Differential response of the NADH oxidase of plasma membranes of rat liver and hepatoma and HeLa cells to thiol reagents

Use of thioglycerol on porous polyurethane as an effective theranostic capping agent for bone tissue engineering

Thiolated biodegradable polyurethane (TG-DPU) was synthesized using a one-pot reaction with thioglycerol adopted as a functionalized chain extender. After characterization of the chemical structure of TG-DPU using proton nuclear magnetic resonance spectroscopy, bone morphogenetic protein (BMP-2) was loaded in the TG-DPU under oxidative conditions to form disulfides between the free thiol of TG-DPU and BMP-2. The interaction between TG-DPU and BMP-2, so-called bioconjugates, was investigated using X-ray photoelectron spectroscopy analysis; the appearance of disulfide (S–S) linkage indicated the formation of a polymer/growth factor conjugate system. The covalently linked bioconjugates provided stability with minimal loss during the drug delivery with prolonged release performance in in vitro release tests. The effects of the drugs delivered by TG-DPU were also confirmed by in vitro alkaline phosphatase tests using pre-osteoblasts and in vivo bone regeneration tests. The drugs effectively induced cell differentiation and promoted mature bone recovery.

Gills as a glutathione-dependent metabolic barrier in Pacific oysters Crassostrea gigas: Absorption, metabolism and excretion of a model electrophile

The mercapturic acid pathway (MAP) is a major phase II detoxification route, comprising the conjugation of electrophilic substances to glutathione (GSH) in a reaction catalyzed by glutathione S-transferase (GST) enzymes. In mammals, GSH-conjugates are exported from cells, and the GSH-constituent amino acids (Glu/Gly) are subsequently removed by ectopeptidases. The resulting Cys-conjugates are reabsorbed and, finally, a mercapturic acid is generated through N-acetylation. This pathway, though very well characterized in mammals, is poorly studied in non-mammalian biological models, such as bivalve mollusks, which are key organisms in aquatic ecosystems, aquaculture activities and environmental studies. In the present work, the compound 1-chloro-2,4-dinitrobenzene (CDNB) was used as a model electrophile to study the MAP in Pacific oysters Crassostrea gigas. Animals were exposed to 10μM CDNB and MAP metabolites were followed over 24h in the seawater and in oyster tissues (gills, digestive gland and hemolymph). A rapid decay was detected for CDNB in the seawater (half-life 1.7h), and MAP metabolites peaked in oyster tissues as soon as 15min for the GSH-conjugate, 1h for the Cys-conjugate, and 4h for the final metabolite (mercapturic acid). Biokinetic modeling of the MAP supports the fast CDNB uptake and metabolism, and indicated that while gills are a key organ for absorption, initial biotransformation, and likely metabolite excretion, hemolymph is a possible milieu for metabolite transport along different tissues. CDNB-induced GSH depletion (4h) was followed by increased GST activity (24h) in the gills, but not in the digestive gland. Furthermore, the transcript levels of glutamate-cysteine ligase, coding for the rate limiting enzyme in GSH synthesis, and two phase II biotransformation genes (GSTpi and GSTo), presented a fast (4h) and robust (∼6-70 fold) increase in the gills. Waterborne exposure to electrophilic compounds affected gills, but not digestive gland, while intramuscular exposure was able to modulate biochemical parameters in both tissues. This study is the first evidence of a fully functional and interorgan MAP pathway in bivalves. Hemolymph was shown to be responsible for the metabolic interplay among tissues, and gills, acting as a powerful GSH-dependent metabolic barrier against waterborne electrophilic substances, possibly also participating in metabolite excretion into the sea water. Altogether, experimental and modeled data fully agree with the existence of a classical mechanism for phase II xenobiotic metabolism and excretion in bivalves.

Stress-induced down-regulation of tumor-associated NADH oxidase during apoptosis in transformed cells

Tumor-associated NADH oxidase (tNOX) is a growth-related protein expressed in transformed cells. tNOX knockdown using RNA interference leads to a significant reduction in HeLa cell proliferation and migration, indicating an important role for tNOX in growth regulation and the cancer phenotype. Here, we show that tNOX is down-regulated during apoptosis in HCT116 cells. Treatment with diverse stresses induced a dose- and time-dependent decrease in tNOX expression that was concurrent with apoptosis. Moreover, shRNA-mediated tNOX knockdown rendered cells susceptible to apoptosis, whereas re-expression of tNOX partially recovered cell proliferation. Our results indicate that tNOX is suppressed during apoptosis and demonstrate that tNOX down-regulation sensitizes cells to stress-induced growth reduction, suggesting that tNOX is required for transformed cell growth.

RNA interference targeting tNOX attenuates cell migration via a mechanism that involves membrane association of Rac

tNOX, a tumor-associated NADH oxidase, is a growth-related protein present in transformed cells. In this study, we employed RNA interference (RNAi)-mediated down-regulation of tNOX protein expression to explore the role of tNOX in regulating cell growth in human cervical adenocarcinoma (HeLa) cells. In this first reported use of RNAi to decrease tNOX expression, we found that HeLa cell growth was significantly inhibited by shRNA-knockdown of tNOX. Furthermore, cell migration and membrane association of Rac were decreased concomitantly with the reduction in tNOX protein expression. These results indicate that shRNA targeting of tNOX inhibits the growth of cervical cancer cells, and reduces cell migration via a decrease in the membrane association of Rac. We propose that tNOX is a potential upstream mediator of Rho activation that plays a role in regulating cell proliferation, migration, and invasion.

Structural changes revealed by Fourier transform infrared and circular dichroism spectroscopic analyses underlie tNOX periodic oscillations

A recurring pattern of spectral changes indicative of periodic changes in the proportion of beta-structure and a-helix of a recombinant ECTO-NOX fusion protein of tNOX, with a cellulose binding domain peptide, was demonstrated by Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopic analyses. The pattern of structural changes correlated with oscillatory patterns of enzymatic activities exhibited by the protein previously interpreted as indicative of a clock function. The pattern consisted of a repeating pattern of oscillations with a period length of 21 min with five maxima (two separated by 5 min and 3 separated by 4 to 4.5 min) within each 21 min repeat. Oscillatory patterns were not obvious in comparable FTIR or CD spectra of albumin, ribonuclease or concanavalin A. The period length was constant at 5, 15, 25, 35 and 45 degrees C (temperature compensated) and oscillations occurred independently of substrate presence. Spectra obtained in deuterium oxide yielded a longer period length of 26 min both for oscillations in enzymatic activity and absorbance ratios determined by FTIR. Taken together the findings suggest that the regular patterns of oscillations exhibited by the ECTO-NOX proteins are accompanied by recurrent global changes in the conformation of the protein backbone that directly modulate enzymatic activity.

Drug delivery strategy utilizing conjugation via reversible disulfide linkages: role and site of cellular reducing activities

The first disulfide linkage-employing drug conjugate that exploits the reversible nature of this unique covalent bond was recently approved for human use. Increasing numbers of drug formulations that incorporate disulfide bonds have been reported, particularly in the next generation macromolecular pharmaceuticals. These are designed to exploit differences in the reduction potential at different locations within and upon cells. The recent characterization of a novel redox enzyme in endosomes and lysosomes adds more excitement to this approach. This review focuses on understanding where and how the disulfide bond in the bioconjugate is reduced upon contact with biological milieu, which affects delivery design and the interpretation of the delivery strategies.

Decomposition Analyses Applied to a Complex Ultradian Biorhythm: The Oscillating NADH Oxidase Activity of Plasma Membranes Having a Potential Time-Keeping (Clock) Function

Seasonal decomposition analyses were applied to the statistical evaluation of an oscillating activity for a plasma membrane NADH oxidase activity with a temperature compensated period of 24 min. The decomposition fits were used to validate the cyclic oscillatory pattern. Three measured values, average percentage error (MAPE), a measure of the periodic oscillation, mean average deviation (MAD), a measure of the absolute average deviations from the fitted values, and mean standard deviation (MSD), the measure of standard deviation from the fitted values plus R-squared and the Henriksson-Merton p value were used to evaluate accuracy.Decomposition was carried out by fitting a trend line to the data, then detrending the data if necessary, by subtracting the trend component. The data, with or without detrending, were then smoothed by subtracting a centered moving average of length equal to the period length determined by Fourier analysis. Finally, the time series were decomposed into cyclic and error components. The findings not only validate the periodic nature of the major oscillations but suggest, as well, that the minor intervening fluctuations also recur within each period with a reproducible pattern of recurrence.

Entrainment in solution of an oscillating NADH oxidase activity from the bovine milk fat globule membrane with a temperature-compensated period length suggestive of an ultradian time-keeping (clock) function

Entrainment in solution of an oscillating activity with a temperature compensated period of 24 min is described for a NADH oxidase (NOX) activity of the bovine milk fat globule membrane, a derivative of the mammary epithelial cell plasma membrane. The period of 24 min remained unchanged at 17 degrees C, 27 degrees C and 37 degrees C whereas the amplitude approximately doubled with each 10 degree C rise in temperature (Q(10)congruent with 2). The periodicity was observed with both intact milk fat globule membranes and with detergent-solubilized membranes, demonstrating that the oscillations did not require an association with membranes. The periodicity was not the result of instrument variation or of chemical interactions among reactants in solution. Preparations with different periodicities entrained (autosynchronized) when mixed. Upon mixing, the preparations exhibited two oscillatory patterns but eventually a single pattern representing the mean of the farthest separated maxima of the two preparations analyzed separately emerged. The cell surface NOX protein is the first reported example of an entrainable biochemical entity with a temperature-compensated periodicity potentially capable of functioning as an ultradian or circadian clock driver.

A site-directed mutagenesis analysis of tNOX functional domains

Constitutive NADH oxidase proteins of the mammalian cell surface exhibit two different activities, oxidation of hydroquinones (or NADH) and protein disulfide-thiol interchange which alternate to yield oscillatory patterns with period lengths of 24 min. A drug-responsive tNOX (tumor-associated NADH oxidase) has a period length of about 22 min. The tNOX cDNA has been cloned and expressed. These two proteins are representative of cycling oxidase proteins of the plant and animal cell surface. In this report, we describe a series of eight amino acid replacements in tNOX which, when expressed in Escherichia coli, were analyzed for enzymatic activity, drug response and period length. Replacement sites selected include six cysteines that lie within the processed plasma membrane (34 kDa) form of the protein, and amino acids located in putative drug and adenine nucleotide (NADH) binding domains. The latter, plus two of the cysteine replacements, resulted in a loss of enzymatic activity. The recombinant tNOX with the modified drug binding site retained activity but the activity was no longer drug-responsive. The four remaining cysteine replacements were of interest in that both activity and drug response were retained but the period length for both NADH oxidation and protein disulfide-thiol interchange was increased from 22 min to 36 or 42 min. The findings confirm the correctness of the drug and adenine nucleotide binding motifs within the tNOX protein and imply a potential critical role of cysteine residues in determining the period length.

NADH oxidase activity (NOX) and enlargement of HeLa cells oscillate with two different temperature-compensated period lengths of 22 and 24 minutes corresponding to different NOX forms

NOX proteins are cell surface-associated and growth-related hydroquinone (NADH) oxidases with protein disulfide-thiol interchange activity. A defining characteristic of NOX proteins is that the two enzymatic activities alternate to generate a regular period length of about 24 min. HeLa cells exhibit at least two forms of NOX. One is tumor-associated (tNOX) and is inhibited by putative quinone site inhibitors (e.g., capsaicin or the antitumor sulfonylurea, LY181984). Another is constitutive (CNOX) and refractory to inhibition. The periodic alternation of activities and drug sensitivity of the NADH oxidase activity observed with intact HeLa cells was retained in isolated plasma membranes and with the solubilized and partially purified enzyme. At least two activities were present. One had a period length of 24 min and the other had a period length of 22 min. The lengths of both the 22 and the 24 min periods were temperature compensated (approximately the same when measured at 17, 27 or 37 degrees C) whereas the rate of NADH oxidation approximately doubled with each 10 degrees C rise in temperature. The rate of increase in cell area of HeLa cells when measured by video-enhanced light microscopy also exhibited a complex period of oscillations reflective of both 22 and 24 min period lengths. The findings demonstrate the presence of a novel oscillating NOX activity at the surface of cancer cells with a period length of 22 min in addition to the constitutive NOX of non-cancer cells and tissues with a period length of 24 min.

Surface oxidase and oxidative stress propagation in aging

This report summarizes new evidence for a plasma-membrane-associated hydroquinone oxidase designated as CNOX (constitutive plasma membrane NADH oxidase) that functions as a terminal oxidase for a plasma membrane oxidoreductase (PMOR) electron transport chain to link the accumulation of lesions in mitochondrial DNA to cell-surface accumulations of reactive oxygen species. Previous considerations of plasma membrane redox changes during aging have lacked evidence for a specific terminal oxidase to catalyze a flow of electrons from cytosolic NADH to molecular oxygen (or to protein disulfides). Cells with functionally deficient mitochondria become characterized by an anaerobic metabolism. As a result, NADH accumulates from the glycolytic production of ATP. Elevated PMOR activity has been shown to be necessary to maintain the NAD(+)/NADH homeostasis essential for survival. Our findings demonstrate that the hyperactivity of the PMOR system results in an NADH oxidase (NOX) activity capable of generating reactive oxygen species at the cell surface. This would serve to propagate the aging cascade both to adjacent cells and to circulating blood components. The generation of superoxide by NOX forms associated with aging is inhibited by coenzyme Q and provides a rational basis for the anti-aging activity of circulating coenzyme Q.

Cell membrane redox systems and transformation

Cell membrane redox systems carry electrons from intracellular donors and transport them to extracellular acceptors. This phenomenon appears to be universal. Numerous reviews have emphasized not only the bioenergetic mechanisms of redox systems but also the antioxidant defense mechanisms in which they participate. Moreover, significant progress has been made in the modulation of the membrane redox systems on cell proliferation. Because membrane redox systems play a key role in the regulation of cell growth, they need to be somehow linked into the signaling pathways resulting in either controlled or unregulated growth by both internal and external signals. Ultimately, these sequential events lead to either normal cell proliferation or cancer cell formation. However, much less is known about the involvement of membrane redox in transformation or tumorgenesis. In this review, the facts and ideas are summarized concerning the redox systems and tumorgenesis in several aspects, such as the regulation of cell growth and the effect on cell differentiation and on signaling pathways. In addition, information on a unique tumor-associated nicotinamide adenine dinucleotide (NADH) oxidase (tNOX) protein is reviewed.

Drug-antibody conjugates with anti-HIV activity

Human immunodeficiency virus (HIV)-specific peptide antibody-brefeldin A conjugates and antibody-glaucarubolone conjugates directed to cell surface viral glycoprotein epitopes were prepared and tested for antiviral activity. A selective response was observed both on survival of cell lines permanently infected with lentiviruses and on HIV infectivity. With human peripheral blood mononuclear cells (PBMCs), the conjugate also was effective in reducing virus titers. The effectiveness of an HIV-specific peptide antibody-brefeldin A conjugate was enhanced by combination with 3'-azido-3'-deoxythymidine (AZT) and was effective against AZT-resistant isolates in combination with AZT. The conjugates reduced virus production in MOLT-4 cells and in HIV-1-infected PBMCs without affecting the viability of uninfected cells.

Use of dipyridyl-dithio substrates to measure directly the protein disulfide-thiol interchange activity of the auxin stimulated NADH: protein disulfide reductase (NADH oxidase) of soybean plasma membranes

Dipyridyl-dithio substrates were cleaved by isolated vesicles of plasma membranes prepared from etiolated hypocotyls of soybean. The cleavage was stimulated by auxins at physiological concentrations. The substrates utilized were principally 2,2'-dithiodipyridine (DTP) and 6,6'-dithiodinicotinic acid (DTNA). The DTP generated 2 moles of 2-pyridinethione whereas the 6,6'-dithiodinicotinic acid generated 2 moles of 6-nicotinylthionine. Both products absorbed at 340 nm. The auxin herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) stimulated the activity approximately 2-fold to a maximum at about 10 microM. Concentrations of 2,4-D greater than 100 microM inhibited the activity. Indole-3-acetic acid stimulated the activity as well. The growth-inactive auxin, 2,3-dichlorophenoxyacetic acid (2,3-D), was without effect. DTNA cleavage correlated with oxidation of NADH and reduction of protein disulfide bonds reported earlier in terms of location at the external plasma membrane surface, absolute specific activity, pH dependence and auxin specificity. The dipyridyl-dithio substrates provide, for the first time, a direct measure of the disulfide-thiol interchange activity of the protein previously measured only indirectly as an auxin-dependent ability of isolated plasma membrane vesicles to restore activity to scrambled and inactive RNase.

Capsaicin-responsive NADH oxidase activities from urine of cancer patients

NADH oxidases of low specific activities from urine of cancer patients were found to be inhibited or stimulated by the vanilloid capsaicin (8-methyl-N-vanillyl-6-noneamide). Similar activities, inhibited or stimulated by capsaicin, were reported previously for sera of cancer patients but not for sera of normal volunteers or for patients with disorders other than cancer. Like those from sera, the activities from urine were resistant to heat and to digestion with proteinase K. Two different fractions with capsaicin-responsive NADH oxidase activities were obtained by FPLC. One fraction in which the 33-kDa band was the major component exhibited NADH oxidase activity stimulated by capsaicin. Another fraction in which 66-kDa and 45-kDa bands were major components exhibited NADH oxidase activities inhibited by capsaicin. A monoclonal antibody generated to a ca 34-kDa form of the NADH oxidase from sera reacted with a urine protein of a ca 33-kDa band in the capsaicin-stimulated fraction. The 33-kDa protein was of low abundance and was estimated to be present in amounts between 5 and 100 microgram/L, depending on the particular patient.

A drug-responsive and protease-resistant peripheral NADH oxidase complex from the surface of HeLa S cells

Our laboratory described a ca. 34-kDa protein of the HeLa S cell surface that bound an antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984) with high affinity and that exhibited NADH oxidase and protein disulfide-thiol interchange activities also inhibited by LY181984. The quinone site inhibitor 8-methyl-N-vanillyl-6-noneamide (capsaicin) also blocked these same enzymatic activities. Using capsaicin inhibition as the criterion, the drug-responsive oxidase was released from the surface of HeLa S cells and purified. The activity of the released capsaicin-inhibited oxidase was resistant to heating at 50 degrees C and to protease digestion. After heating and proteinase K digestion, the activity was isolated in >90% yield by FPLC as an apparent 50- to 60-kDa multimer. Final purification by preparative SDS-PAGE yielded a capsaicin-inhibited NADH oxidase activity of a specific activity indicative of >500-fold purification relative to the plasma membrane. The final activity correlated with a ca. 34-kDa band on SDS-PAGE. Matrix-assisted laser desorption mass spectroscopy as well as reelectrophoresis of the 34-kDa band indicated that the ca. 34-kDa material was a stable mixture of 22-, 17-, and 9.5-kDa components which occasionally migrated as a ca. 52-kDa complex. The purified complex tended to multimerize and formed insoluble 10- to 20-nm-diameter amyloid rods. The components of the purified 34-kDa complex were blocked to N-terminal amino acid sequencing and were resistant to further protease digestion. After multimerization into amyloid rods, the protein remained resistant to proteases even under denaturing conditions and to cyanogen bromide either with or without prior alkylation.

The sulfonylurea-inhibited NADH oxidase activity of HeLa cell plasma membranes has properties of a protein disulfide-thiol oxidoreductase with protein disulfide-thiol interchange activity

Plasma membrane vesicles of HeLa cells are characterized by a drug-responsive oxidation of NADH. The NADH oxidation takes place in an argon or nitrogen atmosphere and in samples purged of oxygen. Direct assay of protein thiols by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB; Ellman's reagent), suggests that protein disulfides may be the natural electron acceptors for NADH oxidation by the plasma membrane vesicles. In the presence of NADH, protein disulfides of the membranes were reduced with a concomitant stoichiometric increase in protein thiols. The increase in protein thiols was inhibited in parallel to the inhibition of NADH oxidation by the antitumor sulfonylurea LY181984 with an EC50 of ca. 30 nM. LY 181984, with an EC50 of 30 nM, also inhibited a protein disulfide-thiol interchange activity based on the restoration of activity to inactive (scrambled) RNase and thiol oxidation. The findings suggest that thiol oxidation, NADH-dependent disulfide reduction (NADH oxidation), and protein disulfide-thiol interchange in the absence of NADH all may be manifestations of the same sulfonylurea binding protein of the HeLa plasma membrane. A surface location of the thiols involved was demonstrated using detergents and the impermeant thiol reagent p-chloromercuriphenylsulfonic acid (PCMPS). The surface location precludes a physiological role of the protein in NADH oxidation. Rather, it may carry out some other role more closely related to a function in growth, such as protein disulfide-thiol interchange coupled to cell enlargement.

NADH oxidase activity from sera altered by capsaicin is widely distributed among cancer patients

A cancer-specific form of NADH oxidase inhibited or stimulated by 1 or 100 microM capsaicin (8-methyl-N-vanillyl-6-noneamide) is present in sera from cancer patients. The capsaicin-inhibited NADH oxidase activity appears to be absent from sera of individuals free of cancer. The capsaicin-inhibited activity is present both in freshly collected sera and in sera stored frozen for varying periods of time. For the latter, an assay was carried out under renaturing conditions in the presence of NADH and reduced glutathione followed by dilute hydrogen peroxide. Inhibition was half maximal at about 1 microM capsaicin. The capsaicin-inhibited activity was found in sera over a broad spectrum of cancer patients including patients with solid cancers (e.g., breast, prostate, lung, ovarian) as well as with leukemias and lymphomas.

A 33.5-kDa heat- and protease-resistant NADH oxidase inhibited by capsaicin from sera of cancer patients

Sera from patients with a variety of cancers, including solid carcinomas, leukemias, and lymphomas, contain a ca. 33.5-kDa protein absent from sera of healthy volunteers or patients not diagnosed as having cancer. The protein exhibits an NADH oxidase activity inhibited by 8-methyl-N-vanillyl-6-noneamide (capsaicin). The activity and the protein are resistant to digestion by proteases (trypsin, chymotrypsin, proteinase K, subtilisin) and to heat. Following protease digestion to reduce the content of major serum proteins, the 33.5-kDa protein could be detected on Western blots of SDS-PAGE transferred to nitrocellulose membranes using polyclonal antisera to a corresponding partially purified 33.5-kDa protein shed into culture media conditioned by growth of HeLa cells. No corresponding protein was seen with control sera. The findings confirm the capsaicin-inhibited NADH oxidase activity of cancer sera as a circulating marker potentially specific to sera of cancer patients and identify a ca. 33.5-kDa protein resistant to proteases and heat as the source of the circulating capsaicin-inhibited NADH oxidase activity.

Is the drug-responsive NADH oxidase of the cancer cell plasma membrane a molecular target for adriamycin?

Enhanced growth inhibition and antitumor responses to adriamycin have been observed repeatedly from several laboratories using impermeant forms of adriamycin where entry into the cell was greatly reduced or prevented. Our laboratory has described an NADH oxidase activity at the external surface of plasma membrane vesicles from tumor cells where inhibition by an antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984), and by the vanilloid, capsaicin (8-methyl-N-vanillyl-6-noneamide) correlated with inhibition of growth. Here we report that the oxidation of NADH by isolated plasma membrane vesicles was inhibited, as well, by adriamycin. An external site of inhibition was indicated from studies where impermeant adriamycin conjugates were used. The EC50 for inhibition of the oxidase of rat hepatoma plasma membranes by adriamycin was several orders of magnitude less than that for rat liver. Adriamycin cross-linked to diferric transferrin and other impermeant supports also was effective in inhibition of NADH oxidation by isolated plasma membrane vesicles and in inhibition of growth of cultured cells. The findings suggest the NADH oxidase of the plasma membrane as a growth-related adriamycin target at the surface of cancer cells responsive to adriamycin. Whereas DNA intercalation remains clearly one of the principal bases for the cytotoxic action of free adriamycin, this second site, possibly related to a more specific antitumor action, may be helpful in understanding the enhanced efficacy reported previously for immobilized adriamycin forms compared to free adriamycin.

A circulating form of NADH oxidase activity responsive to the antitumor sulfonylurea N-4-(methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984) specific to sera from cancer patients

Our laboratory has described a drug-responsive NADH oxidase activity of the external surface of the plasma membrane of HeLa and other cancer cells, but not from normal cells, that was shed into media conditioned by the growth of cancer cells such as HeLa. The shed form of the activity exhibited the same drug responsiveness as the plasma membrane-associated form. In this study, sera from tumor-bearing and control rats, cancer patients, normal volunteers, and patients with diseases other than cancer were collected and assayed for a cancer-specific form of NADH oxidase responsive to the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). With sera from tumor-bearing rats and cancer patients, LY181984 added at a final concentration of 1 microM either inhibited or stimulated the activity. With sera from control rats, normal volunteers, or patients with disorders other than cancer, the drug was without effect on the NADH oxidase activity of the sera. The activity altered by the antitumor sulfonylurea was present both in freshly collected sera and in sera stored frozen. Inhibition was half maximal at about 30 nM LY181984. The sulfonylurea-altered activity was found in sera of nearly 200 cancer patients including patients with solid cancers (e.g., breast, prostate, lung, ovarian) and with leukemias and lymphomas. We postulate that the serum presence of the antitumor sulfonylurea-responsive NADH oxidase represents an origin due to shedding from the patient's cancer. If so, the antitumor-responsive NADH oxidase would represent the first reported cell surface change universally associated with all forms of human cancer.

A protein disulfide-thiol interchange activity of HeLa plasma membranes inhibited by the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984)

Plasma membrane vesicles isolated from HeLa cells grown in suspension culture contain a protein disulfide-thiol interchange (protein disulfide-like) activity. The activity was estimated from the restoration of activity to inactive (scrambled) pancreatic RNAase. RNAase activity was measured either by hydrolysis of cCMP or by a decrease in acid precipitable yeast RNA. The ability of plasma membrane vesicles to restore activity to inactive (scrambled) pancreatic ribonuclease was inhibited by the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). The activity correlated with that of a cyanide-resistant NADH oxidase also associated with the plasma membrane vesicles that exhibited a similar pattern of drug response. The activity was stimulated by reduced glutathione and inhibited by oxidized glutathione but did not depend on either for activity. The antitumor sulfonylurea-inhibited activity was greatest in the presence of reduced glutathione and least in the presence of oxidized glutathione. The antitumor sulfonylurea-inhibited activity was unaffected by a monoclonal antibody to protein disulfide isomerase. Also the antitumor sulfonylurea-inhibited activity was unaffected by peptide antisera to the consensus active site sequence of protein disulfide isomerase. Thus the antitumor sulfonylurea-inhibited activity appeared to reside with a novel cell surface protein capable of oxidation of both NADH and protein thiols and of carrying out a protein disulfide isomerase-like protein disulfide-thiol interchange activity in the absence of NADH or other external reductants.

Impermeant antitumor sulfonylurea conjugates that inhibit plasma membrane NADH oxidase and growth of HeLa cells in culture. Identification of binding proteins from sera of cancer patients

The antitumor sulfonylurea LY237868 (N-(4-aminophenyl-sulfonyl)-N'-(4-chlorophenyl)urea) was conjugated through the A ring to alpha-cyclodextrin or agarose bead material (Affigel 10) to prepare impermeant conjugates for activity measurements and affinity isolation of binding proteins from serum. When conjugated to alpha-cyclodextrin, the resulting LY237868 conjugate inhibited both NADH oxidase activity and growth of HeLa cells in culture. The conjugate was at least one order of magnitude more potent as an inhibitor than the parent compound. These findings confirm previous results that demonstrate an antitumor sulfonylurea-binding protein with NADH oxidase activity at the external plasma membrane surface of HeLa cells that is shed into culture media conditioned by growth of HeLa cells. A comparable activity, responsive to sulfonylurea, was present in sera of cancer patients. LY237868 conjugated to agarose beads as the affinity support bound a large number of serum proteins. However, compared to serum from normal patients, the affinity support bound two proteins of M(r) approx. 33.5 and 29.5 not found in sera of normal patients. The 33.5 kDa protein from human sera reacted with antisera to a 33.5 kDa protein from culture media conditioned by growth of HeLa cells that blocked and immunoprecipitated the sulfonylurea-responsive activity from HeLa cell plasma membranes. The results point to the 33.5 kDa protein from cancer patient sera that bound to the sulfonylurea affinity support as representing the circulating equivalent of the previously identified 34 kDa sulfonylurea-binding protein, with NADH oxidase activity at the external cell surface of cultured HeLa cells and a corresponding 33.5 kDa protein shed into culture media conditioned by growth of HeLa cells.

Antitumor sulfonylurea-inhibited NADH oxidase of cultured HeLa cells shed into media

Conditioned culture media of HeLa S cells contain a soluble NADH oxidase activity inhibited by the antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N' -(4-chlorophenyl)urea (LY181984) similar to that associated with the outer surface of the plasma membrane. This activity was absent from media in which cells had not been grown and was present in conditioned culture media from which cells had been removed by centrifugation both for serum-containing and serum-free media. The Km with respect to NADH and response to thiol reagents were similar to those of the corresponding activity of the plasma membrane of HeLa cells. The conditioned HeLa culture media bound [3H]LY181984 with high affinity. Both antitumor sulfonylurea-inhibited and -resistant forms of the NADH oxidase were isolated by free-flow electrophoresis. The antitumor sulfonylurea-inhibited activity was purified to apparent homogeneity and was identified with a 33.5 kDa protein with an isoelectric point of about pH 4.5. The 33.5 kDa protein from conditioned HeLa culture medium both bound [3H]LY181984 and retained an LY181984-inhibited NADH oxidase activity. A polyclonal antisera was raised in rabbits to the purified 33.5 kDa constituent from conditioned HeLa culture medium. The antisera blocked the activity of the LY181984-inhibited NADH oxidase activity, immunoprecipitated the activity and reacted with a 33.5 kDa protein on Western blots while preimmune sera did not. Also inhibited and immunoprecipitated was NADH oxidase activity from HeLa plasma membranes. The findings are consistent with the 33.5 kDa drug-inhibited NADH oxidase activity of the culture media being a shed form of the corresponding native 34 kDa antitumor sulfonylurea-inhibited NADH oxidase activity of the HeLa cell plasma membrane.