Citrate-Induced p85α⁻PTEN Complex Formation Causes G2/M Phase Arrest in Human Pharyngeal Squamous Carcinoma Cell Lines

Citrate oscillations during cell cycle are a targetable vulnerability in cancer cells

Cell cycle progression is timely interconnected with oscillations in cellular metabolism. Here, we first describe how these metabolic oscillations allow cycling cells to meet the bioenergetic needs specifically for each phase of the cell cycle. In parallel, we highlight how the cytosolic level of citrate is dynamically regulated during these different phases, being low in G1 phase, increasing in S phase, peaking in G2/M, and decreasing in mitosis. Of note, in cancer cells, a dysregulation of such citrate oscillation can support cell cycle progression by promoting a deregulated Warburg effect (aerobic glycolysis), activating oncogenic signaling pathways (such as PI3K/AKT), and promoting acetyl-CoA production via alternative routes, such as overconsumption of acetate. Then, we review how administration of sodium citrate (at high doses) arrests the cell cycle in G0/G1 or G2/M, inhibits glycolysis and PI3K/AKT, induces apoptosis, and significantly reduces tumor growth in various in vivo models. Last, we reason on the possibility to implement citrate administration to reinforce the effectiveness of cell cycle inhibitors to better cure cancer.

Why and how citrate may sensitize malignant tumors to immunotherapy

Immunotherapy, either alone or in combination with chemotherapy, has demonstrated limited efficacy in a variety of solid cancers. Several factors contribute to explaining primary or secondary resistance. Among them, cancer cells, whose metabolism frequently relies on aerobic glycolysis, promote exhaustion of cytotoxic immune cells by diverting the glucose in the tumor microenvironment (TME) to their own profit, while secreting lactic acid that sustains the oxidative metabolism of immunosuppressive cells. Here, we propose to combine current treatment based on the use of immune checkpoint inhibitors (ICIs) with high doses of sodium citrate (SCT) because citrate inhibits cancer cell metabolism (by targeting both glycolysis and oxidative metabolism) and may active anti-tumor immune response. Indeed, as showed in preclinical studies, SCT reduces cancer cell growth, promoting cell death and chemotherapy effectiveness. Furthermore, since the plasma membrane citrate carrier pmCIC is mainly expressed in cancer cells and low or not expressed in immune and non-transformed cells, we argue that the inhibition of cancer cell metabolism by SCT may increase glucose availability in the TME, thus promoting functionality of anti-tumor immune cells. Concomitantly, the decrease in the amount of lactic acid in the TME may reduce the functionality of immunosuppressive cells. Preclinical studies have shown that SCT can enhance the anti-tumor immune response through an enhancement of T cell infiltration and activation, and a repolarization of macrophages towards a TAM1-like phenotype. Therefore, this simple and cheap strategy may have a major impact to increase the efficacy of current immunotherapies in human solid tumors and we encourage testing it in clinical trials.

The dual role of citrate in cancer

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

How Phosphofructokinase-1 Promotes PI3K and YAP/TAZ in Cancer: Therapeutic Perspectives

Simple Summary

We propose that PFK1 promotes a positive feedback loop with PI3K/AKT and YAP/TAZ signaling pathways in cancer cells. Therefore, targeting PFK1 (or its product F-1,6-BP) could improve the efficacy of PI3K and YAP/TAZ inhibitors currently tested in clinical trials. To this aim, we suggest the use of citrate, which is a physiologic and potent inhibitor of PFK1.

Abstract

PI3K/AKT is one of the most frequently altered signaling pathways in human cancers, supporting the activation of many proteins sustaining cell metabolism, proliferation, and aggressiveness. Another important pathway frequently altered in cancer cells is the one regulating the YAP/TAZ transcriptional coactivators, which promote the expression of genes sustaining aerobic glycolysis (such as WNT, MYC, HIF-1), EMT, and drug resistance. Of note, the PI3K/AKT pathway can also regulate the YAP/TAZ one. Unfortunately, although PI3K and YAP inhibitors are currently tested in highly resistant cancers (both solid and hematologic ones), several resistance mechanisms may arise. Resistance mechanisms to PI3K inhibitors may involve the stimulation of alternative pathways (such as RAS, HER, IGFR/AKT), the inactivation of PTEN (the physiologic inhibitor of PI3K), and the expression of anti-apoptotic Bcl-xL and MCL1 proteins. Therefore, it is important to improve current therapeutic strategies to overcome these limitations. Here, we want to highlight how the glycolytic enzyme PFK1 (and its product F-1,6-BP) promotes the activation of both PI3K/AKT and YAP/TAZ pathways by several direct and indirect mechanisms. In turn, PI3K/AKT and YAP/TAZ can promote PFK1 activity and F-1,6-BP production in a positive feedback loop, thus sustaining the Warburg effect and drug resistance. Thus, we propose that the inhibition of PFK1 (and of its key activator PFK2/PFKFB3) could potentiate the sensitivity to PI3K and YAP inhibitors currently tested. Awaiting the development of non-toxic inhibitors of these enzymes, we propose to test the administration of citrate at a high dosage, because citrate is a physiologic inhibitor of both PFK1 and PFK2/PFKFB3. Consistently, in various cultured cancer cells (including melanoma, sarcoma, hematologic, and epithelial cancer cells), this “citrate strategy” efficiently inhibits the IGFR1/AKT pathway, promotes PTEN activity, reduces Bcl-xL and MCL1 expression, and increases sensitivity to standard chemotherapy. It also inhibits the development of sarcoma, pancreatic, mammary HER⁺ and lung RAS-driven tumors in mice without apparent toxicities.

Why may citrate sodium significantly increase the effectiveness of transarterial chemoembolization in hepatocellular carcinoma?

Hepatocellular carcinoma (HCC) represents the third cause of cancer death in men worldwide, and its increasing incidence can be explained by the increasing occurrence of non-alcoholic steatohepatitis (NASH). HCC prognosis is poor, as its 5-year overall survival is approximately 18 % and most cases are diagnosed at an inoperable advanced stage. Moreover, tumor sensitivity to conventional chemotherapeutics (particularly to cisplatin-based regimen), trans-arterial chemoembolization (cTACE), tyrosine kinase inhibitors, anti-angiogenic molecules and immune checkpoint inhibitors is limited. Oncogenic signaling pathways, such as HIF-1α and RAS/PI3K/AKT, may provoke drug resistance by enhancing the aerobic glycolysis ("Warburg effect") in cancer cells. Indeed, this metabolism, which promotes cancer cell development and aggressiveness, also induces extracellular acidity. In turn, this acidity promotes the protonation of drugs, hence abrogating their internalization, since they are most often weakly basic molecules. Consequently, targeting the Warburg effect in these cancer cells (which in turn would reduce the extracellular acidification) could be an effective strategy to increase the delivery of drugs into the tumor. Phosphofructokinase-1 (PFK1) and its activator PFK2 are the main regulators of glycolysis, and they also couple the enhancement of glycolysis to the activation of key signaling cascades and cell cycle progression. Therefore, targeting this "Gordian Knot" in HCC cells would be of crucial importance. Here, we suggest that this could be achieved by citrate administration at high concentration, because citrate is a physiologic inhibitor of PFK1 and PFK2. As shown in various in vitro studies, including HCC cell lines, administration of high concentrations of citrate inhibits PFK1 and PFK2 (and consequently glycolysis), decreases ATP production, counteracts HIF-1α and PI3K/AKT signaling, induces apoptosis, and sensitizes cells to cisplatin treatment. Administration of high concentrations of citrate in animal models (including Ras-driven tumours) has been shown to effectively inhibit cancer growth, reverse cell dedifferentiation, and neutralize intratumor acidity, without apparent toxicity in animal studies. Citrate may also induce a rapid secretion of pro-inflammatory cytokines by macrophages, and it could favour the destruction of cancer stem cells (CSCs) sustaining tumor recurrence. Consequently, this "citrate strategy" could improve the tumor sensitivity to current treatments of HCC by reducing the extracellular acidity, thus enhancing the delivery of chemotherapeutic drugs into the tumor. Therefore, we propose that this strategy should be explored in clinical trials, in particular to enhance cTACE effectiveness.

Understanding the Central Role of Citrate in the Metabolism of Cancer Cells and Tumors: An Update

Citrate plays a central role in cancer cells’ metabolism and regulation. Derived from mitochondrial synthesis and/or carboxylation of α-ketoglutarate, it is cleaved by ATP-citrate lyase into acetyl-CoA and oxaloacetate. The rapid turnover of these molecules in proliferative cancer cells maintains a low-level of citrate, precluding its retro-inhibition on glycolytic enzymes. In cancer cells relying on glycolysis, this regulation helps sustain the Warburg effect. In those relying on an oxidative metabolism, fatty acid β-oxidation sustains a high production of citrate, which is still rapidly converted into acetyl-CoA and oxaloacetate, this latter molecule sustaining nucleotide synthesis and gluconeogenesis. Therefore, citrate levels are rarely high in cancer cells. Resistance of cancer cells to targeted therapies, such as tyrosine kinase inhibitors (TKIs), is frequently sustained by aerobic glycolysis and its key oncogenic drivers, such as Ras and its downstream effectors MAPK/ERK and PI3K/Akt. Remarkably, in preclinical cancer models, the administration of high doses of citrate showed various anti-cancer effects, such as the inhibition of glycolysis, the promotion of cytotoxic drugs sensibility and apoptosis, the neutralization of extracellular acidity, and the inhibition of tumors growth and of key signalling pathways (in particular, the IGF-1R/AKT pathway). Therefore, these preclinical results support the testing of the citrate strategy in clinical trials to counteract key oncogenic drivers sustaining cancer development and resistance to anti-cancer therapies.

Oxidative Stress-Induced Unscheduled CDK1-Cyclin B1 Activity Impairs ER-Mitochondria-Mediated Bioenergetic Metabolism

Targeting the activities of endoplasmic reticulum (ER)-mitochondrial-dependent metabolic reprogramming is considered one of the most promising strategies for cancer treatment. Here, we present biochemical subcellular fractionation, coimmunoprecipitation, gene manipulation, and pharmacologic evidence that induction of mitochondria-localized phospho (p)-cyclin dependent kinase 1 (CDK1) (Thr 161)-cyclin B1 complexes by apigenin in nasopharyngeal carcinoma (NPC) cells impairs the ER-mitochondrial bioenergetics and redox regulation of calcium (Ca⁺⁺) homeostasis through suppressing the B cell lymphoma 2 (BCL-2)/BCL-2/B-cell lymphoma-extra large (BCL-x_L)-modulated anti-apoptotic and metabolic functions. Using a specific inducer, inhibitor, or short hairpin RNA for acid sphingomyelinase (ASM) demonstrated that enhanced lipid raft-associated ASM activity confers alteration of the lipid composition of lipid raft membranes, which leads to perturbation of protein trafficking, and induces formation of p110α free p85α-unphosphorylated phosphatase and tensin homolog deleted from chromosome 10 complexes in the lipid raft membranes, causing disruption of phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt)-GTP-ras-related C3 botulinum toxin substrate 1 (Rac1)-mediated signaling, thus triggering the p-CDK1 (Thr 161))-cyclin B1-mediated BCL-2 (Thr 69/Ser 87)/BCL-x_L (Ser 62) phosphorylation and accompanying impairment of ER-mitochondria-regulated bioenergetic, redox, and Ca⁺⁺ homeostasis. Inhibition of apigenin-induced reactive oxygen species (ROS) generation by a ROS scavenger N-acetyl-L-cysteine blocked the lipid raft membrane localization and activation of ASM and formation of ceramide-enriched lipid raft membranes, returned PI3K-Akt-GTP-Rac1-modulated CDK1-cyclin B1 activity, and subsequently restored the BCL-2/BCL-x_L-regulated ER-mitochondrial bioenergetic activity. Thus, this study reveals a novel molecular mechanism of the pro-apoptotic activity of ASM controlled by oxidative stress to modulate the ER-mitochondrial bioenergetic metabolism, as well as suggests the disruption of CDK1-cyclin B1-mediated BCL-2/BCL-x_L oncogenic activity by triggering oxidative stress-ASM-induced PI3K-Akt-GTP-Rac1 inactivation as a therapeutic approach for NPC.

Gallic Acid Induces S and G2 Phase Arrest and Apoptosis in Human Ovarian Cancer Cells In Vitro

Ovarian cancer (OC) is among the top gynecologic cancers in the US with a death tally of 13,940 in the past year alone. Gallic acid (GA) is a natural compound with pharmacological benefits. In this research, the role of GA on cell proliferation, cell apoptosis, cell cycle-related protein expression was explored in OC cell lines OVCAR-3 and A2780/CP70. After 24,48 and 72 h of GA treatment, the IC50 values in OVCAR-3 cells were 22.14 ± 0.45, 20.36 ± 0.18, 15.13 ± 0.53 μM, respectively and in A2780/CP70 cells IC50 values were 33.53 ± 2.64, 27.18 ± 0.22, 22.81 ± 0.56, respectively. Hoechst 33,342 DNA staining and flow cytometry results showed 20 μM GA exposure could significantly accelerate apoptosis in both OC cell lines and the total apoptotic rate increased from 5.34%(control) to 21.42% in OVCAR-3 cells and from 8.01%(control) to 17.69% in A2780/CP70 cells. Western blot analysis revealed that GA stimulated programmed OC cell death via a p53-dependent intrinsic signaling. In addition, GA arrested cell cycle at the S or G2 phase via p53-p21-Cdc2-cyclin B pathway in the same cells. In conclusion, we provide some evidence of the efficacy of GA in ovarian cancer prevention and therapy.

Subunit P60 of phosphatidylinositol 3-kinase promotes cell proliferation or apoptosis depending on its phosphorylation status

The regulatory subunits (P60 in insects, P85 in mammals) determine the activation of the catalytic subunits P110 in phosphatidylinositol 3-kinases (PI3Ks) in the insulin pathway for cell proliferation and body growth. However, the regulatory subunits also promote apoptosis via an unclear regulatory mechanism. Using Helicoverpa armigera, an agricultural pest, we showed that H. armigera P60 (HaP60) was phosphorylated under insulin-like peptides (ILPs) regulation at larval growth stages and played roles in the insulin/ insulin-like growth factor (IGF) signaling (IIS) to determine HaP110 phosphorylation and cell membrane translocation; whereas, HaP60 was dephosphorylated and its expression increased under steroid hormone 20-hydroxyecdysone (20E) regulation during metamorphosis. Protein tyrosine phosphatase non-receptor type 6 (HaPTPN6, also named tyrosine-protein phosphatase corkscrew-like isoform X1 in the genome) was upregulated by 20E to dephosphorylate HaP60 and HaP110. 20E blocked HaP60 and HaP110 translocation to the cell membrane and reduced their interaction. The phosphorylated HaP60 mediated a cascade of protein phosphorylation and forkhead box protein O (HaFOXO) cytosol localization in the IIS to promote cell proliferation. However, 20E, via G protein-coupled-receptor-, ecdysone receptor-, and HaFOXO signaling axis, upregulated HaP60 expression, and the non-phosphorylated HaP60 interacted with phosphatase and tensin homolog (HaPTEN) to induce apoptosis. RNA interference-mediated knockdown of HaP60 and HaP110 in larvae repressed larval growth and apoptosis. Thus, HaP60 plays dual functions to promote cell proliferation and apoptosis by changing its phosphorylation status under ILPs and 20E regulation, respectively.

The regulatory subunits of phosphatidylinositol 3-kinases (PI3Ks) play very important roles in various pathways by promoting cell proliferation or apoptosis. However, the upstream regulatory mechanism of their opposite functions is unclear. Using a seriously agricultural pest Helicoverpa armigera as a model, we show that ILPs induce HaP60 phosphorylation to increase HaP110 phosphorylation and cell membrane location to promote cell proliferation. 20E promotes HaP60 and HaP110 dephosphorylation that resulted in the cytosol localization and inhibition of PI3K activity. Moreover, 20E elevates HaP60 expression to promote apoptosis. Our study revealed that HaP60 plays dual functions to regulate cell proliferation and apoptosis by changing its phosphorylated status.

Identification of the potential novel biomarkers as susceptibility gene for Wilms tumor

Background

Wilms tumor (WT) is the most common malignant renal tumor in children. The aim of this study was to identify potential susceptibility gene of WT for better prognosis.

Methods

Weighted gene coexpression network analysis is used for the detection of clinically important biomarkers associated with WT.

Results

In the study, 59 tissue samples from National Cancer Institute were pretreated for constructing gene co-expression network, while 224 samples also downloaded from National Cancer Institute were used for hub gene validation and module preservation analysis. Three modules were found to be highly correlated with WT, and 44 top hub genes were identified in these key modules eventually. In addition, both the module preservation analysis and gene validation showed ideal results based on other dataset with 224 samples. Meanwhile, Functional enrichment analysis showed that genes in module were enriched to sister chromatid cohesion, cell cycle, oocyte meiosis.

Conclusion

In summary, we established a gene co-expression network to identify 44 hub genes are closely to recurrence and staging of WT, and 6 of these hub genes was closely related to the poor prognosis of patients. Our findings revealed that those hub genes may be used as potential susceptibility gene for clinical diagnosis and prognosis of this tumor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08034-w.

Inhibition of DNA Repair Pathways and Induction of ROS Are Potential Mechanisms of Action of the Small Molecule Inhibitor BOLD-100 in Breast Cancer

BOLD-100, a ruthenium-based complex, sodium trans-[tetrachloridobis (1H-indazole) ruthenate (III)] (also known as IT-139, NKP1339 or KP1339), is a novel small molecule drug that demonstrated a manageable safety profile at the maximum tolerated dose and modest antitumor activity in a phase I clinical trial. BOLD-100 has been reported to inhibit the upregulation of the endoplasmic reticulum stress sensing protein GRP78. However, response to BOLD-100 varies in different cancer models and the precise mechanism of action in high-response versus low-response cancer cells remains unclear. In vitro studies have indicated that BOLD-100 induces cytostatic rather than cytotoxic effects as a monotherapy. To understand BOLD-100-mediated signaling mechanism in breast cancer cells, we used estrogen receptor positive (ER+) MCF7 breast cancer cells to obtain gene-metabolite integrated models. At 100 μM, BOLD-100 significantly reduced cell proliferation and expression of genes involved in the DNA repair pathway. BOLD-100 also induced reactive oxygen species (ROS) and phosphorylation of histone H2AX, gamma-H2AX (Ser139), suggesting disruption of proper DNA surveillance. In estrogen receptor negative (ER-) breast cancer cells, combination of BOLD-100 with a PARP inhibitor, olaparib, induced significant inhibition of cell growth and xenografts and increased gamma-H2AX. Thus, BOLD-100 is a novel DNA repair pathway targeting agent and can be used with other chemotherapies in ER- breast cancer.