Targeting mitochondria as a therapeutic target in cancer

Mitochondrial bioenergetics of breast cancer

Breast cancer cells exhibit metabolic heterogeneity based on tumour aggressiveness. Glycolysis and mitochondrial respiration are two major metabolic pathways for ATP production. The oxygen flux, oxygen tension, proton leakage, protonmotive force, inner mitochondrial membrane potential, ECAR and electrochemical proton gradient maintain metabolic homeostasis, ATP production, ROS generation, heat dissipation, and carbon flow and are referred to as "sub-domains" of mitochondrial bioenergetics. Tumour aggressiveness is influenced by these mechanisms, especially when breast cancer cells undergo metastasis. These physiological parameters for healthy mitochondria are as crucial as energy demands for tumour growth and metastasis. The instant energy demands are already elucidated under Warburg effects, while these parameters may have dual functionality to maintain cellular bioenergetics and cellular health. The tumour cell might maintain these mitochondrial parameters for mitochondrial health or avoid apoptosis, while energy production could be a second priority. This review focuses explicitly on the crosstalk between metabolic domains and the utilisation of these parameters by breast cancer cells for their progression. Some major interventions are discussed based on mitochondrial bioenergetics that need further investigation. This review highlights the pathophysiological significance of mitochondrial bioenergetics and the regulation of its sub-domains by breast tumour cells for uncontrolled proliferation.

Peripheral CX3CR1+ T cells combined with PD-1 blockade therapy potentiates the anti-tumor efficacy for lung cancer

Identifying tumor-relevant T cell subsets in the peripheral blood (PB) has become a potential strategy for cancer treatment. However, the subset of PB that could be used to treat cancer remains poorly defined. Here, we found that the CX3CR1+ T cell subset in the blood of patients with lung cancer exhibited effector properties and had a higher TCR matching ratio with tumor-infiltrating lymphocytes (TILs) compared to CX3CR1- T cells, as determined by paired single-cell RNA and TCR sequencing. Meanwhile, the anti-tumor activities, effector cytokine production, and mitochondrial function were enhanced in CX3CR1+ T cells both in vitro and in vivo. However, in the co-culture system of H322 cells with T cells, the percentages of apoptotic cells and Fas were substantially higher in CX3CR1+ T cells than those in CX3CR1- T cells. Fas-mediated apoptosis was rescued by treatment with an anti-PD-1 antibody. Accordingly, the combination of adoptive transfer of CX3CR1+ T cells and anti-PD-1 treatment considerably decreased Fas expression and improved the survival of lung xenograft mice. Moreover, an increased frequency of CX3CR1+ T cells in the PB correlated with a better response and prolonged survival of patients with lung cancer who received anti-PD-1 therapy. These findings indicate the promising potential of adoptive transfer of peripheral CX3CR1+ T cells as an individual cancer immunotherapy.

Promising Strategy of mPTP Modulation in Cancer Therapy: An Emerging Progress and Future Insight

Cancer has been progressively a major global health concern. With this developing global concern, cancer determent is one of the most significant public health challenges of this era. To date, the scientific community undoubtedly highlights mitochondrial dysfunction as a hallmark of cancer cells. Permeabilization of the mitochondrial membranes has been implicated as the most considerable footprint in apoptosis-mediated cancer cell death. Under the condition of mitochondrial calcium overload, exclusively mediated by oxidative stress, an opening of a nonspecific channel with a well-defined diameter in mitochondrial membrane allows free exchange between the mitochondrial matrix and the extra mitochondrial cytosol of solutes and proteins up to 1.5 kDa. Such a channel/nonspecific pore is recognized as the mitochondrial permeability transition pore (mPTP). mPTP has been established for regulating apoptosis-mediated cancer cell death. It has been evident that mPTP is critically linked with the glycolytic enzyme hexokinase II to defend cellular death and reduce cytochrome c release. However, elevated mitochondrial Ca2+ loading, oxidative stress, and mitochondrial depolarization are critical factors leading to mPTP opening/activation. Although the exact mechanism underlying mPTP-mediated cell death remains elusive, mPTP-mediated apoptosis machinery has been considered as an important clamp and plays a critical role in the pathogenesis of several types of cancers. In this review, we focus on structure and regulation of the mPTP complex-mediated apoptosis mechanisms and follow with a comprehensive discussion addressing the development of novel mPTP-targeting drugs/molecules in cancer treatment.

Zinc oxide nanoparticles trigger dysfunction of mitochondrial respiratory complexes and repair dynamics in human alveolar cells

Zinc oxide nanoparticles (ZnO NP) are commonly used engineered NPs with extensive usage in consumer products, thus leading to direct exposure to humans. The direct route of exposure is through inhalation. Once inhaled, these particles accumulate in the lungs, increasing the chances of respiratory tract illness through cellular organelle damage. Zinc oxide nanoparticle-treated lung cells are reported to display cytotoxicity, increase DNA damage, and induce oxidative stress. The current study focused on the effects of ZnO NPs on mitochondrial dynamics (fission and fusion) in human lung epithelial cells (A549). The lung cells were exposed to ZnO NPs at 50 and 100 μg/ml concentrations, and their mitochondrial dynamics were assessed to understand the effects of the NPs. Treatment with ZnO NPs reduced the activity of mitochondrial complex I and complex III and altered mitochondrial structural and functional characteristics in a concentration-dependent manner. Zinc oxide nanoparticles exposure showed an increase in small and round-shaped mitochondria. The expression of various fission proteins (Drp1 and Fis1) and fusion proteins (Mfn1, Mfn2, and OPA1) was altered upon exposure to ZnO NPs. Our studies showed dysfunction of the mitochondria induced by ZnO NPs. In fibroblast mitochondrial dynamics, fission symbolizes threshold damage. In this paper, we have shown that the mitochondrial fission phenotype increased upon exposure to ZnO NPs. The paper emphasizes that these particles enter mitochondria, triggering a stress response that results in the removal of mitochondria via fission. It provides relevant data for safety guidelines to ensure the safer use of these particles.

Mitochondria-Shaping Proteins and Chemotherapy

The emergence, in recent decades, of an entirely new area of “Mitochondrial dynamics”, which consists principally of fission and fusion, reflects the recognition that mitochondria play a significant role in human tumorigenesis and response to therapeutics. Proteins that determine mitochondrial dynamics are referred to as “shaping proteins”. Marked heterogeneity has been observed in the response of tumor cells to chemotherapy, which is associated with imbalances in mitochondrial dynamics and function leading to adaptive and acquired resistance to chemotherapeutic agents. Therefore, targeting mitochondria-shaping proteins may prove to be a promising approach to treat chemotherapy resistant cancers. In this review, we summarize the alterations of mitochondrial dynamics in chemotherapeutic processing and the antitumor mechanisms by which chemotherapy drugs synergize with mitochondria-shaping proteins. These might shed light on new biomarkers for better prediction of cancer chemosensitivity and contribute to the exploitation of potent therapeutic strategies for the clinical treatment of cancers.

Structural basis of complex formation between mitochondrial anion channel VDAC1 and Hexokinase-II

Complex formation between hexokinase-II (HKII) and the mitochondrial VDAC1 is crucial to cell growth and survival. We hypothesize that HKII first inserts into the outer membrane of mitochondria (OMM) and then interacts with VDAC1 on the cytosolic leaflet of OMM to form a binary complex. To systematically investigate this process, we devised a hybrid approach. First, we describe membrane binding of HKII with molecular dynamics (MD) simulations employing a membrane mimetic model with enhanced lipid diffusion capturing membrane insertion of its H-anchor. The insertion depth of the H-anchor was then used to derive positional restraints in subsequent millisecond-scale Brownian dynamics (BD) simulations to preserve the membrane-bound pose of HKII during the formation of the HKII/VDAC1 binary complex. Multiple BD-derived structural models for the complex were further refined and their structural stability probed with additional MD simulations, resulting in one stable complex. A major feature in the complex is the partial (not complete) blockade of VDAC1's permeation pathway, a result supported by our comparative electrophysiological measurements of the channel in the presence and absence of HKII. We also show how VDAC1 phosphorylation disrupts HKII binding, a feature that is verified by our electrophysiology recordings and has implications in mitochondria-mediated cell death.

Evidences of a Direct Relationship between Cellular Fuel Supply and Ciliogenesis Regulated by Hypoxic VDAC1-ΔC

Metabolic flexibility is the ability of a cell to adapt its metabolism to changes in its surrounding environment. Such adaptability, combined with apoptosis resistance provides cancer cells with a survival advantage. Mitochondrial voltage-dependent anion channel 1 (VDAC1) has been defined as a metabolic checkpoint at the crossroad of these two processes. Here, we show that the hypoxia-induced cleaved form of VDAC1 (VDAC1-ΔC) is implicated in both the up-regulation of glycolysis and the mitochondrial respiration. We demonstrate that VDAC1-ΔC, due to the loss of the putative phosphorylation site at serine 215, concomitantly with the loss of interaction with tubulin and microtubules, reprograms the cell to utilize more metabolites, favoring cell growth in hypoxic microenvironment. We further found that VDAC1-ΔC represses ciliogenesis and thus participates in ciliopathy, a group of genetic disorders involving dysfunctional primary cilium. Cancer, although not representing a ciliopathy, is tightly linked to cilia. Moreover, we highlight, for the first time, a direct relationship between the cilium and cancer cell metabolism. Our study provides the first new comprehensive molecular-level model centered on VDAC1-ΔC integrating metabolic flexibility, ciliogenesis, and enhanced survival in a hypoxic microenvironment.

Photodynamic therapy on prostate cancer cells involve mitochondria membrane proteins

OBJECTIVE

Photodynamic therapy for prostate cancer has emerged, however the evaluation of its mechanism of action has not yet been clarified. This study aims to explore the mechanism and significance of photodynamic therapy on prostate cancer in vitro.

METHODS

Cultured prostate cancer cells were divided into two groups: untreated and photodynamic therapy treatment. The protein of each group was extracted and analyzed by MALDI-TOF/MSMS method. The significantly expressed proteins were identified in the NCBI human protein database. The change of mitochondrial membrane permeability after photodynamic treatment was examined by transmission electron microscopy.

RESULTS

The total protein content and band distribution of photodynamic treatment group were similar to the control group. Two mitochondrial membrane proteins were down-regulated significantly. They are mitochondrial heat shock protein (HSP60) (Entrez Gene ID: 31542947, PI 5.7, MW: 61016.4, Protein Score: 354, Protein Score C.I.%:100), and voltage-dependent anion channel (VDAC) (Entrez Gene ID: 340201, PI 7.49, MW: 31574.6, Protein Score: 178, Protein Score C.I.%:100). Transmission electron microscopy showed the loss of integrity of mitochondrial membranes.

CONCLUSIONS

Photodynamic therapy changes mitochondrial membrane permeability, leading to the eventual death of cancer cells. The regulation of proteins related to mitochondrial membrane permeability may become an indicator of the efficacy of photodynamic therapy.

A Licorice Roots Extract Induces Apoptosis and Cell Cycle Arrest and Improves Metabolism via Regulating MiRNAs in Liver Cancer Cells

Targeting altered metabolism in cancer provides a promising preventive and therapeutic approach. Natural products interplay between gene expression and metabolism either by targeting altered metabolic enzymes and/or affecting the regulating miRNAs. Licorice is a widely known product used as flavoring agent. Glycyrrhizin and other metabolites were reported to exert several metabolic benefits. Here, we investigated the effect of licorice roots extract on some metabolic pathways and their regulating miRNAs in hepatocellular carcinoma cells. Our data showed various beneficial effects of licorice roots extract including induction of apoptosis and cell cycle arrest. Second, upregulating tumor suppressor miRNAs; let7a-3p, miR-34c-5p, miR-122-5p, miR-126-3p, miR195-5p, miR-199a-5p, miR-206, and miR-326-5p. Third, inhibiting HIF1α, PI3K and C-Myc and activating AMPK and p53. Fourth, inhibiting enzymes of glycolysis; HK-2, LDH-A and PK-M2; pentose phosphate pathway; G6PD and glutaminolysis; glutaminase. However, such an extract upregulated oncogenic miRNAs; miR-21, miR-221, and miR-222. Although the present data highlights the ability of licorice roots extract to enhance apoptosis and cell cycle arrest and correct altered metabolism, it warns against its unfavorable effects, hence, its use for prevention and therapy should proceed with caution. Further experiments are required to investigate whether a specific bioactive ingredient is responsible for upregulating the oncogenic miRNAs.

Combinatory antitumor therapy by cascade targeting of a single drug

Combination therapy has shown its promise in the clinic for enhancing the efficacy of tumor treatment. However, the dose control of multiple drugs and their non-overlapping toxicity from different drugs are still great challenge. In this work, a single model drug, paclitaxel (PTX), is used to realize combination therapy and solve the problems mentioned above. Either PTX or its triphenylphosphine derivative (TPTX) is encapsulated in galactose-modified liposomes (GLips) to obtain GLips-P or GLips-TP, which are simply mixed in different ratios to finely control the proportion of PTX and TPTX. These mixed liposomes, GLips-P/TP, feature a cascade target delivery of PTX, from tissue to cell, and then to organelle. PTX plays a primary role to cause the cytotoxicity by microtubule bindings in cytoplasm, while TPTX is proved to increase the intracellular levels of caspase-3 and caspase-9 that cause apoptosis via a mitochondria-mediated pathway. Notably, GLips-P/TP 3:1 exhibited the significant drug synergy in both cytotoxicity assay of HepG2 cells and the treatment efficacy in Heps xenograft ICR mouse models. This work not only demonstrates the great promise of a cascade targeting delivery for precise tumor treatment, but also offers a novel platform to design combinatory therapy systems using a single drug.

Identification of a new aggressive axis driven by ciliogenesis and absence of VDAC1-ΔC in clear cell Renal Cell Carcinoma patients

Rationale: Renal cell carcinoma (RCC) accounts for about 2% of all adult cancers, and clear cell RCC (ccRCC) is the most common RCC histologic subtype. A hallmark of ccRCC is the loss of the primary cilium, a cellular antenna that senses a wide variety of signals. Loss of this key organelle in ccRCC is associated with the loss of the von Hippel-Lindau protein (VHL). However, not all mechanisms of ciliopathy have been clearly elucidated. Methods: By using RCC4 renal cancer cells and patient samples, we examined the regulation of ciliogenesis via the presence or absence of the hypoxic form of the voltage-dependent anion channel (VDAC1-ΔC) and its impact on tumor aggressiveness. Three independent cohorts were analyzed. Cohort A was from PREDIR and included 12 patients with hereditary pVHL mutations and 22 sporadic patients presenting tumors with wild-type pVHL or mutated pVHL; Cohort B included tissue samples from 43 patients with non-metastatic ccRCC who had undergone surgery; and Cohort C was composed of 375 non-metastatic ccRCC tumor samples from The Cancer Genome Atlas (TCGA) and was used for validation. The presence of VDAC1-ΔC and legumain was determined by immunoblot. Transcriptional regulation of IFT20/GLI1 expression was evaluated by qPCR. Ciliogenesis was detected using both mouse anti-acetylated α-tubulin and rabbit polyclonal ARL13B antibodies for immunofluorescence. Results: Our study defines, for the first time, a group of ccRCC patients in which the hypoxia-cleaved form of VDAC1 (VDAC1-ΔC) induces resorption of the primary cilium in a Hypoxia-Inducible Factor-1 (HIF-1)-dependent manner. An additional novel group, in which the primary cilium is re-expressed or maintained, lacked VDAC1-ΔC yet maintained glycolysis, a signature of epithelial-mesenchymal transition (EMT) and more aggressive tumor progression, but was independent to VHL. Moreover, these patients were less sensitive to sunitinib, the first-line treatment for ccRCC, but were potentially suitable for immunotherapy, as indicated by the immunophenoscore and the presence of PDL1 expression. Conclusion: This study provides a new way to classify ccRCC patients and proposes potential therapeutic targets linked to metabolism and immunotherapy.

The Mitochondrial Genes BAK1, FIS1 and SFN are Linked with Alterations in Mitochondrial Membrane Potential in Barrett's Esophagus

Barrett's esophagus and esophageal cancer lack prognostic markers that allow the tailoring of personalized medicine and biomarkers with potential to provide insight into treatment response. This study aims to characterize mitochondrial function across the metaplasia-dysplasia-adenocarcinoma disease sequence in Barrett's esophagus and examines the functional effect of manipulating mitochondrial genes. Mitochondrial genes of interest were validated in in vitro cell lines across the metaplasia (QH), dysplasia (GO) and adenocarcinoma (OE33) sequence and in in vivo patient tissue samples. These genes were subsequently knocked down in QH and OE33 cells and the functional effect of siRNA-induced knockdown on reactive oxygen species production, mitochondrial mass, mitochondrial membrane potential and cellular metabolism was investigated. Three global mitochondrial genes (BAK1, FIS1 and SFN) were differentially altered across the in vivo Barrett's disease sequence. We also demonstrate that knockdown of BAK1, FIS1 and SFN in vitro resulted in significant alterations in mitochondrial membrane potential; however, no differences in reactive oxygen species or mitochondrial mass were observed. Furthermore, knockdown of these genes in esophageal adenocarcinoma cells significantly altered cellular metabolism. In conclusion, we found that differential expression of BAK1, FIS1, and SFN were altered across the Barrett's disease sequence and manipulation of these genes elicited significant effects on mitochondrial membrane potential.

Filling the Tank: Keeping Antitumor T Cells Metabolically Fit for the Long Haul

Discoveries in tumor immunology and subsequent clinical advances in cancer immunotherapy have revealed that the immune system is not oblivious to tumor progression but heavily interacts with developing neoplasia and malignancy. A major factor preventing immune destruction is the establishment of a highly immunosuppressive tumor microenvironment (TME), which provides architecture to the tumor, supports indirect means of immunosuppression such as the recruitment of tolerogenic cells like regulatory T cells and myeloid-derived suppressor cells (MDSC), and represents a zone of metabolically dearth conditions. T-cell activation and consequent effector function are cellular states characterized by extreme metabolic demands, and activation in the context of insufficient metabolic substrates results in anergy or regulatory differentiation. Thus, T cells must endure both immunosuppression (co-inhibitory molecule ligation, regulatory T cells, and suppressive cytokines) but also a sort of metabolic suppression in the TME. Here I will review the general features of the TME, identify the metabolic demands of activated effector T cells, discuss the known metabolic checkpoints associated with intratumoral T cells, and propose strategies for generating superior antitumor T cells, whether in vitro for adoptive cell therapy or through in vivo reinvigoration of the existing immune response. Cancer Immunol Res; 4(12); 1001-6. ©2016 AACR.

Synthesis and evaluation of 99mTc/Re-tricarbonyl complexes of the triphenylphosphonium cation for mitochondrial targeting

INTRODUCTION

Lipophilic delocalized cations accumulate in tumor cell mitochondria due to their higher transmembrane potential. In this work, this strategy was adopted for the development of ^99mTc tumor-targeted imaging agents.

METHODS

Two tridentate ligands containing the triphenylphosphonium cation, L1 (S-cysteinyl) and L2 (N-iminodiacetate) as well as the respective ^99mTc/ReL1 and ^99mTc/ReL2 tricarbonyl complexes were synthesized. The effect of the ligands and the Re complexes on cell growth in U-87 MG glioblastoma cells was assessed. In vitro stability studies and measurement of logP of the ^99mTc tracers was performed. The cellular and mitochondrial uptake of the ^99mTc tracers in U-87 MG cells was evaluated. Biodistribution of ^99mTcL1 and ^99mTcL2 were performed on SCID mice bearing U-87 MG tumors.

RESULTS

The ligands L1, L2 and the Re1 and ReL2 complexes were characterized spectroscopically. Single products ^99mTcL1 and ^99mTcL2, >90% stable in rat serum, were obtained. LogP was 0.40±0.14 for ^99mTcL1 and -0.02±0.07 for ^99mTcL2. L1, ReL1 and ReL2 caused no notable cytotoxicity and L2 was found to infer 40% inhibition of cellular growth at 10^-5M as well as 80% cell death in culture at 10^-4M. The cell uptake of ^99mTcL1 and ^99mTcL2 over 4h was 1.26±0.08% and 0.06±0.01% respectively, of which 13.41±3.63% and 18.61±6.19% was distributed in the mitochondria respectively. The initial tumor uptake in mice was found to be >1% ID/g for both ^99mTc tracers.

CONCLUSIONS

In vitro mitochondrial and in vivo tumor targeting was observed, better in ^99mTcL1, however these properties should be optimized in future studies. Advances in Knowledge and Implications for Patient Care: Continuous efforts in this direction may lead to a suitable mitochondrial-targeted ^99mTc imaging agent for tumor detection.

Two mutations in mitochondrial ATP6 gene of ATP synthase, related to human cancer, affect ROS, calcium homeostasis and mitochondrial permeability transition in yeast

The relevance of mitochondrial DNA (mtDNA) mutations in cancer process is still unknown. Since the mutagenesis of mitochondrial genome in mammals is not possible yet, we have exploited budding yeast S. cerevisiae as a model to study the effects of tumor-associated mutations in the mitochondrial MTATP6 gene, encoding subunit 6 of ATP synthase, on the energy metabolism. We previously reported that four mutations in this gene have a limited impact on the production of cellular energy. Here we show that two mutations, Atp6-P163S and Atp6-K90E (human MTATP6-P136S and MTATP6-K64E, found in prostate and thyroid cancer samples, respectively), increase sensitivity of yeast cells both to compounds inducing oxidative stress and to high concentrations of calcium ions in the medium, when Om45p, the component of porin complex in outer mitochondrial membrane (OM), was fused to GFP. In OM45-GFP background, these mutations affect the activation of yeast permeability transition pore (yPTP, also called YMUC, yeast mitochondrial unspecific channel) upon calcium induction. Moreover, we show that calcium addition to isolated mitochondria heavily induced the formation of ATP synthase dimers and oligomers, recently proposed to form the core of PTP, which was slower in the mutants. We show the genetic evidence for involvement of mitochondrial ATP synthase in calcium homeostasis and permeability transition in yeast. This paper is a first to show, although in yeast model organism, that mitochondrial ATP synthase mutations, which accumulate during carcinogenesis process, may be significant for cancer cell escape from apoptosis.

Mitochondrial VDAC1: A Key Gatekeeper as Potential Therapeutic Target

Mitochondria are the key source of ATP that fuels cellular functions, and they are also central in cellular signaling, cell division and apoptosis. Dysfunction of mitochondria has been implicated in a wide range of diseases, including neurodegenerative and cardiac diseases, and various types of cancer. One of the key proteins that regulate mitochondrial function is the voltage-dependent anion channel 1 (VDAC1), the most abundant protein on the outer membrane of mitochondria. VDAC1 is the gatekeeper for the passages of metabolites, nucleotides, and ions; it plays a crucial role in regulating apoptosis due to its interaction with apoptotic and anti-apoptotic proteins, namely members of the Bcl-2 family of proteins and hexokinase. Therefore, regulation of VDAC1 is crucial not only for metabolic functions of mitochondria, but also for cell survival. In fact, multiple lines of evidence have confirmed the involvement of VDAC1 in several diseases. Consequently, modulation or dysregulation of VDAC1 function can potentially attenuate or exacerbate pathophysiological conditions. Understanding the role of VDAC1 in health and disease could lead to selective protection of cells in different tissues and diverse diseases. The purpose of this review is to discuss the role of VDAC1 in the pathogenesis of diseases and as a potentially effective target for therapeutic management of various pathologies.

Impact of Diet and Nutrition on Cancer Hallmarks

Diet and nutrition are undeniably two factors that have a major impact on the prevention, progression, and treatment of various cancers. In this review, we will discuss how bioactives from diet and nutritional status affect each of the hallmarks of cancer. We will present recent research and discuss using diet and nutrition as a means to prevent and treat cancer.

Novel mitochondria targeted copper(ii) complexes of ferrocenyl terpyridine and anticancer active 8-hydroxyquinolines showing remarkable cytotoxicity, DNA and protein binding affinity

Mixed-ligand ferrocenyl copper(ii) complexes target the mitochondria of cancer cells showing remarkable cytotoxicity against HeLa and MCF-7 cancer cells while being much less toxic to MCF-10A normal cells.

Mitochondrial dysfunction in cancer chemoprevention by phytochemicals from dietary and medicinal plants

Cancer chemoprevention, a scientific term coined by Dr. Sporn in the late seventies, implies use of natural or synthetic chemicals to block, delay or reverse carcinogenesis. Phytochemicals derived from edible and medicinal plants have been studied rather extensively for cancer chemoprevention using preclinical models in the past few decades. Nevertheless, some of these agents (e.g., isothiocyanates from cruciferous vegetables like broccoli and watercress) have already entered into clinical investigations. Examples of widely studied and highly promising phytochemicals from edible and medicinal plants include cruciferous vegetable constituents (phenethyl isothiocyanate, benzyl isothiocyanate, and sulforaphane), withaferin A (WA) derived from a medicinal plant (Withania somnifera) used heavily in Asia, and an oriental medicine plant component honokiol (HNK). An interesting feature of these structurally-diverse phytochemicals is that they target mitochondria to provoke cancer cell-selective death program. Mechanisms underlying cell death induction by commonly studied phytochemicals have been discussed rather extensively and thus are not covered in this review article. Instead, the primary focus of this perspective is to discuss experimental evidence pointing to mitochondrial dysfunction in cancer chemoprevention by promising phytochemicals.

Overexpressed CISD2 has prognostic value in human gastric cancer and promotes gastric cancer cell proliferation and tumorigenesis via AKT signaling pathway

CDGSH iron sulfur domain 2 (CISD2) is localized in the outer mitochondrial membrane and mediates mitochondrial integrity and lifespan in mammals, but its role in cancer is unknown. In the current study, we reported that CISD2 mRNA and protein expression levels were significantly upregulated in gastric cancer cells compared to normal gastric epithelial cells (P < 0.001). Immunohistochemical analysis of 261 paraffin-embedded archived gastric cancer tissues showed that high CISD2 expression was significantly associated with clinical stage, TNM classifications, venous invasion and lymphatic invasion. Univariate and multivariate analysis indicated that high CISD2 expression was an independent prognostic factor for poorer overall survival in the entire cohort. Overexpressing CISD2 promoted, while silencing CISD2 inhibited, the proliferation of gastric cancer cells. Furthermore, we found that silencing endogenous CISD2 also significantly inhibited the proliferation and tumorigenicity of MGC-803 and SGC-7901 cells not only in vitro but also in vivo in NOD/SCID mice (P < 0.05). Furthermore, we found that CISD2 affected cell proliferation and tumorigenicity of gastric cancer cells through mediating the G1-to-S phase transition. Moreover, we demonstrated that the pro-proliferative effect of CISD2 on gastric cancer cells was associated with downregulation of cyclin-dependent kinase inhibitor p21Cip1 and p27Kip1, and activation of AKT signaling. The findings of this study indicate that CISD2 may promote proliferation and tumorigenicity, potentially representing a novel prognostic marker for overall survival in gastric cancer.

Metabolic Modification in Gastrointestinal Cancer Stem Cells: Characteristics and Therapeutic Approaches

Currently, there is much interest in the characterization of metabolic profiling of cancer stem cells (CSCs), a small subset of tumor cells with self-renewal capacity. Indeed, ever-growing evidence indicate that metabolism and stemness are highly intertwined processes in tumor tissue. In this review, we analyze the potential metabolic targeting strategies for eradicating CSCs that could help to develop a more effective therapeutic approach for gastrointestinal cancers. Indeed, the successful elimination of a tumor requires an anticancer therapy that affects both cancer cells and CSCs. The observation that gastrointestinal CSCs possess higher inducible nitric oxide sinthase (iNOS) expression, lower reactive oxygen species (ROS) production, and a different metabolism respect to no-CSCs tumor cells has paved the way to develop drugs targeting CSC specific signaling. In particular, several studies have highlighted that metformin, aldehyde dehydrogenase 1, and iNOS inhibitors selectively suppressed CSC growth and that combinatorial therapy of them with standard chemotherapeutic drugs had a synergistic effect resulting in reduced tumor burden and delayed tumor recurrence. Thus, the possibility of combining specific CSC metabolism inhibitors with existing therapeutic approaches could have profound anticancer effects, changing the conventional treatment approaches to gastrointestinal cancers. J. Cell. Physiol. 231: 2081-2087, 2016. © 2016 Wiley Periodicals, Inc.

The Tumor Microenvironment Represses T Cell Mitochondrial Biogenesis to Drive Intratumoral T Cell Metabolic Insufficiency and Dysfunction

Although tumor-specific T cells recognize cancer cells, they are often rendered dysfunctional due to an immunosuppressive microenvironment. Here we showed that T cells demonstrated persistent loss of mitochondrial function and mass when infiltrating murine and human tumors, an effect specific to the tumor microenvironment and not merely caused by activation. Tumor-infiltrating T cells showed a progressive loss of PPAR-gamma coactivator 1α (PGC1α), which programs mitochondrial biogenesis, induced by chronic Akt signaling in tumor-specific T cells. Reprogramming tumor-specific T cells through enforced expression of PGC1α resulted in superior intratumoral metabolic and effector function. Our data support a model in which signals in the tumor microenvironment repress T cell oxidative metabolism, resulting in effector cells with metabolic needs that cannot be met. Our studies also suggest that modulation or reprogramming of the altered metabolism of tumor-infiltrating T cells might represent a potential strategy to reinvigorate dysfunctional T cells for cancer treatment.

Ceramide-tamoxifen regimen targets bioenergetic elements in acute myelogenous leukemia

The objective of our study was to determine the mechanism of action of the short-chain ceramide analog, C6-ceramide, and the breast cancer drug, tamoxifen, which we show coactively depress viability and induce apoptosis in human acute myelogenous leukemia cells. Exposure to the C6-ceramide-tamoxifen combination elicited decreases in mitochondrial membrane potential and complex I respiration, increases in reactive oxygen species (ROS), and release of mitochondrial proapoptotic proteins. Decreases in ATP levels, reduced glycolytic capacity, and reduced expression of inhibitors of apoptosis proteins also resulted. Cytotoxicity of the drug combination was mitigated by exposure to antioxidant. Cells metabolized C6-ceramide by glycosylation and hydrolysis, the latter leading to increases in long-chain ceramides. Tamoxifen potently blocked glycosylation of C6-ceramide and long-chain ceramides. N-desmethyltamoxifen, a poor antiestrogen and the major tamoxifen metabolite in humans, was also effective with C6-ceramide, indicating that traditional antiestrogen pathways are not involved in cellular responses. We conclude that cell death is driven by mitochondrial targeting and ROS generation and that tamoxifen enhances the ceramide effect by blocking its metabolism. As depletion of ATP and targeting the "Warburg effect" represent dynamic metabolic insult, this ceramide-containing combination may be of utility in the treatment of leukemia and other cancers.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(iii) complex of terpyridine and curcumin in cancer cells

A mixed-ligand neodymium(iii) complex of ferrocene appended terpyridine and curcumin targets the mitochondria and shows remarkable visible-light induced cytotoxicity in HeLa and MCF-7 cancer cells while being much less toxic in dark and to MCF-10A normal cells.

Remarkable visible light-triggered cytotoxicity of mitochondria targeting mixed-ligand cobalt(iii) complexes of curcumin and phenanthroline bases binding to human serum albumin

Co(iii) complexes of curcumin and phenanthroline bases show remarkable visible-light induced cytotoxicity in HeLa cells but are much less toxic in dark and to normal cells. The complexes bind to HSA with significant affinity.

Mechanistic studies of cancer cell mitochondria- and NQO1-mediated redox activation of beta-lapachone, a potentially novel anticancer agent

Beta-lapachone (beta-Lp) derived from the Lapacho tree is a potentially novel anticancer agent currently under clinical trials. Previous studies suggested that redox activation of beta-Lp catalyzed by

NAD(P)H

quinone oxidoreductase 1 (NQO1) accounted for its killing of cancer cells. However, the exact mechanisms of this effect remain largely unknown. Using chemiluminescence and electron paramagnetic resonance (EPR) spin-trapping techniques, this study for the first time demonstrated the real-time formation of ROS in the redox activation of beta-lapachone from cancer cells mediated by mitochondria and NQO1 in melanoma B16-F10 and hepatocellular carcinoma HepG2 cancer cells. ES936, a highly selective NQO1 inhibitor, and rotenone, a selective inhibitor of mitochondrial electron transport chain (METC) complex I were found to significantly block beta-Lp meditated redox activation in B16-F10 cells. In HepG2 cells ES936 inhibited beta-Lp-mediated oxygen radical formation by ~80% while rotenone exerted no significant effect. These results revealed the differential contribution of METC and NQO1 to beta-lapachone-induced ROS formation and cancer cell killing. In melanoma B16-F10 cells that do not express high NQO1 activity, both NOQ1 and METC play a critical role in beta-Lp redox activation. In contrast, in hepatocellular carcinoma HepG2 cells expressing extremely high NQO1 activity, redox activation of beta-Lp is primarily mediated by NQO1 (METC plays a minor role). These findings will contribute to our understanding of how cancer cells are selectively killed by beta-lapachone and increase our ability to devise strategies to enhance the anticancer efficacy of this potentially novel drug while minimizing its possible adverse effects on normal cells.

Targeting tumour hypoxia to prevent cancer metastasis. From biology, biosensing and technology to drug development: the METOXIA consortium

The hypoxic areas of solid cancers represent a negative prognostic factor irrespective of which treatment modality is chosen for the patient. Still, after almost 80 years of focus on the problems created by hypoxia in solid tumours, we still largely lack methods to deal efficiently with these treatment-resistant cells. The consequences of this lack may be serious for many patients: Not only is there a negative correlation between the hypoxic fraction in tumours and the outcome of radiotherapy as well as many types of chemotherapy, a correlation has been shown between the hypoxic fraction in tumours and cancer metastasis. Thus, on a fundamental basis the great variety of problems related to hypoxia in cancer treatment has to do with the broad range of functions oxygen (and lack of oxygen) have in cells and tissues. Therefore, activation-deactivation of oxygen-regulated cascades related to metabolism or external signalling are important areas for the identification of mechanisms as potential targets for hypoxia-specific treatment. Also the chemistry related to reactive oxygen radicals (ROS) and the biological handling of ROS are part of the problem complex. The problem is further complicated by the great variety in oxygen concentrations found in tissues. For tumour hypoxia to be used as a marker for individualisation of treatment there is a need for non-invasive methods to measure oxygen routinely in patient tumours. A large-scale collaborative EU-financed project 2009-2014 denoted METOXIA has studied all the mentioned aspects of hypoxia with the aim of selecting potential targets for new hypoxia-specific therapy and develop the first stage of tests for this therapy. A new non-invasive PET-imaging method based on the 2-nitroimidazole [(18)F]-HX4 was found to be promising in a clinical trial on NSCLC patients. New preclinical models for testing of the metastatic potential of cells were developed, both in vitro (2D as well as 3D models) and in mice (orthotopic grafting). Low density quantitative real-time polymerase chain reaction (qPCR)-based assays were developed measuring multiple hypoxia-responsive markers in parallel to identify tumour hypoxia-related patterns of gene expression. As possible targets for new therapy two main regulatory cascades were prioritised: The hypoxia-inducible-factor (HIF)-regulated cascades operating at moderate to weak hypoxia (<1% O(2)), and the unfolded protein response (UPR) activated by endoplasmatic reticulum (ER) stress and operating at more severe hypoxia (<0.2%). The prioritised targets were the HIF-regulated proteins carbonic anhydrase IX (CAIX), the lactate transporter MCT4 and the PERK/eIF2α/ATF4-arm of the UPR. The METOXIA project has developed patented compounds targeting CAIX with a preclinical documented effect. Since hypoxia-specific treatments alone are not curative they will have to be combined with traditional anti-cancer therapy to eradicate the aerobic cancer cell population as well.

Compound A398, a novel podophyllotoxin analogue: cytotoxicity and induction of apoptosis in human leukemia cells

Despite advances in oncology research, cancer is one of the leading causes of death worldwide. Thus, there is a demand for the development of more selective and effective antitumor agents. This study showed that A398, a novel podophyllotoxin analogue, was cytotoxic to the HT-29, MCF-7, MOLT-4 and HL-60 tumor cell lines, being less active in human peripheral blood mononuclear cells and normal cell lines FGH and IEC-6. Tests using the HepG2 lineage indicated that its metabolites do not contribute to its cytotoxicity. In the HL-60 cells, A398 induced apoptosis in a time and concentration-dependent manner, promoting mitochondrial depolarization, inhibition of Bcl-2, phosphatidylserine exposure, activation of caspases -8, -9 and -3, and DNA fragmentation. The production of reactive oxygen species does not seem to be a crucial event for the apoptotic process. Pretreatment with specific inhibitors of kinases ERK1/2, JNK and p38 resulted in an increased percentage of death induced by A398. These results indicate that the compound induced apoptosis through activation of intrinsic and extrinsic death pathways with the mechanism involving the inhibition of the MAPKs and Bcl-2. Taken together, our findings suggest that A398 has an anticancer potential, proving itself to be a candidate for preclinical studies.

Profiling and targeting of cellular bioenergetics: inhibition of pancreatic cancer cell proliferation

BACKGROUND

Targeting both mitochondrial bioenergetics and glycolysis pathway is an effective way to inhibit proliferation of tumour cells, including those that are resistant to conventional chemotherapeutics.

METHODS

In this study, using the Seahorse 96-well Extracellular Flux Analyzer, we mapped the two intrinsic cellular bioenergetic parameters, oxygen consumption rate and proton production rate in six different pancreatic cancer cell lines and determined their differential sensitivity to mitochondrial and glycolytic inhibitors.

RESULTS

There exists a very close relationship among intracellular bioenergetic parameters, depletion of ATP and anti-proliferative effects (inhibition of colony-forming ability) in pancreatic cancer cells derived from different genetic backgrounds treated with the glycolytic inhibitor, 2-deoxyglucose (2-DG). The most glycolytic pancreatic cancer cell line was exquisitely sensitive to 2-DG, whereas the least glycolytic pancreatic cancer cell was resistant to 2-DG. However, when combined with metformin, inhibitor of mitochondrial respiration and activator of AMP-activated protein kinase, 2-DG synergistically enhanced ATP depletion and inhibited cell proliferation even in poorly glycolytic, 2-DG-resistant pancreatic cancer cell line. Furthermore, treatment with conventional chemotherapeutic drugs (e.g., gemcitabine and doxorubicin) or COX-2 inhibitor, celecoxib, sensitised the cells to 2-DG treatment.

CONCLUSIONS

Detailed profiling of cellular bioenergetics can provide new insight into the design of therapeutic strategies for inhibiting pancreatic cancer cell metabolism and proliferation.

mitoNEET as a novel drug target for mitochondrial dysfunction

Mitochondrial dysfunction plays an important part in the pathology of several diseases, including Alzheimer's disease and Parkinson's disease. Targeting mitochondrial proteins shows promise in treating and attenuating the neurodegeneration seen in these diseases, especially considering their complex and pleiotropic origins. Recently, the mitochondrial protein mitoNEET [also referred to as CDGSH iron sulfur domain 1 (CISD1)] has emerged as the mitochondrial target of thiazolidinedione drugs such as the antidiabetic pioglitazone. In this review, we evaluate the current understanding regarding how mitoNEET regulates cellular bioenergetics as well as the structural requirements for drug compound association with mitoNEET. With a clear understanding of mitoNEET function, it might be possible to develop therapeutic agents useful in several different diseases including neurodegeneration, breast cancer, diabetes and inflammation.

Investigation of cyanine dyes for in vivo optical imaging of altered mitochondrial membrane potential in tumors

Mitochondrial membrane potential (Δψm ) alteration is an important target for cancer diagnosis. In this study, we designed a series of near-infrared fluorescent cationic cyanine dyes with varying alkyl chain lengths (IC7-1 derivatives) to provide diverse lipophilicities and serum albumin-binding rates, and we evaluated the usefulness of these derivatives for in vivo Δψm imaging. IC7-1 derivatives with side chains from methyl to hexyl (IC7-1-Me to IC7-1-He) were synthesized, and their optical properties were measured. Cellular uptake and intracellular distribution were investigated with depolarized HeLa cells from carbonyl cyanine m-chlorophenylhydrazone (CCCP) treatment using a spectrofluorometer and a fluorescence microscope. Serum albumin-binding rates were evaluated using albumin-binding inhibitors. In vivo optical imaging was performed with HeLa cell xenograft mice following intravenous administration of IC7-1 derivatives with or without warfarin and CCCP as in vivo blocking agents. IC7-1 derivatives showing maximum excitation and emission wavelengths at 823 nm and ~845 nm, respectively, were synthesized. IC7-1-Me to -Bu showed fluorescence in mitochondria that decreased with CCCP treatment in a concentration-dependent manner, which showed that IC7-1-Me to -Bu successfully indicated Δψm . Tumors were clearly visualized after IC7-1-Bu administration. Treatment with warfarin or CCCP significantly decreased IC7-1-Bu fluorescence in the tumor region. In summary, IC7-1-Bu exhibited fluorescence localized to mitochondria dependent on Δψm , which enabled clear in vivo tumor imaging via serum albumin as a drug carrier for effective tumor targeting. Our data suggest that IC7-1-Bu is a promising NIR probe for in vivo imaging of the altered Δψm of tumor cells.

Hypoxic VDAC1: a potential mitochondrial marker for cancer therapy

Finding new therapeutic targets to fight cancer is an ongoing quest. Because of insufficiencies in tumor vasculature, cells often are exposed to a hostile microenvironment that is low in oxygen (hypoxic) and nutrients. Thus, tumor cells face the challenge of finding new sources of energy and defying apoptosis, which allow them to survive, grow, and colonize other tissues. Eradicating specifically these hypoxic cells is one of the many goals of anticancer therapies. The mitochondrial voltage-dependent anion channel (VDAC) is a protein at the crossroads of metabolic and survival pathways. As its name suggests, VDAC is involved in ion transport as well as adenosine triphosphate and NAD(+) transport. We recently reported the presence in tumor cells of a novel hypoxia-induced form of VDAC. This form, a C-terminal truncated protein (VDAC1-ΔC), was associated in some cancer cell lines with a high output of adenosine triphosphate and a strong resistance to chemotherapy-induced apoptosis. Furthermore, VDAC1-ΔC was detected in tissues of 50 % of 46 patients with lung cancer. This review examines the significance of this new form of VDAC1 for anticancer therapy.

Mitochondrial dysfunction and permeability transition in osteosarcoma cells showing the Warburg effect

Metabolic reprogramming in cancer is manifested by persistent aerobic glycolysis and suppression of mitochondrial function and is known as the Warburg effect. The Warburg effect contributes to cancer progression and is considered to be a promising therapeutic target. Understanding the mechanisms used by cancer cells to suppress their mitochondria may lead to development of new approaches to reverse metabolic reprogramming. We have evaluated mitochondrial function and morphology in poorly respiring LM7 and 143B osteosarcoma (OS) cell lines showing the Warburg effect in comparison with actively respiring Saos2 and HOS OS cells and noncancerous osteoblastic hFOB cells. In LM7 and 143B cells, we detected markers of the mitochondrial permeability transition (MPT), such as mitochondrial swelling, depolarization, and membrane permeabilization. In addition, we detected mitochondrial swelling in human OS xenografts in mice and archival human OS specimens using electron microscopy. The MPT inhibitor sanglifehrin A reversed MPT markers and increased respiration in LM7 and 143B cells. Our data suggest that the MPT may play a role in suppression of mitochondrial function, contributing to the Warburg effect in cancer.

Therapeutic potential of a pyridoxal-based vanadium(IV) complex showing selective cytotoxicity for cancer versus healthy cells

Vanadium compounds can exert anticancer effects, partly due to inhibition of tyrosine phosphatases. Here, we report the effect of N,N'-ethylenebis (pyridoxylideneiminato) vanadium (IV) complex (Pyr2 enV(IV)), that induced 93% and 57% of cell mortality in A375 (human melanoma) and A549 (human lung carcinoma) cells, respectively; the mortality was <24% in other cancer cell lines and in human normal epidermal keratinocytes, lung cells and peripheral blood mononuclear cells. The mechanism of Pyr2 enV(IV) effect relied on apoptosis induction; this was triggered by ROS increase, followed by mitochondrial membrane depolarization. Indeed, the addition of N-acetyl cysteine to cell cultures abated Pyr2 enV(IV)-induced apoptosis. These results disclose the pro-apoptotic activity of Pyr2 enV(IV) and its mechanism, relying on intracellular ROS increase.

BAY 87-2243, a highly potent and selective inhibitor of hypoxia-induced gene activation has antitumor activities by inhibition of mitochondrial complex I

The activation of the transcription factor hypoxia-inducible factor-1 (HIF-1) plays an essential role in tumor development, tumor progression, and resistance to chemo- and radiotherapy. In order to identify compounds targeting the HIF pathway, a small molecule library was screened using a luciferase-driven HIF-1 reporter cell line under hypoxia. The high-throughput screening led to the identification of a class of aminoalkyl-substituted compounds that inhibited hypoxia-induced HIF-1 target gene expression in human lung cancer cell lines at low nanomolar concentrations. Lead structure BAY 87-2243 was found to inhibit HIF-1α and HIF-2α protein accumulation under hypoxic conditions in non-small cell lung cancer (NSCLC) cell line H460 but had no effect on HIF-1α protein levels induced by the hypoxia mimetics desferrioxamine or cobalt chloride. BAY 87-2243 had no effect on HIF target gene expression levels in RCC4 cells lacking Von Hippel–Lindau (VHL) activity nor did the compound affect the activity of HIF prolyl hydroxylase-2. Antitumor activity of BAY 87-2243, suppression of HIF-1α protein levels, and reduction of HIF-1 target gene expression in vivo were demonstrated in a H460 xenograft model. BAY 87-2243 did not inhibit cell proliferation under standard conditions. However under glucose depletion, a condition favoring mitochondrial ATP generation as energy source, BAY 87-2243 inhibited cell proliferation in the nanomolar range. Further experiments revealed that BAY 87-2243 inhibits mitochondrial complex I activity but has no effect on complex III activity. Interference with mitochondrial function to reduce hypoxia-induced HIF-1 activity in tumors might be an interesting therapeutic approach to overcome chemo- and radiotherapy-resistance of hypoxic tumors.

Mitochondrial permeability transition pore as a selective target for anti-cancer therapy

Mitochondrial outer membrane permeabilization (MOMP) is the ultimate step in dozens of lethal apoptotic signal transduction pathways which converge on mitochondria. One of the representative systems proposed to be responsible for the MOMP is the mitochondrial permeability transition pore (MPTP). Although the molecular composition of the MPTP is not clearly understood, the MPTP attracts much interest as a promising target for resolving two conundrums regarding cancer treatment: tumor selectivity and resistance to treatment. The regulation of the MPTP is closely related to metabolic reprogramming in cancer cells including mitochondrial alterations. Restoration of deregulated apoptotic machinery in cancer cells by tumor-specific modulation of the MPTP could therefore be a promising anti-cancer strategy. Currently, a number of MPTP-targeting agents are under pre-clinical and clinical studies. Here, we reviewed the structure and regulation of the MPTP as well as the current status of the development of promising MPTP-targeting drugs.