The promising anticancer drug 3-bromopyruvate is metabolized through glutathione conjugation which affects chemoresistance and clinical practice: An evidence-based view

The Promoting Role of HK II in Tumor Development and the Research Progress of Its Inhibitors

Increased glycolysis is a key characteristic of malignant cells that contributes to their high proliferation rates and ability to develop drug resistance. The glycolysis rate-limiting enzyme hexokinase II (HK II) is overexpressed in most tumor cells and significantly affects tumor development. This paper examines the structure of HK II and the specific biological factors that influence its role in tumor development, as well as the potential of HK II inhibitors in antitumor therapy. Furthermore, we identify and discuss the inhibitors of HK II that have been reported in the literature.

Anti-Glycolytic Drugs in the Treatment of Hepatocellular Carcinoma: Systemic and Locoregional Options

Hepatocellular cancer (HCC) is the most common primary liver cancer and the third leading cause of cancer-related death. Locoregional therapies, including transarterial embolization (TAE: bland embolization), chemoembolization (TACE), and radioembolization, have demonstrated survival benefits when treating patients with unresectable HCC. TAE and TACE occlude the tumor's arterial supply, causing hypoxia and nutritional deprivation and ultimately resulting in tumor necrosis. Embolization blocks the aerobic metabolic pathway. However, tumors, including HCC, use the "Warburg effect" and survive hypoxia from embolization. An adaptation to hypoxia through the Warburg effect, which was first described in 1956, is when the cancer cells switch to glycolysis even in the presence of oxygen. Hence, this is also known as aerobic glycolysis. In this article, the adaptation mechanisms of HCC, including glycolysis, are discussed, and anti-glycolytic treatments, including systemic and locoregional options that have been previously reported or have the potential to be utilized in the treatment of HCC, are reviewed.

Glutathione-Mediated Conjugation of Anticancer Drugs: An Overview of Reaction Mechanisms and Biological Significance for Drug Detoxification and Bioactivation

The effectiveness of many anticancer drugs depends on the creation of specific metabolites that may alter their therapeutic or toxic properties. One significant route of biotransformation is a conjugation of electrophilic compounds with reduced glutathione, which can be non-enzymatic and/or catalyzed by glutathione-dependent enzymes. Glutathione usually combines with anticancer drugs and/or their metabolites to form more polar and water-soluble glutathione S-conjugates, readily excreted outside the body. In this regard, glutathione plays a role in detoxification, decreasing the likelihood that a xenobiotic will react with cellular targets. However, some drugs once transformed into thioethers are more active or toxic than the parent compound. Thus, glutathione conjugation may also lead to pharmacological or toxicological effects through bioactivation reactions. My purpose here is to provide a broad overview of the mechanisms of glutathione-mediated conjugation of anticancer drugs. Additionally, I discuss the biological importance of glutathione conjugation to anticancer drug detoxification and bioactivation pathways. I also consider the potential role of glutathione in the metabolism of unsymmetrical bisacridines, a novel prosperous class of anticancer compounds developed in our laboratory. The knowledge on glutathione-mediated conjugation of anticancer drugs presented in this review may be noteworthy for improving cancer therapy and preventing drug resistance in cancers.

2-Deoxy-D-glucose increases the sensitivity of glioblastoma cells to BCNU through the regulation of glycolysis, ROS and ERS pathways: In vitro and in vivo validation

Chloroethylnitrosoureas (CENUs) exert antitumor activity via producing dG-dC interstrand crosslinks (ICLs). However, tumor resistance make it necessary to find novel strategies to improve the therapeutic effect of CENUs. 2-Deoxy-D-glucose (2-DG) is a well-known glycolytic inhibitor, which can reprogram tumor energy metabolism closely related to tumor resistance. Here, we investigated the chemosensitization effect of 2-DG on l,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) against glioblastoma cells and the underlying mechanisms. We found that 2-DG significantly increased the inhibitory effects of BCNU on tumor cells compared with BCNU alone, while 2-DG showed no obvious enhancing effect on the BCNU-induced cytotoxicity for normal HaCaT and HA1800 cells. Proliferation, migration and invasion determinations presented the same trend as survival on tumor cells. 2-DG plus BCNU increased the energy deficiency through a more effective inhibition of glycolytic pathway. Notably, the combination of 2-DG and BCNU aggravated oxidative stress in glioblastoma cells, along with a significant decrease in glutathione (GSH) levels, and an increase in intracellular reactive oxygen species (ROS). Subsequently, we demonstrated that the combination treatment led to increased apoptosis via activating mitochondria and endoplasmic reticulum stress (ERS) related apoptosis pathways. Finally, we found that the dG-dC level was significantly increased after 2-DG pretreatment compared to BCNU alone by HPLC-ESI-MS/MS analysis. Finally, in vivo, 2-DG plus BCNU significantly suppressed tumor growth with lower side effects compared with BCNU alone in tumor-bearing mice. In summary, we proposed that 2-DG may have potential to increase the sensitivity of glioblastoma cells to BCNU by regulating glycolysis, ROS and ERS pathways in clinical setting.

3-Bromopyruvate-mediated MCT1-dependent metabolic perturbation sensitizes triple negative breast cancer cells to ionizing radiation

BACKGROUND

Triple negative breast cancer (TNBC) poses a serious clinical challenge as it is an aggressive form of the disease that lacks estrogen receptor, progesterone receptor, and ERBB2 (formerly HER2) gene amplification, which limits the treatment options. The Warburg phenotype of upregulated glycolysis in the presence of oxygen has been shown to be prevalent in TNBC. Elevated glycolysis satisfies the energy requirements of cancer cells, contributes to resistance to treatment by maintaining redox homeostasis and generating nucleotide precursors required for cell proliferation and DNA repair. Expression of the monocarboxylate transporter 1 (MCT1), which is responsible for the bidirectional transport of lactate, correlates with an aggressive phenotype and poor outcome in several cancer types, including breast cancer. In this study, 3-bromopyruvate (3BP), a lactate/pyruvate analog, was used to selectively target TNBC cells that express MCT1.

METHODS

The cytotoxicity of 3BP was tested in MTT assays using human TNBC cell lines: BT20 (MCT1+/MCT4-), MDA-MB-23 (MCT1-/MCT4+), and BT20 in which MCT1 was knocked down (siMCT1-BT20). The metabolite profile of 3BP-treated and 3BP-untreated cells was investigated using LC-MS/MS. The extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) of BT20 and MDA-MB-231 cells treated with 3BP were measured using a Seahorse XF96 extracellular flux analyzer. The impact of ionizing radiation on cell survival, alone or in combination with 3BP pre-treatment, was evaluated using clonogenic assays.

RESULTS

Metabolomic analyses showed that 3BP causes inhibition of glycolysis, disturbance of redox homeostasis, decreased nucleotide synthesis, and was accompanied by a reduction in medium acidification. In addition, 3BP potentiated the cytotoxic effect of ionizing radiation, a treatment that is frequently used in the management of TNBC.

CONCLUSIONS

Overall, MCT1-mediated metabolic perturbation in combination with radiotherapy is shown to be a promising strategy for the treatment of glycolytic tumors such as TNBC, overcoming the selectivity challenges of targeting glycolysis with glucose analogs.

Mitochondrial Function Are Disturbed in the Presence of the Anticancer Drug, 3-Bromopyruvate

3-bromopuryvate (3-BP) is a compound with unique antitumor activity. It has a selective action against tumor cells that exhibit the Warburg effect. It has been proven that the action of 3-BP is pleiotropic: it acts on proteins, glycolytic enzymes, reduces the amount of ATP, induces the formation of ROS (reactive oxygen species), and induces nuclear DNA damage. Mitochondria are important organelles for the proper functioning of the cell. The production of cellular energy (ATP), the proper functioning of the respiratory chain, or participation in the production of amino acids are one of the many functions of mitochondria. Here, for the first time, we show on the yeast model that 3-BP acts in the eukaryotic cell also by influence on mitochondria and that agents inhibiting mitochondrial function can potentially be used in cancer therapy with 3-BP. We show that cells with functional mitochondria are more resistant to 3-BP than rho⁰ cells. Using an MTT assay (a colorimetric assay for assessing cell metabolic activity), we demonstrated that 3-BP decreased mitochondrial activity in yeast in a dose-dependent manner. 3-BP induces mitochondrial-dependent ROS generation which results in ∆sod2, ∆por1, or ∆gpx1 mutant sensitivity to 3-BP. Probably due to ROS mtDNA lesions rise during 3-BP treatment. Our findings may have a significant impact on the therapy with 3-BP.

Delphinidin Increases the Sensitivity of Ovarian Cancer Cell Lines to 3-Bromopyruvate

3-Bromopyruvic acid (3-BP) is a promising anticancer compound. Two ovary cancer (OC) cell lines, PEO1 and SKOV3, showed relatively high sensitivity to 3-BP (half maximal inhibitory concentration (IC₅₀) of 18.7 and 40.5 µM, respectively). However, the further sensitization of OC cells to 3-BP would be desirable. Delphinidin (D) has been reported to be cytotoxic for cancer cell lines. We found that D was the most toxic for PEO1 and SKOV3 cells from among several flavonoids tested. The combined action of 3-BP and D was mostly synergistic in PEO1 cells and mostly weakly antagonistic in SKOV3 cells. The viability of MRC-5 fibroblasts was not affected by both compounds at concentrations of up to 100 µM. The combined action of 3-BP and D decreased the level of ATP and of dihydroethidium (DHE)-detectable reactive oxygen species (ROS), cellular mobility and cell staining with phalloidin and Mitotracker Red in both cell lines but increased the 2’,7’-dichlorofluorescein (DCFDA)-detectable ROS level and decreased the mitochondrial membrane potential and mitochondrial mass only in PEO1 cells. The glutathione level was increased by 3-BP+D only in SKOV3 cells. These differences may contribute to the lower sensitivity of SKOV3 cells to 3-BP+D. Our results point to the possibility of sensitization of at least some OC cells to 3-BP by D.

Toxicity and metabolism of 3-bromopyruvate in Caenorhabditis elegans

In this study, we aimed to evaluate the toxic effects, changes in life span, and expression of various metabolism-related genes in Caenorhabditis elegans, using RNA interference (RNAi) and mutant strains, after 3-bromopyruvate (3-BrPA) treatment. C. elegans was treated with various concentrations of 3-BrPA on nematode growth medium (NGM) plates, and their survival was monitored every 24 h. The expression of genes related to metabolism was measured by the real-time fluorescent quantitative polymerase chain reaction (qPCR). Nematode survival in the presence of 3-BrPA was also studied after silencing three hexokinase (HK) genes. The average life span of C. elegans cultured on NGM with 3-BrPA was shortened to 5.7 d compared with 7.7 d in the control group. hxk-1, hxk-2, and hxk-3 were overexpressed after the treatment with 3-BrPA. After successfully interfering hxk-1, hxk-2, and hxk-3, the 50% lethal concentration (LC₅₀) of all mutant nematodes decreased with 3-BrPA treatment for 24 h compared with that of the control. All the cyp35 genes tested were overexpressed, except cyp-35B3. The induction of cyp-35A1 expression was most obvious. The LC₅₀ values of the mutant strains cyp-35A1, cyp-35A2, cyp-35A4, cyp-35B3, and cyp-35C1 were lower than that of the control. Thus, the toxicity of 3-BrPA is closely related to its effect on hexokinase metabolism in nematodes, and the cyp-35 family plays a key role in the metabolism of 3-BrPA.

Construction and Evaluation of Folic Acid-Modified 3-Bromopyruvate Cubosomes

Background

Direct 3-bromopyruvate chemotherapy often causes side effects. We thus aimed to construct and evaluate folic acid-modified 3-bromopyruvate liquid crystalline nanoparticles (3BP-LCNP-FA) and assess their targeted antitumor effects in tumor-bearing nude mice.

Material/Methods

A liquid crystalline nanoparticle formulation was screened, and the structure was characterized using polarizing light- and transmission electron microscopy. The folate target was then synthesized and characterized using differential scanning calorimetry and proton nuclear magnetic resonance spectroscopy. In vitro, human CNE-2Z and MDA-MB-231 tumor cells were used to evaluate 3BP-LCNP-FA effects on tumor cell morphology and proliferation. Different drug formulations were administered to tumor-bearing nude mice to observe the treatment effects. Hepatic and renal toxicities were assessed using hematoxylin and eosin-stained liver, kidney, and lung sections along with serological analysis of liver and kidney injury markers (e.g., aspartate aminotransferase, alanine transaminase, blood urea nitrogen, and creatinine). Tumor tissue was observed for changes using proliferating cell nuclear antigen immunohistochemistry and terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

Results

We successfully prepared 3BP-LCNP-FA of spherical shape with uniform size using the aforementioned techniques; drug loading did not alter crystal morphology. These cubosomes exhibited more potent antitumor activity than 3-bromopyruvate alone or non-folic acid-conjugated 3-bromopyruvate liquid crystalline nanoparticles in vitro and in vivo without obvious toxic side effects.

Conclusions

It is possible to successfully construct 3BP-LCNP-FA as a drug delivery vehicle that is more efficacious than 3-bromopyruvate and has no obvious toxic effects. Thus, folic acid-modified cubosomes can be used as effective carriers for targeted drug administration.

The Anticancer Drug 3-Bromopyruvate Induces DNA Damage Potentially Through Reactive Oxygen Species in Yeast and in Human Cancer Cells

3-bromopyruvate (3-BP) is a small molecule with anticancer and antimicrobial activities. 3-BP is taken up selectively by cancer cells’ mono-carboxylate transporters (MCTs), which are highly overexpressed by many cancers. When 3-BP enters cancer cells it inactivates several glycolytic and mitochondrial enzymes, leading to ATP depletion and the generation of reactive oxygen species. While mechanisms of 3-BP uptake and its influence on cell metabolism are well understood, the impact of 3-BP at certain concentrations on DNA integrity has never been investigated in detail. Here we have collected several lines of evidence suggesting that 3-BP induces DNA damage probably as a result of ROS generation, in both yeast and human cancer cells, when its concentration is sufficiently low and most cells are still viable. We also demonstrate that in yeast 3-BP treatment leads to generation of DNA double-strand breaks only in S-phase of the cell cycle, possibly as a result of oxidative DNA damage. This leads to DNA damage, checkpoint activation and focal accumulation of the DNA response proteins. Interestingly, in human cancer cells exposure to 3-BP also induces DNA breaks that trigger H2A.X phosphorylation. Our current data shed new light on the mechanisms by which a sufficiently low concentration of 3-BP can induce cytotoxicity at the DNA level, a finding that might be important for the future design of anticancer therapies.

3-Bromopyruvate regulates the status of glycolysis and BCNU sensitivity in human hepatocellular carcinoma cells

Chloroethylnitrosoureas (CENUs) are bifunctional antitumor alkylating agents, which exert their antitumor activity through inducing the formation of dG-dC interstrand crosslinks (ICLs) within DNA double strand. However, the complex process of tumor biology enables tumor cells to escape the killing triggered by CENUs, as for instance with the detoxifying activity of O⁶-methylguanine DNA methyltransferase (MGMT) to accomplish DNA damage repair. Considering the fact that most tumor cells highly depend on aerobic glycolysis to provide energy for survival even in the presence of oxygen (Warburg effect), inhibition of aerobic glycolysis may be an attractive strategy to overcome the resistance and improve the chemotherapeutic effects of CENUs. Especially, 3-bromopyruvate (3-BrPA), a small molecule alkylating agent, has been emerged as an effective glycolytic inhibitor (energy blocker) in cancer treatment. In view of its tumor specificity and inhibition on cellular multiple targets, it is likely to reduce the chemoresistance when chemotherapeutic drugs are combined with 3-BrPA. In this study, we investigated the effects of 3-BrPA on the chemosensitivity of two human hepatocellular carcinoma (HCC) cell lines to the cytotoxic effects of l,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and the underlying molecular mechanism. The sensitivity of SMMC-7721 and HepG2 cells to BCNU was significantly increased by 2 h pretreatment with micromolar dosage of 3-BrPA. Moreover, 3-BrPA decreased the cellular ATP and GSH levels, and extracellular lactate excreted by tumor cells, and the effects were more effective when 3-BrPA was combined with BCNU. Cellular hexokinase-II (HK-II) activity was also reduced after exposure to the treatment of 3-BrPA plus BCNU. Based on the above results, the effects of 3-BrPA on the formation of dG-dC ICLs induced by BCNU was investigated by stable isotope dilution high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). The results indicated that BCNU produced higher levels of dG-dC ICLs in SMMC-7721 and HepG2 cells pretreated with 3-BrPA compared to that without 3-BrPA pretreatment. Notably, in MGMT-deficient HepG2 cells, the levels of dG-dC ICLs were significantly higher than MGMT-proficient SMMC-7721 cells. In general, these findings revealed that 3-BrPA, as an effective glycolytic inhibitor, may be considered as a potential clinical chemosensitizer to optimize the therapeutic index of CENUs.

Unraveling the Potential Role of Glutathione in Multiple Forms of Cell Death in Cancer Therapy

Glutathione is the principal intracellular antioxidant buffer against oxidative stress and mainly exists in the forms of reduced glutathione (GSH) and oxidized glutathione (GSSG). The processes of glutathione synthesis, transport, utilization, and metabolism are tightly controlled to maintain intracellular glutathione homeostasis and redox balance. As for cancer cells, they exhibit a greater ROS level than normal cells in order to meet the enhanced metabolism and vicious proliferation; meanwhile, they also have to develop an increased antioxidant defense system to cope with the higher oxidant state. Growing numbers of studies have implicated that altering the glutathione antioxidant system is associated with multiple forms of programmed cell death in cancer cells. In this review, we firstly focus on glutathione homeostasis from the perspectives of glutathione synthesis, distribution, transportation, and metabolism. Then, we discuss the function of glutathione in the antioxidant process. Afterwards, we also summarize the recent advance in the understanding of the mechanism by which glutathione plays a key role in multiple forms of programmed cell death, including apoptosis, necroptosis, ferroptosis, and autophagy. Finally, we highlight the glutathione-targeting therapeutic approaches toward cancers. A comprehensive review on the glutathione homeostasis and the role of glutathione depletion in programmed cell death provide insight into the redox-based research concerning cancer therapeutics.

B7-H3 promotes aerobic glycolysis and chemoresistance in colorectal cancer cells by regulating HK2

Accumulating evidence suggests that aerobic glycolysis is important for colorectal cancer (CRC) development. However, the underlying mechanisms have yet to be elucidated. B7-H3, an immunoregulatory protein, is broadly overexpressed by multiple tumor types and plays a vital role in tumor progression. In this study, we found that overexpression of B7-H3 effectively increased the rate of glucose consumption and lactate production, whereas knockdown of B7-H3 had the opposite effect. Furthermore, we showed that B7-H3 increased glucose consumption and lactate production by promoting hexokinase 2 (HK2) expression in CRC cells, and we also found that HK2 was a key mediator of B7-H3-induced CRC chemoresistance. Depletion of HK2 expression or treating cells with HK2 inhibitors could reverse the B7-H3-induced increase in aerobic glycolysis and B7-H3-endowed chemoresistance of cancer cells. Moreover, we verified a positive correlation between the expression of B7-H3 and HK2 in tumor tissues of CRC patients. Collectively, our findings suggest that B7-H3 may be a novel regulator of glucose metabolism and chemoresistance via controlling HK2 expression in CRC cells, a result that could help develop B7-H3 as a promising therapeutic target for CRC treatment.

Tumor Energy Metabolism and Potential of 3-Bromopyruvate as an Inhibitor of Aerobic Glycolysis: Implications in Tumor Treatment

Tumor formation and growth depend on various biological metabolism processes that are distinctly different with normal tissues. Abnormal energy metabolism is one of the typical characteristics of tumors. It has been proven that most tumor cells highly rely on aerobic glycolysis to obtain energy rather than mitochondrial oxidative phosphorylation (OXPHOS) even in the presence of oxygen, a phenomenon called “Warburg effect”. Thus, inhibition of aerobic glycolysis becomes an attractive strategy to specifically kill tumor cells, while normal cells remain unaffected. In recent years, a small molecule alkylating agent, 3-bromopyruvate (3-BrPA), being an effective glycolytic inhibitor, has shown great potential as a promising antitumor drug. Not only it targets glycolysis process, but also inhibits mitochondrial OXPHOS in tumor cells. Excellent antitumor effects of 3-BrPA were observed in cultured cells and tumor-bearing animal models. In this review, we described the energy metabolic pathways of tumor cells, mechanism of action and cellular targets of 3-BrPA, antitumor effects, and the underlying mechanism of 3-BrPA alone or in combination with other antitumor drugs (e.g., cisplatin, doxorubicin, daunorubicin, 5-fluorouracil, etc.) in vitro and in vivo. In addition, few human case studies of 3-BrPA were also involved. Finally, the novel chemotherapeutic strategies of 3-BrPA, including wafer, liposomal nanoparticle, aerosol, and conjugate formulations, were also discussed for future clinical application.

3-Bromopyruvate as a potent anticancer therapy in honor and memory of the late Professor André Goffeau

3-Bromopyruvate (3BP) is a small, highly reactive molecule formed by bromination of pyruvate. In the year 2000, the antitumor properties of 3BP were discovered. Studies using animal models proved its high efficacy for anticancer therapy with no apparent side effects. This was also found to be the case in a limited number of cancer patients treated with 3BP. Due to the "Warburg effect," most tumor cells exhibit metabolic changes, for example, increased glucose consumption and lactic acid production resulting from mitochondrial-bound overexpressed hexokinase 2. Such alterations promote cell migration, immortality via inhibition of apoptosis, and less dependence on the availability of oxygen. Significantly, these attributes also make cancer cells more sensitive to agents, such as 3BP that inhibits energy production pathways without harming normal cells. This selectivity of 3BP is mainly due to overexpressed monocarboxylate transporters in cancer cells. Furthermore, 3BP is not a substrate for any pumps belonging to the ATP-binding cassette superfamily, which confers resistance to a variety of drugs. Also, 3BP has the capacity to induce multiple forms of cell death, by, for example, ATP depletion resulting from inactivation of both glycolytic and mitochondrial energy production pathways. In addition to its anticancer property, 3BP also exhibits antimicrobial activity. Various species of microorganisms are characterized by different susceptibility to 3BP inhibition. Among tested strains, the most sensitive was found to be the pathogenic yeast-like fungus Cryptococcus neoformans. Significantly, studies carried out in our laboratories have shown that 3BP exhibits a remarkable capacity to eradicate cancer cells, fungi, and algae.

The antimetabolite 3-bromopyruvate selectively inhibits Staphylococcus aureus

Increased antibacterial resistance jeopardizes current therapeutic strategies to control infections, soliciting the development of novel antibacterial drugs with new mechanisms of action. This study reports the discovery of potent and selective antistaphylococcal activity of 3-bromopyruvate (3BP), an antimetabolite in preclinical development as an anticancer drug. 3BP showed bactericidal activity against Staphylococcus aureus, with active concentrations comparable with those reported to be effective against cancer cells. In contrast, no relevant activity was observed against other ESKAPE bacteria (Enterococcus faecium, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.). The antistaphylococcal activity of 3BP was confirmed using a panel of human and veterinary strains, including multi-drug-resistant isolates. 3BP showed highest antibacterial activity under conditions that increase its stability (acidic pH) or promote S. aureus fermentative metabolism (anaerobiosis), although 3BP was also able to kill metabolically inactive cells. 3BP showed synergism with gentamicin, and also disrupted preformed S. aureus biofilms at concentrations only slightly higher than those inhibiting planktonic cells. This study unravels novel antibacterial and antibiofilm activities for the anticancer drug 3BP, paving the way for further preclinical studies.

Enhancing anticancer effects, decreasing risks and solving practical problems facing 3-bromopyruvate in clinical oncology: 10 years of research experience

3-Bromopyruvate (3BP) is a promising powerful general anticancer agent. Unfortunately, 3BP release faces many practical and biochemical problems in clinical human oncology, for example, 3BP induces burning venous sensation (during intravenous infusion) and rapid inactivation by thiol groups of glutathione and proteins. 3BP exhibits resistance in glutathione-rich tumors without being able to exert selective targeting. 3BP does not cross the blood–brain barrier and cannot treat nervous system tumors. Importantly, 3BP cannot persist in tumor tissues due to the phenomenon of enhanced permeability and retention effect. Here, the author presents the practical solutions for clinical problems facing 3BP use in clinical oncology, based on over 10 years of experience in 3BP research. Crude (unformulated 3BP that is purchased from chemical companies without being formulated in liposomes or other nanocarriers) should not be administered in clinical oncology. Instead, 3BP is better formulated with liposomes, polyethylene glycol (PEG), PEGylated liposomes (stealth liposomes) or perillyl alcohol that are used currently with many chemotherapeutics for treating clinical tumors in cancer patients. Formulating 3BP with targeted liposomes, for example, with folate, transferrin or other ligands, improves tumor targeting. Formulating 3BP with liposomes, PEG, stealth liposomes or perillyl alcohol may improve its pharmacokinetics, hide it from thiols in the circulation, protect it from serum proteins and enzymes, prevent burning sensation, prolong 3BP’s longevity and facilitate crossing the BBB. Formulating 3BP with stealth liposomes protects 3BP from the reticuloendothelial cells. Liposomal 3BP formulations may retain 3BP better inside the relatively large tumor capillary pores (abolish enhanced permeability and retention effect) sparing normal tissues, facilitate new delivery routes for 3BP (eg, topical and intranasal 3BP administration using perillyl alcohol) and improve cancer cytotoxicity. Formulating 3BP may be promising in overcoming many obstacles in clinical oncology.

Targeting energy metabolism to eliminate cancer cells

Adaptive metabolic responses toward a low oxygen environment are essential to maintain rapid proliferation and are relevant for tumorigenesis. Reprogramming of core metabolism in tumors confers a selective growth advantage such as the ability to evade apoptosis and/or enhance cell proliferation and promotes tumor growth and progression. One of the mechanisms that contributes to tumor growth is the impairment of cancer cell metabolism. In this review, we outline the small-molecule inhibitors identified over the past decade in targeting cancer cell metabolism and the usage of some of these molecules in clinical trials.

Glutathione in Ovarian Cancer: A Double-Edged Sword

Glutathione (GSH) has several roles in a cell, such as a reactive oxygen species (ROS) scavenger, an intervenient in xenobiotics metabolism and a reservoir of cysteine. All of these activities are important in the maintenance of normal cells homeostasis but can also constitute an advantage for cancer cells, allowing disease progression and resistance to therapy. Ovarian cancer is the major cause of death from gynaecologic disease and the second most common gynaecologic malignancy worldwide. In over 50 years, the overall survival of patients diagnosed with epithelial ovarian cancer has not changed, regardless of the efforts concerning early detection, radical surgery and new therapeutic approaches. Late diagnosis and resistance to therapy are the main causes of this outcome, and GSH is profoundly associated with chemoresistance to platinum salts, which, together with taxane-based chemotherapy and surgery, are the main therapy strategies in ovarian cancer treatment. Herein, we present some insights into the role of GSH in the poor prognosis of ovarian cancer, and also point out how some strategies underlying the dependence of ovarian cancer cells on GSH can be further used to improve the effectiveness of therapy.

Drug metabolizing enzymes and their inhibitors' role in cancer resistance

Despite continuous research on chemotherapeutic agents, different mechanisms of resistance have become a major pitfall in cancer chemotherapy. Although, exhaustive efforts are being made by several researchers to target resistance against chemotherapeutic agents, there is another class of resistance mechanism which is almost carrying on unattended. This class of resistance includes pharmacokinetics resistance such as efflux by ABC transporters and drug metabolizing enzymes. ABC transporters are the membrane bound proteins which are responsible for the movement of substrates through the cell membrane. Drug metabolizing enzymes are an integral part of phase-II metabolism that helps in the detoxification of exogenous, endogenous and xenobiotics substrates. These include uridine diphospho-glucuronosyltransferases (UGTs), glutathione-S-transferases (GSTs), dihydropyrimidine dehydrogenases (DPDs) and thiopurine methyltransferases (TPMTs). These enzymes may affect the role of drugs in both positive as well negative manner, depending upon the type of tissue and cells present and when present in tumors, can result in drug resistance. However, the underlying mechanism of resistance by drug metabolizing enzymes is still not clear. Here, we have tried to cover various aspects of these enzymes in relation to anticancer drugs.

3-Bromopyruvate as an Alternative Option for the Treatment of Protothecosis

Protothecosis is an unusual infection of both humans and animals caused by opportunistically pathogenic microalgae of the genus Prototheca. Until now, no standardized treatment protocols exist for the protothecal disease, boosted by a remarkable resistance of Prototheca spp. to a wide array of antimicrobial agents currently available in clinical use. Consequently, there is an urgent need for new effective drugs against Prototheca algae. In this study, the anti-Prototheca activity of 3-bromopyruvate (3BP), either alone or in combination with amphotericin B (AMB) was assessed in vitro, as well as the cytotoxicity of 3BP toward the bovine mammary epithelial cells and murine skin fibroblasts. The mean minimum inhibitory concentrations (MIC) and minimum algaecidal concentrations (MAC) were 0.85 ± 0.21 and 2.25 ± 0.54 mM for Prototheca wickerhamii, 1.25 ± 0.47 and 4.8 ± 1.03 mM for Prototheca blaschkeae, and 1.55 ± 0.69 and 5.6 ± 1.3 mM for Prototheca zopfii gen. 2, respectively. For all Prototheca strains tested, a synergistic interaction between 3BP and AMB was observed, resulting in about 4-fold reduction of their individual MICs, when used together. The elevated content of intracellular glutathione (GSH) was associated with a decreased susceptibility to 3BP. Both epithelial and fibroblast cells retained high viability upon treatment with 3BP at concentrations equivalent to the highest MIC recorded (3 mM) and 10-fold higher (30 mM), with the mean cell viability exceeding 80%, essentially the same as for the untreated cells. The results from these in vitro studies emphasize the high activity of 3BP against the Prototheca algae, its synergistic effect when used in combination with AMB, and the safety of the drug toward the tested mammalian cells. Along with the advantageous physico-chemical and pharmacokinetic properties, 3BP may be considered an effective and safe novel agent against the protothecal disease.