Flexibility and Adaptation of Cancer Cells in a Heterogenous Metabolic Microenvironment

Mitochondrial signaling pathways and their role in cancer drug resistance

Mitochondria, traditionally known as cellular powerhouses, now emerge as critical signaling centers influencing cancer progression and drug resistance. The review highlights the role that apoptotic signaling, DNA mutations, mitochondrial dynamics and metabolism play in the development of resistance mechanisms and the advancement of cancer. Targeted approaches are discussed, with an emphasis on managing mitophagy, fusion, and fission of the mitochondria to make resistant cancer cells more susceptible to traditional treatments. Additionally, metabolic reprogramming can be used to effectively target metabolic enzymes such GLUT1, HKII, PDK, and PKM2 in order to avoid resistance mechanisms. Although there are potential possibilities for therapy, the complex structure of mitochondria and their subtle role in tumor development hamper clinical translation. Novel targeted medicines are put forth, providing fresh insights on combating drug resistance in cancer. The study also emphasizes the significance of glutamine metabolism, mitochondrial respiratory complexes, and apoptotic pathways as potential targets to improve treatment effectiveness against drug-resistant cancers. Combining complementary and nanoparticle-based techniques to target mitochondria has demonstrated encouraging results in the treatment of cancer, opening doors to reduce resistance and enable individualized treatment plans catered to the unique characteristics of each patient. Suggesting innovative approaches such as drug repositioning and mitochondrial drug delivery to enhance the efficacy of mitochondria-targeting therapies, presenting a pathway for advancements in cancer treatment. This thorough investigation is a major step forward in the treatment of cancer and has the potential to influence clinical practice and enhance patient outcomes.

Metabolic vulnerabilities in cancer: A new therapeutic strategy

Cancer metabolism is now a key area for therapeutic intervention, targeting unique metabolic reprogramming crucial for tumor growth and survival. This article reviews the therapeutic potential of addressing metabolic vulnerabilities through glycolysis and glutaminase inhibitors, which disrupt cancer cell metabolism. Challenges such as tumor heterogeneity and adaptive resistance are discussed, with strategies including personalized medicine and predictive biomarkers to enhance treatment efficacy. Additionally, integrating diet and lifestyle changes with metabolic targeting underscores a holistic approach to improving therapy outcomes. The article also examines the benefits of incorporating these strategies into standard care, highlighting the potential for more tailored, safer treatments. In conclusion, exploiting metabolic vulnerabilities promises a new era in oncology, positioning metabolic targeting at the forefront of personalized cancer therapy and transforming patient care.

The gluconeogenesis enzyme PCK2 has a non-enzymatic role in proteostasis in endothelial cells

Endothelial cells (ECs) are highly glycolytic, but whether they generate glycolytic intermediates via gluconeogenesis (GNG) in glucose-deprived conditions remains unknown. Here, we report that glucose-deprived ECs upregulate the GNG enzyme PCK2 and rely on a PCK2-dependent truncated GNG, whereby lactate and glutamine are used for the synthesis of lower glycolytic intermediates that enter the serine and glycerophospholipid biosynthesis pathways, which can play key roles in redox homeostasis and phospholipid synthesis, respectively. Unexpectedly, however, even in normal glucose conditions, and independent of its enzymatic activity, PCK2 silencing perturbs proteostasis, beyond its traditional GNG role. Indeed, PCK2-silenced ECs have an impaired unfolded protein response, leading to accumulation of misfolded proteins, which due to defective proteasomes and impaired autophagy, results in the accumulation of protein aggregates in lysosomes and EC demise. Ultimately, loss of PCK2 in ECs impaired vessel sprouting. This study identifies a role for PCK2 in proteostasis beyond GNG.

Association of metformin use and cancer incidence: a systematic review and meta-analysis

BACKGROUND

Metformin is among the most widely used antidiabetics medications because of its minimal toxicity, favorable safety profile, availability, and low cost. In addition to its role in diabetes management, metformin may reduce cancer risk.

METHODS

We conducted a comprehensive systematic review and meta-analysis to investigate the association between metformin use and cancer risk, with evaluation by specific cancer type when possible. Applicable studies were identified in PubMed/MEDLINE, Embase, Cochrane Library, Web of Science, and Scopus from inception through March 7, 2023, with metformin use categorized as "ever" or "yes" and a cancer diagnosis as the outcome. Article quality was evaluated using National Heart, Lung, and Blood Institute guidelines, and publication bias was evaluated using the Egger test, Begg test, and funnel plots. Pooled relative risk (RR) estimates were calculated using random-effects models, and sensitivity analysis was completed through leave-one-out cross-validation.

RESULTS

We included 166 studies with cancer incidence information in the meta-analysis. Reduced risk for overall cancer was observed in case-control studies (RR = 0.55, 95% confidence interval [CI] = 0.30 to 0.80) and prospective cohort studies (RR = 0.65, 95% CI = 0.37 to 0.93). Metformin use was associated with reduced gastrointestinal (RR = 0.79, 95% CI = 0.73 to 0.85), urologic (RR = 0.88, 95% CI = 0.78 to 0.99), and hematologic (RR = 0.87, 95% CI = 0.75 to 0.99) cancer risk. Statistically significant publication bias was observed within the studies (Egger P < .001).

CONCLUSIONS

Metformin may be associated with a decreased risk of many cancer types, but high heterogeneity and risk of publication bias limit confidence in these results. Additional studies in populations without diabetes are needed to better understand the utility of metformin in cancer prevention.

Targeting Fatty Acid Desaturase I Inhibits Renal Cancer Growth Via ATF3-mediated ER Stress Response

Monounsaturated fatty acids (MUFAs) play a pivotal role in maintaining endoplasmic reticulum (ER) homeostasis, an emerging hallmark of cancer. However, the role of polyunsaturated fatty acid (PUFAs) desaturation in persistent ER stress driven by oncogenic abnormalities remains elusive. Fatty Acid Desaturase 1 (FADS1) is a rate-limiting enzyme controlling the bioproduction of long-chain PUFAs. Our previous research has demonstrated the significant role of FADS1 in cancer survival, especially in kidney cancers. We explored the underlying mechanism in this study. We found that pharmacological inhibition or knockdown of the expression of FADS1 effectively inhibits renal cancer cell proliferation and induces cell cycle arrest. The stable knockdown of FADS1 also significantly inhibits tumor formation in vivo. Mechanistically, we show that while FADS1 inhibition induces ER stress, its expression is also augmented by ER-stress inducers. Notably, FADS1-inhibition sensitized cellular response to ER stress inducers, providing evidence of FADS1's role in modulating the ER stress response in cancer cells. We show that, while FADS1 inhibition-induced ER stress leads to activation of ATF3, ATF3-knockdown rescues the FADS1 inhibition-induced ER stress and cell growth suppression. In addition, FADS1 inhibition results in the impaired biosynthesis of nucleotides and decreases the level of UPD-N-Acetylglucosamine, a critical mediator of the unfolded protein response. Our findings suggest that PUFA desaturation is crucial for rescuing cancer cells from persistent ER stress, supporting FADS1 as a new therapeutic target.

Targeting metabolic adaptive responses induced by glucose starvation inhibits cell proliferation and enhances cell death in osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines

Osimertinib, a tyrosine kinase inhibitor targeting mutant EGFR, has received approval for initial treatment in patients with Non-Small Cell Lung Cancer (NSCLC). While effective in both first- and second-line treatments, patients eventually develop acquired resistance. Metabolic reprogramming represents a strategy through which cancer cells may resist and adapt to the selective pressure exerted by the drug. In the current study, we investigated the metabolic adaptations associated with osimertinib-resistance in NSCLC cells under low glucose culture conditions. We demonstrated that, unlike osimertinib-sensitive cells, osimertinib-resistant cells were able to survive under low glucose conditions by increasing the rate of glucose and glutamine uptake and by shifting towards mitochondrial metabolism. Inhibiting glucose/pyruvate contribution to mitochondrial respiration, glutamine deamination to glutamate, and oxidative phosphorylation decreased the proliferation and survival abilities of osimertinib-resistant cells to glucose starvation. Our findings underscore the remarkable adaptability of osimertinib-resistant NSCLC cells in a low glucose environment and highlight the pivotal role of mitochondrial metabolism in mediating this adaptation. Targeting the metabolic adaptive responses triggered by glucose shortage emerges as a promising strategy, effectively inhibiting cell proliferation and promoting cell death in osimertinib-resistant cells.

Cisplatin and Starvation Differently Sensitize Autophagy in Renal Carcinoma: A Potential Therapeutic Pathway to Target Variegated Drugs Resistant Cancerous Cells

Cisplatin, a powerful chemotherapy medication, has long been a cornerstone in the fight against cancer due to chemotherapeutic failure. The mechanism of cisplatin resistance/failure is a multifaceted and complex issue that consists mainly of apoptosis inhibition through autophagy sensitization. Currently, researchers are exploring ways to regulate autophagy in order to tip the balance in favor of effective chemotherapy. Based on this notion, the current study primarily identifies the differentially expressed genes (DEGs) in cisplatin-treated autophagic ACHN cells through the Illumina Hi-seq platform. A protein-protein interaction network was constructed using the STRING database and KEGG. GO classifiers were implicated to identify genes and their participating biological pathways. ClueGO, David, and MCODE detected ontological enrichment and sub-networking. The network topology was further examined using 12 different algorithms to identify top-ranked hub genes through the Cytoscape plugin Cytohubba to identify potential targets, which established profound drug efficacy under an autophagic environment. Considerable upregulation of genes related to autophagy and apoptosis suggests that autophagy boosts cisplatin efficacy in malignant ACHN cells with minimal harm to normal HEK-293 growth. Furthermore, the determination of cellular viability and apoptosis by AnnexinV/FITC-PI assay corroborates with in silico data, indicating the reliability of the bioinformatics method followed by qRT-PCR. Altogether, our data provide a clear molecular insight into drug efficacy under starved conditions to improve chemotherapy and will likely prompt more clinical trials on this aspect.

Modelling cancer metabolism in vitro: current improvements and future challenges

Advances in cancer biology over the past decades have revealed that metabolic adaptation of cancer cells is an essential aspect of tumorigenesis. However, recent insights into tumour metabolism in vivo have revealed dissimilarities with results obtained in vitro. This is partly due to the reductionism of in vitro cancer models that struggle to reproduce the complexity of tumour tissues. This review describes some of the discrepancies in cancer cell metabolism between in vitro and in vivo conditions, and presents current methodological approaches and tools used to bridge the gap with the clinically relevant microenvironment. As such, these approaches should generate new knowledge that could be more effectively translated into therapeutic opportunities.

Ferroptosis, Metabolic Rewiring, and Endometrial Cancer

Ferroptosis is a newly discovered form of regulated cell death. The main feature of ferroptosis is excessive membrane lipid peroxidation caused by iron-mediated chemical and enzymatic reactions. In normal cells, harmful lipid peroxides are neutralized by glutathione peroxidase 4 (GPX4). When GPX4 is inhibited, ferroptosis occurs. In mammalian cells, ferroptosis serves as a tumor suppression mechanism. Not surprisingly, in recent years, ferroptosis induction has gained attention as a potential anticancer strategy, alone or in combination with other conventional therapies. However, sensitivity to ferroptosis inducers depends on the metabolic state of the cell. Endometrial cancer (EC) is the sixth most common cancer in the world, with more than 66,000 new cases diagnosed every year. Out of all gynecological cancers, carcinogenesis of EC is mostly dependent on metabolic abnormalities. Changes in the uptake and catabolism of iron, lipids, glucose, and glutamine affect the redox capacity of EC cells and, consequently, their sensitivity to ferroptosis-inducing agents. In addition to this, in EC cells, ferroptosis-related genes are usually mutated and overexpressed, which makes ferroptosis a promising target for EC prediction, diagnosis, and therapy. However, for a successful application of ferroptosis, the connection between metabolic rewiring and ferroptosis in EC needs to be deciphered, which is the focus of this review.

GLUT5, GLUT7, and GLUT11 expression and Bcl-2/Bax ratio on Breast Cancer Cell Line MCF-7 Treated with Fructose and Glucose

OBJECTIVE

Fructose and glucose are types of sugars commonly found in the diet that have been linked to cancer development. Glucose transporters (GLUTs) are facilitating the uptake of these hexoses. Expression of GLUT5 is higher in cancer cells than in healthy tissue. GLUT7 and GLUT11 facilitate the transport of glucose and fructose; however, their expression in breast cancer has not been extensively studied. The Bcl-2 family has been known as a regulator of the cell's survival and death. Here, we investigated the effect of the fructose-glucose combination in MCF-7 breast cancer cells on the viability, migration, and expression of GLUT5, GLUT7, GLUT11, and Bcl-2/Bax ratio.

METHODS

Breast cancer cells MCF-7 were treated with fructose, glucose, and combinations of fructose:glucose (75%:25%, 50%:50%, 25%:75%). Cell viability was assessed using an MTT test. Cell migration was examined with a wound-healing assay. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to evaluate the mRNA expression of GLUT5, GLUT7, GLUT11, and Bcl-2/Bax.

RESULTS

The viability and migration of MCF-7 breast cancer cells elevated when treated with a combination of fructose and glucose, and glucose alone, compared to fructose alone. The expression levels of GLUT5 and GLUT7 were highest in combination of fructose:glucose (75%:25%). Conversely, the expression of GLUT11 was consistently low across all treated media. The highest Bcl-2/Bax ratio was shown in fructose:glucose combination (25%:75%).

CONCLUSION

The viability, migration, and Bcl-2/Bax ratio are enhanced in the combination media with higher glucose. In contrast, when the fructose composition was higher in the media, expression of GLUT5 and GLUT7 increased.

Gluconeogenesis Flux in Metabolic Disease

Gluconeogenesis is a critical biosynthetic process that helps maintain whole-body glucose homeostasis and becomes altered in certain medical diseases. We review gluconeogenic flux in various medical diseases, including common metabolic disorders, hormonal imbalances, specific inborn genetic errors, and cancer. We discuss how the altered gluconeogenic activity contributes to disease pathogenesis using data from experiments using isotopic tracer and spectroscopy methodologies. These in vitro, animal, and human studies provide insights into the changes in circulating levels of available gluconeogenesis substrates and the efficiency of converting those substrates to glucose by gluconeogenic organs. We highlight ongoing knowledge gaps, discuss emerging research areas, and suggest future investigations. A better understanding of altered gluconeogenesis flux may ultimately identify novel and targeted treatment strategies for such diseases.

Cellular Adaptation Takes Advantage of Atavistic Regression Programs during Carcinogenesis

Adaptation of cancer cells to extreme microenvironmental conditions (i.e., hypoxia, high acidity, and reduced nutrient availability) contributes to cancer resilience. Furthermore, neoplastic transformation can be envisioned as an extreme adaptive response to tissue damage or chronic injury. The recent Systemic-Evolutionary Theory of the Origin of Cancer (SETOC) hypothesizes that cancer cells "revert" to "primitive" characteristics either ontogenically (embryo-like) or phylogenetically (single-celled organisms). This regression may confer robustness and maintain the disordered state of the tissue, which is a hallmark of malignancy. Changes in cancer cell metabolism during adaptation may also be the consequence of altered microenvironmental conditions, often resulting in a shift toward lactic acid fermentation. However, the mechanisms underlying the robust adaptive capacity of cancer cells remain largely unknown. In recent years, cancer cells' metabolic flexibility has received increasing attention among researchers. Here, we focus on how changes in the microenvironment can affect cancer cell energy production and drug sensitivity. Indeed, changes in the cellular microenvironment may lead to a "shift" toward "atavistic" biologic features, such as the switch from oxidative phosphorylation (OXPHOS) to lactic acid fermentation, which can also sustain drug resistance. Finally, we point out new integrative metabolism-based pharmacological approaches and potential biomarkers for early detection.

The metabolic cross-talk between cancer and T cells

The metabolic cross-talk between cancer cells and T cells dictates cancer formation and progression. These cells possess metabolic plasticity. Thus, they adapt their metabolic profile to meet their phenotypic requirements. However, the nutrient microenvironment of a tumor is a very hostile niche in which these cells are forced to compete for the available nutrients. The hyperactive metabolism of tumor cells often outcompetes the antitumorigenic CD8+ T cells while promoting the protumorigenic exhausted CD8+ T cells and T regulatory (Treg) cells. Thus, cancer cells elude the immune response and spread in an uncontrolled manner. Identifying the metabolic pathways necessary to shift the balance from a protumorigenic to an antitumorigenic immune phenotype is essential to potentiate antitumor immunity.

How Warburg-Associated Lactic Acidosis Rewires Cancer Cell Energy Metabolism to Resist Glucose Deprivation

Lactic acidosis, a hallmark of solid tumour microenvironment, originates from lactate hyperproduction and its co-secretion with protons by cancer cells displaying the Warburg effect. Long considered a side effect of cancer metabolism, lactic acidosis is now known to play a major role in tumour physiology, aggressiveness and treatment efficiency. Growing evidence shows that it promotes cancer cell resistance to glucose deprivation, a common feature of tumours. Here we review the current understanding of how extracellular lactate and acidosis, acting as a combination of enzymatic inhibitors, signal, and nutrient, switch cancer cell metabolism from the Warburg effect to an oxidative metabolic phenotype, which allows cancer cells to withstand glucose deprivation, and makes lactic acidosis a promising anticancer target. We also discuss how the evidence about lactic acidosis' effect could be integrated in the understanding of the whole-tumour metabolism and what perspectives it opens up for future research.

Development of "smart" drug delivery systems for chemo/PDT synergistic treatment

Although chemotherapy and photodynamic therapy (PDT) have been developed for fighting cancer, the complex and heterogeneous nature of tumors makes it difficult for a single therapy to completely inhibit tumor growth. In order to reduce multidrug resistance of cancer cells to chemotherapeutic drugs and overcome low PDT efficiency in the hypoxic tumor microenvironment (TME), chemo/PDT synergistic treatment has received much attention in recent years. Depending on the characteristic signals of TME, various drug delivery systems can be constructed to target tumors and improve the therapeutic efficacy and the pharmacokinetic profile of anticancer drugs. This review highlights the synergistic strategies, treatment protocols, and design of chemo/PDT co-therapy in recent years to explore its scope and limitations. Taking advantage of stimuli-responsive materials and active cancer-targeting agents, cancer-targeting synergistic therapy is presented and discussed, providing ideas and suggestions for the construction of chemo/PDT co-therapy "smart" nanocarriers.

Synchronized, Spontaneous, and Oscillatory Detachment of Eukaryotic Cells: A New Tool for Cell Characterization and Identification

Despite the importance of cell characterization and identification for diagnostic and therapeutic applications, developing fast and label-free methods without (bio)-chemical markers or surface-engineered receptors remains challenging. Here, we exploit the natural cellular response to mild thermal stimuli and propose a label- and receptor-free method for fast and facile cell characterization. Cell suspensions in a dedicated sensor are exposed to a temperature gradient, which stimulates synchronized and spontaneous cell-detachment with sharply defined time-patterns, a phenomenon unknown from literature. These patterns depend on metabolic activity (controlled through temperature, nutrients, and drugs) and provide a library of cell-type-specific indicators, allowing to distinguish several yeast strains as well as cancer cells. Under specific conditions, synchronized glycolytic-type oscillations are observed during detachment of mammalian and yeast-cell ensembles, providing additional cell-specific signatures. These findings suggest potential applications for cell viability analysis and for assessing the collective response of cancer cells to drugs.

The Marine-Derived Macrolactone Mandelalide A Is an Indirect Activator of AMPK

The mandelalides are complex macrolactone natural products with distinct macrocycle motifs and a bioactivity profile that is heavily influenced by compound glycosylation. Mandelalides A and B are direct inhibitors of mitochondrial ATP synthase (complex V) and therefore more toxic to mammalian cells with an oxidative metabolic phenotype. To provide further insight into the pharmacology of the mandelalides, we studied the AMP-activated protein kinase (AMPK) energy stress pathway and report that mandelalide A is an indirect activator of AMPK. Wild-type mouse embryonic fibroblasts (MEFs) and representative human non-small cell lung cancer (NSCLC) cells showed statistically significant increases in phospho-AMPK (Thr172) and phospho-ACC (Ser79) in response to mandelalide A. Mandelalide L, which also harbors an A-type macrocycle, induced similar increases in phospho-AMPK (Thr172) and phospho-ACC (Ser79) in U87-MG glioblastoma cells. In contrast, MEFs co-treated with an AMPK inhibitor (dorsomorphin), AMPKα-null MEFs, or NSCLC cells lacking liver kinase B1 (LKB1) lacked this activity. Mandelalide A was significantly more cytotoxic to AMPKα-null MEFs than wild-type cells, suggesting that AMPK activation serves as a protective response to mandelalide-induced depletion of cellular ATP. However, LKB1 status alone was not predictive of the antiproliferative effects of mandelalide A against NSCLC cells. When EGFR status was considered, erlotinib and mandelalide A showed strong cytotoxic synergy in combination against erlotinib-resistant 11-18 NSCLC cells but not against erlotinib-sensitive PC-9 cells. Finally, prolonged exposures rendered mandelalide A, a potent and efficacious cytotoxin, against a panel of human glioblastoma cell types regardless of the underlying metabolic phenotype of the cell. These results add biological relevance to the mandelalide series and provide the basis for their further pre-clinical evaluation as ATP synthase inhibitors and secondary activators of AMPK.

Targeting epidermal growth factor receptor in paclitaxel-resistant human breast and lung cancer cells with upregulated glucose-6-phosphate dehydrogenase

BACKGROUND

Chemoresistance is a major obstacle to the successful treatment of triple-negative breast cancer (TNBC) and non-small-cell lung cancer (NSCLC). Therapeutic strategies to overcome chemoresistance are necessary to improve the prognosis of patients with these cancers.

METHODS

Paclitaxel-resistant TNBC and NSCLC sublines were generated through continuous paclitaxel treatment over 6 months. The mechanistic investigation was conducted using MTT assay, LC/MS-based metabolite analysis, flow cytometry, western blot analysis, real-time PCR and tumour xenograft experiments.

RESULTS

Glucose-6-phosphate dehydrogenase (G6PD) expression along with an increase in 3-phosphoglycerates and ribulose-5-phosphate production was upregulated in paclitaxel-resistant cells. Blockade of G6PD decreased viability of paclitaxel-resistant cells in vitro and the growth of paclitaxel-resistant MDA/R xenograft tumours in vivo. Mechanistically, activation of the epidermal growth factor receptor (EGFR)/Akt pathway mediates G6PD expression and G6PD-induced cell survival. Blockade of the EGFR pathway inhibited G6PD expression and sensitised those paclitaxel-resistant cells to paclitaxel treatment in vitro and in vivo. Analysis of publicly available datasets revealed an association between G6PD and unfavourable clinical outcomes in patients with breast or lung cancer.

CONCLUSIONS

EGFR signaling-mediated G6PD expression plays a pivotal role in paclitaxel resistance, highlighting the potential of targeting EGFR to overcome paclitaxel resistance in TNBC and NSCLC cells overexpressing G6PD.

(Dis)similarities between the Decidual and Tumor Microenvironment

Placenta-specific trophoblast and tumor cells exhibit many common characteristics. Trophoblast cells invade maternal tissues while being tolerated by the maternal immune system. Similarly, tumor cells can invade surrounding tissues and escape the immune system. Importantly, both trophoblast and tumor cells are supported by an abetting microenvironment, which influences invasion, angiogenesis, and immune tolerance/evasion, among others. However, in contrast to tumor cells, the metabolic, proliferative, migrative, and invasive states of trophoblast cells are under tight regulatory control. In this review, we provide an overview of similarities and dissimilarities in regulatory processes that drive trophoblast and tumor cell fate, particularly focusing on the role of the abetting microenvironments.

Combination strategies to target metabolic flexibility in cancer

Therapeutically interfering with metabolic pathways has great merit to curtail tumor growth because the demand for copious amounts of energy for growth-supporting biomass production is common to all cancer entities. A major impediment to a straight implementation of metabolic cancer therapy is the metabolic flexibility and plasticity of cancer cells (and their microenvironment) resulting in therapy resistance and evasion. Metabolic combination therapies, therefore, are promising as they are designed to target several energetic routes simultaneously and thereby diminish the availability of alternative substrates. Thus, dietary restrictions, specific nutrient limitations, and/or pharmacological interventions impinging on metabolic pathways can be combined to improve cancer treatment efficacy, to overcome therapy resistance, or even act as a preventive measure. Here, we review the most recent developments in metabolic combination therapies particularly highlighting in vivo reports of synergistic effects and available clinical data. We close with identifying the challenges of the field (metabolic tumor heterogeneity, immune cell interactions, inter-patient variabilities) and suggest a "metabo-typing" strategy to tailor evidence-based metabolic combination therapies to the energetic requirements of the tumors and the patient's nutritional habits and status.

Active mitochondrial respiration in cancer: a target for the drug

The relative contribution of mitochondrial respiration and subsequent energy production in malignant cells has remained controversial to date. Enhanced aerobic glycolysis and impaired mitochondrial respiration have gained more attention in the metabolic study of cancer. In contrast to the popular concept, mitochondria of cancer cells oxidize a diverse array of metabolic fuels to generate a majority of the cellular energy by respiration. Several mitochondrial respiratory chain (MRC) subunits' expressions are critical for the growth, metastasis, and cancer cell invasion. Also, the assembly factors, which regulate the integration of individual MRC complexes into native super-complexes, are upregulated in cancer. Moreover, a series of anti-cancer drugs function by inhibiting respiration and ATP production. In this review, we have specified the roles of mitochondrial fuels, MRC subunits, and super-complex assembly factors that promote active respiration across different cancer types and discussed the potential roles of MRC inhibitor drugs in controlling cancer.

Fasting improves therapeutic response in hepatocellular carcinoma through p53-dependent metabolic synergism

Cancer cells voraciously consume nutrients to support their growth, exposing metabolic vulnerabilities that can be therapeutically exploited. Here, we show in hepatocellular carcinoma (HCC) cells, xenografts, and patient-derived organoids that fasting improves sorafenib efficacy and acts synergistically to sensitize sorafenib-resistant HCC. Mechanistically, sorafenib acts noncanonically as an inhibitor of mitochondrial respiration, causing resistant cells to depend on glycolysis for survival. Fasting, through reduction in glucose and impeded AKT/mTOR signaling, prevents this Warburg shift. Regulating glucose transporter and proapoptotic protein expression, p53 is necessary and sufficient for the sorafenib-sensitizing effect of fasting. p53 is also crucial for fasting-mediated improvement of sorafenib efficacy in an orthotopic HCC mouse model. Together, our data suggest fasting and sorafenib as rational combination therapy for HCC with intact p53 signaling. As HCC therapy is currently severely limited by resistance, these results should instigate clinical studies aimed at improving therapy response in advanced-stage HCC.

Salubrinal Enhances Cancer Cell Death during Glucose Deprivation through the Upregulation of xCT and Mitochondrial Oxidative Stress

Cancer cells have the metabolic flexibility to adapt to heterogeneous tumor microenvironments. The integrated stress response (ISR) regulates the cellular adaptation response during nutrient stress. However, the issue of how the ISR regulates metabolic flexibility is still poorly understood. In this study, we activated the ISR using salubrinal in cancer cells and found that salubrinal repressed cell growth, colony formation, and migration but did not induce cell death in a glucose-containing condition. Under a glucose-deprivation condition, salubrinal induced cell death and increased the levels of mitochondrial reactive oxygen species (ROS). We found that these effects of salubrinal and glucose deprivation were associated with the upregulation of xCT (SLC7A11), which functions as an antiporter of cystine and glutamate and maintains the level of glutathione to maintain redox homeostasis. The upregulation of xCT did not protect cells from oxidative stress-mediated cell death but promoted it during glucose deprivation. In addition, the supplementation of ROS scavenger N-acetylcysteine and the maintenance of intracellular levels of amino acids via sulfasalazine (xCT inhibitor) or dimethyl-α-ketoglutarate decreased the levels of mitochondrial ROS and protected cells from death. Our results suggested that salubrinal enhances cancer cell death during glucose deprivation through the upregulation of xCT and mitochondrial oxidative stress.

Detection of Lung Cancer via Blood Plasma and 1H-NMR Metabolomics: Validation by a Semi-Targeted and Quantitative Approach Using a Protein-Binding Competitor

Metabolite profiling of blood plasma, by proton nuclear magnetic resonance (¹H-NMR) spectroscopy, offers great potential for early cancer diagnosis and unraveling disruptions in cancer metabolism. Despite the essential attempts to standardize pre-analytical and external conditions, such as pH or temperature, the donor-intrinsic plasma protein concentration is highly overlooked. However, this is of utmost importance, since several metabolites bind to these proteins, resulting in an underestimation of signal intensities. This paper describes a novel ¹H-NMR approach to avoid metabolite binding by adding 4 mM trimethylsilyl-2,2,3,3-tetradeuteropropionic acid (TSP) as a strong binding competitor. In addition, it is demonstrated, for the first time, that maleic acid is a reliable internal standard to quantify the human plasma metabolites without the need for protein precipitation. Metabolite spiking is further used to identify the peaks of 62 plasma metabolites and to divide the ¹H-NMR spectrum into 237 well-defined integration regions, representing these 62 metabolites. A supervised multivariate classification model, trained using the intensities of these integration regions (areas under the peaks), was able to differentiate between lung cancer patients and healthy controls in a large patient cohort (n = 160), with a specificity, sensitivity, and area under the curve of 93%, 85%, and 0.95, respectively. The robustness of the classification model is shown by validation in an independent patient cohort (n = 72).