A Top-Down Proteomic Assay to Evaluate KRAS4B-Compound Engagement

Development of new targeted inhibitors for oncogenic KRAS mutants may benefit from insight into how a given mutation influences the accessibility of protein residues and how compounds interact with mutant or wild-type KRAS proteins. Targeted proteomic analysis, a key validation step in the KRAS inhibitor development process, typically involves both intact mass- and peptide-based methods to confirm compound localization or quantify binding. However, these methods may not always provide a clear picture of the compound binding affinity for KRAS, how specific the compound is to the target KRAS residue, and how experimental conditions may impact these factors. To address this, we have developed a novel top-down proteomic assay to evaluate in vitro KRAS4B-compound engagement while assessing relative quantitation in parallel. We present two applications to demonstrate the capabilities of our assay: maleimide-biotin labeling of a KRAS4BG12D cysteine mutant panel and treatment of three KRAS4B proteins (WT, G12C, and G13C) with small molecule compounds. Our results show the time- or concentration-dependence of KRAS4B-compound engagement in context of the intact protein molecule while directly mapping the compound binding site.

Revealing the mechanism of action of a first-in-class covalent inhibitor of KRASG12C (ON) and other functional properties of oncogenic KRAS by 31P NMR

Individual oncogenic KRAS mutants confer distinct differences in biochemical properties and signaling for reasons that are not well understood. KRAS activity is closely coupled to protein dynamics and is regulated through two interconverting conformations: state 1 (inactive, effector binding deficient) and state 2 (active, effector binding enabled). Here, we use 31P NMR to delineate the differences in state 1 and state 2 populations present in WT and common KRAS oncogenic mutants (G12C, G12D, G12V, G13D, and Q61L) bound to its natural substrate GTP or a commonly used nonhydrolyzable analog GppNHp (guanosine-5'-[(β,γ)-imido] triphosphate). Our results show that GppNHp-bound proteins exhibit significant state 1 population, whereas GTP-bound KRAS is primarily (90% or more) in state 2 conformation. This observation suggests that the predominance of state 1 shown here and in other studies is related to GppNHp and is most likely nonexistent in cells. We characterize the impact of this differential conformational equilibrium of oncogenic KRAS on RAF1 kinase effector RAS-binding domain and intrinsic hydrolysis. Through a KRAS G12C drug discovery, we have identified a novel small-molecule inhibitor, BBO-8956, which is effective against both GDP- and GTP-bound KRAS G12C. We show that binding of this inhibitor significantly perturbs state 1-state 2 equilibrium and induces an inactive state 1 conformation in GTP-bound KRAS G12C. In the presence of BBO-8956, RAF1-RAS-binding domain is unable to induce a signaling competent state 2 conformation within the ternary complex, demonstrating the mechanism of action for this novel and active-conformation inhibitor.

FLAG-KRAS4B as a Model System for KRAS4B Proteoform and PTM Evaluation by Mass Spectrometry

Prior analysis of intact and modified protein forms (proteoforms) of KRAS4B isolated from cell lines and tumor samples by top-down mass spectrometry revealed the presence of novel posttranslational modifications (PTMs) and potential evidence of context-specific KRAS4B modifications. However, low endogenous proteoform signal resulted in ineffective characterization, making it difficult to visualize less abundant PTMs or perform follow-up PTM validation using standard proteomic workflows. The NCI RAS Initiative has developed a model system, whereby KRAS4B bearing an N-terminal FLAG tag can be stably expressed within a panel of cancer cell lines. Herein, we present a method for combining immunoprecipitation with complementary proteomic methods to directly analyze N-terminally FLAG-tagged KRAS4B proteoforms and PTMs. We provide detailed protocols for FLAG-KRAS4B purification, proteoform analysis by targeted top-down LC-MS/MS, and validation of abundant PTMs by bottom-up LC-MS/MS with example results.

High-Throughput Cell-Based Screening of Small Molecule KRAS Signaling Inhibitors Using a Homogeneous Time-Resolved Fluorescence (HTRF) Assay

With recent advances proving that effective inhibition of KRAS is possible, there have been significant efforts made to develop inhibitors of specific mutant alleles. Here we describe a detailed protocol that employs homogeneous time-resolved fluorescence (HTRF) to identify compounds acting on KRAS signaling in malignant cell lines. This method allows for high-throughput, cell-based screens of large compound libraries for the development of RAS-targeted therapeutics.

MALDI-TOF Mass Spectrometry-Based Assay for Measuring Covalent Target Engagement of KRAS G12C Inhibitors

MALDI-TOF mass spectrometry enables high-throughput screening of covalent fragment libraries and SAR compound progressions of selective KRAS G12C inhibitors. Using the MALDI-TOF platform instead of the more traditional ESI-MS TOF/orbitrap instrumentation can radically shorten sample acquisition time, allowing up to 384 samples to be screened in 30 min. The typical throughput for a covalent library screen is 1152 samples per 8 h, including processing, calculation, and reporting steps. The throughput can be doubled without any significant assay modification.

NMR 1H, 13C, 15N backbone resonance assignments of the T35S and oncogenic T35S/Q61L mutants of human KRAS4b in the active, GppNHp-bound conformation

RAS proteins cycling between the active-form (GTP-bound) and inactive-form (GDP-bound) play a key role in cell signaling pathways that control cell survival, proliferation, and differentiation. Mutations at codon 12, 13, and 61 in RAS are known to attenuate its GTPase activity favoring the RAS active state and constitutively active downstream signaling. This hyperactivation accounts for various malignancies including pancreatic, lung, and colorectal cancers. Active KRAS is found to exist in equilibrium between two rapidly interconverting conformational states (State1-State2) in solution. Due to this dynamic feature of the protein, the ¹H-¹⁵N correlation cross-peak signals of several amino acid (AA) residues of KRAS belonging to the flexible loop regions are absent from its 2D ¹H-¹⁵N HSQC spectrum within and near physiological solution pH. A threonine to serine mutation at position 35 (T35S) shifts the interconverting equilibrium to State1 conformation and enables the emergence of such residues in the 2D ¹H-¹⁵N HSQC spectrum due to gained conformational rigidity. We report here the ¹H^N, ¹⁵N, and ¹³C backbone resonance assignments for the 19.2 kDa (AA 1-169) protein constructs of KRAS-GppNHp harboring T35S mutation (KRAS^T35S/C118S-GppNHp) and of its oncogenic counterpart harboring the Q61L mutation (KRAS^{T35S/Q61L/C118S}-GppNHp) using heteronuclear, multidimensional NMR spectroscopy at 298 K. High resolution NMR data allowed the unambiguous assignments of ¹H-¹⁵N correlation cross-peaks for all the residues except for Met1. Furthermore, 2D ¹H-¹⁵N HSQC overlay of two proteins assisted in determination of Q61L mutation-induced chemical shift perturbations for select residues in the regions of P-loop, Switch-II, and helix α3.

Nitric oxide (NO) releasing poly ADP-ribose polymerase 1 (PARP-1) inhibitors targeted to glutathione S-transferase P1-overexpressing cancer cells

We report the antitumor effects of nitric oxide (NO) releasing derivatives of the PARP-1 inhibitor olaparib (1). Compound 5b was prepared by coupling the carboxyl group of 3b and the free amino group of arylated diazeniumdiolated piperazine 4. Analogue 5a has the same structure except that the F is replaced by H. Compound 13 is the same as 5b except that a Me2N-N(O)═NO- group was added para and ortho to the nitro groups of the dinitrophenyl ring. The resulting prodrugs are activated by glutathione in a reaction accelerated by glutathione S-transferase P1 (GSTP1), an enzyme frequently overexpressed in cancers. This metabolism generates NO plus a PARP-1 inhibitor simultaneously, consuming reducing equivalents, leading to DNA damage concomitant with inhibition of DNA repair, and in the case of 13 inducing cross-linking glutathionylation of proteins. Compounds 5b and 13 reduced the growth rates of A549 human lung adenocarcinoma xenografts with no evidence of systemic toxicity.

Co-transcriptional production of RNA-DNA hybrids for simultaneous release of multiple split functionalities

Control over the simultaneous delivery of different functionalities and their synchronized intracellular activation can greatly benefit the fields of RNA and DNA biomedical nanotechnologies and allow for the production of nanoparticles and various switching devices with controllable functions. We present a system of multiple split functionalities embedded in the cognate pairs of RNA-DNA hybrids which are programmed to recognize each other, re-associate and form a DNA duplex while also releasing the split RNA fragments which upon association regain their original functions. Simultaneous activation of three different functionalities (RNAi, Förster resonance energy transfer and RNA aptamer) confirmed by multiple in vitro and cell culture experiments prove the concept. To automate the design process, a novel computational tool that differentiates between the thermodynamic stabilities of RNA-RNA, RNA-DNA and DNA-DNA duplexes was developed. Moreover, here we demonstrate that besides being easily produced by annealing synthetic RNAs and DNAs, the individual hybrids carrying longer RNAs can be produced by RNA polymerase II-dependent transcription of single-stranded DNA templates.

Abstract 3334: GSTP1-activated nitric oxide-releasing/PARP inhibitor hybrid prodrugs induce cancer cell death through ROS/RNS, DNA damage, ER stress, and apoptosis

Poly [ADP-ribose] polymerase (PARP) has been recognized as a potential molecular target in cancer therapy. PARP inhibitors have been evaluated in clinical trials, both in combination with DNA damaging chemotherapy, and also as single agents in patients with BRCA deficiencies. However, there are problems associated with the clinical applicability of PARP inhibitors that include theoretical genotoxicity of these DNA damage repair inhibitors, and increased toxicity in combination with chemotherapy. Therefore targeted delivery of PARP inhibitors selectively to cancer cells would be clinically beneficial.

Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs developed in our laboratory have proven effective as anticancer agents in a number of in vitro and in vivo models. The lead prodrug JS-K exhibits a multifaceted mechanism of action that includes generation of oxidative/nitrosative stress and DNA damage. We hypothesized that inhibiting PARP may increase effectiveness of JS-K. More importantly, creating a PARP inhibitor prodrug that is activated specifically in the cancer cell could diminish dose-limiting adverse events observed in clinical trials.

Using structure-based molecular modeling approaches we have designed and synthesized novel diazeniumdiolate/PARP inhibitor hybrid prodrugs that are activated by glutathione S-transferase P1 (GSTP1), an enzyme frequently overexpressed by cancer cells. This GSTP1-catalyzed activation allows for the selective delivery of nitric oxide and PARP inhibitor simultaneously to the cancer cell. Biological evaluation of the prodrugs in vitro in lung adenocarcinoma and leukemia cells reveals that their mechanism of action involves oxidative/nitrosative stress associated with NO release and depletion of cellular GSH, leading to DNA strand break damage. The compounds induce aryl-mediated crosslinking glutathionylation of cellular thiols that is irreversible, and may lead to observed endoplasmic reticulum (ER) stress. The tumor suppressor p53 pathway is involved in cells bearing wildtype p53. We have also observed the activation of stress kinases p38 and SAPK/JNK. All of the above events led to initiation of apoptosis through both intrinsic and extrinsic pathways.

Cancer cells often exhibit specific stress-related phenotypes, caused by insults such as reactive oxygen species, DNA damage, metabolic stress, or ER stress, and agents that further enhance these stresses could be developed as potential therapies. GSTP1-activated diazeniumdiolate/PARP inhibitor hybrid prodrugs selectively induce cancer cell death through ROS/DNA damage and ER stress overload, leading to apoptosis.

Citation Format: Anna E. Maciag, Joseph E. Saavedra, Ryan J. Holland, Youseung Kim, Vandana Kumari, Christina E. Luthers, Waheed S. Sehareen, Xinhua Ji, Lucy M. Anderson, Larry K. Keefer. GSTP1-activated nitric oxide-releasing/PARP inhibitor hybrid prodrugs induce cancer cell death through ROS/RNS, DNA damage, ER stress, and apoptosis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3334. doi:10.1158/1538-7445.AM2013-3334

Abstract 2922: Stoichiometric depletion of glutathione by anticancer agent JS-K

JS-K is a nitric oxide (NO)-releasing drug of the O2-arylated diazeniumdiolate family that has demonstrated pronounced cytotoxicity and antitumor properties in a variety of cancer models. It is activated for NO release by reaction with glutathione (GSH), a step that consumes an equivalent of GSH, effectively irreversibly. The two equivalents of NO thus released can be oxidized intracellularly, leading to S-nitrosylation and S-glutathionylation of GSH in a cascade of further reactions that consume additional equivalents of GSH and generate GSH disulfide (GSSG). The GSH/GSSG redox couple is the major redox buffer of the cell, helping maintain a reducing environment under basal conditions. Here we show that depletion of GSH on treating U937 leukemia cells with JS-K markedly raises the reduction potential of the cell, 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. The data indicate that multiplicative depletion of reduced GSH and deregulation of intracellular redox balance are important steps in the mechanism of JS-K's cytotoxic action.

An additional GSH-consuming pathway was found to occur with Double JS-K, an aryl bis(diazeniumdiolate) created with the purpose of doubling the payload of NO. Double JS-K caused pronounced protein glutathionylation, in contrast to its monovalent counterpart. Serving as a bivalent electrophile, Double JS-K irreversibly crosslinked GSH to protein thiols through its aromatic linker. The results provide a previously unrecognized component of the multifaceted mechanism of action of bivalent electrophiles of the arylated diazeniumdiolate class.

Citation Format: Ryan J. Holland, Anna E. Maciag, Robert Y.-S. Cheng, Luis G. Rodriguez, Joseph E. Saavedra, Lucy M. Anderson, Larry K. Keefer. Stoichiometric depletion of glutathione by anticancer agent JS-K. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2922. doi:10.1158/1538-7445.AM2013-2922

Activation of different split functionalities on re-association of RNA-DNA hybrids

Split-protein systems, an approach that relies on fragmentation of proteins with their further conditional re-association to form functional complexes, are increasingly used for various biomedical applications. This approach offers tight control of protein functions and improved detection sensitivity. Here we report a similar technique based on a pair of RNA-DNA hybrids that can be used generally for triggering different split functionalities. Individually, each hybrid is inactive but when two cognate hybrids re-associate, different functionalities are triggered inside mammalian cells. As a proof of concept, this work mainly focuses on the activation of RNA interference. However, the release of other functionalities (such as resonance energy transfer and RNA aptamer) is also shown. Furthermore, in vivo studies demonstrate a significant uptake of the hybrids by tumours together with specific gene silencing. This split-functionality approach presents a new route in the development of 'smart' nucleic acid-based nanoparticles and switches for various biomedical applications.

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 O²-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.

Cross-linking protein glutathionylation mediated by O2-arylated bis-diazeniumdiolate "Double JS-K"

Attachment of glutathione (GSH) to cysteine residues in proteins (S-glutathionylation) is a reversible post-translational modification that can profoundly alter protein structure and function. Often serving in a protective role, for example, by temporarily saving protein thiols from irreversible oxidation and inactivation, glutathionylation can be identified and semiquantitatively assessed using anti-GSH antibodies, thought to be specific for recognition of the S-glutathionylation modification. Here, we describe an alternate mechanism of protein glutathionylation in which the sulfur atoms of the GSH and the protein's thiol group are covalently bound via a cross-linking agent, rather than through a disulfide bond. This form of thiol cross-linking has been shown to occur and has been confirmed by mass spectrometry at the solution chemistry level, as well as in experiments documenting the potent antiproliferative activity of the bis-diazeniumdiolate Double JS-K in H1703 cells in vitro and in vivo. The modification is recognized by the anti-GSH antibody as if it were authentic S-glutathionylation, requiring mass spectrometry to distinguish between them.

Diazeniumdiolated carbamates: a novel class of nitric oxide donors

We report an indirect method for synthesis of previously inaccessible diazeniumdiolated carbamates. Synthesis involves use of previously reported triisopropylsilyloxymethylated isopropylamine diazeniumdiolate (TOM-ylated IPA/NO). These novel diazeniumdiolated carbamate prodrugs upon activation release nitric oxide (NO) similar to their secondary amine counterparts. They are also efficient sources of intracellular NO. These prodrugs may have potential applications as therapeutic NO-donors.

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.

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.

Abstract C180: The effect of JS-K, a lead O2-arylated diazeniumdiolate anticancer agent, on the cellular glutathione status

JS-K is an O2-arylated diazeniumdiolate prodrug which has demonstrated pronounced selective cytotoxicity and antitumorigenic properties in a variety of cancer models both in vitro and in vivo. Mass spectrometric studies of the metabolic fate of JS-K were undertaken to understand the origin of the cytotoxicity. Consistent with model chemical reactions, the first step in the cellular metabolism of JS-K is the de-arylation of the diazeniumdiolate by glutathione (GSH) via a nucleophilic aromatic substitution reaction, forming a dinitrophenyl-GSH adduct, with the daizeniumdiolate ion by-product ultimately releasing nitric oxide (NO). A consequence of this metabolism and NO-generation is a rapid and pronounced depletion of cellular GSH concurrent with a rise in oxidized glutathione (GSSG). The GSH/GSSG redox couple, considered to be the major redox buffer of the cell, helps maintain a reducing environment under basal conditions. The depletion of GSH through drug conjugation and subsequent oxidation results in a rapid rise in the oxidation potential of the cellular environment, an increase of 30 mV in the first 30 min of treatment, initiating the stress signaling pathways which lead to extrinsic/intrinsic apoptosis. Preventing this rise in the oxidation potential by pre-treating cells with known antioxidant N-acetylcysteine inhibited the downstream signaling events leading to apoptosis. These data indicate that depletion of the glutathione pool is a crucial first step in the mechanism of JS-K cytotoxicity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C180.

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 V-PROLI/NO Inhibits Cellular Uptake of Proline

V-PYRRO/NO is a well studied nitric oxide (NO) prodrug which has been shown to protect human liver cells from arsenic, acetaminophen, and other toxic assaults in vivo. Its proline-based analogue, V-PROLI/NO, was designed to be a more biocompatible form that decomposes to the naturally occurring metabolites of proline, NO, and glycolaldehyde. Like V-PYRRO/NO, this cytochrome P450-activated prodrug was previously assumed to passively diffuse through the cellular membrane. Using (14)C-labeled proline in a competition assay, we show that V-PROLI/NO is transported through proline transporters into multiple cell lines. A fluorescent NO-sensitive dye (DAF-FM diacetate) and nitrite excretion indicated elevated intracellular NO release after metabolism over V-PYRRO/NO. These results also allowed us to predict and design a more permeable analogue, V-SARCO/NO. We report a proline transporter-based strategy for the selective transport of NO prodrugs that may have enhanced efficacy and aid in development of further NO prodrugs with increased permeability.

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.

Macrophage-dependent nitric oxide expression regulates tumor cell detachment and metastasis after IL-2/anti-CD40 immunotherapy

Immunotherapy with IL-2 and anti-CD40 induces the expression of NOS2 in tumor-associated macrophages, and its expression is required for the inhibition of tumor metastasis.

Using an orthotopic model of renal cell carcinoma, we showed previously that IL-2/anti-CD40 immunotherapy resulted in synergistic anti-tumor responses, whereas IL-2 or α-CD40 alone mediated partial transient anti-tumor effects. We now show that treatment of tumor-bearing mice with IL-2/α-CD40, but not IL-2 or α-CD40, induced significant nitric oxide synthase (NOS) 2 expression in tumor-associated macrophages. In control-treated mice (low NO), NOS2 inhibition reduced tumor burden. However, during immunotherapy (high NO), NOS2 inhibition or macrophage depletion reversed the ability of IL-2/α-CD40 treatment to reduce lung metastases but had no effect on primary tumor burden. Furthermore, IL-2/α-CD40 induced the IFN-γ– and NO-dependent decrease in matrix metalloproteinase (MMP) expression and activity, concomitant with increases in tissue inhibitor of metalloproteinase (TIMP) 1 and E-cadherin expression within tumors. Finally, treatment of tumor-bearing mice with the NO donor JS-K significantly reduced metastases. These data differentiate the mechanism for primary anti-tumor effects of IL-2/α-CD40 immunotherapy, which are independent of NO, from the NO-dependent inhibition of metastases. Furthermore, reduced MMP9 activity implicates M1-polarized macrophages within the tumor microenvironment as critical components of therapeutic response. Our data demonstrate the mechanistic basis for IL-2/α-CD40–mediated control of metastases and suggest that the context-dependent application of NO donors may hold promise for prevention of metastatic disease.

"Click" reaction in conjunction with diazeniumdiolate chemistry: developing high-load nitric oxide donors

The use of Cu(I)-catalyzed "click" reactions of alkyne-substituted diazeniumdiolate prodrugs with bis- and tetrakis-azido compounds is described. The "click" reaction for the bis-azide using CuSO(4)/Na-ascorbate predominantly gave the expected bis-triazole. However, CuI/diisopropylethylamine predominantly gave uncommon triazolo-triazole products as a result of oxidative coupling. Neither set of "click" conditions showed evidence of compromising the integrity of the diazeniumdiolate groups. The chemistry developed has applications in the synthesis of polyvalent and dendritic nitric oxide donors.

Abstract 4547: Diazeniumdiolate-based nitric oxide-releasing prodrugs kill lung adenocarcinoma cells in culture and in vivo through alterations in cellular redox balance leading to mitochondrially-mediated apoptosis

Lung cancer is the most common and among the most deadly of human malignancies. Early detection is unusual and there are no completely effective therapies in most cases. Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs are a growing class of promising NO-based therapeutics. Here we show that JS-K (O2-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate) and its homopiperazine analogue are potent tumoristatic agents against non-small cell lung cancer (NSCLC) cells both in vitro and as xenografts in mice. Drug treatment led to 75 - 85% reduction of the growth of H1703 cells in vivo.

The diazeniumdiolate-based NO-releasing compounds displayed a multifaceted mode of action, involving oxidative/nitrosative stress, DNA strand break damage, MnSOD tyrosine nitration and activation of cellular stress signaling. In the NSCLC cells the drugs altered glutathione homeostasis to increase the ratio of oxidized to reduced forms. Altered cellular redox potential associated with Bax dimerization and translocation to mitochondria. Apoptosis was triggered by disruption of the mitochondrial membrane potential leading to membrane permeabilization and cytochrome c release. Apoptosis was induced via a caspase-dependent mechanism and was p53 independent. Activation of effector caspases 3 and 7, cleavage of their nuclear substrate PARP, and morphological changes specific for apoptosis were detected in less than one hour after drug treatment.

The effectiveness of the drugs was significantly correlated with pre-existing high levels of reactive oxygen species (ROS). Many cancer cell types, especially in advanced stage tumors, exhibit increased levels of ROS, and these high-ROS cells are likely to be more vulnerable to damage by further ROS/RNS released from exogenous sources than nonmalignant cells. In the present work, we have identified a subset of 30% of lung adenocarcinoma cell lines that are characterized by high levels of ROS and show that this property of lung cancer cells could be exploited for therapeutic benefits. The levels of endogenous ROS correlated significantly with the drug's toxicity measured as IC50 values. Low levels of peroxide-scavengers peroxiredoxins 1 and 6, and of the DNA repair enzyme OGG1, predispose for the drug's toxicity and could be biomarkers for sensitive tumors. Taken together, the data suggest that diazeniumdiolate-based NO-releasing prodrugs may have application as a personalized therapy for lung cancer, against tumors characterized by high levels of ROS and/or low levels of antioxidant defense/DNA repair mechanisms.

Funded in part under contract HHSN261200800001E

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4547.

Abstract 4116: Relationship between K-ras 4A and superoxide in lung adenocarcinoma cell lines

The K-ras gene is mutated in 30-50% of human lung adenocarcinomas, and even more frequently in cancers of colon and pancreas. It exists in two protein isoforms, K-ras 4A and 4B. Their amino acid sequence is very similar, except for marked differences in the hypervariable domain near the carboxyl terminus. K-ras 4B, with a polylysine tail, is unique among the ras gene products and is the dominant K-ras isoform in most tissues. Wild-type K-ras 4B has tumor suppressor activity (Zhang et al. Nature Gen. 29:25, 2001), whereas K-ras 4A was recently found to be necessary for lung tumor development in mice (To et al. Nature Gen. 40:1240, 2008). In search of an oncogenic function for K-ras 4A in lung cancer, we previously demonstrated a highly significant (P<0.01) positive correlation between K-ras 4A expression, at both mRNA and protein levels, and superoxide amounts in a panel of 11 human lung adenocarcinoma cell lines (Proc. Am. Assoc. for Cancer Research 50: (#437)). Superoxide has been widely implicated in cancer causation and progression. In the present study, we test whether there is a cause-effect relationship between expression of K-ras 4A and superoxide production. Cell line H441 expresses high levels of both superoxide and K-ras 4A. Superoxide levels were determined using a nitroblue tetrazolium (NBT) assay and K-ras 4A protein levels quantified by immunoblot with a specific antibody. Results are means ± SEMs. The effect of reduced levels of K-ras 4A on superoxide production was determined using a K-ras 4A silencing siRNA, which reduced K-ras 4A protein by 60.2 ± 3.0% after 72 hours of siRNA treatment. This reduction had no effect on superoxide (control 1.13 ± 0.08, siRNA 1.17 ± 0.08 nmol NBT reduced/ug protein). The effect of reduced levels of superoxide on K-ras 4A expression was determined using 5 mM Tiron, an electron scavenger. A 36% decrease in superoxide did not affect K-ras 4A protein levels (control 26.90 ± 0.89 vs. Tiron-treated 26.89 ± 1.91, arbitrary units). If these preliminary results are confirmed with additional cell lines and reagents, they may suggest that both expression of K-ras 4A and production of superoxide are controlled by another, pro-oncogenic factor or set of conditions. In view of the importance of both K-ras and superoxide in cancer, discovery of this putative central pro-oncogenic regulator might offer an important preventive and therapeutic target in lung cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4116.

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.

Glycosylated PROLI/NO derivatives as nitric oxide prodrugs

GlcNAc-PROLI/NO prodrugs that are activated by N-acetylglucosaminidase to release nitric oxide (NO) are described. A classical acid-amine coupling is used to bifunctionalize these PROLI/NO prodrugs, which on activation generate up to 4 mol of NO, a peptide residue, and an N-acetylglucosamine residue. Many of the prodrugs synthesized are efficient sources of intracellular NO.

Abstract C102: Reactive oxygen species-related killing of lung adenocarcinoma cells in culture and in vivo by diazeniumdiolate-based nitric oxide-releasing prodrugs

Lung cancer is the most common and among the most deadly of human malignancies. Early detection is unusual and there are no completely effective therapies in most cases. Diazeniumdiolate-based nitric oxide (NO) - releasing prodrugs are a growing class of promising NO-based therapeutics. Here we show that JS-K (O2-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate) and its homopiperazine analogue JS-36-25 are potent tumoristatic agents against lung adenocarcinoma cells both in vitro and as xenografts in mice. JS-K treatment led to 75% reduction of the growth of H1703 cells in vivo, and JS-36-25 appears to be even more effective, leading to 85% reduction of the tumors. We have shown previously that JS-36-25 has diminished reactivity towards glutathione. This drug property may translate to a prolonged half-life in blood, allowing selective accumulation of JS-36-25 in the tumor. This would explain its possibly higher in vivo efficacy compared to JS-K.

Differential lung cancer cells’ responsiveness to both prodrugs appears to be related to their endogenous levels of reactive oxygen species (ROS). The level of endogenous ROS correlated significantly with the drugs’ toxicity measured as IC50 values. The treatment of the lung adenocarcinoma cells with JS-K or JS-36-25 resulted in significant, 2-fold increase in ROS/RNS generation in the cells with high basal levels of ROS. The oxidative/nitrosative stress resulted in significant DNA strand break damage in less than 1 hour of incubation with 1 µM drug. Activation of SAPK/JNK stress pathway was observed within 30 minutes after the treatment was initiated. Initiation of apoptosis occurred early, after 1 hour of incubation with 1 µM compound, as indicated by FACS analysis, as well activation of caspases 3 and 7 and PARP cleavage. Taken together, the data suggest that diazeniumdiolate-based NO - releasing prodrugs may have application as a personalized therapy for lung cancer in patients whose tumors are characterized by high levels of ROS.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C102.

The nitric oxide prodrug JS-K and its structural analogues as cancer therapeutic agents

Nitric oxide (NO) prodrugs of the diazeniumdiolate class are routinely used as reliable sources of nitric oxide in chemical and biological laboratory settings. O(2)-(2,4-dinitrophenyl) diazeniumdiolates, which are derivatized forms of ionic diazeniumdiolates, have been found to show potent anti-proliferative activity in a variety of cancer cells, presumably through the effects of NO. One important member of this class of diazeniumdiolates, O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K), has shown promise as a novel cancer therapeutic agent in a number of animal models. This review describes the developments in chemical and biochemical characterization and structure-activity relationship of JS-K and its analogues. In addition, some molecular mechanistic insights into the observed anti-proliferative activity of JS-K are discussed. Finally, a structural motif is presented for O(2)-(aryl) diazeniumdiolate nitric oxide prodrugs that show potency comparable with that of JS-K.

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.

JS-K, an arylating nitric oxide (NO) donor, has synergistic anti-leukemic activity with cytarabine (ARA-C)

We have designed prodrugs that release nitric oxide (NO) on metabolism by glutathione S-transferases (GST). This design exploits the upregulation of GST in acute myeloid leukemia (AML) cells. O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K, a member of this class) has potent anti-leukemic activity. HL-60 myeloid leukemia cells were used for in vitro studies of the combination of JS-K with daunorubicin (DAUNO), cytarabine (ARA-C) or etoposide (ETOP) using the median effect method to determine synergistic, antagonistic, or additive effects. Combinations of JS-K added simultaneously, 2h before or 2h after the other compounds were used. JS-K and DAUNO were antagonistic in all three drug sequences. JS-K and ETOP were also antagonistic but to a lesser degree. JS-K and ARA-C showed strong synergy. The combination index at the 50% fraction affected was 0.37+/-0.23, 0.24+/-0.27, and 0.15+/-0.11 for simultaneous, JS-K first and ARA-C first additions, respectively. JS-K by itself induced DNA strand breaks at relatively high concentrations. However, at submicromolar concentrations, it significantly augmented ARA-C-induced DNA strand breaks. NMR spectroscopy revealed no evidence of chemical interaction between JS-K and the other chemotherapeutic agents. We conclude that ARA-C and JS-K have synergistic anti-leukemic activity and warrant further exploration in combination.

Aryl bis(diazeniumdiolates): potent inducers of S-glutathionylation of cellular proteins and their in vitro antiproliferative activities

A number of bis(diazeniumdiolates) that we designed to release up to 4 mol of nitric oxide (NO) and that are structural analogues of the NO prodrug and anticancer lead compound O(2)-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2- diolate (PABA/NO) were synthesized and studied. A majority of these compounds yielded higher levels of NO, were better inhibitors of proliferation of a number of cancer cell lines, and more rapidly induced substantially increased levels of S-glutathionylation of cellular proteins in comparison with PABA/NO. In most cases, the antiproliferative activity and extents of S-glutathionylation correlated well with levels of intracellular NO release. We report bis(diazeniumdiolates) to be a class of S-glutathionylating agents with potent antiproliferative and S-glutathionylating activity.

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

Nitric oxide (NO) prodrugs such as O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) are a growing class of promising NO-based therapeutics. Nitric oxide release from the anti-cancer lead compound, JS-K, is proposed to occur through a nucleophilic aromatic substitution by glutathione (GSH) catalyzed by glutathione S-transferase (GST) to form a diazeniumdiolate anion that spontaneously releases NO. In this study, a number of structural analogues of JS-K were synthesized and their chemical and biological properties were compared with those of JS-K. The homopiperazine analogue of JS-K showed anti-cancer activity that is comparable with that of JS-K but with a diminished reactivity towards both GSH and GSH/GST; both the aforementioned compounds displayed no cytotoxic activity towards normal renal epithelial cell line at concentrations where they significantly diminished the proliferation of a panel of renal cancer cell lines. These properties may prove advantageous in the further development of this class of nitric oxide prodrugs as cancer therapeutic agents.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.