Mechanism for ribonucleotide reductase inactivation by the anticancer drug gemcitabine

Ribonucleotide reductase inhibition improves the symptoms of a Caenorhabditis elegans model of Alzheimer's disease

Alzheimer's disease is the main cause of aging-associated dementia, for which there is no effective treatment. In this work, we reanalyze the information of a previous genome wide association study, using a new pipeline design to identify novel potential drugs. With this approach, ribonucleoside-diphosphate reductase gene (RRM2B) emerged as a candidate target and its inhibitor, 2', 2'-difluoro 2'deoxycytidine (gemcitabine), as a potential pharmaceutical drug against Alzheimer's disease. We functionally verified the effect of inhibiting the RRM2B homolog, rnr-2, in an Alzheimer's model of Caenorhabditis elegans, which accumulates human Aβ1-42 peptide to an irreversible paralysis. RNA interference against rnr-2 and also treatment with 200 ng/ml of gemcitabine, showed an improvement of the phenotype. Gemcitabine treatment increased the intracellular ATP level 3.03 times, which may point to its mechanism of action. Gemcitabine has been extensively used in humans for cancer treatment but at higher concentrations. The 200 ng/ml concentration did not exert a significant effect over cell cycle, or affected cell viability when assayed in the microglia N13 cell line. Thus, the inhibitory drug of the RRM2B activity could be of potential use to treat Alzheimer's disease and particularly gemcitabine might be considered as a promising candidate to be repurposed for its treatment.

Overcoming Microbiome-Acquired Gemcitabine Resistance in Pancreatic Ductal Adenocarcinoma

Gastrointestinal cancers (GICs) are one of the most recurrent diseases in the world. Among all GICs, pancreatic cancer (PC) is one of the deadliest and continues to disrupt people's lives worldwide. The most frequent pancreatic cancer type is pancreatic ductal adenocarcinoma (PDAC), representing 90 to 95% of all pancreatic malignancies. PC is one of the cancers with the worst prognoses due to its non-specific symptoms that lead to a late diagnosis, but also due to the high resistance it develops to anticancer drugs. Gemcitabine is a standard treatment option for PDAC, however, resistance to this anticancer drug develops very fast. The microbiome was recently classified as a cancer hallmark and has emerged in several studies detailing how it promotes drug resistance. However, this area of study still has seen very little development, and more answers will help in developing personalized medicine. PC is one of the cancers with the highest mortality rates; therefore, it is crucial to explore how the microbiome may mold the response to reference drugs used in PDAC, such as gemcitabine. In this article, we provide a review of what has already been investigated regarding the impact that the microbiome has on the development of PDAC in terms of its effect on the gemcitabine pathway, which may influence the response to gemcitabine. Therapeutic advances in this type of GIC could bring innovative solutions and more effective therapeutic strategies for other types of GIC, such as colorectal cancer (CRC), due to its close relation with the microbiome.

RRM2 enhances MYCN-driven neuroblastoma formation and acts as a synergistic target with CHK1 inhibition

High-risk neuroblastoma, a pediatric tumor originating from the sympathetic nervous system, has a low mutation load but highly recurrent somatic DNA copy number variants. Previously, segmental gains and/or amplifications allowed identification of drivers for neuroblastoma development. Using this approach, combined with gene dosage impact on expression and survival, we identified ribonucleotide reductase subunit M2 (RRM2) as a candidate dependency factor further supported by growth inhibition upon in vitro knockdown and accelerated tumor formation in a neuroblastoma zebrafish model coexpressing human RRM2 with MYCN. Forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition, while high RRM2 expression in human neuroblastomas correlates with high CHK1 activity. MYCN-driven zebrafish tumors with RRM2 co-overexpression exhibit differentially expressed DNA repair genes in keeping with enhanced ATR-CHK1 signaling activity. In vitro, RRM2 inhibition enhances intrinsic replication stress checkpoint addiction. Last, combinatorial RRM2-CHK1 inhibition acts synergistic in high-risk neuroblastoma cell lines and patient-derived xenograft models, illustrating the therapeutic potential.

Resistance to Gemcitabine in Pancreatic Ductal Adenocarcinoma: A Physiopathologic and Pharmacologic Review

Pancreatic ductal adenocarcinoma (PDAC) is a very aggressive tumor with a poor prognosis and inadequate response to treatment. Many factors contribute to this therapeutic failure: lack of symptoms until the tumor reaches an advanced stage, leading to late diagnosis; early lymphatic and hematic spread; advanced age of patients; important development of a pro-tumoral and hyperfibrotic stroma; high genetic and metabolic heterogeneity; poor vascular supply; a highly acidic matrix; extreme hypoxia; and early development of resistance to the available therapeutic options. In most cases, the disease is silent for a long time, andwhen it does become symptomatic, it is too late for ablative surgery; this is one of the major reasons explaining the short survival associated with the disease. Even when surgery is possible, relapsesare frequent, andthe causes of this devastating picture are the low efficacy ofand early resistance to all known chemotherapeutic treatments. Thus, it is imperative to analyze the roots of this resistance in order to improve the benefits of therapy. PDAC chemoresistance is the final product of different, but to some extent, interconnected factors. Surgery, being the most adequate treatment for pancreatic cancer and the only one that in a few selected cases can achieve longer survival, is only possible in less than 20% of patients. Thus, the treatment burden relies on chemotherapy in mostcases. While the FOLFIRINOX scheme has a slightly longer overall survival, it also produces many more adverse eventsso that gemcitabine is still considered the first choice for treatment, especially in combination with other compounds/agents. This review discusses the multiple causes of gemcitabine resistance in PDAC.

Wirelessly Activated Nanotherapeutics for In Vivo Programmable Photodynamic-Chemotherapy of Orthotopic Bladder Cancer

Photochemical internalization (PCI) is a promising intervention using photodynamic therapy (PDT) to enhance the activity of chemotherapeutic drugs. However, current bladder cancer treatments involve high-dose chemotherapy and high-irradiance PDT which cause debilitating side effects. Moreover, low penetration of light and drugs in target tissues and cumbersome light delivery procedures hinder the clinical utility of PDT and chemotherapy combination for PCI. To circumvent these challenges, a photodynamic-chemotherapy approach is developed comprising tumor-targeting glycosylated nanocarriers, coloaded with chlorin e6 (Ce6) and gemcitabine elaidate (GemE), and a miniaturized implantable wirelessly powered light-emitting diode (LED) as a light source. The device successfully delivers four weekly light doses to the bladder while the nanocarrier promoted the specific accumulation of drugs in tumors. This approach facilitates the combination of low-irradiance PDT (1 mW cm-2 ) and low-dose chemotherapy (≈1500× lower than clinical dose) which significantly cures and controls orthotopic disease burden (90% treated vs control, 35%) in mice, demonstrating a potential new bladder cancer treatment option.

Tumor-targeted Drug Delivery by Nanocomposites

BACKGROUND

Tumor-targeted delivery by nanoparticles is a great achievement towards the use of highly effective drug at very low doses. The conventional development of tumor-targeted delivery by nanoparticles is based on enhanced permeability and retention (EPR) effect and endocytosis based on receptor-mediated are very demanding due to the biological and natural complications of tumors as well as the restrictions on the design of the accurate nanoparticle delivery systems.

METHODS

Different tumor environment stimuli are responsible for triggered multistage drug delivery systems (MSDDS) for tumor therapy and imaging. Physicochemical properties, such as size, hydrophobicity and potential transform by MSDDS because of the physiological blood circulation different, intracellular tumor environment. This system accomplishes tumor penetration, cellular uptake improved, discharge of drugs on accurate time, and endosomal discharge.

RESULTS

Maximum drug delivery by MSDDS mechanism to target therapeutic cells and also tumor tissues and sub cellular organism. Poorly soluble compounds and bioavailability issues have been faced by pharmaceutical industries, which are resolved by nanoparticle formulation.

CONCLUSION

In our review, we illustrate different types of triggered moods and stimuli of the tumor environment, which help in smart multistage drug delivery systems by nanoparticles, basically a multi-stimuli sensitive delivery system, and elaborate their function, effects, and diagnosis.

Quantifying cell cycle-dependent drug sensitivities in cancer using a high throughput synchronisation and screening approach

BACKGROUND

Chemotherapy and targeted agent anti-cancer efficacy is largely dependent on the proliferative state of tumours, as exemplified by agents that target DNA synthesis/replication or mitosis. As a result, cell cycle specificities of a number of cancer drugs are well known. However, they are yet to be described in a quantifiable manner.

METHODS

A scalable cell synchronisation protocol used to screen a library of 235 anti-cancer compounds exposed over six hours in G1 or S/G2 accumulated AsPC-1 cells to generate a cell cycle specificity (CCS) score.

FINDINGS

The synchronisation method was associated with reduced method-related cytotoxicity compared to nocodazole, delivering sufficient cell cycle purity and cell numbers to run high-throughput drug library screens. Compounds were identified with G1 and S/G2-associated specificities that, overall, functionally matched with a compound's target/mechanism of action. This annotation was used to describe a synergistic schedule using the CDK4/6 inhibitor, palbociclib, prior to gemcitabine/AZD6738 as well as describe the correlation between the CCS score and published synergistic/antagonistic drug schedules.

INTERPRETATION

This is the first highly quantitative description of cell cycle-dependent drug sensitivities that utilised a tractable and tolerated method with potential uses outside the present study. Drug treatments such as those shown to be G1 or S/G2 associated may benefit from scheduling considerations such as after CDK4/6 inhibitors and being first in drug sequences respectively.

FUNDING

Cancer Research UK (CRUK) Institute core grants C14303/A17197 and C9545/A29580. The Li Ka Shing Centre where this work was performed was generously funded by CK Hutchison Holdings Limited, the University of Cambridge, CRUK, The Atlantic Philanthropies and others.

Drug-metabolizing enzymes: role in drug resistance in cancer

Although continuous researches are going on for the discovery of new chemotherapeutic agents, resistance to these anticancer agents has made it really difficult to reach the fruitful results. There are many causes for this resistance that are being studied by the researchers across the world, but still, success is far because there are several factors that are going along unattended or have been studied less. Drug-metabolizing enzymes (DMEs) are one of these factors, on which less study has been conducted. DMEs include Phase I and Phase II enzymes. Cytochrome P450s (CYPs) are major Phase I enzymes while glutathione-S-transferases (GSTs), UDP-glucuronosyltransferases (UGTs), dihydropyrimidine dehydrogenases are the major enzymes belonging to the Phase II enzymes. These enzymes play an important role in detoxification of the xenobiotics as well as the metabolism of drugs, depending upon the tissue in which they are expressed. When present in tumorous tissues, they cause resistance by metabolizing the drugs and rendering them inactive. In this review, the role of these various enzymes in anticancer drug metabolism and the possibilities for overcoming the resistance have been discussed.

Nanomedicines guided nanoimaging probes and nanotherapeutics for early detection of lung cancer and abolishing pulmonary metastasis: Critical appraisal of newer developments and challenges to clinical transition

Lung cancer (LC) is the second most prevalent type of cancer and primary cause of mortality among both men and women, worldwide. The most commonly employed diagnostic modalities for LC include chest X-ray (CXR), magnetic-resonance-imaging (MRI), computed tomography (CT-scan), and fused-positron-emitting-tomography-CT (PET-CT). Owing to several limitations associated with the use of conventional diagnostic tools such as radiation burden to the patient, misleading diagnosis ("missed lung cancer"), false staging and low sensitivity and resolution, contemporary diagnostic regimen needed to be employed for screening of LC. In recent decades, nanotechnology-guided interventions have been transpired as emerging nanoimaging probes for detection of LC at advanced stages, while producing signal amplification, better resolution for surface and deep tissue imaging, and enhanced translocation and biodistribution of imaging probes within the cancerous tissues. Besides enormous potential of nanoimaging probes, nanotechnology-based advancements have also been evidenced for superior efficacy for treatment of LC and abolishing pulmonary metastasis (PM). The success of nanotherapeutics is due to their ability to maximise translocation and biodistribution of anti-neoplastic agents into the tumor tissues, improve pharmacokinetic profiles of anti-metastatic agents, optimise target-specific drug delivery, and control release kinetics of encapsulated moieties in target tissues. This review aims to overview and critically discuss the superiority of nanoimaging probes and nanotherapeutics over conventional regimen for early detection of LC and abolishing PM. Current challenges to clinical transition of nanoimaging probes and therapeutic viability of nanotherapeutics for treatment for LC and PM have also been pondered.

Computational Approaches Towards Kinases as Attractive Targets for Anticancer Drug Discovery and Development

BACKGROUND

One of the major goals of computational chemists is to determine and develop the pathways for anticancer drug discovery and development. In recent past, high performance computing systems elicited the desired results with little or no side effects. The aim of the current review is to evaluate the role of computational chemistry in ascertaining kinases as attractive targets for anticancer drug discovery and development.

METHODS

Research related to computational studies in the field of anticancer drug development is reviewed. Extensive literature on achievements of theorists in this regard has been compiled and presented with special emphasis on kinases being the attractive anticancer drug targets.

RESULTS

Different approaches to facilitate anticancer drug discovery include determination of actual targets, multi-targeted drug discovery, ligand-protein inverse docking, virtual screening of drug like compounds, formation of di-nuclear analogs of drugs, drug specific nano-carrier design, kinetic and trapping studies in drug design, multi-target QSAR (Quantitative Structure Activity Relationship) model, targeted co-delivery of anticancer drug and siRNA, formation of stable inclusion complex, determination of mechanism of drug resistance, and designing drug like libraries for the prediction of drug-like compounds. Protein kinases have gained enough popularity as attractive targets for anticancer drugs. These kinases are responsible for uncontrolled and deregulated differentiation, proliferation, and cell signaling of the malignant cells which result in cancer.

CONCLUSION

Interest in developing drugs through computational methods is a growing trend, which saves equally the cost and time. Kinases are the most popular targets among the other for anticancer drugs which demand attention. 3D-QSAR modelling, molecular docking, and other computational approaches have not only identified the target-inhibitor binding interactions for better anticancer drug discovery but are also designing and predicting new inhibitors, which serve as lead for the synthetic preparation of drugs. In light of computational studies made so far in this field, the current review highlights the importance of kinases as attractive targets for anticancer drug discovery and development.

Anti-tumour activity of a first-in-class agent NUC-1031 in patients with advanced cancer: results of a phase I study

Background

Gemcitabine is used to treat a wide range of tumours, but its efficacy is limited by cancer cell resistance mechanisms. NUC-1031, a phosphoramidate modification of gemcitabine, is the first anti-cancer ProTide to enter the clinic and is designed to overcome these key resistance mechanisms.

Methods

Sixty-eight patients with advanced solid tumours who had relapsed after treatment with standard therapy were recruited to a dose escalation study to determine the recommended Phase II dose (RP2D) and assess the safety of NUC-1031. Pharmacokinetics and anti-tumour activity was also assessed.

Results

Sixty-eight patients received treatment, 50% of whom had prior exposure to gemcitabine. NUC-1031 was well tolerated with the most common Grade 3/4 adverse events of neutropaenia, lymphopaenia and fatigue occurring in 13 patients each (19%). In 49 response-evaluable patients, 5 (10%) achieved a partial response and 33 (67%) had stable disease, resulting in a 78% disease control rate. C_max levels of the active intracellular metabolite, dFdCTP, were 217-times greater than those reported for equimolar doses of gemcitabine, with minimal toxic metabolite accumulation. The RP2D was determined as 825 mg/m² on days 1, 8 and 15 of a 28-day cycle.

Conclusions

NUC-1031 was well tolerated and demonstrated clinically significant anti-tumour activity, even in patients with prior gemcitabine exposure and in cancers not traditionally perceived as gemcitabine-responsive.

ZH-1 enhances the anticancer activity of gemcitabine via deoxyribonucleotide synthesis and apoptotic pathway against A549 cells

The purpose of this study was to investigate the inhibitory effect of ZH-1 ((6S,9aS,6aR,9bR)-6-(phenylcarbonyl)-6,6a,9a,9b-tetrahydro-8H-azolidino[3,4-a]b enzo [e]indolizine-7,9-dione) and its potential interaction with gemcitabine in A549 cells. MTT assay showed that the combined use of gemcitabine and ZH-1 presented a significant inhibition effect on A549 cell growth with the cell viability from 82.3 ± 5.6% to 51.0 ± 6.6%. The CI value was 0.60 suggesting a synergistic effect between these two drugs. HPLC-MS/MS data indicated that combined treatment with gemcitabine and ZH-1 induced a significant decrease in deoxyadenosine triphosphate, deoxycytidine triphosphate, deoxyguanosine triphosphate and deoxythymidine triphosphate levels compared with use of gemcitabine alone. Five RNs as well as seven dRNs were considered to be significantly contributive to the discrimination of samples. Furthermore, western blot analysis revealed that the combination treatment caused A549 cell apoptosis via the intrinsic pathway by up-regulating Bax/Bcl-2 ratio, activating caspase-9, caspase-3 and poly-ADP-ribose polymerase, and promoting caspase-7, caspase-9 and poly-ADP-ribose polymerase cleavage. Collectively, the combined treatment with gemcitabine and ZH-1 exerted a strong synergistic action on anticancer activity through growth inhibition, perturbations in ribonucleotides and deoxyribonucleotides and the activation of intrinsic apoptotic signaling pathway.

Drug sensitivity and resistance testing identifies PLK1 inhibitors and gemcitabine as potent drugs for malignant peripheral nerve sheath tumors

Patients with malignant peripheral nerve sheath tumor (MPNST), a rare soft tissue cancer associated with loss of the tumor suppressor neurofibromin (NF1), have poor prognosis and typically respond poorly to adjuvant therapy. We evaluated the effect of 299 clinical and investigational compounds on seven MPNST cell lines, two primary cultures of human Schwann cells, and five normal bone marrow aspirates, to identify potent drugs for MPNST treatment with few side effects. Top hits included Polo-like kinase 1 (PLK1) inhibitors (volasertib and BI2536) and the fluoronucleoside gemcitabine, which were validated in orthogonal assays measuring viability, cytotoxicity, and apoptosis. DNA copy number, gene expression, and protein expression were determined for the cell lines to assess pharmacogenomic relationships. MPNST cells were more sensitive to BI2536 and gemcitabine compared to a reference set of 94 cancer cell lines. PLK1, RRM1, and RRM2 mRNA levels were increased in MPNST compared to benign neurofibroma tissue, and the protein level of PLK1 was increased in the MPNST cell lines compared to normal Schwann cells, indicating an increased dependence on these drug targets in malignant cells. Furthermore, we observed an association between increased mRNA expression of PLK1, RRM1, and RRM2 in patient samples and worse disease outcome, suggesting a selective benefit from inhibition of these genes in the most aggressive tumors.

Profiling ribonucleotide and deoxyribonucleotide pools perturbed by gemcitabine in human non-small cell lung cancer cells

In this study, we investigated the dosage effect of gemcitabine, an inhibitor of ribonucleotide reductase (RR), on cellular levels of ribonucleotides and deoxyribonucleotides using high performance liquid chromatography-electrospray ionization tandem mass spectrometric method. As anticipated, after 4-h incubation of non-small cell lung cancer (A549) cells with gemcitabine at 0.5 and 2 μM, there were consistent reductions in levels of deoxyribonucleoside diphosphates (dNDP) and their corresponding deoxyribonucleoside triphosphates (dNTP). However, after 24-h exposure to 0.5 μM gemcitabine, the amounts of dNTP were increased by about 3 fold, whereas cells after 24-h 2 μM gemcitabine treatment exhibited deoxycytidine diphosphate (dCDP), deoxyadenosine diphosphate (dADP) and deoxyguanosine diphosphate (dGDP) levels less than 50% of control values, with deoxycytidine triphosphate (dCTP) and deoxyguanosine triphosphate (dGTP) returning to the control level. Using cell cycle analysis, we found that 24-h incubation at 0.5 μM gemcitabine resulted in a significant increase in S phase arrest, while 2 μM treatment increased G0/G1 population. Our data demonstrated the correlation between the level of RR and the increased levels of dNTPs in the group of 0.5 μM treatment for 24-h with a markedly reduced level of dFdCTP. Accordingly, we proposed that the dosage of dFdC could determine the arrested phase of cell cycle, in turn affecting the recovery of dNTPs pools.

RRM1 *151A>T, RRM1 -756T>C, and RRM1 -585T>Gis associated with increased susceptibility of lung cancer in Chinese patients

Ribonucleotide reductase M1 (RRM1) is a crucial gene in DNA repair. Recent studies have shown that RRM1 expression can be a powerful predictor of survival or chemotherapy sensitivity in patients presenting with carcinomas who are treated with adjuvant gemcitabine-based chemotherapy including lung cancer. However, the relationship between the single nucleotide polymorphisms (SNP) of RRM1 and the susceptibility of lung cancer to chemotherapy has not been well addressed. We detected six tag SNPs of RRM1 genotypes in a cohort of 1007 patients with primary lung cancer and 1007 age- and sex-matched population controls using SNaPshot detection technology. Logistic regression, odds ratios (OR), and 95% confidence intervals were calculated to estimate lung cancer risk associated with SNP genotypes and haplotypes, after adjusting for case-control matching factors. Compared with the T/T and A/T genotype of RRM1 *151A>T, the A/A genotype had an increased risk for overall lung cancer (adjusted OR, 1.33). Additionally, the T/T+T/C genotypes of RRM1 -756T>C were risk factors that increased the susceptibility to lung cancer (adjusted OR 1.54, as compared with the C/C genotype). While the T/T+G/T genotypes of RRM1 -585T>G behaved as protective factors to increase the susceptibility to lung cancer (adjusted OR 0.44, as compared with the C/C genotype). In summary, this is the first study to systematically identify the relationship between the polymorphisms of RRM1 and individual susceptibility to lung cancer. It is anticipated that the RRM1 *151A>T, RRM1 -756T>C, and RRM1 -585T>G polymorphisms will improve the predictive prognosis of lung cancer sensitivity.

The MEK1/2 Inhibitor Pimasertib Enhances Gemcitabine Efficacy in Pancreatic Cancer Models by Altering Ribonucleotide Reductase Subunit-1 (RRM1)

PURPOSE

Gemcitabine, a nucleoside analogue, is an important treatment for locally advanced and metastatic pancreatic ductal adenocarcinoma (PDAC) but provides only modest survival benefit. Targeting downstream effectors of the RAS/ERK signaling pathway by direct inhibition of MEK1/2 proteins is a promising therapeutic strategy, as aberrant activation of this pathway occurs frequently in PDAC. In this study, the ability of pimasertib, a selective allosteric MEK1/2 inhibitor, to enhance gemcitabine efficacy was tested and the molecular mechanism of their interaction was investigated.

EXPERIMENTAL DESIGN

Cell survival and apoptosis were assessed by MTT and Caspase 3/7 Glo assays in human pancreatic cancer cell lines. Protein expression was detected by immunoblotting. The in vivo sensitivity of gemcitabine with pimasertib was evaluated in an orthotopic model of pancreatic tumor.

RESULTS

Synergistic activity was observed when gemcitabine was combined sequentially with pimasertib, in human pancreatic cancer cells. In particular, pimasertib reduced ribonucleotide reductase subunit 1 (RRM1) protein, and this was associated with sensitivity to gemcitabine. Pretreatment with MG132 impaired reduction of RRM1 protein induced by pimasertib, suggesting that RRM1 is degraded posttranslationally. Immunoprecipitation indicated enhanced MDM2-mediated polyubiquitination of RRM1 through Lys-48-mediated linkage following pimasertib treatment, an effect mediated, in part, by AKT. Finally, the combination treatment with pimasertib and gemcitabine caused significant tumor growth delays in an orthotopic pancreatic cancer model, with RRM1 downregulation in pimasertib-treated mice.

CONCLUSIONS

These results confirm an important role of RRM1 in gemcitabine response and indicate MEK as a potential target to sensitize gemcitabine therapy for PDAC. Clin Cancer Res; 21(24); 5563-77. ©2015 AACR.

Curaxin CBL0137 eradicates drug resistant cancer stem cells and potentiates efficacy of gemcitabine in preclinical models of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) continues to be one of the deadliest cancers due to the absence of effective treatment. Curaxins are a class of small molecules with anti-cancer activity demonstrated in different models of cancer in mice. The lead curaxin compound, CBL0137, recently entered Phase I clinical trials. Curaxins modulate several important signaling pathways involved in the pathogenesis of PDA through inhibition of chromatin remodeling complex FACT. FACT is overexpressed in multiple types of tumor, with one of the highest rate of overexpression in PDA (59%). In this study, the efficacy of CBL0137 alone or in combination with current standard of care, gemcitabine, was tested against different models of PDA in vitro and in mouse models. It was found that CBL0137 alone is a potent inducer of apoptosis in pancreatic cancer cell lines and is toxic not only for proliferating bulk tumor cells, but also for pancreatic cancer stem cells. In mice, CBL0137 was effective against several PDA models, including orthotopic gemcitabine resistant PANC-1 model and patient derived xenografts, in which CBL0137 anti-tumor effect correlated with overexpression of FACT. Moreover, we observed synergy of CBL0137 with gemcitabine which may be explained by the ability of CBL0137 to inhibit several transcriptional programs induced by gemcitabine, including NF-kappaB response and expression of ribonucleotide reductase, one of the targets of gemcitabine in cells. This data suggest testing of CBL0137 efficacy in Phase II trial in PDA patients alone and in combination with gemcitabine.

Nanotechnology approaches for inhalation treatment of lung diseases

Local administration of therapeutics by inhalation for treatment of lung diseases has the ability to deliver drugs, nucleic acids and peptides specifically to the site of their action and therefore enhance the efficacy of the treatment, limit the penetration of nebulized therapeutic agent(s) into the bloodstream and consequently decrease adverse systemic side effects of the treatment. Nanotechnology allows for a further enhancement of the treatment efficiency. The present review analyzes modern therapeutic approaches of inhaled nanoscale-based pharmaceutics for the detection and treatment of various lung diseases.

Potent effect of adenoviral vector expressing short hairpin RNA targeting ribonucleotide reductase large subunit M1 on cell viability and chemotherapeutic sensitivity to gemcitabine in non-small cell lung cancer cells

BACKGROUND

Ribonucleotide reductase large subunit (RRM1) is the main enzyme responsible for synthesis of the deoxyribonucleotides used during DNA synthesis. It is also a cellular target for gemcitabine (GEM). Overexpression of RRM1 is reportedly associated with resistance to GEM and the poor prognosis for many types of malignant tumours. Aim of the present study is to establish gene therapy against RRM1-overexpressing tumours.

METHOD

An adenoviral vector that encoded a short hairpin siRNA targeting the RRM1 gene (Ad-shRRM1) was constructed. Two RRM1-overexpressing non-small cell lung cancer (NSCLC) lines, MAC10 and RERF-LC-MA, were used. Finally, a human tumour xenograft model in nude mice was prepared by subcutaneously implanting tumours derived from RERF-LC-MA cells.

RESULTS

Ad-shRRM1 effectively downregulated RRM1 mRNA and protein in both types of NSCLC cells and significantly reduced the percentage of viable cells as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (p<0.005). Caspase 3/7 analysis revealed that transfection with Ad-RRM1 increased the percentage of apoptotic cells in culture containing either type of RRM1-overexpressing cell (p<0.001). Treatment with Ad-shRRM1 exerted a potent antitumour effect against the RRM1-overexpressing RERF-LC-MA xenografts (p<0.05). Furthermore, Ad-shRRM1-mediated inhibition of RRM1 specifically increased sensitivity to gemcitabine of each type of RRM1-overexpressing tumour cell. Combination treatment with Ad-shRRM1 and GEM exerted significantly greater inhibition on cell proliferation than Ad-shRRM1 or GEM treatment alone.

CONCLUSION

RRM1 appeared to be a promising target for gene therapy, and Ad-shRRM1 had strong antitumour effects, specifically anti-proliferative and pro-apoptotic effects, against NSCLC cells that overexpressed RRM1. Combination therapy with Ad-shRRM1 and GEM may become a new treatment option for patients with NSCLC.

A patient-derived subrenal capsule xenograft model can predict response to adjuvant therapy for cancers in the head of the pancreas

BACKGROUND

Although gemcitabine is commonly used as adjuvant therapy for pancreatic adenocarcinoma and pancreaticobiliary-type periampullary cancers, not all patients appear to benefit. This translational study evaluates the potential of a patient-derived subrenal capsule pancreatic cancer xenograft (SRCPCX) model to identify within eight weeks after surgery those tumours which will respond to gemcitabine.

METHODS

SRCPCXs from 32 pancreatectomy patients were established in six to ten NOD/SCID mice per patient. After four weeks the mice were randomly assigned to receive gemcitabine or saline for four more weeks. After eight weeks, gemcitabine response in the grafts was evaluated by the percentage of tumour growth inhibition (%TGI), histological morphology and immunohistochemical markers (Ki-67, CK7 and cleaved caspase-3). These were collated into an Overall Response. Survival was assessed by Kaplan-Meier and Cox multivariate analyses.

RESULTS

375 of 450 pieces of tissue from 27 of 31 patients were evaluable. In 90% of patients, histopathological and immunostaining features of saline-treated control grafts were concordant with their original tumours. At follow up, six of 15 patients whose tumours had an Overall Response to gemcitabine died, compared with ten of 12 whose tumours did not respond (P = 0.025, Fisher's exact test). This was associated with improved survival on Kaplan-Meier analysis (P = 0.013). Cox multivariate analysis indicated that Overall Response, stage and grade were independent predictors of survival.

CONCLUSION

This SRCPCX model retains major histopathological and immunohistochemical characteristics of the original tumour and when a combination of measures is used, enables early assessment of tumour sensitivity to gemcitabine in pancreatic cancers.

Yeast Phenomics: An Experimental Approach for Modeling Gene Interaction Networks that Buffer Disease

The genome project increased appreciation of genetic complexity underlying disease phenotypes: many genes contribute each phenotype and each gene contributes multiple phenotypes. The aspiration of predicting common disease in individuals has evolved from seeking primary loci to marginal risk assignments based on many genes. Genetic interaction, defined as contributions to a phenotype that are dependent upon particular digenic allele combinations, could improve prediction of phenotype from complex genotype, but it is difficult to study in human populations. High throughput, systematic analysis of S. cerevisiae gene knockouts or knockdowns in the context of disease-relevant phenotypic perturbations provides a tractable experimental approach to derive gene interaction networks, in order to deduce by cross-species gene homology how phenotype is buffered against disease-risk genotypes. Yeast gene interaction network analysis to date has revealed biology more complex than previously imagined. This has motivated the development of more powerful yeast cell array phenotyping methods to globally model the role of gene interaction networks in modulating phenotypes (which we call yeast phenomic analysis). The article illustrates yeast phenomic technology, which is applied here to quantify gene X media interaction at higher resolution and supports use of a human-like media for future applications of yeast phenomics for modeling human disease.

Predicting chemosensitivity to gemcitabine and cisplatin based on gene polymorphisms and mRNA expression in non-small-cell lung cancer cells

Aim: We used a panel of 17 non-small-cell lung cancer cell lines to investigate whether the presence of polymorphisms in the RRM1, ERCC1, ABCB1 and MTHFR genes and alterations in their mRNA expression can affect the in vitro chemosensitivity to cisplatin and gemcitabine. Materials & methods: Polymorphisms in these genes were evaluated by direct sequencing. mRNA expression levels were assessed by realtime PCR. In vitro chemosensitivity to cisplatin and gemcitabine was expressed as IC50 values, using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Results: There was a significant, positive correlation between RRM1 mRNA expression and IC50 values for gemcitabine (r = 0.6533, p = 0.0045), and there was a significant, negative correlation between ABCB1 mRNA expression and IC50 values for cisplatin (r = -0.5459, p = 0.0287). When examining the association between the polymorphisms and IC50, we found that only the MTHFR 1298A>C polymorphism showed a tendency to be more chemosensitive to gemcitabine (p = 0.0440). Conclusion: These in vitro results suggest that mRNA expression levels of the RRM1 and ABCB1 genes may be useful indicators of chemosensitivity to gemcitabine and cisplatin, respectively. The MTHFR 1298A>C polymorphism was associated with gemcitabine chemosensitivity, which require further functional analysis with co-expressed genes and should be explored in prospective clinical studies to determine its potential clinical application as a predictive biomarker.

Original submitted 11 February 2014; Revision submitted 3 November 2014

One-electron oxidation of gemcitabine and analogs: mechanism of formation of C3' and C2' sugar radicals

Gemcitabine is a modified cytidine analog having two fluorine atoms at the 2'-position of the ribose ring. It has been proposed that gemcitabine inhibits RNR activity by producing a C3'• intermediate via direct H3'-atom abstraction followed by loss of HF to yield a C2'• with 3'-keto moiety. Direct detection of C3'• and C2'• during RNR inactivation by gemcitabine still remains elusive. To test the influence of 2'- substitution on radical site formation, electron spin resonance (ESR) studies are carried out on one-electron oxidized gemcitabine and other 2'-modified analogs, i.e., 2'-deoxy-2'-fluoro-2'-C-methylcytidine (MeFdC) and 2'-fluoro-2'-deoxycytidine (2'-FdC). ESR line components from two anisotropic β-2'-F-atom hyperfine couplings identify the C3'• formation in one-electron oxidized gemcitabine, but no further reaction to C2'• is found. One-electron oxidized 2'-FdC is unreactive toward C3'• or C2'• formation. In one-electron oxidized MeFdC, ESR studies show C2'• production presumably from a very unstable C3'• precursor. The experimentally observed hyperfine couplings for C2'• and C3'• match well with the theoretically predicted ones. C3'• to C2'• conversion in one-electron oxidized gemcitabine and MeFdC has theoretically been modeled by first considering the C3'• and H3O(+) formation via H3'-proton deprotonation and the subsequent C2'• formation via HF loss induced by this proximate H3O(+). Theoretical calculations show that in gemcitabine, C3'• to C2'• conversion in the presence of a proximate H3O(+) has a barrier in agreement with the experimentally observed lack of C3'• to C2'• conversion. In contrast, in MeFdC, the loss of HF from C3'• in the presence of a proximate H3O(+) is barrierless resulting in C2'• formation which agrees with the experimentally observed rapid C2'• formation.

A kinome screen identifies checkpoint kinase 1 (CHK1) as a sensitizer for RRM1-dependent gemcitabine efficacy

Gemcitabine is among the most efficacious and widely used antimetabolite agents. Its molecular targets are ribonucleotide reductase M1 (RRM1) and elongating DNA. Acquired and de novo resistance as a result of RRM1 overexpression are major obstacles to therapeutic efficacy. We deployed a synthetic lethality screen to investigate if knockdown of 87 selected protein kinases by siRNA could overcome RRM1-dependent gemcitabine resistance in high and low RRM1-expressing model systems. The models included genetically RRM1-modified lung and breast cancer cell lines, cell lines with gemcitabine-induced RRM1 overexpression, and a series of naturally gemcitabine-resistant cell lines. Lead molecular targets were validated by determination of differential gemcitabine activity using cell lines with and without target knock down, and by assessing synergistic activity between gemcitabine and an inhibitor of the lead target. CHK1 was identified has the kinase with the most significant and robust interaction, and it was validated using AZD7762, a small-molecule ATP-competitive inhibitor of CHK1 activation. Synergism between CHK1 inhibition and RRM1-dependent gemcitabine efficacy was observed in cells with high RRM1 levels, while antagonism was observed in cells with low RRM1 levels. In addition, four cell lines with natural gemcitabine resistance demonstrated improved gemcitabine efficacy after CHK1 inhibition. In tumor specimens from 187 patients with non-small-cell lung cancer, total CHK1 and RRM1 in situ protein levels were significantly (p = 0.003) and inversely correlated. We conclude that inhibition of CHK1 may have its greatest clinical utility in malignancies where gemcitabine resistance is a result of elevated RRM1 levels. We also conclude that CHK1 inhibition in tumors with low RRM1 levels may be detrimental to gemcitabine efficacy.

Overcoming nucleoside analog chemoresistance of pancreatic cancer: a therapeutic challenge

Clinical refractoriness to nucleoside analogs (e.g., gemcitabine, capecitabine) is a major scientific problem and is one of the main reasons underlying the extremely poor prognostic state of pancreatic cancer. The drugs' effects are suboptimal partly due to cellular mechanisms limiting their transport, activation, and overall efficacy. Nonetheless, novel therapeutic approaches are presently under study to circumvent nucleoside analog resistance in pancreatic cancer. With these new approaches come additional challenges to be addressed. This review describes the determinants of chemoresistance in the gemcitabine cytotoxicity pathways, provides an overview of investigational approaches for overcoming chemoresistance, and discusses new challenges presented. Understanding the future directions of the field may assist in the successful development of novel treatment strategies for enhancing chemotherapeutic efficacy in pancreatic cancer.

Targeting the Large Subunit of Human Ribonucleotide Reductase for Cancer Chemotherapy

Ribonucleotide reductase (RR) is a crucial enzyme in de novo DNA synthesis, where it catalyses the rate determining step of dNTP synthesis. RRs consist of a large subunit called RR1 (α), that contains two allosteric sites and one catalytic site, and a small subunit called RR2 (β), which houses a tyrosyl free radical essential for initiating catalysis. The active form of mammalian RR is an α_nβ_m hetero oligomer. RR inhibitors are cytotoxic to proliferating cancer cells. In this brief review we will discuss the three classes of RR, the catalytic mechanism of RR, the regulation of the dNTP pool, the substrate selection, the allosteric activation, inactivation by ATP and dATP, and the nucleoside drugs that target RR. We will also discuss possible strategies for developing a new class of drugs that disrupts the RR assembly.

RRM1 expression and clinical outcome of gemcitabine-containing chemotherapy for advanced non-small-cell lung cancer: a meta-analysis

BACKGROUND

The predictive value of RRM1 to therapeutic efficacy of gemicitabine-containing chemotherapy in patients with advanced non-small-cell lung cancer (NSCLC) remains disputable. This meta-analysis is performed to systematically evaluate whether RRM1 expression is associated with the clinical outcome of gemcitabine-containing regimen in advanced NSCLC.

METHODS

An electronic search was conducted using the databases Pubmed, Medline, EMBASE, Cochrane library and CNKI, from inception to May, 2011. A systemic review of the studies on the association between RRM1 expression in advanced NSCLC and clinical outcome of gemcitabine-containing regimen was performed. Pooled odds ratios (OR) for the response rate, weighted median survival and time to progression were calculated using the software Revman 5.0.

RESULTS

The search strategy identified 18 eligible studies (n=1243). Response rate to gemcitabine-containing regimen was significantly higher in patients with low/negative RRM1 (OR=0.31, 95% CI 0.21-0.45, P<0.00001). NSCLC patients with low/negative RRM1 who were treated with gemicitabine-containing regimen survived 3.94 months longer (95% CI 2.15-5.73, P<0.0001) and had longer time to progression for 2.64 months (95% CI 0.39-4.89, P=0.02) than those with high/positive RRM1.

CONCLUSIONS

Low/negative RRM1 expression in advanced NSCLC was associated with higher response rate to gemcitabine-containing regimen and better prognosis. Large phase III randomized trials are required to identify whether RRM1 detection is clinically valuable for predicting the prognosis and sensitivity to gemcitabine-containing regimen in advanced NSCLC.

Modulation of the ribonucleotide reductase M1-gemcitabine interaction in vivo by N-ethylmaleimide

Ribonucleotide reductase M1 (RRM1) is the regulatory subunit of the holoenzyme that catalyzes the conversion of ribonucleotides to 2'-deoxyribonucleotides. Its function is indispensible in cell proliferation and DNA repair. It also serves as a biomarker of therapeutic efficacy of the antimetabolite drug gemcitabine (2',2'-difluoro-2'-deoxycytidine) in various malignancies. However, a mechanistic explanation remains to be determined. This study investigated how the alkylating agent N-ethylmaleimide (NEM) interacts with the inhibitory activity of gemcitabine on its target protein RRM1 in vivo. We found, when cells were treated with gemcitabine in the presence of NEM, a novel 110 kDa band, along with the 90 kDa native RRM1 band, appeared in immunoblots. This 110 kDa band was identified as RRM1 by mass spectrometry (LC-MS/MS) and represented a conformational change resulting from covalent labeling by gemcitabine. It is specific to gemcitabine/NEM, among 11 other chemotherapy drugs tested. It was also detectable in human tumor xenografts in mice treated with gemcitabine. Among mutations of seven residues essential for RRM1 function, C218A, C429A, and E431A abolished the conformational change, while N427A, C787A, and C790A diminished it. C444A was unique since it was able to alter the conformation even in absence of gemcitabine treatment. We conclude that the thiol alkylator NEM can stabilize the gemcitabine-induced conformational change of RRM1, and this stabilized RRM1 conformation has the potential to serve as a specific biomarker of gemcitabine's therapeutic efficacy.

Stearoyl gemcitabine nanoparticles overcome resistance related to the over-expression of ribonucleotide reductase subunit M1

Gemcitabine is a deoxycytidine analog used in the treatment of various solid tumors. However, tumors often develop resistances over time, which becomes a major issue for most gemcitabine-related chemotherapies. In the present study, a previously reported stearoyl gemcitabine nanoparticle formulation (GemC18-NPs) was evaluated for its ability to overcome gemcitabine resistance. In the wild type CCRF-CEM human leukemia cells, the IC(50) value of GemC18-NPs was 9.5-fold greater than that of gemcitabine hydrochloride (HCl). However, in the CCRF-CEM-AraC-8C cells that are deficient in the human equilibrative nucleoside transporter-1, the IC(50) of GemC18-NPs was only 3.4-fold greater than that in the parent CCRF-CEM cells, whereas the IC(50) of gemcitabine HCl was 471-fold greater than that in the parent CCRF-CEM cells. The GemC18-NPs were also more cytotoxic than gemcitabine HCl in the deoxycytidine kinase deficient (CCRF-CEM/dCK(-/-)) tumor cells. Similar to gemcitabine HCl, GemC18-NPs induced apoptosis through caspase activation. Another gemcitabine-resistant tumor cell line, TC-1-GR, was developed in our laboratory. In the TC-1-GR cells, the IC(50) of GemC18-NPs was only 5% of that of gemcitabine HCl. Importantly, GemC18-NPs effectively controlled the growth of gemcitabine resistant TC-1-GR tumors in mice, whereas the molar equivalent dose of gemcitabine HCl did not show any activity against the growth of the TC-1-GR tumors. Proteomics analysis revealed that the TC-1-GR cells over-expressed ribonucleotide reductase M1, which was likely the cause of the acquired gemcitabine resistance in the TC-1-GR cells. To our best knowledge, this represents the first report demonstrating that a nanoparticle formulation of gemcitabine overcomes gemcitabine resistance related to ribonucleotide reductase M1 over-expression.

The ribonucleotide reductase large subunit (RRM1) as a predictive factor in patients with cancer

The large subunit of human ribonucleotide reductase, RRM1, is involved in the regulation of cell proliferation, cell migration, tumour and metastasis development, and the synthesis of deoxyribonucleotides for DNA synthesis. It is also a cellular target for the chemotherapeutic agent, gemcitabine. RRM1 has been studied in a large number of patients with different types of cancer, such as non-small-cell lung cancer, pancreatic cancer, breast cancer, and biliary tract cancer, to establish its prognostic or predictive value when patients were treated with gemcitabine, and mRNA expression and genetic variants as determined by genotyping have in some cases been associated with clinical outcome of patients with cancer. Here, we review preclinical and clinical studies of RRM1 assessment and discuss the further steps in the development of this clinically pertinent biomarker.

Liquid chromatographic methods for the determination of endogenous nucleotides and nucleotide analogs used in cancer therapy: a review

Endogenous ribonucleotides and deoxyribonucleotides play a crucial role in cell function. The determination of their levels is of fundamental interest in numerous applications such as energy metabolism, biochemical processes, or in understanding the mechanism of nucleoside analog compounds. Nucleoside analogs are widely used in anticancer therapy. Their mechanisms of action are related to their structural similarity with natural nucleotides. Numerous assays have been described for the determination of endogenous nucleotides or anticancer nucleotide analogs in different matrices such as cellular cultures, tissue or peripheral blood mononuclear cells. The determination of these compounds is challenging due to the large difference of concentrations between ribonucleotides and deoxyribonucleotides, the presence of numerous endogenous interferences in complex matrices and the high polarity of the molecules due to the phosphate moiety. The extraction was generally performed at low temperature and was based on protein precipitation using acid or solvent mixture. This first phase could be coupled with extraction or cleaning step of the supernatant. Liquid chromatography coupled with UV detection and based on ion-exchange chromatography using non-volatile high salt concentrations was largely described for the quantification of nucleotides. However, the development of LC-MS and LC-MS/MS during the last ten years has constituted a sensitive and specific tool. In this case, analytical column was mostly constituted by graphite or C18 stationary phase. Mobile phase was usually based on a mixture of ammonium buffer and acetonitrile and in several assays included a volatile ion-pairing agent. Mass spectrometry detection was performed either with positive or negative electrospray mode according to compounds and mobile phase components. The purpose of the current review is to provide an overview of the most recent chromatographic assays (over the past ten years) developed for the determination of endogenous nucleotides and nucleotide analogs used in cancer therapy. We focused on sample preparation, chromatographic separation and quantitative considerations.

Imexon enhances gemcitabine cytotoxicity by inhibition of ribonucleotide reductase

PURPOSE

Gemcitabine (GEM) is currently the standard first line treatment for pancreatic cancer; however, the overall survival of patients with this disease remains poor. Imexon is a pro-oxidant small molecule which produced a high response rate in combination with GEM in a phase I trial in pancreatic cancer. In this study, we investigate the combination of GEM with a novel redox-active agent, imexon, in vitro and in vivo.

METHODS

Median effect analysis was used for in vitro combination cytotoxicity. The effect of imexon on GEM metabolism and uptake into cells and into DNA and effects on ribonucleotide reductase (RNR) were examined in vitro. The pharmacokinetics and antitumor efficacy of the imexon/GEM combination was evaluated in mouse models.

RESULTS

In three human pancreatic cancer lines, there was additivity for the imexon/GEM combination. There was significantly greater efficacy for the drug combination in Panc-1 xenograft tumors. A pharmacokinetic study in mice showed a near doubling in the AUC of imexon when GEM was co-administered, with no effect of imexon on GEM's pharmacokinetic disposition. In vitro, imexon did not alter GEM's metabolism or uptake into DNA, but significantly inhibited RNR, and this effect was greater when combined with GEM.

CONCLUSIONS

These results suggest that the interaction between imexon and GEM may be due to complimentary inhibition of RNR plus an enhanced exposure to imexon when the GEM is administered in vivo. This combination is currently being tested in a randomized phase II trial in pancreatic cancer.

RRM1 single nucleotide polymorphism -37C-->A correlates with progression-free survival in NSCLC patients after gemcitabine-based chemotherapy

Background

The ribonucleotide reductase M1 (RRM1) gene encodes the regulatory subunit of ribonucleotide reductase, the molecular target of gemcitabine. The overexpression of RRM1 mRNA in tumor tissues is reported to be associated with gemcitabine resistance. Thus, single nucleotide polymorphisms (SNPs) of the RRM1 gene are potential biomarkers of the response to gemcitabine chemotherapy. We investigated whether RRM1 expression in peripheral blood mononuclear cells (PBMCs) or SNPs were associated with clinical outcome after gemcitabine-based chemotherapy in advanced non-small cell lung cancer (NSCLC) patients.

Methods

PBMC samples were obtained from 62 stage IIIB and IV patients treated with gemcitabine-based chemotherapy. RRM1 mRNA expression levels were assessed by real-time PCR. Three RRM1 SNPs, -37C→A, 2455A→G and 2464G→A, were assessed by direct sequencing.

Results

RRM1 expression was detectable in 57 PBMC samples, and SNPs were sequenced in 56 samples. The overall response rate to gemcitabine was 18%; there was no significant association between RRM1 mRNA expression and response rate (P = 0.560). The median progression-free survival (PFS) was 23.3 weeks in the lower expression group and 26.9 weeks in the higher expression group (P = 0.659). For the -37C→A polymorphism, the median PFS was 30.7 weeks in the C(-)37A group, 24.7 weeks in the A(-)37A group, and 23.3 weeks in the C(-)37C group (P = 0.043). No significant difference in PFS was observed for the SNP 2455A→G or 2464G→A.

Conclusions

The RRM1 polymorphism -37C→A correlated with PFS in NSCLC patients treated with gemcitabine-based chemotherapy. No significant correlation was found between PBMC RRM1 mRNA expression and the efficacy of gemcitabine.

Insight into the mechanism of inactivation of ribonucleotide reductase by gemcitabine 5'-diphosphate in the presence or absence of reductant

Gemcitabine 5'-diphosphate (F(2)CDP) is a potent inhibitor of ribonucleotide reductases (RNRs), enzymes that convert nucleotides (NDPs) to deoxynucleotides and are essential for DNA replication and repair. The Escherichia coli RNR, an alpha2beta2 complex, when incubated with 1 equiv of F(2)CDP catalyzes the release of two fluorides and cytosine concomitant with enzyme inactivation. In the presence of reductant (thioredoxin/thioredoxin reductase/NADPH or DTT), the enzyme inactivation results from its covalent labeling of alpha with the sugar of F(2)CDP (one label/alpha2beta2). SDS-PAGE analysis of the inactivated RNR without boiling of the sample reveals that alpha migrates as an 87 and 110 kDa protein in a ratio of 0.6:0.4. When the reductant is omitted, RNR is inactivated by loss of the essential tyrosyl radical and formation of a new radical. Inactivation studies with C225S-alpha in the presence or absence of reductants, reveal it behaves like wt-RNR in the absence of reductant. Inactivated C225S-alpha migrates as an 87 kDa protein and is not covalently modified. C225 is one of the cysteines in RNR's active site that supplies reducing equivalents to make dNDPs. To identify the new radical formed, [1'-(2)H]-F(2)CDP was studied with wt- and C225S-RNR by 9 and 140 GHz EPR spectroscopy. These studies revealed that the new radical is a nucleotide derived with g values of g(x) 2.00738, g(y) 2.00592, and g(z) 2.00230 and with altered hyperfine interactions (apparent triplet collapsed to a doublet) relative to [1'-(1)H]-F(2)CDP. The EPR features are very similar to those we recently reported for the nucleotide radical generated with CDP and E441Q-RNR.

Disulfiram/copper complex inhibiting NFkappaB activity and potentiating cytotoxic effect of gemcitabine on colon and breast cancer cell lines

Most of the gemcitabine (dFdC) resistant cell lines manifested high NFkappaB activity. The NFkappaB activity can be induced by dFdC and 5-FU exposure. The chemosensitizing effect of disulfiram (DS), an anti-alcoholism drug and NFkappaB inhibitor, and copper (Cu) on the chemoresistant cell lines was examined. The DS/Cu complex significantly enhanced the cytotoxicity of dFdC (resistant cells: 12.2-1085-fold) and completely reversed the dFdC resistance in the resitant cell lines. The dFdC-induced NFkappaB activity was markedly inhibited by DS/Cu complex. The data from this study indicated that DS may be used in clinic to improve the therapeutic effect of dFdC in breast and colon cancer patients.

Effect of hyperthermia combined with gemcitabine on apoptotic cell death in cultured human pancreatic cancer cell lines

BACKGROUND AND AIM

It is reported that NF-kappaB is activated by chemotherapy in some cancer cell lines and NF-kappaB activation is one of the mechanisms by which tumors are induced to become resistant to chemotherapy. We reported that heat-treatment-induced heat shock protein 70 (Hsp70) could inhibit I-kappa-B kinase, resulting in the inhibition of NF-kappaB activation. Therefore, we speculated that activated NF-kappaB in a pancreatic cell line might be inhibited by heat treatment, resulting in the enhancement of gemcitabine-induced cytotoxicity.

METHODS

We used the human pancreatic carcinoma cell lines AsPC-1 and MIAPaCa-2. Both cell lines were treated with various concentrations (0, 5, 10, 20, and 30 microM) of gemcitabine for 24 h. Heat treatment (43 degrees C, 1 h) was performed at various times relative to gemcitabine treatment. The effect of gemcitabine and heat treatment on cell survival was determined by WST-8 assay. The status of NF-kappaB in carcinoma cells exposed to gemcitabine was investigated by electrophoretic mobility shift assay and immunocytochemistry. We analyzed apoptosis and necrosis in AsPC-1 and MIAPaCa-2 cells by flow cytometry. Furthermore, the levels of Hsp70, cyclin D1, caspase-3, and vascular endothelial growth factor in each treatment group were detected by western blotting.

RESULTS

(1) Significant cytotoxicity was observed with gemcitabine. (2) Gemcitabine activated NF-kappaB binding activity in both cell lines. (3) Heat treatment inhibited the gemcitabine-induced activation of NF-kappaB. (4) Heat treatment enhanced the cytotoxicity of gemcitabine, especially when heat treatment was performed 24 h before gemcitabine was given. (5) The levels of Hsp70 were increased by heat treatment. Gemcitabine did not affect the protein level of Hsp70. The levels of pro-caspase-3 were decreased by heat treatment combined with gemcitabine.

CONCLUSIONS

Heat treatment inhibited gemcitabine-induced activation of NF-kappaB, resulting in the enhancement of the cytotoxicity of gemcitabine.

Understanding Ribonucleotide Reductase Inactivation by Gemcitabine

This paper focuses on the inhibition of ribonucleotide reductase (RNR) by gemcitabine, 2',2'-difluoro-2'-deoxycytidine (dFdC), a deoxycytidine analogue that is a very active drug against solid tumors and is currently commercialized as gemzar. RNR inactivation is reductant-dependent and occurs in a very different way from that of other known substrate analogues. In the presence of reductants monomer R1 of RNR is inhibited, whereas in the absence of reductants the radical is lost and monomer R2 is inhibited. As inside the cell reductants are available, it is likely that R1 inactivation is the most favorable mechanism responsible for drug cytotoxicity. This inhibition pathway has been unknown to date, but we have conducted a theoretical study that has led us to the first proposal of a mechanism for RNR inhibition by dFdC in the presence of reductants.

Enzyme ribonucleotide reductase: unraveling an enigmatic paradigm of enzyme inhibition by furanone derivatives

Several 2'-substituted-2'-deoxyribonucleotides are potent inactivators of the enzyme ribonucleotide reductase (RNR), by destroying the essential tyrosyl radical located in subunit R2 or/and covalently alkylating the subunit R1. In the absence of external reductants, the inactivation is achieved by alkylation of subunit R1 by a methylene-3(2H)-furanone. The furanone is generated in solution through degradation of a keto-deoxyribonucleotide intermediate, produced during the inhibitory mechanism of a wide group of 2'-substituted inhibitors, and is easily detected experimentally by UV spectroscopy. Interestingly, the same keto-deoxyribonucleotide is also a proposed intermediate of the normal substrate pathway, but by some unknown reason, it does not dissociate from the active site and does not inactivate the enzyme. Therefore, if the currently accepted mechanism for substrate reduction is correct, there must be some specific reason that makes such a reactive intermediate behave differently, not dissociating from the active site during substrate reduction. In this article, we propose to validate the current substrate mechanism by showing that the keto-deoxyribonucleotide dissociates from the active site only in the case of the inhibitors, and therefore, it corresponds to a viable intermediate in the substrate mechanism. Furthermore, we answer unexplained experimental observations that concern the predomination of the normal reduction mechanism over the abnormal ketone formation in the FdNDP and the release of F(-), either in the normal or in the abnormal turnover. For that purpose, we have investigated the interaction between the enzyme and this keto-deoxyribonucleotide generated from the normal substrate and from two widely studied representative inhibitors. A model containing 140 atoms was used to represent the desired structures. The results allowed us to conclude that the solvation free energy of the 2'-substituents, its influence inside the active site, and the charge transfer mechanism from a protein side chain to solution are the thermodynamic driving forces for the intermediate dissociation and subsequent RNR inhibition. Such charge transfer cannot be accomplished by the natural substrate, preventing its dissociation. These results elucidate a paradox which has been unexplained for more than 20 years and further validates both the proposed substrate and inhibition chemical mechanisms.

Ribonucleotide reductase M1 (RRM1) 2464G>A polymorphism shows an association with gemcitabine chemosensitivity in cancer cell lines

OBJECTIVES

Significant variability in the efficacy and toxicity of an anticancer drug is observed in cancer patients. Currently, there are no standard tools for prediction of a patient's tumor response or his risk of adverse events to chemotherapy.

METHODS

We investigate an association between polymorphisms of gemcitabine metabolism-related genes and its chemosensitivity in vitro using 62 human cancer cell lines of various origins. Polymorphisms of gemcitabine metabolism-related genes of deoxycytidine monophosphate deaminase (DCTD), deoxycytidine kinase (DCK) and ribonucleotide reductase M1 (RRM1) were evaluated using the CEQ8000 Genetic analysis system and GeneDoc software. Chemosensitivity of gemcitabine was expressed as an IC50 using MTT assay.

RESULTS

The frequency of the polymorphisms was 21% in DCTD 315T>C, 45.2% in RRM1 1082C>A, 59.7% in RRM1 2455A>G, and 79% in RRM1 2464G>A. When examining the association between these polymorphisms and IC50, only the RRM1 2464G>A showed the tendency to be more chemosensitive to gemcitabine (P=0.011), and haplotypes containing 2464G>A polymorphism also showed the association with chemosensitivity when compared to wild-type RRM1 (G2464G). We could not see the significant differences of mRNA expression level with real-time PCR between cell lines according to G2464A polymorphism. In oligonucleotide microarray 73 GenBank Accession Number (69 genes) were selected which expressed differently between RRM1 wild-type and the G2464A polymorphism.

CONCLUSIONS

RRM1 2464G>A polymorphism demonstrated an association with gemcitabine sensitivity, which needs functional studies with co-expressing genes and prospective clinical studies for the clinical application as a predictive bio-marker.

Computational studies on class I ribonucleotide reductase: understanding the mechanisms of action and inhibition of a cornerstone enzyme for the treatment of cancer

This review provides a synthesis of recent work, using computational methods, on the action and inhibition mechanisms of class I ribonucleotide reductase (RNR). This enzyme catalyzes the rate-limiting step of the pathway for the synthesis of DNA monomers and, therefore, has long been regarded as an important target for therapies aiming to control pathologies that depend strongly on DNA replication. In fact, over the last years, several molecules, which are able to impair RNR activity by different mechanisms, have been applied effectively in anti-cancer, anti-viral and anti-parasite therapies. A better understanding of the chemical mechanisms involved in normal catalysis and in inhibition of the enzyme is important for the rational design of more specific and effective inhibitor compounds. To achieve this goal, computational methods, particularly quantum chemical calculations, have been used more and more frequently. The ever-growing capabilities of these methods together with undeniable advantages make it a stimulating area for research purposes.

Theoretical Study on the Inhibition of Ribonucleotide Reductase by 2‘-Mercapto-2‘-deoxyribonucleoside-5‘-diphosphates

Ribonucleotide reductase (RNR) is responsible for the reduction of ribonucleotides into the correspondent 2'-deoxyribonucleotides in the only physiological process that yields the monomers of DNA. The enzyme has thus become an attractive target for chemotherapies that fight proliferation-based diseases, specifically cancer and infections by some viruses and parasites. 2'-Mercapto-2'-deoxyribonucleoside-5'-diphosphates (SHdNDP) are mechanism-based inhibitors of RNR and therefore potential chemotherapeutic agents for those indications. Previous experimental studies established the in vitro and in vivo activity of SHdNDP. In the in vitro studies, it was observed that the activity was dependent on the oxidative status of the medium, with the inactivation of RNR only occurring when molecular oxygen was available. To better understand the mechanism involved in RNR inactivation by SHdNDP, we performed theoretical calculations on the possible reactions between the inhibitors and the RNR active site. As a result, we propose the possible mechanistic pathways for the chemical events that occur in the absence and in the presence of O2. They correspond to a refinement and a complement of those proposed in the literature.

Ribonucleotide activation by enzyme ribonucleotide reductase: understanding the role of the enzyme

This article focuses on the first step of the catalytic mechanism for the reduction of ribonucleotides catalyzed by the enzyme Ribonucleotide Reductase (RNR). This corresponds to the activation of the substrate. In this work a large model of the active site region involving 130 atoms was used instead of the minimal gas phase models used in previous works. The ONIOM method was employed to deal with such a large system. The results gave additional information, which previous small models could not provide, allowing a much clearer evaluation of the role of the enzyme in this step. Enzyme-substrate interaction energies, specific transition state stabilization, and substrate steric strain energies were obtained. It was concluded that the transition state is stabilized in 4.0 kcal/mol by specific enzyme-substrate interactions. However, this stabilization is cancelled by the cost in conformational energy for the enzyme to adopt the transition state geometry; the overall result is that the enzyme machinery does not lead to a rate enhancement in this step. It was also found that the substrate binds to the active site with almost no steric strain, emphasizing the complementarity and specificity of the RNR active site for nucleotide binding. The main role of the enzyme at the very beginning of the catalytic cycle was concluded to be to impose stereospecifity upon substrate activation and to protect the enzyme radical from the solvent, rather than to be an reaction rate enhancement.