perglycolysis rather than oxidative phosphorylation. This phenomenon is called the "Warburg effect". The mechanism of glycolysis in tumor cells is more complicated, which is caused by the comprehensive regulation of multiple factors. Abnormal enzyme metabolism is one of the main influencing factors and inhibiting the three main rate-limiting enzymes in glycolysis is thought to be important strategy for cancer treatment. Therefore, numerous inhibitors of glycolysis rate-limiting enzyme have been developed in recent years, such as the latest HKII inhibitor and PKM2 inhibitor Pachymic acid (PA) and N-(4-(3-(3-(methylamino)-3-oxopropyl)-5-(4'-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-pyrazol-1-yl)phenyl)propiolamide. The review focuses on source, structure-activity relationship, bioecological activity and mechanism of the three main rate-limiting enzymes inhibitors, and hopes to guide the future research on the design and synthesis of rate-limiting enzyme inhibitors.

Pyruvate kinase M2 (PKM2) in cancer and cancer therapeutics

Pyruvate kinase M2 (PKM2), a key rate-limiting enzyme of glycolysis, is a critical regulator in tumor metabolism. PKM2 has been demonstrated to overexpressed in various cancers and promoted proliferation and metastasis of tumor cells. The errant expression of PKM2 has inspired people to investigate the function of PKM2 and the therapeutic potential in cancer. In addition, some studies have shown that the upregulation of PKM2 in tumor tissues is associated with the altered expression of lncRNAs and the poor survival. Therefore, researchers have begun to unravel the specific molecular mechanisms of lncRNA-mediated PKM2 expression in cancer metabolism. As the tumor microenvironment (TME) is essential in tumor development, it is necessary to identify the role of PKM2 in TME. In this review, we will introduce the role of PKM2 in different cancers as well as TME, and summarize the molecular mechanism of PKM2-related lncRNAs in cancer metabolism. We expect that this work will lead to a better understanding of the molecular mechanisms of PKM2 that may help in developing therapeutic strategies in clinic for researchers.

The Role of PKM2 in Metabolic Reprogramming: Insights into the Regulatory Roles of Non-Coding RNAs

Pyruvate kinase is a key regulator in glycolysis through the conversion of phosphoenolpyruvate (PEP) into pyruvate. Pyruvate kinase exists in various isoforms that can exhibit diverse biological functions and outcomes. The pyruvate kinase isoenzyme type M2 (PKM2) controls cell progression and survival through the regulation of key signaling pathways. In cancer cells, the dimer form of PKM2 predominates and plays an integral role in cancer metabolism. This predominance of the inactive dimeric form promotes the accumulation of phosphometabolites, allowing cancer cells to engage in high levels of synthetic processing to enhance their proliferative capacity. PKM2 has been recognized for its role in regulating gene expression and transcription factors critical for health and disease. This role enables PKM2 to exert profound regulatory effects that promote cancer cell metabolism, proliferation, and migration. In addition to its role in cancer, PKM2 regulates aspects essential to cellular homeostasis in non-cancer tissues and, in some cases, promotes tissue-specific pathways in health and diseases. In pursuit of understanding the diverse tissue-specific roles of PKM2, investigations targeting tissues such as the kidney, liver, adipose, and pancreas have been conducted. Findings from these studies enhance our understanding of PKM2 functions in various diseases beyond cancer. Therefore, there is substantial interest in PKM2 modulation as a potential therapeutic target for the treatment of multiple conditions. Indeed, a vast plethora of research has focused on identifying therapeutic strategies for targeting PKM2. Recently, targeting PKM2 through its regulatory microRNAs, long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) has gathered increasing interest. Thus, the goal of this review is to highlight recent advancements in PKM2 research, with a focus on PKM2 regulatory microRNAs and lncRNAs and their subsequent physiological significance.

Simultaneous Inhibition of Ornithine Decarboxylase 1 and Pyruvate Kinase M2 Exerts Synergistic Effects Against Hepatocellular Carcinoma Cells

Purpose

Previously, we showed that lactate promoted the proliferation and mobility of hepatocellular carcinoma (HCC) cells by increasing the expression of ornithine decarboxylase 1 (ODC1). In this study, we determined the relationship between ODC1 and pyruvate kinase M2 (PKM2, a key lactate metabolism enzyme), and determined the combined effects of difluoromethylornithine (DFMO; an ODC1 inhibitor) and compound 3k (a PKM2 inhibitor) on HCC cells.

Methods

First, the relationship between PKM2 and ODC1 was analyzed using Western blotting, Cell Counting Kit (CCK)-8 assays, transwell assays, bioinformatics, quantitative real-time fluorescent PCR (qRT-PCR), and immunohistochemical staining. Thereafter, the ODC1 inhibitor DFMO and the PKM2 inhibitor compound 3k were employed. Their combined effects on HCC cell proliferation and mobility were evaluated via CCK-8 assay, flow cytometry, a subcutaneous xenograft tumor model in mice, wound healing assays, and transwell assays. Additionally, the effects of DFMO and compound 3k on the epithelial–mesenchymal transition phenotype and the AKT/GSK-3β/β-catenin pathway were explored using Western blotting and immunofluorescence.

Results

PKM2 knockdown significantly decreased the ODC1 expression, and the proliferation and invasion of HCC cells, while ODC1 overexpression reversed the inhibitory effects of PKM2 knockdown. Similarly, inhibition of ODC1 also decreased the expression of PKM2 via reducing the c-myc-induced transcription. PKM2 was co-expressed with ODC1 in HCC samples, while simultaneously upregulated PKM2 and ODC1 led to the poorest survival outcome. DFMO and compound 3k synergistically inhibited HCC cell proliferation, induced apoptosis, and suppressed cell mobility, as well as the EMT phenotype and the AKT/GSK-3β/β-catenin pathway. The AKT activator SC79 reversed the inhibitory effects.

Conclusion

PKM2/ODC1 are involved in a positive feedback loop. The simultaneous inhibition of ODC1 and PKM2 using DFMO and compound 3k exerts synergistic effects against HCC cells via the AKT/GSK-3β/β-catenin pathway. Thus, DFMO combined with compound 3k may be a novel effective strategy for treating HCC.

Pyruvate Kinase M2 and Cancer: The Role of PKM2 in Promoting Tumorigenesis

Pyruvate kinase plays a pivotal role in regulating cell metabolism. The final and rate-limiting step of glycolysis is the conversion of Phosphoenolpyruvate (PEP) to Pyruvate, which is catalyzed by Pyruvate Kinase. There are four isomeric, tissue-specific forms of Pyruvate Kinase found in mammals: PKL, PKR, PKM1, and PKM2. PKM1 and PKM2 are formed bya single mRNA transcript of the PKM gene by alternative splicing. The oligomers of PKM2 exist in high activity tetramer and low activity dimer forms. The dimer PKM2 regulates the rate-limiting step of glycolysis that shifts the glucose metabolism from the normal respiratory chain to lactate production in tumor cells. Besides its role as a metabolic regulator, it also acts as protein kinase, which contributes to tumorigenesis. This review is focused on the metabolic role of pyruvate kinase M2 in normal cells vs. cancerous cells and its regulation at the transcriptional level. The review also highlights the role of PKM2 as a potential diagnostic marker and as a therapeutic target in cancer treatment.

Unlocking the Potential of HK2 in Cancer Metabolism and Therapeutics

Glycolysis is a tightly regulated process in which several enzymes, such as Hexokinases (HKs), play crucial roles. Cancer cells are characterized by specific expression levels of several isoenzymes in different metabolic pathways and these features offer possibilities for therapeutic interventions. Overexpression of HKs (mostly of the HK2 isoform) have been consistently reported in numerous types of cancer. Moreover, deletion of HK2 has been shown to decrease cancer cell proliferation without explicit side effects in animal models, which suggests that targeting HK2 is a viable strategy for cancer therapy. HK2 inhibition causes a substantial decrease of glycolysis that affects multiple pathways of central metabolism and also destabilizes the mitochondrial outer membrane, ultimately enhancing cell death. Although glycolysis inhibition has met limited success, partly due to low selectivity for specific isoforms and excessive side effects of the reported HK inhibitors, there is ample ground for progress. The current review is focused on HK2 inhibition, envisaging the development of potent and selective anticancer agents. The information on function, expression, and activity of HKs is presented, along with their structures, known inhibitors, and reported effects of HK2 ablation/inhibition. The structural features of the different isozymes are discussed, aiming to stimulate a more rational approach to the design of selective HK2 inhibitors with appropriate drug-like properties. Particular attention is dedicated to a structural and sequence comparison of the structurally similar HK1 and HK2 isoforms, aiming to unveil differences that could be explored therapeutically. Finally, several additional catalytic- and non-catalytic roles on different pathways and diseases, recently attributed to HK2, are reviewed and their implications briefly discussed.

PKM2 regulates angiogenesis of VR-EPCs through modulating glycolysis, mitochondrial fission, and fusion

Vascular resident endothelial progenitor cells (VR-EPCs) have a certain ability to differentiate into endothelial cells (ECs) and participate in the process of angiogenesis. Glycolysis and mitochondrial fission and fusion play a pivotal role in angiogenesis. Pyruvate kinase muscle isoenzyme 2 (PKM2), which mediates energy metabolism and mitochondrial morphology, is regarded as the focus of VR-EPCs angiogenesis in our study. VR-EPCs were isolated from the hearts of 12-weeks-old Sprague-Dawley rats. The role of PKM2 on angiogenesis was evaluated by tube formation assay, wound healing assay, transwell assay, and chick chorioallantoic membrane assay. Western blot analysis, flow cytometry, mitochondrial membrane potential detection, reactive oxygen species (ROS) detection, immunofluorescence staining, and quantitative real-time polymerase chain reaction were used to investigate the potential mechanism of PKM2 for regulating VR-EPCs angiogenesis. We explored the function of PKM2 on the angiogenesis of VR-EPCs. DASA-58 (the activator of PKM2) promoted VR-EPCs proliferation and PKM2 activity, it also could promote angiogenic differentiation. At the same time, DASA-58 significantly enhanced glycolysis, mitochondrial fusion, slightly increased mitochondrial membrane potential, and maintained ROS at a low level. C3k, an inhibitor of PKM2, inhibited PKM2 activity, expression of angiogenesis-related genes and tube formation. Besides, C3k drastically reduced glycolysis and mitochondrial membrane potential while significantly promoting mitochondrial fission and ROS level. Activation of PKM2 could promote VR-EPCs angiogenesis through modulating glycolysis, mitochondrial fission and fusion. By contrast, PKM2 inhibitor has opposite effects.

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.

Shikonin derivatives for cancer prevention and therapy

Phytochemicals gained considerable interest during the past years as source to develop new treatment options for chemoprevention and cancer therapy. Motivated by the fact that a majority of established anticancer drugs are derived in one way or another from natural resources, we focused on shikonin, a naphthoquinone with high potentials to be further developed as preventive or therapeutic drug to fight cancer. Shikonin is the major chemical component of Lithospermum erythrorhizon (Purple Cromwell) roots. Traditionally, the root extract has been applied to cure dermatitis, burns, and wounds. Over the past three decades, the anti-inflammatory and anticancer effects of root extracts, isolated shikonin as well as semi-synthetic and synthetic derivatives and nanoformulations have been described. In vitro and in vivo experiments were conducted to understand the effect of shikonin at cellular and molecular levels. Preliminary clinical trials indicate the potential of shikonin for translation into clinical oncology. Shikonin exerts additive and synergistic interactions in combination with established chemotherapeutics, immunotherapeutic approaches, radiotherapy and other treatment modalities, which further underscores the potential of this phytochemical to be integrated into standard treatment regimens.

Pyruvate kinase M2: A multifarious enzyme in non-canonical localization to promote cancer progression

Rewiring glucose metabolism, termed as Warburg effect or aerobic glycolysis, is a common signature of cancer cells to meet their high energetic and biosynthetic demands of rapid growth and proliferation. Pyruvate kinase M2 isoform (PKM2) is a key player in such metabolic reshuffle, which functions as a rate-limiting glycolytic enzyme in the cytosol of highly-proliferative cancer cells. During the recent decades, PKM2 has been extensively studied in non-canonical localizations such as nucleus, mitochondria, and extracellular secretion, and pertained to novel biological functions in tumor progression. Such functions of PKM2 open a new avenue for cancer researchers. This review summarizes up-to-date functions of PKM2 at various subcellular localizations of cancer cells and draws attention to the translocation of PKM2 from cytosol into the nucleus induced by posttranslational modifications. Moreover, PKM2 in tumor cells could have an important role in resistance acquisition processes against various chemotherapeutic drugs, which have raised a concern on PKM2 as a potential therapeutic target. Finally, we summarize the current status and future perspectives to improve the potential of PKM2 as a therapeutic target for the development of anticancer therapeutic strategies.

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.

Pancreatic cancer stem cells: Perspectives on potential therapeutic approaches of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma is one of the most aggressive solid tumours of the pancreas, characterised by a five-year survival rate less than 8%. Recent reports that pancreatic cancer stem cells (PCSCs) contribute to the tumorigenesis, progression, and chemoresistance of pancreatic cancer have prompted the investigation of new therapeutic approaches able to directly target PCSCs. In the present paper the non-cancer related drugs that have been proposed to target CSCs that could potentially combat pancreatic cancer are reviewed and evaluated. The role of some pathways and deregulated proteins in PCSCs as new therapeutic targets are also discussed with a focus on selected specific inhibitors. Finally, advances in the development of nanoparticles for targeting PCSCs and site-specific drug delivery are highlighted, and their limitations considered.

Discovery of Pyruvate Kinase as a Novel Target of New Fungicide Candidate 3-(4-Methyl-1,2,3-thiadiazolyl)-6-trichloromethyl-[1,2,4]-triazolo-[3,4- b][1,3,4]-thiadizole

Target identification is an essential basis for novel-pesticide development in new molecular design and lead optimization. 3-(4-Methyl-1,2,3-thiadiazolyl)-6-trichloromethyl[1,2,4]triazolo[3,4- b][1,3,4]thiadizole (YZK-C22) is a novel fungicide candidate with specific antifungal activity. We investigated its mode of action, and our studies indicated that YZK-C22 showed no cross resistance against Saccharomyces cerevisiae mutants with classic fungicide targets. Mec1 and Rad53 are two kinases that respond to DNA-replication damage, and the efficacy test showed that YZK-C22 could not perform its fungicidal activity by inhibiting DNA repair. Target screening by drug-affinity-responsive target stability (DARTS) showed that pyruvate kinase (PK), a key enzyme in the glycolytic pathway, was the potent new fungicidal target of YZK-C22. Fifty-eight differentially expressed proteins (DEPs) primarily involved in the metabolic process were identified by isobaric tags for relative and absolute quantification analysis (iTRAQ) in S. cerevisiae, and protein expression in the citrate cycle decreased with treatment of 5 mg/L YZK-C22, which was consistent with the results of DARTS. Molecular-docking analysis further validated that YZK-C22 could dock into the active center of PK instead of phosphoenolpyruvate. The enzyme activity of PK from S. cerevisiae was competitively inhibited with a K_i of 3.33 ± 0.28 μmol/L, and the cell-growth inhibition of S. cerevisiae was released by supplementation with pyruvic acid, whereas the growth of S. cerevisiae was not recovered by adding PK's substrate (phosphoenolpyruvate) or allosteric regulator (fructose-1,6-bisphosphate). The present studies uncovered and validated the primary target of the new, potent fungicidal candidate YZK-C22; our results provide a successful, valuable, and applicable case of target discovery and identification for novel-fungicide development.

Pyruvate Kinase Isozyme M2 Plays a Critical Role in the Interactions Between Pancreatic Stellate Cells and Cancer Cells

BACKGROUND

The interaction between pancreatic cancer cells and pancreatic stellate cells plays a pivotal role in the progression of pancreatic cancer. Pyruvate kinase isozyme M2 is a key enzyme in glycolysis. Previous studies have shown that pyruvate kinase isozyme M2 is overexpressed in pancreatic cancer and that it regulates the aggressive behaviors of pancreatic cancer cells.

AIMS

To clarify the role of pyruvate kinase isozyme M2 in the interactions between pancreatic cancer cells and pancreatic stellate cells.

METHODS

Pyruvate kinase isozyme M2-knockdown pancreatic cancer cells (Panc-1 and SUIT-2 cells) and pancreatic stellate cells were generated by the introduction of small interfering RNA-expressing vector against pyruvate kinase isozyme M2. Cell proliferation, migration, and epithelial-mesenchymal transition were examined in vitro. The impact of pyruvate kinase isozyme M2 knockdown on the growth of subcutaneous tumors was examined in nude mice in vivo.

RESULTS

Pyruvate kinase isozyme M2-kockdown pancreatic cancer cells and pancreatic stellate cells showed decreased proliferation and migration compared to their respective control cells. Pancreatic stellate cell-induced proliferation, migration, and epithelial-mesenchymal transition were inhibited when pyruvate kinase isozyme M2 expression was knocked down in pancreatic cancer cells. In vivo, co-injection of pancreatic stellate cells increased the size of the tumor developed by the control SUIT-2 cells, but the effects were less evident when pyruvate kinase isozyme M2 was knocked down in SUIT-2 cells or pancreatic stellate cells.

CONCLUSIONS

Our results suggested a critical role of pyruvate kinase isozyme M2 in the interaction between pancreatic cancer cells and pancreatic stellate cells.

Anti-cancer effect of a novel 2,3-didithiocarbamate-substituted naphthoquinone as a tumor metabolic suppressor in vitro and in vivo

Tumor cells reprogram their cellular metabolism by switching from oxidative phosphorylation to aerobic glycolysis to support aberrant cell proliferation. Suppressing tumor cell metabolism has become an attractive strategy for treating cancer patients. In this study, we identified a 2,3-didithiocarbamate-substituted naphthoquinone 3i that inhibited the proliferation of tumor cells by disturbing their metabolism. Compound 3i reduced cancer cell viability with IC50 values from 50 nM to 150 nM against HCT116, MCF7, MDA-MB231, HeLa, H1299 and B16 cells. Further, compound 3i was found to suppress ATP production in cultured cancer cells, inhibit the M2 isoform of pyruvate kinase (PKM2) which is a rate-limiting enzyme in the glycolytic pathway and block the subsequent transcription of the downstream genes GLUT1, LDH and CCND1. In addition, exposure to compound 3i significantly suppressed tumor growth in a B16 melanoma transplantation mouse model and a spontaneous breast carcinoma mouse model in vivo. The identification of compound 3i as a tumor metabolic suppressor not only offers a candidate compound for cancer therapy, but also provides a tool for an in-depth study of tumor metabolism.

The fiber arrangement of the pathological human tympanic membrane

Aerobic glycolysis is an important metabolic adaptation of cancer cells. There is growing evidence that oxidative phosphorylation is also an active metabolic pathway in many tumors, including in high grade serous ovarian cancer. Metastasized ovarian tumors use fatty acids for their energy needs. There is also evidence of ovarian cancer stem cells privileging oxidative phosphorylation (OXPHOS) for their metabolic needs. Metformin and thiazolidinediones such as rosiglitazone restrict tumor growth by inhibiting specific steps in the mitochondrial electron transport chain. These observations suggest that strategies to interfere with oxidative phosphorylation should be considered for the treatment of ovarian tumors. Here, we review the literature that supports this hypothesis and describe potential agents and critical control points in the oxidative phosphorylation pathway that can be targeted using small molecule agents. In this review, we also discuss potential barriers that can reduce the efficacy of the inhibitors of oxidative phosphorylation.