Pyruvate kinase M2-specific siRNA induces apoptosis and tumor regression

RNA structure in alternative splicing regulation: from mechanism to therapy

Alternative splicing is a highly intricate process that plays a crucial role in post-transcriptional regulation and significantly expands the functional proteome of a limited number of coding genes in eukaryotes. Its regulation is multifactorial, with RNA structure exerting a significant impact. Aberrant RNA conformations lead to dysregulation of splicing patterns, which directly affects the manifestation of disease symptoms. In this review, the molecular mechanisms of RNA secondary structure-mediated splicing regulation are summarized, with a focus on the complex interplay between aberrant RNA conformations and disease phenotypes resulted from splicing defects. This study also explores additional factors that reshape structural conformations, enriching our understanding of the mechanistic network underlying structure-mediated splicing regulation. In addition, an emphasis has been placed on the clinical role of targeting aberrant splicing corrections in human diseases. The principal mechanisms of action behind this phenomenon are described, followed by a discussion of prospective development strategies and pertinent challenges.

Discovery of Cell-Permeable Allosteric Inhibitors of Liver Pyruvate Kinase: Design and Synthesis of Sulfone-Based Urolithins

Metabolic dysfunction-associated fatty liver disease (MAFLD) presents a significant global health challenge, characterized by the accumulation of liver fat and impacting a considerable portion of the worldwide population. Despite its widespread occurrence, effective treatments for MAFLD are limited. The liver-specific isoform of pyruvate kinase (PKL) has been identified as a promising target for developing MAFLD therapies. Urolithin C, an allosteric inhibitor of PKL, has shown potential in preliminary studies. Expanding upon this groundwork, our study delved into delineating the structure-activity relationship of urolithin C via the synthesis of sulfone-based urolithin analogs. Our results highlight that incorporating a sulfone moiety leads to substantial PKL inhibition, with additional catechol moieties further enhancing this effect. Despite modest improvements in liver cell lines, there was a significant increase in inhibition observed in HepG2 cell lysates. Specifically, compounds 15d, 9d, 15e, 18a, 12d, and 15a displayed promising IC50 values ranging from 4.3 µM to 18.7 µM. Notably, compound 15e not only demonstrated a decrease in PKL activity and triacylglycerol (TAG) content but also showed efficient cellular uptake. These findings position compound 15e as a promising candidate for pharmacological MAFLD treatment, warranting further research and studies.

An evolutionarily conserved mechanism controls reversible amyloids of pyruvate kinase via pH-sensing regions

Amyloids are known as irreversible aggregates associated with neurodegenerative diseases. However, recent evidence shows that a subset of amyloids can form reversibly and fulfill essential cellular functions. Yet, the molecular mechanisms regulating functional amyloids and distinguishing them from pathological aggregates remain unclear. Here, we investigate the conserved principles of amyloid reversibility by studying the essential metabolic enzyme pyruvate kinase (PK) in yeast and human cells. We demonstrate that yeast PK (Cdc19) and human PK (PKM2) form reversible amyloids through a pH-sensitive amyloid core. Stress-induced cytosolic acidification promotes aggregation via protonation of specific glutamate (yeast) or histidine (human) residues within the amyloid core. Mutations mimicking protonation cause constitutive PK aggregation, while non-protonatable PK mutants remain soluble even upon stress. Physiological PK aggregation is coupled to metabolic rewiring and glycolysis arrest, causing severe growth defects when misregulated. Our work thus identifies an evolutionarily conserved, potentially widespread mechanism regulating functional amyloids during stress.

PKM2 promotes myoblast growth and inosine monophosphate-specific deposition in Jingyuan chicken

Inosine monophosphate (IMP) is widely regarded as an important indicator for evaluating the flavour of poultry meat. However, little is known about the molecular mechanisms affecting the specific deposition of IMP. In this study, we functionally verified PKM2 (Pyruvate kinase M2), a candidate gene related to IMP synthesis, in order to reveal the important role of PKM2 in meat flavour and muscle development of Jingyuan chickens. The results showed that the IMP content in breast muscle of Jingyuan chickens was negatively correlated with PKM2 mRNA expression (r = -0.1710), while the IMP content in leg muscle was significantly positively correlated with PKM2 mRNA expression (r = 0.7350) (P < 0.05). During myogenesis, PKM2 promoted the proliferation rate of myoblasts and the expression of proliferation marker genes, inhibited the apoptosis rate and the expression of apoptosis marker genes, and decreased the expression of differentiation marker genes. Up-regulation of PKM2 enhanced the expression of key genes in the purine metabolic pathway and the de novo synthesis pathway of IMP, and suppressed the expression of key genes in the salvage pathway. ELISA assays showed that PKM2 decreased IMP and hypoxanthine (HX) contents, while adenosine triphosphate (ATP) and uric acid (UA) contents were clearly elevated. In summary, these studies revealed that PKM2 regulates myogenesis and specific deposition of IMP, which can be used to improve the quality of Jingyuan chicken meat.

Delving into the Metabolism of Sézary Cells: A Brief Review

Primary cutaneous lymphomas (PCLs) are a heterogeneous group of lymphoproliferative disorders caused by the accumulation of neoplastic T or B lymphocytes in the skin. Sézary syndrome (SS) is an aggressive and rare form of cutaneous T cell lymphoma (CTCL) characterized by an erythroderma and the presence of atypical cerebriform T cells named Sézary cells in skin and blood. Most of the available treatments for SS are not curative, which means there is an urgent need for the development of novel efficient therapies. Recently, targeting cancer metabolism has emerged as a promising strategy for cancer therapy. This is due to the accumulating evidence that metabolic reprogramming highly contributes to tumor progression. Genes play a pivotal role in regulating metabolic processes, and alterations in these genes can disrupt the delicate balance of metabolic pathways, potentially contributing to cancer development. In this review, we discuss the importance of targeting energy metabolism in tumors and the currently available data on the metabolism of Sézary cells, paving the way for potential new therapeutic approaches aiming to improve clinical outcomes for patients suffering from SS.

Current Advances on Nanomaterials Interfering with Lactate Metabolism for Tumor Therapy

Increasing numbers of studies have shown that tumor cells prefer fermentative glycolysis over oxidative phosphorylation to provide a vast amount of energy for fast proliferation even under oxygen-sufficient conditions. This metabolic alteration not only favors tumor cell progression and metastasis but also increases lactate accumulation in solid tumors. In addition to serving as a byproduct of glycolytic tumor cells, lactate also plays a central role in the construction of acidic and immunosuppressive tumor microenvironment, resulting in therapeutic tolerance. Recently, targeted drug delivery and inherent therapeutic properties of nanomaterials have attracted great attention, and research on modulating lactate metabolism based on nanomaterials to enhance antitumor therapy has exploded. In this review, the advanced tumor therapy strategies based on nanomaterials that interfere with lactate metabolism are discussed, including inhibiting lactate anabolism, promoting lactate catabolism, and disrupting the "lactate shuttle". Furthermore, recent advances in combining lactate metabolism modulation with other therapies, including chemotherapy, immunotherapy, photothermal therapy, and reactive oxygen species-related therapies, etc., which have achieved cooperatively enhanced therapeutic outcomes, are summarized. Finally, foreseeable challenges and prospective developments are also reviewed for the future development of this field.

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.

Mint3-depletion-induced energy stress sensitizes triple-negative breast cancer to chemotherapy via HSF1 inactivation

Given the lack of therapeutic targets, the conventional approach for managing triple-negative breast cancer (TNBC) involves the utilization of cytotoxic chemotherapeutic agents. However, most TNBCs acquire resistance to chemotherapy, thereby lowering the therapeutic outcome. In addition to oncogenic mutations in TNBC, microenvironment-induced mechanisms render chemoresistance more complex and robust in vivo. Here, we aimed to analyze whether depletion of Munc18-1 interacting protein 3 (Mint3), which activates hypoxia-inducible factor 1 (HIF-1) during normoxia, sensitizes TNBC to chemotherapy. We found that Mint3 promotes the chemoresistance of TNBC in vivo. Mint3 depletion did not affect the sensitivity of human TNBC cell lines to doxorubicin and paclitaxel in vitro but sensitized tumors of these cells to chemotherapy in vivo. Transcriptome analyses revealed that the Mint3-HIF-1 axis enhanced heat shock protein 70 (HSP70) expression in tumors of TNBC cells. Administering an HSP70 inhibitor enhanced the antitumor activity of doxorubicin in TNBC tumors, similar to Mint3 depletion. Mint3 expression was also correlated with HSP70 expression in human TNBC specimens. Mechanistically, Mint3 depletion induces glycolytic maladaptation to the tumor microenvironment in TNBC tumors, resulting in energy stress. This energy stress by Mint3 depletion inactivated heat shock factor 1 (HSF-1), the master regulator of HSP expression, via the AMP-activated protein kinase/mechanistic target of the rapamycin pathway following attenuated HSP70 expression. In conclusion, Mint3 is a unique regulator of TNBC chemoresistance in vivo via metabolic adaptation to the tumor microenvironment, and a combination of Mint3 inhibition and chemotherapy may be a good strategy for TNBC treatment.

The Complex Effects of PKM2 and PKM2:IP3R Disruption on Intracellular Ca2+ Handling and Cellular Functions

Pyruvate kinase M (PKM) 2 was described to interact with the inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and suppress its activity. To further investigate the physiological importance of the PKM2:IP3R interaction, we developed and characterized HeLa PKM2 knockout (KO) cells. In the HeLa PKM2 KO cells, the release of Ca2+ to the cytosol appears to be more sensitive to low agonist concentrations than in HeLa wild-type (WT) cells. However, upon an identical IP3-induced Ca2+ release, Ca2+ uptake in the mitochondria is decreased in HeLa PKM2 KO cells, which may be explained by the smaller number of contact sites between the ER and the mitochondria. Furthermore, in HeLa PKM2 KO cells, mitochondria are more numerous, though they are smaller and less branched and have a hyperpolarized membrane potential. TAT-D5SD, a cell-permeable peptide representing a sequence derived from IP3R1 that can disrupt the PKM2:IP3R interaction, induces Ca2+ release into the cytosol and Ca2+ uptake into mitochondria in both HeLa WT and PKM2 KO cells. Moreover, TAT-D5SD induced apoptosis in HeLa WT and PKM2 KO cells but not in HeLa cells completely devoid of IP3Rs. These results indicate that PKM2 separately regulates cytosolic and mitochondrial Ca2+ handling and that the cytotoxic effect of TAT-D5SD depends on IP3R activity but not on PKM2. However, the tyrosine kinase Lck, which also interacts with the D5SD sequence, is expressed neither in HeLa WT nor PKM2 KO cells, and we can also exclude a role for PKM1, which is upregulated in HeLa PKM2 KO cells, indicating that the TAT-D5SD peptide has a more complex mode of action than anticipated.

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 essential molecular requirements for the transformation of normal cells into established cancer cells, with implications for a novel anti-cancer agent

BACKGROUND

Normal adult mammalian cells can respond to oncogenic somatic mutations by committing suicide through a well-described, energy dependent process termed apoptosis. Cancer cells avoid oncogene promoted apoptosis. Oncogenic somatic mutations are widely acknowledged to be the cause of the relentless unconstrained cell proliferation which characterises cancer. But how does the normal cell with the very first oncogenic mutation survive to proliferate without undergoing apoptosis?

NEW FINDINGS

The phenomena of malignant transformation by somatic mutation, apoptosis, aneuploidy, aerobic glycolysis and Cdk4 upregulation in carcinogenesis have each been extensively discussed separately in the literature but an overview explaining how they may be linked at the initiation of the cancer process has not previously proposed.

CONCLUSION

A hypothesis is presented to explain how in addition to the initial oncogenic mutation, the expression of certain key normal genes is, counter-intuitively, also required for successful malignant transformation from a normal cell to a cancer cell. The hypothesis provides an explanation for how the cyclic amphiphilic peptide HILR-056, derived from peptides with homology to a hexapeptide in the C-terminal region of Cdk4, kill cancer cells but not normal cell by necrosis rather than apoptosis.

Association of PKLR gene copy number, expression levels and enzyme activity with 2,3,7,8-TCDD exposure in individuals exposed to Agent Orange/Dioxin in Vietnam

2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is the most toxic congener of dioxin and has serious long-term effects on the environment and human health. Pyruvate Kinase L/R (PKLR) gene expression levels and gene variants are associated with pyruvate kinase enzyme deficiency, which has been identified as the cause of several diseases linked to dioxin exposure. In this study, we estimated PKLR gene copy number and gene expression levels using real-time quantitative PCR (RT-qPCR) assays, genotyped PKLR SNP rs3020781 by Sanger sequencing, and quantified plasma pyruvate kinase enzyme activity in 100 individuals exposed to Agent Orange/Dioxin near Bien Hoa and Da Nang airfields in Vietnam and 100 healthy controls. The means of PKLR copy numbers and PKLR gene expression levels were significantly higher, while pyruvate kinase enzyme activity was significantly decreased in Agent Orange/Dioxin-exposed individuals compared to healthy controls (P < 0.0001). Positive correlations of PKLR gene copy number and gene expression with 2,3,7,8-TCDD concentrations were observed (r = 0.2, P = 0.045 and r = 0.54, P < 0.0001, respectively). In contrast, pyruvate kinase enzyme activity was inversely correlated with 2,3,7,8-TCDD concentrations (r = -0.52, P < 0.0001). PKLR gene copy number and gene expression levels were also inversely correlated with pyruvate kinase enzyme activity. Additionally, PKLR SNP rs3020781 was found to be associated with 2,3,7,8-TCDD concentrations and PKLR gene expression. In conclusion, PKLR copy number, gene expression levels, and pyruvate kinase enzyme activity are associated with 2,3,7,8-TCDD exposure in individuals living in Agent Orange/Dioxin-contaminated areas.

Anti-tumor effects of novel alkannin derivatives with potent selectivity on comprehensive analysis

BACKGROUND

Therapeutic approaches based on glycolysis and energy metabolism of tumor cells are new promising strategies for the treatment of cancer. Currently, researches on the inhibition of pyruvate kinase M2, a key rate limiting enzyme in glycolysis, have been corroborated as an effective cancer therapy. Alkannin is a potent pyruvate kinase M2 inhibitor. However, its non-selective cytotoxicity has affected its subsequent clinical application. Thus, it needs to be structurally modified to develop novel derivatives with high selectivity.

PURPOSE

Our study aimed to ameliorate the toxicity of alkannin through structural modification and elucidate the mechanism of the superior derivative 23 in lung cancer therapy.

METHODS

On the basis of the principle of collocation, different amino acids and oxygen-containing heterocycles were introduced into the hydroxyl group of the alkannin side chain. We examined the cell viability of all derivatives on three tumor cells (HepG2, A549 and HCT116) and two normal cells (L02 and MDCK) by MTT assay. Besides, the effect of derivative 23 on the morphology of A549 cells as observed by Giemsa and DAPI staining, respectively. Flow cytometry was performed to assess the effects of derivative 23 on apoptosis and cell cycle arrest. To further assess the effect of derivative 23 on the Pyruvate kinase M2 in glycolysis, an enzyme activity assay and western blot assay were performed. Finally, in vivo the antitumor activity and safety of the derivative 23 were evaluated by using Lewis mouse lung cancer xenograft model.

RESULTS

Twenty-three novel alkannin derivatives were designed and synthesized to improve the cytotoxicity selectivity. Among these derivatives, derivative 23 showed the highest cytotoxicity selectivity between cancer and normal cells. The anti-proliferative activity of derivative 23 on A549 cells (IC₅₀ = 1.67 ± 0.34 μM) was 10-fold higher than L02 cells (IC₅₀ = 16.77 ± 1.44 μM) and 5-fold higher than MDCK cells (IC₅₀ = 9.23 ± 0.29 μM) respectively. Subsequently, fluorescent staining and flow cytometric analysis showed that derivative 23 was able to induce apoptosis of A549 cells and arrest the cell cycle in the G0/G1 phase. In addition, the mechanistic studies suggested derivative 23 was an inhibitor of pyruvate kinase; it could regulate glycolysis by inhibiting the activation of the phosphorylation of PKM2/STAT3 signaling pathway. Furthermore, studies in vivo demonstrated derivative 23 significantly inhibited the growth of xenograft tumor.

CONCLUSION

In this study, alkannin selectivity is reported to be significantly improved following structural modification, and derivative 23 is first shown to be able to inhibit lung cancer growth via the PKM2/STAT3 phosphorylation signaling pathway in vitro, indicating the potential value of derivative 23 in treating lung cancer.

Isoform specific knockdown of the ETS transcription factor Pointed in Drosophila S2 cells

Alternate splicing of the pointed ( pnt ) gene locus produces two major isoforms, PntP1 and PntP2. Understanding their individual contributions to key developmental processes and identification of their genome-wide transcriptional targets has been hampered by a number of factors including their essential roles during embryonic development, and co-expression in several tissues. siRNAs were designed to target isoform-specific exons that code for the unique N-terminal region of either PntP1 or PntP2. The efficacy and specificity of the siRNAs were examined by co-transfection of isoform specific siRNAs with plasmids encoding epitope tagged PntP1 or PntP2 in Drosophila S2 cells. All P1-specific siRNAs were demonstrated to knockdown PntP1 protein level to greater than 95%, while having nominal impact on PntP2 level. Similarly, PntP2 siRNAs while ineffective at eliminating PntP1, were shown to reduce PntP2 protein level by 87-99%.

Exploration of Novel Urolithin C Derivatives as Non-Competitive Inhibitors of Liver Pyruvate Kinase

The inhibition of liver pyruvate kinase could be beneficial to halt or reverse non-alcoholic fatty liver disease (NAFLD), a progressive accumulation of fat in the liver that can lead eventually to cirrhosis. Recently, urolithin C has been reported as a new scaffold for the development of allosteric inhibitors of liver pyruvate kinase (PKL). In this work, a comprehensive structure-activity analysis of urolithin C was carried out. More than 50 analogues were synthesized and tested regarding the chemical features responsible for the desired activity. These data could pave the way to the development of more potent and selective PKL allosteric inhibitors.

PKM2/PDK1 dual-targeted shikonin derivatives restore the sensitivity of EGFR-mutated NSCLC cells to gefitinib by remodeling glucose metabolism

Pyruvate kinase 2 (PKM2) and pyruvate dehydrogenase kinase 1 (PDK1) are two key enzymes in tumor glucose metabolism pathway that not only promote tumor growth and proliferation through accelerating aerobic glycolysis, but also contribute to drug resistance of non-small cell lung cancer (NSCLC). Considering that targeting PKM2 or PDK1 alone seems insufficient to remodel abnormal glucose metabolism to achieve significant antitumor activity, we proposed a "two-step approach" that regulates PKM2 and PDK1 synchronously. Firstly, we found that the combination of ML265 (PKM2 activator) and AZD7545 (PDK1 inhibitor) could synergistically inhibit proliferation and induce apoptosis in H1299 cells. Base on this, we designed a series of novel shikonin (SK) thioether derivatives as PKM2/PDK1 dual-target agents, among which the most potent compound E5 featuring a 2-methyl substitution on the benzene ring exerted significantly increased inhibitory activity toward EGFR mutant NSCLC cell H1975 (IC₅₀ = 1.51 μmol/L), which was 3 and 17-fold more active than the lead compound SK (IC₅₀ = 4.56 μmol/L) and the positive control gefitinib (IC₅₀ = 25.56 μmol/L), respectively. Additionally, E5 also showed good anti-tumor activity in xenografted mouse models, with significantly lower toxicity side effects than SK. Moreover, E5 also inhibited the entry of PKM2 into nucleus to regulate the transcriptional activation of oncogenes, thus restoring the sensitivity of H1975 cell to gefitinib. Collectively, these data demonstrate that E5, a dual inhibitor of PKM2/PDK1, may be a promising adjunct to gefitinib in the treatment of EGFR-TKIs resistant NSCLC, deserving further investigation.

Selective Covalent Targeting of Pyruvate Kinase M2 Using Arsenous Warheads

There is growing interest in covalent targeted inhibitors in drug discovery against previously "undruggable" sites and targets. These molecules typically feature an electrophilic warhead that reacts with nucleophilic groups of protein residues, most notably the thiol group of cysteines. One main challenge in the field is to develop versatile utilizable warheads. Here, we characterize the unique features of novel arsenous warheads for reaction with thiol species in a reversible manner and further demonstrate that organoarsenic probes can be chemically tuned toward specific molecular targets by developing selective and potent inhibitors of pyruvate kinase M2 (PKM2). We show that compound 24 is a covalent and allosteric inhibitor of PKM2 and its orally bioavailable prodrug 25 exerts efficacious inhibition of PKM2-dependent tumor growth in vitro and in vivo. Our results introduce 25 and its derivatives as useful pharmacological tools and provide a general road map for targeting the protein cysteinome using arsenous warheads.

Expression of PKM2 in wound keratinocytes is coupled to angiogenesis during skin repair in vivo and in HaCaT keratinocytes in vitro

An injured skin is rapidly restored in a manner of wound healing. We have previously shown that intact insulin signaling and glucose uptake are fundamental to proper wound closure. Consequently, under exacerbated inflammation, compromised insulin action and glucose uptake lead to impaired healing. However, in spite of the increased attention to cell metabolism during tissue regeneration, metabolic mediators that govern cellular and physiological processes throughout skin repair remained largely elusive. Through assessment of mRNA using real-time PCR and protein blot analysis, we report that healing of cutaneous wounds comprise a boosted expression of genes involved in glycolysis, oxidative phosphorylation, pentose phosphate shunt, and glutamine anaplerosis. We further focused on the functional role of pyruvate kinase M (PKM) isoenzymes that catalyze the final and rate-limiting step of glycolysis. Whereas the expression of the metabolic constitutively active Pkm1 isozyme remained almost unchanged, Pkm2 is augmented during the inflammatory phase of healing. The immunohistochemistry and RNA in situ hybridization analysis showed a confined Pkm2 expression to keratinocytes of the hyperproliferative epithelium and, to a lesser extent, infiltrating neutrophils and monocytes as well as later on in macrophages. Notably, the expression of Pkm2 in keratinocytes facing the wound bed side colocalized with VEGF expression. The in vitro knockdown of PKM2 in HaCaT keratinocytes using small interfering (si) RNA confirmed an acute role for PKM2 in facilitating the complete induction of VEGF mRNA and protein expression in keratinocytes; this function is mainly HIF-1α independent. KEY MESSAGES: • Wound healing involves activation of glycolysis, oxidative phosphorylation, pentos-phosphate shunt, and replenishment of tri-carboxylic acid (TCA) cycle through glutamine anaplerosis. • The pyruvate kinase M2 (PKM2) isoform is upregulated during the inflammatory phase of cutaneous healing, mainly in keratinocytes of hyperproliferative epithelia. • In vivo, the expression of VEGF in wound keratinocytes is colocalized with PKM2. • PKM2 is required for full induction of VEGF in HaCaT keratinocytes in vitro.

Long Non-coding RNA UCA1a Promotes Proliferation via PKM2 in Cervical Cancer

Cervical cancer is a common malignancy that affects women worldwide. The long non-coding RNA (lncRNA) urothelial cancer-associated 1a (UCA1a) is reported to be significantly upregulated in cervical cancer. However, the exact role of UCA1a in cervical cancer remains unknown. This study aimed to identify two core promoter regions in UCA1a, which are essential for CEBPA-dependent transcription and FOXL1-, FOXL4-, and FOXL6-dependent activation, respectively. RNA sequencing results showed that overexpression of UCA1a resulted in extensive changes in the gene expression profile of HeLa cells, especially in the signaling pathway that regulates tumorgenesis. Mass spectrometry assay was conducted to show that pyruvate kinase M2 (PKM2) was a UCA1a-interacting protein. The 400 ~ 800 nt long region of UCA1a at the 5' end and the A1B domain of PKM2 were critical for the UCA1a-PKM2 interaction. Functional assays were performed to show that PKM2 was sufficient and necessary for UCA1a-induced proliferation of HeLa cells, which was partly due to the regulating of nuclear translocation and stabilization of PKM2. These findings provide a novel mechanism for UCA1a to regulate Hela cells by ubiquitination degradation of PKM2 and suggest that UCA1a may play a key role in the progression of cervical cancer.

[Shikonin induces hepatocellular carcinoma cell apoptosis by suppressing PKM2/PHD3/HIF-1α signaling pathway]

OBJECTIVE

To investigate the mechanism of shikonin-induced death of human hepatocellular carcinoma SMMC-7721 cells.

METHODS

Cultured SMMC-7721 cells and normal hepatocytes (L-02 cells) were treated with 4, 8, or 16 μmol/L shikonin, and the changes in cell viability was assessed using MTT assay. The levels of ATP and lactic acid in the cell cultures were detected using commercial kits. Co-immunoprecipitation and immunofluorescence staining were used to determine the relationship among pyruvate kinase M2 (PKM2), prolyl hydroxylase 3 (PHD3), and hypoxia-inducible factor-1α (HIF-1α). The expressions of PHD3, PKM2, HIF-1α, Bax, cleaved caspase-3, and Bcl-2 in SMMC-7721 cells were detected with Western blotting, and cell apoptosis was analyzed with annexin V-FITC/PI staining. The effects of RNA interference of PKM2 on PHD3 and HIF-1α expressions in SMMC-7721 cells were detected using Western blotting.

RESULTS

The IC₅₀ of shikonin against SMMC-7721 and L-02 cells was 8.041 μmol/L and 31.75 μmol/L, respectively. Treatment with shikonin significantly inhibited the protein expressions of PKM2, HIF-1α and PHD3 and nuclear translocation of PKM2 and HIF-1α in SMMC-7721 cells. Coimmunoprecipitation and immunofluorescence staining confirmed that shikonin inhibited the formation of PKM2/PHD3/HIF-1α complex and significantly reduced the contents of lactic acid and ATP in SMMC-7721 cells (P < 0.05). The expressions of PHD3 and HIF-1α decreased significantly after PKM2 knockdown (P < 0.05). Shikonin treatment significantly increased the apoptosis rate, enhanced the expressions of Bax and cleaved caspase-3, and decreased Bcl-2 expression in SMMC-7721 cells (P < 0.05).

CONCLUSIONS

Shikonin induces apoptosis of SMMC-7721 cells possibly by inhibiting aerobic glycolysis through the PKM2/PHD3/HIF-1α signaling pathway to cause energy supply dysfunction in the cells.

Aberrant splicing in human cancer: An RNA structural code point of view

Alternative splicing represents an essential process that occurs widely in eukaryotes. In humans, most genes undergo alternative splicing to ensure transcriptome and proteome diversity reflecting their functional complexity. Over the last decade, aberrantly spliced transcripts due to mutations in cis- or trans-acting splicing regulators have been tightly associated with cancer development, largely drawing scientific attention. Although a plethora of single proteins, ribonucleoproteins, complexed RNAs, and short RNA sequences have emerged as nodal contributors to the splicing cascade, the role of RNA secondary structures in warranting splicing fidelity has been underestimated. Recent studies have leveraged the establishment of novel high-throughput methodologies and bioinformatic tools to shed light on an additional layer of splicing regulation in the context of RNA structural elements. This short review focuses on the most recent available data on splicing mechanism regulation on the basis of RNA secondary structure, emphasizing the importance of the complex RNA G-quadruplex structures (rG4s), and other specific RNA motifs identified as splicing silencers or enhancers. Moreover, it intends to provide knowledge on newly established techniques that allow the identification of RNA structural elements and highlight the potential to develop new RNA-oriented therapeutic strategies against cancer.

Knowledge-driven design and optimization of potent symmetric anticancer molecules: A case study on PKM2 activators

BACKGROUND

Pyruvate kinase M2 (PKM2) is preferentially expressed as a low-activity dimer over the active tetramer in proliferating tumor cells, resulting in metabolic reprogramming to achieve high energy requirements and nutrient uptake. This leads to a shift from the normal glycolytic pathway causing tumor cells to proliferate uncontrollably. This study utilizes knowledge-based drug discovery to determine the critical features from experimentally known PKM2 activators and design compounds that would significantly confer a stable structural and functional edge over the known compounds which are still at the preclinical stage.

METHODS

Conscientious molecular modeling studies were carried out and critical structural features were identified and validated from the knowledge of experimentally known PKM2 activators to confer high-binding affinities. A virtual library of 200 palindromic and non-palindromic activators was designed based on these identified critical features to target a distinct activator binding-site. This binding would favor specific dimer-dimer association and subsequent protein tetramerization. The resultant compounds strongly correlated with identified structural features and binding affinities which further strengthened our findings. The designed activators were then subjected to pharmacokinetic profiling and toxicity prediction, followed by free-binding energy calculations and MD simulations.

RESULTS

All the virtually designed activators comprising the identified critical features were observed to confer high-binding affinities ranging from -9.1 to -15.0 kcal/mol to the receptor protein. The designed activators also demonstrated optimum pharmacokinetic and toxicity profiles.

CONCLUSION

The best activators selected for MD simulations studies were conclusively observed to stabilize the required tetrameric conformation suggesting that these activators could potentially target PKM2 tetramerization that might restore the normal glycolytic pathway and suppress tumor progression.

PKM2 promotes pulmonary fibrosis by stabilizing TGF-β1 receptor I and enhancing TGF-β1 signaling

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease, and the molecular mechanisms remain poorly understood. Our findings demonstrated that pyruvate kinase M2 (PKM2) promoted fibrosis progression by directly interacting with Smad7 and reinforcing transforming growth factor-β1 (TGF-β1) signaling. Total PKM2 expression and the portion of the tetrameric form elevated in lungs and fibroblasts were derived from mice with bleomycin (BLM)-induced pulmonary fibrosis. Pkm2 deletion markedly alleviated BLM-induced fibrosis progression, myofibroblast differentiation, and TGF-β1 signaling activation. Further study showed that PKM2 tetramer enhanced TGF-β1 signaling by directly binding with Smad7 on its MH2 domain, and thus interfered with the interaction between Smad7 and TGF-β type I receptor (TβR1), decreased TβR1 ubiquitination, and stabilized TβR1. Pharmacologically enhanced PKM2 tetramer by TEPP-46 promoted BLM-induced pulmonary fibrosis, while tetramer disruption by compound 3k alleviated fibrosis progression. Our results demonstrate how PKM2 regulates TGF-β1 signaling and is a key factor in fibrosis progression.

Targeting Glucose Metabolism Enzymes in Cancer Treatment: Current and Emerging Strategies

Simple Summary

Reprogramming of glucose metabolism is a hallmark of cancer and can be targeted by therapeutic agents. Some metabolism regulators, such as ivosidenib and enasidenib, have been approved for cancer treatment. Currently, more advanced and effective glucose metabolism enzyme-targeted anticancer drugs have been developed. Furthermore, some natural products have shown efficacy in killing tumor cells by regulating glucose metabolism, offering novel therapeutic opportunities in cancer. However, most of them have failed to be translated into clinical applications due to low selectivity, high toxicity, and side effects. Recent studies suggest that combining glucose metabolism modulators with chemotherapeutic drugs, immunotherapeutic drugs, and other conventional anticancer drugs may be a future direction for cancer treatment.

Abstract

Reprogramming of glucose metabolism provides sufficient energy and raw materials for the proliferation, metastasis, and immune escape of cancer cells, which is enabled by glucose metabolism-related enzymes that are abundantly expressed in a broad range of cancers. Therefore, targeting glucose metabolism enzymes has emerged as a promising strategy for anticancer drug development. Although several glucose metabolism modulators have been approved for cancer treatment in recent years, some limitations exist, such as a short half-life, poor solubility, and numerous adverse effects. With the rapid development of medicinal chemicals, more advanced and effective glucose metabolism enzyme-targeted anticancer drugs have been developed. Additionally, several studies have found that some natural products can suppress cancer progression by regulating glucose metabolism enzymes. In this review, we summarize the mechanisms underlying the reprogramming of glucose metabolism and present enzymes that could serve as therapeutic targets. In addition, we systematically review the existing drugs targeting glucose metabolism enzymes, including small-molecule modulators and natural products. Finally, the opportunities and challenges for glucose metabolism enzyme-targeted anticancer drugs are also discussed. In conclusion, combining glucose metabolism modulators with conventional anticancer drugs may be a promising cancer treatment strategy.

Single-Cell FISH Analysis Reveals Distinct Shifts in PKM Isoform Populations during Drug Resistance Acquisition

The Warburg effect, i.e., the utilization of glycolysis under aerobic conditions, is recognized as a survival advantage of cancer cells. However, how the glycolytic activity is affected during drug resistance acquisition has not been explored at single-cell resolution. Because the relative ratio of the splicing isoform of pyruvate kinase M (PKM), PKM2/PKM1, can be used to estimate glycolytic activity, we utilized a single-molecule fluorescence in situ hybridization (SM-FISH) method to simultaneously quantify the mRNA levels of PKM1 and PKM2. Treatment of HCT116 cells with gefitinib (GE) resulted in two distinct populations of cells. However, as cells developed GE resistance, the GE-sensitive population with reduced PKM2 expression disappeared, and GE-resistant cells (Res) demonstrated enhanced PKM1 expression and a tightly regulated PKM2/PKM1 ratio. Our data suggest that maintaining an appropriate PKM2 level is important for cell survival upon GE treatment, whereas increased PKM1 expression becomes crucial in GE Res. This approach demonstrates the importance of single-cell-based analysis for our understanding of cancer cell metabolic responses to drugs, which could aid in the design of treatment strategies for drug-resistant cancers.

Mitochondrial PKM2 deacetylation by procyanidin B2-induced SIRT3 upregulation alleviates lung ischemia/reperfusion injury

Apoptosis is a critical event in the pathogenesis of lung ischemia/reperfusion (I/R) injury. Sirtuin 3 (SIRT3), an important deacetylase predominantly localized in mitochondria, regulates diverse physiological processes, including apoptosis. However, the detailed mechanisms by which SIRT3 regulates lung I/R injury remain unclear. Many polyphenols strongly regulate the sirtuin family. In this study, we found that a polyphenol compound, procyanidin B2 (PCB2), activated SIRT3 in mouse lungs. Due to this effect, PCB2 administration attenuated histological lesions, relieved pulmonary dysfunction, and improved the survival rate of the murine model of lung I/R injury. Additionally, this treatment inhibited hypoxia/reoxygenation (H/R)-induced A549 cell apoptosis and rescued Bcl-2 expression. Using Sirt3-knockout mice and specific SIRT3 knockdown in vitro, we further found that SIRT3 strongly protects against lung I/R injury. Sirt3 deficiency or enzymatic inactivation substantially aggravated lung I/R-induced pulmonary lesions, promoted apoptosis, and abolished PCB2-mediated protection. Mitochondrial pyruvate kinase M2 (PKM2) inhibits apoptosis by stabilizing Bcl-2. Here, we found that PKM2 accumulates and is hyperacetylated in mitochondria upon lung I/R injury. By screening the potential sites of PKM2 acetylation, we found that SIRT3 deacetylates the K433 residue of PKM2 in A549 cells. Transfection with a deacetylated mimic plasmid of PKM2 noticeably reduced apoptosis, while acetylated mimic transfection abolished the protective effect of PKM2. Furthermore, PKM2 knockdown or inhibition in vivo significantly abrogated the antiapoptotic effects of SIRT3 upregulation. Collectively, this study provides the first evidence that the SIRT3/PKM2 pathway is a protective target for the suppression of apoptosis in lung I/R injury. Moreover, this study identifies K433 deacetylation of PKM2 as a novel modification that regulates its anti-apoptotic activity. In addition, PCB2-mediated modulation of the SIRT3/PKM2 pathway may significantly protect against lung I/R injury, suggesting a novel prophylactic strategy for lung I/R injury.

Chemoproteomics reveals berberine directly binds to PKM2 to inhibit the progression of colorectal cancer

Colorectal cancer is one of the most serious tumors and berberine can inhibit the recurrence and transformation of colorectal adenoma into colorectal cancer. However, the direct binding target proteins of berberine in inhibiting colorectal cancer remain unclear. In this study, the chemical proteomics method was used and demonstrated that berberine is directly bound to pyruvate kinase isozyme type M2 (PKM2) in colorectal cancer cells. The triangular N-O-O triangular structure of berberine contributed to hydrophobic interaction with I119 amino acid residues and π-π interaction with F244 amino acid residues of PKM2 protein. Moreover, berberine was shown to inhibit the reprogramming of glucose metabolism and the phosphorylation of STAT3, down regulate the expression of Bcl-2 and Cyclin D1 genes, ultimately inhibiting the progression of colorectal cancer. This study uncovered the direct binding target protein and mechanism of berberine to improve metabolic reprogramming in colorectal cancer, which is helpful to guide the optimization of berberine.

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Berberine directly targets PKM2 to inhibit colorectal cancer

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Berberine forms hydrophobic interaction with I119 and π-π interaction with F244 of PKM2

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P-aminobenzoic acid-berberine ester was synthesized to improve the biological activity

Pyruvate Kinase M2 Protects Heart from Pressure Overload-Induced Heart Failure by Phosphorylating RAC1

Background

Heart failure, caused by sustained pressure overload, remains a major public health problem. PKM (pyruvate kinase M) acts as a rate‐limiting enzyme of glycolysis. PKM2 (pyruvate kinase M2), an alternative splicing product of PKM, plays complex roles in various biological processes and diseases. However, the role of PKM2 in the development of heart failure remains unknown.

Methods and Results

Cardiomyocyte‐specific Pkm2 knockout mice were generated by crossing the floxed Pkm2 mice with α‐MHC (myosin heavy chain)‐Cre transgenic mice, and cardiac specific Pkm2 overexpression mice were established by injecting adeno‐associated virus serotype 9 system. The results showed that cardiomyocyte‐specific Pkm2 deletion resulted in significant deterioration of cardiac functions under pressure overload, whereas Pkm2 overexpression mitigated transverse aortic constriction‐induced cardiac hypertrophy and improved heart functions. Mechanistically, we demonstrated that PKM2 acted as a protein kinase rather than a pyruvate kinase, which inhibited the activation of RAC1 (rho family, small GTP binding protein)‐MAPK (mitogen‐activated protein kinase) signaling pathway by phosphorylating RAC1 in the progress of heart failure. In addition, blockade of RAC1 through NSC23766, a specific RAC1 inhibitor, attenuated pathological cardiac remodeling in Pkm2 deficiency mice subjected to transverse aortic constriction.

Conclusions

This study revealed that PKM2 attenuated overload‐induced pathological cardiac hypertrophy and heart failure, which provides an attractive target for the prevention and treatment of cardiomyopathies.

Targeting Protein Kinases and Epigenetic Control as Combinatorial Therapy Options for Advanced Prostate Cancer Treatment

Prostate cancer (PC), the fifth leading cause of cancer-related mortality worldwide, is known as metastatic bone cancer when it spreads to the bone. Although there is still no effective treatment for advanced/metastatic PC, awareness of the molecular events that contribute to PC progression has opened up opportunities and raised hopes for the development of new treatment strategies. Androgen deprivation and androgen-receptor-targeting therapies are two gold standard treatments for metastatic PC. However, acquired resistance to these treatments is a crucial challenge. Due to the role of protein kinases (PKs) in the growth, proliferation, and metastases of prostatic tumors, combinatorial therapy by PK inhibitors may help pave the way for metastatic PC treatment. Additionally, PC is known to have epigenetic involvement. Thus, understanding epigenetic pathways can help adopt another combinatorial treatment strategy. In this study, we reviewed the PKs that promote PC to advanced stages. We also summarized some PK inhibitors that may be used to treat advanced PC and we discussed the importance of epigenetic control in this cancer. We hope the information presented in this article will contribute to finding an effective treatment for the management of advanced PC.

PKM2 Is Essential for Bladder Cancer Growth and Maintenance

Pyruvate kinase M2 (PKM2) has been shown to promote tumorigenesis by facilitating the Warburg effect and enhancing the activities of oncoproteins. However, this paradigm has recently been challenged by studies in which the absence of PKM2 failed to inhibit and instead accelerated tumorigenesis in mouse models. These results seem inconsistent with the fact that most human tumors overexpress PKM2. To further elucidate the role of PKM2 in tumorigenesis, we investigated the effect of PKM2 knockout in oncogenic HRAS-driven urothelial carcinoma. While PKM2 ablation in mouse urothelial cells did not affect tumor initiation, it impaired the growth and maintenance of HRAS-driven tumors. Chemical inhibition of PKM2 recapitulated these effects. Both conditions substantially reduced complex formation of PKM2 with STAT3, their nuclear translocation, and HIF1α- and VEGF-related angiogenesis. The reduction in nuclear STAT3 in the absence of PKM2 also correlated with decreased autophagy and increased apoptosis. Time-controlled, inducible PKM2 overexpression in simple urothelial hyperplasia did not trigger tumorigenesis, while overexpression of PKM2, but not PKM1, in nodular urothelial hyperplasia with angiogenesis strongly accelerated tumorigenesis. Finally, in human patients, PKM2 was overexpressed in low-grade nonmuscle-invasive and high-grade muscle-invasive bladder cancer. Based on these data, PKM2 is not required for tumor initiation but is essential for tumor growth and maintenance by enhancing angiogenesis and metabolic addiction. The PKM2-STAT3-HIF1α/VEGF signaling axis may play a critical role in bladder cancer and may serve as an actionable therapeutic target.

SIGNIFICANCE

Genetic manipulation and pharmacologic inhibition of PKM2 in mouse urothelial lesions highlight its essential role in promoting angiogenesis and metabolic addiction, events indispensable for tumor growth and maintenance.

A responsive fluorescent probe for detecting and imaging pyruvate kinase M2 in live cells

In this study, we designed and testified a fluorescent probe zy-2 for specific and responsive imaging of pyruvate kinase M2 (PKM2), which can be excited by 419 nm light. A...

ASO-based PKM splice-switching therapy inhibits hepatocellular carcinoma growth

The M2 pyruvate kinase (PKM2) isoform is upregulated in most cancers and plays a crucial role in regulation of the Warburg effect, which is characterized by the preference for aerobic glycolysis over oxidative phosphorylation for energy metabolism. PKM2 is an alternative-splice isoform of the PKM gene and is a potential therapeutic target. Antisense oligonucleotides (ASO) that switch PKM splicing from the cancer-associated PKM2 to the PKM1 isoform have been shown to induce apoptosis in cultured glioblastoma cells when delivered by lipofection. Here, we explore the potential of ASO-based PKM splice switching as a targeted therapy for liver cancer. A more potent lead cEt/DNA ASO induced PKM splice-switching and inhibited the growth of cultured hepatocellular carcinoma (HCC) cells. This PKM isoform switch increased pyruvate-kinase activity and altered glucose metabolism. In an orthotopic HCC xenograft mouse model, the lead ASO and a second ASO targeting a non-overlapping site inhibited tumor growth. Finally, in a genetic HCC mouse model, a surrogate mouse-specific ASO induced Pkm splice switching and inhibited tumorigenesis, without observable toxicity. These results lay the groundwork for a potential ASO-based splicing therapy for HCC.

Silencing of Pyruvate Kinase M2 via a Metal-Organic Framework Based Theranostic Gene Nanomedicine for Triple-Negative Breast Cancer Therapy

Triple-negative breast cancer (TNBC) is typically associated with poor prognosis due to its only partial response to chemotherapy and lack of clinically established targeted therapies coupled with an aggressive disease course. Aerobic glycolysis is a hallmark of reprogrammed metabolic activity in cancer cells, which can be repressed by small-interfering RNA (siRNA). However, the lack of effective carriers to deliver vulnerable siRNA restricts the clinical potentials of glycolysis-based gene therapy for TNBC. Herein, we develop a tumor-targeted, biomimetic manganese dioxide (MnO₂)-shrouded metal-organic framework (MOF) based nanomedicine to deliver siRNA against pyruvate kinase muscle isozyme M2 (siPKM2), wherein PKM2 is a rate-limiting enzyme in glycolysis, to inhibit the reprogrammed glycolysis of TNBC. This MOF-based genetic nanomedicine shows excellent monodispersity and stability and protects siPKM2 against degradation by nucleases. The nanomedicine not only substantially blocks the glycolytic pathway but also improves intracellular hypoxia in TNBC cells, with a resultant O₂-enhanced anticancer effect. In the mice orthotopic TNBC model, the nanomedicine shows a remarkable therapeutic effect. Meanwhile, the Mn²⁺ ions released from acid microenvironment-responsive MnO₂ enable in vivo monitoring of the therapeutic process with magnetic resonance imaging (MRI). Our study shows great promise with this MRI-visible MOF-based nanomedicine for treating TNBC by inhibition of glycolysis via the RNA interference.

Photodynamic therapy induces human esophageal carcinoma cell pyroptosis by targeting the PKM2/caspase-8/caspase-3/GSDME axis

Photodynamic therapy (PDT) uses a photosensitizer (PS) and visible light to induce cancer cell death. Pyroptosis is a new type of programmed cell death that is associated with the gasdermin protein family. However, the precise mechanism of pyroptosis in PDT-induced suppression of esophageal cancer remains unknown. We demonstrate that PDT can induce gasdermin E (GSDME)-mediated pyroptosis, which is characterized by the formation of pyroptotic blebs in esophageal squamous cell carcinoma (ESCC), which burst and release intracellular contents and pro-inflammatory mediators. Mechanistically, PDT may inhibit pyruvate kinase M2 (PKM2) and consequently, activate caspase-8 and caspase-3, which ultimately releases N-GSDME and triggers pyroptosis in ESCC. Moreover, PDT decreased the efficiency of pyroptosis in the presence of a glycolytic inhibitor. Overall, our results show that PDT induces pyroptosis in ESCC by targeting the PKM2/caspase-8/caspase-3/GSDME axis. This is the first in-depth study of the specific mechanism underlying PKM2-mediated pyroptosis under PDT in ESCC, and potentially has great implications for the clinical application of PDT in ESCC.

TEPP-46-Based AIE Fluorescent Probe for Detection and Bioimaging of PKM2 in Living Cells

Pyruvate kinase (PK) M2 (PKM2), a glycolytic enzyme, is a hallmark of different types of tumors and plays a significant role in the Warburg effect. However, there is no fluorescent probe for PKM2 that has been reported yet. In this study, TEPC466, a novel TEPP-46-based aggregation-induced emission (AIE) probe for the detection of PKM2, was designed, synthesized, and fully characterized by ¹H NMR, ¹³C NMR, and high-resolution mass spectrometry. When the fluorescent agent, coumarine, was conjugated to TEPP-46, the bioprobe TEPC466 showed a high degree of selectivity and sensitivity for the detection of PKM2 protein via the AIE effect. TEPC466 was then successfully applied in imaging the PKM2 protein in colorectal cancer cells with low toxicity. Moreover, structure-based modeling and the PK activity assay confirmed that TEPC466 has a better binding with PKM2 than TEPP-46, which suggests that TEPC466 could also be a good agonist of PKM2. Taken together, the bioprobe shows potential in selective detection of PKM2 and provides a useful tool for cancer diagnosis and therapy.

The Mechanism of Warburg Effect-Induced Chemoresistance in Cancer

Although chemotherapy can improve the overall survival and prognosis of cancer patients, chemoresistance remains an obstacle due to the diversity, heterogeneity, and adaptability to environmental alters in clinic. To determine more possibilities for cancer therapy, recent studies have begun to explore changes in the metabolism, especially glycolysis. The Warburg effect is a hallmark of cancer that refers to the preference of cancer cells to metabolize glucose anaerobically rather than aerobically, even under normoxia, which contributes to chemoresistance. However, the association between glycolysis and chemoresistance and molecular mechanisms of glycolysis-induced chemoresistance remains unclear. This review describes the mechanism of glycolysis-induced chemoresistance from the aspects of glycolysis process, signaling pathways, tumor microenvironment, and their interactions. The understanding of how glycolysis induces chemoresistance may provide new molecular targets and concepts for cancer therapy.

LncRNA MALAT1 promotes breast cancer progression by sponging miR101-3p to mediate mTOR/PKM2 signal transmission

Breast cancer (BC) is a common malignant tumor in women and exhibits a poor prognosis. This study examined the role and underlying mechanisms of long non-coding RNA (lncRNA), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in BC pathogenesis. The MALAT1 expression levels in BC cells and tissues were measured using quantitative reverse transcription-polymerase chain reactions. CCK-8 kits and wound healing and transwell assays were used to evaluate the cell growth, invasion, and migration of BC. Bioinformatics and dual-luciferase reporter analyses were conducted to identify MALAT1's potential targets. The protein levels in the mTOR/PKM2 pathway were assessed using Western blot analyses. The MALAT1 overexpressions in the BC tissues and cells were considered to be a predictor of poor prognosis. Therefore, MALAT1 downregulation significantly inhibited BC progression, including cell growth, invasion, and migration. MALAT1 was anticipated to be an miR-101-3p target according to the dual-luciferase reporter gene assay results. The miR-101-3p levels were indirectly proportional to the MALAT1 expressions and the suppressed BC cells. Additionally, the mTOR/PKM2 pathway was directly targeted by miR-101-3p. MALAT1 overexpression significantly decreased the miR-101-3p gene levels and increased the mTOR/PKM2 pathway protein expressions. This miR-101-3p inhibition blocked MALAT1. These findings suggest that lncRNA MALAT1 is related to BC pathogenesis using the miR101-3p/mTOR/PKM2 pathway and is a potential therapeutic target.

PKM1 Exerts Critical Roles in Cardiac Remodeling Under Pressure Overload in the Heart

BACKGROUND

Metabolic remodeling precedes most alterations during cardiac hypertrophic growth under hemodynamic stress. The elevation of glucose utilization has been recognized as a hallmark of metabolic remodeling. However, its role in cardiac hypertrophic growth and heart failure in response to pressure overload remains to be fully illustrated. Here, we aimed to dissect the role of cardiac PKM1 (pyruvate kinase muscle isozyme 1) in glucose metabolic regulation and cardiac response under pressure overload.

METHODS

Cardiac-specific deletion of PKM1 was achieved by crossing the floxed PKM1 mouse model with the cardiomyocyte-specific Cre transgenic mouse. PKM1 transgenic mice were generated under the control of tetracycline response elements, and cardiac-specific overexpression of PKM1 was induced by doxycycline administration in adult mice. Pressure overload was triggered by transverse aortic constriction. Primary neonatal rat ventricular myocytes were used to dissect molecular mechanisms. Moreover, metabolomics and nuclear magnetic resonance spectroscopy analyses were conducted to determine cardiac metabolic flux in response to pressure overload.

RESULTS

We found that PKM1 expression is reduced in failing human and mouse hearts. It is important to note that cardiomyocyte-specific deletion of PKM1 exacerbates cardiac dysfunction and fibrosis in response to pressure overload. Inducible overexpression of PKM1 in cardiomyocytes protects the heart against transverse aortic constriction-induced cardiomyopathy and heart failure. At the mechanistic level, PKM1 is required for the augmentation of glycolytic flux, mitochondrial respiration, and ATP production under pressure overload. Furthermore, deficiency of PKM1 causes a defect in cardiomyocyte growth and a decrease in pyruvate dehydrogenase complex activity at both in vitro and in vivo levels.

CONCLUSIONS

These findings suggest that PKM1 plays an essential role in maintaining a homeostatic response in the heart under hemodynamic stress.

Dual Covalent Inhibition of PKM and IMPDH Targets Metabolism in Cutaneous Metastatic Melanoma

Overcoming acquired drug resistance is a primary challenge in cancer treatment. Notably, more than 50% of patients with BRAFV600E cutaneous metastatic melanoma (CMM) eventually develop resistance to BRAF inhibitors. Resistant cells undergo metabolic reprogramming that profoundly influences therapeutic response and promotes tumor progression. Uncovering metabolic vulnerabilities could help suppress CMM tumor growth and overcome drug resistance. Here we identified a drug, HA344, that concomitantly targets two distinct metabolic hubs in cancer cells. HA344 inhibited the final and rate-limiting step of glycolysis through its covalent binding to the pyruvate kinase M2 (PKM2) enzyme, and it concurrently blocked the activity of inosine monophosphate dehydrogenase, the rate-limiting enzyme of de novo guanylate synthesis. As a consequence, HA344 efficiently targeted vemurafenib-sensitive and vemurafenib-resistant CMM cells and impaired CMM xenograft tumor growth in mice. In addition, HA344 acted synergistically with BRAF inhibitors on CMM cell lines in vitro. Thus, the mechanism of action of HA344 provides potential therapeutic avenues for patients with CMM and a broad range of different cancers. SIGNIFICANCE: Glycolytic and purine synthesis pathways are often deregulated in therapy-resistant tumors and can be targeted by the covalent inhibitor described in this study, suggesting its broad application for overcoming resistance in cancer.

A short review on cross-link between pyruvate kinase (PKM2) and Glioblastoma Multiforme

Pyruvate kinase (PK) catalyzes the last irreversible reaction of glycolysis pathway, generating pyruvate and ATP, from Phosphoenol Pyruvate (PEP) and ADP precursors. In mammals, four different tissue-specific isoforms (M1, M2, L and R) of PK exist, which are translated from two genes (PKL and PKR). PKM2 is the highly expressed isoform of PK in cancers, which regulates the aerobic glycolysis via reprogramming cancer cell's metabolic pathways to provide an anabolic advantage to the tumor cells. In addition to the established role of PKM2 in aerobic glycolysis of multiple cancer types, various recent findings have highlighted the non-metabolic functions of PKM2 in brain tumor development. Nuclear PKM2 acts as a co-activator and directly regulates gene transcription. PKM2 dependent transactivation of various oncogenic genes is instrumental in the progression and aggressiveness of Glioblastoma Multiforme (GBM). Also, PKM2 acts as a protein kinase in histone modification which regulates gene expression and tumorigenesis. Ongoing research has explored novel regulatory mechanisms of PKM2 and its association in GBM progression. This review enlists and summarizes the metabolic and non-metabolic roles of PKM2 at the cellular level, and its regulatory function highlights the importance of the nuclear functions of PKM2 in GBM progression, and an emerging role of PKM2 as novel cancer therapeutics.

Activator-Mediated Pyruvate Kinase M2 Activation Contributes to Endotoxin Tolerance by Promoting Mitochondrial Biogenesis

Pyruvate kinase M2 (PKM2) is a key glycolysis enzyme, and its effect on macrophages has not been entirely elucidated. Here, we identified that the PKM2 small-molecule agonist TEPP-46 mediated PKM2 activation by inducing the formation of PKM2 tetramer and promoted macrophage endotoxin tolerance. Lipopolysaccharide (LPS)-tolerant mice had higher expression of the PKM2 tetramer, which was associated with a reduced in vivo immune response to LPS. Pretreatment of macrophages with TEPP-46 resulted in tolerance to LPS stimulation, as demonstrated by a significant reduction in the production of TNF-α and IL-6. We found that TEPP-46 induced mitochondrial biogenesis in macrophages. Inhibition of mitochondrial biogenesis by mtTFA knockdown effectively inhibited TEPP-46-mediated macrophage tolerance to endotoxins. We discovered that TEPP-46 promoted the expression of PGC-1α and that PGC-1α was the key regulator of mitochondrial biogenesis in macrophages induced by TEPP-46. PGC-1α was negatively regulated by the PI3K/Akt signaling pathway. Knockdown of PKM2 or PGC-1α uniformly inhibited TEPP-46-mediated endotoxin tolerance by inhibiting mitochondrial biogenesis. In addition, TEPP-46 protected mice from lethal endotoxemia and sepsis. Collectively, these findings reveal novel mechanisms for the metabolic control of inflammation and for the induction of endotoxin tolerance by promoting mitochondrial biogenesis. Targeting PKM2 appears to be a new therapeutic option for the treatment of sepsis and other inflammatory diseases.

Metabolic Reprogramming of Fibroblasts as Therapeutic Target in Rheumatoid Arthritis and Cancer: Deciphering Key Mechanisms Using Computational Systems Biology Approaches

Fibroblasts, the most abundant cells in the connective tissue, are key modulators of the extracellular matrix (ECM) composition. These spindle-shaped cells are capable of synthesizing various extracellular matrix proteins and collagen. They also provide the structural framework (stroma) for tissues and play a pivotal role in the wound healing process. While they are maintainers of the ECM turnover and regulate several physiological processes, they can also undergo transformations responding to certain stimuli and display aggressive phenotypes that contribute to disease pathophysiology. In this review, we focus on the metabolic pathways of glucose and highlight metabolic reprogramming as a critical event that contributes to the transition of fibroblasts from quiescent to activated and aggressive cells. We also cover the emerging evidence that allows us to draw parallels between fibroblasts in autoimmune disorders and more specifically in rheumatoid arthritis and cancer. We link the metabolic changes of fibroblasts to the toxic environment created by the disease condition and discuss how targeting of metabolic reprogramming could be employed in the treatment of such diseases. Lastly, we discuss Systems Biology approaches, and more specifically, computational modeling, as a means to elucidate pathogenetic mechanisms and accelerate the identification of novel therapeutic targets.

Animal Models: A Useful Tool to Unveil Metabolic Changes in Hepatocellular Carcinoma

Simple Summary

Hepatocellular carcinoma (HCC) represents an important health problem. At the moment, systemic therapies offered only modest clinical benefits. Thus, HCC represents a cancer extremely difficult to treat, and therapeutic breakthroughs are urgently needed. Metabolic reprogramming of neoplastic cells has been recognized as one of the core hallmarks of cancer. Experimental animal models represent an important tool that allows to investigate metabolic changes underlying HCC development and progression. In the present review, we characterize available rodent models of hepatocarcinogenesis. Moreover, we discuss the possibility that pharmacological targeting of Warburg metabolism may represent an additional tool to improve already available therapeutic approaches for HCC.

Abstract

Hepatocellular carcinoma (HCC) is one the most frequent and lethal human cancers. At present, no effective treatment for advanced HCC exist; therefore, the overall prognosis for HCC patients remains dismal. In recent years, a better knowledge of the signaling pathways involved in the regulation of HCC development and progression, has led to the identification of novel potential targets for therapeutic strategies. However, the obtained benefits from current therapeutic options are disappointing. Altered cancer metabolism has become a topic of renewed interest in the last decades, and it has been included among the core hallmarks of cancer. In the light of growing evidence for metabolic reprogramming in cancer, a wide number of experimental animal models have been exploited to study metabolic changes characterizing HCC development and progression and to further expand our knowledge of this tumor. In the present review, we discuss several rodent models of hepatocarcinogenesis, that contributed to elucidate the metabolic profile of HCC and the implications of these changes in modulating the aggressiveness of neoplastic cells. We also highlight the apparently contrasting results stemming from different animal models. Finally, we analyze whether these observations could be exploited to improve current therapeutic strategies for HCC.

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.

Efficacy and mechanism of combination of oxaliplatin with PKM2 knockdown in colorectal cancer

M2 isomer of pyruvate kinase (PKM2), a key enzyme in aerobic glycolysis, is closely related to cancer development and progression. Suppression of PKM2 exhibits synergistic effects with docetaxel in lung cancer, but the therapeutic potential in colorectal cancer (CRC) is unclear. The aim of the present study was to explore the synergic effects and mechanism of knocking down PKM2 combined with oxaliplatin (a chemosensitizer) treatment in two CRC cell lines (HCT116 and DLD1). The PKM2 gene was initially knocked down using small interfering (si)RNAs (si155 and si156). Subsequently, the effects of PKM2-siRNAs and oxaliplatin, on CRC cells were determined using MTS, cell cycle analysis and apoptosis assays. The mechanism of targeting PKM2 was explored by detecting glucose uptake, lactate secretion fluxes, and the levels of glucose-6-phosphate dehydrogenase (G6PD) mRNA, glutathione (GSH) and reactive oxygen species (ROS). Cell viability in the experimental groups (PKM2-siRNAs, oxaliplatin, PKM2-siRNAs + oxaliplatin) was significantly reduced compared with the control group, and combination treatments (PKM2-siRNAs + oxaliplatin) were more effective than single treatments (PKM2-siRNAs and oxaliplatin only groups). Similar results were observed with the apoptosis assay. The combination groups showed synergistic effects compared with both single treatment groups. Furthermore, glucose uptake and lactate secretion and mRNA levels of G6PD and PKM2 were decreased after PKM2 knockdown in the PKM2-siRNAs and PKM2-siRNAs + oxaliplatin groups. The GSH levels in the PKM2-siRNAs group was significantly lower compared with the negative control group. The ROS levels in the PKM2-siRNAs groups were also significantly increased. The combination of PKM2-siRNAs and oxaliplatin had synergistic effects on CRC cells (HCT116 and DLD1). PKM2 silencing may alter energy metabolism in cancer cells and initiate ROS-induced apoptosis after downregulation of the pentose phosphate pathway by PKM2-siRNAs.

Oxymatrine Inhibits Colorectal Cancer Metastasis via Attenuating PKM2-Mediated Aerobic Glycolysis

Background

Colorectal cancer (CRC), a type of highly occurred intestinal cancer at present, is prone to metastasis at the later stage of chemotherapy. Looking for the anti-metastatic agents from natural compounds attracted much concern. Here, it aims to demonstrate whether oxymatrine, an anti-cancer natural compound, has anti-metastatic activity and its potential significance in clinic.

Materials and Methods

Wound healing assay and transwell assay were for evaluating the effect of oxymatrine on cell migration and invasion in vitro. Anti-metastatic action in vivo was determined by hepatic metastasis of colorectal cancer cells in mice.

Results

Oxymatrine can significantly inhibit cancer cell migration and invasion in vitro. The production of ATP, pyruvate, and lactate was suppressed in CRC cells under the treatment of oxymatrine, as well as the glucose consumption. Meantime, extracellular acidification rates (ECR) were evidently attenuated although the oxygen consumption rates (OCR) were not affected. Both clued that oxymatrine inhibition of metastasis is possibly related to blocking aerobic glycolysis. Subsequent results indicated that pyruvate kinase M2 (PKM2) not hexokinase (HK) and phosphofructokinase (PFK) were involved in oxymatrine blocking glycolysis as the PKM2 kinase activity and expression were inhibited by oxymatrine and the PKM2 activator, TEPP-46, can reverse in part the effect of oxymatrine induced in CRC cells. Furthermore, this process was also mediated by inhibition of glucose transporter 1 (GLUT1). Finally, the in vivo metastatic model in mice showed both 20 mg/kg and 40 mg/kg oxymatrine significantly inhibit liver metastasis of CRC cells in mice, and PKM2 and GLUT1 expression in liver of the oxymatrine-treated group is declined.

Conclusion

Oxymatrine exerted anti-metastatic activity dependent on inhibition of PKM2-mediated aerobic glycolysis. It is not only an anti-cancer agent but also a potential anti-metastatic compound with clinical application significance.

[Gefitinib inhibits glycolysis and induces programmed cell death in non-small cell lung cancer cells]

OBJECTIVE

To observe the cell death pattern induced by gefitinib in non-small cell lung cancer A549 and H1975 cells and explore the possible mechanism in light of glycolysis.

METHODS

The inhibitory effects of gefitinib at 20, 30, or 40 μmol/L in A549 cells and at 20, 40, or 80 μmol/L in H1975 cells were examined using MTT assay. The changes of lactic acid level in the cells were determined with a lactic acid kit, and the expression levels of glycolysis-related proteins (PKM2 and HK2) and the proteins in PI3K-Akt-mTOR signaling pathway were detected using Western blotting. 2-NBDG was used for detecting glucose uptake capacity of the cells, and ATP kit was used to detect the intracellular ATP level. The mitochondrial membrane potential of the cells was examined with the JC-1 kit, and cell apoptosis was analyzed with Annexin V-FITC/PI double staining. The relative expression levels of the apoptotic proteins Bax and Bcl-2 and the autophagy marker protein LC3B were detected with Western blotting.

RESULTS

MTT assay showed that gefitinib inhibited the proliferation of A549 and H1975 cells in a time- and dose-dependent manner (P &lt; 0.05). The IC₅₀ of gefitinib at 24, 48 and 72 h was 48.6, 28.6 and 19.7 μmol/L in A549 cells and was 321.6, 49.1 and 14.6 μmol/L in H1975 cells, respectively. Gefitinib significantly lowered intracellular lactic acid level of the cells (P &lt; 0.05) and down-regulated the expressions of PKM2 and HK2 proteins (P &lt; 0.05) and PI3K-Akt-mTOR signaling pathway-associated proteins (P &lt; 0.05). Gefitinib obviously inhibited glucose uptake and ATP levels in both A549 and H1975 cells (P &lt; 0.05). Treatment with gefitinib induced obviously enhanced apoptosis in the cells, resulting in apoptosis rates of (10.77± 1.0)%, (14.5±0.4)%, (17.4±0.2)% and (32.1±0.6)% at 0, 20, 30 and 40 μmol/L in A549 cells (P &lt; 0.05) and of (10.5±0.6)%, (13.2± 0.92)%, (18.9±0.98)% and (35.1±1.4)% at 0, 20, 40 and 80 μmol/L in H1975 cells, respectively (P &lt; 0.05). The protein expression of Bax increased and that of Bcl-2 decreased following gefitinib treatment in the cells (P &lt; 0.05). Gefitinib significantly increased autophagy in A549 and H1975 cells as shown by increased LC3B expressions following the treatment (P &lt; 0.05).

CONCLUSIONS

Gefitinib can inhibit the proliferation, induce apoptosis and increase autophagy in A549 and H1975 cells. Gefitinib induces apoptosis of the cells possibly by affecting glycolysis and PI3K-Akt-mTOR signaling pathway.

Identification of Gliotoxin isolated from marine fungus as a new pyruvate kinase M2 inhibitor

Pyruvate kinase M2 (PKM2) functions as an important rate-limiting enzyme of aerobic glycolysis that is involved in tumor initiation and progression. However, there are few studies on effective PKM2 inhibitors. Gliotoxin is a marine-derived fungal secondary metabolite with multiple biological activities, including immunosuppression, cytotoxicity, and et al. In this study, we found that Gliotoxin directly bound to PKM2 and inhibited its glycolytic activity in a dose-dependent manner accompanied by the decreases in glucose consumption and lactate production in the human glioma cell line U87. Moreover, Gliotoxin suppressed tyrosine kinase activity of PKM2, leading to a dramatic reduction in Stat3 phosphorylation in U87 cells. Furthermore, Gliotoxin suppressed cell viability in U87 cells, and cytotoxicity of Gliotoxin on U87 cells was obviously augmented under hypoxia condition compared to normal condition. Finally, Gliotoxin was demonstrated to induce cell apoptosis of U87 cells and synergize with temozolomide. Our findings identify Gliotoxin as a new PKM2 inhibitor with anti-tumor activity, which lays the foundation for the development of Gliotoxin as a promising anti-tumor drug in the future.

FA-SAT ncRNA interacts with PKM2 protein: depletion of this complex induces a switch from cell proliferation to apoptosis

FA-SAT is a highly conserved satellite DNA sequence transcribed in many Bilateria species. To disclose the cellular and functional profile of FA-SAT non-coding RNAs, a comprehensive experimental approach, including the transcripts location in the cell and in the cell cycle, the identification of its putative protein interactors, and silencing/ectopic expression phenotype analysis, was performed. FA-SAT non-coding RNAs play a nuclear function at the G1 phase of the cell cycle and the interactomic assay showed that the PKM2 protein is the main interactor. The disruption of the FA-SAT non-coding RNA/PKM2 protein complex, by the depletion of either FA-SAT or PKM2, results in the same phenotype-apoptosis, and the ectopic overexpression of FA-SAT did not affect the cell-cycle progression, but promotes the PKM2 nuclear accumulation. Overall, our data first describe the importance of this ribonucleoprotein complex in apoptosis and cell-cycle progression, what foresees a promising novel candidate molecular target for cancer therapy and diagnosis.