The antiproliferative effects of phenoxodiol are associated with inhibition of plasma membrane electron transport in tumour cell lines and primary immune cells

Ecto-NOX Disulfide-Thiol Exchanger 2 (ENOX2/tNOX) Is a Potential Prognostic Marker in Primary Malignant Melanoma and May Serve as a Therapeutic Target

With an increasing incidence of malignant melanoma, new prognostic biomarkers for clinical decision making have become more important. In this study, we evaluated the role of ecto-NOX disulfide-thiol exchanger 2 (ENOX2/tNOX), a cancer- and growth-associated protein, in the prognosis and therapy of primary malignant melanoma. We conducted a tissue microarray analysis of immunohistochemical ENOX2 protein expression and The Cancer Genome Atlas (TCGA) ENOX2 RNA expression analysis, as well as viability assays and Western blots of melanoma cell lines treated with the ENOX2 inhibitor phenoxodiol (PXD) and BRAF inhibitor (BRAFi) vemurafenib. We discovered that high ENOX2 expression is associated with decreased overall (OS), disease-specific (DSS) and metastasis-free survival (MFS) in primary melanoma (PM) and a reduction in electronic tumor-infiltrating lymphocytes (eTILs). A gradual rise in ENOX2 expression was found with an increase in malignant potential from benign nevi (BNs) via PMs to melanoma metastases (MMs), as well as with an increasing tumor thickness and stage. These results highlight the important role of ENOX2 in cancer growth, progression and metastasis. The ENOX2 expression was not limited to malignant cell lines but could also be found in keratinocytes, fibroblasts and melanocytes. The viability of melanoma cell lines could be inhibited by PXD. A reduced induction of phospho-AKT under PXD could prevent the development of acquired BRAFi resistance. In conclusion, ENOX2 may serve as a potential prognostic marker and therapeutic target in malignant melanoma.

The role of isoflavones in augmenting the effects of radiotherapy

Cancer is one of the major health problems and the second cause of death worldwide behind heart disease. The traditional soy diet containing isoflavones, consumed by the Asian population in China and Japan has been identified as a protective factor from hormone-related cancers. Over the years the research focus has shifted from emphasizing the preventive effect of isoflavones from cancer initiation and promotion to their efficacy against established tumors along with chemo- and radiopotentiating effects. Studies performed in mouse models and results of clinical trials emphasize that genistein or a mixture of isoflavones, containing in traditional soy diet, could be utilized to both potentiate the response of cancer cells to radiotherapy and reduce radiation-induced toxicity in normal tissues. Currently ongoing clinical research explores a potential of another significant isoflavone, idronoxil, also known as phenoxodiol, as radiation enhancing agent. In the light of the recent clinical findings, this article reviews the accumulated evidence which support the clinically desirable interactions of soy isoflavones with radiation therapy resulting in improved tumor treatment. This review discusses important aspects of the development of isoflavones as anticancer agents, and mechanisms potentially relevant to their activity in combination with radiation therapy of cancer. It gives a critical overview of studies characterizing isoflavone targets such as topoisomerases, ENOX2/PMET, tyrosine kinases and ER receptor signaling, and cellular effects on the cell cycle, DNA damage, cell death, and immune responses.

Synthesis, characterization of ruthenium(II), nickel(II), palladium(II), and platinum(II) triphenylphosphine-based complexes bearing an ONS-donor chelating agent: Interaction with biomolecules, antioxidant, in vitro cytotoxic, apoptotic activity and cell cycle analysis

Four new transition metal complexes, [M(PPh₃)(L)]^.CH₃OH (M = Ni(II) (1), Pd(II) (2)) [Pt (PPh₃)₂(HL)]Cl (3) and [Ru(CO)(PPh₃)₂(L)] (4) (H₂L = 2,4-dihydroxybenzaldehyde-S-methyldithiocarbazate, PPh₃ = triphenylphosphine) have been synthesized and characterized by elemental analyses (C, H, N), FTIR, NMR (¹H, ³¹P), ESI-MS and UV-visible spectroscopy. The molecular structure of (1) and (2) complexes was confirmed by single-crystal X-ray crystallography. It showed a distorted square planar geometry for both complexes around the metal center, and the H₂L adopt a bi-negative tridentate chelating mode. The interaction with biomolecules viz., calf thymus DNA (ct DNA), yeast RNA (tRNA), and BSA (bovine serum albumin) was examined by both UV-visible and fluorescence spectroscopies. The antioxidant activity of all compounds is discussed on basis of DPPH^• (2,2-diphenyl-1-picrylhydrazyl) scavenging activity and showed better antioxidant activity for complexes compared to the ligand. The in vitro cytotoxicity of the compounds was tested on human (breast cancer (MCF7), colon cancer (HCT116), liver cancer (HepG2), and normal lung fibroblast (WI38)) cell lines, showing that complex (1) the most potent against MCF7 and complex (4) against HCT116 cell lines based on IC₅₀ and selective indices (SI) values. So, both complexes were chosen for further studies such as DNA fragmentation, cell apoptosis, and cell cycle analyses. Complex (1) induced MCF7 cell death by cellular apoptosis and arrest cells at S phase. Complex (4) induced HCT116 cell death predominantly by cellular necrosis and arrested cell division at G2/M phase due to DNA damage.

NOX66 as Monotherapy, and in Combination With Carboplatin, in Patients With Refractory Solid Tumors: Phase Ia/b Study

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NOX66 contains idronoxil, formulated as a rectal suppository.

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CEP-1 is the first study to assess NOX66 in patients with refractory solid tumors.

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NOX66 was well tolerated at 400/800 mg as monotherapy and combined with carboplatin.

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The safety profile justifies continuation of the NOX66 clinical research program.

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Early results suggest most patients had stable disease by study end

Background

Although oral and intravenous forms of idronoxil have been well tolerated, the safety of NOX66, with idronoxil formulated as a rectal suppository, is not known. This Phase Ia/b clinical study (protocol No. NOX66-001A), known as Chemotherapy Enhancement Program-1, is the first to assess NOX66 in patients with refractory solid tumors.

Objective

The study aimed to determine the safety profile of NOX66 both as a monotherapy and in combination with carboplatin, and to evaluate whether or not NOX66 has a meaningful anticancer effect when combined with carboplatin in this patient population.

Methods

Chemotherapy Enhancement Program-1 was a multicenter, open-label, nonrandomized, 2-dose cohort study of NOX66 as monotherapy (Phase Ia) and in combination with carboplatin (Phase Ib). Patients with refractory solid tumors who had stopped responding to standard treatments were eligible to participate. Twenty patients were screened and 19 enrolled in the study. They were divided into 2 groups: cohort 1 (n = 8) received 1 suppository daily (400 mg) and cohort 2 (n = 11) received 2 suppositories daily (800 mg) for 14 consecutive days followed by 7 days of rest. Patients who completed Phase Ia without significant toxicity continued to Phase Ib, where NOX66 was combined with carboplatin for up to 6x 28-day treatment cycles, with low-dose carboplatin (600 mg) for cycles 1B through 3B and standard dose carboplatin (900 mg) for cycles 4B through 6B. The main outcomes assessed were safety (n = 18) and efficacy signals (n = 14).

Results

NOX66 generally was well tolerated at 400 mg and 800 mg, both as monotherapy and in combination with carboplatin in patients with refractory solid tumors. The safety profile was consistent for oncology patients, with 77.8% experiencing at least 1 treatment-emergent adverse event. The most common adverse events were blood and lymphatic system disorders (44.4%), with only anemia considered as possibly related to NOX66. Although the study was primarily designed to assess safety and tolerability, the efficacy measurements demonstrated that most patients had stable disease or better by study end.

Conclusions

The favorable safety profile of NOX66 provides reassurance to justify continuation of clinical research. The efficacy findings are encouraging in terms of the chemosensitizing potential of NOX66 in refractory solid tumors. (Curr Ther Res Clin Exp. 2021; 82:XXX–XXX)

A simple indirect colorimetric assay for measuring mitochondrial energy metabolism based on uncoupling sensitivity

Purpose

Cancer cells rapidly adjust their balance between glycolytic and mitochondrial ATP production in response to changes in their microenvironment and to treatments like radiation and chemotherapy. Reliable, simple, high throughput assays that measure the levels of mitochondrial energy metabolism in cells are useful determinants of treatment effects. Mitochondrial metabolism is routinely determined by measuring the rate of oxygen consumption (OCR). We have previously shown that indirect inhibition of plasma membrane electron transport (PMET) by the mitochondrial uncoupler, FCCP, may also be a reliable measure of mitochondrial energy metabolism. Here, we aimed to validate these earlier findings by exploring the relationship between stimulation of oxygen consumption by FCCP and inhibition of PMET.

Methods

We measured PMET by reduction of the cell impermeable tetrazolium salt WST-1/PMS. We characterised the effect of different growth conditions on the extent of PMET inhibition by FCCP. Next, we compared FCCP-mediated PMET inhibition with FCCP-mediated stimulation of OCR using the Seahorse XF96e flux analyser, in a panel of cancer cell lines.

Results

We found a strong inverse correlation between stimulation of OCR and PMET inhibition by FCCP. PMET and OCR were much more severely affected by FCCP in cells that rely on mitochondrial energy production than in cells with a more glycolytic phenotype.

Conclusion

Indirect inhibition of PMET by FCCP is a reliable, simple and inexpensive high throughput assay to determine the level of mitochondrial energy metabolism in cancer cells.

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WST-1/PMS dye reduction measures NADH-driven plasma membrane electron transport.

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FCCP stimulates mitochondrial oxygen consumption and inhibits dye reduction.

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The FCCP effect on dye reduction and oxygen consumption is inversely correlated.

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FCCP-mediated inhibition of dye reduction is a measure of mitochondrial metabolism.

Triggering of eryptosis, the suicidal erythrocyte death, by phenoxodiol

Phenoxodiol is used for the treatment of malignancy. The substance is effective by triggering suicidal tumor cell death or apoptosis. At least in theory, phenoxodiol could similarly stimulate suicidal erythrocyte death or eryptosis. Eryptosis is characterized by cell shrinkage and breakdown of cell membrane asymmetry with phosphatidylserine translocation to the erythrocyte surface. Signaling of eryptosis includes increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), formation of reactive oxygen species (ROS), and increase of ceramide abundance at the cell surface. The present study explored whether phenoxodiol induces eryptosis and whether it modifies Ca²⁺ entry, ROS, and ceramide. Using flow cytometry, phosphatidylserine exposure at the cell surface was quantified from annexin V binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3 fluorescence, ROS from DCFDA-dependent fluorescence, and ceramide abundance utilizing specific antibodies. A 48-h exposure of human erythrocytes to phenoxodiol (100 μg/ml [416 μM]) significantly increased the percentage of annexin V binding cells, significantly decreased average forward scatter and Fluo3 fluorescence and significantly increased ceramide abundance, but did not significantly modify DCFDA fluorescence. The effect of phenoxodiol on annexin V binding tended to decrease following removal of extracellular Ca²⁺, an effect, however, not reaching statistical significance. In conclusion, phenoxodiol triggers eryptosis, an effect paralleled by increase of ceramide abundance.

Preparation, characterization and in vitro biological evaluation of (1:2) phenoxodiol-β-cyclodextrin complex

Phenoxodiol is an isoflavone analogue that possesses potent anticancer properties. However, the poor water solubility of phenoxodiol limits its overall efficacy as an anticancer agent. To overcome this, β-cyclodextrin was used to encapsulate phenoxodiol. The phenoxodiol-β-cyclodextrin complex was prepared via a modified co-evaporation method and characterized by ¹H NMR and X-ray crystallography, revealing a 1:2 stoichiometry. The 2D ROESY NMR spectroscopy suggested the limited motion of phenoxodiol within the cavity of β-cyclodextrin while the X-ray crystal data displays by far the best 'ship-in-a-bottle' case of 1:2 inclusion complex. The aqueous solubility of the phenoxodiol in β-cyclodextrin had improved and the in vitro biological evaluation revealed enhanced anti-proliferative activity against three cancer cell lines. Additionally, the toxicity of the complex against normal human cell line was 2.5 times lower. These data indicates that the encapsulation of phenoxodiol into β-cyclodextrin leads to an improvement in its overall water solubility and biological activity.

Functional Mitochondria in Health and Disease

The ability to rapidly adapt cellular bioenergetic capabilities to meet rapidly changing environmental conditions is mandatory for normal cellular function and for cancer progression. Any loss of this adaptive response has the potential to compromise cellular function and render the cell more susceptible to external stressors such as oxidative stress, radiation, chemotherapeutic drugs, and hypoxia. Mitochondria play a vital role in bioenergetic and biosynthetic pathways and can rapidly adjust to meet the metabolic needs of the cell. Increased demand is met by mitochondrial biogenesis and fusion of individual mitochondria into dynamic networks, whereas a decrease in demand results in the removal of superfluous mitochondria through fission and mitophagy. Effective communication between nucleus and mitochondria (mito-nuclear cross talk), involving the generation of different mitochondrial stress signals as well as the nuclear stress response pathways to deal with these stressors, maintains bioenergetic homeostasis under most conditions. However, when mitochondrial DNA (mtDNA) mutations accumulate and mito-nuclear cross talk falters, mitochondria fail to deliver critical functional outputs. Mutations in mtDNA have been implicated in neuromuscular and neurodegenerative mitochondriopathies and complex diseases such as diabetes, cardiovascular diseases, gastrointestinal disorders, skin disorders, aging, and cancer. In some cases, drastic measures such as acquisition of new mitochondria from donor cells occurs to ensure cell survival. This review starts with a brief discussion of the evolutionary origin of mitochondria and summarizes how mutations in mtDNA lead to mitochondriopathies and other degenerative diseases. Mito-nuclear cross talk, including various stress signals generated by mitochondria and corresponding stress response pathways activated by the nucleus are summarized. We also introduce and discuss a small family of recently discovered hormone-like mitopeptides that modulate body metabolism. Under conditions of severe mitochondrial stress, mitochondria have been shown to traffic between cells, replacing mitochondria in cells with damaged and malfunctional mtDNA. Understanding the processes involved in cellular bioenergetics and metabolic adaptation has the potential to generate new knowledge that will lead to improved treatment of many of the metabolic, degenerative, and age-related inflammatory diseases that characterize modern societies.

Redox Signaling and Bioenergetics Influence Lung Cancer Cell Line Sensitivity to the Isoflavone ME-344

ME-344 [(3R,4S)-3,4-bis(4-hydroxyphenyl)-8-methyl-3,4-dihydro-2H-chromen-7-ol] is a second-generation derivative natural product isoflavone presently under clinical development. ME-344 effects were compared in lung cancer cell lines that are either intrinsically sensitive or resistant to the drug and in primary immortalized human lung embryonic fibroblasts (IHLEF). Cytotoxicity at low micromolar concentrations occurred only in sensitive cell lines, causing redox stress, decreased mitochondrial ATP production, and subsequent disruption of mitochondrial function. In a dose-dependent manner the drug caused instantaneous and pronounced inhibition of oxygen consumption rates (OCR) in drug-sensitive cells (quantitatively significantly less in drug-resistant cells). This was consistent with targeting of mitochondria by ME-344, with specific effects on the respiratory chain (resistance correlated with higher glycolytic indexes). OCR inhibition did not occur in primary IHLEF. ME-344 increased extracellular acidification rates in drug-resistant cells (significantly less in drug-sensitive cells), implying that ME-344 targets mitochondrial proton pumps. Only in drug-sensitive cells did ME-344 dose-dependently increase the intracellular generation of reactive oxygen species and cause oxidation of total (mainly glutathione) and protein thiols and the concomitant immediate increases in NADPH levels. We conclude that ME-344 causes complex, redox-specific, and mitochondria-targeted effects in lung cancer cells, which differ in extent from normal cells, correlate with drug sensitivity, and provide indications of a beneficial in vitro therapeutic index.

NADH-linked metabolic plasticity of MCF-7 breast cancer cells surviving in a nutrient-deprived microenvironment

Characteristic of the tumor microenvironment are fluctuating gradients of reduced nutrient levels and released lactate. A fundamental issue is how tumor cells modulate their metabolic activity when both glucose and glutamine levels become limiting in the presence of high exogenous lactate. For functional analyses, the activities of pyruvate kinase, lactate dehydrogenase (LDH) and plasma membrane NADH oxidase (NOX) as well as cell growth were measured in breast cancer MCF-7 cells cultured in medium containing various concentrations of these metabolites. After 3 days at glucose concentrations below 2.5 mM, cell number was higher with 0.1 mM than with 1.0 mM glutamine, indicating that the glucose/glutamine balance is important for growth. On the other hand, NOX activity increased with increasing glucose >2.5 mM, but only with low glutamine (0.1 mM). Pyruvate kinase activity also increased, with LDH activity remaining 2-3-fold lower. Here NOX could have a complementary role in reoxidizing NADH for glycolysis. Exogenous lactate supported cell survival at limiting concentrations of glucose and glutamine while increasing NOX and pyruvate kinase activities as well as NADH levels. It is proposed that lactate supports cell survival by fuelling gluconeogenesis and/or the TCA cycle in mitochondria, from where NADH could be shuttled to the cytosol and reoxidized by NOX. Cell survival and the metabolic phenotype are thus interrelated to the dynamics of NADH and plasma membrane NOX activity, which are regulated by the balance of glucose/glutamine levels, in conjunction with lactate in a precarious tumor microenvironment.

Cytotoxic constituents from the rhizomes of Curcuma zedoaria

Curcuma zedoaria also known as Temu putih is traditionally used in food preparations and treatment of various ailments including cancer. The cytotoxic activity of hexane, dichloromethane, ethyl acetate, methanol, and the methanol-soxhlet extracts of Curcuma zedoaria rhizomes was tested on two human cancer cell lines (Ca Ski and MCF-7) and a noncancer cell line (HUVEC) using MTT assay. Investigation on the chemical components in the hexane and dichloromethane fractions gave 19 compounds, namely, labda-8(17),12 diene-15,16 dial (1), dehydrocurdione (2), curcumenone (3), comosone II (4), curcumenol (5), procurcumenol (6), germacrone (7), zerumbone epoxide (8), zederone (9), 9-isopropylidene-2,6-dimethyl-11-oxatricyclo[6.2.1.0^1,5]undec-6-en-8-ol (10), furanodiene (11), germacrone-4,5-epoxide (12), calcaratarin A (13), isoprocurcumenol (14), germacrone-1,10-epoxide (15), zerumin A (16), curcumanolide A (17), curcuzedoalide (18), and gweicurculactone (19). Compounds (1–19) were evaluated for their antiproliferative effect using MTT assay against four cancer cell lines (Ca Ski, MCF-7, PC-3, and HT-29). Curcumenone (3) and curcumenol (5) displayed strong antiproliferative activity (IC₅₀ = 8.3 ± 1.0 and 9.3 ± 0.3 μg/mL, resp.) and were found to induce apoptotic cell death on MCF-7 cells using phase contrast and Hoechst 33342/PI double-staining assay. Thus, the present study provides basis for the ethnomedical application of Curcuma zedoaria in the treatment of breast cancer.

A first-in-human dose-escalation study of ME-143, a second generation NADH oxidase inhibitor, in patients with advanced solid tumors

Background ME-143, a second-generation tumor-specific NADH oxidase inhibitor, is broadly active against human cancers in vitro and in vivo. This first-in-human dose-escalation study evaluated the dose-limiting toxicities (DLTs), pharmacokinetics, safety, tolerability, and preliminary anti-tumor activity of ME-143 in patients with advanced solid tumors. Methods Patients with advanced solid tumors were treated in a 3 + 3 escalation design. ME-143 was administered via intravenous infusion on days 1, 8, and 15 of the first 28-day cycle, and weekly thereafter; the final cohort received twice-weekly treatment. Samples for pharmacokinetic analysis were collected during cycle 1. Treatment continued until disease progression or unacceptable toxicity. Results Eighteen patients were treated: 2.5 mg/kg (n = 3); 5 mg/kg (n = 3); 10 mg/kg (n = 3); 20 mg/kg (n = 6); 20 mg/kg twice-weekly (n = 3). There were no DLTs observed. Nearly all treatment-related toxicities were grade 1/2, specifically (all grades) nausea (22 %) and fatigue (17 %). Two patients experienced infusion reactions at the 20 mg/kg dose level, one of which was grade 4. Stable disease was documented in three patients with colorectal cancer, cholangiocarcinoma, and anal cancer. Pharmacokinetic exposures were linear and dose-dependent, with a half-life of approximately 5 h. Conclusions ME-143 was well-tolerated when administered intravenously at the maximally administered/recommended phase 2 dose of 20 mg/kg once weekly to patients with advanced solid tumors. Though limited clinical activity was observed with monotherapy, inhibitors of tumor-specific NADH oxidase such as ME-143 may derive their greatest benefit in combination with cytotoxic chemotherapy.

Mitochondrial genome-knockout cells demonstrate a dual mechanism of action for the electron transport complex I inhibitor mycothiazole

Mycothiazole, a polyketide metabolite isolated from the marine sponge Cacospongia mycofijiensis, is a potent inhibitor of metabolic activity and mitochondrial electron transport chain complex I in sensitive cells, but other cells are relatively insensitive to the drug. Sensitive cell lines (IC(50) 0.36-13.8 nM) include HeLa, P815, RAW 264.7, MDCK, HeLa S3, 143B, 4T1, B16, and CD4/CD8 T cells. Insensitive cell lines (IC(50) 12.2-26.5 μM) include HL-60, LN18, and Jurkat. Thus, there is a 34,000-fold difference in sensitivity between HeLa and HL-60 cells. Some sensitive cell lines show a biphasic response, suggesting more than one mechanism of action. Mitochondrial genome-knockout ρ(0) cell lines are insensitive to mycothiazole, supporting a conditional mitochondrial site of action. Mycothiazole is cytostatic rather than cytotoxic in sensitive cells, has a long lag period of about 12 h, and unlike the complex I inhibitor, rotenone, does not cause G(2)/M cell cycle arrest. Mycothiazole decreases, rather than increases the levels of reactive oxygen species after 24 h. It is concluded that the cytostatic inhibitory effects of mycothiazole on mitochondrial electron transport function in sensitive cell lines may depend on a pre-activation step that is absent in insensitive cell lines with intact mitochondria, and that a second lower-affinity cytotoxic target may also be involved in the metabolic and growth inhibition of cells.

Preclinical genotoxicology of nor-β-lapachone in human cultured lymphocytes and Chinese hamster lung fibroblasts

Nor-β-lapachone has shown several biological properties. Regarding cytotoxic activity against cancer cell lines, it has been recognized as an important prototype. However, quinonoid drugs present a major challenge because of their toxicity. In this study, we evaluated the cytotoxicity and genetic toxicity of nor-β-lapachone in human lymphocytes and HL-60 leukemia cells and murine V79 fibroblasts, to shed some light on its selectivity toward cancer cells. As measured by MTT test, exposure of V79 cells to nor-β-lapachone resulted in a weak cytotoxicity (IC(50) = 13.41 μM), and at a concentration up to 21.9 μM, no cytotoxic effect was observed in lymphocytes, while in HL-60 cells, nor-β-lapachone elicited significantly greater cytotoxicity (IC(50) = 1.89 μM). Cultures coexposed to GSH-OEt showed an increased viability, which may indicate a neutralization of ROS generated by quinonoid treatment. In fact, only the highest concentrations of nor-β-lapachone (10 or 20 μM) caused an increase in oxidative stress in nontumor levels cells as measured by TBARS and nitrite/nitrate detection. This was accompanied by an alteration in intracellular thiol content. However, NAC pre-exposure restored the redox equilibrium of the cells and the concentration of thiol levels to control values. Nor-β-lapachone at 2.5 and 5 μM failed to induce DNA damage in nontumor cells, but at the highest concentrations tested, it induced single and double DNA strand breaks and increased the frequency of chromosomal aberrations. Interestingly, these damages were prevented by NAC pretreatment or exacerbated by prior exposure to the GSH-depleting agent 1-bromoheptane. In electrochemical experiments, nor-β-lapachone at the same concentrations as those used in genotoxic tests did not damage DNA directly, but at the highest concentration tested (200 μM), it caused a very weak DNA interaction. Corroborating electrochemical data, oxidative modifications of DNA bases were observed, as checked by DNA repair enzymes EndoIII and FPG, which reinforced the indirect actions caused by nor-β-lapachone through ROS generation and not via DNA intercalation. The DNA repair capacities were higher for nontumor cells than for leukemia cells, which may be related to the selective cytoxicity of nor-β-lapachone toward cancer cells. Our data suggest that ROS play an important role in nor-β-lapachone toxicity and that its DNA-damaging effect occurs only at concentrations several times higher than that needed for its antiproliferative effect on cancer cells.

Plasma membrane electron transport in pancreatic β-cells is mediated in part by NQO1

Plasma membrane electron transport (PMET), a cytosolic/plasma membrane analog of mitochondrial electron transport, is a ubiquitous system of cytosolic and plasma membrane oxidoreductases that oxidizes cytosolic NADH and NADPH and passes electrons to extracellular targets. While PMET has been shown to play an important role in a variety of cell types, no studies exist to evaluate its function in insulin-secreting cells. Here we demonstrate the presence of robust PMET activity in primary islets and clonal β-cells, as assessed by the reduction of the plasma membrane-impermeable dyes WST-1 and ferricyanide. Because the degree of metabolic function of β-cells (reflected by the level of insulin output) increases in a glucose-dependent manner between 4 and 10 mM glucose, PMET was evaluated under these conditions. PMET activity was present at 4 mM glucose and was further stimulated at 10 mM glucose. PMET activity at 10 mM glucose was inhibited by the application of the flavoprotein inhibitor diphenylene iodonium and various antioxidants. Overexpression of cytosolic NAD(P)H-quinone oxidoreductase (NQO1) increased PMET activity in the presence of 10 mM glucose while inhibition of NQO1 by its inhibitor dicoumarol abolished this activity. Mitochondrial inhibitors rotenone, antimycin A, and potassium cyanide elevated PMET activity. Regardless of glucose levels, PMET activity was greatly enhanced by the application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle. We propose a model for the role of PMET as a regulator of glycolytic flux and an important component of the metabolic machinery in β-cells.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Pharmacokinetics of phenoxodiol, a novel isoflavone, following intravenous administration to patients with advanced cancer

Background

Phenoxodiol is a novel isoflavone currently being studied in clinical trials for the treatment of cancer. This study reports the pharmacokinetics of phenoxodiol in patients with cancer.

Methods

The pharmacokinetics of phenoxodiol was studied following a single intravenous (iv) bolus dose and during a continuous intravenous infusion. Three men with prostate cancer and 3 women with breast cancer received IV bolus phenoxodiol (5 mg/kg) and plasma was sampled for free and total phenoxodiol levels. On a separate occasion 5 of the same patients received a continuous intravenous infusion of phenoxodiol (2 mg/kg/h) and plasma was again sampled for free and total phenoxodiol levels. Phenoxodiol was measured using gradient HPLC with ultraviolet detection.

Results

Following bolus injection, free and total phenoxodiol appeared to follow first order pharmacokinetics. The elimination half-lives for free and total phenoxodiol were 0.67 ± 0.53 h and 3.19 ± 1.93 h, respectively, while the total plasma clearance rates were 2.48 ± 2.33 L/h and 0.15 ± 0.08 L/h, respectively. The respective apparent volumes of distribution were 1.55 ± 0.69 L/kg and 0.64 ± 0.51 L/kg. During continuous intravenous infusion, free phenoxodiol accumulated rapidly to reach a mean concentration at steady state of 0.79 ± 0.14 μg/ml after 0.87 ± 0.18 h. The apparent accumulation half-life of free phenoxodiol was 0.17 ± 0.04 h while the plasma clearance during continuous infusion was 1.29 ± 0.23 L/h.

Conclusions

Phenoxodiol has a short plasma half-life, particularly in the free form, leading to a rapid attainment of steady state levels during continuous intravenous infusion.

Trial registration

Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12610000334000

Clinical pharmacology of isoflavones and its relevance for potential prevention of prostate cancer

Isoflavones are phytoestrogens that have pleiotropic effects in a wide variety of cancer cell lines. Many of these biological effects involve key components of signal transduction pathways within cancer cells, including prostate cancer cells. Epidemiological studies have raised the hypothesis that isoflavones may play an important role in the prevention and modulation of prostate cancer growth. Since randomized phase III trials of isoflavones in prostate cancer prevention are currently lacking, the best evidence for this concept is presently provided by case control studies. However, in vitro data are much more convincing in regard to the activity of a number of isoflavones, and have led to the development of genistein and phenoxodiol in the clinic as potential treatments for cancer. In addition, the potential activity of isoflavones in combination with cytotoxics or radiotherapy warrants further investigation. This review focuses on the clinical pharmacology of isoflavones and its relevance to their development for use in the prevention of prostate cancer, and it evaluates some of the conflicting data in the literature.

The expression of sphingosine kinase-1 in head and neck carcinoma

Sphingosine kinase-1 (SPHK1) modulates the proliferation, apoptosis and differentiation of keratinocytes through the regulation of ceramide and sphingosine-1-phosphate levels. However, studies on the expression of SPHK1 in human head and neck squamous cell carcinoma (HNSCC) specimens are lacking. Therefore, the aim of the present work was to evaluate SPHK1 expression in human primary HNSCCs and to correlate the results with clinical and anatomopathological parameters. We investigated the expression of this protein by immunohistochemistry performed in tissue microarrays of HNSCC and in an independent cohort of 37 paraffin-embedded specimens. SPHK1 expression was further validated by real-time PCR performed on laser capture-microdissected tissue samples. The positive rate of SPHK1 protein in the cancerous tissues was significantly higher (74%) than that in the nontumor oral tissues (23%), and malignant tissues showed stronger immunoreactivity for SPHK1 than normal matching samples. These results were confirmed by real-time PCR quantification of SPHK1 mRNA. Interestingly, the positive expression of SPHK1 was associated with shorter patient survival time (Kaplan-Meier survival curves) and with the loss of p21 expression. Taken together, these results demonstrate that SPHK1 is upregulated in HNSCC and provide clues of the role SPHK1 might play in tumor progression.

Phenoxodiol: pharmacology and clinical experience in cancer monotherapy and in combination with chemotherapeutic drugs

BACKGROUND

Phenoxodiol is a synthetic derivative of the naturally occurring plant isoflavone genistein. The observation that an inverse relationship exists between dietary intake of isoflavones and cancer incidence has led to the evaluation of these compounds in cancer therapy.

OBJECTIVE

This article reviews the mechanisms of action of phenoxodiol and the completed and ongoing clinical studies evaluating this drug.

RESULTS/CONCLUSIONS

By altering the chemical structure of genistein, the new compound phenoxodiol showed increased anticancer activity without any increase in toxicity. In addition to its direct cytotoxic activity against different cancers, phenoxodiol sensitizes chemoresistant ovarian cancer cells to platinum and taxane drugs, as well as gemcitabine and topotecan. The US Food and Drug Administration has granted 'fast track' status to the development of phenoxodiol as chemosensitizer for platinum and taxane drugs used in the treatment of recurrent ovarian cancer.

Flavonoids, phenoxodiol, and a novel agent, triphendiol, for the treatment of pancreaticobiliary cancers

Flavonoids, in particular the isoflavones, are naturally occurring compounds found in soy and textured vegetables that have antiproliferative effects on a variety of cancer types. Phenoxodiol is a derivative of the isoflavone genisten that is 5-20 times more potent than genisten. Triphendiol is a derivative of phenoxodiol that has superior anticancer activity against pancreatic and bile duct cancers. This review will focus on the mechanisms of action and activity of two isoflavone derivatives, phenoxodiol and triphendiol, in various tumor types, especially pancreaticobiliary cancers. Triphendiol induces apoptosis in pancreatic cell lines by both caspase-mediated and caspase-independent mechanisms. The addition of triphendiol to gemcitabine is synergistic in in vitro and in vivo models of pancreatic cancer and represents a novel combination of drugs for pancreatic cancer patients.

The anti-cancer drug, phenoxodiol, kills primary myeloid and lymphoid leukemic blasts and rapidly proliferating T cells

BACKGROUND

The redox-active isoflavene anti-cancer drug, phenoxodiol, has previously been shown to inhibit plasma membrane electron transport and cell proliferation and promote apoptosis in a range of cancer cell lines and in anti-CD3/anti-CD28-activated murine splenocytes but not in non-transformed WI-38 cells and human umbilical vein endothelial cells.

DESIGN AND METHODS

We determined the effects of phenoxodiol on plasma membrane electron transport, MTT responses and viability of activated and resting human T cells. In addition, we evaluated the effect of phenoxodiol on the viability of leukemic cell lines and primary myeloid and lymphoid leukemic blasts.

RESULTS

We demonstrated that phenoxodiol inhibited plasma membrane electron transport and cell proliferation (IC(50) 46 microM and 5.4 microM, respectively) and promoted apoptosis of rapidly proliferating human T cells but did not affect resting T cells. Phenoxodiol also induced apoptosis in T cells stimulated in HLA-mismatched allogeneic mixed lymphocyte reactions. Conversely, non-proliferating T cells in the mixed lymphocyte reaction remained viable and could be restimulated in a third party mixed lymphocyte reaction, in the absence of phenoxodiol. In addition, we demonstrated that leukemic blasts from patients with primary acute myeloid leukemia (n=22) and acute lymphocytic leukemia (n=8) were sensitive to phenoxodiol. The lymphocytic leukemic blasts were more sensitive than the myeloid leukemic blasts to 10 muM phenoxodiol exposure for 24h (viability of 23+/-4% and 64+/-5%, respectively, p=0.0002).

CONCLUSIONS

The ability of phenoxodiol to kill rapidly proliferating lymphocytes makes this drug a promising candidate for the treatment of pathologically-activated lymphocytes such as those in acute lymphoid leukemia, or diseases driven by T-cell proliferation such as auto-immune diseases and graft-versus-host disease.

Phenoxodiol, an anticancer isoflavene, induces immunomodulatory effects in vitro and in vivo

Phenoxodiol (PXD) is a synthetic analogue of the plant isoflavone genistein with improved anticancer efficacy. Various properties and mechanisms of action have been attributed to the drug, the most important being its ability to sensitize resistant tumour cells to chemotherapy, which led to its fast track FDA approval for phase II/III clinical trials. In this study, we examined the effects of PXD on human peripheral blood mononuclear cells (PBMC) and its potential role in regulating immune responses. We show that PXD, at concentrations ≥1 μg/ml (4 μM), inhibited proliferation and reduced the viability of healthy donor-derived PBMC. In contrast, lower PXD concentrations (0.05–0.5 μg/ml) augmented, upon 3-day incubation, PBMC cytotoxicity. Experiments with purified CD56⁺ lymphocytes revealed that PXD enhanced the lytic function of natural killer (NK) cells by directly stimulating this lymphocytic subpopulation. Furthermore, in an in vivo colon cancer model, Balb/C mice administered low-dose PXD, exhibited significantly reduced tumour growth rates and prolonged survival (in 40% of the animals). Ex vivo results showed that PXD stimulated both NK and tumour-specific cell lytic activity. We conclude that PXD, when administered at low concentrations, can act as an immunomodulator, enhancing impaired immune responses, often seen in cancer-bearing individuals.

Future directions in the management of epithelial ovarian cancer

Epithelial ovarian cancer can be a difficult malignancy to manage, partially owing to its heterogenous biology. Whilst desirable, screening designed to reduce mortality has not yet proven effective, though results of ongoing studies are awaited. In this brief review, we attempt to highlight some important issues in the current management of primary and recurrent ovarian cancer, and to place these issues in the context of cutting-edge approaches to targeted therapy and its combination with chemotherapy, as well as other novel treatment strategies. It is hoped that this will lead to further improvements in progression-free and overall survival for patients with ovarian cancer, whilst maintaining their quality of life for as much of the disease journey as possible.

Anti-tumor activity of phenoxodiol: from bench to clinic

A major limitation in the treatment of cancers is the prevalence of chemoresistant tumors. Chemotherapy agents induce cell death by activating apoptosis. However, most cancer cells express high levels of antiapoptotic proteins and, hence, are chemoresistant. Phenoxodiol, a novel isoflavone derivative, has been shown to induce apoptosis both in vitro and in vivo, even in chemoresistant cancer cells. In addition, phenoxodiol has been shown to chemosensitize resistant cancer cells to commonly used chemotherapy agents, such as carboplatin and paclitaxel. This review will discuss the characterization of phenoxodiol’s molecular mechanism and its current state in the clinic.

Antitumor activity of bis-indole derivatives

This paper reports the synthesis of compounds formed by two indole systems separated by a heterocycle (pyridine or piperazine). As a primary screening, the new compounds were submitted to the National Cancer Institute for evaluation of antitumor activity in the human cell line screen. The pyridine derivatives were far more active than the piperazine derivatives. For the study of the mechanism of action, the most active compounds were subjected to COMPARE analysis and to further biological tests including proteasome inhibition and inhibition of plasma membrane electron transport. The compound bearing the 5-methoxy-2-indolinone moiety was subjected to the first in vivo experiment (hollow fiber assay) and was active. It was therefore selected for the second in vivo experiment (human tumor xenograft in mice). In conclusion we demonstrated that this approach was successful, since some of the compounds described are much more active than the numerous, so far prepared and tested 3-indolylmethylene-2-indolinones.