A combination of 2-deoxy-D-glucose and 6-aminonicotinamide induces cell cycle arrest and apoptosis selectively in irradiated human malignant cells. Tumour Biol. 2012;33:1021-1030. [PMID: 22328137 DOI: 10.1007/s13277-012-0335-1]

Combined inhibition of pyruvate dehydrogenase kinase 1 and lactate dehydrogenase a induces metabolic and signaling reprogramming and enhances lung adenocarcinoma cell killing

Lung adenocarcinoma (LUAD) is one of the most prevalent and aggressive types of lung cancer. Metabolic reprogramming plays a critical role in the development and progression of LUAD. Pyruvate dehydrogenase kinase 1 (PDK1) and lactate dehydrogenase A (LDHA) are two key enzymes involved in glucose metabolism, whilst their aberrant expressions are often associated with tumorigenesis. Herein, we investigated the anticancer effects of combined inhibition of PDK1 and LDHA in LUAD in vitro and in vivo and its underlying mechanisms of action. The combination of a PDK1 inhibitor, 64, and a LDHA inhibitor, NHI-Glc-2, led to a synergistic growth inhibition in 3 different LUAD cell lines and more than additively suppressed tumor growth in the LUAD xenograft H1975 model. This combination also inhibited cellular migration and colony formation, while it induced a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) resulting in mitochondrial depolarization and apoptosis in LUAD cells. These effects were related to modulation of multiple cell signaling pathways, including AMPK, RAS/ERK, and AKT/mTOR. Our findings demonstrate that simultaneous inhibition of multiple glycolytic enzymes (PDK1 and LDHA) is a promising novel therapeutic approach for LUAD.

Proteomic Analysis Reveals Differential Protein Expression Induced by Inhibition of Prolyl Oligopeptidase in Filarial Parasites

Prolyl oligopeptidase (POP) plays a crucial role in the processing and degradation of neuropeptides and regulates inositol trisphosphate (IP3) signaling in mammals. We have reported that POP inhibition leads to IP3-mediated calcium efflux leading to mitochondrial-mediated apoptosis in the filarial parasite Setaria cervi. This study further elucidates the effect of altered calcium homeostasis on the proteome of filarial parasites. Adult parasites were treated with POP's specific inhibitor, Z-Pro-prolinal (ZPP), for 7 h. Cytosolic and mitochondrial proteome was analyzed using 2D gel electrophoresis coupled with MALDI-MS/MS. Phosphoproteins were also analyzed in the cytosolic fraction of the parasites. The phosphoprotein analysis revealed 7, and 9 spots in the cytosolic fraction of control and ZPP-treated parasites, respectively. The two identified protein spots in the treated set were found to be involved in G protein signaling. In cytosolic fraction, 109 and 112 protein spots were observed in control and treated parasites, respectively. Of these, 56 upregulated and 32 downregulated protein spots were observed in the treated set. On the other hand, 50 and 47 protein spots were detected in the mitochondrial fraction of control and treated parasites, respectively. Of these spots, 18 upregulated and 12 down-regulated protein spots were found in treated parasites. In silico analysis showed that the identified proteins were involved in energy metabolism, calcium signaling, stress response, and cytoskeleton organization. These findings correlate with our previous results suggesting the important regulatory role of POP in signaling and different metabolic pathways of filarial parasites.

Revisiting the Warburg Effect: Diet-Based Strategies for Cancer Prevention

It is widely acknowledged that cancer cell energy metabolism relies mainly on anaerobic glycolysis; this phenomenon is described as the Warburg effect. However, whether the Warburg effect is caused by genetic dysregulation in cancer or is the cause of cancer remains unknown. The exact reasons and physiology of this abnormal metabolism are unclear; therefore, many researchers have attempted to reduce malignant cell growth in tumors in preclinical and clinical studies. Anticancer strategies based on the Warburg effect have involved the use of drug compounds and dietary changes. We recently reviewed applications of the Warburg effect to understand the benefits of this unusual cancer-related metabolism. In the current article, we summarize diet strategies for cancer treatment based on the Warburg effect.

Cancer Metabolism and the Evasion of Apoptotic Cell Death

Cellular growth and proliferation depend upon the acquisition and synthesis of specific metabolites. These metabolites fuel the bioenergy, biosynthesis, and redox potential required for duplication of cellular biomass. Multicellular organisms maintain tissue homeostasis by balancing signals promoting proliferation and removal of cells via apoptosis. While apoptosis is in itself an energy dependent process activated by intrinsic and extrinsic signals, whether specific nutrient acquisition (elevated or suppressed) and their metabolism regulates apoptosis is less well investigated. Normal cellular metabolism is regulated by lineage specific intrinsic features and microenvironment driven extrinsic features. In the context of cancer, genetic abnormalities, unconventional microenvironments and/or therapy engage constitutive pro-survival signaling to re-program and rewire metabolism to maintain survival, growth, and proliferation. It thus becomes particularly relevant to understand whether altered nutrient acquisition and metabolism in cancer can also contribute to the evasion of apoptosis and consequently therapy resistance. Our review attempts to dissect a causal relationship between two cancer hallmarks, i.e., deregulated cellular energetics and the evasion of programmed cell death with primary focus on the intrinsic pathway of apoptosis.

Hepatic peroxisome proliferator-activated receptor γ coactivator 1β drives mitochondrial and anabolic signatures that contribute to hepatocellular carcinoma progression in mice

The peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1β (PGC-1 β) is a master regulator of mitochondrial biogenesis and oxidative metabolism as well as of antioxidant defense. Specifically, in the liver, PGC-1β also promotes de novo lipogenesis, thus sustaining cellular anabolic processes. Given the relevant pathogenic role of mitochondrial and fatty acid metabolism in hepatocarcinoma (HCC), here we pointed to PGC-1β as a putative novel transcriptional player in the development and progression of HCC. For this purpose, we generated both hepatic-specific PGC-1β-overexpressing (LivPGC-1β) and PGC-1β knockout (LivPGC-1βKO) mice, and we challenged them with both chemical and genetic models of hepatic carcinogenesis. Our results demonstrate a pivotal role of PGC-1β in driving liver tumor development. Indeed, whereas mice overexpressing PGC-1β show greater tumor susceptibility, PGC-1β knockout mice are protected from carcinogenesis. High levels of PGC-1β are able to boost reactive oxygen species (ROS) scavenger expression, therefore limiting the detrimental ROS accumulation and, consequently, apoptosis. Moreover, it supports tumor anabolism, enhancing the expression of genes involved in fatty acid and triglyceride synthesis. Accordingly, the specific hepatic ablation of PGC-1β promotes the accumulation of ROS-driven macromolecule damage, finally limiting tumor growth.

CONCLUSION

The present data elect hepatic PGC-1β as a transcriptional gatekeeper of mitochondrial function and redox status in HCC, orchestrating different metabolic programs that allow tumor progression. (Hepatology 2018;67:884-898).

Improving radiotherapy in cancer treatment: Promises and challenges

Effective radiotherapy for cancer has relied on the promise of maximally eradicating tumor cells while minimally killing normal cells. Technological advancement has provided state-of-the-art instrumentation that enables delivery of radiotherapy with great precision to tumor lesions with substantial reduced injury to normal tissues. Moreover, better understanding of radiobiology, particularly the mechanisms of radiation sensitivity and resistance in tumor lesions and toxicity in normal tissues, has improved the treatment efficacy of radiotherapy. Previous mechanism-based studies have identified many cellular targets that can affect radiation sensitivity, notably reactive oxygen species, DNA-damaging response signals, and tumor microenvironments. Several radiation sensitizers and protectors have been developed and clinically evaluated; however, many of these results are inconclusive, indicating that improvement remains needed. In this era of personalized medicine in which patients’ genetic variations, transcriptome and proteomics, tumor metabolism and microenvironment, and tumor immunity are available. These new developments have provided opportunity for new target discovery. Several radiotherapy sensitivity-associated “gene signatures” have been reported although clinical validations are needed. Recently, several immune modifiers have been shown to associate with improved radiotherapy in preclinical models and in early clinical trials. Combination of radiotherapy and immunocheckpoint blockade has shown promising results especially in targeting metastatic tumors through abscopal response. In this article, we succinctly review recent advancements in the areas of mechanism-driven targets and exploitation of new targets from current radio-oncogenomic and radiation-immunotherapeutic approaches that bear clinical implications for improving the treatment efficacy of radiotherapy.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

Deltamethrin induced RIPK3-mediated caspase-independent non-apoptotic cell death in rat primary hepatocytes

Deltamethrin (DLM), a synthetic pyrethroid insecticide, is used all over the world for indoor and field pest management. In the present study, we investigated the elicited pathogenesis of DLM-induced hepatotoxicity in rat primary hepatocytes. DLM-induced cell death was accompanied with increased ROS generation, decreased mitochondrial membrane potential and G2/M arrest. Pre-treatment with N-acetyl cysteine/butylated hydroxyanisole/IM54 could partly rescue hepatocytes suggesting that ROS might play a role in DLM-induced toxicity. Interestingly, DLM treatment resulted in a caspase-independent but non-apoptotic cell death. Pre-treatment with pan-caspase inhibitor (ZVAD-FMK) could not rescue hepatocytes. Unaltered caspase-3 activity and absence of cleaved caspase-3 also corroborated our findings. Further, LDH release and Transmission electron microscopy (TEM) analysis demonstrated that DLM incites membrane disintegrity and necrotic damage. Immunochemical staining revealed an increased expression of inflammatory markers (TNFα, NFκB, iNOS, COX-2) following DLM treatment. Moreover, the enhanced RIPK3 expression in DLM treated groups and prominent rescue from cell death by GSK-872 indicated that DLM exposure could induce programmed necrosis in hepatocytes. The present study demonstrates that DLM could induce hepatotoxicity via non-apoptotic mode of cell death.

Targeting Cancer Metabolism - Revisiting the Warburg Effects

After more than half of century since the Warburg effect was described, this atypical metabolism has been standing true for almost every type of cancer, exhibiting higher glycolysis and lactate metabolism and defective mitochondrial ATP production. This phenomenon had attracted many scientists to the problem of elucidating the mechanism of, and reason for, this effect. Several models based on oncogenic studies have been proposed, such as the accumulation of mitochondrial gene mutations, the switch from oxidative phosphorylation respiration to glycolysis, the enhancement of lactate metabolism, and the alteration of glycolytic genes. Whether the Warburg phenomenon is the consequence of genetic dysregulation in cancer or the cause of cancer remains unknown. Moreover, the exact reasons and physiological values of this peculiar metabolism in cancer remain unclear. Although there are some pharmacological compounds, such as 2-deoxy-D-glucose, dichloroacetic acid, and 3-bromopyruvate, therapeutic strategies, including diet, have been developed based on targeting the Warburg effect. In this review, we will revisit the Warburg effect to determine how much scientists currently understand about this phenomenon and how we can treat the cancer based on targeting metabolism.

ROS homeostasis and metabolism: a dangerous liason in cancer cells

Tumor cells harbor genetic alterations that promote a continuous and elevated production of reactive oxygen species. Whereas such oxidative stress conditions would be harmful to normal cells, they facilitate tumor growth in multiple ways by causing DNA damage and genomic instability, and ultimately, by reprogramming cancer cell metabolism. This review outlines the metabolic-dependent mechanisms that tumors engage in when faced with oxidative stress conditions that are critical for cancer progression by producing redox cofactors. In particular, we describe how the mitochondria has a key role in regulating the interplay between redox homeostasis and metabolism within tumor cells. Last, we will discuss the potential therapeutic use of agents that directly or indirectly block metabolism.

Particle size tailoring of ursolic acid nanosuspensions for improved anticancer activity by controlled antisolvent precipitation

The present study was aimed at tailoring the particle size of ursolic acid (UA) nanosuspension for improved anticancer activity. UA nanosuspensions were prepared by antisolvent precipitation using a four-stream multi-inlet vortex mixer (MIVM) under defined conditions of varying solvent composition, drug feeding concentration or stream flow rate. The resulting products were characterized for particle size and polydispersity. Two of the UA nanosuspensions with mean particle sizes of 100 and 300 nm were further assessed for their in-vitro activity against MCF-7 breast cancer cells using fluorescence microscopy with 4',6-diamidino-2-phenylindole (DAPI) staining, as well as flow cytometry with propidium (PI) staining and with double staining by fluorescein isothiocyanate. It was revealed that the solvent composition, drug feeding concentration and stream flow rate were critical parameters for particle size control of the UA nanosuspensions generated with the MIVM. Specifically, decreasing the UA feeding concentration or increasing the stream flow rate or ethanol content resulted in a reduction of particle size. Excellent reproducibility for nanosuspension production was demonstrated for the 100 and 300 nm UA preparations with a deviation of not more than 5% in particle size from the mean value of three independent batches. Fluorescence microscopy and flow cytometry revealed that these two different sized UA nanosuspensions, particularly the 300 nm sample, exhibited a higher anti-proliferation activity against the MCF-7 cells and afforded a larger population of these cells in both early and late apoptotic phases. In conclusion, MIVM is a robust and pragmatic tool for tailoring the particle size of the UA nanosuspension. Particle size appears to be a critical determinant of the anticancer activity of the UA nanoparticles.

The Warburg effect: evolving interpretations of an established concept

Metabolic reprogramming and altered bioenergetics have emerged as hallmarks of cancer and an area of active basic and translational cancer research. Drastically upregulated glucose transport and metabolism in most cancers regardless of the oxygen supply, a phenomenon called the Warburg effect, is a major focuses of the research. Warburg speculated that cancer cells, due to defective mitochondrial oxidative phosphorylation (OXPHOS), switch to glycolysis for ATP synthesis, even in the presence of oxygen. Studies in the recent decade indicated that while glycolysis is indeed drastically upregulated in almost all cancer cells, mitochondrial respiration continues to operate normally at rates proportional to oxygen supply. There is no OXPHOS-to-glycolysis switch but rather upregulation of glycolysis. Furthermore, upregulated glycolysis appears to be for synthesis of biomass and reducing equivalents in addition to ATP production. The new finding that a significant amount of glycolytic intermediates is diverted to the pentose phosphate pathway (PPP) for production of NADPH has profound implications in how cancer cells use the Warburg effect to cope with reactive oxygen species (ROS) generation and oxidative stress, opening the door for anticancer interventions taking advantage of this. Recent findings in the Warburg effect and its relationship with ROS and oxidative stress controls will be reviewed. Cancer treatment strategies based on these new findings will be presented and discussed.

Inhibitors of glucose transport and glycolysis as novel anticancer therapeutics

Metabolic reprogramming and altered energetics have become an emerging hallmark of cancer and an active area of basic, translational, and clinical cancer research in the recent decade. Development of effective anticancer therapeutics may depend on improved understanding of the altered cancer metabolism compared to that of normal cells. Changes in glucose transport and glycolysis, which are drastically upregulated in most cancers and termed the Warburg effect, are one of major focuses of this new research area. By taking advantage of the new knowledge and understanding of cancer’s mechanisms, numerous therapeutic agents have been developed to target proteins and enzymes involved in glucose transport and metabolism, with promising results in cancer cells, animal tumor models and even clinical trials. It has also been hypothesized that targeting a pathway or a process, such as glucose transport or glucose metabolism, rather than a specific protein or enzyme in a signaling pathway may be more effective. This is based on the observation that cancer somehow can always bypass the inhibition of a target drug by switching to a redundant or compensatory pathway. In addition, cancer cells have higher dependence on glucose. This review will provide background information on glucose transport and metabolism in cancer, and summarize new therapeutic developments in basic and translational research in these areas, with a focus on glucose transporter inhibitors and glycolysis inhibitors. The daunting challenges facing both basic and clinical researchers of the field are also presented and discussed.

Redox proteins and radiotherapy

Although conventional radiotherapy can directly damage DNA and other organic molecules within cells, most of the damage and the cytotoxicity of such ionising radiation, comes from the production of ions and free radicals produced via interactions with water. This 'indirect effect', a form of oxidative stress, can be modulated by a variety of systems within cells that are in place to, in normal situations, maintain homeostasis and redox balance. If cancer cells express high levels of antioxidant redox proteins, they may be more resistant to radiation and so targeting such systems may be a profitable strategy to increase therapeutic efficacy of conventional radiotherapy. An overview, with exemplars, of the main systems regulating redox homeostasis is supplied and discussed in relation to their use as prognostic and predictive biomarkers, and how targeting such proteins and systems may increase radiosensitivity and, potentially, improve the radiotherapeutic response.

Association between glutathione S-transferase T1 null genotype and gastric cancer risk: a meta-analysis of 48 studies

BACKGROUND

Glutathione S-transferases (GSTs) have proved to be involved in the detoxifying several carcinogens and may play an important role in carcinogenesis of cancer. Previous studies on the association between Glutathione S-transferase T1 (GSTT1) polymorphism and gastric cancer risk reported inconclusive results. To clarify the possible association, we conducted a meta-analysis of eligible studies.

METHODS

We searched in the Pubmed, Embase, and Wangfang Medicine databases for studies assessing the association between GSTT1 null genotype and gastric cancer risk. The pooled odds ratio (OR) and its 95% confidence interval (95%CI) was calculated to assess the strength of the association. A total of 48 studies with a total of 24,440 individuals were ultimately eligible for meta-analysis.

RESULTS

Overall, GSTT1 null genotype was significantly associated with increased risk of gastric cancer (Random-effect OR = 1.23, 95%CI 1.13-1.35, P OR <0.001, I(2) = 45.5%). Significant association was also found in Caucasians, East Asians, and Indians (P Caucasians = 0.010; P East Asians = 0.003; P Indians = 0.017). After adjusting for other confounding variables, GSTT1 null genotype was also significantly associated with increased risk of gastric cancer (Random-effect OR = 1.43, 95%CI 1.20-1.71, P OR <0.001, I(2) = 48.1%).

CONCLUSION

The meta-analysis provides strong evidence for the significant association between GSTT1 null genotype and increased risk of gastric cancer.

Radiosensitization by 2-deoxy-D-glucose and 6-aminonicotinamide involves activation of redox sensitive ASK1-JNK/p38MAPK signaling in head and neck cancer cells

Our previous studies on simultaneous inhibition of glycolysis by 2-deoxy-D-glucose (2-DG) and pentose phosphate activity by 6-aminonicotinamide (6-AN) have been shown to induce oxidative stress mediated selective radiosensitization in wide range of human malignant cells. However, the mechanism of radiosensitization induced by this combination (2-DG+6-AN) is not completely understood. Since activation of apoptotic signal regulating kinase (ASK1) and subsequent apoptosis are implicated in oxidative stress response, the role of ASK1 activation in radiosensitization by this combination was investigated in the present study. Our results demonstrated that redox alterations induced by this combination activated ASK1 and subsequent apoptosis during radiosensitization of head and neck carcinoma cells (KB). In addition, mRNA and protein expression of thioredoxin and thioredoxin reductase decreased significantly under similar treatment conditions. Further, the downstream targets such as JNK and p38MAPK were also activated by this combination, and their pharmacological inhibition by SP600125 and SB201291 respectively resulted in suppression of 2-DG+6-AN mediated apoptosis in irradiated KB cells. Interestingly, the activation of ASK1 was mediated by hydrogen peroxide rather than superoxide anions as PEG-catalase but not PEG-SOD suppressed its activation. Our observations clearly suggest that redox alterations by inhibition of glucose metabolism serves as a molecular switch that activate ASK1-JNK/p38MAPK signaling in malignant cells during radiosensitization by 2-DG+6-AN. The present study emphasizes the importance of redox alterations in determining radiosensitivity of tumor cells that may greatly influence the outcome of radiation therapy.

2-Deoxy-D-glucose and 6-aminonicotinamide-mediated Nrf2 down regulation leads to radiosensitization of malignant cells via abrogation of GSH-mediated defense

Enhanced level of nuclear erythroid-related factor-2 (Nrf2) has been associated with cancer chemo/radioresistance. Therefore, the role of Nrf2 in radiosensitization of malignant cells induced by a combination of 2-deoxy-D-Glucose (2-DG) and 6-aminonicotinamide (6-AN) was investigated. Two established human malignant cells lines namely KB (head and neck squamous carcinoma) and BMG-1 (cerebral glioma) were used. Following treatment with a combination of 2-DG (5 mM) and 6-AN (5 μM), irradiated (2Gy) KB and BMG-1 cells were assessed for protein level of Nrf2, Keap1 and γ-glutamylcysteine synthetase (γ-GCS) by western blotting and mRNA expression of γ-GCS, glutathione reductase (GR) and glutathione peroxidase (GPx1) by RT-PCR at 24 hours post treatment. A significant decrease in the level of Nrf2 with a concomitant increase in Keap1 was observed in both the irradiated malignant cells at 24 hours following treatment with combination (2-DG + 6-AN). Down regulation of γ-GCS, GR and GPx1 at 24 hours following treatment with combination (2-DG + 6-AN) resulted in abrogation of glutathione (GSH)-mediated defense in both the irradiated malignant cells. Eventual accumulation of ROS led to radiosensitization of both the malignant cells. These results indicate that deregulated Nrf2-Keap1 signalling leads to the radiosensitization of malignant cells due to abrogated glutathione defense. Metabolic modification-mediated down regulation of Nfr2 and its downstream signalling may have a potential of improving tumour radiotherapy.