Free radical formation by antitumor quinones

Chemical Characterization, DNA-Damage Protection, Antiproliferative Activity and in Silico Studies of the Essential Oils from Perralderia coronopifolia Coss

In this study, for the first time, we analyzed the chemical composition of essential oils (EOs) steam-distilled from the flowers and leaves of Perralderia coronopifolia by GC-FID/MS. The objective was to explore new anticancer and antioxidant bioactive substances and understand their mechanisms of action through the use of plant-derived natural products. The major chemical components characterizing the EOs were cis-chrysanthenyl acetate 1, 6-oxocyclonerolidol 2, cis-8-acetoxychrysanthenyl acetate 3, and 6α-hydroxycyclonerolidol 4, respectively. Furthermore, the EOs inhibited cell proliferation in HeLa (human cervix carcinoma) and PC3 (human prostate cancer) cells and protected plasmid DNA from oxidative damage caused by UV-photolyzed H2 O2 . Employing a molecular docking study, we elucidated the main compounds' inhibition mechanisms. Consequently, the antitumor activity could be related to the inhibitory property of compound 3 against CDC25B phosphatase. The evaluation of ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties and the density functional theory (DFT) calculations of the major compounds, especially compound 3, offer potential insights for designing and developing new cancer drug candidates. In conclusion, our study provides a framework for future research and development in the field by establishing a scientific foundation for the use of Perralderia coronopifolia essential oils as a prospective source of antioxidant and anticancer agents.

How a natural antibiotic uses oxidative stress to kill oxidant-resistant bacteria

Natural products that possess antibiotic and antitumor qualities are often suspected of working through oxidative mechanisms. In this study, two quinone-based small molecules were compared. Menadione, a classic redox-cycling compound, was confirmed to generate high levels of reactive oxygen species inside Escherichia coli. It inactivated iron-cofactored enzymes and blocked growth. However, despite the substantial levels of oxidants that it produced, it was unable to generate significant DNA damage and was not lethal. Streptonigrin, in contrast, was poorer at redox cycling and did not inactivate enzymes or block growth; however, even in low doses, it damaged DNA and killed cells. Its activity required iron and oxygen, and in vitro experiments indicated that its quinone moiety transferred electrons through the adjacent iron atom to oxygen. Additionally, in vitro experiments revealed that streptonigrin was able to damage DNA without inhibition by catalase, indicating that hydrogen peroxide was not involved. We infer that streptonigrin can reduce bound oxygen directly to a ferryl species, which then oxidizes the adjacent DNA, without release of superoxide or hydrogen peroxide intermediates. This scheme allows streptonigrin to kill a bacterial cell without interference by scavenging enzymes. Moreover, its minimal redox-cycling behavior avoids alerting either the OxyR or the SoxRS systems, which otherwise would block killing. This example highlights qualities that may be important in the design of oxidative drugs. These results also cast doubt on proposals that bacteria can be killed by stressors that merely stimulate intracellular O2- and H2O2 formation.

Cardioprotective effect of Justicia gendarussa on doxorubicin induced toxicity in mice

Justicia gendarussa Burm.f, belonging to the family Acanthaceae, is widely used for various ailments traditionally. Antioxidant, anti-arthritic, anti-inflammatory, analgesic, anticancerous, properties of the plant have been widely reported. The present study analyzed the cardioprotective effect of J. gendarussa on doxorubicin (DOX) induced toxicity in mice. Ethanolic extract of J. gendarussa was administered orally for 7 consecutive days. The alterations in oxido-reduction status, biochemical and histopathological parameters were analyzed in heart tissue. DOX increased superoxide dismutase (SOD) and catalase activities to 3.4 ± 0.5 and 3.68 ± 1 from their normal values 2.43 ± 0.8 and 2.72 ± 0.88, respectively. The increased activities of both the enzymes were found reduced to 3.12 ± 0.24 and 3.41 ± 0.65 by the treatment of the extract. Similarly, DOX elevated glutathione peroxidase (GPx) activity to 44.6 ± 3.71 from the normal level 32.33 ± 3.41. DOX decreased the glutathione (GSH) level to 15.66 ± 2.51 from the normal values 31.66 ± 4.05. Upon treatment, GPx activity and GHS level found restored. The increased lipid peroxidation 2.53 ± 0.25 of DOX was also decreased to 2.0 ± 0.34 by the extract. Histopathology observations substantiate the protective effect of J. gendarussa extract. In conclusion, DOX-induced disturbance of oxido-reduction status and histopathology of heart attenuated closer to the normal indicating the protective effect of J. gendarussa against DOX-induced toxicity in cardiomyocytes.

Sustainable Synthesis, Antiproliferative and Acetylcholinesterase Inhibition of 1,4- and 1,2-Naphthoquinone Derivatives

This work describes the design, sustainable synthesis, evaluation of electrochemical and biological properties against HepG2 cell lines, and AChE enzymes of different substituted derivatives of 1,4- and 1,2-naphthoquinones (NQ). A microwave-assisted protocol was optimized with success for the synthesis of the 2-substituted-1,4-NQ series and extended to the 4-substituted-1,2-NQ family, providing an alternative and more sustainable approach to the synthesis of naphthoquinones. The electrochemical properties were studied by cyclic voltammetry, and the redox potentials related to the molecular structural characteristics and the biological properties. Compounds were tested for their potential anti-cancer activity against a hepatocellular carcinoma cell line, HepG2, using MTT assay, and 1,2-NQ derivatives were found to be more active than their 1,4-NQ homologues (3a-f), with the highest cytotoxic potential found for compound 4a (EC₅₀ = 3 μM). The same trend was found for the inhibitory action against acetylcholinesterase, with 1,2-NQ derivatives showing higher inhibition_50µM than their 1,4-NQ homologues, with 4h being the most potent compound (Inhibition_50µM = 85%). Docking studies were performed for the 1,2-NQ derivatives with the highest inhibitions, showing dual binding interactions with both CAS and PAS sites, while the less active 1,4-NQ derivatives showed interactions with PAS and the mid-gorge region.

The Interaction of Anthracycline Based Quinone-Chelators with Model Lipid Membranes: 1H NMR and MD Study

Anthracycline antibiotics, e.g., doxorubicin, daunomycin, and other anthraquinones, are an important family of antitumor agents widely used in chemotherapy, which is currently the principal method for treating many malignancies. Thus, development of improved antitumor drugs with enhanced efficacy remains a high priority. Interaction of anthraquinone-based anticancer drugs with cell membranes attracts significant attention due to its importance in the eventual overcoming of multidrug resistance (MDR). The use of drugs able to accumulate in the cell membrane is one of the possible ways of overcoming MDR. In the present work, the aspects of interaction of anthraquinone 2-phenyl-4-(butylamino)naphtho[2,3-h]quinoline-7,12-dione) (Q1) with a model membrane were studied by means of NMR and molecular dynamics simulations. A fundamental shortcoming of anthracycline antibiotics is their high cardiotoxicity caused by reactive oxygen species (ROS). The important feature of Q1 is its ability to chelate transition metal ions responsible for ROS generation in vivo. In the present study, we have shown that Q1 and its chelating complexes penetrated into the lipid membrane and were located in the hydrophobic part of the bilayer near the bilayer surface. The chelate complex formation of Q1 with metal ions increased its penetration ability. In addition, it was found that the interaction of Q1 with lipid molecules could influence lipid mobility in the bilayer. The obtained results have an impact on the understanding of molecular mechanisms of Q1 biological activity.

Nanotherapeutic Intervention in Photodynamic Therapy for Cancer

The clinical need for photodynamic therapy (PDT) has been growing for several decades. Notably, PDT is often used in oncology to treat a variety of tumors since it is a low-risk therapy with excellent selectivity, does not conflict with other therapies, and may be repeated as necessary. The mechanism of action of PDT is the photoactivation of a particular photosensitizer (PS) in a tumor microenvironment in the presence of oxygen. During PDT, cancer cells produce singlet oxygen (¹O₂) and reactive oxygen species (ROS) upon activation of PSs by irradiation, which efficiently kills the tumor. However, PDT's effectiveness in curing a deep-seated malignancy is constrained by three key reasons: a tumor's inadequate PS accumulation in tumor tissues, a hypoxic core with low oxygen content in solid tumors, and limited depth of light penetration. PDTs are therefore restricted to the management of thin and superficial cancers. With the development of nanotechnology, PDT's ability to penetrate deep tumor tissues and exert desired therapeutic effects has become a reality. However, further advancement in this field of research is necessary to address the challenges with PDT and ameliorate the therapeutic outcome. This review presents an overview of PSs, the mechanism of loading of PSs, nanomedicine-based solutions for enhancing PDT, and their biological applications including chemodynamic therapy, chemo-photodynamic therapy, PDT-electroporation, photodynamic-photothermal (PDT-PTT) therapy, and PDT-immunotherapy. Furthermore, the review discusses the mechanism of ROS generation in PDT advantages and challenges of PSs in PDT.

New Iron Metabolic Pathways and Chelation Targeting Strategies Affecting the Treatment of All Types and Stages of Cancer

There is new and increasing evidence from in vitro, in vivo and clinical studies implicating the pivotal role of iron and associated metabolic pathways in the initiation, progression and development of cancer and in cancer metastasis. New metabolic and toxicity mechanisms and pathways, as well as genomic, transcription and other factors, have been linked to cancer and many are related to iron. Accordingly, a number of new targets for iron chelators have been identified and characterized in new anticancer strategies, in addition to the classical restriction of/reduction in iron supply, the inhibition of transferrin iron delivery, the inhibition of ribonucleotide reductase in DNA synthesis and high antioxidant potential. The new targets include the removal of excess iron from iron-laden macrophages, which affects anticancer activity; the modulation of ferroptosis; ferritin iron removal and the control of hyperferritinemia; the inhibition of hypoxia related to the role of hypoxia-inducible factor (HIF); modulation of the function of new molecular species such as STEAP4 metalloreductase and the metastasis suppressor N-MYC downstream-regulated gene-1 (NDRG1); modulation of the metabolic pathways of oxidative stress damage affecting mitochondrial function, etc. Many of these new, but also previously known associated iron metabolic pathways appear to affect all stages of cancer, as well as metastasis and drug resistance. Iron-chelating drugs and especially deferiprone (L1), has been shown in many recent studies to fulfill the role of multi-target anticancer drug linked to the above and also other iron targets, and has been proposed for phase II trials in cancer patients. In contrast, lipophilic chelators and their iron complexes are proposed for the induction of ferroptosis in some refractory or recurring tumors in drug resistance and metastasis where effective treatments are absent. There is a need to readdress cancer therapy and include therapeutic strategies targeting multifactorial processes, including the application of multi-targeting drugs involving iron chelators and iron-chelator complexes. New therapeutic protocols including drug combinations with L1 and other chelating drugs could increase anticancer activity, decrease drug resistance and metastasis, improve treatments, reduce toxicity and increase overall survival in cancer patients.

Concept of Hybrid Drugs and Recent Advancements in Anticancer Hybrids

Cancer is a complex disease, and its treatment is a big challenge, with variable efficacy of conventional anticancer drugs. A two-drug cocktail hybrid approach is a potential strategy in recent drug discovery that involves the combination of two drug pharmacophores into a single molecule. The hybrid molecule acts through distinct modes of action on several targets at a given time with more efficacy and less susceptibility to resistance. Thus, there is a huge scope for using hybrid compounds to tackle the present difficulties in cancer medicine. Recent work has applied this technique to uncover some interesting molecules with substantial anticancer properties. In this study, we report data on numerous promising hybrid anti-proliferative/anti-tumor agents developed over the previous 10 years (2011–2021). It includes quinazoline, indole, carbazole, pyrimidine, quinoline, quinone, imidazole, selenium, platinum, hydroxamic acid, ferrocene, curcumin, triazole, benzimidazole, isatin, pyrrolo benzodiazepine (PBD), chalcone, coumarin, nitrogen mustard, pyrazole, and pyridine-based anticancer hybrids produced via molecular hybridization techniques. Overall, this review offers a clear indication of the potential benefits of merging pharmacophoric subunits from multiple different known chemical prototypes to produce more potent and precise hybrid compounds. This provides valuable knowledge for researchers working on complex diseases such as cancer.

Controlled masking and targeted release of redox-cycling ortho-quinones via a C-C bond-cleaving 1,6-elimination

Natural products that contain ortho-quinones show great potential as anticancer agents but have been largely discarded from clinical development because their redox-cycling behaviour results in general systemic toxicity. Here we report conjugation of ortho-quinones to a carrier, which simultaneously masks their underlying redox activity. C-benzylation at a quinone carbonyl forms a redox-inactive benzyl ketol. Upon a specific enzymatic trigger, an acid-promoted, self-immolative C-C bond-cleaving 1,6-elimination mechanism releases the redox-active hydroquinone inside cells. By using a 5-lipoxygenase modulator, β-lapachone, we created cathepsin-B-cleavable quinone prodrugs. We applied the strategy for intracellular release of β-lapachone upon antibody-mediated delivery. Conjugation of protected β-lapachone to Gem-IgG1 antibodies, which contain the variable region of gemtuzumab, results in homogeneous, systemically non-toxic and conditionally stable CD33+-specific antibody-drug conjugates with in vivo efficacy against a xenograft murine model of acute myeloid leukaemia. This protection strategy could allow the use of previously overlooked natural products as anticancer agents, thus extending the range of drugs available for next-generation targeted therapeutics.

Mycothiol Peroxidase Activity as a Part of the Self-Resistance Mechanisms against the Antitumor Antibiotic Cosmomycin D

Antibiotic-producing microorganisms usually require one or more self-resistance determinants to survive antibiotic production. The effectors of these mechanisms are proteins that inactivate the antibiotic, facilitate its transport, or modify the target to render it insensitive to the molecule. Streptomyces bacteria biosynthesize various bioactive natural products and possess resistance systems for most metabolites, which are coregulated with antibiotic biosynthesis genes. Streptomyces olindensis strain DAUFPE 5622 produces the antitumor antibiotic cosmomycin D (COSD), a member of the anthracycline family. In this study, we propose three self-resistance mechanisms, anchored or based in the COSD biosynthetic gene cluster. These include cosIJ (an ABC transporter), cosU (a UvrA class IIa protein), and a new self-resistance mechanism encoded by cosP, which shows response against peroxides by the enzyme mycothiol peroxidase (MPx). Activity-based investigations of MPx and its mutant enzyme confirmed peroxidation during the production of COSD. Overexpression of the ABC transporter, the UvrA class IIa protein, and the MPx led to an effective response against toxic anthracyclines, such as cosmomycins. Our findings help to understand how thiol peroxidases play an antioxidant role in the anthracycline producer S. olindensis DAUFPE 5622, a mechanism which has been reported for neoplastic cells that are resistant to doxorubicin (DOX).

IMPORTANCE Anthracycline compounds are DNA intercalating agents widely used in cancer chemotherapeutic protocols. This work focused on the self-resistance mechanisms developed by the cosmomycin-producing bacterium Streptomyces olindensis. Our findings showed that cysteine peroxidases, such as mycothiol peroxidase, encoded by the gene cosP, protected S. olindensis against peroxidation during cosmomycin production. This observation can contribute to much better understanding of resistance both in the producers, eventually enhancing production, and in some tumoral cell lines.

The Interplay of Ascorbic Acid with Quinones-Chelators—Influence on Lipid Peroxidation: Insight into Anticancer Activity

Ascorbic acid is a multifaceted compound that can perform both antioxidant and pro-oxidant activities in the redox reactions induced by transition metal ions, so its role in nature and especially in the human body is still the subject of debate. In the present study, we have examined the influence of ascorbic acid on lipid peroxidation in a model system that mimics the cell membrane, namely micelles of linoleic acid (LA), induced by chelate complexes of iron and copper ions with quinone-chelator 2-phenyl-4-(butylamino)-naphtholquinoline-7,12-dione (Q1). This quinone effectively generates reactive oxygen species and semiquinone radicals inside cancer cells via a cycling redox reaction. Here it was demonstrated that in the absence of quinone-chelator ascorbic acid significantly accelerates the lipid peroxidation induced by both Fe(II) and Cu(II) ions. It has been shown also that Q1 chelate complexes with Fe(II) and Cu(II) ions are redox active in the LA micelles oxidation. No effect of ascorbate was detected on the reactivity of chelate complex with Fe(II) ions. On the other hand, ascorbate performs pro-oxidant activity in Q1-Cu(II) complex induced reaction. We can conclude that ascorbate-driven redox cycling of Q1 may promote its anti-tumor activity.

Mechanistic Insights of Chelator Complexes with Essential Transition Metals: Antioxidant/Pro-Oxidant Activity and Applications in Medicine

The antioxidant/pro-oxidant activity of drugs and dietary molecules and their role in the maintenance of redox homeostasis, as well as the implications in health and different diseases, have not yet been fully evaluated. In particular, the redox activity and other interactions of drugs with essential redox metal ions, such as iron and copper, need further investigation. These metal ions are ubiquitous in human nutrition but also widely found in dietary supplements and appear to exert major effects on redox homeostasis in health, but also on many diseases of free radical pathology. In this context, the redox mechanistic insights of mainly three prototype groups of drugs, namely alpha-ketohydroxypyridines (alpha-hydroxypyridones), e.g., deferiprone, anthraquinones, e.g., doxorubicin and thiosemicarbazones, e.g., triapine and their metal complexes were examined; details of the mechanisms of their redox activity were reviewed, with emphasis on the biological implications and potential clinical applications, including anticancer activity. Furthermore, the redox properties of these three classes of chelators were compared to those of the iron chelating drugs and also to vitamin C, with an emphasis on their potential clinical interactions and future clinical application prospects in cancer, neurodegenerative and other diseases.

Ascorbate-and iron-driven redox activity of Dp44mT and emodin facilitates peroxidation of micelles and bicelles

BACKGROUND

Iron (Fe)-induced oxidative stress leads to reactive oxygen species that damage biomembranes, with this mechanism being involved in the activity of some anti-cancer chemotherapeutics.

METHODS

Herein, we compared the effect of Fe complexes of the ligand, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), or the potential ligand, Emodin, on lipid peroxidation in cell membrane models (micelles and bicelles). These studies were performed in the presence of hydrogen peroxide (H₂O₂) and the absence or presence of ascorbate.

RESULTS

In the absence of ascorbate, Fe(II)/Emodin mixtures incubated with H₂O₂ demonstrated slight pro-oxidant properties on micelles versus Fe(II) alone, while the Fe(III)-Dp44mT complex exhibited marked antioxidant properties. Examining more physiologically relevant phospholipid-containing bicelles, the Fe(II)- and Fe(III)-Dp44mT complexes demonstrated antioxidant activity without ascorbate. Upon adding ascorbate, there was a significant increase in the peroxidation of micelles and bicelles in the presence of unchelated Fe(II) and H₂O₂. The addition of ascorbate to Fe(III)-Dp44mT substantially increased the peroxidation of micelles and bicelles, with the Fe(III)-Dp44mT complex being reduced by ascorbate to the Fe(II) state, explaining the increased reactivity. Electron paramagnetic resonance spectroscopy demonstrated ascorbyl radical anion generation after mixing ascorbate and Emodin, with signal intensity being enhanced by H₂O₂. This finding suggested Emodin semiquinone radical formation that could play a role in its reactivity via ascorbate-driven redox cycling. Examining cultured melanoma cells in vitro, ascorbate at pharmacological levels enhanced the anti-proliferative activity of Dp44mT and Emodin.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Ascorbate-driven redox cycling of Dp44mT and Emodin promotes their anti-proliferative activity.

Electrochemistry of Quinones with Respect to their Role in Biomedical Chemistry

Quinones are ubiquitous in nature and form one of the largest class of antitumor agents approved for clinical use. They are known to be efficient in inhibiting cancer cells growth. Under physiological conditions they can undergo non-enzymatic one-electron reduction to give the moderately toxic species of semiquinone radical-anion. Thus, electrochemical study of quinones might provide a basic knowledge on semi-quinone radicals formation in both in vivo and in vitro under different media. Several processes are outlined briefly and discussed in the present article. Previously we investigated the electrochemical and spectral properties of ω-N-quinonyl amino acids. Such quinone-bearing peptides are known to be cytotoxic and of potential clinical significance. We were able to prove that the ω-amino quinonyl compounds are very effective in producing stable semiquinone radicals. Moreover, a direct relation was found between the first reduction potentials of the quinonyl moiety and their reactivity towards the ω-amino acids. In order to increase our knowledge of such amino quinonyl compounds and enlarge the arsenal of such cytotoxic compounds, a series of N,N-diquinonyl amines (1-6) bearing an internal proton (stems from the NH moiety) were synthesized. Their electron-transfer capabilities were probed by cyclic voltammetry measurements, in dichloromethane. It was found that the acidic NH group linking the two quinonyl moieties undergoes an initial electrochemical reduction step and generates a nitride anion. This step is followed by further reductions to yield quasi-stable semiquinone radicals and polyanions, Since these acidic diquinones (1-6) serve also as a source of internal proton donors even in non-polar medium, they might cause protonation of basic radical-anions and polyanion intermediates during the various electrochemical stages. The processes are demonstrated and discussed by analyzing different mechanistic schemes. The successful generation of relatively stable semiquinone radicals is a prerequisite for the manifestation of site directed antitumor activity by these bis-quinonyl amino derivatives. Based on the values of their redox potentials some of them could be promising candidates for clinical development.

Pre-Clinical Activity of Amino-Alcohol Dimeric Naphthoquinones as Potential Therapeutics for Acute Myeloid Leukemia

BACKGROUND

The clinical outcomes of patients with acute myeloid leukemia (AML) remain unsatisfactory, therefore the development of more efficacious and better-tolerated therapy for AML is critical. We have previously reported the anti-leukemic activity of synthetic halohydroxyl dimeric naphthoquinones (BiQ) and aziridinyl BiQ.

OBJECTIVE

This study aimed to improve the potency and bioavailability of BiQ compounds and investigate the anti-leukemic activity of the lead compound in vitro and in a human AML xenograft mouse model.

METHODS

We designed, synthesized, and performed structure-activity relationship of several rationally designed BiQ analogues that possess amino alcohol functional groups on the naphthoquinone core rings. The compounds were screened for anti-leukemic activity and the mechanism as well as in vivo tolerability and efficacy of our lead compound was investigated.

RESULTS

We report that a dimeric naphthoquinone (designated BaltBiQ) demonstrated potent nanomolar anti-leukemic activity in AML cell lines. BaltBiQ treatment resulted in the generation of reactive oxygen species, induction of DNA damage, and inhibition of indoleamine dioxygenase 1. Although BaltBiQ was tolerated well in vivo, it did not significantly improve survival as a single agent, but in combination with the specific Bcl-2 inhibitor, Venetoclax, tumor growth was significantly inhibited compared to untreated mice.

CONCLUSION

We synthesized a novel amino alcohol dimeric naphthoquinone, investigated its main mechanisms of action, reported its in vitro anti-AML cytotoxic activity, and showed its in vivo promising activity combined with a clinically available Bcl-2 inhibitor in a patient-derived xenograft model of AML.

Potential Anti-Tumor Activity of Kefir-Induced Juglone and Resveratrol Fractions Against Ehrlich Ascites Carcinoma-Bearing BALB/C Mice

We investigated the potential influence of kefir-induced juglone and resveratrol fractions (JRK) against Ehrlich Ascites Carcinoma (EAC) bearing BALB/c male mice. Kefir yeast was grown in the cell culture supplemented with juglone and resveratrol (1:2). After 48 h incubation, JRK solution was applied (0.1 mL/day i.p.) to the EAC-bearing mice throughout five days. Molecular regulatory mechanisms of apoptotic and anti-apoptotic pathway components were evaluated in the plasma of mice and isolated EAC cells with ELISA, qRT-PCR, and immunocytchemical experiments. EAC-induced upregulation in Bcl-2 and downregulation in Caspase-3 were normalized with JRK in the plasma of mice. Additionally, JRK upregulated the expression levels of apoptotic Bax, p53, Caspase-3,8,9, and APAF-1 proteins together with BAX, CASPASE-8, and CASPASE-9 genes in isolated EAC cells. These changes were also associated with decreased expression levels of anti-apoptotic Bcl-2 and Bcl-xl proteins. Immunocytochemical studies also confirmed the activation of apoptotic pathways and repression of anti-apoptotic proteins in EAC cells with JRK treatment. JRK activates apoptotic pathway and inhibits anti-apoptotic genes and proteins in Ehrlich ascites carcinoma- bearing BALB/c mice that could be beneficial in cancer treatment.

Characterization and trypanocidal activity of a β-lapachone-containing drug carrier

The treatment of Chagas disease (CD), a neglected parasitic condition caused by Trypanosoma cruzi, is still based on only two drugs, nifurtimox (Nif) and benznidazole (Bz), both of which have limited efficacy in the late chronic phase and induce severe side effects. This scenario justifies the continuous search for alternative drugs, and in this context, the natural naphthoquinone β-lapachone (β-Lap) and its derivatives have demonstrated important trypanocidal activities. Unfortunately, the decrease in trypanocidal activity in the blood, high toxicity to mammalian cells and low water solubility of β-Lap limit its systemic administration and, consequently, clinical applications. For this reason, carriers as drug delivery systems can strategically maximize the therapeutic effects of this drug, overcoming the above mentioned restrictions. Accordingly, the aim of this study is to investigate the in vitro anti-T. cruzi effects of β-Lap encapsulated in2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) and its potential toxicity to mammalian cells.

Inhibition of Staphylococcus aureus TetK and MsrA efflux pumps by hydroxyamines derived from lapachol and norlachol

The present study aimed to evaluate the in vitro efflux pump inhibitory capacity of hydroxyamines derived from lapachol and norlachol, where compounds 3, 4, and 5 were tested against the S. aureus strains: RN4220 carrying the pUL5054 plasmid; and IS-58, endowed with the PT181 plasmid. The substances were synthesized from 2-hydroxy-quinones, lapachol and nor-lapachol obtaining the corresponding 2-methoxylated derivatives via dimethyl sulfate alkylation in a basic medium, which then reacted chemoselectively with 2-ethanolamine and 3-propanolamine to form the corresponding amino alcohols. The antibacterial action of the substances was quantified by determining the Minimum Inhibitory Concentration (MIC), while a microdilution assay was carried out to ascertain efflux pump inhibition of Staphylococcus aureus strains carrying the MsrA macrolide and the TetK tetracycline efflux pumps with the substances at a sub-inhibitory concentration. The results were subjected to statistical analysis by an ANOVA test and Bonferroni post hoc test. The MIC from the substances exhibited a value ≥ 1024 µg/mL. However, a significant reduction (p < 0.0001) of the erythromycin, tetracycline and ethidium bromide MIC was demonstrated when these were in combination with the substances, with this effect being due to a supposed efflux pump inhibition. The tested substances demonstrated effectiveness at decreasing the MIC of erythromycin, tetracycline and ethidium bromide, potentially by inhibiting the MsrA macrolide and the TetK tetracycline efflux pumps present in the tested S. aureus strains.

Designing a high-performance smart drug delivery system for the synergetic co-absorption of DOX and EGCG on ZIF-8

Due to the extreme pore volume and valuable surface area, zeolitic imidazole frameworks (ZIFs) are promising vehicles that enhance the delivery of therapeutic agents to tissues. Furthermore, these nanoporous materials have high stability in the pH and temperature of the surrounding healthy cells (37 °C and pH = 7) and an exotic potential to deform in carcinogenic environment (T > 37 °C and pH ∼ 5.5), which make them perfect smart drug delivery vehicle candidates. In this work, a series of molecular dynamics (MD) and metadynamics simulations have been performed to gain molecular insight into the mechanisms involved in the process of co-loading of doxorubicin (DOX) and EpiGalloCatechin-3 Gallate (EGCG) on ZIF-8, which form a smart drug delivery system (SDDS). The obtained results revealed that DOX was adsorbed on the carrier mostly through electrostatic interactions (E coul = ∼-1200 kJ mol-1, E tot = -1700 kJ mol-1), and EGCG was stacked on ZIF-8 mainly via van der Waals interactions (E L-J = ∼-600 kJ mol-1, E tot = ∼-1200 kJ mol-1). It is worth mentioning that the drug-drug L-J interactions (E L-J = ∼500 kJ mol-1) were also important in the co-loading process. The insertion of DOX and EGCG as additive agents to the initial ZIF-8/EGCG and ZIF-8/DOX systems led to the enhancement of the drug-carrier pair interactions to about ∼-2300 kJ mol-1 and ∼-2000 kJ mol-1, respectively. This finding implied that the drug-drug interactions had a complementary role in the development of SDDS via ZIF-8. From the metadynamics simulation, it was found that the geometry of the drugs is a determining factor in an efficient co-loading SDDS.

In silico evaluation of the antibacterial and modulatory activity of lapachol and nor-lapachol derivates

The aim of this research was to investigate the pharmacological properties of 2-(2-hydroxyethylamine)-3-(3-methyl-2-butenyl)-1,4-dihydro-1,4-naphthalenedione, 2-(2-hydroxy-ethylamine)-3-(2-methyl-propenyl)-[1,4]naphthoquinone and 2-(3-hydroxy-propylamine)-3-(3-methyl-2-butenyl)-[1,4]naphthoquinone using computational prediction models, in addition to evaluating the in vitro antibacterial and modulatory activity of these compounds against bacterial ATCC strains and clinical isolates. The substances were synthesized from 2-hydroxy-quinones, lapachol and nor-lapachol obtaining the corresponding 2-methoxylated derivatives via dimethyl sulfate alkylation in a basic medium, these then reacted chemoselectively with 2-ethanolamine and 3-propanolamine to form the corresponding amino alcohols. The antibacterial activity and modulatory activity of the substances were assayed by broth microdilution method to determine the Minimum Inhibitory Concentration (MIC). The molecular structures were analyzed using the ChEMBL database to predict possible pharmacological targets, which pointed to the molecule 2- (2-hydroxy-ethylamine)-3-(2-methyl-propenyl)-[1,4]naphthoquinone as a probable antibacterial agent for the proteins Replicative DNA helicase and RecA. The compounds had a low molecular weight and a small number of rotatable bonds. The MICs of the substances were not clinically significant, however, the association with gentamicin and amikacin reduced the MICs of these antibiotics. In conclusion, the combination of these substances with aminoglycosides may be a therapeutic alternative to bacterial resistance and the reduction of side effects.

The diverse mechanisms and anticancer potential of naphthoquinones

Cancer is one of the leading causes of death around the world and although the different clinical approaches have helped to increase survival rates, incidence is still high and so its mortality. Chemotherapy is the only approach which is systemic, reaching cancer cells in all body tissues and the search for new potent and selective drugs is still an attractive field within cancer research. Naphthoquinones, natural and synthetic, have garnered much attention in the scientific community due to their pharmacological properties, among them anticancer action, and potential therapeutic significance. Many mechanisms of action have been reported which also depend on structural differences among them. Here, we describe some of the most relevant mechanisms of action reported so far for naphthoquinones and highlight novel targets which are being described in the literature. Furthermore, we gather some of the most impressive efforts done by researchers to harness the anticancer properties of these compounds through specifically designed structural modifications.

Juglone in Oxidative Stress and Cell Signaling

Juglone (5-hydroxyl-1,4-naphthoquinone) is a phenolic compound found in walnuts. Because of the antioxidant capacities of phenolic compounds, juglone may serve to combat oxidative stress, thereby protecting against the development of various diseases and aging processes. However, being a quinone molecule, juglone could also act as a redox cycling agent and produce reactive oxygen species. Such prooxidant properties of juglone may confer health effects, such as by killing cancer cells. Further, recent studies revealed that juglone influences cell signaling. Notably, juglone is an inhibitor of Pin1 (peptidyl-prolyl cis/trans isomerase) that could regulate phosphorylation of Tau, implicating potential effects of juglone in Alzheimer’s disease. Juglone also activates mitogen-activated protein kinases that could promote cell survival, thereby protecting against conditions such as cardiac injury. This review describes recent advances in the understanding of the effects and roles of juglone in oxidative stress and cell signaling.

Combined Effect of Bortezomib and Menadione Sodium Bisulfite on Proteasomes of Tumor Cells: The Dramatic Decrease of Bortezomib Toxicity in a Preclinical Trial

Tumor growth is associated with elevated proteasome expression and activity. This makes proteasomes a promising target for antitumor drugs. Current antitumor drugs such as bortezomib that inhibit proteasome activity have significant side effects. The purpose of the present study was to develop effective low-toxic antitumor compositions with combined effects on proteasomes. For compositions, we used bortezomib in amounts four and ten times lower than its clinical dose, and chose menadione sodium bisulfite (MSB) as the second component. MSB is known to promote oxidation of NADH, generate superoxide radicals, and as a result damage proteasome function in cells that ensure the relevance of MSB use for the composition development. The proteasome pool was investigated by the original native gel electrophoresis method, proteasome chymotrypsin-like activity-by Suc-LLVY-AMC-hydrolysis. For the compositions, we detected 10 and 20 μM MSB doses showing stronger proteasome-suppressing and cytotoxic in cellulo effects on malignant cells than on normal ones. MSB indirectly suppressed 26S-proteasome activity in cellulo, but not in vitro. At the same time, MSB together with bortezomib displayed synergetic action on the activity of all proteasome forms in vitro as well as synergetic antitumor effects in cellulo. These findings determine the properties of the developed compositions in vivo: antitumor efficiency, higher (against hepatocellular carcinoma and mammary adenocarcinoma) or comparable to bortezomib (against Lewis lung carcinoma), and drastically reduced toxicity (LD50) relative to bortezomib. Thus, the developed compositions represent a novel generation of bortezomib-based anticancer drugs combining high efficiency, low general toxicity, and a potentially expanded range of target tumors.

Highly selective anthraquinone-chalcone hybrids as potential antileukemia agents

A series of 23 novel anthraquinone-chalcone hybrids containing amide function was synthesized and structurally characterized. Sixteen compounds exerted strong cytotoxic activities against K562, Jurkat and HL-60 leukemia cell lines and significantly lower cytotoxic effects against normal MRC-5 cells, indicating very high selectivity in their anticancer action. The compounds 6g, 6u and 6v activate apoptosis in K562 cells through the extrinsic and intrinsic apoptotic pathway. The compound 6e triggered apoptosis in K562 cells only through the extrinsic apoptotic pathway. Treatment of K562 cells with each of these four compounds caused decrease in the expression levels of MMP2, MMP9, and VEGF, suggesting their anti-invasive, antimetastatic and antiangiogenic properties. The compounds 6g and 6v downregulated expression levels of miR-155 in K562 cells, while compounds 6e and 6u upregulated miR-155 levels in treated cells, in comparison with control cells. The structure-based 3-D QSAR models for 6f, 6e, 6i and 6l describe pro-apoptotic activity against caspase-3.

Redox-Active Quinone Chelators: Properties, Mechanisms of Action, Cell Delivery, and Cell Toxicity

SIGNIFICANCE

Chemotherapy is currently the principal method for treating many malignancies. Thus, the development of improved antitumor drugs with enhanced efficacy and selectivity remains a high priority. Recent Advances: Anthracycline antibiotics (AAs), for example, doxorubicin, daunomycin, and mitomycin C, belong to an important family of antitumor agents widely used in chemotherapy. These compounds are all quinones. They are, thus, capable of being reduced by appropriate chemicals or reductases. One of their important properties is that under aerobic conditions their reduced forms undergo oxidation, with concomitant generation of reactive oxygen species (ROS), namely, superoxide anion radicals, hydrogen peroxide, and hydroxyl radicals. The presence of metal ions is essential for the generation of ROS by AAs in biological systems.

CRITICAL ISSUES

A fundamental shortcoming of the AAs is their high cardiotoxicity. We have proposed, and experimentally realized, a new type of quinones that is capable of coordinating metal ions. We have demonstrated in vitro that they can be reduced by electron transfer chains and glutathione with concomitant generation of ROS. They can also produce ROS under photo-excitation. The mechanisms of these reactions have been characterized by using nuclear magnetic resonance and electron paramagnetic resonance.

FUTURE DIRECTIONS

To enhance their therapeutic effectiveness, and decrease cardiotoxicity and other side effects, we intend to conjugate the quinone chelators with monoclonal antibodies and peptide hormones that are specifically targeted to receptors on the cancer cell surface. Some such candidates have already been synthesized. An alternative approach for delivery of our compounds involves the use of specific peptide-based nanoparticles. In addition, our novel approach for treating malignancies is also suitable for photodynamic therapy. Antioxid. Redox Signal. 28, 1394-1403.

In Vitro Inhibition of Helicobacter pylori Growth by Redox Cycling Phenylaminojuglones

Infection by Helicobacter pylori increases 10 times the risk of developing gastric cancer. Juglone, a natural occurring 1,4-naphthoquinone, prevents H. pylori growth by interfering with some of its critical metabolic pathways. Here, we report the design, synthesis, and in vitro evaluation of a series of juglone derivatives, namely, 2/3-phenylaminojuglones, as potential H. pylori growth inhibitors. Results show that 5 out of 12 phenylaminojuglones (at 1.5 μg/mL) were 1.5-2.2-fold more active than juglone. Interestingly, most of the phenylaminojuglones (10 out of 12) were 1.1-2.8 fold more active than metronidazole, a known H. pylori growth inhibitor. The most active compound, namely, 2-((3,4,5-trimethoxyphenyl)amino)-5-hydroxynaphthalene-1,4-dione 7, showed significant higher halo of growth inhibitions (HGI = 32.25 mm) to that of juglone and metronidazole (HGI = 14.50 and 11.67 mm). Structural activity relationships of the series suggest that the nature and location of the nitrogen substituents in the juglone scaffold, likely due in part to their redox potential, may influence the antibacterial activity of the series.

Antiproliferative Effects of Mitoxantrone in Adr-Sensitive and Adr-Resistant P388 Leukemia Cells Enhanced by Vitamin K3

Vitamin K3 was employed as a resistance-modifying agent to Investigate its activity in enhancing mitoxantrone (MITO)-induced cytotoxicity in parental (P388/S) and multidrug resistant (P388/ADR) P388 leukemia cells. Vitamin K3 potentiated the antitumor effects of MITO in P388/S and P388/ ADR tumor cells as monitored by inhibition of tumor cell survival (MTT assay). MITO and vitamin K3 in combination effected an enhanced inhibition of [3H]thymidine (DNA synthesis) and [3H]uridine (RNA synthesis) and also Increased the life span of the sensitive and resistant tumor-bearing animals. The effect of vitamin K3 on the induction of DNA strand breaks by MITO was also examined. Increased fragmentation of DNA was illustrated in the sensitive and resistant P388 leukemia cells exposed to the combination. Observations indicate the restoration of sensitivity in P388/ADR cells to MITO by vitamin K3 that may be due to its ability to increase the MITO-induced DNA strand breaks.

p-Coumaric acid mediated protection of H9c2 cells from Doxorubicin-induced cardiotoxicity: Involvement of augmented Nrf2 and autophagy

Doxorubicin (Dox) is a widely administered chemotherapeutic drug and incidences of cardiotoxicity associated with its administration have been of general concern. Extensive research proposes several mechanisms as a cause of Dox induced cardiotoxicity. However, none of these studies have been able to suggest a find one, cure all antidote for the same. To this end, several studies involving plant based compounds or natural products have gained acclaim for their ability to address at least one factor contributing to drug induced pathogenesis. We had previously reported that p-coumaric (pCA) has a protective effect on Dox induced oxidative stress in rat-derived cardiomyoblasts. In this study we investigated the effects of pCA on the regulation of Nrf-2, mitochondrial viability, autophagy and apoptosis in Doxorubicin treated H9c2 cardiomyocytes. ROS induced mitochondrial stress, changes in mitochondrial membrane potential, loss of membrane integrity; nuclear damage as single/double stranded breaks, autophagy and the effects of pre and co-treatment of pCA on Nrf-2 mediated signaling was evaluated by various approaches. The effect of pCA on drug uptake was evaluated through confocal Raman Spectroscopy. We find that nuclear translocation of Nrf-2 is prominently marked by protein-specific antibody conjugated fluorophore in Dox treated cells especially. Cell survival is mediated to a certain extent by the expression of the anti-apoptotic BCl2 in pCA treated cells. However, mRNA levels of autophagy related (Atg) genes suggest that autophagy plays a decisive role in deciding cellular fate. Caspase-3 activation is also observed in pCA treated cells which suggest an alternative function of caspase-3 in pCA mediated cell survival. Expression of antioxidant enzymes confirm the oxidative stress induced by Dox treatment in cells and the modulation of cell redox homeostasis through treatment with pCA.

In vitro and in vivo metabolic activation of rhein and characterization of glutathione conjugates derived from rhein

Rhein (RH), 4,5-dihydroxyanthrauinone-2-carboxylic acid, is found in rhubarb (Dahuang), a traditional herbal medicine. RH has reportedly demonstrated multiple pharmacologic properties. Previous studies have also shown that RH induced hepatotoxicity, but the mechanisms of the adverse effect remain unknown. The major objective of the present study was to study the metabolic pathways of RH in order to identify potential reactive metabolites. One mono-hydroxylation metabolite (M1) was detected in urine and bile of rats given RH. M1 was also observed in rat and human liver microsomal incubations after exposure to RH. A total of three (GSH) conjugates (M2, M3 and M5) were detected in bile of rats treated with RH. We concluded that M2-M3 were directly derived from parent compound RH through spontaneous reaction with GSH. M5 was derived from M1 by reaction with GSH, which required cytoslic GSTs. M5 was further metabolized to the corresponding NAC conjugate (mercapturic acid) and was excreted in urine. P450 2C9 was mainly involved in the oxidation of RH.

Apoptosis inducing factor (AIF) mediates lethal redox stress induced by menadione

Mitochondrial apoptosis inducing factor (AIF) is a redox-active enzyme that participates to the biogenesis/maintenance of complex I of the respiratory chain, yet also contributes to catabolic reactions in the context of regulated cell death when AIF translocates to the cytosol and to the nucleus. Here we explore the contribution of AIF to cell death induced by menadione (2-methyl-1,4-naphtoquinone; also called vitamin K3) in conditions in which this pro-oxidant does not cause the mitochondrial release of AIF, yet causes caspase-independent cell killing. Depletion of AIF from human cancer cells reduced the cytotoxicity of menadione. This cytoprotective effect was accompanied by the maintenance of high levels of reduced glutathione (GSH), which are normally depleted by menadione. In addition, AIF depletion reduced the arylation of cellular proteins induced by menadione. This menadione-triggered arylation, which can be measured by a fluorescence assay, is completely suppressed by addition of exogenous glutathione or N-acetyl cysteine. Complex I inhibition by Rotenone did not mimic the cytoprotective action of AIF depletion. Altogether, these results are compatible with the hypothesis that mitochondrion-sessile AIF facilitates lethal redox cycling of menadione, thereby precipitating protein arylation and glutathione depletion.

The BET bromodomain inhibitor exerts the most potent synergistic anticancer effects with quinone-containing compounds and anti-microtubule drugs

BET bromodomain inhibitors are very promising novel anticancer agents, however, single therapy does not cause tumor regression in mice, suggesting the need for combination therapy. After screening a library of 2697 small molecule compounds, we found that two classes of compounds, the quinone-containing compounds such as nanaomycin and anti-microtubule drugs such as vincristine, exerted the best synergistic anticancer effects with the BET bromodomain inhibitor JQ1 in neuroblastoma cells. Mechanistically, the quinone-containing compound nanaomycin induced neuroblastoma cell death but also activated the Nrf2-antioxidant signaling pathway, and the BET bromodomain proteins BRD3 and BRD4 formed a protein complex with Nrf2. Treatment with JQ1 blocked the recruitment of Nrf2 to the antioxidant responsive elements at Nrf2 target gene promoters, and JQ1 exerted synergistic anticancer effects with nanaomycin by blocking the Nrf2-antioxidant signaling pathway. JQ1 and vincristine synergistically induced neuroblastoma cell cycle arrest at the G₂/M phase, aberrant mitotic spindle assembly formation and apoptosis, but showed no effect on cell survival in normal non-malignant cells. Importantly, co-treatment with JQ1 and vincristine synergistically suppressed tumor progression in neuroblastoma-bearing mice. These results strongly suggest that patients treated with BET bromodomain inhibitors in clinical trials should be co-treated with vincristine.

Distinct activation mechanisms trigger the trypanocidal activity of DNA damaging prodrugs

Quinone‐based compounds have been exploited to treat infectious diseases and cancer, with such chemicals often functioning as inhibitors of key metabolic pathways or as prodrugs. Here, we screened an aziridinyl 1,4‐benzoquinone (ABQ) library against the causative agents of trypanosomiasis, and cutaneous leishmaniasis, identifying several potent structures that exhibited EC₅₀ values of <100 nM. However, these compounds also displayed significant toxicity towards mammalian cells indicating that they are not suitable therapies for systemic infections. Using anti‐T. brucei ABQs as chemical probes, we demonstrated that these exhibit different trypanocidal modes of action. Many functioned as type I nitroreductase (TbNTR) or cytochrome P450 reductase (TbCPR) dependent prodrugs that, following activation, generate metabolites which promote DNA damage, specifically interstrand crosslinks (ICLs). Trypanosomes lacking TbSNM1, a nuclease that specifically repairs ICLs, are hypersensitive to most ABQ prodrugs, a phenotype exacerbated in cells also engineered to express elevated levels of TbNTR or TbCPR. In contrast, ABQs that contain substituent groups on the biologically active aziridine do not function as TbNTR or TbCPR‐activated prodrugs and do not promote DNA damage. By unravelling how ABQs mediate their activities, features that facilitate the desired anti‐parasitic growth inhibitory effects could be incorporated into new, safer compounds targeting these neglected tropical diseases.

Flavoenzyme-mediated reduction reactions and antitumor activity of nitrogen-containing tetracyclic ortho-quinone compounds and their nitrated derivatives

Nitrogen-based tetracyclic ortho-quinones (naphtho[1'2':4.5]imidazo[1,2-a]pyridine-5,6-diones, NPDOs) and their nitro-substituted derivatives (nitro-(P)NPDOs) were obtained by condensation of substituted 2,3-dichloro-1,4-naphthoquinones with 2-amino-pyridine and -pyrimidine and nitration at an elevated temperature. The structural features of the compounds as well as their global and regional electrophilic potency were characterized by means of DFT computation. The compounds were highly reactive substrates of single- and two-electron (hydride) - transferring P-450R (CPR; EC 1.6.2.4) and NQO-1 (DTD; EC 1.6.99.2), respectively, concomitantly producing reactive oxygen species. Their catalytic efficiency defined in terms of the apparent second-order rate constant (k_cat/K_{M (Q)}) values in P-450R- and NQO-1-mediated reactions varied in the range of 3-6 × 10⁷ M^-1 s^-1 and 1.6-7.4 × 10⁸ M^-1 s^-1, respectively. The cytotoxic activities of the compounds on tumor cell lines followed the concentration-dependent manner exhibiting relatively high cytotoxic potency against breast cancer MCF-7, with CL₅₀ values of 0.08-2.02 µM L^-1 and lower potency against lung cancer A-549 (CL₅₀ = 0.28-7.66 µM L^-1). 3-nitro-pyrimidino-NPDO quinone was the most active compound against MCF-7 with CL₅₀ of 0.08 ± 0.01 µM L^-1 (0.02 µg mL^-1)) which was followed by 3-nitro-NPDO with CL₅₀ of 0.12 ± 0.03 µM L^-1 (0.035 µg mL^-1)) and 0.28 ± 0.08 µM L^-1 (0.08 µg mL^-1) on A-549 and MCF-7 cells, respectively, while 1- and 4-nitro-quinoidals produced the least cytotoxic effects. Tumor cells quantified by AO/EB staining showed that the cell death induced by the compounds occurs primarily through apoptosis.

Rethinking Drugs from Chemistry to Therapeutic Opportunities: Pixantrone beyond Anthracyclines

Pixantrone (6,9-bis[(2-aminoethyl)amino]benzo[g]isoquinoline-5,10-dione) has been approved by the European Medicines Agency for the treatment of refractory or relapsed non-Hodgkin's lymphoma (NHL). It is popularly referred to as a novel aza-anthracenedione, and as such it is grouped with anthracycline-like drugs. Preclinical development of pixantrone was in fact tailored to retain the same antitumor activity as that of anthracyclines or other anthracenediones while also avoiding cardiotoxicity that dose-limits clinical use of anthracycline-like drugs. Preliminary data in laboratory animals showed that pixantrone was active, primarily in hematologic malignancies, but caused significantly less cardiotoxicity than doxorubicin or mitoxantrone. Pixantrone was cardiac tolerable also in animals pretreated with doxorubicin, which anticipated a therapeutic niche for pixantrone to treat patients with a history of prior exposure to anthracyclines. This is the case for patients with refractory/relapsed NHL. Pixantrone clinical development, regulatory approval, and penetration in clinical practice were nonetheless laborious if not similar to a rocky road. Structural and nominal similarities with mitoxantrone and anthracyclines may have caused a negative influence, possibly leading to a general perception that pixantrone is a "me-too" anthracycline. Recent insights suggest this is not the case. Pixantrone shows pharmacological and toxicological mechanisms of action that are difficult to reconcile with anthracycline-like drugs. Pixantrone is a new drug with its own characteristics. For example, pixantrone causes mis-segregation of genomic material in cancer cells and inhibits formation of toxic anthracycline metabolites in cardiac cells. Understanding the differences between pixantrone and anthracyclines or mitoxantrone may help one to appreciate how it worked in the phase 3 study that led to its approval in Europe and how it might work in many more patients in everyday clinical practice, were it properly perceived as a drug with its own characteristics and therapeutic potential. The road is rocky but not a dead-end.

Metabolic Activation of Rhein: Insights into the Potential Toxicity Induced by Rhein-Containing Herbs

Rhein is a major component of the many medicinal herbs such as rhubarb. Despite wide use, intoxication cases associated with rhein-containing herbs are often reported. The present work aimed to investigate if rhein was subject to metabolic activation leading to toxicity. Upon incubations with different species of liver microsomes, three monoglucuronides were identified, corresponding to two hydroxyl glucuronides and one acyl glucuronide via the carboxyl group, respectively. Further study revealed that rhein acyl glucuronide was chemically reactive, and showed cytotoxicity toward hepatocarcinoma cells. In addition, significant species differences in glucuronidation of rhein were observed between laboratory animals and humans. Reaction phenotyping experiments demonstrated that rhein acyl glucuronide was catalyzed predominantly by uridine 5'-diphospho-glucuronosyltransferase 1A1, 1A9, and 2B7. Taken together, the present study confirmed that rhein could be metabolically activated via the formation of acyl glucuronide, especially in human.

Anthraquinones As Pharmacological Tools and Drugs

Anthraquinones (9,10-dioxoanthracenes) constitute an important class of natural and synthetic compounds with a wide range of applications. Besides their utilization as colorants, anthraquinone derivatives have been used since centuries for medical applications, for example, as laxatives and antimicrobial and antiinflammatory agents. Current therapeutic indications include constipation, arthritis, multiple sclerosis, and cancer. Moreover, biologically active anthraquinones derived from Reactive Blue 2 have been utilized as valuable tool compounds for biochemical and pharmacological studies. They may serve as lead structures for the development of future drugs. However, the presence of the quinone moiety in the structure of anthraquinones raises safety concerns, and anthraquinone laxatives have therefore been under critical reassessment. This review article provides an overview of the chemistry, biology, and toxicology of anthraquinones focusing on their application as drugs.

Divergent non-heme iron enzymes in the nogalamycin biosynthetic pathway

Nogalamycin, an aromatic polyketide displaying high cytotoxicity, has a unique structure, with one of the carbohydrate units covalently attached to the aglycone via an additional carbon-carbon bond. The underlying chemistry, which implies a particularly challenging reaction requiring activation of an aliphatic carbon atom, has remained enigmatic. Here, we show that the unusual C5''-C2 carbocyclization is catalyzed by the non-heme iron α-ketoglutarate (α-KG)-dependent SnoK in the biosynthesis of the anthracycline nogalamycin. The data are consistent with a mechanistic proposal whereby the Fe(IV) = O center abstracts the H5'' atom from the amino sugar of the substrate, with subsequent attack of the aromatic C2 carbon on the radical center. We further show that, in the same metabolic pathway, the homologous SnoN (38% sequence identity) catalyzes an epimerization step at the adjacent C4'' carbon, most likely via a radical mechanism involving the Fe(IV) = O center. SnoK and SnoN have surprisingly similar active site architectures considering the markedly different chemistries catalyzed by the enzymes. Structural studies reveal that the differences are achieved by minor changes in the alignment of the substrates in front of the reactive ferryl-oxo species. Our findings significantly expand the repertoire of reactions reported for this important protein family and provide an illustrative example of enzyme evolution.

Hydroxylated Dimeric Naphthoquinones Increase the Generation of Reactive Oxygen Species, Induce Apoptosis of Acute Myeloid Leukemia Cells and Are Not Substrates of the Multidrug Resistance Proteins ABCB1 and ABCG2

Selective targeting of the oxidative state, which is a tightly balanced fundamental cellular property, is an attractive strategy for developing novel anti-leukemic chemotherapeutics with potential applications in the treatment of acute myeloid leukemia (AML), a molecularly heterogeneous disease. Dimeric naphthoquinones (BiQs) with the ability to undergo redox cycling and to generate reactive oxygen species (ROS) in cancer cells are a novel class of compounds with unique characteristics that make them excellent candidates to be tested against AML cells. We evaluated the effect of two BiQ analogues and one monomeric naphthoquinone in AML cell lines and primary cells from patients. All compounds possess one halogen and one hydroxyl group on the quinone cores. Dimeric, but not monomeric, naphthoquinones demonstrated significant anti-AML activity in the cell lines and primary cells from patients with favorable therapeutic index compared to normal hematopoietic cells. BiQ-1 effectively inhibited clonogenicity and induced apoptosis as measured by Western blotting and Annexin V staining and mitochondrial membrane depolarization by flow cytometry. BiQ-1 significantly enhances intracellular ROS levels in AML cells and upregulates expression of key anti-oxidant protein, Nrf2. Notably, systemic exposure to BiQ-1 was well tolerated in mice. In conclusion, we propose that BiQ-induced therapeutic augmentation of ROS in AML cells with dysregulation of antioxidants kill leukemic cells while normal cells remain relatively intact. Further studies are warranted to better understand this class of potential chemotherapeutics.

Interaction of p-synephrine with p-chloranil: experimental design and multiple response optimization

A multivariate factorial design was proposed for determination ofp-synephrine. Novelty of present approach stems from consolidating multiple responses into a unified performance characteristic.