Effects of 1,2-naphthoquinones on human tumor cell growth and lack of cross-resistance with other anticancer agents

Interactions of the antioxidant enzymes NAD(P)H: Quinone oxidoreductase 1 (NQO1) and NRH: Quinone oxidoreductase 2 (NQO2) with pharmacological agents, endogenous biochemicals and environmental contaminants

NAD(P)H

Quinone Oxidoreductase 1 (NQO1) is an antioxidant enzyme that catalyzes the two-electron reduction of several different classes of quinone-like compounds (quinones, quinone imines, nitroaromatics, and azo dyes). One-electron reduction of quinone or quinone-like metabolites is considered to generate semiquinones to initiate redox cycling that is responsible for the generation of reactive oxygen species and oxidative stress and may contribute to the initiation of adverse drug reactions and adverse health effects. On the other hand, the two-electron reduction of quinoid compounds appears important for drug activation (bioreductive activation) via chemical rearrangement or autoxidation. Two-electron reduction decreases quinone levels and opportunities for the generation of reactive species that can deplete intracellular thiol pools. Also, studies have shown that induction or depletion (knockout) of NQO1 were associated with decreased or increased susceptibilities to oxidative stress, respectively. Moreover, another member of the quinone reductase family, NRH: Quinone Oxidoreductase 2 (NQO2), has a significant functional and structural similarity with NQO1. The activity of both antioxidant enzymes, NQO1 and NQO2, becomes critically important when other detoxification pathways are exhausted. Therefore, this article summarizes the interactions of NQO1 and NQO2 with different pharmacological agents, endogenous biochemicals, and environmental contaminants that would be useful in the development of therapeutic approaches to reduce the adverse drug reactions as well as protection against quinone-induced oxidative damage. Also, future directions and areas of further study for NQO1 and NQO2 are discussed.

Molecular mechanism and health effects of 1,2-Naphtoquinone

Extensive literature regarding the health side effects of ambient pollutants (AP) are available, such as diesel exhaust particles (DEPs), but limited studies are available on their electrophilic contaminant 1,2-Naphthoquinone (1,2-NQ), enzymatically derived from naphthalene. This review summarizes relevant toxicologic and biological properties of 1,2-NQ as an environmental pollutant or to a lesser degree as a backbone in drug development to treat infectious diseases. It presents evidence of 1,2-NQ-mediated genotoxicity, neurogenic inflammation, and cytotoxicity due to several mechanistic properties, including the production of reactive oxygen species (ROS), that promote cell damage, carcinogenesis, and cell death. Many signal transduction pathways act as a vulnerable target for 1,2-NQ, including kappaB kinase b (IKKbeta) and protein tyrosine phosphatase 1B (PTP1B). Antioxidant molecules act in defense against ROS/RNS-mediated 1,2-NQ responses to injury. Nonetheless, its inhibitory effects at PTP1B, altering the insulin signaling pathway, represents a new therapeutic target to treat diabetes type 2. Questions exist whether exposure to 1,2-NQ may promote arylation of the Keap1 factor, a negative regulator of Nrf2, as well as acting on the sepiapterin reductase activity, an NADPH-dependent enzyme which catalyzes the formation of critical cofactors in aromatic amino acid metabolism and nitric oxide biosynthesis. Exposure to 1,2-NQ is linked to neurologic, behavioral, and developmental disturbances as well as increased susceptibility to asthma. Limited new knowledge exists on molecular modeling of quinones molecules as antitumoral and anti-microorganism agents. Altogether, these studies suggest that 1,2-NQ and its intermediate compounds can initiate a number of pathological pathways as AP in living organisms but it can be used to better understand molecular pathways.

Facile Synthesis of Naphtha-quinoxaline Derivatives from β-lapachone Using Graphene Oxide as Catalyst

Objective:

To develop efficient method for the synthesis of naphtha-quinoxaline derivatives via the reaction of β-lapachone with various 1,2-diamines.

Methods:

A mixture of β-lapachone (1mmol), 1,2-diamine (1mmol) and graphene oxide (20mg) in methanol (3mL) was heated at 60°C, under constant stirring for appropriate time. After completion of the reaction, the catalyst was filtered off, washed with ethyl acetate (3x3mL) and the combined filtrate was washed with H2O, dried (anhy. Na2SO4) and concentrated under vacuum. The residue was chromatographed over a column of silica gel eluting with a mixture of hexane and ethyl acetate in different ratios, to afford the desired product. All synthesized compounds were assigned with the help of analytical and 1H, 13C NMR, IR, and mass spectral studies.

Results:

To establish the catalytic role of GO in the synthesis of naphtha-quinoxaline derivatives, the reaction of β-lapachone with 3,4-diaminotoluene was selected as a model reaction. The catalytic activity of graphene oxide in comparison with other catalysts like acidic resin amberlyst-15 and solid acid catalyst like montmorillonite K-10 were studied. The reaction was also observed in various solvents such as water, acetonitrile, toluene, dichloromethane, ethanol and 1,4-dioxane using GO as a catalyst. Excellent yields were obtained at 60°C in methanol. The efficacy of the present protocol was investigated by the reaction of β- lapachone with other 1,2-diamines.

Conclusion:

An attractive green metal free carbocatalyst Graphene Oxide (GO) has been successfully utilized for the expedient synthesis of naphtha-quinoxaline derivatives. GO showed high catalytic activity which is attested by the desired products being produced in shorter time. The main advantage of this method is the reusability of the catalyst which makes the procedure sustainable.

A novel 1,4-naphthoquinone-derived compound induces apoptotic cell death in breast cancer cells

Breast cancer is the most-diagnosed cancer type among women. The triple-negative subtype is an especially aggressive type of breast cancer. Although chemotherapy is almost the only option for the treatment of triple-negative breast cancer (TNBC), currently used chemotherapeutics are not effective enough, considering the poor survival rate of patients. Therefore, novel compounds need to be developed to improve survival rates. It has been known that quinonic compounds, which are found in nature, have antibacterial, antifungal, and antitumorigenic properties. Naphthoquinones are members of the quinone family and are widely used in research due to their promising properties. In this study, we evaluated the cytotoxic activity of a novel naphthoquinone-derived compound (1,4-naphthoquinone (1,4-NQ)) against two different breast cancer cells: a hormone-responsive cell line (MCF-7) and a triple-negative cell line (MDA-MB-231). As a result, 1,4-NQ decreased cell viability in both tested cell lines in a dose-dependent manner. Increased apoptotic markers (presence of pyknotic nuclei, annexin-V positivity, caspase 3/7 activity, and decreased mitochondrial membrane potential) and DNA damage were especially observed in MDA-MB-231 cells after treatment with the compound. Considering the promising cytotoxic effect of the compound, 1,4-NQ needs further evaluation as a potential candidate for the treatment of TNBC.

Pharmacological stimulation of NQO1 decreases NADPH levels and ameliorates acute pancreatitis in mice

Reactive oxygen species (ROS) regulates the activation of inflammatory cascades and tissue damage in acute pancreatitis. NADPH oxidase (NOX) is upregulated in pancreatitis and is one of the major enzymes involved in ROS production using NADPH as a general rate-limiting substrate. Dunnione, a well-known substrate of NAD(P)H:quinone oxidoreductase 1 (NQO1), reduces the ratio of cellular NADPH/NADP⁺ through the enzymatic action of NQO1. This study assessed whether a reduction in cellular NADPH/NADP⁺ ratio can be used to regulate caerulein-induced pancreatic damage associated with NOX-induced ROS production in animal models. Dunnione treatment significantly reduced the cellular NADPH/NADP⁺ ratio and NOX activity through the enzymatic action of NQO1 in the pancreas of the caerulein-injection group. Similar to these results, total ROS production and expressions of mRNA and protein for NOX subunits Nox1, p27^phox, p47^phox, and p67^phox also decreased in the dunnione-treated group. In addition, caerulein-induced pancreatic inflammation and acinar cell injury were significantly reduced by dunnione treatment. This study is the first to demonstrate that modulation of the cellular NADPH:NADP⁺ ratio by enzymatic action of NQO1 protects acute pancreatitis through the regulation of NOX activity. Furthermore, these results suggest that modulation of the NADPH:NADP⁺ ratio in cells by NQO1 may be a novel therapeutic strategy for acute pancreatitis.

Synthesis and antitumor activity evaluation of novel substituted 5H-benzo[i][1,3,4]thiadiazolo[3,2-a]quinazoline-6,7-diones

A series of novel substituted 5H-benzo[i][1,3,4]thiadiazolo[3,2-a]quinazoline-6,7-diones were synthesized and all compounds exhibited excellent antitumor activities.

Dunnione ameliorates cisplatin-induced small intestinal damage by modulating NAD(+) metabolism

Although cisplatin is a widely used anticancer drug for the treatment of a variety of tumors, its use is critically limited because of adverse effects such as ototoxicity, nephrotoxicity, neuropathy, and gastrointestinal damage. Cisplatin treatment increases oxidative stress biomarkers in the small intestine, which may induce apoptosis of epithelial cells and thereby elicit damage to the small intestine. Nicotinamide adenine dinucleotide (NAD(+)) is a cofactor for various enzymes associated with cellular homeostasis. In the present study, we demonstrated that the hyper-activation of poly(ADP-ribose) polymerase-1 (PARP-1) is closely associated with the depletion of NAD(+) in the small intestine after cisplatin treatment, which results in downregulation of sirtuin1 (SIRT1) activity. Furthermore, a decrease in SIRT1 activity was found to play an important role in cisplatin-mediated small intestinal damage through nuclear factor (NF)-κB p65 activation, facilitated by its acetylation increase. However, use of dunnione as a strong substrate for the NADH:quinone oxidoreductase 1 (NQO1) enzyme led to an increase in intracellular NAD(+) levels and prevented the cisplatin-induced small intestinal damage correlating with the modulation of PARP-1, SIRT1, and NF-κB. These results suggest that direct modulation of cellular NAD(+) levels by pharmacological NQO1 substrates could be a promising therapeutic approach for protecting against cisplatin-induced small intestinal damage.

Dunnione ameliorates cisplatin ototoxicity through modulation of NAD(+) metabolism

Ototoxicity is an important issue in patients receiving cisplatin chemotherapy. Numerous studies have demonstrated that cisplatin-induced ototoxicity is related to oxidative stress and DNA damage. However, the precise mechanism underlying cisplatin-associated ototoxicity is still unclear. The cofactor nicotinamide adenine dinucleotide (NAD(+)) has emerged as an important regulator of energy metabolism and cellular homeostasis. Here, we demonstrate that the levels and activities of sirtuin-1 (SIRT1) are suppressed by the reduction of intracellular NAD(+) levels in cisplatin-mediated ototoxicity. We provide evidence that the decreases in SIRT1 activity and expression facilitated by increasing poly(ADP-ribose) polymerase-1 (PARP-1) activation and microRNA-34a levels through cisplatin-mediated p53 activation aggravate the associated ototoxicity. Furthermore, we show that the induction of cellular NAD(+) levels using dunnione, which targets intracellular NQO1, prevents the toxic effects of cisplatin through the regulation of PARP-1 and SIRT1 activity. These results suggest that direct modulation of cellular NAD(+) levels by pharmacological agents could be a promising therapeutic approach for protection from cisplatin-induced ototoxicity.

Solid-phase organic synthesis of 2-tridecanyl-1,4-naphthoquinone and 2-tridecanyl-1,4-naphthodiol that form redox-active micelles and vesicles

The solid-phase synthesis of new amphiphilic compounds is reported. It is based on a newly designed 1,4-naphthoquinone derivative that contains polar and nonpolar groups and self-assembles into micelles or vesicles in water depending on the concentration. They also display redox-active properties.

Different cytotoxicities and cellular localizations of novel quindoline derivatives with or without boronic acid modifications in cancer cells

The synthesis of a 4 × 4 series of novel quindoline derivatives with or without boronic acid modifications and their cytotoxicities, cellular localizations, and implications on cancer cells are presented and discussed.

Novel o-naphthoquinones induce apoptosis of EL-4 T lymphoma cells through the increase of reactive oxygen species

Novel β-lapachone analogs 2-phenyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ1), 2-p-tolyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ3) and 2-methyl-2-phenyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ7), which have trypanocidal activity, were assayed for cytotoxic effects on murine EL-4 T lymphoma cells. The NQs inhibited the proliferation of EL-4 cells at concentrations above 1μM. Nuclear staining of the EL-4 cells revealed chromatin condensation and a nuclear morphology compatible with the induction of apoptosis. Flow cytometry assays with annexin V-FITC and propidium iodide confirmed the cell death by apoptosis. Using electron paramagnetic resonance (EPR), a semiquinone radical was detected in EL-4 cells treated with NQs. In addition, a decrease in the GSH level in parallel with reactive oxygen species (ROS) production was observed. Preincubation with n-acetyl-l-cysteine (NAC) was able to reverse the inhibitory effects of the NQs on cell proliferation, indicating that ROS generation is involved in NQ-induced apoptosis. In addition, the NQs induced a decrease in the mitochondrial membrane potential and increased the proteolytic activation of caspases 9 and 3 and the cleavage of Poly (ADP-Ribose) Polymerase (PARP). In conclusion, these results indicate that redox cycling is induced by the NQs in the EL-4 cell line, with the generation of ROS and other free radicals that could inhibit cellular proliferation as a result of the induction of the intrinsic apoptosis pathway.

The naphthoquinones, vitamin K3 and its structural analogue plumbagin, are substrates of the multidrug resistance linked ATP binding cassette drug transporter ABCG2

Vitamin K3 (menadione; 2-methyl-1,4-naphthoquinone) is a structural precursor of vitamins K1 and K2, which are essential for blood clotting. The naturally occurring structural analogue of this vitamin, plumbagin (5-hydroxy-menadione), is known to modulate cellular proliferation, apoptosis, carcinogenesis, and radioresistance. We here report that both vitamin K3 and plumbagin are substrates of the multidrug resistance-linked ATP binding cassette drug transporter, ABCG2. Vitamin K3 and plumbagin specifically inhibited the ABCG2-mediated efflux of mitoxantrone but did not have any effect on the ABCB1-mediated efflux of rhodamine 123. This inhibition of ABCG2 function was due to their interaction at the substrate-binding site(s). Vitamin K3 and plumbagin inhibited the binding of [(125)I]iodoarylazidoprazosin, a substrate of ABCG2, to this transporter in a concentration-dependent manner with IC(50) values of 7.3 and 22.6 micromol/L, respectively, but had no effect on the binding of the photoaffinity analogue to ABCB1. Both compounds stimulated ABCG2-mediated ATP hydrolysis and also inhibited the mitoxantrone-stimulated ATPase activity of the ABCG2 transporter, but did not have any significant effect on the ATPase activity of ABCB1. In a cytotoxicity assay, ABCG2-expressing HEK cells were 2.8- and 2.3-fold resistant to plumbagin and vitamin K3, respectively, compared with the control cells, suggesting that they are substrates of this transporter. Collectively, these data show for the first time that vitamin K3 is a substrate of the ABCG2 transporter. Thus, ABCG2 may have a role in the regulation of vitamin K3 levels in the body. In addition, vitamin K3 and its structural derivative, plumbagin, could potentially be used to modulate ABCG2 function.

Beta-lapachone inhibits proliferation and induces apoptosis in retinoblastoma cell lines

AIMS

To investigate the cytotoxicity of beta-lapachone, a potent agent that may selectively target tumour cells, in retinoblastoma (RB) cell lines.

METHODS

Growth inhibitory effects of beta-lapachone were evaluated in Y79, WERI-RB1, and RBM human retinoblastoma cell lines. Pro-apoptotic effects of beta-lapachone were evaluated in Y79 cells by detection of caspase 3/7 activity, by enzyme-linked immunosorbent assay for nucleosome fragments, and by cellular morphological analysis.

RESULTS

Beta-lapachone induced significant dose-dependent growth inhibitory effects in all three retinoblastoma cell lines. The 50% growth inhibitory concentration (IC(50)) of this agent was 1.9 microM in Y79 cells, 1.3 microM in WERI-RB1 cells, and 0.9 microM in RBM cells. Beta-lapachone also induced proapoptotic effects in RB cells. Treatment of Y79 cells with 1.9 microM beta-lapachone (IC(50)) resulted in a peak, fourfold induction of caspase 3/7 activity at 72 h post-treatment; a peak, 5.6-fold increase in nucleosome fragments at 96 h post-treatment; and a peak, 1.7-fold increase in the frequency of apoptotic cells at 48 h post-treatment, relative to vehicle-treated controls.

CONCLUSION

Beta-lapachone induced potent cytotoxic effects in RB cell lines at low micromolar concentrations, suggesting this agent could be useful in the clinical management of RB.

Development of beta-lapachone prodrugs for therapy against human cancer cells with elevated NAD(P)H:quinone oxidoreductase 1 levels

beta-Lapachone, an o-naphthoquinone, induces a novel caspase- and p53-independent apoptotic pathway dependent on NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 reduces beta-lapachone to an unstable hydroquinone that rapidly undergoes a two-step oxidation back to the parent compound, perpetuating a futile redox cycle. A deficiency or inhibition of NQO1 rendered cells resistant to beta-lapachone. Thus, beta-lapachone has great potential for the treatment of specific cancers with elevated NQO1 levels (e.g., breast, non-small cell lung, pancreatic, colon, and prostate cancers). We report the development of mono(arylimino) derivatives of beta-lapachone as potential prodrugs. These derivatives are relatively nontoxic and not substrates for NQO1 when initially diluted in water. In solution, however, they undergo hydrolytic conversion to beta-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. NQO1 enzyme assays, UV-visible spectrophotometry, high-performance liquid chromatography-electrospray ionization-mass spectrometry, and nuclear magnetic resonance analyses confirmed and monitored conversion of each derivative to beta-lapachone. Once converted, beta-lapachone derivatives caused NQO1-dependent, mu-calpain-mediated cell death in human cancer cells identical to that caused by beta-lapachone. Interestingly, coadministration of N-acetyl-l-cysteine, prevented derivative-induced cytotoxicity but did not affect beta-lapachone lethality. Nuclear magnetic resonance analyses indicated that prevention of beta-lapachone derivative cytotoxicity was the result of direct modification of these derivatives by N-acetyl-l-cysteine, preventing their conversion to beta-lapachone. The use of beta-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation.

2-Phenyl-β-lapachone can affect mitochondrial function by redox cycling mediated oxidation

2-Phenyl-beta-lapachone (3,4-dihydro-2-methyl-2-phenyl-2H-naphtho[1,2b]pyran-5,6-dione) (2PBL) is a o-naphthoquinone synthesized as a possible antitumoral agent. The addition of micromolar concentrations of 2PBL to rat liver mitochondria (in the presence of malate-glutamate or succinate, as respiratory substrates): (1) stimulated O(2) consumption in state 4 and inhibited O(2) consumption in state 3, thus decreasing respiratory control index (RCI); and (2) collapsed the mitochondrial membrane potential. The addition of 2PBL to rat liver submitochondrial particles: (1) stimulated NADH oxidation in the presence of rotenone, antimycin, myxothiazol or cyanide; (2) stimulated (.-)O(2)(-) production in the presence of NADH and antimycin; and (3) led to 2PBL semiquinone radical production. Control studies carried out with two p-naphthoquinones, menadione and atovaquone, did not produced equivalent effects. These findings support the hypothesis that 2PBL, undergoes redox cycling and affects mitochondrial function. The 2PBL effect is complex, involving inhibition of electron transfer, uncoupling of oxidative phosphorylation, collapse of mitochondrial membrane potential and (.-)O(2)(-) production by redox cycling. The mitochondrion could be a target organelle for 2PBL cytotoxicity.

Antioxidant activity and characterization of volatile constituents of Taheebo (Tabebuia impetiginosa Martius ex DC)

Volatiles were isolated from the dried inner bark of Tabebuia impetiginosa using steam distillation under reduced pressure followed by continuous liquid-liquid extraction. The extract was analyzed by gas chromatography and gas chromatography-mass spectrometry. The major volatile constituents of T. impetiginosa were 4-methoxybenzaldehyde (52.84 microg/g), 4-methoxyphenol (38.91 microg/g), 5-allyl-1,2,3-trimethoxybenzene (elemicin; 34.15 microg/g), 1-methoxy-4-(1E)-1-propenylbenzene (trans-anethole; 33.75 microg/g), and 4-methoxybenzyl alcohol (30.29 microg/g). The antioxidant activity of the volatiles was evaluated using two different assays. The extract exhibited a potent inhibitory effect on the formation of conjugated diene hydroperoxides (from methyl linoleate) at a concentration of 1000 microg/mL. The extract also inhibited the oxidation of hexanal for 40 days at a level of 5 microg/mL. The antioxidative activity of T. impetiginosa volatiles was comparable with that of the well-known antioxidants, alpha-tocopherol, and butylated hydroxytoluene.

Induction of apoptosis in human cancer cell lines by diospyrin, a plant-derived bisnaphthoquinonoid, and its synthetic derivatives

Diospyrin, a bisnaphthoquinonoid natural product, and three synthetic derivatives have been tested for their action in four human cancer cell lines: acute myeloblastic leukemia (HL-60), chronic myelogenic leukemia (K-562), breast adenocarcinoma (MCF-7) and cervical epithelial carcinoma (HeLa). In cells grown in appropriate media several derivatives elicited cytotoxicity as assessed by Trypan Blue dye exclusion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide reduction and DNA synthesis. Diethyl ether derivative (D7) was most effective in this regard while the parent compound diospyrin (D1) was least active (D7>D3>D2>D1). D7 was not cytotoxic toward normal human lymphocytes, suggesting its action is specific for tumor cells. On microscopic examination D7-treated cells exhibited characteristic morphological features of apoptosis, such as cell shrinkage and formation of apoptotic bodies. Fluorescent staining with propidium iodide revealed distinct chromatin condensation and nuclear fragmentation. The apoptotic index paralleled cytotoxic parameters, and fragmented DNA extracted free of genomic DNA displayed on gel electrophoresis a typical ladder pattern. D7-induced apoptosis was mediated via activation of caspase 3 and caspase 8.

Synthesis and preliminary pharmacological evaluation of new (+/-) 1,4-naphthoquinones structurally related to lapachol

Seven new 1,4-naphthoquinones structurally related to lapachol were synthesized from lawsone and oxygenated arylmercurials. These compounds can also be seen as pterocarpan derivatives where the A-ring was substituted by the 1,4-naphthoquinone nucleus. Pharmacological screening provided evidence of significant biological activities, including effects against proliferation of the MCF-7 human breast cancer cell line, against Herpes Simplex Virus type 2 infection, and against snake poison-induced myotoxicity. One derivative displaced flunitrazepam binding and showed benzodiazepine-like activity, suggesting novel neuroactive structural motifs.

Role of glutathione depletion and reactive oxygen species generation in apoptotic signaling in a human B lymphoma cell line

The primary objective of this study was to determine the sequence of biochemical signaling events that occur after modulation of the cellular redox state in the B cell lymphoma line, PW, with emphasis on the role of mitochondrial signaling. L-Buthionine sulphoximine (BSO), which inhibits gamma glutamyl cysteine synthetase (gammaGCS), was used to modulate the cellular redox status. The sequence and role of mitochondrial events and downstream apoptotic signals and mediators was studied. After BSO treatment, there was an early decline in cellular glutathione (GSH), followed by an increase in reactive oxygen species (ROS) production, which induced a variety of apoptotic signals (detectable at different time points) in the absence of any external apoptotic stimuli. The sequence of biochemical events accompanying apoptosis included a 95% decrease in total GSH and a partial (25%) preservation of mitochondrial GSH, without a significant increase in ROS production at 24h. Early activation and nuclear translocation of the nuclear factor kappa B subunit Rel A was observed at approximately 3h after BSO treatment. Cytochrome c release into the cytosol was also seen after 24h of BSO treatment. p53 protein expression was unchanged after redox modulation for up to 72 h, and p21waf1 independent loss of cellular proliferation was observed. Surprisingly, a truncated form of p53 was expressed in a time-dependent manner, beginning at 24h after BSO incubation. Irreversible commitment to apoptosis occurred between 48 and 72 h after BSO treatment when mitochondrial GSH was depleted, and there was an increase in ROS production. Procaspase 3 protein levels showed a time-dependent reduction following incubation with BSO, notably after 48 h, that corresponded with increasing ROS levels. At 96 h, caspase 3 cleavage products were detectable. The pan-caspase inhibitor zVADfmk, partially blocked the induction of apoptosis at 48 h, and was ineffective after 72 h. PW cells could be rescued from apoptosis by removing them from BSO after up to 48, but not 72 h incubation with BSO. Mitochondrial transmembrane potential (DeltaPsi(m)) remained intact in most of the cells during the 72 h observation period, indicating that DeltaPsi(m) dissipation is not an early signal for the induction of redox dependent apoptosis in PW cells. These data suggest that a decrease in GSH alone can act as a potent early activator of apoptotic signaling. Increased ROS production following mitochondrial GSH depletion, represents a crucial event, which irreversibly commits PW cells to apoptosis.

Preparation and cytotoxicity toward cancer cells of mono(arylimino) derivatives of beta-lapachone

A regio- and stereospecific synthesis of monoarylimino o-quinones derived from beta-lapachone (1) was achieved by treatment of the quinone with a slight excess of an arylamine in the presence of an excess of triethylamine/titanium tetrachloride 4:1. Imine formation occurred exclusively at position 6, giving the Z diastereomer, as determined by single-crystal X-ray analysis. In vitro tests for cytotoxicity in 55 human cancer cell cultures showed a substantial loss in activity for the p-nitrophenylimine (5), whereas the phenylimine (2), p-methylphenylimine (3), and p-methoxyphenylimine (4) retained (or bettered) most of the cytotoxicity and selectivity of the parent quinone. Preliminary in vivo testing in hollow fiber assays against a standard panel of 12 human tumor cell lines showed that although beta-lapachone failed, compounds 2 and 3 had good scores with net cell kills.

Cellular and molecular responses to topoisomerase I poisons. Exploiting synergy for improved radiotherapy

The efficacy of topoisomerase (Topo) I-active drugs may be improved by better understanding the molecular and cellular responses of tumor compared to normal cells after genotoxic insults. Ionizing radiation (IR) + Topo I-active drugs (e.g., Topotecan) caused synergistic cell killing in various human cancer cells, even in cells from highly radioresistant tumors. Topo I poisons had to be added either during or immediately after IR. Synergy was caused by DNA lesion modification mechanisms as well as by concomitant stimulation of two pathways of cell death: necrosis (IR) + apoptosis (Topo I poisons). Cumulative data favor a mechanism of synergistic cell killing caused by altered DNA lesion modification and enhanced apoptosis. However, alterations in cell cycle regulation may also play a role in the synergy between these two agents in certain human cancers. We recently showed that NF-kappa B, a known anti-apoptotic factor, was activated in various cancer cells after poisoning Topo I using clinically active drugs. NF-kappa B activation was dependent on initial nuclear DNA damage followed by cytoplasmic signaling events. Cytoplasmic signaling leading to NF-kappa B activation after Topo I poisons was diminished in cytoplasts (lacking nuclei) and in CEM/C2 cells that expressed a mutant Topo I protein that did not interact with Topo I-active drugs. NF-kappa B activation was intensified in S-phase and blocked by aphidicolin, suggesting that activation was a result of double-strand break formation due to Topo I poisoning and DNA replication. Dominant-negative I kappa B expression augmented Topo I poison-mediated apoptosis. Elucidation of molecular signal transduction pathways after Topo I drug-IR combinations may lead to improved radiotherapy by blocking anti-apoptotic NF-kappa B responses. Recent data also indicate that synergy caused by IR + Topo I poisons is different from radiosensitization by beta-lapachone (beta-lap), a "reported" Topo I and II-alpha poison in vitro. In fact, beta-lap does not kill cells by poisoning either Topo I or II-alpha in vivo. Instead, the compound is "activated" by an IR (damage)-inducible enzyme, NAD(P)H:quinone oxidoreductase (NQO1), a gene cloned as x-ray-inducible transcript #3, xip3. Unlike the lesion modification pathway induced by IR + Topo I drugs, beta-lap kills cells via NQO1 futile cycle metabolism. Downstream apoptosis caused by beta-lap appears to be noncaspase-mediated, involving calpain or a calpain-like protease. Thus, although Topo I poisons or beta-lap in combination with IR both synergistically kill cancer cells, the mechanisms are very different.