NQO1-activated phenothiazinium redox cyclers for the targeted bioreductive induction of cancer cell apoptosis

Small-molecule redox modulators with anticancer activity: A comprehensive mechanistic update

The pursuit of effective anticancer therapies has led to a burgeoning interest in the realm of redox modulation. This review provides a comprehensive exploration of the intricate mechanisms by which diverse anticancer molecules leverage redox pathways for therapeutic intervention. Redox modulation, encompassing the fine balance of oxidation-reduction processes within cells, has emerged as a pivotal player in cancer treatment. This review delves into the multifaceted mechanisms of action employed by various anticancer compounds, including small molecules and natural products, to disrupt cancer cell proliferation and survival. Beginning with an examination of the role of redox signaling in cancer development and resistance, the review highlights how aberrant redox dynamics can fuel tumorigenesis. It then meticulously dissects the strategies employed by anticancer agents to induce oxidative stress, perturb redox equilibrium, and trigger apoptosis within cancer cells. Furthermore, the review explores the challenges and potential side effects associated with redox-based treatments, along with the development of novel redox-targeted agents. In summary, this review offers a profound understanding of the dynamic interplay between redox modulation and anticancer molecules, presenting promising avenues to revolutionize cancer therapy and enhance patient outcomes.

Improved Bladder Tumor RNA Isolation from Archived Tissues Using Methylene Blue for Normalization, Multiplex RNA Hybridization, Sequencing and Subtyping

Methylene blue (MB) is a dye used for histology with clinical importance and intercalates into nucleic acids. After MB staining of formalin fixed paraffin embedded (FFPE) muscle invasive bladder cancer (MIBC) and normal urothelium, specific regions could be microdissected. It is not known if MB influences RNA used for gene expression studies. Therefore, we analyzed MIBC using five different RNA isolation methods comparing patient matched FFPE and fresh frozen (FF) tissues pre-stained with or without MB. We demonstrate a positive impact of MB on RNA integrity with FF tissues using real time PCR with no interference of its chemical properties. FFPE tissues showed no improvement of RNA integrity, which we propose is due to formalin induced nucleotide crosslinks. Using direct multiplex RNA hybridization the best genes for normalization of MIBC and control tissues were identified from 34 reference genes. In addition, 5SrRNA and 5.8SrRNA were distinctive reference genes detecting <200 bp fragments important for mRNA analyses. Using these normalized RNAs from MB stained MIBC and applying multiplex RNA hybridization and mRNA sequencing, a minimal gene expression panel precisely identified luminal and basal MIBC tumor subtypes, important for diagnosis, prognosis and chemotherapy response.

Effects of toluidine blue O and methylene blue on growth and viability of pancreatic cancer cells

Amyloid precursor-like protein-2 (APLP2) and its C-terminal fragments (CTFs) are expressed at high levels in pancreatic cancer cells and knockdown of APLP2 expression inhibits tumor growth. CTFs are released from APLP2 by beta-secretase (BACE). In this study, our goal was to determine whether methylene blue (MethB) and toluidine blue O (TBO) could be used to slow down the growth and viability of pancreatic cancer cells (Hs 766T). We found that TBO and MethB decreased the growth and viability of Hs 766T cells in a dose- and time-dependent manner compared to vehicle-treated control, as demonstrated by MTT and trypan blue exclusion assays. Although TBO led to decreased expression of APLP2, MethB did not show any significant effect on APLP2. However, both MethB and TBO reduced BACE activity and the levels of APLP2 CTFs in Hs 766T cells. In conclusion, MethB and TBO may be valuable candidates for the treatment of pancreatic cancer by targeting APLP2 processing.

The Role of ROS as a Double-Edged Sword in (In)Fertility: The Impact of Cancer Treatment

Simple Summary

Tumor cells are highly resistant to oxidative stress, but beyond a certain threshold, it may lead to apoptosis/necrosis. Thus, induced loss of redox balance can be a strategy used in anticancer therapies. However, the effectiveness of drugs contrasts with unknown mechanisms involved in the loss of fertility. Considering that cancer patients’ life expectancy is increasing, it raises concerns about the unknown adverse effects. Therefore, new strategies should be pursued alongside explaining to the patients their options regarding the reproduction side effects.

Abstract

Tumor cells are highly resistant to oxidative stress resulting from the imbalance between high reactive oxygen species (ROS) production and insufficient antioxidant defenses. However, when intracellular levels of ROS rise beyond a certain threshold, largely above cancer cells’ capacity to reduce it, they may ultimately lead to apoptosis or necrosis. This is, in fact, one of the molecular mechanisms of anticancer drugs, as most chemotherapeutic treatments alter redox homeostasis by further elevation of intracellular ROS levels or inhibition of antioxidant pathways. In traditional chemotherapy, it is widely accepted that most therapeutic effects are due to ROS-mediated cell damage, but in targeted therapies, ROS-mediated effects are mostly unknown and data are still emerging. The increasing effectiveness of anticancer treatments has raised new challenges, especially in the field of reproduction. With cancer patients’ life expectancy increasing, many aiming to become parents will be confronted with the adverse effects of treatments. Consequently, concerns about the impact of anticancer therapies on reproductive capacity are of particular interest. In this review, we begin with a short introduction on anticancer therapies, then address ROS physiological/pathophysiological roles in both male and female reproductive systems, and finish with ROS-mediated adverse effects of anticancer treatments in reproduction.

Induced photo-cytotoxicity on prostate cancer cells with the photodynamic action of toluidine Blue ortho

BACKGROUND

Photodynamic therapy (PDT) has become an advantageous therapeutic approach for the treatment of select cancers and microbial infections. PDT generates toxic reactive oxygen species as an end product of the interaction between the photosensitizer and light with an appropriate wavelength. Toluidine blue ortho is a photosensitizer that is commonly used in the photodynamic treatment of bacterial infection and a promising photosensitizer for cancer treatment. This study aims to evaluate the potential photo-cytotoxicity of toluidine blue ortho-mediated photodynamic therapy on PC-3 prostate cancer cells.

METHODS

In this study toluidine blue ortho-mediated photodynamic therapy was assessed on PC-3 cancer cells with various photosensitizer concentrations and light energy densities of the 655-nm diode laser. MTT analysis was used for the determination of the cytotoxicity on the cells and viability/cytotoxicity assay was used for live/dead cell staining after the applications. The mechanism of this application was further analyzed with the determination of intracellular reactive oxygen species and nitric oxide release.

RESULTS

The light applications and the photosensitizer alone did not inhibit the cell viability of PC-3 cells. 20 J/cm² laser energy density together with 100 μM photosensitizer concentration resulted in maximum cancer cell death with a rate of approximately 89 %. The level of intracellular reactive oxygen species increased with the increasing parameters of the applications that resulted in more cell death.

CONCLUSION

This study showed the successful anticancer activity of toluidine blue ortho upon irradiation with 655 nm of laser light against PC-3 cancer cells and it was mediated with the production of reactive oxygen species.

Fluorescent redox-dependent labeling of lipid droplets in cultured cells by reduced phenazine methosulfate

Natural and synthetic phenazines are widely used in biomedical sciences. In dehydrogenase histochemistry, phenazine methosulfate (PMS) is applied as a redox reagent for coupling reduced coenzymes to the reduction of tetrazolium salts into colored formazans. PMS is also currently used for cytotoxicity and viability assays of cell cultures using sulfonated tetrazoliums. Under UV (340 nm) excitation, aqueous solutions of the cationic PMS show green fluorescence (λem: 526 nm), whereas the reduced hydrophobic derivative (methyl-phenazine, MPH) shows blue fluorescence (λem: 465 nm). Under UV (365 nm) excitation, cultured cells (LM2, IGROV-1, BGC-1, and 3T3-L1 adipocytes) treated with PMS (5 μg/mL, 30 min) showed cytoplasmic granules with bright blue fluorescence, which correspond to lipid droplets labeled by the lipophilic methyl-phenazine. After formaldehyde fixation blue-fluorescing droplets could be stained with oil red O. Interestingly, PMS-treated 3T3-L1 adipocytes observed under UV excitation 24 h after labeling showed large lipid droplets with a weak green emission within a diffuse pale blue-fluorescing cytoplasm, whereas a strong green emission was observed in small lipid droplets. This fluorescence change from blue to green indicates that reoxidation of methyl-phenazine to PMS can occur. Regarding cell uptake and labeling mechanisms, QSAR models predict that the hydrophilic PMS is not significantly membrane-permeant, so most PMS reduction is expected to be extracellular and associated with a plasma membrane NAD(P)H reductase. Once formed, the lipophilic and blue-fluorescing methyl-phenazine enters live cells and mainly accumulates in lipid droplets. Overall, the results reported here indicate that PMS is an excellent fluorescent probe to investigate labeling and redox dynamics of lipid droplets in cultured cells.

Comparative Study Regarding the Properties of Methylene Blue and Proflavine and Their Optimal Concentrations for In Vitro and In Vivo Applications

Methylene blue and proflavine are fluorescent dyes used to stain nucleic acid from the molecular level to the tissue level. Already clinically used for sentinel node mapping, detection of neuroendocrine tumors, methemoglobinemia, septic shock, ifosfamide-induced encephalopathy, and photodynamic inactivation of RNA viruses, the antimicrobial, anti-inflammatory, and antioxidant effect of methylene blue has been demonstrated in different in vitro and in vivo studies. Proflavine was used as a disinfectant and bacteriostatic agent against many gram-positive bacteria, as well as a urinary antiseptic involved in highlighting cell nuclei. At the tissue level, the anti-inflammatory effects of methylene blue protect against pulmonary, renal, cardiac, pancreatic, ischemic-reperfusion lesions, and fevers. First used for their antiseptic and antiviral activity, respectively, methylene blue and proflavine turned out to be excellent dyes for diagnostic and treatment purposes. In vitro and in vivo studies demonstrated that both dyes are efficient as perfusion and tissue tracers and permitted to evaluate the minimal efficient concentration in different species, as well as their pharmacokinetics and toxicity. This review aims to identify the optimal concentrations of methylene blue and proflavine that can be used for in vivo experiments to highlight the vascularization of the skin in the case of a perforasome (both as a tissue tracer and in vascular mapping), as well as their effects on tissues. This review is intended to be a comparative and critical presentation of the possible applications of methylene blue (MB) and proflavine (PRO) in the surgical field, and the relevant biomedical findings from specialized literature to date are discussed as well.

Understanding of ROS-Inducing Strategy in Anticancer Therapy

Redox homeostasis is essential for the maintenance of diverse cellular processes. Cancer cells have higher levels of reactive oxygen species (ROS) than normal cells as a result of hypermetabolism, but the redox balance is maintained in cancer cells due to their marked antioxidant capacity. Recently, anticancer therapies that induce oxidative stress by increasing ROS and/or inhibiting antioxidant processes have received significant attention. The acceleration of accumulative ROS disrupts redox homeostasis and causes severe damage in cancer cells. In this review, we describe ROS-inducing cancer therapy and the anticancer mechanism employed by prooxidative agents. To understand the comprehensive biological response to certain prooxidative anticancer drugs such as 2-methoxyestradiol, buthionine sulfoximine, cisplatin, doxorubicin, imexon, and motexafin gadolinium, we propose and visualize the drug-gene, drug-cell process, and drug-disease interactions involved in oxidative stress induction and antioxidant process inhibition as well as specific side effects of these drugs using pathway analysis with a big data-based text-mining approach. Our review will be helpful to improve the therapeutic effects of anticancer drugs by providing information about biological changes that occur in response to prooxidants. For future directions, there is still a need for pharmacogenomic studies on prooxidative agents as well as the molecular mechanisms underlying the effects of the prooxidants and/or antioxidant-inhibitor agents for effective anticancer therapy through selective killing of cancer cells.

Repurposing the Electron Transfer Reactant Phenazine Methosulfate (PMS) for the Apoptotic Elimination of Malignant Melanoma Cells through Induction of Lethal Oxidative and Mitochondriotoxic Stress

Redox-directed pharmacophores have shown potential for the apoptotic elimination of cancer cells through chemotherapeutic induction of oxidative stress. Phenazine methosulfate (PMS), a N-alkylphenazinium cation-based redox cycler, is used widely as an electron transfer reactant coupling NAD(P)H generation to the reduction of tetrazolium salts in biochemical cell viability assays. Here, we have explored feasibility of repurposing the redox cycler PMS as a superoxide generating chemotherapeutic for the pro-oxidant induction of cancer cell apoptosis. In a panel of malignant human melanoma cells (A375, G361, LOX), low micromolar concentrations of PMS (1-10 μM, 24 h) displayed pronounced apoptogenicity as detected by annexin V-ITC/propidium iodide flow cytometry, and PMS-induced cell death was suppressed by antioxidant (NAC) or pan-caspase inhibitor (zVAD-fmk) cotreatment. Gene expression array analysis in A375 melanoma cells (PMS, 10 µM; 6 h) revealed transcriptional upregulation of heat shock (HSPA6, HSPA1A), oxidative (HMOX1) and genotoxic (EGR1, GADD45A) stress responses, confirmed by immunoblot detection demonstrating upregulation of redox regulators (NRF2, HO-1, HSP70) and modulation of pro- (BAX, PUMA) and anti-apoptotic factors (Bcl-2, Mcl-1). PMS-induced oxidative stress and glutathione depletion preceded induction of apoptotic cell death. Furthermore, the mitochondrial origin of PMS-induced superoxide production was substantiated by MitoSOX-Red live cell fluorescence imaging, and PMS-induced mitochondriotoxicity (as evidenced by diminished transmembrane potential and oxygen consumption rate) was observable at early time points. After demonstrating NADPH-driven (SOD-suppressible) superoxide radical anion generation by PMS employing a chemical NBT reduction assay, PMS-induction of oxidative genotoxic stress was substantiated by quantitative Comet analysis that confirmed the introduction of formamido-pyrimidine DNA glycosylase (Fpg)-sensitive oxidative DNA lesions in A375 melanoma cells. Taken together, these data suggest feasibility of repurposing the biochemical reactant PMS as an experimental pro-oxidant targeting mitochondrial integrity and redox homeostasis for the apoptotic elimination of malignant melanoma cells.

Micro/nanomachines: what is needed for them to become a real force in cancer therapy?

Conventional drug delivery systems face several issues in medical applications, such as cyto/genotoxicity and off-targeting. These issues are particularly significant for cancer therapeutics because many of the currently used systems are toxic in their free form. Self-propelled autonomous micro/nanomachines offer promising alternative drug delivery systems based on high cargo loading, fast autonomous movement, precise targeting and the on-demand release of therapeutics in vivo. With this unique set of properties, it is not surprising that they are receiving considerable research attention. However, much less is reported about the drawbacks that hinder their systemic in vivo application. In this review, a biomedical perspective is used to assess micro/nanomotor-based anticancer drug delivery systems reported to date. Advantages along with present issues are highlighted and recommendations which need to be considered to develop an effective biocompatible micro/nanomotor-based delivery system for cancer therapy are discussed.

A smart multifunctional drug delivery nanoplatform for targeting cancer cells

Wirelessly guided magnetic nanomachines are promising vectors for targeted drug delivery, which have the potential to minimize the interaction between anticancer agents and healthy tissues. In this work, we propose a smart multifunctional drug delivery nanomachine for targeted drug delivery that incorporates a stimuli-responsive building block. The nanomachine consists of a magnetic nickel (Ni) nanotube that contains a pH-responsive chitosan hydrogel in its inner cavity. The chitosan inside the nanotube serves as a matrix that can selectively release drugs in acidic environments, such as the extracellular space of most tumors. Approximately a 2.5 times higher drug release from Ni nanotubes at pH = 6 is achieved compared to that at pH = 7.4. The outside of the Ni tube is coated with gold. A fluorescein isothiocyanate (FITC) labeled thiol-ssDNA, a biological marker, was conjugated on its surface by thiol-gold click chemistry, which enables traceability. The Ni nanotube allows the propulsion of the device by means of external magnetic fields. As the proposed nanoarchitecture integrates different functional building blocks, our drug delivery nanoplatform can be employed for carrying molecular drug conjugates and for performing targeted combinatorial therapies, which can provide an alternative and supplementary solution to current drug delivery technologies.

The variable chemotherapeutic response of Malabaricone-A in leukemic and solid tumor cell lines depends on the degree of redox imbalance

PURPOSE

The 'two-faced' character of reactive oxygen species (ROS) plays an important role in cancer biology by acting as secondary messengers in intracellular signaling cascades, enhancing cell proliferation and survival, thereby sustaining the oncogenic phenotype. Conversely, enhanced generation of ROS can trigger an oxidative assault leading to a redox imbalance translating into an apoptotic cell death. Intrinsically, cancer cells have higher basal levels of ROS which if supplemented by additional oxidative insult by pro-oxidants can be cytotoxic, an example being Malabaricone-A (MAL-A). MAL-A is a plant derived diarylnonanoid, purified from fruit rind of the plant Myristica malabarica whose anti-cancer activity has been demonstrated in leukemic cell lines, the modality of cell death being apoptosis. This study aimed to compare the degree of effectiveness of MAL-A in leukemic vs. solid tumor cell lines.

METHODS

The cytotoxicity of MAL-A was evaluated by the MTS-PMS cell viability assay in leukemic cell lines (MOLT3, K562 and HL-60) and compared with solid tumor cell lines (MCF7, A549 and HepG2); further studies then proceeded with MOLT3 vs. MCF7 and A549. The contribution of redox imbalance in MAL-A induced cytotoxicity was confirmed by pre-incubating cells with an antioxidant, N-acetyl-L-cysteine (NAC) or a thiol depletor, buthionine sulfoximine (BSO). MAL-A induced redox imbalance was quantitated by flow cytometry, by measuring the generation of ROS and levels of non protein thiols using dichlorofluorescein diacetate (CM-H2DCFDA) and 5-chloromethylfluorescein diacetate (CMFDA) respectively. The activities of glutathione peroxidase (GPx), superoxide dismutase, catalase (CAT), NAD(P)H dehydrogenase (quinone 1) NQO1 and glutathione-S-transferase GST were measured spectrophotometrically. The mitochondrial involvement of MAL-A induced cell death was measured by evaluation of cardiolipin peroxidation using 10-N-nonyl acridine orange (NAO), transition pore activity with calcein-AM, while the mitochondrial transmembrane electrochemical gradient (∆ψ(m)) was measured by JC-1, fluorescence being acquired in a flow cytometer. The apoptotic mode of cell death was evaluated by double staining with annexin V-FITC and propidium iodide (PI), cell cycle analysis by flow cytometry and caspase-3 activity spectrophotometrically. The expression of Nrf2 and HO-1 was examined by western blotting.

RESULTS

MAL-A demonstrated a higher degree of cytotoxicity in three leukemic cell lines whose IC50 ranged from 12.70 ± 0.10 to 18.10 ± 0.95 µg/ml, whereas in three solid tumor cell lines, the IC50 ranged from 28.10 ± 0.58 to 55.26 ± 5.90 µg/ml. This higher degree of cytotoxicity in MOLT3, a leukemic cell line was due to a higher induction of redox imbalance, evident by both an increased generation of ROS and concomitant depletion of thiols. This was confirmed by pre-incubation with NAC and BSO, wherein NAC decreased MAL-A induced cytotoxicity by 2.04 fold while BSO enhanced MAL-A cytotoxicity and decreased the IC50 by 5.60 fold. However, in solid tumor cell lines (MCF7 and A549), NAC minimally decreased MAL-A induced cytotoxicity, and BSO increased the IC50 by 1.96 and 2.39 fold respectively. Furthermore, the generation of ROS by MAL-A increased maximally in MOLT3 as the fluorescence increased from 44.28 ± 7.85 to 273.99 ± 32.78, and to a lesser degree in solid tumor cell lines, MCF7 (44.28 ± 14.89 to 207.97 ± 70.64) and A549 (37.87 ± 3.24 to 147.12 ± 38.53). In all three cell lines there was a concomitant depletion of thiols as in MOLT3, the GMFC decreased from 340.65 ± 60.39 to 62.67 ± 11.32, in MCF7 (277.82 ± 50.32 to 100.39 ± 31.93) and in A549 (274.05 ± 59.13 to 83.15 ± 21.43). In MOLT3 as compared to MCF7 and A549, decrease in the activities of GPx, CAT, NQO1 and GST was substantially greater. In all cell lines, the MAL-A induced redox imbalance translated into triggering of initial mitochondrial apoptotic events. Here again, MAL-A induced a higher degree of cardiolipin peroxidation in MOLT3 (67.01%) than MCF7 and A549 (29.15% and 44.30%), as also down regulated the mitochondrial transition pore activity from baseline to a higher extent, GMFC being 48.05 ± 2.37 to 10.70 ± 3.97 (MOLT3), 43.55 ± 3.36 to 15.36 ± 0.60 (MCF7) and 39.58 ± 0.4 to 12.65 ± 1.56 (A549). Perturbation of mitochondrial membrane potential evident by a decrease in the ratio of red/green (J-aggregates/monomers) was 134 fold (14.73/0.11) in MOLT3, 45 fold in MCF7 (20.72/0.46) and 34 fold in A549 (22.01/0.64). The extent of apoptosis using a similar concentration of MAL-A was maximal in MOLT3, wherein a 105 fold increase in annexin V binding was evident (0.83 ± 0.51 to 87.08 ± 9.85%) whereas it increased by 43.11 fold in MCF7 (0.69 ± 0.30 to 29.75 ± 11.79%) and 47.52 fold in A549 (0.61 ± 0.31 to 28.99 ± 17.21%). MAL-A induced apoptosis was also associated with a higher degree of caspase-3 activity in MOLT3 vs. MCF7 or A549 which translated into halting of cell cycle progression, evident by an increment in the sub-G0/G1 population [19.26 fold in MOLT3 (0.95 ± 0.45 vs. 18.30 ± 1.90%), 11.01 fold in MCF7 (0.97 ± 0.37 vs. 10.68 ± 0.69%) and 8.58 fold in A549 (1.06 ± 0.45 vs. 9.10 ± 1.05%)]. MAL-A effectively inhibited Nrf2 and HO-1, more prominently in MOLT3. Furthermore, the decreased expression of Nrf2 in MOLT3 correlated with the decreased activities of NQO1 and GST, suggesting that targeting of the Nrf2 anti-oxidant pathway could be considered.

CONCLUSION

Taken together, MAL-A a pro-oxidant compound is likely to be more effective in leukemias, meriting further pharmacological consideration.

Methylene blue-induced neuronal protective mechanism against hypoxia-reoxygenation stress

Brain ischemia and reperfusion (I/R) injury occurs in various pathological conditions, but there is no effective treatment currently available in clinical practice. Methylene blue (MB) is a century-old drug with a newly discovered protective function in the ischemic stroke model. In the current investigation we studied the MB-induced neuroprotective mechanism focusing on stabilization and activation of hypoxia-inducible factor-1α (HIF-1α) in an in vitro oxygen and glucose deprivation (OGD)-reoxygenation model.

METHODS

HT22 cells were exposed to OGD (0.1% O2, 6h) and reoxygenation (21% O2, 24h). Cell viability was determined with the calcein AM assay. The dynamic change of intracellular O2 concentration was monitored by fluorescence lifetime imaging microscopy (FLTIM). Glucose uptake was quantified using the 2-[N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino]-2-Deoxy-d-Glucose (2-NBDG) assay. ATP concentration and glycolytic enzyme activity were examined by spectrophotometry. Protein content changes were measured by immunoblot: HIF-1α, prolyl hydroxylase 2 (PHD2), erythropoietin (EPO), Akt, mTOR, and PIP5K. The contribution of HIF-1α activation in the MB-induced neuroprotective mechanism was confirmed by blocking HIF-1α activation with 2-methoxyestradiol-2 (2-MeOE2) and by transiently transfecting constitutively active HIF-1α.

RESULTS

MB increases cell viability by about 50% vs. OGD control. Compared to the corresponding control, MB increases intracellular O2 concentration and glucose uptake as well as the activities of hexokinase and G-6-PDH, and ATP concentration. MB activates the EPO signaling pathway with a corresponding increase in HIF-1α. Phosphorylation of Akt was significantly increased with MB treatment followed by activation of the mTOR pathway. Importantly, we observed, MB increased nuclear translocation of HIF-1α vs. control (about three folds), which was shown by a ratio of nuclear:cytoplasmic HIF-1α protein content.

CONCLUSION

We conclude that MB protects the hippocampus-derived neuronal cells against OGD-reoxygenation injury by enhancing energy metabolism and increasing HIF-1α protein content accompanied by an activation of the EPO signaling pathway.

In vivo pump-probe optical coherence tomography imaging in Xenopus laevis

Currently, optical coherence tomography (OCT), is not capable of obtaining molecular information often crucial for identification of disease. To enable molecular imaging with OCT, we have further developed a technique that harnesses transient changes in light absorption in the sample to garner molecular information. A Fourier-domain Pump-Probe OCT (PPOCT) system utilizing a 532 nm pump and 830 nm probe has been developed for imaging hemoglobin. Methylene blue, a biological dye with well-know photophysics, was used to characterize the system before investigating the origin of the hemoglobin PPOCT signal. The first in vivo PPOCT images were recorded of the vasculature in Xenopus laevis. The technique was shown to work equally well in flowing and nonflowing vessels. Furthermore, PPOCT was compared with other OCT extensions which require flow, such as Doppler OCT and phase-variance OCT. PPOCT was shown to better delineate tortuous vessels, where nodes often restrict Doppler and phase-variance reconstruction.

The quinone methide aurin is a heat shock response inducer that causes proteotoxic stress and Noxa-dependent apoptosis in malignant melanoma cells

Pharmacological induction of proteotoxic stress is rapidly emerging as a promising strategy for cancer cell-directed chemotherapeutic intervention. Here, we describe the identification of a novel drug-like heat shock response inducer for the therapeutic induction of proteotoxic stress targeting malignant human melanoma cells. Screening a focused library of compounds containing redox-directed electrophilic pharmacophores employing the Stress & Toxicity PathwayFinder(TM) PCR Array technology as a discovery tool, a drug-like triphenylmethane-derivative (aurin; 4-[bis(p-hydroxyphenyl)methylene]-2,5-cyclohexadien-1-one) was identified as an experimental cell stress modulator that causes (i) heat shock factor transcriptional activation, (ii) up-regulation of heat shock response gene expression (HSPA6, HSPA1A, DNAJB4, HMOX1), (iii) early unfolded protein response signaling (phospho-PERK, phospho-eIF2α, CHOP (CCAAT/enhancer-binding protein homologous protein)), (iv) proteasome impairment with increased protein-ubiquitination, and (v) oxidative stress with glutathione depletion. Fluorescence polarization-based experiments revealed that aurin displays activity as a geldanamycin-competitive Hsp90α-antagonist, a finding further substantiated by molecular docking and ATPase inhibition analysis. Aurin exposure caused caspase-dependent cell death in a panel of human malignant melanoma cells (A375, G361, LOX-IMVI) but not in non-malignant human skin cells (Hs27 fibroblasts, HaCaT keratinocytes, primary melanocytes) undergoing the aurin-induced heat shock response without impairment of viability. Aurin-induced melanoma cell apoptosis depends on Noxa up-regulation as confirmed by siRNA rescue experiments demonstrating that siPMAIP1-based target down-regulation suppresses aurin-induced cell death. Taken together, our data suggest feasibility of apoptotic elimination of malignant melanoma cells using the quinone methide-derived heat shock response inducer aurin.

Methylene blue inhibits the asexual development of vivax malaria parasites from a region of increasing chloroquine resistance

OBJECTIVES

Methylene blue, once discarded due to its unsettling yet mild side effects, has now found a renewed place in the pharmacopoeia of modern medicine. The continued spread of drug-resistant Plasmodium vivax and Plasmodium falciparum has also led to a recent re-examination of methylene blue's potent antimalarial properties. Here we examine the ex vivo susceptibility profile of Plasmodium spp. isolates to methylene blue; the isolates were from a region on the Thai-Myanmar border where there are increasing rates of failure when treating vivax malaria with chloroquine.

METHODS

To do this we used a newly developed ex vivo susceptibility assay utilizing flow cytometry and a portable flow cytometer with a near-UV laser.

RESULTS

P. vivax (median methylene blue IC50 3.1 nM, IQR 1.7-4.3 nM) and P. falciparum (median methylene blue IC50 1.8 nM, IQR 1.6-2.3 nM) are susceptible to methylene blue treatment at physiologically relevant levels. Unfortunately, the addition of chloroquine to combination treatments with methylene blue significantly reduces the ex vivo effectiveness of this molecule.

CONCLUSIONS

Our data support further efforts to employ methylene blue as a safe, low-cost antimalarial to treat drug-resistant malaria.

Chemical and biological mechanisms of pathogen reduction technologies

Within the last decade new technologies have been developed and implemented which employ light, often in the presence of a photosensitizer, to inactivate pathogens that reside in human blood products for the purpose of transfusion. These pathogen reduction technologies attempt to find the proper balance between pathogen kill and cell quality. Each system utilizes various chemistries that not only impact which pathogens they can inactivate and how, but also how the treatments affect the plasma and cellular proteins and to what degree. This paper aims to present the various chemical mechanisms for pathogen reduction in transfusion medicine that are currently practiced or in development.

Calcium carbonate microparticle growth controlled by a conjugate drug-copolymer and crystallization time

The influence of crystallization reaction time on CaCO3 microparticle growth from supersaturate aqueous solutions, in the presence of a conjugate drug-copolymer, has been investigated. The polymer conjugate, P(NVP-MA-Ox), is based on poly(N-vinylpyrrolidone-co-maleic anhydride) as the support and 2-amino-5-(4-methoxyphenyl)-1,3,4-oxadiazole as the drug. The microparticles are characterized by optical, scanning and transmission electron microscopy, dynamic light scattering, X-ray diffraction, flow particle image analysis and particle charge density. X-ray diffraction (XRD) investigations showed that calcite polymorph content increased with an increase in crystallization time, even if the electrostatic interactions between Ca(2+) and polyanionic sites of P(NVP-MA-Ox) structure conduct to an increased vaterite phase stability. The strong particle size increase after 6 h of ageing can be ascribed to partially vaterite recrystallization and adsorption of nano-scaled calcite crystallite nuclei at microparticles surfaces. The pH stability of the particles was shown by zeta potential changes and their adsorption capacity as a function of their composition, and characteristics were tested using methylene blue. The sorption capacity of composite materials was strongly influenced by the ratio between polymorphs in the composites, and increased with the increase of calcite content and ageing time.

Convenient microtiter plate-based, oxygen-independent activity assays for flavin-dependent oxidoreductases based on different redox dyes

Flavin-dependent oxidoreductases are increasingly recognized as important biocatalysts for various industrial applications. In order to identify novel activities and to improve these enzymes in engineering approaches, suitable screening methods are necessary. We developed novel microtiter-plate-based assays for flavin-dependent oxidases and dehydrogenases using redox dyes as electron acceptors for these enzymes. 2,6-dichlorophenol-indophenol, methylene green, and thionine show absorption changes between their oxidized and reduced forms in the visible range, making it easy to judge visually changes in activity. A sample set of enzymes containing both flavoprotein oxidases and dehydrogenases - pyranose 2-oxidase, pyranose dehydrogenase, cellobiose dehydrogenase, D-amino acid oxidase, and L-lactate oxidase - was selected. Assays for these enzymes are based on a direct enzymatic reduction of the redox dyes and not on the coupled detection of a reaction product as in the frequently used assays based on hydrogen peroxide formation. The different flavoproteins show low Michaelis constants with these electron acceptor substrates, and therefore these dyes need to be added in only low concentrations to assure substrate saturation. In conclusion, these electron acceptors are useful in selective, reliable and cheap MTP-based screening assays for a range of flavin-dependent oxidoreductases, and offer a robust method for library screening, which could find applications in enzyme engineering programs.

D-Penicillamine targets metastatic melanoma cells with induction of the unfolded protein response (UPR) and Noxa (PMAIP1)-dependent mitochondrial apoptosis

D-Penicillamine (3,3-dimethyl-D-cysteine; DP) is an FDA-approved redox-active D-cysteine-derivative with antioxidant, disulfide-reducing, and metal chelating properties used therapeutically for the control of copper-related pathology in Wilson's disease and reductive cystine-solubilization in cystinuria. Based on the established sensitivity of metastatic melanoma cells to pharmacological modulation of cellular oxidative stress, we tested feasibility of using DP for chemotherapeutic intervention targeting human A375 melanoma cells in vitro and in vivo. DP treatment induced caspase-dependent cell death in cultured human metastatic melanoma cells (A375, G361) without compromising viability of primary epidermal melanocytes, an effect not observed with the thiol-antioxidants N-acetyl-L-cysteine (NAC) and dithiothreitol. Focused gene expression array analysis followed by immunoblot detection revealed that DP rapidly activates the cytotoxic unfolded protein response (UPR; involving phospho-PERK, phospho-eIF2α, Grp78, CHOP, and Hsp70) and the mitochondrial pathway of apoptosis with p53 upregulation and modulation of Bcl-2 family members (involving Noxa, Mcl-1, and Bcl-2). DP (but not NAC) induced oxidative stress with early impairment of glutathione homeostasis and mitochondrial transmembrane potential. SiRNA-based antagonism of PMAIP1 expression blocked DP-induced upregulation of the proapoptotic BH3-only effector Noxa and prevented downregulation of the Noxa-antagonist Mcl-1, rescuing melanoma cells from DP-induced apoptosis. Intraperitoneal administration of DP displayed significant antimelanoma activity in a murine A375 xenograft model. It remains to be seen if melanoma cell-directed induction of UPR and apoptosis using DP or improved DP-derivatives can be harnessed for future chemotherapeutic intervention.

GS-2, a pyrazolo[1,5-a]indole derivative with inhibitory activity of topoisomerases, exerts its potent cytotoxic activity by ROS generation

Pyrazolo[1,5-a]indole derivatives, a new type of topoisomerase (topo) inhibitor, demonstrate a broad spectrum of antitumor activities. However, the mechanism underlying the induced cytotoxicity remains unclear. In this study, we investigated whether GS-2, one of the derivatives, altered the levels of ROS in breast cancer MDA-231 cells and whether these ROS contributed to the observed antitumoral activity. Our data revealed that GS-2 caused a time- and dose-dependent elevation of intracellular ROS level in MDA-231 cells. GS-2 subsequently elicited notable inhibition on the expression of topos, DNA damage, activation of caspase-3, -9. The loss of mitochondrial membrane potential (MMP) was observed during the induction. The addition of N-acetyl cysteine (NAC, a well-known antioxidant) could effectively attenuate the GS-2-induced ROS enhancement and subsequent apoptosis. NAC attenuated the induced inhibition on expression of topos, indicating that topos might be the target of GS-2-induced ROS. The finding of the induced ROS provides new evidence for the molecular mechanisms of antitumor activity of pyrazolo[1,5-a]indole derivatives.

Phenotypic identification of the redox dye methylene blue as an antagonist of heat shock response gene expression in metastatic melanoma cells

Repurposing approved and abandoned non-oncological drugs is an alternative developmental strategy for the identification of anticancer therapeutics that has recently attracted considerable attention. Due to the essential role of the cellular heat shock response in cytoprotection through the maintenance of proteostasis and suppression of apoptosis, small molecule heat shock response antagonists can be harnessed for targeted induction of cytotoxic effects in cancer cells. Guided by gene expression array analysis and a phenotypic screen interrogating a collection of 3,7-diamino-phenothiazinium derivatives, we have identified the redox-drug methylene blue (MB), used clinically for the infusional treatment of methemoglobinemia, as a negative modulator of heat shock response gene expression in human metastatic melanoma cells. MB-treatment blocked thermal (43 °C) and pharmacological (celastrol, geldanamycin) induction of heat shock response gene expression, suppressing Hsp70 (HSPA1A) and Hsp27 (HSPB1) upregulation at the mRNA and protein level. MB sensitized melanoma cells to the apoptogenic activity of geldanamycin, an Hsp90 antagonist known to induce the counter-regulatory upregulation of Hsp70 expression underlying cancer cell resistance to geldanamycin chemotherapy. Similarly, MB-cotreatment sensitized melanoma cells to other chemotherapeutics (etoposide, doxorubicin). Taken together, these data suggest feasibility of repurposing the non-oncological redox drug MB as a therapeutic heat shock response antagonist for cancer cell chemosensitization.

Discovery of antimicrobial ribonucleotide reductase inhibitors by screening in microwell format

Ribonucleotide reductase (RNR) catalyzes reduction of the four different ribonucleotides to their corresponding deoxyribonucleotides and is the rate-limiting enzyme in DNA synthesis. RNR is a well-established target for the antiproliferative drugs Gemzar and Hydrea, for antisense therapy, and in combination chemotherapies. Surprisingly, few novel drugs that target RNR have emerged, partly because RNR activity assays are laboratory-intense and exclude high-throughput methodologies. Here, we present a previously undescribed PCR-based assay for RNR activity measurements in microplate format. We validated the approach by screening a diverse library of 1,364 compounds for inhibitors of class I RNR from the opportunistic pathogen Pseudomonas aeruginosa, and we identified 27 inhibitors with IC(50) values from ∼200 nM to 30 μM. Interestingly, a majority of the identified inhibitors have been found inactive in human cell lines as well as in anticancer and in vivo tumor tests as reported by the PubChem BioAssay database. Four of the RNR inhibitors inhibited growth of P. aeruginosa, and two were also found to affect the transcription of RNR genes and to decrease the cellular deoxyribonucleotide pools. This unique PCR-based assay works with any RNR enzyme and any substrate nucleotide, and thus opens the door to high-throughput screening for RNR inhibitors in drug discovery.

Thiostrepton is an inducer of oxidative and proteotoxic stress that impairs viability of human melanoma cells but not primary melanocytes

Pharmacological induction of oxidative and proteotoxic stress has recently emerged as a promising strategy for chemotherapeutic intervention targeting cancer cells. Guided by a differential phenotypic drug screen for novel lead compounds that selectively induce melanoma cell apoptosis without compromising viability of primary human melanocytes, we have focused on the cyclic pyridinyl-polythiazolyl peptide-antimicrobial thiostrepton. Using comparative gene expression-array analysis, the early cellular stress response induced by thiostrepton was examined in human A375 metastatic melanoma cells and primary melanocytes. Thiostrepton displayed selective antimelanoma activity causing early induction of proteotoxic stress with massive upregulation of heat shock (HSPA6, HSPA1A, DNAJB4, HSPB1, HSPH1, HSPA1L, CRYAB, HSPA5, DNAJA1), oxidative stress (HMOX1, GSR, SOD1), and ER stress response (DDIT3) gene expression, confirmed by immunodetection (Hsp70, Hsp70B', HO-1, phospho-eIF2α). Moreover, upregulation of p53, proapoptotic modulation of Bcl-2 family members (Bax, Noxa, Mcl-1, Bcl-2), and induction of apoptotic cell death were observed. Thiostrepton rapidly induced cellular oxidative stress followed by inactivation of chymotrypsin-like proteasomal activity and melanoma cell-directed accumulation of ubiquitinated proteins, not observed in melanocytes that were resistant to thiostrepton-induced apoptosis. Proteotoxic and apoptogenic effects were fully antagonized by antioxidant intervention. In RPMI 8226 multiple myeloma cells, known to be exquisitely sensitive to proteasome inhibition, early proteotoxic and apoptogenic effects of thiostrepton were confirmed by array analysis indicating pronounced upregulation of heat shock response gene expression. Our findings demonstrate that thiostrepton displays dual activity as a selective prooxidant and proteotoxic chemotherapeutic, suggesting feasibility of experimental intervention targeting metastatic melanoma and other malignancies including multiple myeloma.

Dicoumarol activates Ca2+-permeable cation channels triggering erythrocyte cell membrane scrambling

Dicoumarol, a widely used anticoagulant, may cause anemia, which may result from enhanced erythrocyte loss due to bleeding or due to accelerated erythrocyte death. Erythrocytes may undergo suicidal death or eryptosis, characterized by cell shrinkage and phospholipid scrambling of the cell membrane. Eryptosis may be triggered by increase of cytosolic Ca(2+)-activity ([Ca(2+)](i)). The present study explored, whether dicoumarol induces eryptosis. [Ca(2+)](i) was estimated from Fluo3-fluorescence, cation channel activity utilizing whole cell patch clamp, cell volume from forward scatter, phospholipid scrambling from annexin-V-binding, and hemolysis from haemoglobin release. Exposure of erythrocytes for 48 hours to dicoumarol (=10 μM) significantly increased [Ca(2+)](i), enhanced cation channel activity, decreased forward scatter, triggered annexin-V-binding and elicited hemolysis. Following exposure to 30 μM dicoumarol, annexin-V-binding affected approximately 15%, and hemolysis 2% of treated erythrocytes. The stimulation of annexin-V-binding by dicoumarol was abrogated in the nominal absence of Ca(2+). In conclusion, dicoumarol stimulates suicidal death of erythrocytes by stimulating Ca(2+) entry and subsequent triggering of Ca(2+) dependent cell membrane scrambling.

Magnetic carbon nanotubes with particle-free surfaces and high drug loading capacity

Open-ended, multi-wall carbon nanotubes (CNTs) with magnetic nanoparticles encapsulated within their graphitic walls (magCNTs) were fabricated by a combined action of templated growth and a ferrofluid catalyst/carbon precursor, and tested as drug hosts. The hybrid nanotubes are stable under extreme pH conditions due to particle protection provided by the graphitic shell. The magCNTs are promising for high capacity drug loading given that the magnetic functionalization did not block any of the active sites available for drug attachment, either from the CNT internal void or on the internal and external surfaces. This is in contrast to typical approaches of loading CNTs with particles that proceed through surface attachment or capillary filling of the tube interior. Additionally, the CNTs exhibit enhanced hydrophilic character, as shown by water adsorption measurements, which make them suitable for biological applications. The morphological and structural characteristics of the hybrid CNTs are evaluated in conjunction to their magnetic properties and ability for drug loading (diaminophenothiazine). The fact that the magnetic functionality is provided from 'inside the walls' can allow for multimode functionalization of the graphitic surfaces and makes the magCNTs promising for targeted therapeutic applications.

The redox antimalarial dihydroartemisinin targets human metastatic melanoma cells but not primary melanocytes with induction of NOXA-dependent apoptosis

Recent research suggests that altered redox control of melanoma cell survival, proliferation, and invasiveness represents a chemical vulnerability that can be targeted by pharmacological modulation of cellular oxidative stress. The endoperoxide artemisinin and semisynthetic artemisinin-derivatives including dihydroartemisinin (DHA) constitute a major class of antimalarials that kill plasmodium parasites through induction of iron-dependent oxidative stress. Here, we demonstrate that DHA may serve as a redox chemotherapeutic that selectively induces melanoma cell apoptosis without compromising viability of primary human melanocytes. Cultured human metastatic melanoma cells (A375, G361, LOX) were sensitive to DHA-induced apoptosis with upregulation of cellular oxidative stress, phosphatidylserine externalization, and activational cleavage of procaspase 3. Expression array analysis revealed DHA-induced upregulation of oxidative and genotoxic stress response genes (GADD45A, GADD153, CDKN1A, PMAIP1, HMOX1, EGR1) in A375 cells. DHA exposure caused early upregulation of the BH3-only protein NOXA, a proapototic member of the Bcl2 family encoded by PMAIP1, and genetic antagonism (siRNA targeting PMAIP1) rescued melanoma cells from apoptosis indicating a causative role of NOXA-upregulation in DHA-induced melanoma cell death. Comet analysis revealed early DHA-induction of genotoxic stress accompanied by p53 activational phosphorylation (Ser 15). In primary human epidermal melanocytes, viability was not compromised by DHA, and oxidative stress, comet tail moment, and PMAIP1 (NOXA) expression remained unaltered. Taken together, these data demonstrate that metastatic melanoma cells display a specific vulnerability to DHA-induced NOXA-dependent apoptosis and suggest feasibility of future anti-melanoma intervention using artemisinin-derived clinical redox antimalarials.

Tumor Growth Inhibitory Effect of Juglone and Its Radiation Sensitizing Potential

The present study aimed at evaluating the anticancer and radiosensitizing potential of juglone against a chemoresistant and radioresistant tumor (B16F1 melanoma) growing on C57BL/6J mice. Volume doubling time, growth delay, and median survival were used to assess the in vivo anticancer and radiosensitizing potential of juglone. In vitro radiosensitizing potential of juglone was studied using clonogenic, comet, and reactive oxygen species induction assays. Treatment of tumor-bearing mice with sublethal doses of juglone caused a dose-dependent inhibition of tumor growth as evident from the growth delay and median survival values. Comet assay using tumor tissue and blood showed differential toxicity of juglone, where higher levels of DNA damage was seen in tumor tissue compared with blood cells. Pretreatment of tumor-bearing mice with optimum dose of juglone before radiation resulted in significant tumor growth inhibition compared with radiation alone. From the clonogenic assay, the authors observed a sensitization enhancement ratio of 1.37 for the combination treatment compared with radiation alone. Furthermore, comet assay studies revealed the potential of juglone to enhance the radiation-induced DNA damage and cause a delay in its repair. Juglone pretreatment before radiation also resulted in a significant elevation in the intracellular reactive oxygen species levels compared with radiation alone. In conclusion, the results of this study show the potential of juglone to inhibit the growth of melanoma in vivo. The study also revealed the potential of juglone to augment the radiation-induced cell death of melanoma cells, which may be attributed to oxidative stress–mediated DNA damage and its delayed repair.

Antimicrobial mechanisms behind photodynamic effect in the presence of hydrogen peroxide

This study describes the use of methylene blue (MB) plus light (photodynamic inactivation, PDI) in the presence of hydrogen peroxide (H(2)O(2)) to kill Staphylococcus aureus, Escherichia coli, and Candida albicans. When H(2)O(2) was added to MB plus light there was an increased antimicrobial effect, which could be due to a change in the type of ROS generated or increased microbial uptake of MB. To clarify the mechanism, the production of ROS was investigated in the presence and absence of H(2)O(2). It was observed that ROS production was almost inhibited by the presence of H(2)O(2) when cells were not present. In addition, experiments using different sequence combinations of MB and H(2)O(2) were performed and MB optical properties inside the cell were analyzed. Spectroscopy experiments suggested that the amount of MB was higher inside the cells when H(2)O(2) was used before or simultaneously with PDI, and ROS formation inside C. albicans cells confirmed that ROS production is higher in the presence of H(2)O(2). Moreover enzymatic reduction of MB by E. coli during photosensitizer uptake to the photochemically inactive leucoMB could be reversed by the oxidative effects of hydrogen peroxide, increasing ROS formation inside the microorganism. Therefore, the combination of a photosensitizer such as MB and H(2)O(2) is an interesting approach to improve PDI efficiency.

DCPIP (2,6-dichlorophenolindophenol) as a genotype-directed redox chemotherapeutic targeting NQO1*2 breast carcinoma

Accumulative experimental evidence suggests feasibility of chemotherapeutic intervention targeting human cancer cells by pharmacological modulation of cellular oxidative stress. Current efforts aim at personalization of redox chemotherapy through identification of predictive tumour genotypes and redox biomarkers. Based on earlier research demonstrating that anti-melanoma activity of the pro-oxidant 2,6-dichlorophenolindophenol (DCPIP) is antagonized by cellular NAD(P)H:quinone oxidoreductase (NQO1) expression, this study tested DCPIP as a genotype-directed redox chemotherapeutic targeting homozygous NQO1*2 breast carcinoma, a common missense genotype [rs1800566 polymorphism; NP_000894.1:p.Pro187Ser] encoding a functionally impaired NQO1 protein. In a panel of cultured breast carcinoma cell lines and NQO1-transfectants with differential NQO1 expression levels, homozygous NQO1*2 MDA-MB231 cells were hypersensitive to DCPIP-induced caspase-independent cell death that occurred after early onset of oxidative stress with glutathione depletion and loss of genomic integrity. Array analysis revealed upregulated expression of oxidative (GSTM3, HMOX1, EGR1), heat shock (HSPA6, HSPA1A, CRYAB) and genotoxic stress response (GADD45A, CDKN1A) genes confirmed by immunoblot detection of HO-1, Hsp70, Hsp70B', p21 and phospho-p53 (Ser15). In a murine xenograft model of human homozygous NQO1*2-breast carcinoma, systemic administration of DCPIP displayed significant anti-tumour activity, suggesting feasibility of redox chemotherapeutic intervention targeting the NQO1*2 genotype.

The malondialdehyde-derived fluorophore DHP-lysine is a potent sensitizer of UVA-induced photooxidative stress in human skin cells

Light-driven electron and energy transfer involving non-DNA skin chromophores as endogenous photosensitizers induces oxidative stress in UVA-exposed human skin, a process relevant to photoaging and photocarcinogenesis. Malondialdehyde is an electrophilic dicarbonyl-species derived from membrane lipid peroxidation. Here, we present experimental evidence suggesting that the malondialdehyde-derived protein epitope dihydropyridine (DHP)-lysine is a potent endogenous UVA-photosensitizer of human skin cells. Immunohistochemical analysis revealed the abundant occurrence of malondialdehyde-derived and DHP-lysine epitopes in human skin. Using the chemically protected dihydropyridine-derivative (2S)-Boc-2-amino-6-(3,5-diformyl-4-methyl-4H-pyridin-1-yl)-hexanoic acid-t-butylester as a model of peptide-bound DHP-lysine, photodynamic inhibition of proliferation and induction of cell death were observed in human skin Hs27 fibroblasts as well as primary and HaCaT keratinocytes exposed to the combined action of UVA and DHP-lysine. DHP-lysine photosensitization induced intracellular oxidative stress, p38 MAPkinase activation, and upregulation of heme oxygenase-1 expression. Consistent with UVA-driven ROS formation from DHP-lysine, formation of superoxide, hydrogen peroxide, and singlet oxygen was detected in chemical assays, but little protection was achieved using SOD or catalase during cellular photosensitization. In contrast, inclusion of NaN(3) completely abolished DHP-photosensitization. Taken together, these data demonstrate photodynamic activity of DHP-lysine and support the hypothesis that malondialdehyde-derived protein-epitopes may function as endogenous sensitizers of UVA-induced oxidative stress in human skin.

GLO1 overexpression in human malignant melanoma

Glyoxalase I [lactoylglutathione lyase (EC 4.4.1.5) encoded by GLO1] is a ubiquitous cellular defense enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis. Accumulative evidence suggests an important role of GLO1 expression in protection against methylglyoxal-dependent protein adduction and cellular damage associated with diabetes, cancer, and chronological aging. On the basis of the hypothesis that GLO1 upregulation may play a functional role in glycolytic adaptations of cancer cells, we examined GLO1 expression status in human melanoma tissue. Quantitative reverse transcription polymerase chain reaction analysis of a cDNA tissue array containing 40 human melanoma tissues (stages III and IV) and 13 healthy controls revealed pronounced upregulation of GLO1 expression at the mRNA level. Immunohistochemical analysis of a melanoma tissue microarray confirmed upregulation of glyoxalase I protein levels in malignant melanoma tissue versus healthy human skin. Consistent with an essential role of GLO1 in melanoma cell defense against methylglyoxal cytotoxicity, siRNA interference targeting GLO1-expression (siGLO1) sensitized A375 and G361 human metastatic melanoma cells towards the antiproliferative, apoptogenic, and oxidative stress-inducing activity of exogenous methylglyoxal. Protein adduction by methylglyoxal was increased in siGLO1-transfected cells as revealed by immunodetection using a monoclonal antibody directed against the major methylglyoxal-derived epitope argpyrimidine that detected a single band of methylglyoxal-adducted protein in human LOX, G361, and A375 total cell lysates. Using two-dimensional proteomics followed by mass spectrometry the methylglyoxal-adducted protein was identified as heat shock protein 27 (Hsp27; HSPB1). Taken together, our data suggest a function of GLO1 in the regulation of detoxification and target adduction by the glycolytic byproduct methylglyoxal in malignant melanoma.

The topical antimicrobial zinc pyrithione is a heat shock response inducer that causes DNA damage and PARP-dependent energy crisis in human skin cells

The differentiated epidermis of human skin serves as an essential barrier against environmental insults from physical, chemical, and biological sources. Zinc pyrithione (ZnPT) is an FDA-approved microbicidal agent used worldwide in clinical antiseptic products, over-the-counter topical antimicrobials, and cosmetic consumer products including antidandruff shampoos. Here we demonstrate for the first time that cultured primary human skin keratinocytes and melanocytes display an exquisite vulnerability to nanomolar concentrations of ZnPT resulting in pronounced induction of heat shock response gene expression and impaired genomic integrity. In keratinocytes treated with nanomolar concentrations of ZnPT, expression array analysis revealed massive upregulation of genes encoding heat shock proteins (HSPA6, HSPA1A, HSPB5, HMOX1, HSPA1L, and DNAJA1) further confirmed by immunodetection. Moreover, ZnPT treatment induced rapid depletion of cellular ATP levels and formation of poly(ADP-ribose) polymers. Consistent with an involvement of poly(ADP-ribose) polymerase (PARP) in ZnPT-induced energy crisis, ATP depletion could be antagonized by pharmacological inhibition of PARP. This result was independently confirmed using PARP-1 knockout mouse embryonic fibroblasts that were resistant to ATP depletion and cytotoxicity resulting from ZnPT exposure. In keratinocytes and melanocytes, single-cell gel electrophoresis and flow cytometric detection of gamma-H2A.X revealed rapid induction of DNA damage in response to ZnPT detectable before general loss of cell viability occurred through caspase-independent pathways. Combined with earlier experimental evidence that documents penetration of ZnPT through mammalian skin, our findings raise the possibility that this topical antimicrobial may target and compromise keratinocytes and melanocytes in intact human skin.

Redox-directed cancer therapeutics: molecular mechanisms and opportunities

Redox dysregulation originating from metabolic alterations and dependence on mitogenic and survival signaling through reactive oxygen species represents a specific vulnerability of malignant cells that can be selectively targeted by redox chemotherapeutics. This review will present an update on drug discovery, target identification, and mechanisms of action of experimental redox chemotherapeutics with a focus on pro- and antioxidant redox modulators now in advanced phases of preclinal and clinical development. Recent research indicates that numerous oncogenes and tumor suppressor genes exert their functions in part through redox mechanisms amenable to pharmacological intervention by redox chemotherapeutics. The pleiotropic action of many redox chemotherapeutics that involves simultaneous modulation of multiple redox sensitive targets can overcome cancer cell drug resistance originating from redundancy of oncogenic signaling and rapid mutation.Moreover, some redox chemotherapeutics may function according to the concept of synthetic lethality (i.e., drug cytotoxicity is confined to cancer cells that display loss of function mutations in tumor suppressor genes or upregulation of oncogene expression). The impressive number of ongoing clinical trials that examine therapeutic performance of novel redox drugs in cancer patients demonstrates that redox chemotherapy has made the crucial transition from bench to bedside.

Targeting cancer cells by ROS-mediated mechanisms: a radical therapeutic approach?

Increased generation of reactive oxygen species (ROS) and an altered redox status have long been observed in cancer cells, and recent studies suggest that this biochemical property of cancer cells can be exploited for therapeutic benefits. Cancer cells in advanced stage tumours frequently exhibit multiple genetic alterations and high oxidative stress, suggesting that it might be possible to preferentially eliminate these cells by pharmacological ROS insults. However, the upregulation of antioxidant capacity in adaptation to intrinsic oxidative stress in cancer cells can confer drug resistance. Abrogation of such drug-resistant mechanisms by redox modulation could have significant therapeutic implications. We argue that modulating the unique redox regulatory mechanisms of cancer cells might be an effective strategy to eliminate these cells.

Antimelanoma activity of the redox dye DCPIP (2,6-dichlorophenolindophenol) is antagonized by NQO1

Altered redox homeostasis involved in the control of cancer cell survival and proliferative signaling represents a chemical vulnerability that can be targeted by prooxidant redox intervention. Here, we demonstrate that the redox dye 2,6-dichlorophenolindophenol (DCPIP) may serve as a prooxidant chemotherapeutic targeting human melanoma cells in vitro and in vivo. DCPIP-apoptogenicity observed in the human melanoma cell lines A375 and G361 was inversely correlated with NAD(P)H:quinone oxidoreductase (NQO1) expression levels. In A375 cells displaying low NQO1 activity, DCPIP induced apoptosis with procaspase-3 and PARP cleavage, whereas G361 cells expressing high levels of enzymatically active NQO1 were resistant to DCPIP-cytotoxicity. Genetic (siRNA) or pharmacological (dicoumarol) antagonism of NQO1 strongly sensitized G361 cells to DCPIP apoptogenic activity. DCPIP-cytotoxicity was associated with the induction of oxidative stress and rapid depletion of glutathione in A375 and NQO1-modulated G361 cells. Expression array analysis revealed a DCPIP-induced stress response in A375 cells with massive upregulation of genes encoding Hsp70B' (HSPA6), Hsp70 (HSPA1A), heme oxygenase-1 (HMOX1), and early growth response protein 1 (EGR1) further confirmed by immunodetection. Systemic administration of DCPIP displayed significant antimelanoma activity in the A375 murine xenograft model. These findings suggest feasibility of targeting tumors that display low NQO1 enzymatic activity using DCPIP.

The cinnamon-derived Michael acceptor cinnamic aldehyde impairs melanoma cell proliferation, invasiveness, and tumor growth

Redox dysregulation in cancer cells represents a chemical vulnerability that can be targeted by pro-oxidant redox intervention. Dietary constituents that contain an electrophilic Michael acceptor pharmacophore may therefore display promising chemopreventive and chemotherapeutic anti-cancer activity. Here, we demonstrate that the cinnamon-derived dietary Michael acceptor trans-cinnamic aldehyde (CA) impairs melanoma cell proliferation and tumor growth. Feasibility of therapeutic intervention using high doses of CA (120 mg/kg, po, daily, 10 days) was demonstrated in a human A375 melanoma SCID mouse xenograft model. Low-micromolar concentrations (IC(50)< 10 microM) of CA, but not closely related CA derivatives devoid of Michael acceptor activity, suppressed proliferation of human metastatic melanoma cell lines (A375, G361, LOX) with G1 cell-cycle arrest, elevated intracellular ROS, and impaired invasiveness. Expression array analysis revealed that CA induced an oxidative stress response in A375 cells, up-regulating heme oxygenase 1, sulfiredoxin 1 homolog, thioredoxin reductase 1, and other genes, including the cell-cycle regulator and stress-responsive tumor suppressor gene cyclin-dependent kinase inhibitor 1A, a key mediator of G1-phase arrest. CA, but not Michael-inactive derivatives, inhibited NF-kappaB transcriptional activity and TNFalpha-induced IL-8 production in A375 cells. These findings support a previously unrecognized role of CA as a dietary Michael acceptor with potential anti-cancer activity.

The experimental chemotherapeutic N6-furfuryladenosine (kinetin-riboside) induces rapid ATP depletion, genotoxic stress, and CDKN1A(p21) upregulation in human cancer cell lines

Cytokinins and cytokinin nucleosides are purine derivatives with potential anticancer activity. N(6)-furfuryladenosine (FAdo, kinetin-riboside) displays anti-proliferative and apoptogenic activity against various human cancer cell lines, and FAdo has recently been shown to suppress tumor growth in murine xenograft models of human leukemia and melanoma. In this study, FAdo-induced genotoxicity, stress response gene expression, and cellular ATP depletion were examined as early molecular consequences of FAdo exposure in MiaPaCa-2 pancreas carcinoma, A375 melanoma, and other human cancer cell lines. FAdo, but not adenosine or N(6)-furfuryladenine (FA), displayed potent anti-proliferative activity that was also observed in human primary fibroblasts and keratinocytes. Remarkably, massive ATP depletion and induction of genotoxic stress as assessed by the alkaline comet assay occurred within 60-180min of exposure to low micromolar concentrations of FAdo. This was followed by rapid upregulation of CDKN1A and other DNA damage/stress response genes (HMOX1, DDIT3, and GADD45A) as revealed by expression array and Western analysis. Pharmacological and siRNA-based genetic inhibition of adenosine kinase (ADK) suppressed FAdo cytotoxicity and also prevented ATP depletion and p21 upregulation suggesting the importance of bioconversion of FAdo into the nucleotide form required for drug action. Taken together our data suggest that early induction of genotoxicity and energy crisis are important causative factors involved in FAdo cytotoxicity.

NAD(P)H quinone oxidoreductase 1 is essential for ozone-induced oxidative stress in mice and humans

One host susceptibility factor for ozone identified in epidemiologic studies is NAD(P)H quinone oxidoreductase 1 (NQO1). We hypothesized that after ozone exposure, NQO1 is required to increase 8-isoprostane (also known as F(2)-isoprostane) production, a recognized marker of ozone-induced oxidative stress, and to enhance airway inflammation and hyperresponsiveness. In this report, we demonstrate that in contrast to wild-type mice, NQO1-null mice are resistant to ozone and have blunted responses, including decreased production of F(2)-isoprostane and keratinocyte chemokine, decreased airway inflammation, and diminished airway hyperresponsiveness. Importantly, these results in mice correlate with in vitro findings in humans. In primary human airway epithelial cells, inhibition of NQO1 by dicumarol blocks ozone-induced F(2)-isoprostane production and IL-8 gene expression. Together, these results demonstrate that NQO1 modulates cellular redox status and influences the biologic and physiologic effects of ozone.

Cinnamoyl-based Nrf2-activators targeting human skin cell photo-oxidative stress

Strong experimental evidence suggests the involvement of photo-oxidative stress mediated by reactive oxygen species as a crucial mechanism of solar damage relevant to human skin photoaging and photocarcinogenesis. Based on the established role of antioxidant response element (ARE)-mediated gene expression in cancer chemoprevention, we tested the hypothesis that small molecule Nrf2-activators may serve a photo-chemopreventive role by targeting skin cell photo-oxidative stress. A luciferase-based reporter gene assay was used as a primary screen for the identification of novel agents that modulate the Nrf2-Keap1 signaling pathway. A series of cinnamoyl-based electrophilic Michael acceptors including cinnamic aldehyde and methyl-1-cinnamoyl-5-oxo-2-pyrrolidine-carboxylate was identified as potent Nrf2-activators. Hit confirmation was performed in a secondary screen, based on immunodetection of Nrf2 protein upregulation in human Hs27 skin fibroblasts, HaCaT keratinocytes, and primary skin keratinocytes. Bioefficacy profiling of positive test compounds in skin cells demonstrated compound-induced upregulation of hemeoxygenase I and NAD(P)H-quinone oxidoreductase, two Nrf2 target genes involved in the cellular antioxidant response. Pretreatment with cinnamoyl-based Nrf2-activators suppressed intracellular oxidative stress and protected against photo-oxidative induction of apoptosis in skin cells exposed to high doses of singlet oxygen. Our pilot studies suggest feasibility of developing cinnamoyl-based Nrf2-activators as novel photo-chemopreventive agents targeting skin cell photo-oxidative stress.