PK-M2-mediated metabolic changes in breast cancer cells induced by ionizing radiation

M2 isoform of pyruvate kinase rewires glucose metabolism during radiation therapy to promote an antioxidant response and glioblastoma radioresistance

BACKGROUND

Resistance to existing therapies is a significant challenge in improving outcomes for glioblastoma (GBM) patients. Metabolic plasticity has emerged as an important contributor to therapy resistance, including radiation therapy (RT). Here, we investigated how GBM cells reprogram their glucose metabolism in response to RT to promote radiation resistance.

METHODS

Effects of radiation on glucose metabolism of human GBM specimens were examined in vitro and in vivo with the use of metabolic and enzymatic assays, targeted metabolomics, and FDG-PET. Radiosensitization potential of interfering with M2 isoform of pyruvate kinase (PKM2) activity was tested via gliomasphere formation assays and in vivo human GBM models.

RESULTS

Here, we show that RT induces increased glucose utilization by GBM cells, and this is accompanied with translocation of GLUT3 transporters to the cell membrane. Irradiated GBM cells route glucose carbons through the pentose phosphate pathway (PPP) to harness the antioxidant power of the PPP and support survival after radiation. This response is regulated in part by the PKM2. Activators of PKM2 can antagonize the radiation-induced rewiring of glucose metabolism and radiosensitize GBM cells in vitro and in vivo.

CONCLUSIONS

These findings open the possibility that interventions designed to target cancer-specific regulators of metabolic plasticity, such as PKM2, rather than specific metabolic pathways, have the potential to improve the radiotherapeutic outcomes in GBM patients.

Glioblastomas: Hijacking Metabolism to Build a Flexible Shield for Therapy Resistance

Significance: Glioblastomas (GBMs) are among the most lethal tumors despite the almost exclusive localization to the brain. This is largely due to therapeutic resistance. Radiation and chemotherapy significantly increase the survival for GBM patients, however, GBMs always recur, and the median overall survival is just over a year. Proposed reasons for such intractable resistance to therapy are numerous and include tumor metabolism, in particular, the ability of tumor cells to reconfigure metabolic fluxes on demand (metabolic plasticity). Understanding how the hard-wired, oncogene-driven metabolic tendencies of GBMs intersect with flexible, context-induced metabolic rewiring promises to reveal novel approaches for combating therapy resistance. Recent Advances: Personalized genome-scale metabolic flux models have recently provided evidence that metabolic flexibility promotes radiation resistance in cancer and identified tumor redox metabolism as a major predictor for resistance to radiation therapy (RT). It was demonstrated that radioresistant tumors, including GBM, reroute metabolic fluxes to boost the levels of reducing factors of the cell, thus enhancing clearance of reactive oxygen species that are generated during RT and promoting survival. Critical Issues: The current body of knowledge from published studies strongly supports the notion that robust metabolic plasticity can act as a (flexible) shield against the cytotoxic effects of standard GBM therapies, thus driving therapy resistance. The limited understanding of the critical drivers of such metabolic plasticity hampers the rational design of effective combination therapies. Future Directions: Identifying and targeting regulators of metabolic plasticity, rather than specific metabolic pathways, in combination with standard-of-care treatments have the potential to improve therapeutic outcomes in GBM. Antioxid. Redox Signal. 39, 957-979.

GTP signaling links metabolism, DNA repair, and responses to genotoxic stress

How cell metabolism regulates DNA repair is incompletely understood. Here, we define a GTP-mediated signaling cascade that links metabolism to DNA repair and has significant therapeutic implications. GTP, but not other nucleotides, regulates the activity of Rac1, a G protein, that promotes the dephosphorylation of serine 323 on Abl-interactor 1 (Abi-1) by protein phosphatase 5 (PP5). Dephosphorylated Abi-1, a protein previously not known to activate DNA repair, promotes non-homologous end joining. In patients and mouse models of glioblastoma, Rac1 and dephosphorylated Abi-1 mediate DNA repair and resistance to standard of care genotoxic treatments. The GTP-Rac1-PP5-Abi-1 signaling axis is not limited to brain cancer, as GTP supplementation promotes DNA repair and Abi-1-S323 dephosphorylation in non-malignant cells and protects mouse tissues from genotoxic insult. This unexpected ability of GTP to regulate DNA repair independently of deoxynucleotide pools has important implications for normal physiology and cancer treatment.

Novel insight into metabolic reprogrammming in cancer radioresistance: A promising therapeutic target in radiotherapy

Currently, cancer treatment mainly consists of surgery, radiotherapy, chemotherapy, immunotherapy, and molecular targeted therapy, of which radiotherapy is one of the major pillars. However, the occurrence of radioresistance largely limits its therapeutic effect. Metabolic reprogramming is an important hallmark in cancer progression and treatment resistance. In radiotherapy, DNA breakage is the major mechanism of cell damage, and in turn, cancer cells are prone to increase the metabolic flux of glucose, glutamine, serine, arginine, fatty acids etc., thus providing sufficient substrates and energy for DNA damage repair. Therefore, studying the linkage between metabolic reprogramming and cancer radioresistance may provide new ideas for improving the efficacy of tumor therapy. This review mainly focuses on the role of metabolic alterations, including glucose, amino acid, lipid, nucleotide and other ion metabolism, in radioresistance, and proposes possible therapeutic targets to improve the efficacy of cancer radiotherapy.

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

Radiosensitizing Pancreatic Cancer via Effective Autophagy Inhibition

Despite aggressive treatments, pancreatic ductal adenocarcinoma (PDAC) remains an intractable disease, largely because it is refractory to therapeutic interventions. To overcome its nutrient-poor microenvironment, PDAC heavily relies on autophagy for metabolic needs to promote tumor growth and survival. Here, we explore autophagy inhibition as a method to enhance the effects of radiotherapy on PDAC tumors. Hydroxychloroquine is an autophagy inhibitor at the focus of many PDAC clinical trials, including in combination with radiotherapy. However, its acid-labile properties likely reduce its intratumoral efficacy. Here, we demonstrate that EAD1, a synthesized analogue of HCQ, is a more effective therapeutic for sensitizing PDAC tumors of various KRAS mutations to radiotherapy. Specifically, in vitro models show that EAD1 is an effective inhibitor of autophagic flux in PDAC cells, accompanied by a potent inhibition of proliferation. When combined with radiotherapy, EAD1 is consistently superior to HCQ not only as a single agent, but also in radiosensitizing PDAC cells, and perhaps most importantly, in decreasing the self-renewal capacity of PDAC cancer stem cells (PCSC). The more pronounced sensitizing effects of autophagy inhibitors on pancreatic stem over differentiated cells points to a new understanding that PCSCs may be more dependent on autophagy to counter the effects of radiation toxicity, a potential mechanism explaining the resistance of PCSCs to radiotherapy. Finally, in vivo subcutaneous tumor models demonstrate that combination of radiotherapy and EAD1 is the most successful at controlling tumor growth. The models also confirmed a similar toxicity profile between EAD1 and Hydroxychloroquine.

Pyruvate Kinase Is Required for Sex Pheromone Biosynthesis in Helicoverpa armigera

Pyruvate kinase (PYK) is a speed-limited enzyme of glycolysis that catalyzes the formation of pyruvate, and plays an important role in acetyl-CoA synthesis. The acetyl-CoA is the precursor of sex pheromone biosynthesis in Helicoverpa armigera. However, the role of PYK in sex pheromone biosynthesis remains elusive. Here, PYK in H. armigera (HaPYK) was found to be highly expressed in the pheromone glands (PGs). The developmental expression profile of HaPYK was consistent with the fluctuation of sex pheromone release. Function analysis revealed that the knockdown of HaPYK led to a decrease in the levels of pyruvic acid and acetyl-CoA in PGs, which in turn caused a significant decrease in cis-11-hexadecenal (Z11-16: Ald) production, female capability to attract males, and mating frequency. Further study demonstrated that sugar feeding (5% sugar) increased the transcription and enzyme activity of HaPYK, thereby facilitating sex pheromone biosynthesis. Moreover, pheromone biosynthesis activating neuropeptide (PBAN) upregulated HaPYK activity through protein kinase C (PKC), as shown by PKC-specific inhibitor analysis. Altogether, our results revealed that PBAN activated HaPYK by Ca²⁺/PKC, thereby regulating the synthesis of pyruvate and subsequent acetyl-CoA, ensuring the supply of sex pheromone precursor, and finally facilitating sex pheromone biosynthesis and mating behavior.

Targeting Pyruvate Kinase M2 Phosphorylation Reverses Aggressive Cancer Phenotypes

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype with low survival rate and a lack of biomarkers and targeted treatments. Here, we target pyruvate kinase M2 (PKM2), a key metabolic component of oncogenesis. In patients with TNBC, PKM2pS37 was identified as a prominent phosphoprotein corresponding to the aggressive breast cancer phenotype that showed a characteristic nuclear staining pattern and prognostic value. Phosphorylation of PKM2 at S37 was connected with a cyclin-dependent kinase (CDK) pathway in TNBC cells. In parallel, pyruvate kinase activator TEPP-46 bound PKM2pS37 and reduced its nuclear localization. In a TNBC mouse xenograft model, treatment with either TEPP-46 or the potent CDK inhibitor dinaciclib reduced tumor growth and diminished PKM2pS37. Combinations of dinaciclib with TEPP-46 reduced cell invasion, impaired redox balance, and triggered cancer cell death. Collectively, these data support an approach to identify PKM2pS37-positive TNBC and target the PKM2 regulatory axis as a potential treatment. SIGNIFICANCE: PKM2 phosphorylation marks aggressive breast cancer cell phenotypes and targeting PKM2pS37 could be an effective therapeutic approach for treating triple-negative breast cancer.

Offset of apparent hyperpolarized 13 C lactate flux by the use of adjuvant metformin in ionizing radiation therapy in vivo

An increase in hyperpolarized (HP) [1-13 C]lactate production has been suggested as a biomarker for cancer occurrence as well as for response monitoring of cancer treatment. Recently, the use of metformin has been suggested as an anticancer or adjuvant treatment. By regulating the cytosolic NAD+ /NADH redox state, metformin stimulates lactate production and increases the HP [1-13 C]lactate conversion rate in the kidney, liver, and heart. In general, increased HP [1-13 C]lactate is regarded as a sign of cancer occurrence or tumor growth. Thus, the relationship between the tumor suppression effect of metformin and the change in metabolism monitored by HP [1-13 C]pyruvate MRS in cancer treatment needs to be investigated. The present study was performed using a brain metastasis animal model with MDA-MB-231(BR)-Luc breast cancer cells. HP [1-13 C]pyruvate MRS, T2 -weighted MRI, and bioluminescence imaging were performed in groups treated with metformin or adjuvant metformin and radiation therapy. Metformin treatment alone did not display a tumor suppression effect, and the HP [1-13 C]lactate conversion rate increased. In radiation therapy, the HP [1-13 C]lactate conversion rate decreased with tumor suppression, with a p-value of 0.028. In the adjuvant metformin and radiation treatment, the tumor suppression effect increased, with a p-value of 0.001. However, the apparent HP [1-13 C]lactate conversion rate (Kpl ) was observed to be offset by two opposite effects: a decrease on radiation therapy and an increase caused by metformin treatment. Although HP [1-13 C]pyruvate MRS could not evaluate the tumor suppression effect of adjuvant metformin and radiation therapy due to the offset phenomenon, metabolic changes following only metformin pre-treatment could be monitored. Therefore, our results indicate that the interpretation of HP [1-13 C]pyruvate MRS for response monitoring of cancer treatment should be carried out with caution when metformin is used as an adjuvant cancer therapy.

Metabolic changes in triple negative breast cancer-focus on aerobic glycolysis

Among breast cancer subtypes, the triple negative breast cancer (TNBC) has the worst prognosis. In absence of any permitted targeted therapy, standard chemotherapy is the mainstay for TNBC treatment. Hence, there is a crucial need to identify potential druggable targets in TNBCs for its effective treatment. In recent times, metabolic reprogramming has emerged as cancer cells hallmark, wherein cancer cells display discrete metabolic phenotypes to fuel cell progression and metastasis. Altered glycolysis is one such phenotype, in which even in oxygen abundance majority of cancer cells harvest considerable amount of energy through elevated glycolytic-flux. In the present review, we attempt to summarize the role of key glycolytic enzymes i.e. HK, Hexokinase; PFK, Phosphofructokinase; PKM2, Pyruvate kinase isozyme type 2; and LDH, Lactate dehydrogenase in TNBCs, and possible therapeutic options presently available.

Metabolic gene signature for predicting breast cancer recurrence using transcriptome analysis

Background: The study aimed at identifying a metabolic gene signature for stratifying the risk of recurrence in breast cancer. Materials & methods: The data of patients were obtained from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database. The limma package was used to identify differentially expressed metabolic genes, and a metabolic gene signature was constructed. Results: A five-gene metabolic signature was established that demonstrated satisfactory accuracy and predictive power in both training and validation cohorts. Also, a nomogram for predicting recurrence-free survival was established using a combination of the metabolism gene risk score and the clinicopathological features. Conclusions: The proposed metabolic gene signature and nomogram have a significant prognostic value and may improve the recurrence risk stratification for breast cancer patients.