Pro- and antitumor effects of mitochondrial reactive oxygen species

Advances in research on the relationship between mitochondrial function and colorectal cancer: a bibliometric study from 2013 to 2023

The study provides a thorough examination of literature from 2013 to 2023, delving into the intricate relationship between mitochondrial function and colorectal cancer (CRC). It offers a concise overview of the current landscape and emerging trends in this rapidly evolving research area. The findings indicate a consistent rise in annual publications, reflecting growing interest and significant potential in the field. China emerges as the leading contributor, followed by the United States and India. However, despite China's dominance in output, its average citation rate is lower than that of the US, which leads in citations per publication, highlighting a noticeable disparity. In the realm of research institutions, Shanghai Jiao Tong University and China Medical University are identified as major contributors, yet the potential for inter-institutional collaboration remains largely untapped, suggesting avenues for future synergy. Internationally, China-US collaborations are particularly robust, fostering cross-border knowledge exchange. Hyun Jin Won and Li Wei are recognized as prolific authors, while Ahmedin Jemal is an influential co-cited scholar, noted for his seminal contributions. Keyword analysis reveals research focus areas, such as the complex CRC tumor microenvironment, molecular mechanisms of oxidative stress, and key multidrug resistance pathways. It also highlights the promising potential of mitochondria-targeted therapies and nanomolecular technologies in clinical practice, signaling their growing significance in addressing complex health challenges. The study underscores the imperative to validate complex mitochondrial mechanisms and signaling pathways in CRC, with a particular emphasis on translating these insights into drug targets for clinical trials. Advancing this research is expected to refine and enhance CRC treatment strategies. Additionally, it highlights the urgency of validating mitochondrial complexities in CRC, advocating for collaborative efforts to link these mechanisms with tailored therapeutic interventions for clinical testing. This integrated approach promises significant advancements in developing effective, targeted CRC treatments, ultimately improving patient outcomes.

Targeting mitochondrial damage: shining a new light on immunotherapy

Mitochondrial damage has a particular impact on the immune system and tumor microenvironment, which can trigger cell stress, an inflammatory response, and disrupt immune cell function, thus all of which can accelerate the progression of the tumor. Therefore, it is of essence to comprehend how the immune system function and the tumor microenvironment interact with mitochondrial dysfunction for cancer treatment. Preserving the integrity of mitochondria or regulating the function of immune cells, such as macrophages, may enhance the efficacy of cancer therapy. Future research should concentrate on the interactions among mitochondria, the immune system, and the tumor microenvironment to identify new therapeutic strategies.

Subclinical dose irradiation triggers human breast cancer migration via mitochondrial reactive oxygen species

BACKGROUND

Despite technological advances in radiotherapy, cancer cells at the tumor margin and in diffusive infiltrates can receive subcytotoxic doses of photons. Even if only a minority of cancer cells are concerned, phenotypic consequences could be important considering that mitochondrial DNA (mtDNA) is a primary target of radiation and that damage to mtDNA can persist. In turn, mitochondrial dysfunction associated with enhanced mitochondrial ROS (mtROS) production could promote cancer cell migration out of the irradiation field in a natural attempt to escape therapy. In this study, using MCF7 and MDA-MB-231 human breast cancer cells as models, we aimed to elucidate the molecular mechanisms supporting a mitochondrial contribution to cancer cell migration induced by subclinical doses of irradiation (< 2 Gy).

METHODS

Mitochondrial dysfunction was tested using mtDNA multiplex PCR, oximetry, and ROS-sensitive fluorescent reporters. Migration was tested in transwells 48 h after irradiation in the presence or absence of inhibitors targeting specific ROS or downstream effectors. Among tested inhibitors, we designed a mitochondria-targeted version of human catalase (mtCAT) to selectively inactivate mitochondrial H2O2.

RESULTS

Photon irradiation at subclinical doses (0.5 Gy for MCF7 and 0.125 Gy for MDA-MB-231 cells) sequentially affected mtDNA levels and/or integrity, increased mtROS production, increased MAP2K1/MEK1 gene expression, activated ROS-sensitive transcription factors NF-κB and AP1 and stimulated breast cancer cell migration. Targeting mtROS pharmacologically by MitoQ or genetically by mtCAT expression mitigated migration induced by a subclinical dose of irradiation.

CONCLUSION

Subclinical doses of photon irradiation promote human breast cancer migration, which can be countered by selectively targeting mtROS.

Role of reactive oxygen species in myelodysplastic syndromes

Reactive oxygen species (ROS) serve as typical metabolic byproducts of aerobic life and play a pivotal role in redox reactions and signal transduction pathways. Contingent upon their concentration, ROS production not only initiates or stimulates tumorigenesis but also causes oxidative stress (OS) and triggers cellular apoptosis. Mounting literature supports the view that ROS are closely interwoven with the pathogenesis of a cluster of diseases, particularly those involving cell proliferation and differentiation, such as myelodysplastic syndromes (MDS) and chronic/acute myeloid leukemia (CML/AML). OS caused by excessive ROS at physiological levels is likely to affect the functions of hematopoietic stem cells, such as cell growth and self-renewal, which may contribute to defective hematopoiesis. We review herein the eminent role of ROS in the hematological niche and their profound influence on the progress of MDS. We also highlight that targeting ROS is a practical and reliable tactic for MDS therapy.

A pH-Sensitive Nanoparticle as Reactive Oxygen Species Amplifier to Regulate Tumor Microenvironment and Potentiate Tumor Radiotherapy

Background

Radiotherapy is a widely used clinical tool for tumor treatment but can cause systemic toxicity if excessive radiation is administered. Although numerous nanoparticles have been developed as radiosensitizers to reduce the required dose of X-ray irradiation, they often have limitations, such as passive reliance on radiation-induced apoptosis in tumors, and little consider the unique tumor microenvironment that contributes radiotherapy resistance.

Methods

In this study, we developed and characterized a novel self-assembled nanoparticle containing dysprosium ion and manganese ion (Dy/Mn-P). We systematically investigated the potential of Dy/Mn-P nanoparticles (NPs) as a reactive oxygen species (ROS) amplifier and radiosensitizer to enhance radiation therapy and modulate the tumor microenvironment at the cellular level. Additionally, we evaluated the effect of Dy/Mn-P on the stimulator of interferon genes (STING), an innate immune signaling pathway.

Results

Physicochemical analysis demonstrated the prepared Dy/Mn-P NPs exhibited excellent dispersibility and stability, and degraded rapidly at lower pH values. Furthermore, Dy/Mn-P was internalized by cells and exhibited selective toxicity towards tumor cells compared to normal cells. Our findings also revealed that Dy/Mn-P NPs improved the tumor microenvironment and significantly increased ROS generation under ionizing radiation, resulting in a ~70% increase in ROS levels compared to radiation therapy alone. This enhanced ROS generation inhibited ~92% of cell clone formation and greatly contributed to cytoplasmic DNA exposure. Subsequently, the activation of the STING pathway was observed, leading to the secretion of pro-inflammatory immune factors and maturation of dendritic cells (DCs).

Conclusion

Our study demonstrates that Dy/Mn-P NPs can potentiate tumor radiotherapy by improving the tumor microenvironment and increasing endogenous ROS levels within the tumor. Furthermore, Dy/Mn-P can amplify the activation of the STING pathway during radiotherapy, thereby triggering an anti-tumor immune response. This novel approach has the potential to expand the application of radiotherapy in tumor treatment.

Complex II ambiguities-FADH2 in the electron transfer system

The prevailing notion that reduced cofactors NADH and FADH2 transfer electrons from the tricarboxylic acid cycle to the mitochondrial electron transfer system creates ambiguities regarding respiratory Complex II (CII). CII is the only membrane-bound enzyme in the tricarboxylic acid cycle and is part of the electron transfer system of the mitochondrial inner membrane feeding electrons into the coenzyme Q-junction. The succinate dehydrogenase subunit SDHA of CII oxidizes succinate and reduces the covalently bound prosthetic group FAD to FADH2 in the canonical forward tricarboxylic acid cycle. However, several graphical representations of the electron transfer system depict FADH2 in the mitochondrial matrix as a substrate to be oxidized by CII. This leads to the false conclusion that FADH2 from the β-oxidation cycle in fatty acid oxidation feeds electrons into CII. In reality, dehydrogenases of fatty acid oxidation channel electrons to the Q-junction but not through CII. The ambiguities surrounding Complex II in the literature and educational resources call for quality control, to secure scientific standards in current communications of bioenergetics, and ultimately support adequate clinical applications. This review aims to raise awareness of the inherent ambiguity crisis, complementing efforts to address the well-acknowledged issues of credibility and reproducibility.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Weak Radiofrequency Field Effects on Chemical Parameters That Characterize Oxidative Stress in Human Fibrosarcoma and Fibroblast Cells

In the last few decades, evidence has surfaced that weak radiofrequency (RF) fields can influence biological systems. This work aims to improve our understanding of how externally applied weak RF fields alter concentrations of chemical parameters that characterize oxidative stress. We conducted a series of experiments to investigate the effects of applying weak RF magnetic fields within the 3-5 MHz region on mitochondrial respiration in both human fibrosarcoma and fibroblast cells over a period of four days. Our experimental data show that RF fields between 3 and 5 MHz were able to change the modulation of mitochondrial signaling by changing the cell growth, mitochondrial mass, and oxidative stress. Exposure to RF fields at 4.2 MHz significantly increased the mitochondrial mass and oxidative stress in fibrosarcoma cells. There are substantial concerns that extended exposure to weak RF fields can lead to health effects. The ability to control these parameters by external magnetic fields may have important clinical implications.

Metal selenide nanomaterials for biomedical applications

Metal selenide nanomaterials have received enormous attention as they possess diverse compositions, microstructures, and properties. The combination of selenium with various metallic elements gives the metal selenide nanomaterials distinctive optoelectronic and magnetic properties, such as strong near-infrared absorption, excellent imaging properties, good stability, and long in vivo circulation. This makes metal selenide nanomaterials advantageous and promising for biomedical applications. This paper summarizes the research progress in the last five years in the controlled synthesis of metal selenide nanomaterials in different dimensions and with different compositions and structures. Then we discuss how surface modification and functionalization strategies are well-suited for biomedical fields, including tumor therapy, biosensing, and antibacterial biological applications. The future trends and issues of metal selenide nanomaterials in the biomedical field are also discussed.

Comparative proteomic analysis of the mitochondria of menstrual stem cells and ovarian cancer cells

Mitochondrial transplantation is a popular field of research in cell-free therapy. Menstrual stem cells (MenSCs) are potential donor cells for provision of foreign mitochondria. The present study aimed to investigate the potential effects of MenSC-derived mitochondria on ovarian cancer from the perspective of protein expression profiling. MenSCs were harvested from menstrual blood. The mitochondria were isolated from MenSCs and ovarian cancer cell line SKOV3. A label-free mitochondria proteomics and analysis were performed by comparing the protein expression in mitochondria of MenSCs and SKOV3 cells. The differentially expressed proteins with fold-change >2 were analyzed by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway and protein domain enrichment, protein interaction networks and parallel reaction monitoring (PRM) analysis. In total, 592 proteins that were found to have increased expression in the mitochondria of MenSCs were analyzed. Functional enrichment analysis revealed these proteins were enriched in metabolism-associated pathway entries including 'oxidative phosphorylation' (OXPHOS) pathway. PRM analysis confirmed that four of 6 candidate proteins in the OXPHOS pathway showed similar increasing trends. The protein domain enrichment analysis showed that domains such as 'thioredoxin domain' were significantly enriched. Based on these findings, it was hypothesized that mitochondria from MenSCs have the potential to enhance progression of ovarian cancer likely mediated by the enrichment of OXPHOS-associated metabolic pathways.

Synergistic Combination of Luteolin and Asiatic Acid on Cervical Cancer In Vitro and In Vivo

Cervical cancer is an important issue globally because it is the second most common gynecological malignant tumor and conventional treatment effects have been shown to be limited. Lut and AsA are plant-derived natural flavonoid and triterpenoid products that have exhibited anticancer activities and can modulate various signaling pathways. Thus, the aim of the present study was to evaluate whether Lut combined with AsA could enhance the anticancer effect to inhibit cervical cancer cell proliferation and examine the underlying molecular mechanisms in vitro and in vivo. The results of a CCK-8 assay showed that Lut combined with AsA more effectively inhibited the proliferation of CaSki and HeLa cells than Lut or AsA treatment alone. Lut combined with AsA caused apoptosis induction and sub-G1-phase arrest in CaSki and HeLa cells, as confirmed by flow cytometry, mitoROS analysis, antioxidant activity measurement and western blot assay. In addition, Lut combined with AsA significantly inhibited the cell migration ability of CaSki and HeLa cells in a wound-healing assay. Furthermore, Lut combined with AsA induced apoptosis and inhibited migration through downregulated PI3K/AKT (PI3K, AKT and p70S6K), JNK/p38 MAPK and FAK (integrin β1, paxillin and FAK) signaling and upregulated ERK signaling. In an in vivo study, Lut combined with AsA markedly inhibited cervical cancer cell-derived xenograft tumor growth. Collectively, the present study showed that Lut combined with AsA may be used as an anticancer agent to improve the prognosis of cervical cancer. Indeed, with additional research to develop standardized dosages, Lut and AsA combination therapy could also be applied in clinical medicine.

Targeting Mitochondrial Metabolism to Reverse Radioresistance: An Alternative to Glucose Metabolism

Radiotherapy failure and poor tumor prognosis are primarily attributed to radioresistance. Improving the curative effect of radiotherapy and delaying cancer progression have become difficult problems for clinicians. Glucose metabolism has long been regarded as the main metabolic process by which tumor cells meet their bioenergetic and anabolic needs, with the complex interactions between the mitochondria and tumors being ignored. This misconception was not dispelled until the early 2000s; however, the cellular molecules and signaling pathways involved in radioresistance remain incompletely defined. In addition to being a key metabolic site that regulates tumorigenesis, mitochondria can influence the radiation effects of malignancies by controlling redox reactions, participating in oxidative phosphorylation, producing oncometabolites, and triggering apoptosis. Therefore, the mitochondria are promising targets for the development of novel anticancer drugs. In this review, we summarize the internal relationship and related mechanisms between mitochondrial metabolism and cancer radioresistance, thus exploring the possibility of targeting mitochondrial signaling pathways to reverse radiation insensitivity. We suggest that attention should be paid to the potential value of mitochondria in prolonging the survival of cancer patients.

Reduced Nucleotides, Thiols and O2 in Cellular Redox Balance: A Biochemist's View

In the present review, which is aimed at researchers, teachers and students in life sciences, we try to show how the physicochemical properties of the elements and molecules define the concept of redox balance. Living organism are open systems traversed by fluxes of energy and matter. During catabolic oxidative metabolism, matter-mostly hydrogenated organic molecules-is oxidized and ultimately released as CO₂. Electrons are passed over to coupling molecules, such as NAD+ and FAD, whose reduced forms serve as electrons donors in anabolic reactions. Early photosynthetic activity led to the accumulation of O₂ and the transformation of the reduction to an oxidizing atmosphere, favoring the development of oxidative metabolism in living organisms. We focus on the specific properties of O₂ that provide the chemical energy for the combustion reactions occurring in living cells. We explain the concepts of redox potential and redox balance in complex systems such as living cells, we present the main redox couples involved in cellular redox balance and we discuss the chemical properties underlying their cellular roles and, in particular, their antioxidant properties in the defense against reactive oxygen species (ROS). Finally, we try to provide an integrative view emphasizing the interplay between metabolism, oxidative stress and metabolic compartmentation in mammalian cells.

MitoQ Inhibits Human Breast Cancer Cell Migration, Invasion and Clonogenicity

To successfully generate distant metastases, metastatic progenitor cells must simultaneously possess mesenchymal characteristics, resist to anoïkis, migrate and invade directionally, resist to redox and shear stresses in the systemic circulation, and possess stem cell characteristics. These cells primarily originate from metabolically hostile areas of the primary tumor, where oxygen and nutrient deprivation, together with metabolic waste accumulation, exert a strong selection pressure promoting evasion. Here, we followed the hypothesis according to which metastasis as a whole implies the existence of metabolic sensors. Among others, mitochondria are singled out as a major source of superoxide that supports the metastatic phenotype. Molecularly, stressed cancer cells increase mitochondrial superoxide production, which activates the transforming growth factor-β pathway through src directly within mitochondria, ultimately activating focal adhesion kinase Pyk2. The existence of mitochondria-targeted antioxidants constitutes an opportunity to interfere with the metastatic process. Here, using aggressive triple-negative and HER2-positive human breast cancer cell lines as models, we report that MitoQ inhibits all the metastatic traits that we tested in vitro. Compared to other mitochondria-targeted antioxidants, MitoQ already successfully passed Phase I safety clinical trials, which provides an important incentive for future preclinical and clinical evaluations of this drug for the prevention of breast cancer metastasis.

MitoQ Prevents Human Breast Cancer Recurrence and Lung Metastasis in Mice

Simple Summary

Entry in the metastatic phase is often devastating for cancer patients. Metastases originate from metastatic progenitor cells that are selected in the primary tumor and which simultaneously possess several phenotypic capabilities, including migration, invasion, and clonogenicity. We previously provided in vitro evidence that these features are collectively enforced by mitochondrial superoxide in a paradigm where mitochondria act as metabolic sensors of the tumor microenvironment and produce subcytotoxic levels of superoxide to prime metastatic progenitor cells. We also showed that these metastatic traits can be collectively countered by MitoQ, a mitochondria-targeted antioxidant that selectively deactivates mitochondrial superoxide. Here, we further establish that MitoQ prevents primary tumor recurrence after surgery, tumor take and metastasis as a whole, notably in a model of human breast cancer in mice. Since MitoQ already successfully passed Phase I clinical trials, our findings support the development of this drug as a preventive treatment against breast cancer metastasis.

Abstract

In oncology, the occurrence of distant metastases often marks the transition from curative to palliative care. Such outcome is highly predictable for breast cancer patients, even if tumors are detected early, and there is no specific treatment to prevent metastasis. Previous observations indicated that cancer cell mitochondria are bioenergetic sensors of the tumor microenvironment that produce superoxide to promote evasion. Here, we tested whether mitochondria-targeted antioxidant MitoQ is capable to prevent metastasis in the MDA-MB-231 model of triple-negative human breast cancer in mice and in the MMTV-PyMT model of spontaneously metastatic mouse breast cancer. At clinically relevant doses, we report that MitoQ not only prevented metastatic take and dissemination, but also local recurrence after surgery. We further provide in vitro evidence that MitoQ does not interfere with conventional chemotherapies used to treat breast cancer patients. Since MitoQ already successfully passed Phase I safety clinical trials, our preclinical data collectively provide a strong incentive to test this drug for the prevention of cancer dissemination and relapse in clinical trials with breast cancer patients.

Ginsenoside Rh2 stimulates the production of mitochondrial reactive oxygen species and induces apoptosis of cervical cancer cells by inhibiting mitochondrial electron transfer chain complex

Ginsenoside Rh2 (G-Rh2) is a monomeric compound that extracted from ginseng and possesses anti-cancer activities both in vitro and in vivo. Previously, we reported that G-Rh2 induces apoptosis in HeLa cervical cancer cells and that the process was related to reactive oxygen species (ROS) accumulation and mitochondrial dysfunction. However, the upstream mechanisms of G-Rh2, along with its cellular targets, remain to be elucidated. In the present study, the Cell Counting Kit-8 assay, flow cytometry and Hoechst staining revealed that G-Rh2 significantly inhibited cell viability and induced apoptosis of cervical cancer cells. However, G-Rh2 was demonstrated to be non-toxic to End1/e6e7 cells. JC-1, rhodamine 123 staining, oxidative phosphorylation and glycolysis capacity assays demonstrated that G-Rh2 exposure caused an immediate decrease in mitochondrial transmembrane potential due to its inhibition of mitochondrial oxidative phosphorylation, as well as glycolysis, both of which reduced cellular ATP production. Western blotting and electron transport chain (ETC) activity assays revealed that G-Rh2 significantly inhibited the activity of ETC complexes I, III and V. Overexpression of ETC complex III partially significantly restored mitochondrial ROS and inhibited the apoptosis of cervical cancer cells induced by G-Rh2. The predicted results of binding energy in molecular docking, confirmed that G-Rh2 was highly likely to induce mitochondrial ROS production and promote cell apoptosis by targeting the ETC complex, especially for ETC complex III. Taken together, the present results revealed the potential anti-cervical cancer activity of G-Rh2 and provide direct evidence for the contribution of impaired ETC complex activity to cervical cancer cell death.

Metformin Potentiates the Anticancer Effect of Everolimus on Cervical Cancer In Vitro and In Vivo

Simple Summary

Recent studies have shown that metformin combined with clinical chemotherapeutic drugs could cause decreased cell toxicity and attenuate tumor resistance in various types of cancer. The aim of the present study was to elucidate whether combined treatment with metformin and everolimus has a synergistic anticancer effect in human cervical cancer in vitro and in vivo. The results showed that this combined treatment synergistically inhibited the growth of human cervical cancer cell lines and xenografts in nude mice, and induced caspase-dependent apoptosis, promoting sub-G1- and G0/G1-phase arrest and enhancing mtROS production. Combined treatment also synergistically inactivated PI3K/AKT signaling and activated MAPKs signaling in cervical cancer. Our data suggested that metformin potentiates the anticancer effect of everolimus on cervical cancer, and combined treatment provides a novel therapeutic strategy for patients with cervical cancer.

Abstract

Cervical cancer is globally the fourth most common cancer in women. Metformin is a widely used drug for the treatment of type II diabetes and has been shown to possess important anticancer properties in cervical cancer. Everolimus is an mTOR inhibitor and is widely used to treat NETs, RCC, TSC, and breast cancers. The present study investigated the anticancer effects of metformin and everolimus in cervical cancer, when used alone or in combination. CaSki and C33A human cervical cancer cells were treated with different concentrations of everolimus alone or in combination with metformin. Cell viability was assessed using a CCK-8 assay. Cell apoptosis, cell-cycle, and mtROS analyses were conducted using flow cytometry. Target protein levels were analyzed by Western blotting. Related mechanisms were confirmed using appropriate inhibitors (z-VAD-fmk and BIRB796). The in vitro results were further confirmed in a xenograft tumor study. Both metformin and everolimus, when used alone, were moderately effective in inhibiting cell proliferation and inducing cell apoptosis of CaSki and C33A cells. When used in combination, these two drugs synergistically inhibited the growth of human cervical cancer cells and xenografts in nude mice, promoted sub-G1- and G0/G1-phase cell-cycle arrest, and enhanced mtROS production. The protein expressions of PI3K (p110α) and p-AKT were significantly downregulated, while P27, P21, p-p38, p-ERK, and p-JNK were upregulated following combined treatment. These results revealed that metformin potentiates the anticancer effect of everolimus on cervical cancer, and combination treatment with metformin and everolimus provides a novel therapeutic strategy for patients with cervical cancer.

Antioxidant activity of sulfated Porphyra yezoensis polysaccharides and their regulating effect on calcium oxalate crystal growth

The nucleation, growth and aggregation of calcium oxalate (CaOx) crystals and the oxidative damage of renal tubular epithelial cells are the key factors to induce kidney stones. In this study, degraded Porphyra yezoensis polysaccharide (PYP0) with 14.14% sulfate group (-OSO₃^-) content was modified via the sulfur trioxide-pyridine method to obtain three kinds of sulfated P. yezoensis polysaccharides (PYPs), namely, PYPS1, PYPS2, and PYPS3, with -OSO₃^- group contents of 17.11%, 20.28%, and 27.14% respectively. Fourier transform infrared spectroscopy, ¹H NMR, and ¹³C NMR analyses showed that the -OSO₃^- groups replaced the hydroxyl groups at the C2, C4, and C6 positions on (1 → 3)-linked β-D-galactose, the basic structural skeleton unit of PYP0. The antioxidant activity of the PYPSs increased after sulfation, and their scavenging capacity for OH and DPPH free radicals was enhanced with the increase in their -OSO₃^- group content. Calcium oxalate (CaOx) crystal growth experiments showed that sulfated PYPs promoted the conversion of the thermodynamically stable and sharp CaOx monohydrate (COM) crystals into the thermodynamically unstable and round CaOx dihydrate crystals. With the increase in the -OSO₃^- group content of the polysaccharides, the concentration of soluble Ca²⁺ ions in the supernatant increased and the amount of CaOx precipitate decreased. PYPs were nontoxic to human kidney proximal tubular epithelial cells (HK-2) and could protect HK-2 from oxidative damage caused by nano-COM and reduce the level of reactive oxygen species in cells. PYPS3, which had the highest degree of sulfation, had the best protective capability. The results of this work showed that sulfation improved the biological activity of PYPs. This study could provide inspiration for the development of new drugs for the prevention and treatment of kidney stones.

Exploring Molecular Approaches in Amyotrophic Lateral Sclerosis: Drug Targets from Clinical and Pre-Clinical Findings

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease (MND) characterized by the death of upper and lower motor neurons (corticospinal tract) in the motor cortex, basal ganglia, brain stem, and spinal cord. The patient experiences the sign and symptoms between 55 to 75 years of age, which include impaired motor movement, difficulty in speaking and swallowing, grip loss, muscle atrophy, spasticity, and sometimes associated with memory and cognitive impairments. Median survival is 3 to 5 years after diagnosis and 5 to 10% of the patients live for more than 10 years. The limited intervention of pharmacologically active compounds, that are used clinically, is majorly associated with the narrow therapeutic index. Pre-clinically established experimental models, where neurotoxin methyl mercury mimics the ALS like behavioural and neurochemical alterations in rodents associated with neuronal mitochondrial dysfunctions and downregulation of adenyl cyclase mediated cAMP/CREB, is the main pathological hallmark for the progression of ALS in central as well in the peripheral nervous system. Despite the considerable investigation into neuroprotection, it still constrains treatment choices to strong care and organization of ALS complications. Therefore, this current review specially targeted the investigation of clinical and pre-clinical features available for ALS to understand the pathogenic mechanisms and to explore the pharmacological interventions associated with the up-regulation of intracellular adenyl cyclase/cAMP/ CREB and activation of mitochondrial-ETC coenzyme-Q10 as a future drug target in the amelioration of ALS mediated motor neuronal dysfunctions.

Hereditary Leiomyomatosis and Renal Cell Cancer: Recent Insights Into Mechanisms and Systemic Treatment

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is a rare autosomal dominant hereditary cancer syndrome characterized by a predisposition to cutaneous leiomyomas, uterine leiomyomas, and renal cell carcinoma (RCC). It is known to be caused by germline mutations of the fumarate hydratase (FH) gene, which encodes an enzyme component of the citric acid cycle and catalyzes the conversion of fumarate to L-malate. Currently, there is no standardized treatment for HLRCC, which may be due in part to a lack of understanding of the underlying mechanisms. Here, the underlying molecular mechanisms by which the inactivation of FH causes HLRCC are discussed. Additionally, potential therapeutic pharmacological strategies are also summarized to provide new perspectives for the prevention and treatment of HLRCC.

Hypoxia Signaling in Cancer: From Basics to Clinical Practice

Cancer hypoxia, recognized as one of the most important hallmarks of cancer, affects gene expression, metabolism and ultimately tumor biology-related processes. Major causes of cancer hypoxia are deficient or inappropriate vascularization and systemic hypoxia of the patient (frequently induced by anemia), leading to a unique form of genetic reprogramming by hypoxia induced transcription factors (HIF). However, constitutive activation of oncogene-driven signaling pathways may also activate hypoxia signaling independently of oxygen supply. The consequences of HIF activation in tumors are the angiogenic phenotype, a novel metabolic profile and the immunosuppressive microenvironment. Cancer hypoxia and the induced adaptation mechanisms are two of the major causes of therapy resistance. Accordingly, it seems inevitable to combine various therapeutic modalities of cancer patients by existing anti-hypoxic agents such as anti-angiogenics, anti-anemia therapies or specific signaling pathway inhibitors. It is evident that there is an unmet need in cancer patients to develop targeted therapies of hypoxia to improve efficacies of various anti-cancer therapeutic modalities. The case has been opened recently due to the approval of the first-in-class HIF2α inhibitor.

Mitochondrial Transfer in Cancer: A Comprehensive Review

Depending on their tissue of origin, genetic and epigenetic marks and microenvironmental influences, cancer cells cover a broad range of metabolic activities that fluctuate over time and space. At the core of most metabolic pathways, mitochondria are essential organelles that participate in energy and biomass production, act as metabolic sensors, control cancer cell death, and initiate signaling pathways related to cancer cell migration, invasion, metastasis and resistance to treatments. While some mitochondrial modifications provide aggressive advantages to cancer cells, others are detrimental. This comprehensive review summarizes the current knowledge about mitochondrial transfers that can occur between cancer and nonmalignant cells. Among different mechanisms comprising gap junctions and cell-cell fusion, tunneling nanotubes are increasingly recognized as a main intercellular platform for unidirectional and bidirectional mitochondrial exchanges. Understanding their structure and functionality is an important task expected to generate new anticancer approaches aimed at interfering with gains of functions (e.g., cancer cell proliferation, migration, invasion, metastasis and chemoresistance) or damaged mitochondria elimination associated with mitochondrial transfer.

Mitochondrial Reactive Oxygen Species and Mitophagy: A Complex and Nuanced Relationship

Significance: Mitochondria represent a major source of intracellular reactive oxygen species (ROS) generation. This is often a consequence of oxidative phosphorylation, which can produce ROS as a result of leakage from the electron transport chain. In addition, quality control mechanisms exist to protect cells from cytotoxic ROS production. One such mechanism is selective autophagic degradation of ROS-producing mitochondria, termed mitophagy, that ultimately results in elimination of mitochondria in the lysosome. Recent Advances: However, while the relationship between mitophagy and ROS production is clearly interwoven, it is yet to be fully untangled. In some circumstances, mitochondrial ROS (mtROS) are elevated as a consequence of mitophagy induction. Critical Issues: In this review, we discuss mtROS generation and their detrimental effects on cellular viability. In addition, we consider the cellular defense mechanisms that the eukaryotic cell uses to abrogate superfluous oxidative stress. In particular, we delve into the prominent mechanisms governing mitophagy induction that bear on oxidative stress. Future Directions: Finally, we examine the pathological conditions associated with defective mitophagy, where additional research may help to facilitate understanding.

The Impact of Mitochondrial Fission-Stimulated ROS Production on Pro-Apoptotic Chemotherapy

Cancer is one of the world's deadliest afflictions. Despite recent advances in diagnostic and surgical technologies, as well as improved treatments of some individual tumor types, there is currently no universal cure to prevent or impede the uncontrolled proliferation of malignant cells. Targeting tumors by inducing apoptosis is one of the pillars of cancer treatment. Changes in mitochondrial morphology precede intrinsic apoptosis, but mitochondrial dynamics has only recently been recognized as a viable pharmacological target. In many cancers, oncogenic transformation is accompanied by accumulation of elevated cellular levels of ROS leading to redox imbalance. Hence, a common chemotherapeutic strategy against such tumor types involves deploying pro-oxidant agents to increase ROS levels above an apoptotic death-inducing threshold. The aim of this chapter is to investigate the benefit of stimulating mitochondrial fission-dependent production of ROS for enhanced killing of solid tumors. The main question to be addressed is whether a sudden and abrupt change in mitochondrial shape toward the fragmented phenotype can be pharmacologically harnessed to trigger a burst of mitochondrial ROS sufficient to initiate apoptosis specifically in cancer cells but not in non-transformed healthy tissues.

A versatile EPR toolbox for the simultaneous measurement of oxygen consumption and superoxide production

In this paper, we describe an assay to analyze simultaneously the oxygen consumption rate (OCR) and superoxide production in a biological system. The analytical set-up uses electron paramagnetic resonance (EPR) spectroscopy with two different isotopically-labelled sensors: ¹⁵N-PDT (4-oxo-2,2,6,6-tetramethylpiperidine-d₁₆-¹⁵N-1-oxyl) as oxygen-sensing probe and ¹⁴N-CMH (1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine, a cyclic hydroxylamine, as sensor of reactive oxygen species (ROS). The superoxide contribution to CMH oxidation is assessed using SOD or PEGSOD as controls. Because the EPR spectra are not superimposable, the variation of EPR linewidth of ¹⁵N-PDT (linked to OCR) and the formation of the nitroxide from ¹⁴N-CMH (linked to superoxide production) can be recorded simultaneously over time on a single preparation. The EPR toolbox was qualified in biological systems of increasing complexity. First, we used an enzymatic assay based on the hypoxanthine (HX)/xanthine oxidase (XO) which is a well described model of oxygen consumption and superoxide production. Second, we used a cellular model of superoxide production using macrophages exposed to phorbol 12-myristate 13-acetate (PMA) which stimulates the NADPH oxidase (NOX) to consume oxygen and produce superoxide. Finally, we exposed isolated mitochondria to established inhibitors of the electron transport chain (rotenone and metformin) in order to assess their impact on OCR and superoxide production. This EPR toolbox has the potential to screen the effect of intoxicants or drugs targeting the mitochondrial function.

•

OCR and superoxide production are crucial to assess mitochondrial (dys)function.

•

The EPR toolbox analyzes simultaneously the OCR and superoxide production.

•

The EPR toolbox was validated in enzymatic system, cells and isolated mitochondria.

•

The EPR toolbox has the potential to screen compounds altering mitochondrial function.

Targeting Mitochondrial Singlet Oxygen Dynamics Offers New Perspectives for Effective Metabolic Therapies of Cancer

The occurrence of mitochondrial respiration has allowed evolution toward more complex and advanced life forms. However, its dysfunction is now also seen as the most probable cause of one of the biggest scourges in human health, cancer. Conventional cancer treatments such as chemotherapy, which mainly focus on disrupting the cell division process, have shown being effective in the attenuation of various cancers but also showing significant limits as well as serious sides effects. Indeed, the idea that cancer is a metabolic disease with mitochondria as the central site of the pathology is now emerging, and we provide here a review supporting this "novel" hypothesis re-actualizing past century Otto Warburg's thoughts. Our conclusion, while integrating literature, is that mitochondrial activity and, in particular, the activity of cytochrome c oxidase, complex IV of the ETC, plays a fundamental role in the effectiveness or non-effectiveness of chemotherapy, immunotherapy and probably radiotherapy treatments. We therefore propose that cancer cells mitochondrial singlet oxygen (¹O₂) dynamics may be an efficient target for metabolic therapy development.

Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

Photodynamic therapy (PDT) is an effective and promising cancer treatment. PDT directly generates reactive oxygen species (ROS) through photochemical reactions. This oxygen-dependent exogenous ROS has anti-cancer stem cell (CSC) effect. In addition, PDT may also increase ROS production by altering metabolism, endoplasmic reticulum stress, or potential of mitochondrial membrane. It is known that the half-life of ROS in PDT is short, with high reactivity and limited diffusion distance. Therefore, the main targeting position of PDT is often the subcellular localization of photosensitizers, which is helpful for us to explain how PDT affects CSC characteristics, including differentiation, self-renewal, apoptosis, autophagy, and immunogenicity. Broadly speaking, excess ROS will damage the redox system and cause oxidative damage to molecules such as DNA, change mitochondrial permeability, activate unfolded protein response, autophagy, and CSC resting state. Therefore, understanding the molecular mechanism by which ROS affect CSCs is beneficial to improve the efficiency of PDT and prevent tumor recurrence and metastasis. In this article, we review the effects of two types of photochemical reactions on PDT, the metabolic processes, and the biological effects of ROS in different subcellular locations on CSCs.

Mitochondria Participate in Chemoresistance to Cisplatin in Human Ovarian Cancer Cells

Ovarian cancer is an aggressive disease that affects about 300,000 patients worldwide, with a yearly death count of about 185,000. Following surgery, treatment involves adjuvant or neoadjuvant administration of taxane with platinum compounds cisplatin or carboplatin, which alkylate DNA through the same chemical intermediates. However, although platinum-based therapy can cure patients in a number of cases, a majority of them discontinues treatment owing to side effects and to the emergence of resistance. In this study, we focused on resistance to cisplatin and investigated whether metabolic changes could be involved. As models, we used matched pairs of cisplatin-sensitive (SKOV-3 and COV-362) and cisplatin-resistant (SKOV-3-R and COV-362-R) human ovarian carcinoma cells that were selected in vitro following exposure to increasing doses of the chemotherapy. Metabolic comparison revealed that resistant cells undergo a shift toward a more oxidative metabolism. The shift goes along with a reorganization of the mitochondrial network, with a generally increased mitochondrial compartment. More functional mitochondria in cisplatin-resistant compared with cisplatin-sensitive cells were associated to enzymatic changes affecting either the electron transport chain (SKOV-3/SKOV-3-R model) or mitochondrial coupling (COV-362/COV-362-R model). Our findings further indicate that the preservation of functional mitochondria in these cells could be due to an increased mitochondrial turnover rate, suggesting mitophagy inhibition as a potential strategy to tackle cisplatin-resistant human ovarian cancer progression. IMPLICATIONS: Besides classical mechanisms related to drug efflux and target modification, we report that preserving functional mitochondria is a strategy used by human ovarian cancer cells to resist to cisplatin chemotherapy.

Mitochondrial Dysfunction at the Center of Cancer Therapy

Significance: Mitochondria undergo constant morphological changes through fusion, fission, and mitophagy. As the key organelle in cells, mitochondria are responsible for numerous essential cellular functions such as metabolism, regulation of calcium (Ca²⁺), generation of reactive oxygen species, and initiation of apoptosis. Unsurprisingly, mitochondrial dysfunctions underlie many pathologies including cancer. Recent Advances: Currently, the gold standard for cancer treatment is chemotherapy, radiation, and surgery. However, the efficacy of these treatments varies across different cancer cells. It has been suggested that mitochondria may be at the center of these diverse responses. In the past decade, significant advances have been made in understanding distinct types of mitochondrial dysfunctions in cancer. Through investigations of underlying mechanisms, more effective treatment options are developed. Critical Issues: We summarize various mitochondria dysfunctions in cancer progression that have led to the development of therapeutic options. Current mitochondrial-targeted therapies and challenges are discussed. Future Directions: To address the "root" of cancer, utilization of mitochondrial-targeted therapy to target cancer stem cells may be valuable. Investigation of other areas such as mitochondrial trafficking may offer new insights into cancer therapy. Moreover, common antibiotics could be explored as mitocans, and synthetic lethality screens can be utilized to overcome the plasticity of cancer cells.

The Role of Nrf2 signaling in cancer stem cells: From stemness and self-renewal to tumorigenesis and chemoresistance

Cancer stem cells (CSCs) are subpopulation of tumor mass with exclusive abilities in self-renewing, stemness maintaining, and differentiation into the various non-stem cancer cells to provoke tumorigenesis, metastasis dissemination, drug-resistant, and cancer recurrence. Reactive oxygen species (ROS) impair cellular function by oxidizing cell components containing proteins, lipids, and DNA. Tumor oxidant status is elevated due to high metabolic activity under influence of abnormal growth factors, cytokines and function ROS-producing enzymes, including nitric oxide synthases, cyclooxygenases, and lipoxygenases. Nuclear factor-erythroid 2-related factor 2 (NRF2) is a transcriptional master regulator element which is believed to recognize cellular oxidative stress followed by binding to promoter of cyto-protective and anti-oxidative genes to maintain cellular redox status through promoting antioxidant response participants (glutathione peroxidase, glutathione reductase, thioredoxin reductase, ferritin, NADPH: quinone oxidoreductase 1). However, Nrf2 signaling protects malignant cells from ROS damage against tumor growth and chemoresistance. In addition, Nrf2 is able to participate in differentiation of certain stem cells by modulating autophagy procedure, also NRF2 provokes DNA damage response and facilitates drug metabolism and drug resistance by controlling of downstream enzyme and transporter members. In this review, we discuss the role of NRF2 in stemness, self-renewal ability, tumorigenesis and chemoresistance of CSCs.

The impact of aneuploidy on cellular homeostasis

Genomic instability is a common feature of tumours that has a wide range of disruptive effects on cellular homeostasis. In this review we briefly discuss how instability comes about, then focus on the impact of gain or loss of DNA (aneuploidy) on oxidative stress. We discuss several mechanisms that lead from aneuploidy to the production of reactive oxygen species, including the effects on protein complex stoichiometry, endoplasmic reticulum stress and metabolic disruption. Each of these are involved in positive feedback loops that amplify relatively minor genetic changes into major cellular disruption or cell death, depending on the capacity of the cell to induce antioxidants or processes such as mitophagy that can moderate the disruption. Finally we examine the direct effects of reactive oxygen species on mitosis and how oxidative stress can compromise centrosome number, cytoskeletal integrity and signalling processes that are vital for mitotic fidelity.

mTORC1 as a Regulator of Mitochondrial Functions and a Therapeutic Target in Cancer

Continuous proliferation of tumor cells requires constant adaptations of energy metabolism to rapidly fuel cell growth and division. This energetic adaptation often comprises deregulated glucose uptake and lactate production in the presence of oxygen, a process known as the "Warburg effect." For many years it was thought that the Warburg effect was a result of mitochondrial damage, however, unlike this proposal tumor cell mitochondria maintain their functionality, and is essential for integrating a variety of signals and adapting the metabolic activity of the tumor cell. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of numerous cellular processes implicated in proliferation, metabolism, and cell growth. mTORC1 controls cellular metabolism mainly by regulating the translation and transcription of metabolic genes, such as peroxisome proliferator activated receptor γ coactivator-1 α (PGC-1α), sterol regulatory element-binding protein 1/2 (SREBP1/2), and hypoxia inducible factor-1 α (HIF-1α). Interestingly it has been shown that mTORC1 regulates mitochondrial metabolism, thus representing an important regulator in mitochondrial function. Here we present an overview on the role of mTORC1 in the regulation of mitochondrial functions in cancer, considering new evidences showing that mTORC1 regulates the translation of nucleus-encoded mitochondrial mRNAs that result in an increased ATP mitochondrial production. Moreover, we discuss the relationship between mTORC1 and glutaminolysis, as well as mitochondrial metabolites. In addition, mitochondrial fission processes regulated by mTORC1 and its impact on cancer are discussed. Finally, we also review the therapeutic efficacy of mTORC1 inhibitors in cancer treatments, considering its use in combination with other drugs, with particular focus on cellular metabolism inhibitors, that could help improve their anti neoplastic effect and eliminate cancer cells in patients.