Synthesis, mechanistic studies, and anti-proliferative activity of glutathione/glutathione S-transferase-activated nitric oxide prodrugs

An overview of phenylsulfonylfuroxan-based nitric oxide donors for cancer treatment

Nitric oxide (NO) is a gaseous molecule integral to numerous physiological processes, including tumor modulation, cardiovascular regulation, and systemic physiological functions. Its dual role in promoting and inhibiting tumor growth makes it a focal point of contemporary oncological research. Phenylsulfonylfuroxan, a classical NO donor, has been shown to significantly elevate NO levels, thereby inducing apoptosis and inhibiting proliferation and metastasis in tumor cells. It enhances the efficacy of chemotherapy, radiotherapy, and immunotherapy, reverses multidrug resistance (MDR), and impedes tumor progression. Notably, phenylsulfonylfuroxan have the ability to trigger ferroptosis in cancer cells by binding covalently to inhibit glutathione peroxidase 4 (GPX4). Recent developments in phenylsulfonylfuroxan-based therapies have positioned them as crucial in the advancement of cancer treatment modalities. This review elucidates the mechanism by which phenylsulfonylfuroxan releases NO and summarizes the significant advancements over the past 16 years in the research and development of phenylsulfonylfuroxan conjugates with various anticancer agents for targeted cancer therapy.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

Role of human glutathione transferases in biotransformation of the nitric oxide prodrug JS-K

Nitric oxide (NO) plays a prominent physiological role as a low-molecular-mass signal molecule involved in diverse biological functions. Great attention has been directed to pharmacologically modulating the release of NO for various therapeutic applications. We have focused on O2-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) as an example of diazeniumdiolate prodrugs with potential for cancer chemotherapy. JS-K is reportedly activated by glutathione conjugation by glutathione transferase (GST), but the scope of activities among the numerous members of the GSTome is unknown. We demonstrate that all human GSTs tested except GST T1-1 are active with JS-K as a substrate, but their specific activities are notably spanning a > 100-fold range. The most effective enzyme was the mu class member GST M2-2 with a specific activity of 273 ± 5 µmol min-1 mg-1 and the kinetic parameters Km 63 µM, kcat 353 s-1, kcat/Km 6 × 106 M-1 s-1. The abundance of the GSTs as an ensemble and their high catalytic efficiency indicate that release of NO occurs rapidly in normal tissues such that this influence must be considered in clarification of the tumor-killing effect of JS-K.

Exogenous NO induces apoptosis of hepatocellular carcinoma cells via positive p38/JNK signaling pathway and negative ERK signaling pathways

JS-K as an exogenous NO donor could release NO after activation by glutathione S-transferases (GSTs). The present study explores the effects of JS-K on MAPK pathway in HepG2 and Bel-7402 cells. JS-K significantly prompted apoptosis and SB203580 (a p38 inhibitor) and SP600125 (a JNK inhibitor) prior to JS-K could partly reverse apoptosis and activation of cleaved-caspase-3 and cleaved PARP. However, U0126 (a MEK inhibitor) strengthened the cell apoptosis and the expressions of cleaved-caspase-3 and cleaved PARP. JS-K caused phosphorylation of p38 MAPK and JNK but attenuated phosphorylation of ERK, which were reversed by Carboxy-PTIO (a NO scavenger). Meanwhile, the phosphorylation of HSP27, c-JUN and ATF-2 were activated in JS-K-treated cells. SB203580 and SP600125 could attenuate phosphorylation of p38 MAPK and JNK, respectively. The phosphorylation in downstream substrates of p38 MAPK and JNK was also abolished by SB203580 and SP600125 in JS-K-treated cells. Additionally, JS-K decreased phosphorylation of c-Raf, which subsequently caused a decrease of MEK1/2 phosphorylation. Several downstream targets of ERK1/2 including p90RSK and transcription factors (e.g., Elk-1, c-Myc and c-Fos) were inhibited. U0126 potentiated JS-K-induced inhibitory effect of Raf/MEK/ERK pathway. The same results were also observed in the downstream substrates of ERK1/2 including p90RSK, Elk-1, c-Myc and c-Fos. Moreover, Carboxy-PTIO abolished the inhibitory effect of Raf/MEK/ERK pathway triggered by JS-K. Finally, JS-K significantly suppressed the growth of rat primary hepatic carcinoma via MAPK pathway in vivo. Taken together, JS-K can induce hepatocellular carcinoma cells apoptosis through its activation of JNK and p38 MAPK and inactivation of Raf/MEK/ERK signaling pathways.

Glutathione, an Antioxidant Tripeptide: Dual Roles in Carcinogenesis and Chemoprevention

Glutathione (GSH or reduced glutathione) is a tripeptide of gamma-Glutamyl-cysteinylglycine and the predominant intracellular antioxidant in many organisms including humans. GSH and associated enzymes are controlled by a transcription factor-nuclear factor-2 related erythroid factor-2 (Nrf2). In cellular milieu, GSH protects the cells essentially against a wide variety of free radicals including reactive oxygen species, lipid hydroperoxides, xenobiotic toxicants, and heavy metals. It has two forms, the reduced form or reduced glutathione (GSH) and oxidized form (GSSG), where two GSH moieties combine by sulfhydryl bonds. Glutathione peroxidase (GPx) and glutathione-s-transferase (GST) essentially perform the detoxification reactions using GSH, converting it into GSSG. Glutathione reductase (GR) operates the salvage pathway by converting GSSG to GSH with the expense of NADPH and restores the cellular GSH pool. Hence, GSH and GSH-dependent enzymes are necessary for maintaining the normal redox balance in the body and help in cell survival under stress conditions. In addition, GST removes various carcinogenic compounds offering a chemopreventive property, whereas the GSH system plays a significant role in regulating the cellular survival by offering redox stability in a variety of cancers including prostate, lung, breast, and colon cancer. Studies have also indicated that GSH inhibitors, such as buthionine sulfoximine, improve the chemo-sensitivity in cancer cells. In addition, GSH and dependent enzymes provide a survival advantage for cancer cells against chemotherapeutic drugs and radiotherapy.

JS-K, a nitric oxide donor, induces autophagy as a complementary mechanism inhibiting ovarian cancer

BACKGROUND

Ovarian cancer (OC) is the second most frequent gynecological cancer and is associated with a poor prognosis because OC progression is often asymptoma-tic and is detected at a late stage. There remains an urgent need for novel targeted therapies to improve clinical outcomes in ovarian cancer. As a nitric oxide prodrug, JS-K is reported highly cytotoxic to human cancer cells such as acute myeloid leukemia, multiple myeloma and breast cancer. This study is aim to investigate the influence of JS-K on proliferation and apoptosis in ovarian cancer cells and explored possible autophagy-related mechanisms, which will contribute to future ovarian cancer therapy and supply theory support that JS-K holds great promise as a novel therapeutic agent against ovarian cancer.

METHODS

The cytotoxicity, extracellular ROS/RNS activity and apoptotic effect of JS-K and indicated inhibitors on ovarian cancer cells in vitro were evaluated by MTT assay, extracellular ROS/RNS assay, caspases activities assay and western blot. Further autophagy effect of JS-K and indicated inhibitors were examined by MTT assay, cell transfection, immunofluorescence analysis, transmission electron microscopy (TEM) analysis and western blot on ovarian cancer cells in vitro. In vivo, the BALB/c-nude female mice with SKOV3 ovarian cancer cells xenograft were used to examine the efficacy of JS-K treatment on tumor growth. PCNA and p62 proteins were analyzed by immunohistochemistry.

RESULTS

In vitro, JS-K inhibited the proliferation of ovarian cancer cells, induced apoptosis and cell nucleus shrinkage, enhanced the enzymatic activity of caspase-3/7/8/9, and significantly increased the production of ROS/RNS in ovarian cancer A2780 and SKOV3 cells, these effects were attenuated by inhibition of NAC. In addition, JS-K induced autophagy-related proteins and autophagosomes changes in ovarian cancer A2780 and SKOV3 cells. In vivo, JS-K inhibited tumor growth, decreased p62 protein expression and increased the expression levels of PCNA in xenograft models which were established using SKOV3 ovarian cancer cells.

CONCLUSION

Taken together, we demonstrated that ROS/RNS stress-mediated apoptosis and autophagy are mechanisms by which SKOV3 cells undergo cell death after treatment with JS-K in vitro. Moreover, JS-K inhibited SKOV3 tumor growth in vivo. An alternative therapeutic approach for triggering cell death in cancer cells could constitute a useful multimodal therapies for treating ovarian cancer, which is known for its resistance to apoptosis-inducing drugs.

JS-K induces reactive oxygen species-dependent anti-cancer effects by targeting mitochondria respiratory chain complexes in gastric cancer

As a nitric oxide (NO) donor prodrug, JS‐K inhibits cancer cell proliferation, induces the differentiation of human leukaemia cells, and triggers apoptotic cell death in various cancer models. However, the anti‐cancer effect of JS‐K in gastric cancer has not been reported. In this study, we found that JS‐K inhibited the proliferation of gastric cancer cells in vitro and in vivo and triggered mitochondrial apoptosis. Moreover, JS‐K induced a significant accumulation of reactive oxygen species (ROS), and the clearance of ROS by antioxidant reagents reversed JS‐K‐induced toxicity in gastric cancer cells and subcutaneous xenografts. Although JS‐K triggered significant NO release, NO scavenging had no effect on JS‐K‐induced toxicity in vivo and in vitro. Therefore, ROS, but not NO, mediated the anti‐cancer effects of JS‐K in gastric cancer. We also explored the potential mechanism of JS‐K‐induced ROS accumulation and found that JS‐K significantly down‐regulated the core proteins of mitochondria respiratory chain (MRC) complex I and IV, resulting in the reduction of MRC complex I and IV activity and the subsequent ROS production. Moreover, JS‐K inhibited the expression of antioxidant enzymes, including copper‐zinc‐containing superoxide dismutase (SOD1) and catalase, which contributed to the decrease of antioxidant enzymes activity and the subsequent inhibition of ROS clearance. Therefore, JS‐K may target MRC complex I and IV and antioxidant enzymes to exert ROS‐dependent anti‐cancer function, leading to the potential usage of JS‐K in the prevention and treatment of gastric cancer.

Glutathione S-transferase π: a potential role in antitumor therapy

Glutathione S-transferase π (GSTπ) is a Phase II metabolic enzyme that is an important facilitator of cellular detoxification. Traditional dogma asserts that GSTπ functions to catalyze glutathione (GSH)-substrate conjunction to preserve the macromolecule upon exposure to oxidative stress, thus defending cells against various toxic compounds. Over the past 20 years, abnormal GSTπ expression has been linked to the occurrence of tumor resistance to chemotherapy drugs, demonstrating that this enzyme possesses functions beyond metabolism. This revelation reveals exciting possibilities in the realm of drug discovery, as GSTπ inhibitors and its prodrugs offer a feasible strategy in designing anticancer drugs with the primary purpose of reversing tumor resistance. In connection with the authors' current research, we provide a review on the biological function of GSTπ and current developments in GSTπ-targeting drugs, as well as the prospects of future strategies.

JS-K as a nitric oxide donor induces apoptosis via the ROS/Ca2+/caspase-mediated mitochondrial pathway in HepG2 cells

JS-K, (O²-(2, 4-dinitrophenyl) 1-[(4-ethoxycarbonyl) piperazin-1-yl] diazen 1-ium-1, 2-diolate), is a novel diazeniumdiolate-based nitric oxide donor prodrug. The present study investigated the relationship between reactive oxygen species (ROS) elevation, Ca²⁺ overload and mitochondrial disruption in JS-K-induced apoptosis. JS-K could significantly inhibit cell growth and induce apoptosis in a dose-dependent manner. Meanwhile, JS-K caused the accumulation of ROS, overload of Ca²⁺, decrease of mitochondrial membrane potential, release of cytochrome c (Cyt c) from mitochondria to the cytoplasm, increase of Bax-to-Bcl-2 ratio and activation of caspase- 9/3. NAC (an antioxidant) or BAPTA (an intracellular Ca²⁺ chelator) could partially reverse the above events, while BAPTA had little effect on the levels of ROS. Furthermore, pre-treatment with Carboxy-PTIO (a NO scavenger) significantly blocked the increasing of ROS, cytosolic Ca²⁺ and reversed the loss of mitochondrial membrane potential in JS-K-induced apoptosis. Taken together, the results suggested that NO released from JS-K could significantly induce HepG2 cell apoptosis through a ROS/Ca²⁺/caspase-mediated mitochondrial pathway.

Glutathione transferases: substrates, inihibitors and pro-drugs in cancer and neurodegenerative diseases

Glutathione transferase classical GSH conjugation activity plays a critical role in cellular detoxification against xenobiotics and noxious compounds as well as against oxidative stress. However, this feature is also exploited by cancer cells to acquire drug resistance and improve their survival. As a result, various members of the family were found overexpressed in a number of different cancers. Moreover several GST polymorphisms, ranging from null phenotypes to point mutations, were detected in members of the family and found to correlate with the onset of neuro-degenerative diseases. In the last decades, a great deal of research aimed at clarifying the role played by GSTs in drug resistance, at developing inhibitors to counteract this activity but also at exploiting GSTs for prodrugs specific activation in cancer cells. Here we summarize some of the most important achievements reached in this lively area of research.

Design, Synthesis, and Evaluation of Diazeniumdiolate-Based DNA Cross-Linking Agents Activatable by Glutathione S-Transferase

A novel class of O²-(2,4-dinitrophenyl)-1-[N,N-bis(2-substituted ethyl)amino]diazen-1-ium-1,2-diolates 4-6 were designed, synthesized, and biologically evaluated. The most active compound 6 caused significant DNA damage by releasing N,N-bis(2-TsO ethyl)amine and two molecules of nitric oxide (NO) after activation by GST/GSH in cancer cells, being more cytotoxic against three cancer cell lines than a well-known diazeniumdiolate-based anticancer agent JS-K, suggesting that the strategy has potential to extend to other O²-derived diazeniumdiolates to improve anticancer activity.

Nitric oxide release triggered by two-photon excited photoluminescence of engineered nanomaterials

A new strategy toward controllable release of NO for therapeutic purpose is described. Mn(2+)-doped ZnS quantum dots with NIR-II to visible upconversion properties were encapsulated by chitosan, with which photochemical NO precursors were conjugated to generate nanostructured materials capable of releasing NO under NIR-II irradiation.

Mechanism of action for the cytotoxic effects of the nitric oxide prodrug JS-K in murine erythroleukemia cells

The nitric oxide (NO) prodrug JS-K, a promising anti-cancer agent, consists of a diazeniumdiolate group necessary for the release of NO as well as an arylating ring. In this study, we research the mechanism by which JS-K kills a murine erythroleukemia cell line and determine the roles of NO and arylation in the process. Our studies indicate that JS-K inhibits the PI 3-kinase/Akt and MAP kinase pathways. This correlates with the activation of the tumor suppressor FoxO3a and increased expression of various caspases, leading to apoptosis. The arylating capability of JS-K appears to be sufficient for inducing these biological effects. Overall, these data suggest that JS-K kills tumor cells by arylating and inactivating signaling molecules that block the activation of a tumor suppressor.

Role of glutathione in cancer progression and chemoresistance

Glutathione (GSH) plays an important role in a multitude of cellular processes, including cell differentiation, proliferation, and apoptosis, and disturbances in GSH homeostasis are involved in the etiology and progression of many human diseases including cancer. While GSH deficiency, or a decrease in the GSH/glutathione disulphide (GSSG) ratio, leads to an increased susceptibility to oxidative stress implicated in the progression of cancer, elevated GSH levels increase the antioxidant capacity and the resistance to oxidative stress as observed in many cancer cells. The present review highlights the role of GSH and related cytoprotective effects in the susceptibility to carcinogenesis and in the sensitivity of tumors to the cytotoxic effects of anticancer agents.

Glutathione Transferase (GST)-Activated Prodrugs

Glutathione transferase (formerly GST) catalyzes the inactivation of various electrophile-producing anticancer agents via conjugation to the tripeptide glutathione. Moreover, several data link the overexpression of some GSTs, in particular GSTP1-1, to both natural and acquired resistance to various structurally unrelated anticancer drugs. Tumor overexpression of these proteins has provided a rationale for the search of GST inhibitors and GST activated cytotoxic prodrugs. In the present review we discuss the current structural and pharmacological knowledge of GST-activated cytotoxic compounds.

Effects of the nitric oxide donor JS-K on the blood-tumor barrier and on orthotopic U87 rat gliomas assessed by MRI

Nitric oxide (NO) released from NO donors can be cytotoxic in tumor cells and can enhance the transport of drugs into brain tumors by altering blood-tumor barrier permeability. The NO donor JS-K [O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate] releases NO upon enzymatic activation selectively in cells overexpressing glutathione-S-transferases (GSTs) such as gliomas. Thus, JS-K-dependent NO effects - especially on cell viability and vascular permeability - were investigated in U87 glioma cells in vitro and in an orthotopic U87 xenograft model in vivo by magnetic resonance imaging (MRI). In vitro experiments showed dose-dependent antiproliferative and cytotoxic effects in U87 cells. In addition, treatment of U87 cells with JS-K resulted in a dose-dependent activation of soluble guanylate cyclase and intracellular accumulation of cyclic guanosine monophosphate (cGMP) which was irreversibly inhibited by the selective inhibitor of soluble guanylate cyclase ODQ (1H-[1,2,4]oxadiazolo(4,3a)quinoxaline-1-one). Using dynamic contrast enhanced MRI (DCE-MRI) as a minimally invasive technique, we demonstrated for the first time a significant increase in the DCE-MRI read-out initial area under the concentration curve (iAUC60) indicating an acute increase in blood-tumor barrier permeability after i.v. treatment with JS-K. Repeated MR imaging of animals with intracranial U87 gliomas under treatment with JS-K (3.5 μmol/kg JS-K 3×/week) and of untreated controls on day 12 and 19 after tumor inoculation revealed no significant changes in tumor growth, edema formation or tumor perfusion. Immunohistochemical workup of the brains showed a significant antiproliferative effect of JS-K in the gliomas. Taken together, in vitro and in vivo data suggest that JS-K has antiproliferative effects in U87 gliomas and opens the blood-tumor barrier by activation of the NO/cGMP signaling pathway. This might be a novel approach to facilitate entry of therapeutic drugs into brain tumors. DCE-MRI is a non-invasive, repeatable imaging modality to monitor biological effects of NO donors and other experimental therapeutics in intracranial tumor models.

Nitric oxide-releasing prodrug triggers cancer cell death through deregulation of cellular redox balance

JS-K is a nitric oxide (NO)-releasing prodrug of the O (2)-arylated diazeniumdiolate family that has demonstrated pronounced cytotoxicity and antitumor properties in a variety of cancer models both in vitro and in vivo. The current study of the metabolic actions of JS-K was undertaken to investigate mechanisms of its cytotoxicity. Consistent with model chemical reactions, the activating step in the metabolism of JS-K in the cell is the dearylation of the diazeniumdiolate by glutathione (GSH) via a nucleophilic aromatic substitution reaction. The resulting product (CEP/NO anion) spontaneously hydrolyzes, releasing two equivalents of NO. The GSH/GSSG redox couple is considered to be the major redox buffer of the cell, helping maintain a reducing environment under basal conditions. We have quantified the effects of JS-K on cellular GSH content, and show that JS-K markedly depletes GSH, due to JS-K's rapid uptake and cascading release of NO and reactive nitrogen species. The depletion of GSH results in alterations in the redox potential of the cellular environment, initiating MAPK stress signaling pathways, and inducing apoptosis. Microarray analysis confirmed signaling gene changes at the transcriptional level and revealed alteration in the expression of several genes crucial for maintenance of cellular redox homeostasis, as well as cell proliferation and survival, including MYC. Pre-treating cells with the known GSH precursor and nucleophilic reducing agent N-acetylcysteine prevented the signaling events that lead to apoptosis. These data indicate that multiplicative depletion of the reduced glutathione pool and deregulation of intracellular redox balance are important initial steps in the mechanism of JS-K's cytotoxic action.

Glutathione and glutathione analogues; therapeutic potentials

BACKGROUND

Glutathione (GSH) and related enzymes are critical to cell protection from toxins, both endogenous and environmental, including a number of anti-cancer cytotoxic agents.

SCOPE OF REVIEW

Enhancing GSH and associated enzymes represents a longtime and persistent aim in the search for cytoprotective strategies against cancer, neurologic degeneration, pulmonary and inflammatory conditions, as well as cardiovascular ailments. The challenge is to identify effective GSH analogues or precursors that generate mimic molecules with glutathione's cellular protective effects. This review will provide an update on these efforts. Much effort has also been directed at depleting cellular GSH and related cytoprotective effects, in order to sensitize established tumors to the cytotoxic effects of anti-cancer agents. Efforts to deplete GSH have been limited by the challenge of selectivity doing so in tumor and not in normal tissue so as to avoid enhancing the toxicity of anti-cancer drugs. This review will also provide an update of efforts at overcoming the challenge of targeting the desired GSH depletion to tumor cells.

MAJOR CONCLUSIONS

This chapter provides a brief background and update of progress in the development and use of GSH analogues in the therapeutic setting, including the pharmacological aspects of these compounds.

GENERAL SIGNIFICANCE

This is an area of enormous research activity, and major advances promise the advent of novel therapeutic opportunities in the near future. This article is part of a Special Issue entitled Cellular functions of glutathione.

Structural modifications modulate stability of glutathione-activated arylated diazeniumdiolate prodrugs

JS-K, a diazeniumdiolate-based nitric oxide (NO)-releasing prodrug, is currently in late pre-clinical development as an anti-cancer drug candidate. This prodrug was designed to be activated by glutathione (GSH) to release NO. To increase the potency of JS-K, we are investigating the effect of slowing the reaction of the prodrugs with GSH. Herein, we report the effect of replacement of nitro group(s) by other electron-withdrawing group(s) in JS-K and its homo-piperazine analogues on GSH activation and the drugs' biological activity. We show that nitro-to-cyano substitution increases the half-life of the prodrug in the presence of GSH without compromising the compound's in vivo antitumor activity.

Synthesis and characterization of a multi-arm poly(acrylic acid) star polymer for application in sustained delivery of cisplatin and a nitric oxide prodrug

Functionalized polymeric nanocarriers have been recognized as drug delivery platforms for delivering therapeutic concentrations of chemotherapies. Of this category, star-shaped multiarm polymers are emerging candidates for targeted delivery of anti-cancer drugs, due to their compact structure, narrow size distribution, large surface area and high water solubility. In this study, we synthesized a multi-arm poly(acrylic acid) star polymer via MADIX/RAFT polymerization and characterized it using NMR and size exclusion chromatography. The poly(acrylic acid) star polymer demonstrated excellent water solubility and extremely low viscosity, making it highly suited for targeted drug delivery. Subsequently, we selected a hydrophilic drug, cisplatin, and a hydrophobic nitric oxide-donating prodrug, O²-(2,4-dinitrophenyl) 1-[4-(2-hydroxy)ethyl]-3-methylpiperazin-1-yl]diazen-1-ium-1,2-diolate, as two model compounds to evaluate the feasibility of using poly(acrylic acid) star polymers for delivery of chemotherapeutics. After synthesizing and characterizing two poly(acrylic acid) star polymer-based nanoconjugates, poly(acrylic acid)-cisplatin (acid-Pt) and poly(acrylic acid)-nitric oxide prodrug (acid-NO), the in vitro drug release kinetics of both acid-Pt and acid-NO were determined at physiological conditions. In summary, we have designed and evaluated a polymeric nanocarrier for sustained-delivery of chemotherapies, either as a single treatment or a combination therapy regimen.

JS-K, a glutathione S-transferase-activated nitric oxide donor with antineoplastic activity in malignant gliomas

BACKGROUND

Glutathione S-transferases (GSTs) control multidrug resistance and are upregulated in many cancers, including malignant gliomas. The diazeniumdiolate JS-K generates nitric oxide (NO) on enzymatic activation by glutathione and GST, showing promising NO-based anticancer efficacy.

OBJECTIVE

To evaluate the role of NO-based antitumor therapy with JS-K in U87 gliomas in vitro and in vivo.

METHODS

U87 glioma cells and primary glioblastoma cell lines were exposed to JS-K and a variety of inhibitors to study cell death by necrosis, apoptosis, and other mechanisms. GST expression was evaluated by immunocytochemistry, polymerase chain reaction, and Western blot, and NO release from JS-K was studied with a NO assay. The growth-inhibitory effect of JS-K was studied in a U87 xenograft model in vivo.

RESULTS

Dose-dependent inhibition of cell proliferation was observed in human U87 glioma cells and primary glioblastoma cells in vitro. Cell death was partially induced by caspase-dependent apoptosis, which could be blocked by Z-VAD-FMK and Q-VD-OPH. Inhibition of GST by sulfasalazine, cGMP inhibition by ODQ, and MEK1/2 inhibition by UO126 attenuated the antiproliferative effect of JS-K, suggesting the involvement of various intracellular death signaling pathways. Response to JS-K correlated with mRNA and protein expression of GST and the amount of NO released by the glioma cells. Growth of U87 xenografts was reduced significantly, with immunohistochemical evidence for increased necrosis and apoptosis and reduced proliferation.

CONCLUSION

Our data show for the first time the potent antiproliferative effect of JS-K in gliomas in vitro and in vivo. These findings warrant further investigation of this novel NO-releasing prodrug in gliomas.

Thiol Modification By Pharmacologically Active Agents of the Diazeniumdiolate Class

Promising drug candidates of the diazeniumdiolate (NONOate) chemical family include several types of thiol modification among their mechanisms of action: 1) drugs designed to release nitric oxide (NO) on reaction with the thiol group of glutathione (GSH) arylate the GSH, a step that removes reducing equivalents from the cell; (2) a similar reaction of the drug with the thiol group of a protein changes its structure, leading to potentially impaired function and cell death; (3) the NO generated as a byproduct in the above reactions can undergo oxidation, leading to S-nitrosylation and S-glutathionylation; and (4) diazeniumdiolates can also generate nitroxyl, which reacts with thiol groups to form disulfides or sulfinamides.

Nitric Oxide-Releasing Hybrid Drugs Target Cellular Processes Through S-Nitrosylation

Nitric oxide (NO)-releasing agents such as JS-K and NO-releasing hybrids such as NO- and NONO-nonsteroidal anti-inflammatory drugs are novel agents with great potential for controlling cancer. Although studied extensively, a key question pertaining to their molecular targets and mechanism of action remains unclear: the role of NO in the overall biological effect of these agents. It has been shown that NO can directly modify sulfhydryl residues of proteins through S-nitrosylation and induce apoptosis. We showed that 3 structurally diverse NO-nonsteroidal anti-inflammatory drugs S-nitrosylated nuclear factor-κB p65 in vitro and in vivo and also showed that these agents S-nitrosylated caspase-3 in vivo. JS-K reduced nuclear β-catenin and cyclin D1 protein levels without affecting cytosolic β-catenin expression. On the basis of a time course study, S-nitrsolyation of nuclear β-catenin was determined to precede its degradation. These data provide a mechanistic role for NO and a rationale for the chemopreventive effects of these novel agents.

Activation of the c-Jun N-terminal kinase/activating transcription factor 3 (ATF3) pathway characterizes effective arylated diazeniumdiolate-based nitric oxide-releasing anticancer prodrugs

Improved therapies are needed for nonsmall cell lung cancer. Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs are a growing class of promising NO-based therapeutics. Recently, we have shown that O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K, 1) is effective against nonsmall cell lung cancer (NSCLC) cells in culture and in vivo. Here we report mechanistic studies with compound 1 and its homopiperazine analogue and structural modification of these into more stable prodrugs. Compound 1 and its homopiperazine analogue were potent cytotoxic agents against NSCLC cells in vitro and in vivo, concomitant with activation of the SAPK/JNK stress pathway and upregulation of its downstream effector ATF3. Apoptosis followed these events. An aryl-substituted analogue, despite extended half-life in the presence of glutathione, did not activate JNK or have antitumor activity. The data suggest that rate of reactivity with glutathione and activation of JNK/ATF3 are determinants of cancer cell killing by these prodrugs.

The nitric oxide prodrug JS-K is effective against non-small-cell lung cancer cells in vitro and in vivo: involvement of reactive oxygen species

Non-small-cell lung cancer is among the most common and deadly forms of human malignancies. Early detection is unusual, and there are no curative therapies in most cases. Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs are a growing class of promising NO-based therapeutics. Here, we show that O(2)-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) is a potent cytotoxic agent against a subset of human non-small-cell lung cancer cell lines both in vitro and as xenografts in mice. JS-K treatment led to 75% reduction in the growth of H1703 lung adenocarcinoma cells in vivo. Differences in sensitivity to JS-K in different lung cancer cell lines seem to be related to their endogenous levels of reactive oxygen species (ROS)/reactive nitrogen species (RNS). Other related factors, levels of peroxiredoxin 1 (PRX1) and 8-oxo-deoxyguanosine glycosylase (OGG1), also correlated with drug sensitivity. Treatment of the lung adenocarcinoma cells with JS-K resulted in oxidative/nitrosative stress in cells with high basal levels of ROS/RNS, which, combined with the arylating properties of the compound, was reflected in glutathione depletion and alteration in cellular redox potential, mitochondrial membrane permeabilization, and cytochrome c release. Inactivation of manganese superoxide dismutase by nitration was associated with increased superoxide and significant DNA damage. Apoptosis followed these events. Taken together, the data suggest that diazeniumdiolate-based NO-releasing prodrugs may have application as a personalized therapy for lung cancers characterized by high levels of ROS/RNS. PRX1 and OGG1 proteins, which can be easily measured, could function as biomarkers for identifying tumors sensitive to the therapy.

JS-K, a nitric oxide-releasing prodrug, modulates ß-catenin/TCF signaling in leukemic Jurkat cells: evidence of an S-nitrosylated mechanism

β-Catenin is a central player of the Wnt signaling pathway that regulates cell-cell adhesion and may promote leukemia cell proliferation. We examined whether JS-K, an NO-donating prodrug, modulates the Wnt/β-catenin/TCF-4 signaling pathway in Jurkat T-Acute Lymphoblastic Leukemia cells. JS-K inhibited Jurkat T cell growth in a concentration and time-dependent manner. The IC(50)s for cell growth inhibition were 14±0.7 and 9±1.2μM at 24 and 48h, respectively. Treatment of the cells with JS-K for 24h, caused a dose-dependent increase in apoptosis from 16±3.3% at 10μM to 74.8±2% at 100μM and a decrease in proliferation. This growth inhibition was also due, in part, to alterations in the different phases of the cell cycle. JS-K exhibited a dose-dependent cytotoxicity as measured by LDH release at 24h. However, between 2 and 8h, LDH release was less than 20% for any indicated JS-K concentration. The β-catenin/TCF-4 transcriptional inhibitory activity was reduced by 32±8, 63±5, and 93±2% at 2, 10, and 25μM JS-K, respectively, based on luciferase reporter assays. JS-K reduced nuclear β-catenin and cyclin D1 protein levels, but cytosolic β-catenin expression did not change. Based on a time-course assay of S-nitrosylation of proteins by a biotin switch assay, S-nitrsolyation of nuclear β-catenin was determined to precede its degradation. A comparison of the S-nitrosylated nuclear β-catenin to the total nuclear β-catenin showed that β-catenin protein levels were degraded at 24h, while S-nitrosylation of β-catenin occurred earlier at 0-6h. The NO scavenger PTIO abrogated the JS-K mediated degradation of β-catenin demonstrating the need for NO.

Nitrogen-bound diazeniumdiolated amidines

In contrast to amidines bearing ionizable alpha-CH bonds, which react with nitric oxide (NO) to add diazeniumdiolate groups at their alpha-carbons, benzamidine forms an N-bound diazeniumdiolate that can be further derivatized at the other amidine nitrogen and/or the terminal oxygen to form caged NO compounds as potential NO prodrugs.

Localization of hydrophobic N-diazeniumdiolates in aqueous micellar solution

The interaction of phenyl-substituted zwitterionic N-diazeniumdiolates PhCH(2)N[N(O)NO](-)(CH(2))(2)NH(3)(+) (1) and PhCH(2)N[N(O)NO](-)(CH(2))(2)NH(2)(+)CH(2)Ph (2) with aqueous micellar solutions of prototypal surfactants was investigated by means of UV/vis and (1)H NMR spectroscopy in order to establish the localization of hydrophobic N-diazeniumdiolates in micelles as a model for the binding of the NO donors in biological membranes. In the presence of sodium dodecyl sulfate (SDS), significant shifts of the apparent pK(a) values of 1 and 2 were observed, suggesting strong electrostatic interaction between the diazeniumdiolates and the negatively charged SDS micelles. No effect on both pK(a) and rate of NO release was found in the presence of Triton X-100. The solubilization site of micellar bound N-diazeniumdiolates was established by (1)H NMR spectroscopic studies, taking advantage of the spectroscopic effects induced by CH-pi interactions. The spectra indicate that in alkaline solutions of SDS 1 resides preferably at the micellar surface within the interfacial region, whereas the more hydrophobic NO donor 2 penetrates into the apolar region of the micelle. This suggests hydrophobic interaction as the main driving force for micellar binding of 2 in alkaline solution. Similar studies in presence of Triton X-100 indicate that 1 and 2 are adsorbed within the poly(oxyethylene) layer of the micellar surface rather than penetrating the palisade layer of the micelles. In alkaline solutions of hexadecyltrimethylammonium bromide (CTAB), 1 and 2 bind to the cationic micellar aggregates, whereby the solubilization site strongly depends on the hydrophobicity of the substrate. Up to a moderate pH of 8, the hydrophobic NO donor 2 penetrates the hydrocarbon region of the micelles. As a result, the rate of NO release from 2 is noticeably inhibited by the micellar aggregates due to the higher local concentration of hydroxide ions along the micelle-water interface. From solubilization studies, guidelines for the development and application of future NONOates can be derived. The rate of NO release from micellar bound diazeniumdiolates is determined by the surface charge of the micelles. This ability to tune stability is significant for the design and selection of potential NO delivery systems (drug formulations).

Broad-Spectrum Anti-Cancer Activity of O-Arylated Diazeniumdiolates

O(2)-(2,4-Dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) and O(2)-{2,4-dinitro-5-[4-(N-methylamino)be nzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate (PABA/NO) are O(2)-arylated diazeniumdiolates that have shown promising in vivo activity in a variety of rodent cancer models, including prostate cancer, leukemia, liver cancer, multiple myeloma, and ovarian cancer. This compound class was designed to be activated for anti-cancer effects by glutathione-S-transferase (GST)-induced release of cytotoxic nitric oxide (NO), but mechanistic studies have implicated a variety of pathways, some GST/NO-related, some not. Current work is focused on improving formulations and other drug development activities, as well as exploring possible new applications of these agents and their analogs. The selectivity of these drugs for attacking tumors while exhibiting little toxicity toward normal tissues suggests considerable promise for the treatment of various tumor types.

Nucleophilic reactivity of thiolate, hydroxide and phenolate ions towards a model O-arylated diazeniumdiolate prodrug in aqueous and cationic surfactant media

The kinetics of aromatic nucleophilic substitution of the nitric oxide generating diazeniumdiolate ion, DEA/NO, by thiols, (L-glutathione, L-cysteine, DL-homocysteine, 1-propanethiol, 2-mercaptoethanol and sodium thioglycolate) from the prodrug, DNP-DEA/NO, has been examined in aqueous solution and in solutions of cationic DOTAP vesicles. Second-order rate constants in buffered aqueous solutions (k(RS(-) ) = 3.48 - 30.9 M(-1)s(-1); 30 °C) gave a linear Brønsted plot (β(nuc) = 0.414 ± 0.068) consistent with rate-limiting S(N)Ar nucleophilic attack by thiolate ions. Cationic DOTAP vesicles catalyze the thiolysis reactions with rate enhancements between 11 and 486-fold in Tris-HCl buffered solutions at pH 7.4. The maximum rate increase was obtained with thioglycolate ion. Thiolysis data are compared to data for nucleophilic displacement by phenolate (k(PhO(-) ) = 0.114 M(-1)s(-1)) and hydroxide (k(OH(-) ) = 1.82 × 10(-2) M(-1)s(-1), 37 °C) ions. The base hydrolysis reaction is accelerated by CTAB micelles and DODAC vesicles with vesicles being ca 3-fold more effective as catalysts. Analysis of the data using pseudophase ion-exchange formalism implies that the rate enhancement of the thiolysis and base hydrolysis reactions is due primarily to reactant concentration in the surfactant pseudophase.

Stabilization of the nitric oxide (NO) prodrugs and anticancer leads, PABA/NO and Double JS-K, through incorporation into PEG-protected nanoparticles

We report the stabilization of the nitric oxide (NO) prodrugs and anticancer lead compounds, PABA/NO (O(2)-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate) and "Double JS-K" 1,5-bis-{1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diol-2-ato}-2,4-dinitrobenzene, through their incorporation into polymer-protected nanoparticles. The prodrugs were formulated in block copolymer-stabilized nanoparticles with sizes from 220 to 450 nm by a novel rapid precipitation process. The block copolymers, with polyethylene glycol (PEG) soluble blocks, provide a steric barrier against NO prodrug activation by glutathione. Too rapid activation and NO release has been a major barrier to effective administration of this class of compounds. The nanoparticle stabilized PABA/NO are protected from attack by glutathione as evidenced by a significant increase in time taken for 50% decomposition from 15 min (unformulated) to 5 h (formulated); in the case of Double JS-K, the 50% decomposition time was extended from 4.5 min (unformulated) to 40 min (formulated). The more hydrophobic PABA/NO produced more stable nanoparticles and correspondingly more extended release times in comparison with Double JS-K. The hydrophobic blocks of the polymer were either polystyrene or polylactide. Both blocks produced nanoparticles of approximately the same size and release kinetics. This combination of PEG-protected nanoparticles with sizes appropriate for cancer targeting by enhanced permeation and retention (EPR) and delayed release of NO may afford enhanced therapeutic benefit.

Synthesis and evaluation of piperazine and homopiperazine analogues of JS-K, an anti-cancer lead compound

Here we report a number of novel JS-K structural analogues with sub-micromolar anti-proliferative activities against human leukemia cell lines HL-60 and U937; JS-K is the anti-cancer lead compound O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate. The ability of these compounds to generate intracellular nitric oxide correlated well with their observed anti-proliferative effects: analogues that had potent inhibitory activity against leukemia cells formed elevated levels of intracellular nitric oxide.

Gene expression profiling for nitric oxide prodrug JS-K to kill HL-60 myeloid leukemia cells

The nitric oxide (NO) prodrug JS-K is shown to have anticancer activity. To profile the molecular events associated with the anticancer effects of JS-K, HL-60 leukemia cells were treated with JS-K and subjected to microarray and real-time RT-PCR analysis. JS-K induced concentration- and time-dependent gene expression changes in HL-60 cells corresponding to the cytolethality effects. The apoptotic genes (caspases, Bax, and TNF-alpha) were induced, and differentiation-related genes (CD14, ITGAM, and VIM) were increased. For acute phase protein genes, some were increased (TP53, JUN) while others were suppressed (c-myc, cyclin E). The expression of anti-angiogenesis genes THBS1 and CD36 and genes involved in tumor cell migration such as tissue inhibitors of metalloproteinases, were also increased by JS-K. Confocal analysis confirmed key gene changes at the protein levels. Thus, multiple molecular events are associated with JS-K effects in killing HL-60, which could be molecular targets for this novel anticancer NO prodrug.