ROS-activated anticancer prodrugs: a new strategy for tumor-specific damage

Impact of ROS Generated by Chemical, Physical, and Plasma Techniques on Cancer Attenuation

For the last few decades, while significant improvements have been achieved in cancer therapy, this family of diseases is still considered one of the deadliest threats to human health. Thus, there is an urgent need to find novel strategies in order to tackle this vital medical issue. One of the most pivotal causes of cancer initiation is the presence of reactive oxygen species (ROS) inside the body. Interestingly, on the other hand, high doses of ROS possess the capability to damage malignant cells. Moreover, several important intracellular mechanisms occur during the production of ROS. For these reasons, inducing ROS inside the biological system by utilizing external physical or chemical methods is a promising approach to inhibit the growth of cancer cells. Beside conventional technologies, cold atmospheric plasmas are now receiving much attention as an emerging therapeutic tool for cancer treatment due to their unique biophysical behavior, including the ability to generate considerable amounts of ROS. This review summarizes the important mechanisms of ROS generated by chemical, physical, and plasma approaches. We also emphasize the biological effects and cancer inhibition capabilities of ROS.

Astrakurkurone, a sesquiterpenoid from wild edible mushroom, targets liver cancer cells by modulating Bcl-2 family proteins

Induction of apoptosis is the target of choice for modern chemotherapeutic treatment of cancer, where lack of potent "target-specific" drugs has led to extensive research on anticancer compounds from natural sources. In our study, we have used astrakurkurone, a triterpene isolated from wild edible mushroom, Astraeus hygrometricus. We have discussed the structure and stability of astrakurkurone employing single-crystal X-ray crystallography and studied its potential apoptogenicity in hepatocellular carcinoma (HCC) cells. Our experiments reveal that it is cytotoxic against the HCC cell lines (Hep 3B and Hep G2) at significantly low doses. Further investigations indicated that astrakurkurone acts by inducing apoptosis in the cells, disrupting mitochondrial membrane potential and inducing the expression of Bcl-2 family proteins, for example, Bax, and the downstream effector caspases 3 and 9. A molecular docking study also predicted direct interactions of the drug with antiapoptotic proteins Bcl-2 and Bcl-xL. Thus, astrakurkurone could become a valuable addition to the conventional repertoire of future anticancer drugs. © 2019 IUBMB Life, 1-11, 2019.

Recent Advances on Reactive Oxygen Species-Responsive Delivery and Diagnosis System

Reactive oxygen species (ROS) play crucial roles in biological metabolism and intercellular signaling. However, ROS level is dramatically elevated due to abnormal metabolism during multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. By taking advantage of the discrepancy of ROS levels between normal and diseased tissues, a variety of ROS-sensitive moieties or linkers have been developed to design ROS-responsive systems for the site-specific delivery of drugs and genes. In this review, we summarized the ROS-responsive chemical structures, mechanisms, and delivery systems, focusing on their current advances for precise drug/gene delivery. In particular, ROS-responsive nanocarriers, prodrugs, and supramolecular hydrogels are summarized in terms of their application for drug/gene delivery, and common strategies to elevate or diminish cellular ROS concentrations, as well as the recent development of ROS-related imaging probes were also discussed.

Prodrugs for targeted cancer therapy

Introduction: Prodrugs have been used to improve the selectivity and efficacy of cancer therapy by targeting unique abnormal markers that are overexpressed by cancer cells and are absent in normal tissues. In this context, different strategies have been exploited and new ones are being developed each year. Areas covered: In this review, an integrated view of the potential use of prodrugs in targeted cancer therapy is provided. Passive and active strategies are discussed in light of the advantages of each one and some successful examples are provided, as well as the clinical status of several prodrugs. Among them, antibody-drug conjugates (ADCs) are the most commonly used. However, several drawbacks, including limited prodrug uptake, poor pharmacokinetics, immunogenicity problems, difficulties in selective targeting and gene expression, and optimized bystander effects limit their clinical applications. Expert opinion: Despite the efforts of different companies and research groups, several drawbacks, such as the lack of relevant in vivo models, complexity of the human metabolism, and economic limitations, have hampered the development of new prodrugs for targeted cancer therapy. As a result, we believe that the combination of prodrugs with cancer nanotechnology and other newly developed approaches, such as aptamer-conjugated nanomaterials, are efficient strategies.

Novel dual-action prodrug triggers apoptosis in glioblastoma cells by releasing a glutathione quencher and lysine-specific histone demethylase 1A inhibitor

Targeting epigenetic mechanisms has shown promise against several cancers but has so far been unsuccessful against glioblastoma (GBM). Altered histone 3 lysine 4 methylation and increased lysine‐specific histone demethylase 1A (LSD1) expression in GBM tumours nonetheless suggest that epigenetic mechanisms are involved in GBM. We engineered a dual‐action prodrug, which is activated by the high hydrogen peroxide levels associated with GBM cells. This quinone methide phenylaminecyclopropane prodrug releases the LSD1 inhibitor 2‐phenylcyclopropylamine with the glutathione scavenger para‐quinone methide to trigger apoptosis in GBM cells. Quinone methide phenylaminocyclopropane impaired GBM cell behaviours in two‐dimensional and three‐dimensional assays, and triggered cell apoptosis in several primary and immortal GBM cell cultures. These results support our double‐hit hypothesis of potentially targeting LSD1 and quenching glutathione, in order to impair and kill GBM cells but not healthy astrocytes. Our data suggest this strategy is effective at selectively targeting GBM and potentially other types of cancers.

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Organoselenium Compounds as Novel Adjuvants of Chemotherapy Drugs-A Promising Approach to Fight Cancer Drug Resistance

Malignant diseases present a serious public health burden and their treatment with traditional chemotherapy cannot be considered an all-round solution, due to toxic side effects. Selenium compounds (Se-compounds) have received substantial attention in medicinal chemistry, especially in experimental chemotherapy, both as cytotoxic agents and adjuvants in chemotherapy. A checkerboard microplate method was applied to study the drug interactions of Se-compounds and clinically relevant chemotherapeutic drugs against the multidrug-resistant (MDR) subtype of mouse t-lymphoma cells overexpressing the ABCB1 transporter. Se-compounds showed synergistic interactions with chemotherapeutic agents targeting the topoisomerase enzymes or the microtubule apparatus. The ketone-containing selenoesters showed synergism at lower concentrations (1.25 µM). Most of the tested compounds interacted antagonistically with alkylating agents and verapamil. A thiophene-containing Se-compound showed synergism with all tested drugs, except cisplatin. While the exact mechanism of drug interactions is yet unknown, the potency of the selenocompounds as efflux pump inhibitors or the potentiation of their efficacy as reactive oxygen species modulators may play a role in their complementary activity against the tested MDR lymphoma cell line.

Enhanced Tumor Selectivity of 5-Fluorouracil Using a Reactive Oxygen Species-Activated Prodrug Approach

We report the design, synthesis, and evaluation of novel 5-fluorouracil (5FU) prodrugs 1a,1b that are efficiently activated by the high level of reactive oxygen species (ROS) in cancer cells. Prodrugs 1a,1b selectively kill cancer cells over normal cells and are well-tolerated in mice. The strategy described herein can extend application of chemotherapeutic drugs.

Click and release: bioorthogonal approaches to “on-demand” activation of prodrugs

This review summarizes recent developments in using bioorthogonal chemistry in prodrug design for the delivery of traditional small molecule- and gasotransmitter-based therapeutics.

Utilization of Reactive Oxygen Species Targeted Therapy to Prolong the Efficacy of BRAF Inhibitors in Melanoma

BRAF mutations occur in about 50% of melanoma patients. FDA approved BRAF and MEK inhibitors have improved the prognosis of patients with BRAF mutations. However, all responders develop resistance typically within one year of treatment. Recent observations demonstrate that BRAF inhibitors induce reactive oxygen species (ROS) in melanoma cells. A100, identified from a library screen, is a ROS-activated prodrug that self-cyclizes into a stable bicyclic ring and causes DNA double strand breaks. We proposed to examine if ROS activated therapy will inhibit tumor growth and evade resistance to BRAF inhibitors. In this study, the BRAF inhibitor dabrafenib was used to generate resistant cell lines (A375DR, SK-MEL-24DR and WM-115DR). Flow cytometry experiments showed that ROS levels are increased in these dabrafenib-resistant cells as compared to parental cells, assessed by both the H2DCFDA and MitoSOX assays. Furthermore, we observed that resistant cells had increased levels of the mitochondrial enzymes SOD2 and PRDX1, which function to reduce ROS levels in the mitochondria. We found that A100 sensitized the resistant melanoma cells to dabrafenib and induced DNA damage. Co-treatment of both A100 and dabrafenib significantly suppressed in vitro cell proliferation and three- dimensional (3D) matrigel growth. This study suggests that the combination of A100 with a BRAF inhibitor could be a potential strategy to treat melanoma patients with BRAF mutations.

Heterogeneous Fenton Reaction Enabled Selective Colon Cancerous Cell Treatment

A selective colon cancer cell therapy was effectively achieved with catalase-mediated intra-cellular heterogeneous Fenton reactions triggered by cellular uptake of SnFe2O4 nanocrystals. The treatment was proven effective for eradicating colon cancer cells, whereas was benign to normal colon cells, thus effectively realizing the selective colon cancer cell therapeutics. Cancer cells possess much higher innate hydrogen peroxide (H2O2) but much lower catalase levels than normal cells. Catalase, an effective H2O2 scavenger, prevented attacks on cells by reactive oxygen species induced from H2O2. The above intrinsic difference between cancer and normal cells was utilized to achieve selective colon cancer cell eradication through endocytosing efficient heterogeneous Fenton catalysts to trigger the formation of highly reactive oxygen species from H2O2. In this paper, SnFe2O4 nanocrystals, a newly noted outstanding paramagnetic heterogeneous Fenton catalyst, have been verified an effective selective colon cancerous cell treatment reagent of satisfactory blood compatibility.

Discovery and Optimization of Novel Hydrogen Peroxide Activated Aromatic Nitrogen Mustard Derivatives as Highly Potent Anticancer Agents

We describe several new aromatic nitrogen mustards with various aromatic substituents and boronic esters that can be activated with H₂O₂ to efficiently cross-link DNA. In vitro studies demonstrated the anticancer potential of these compounds at lower concentrations than those of other clinically used chemotherapeutics, such as melphalan and chlorambucil. In particular, compound 10, bearing an amino acid ester chain, is selectively cytotoxic toward breast cancer and leukemia cells that have inherently high levels of reactive oxygen species. Importantly, 10 was 10-14-fold more efficacious than melphalan and chlorambucil for triple-negative breast-cancer (TNBC) cells. Similarly, 10 is more toxic toward primary chronic-lymphocytic-leukemia cells than either chlorambucil or the lead compound, 9. The introduction of an amino acid side chain improved the solubility and permeability of 10. Furthermore, 10 inhibited the growth of TNBC tumors in xenografted mice without obvious signs of general toxicity, making this compound an ideal drug candidate for clinical development.

H2O2/Peroxynitrite-Activated Hydroxamic Acid HDAC Inhibitor Prodrugs Show Antileukemic Activities against AML Cells

Occurrence of acute myeloid leukemia (AML) results in abundant endogenous reactive oxygen species (ROS)/reactive nitrogen species (RNS) in AML cells and in disease-relevant microenvironments. Histone deacetylase inhibitor (HDACi) prodrug approach was designed accordingly by masking the hydroxamic acid zinc binding group with hydrogen peroxide (H₂O₂)/peroxynitrite (PNT)-sensitive, self-immolative aryl boronic acid moiety. Model prodrugs 5-82 and 5-23 were activated in AML cells to release cytotoxic HDACis, evidenced by inducing acetylation markers and reducing viability of AML cells. Intracellular activation and antileukemic activities of prodrug were increased or decreased by ROS/PNT inducers and scavengers, respectively. Prodrugs 5-82 and 5-23 also enhanced the potency of chemotherapy drug cytarabine, supporting the potentials of this prodrug class in combinatorial treatment.

Synthesis and Evaluation of Hydrogen Peroxide Sensitive Prodrugs of Methotrexate and Aminopterin for the Treatment of Rheumatoid Arthritis

A series of novel hydrogen peroxide sensitive prodrugs of methotrexate (MTX) and aminopterin (AMT) were synthesized and evaluated for therapeutic efficacy in mice with collagen induced arthritis (CIA) as a model of chronic rheumatoid arthritis (RA). The prodrug strategy selected is based on ROS-labile 4-methylphenylboronic acid promoieties linked to the drugs via a carbamate linkage or a direct C-N bond. Activation under pathophysiological concentrations of H₂O₂ proved to be effective, and prodrug candidates were selected in agreement with relevant in vitro physicochemical and pharmacokinetic assays. Selected candidates showed moderate to good solubility, high chemical and enzymatic stability, and therapeutic efficacy comparable to the parent drugs in the CIA model. Importantly, the prodrugs displayed the expected safer toxicity profile and increased therapeutic window compared to MTX and AMT while maintaining a comparable therapeutic efficacy, which is highly encouraging for future use in RA patients.

N- and S-donor leaving groups in triazole-based ruthena(ii)cycles: potent anticancer activity, selective activation, and mode of action studies

The functionalization of cycloruthenated triazole arene complexes with N- or S-donors affords pH or redox-activatable complexes with high cytotoxic activities.

Screening of ferrocenyl–phosphines identifies a gold-coordinated derivative as a novel anticancer agent for hematological malignancies

The development of new organometallic compounds as anticancer agents is currently an active area of research. Here, we report the design, synthesis and characterization of a panel of 10 new ferrocenyl–phosphine derivatives (FD1–FD10) and the analysis of their anti-proliferative activities in hematolymphoid cells representing non-Hodgkin cutaneous T-cell lymphoma (CTCL). The gold-coordinated ferrocenyl–phosphine complex FD10 exhibited a significant and dose-dependent cytotoxicity in 4 different CTCL cell lines – HuT78, HH, MJ and MyLa. FD10 concentrations causing 50% cell growth inhibition (IC₅₀) of HuT78, HH, MJ and MyLa cells at 24 h were recorded to be 5.55 ± 0.20, 7.80 ± 0.09, 3.16 ± 0.10 and 6.46 ± 0.24 μM respectively. Further mechanistic studies showed that FD10 induced apoptosis in CTCL cells by an intrinsic pathway mediated via the activation of caspase-3 and poly(ADP-ribose)polymerase. It suppressed the expression and activity of STAT3 oncoprotein in CTCL cells. FD10 caused robust G0/G1 phase cell cycle arrest and reduced the expression levels of Akt S473 phosphorylation and c-Myc, both are key cell cycle regulator proteins. Taken together, this study highlights anticancer properties of the ferrocenyl–phosphine gold organometallic complex FD10 and suggests that further development of this novel class of molecule may contribute to new drug discovery for certain hematolymphoid malignancies.

Development of organometallic compounds as novel anticancer agents.

In vitro and in vivo antitumour effects of phenylboronic acid against mouse mammary adenocarcinoma 4T1 and squamous carcinoma SCCVII cells

The cytotoxic activity of phenylboroxine acid was evaluated in vitro on mouse mammary adenocarcinoma 4T1, mouse squamous cell carcinoma SCCVII, hamster lung fibroblast V79 and mouse dermal fibroblasts L929 cell lines. The cytotoxic effects were dose dependent for all tested tumour and non-tumour cell lines. Under in vivo conditions, three application routes of phenylboronic acid were studied: intra-peritoneal (i.p.), intra-tumour (i.t.) and per-oral. After tumour transplantation in syngeneic mice, phenylboronic acid was shown to slow the growth of both tumour cell lines (4T1 and SCCVII) compared with the control. The inhibitory effects were pronounced during the application of phenylboronic acid. For both tested tumour cell lines, the most prominent antitumour effect was obtained by intraperitoneal administration, followed significantly by oral administration.

Synthesis and in vitro Biological Evaluation of Ferrocenyl Side-Chain-Functionalized Paclitaxel Derivatives

Taxanes, including paclitaxel, are widely used in cancer therapy. In an attempt to overcome some of the disadvantages entailed with taxane chemotherapy, we devised the synthesis of ferrocenyl-functionalized paclitaxel derivatives and studied their biological properties. The cytotoxic activity was measured with a panel of human cancer cell lines of various tissue origin, including multidrug-resistant lines. A structure-activity study of paclitaxel ferrocenylation revealed the N-benzoyl-ferrocenyl-substituted derivative to be the most cytotoxic. In contrast, substitution of the 3'-phenyl group of paclitaxel with a ferrocenyl moiety led to less potent antiproliferative compounds. However, these agents were able to overcome multidrug resistance, as they were virtually unrecognized by ABCB1, a major cellular exporter of taxanes. Interestingly, the redox properties of these ferrocenyl derivatives appear to play a less important role in their mode of action, as there was no correlation between intracellular redox activity and cytotoxicity/cell-cycle distribution. The antiproliferative activity of ferrocenyl taxanes strongly depends on the substitution position, and good tubulin polymerization inducers, as confirmed by molecular docking, were usually more cytotoxic, whereas compounds with stronger pro-oxidative properties exhibited lower antiproliferative activity.

Juglanin inhibits lung cancer by regulation of apoptosis, ROS and autophagy induction

Juglanin (Jug) is obtained from the crude extract of Polygonum aviculare, exerting suppressive activity against cancer cell progression in vitro and in vivo. Juglanin administration causes apoptosis and reactive oxygen species (ROS) in different types of cells through regulating various signaling pathways. In our study, the effects of juglanin on non-small cell lung cancer were investigated. A significant role of juglanin in suppressing lung cancer growth was observed. Juglanin promoted apoptosis in lung cancer cells through increasing Caspase-3 and poly ADP-ribose polymerase (PARP) cleavage, which is regulated by TNF-related apoptosis-inducing ligand/Death receptors (TRAIL/DRs) relied on p53 activation. Anti-apoptotic members Bcl-2 and Bcl-xl were reduced, and pro-apoptotic members Bax and Bad were enhanced in cells and animals receiving juglanin. Additionally, nuclear factor-κB (NF-κB), phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinases (MAPKs) activation were inhibited by juglanin. Further, juglanin improved ROS and induced autophagy. ROS inhibitor N-acetyl-l-cysteine (NAC) reversed apoptosis induced by juglanin in cancer cells. The formation of autophagic vacoules and LC3/autophagy gene7 (ATG7)/Beclin1 (ATG6) over-expression were observed in juglanin-treated cells. Also, juglanin administration to mouse xenograft models inhibited lung cancer progression. Our study demonstrated that juglanin could be a promising candidate against human lung cancer progression.

Superantigen staphylococcal enterotoxin C1 inhibits the growth of bladder cancer

Superantigens can induce cell-mediated cytotoxicity preferentially against MHC II-positive target cells with large amounts of inflammatory cytokines releasing. In this study, superantigen staphylococcal enterotoxin C (SEC) 1 was investigated to evaluate its potential in bladder cancer immunotherapy in vitro and in vivo. Our results revealed that SEC1 could stimulate the proliferation of human peripheral blood mononuclear cells (PBMCs) in a dose-dependent manner, accompanied with the release of interleukin-2, interferon-γ, and tumor necrosis factor-α, and increased the population of CD4+ T cells and CD8+ T cells. PBMCs stimulated by SEC1 could initiate significant cytotoxicity towards human bladder cancer cells in vitro. The results of in vivo antitumor experiment indicated that SEC1 could decrease the rate of tumor formation and prolong the survival time of tumor-bearing mice. Our study demonstrated that SEC1 inhibited the growth of bladder cancer. And it is also suggested that SEC1 may become a candidate for bladder cancer immunotherapy.

Mertensene, a Halogenated Monoterpene, Induces G2/M Cell Cycle Arrest and Caspase Dependent Apoptosis of Human Colon Adenocarcinoma HT29 Cell Line through the Modulation of ERK-1/-2, AKT and NF-κB Signaling

Conventional treatment of advanced colorectal cancer is associated with tumor resistance and toxicity towards normal tissues. Therefore, development of effective anticancer therapeutic alternatives is still urgently required. Nowadays, marine secondary metabolites have been extensively investigated due to the fact that they frequently exhibit anti-tumor properties. However, little attention has been given to terpenoids isolated from seaweeds. In this study, we isolated the halogenated monoterpene mertensene from the red alga Pterocladiella capillacea (S.G. Gmelin) Santelices and Hommersand and we highlight its inhibitory effect on the viability of two human colorectal adenocarcinoma cell lines HT29 and LS174. Interestingly, exposure of HT29 cells to different concentrations of mertensene correlated with the activation of MAPK ERK-1/-2, Akt and NF-κB pathways. Moreover, mertensene-induced G2/M cell cycle arrest was associated with a decrease in the phosphorylated forms of the anti-tumor transcription factor p53, retinoblastoma protein (Rb), cdc2 and chkp2. Indeed, a reduction of the cellular level of cyclin-dependent kinases CDK2 and CDK4 was observed in mertensene-treated cells. We also demonstrated that mertensene triggers a caspase-dependent apoptosis in HT29 cancer cells characterized by the activation of caspase-3 and the cleavage of poly (ADP-ribose) polymerase (PARP). Besides, the level of death receptor-associated protein TRADD increased significantly in a concentration-dependent manner. Taken together, these results demonstrate the potential of mertensene as a drug candidate for the treatment of colon cancer.

TRAIL, Wnt, Sonic Hedgehog, TGFβ, and miRNA Signalings Are Potential Targets for Oral Cancer Therapy

Clinical studies and cancer cell models emphasize the importance of targeting therapies for oral cancer. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is highly expressed in cancer, and is a selective killing ligand for oral cancer. Signaling proteins in the wingless-type mouse mammary tumor virus (MMTV) integration site family (Wnt), Sonic hedgehog (SHH), and transforming growth factor β (TGFβ) pathways may regulate cell proliferation, migration, and apoptosis. Accordingly, the genes encoding these signaling proteins are potential targets for oral cancer therapy. In this review, we focus on recent advances in targeting therapies for oral cancer and discuss the gene targets within TRAIL, Wnt, SHH, and TGFβ signaling for oral cancer therapies. Oncogenic microRNAs (miRNAs) and tumor suppressor miRNAs targeting the genes encoding these signaling proteins are summarized, and the interactions between Wnt, SHH, TGFβ, and miRNAs are interpreted. With suitable combination treatments, synergistic effects are expected to improve targeting therapies for oral cancer.

Stressor-driven extracellular acidosis as tumor inducer via aberrant enzyme activation: A review on the mechanisms and possible prophylaxis

When the extracellular pH of human body vacillates in either direction, tissue homeostasis is compromised. Fluctuations in acidity have been linked to a wide variety of pathological conditions, including bone loss, cancer, allergies, and auto-immune diseases. Stress conditions affect oxygen tension, and the resultant hypoxia modulates the expression and/or activity of membrane-tethered transporters/pumps, transcription factors, enzymes and intercellular junctions. These modifications provoke erratic gene expression, aberrant tissue remodeling and oncogenesis. While the physiological optimization of pH in tissues is practically challenging, it is at least theoretically achievable and can be considered as a possible therapy to resolve a broad array of diseases.

Hydrogen peroxide activated quinone methide precursors with enhanced DNA cross-linking capability and cytotoxicity towards cancer cells

Quinone methide (QM) formation induced by endogenously generated H₂O₂ is attractive for biological and biomedical applications. To overcome current limitations due to low biological activity of H₂O₂-activated QM precursors, we are introducing herein several new arylboronates with electron donating substituents at different positions of benzene ring and/or different neutral leaving groups. The reaction rate of the arylboronate esters with H₂O₂ and subsequent bisquinone methides formation and DNA cross-linking was accelerated with the application of Br as a leaving group instead of acetoxy groups. Additionally, a donating group placed meta to the nascent exo-methylene group of the quinone methide greatly improves H₂O₂-induced DNA interstrand cross-link formation as well as enhances the cellular activity. Multiple donating groups decrease the stability and DNA cross-linking capability, which lead to low cellular activity. A cell-based screen demonstrated that compounds 2a and 5a with a OMe or OH group dramatically inhibited the growth of various tissue-derived cancer cells while normal cells were less affected. Induction of H2AX phosphorylation by these compounds in CLL lymphocytes provide evidence for a correlation between cell death and DNA damage. The compounds presented herein showed potent anticancer activities and selectivity, which represent a novel scaffold for anticancer drug development.

A Boronic Acid Conjugate of Angiogenin that Shows ROS-Responsive Neuroprotective Activity

Angiogenin (ANG) is a human ribonuclease that is compromised in patients with amyotrophic lateral sclerosis (ALS). ANG also promotes neovascularization, and can induce hemorrhage and encourage tumor growth. The causal neurodegeneration of ALS is associated with reactive oxygen species, which are also known to elicit the oxidative cleavage of carbon-boron bonds. We have developed a synthetic boronic acid mask that restrains the ribonucleolytic activity of ANG. The masked ANG does not stimulate endothelial cell proliferation but protects astrocytes from oxidative stress. By differentiating between the two dichotomous biological activities of ANG, this strategy could provide a viable pharmacological approach for the treatment of ALS.

DNA Adduct Profiles Predict in Vitro Cell Viability after Treatment with the Experimental Anticancer Prodrug PR104A

PR104A is an experimental DNA-alkylating hypoxia-activated prodrug that can also be activated in an oxygen-independent manner by the two-electron aldo-keto reductase 1C3. Nitroreduction leads to the formation of cytotoxic hydroxylamine (PR104H) and amine (PR104M) metabolites, which induce DNA mono and cross-linked adducts in cells. PR104A-derived DNA adducts can be utilized as drug-specific biomarkers of efficacy and as a mechanistic tool to elucidate the cellular and molecular effects of PR104A. Toward this goal, a mass spectrometric bioanalysis approach based on a stable isotope-labeled adduct mixture (SILAM) and selected reaction monitoring (SRM) data acquisition for relative quantitation of PR104A-derived DNA adducts in cells was developed. Use of this SILAM-based approach supported simultaneous relative quantitation of 33 PR104A-derived DNA adducts in the same sample, which allowed testing of the hypothesis that the enhanced cytotoxicity, observed by preconditioning cells with the transcription-activating isothiocyanate sulforaphane, is induced by an increased level of DNA adducts induced by PR104H and PR104M, but not PR104A. By applying the new SILAM-SRM approach, we found a 2.4-fold increase in the level of DNA adducts induced by PR104H and PR104M in HT-29 cells preconditioned with sulforaphane and a corresponding 2.6-fold increase in cytotoxicity. These results suggest that DNA adduct levels correlate with drug potency and underly the possibility of monitoring PR104A-derived DNA adducts as biomarkers of efficacy.

Catalase-Modulated Heterogeneous Fenton Reaction for Selective Cancer Cell Eradication: SnFe2O4 Nanocrystals as an Effective Reagent for Treating Lung Cancer Cells

Heterogeneous Fenton reactions have been proven to be an effective and promising selective cancer cell treatment method. The key working mechanism for this method to achieve the critical therapeutic selectivity however remains unclear. In this study, we proposed and demonstrated for the first time the critical role played by catalase in realizing the therapeutic selectivity for the heterogeneous Fenton reaction-driven cancer cell treatment. The heterogeneous Fenton reaction, with the lattice ferric ions of the solid catalyst capable of converting H₂O₂ to highly reactive hydroxyl radicals, can effectively eradicate cancer cells. In this study, SnFe₂O₄ nanocrystals, a recently discovered outstanding heterogeneous Fenton catalyst, were applied for selective killing of lung cancer cells. The SnFe₂O₄ nanocrystals, internalized into the cancer cells, can effectively convert endogenous H₂O₂ into highly reactive hydroxyl radicals to invoke an intensive cytotoxic effect on the cancer cells. On the other hand, catalase, present at a significantly higher concentration in normal cells than in cancer cells, remarkably can impede the apoptotic cell death induced by the internalized SnFe₂O₄ nanocrystals. According to the results obtained from the in vitro cytotoxicity study, the relevant oxidative attacks were effectively suppressed by the presence of normal physiological levels of catalase. The SnFe₂O₄ nanocrystals were thus proved to effect apoptotic cancer cell death through the heterogeneous Fenton reaction and were benign to cells possessing normal physiological levels of catalase. The catalase modulation of the involved heterogeneous Fenton reaction plays the key role in achieving selective cancer cell eradication for the heterogeneous Fenton reaction-driven cancer cell treatment.

Reactive-Oxygen-Species-Responsive Drug Delivery Systems: Promises and Challenges

Given the increasing evidence indicates that many pathological conditions are associated with elevated reactive oxygen species (ROS) levels, there have been growing research efforts focused on the development of ROS-responsive carrier systems because of their promising potential to realize more specific diagnosis and effective therapy. By judicious utilization of ROS-responsive functional moieties, a wide range of carrier systems has been designed for ROS-mediated drug delivery. In this review article, insights into design principle and recent advances on the development of ROS-responsive carrier systems for drug delivery applications are provided alongside discussion of their in vitro and in vivo evaluation. In particular, the discussions in this article will mainly focus on polymeric nanoparticles, hydrogels, inorganic nanoparticles, and activatable prodrugs that have been integrated with diverse ROS-responsive moieties for spatiotemporally controlled release of drugs for effective therapy.

Copper (II) complexes possessing alkyl-substituted polypyridyl ligands: Structural characterization and in vitro antitumor activity

In an effort to find alternatives to the antitumor drug cisplatin, a series of copper (II) complexes possessing alkyl-substituted polypyridyl ligands have been synthesized. Eight new complexes are reported herein: μ-dichloro-bis{2,9-di-sec-butyl-1,10-phenanthrolinechlorocopper(II)} {[(^di-sec-butylphen)ClCu(μ-Cl)₂CuCl(^di-sec-butylphen)]}(1), 2-sec-butyl-1,10-phenanthrolinedichlorocopper(II) {^{[mono-sec-butyl}phen) CuCl₂} (2), 2,9-di-n-butyl-1,10-phenanthrolinedichlorocopper(II) {[^di-n-butylphen) CuCl₂}(3), 2-n-butyl-1,10-phenanthrolinedichlorocopper(II) {[^mono-n-butylphen) CuCl₂} (4), 2,9-di-methyl-1,10-phenanthrolineaquadichlorocopper(II) {[^di-methylphen) Cu(H₂O)Cl₂}(5), μ-dichloro-bis{6-sec-butyl-2,2'-bipyridinedichlorocopper(II)} {(^{mono-sec-butyl}bipy) ClCu(μ-Cl)₂CuCl(^{mono-sec-butyl}bipy)} (6), 6,6'-di-methyl-2,2'-bipyridinedichlorocopper(II) {^{6,6'-di-methyl}bipy) CuCl₂} (7), and 4,4'-dimethyl-2,2'-bipyridinedichlorocopper(II) {^{4,4'-di-methyl}bipy) CuCl₂} (8). These complexes have been characterized via elemental analysis, UV-vis spectroscopy, and mass spectrometry. Single crystal X-ray diffraction experiments revealed the complexes synthesized with the ^di-sec-butylphen ligand (1) and ^{mono-sec-butyl}bipy ligand (6) crystallized as dimers in which two copper(II) centers are bridged by two chloride ligands. Conversely, complexes 2, 7, and 8 were isolated as monomeric species possessing distorted tetrahedral geometries, and the [(^di-methylphen)Cu(H₂O)Cl₂] (5) complex was isolated as a distorted square pyramidal monomer possessing a coordinating aqua ligand. Compounds 1-8 were evaluated for their in vitro antitumor efficacy. Compounds 1, 5, and 7 in particular were found to exhibit remarkable activity against human derived lung cancer cells, yet this class of copper(II) compounds had minimal cytotoxic effect on non-cancerous cells. In vitro control experiments indicate the activity of the copper(II) complexes most likely does not arise from the formation of CuCl₂ and free polypyridyl ligand, and preliminary solution state studies suggest these compounds are generally stable in biological buffer. The results presented herein suggest further development of this class of copper-based drugs as potential anti-cancer therapies should be pursued.

Decoding Warburg's hypothesis: tumor-related mutations in the mitochondrial respiratory chain

Otto Warburg observed that cancer cells derived their energy from aerobic glycolysis by converting glucose to lactate. This mechanism is in opposition to the higher energy requirements of cancer cells because oxidative phosphorylation (OxPhos) produces more ATP from glucose. Warburg hypothesized that this phenomenon occurs due to the malfunction of mitochondria in cancer cells. The rediscovery of Warburg's hypothesis coincided with the discovery of mitochondrial tumor suppressor genes that may conform to Warburg's hypothesis along with the demonstrated negative impact of HIF-1 on PDH activity and the activation of HIF-1 by oncogenic signals such as activated AKT. This work summarizes the alterations in mitochondrial respiratory chain proteins that have been identified and their involvement in cancer. Also discussed is the fact that most of the mitochondrial mutations have been found in homoplasmy, indicating a positive selection during tumor evolution, thereby supporting their causal role.

Synthesis and mechanisms of action of novel harmine derivatives as potential antitumor agents

A series of novel harmine derivatives bearing a benzylindine substituent in position-1 of β-carboline ring were synthesized and evaluated as antitumor agents. The N2-benzylated β-carboline derivatives 3a–g represented the most interesting anticancer activities and compound 3c was found to be the most active agent to diverse cancer cell lines such as gastric carcinoma, melanoma and colorectal cancer. Notably, compound 3c showed low toxicity to normal cells. The treatment significantly induced cell apoptosis. Mechanistically, PI3K/AKT signaling pathway mediated compound 3c-induced apoptosis. Compound 3c inhibited phosphorylation of AKT and promoted the production of reactive oxygen species (ROS). The ROS scavenger, LNAC and GSH, could disturb the effect of compound 3c induced apoptosis and PI3K activity inhibitor LY294002 synergistically enhanced compound 3c efficacy. Moreover, the results from nude mice xenograft model showed that compound 3c treatment effectively inhibited tumor growth and decreased tumor weight. Collectively, our results demonstrated that compound 3c exerts apoptotic effect in cancer cells via suppression of phosphorylated AKT and evocation of ROS generation, which suggested that compound 3c might be served as a promising therapeutic agent for cancer treatment.

Excessive Reactive Oxygen Species and Exotic DNA Lesions as an Exploitable Liability

Although the terms "excessive reactive oxygen species (ROS)" and "oxidative stress" are widely used, the implications of oxidative stress are often misunderstood. ROS are not a single species but a variety of compounds, each with unique biochemical properties and abilities to react with biomolecules. ROS cause activation of growth signals through thiol oxidation and may lead to DNA damage at elevated levels. In this review, we first discuss a conceptual framework for the interplay of ROS and antioxidants. This review then describes ROS signaling using FLT3-mediated growth signaling as an example. We then focus on ROS-mediated DNA damage. High concentrations of ROS result in various DNA lesions, including 8-oxo-7,8-dihydro-guanine, oxazolone, DNA-protein cross-links, and hydantoins, that have unique biological impacts. Here we delve into the biochemistry of nine well-characterized DNA lesions. Within each lesion, the types of repair mechanisms, the mutations induced, and their effects on transcription and replication are discussed. Finally, this review will discuss biochemically inspired implications for cancer therapy. Several teams have put forward designs to harness the excessive ROS and the burdened DNA repair systems of tumor cells for treating cancer. We discuss inhibition of the antioxidant system, the targeting of DNA repair, and ROS-activated prodrugs.

Anticancer effect of icaritin inhibits cell growth of colon cancer through reactive oxygen species, Bcl-2 and cyclin D1/E signaling

Icaritin has an advantage in enhancing immunity. Besides, with its anticancer effect, it may be of great help in cancer treatment and recovery of cancer patients. As a result, icaritin is likely to become a novel anticancer drug. However, the anticancer effect of icaritin against colon cancer has not been elucidated thus far. The present study investigated the latent anticancer effect of icaritin on the inhibition of colon cancer cell growth by regulating reactive oxygen species (ROS), B-cell lymphoma (Bcl)-2 and cyclin D1/E signaling. The COLO-205 colon cancer cell line was used as a colon cancer cell model in the present study. First, cell growth and apoptosis were measured to analyze the anticancer effect of icaritin against colon cancer. Next, the possible mechanism of icaritin against colon cancer, including ROS, Bcl-2, cyclin D1, cyclin E and caspase-3/9, was explored. The results revealed that icaritin could inhibit cell growth and induce the apoptosis of COLO-205 cells. In addition, icaritin significantly induced ROS generation, suppressed Bcl-2, cyclin D1 and cyclin E protein expression, and activated caspase-3/9 activity in COLO-205 cells. The present findings demonstrated that icaritin exerted antiproliferative and anticancer effects against colon cancer through the activation of ROS generation and the suppression of Bcl-2, cyclin D1 and cyclin E signaling.

Birth of MTH1 as a therapeutic target for glioblastoma: MTH1 is indispensable for gliomatumorigenesis

Malignant glioma is the most common primary tumor of the central nervous system. Chemotherapy and radiotherapy are the most common therapeutic approaches in glioma therapy. Both processes mainly kill cancer cells through generating high Reactive Oxygen Species (ROS) and lead to oxidative DNA damage. However, tumor resistance to ROS is always a challenge for cancer treatment. Human Mut T homolog 1 (MTH1, also known as NUDT1) is regarded as a protector of nucleotides against oxidization. Recent reports have verified that overexpression of MTH1 could remove oxidized dNTP pools. Here, we find that MTH1 is overexpressed both at mRNA and protein levels in GBM. MTH1 silencing inhibits colony formation; tumor spheres formation and xenograft tumor growth, and more importantly, the viability of glioma cells is significantly decreased in H2O2 after MTH1 was knocked down in glioma. PI staining show that H2O2 cause more glioma cell death after MTH1 silencing. So we speculate that overexpression of MTH1 is crucial for glioma survival, suppression of its expression can inhibit cancer cell survival in vitro and in vivo, MTH1 may be a potential target for human glioma therapy in future.

Preparation of Conjugated Polymer Grafted with H2O2-Sensitive Prodrug for Cell Imaging and Tumor Cell Killing

In this work, a new conjugated polymer poly(fluorene-co-phenylene) derivative containing pendent quaternized chlormethine (PFP-Chl) was synthesized by covalent linking small molecular prodrug groups onto conjugated polymer side chains. H2O2-sensitive prodrug with an eight-member-cyclic boronate ester structure could suffer from H2O2-triggered nitrogen mustard release and further DNA cross-linking and alkylation. PFP-Chl combines therapeutic characteristic with excellent optical property of conjugated polymers. It is found that PFP-Chl could enter into cells by endocytosis to simultaneously exhibit abilities of fluorescent imaging and tumor cell inhibition.

A ROS-Activatable Agent Elicits Homologous Recombination DNA Repair and Synergizes with Pathway Compounds

We designed ROS-activated cytotoxic agents (RACs) that are active against AML cancer cells. In this study, the mechanism of action and synergistic effects against cells coexpressing the AML oncogenes MLL-AF9 fusion and FLT3-ITD were investigated. One RAC (RAC1) had an IC50 value of 1.8±0.3 μm, with ninefold greater selectivity for transformed cells compared to untransformed cells. Treatment induced DNA strand breaks, apoptosis, and cell cycle arrest. Proteomics and transcriptomics revealed enhanced expression of the pentose phosphate pathway, DNA repair, and pathways common to cell stress. Western blotting confirmed repair by homologous recombination. Importantly, RAC1 treatment was synergistic in combination with multiple pathway-targeting therapies in AML cells but less so in untransformed cells. Together, these results demonstrate that RAC1 can selectively target poor prognosis AML and that it does so by creating DNA double-strand breaks that require homologous recombination.

Leinamycin E1 acting as an anticancer prodrug activated by reactive oxygen species

Leinamycin (LNM) is a potent antitumor antibiotic produced by Streptomyces atroolivaceus S-140, featuring an unusual 1,3-dioxo-1,2-dithiolane moiety that is spiro-fused to a thiazole-containing 18-membered lactam ring. Upon reductive activation in the presence of cellular thiols, LNM exerts its antitumor activity by an episulfonium ion-mediated DNA alkylation. Previously, we have cloned the lnm gene cluster from S. atroolivaceus S-140 and characterized the biosynthetic machinery responsible for the 18-membered lactam backbone and the alkyl branch at C3 of LNM. We now report the isolation and characterization of leinamycin E1 (LNM E1) from S. atroolivacues SB3033, a ΔlnmE mutant strain of S. atroolivaceus S-140. Complementary to the reductive activation of LNM by cellular thiols, LNM E1 can be oxidatively activated by cellular reactive oxygen species (ROS) to generate a similar episulfonium ion intermediate, thereby alkylating DNA and leading to eventual cell death. The feasibility of exploiting LNM E1 as an anticancer prodrug activated by ROS was demonstrated in two prostate cancer cell lines, LNCaP and DU-145. Because many cancer cells are under higher cellular oxidative stress with increased levels of ROS than normal cells, these findings support the idea of exploiting ROS as a means to target cancer cells and highlight LNM E1 as a novel lead for the development of anticancer prodrugs activated by ROS. The structure of LNM E1 also reveals critical new insights into LNM biosynthesis, setting the stage to investigate sulfur incorporation, as well as the tailoring steps that convert the nascent hybrid peptide-polyketide biosynthetic intermediate into LNM.

UV-Induced DNA Interstrand Cross-Linking and Direct Strand Breaks from a New Type of Binitroimidazole Analogue

Four novel photoactivated binitroimidazole prodrugs were synthesized. These agents produced DNA interstrand cross-links (ICLs) and direct strand breaks (DSB) upon UV irradiation, whereas no or very few DNA ICLs and DSBs were observed without UV treatment. Although these four molecules (1-4) contain the same binitroimidazole moiety, they bear four different leaving groups, which resulted in their producing different yields of DNA damage. Compound 4, with nitrogen mustard as a leaving group, showed the highest ICL yield. Surprisingly, compounds 1-3, without any alkylating functional group, also induced DNA ICL formation, although they did so with lower yields, which suggested that the binitroimidazole moiety released from UV irradiation of 1-3 is capable of cross-linking DNA. The DNA cross-linked products induced by these compounds were completely destroyed upon 1.0 M piperidine treatment at 90 °C (leading to cleavage at dG sites), which revealed that DNA cross-linking mainly occurred via alkylation of dGs. We proposed a possible mechanism by which alkylating agents were released from these compounds. HRMS and NMR analysis confirmed that free nitrogen mustards were generated by UV irradiation of 4. Suppression of DNA ICL and DSB formation by a radical trap, TEMPO, indicated the involvement of free radicals in the photo reactions of 3 and 4 with DNA. On the basis of these data, we propose that UV irradiation of compounds 1-4 generated a binitroimidazole intermediate that cross-links DNA. The higher ICL yield observed with 4 resulted from the amine effector nitrogen mustard released from UV irradiation.

Design of a hydrogen peroxide-activatable agent that specifically targets cancer cells

Some cancers, like acute myeloid leukemia (AML), use reactive oxygen species to endogenously activate cell proliferation and angiogenic signaling cascades. Thus many cancers display increases in reactive oxygen like hydrogen peroxide concentrations. To translate this finding into a therapeutic strategy we designed new hydrogen peroxide-activated agents with two key molecular pharmacophores. The first pharmacophore is a peroxide-acceptor and the second is a pendant amine. The acceptor is an N-(2,5-dihydroxyphenyl)acetamide susceptible to hydrogen peroxide oxidation. We hypothesized that selectivity between AML and normal cells could be achieved by tuning the pendant amine. Synthesis and testing of fourteen compounds that differed at the pendent amine led to the identification of an agent (14) with 2μM activity against AML cancer cells and an eleven fold-lower activity in healthy CD34+ blood stem cells. Interestingly, analysis shows that upon oxidation the pendant amine cyclizes, ejecting water, with the acceptor to give a bicyclic compound capable of reacting with nucleophiles. Preliminary mechanistic investigations show that AML cells made from addition of two oncogenes (NrasG12D and MLL-AF9) increase the ROS-status, is initially an anti-oxidant as hydrogen peroxide is consumed to activate the pro-drug, and cells respond by upregulating electrophilic defense as visualized by Western blotting of KEAP1. Thus, using this chemical approach we have obtained a simple, potent, and selective ROS-activated anti-AML agent.