A strategically designed small molecule attacks alpha-ketoglutarate dehydrogenase in tumor cells through a redox process

Mitochondria in cancer metabolism, an organelle whose time has come?

Mitochondria have long been controversial organelles in cancer. Early discoveries in cancer metabolism placed much emphasis on cytosolic contributions. Initial debate focused on if mitochondria had a role in cancer formation and progression at all. More recently the contributions of mitochondria to cancer development and progression have become firmly established. This has led to the identification of novel targets and inhibitors being studied as new therapeutic approaches. This review will summarize the role of mitochondria in cancer and highlight several agents under development.

The potential of metabolic profiling for vaccine development

Recent technological advances have provided deeper insights into the role of small molecules in biological processes. Metabolic profiling has thus entered the arena of -omics studies and rapidly proven its value both as stand-alone and as complement to other more advanced approaches, notably transcriptomics. Here we describe the potential of metabolic profiling for vaccinology embedded in the context of infection and immunity. This discussion is preceded by a description of the relevant technical and analytical tools for biological interpretation of metabolic data. Although not as widely applied as other -omics technologies, we believe that metabolic profiling can make important contributions to the better understanding of mechanisms underlying vaccine-induced responses and their effects on the prevention of infection or disease.

Therapeutic potential of CPI-613 for targeting tumorous mitochondrial energy metabolism and inhibiting autophagy in clear cell sarcoma

Clear cell sarcoma (CCS) is an aggressive type of soft tissue tumor that is associated with high rates of metastasis. In the present study, we found that CPI-613, which targets tumorous mitochondrial energy metabolism, induced autophagosome formation followed by lysosome fusion in HS-MM CCS cells in vitro. Interestingly, CPI-613 along with chloroquine, which inhibits the fusion of autophagosomes with lysosomes, significantly induced necrosis of HS-MM CCS cell growth in vitro. Subsequently, we established a murine orthotropic metastatic model of CCS and evaluated the putative suppressive effect of a combination of CPI-613 and chloroquine on CCS progression. Injection of HS-MM into the aponeuroses of the thigh, the most frequently affected site in CCS, resulted in massive metastasis in SCID-beige mice. By contrast, intraperitoneal administration of CPI-613 (25 mg/kg) and chloroquine (50 mg/kg), two days a week for two weeks, significantly decreased tumor growth at the injection site and abolished metastasis. The present results imply the inhibitory effects of a combination of CPI-613 and chloroquine on the progression of CCS.

Pancreatic Cancer Metabolism: Molecular Mechanisms and Clinical Applications

PURPOSE OF REVIEW

Pancreatic adenocarcinoma is a leading cause of cancer mortality in western countries with a uniformly poor prognosis. Unfortunately, there has been little in the way of novel therapeutics for this malignancy over the last several decades. Derangements in metabolic circuitry favoring excess glycolysis are increasingly recognized as a key hallmark of cancer.

RECENT FINDINGS

The role of alterations in glutamine metabolism in pancreatic tumor progression has been elucidated in animal models and human cells lines, and there has been considerable interest in exploiting these aberrations for the treatment of pancreatic cancer. Other strategies targeting NQO1/GLS1 inhibition, NAD+ synthesis, and TCA cycle intermediates are being actively studied in the clinic. Aberrant metabolism in pancreatic cancer poses a unique therapeutic strategy. We review preclinical and clinical studies looking to exploit alterations in the metabolic circuitry of pancreatic cancer.

A Phase I Study of CPI-613 in Combination with High-Dose Cytarabine and Mitoxantrone for Relapsed or Refractory Acute Myeloid Leukemia

Purpose: CPI-613, a lipoate analogue that inhibits pyruvate dehydrogenase (PDH) and α-ketogluterate dehydrogenase (KGDH), has activity in patients with myeloid malignancies. This study explored the role of mitochondrial metabolism in chemotherapy response and determined the MTD, efficacy, and safety of CPI-613 combined with high-dose cytarabine and mitoxantrone in patients with relapsed or refractory acute myeloid leukemia.Experimental Design: The role of mitochondrial response to chemotherapy was assessed in cell lines and animal models. A phase I study of CPI-613 plus cytarabine and mitoxantrone was conducted in patients with relapsed or refractory AML.Results: Exposure to chemotherapy induced mitochondrial oxygen consumption that depended on PDH. CPI-613 sensitized AML cells to chemotherapy indicating that mitochondrial metabolism is a source of resistance. Loss of p53 did not alter response to CPI-613. The phase I study enrolled 67 patients and 62 were evaluable for response. The overall response rate was 50% (26CR+5CRi/62). Median survival was 6.7 months. In patients over 60 years old, the CR/CRi rate was 47% (15/32) with a median survival of 6.9 months. The response rate for patients with poor-risk cytogenetics also was encouraging with 46% (11/24 patients) achieving a CR or CRi. RNA sequencing analysis of a subset of baseline bone marrow samples revealed a gene expression signature consistent with the presence of B cells in the pretreatment marrow of responders.Conclusions: The addition of CPI-613 to chemotherapy is a promising approach in older patients and those with poor-risk cytogenetics. Clin Cancer Res; 24(9); 2060-73. ©2018 AACR.

Pyruvate attenuates the anti-neoplastic effect of carnosine independently from oxidative phosphorylation

Here we analyzed whether the anti-neoplastic effect of carnosine, which inhibits glycolytic ATP production, can be antagonized by ATP production via oxidative phosphorylation fueled by pyruvate. Therefore, glioblastoma cells were cultivated in medium supplemented with glucose, galactose or pyruvate and in the presence or absence of carnosine. CPI-613 was employed to inhibit the entry of pyruvate into the tricarboxylic acid cycle and 2,4-dinitrophenol to inhibit oxidative phosphorylation. Energy metabolism and viability were assessed by cell based assays and histochemistry.ATP in cell lysates and dehydrogenase activity in living cells revealed a strong reduction of viability under the influence of carnosine when cells received glucose or galactose but not in the presence of pyruvate. CPI-613 and 2,4-dinitrophenol reduced viability of cells cultivated in pyruvate, but no effect was seen in the presence of glucose. No effect of carnosine on viability was observed in the presence of glucose and pyruvate even in the presence of 2,4-dinitrophenol or CPI-613.In conclusion, glioblastoma cells produce ATP from pyruvate via the tricarboxylic acid cycle and oxidative phosphorylation in the absence of a glycolytic substrate. In addition, pyruvate attenuates the anti-neoplastic effect of carnosine, even when ATP production via tricarboxylic acid cycle and oxidative phosphorylation is blocked. We also observed an inhibitory effect of carnosine on the tricarboxylic acid cycle and a stimulating effect of 2,4-dinitrophenol on glycolytic ATP production.

Canagliflozin mediated dual inhibition of mitochondrial glutamate dehydrogenase and complex I: an off-target adverse effect

Recent FDA Drug Safety Communications report an increased risk for acute kidney injury in patients treated with the gliflozin class of sodium/glucose co-transport inhibitors indicated for treatment of type 2 diabetes mellitus. To identify a potential rationale for the latter, we used an in vitro human renal proximal tubule epithelial cell model system (RPTEC/TERT1), physiologically representing human renal proximal tubule function. A targeted metabolomics approach, contrasting gliflozins to inhibitors of central carbon metabolism and mitochondrial function, revealed a double mode of action for canagliflozin, but not for its analogs dapagliflozin and empagliflozin. Canagliflozin inhibited the glutamate dehydrogenase (GDH) and mitochondrial electron transport chain (ETC) complex I at clinically relevant concentrations. This dual inhibition specifically prevented replenishment of tricarboxylic acid cycle metabolites by glutamine (anaplerosis) and thus altered amino acid pools by increasing compensatory transamination reactions. Consequently, canagliflozin caused a characteristic intracellular accumulation of glutamine, glutamate and alanine in confluent, quiescent RPTEC/TERT1. Canagliflozin, but none of the classical ETC inhibitors, induced cytotoxicity at particularly low concentrations in proliferating RPTEC/TERT1, serving as model for proximal tubule regeneration in situ. This finding is testimony of the strong dependence of proliferating cells on glutamine anaplerosis via GDH. Our discovery of canagliflozin-mediated simultaneous inhibition of GDH and ETC complex I in renal cells at clinically relevant concentrations, and their particular susceptibility to necrotic cell death during proliferation, provides a mechanistic rationale for the adverse effects observed especially in patients with preexisting chronic kidney disease or previous kidney injury characterized by sustained regenerative tubular epithelial cell proliferation.

Inhibition of mitochondrial 2-oxoglutarate dehydrogenase impairs viability of cancer cells in a cell-specific metabolism-dependent manner

2-Oxoglutarate dehydrogenase (OGDH) of the tricarboxylic acid (TCA) cycle is often implied to be inactive in cancer, but this was not experimentally tested. We addressed the question through specific inhibition of OGDH by succinyl phosphonate (SP). SP action on different cancer cells was investigated using indicators of cellular viability and reactive oxygen species (ROS), metabolic profiling and transcriptomics. Relative sensitivity of various cancer cells to SP changed with increasing SP exposure and could differ in the ATP- and NAD(P)H-based assays. Glioblastoma responses to SP revealed metabolic sub-types increasing or decreasing cellular ATP/NAD(P)H ratio under OGDH inhibition. Cancer cell homeostasis was perturbed also when viability indicators were SP-resistant, e.g. in U87 and N2A cells. The transcriptomics database analysis showed that the SP-sensitive cells, such as A549 and T98G, exhibit the lowest expression of OGDH compared to other TCA cycle enzymes, associated with higher expression of affiliated pathways utilizing 2-oxoglutarate. Metabolic profiling confirmed the dependence of cellular SP reactivity on cell-specific expression of the pathways. Thus, oxidative decarboxylation of 2-oxoglutarate is significant for the interdependent homeostasis of NAD(P)H, ATP, ROS and key metabolites in various cancer cells. Assessment of cell-specific responses to OGDH inhibition is of diagnostic value for anticancer strategies.

Recent advances in understanding and managing T-cell lymphoma

Owing to the rarity of peripheral T-cell lymphoma (PTCL) and the heterogeneity of subtypes, there are no compelling data to guide the therapeutic approaches for such patients. Over the years, there have been remarkable advances in molecular subtyping and treatment of PTCL, although there are still many areas to be explored. In this review, we summarize recent updates on the evolution of understanding and treatment for PTCL.

Differential Aspartate Usage Identifies a Subset of Cancer Cells Particularly Dependent on OGDH

Although aberrant metabolism in tumors has been well described, the identification of cancer subsets with particular metabolic vulnerabilities has remained challenging. Here, we conducted an siRNA screen focusing on enzymes involved in the tricarboxylic acid (TCA) cycle and uncovered a striking range of cancer cell dependencies on OGDH, the E1 subunit of the alpha-ketoglutarate dehydrogenase complex. Using an integrative metabolomics approach, we identified differential aspartate utilization, via the malate-aspartate shuttle, as a predictor of whether OGDH is required for proliferation in 3D culture assays and for the growth of xenograft tumors. These findings highlight an anaplerotic role of aspartate and, more broadly, suggest that differential nutrient utilization patterns can identify subsets of cancers with distinct metabolic dependencies for potential pharmacological intervention.

The emerging role and targetability of the TCA cycle in cancer metabolism

The tricarboxylic acid (TCA) cycle is a central route for oxidative phosphorylation in cells, and fulfills their bioenergetic, biosynthetic, and redox balance requirements. Despite early dogma that cancer cells bypass the TCA cycle and primarily utilize aerobic glycolysis, emerging evidence demonstrates that certain cancer cells, especially those with deregulated oncogene and tumor suppressor expression, rely heavily on the TCA cycle for energy production and macromolecule synthesis. As the field progresses, the importance of aberrant TCA cycle function in tumorigenesis and the potentials of applying small molecule inhibitors to perturb the enhanced cycle function for cancer treatment start to evolve. In this review, we summarize current knowledge about the fuels feeding the cycle, effects of oncogenes and tumor suppressors on fuel and cycle usage, common genetic alterations and deregulation of cycle enzymes, and potential therapeutic opportunities for targeting the TCA cycle in cancer cells. With the application of advanced technology and in vivo model organism studies, it is our hope that studies of this previously overlooked biochemical hub will provide fresh insights into cancer metabolism and tumorigenesis, subsequently revealing vulnerabilities for therapeutic interventions in various cancer types.

Examination of the superoxide/hydrogen peroxide forming and quenching potential of mouse liver mitochondria

Pyruvate dehydrogenase (PDHC) and α-ketoglutarate dehydrogenase complex (KGDHC) are important sources of reactive oxygen species (ROS). In addition, it has been found that mitochondria can also serve as sinks for cellular hydrogen peroxide (H₂O₂). However, the ROS forming and quenching capacity of liver mitochondria has never been thoroughly examined. Here, we show that mouse liver mitochondria use catalase, glutathione (GSH), and peroxiredoxin (PRX) systems to quench ROS. Incubation of mitochondria with catalase inhibitor 3-amino-1,2,4-triazole (triazole) induced a significant increase in pyruvate or α-ketoglutarate driven O₂^-/H₂O₂ formation. 1-Choro-2,4-dinitrobenzene (CDNB), which depletes glutathione (GSH), elicited a similar effect. Auranofin (AF), a thioredoxin reductase-2 (TR2) inhibitor which disables the PRX system, did not significantly change O₂^-/H₂O₂ formation. By contrast catalase, GSH, and PRX were all required to scavenging extramitochondrial H₂O₂. In this study, the ROS forming potential of PDHC, KGDHC, Complex I, and Complex III was also profiled. Titration of mitochondria with 3-methyl-2-oxovaleric acid (KMV), a specific inhibitor for O₂^-/H₂O₂ production by KGDHC, induced a ~86% and ~84% decrease in ROS production during α-ketoglutarate and pyruvate oxidation. Titration of myxothiazol, a Complex III inhibitor, decreased O₂^-/H₂O₂ formation by ~45%. Rotenone also lowered ROS production in mitochondria metabolizing pyruvate or α-ketoglutarate indicating that Complex I does not contribute to ROS production during forward electron transfer from NADH. Taken together, our results indicate that KGDHC and Complex III are high capacity sites for O₂^-/H₂O₂ production in mouse liver mitochondria. We also confirm that catalase plays a role in quenching either exogenous or intramitochondrial H₂O₂.

Safety and tolerability of the first-in-class agent CPI-613 in combination with modified FOLFIRINOX in patients with metastatic pancreatic cancer: a single-centre, open-label, dose-escalation, phase 1 trial

Background

Pancreatic cancer statistics are dismal, with a five-year survival of less than 10%, and over 50% of patients presenting with metastatic disease. Metabolic reprogramming is an emerging hallmark of pancreatic adenocarcinoma, including aerobic glycolysis, oxidative phosphorylation, glutaminolysis, lipogenesis and lipolysis, autophagic status, and anti-oxidative stress. CPI-613 is a novel anti-cancer agent that selectively targets the altered form of mitochondrial energy metabolism in tumor cells, causing changes in mitochondrial enzyme activities and redox status which lead to apoptosis, necrosis and autophagy of tumor cells.

Methods

This is a phase 1 study to determine the maximum-tolerated dose (MTD) of CPI-613 when used in combination with modified FOLFIRINOX (oxaliplatin at 65 mg/m² and irinotecan at 140 mg/m², and fluorouracil 400 mg/m² bolus and 2400 mg/m² over 46 h) in combination with CPI-613 in patients with newly diagnosed metastatic pancreatic adenocarcinoma with good bone marrow, liver and kidney function and good performance status (NCT01835041 – closed to recruitment). A two-stage dose-escalation scheme (single patient and traditional 3+3 design) was applied. In the single patient stage, one patient was accrued per dose level. The starting dose of CPI-613 was 500 mg/m²/day; the dose level was then escalated by doubling the previous dose if there was no toxicity greater than Grade 2 within 4 weeks attributed as probably or definitely related to CPI-613. The traditional 3+3 dose-escalation stage was triggered if toxicity attributed as probably or definitely related to CPI-613 was ≥ Grade 2. The dose level for CPI-613 for the first cohort in the traditional dose-escalation stage was the same as used in the last cohort of the single patient dose-escalation stage. Secondary objectives were safety, preliminary efficacy, and tissue collection for future analyses. Response rates, progression-free survival and overall survival data were assessed in the patients treated at the MTD.

Findings

Twenty patients were enrolled April 22, 2013 – January 8, 2016. The MTD of CPI-613 was 500 mg/m². The median number of treatment cycles administered at the MTD was 11 (interquartile range, 4–19). Two patients enrolled at a higher dose (1000 mg/m²) both experienced a DLT (dose limiting toxicity). There were 2 unexpected serious adverse events (SAEs), both for the first patient enrolled: 1) possible leaching due to infusion of CPI-613 via non-PVC tubing, and 2) the patient re- accessed her port at home after accidental de-access. Neither incident resulted in a negative clinical outcome. Expected SAEs were: thrombocytopenia, anemia and lymphopenia (all for Patient #2, with anemia and lymphopenia being a DLT); hyperglycemia (Patient #7); hypokalemia, hypoalbuminemia and sepsis (Patient #11); and neutropenia (Patient #20). There was no grade 5 toxicity. For the 18 patients treated at the MTD, the most common Grade 3–4 toxicities were hypokalemia (6/18, 33%), diarrhea (5/18, 28%) and abdominal pain (4/18, 22%). Sensorial neuropathy (17/18, 94%) was managed with dose de-escalation or discontinuation per standard of care. None of the patients experienced grade 4 or 5 neuropathy. No patients died while on active treatment; 11 study participants died, with cause of death as terminal pancreatic cancer.

Among the 18 patients treated with the MTD, there were 3 patients with a complete response (CR), 1 with a non-CR/non-progressive disease, 7 with a partial response (PR), 3 with stable disease, and 4 with PD. The partial + complete response rate was 61% (11/18).

Interpretation

The treatment was well tolerated and all end points were met. The intriguing signal of efficacy will require validation in a phase 2 study.

Funding

Comprehensive Cancer Center of Wake Forest Baptist Medical Center

The α-ketoglutarate dehydrogenase complex in cancer metabolic plasticity

Deregulated metabolism is a well-established hallmark of cancer. At the hub of various metabolic pathways deeply integrated within mitochondrial functions, the α-ketoglutarate dehydrogenase complex represents a major modulator of electron transport chain activity and tricarboxylic acid cycle (TCA) flux, and is a pivotal enzyme in the metabolic reprogramming following a cancer cell’s change in bioenergetic requirements. By contributing to the control of α-ketoglutarate levels, dynamics, and oxidation state, the α-ketoglutarate dehydrogenase is also essential in modulating the epigenetic landscape of cancer cells. In this review, we will discuss the manifold roles that this TCA enzyme and its substrate play in cancer.

Amplification of USP13 drives ovarian cancer metabolism

Dysregulated energetic metabolism has been recently identified as a hallmark of cancer. Although mutations in metabolic enzymes hardwire metabolism to tumourigenesis, they are relatively infrequent in ovarian cancer. More often, cancer metabolism is re-engineered by altered abundance and activity of the metabolic enzymes. Here we identify ubiquitin-specific peptidase 13 (USP13) as a master regulator that drives ovarian cancer metabolism. USP13 specifically deubiquitinates and thus upregulates ATP citrate lyase and oxoglutarate dehydrogenase, two key enzymes that determine mitochondrial respiration, glutaminolysis and fatty acid synthesis. The USP13 gene is co-amplified with PIK3CA in 29.3% of high-grade serous ovarian cancers and its overexpression is significantly associated with poor clinical outcome. Inhibiting USP13 remarkably suppresses ovarian tumour progression and sensitizes tumour cells to the treatment of PI3K/AKT inhibitor. Our results reveal an important metabolism-centric role of USP13, which may lead to potential therapeutics targeting USP13 in ovarian cancers.

Cancer cells need to reprogramme their metabolism to allow rapid cell proliferation. Here, the authors show that USP13 is amplified in ovarian cancer and its protein product, a deubiquitinase, drives tumour progression by rewiring the metabolism of cancer cells by stabilising two critical metabolic enzymes.

The disulfide compound α-lipoic acid and its derivatives: A novel class of anticancer agents targeting mitochondria

The endogenous disulfide α-lipoic acid (LA) is an essential mitochondrial co-factor. In addition, LA and its reduced counterpart dihydro lipoic acid form a potent redox couple with antioxidative functions, for which it is used as dietary supplement and therapeutic. Recently, it has gained attention due to its cytotoxic effects in cancer cells, which is the key aspect of this review. We initially recapitulate the dietary occurrence, gastrointestinal absorption and pharmacokinetics of LA, illustrating its diverse antioxidative mechanisms. We then focus on its mode of action in cancer cells, in which it triggers primarily the mitochondrial pathway of apoptosis, whereas non-transformed primary cells are hardly affected. Furthermore, LA impairs oncogenic signaling and displays anti-metastatic potential. Novel LA derivatives such as CPI-613, which target mitochondrial energy metabolism, are described and recent pre-clinical studies are presented, which demonstrate that LA and its derivatives exert antitumor activity in vivo. Finally, we highlight clinical studies currently performed with the LA analog CPI-613. In summary, LA and its derivatives are promising candidates to complement the arsenal of established anticancer drugs due to their mitochondria-targeted mode of action and non-genotoxic properties.

Structural alterations by five disease-causing mutations in the low-pH conformation of human dihydrolipoamide dehydrogenase (hLADH) analyzed by molecular dynamics - Implications in functional loss and modulation of reactive oxygen species generation by pathogenic hLADH forms

Human dihydrolipoamide dehydrogenase (hLADH) is a flavoenzyme component (E3) of the human alpha-ketoglutarate dehydrogenase complex (α-KGDHc) and few other dehydrogenase complexes. Pathogenic mutations of hLADH cause severe metabolic diseases (atypical forms of E3 deficiency) that often escalate to cardiological or neurological presentations and even premature death; the pathologies are generally accompanied by lactic acidosis. hLADH presents a distinct conformation under acidosis (pH 5.5–6.8) with lower physiological activity and the capacity of generating reactive oxygen species (ROS). It has been shown by our laboratory that selected pathogenic mutations, besides lowering the physiological activity of hLADH, significantly stimulate ROS generation by hLADH, especially at lower pH, which might play a role in the pathogenesis of E3-deficiency in respective cases. Previously, we generated by molecular dynamics (MD) simulation the low-pH hLADH structure and analyzed the structural changes induced in this structure by eight of the pathogenic mutations of hLADH. In the absence of high resolution mutant structures these pieces of information are crucial for the mechanistic investigation of the molecular pathogeneses of the hLADH protein. In the present work we analyzed by molecular dynamics simulation the structural changes induced in the low-pH conformation of hLADH by five pathogenic mutations of hLADH; the structures of these disease-causing mutants of hLADH have never been examined before.

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5 disease-causing mutants of hLADH were subjected to MD to reveal structural changes.

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MD simulations were carried out both in vacuum and in water supplemented with ions.

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Functional regions significantly affected by mutation were identified.

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Implicated residues are to be targeted in mechanistic studies of hLADH dysfunction.

Current Approaches in the Treatment of Relapsed and Refractory Acute Myeloid Leukemia

The limited sensitivity of the historical treatment response criteria for acute myeloid leukemia (AML) has resulted in a different paradigm for treatment compared with most other cancers presenting with widely disseminated disease. Initial cytotoxic induction chemotherapy is often able to reduce tumor burden to a level sufficient to meet the current criteria for "complete" remission. Nevertheless, most AML patients ultimately die from their disease, most commonly as clinically evident relapsed AML. Despite a variety of available salvage therapy options, prognosis in patients with relapsed or refractory AML is generally poor. In this review, we outline the commonly utilized salvage cytotoxic therapy interventions and then highlight novel investigational efforts currently in clinical trials using both pathway-targeted agents and immunotherapy based approaches. We conclude that there is no current standard of care for adult relapsed or refractory AML other than offering referral to an appropriate clinical trial.

The RNA-binding protein HuR is essential for the B cell antibody response

Post-transcriptional regulation of mRNA by the RNA-binding protein HuR (encoded by Elavl1) is required in B cells for the germinal center reaction and for the production of class-switched antibodies in response to thymus-independent antigens. Transcriptome-wide examination of RNA isoforms and their abundance and translation in HuR-deficient B cells, together with direct measurements of HuR-RNA interactions, revealed that HuR-dependent splicing of mRNA affected hundreds of transcripts, including that encoding dihydrolipoamide S-succinyltransferase (Dlst), a subunit of the 2-oxoglutarate dehydrogenase (α-KGDH) complex. In the absence of HuR, defective mitochondrial metabolism resulted in large amounts of reactive oxygen species and B cell death. Our study shows how post-transcriptional processes control the balance of energy metabolism required for the proliferation and differentiation of B cells.

Glutamate dehydrogenase 1 signals through antioxidant glutathione peroxidase 1 to regulate redox homeostasis and tumor growth

How mitochondrial glutaminolysis contributes to redox homeostasis in cancer cells remains unclear. Here we report that the mitochondrial enzyme glutamate dehydrogenase 1 (GDH1) is commonly upregulated in human cancers. GDH1 is important for redox homeostasis in cancer cells by controlling the intracellular levels of its product alpha-ketoglutarate and subsequent metabolite fumarate. Mechanistically, fumarate binds to and activates a reactive oxygen species scavenging enzyme glutathione peroxidase 1. Targeting GDH1 by shRNA or a small molecule inhibitor R162 resulted in imbalanced redox homeostasis, leading to attenuated cancer cell proliferation and tumor growth.

Investigational cancer drugs targeting cell metabolism in clinical development

Introduction: Malignant cell transformation and tumor progression are associated with alterations in glycolysis, fatty acid synthesis, amino acid delivery and production of reactive oxygen species. With increased understanding of the role of metabolism in tumors, there has been interest in developing agents that target tumor specific metabolic pathways. Numerous promising agents targeting altered metabolic pathways are currently in Phase I - III clinical trials. Areas covered: This paper reviews the early phase clinical trial development of these agents and provides perspective on the future direction of this emerging field. Specifically, the authors describe novel and repurposed therapies, focusing on the effects of each agent on tumor metabolism and results from relevant Phase I and II clinical trials. Expert opinion: Metabolism modulating agents, alone and in combinations with other classes of agents, have shown efficacy in the treatment of neoplasm, which, the authors believe, will bear positive results in future studies. Because of the significant crosstalk between metabolic pathways and oncogenic signaling pathways, the authors also believe that combining metabolic modifiers with targeted agents will be an important strategy. An increased understanding of cancer metabolism, in addition to the continued study of metabolic modulators, should lead to further advances in this nascent therapeutic field in the future.

S-glutathionylation reactions in mitochondrial function and disease

Mitochondria are highly efficient energy-transforming organelles that convert energy stored in nutrients into ATP. The production of ATP by mitochondria is dependent on oxidation of nutrients and coupling of exergonic electron transfer reactions to the genesis of transmembrane electrochemical potential of protons. Electrons can also prematurely “spin-off” from prosthetic groups in Krebs cycle enzymes and respiratory complexes and univalently reduce di-oxygen to generate reactive oxygen species (ROS) superoxide (O₂•⁻) and hydrogen peroxide (H₂O₂), important signaling molecules that can be toxic at high concentrations. Production of ATP and ROS are intimately linked by the respiratory chain and the genesis of one or the other inherently depends on the metabolic state of mitochondria. Various control mechanisms converge on mitochondria to adjust ATP and ROS output in response to changing cellular demands. One control mechanism that has gained a high amount of attention recently is S-glutathionylation, a redox sensitive covalent modification that involves formation of a disulfide bridge between glutathione and an available protein cysteine thiol. A number of S-glutathionylation targets have been identified in mitochondria. It has also been established that S-glutathionylation reactions in mitochondria are mediated by the thiol oxidoreductase glutaredoxin-2 (Grx2). In the following review, emerging knowledge on S-glutathionylation reactions and its importance in modulating mitochondrial ATP and ROS production will be discussed. Major focus will be placed on Complex I of the respiratory chain since (1) it is a target for reversible S-glutathionylation by Grx2 and (2) deregulation of Complex I S-glutathionylation is associated with development of various disease states particularly heart disease. Other mitochondrial enzymes and how their S-glutathionylation profile is affected in different disease states will also be discussed.

Caloric restriction mimetics: towards a molecular definition

Caloric restriction, be it constant or intermittent, is reputed to have health-promoting and lifespan-extending effects. Caloric restriction mimetics (CRMs) are compounds that mimic the biochemical and functional effects of caloric restriction. In this Opinion article, we propose a unifying definition of CRMs as compounds that stimulate autophagy by favouring the deacetylation of cellular proteins. This deacetylation process can be achieved by three classes of compounds that deplete acetyl coenzyme A (AcCoA; the sole donor of acetyl groups), that inhibit acetyl transferases (a group of enzymes that acetylate lysine residues in an array of proteins) or that stimulate the activity of deacetylases and hence reverse the action of acetyl transferases. A unifying definition of CRMs will be important for the continued development of this class of therapeutic agents.

Translational assessment of mitochondrial dysfunction of pancreatic cancer from in vitro gene microarray and animal efficacy studies, to early clinical studies, via the novel tumor-specific anti-mitochondrial agent, CPI-613

STUDY RATIONALE AND OBJECTIVES

Via genetic alterations, malignant transformation and proliferation are associated with extensive alterations of mitochondrial energy metabolism of tumor cells. Thus, inhibition of the altered form of mitochondrial energy metabolism of tumor cells may be an effective therapy for cancers. This study performed translational assessment of mitochondrial dysfunction of pancreatic cancer from in vitro gene microarray and animal efficacy studies, to early clinical studies, via the novel tumor-specific anti-mitochondrial agent, CPI-613.

METHODS

The gene profiles of BxPC-3 human pancreatic tumor cells and non-transformed NIH-3T3 mouse fibroblast cells (negative control), after CPI-613 or sham treatment, were assessed and compared using microarray technique. The anti-cancer efficacies of CPI-613 and Gemcitabine were assessed and compared in mice with xenograft from inoculation of BxPC-3 human pancreatic tumor cells, based on the degree of tumor growth inhibition and prolongation of survival when compared to vehicle treatment. The anti-cancer activities, according to overall survival (OS), of CPI-613 alone and in combination with Gemcitabine were assessed in patients with Stage IV pancreatic cancer.

RESULTS

Microarray studies indicated that CPI-613 down-regulated the expression of Cyclin D3, E1, E2, F, A2, B1 and CDK2 genes of BxPC-3 pancreatic cancer cells but not non-transformed NIH-3T3 mouse fibroblast cells (negative control). In mice with pancreatic carcinoma xenografts, four weekly intraperitoneal injections of either CPI-613 (25 mg/kg/administration) or Gemcitabine (50 mg/kg/administration) inhibited tumor growth and prolonged survival when compared to vehicle treatment. The degree of tumor growth inhibition was ~2×, and prolongation of survival was ~4×, greater with CPI-613 treatment than with Gemcitabine treatment. In patients with Stage IV advanced pancreatic cancer, CPI-613 at 420-1,300 mg/m(2), given twice weekly for three weeks followed by a week of rest (i.e., 3-week-on-1-week-off) as monotherapy, provided median OS of 15 months in three patients. CPI-613 at 150-320 mg/m(2) given twice weekly on the 3-week-on-1-week-off dosing schedule, coinciding with Gemcitabine (1,000 mg/m(2)) given once weekly on the 3-week-on-1-week-off dosing schedule, provided median OS of 17.8 months in four patients. These median OS values from CPI-613 monotherapy and CPI-613 + Gemcitabine treatment tend to be longer than those in patients treated with Abraxane + Gemcitabine combination or FOLFININOX (median OS ~12 months).

CONCLUSIONS

The dysfunctional mitochondria of pancreatic cancer cells was translationable from in vitro gene alteration and animal tumor model studies to patients with advanced Stage IV pancreatic cancer, as reflected by the anti-cancer activities of the tumor-specific anti-mitochondrial agent, CPI-613, in these studies.

A phase I study of the first-in-class antimitochondrial metabolism agent, CPI-613, in patients with advanced hematologic malignancies

PURPOSE

The lipoate derivative CPI-613 is a first-in-class agent that targets mitochondrial metabolism. This study determined the effects of CPI-613 on mitochondrial function and defined the MTD, pharmacokinetics, and safety in patients with relapsed or refractory hematologic malignancies.

EXPERIMENTAL DESIGN

Human leukemia cell lines were exposed to CPI-613 and mitochondrial function was assayed. A phase I trial was conducted in which CPI-613 was given as a 2-hour infusion on days 1 and 4 for 3 weeks every 28 days.

RESULTS

CPI-613 inhibited mitochondrial respiration of human leukemia cells consistent with the proposed mechanism of action. In the phase I trial, 26 patients were enrolled. CPI-613 was well tolerated with no marrow suppression observed. When the infusion time was shortened to 1 hour, renal failure occurred in 2 patients. At 3,780 mg/m(2), there were two dose-limiting toxicities (DLT). At a dose of 2,940 mg/m(2) over 2 hours, no DLTs were observed, establishing this as the MTD. Renal failure occurred in a total of 4 patients and resolved in all but 1, who chose hospice care. CPI-613 has a triphasic elimination with an alpha half-life of approximately 1.34 hours. Of the 21 evaluable, heavily pretreated patients, 4 achieved an objective response and 2 achieved prolonged stabilization of disease for a clinical benefit rate of 29%. Following drug exposure, gene expression profiles of peripheral blood mononuclear cells from responders demonstrated immune activation.

CONCLUSION

CPI-613 inhibits mitochondrial function and demonstrates activity in a heavily pretreated cohort of patients.

Obstructive jaundice and carcinoma of the gallbladder

The Warburg effect is a metabolic phenomenon characterized by increased glycolytic activity, decreased mitochondrial oxidative phosphorylation, and the production of lactate. This metabolic phenotype is characterized in rapidly proliferative cell types such as cancerous cells and embryonic stem cells. We hypothesized that a Warburg-like metabolism could be achieved in other cell types by treatment with pharmacological agents, which might, in turn, facilitate nuclear reprogramming. The aim of this study was to treat fibroblasts with CPI-613 and PS48 to induce a Warburg-like metabolic state. We demonstrate that treatment with both drugs altered the expression of 69 genes and changed the level of 21 metabolites in conditioned culture media, but did not induce higher proliferation compared to the control treatment. These results support a role for the reverse Warburg effect, whereby cancer cells induce cancer-associated fibroblast cells in the surrounding stroma to exhibit the metabolically characterized Warburg effect. Cancer-associated fibroblasts then produce and secrete metabolites such as pyruvate to supply the cancerous cells, thereby supporting tumor growth and metastasis. While anticipating an increase in the production of lactate and increased cellular proliferation, both hallmarks of the Warburg effect, we instead observed increased secretion of pyruvate without changes in proliferation.