New tricks for old drugs: the anticarcinogenic potential of DNA repair inhibitors

Enhanced Chemodynamic Therapy Mediated by a Tumor-Specific Catalyst in Synergy with Mitophagy Inhibition Improves the Efficacy for Endometrial Cancer

Chemodynamic therapy (CDT) relies on the tumor microenvironment (e.g., high H2 O2 level) responsive Fenton-like reactions to produce hydroxyl radicals (·OH) against tumors. However, endogenous H2 O2 is insufficient for effective chemodynamic responses. An NAD(P)H: quinone oxidoreductase 1 (NQO1)high catalase (CAT)low therapeutic window for the use of NQO1 bioactive drug β-lapachone (β-Lap) is first identified in endometrial cancer (EC). Accompanied by NADH depletion, NQO1 catalyzes β-Lap to produce excess H2 O2 and initiate oxidative stress, which selectively suppress NQO1high EC cell proliferation, induce DNA double-strand breaks, and promote apoptosis. Moreover, shRNA-mediated NQO1 knockdown or dicoumarol rescues NQO1high EC cells from β-Lap-induced cytotoxicity. Arginine-glycine-aspartic acid (RGD)-functionalized iron-based metal-organic frameworks (MOF(Fe)) further promote the conversion of the accumulated H2 O2 into highly oxidative ·OH, which in turn, exacerbates the oxidative damage to RGD-positive target cells. Furthermore, mitophagy inhibition by Mdivi-1 blocks a powerful antioxidant defense approach, ultimately ensuring the anti-tumor efficacy of stepwise-amplified reactive oxygen species signals. The tumor growth inhibition rate (TGI) is about 85.92%. However, the TGI of MOF(Fe)-based synergistic antitumor therapy decreases to only 50.46% in NQO1-deficient KLE tumors. Tumor-specific chemotherapy and CDT-triggered therapeutic modality present unprecedented therapeutic benefits in treating NQO1high EC.

Naphthoquinones and derivatives as potential anticancer agents: An updated review

One of the leading global causes of death is cancer; even though several treatment methods have improved survival rates, the incidence and fatality rates remain high. Naphthoquinones are a type of quinone that is found in nature and has vital biological roles. These chemicals have anticancer (antineoplastic), analgesic, anti-inflammatory, antimalarial, antifungal, antiviral, antitrypanosomal, antischistosomal, leishmanicidal, and anti-ulcerative effects. Direct addition of a substituent group to the 1,4-naphthoquinone ring can alter the naphthoquinone's oxidation/reduction and acid/base characteristics, and the activity can be altered. Because of their pharmacological properties, such as anticancer activity and probable therapeutic application, naphthoquinones have greatly interested the scientific community. Some chemicals having a quinone ring in malignant cells have been found to have antiproliferative effects. Naphthoquinones' deadly impact is connected with the inhibition of electron transporters, the uncoupling of oxidative phosphorylation, the creation of ROS, and the formation of protein adducts, notably with -SH enzyme groups. This review article aims to discuss naphthoquinones and their derivatives, which act against cancer and their future perspectives. This review covers several studies highlighting the potent anticancer properties of naphthoquinones. Further, various proposed mechanisms of anticancer actions of naphthoquinones have been summarized in this review.

DNA damage induced by KP372-1 hyperactivates PARP1 and enhances lethality of pancreatic cancer cells with PARP inhibition

The overall prognosis for pancreatic cancer remains dismal and potent chemotherapeutic agents that selectively target this cancer are critically needed. Elevated expression of NAD(P)H:quinone oxidoreductase 1 (NQO1) is frequent in pancreatic cancer, and it offers promising tumor-selective targeting. Recently, KP372-1 was identified as a novel NQO1 redox cycling agent that induces cytotoxicity in cancer cells by creating redox imbalance; however, the mechanistic basis of KP372-1-induced cytotoxicity remains elusive. Here, we show that KP372-1 sensitizes NQO1-expressing pancreatic cancer cells and spares immortalized normal pancreatic duct cells, hTERT-HPNE. Notably, we found that KP372-1 is ~ 10- to 20-fold more potent than β-lapachone, another NQO1 substrate, against pancreatic cancer cells. Mechanistically, our data strongly suggest that reactive oxygen species produced by NQO1-dependent redox cycling of KP372-1 cause robust DNA damage, including DNA breaks. Furthermore, we found that KP372-1-induced DNA damage hyperactivates the central DNA damage sensor protein poly(ADP-ribose) polymerase 1 (PARP1) and activates caspase-3 to initiate cell death. Our data also show that the combination of KP372-1 with PARP inhibition creates enhanced cytotoxicity in pancreatic cancer cells. Collectively, our study provides mechanistic insights into the cytotoxicity instigated by KP372-1 and lays an essential foundation to establish it as a promising chemotherapeutic agent against cancer.

Applications and strategies in nanodiagnosis and nanotherapy in lung cancer

Lung cancer is the second most common cancer and the leading cause of death in both men and women in the world. Lung cancer is heterogeneous in nature and diagnosis is often at an advanced stage as it develops silently in the lung and is frequently associated with high mortality rates. Despite the advances made in understanding the biology of lung cancer, progress in early diagnosis, cancer therapy modalities and considering the mechanisms of drug resistance, the prognosis and outcome still remains low for many patients. Nanotechnology is one of the fastest growing areas of research that can solve many biological problems such as cancer. A growing number of therapies based on using nanoparticles (NPs) have successfully entered the clinic to treat pain, cancer, and infectious diseases. Recent progress in nanotechnology has been encouraging and directed to developing novel nanoparticles that can be one step ahead of the cancer reducing the possibility of multi-drug resistance. Nanomedicine using NPs is continuingly impacting cancer diagnosis and treatment. Chemotherapy is often associated with limited targeting to the tumor, side effects and low solubility that leads to insufficient drug reaching the tumor. Overcoming these drawbacks of chemotherapy by equipping NPs with theranostic capability which is leading to the development of novel strategies. This review provides a synopsis of current progress in theranostic applications for lung cancer diagnosis and therapy using NPs including liposome, polymeric NPs, quantum dots, gold NPs, dendrimers, carbon nanotubes and magnetic NPs.

Phase 1 study of ARQ 761, a β-lapachone analogue that promotes NQO1-mediated programmed cancer cell necrosis

BACKGROUND

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a two-electron oxidoreductase expressed in multiple tumour types. ARQ 761 is a β-lapachone (β-lap) analogue that exploits the unique elevation of NQO1 found in solid tumours to cause tumour-specific cell death.

METHODS

We performed a 3+3 dose escalation study of 3 schedules (weekly, every other week, 2/3 weeks) of ARQ 761 in patients with refractory advanced solid tumours. Tumour tissue was analysed for NQO1 expression. After 20 patients were analysed, enrolment was restricted to patients with NQO1-high tumours (H-score ≥ 200).

RESULTS

A total of 42 patients were treated. Median number of prior lines of therapy was 4. Maximum tolerated dose was 390 mg/m² as a 2-h infusion every other week. Dose-limiting toxicity was anaemia. The most common treatment-related adverse events were anaemia (79%), fatigue (45%), hypoxia (33%), nausea (17%), and vomiting (17%). Transient grade 3 hypoxia, reflecting possible methemoglobinaemia, occurred in 26% of patients. Among 32 evaluable patients, best response was stable disease (n = 12); 6 patients had tumour shrinkage. There was a trend towards improved efficacy in NQO1-high tumours (P = 0.06).

CONCLUSIONS

ARQ 761 has modest single-agent activity, which appears associated with tumour NQO1 expression. Principal toxicities include anaemia and possible methemoglobinaemia.

Intermolecular Interactions between Coencapsulated Drugs Inhibit Drug Crystallization and Enhance Colloidal Stability of Polymeric Micelles

Novel "pairs" of drugs possessing pharmacological synergies could be encapsulated into polymeric micelles and exert superb therapeutic effects in vivo upon intravenous administration, with the prerequisite that the micelles remain stable. NADP(H) quinone oxidoreductase 1 (NQO1) inhibitors, such as β-lapachone (LPC) and tanshinone IIA (THA), are structurally and pharmacologically similar molecules that are poorly water-soluble, crystallize extremely fast, and demonstrate synergistic anticancer effect when used together with paclitaxel (PTX). However, when coencapsulated with PTX in poly(ethylene glycol)-b-poly(d,l-lactic acid) (PEG-PLA) micelles, only PTX/LPC but not the PTX/THA pair yields satisfactory colloidal stability. To reveal the molecular mechanism contributing to the colloidal stability of the coencapsulated micelles, we investigated the molecular interactions of PTX/LPC and PTX/THA, through both experimental methods (crystallization kinetics, ¹³C NMR) and molecular dynamic simulation. We observed that PTX was capable of inhibiting LPC but not THA crystallization both in an aqueous environment and in the solid state, which could be attributed to the strong hetero-intermolecular interactions (π-π, H-bonding) between LPC and PTX, which disrupted the homo-intermolecular interactions between LPC molecules and thus formed a favorable miscible binary system. In comparison, the lack of a strong PTX/THA interaction left the strong THA/THA stacking interaction undisturbed and the fast THA crystallization tendency unrestrained. We conclude that the intermolecular interactions, i.e., the "pharmaceutical synergy", between the coencapsulated drugs critically control the colloidal stability of polymeric micelles and, therefore, should be evaluated when coencapsulated drug delivery systems are designed for optimal therapeutic benefits.

Using a novel NQO1 bioactivatable drug, beta-lapachone (ARQ761), to enhance chemotherapeutic effects by metabolic modulation in pancreatic cancer

Novel, tumor-selective therapies are needed to increase the survival rate of pancreatic cancer patients. K-Ras-mutant-driven NAD(P)H:quinone oxidoreductase 1 (NQO1) is over-expressed in pancreatic tumor versus associated normal tissue, while catalase expression is lowered compared to levels in associated normal pancreas tissue. ARQ761 undergoes a robust, futile redox cycle in NQO1+ cancer cells, producing massive hydrogen peroxide (H2 O2 ) levels; normal tissues are spared by low NQO1 and high catalase expression. DNA damage created by ARQ761 in pancreatic cancer cells "hyperactivates" PARP1, causing metabolic catastrophe and NAD ± keresis cell death. NQO1: catalase levels (high in tumor, low in normal tissue) are an attractive therapeutic window to treat pancreatic cancer. Based on a growing body of literature, we are leading a clinical trial to evaluate the combination of ARQ761 and chemotherapy in patients with pancreatic cancer.

The value of pyrans as anticancer scaffolds in medicinal chemistry

Pyran-based heterocycles are promising for anticancer drug discovery.

A comprehensive look of poly(ADP-ribose) polymerase inhibition strategies and future directions for cancer therapy

The finding of promising drugs represents a huge challenge in cancer therapeutics, therefore it is important to seek out novel approaches and elucidate essential cellular processes in order to identify potential drug targets. Studies on DNA repair pathway suggested that an enzyme, PARP, which plays a significant role in DNA repair responses, could be targeted in cancer therapy. Hence, the efficacy of PARP inhibitors in cancer therapy has been investigated and has progressed from the laboratory to clinics, with olaparib having already been approved by the US FDA for ovarian cancer treatment. Here, we have discussed the development of PARP inhibitors, strategies to improve their selectivity and efficacy, including innovative combinational and synthetic lethality approaches to identify effective PARP inhibitors in cancer treatment.

β-Lapachone and Paclitaxel Combination Micelles with Improved Drug Encapsulation and Therapeutic Synergy as Novel Nanotherapeutics for NQO1-Targeted Cancer Therapy

β-Lapachone (LPC) is a novel cytotoxic agent that is bioactivated by NADP(H): quinone oxidoreductase 1 (NQO1), an enzyme elevated in a variety of tumors, such as non-small cell lung cancer (NSCLC), pancreatic cancer, liver cancer, and breast cancer. Despite its unique mechanism of action, its clinical evaluation has been largely hindered by low water solubility, short blood half-life, and narrow therapeutic window. Although encapsulation into poly(ethylene glycol)-b-poly(D,L-lactic acid) (PEG-PLA) micelles could modestly improve its solubility and prolong its half-life, the extremely fast intrinsic crystallization tendency of LPC prevents drug loading higher than ∼2 wt %. The physical stability of the LPC-loaded micelles is also far from satisfactory for further development. In this study, we demonstrate that paclitaxel (PTX), a front-line drug for many cancers, can provide two functions when coencapsulated together with LPC in the PEG-PLA micelles; first, as a strong crystallization inhibitor for LPC, thus to significantly increase the LPC encapsulation efficiency in the micelle from 11.7 ± 2.4% to 100.7 ± 2.2%. The total drug loading efficiency of both PTX and LPC in the combination polymeric micelle reached 100.3 ± 3.0%, and the drug loading density reached 33.2 ± 1.0%. Second, the combination of LPC/PTX demonstrates strong synergistic cytotoxicity effect against the NQO1 overexpressing cancer cells, including A549 NSCLC cells, and several pancreatic cancer cells (combination index <1). In vitro drug release study showed that LPC was released faster than PTX either in phosphate-buffered saline (PH = 7.4) or in 1 M sodium salicylate, which agrees with the desired dosing sequence of the two drugs to exert synergistic pharmacologic effect at different cell checkpoints. The PEG-PLA micelles coloaded with LPC and PTX offer a novel nanotherapeutic, with high drug loading, sufficient physical stability, and biological synergy to increase drug delivery efficiency and optimize the therapeutic window for NOQ1-targeted therapy of cancer.

NAMPT inhibition sensitizes pancreatic adenocarcinoma cells to tumor-selective, PAR-independent metabolic catastrophe and cell death induced by β-lapachone

Nicotinamide phosphoribosyltransferase (NAMPT) inhibitors (e.g., FK866) target the most active pathway of NAD(+) synthesis in tumor cells, but lack tumor-selectivity for use as a single agent. Reducing NAD(+) pools by inhibiting NAMPT primed pancreatic ductal adenocarcinoma (PDA) cells for poly(ADP ribose) polymerase (PARP1)-dependent cell death induced by the targeted cancer therapeutic, β-lapachone (β-lap, ARQ761), independent of poly(ADP ribose) (PAR) accumulation. β-Lap is bioactivated by NADPH:quinone oxidoreductase 1 (NQO1) in a futile redox cycle that consumes oxygen and generates high levels of reactive oxygen species (ROS) that cause extensive DNA damage and rapid PARP1-mediated NAD(+) consumption. Synergy with FK866+β-lap was tumor-selective, only occurring in NQO1-overexpressing cancer cells, which is noted in a majority (∼85%) of PDA cases. This treatment strategy simultaneously decreases NAD(+) synthesis while increasing NAD(+) consumption, reducing required doses and treatment times for both drugs and increasing potency. These complementary mechanisms caused profound NAD(P)(+) depletion and inhibited glycolysis, driving down adenosine triphosphate levels and preventing recovery normally observed with either agent alone. Cancer cells died through an ROS-induced, μ-calpain-mediated programmed cell death process that kills independent of caspase activation and is not driven by PAR accumulation, which we call NAD(+)-Keresis. Non-overlapping specificities of FK866 for PDA tumors that rely heavily on NAMPT-catalyzed NAD(+) synthesis and β-lap for cancer cells with elevated NQO1 levels affords high tumor-selectivity. The concept of reducing NAD(+) pools in cancer cells to sensitize them to ROS-mediated cell death by β-lap is a novel strategy with potential application for pancreatic and other types of NQO1+ solid tumors.

Investigation on the electrochemistry and cytotoxicity of the natural product marcanine A and its synthetic derivatives

The electrochemistry and cytotoxicity of marcanine A were investigated by electrochemical, computational and cellular studies.

Tumor-selective, futile redox cycle-induced bystander effects elicited by NQO1 bioactivatable radiosensitizing drugs in triple-negative breast cancers

AIMS

β-Lapachone (β-lap), a novel radiosensitizer with potent antitumor efficacy alone, selectively kills solid cancers that over-express

NAD(P)H

quinone oxidoreductase 1 (NQO1). Since breast or other solid cancers have heterogeneous NQO1 expression, therapies that reduce the resistance (e.g., NQO1(low)) of tumor cells will have significant clinical advantages. We tested whether NQO1-proficient (NQO1(+)) cells generated sufficient hydrogen peroxide (H2O2) after β-lap treatment to elicit bystander effects, DNA damage, and cell death in neighboring NQO1(low) cells.

RESULTS

β-Lap showed NQO1-dependent efficacy against two triple-negative breast cancer (TNBC) xenografts. NQO1 expression variations in human breast cancer patient samples were noted, where ~60% cancers over-expressed NQO1, with little or no expression in associated normal tissue. Differential DNA damage and lethality were noted in NQO1(+) versus NQO1-deficient (NQO1(-)) TNBC cells and xenografts after β-lap treatment. β-Lap-treated NQO1(+) cells died by programmed necrosis, whereas co-cultured NQO1(-) TNBC cells exhibited DNA damage and caspase-dependent apoptosis. NQO1 inhibition (dicoumarol) or H2O2 scavenging (catalase [CAT]) blocked all responses. Only NQO1(-) cells neighboring NQO1(+) TNBC cells responded to β-lap in vitro, and bystander effects correlated well with H2O2 diffusion. Bystander effects in NQO1(-) cells in vivo within mixed 50:50 co-cultured xenografts were dramatic and depended on NQO1(+) cells. However, normal human cells in vitro or in vivo did not show bystander effects, due to elevated endogenous CAT levels. Innovation and Conclusions: NQO1-dependent bystander effects elicited by NQO1 bioactivatable drugs (β-lap or deoxynyboquinone [DNQ]) likely contribute to their efficacies, killing NQO1(+) solid cancer cells and eliminating surrounding heterogeneous NQO1(low) cancer cells. Normal cells/tissue are protected by low NQO1:CAT ratios.

Photophysics and photochemistry of the β-lapachone derived diphenyldihydrodioxin: generation and characterization of its cation radical

The cation radical derived from β-lapachone diphenyldihydrodioxin can be thermally or photochemically generated.

Dissimilar effects of β-lapachone- and hydroxyurea-induced DNA replication stress in root meristem cells of Allium cepa

Two anticancer drugs, β-lapachone (β-lap, a naphthoquinone) and hydroxyurea (HU, an inhibitor of ribonucleotide reductase), differently affect nuclear morphology and cell cycle control mechanisms in root meristem cells of Allium cepa. The 18 h treatment with 100 μM β-lap results in a lowered number of M-phase cells, increased occurrence of mitotic abnormalities, including over-condensation of chromosomes, their enhanced stickiness, formation of anaphase bridges, micronucleation and reduced mitotic spindles. Following prolonged incubations using high doses of β-lap, cell nuclei reveal dark-red fluorescence evenly distributed in chromatin surrounding the unstained regions of nucleoli. Both drugs generate H2O2 and induce DNA double strand breaks, which is correlated with γ-phoshorylation of H2AX histones. However, the extent of H2AX phosphorylation (including the frequency of γ-H2AX foci and the relative number cells creating phospho-H2AX domains) is considerably reduced in root meristem cells treated jointly with the β-lap/HU mixture. Furthermore, various effects of caffeine (an inhibitor of ATM/ATR cell cycle checkpoint kinases) on β-lap- and HU-induced γ-phoshorylation of H2AX histones and the protective activity of HU against β-lap suggest that their genotoxic activities are largely dissimilar. β-Lap treatment results in the induction of apoptosis-like programmed cell death, while HU treatment leads to cell adaptation to replication stress and promotion of abnormal nuclear divisions with biphasic interphase/mitotic states of chromatin condensation.

β-Lapachone alleviates alcoholic fatty liver disease in rats

Alcohol-induced liver injury is the most common liver disease in which fatty acid metabolism is altered. It is thought that altered NAD(+)/NADH redox potential by alcohol in the liver causes fatty liver by inhibiting fatty acid oxidation and the activity of tricarboxylic acid cycle reactions. β-Lapachone (βL), a naturally occurring quinone, has been shown to stimulate fatty acid oxidation in an obese mouse model by activating adenosine monophosphate-activated protein kinase (AMPK). In this report, we clearly show that βL reduced alcohol-induced hepatic steatosis and induced fatty acid oxidizing capacity in ethanol-fed rats. βL treatment markedly decreased hepatic lipids while serum levels of lipids and lipoproteins were increased in rats fed ethanol-containing liquid diets with βL administration. Furthermore, inhibition of lipolysis, enhancement of lipid mobilization to mitochondria and upregulation of mitochondrial β-oxidation activity in the soleus muscle were observed in ethanol/βL-treated animals compared to the ethanol-fed rats. In addition, the activity of alcohol dehydrogenase, but not aldehyde dehydrogenase, was significantly increased in rats fed βL diets. βL-mediated modulation of NAD(+)/NADH ratio led to the activation of AMPK signaling in these animals.

CONCLUSION

Our results suggest that improvement of fatty liver by βL administration is mediated by the upregulation of apoB100 synthesis and lipid mobilization from the liver as well as the direct involvement of βL on NAD(+)/NADH ratio changes, resulting in the activation of AMPK signaling and PPARα-mediated β-oxidation. Therefore, βL-mediated alteration of NAD(+)/NADH redox potential may be of potential therapeutic benefit in the clinical setting.

Catalase abrogates β-lapachone-induced PARP1 hyperactivation-directed programmed necrosis in NQO1-positive breast cancers

Improving patient outcome by personalized therapy involves a thorough understanding of an agent's mechanism of action. β-Lapachone (clinical forms, Arq501/Arq761) has been developed to exploit dramatic cancer-specific elevations in the phase II detoxifying enzyme NAD(P)H:quinone oxidoreductase (NQO1). NQO1 is dramatically elevated in solid cancers, including primary and metastatic [e.g., triple-negative (ER-, PR-, Her2/Neu-)] breast cancers. To define cellular factors that influence the efficacy of β-lapachone using knowledge of its mechanism of action, we confirmed that NQO1 was required for lethality and mediated a futile redox cycle where ∼120 moles of superoxide were formed per mole of β-lapachone in 2 minutes. β-Lapachone induced reactive oxygen species (ROS), stimulated DNA single-strand break-dependent poly(ADP-ribose) polymerase-1 (PARP1) hyperactivation, caused dramatic loss of essential nucleotides (NAD(+)/ATP), and elicited programmed necrosis in breast cancer cells. Although PARP1 hyperactivation and NQO1 expression were major determinants of β-lapachone-induced lethality, alterations in catalase expression, including treatment with exogenous enzyme, caused marked cytoprotection. Thus, catalase is an important resistance factor and highlights H2O2 as an obligate ROS for cell death from this agent. Exogenous superoxide dismutase enhanced catalase-induced cytoprotection. β-Lapachone-induced cell death included apoptosis-inducing factor (AIF) translocation from mitochondria to nuclei, TUNEL+ staining, atypical PARP1 cleavage, and glyceraldehyde 3-phosphate dehydrogenase S-nitrosylation, which were abrogated by catalase. We predict that the ratio of NQO1:catalase activities in breast cancer versus associated normal tissue are likely to be the major determinants affecting the therapeutic window of β-lapachone and other NQO1 bioactivatable drugs.

Peroxiredoxin 1 knockdown potentiates β-lapachone cytotoxicity through modulation of reactive oxygen species and mitogen-activated protein kinase signals

Peroxiredoxin (Prx) 1 is a member of the thiol-specific peroxidases family and plays diverse roles such as H2O2 scavenger, redox signal transducer and molecular chaperone. Prx1 has been reported to be involved in protecting cancer cells against various therapeutic challenges. We investigated how modulations of intracellular redox system affect cancer cell sensitivity to reactive oxygen species (ROS)-generating drugs. We observed that stable and transient Prx1 knockdown significantly enhanced HeLa cell sensitivity to β-lapachone (β-lap), a potential anticancer agent. Prx1 knockdown markedly potentiated 2 µM β-lap-induced cytotoxicity through ROS accumulation. This effect was largely NAD(P)H:quinone oxidoreductase 1 dependent and associated with a decrease in poly(ADP-ribose) polymerase 1 protein levels, phosphorylation of JNK, p38 and Erk proteins in mitogen-activated protein kinase (MAPK) pathways and a decrease in thioredoxin 1 (Trx1) protein levels. Trx1 serves as an electron donor for Prx1 and is overexpressed in Prx1 knockdown cells. Based on the fact that Prx1 is a major ROS scavenger and a partner of at least ASK1 and JNK, two key components of MAPK pathways, we propose that Prx1 knockdown-induced sensitization to β-lap is achieved through combined action of accumulation of ROS and enhancement of MAPK pathway activation, leading to cell apoptosis. These data support the view that modulation of intracellular redox state could be an alternative approach to enhance cancer cell sensitivity to ROS-generating drugs or to overcome some types of drug resistance.

Structural simplification of bioactive natural products with multicomponent synthesis. 4. 4H-pyrano-[2,3-b]naphthoquinones with anticancer activity

4H-Pyrano-[2,3-b]naphthoquinone is a structural motif commonly found in natural products manifesting anticancer activities. As part of a program aimed at structural simplification of bioactive natural products utilizing multicomponent synthetic processes, we developed a compound library based on this heterocyclic scaffold. We found that several library members displayed low micromolar antiproliferative activity and induced apoptosis in human cancer cells. Selected compounds showed promising activity against cancer cell lines resistant to proapoptotic stimuli, demonstrating their potential in treating cancers with dismal prognoses.

The effects of resveratrol and selected metabolites on the radiation and antioxidant response

Excess reactive oxygen species (ROS) generated from ionizing radiation (IR) or endogenous sources like cellular respiration and inflammation produce cytotoxic effects that can lead to carcinogenesis. Resveratrol (RSV), a polyphenol with antioxidant and anticarcinogenic capabilities, has shown promise as a potential radiation modifier. The present study focuses on examining the effects of RSV or RSV metabolites as a radiation modifier in normal tissue. RSV or a RSV metabolite, piceatannol (PIC) did not protect human lung fibroblasts (1522) from the radiation-induced cell killing. Likewise, neither RSV nor PIC afforded protection against lethal total body IR in C3H mice. Additional research has shown protection in cells against hydrogen peroxide when treated with RSV. Therefore, clonogenic survival was measured in 1522 cells with RSV and RSV metabolites. Only the RSV derivative, piceatannol (PIC), showed protection against hydrogen peroxide mediated cytotoxicity; whereas, RSV enhanced hydrogen peroxide sensitivity at a 50 µM concentration; the remaining metabolites evaluated had little to no effect on survival. PIC also showed enhancement to peroxide exposure at a higher concentration (150 µM). A potential mechanism for RSV-induced sensitivity to peroxides could be its ability to block 1522 cells in the S-phase, which is most sensitive to hydrogen peroxide treatment. In addition, both RSV and PIC can be oxidized to phenoxyl radicals and quinones, which may exert cytotoxic effects. These cytotoxic effects were abolished when HBED, a metal chelator, was added. Taken together RSV and many of its metabolic derivatives are not effective as chemical radioprotectors and should not be considered for clinical use.

Photosensitization Mechanisms of Triplet Excited State β-Lapachone. A Density Functional Theory Study

β-Lapachone is a natural product with multiple pharmacological activities and mechanistic studies indicated that reactive oxygen species (ROS) generated by β-lapachone play significant roles in its pharmacological actions. As photosensitization is an important ROS-generating pathway, in the present work, the photosensitization mechanisms of β-lapachone are explored on the basis of density functional theory estimated triplet excited state characters. Starting from triplet excited state β-lapachone, the possible generating pathways of 1O2 and O2·– are elucidated and the solvent effects on the photosensitizing reactions are also discussed.

The small GTPase RhoA localizes to the nucleus and is activated by Net1 and DNA damage signals

Background

Rho GTPases control many cellular processes, including cell survival, gene expression and migration. Rho proteins reside mainly in the cytosol and are targeted to the plasma membrane (PM) upon specific activation by guanine nucleotide exchange factors (GEFs). Accordingly, most GEFs are also cytosolic or associated with the PM. However, Net1, a RhoA-specific GEF predominantly localizes to the cell nucleus at steady-state. Nuclear localization for Net1 has been seen as a mechanism for sequestering the GEF away from RhoA, effectively rendering the protein inactive. However, considering the prominence of nuclear Net1 and the fact that a biological stimulus that promotes Net1 translocation out the nucleus to the cytosol has yet to be discovered, we hypothesized that Net1 might have a previously unidentified function in the nucleus of cells.

Principal Findings

Using an affinity precipitation method to pulldown the active form of Rho GEFs from different cellular fractions, we show here that nuclear Net1 does in fact exist in an active form, contrary to previous expectations. We further demonstrate that a fraction of RhoA resides in the nucleus, and can also be found in a GTP-bound active form and that Net1 plays a role in the activation of nuclear RhoA. In addition, we show that ionizing radiation (IR) specifically promotes the activation of the nuclear pool of RhoA in a Net1-dependent manner, while the cytoplasmic activity remains unchanged. Surprisingly, irradiating isolated nuclei alone also increases nuclear RhoA activity via Net1, suggesting that all the signals required for IR-induced nuclear RhoA signaling are contained within the nucleus.

Conclusions/Significance

These results demonstrate the existence of a functional Net1/RhoA signaling pathway within the nucleus of the cell and implicate them in the DNA damage response.

Breast cancer stem cells: treatment resistance and therapeutic opportunities

The clinical and pathologic heterogeneity of human breast cancer has long been recognized. Now, molecular profiling has enriched our understanding of breast cancer heterogeneity and yielded new prognostic and predictive information. Despite recent therapeutic advances, including the HER2-specific agent, trastuzumab, locoregional and systemic disease recurrence remain an ever-present threat to the health and well being of breast cancer survivors. By definition, disease recurrence originates from residual treatment-resistant cells, which regenerate at least the initial breast cancer phenotype. The discovery of the normal breast stem cell has re-ignited interest in the identity and properties of breast cancer stem-like cells and the relationship of these cells to the repopulating ability of treatment-resistant cells. The cancer stem cell model of breast cancer development contrasts with the clonal evolution model, whereas the mixed model draws on features of both. Although the origin and identity of breast cancer stem-like cells is contentious, treatment-resistant cells survive and propagate only because aberrant and potentially druggable signaling pathways are recruited. As a means to increase the rates of breast cancer cure, several approaches to specific targeting of the treatment-resistant cell population exist and include methods for addressing the problem of radioresistance in particular.

Prostate cancer radiosensitization through poly(ADP-Ribose) polymerase-1 hyperactivation

The clinical experimental agent, β-lapachone (β-lap; Arq 501), can act as a potent radiosensitizer in vitro through an unknown mechanism. In this study, we analyzed the mechanism to determine whether β-lap may warrant clinical evaluation as a radiosensitizer. β-Lap killed prostate cancer cells by NAD(P)H:quinone oxidoreductase 1 (NQO1) metabolic bioactivation, triggering a massive induction of reactive oxygen species, irreversible DNA single-strand breaks (SSB), poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation, NAD(+)/ATP depletion, and μ-calpain-induced programmed necrosis. In combination with ionizing radiation (IR), β-lap radiosensitized NQO1(+) prostate cancer cells under conditions where nontoxic doses of either agent alone achieved threshold levels of SSBs required for hyperactivation of PARP-1. Combination therapy significantly elevated SSB level, γ-H2AX foci formation, and poly(ADP-ribosylation) of PARP-1, which were associated with ATP loss and induction of μ-calpain-induced programmed cell death. Radiosensitization by β-lap was blocked by the NQO1 inhibitor dicoumarol or the PARP-1 inhibitor DPQ. In a mouse xenograft model of prostate cancer, β-lap synergized with IR to promote antitumor efficacy. NQO1 levels were elevated in ∼60% of human prostate tumors evaluated relative to adjacent normal tissue, where β-lap might be efficacious alone or in combination with radiation. Our findings offer a rationale for the clinical utilization of β-lap (Arq 501) as a radiosensitizer in prostate cancers that overexpress NQO1, offering a potentially synergistic targeting strategy to exploit PARP-1 hyperactivation.

Differential oxidative stress gene expression profile in mouse brain after proton exposure

Radiation is known to potentially interfere with cellular functions at all levels of cell organization. The radiation-induced stress response is very complex and involves altered expression of many genes. Identification of specific genes may allow the determination of pathways important in radiation responses. Although several radiation-related research have been studied extensively, the molecular and cellular processes affected by proton exposure remain poorly understood. Our earlier reports have shown that proton radiation induces reactive oxygen species (ROS) formation and lipid peroxidation and inhibits antioxidants, superoxide dismutase, and glutathione. Therefore, in this present study, we used quantitative real-time reverse transcription polymerase chain reaction approach and showed the modulation of several genes including oxidative stress, antioxidants defense mechanism, ROS metabolism, and oxygen transporters related genes expression in 2-Gy proton-exposed mouse brain. Literature evidences suggest that change in oxidants and antioxidants levels induce DNA damage, followed by cell death. In conclusion, changes in the gene profile of mouse brain after proton irradiation are complex and the exposed cells might undergo programmed cell death through alteration of genes responsible for oxidative stress signaling mechanism.

Beta-lapachone micellar nanotherapeutics for non-small cell lung cancer therapy

Lung cancer is the leading cause of cancer-related deaths with current chemotherapies lacking adequate specificity and efficacy. Beta-lapachone (beta-lap) is a novel anticancer drug that is bioactivated by NAD(P)H:quinone oxidoreductase 1, an enzyme found specifically overexpressed in non-small cell lung cancer (NSCLC). Herein, we report a nanotherapeutic strategy that targets NSCLC tumors in two ways: (a) pharmacodynamically through the use of a bioactivatable agent, beta-lap, and (b) pharmacokinetically by using a biocompatible nanocarrier, polymeric micelles, to achieve drug stability, bioavailability, and targeted delivery. Beta-lap micelles produced by a film sonication technique were small ( approximately 30 nm), displayed core-shell architecture, and possessed favorable release kinetics. Pharmacokinetic analyses in mice bearing subcutaneous A549 lung tumors showed prolonged blood circulation (t(1/2), approximately 28 h) and increased accumulation in tumors. Antitumor efficacy analyses in mice bearing subcutaneous A549 lung tumors and orthotopic Lewis lung carcinoma models showed significant tumor growth delay and increased survival. In summary, we have established a clinically viable beta-lap nanomedicine platform with enhanced safety, pharmacokinetics, and antitumor efficacy for the specific treatment of NSCLC tumors.

The trypanocidal activity of naphthoquinones: a review

Naphthoquinones are compounds present in several families of higher plants. Their molecular structures confer redox properties, and they are involved in multiple biological oxidative processes. In folk medicine, especially among Indian populations, plants containing naphthoquinones have been employed for the treatment of various diseases. The biological redox cycle of quinones can be initiated by one electron reduction leading to the formation of semiquinones, unstable intermediates that react rapidly with molecular oxygen, generating free radicals. Alternatively, the reduction by two electrons, mediated by DT-diphorase, leads to the formation of hydroquinone. Lapachol, alpha-lapachone and beta-lapachone, which are isolated from the heartwood of trees of the Bignoniaceae family, are examples of bioactive naphthoquinones. In this review, we will discuss studies investigating the activity of these natural products and their derivatives in the context of the search for alternative drugs for Chagas disease, caused by Trypanosoma cruzi, a neglected illness that is endemic in Latin America.

Jacaranda--an ethnopharmacological and phytochemical review

The genus Jacaranda, an important representative of the tribe Tecomeae in the family Bignoniaceae, is interesting from both biological and chemical perspectives. In this review, a contemporary summary of biological and pharmacological research on Jacaranda species will be presented and critically evaluated. Significant findings in the treatment of protozoa-caused diseases as well as of skin illnesses have been presented in ethnobotanical reports and recent studies were performed on crude extracts for certain Jacaranda species. Jacaranone, the most important constituent isolated is known to possess anti-cancer activity. Recently, high cutaneous toxicity together with moderate activity against leishmaniasis was described. Very few additional data are available on the biological activities and cytotoxicity of pure compounds from Jacaranda. Thirteen of the forty-nine distinguished species of Jacaranda have been reported in scientific literature as ethnobotanically used or phytochemically investigated. However, information about a chemical profile is available only for six species. The following article gives a critical assessment of the literature to date and aims to show that the pharmaceutical potential of this genus has been underestimated and deserves closer attention.

DNA damage-induced cell death: lessons from the central nervous system

DNA damage can, but does not always, induce cell death. While several pathways linking DNA damage signals to mitochondria-dependent and -independent death machineries have been elucidated, the connectivity of these pathways is subject to regulation by multiple other factors that are not well understood. We have proposed two conceptual models to explain the delayed and variable cell death response to DNA damage: integrative surveillance versus autonomous pathways. In this review, we discuss how these two models may explain the in vivo regulation of cell death induced by ionizing radiation (IR) in the developing central nervous system, where the death response is regulated by radiation dose, cell cycle status and neuronal development.

Nonhomologous end joining is essential for cellular resistance to the novel antitumor agent, beta-lapachone

Commonly used antitumor agents, such as DNA topoisomerase I/II poisons, kill cancer cells by creating nonrepairable DNA double-strand breaks (DSBs). To repair DSBs, error-free homologous recombination (HR), and/or error-prone nonhomologous end joining (NHEJ) are activated. These processes involve the phosphatidylinositol 3'-kinase-related kinase family of serine/threonine enzymes: ataxia telangiectasia mutated (ATM), ATM- and Rad3-related for HR, and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) for NHEJ. Alterations in these repair processes can cause drug/radiation resistance and increased genomic instability. beta-Lapachone (beta-lap; also known as ARQ 501), currently in phase II clinical trials for the treatment of pancreatic cancer, causes a novel caspase- and p53-independent cell death in cancer cells overexpressing NAD(P)H:quinone oxidoreductase-1 (NQO1). NQO1 catalyzes a futile oxidoreduction of beta-lap leading to reactive oxygen species generation, DNA breaks, gamma-H2AX foci formation, and hyperactivation of poly(ADP-ribose) polymerase-1, which is required for cell death. Here, we report that beta-lap exposure results in NQO1-dependent activation of the MRE11-Rad50-Nbs-1 complex. In addition, ATM serine 1981, DNA-PKcs threonine 2609, and Chk1 serine 345 phosphorylation were noted; indicative of simultaneous HR and NHEJ activation. However, inhibition of NHEJ, but not HR, by genetic or chemical means potentiated beta-lap lethality. These studies give insight into the mechanism by which beta-lap radiosensitizes cancer cells and suggest that NHEJ is a potent target for enhancing the therapeutic efficacy of beta-lap alone or in combination with other agents in cancer cells that express elevated NQO1 levels.

An NQO1- and PARP-1-mediated cell death pathway induced in non-small-cell lung cancer cells by beta-lapachone

Lung cancer is the number one cause of cancer-related deaths in the world. Patients treated with current chemotherapies for non-small-cell lung cancers (NSCLCs) have a survival rate of approximately 15% after 5 years. Novel approaches are needed to treat this disease. We show elevated NAD(P)H:quinone oxidoreductase-1 (NQO1) levels in tumors from NSCLC patients. beta-Lapachone, an effective chemotherapeutic and radiosensitizing agent, selectively killed NSCLC cells that expressed high levels of NQO1. Isogenic H596 NSCLC cells that lacked or expressed NQO1 along with A549 NSCLC cells treated with or without dicoumarol, were used to elucidate the mechanism of action and optimal therapeutic window of beta-lapachone. NSCLC cells were killed in an NQO1-dependent manner by beta-lapachone (LD50, approximately 4 microM) with a minimum 2-h exposure. Kinetically, beta-lapachone-induced cell death was characterized by the following: (i) dramatic reactive oxygen species (ROS) formation, eliciting extensive DNA damage; (ii) hyperactivation of poly(ADP-ribose)polymerase-1 (PARP-1); (iii) depletion of NAD+/ATP levels; and (iv) proteolytic cleavage of p53/PARP-1, indicating mu-calpain activation and apoptosis. Beta-lapachone-induced PARP-1 hyperactivation, nucleotide depletion, and apoptosis were blocked by 3-aminobenzamide, a PARP-1 inhibitor, and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), a Ca2+ chelator. NQO1- cells (H596, IMR-90) or dicoumarol-exposed NQO1+ A549 cells were resistant (LD50, >40 microM) to ROS formation and all cytotoxic effects of beta-lapachone. Our data indicate that the most efficacious strategy using beta-lapachone in chemotherapy was to deliver the drug in short pulses, greatly reducing cytotoxicity to NQO1- "normal" cells. beta-Lapachone killed cells in a tumorselective manner and is indicated for use against NQO1+ NSCLC cancers.

DNA repair inhibitors in cancer treatment

Chemotherapy and radiation are two important modalities for cancer treatment. Many agents in clinical used have the ability to induce DNA damage, however they may be highly cytotoxic as a secondary effect. Different mechanisms are involved both, in detection and repair of DNA damage. The modulation of these pathways, has a great impact on clinical outcome and is frequently responsible of therapeutic resistance. Therefore, pharmacological inhibition of DNA damage repair pathways has been explored as a useful strategy to enhance chemo and radiosensitivity, thus it could be used for reversing drug resistance. Different agents have shown excellent results in preclinical studies in combination with radiation or chemotherapy. Early phase clinical trials are now being carried out using different DNA repair inhibitors targeting several enzymes such as PARP, DNA-PK or MGMT.