Identification of thymidylate synthase as a potential therapeutic target for lung cancer

Novel mass spectrometry-based assay for thymidylate synthase activity

Thymidylate synthase (TS) is an enzyme responsible for the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), with the co-substrate 5,10-methylenetetrahydrofolate (5,10-CH2-THF) as the methyl donor. TS is the only enzyme capable of de novo biosynthesis of dTMP in humans, a nucleotide crucial for DNA synthesis and therefore cell proliferation and survival. As such, TS is a major drug target in chemotherapy by compounds such as 5-fluorouracil. Due to the clinical and physiological importance of TS, the ability to accurately assay its activity is crucial. Several assays have been developed for this purpose, relying on spectrophotometry or radioisotope labeling methods. In this study, we have developed a liquid chromatography - mass spectrometry-based method for assessing TS activity by direct and specific measurement of the reaction product, dTMP. The assay was tested on mouse liver homogenates. We noted that excessive 5,10-CH2-THF concentration (400 µM) led to substrate inhibition and therefore 200 µM was used. The activity assayed at 1 µM dUMP was linear with protein content and time (up to 60 min) and was 0.56 ± 0.12 pmol/mg protein/min, in line with previously reported values. Additionally, by using a high mass resolution Orbitrap instrument side reactions were monitored, revealing major changes in folate pools and nucleotide metabolism. These findings highlight the value of the developed TS assay for routine TS activity monitoring in complex matrixes such as clinical material.

Genome-scale CRISPR-Cas9 screen identifies PAICS as a therapeutic target for EGFR wild-type non-small cell lung cancer

Epidermal growth factor receptor-targeted (EGFR-targeted) therapies show promise for non-small cell lung cancer (NSCLC), but they are ineffective in a third of patients who lack EGFR mutations. This underlines the need for personalized treatments for patients with EGFR wild-type NSCLC. A genome-wide CRISPR/Cas9 screen has identified the enzyme phosphoribosylaminoimidazole carboxylase/phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS), which is vital in de novo purine biosynthesis and tumor development, as a potential drug target for EGFR wild-type NSCLC. We have further confirmed that PAICS expression is significantly increased in NSCLC tissues and correlates with poor patient prognosis. Knockdown of PAICS resulted in a marked reduction in both in vitro and in vivo proliferation of EGFR wild-type NSCLC cells. Additionally, PAICS silencing led to cell-cycle arrest in these cells, with genes involved in the cell cycle pathway being differentially expressed. Consistently, an increase in cell proliferation ability and colony number was observed in cells with upregulated PAICS in EGFR wild-type NSCLC. PAICS silencing also caused DNA damage and cell-cycle arrest by interacting with DNA repair genes. Moreover, decreased IMPDH2 activity and activated PI3K-AKT signaling were observed in NSCLC cells with EGFR mutations, which may compromise the effectiveness of PAICS knockdown. Therefore, PAICS plays an oncogenic role in EGFR wild-type NSCLC and represents a potential therapeutic target for this disease.

Discovery of 5'-Substituted 5-Fluoro-2'-deoxyuridine Monophosphate Analogs: A Novel Class of Thymidylate Synthase Inhibitors

5-Fluorouracil and 5-fluorouracil-based prodrugs have been used clinically for decades to treat cancer. Their anticancer effects are most prominently ascribed to inhibition of thymidylate synthase (TS) by metabolite 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP). However, 5-fluorouracil and FdUMP are subject to numerous unfavorable metabolic events that can drive undesired systemic toxicity. Our previous research on antiviral nucleotides suggested that substitution at the nucleoside 5'-carbon imposes conformational restrictions on the corresponding nucleoside monophosphates, rendering them poor substrates for productive intracellular conversion to viral polymerase-inhibiting triphosphate metabolites. Accordingly, we hypothesized that 5'-substituted analogs of FdUMP, which is uniquely active at the monophosphate stage, would inhibit TS while preventing undesirable metabolism. Free energy perturbation-derived relative binding energy calculations suggested that 5'(R)-CH3 and 5'(S)-CF3 FdUMP analogs would maintain TS potency. Herein, we report our computational design strategy, synthesis of 5'-substituted FdUMP analogs, and pharmacological assessment of TS inhibitory activity.

Design, synthesis and biological evaluation of new eugenol derivatives containing 1,3,4-oxadiazole as novel inhibitors of thymidylate synthase

We report the preparation and cytotoxicity of two new eugenol derivatives that contain 1,3,4-oxadiazole, as novel inhibitors of thymidylate synthase; these derivatives are shown to be promising chemotherapeutic agents.

Targeting Thymidylate Synthase and tRNA-Derived Non-Coding RNAs Improves Therapeutic Sensitivity in Colorectal Cancer

Some colorectal cancer (CRC) patients are resistant to 5-fluorouracil (5-FU), and high expression levels of thymidylate synthase (TS) contribute to this resistance. This study investigated whether quercetin, a representative polyphenol compound, could enhance the effect of 5-FU in CRC cells. Quercetin suppressed TS levels that were increased by 5-FU in CRC cells and promoted the expression of p53. Quercetin also induced intracellular and mitochondrial reactive oxygen species (ROS) production and Ca2+ dysregulation in a 5-FU-independent pathway in CRC cells. Furthermore, quercetin decreased mitochondrial membrane potential in CRC cells and inhibited mitochondrial respiration. Moreover, quercetin regulated the expression of specific tiRNAs, including tiRNAHisGTG, and transfection of a tiRNAHisGTG mimic further enhanced the apoptotic effect of quercetin in CRC cells. An enhanced sensitivity to 5-FU was also confirmed in colitis-associated CRC mice treated with quercetin. The treatment of quercetin decreased survival rates of the CRC mouse model, with reductions in the number of tumors and in the disease activity index. Also, quercetin suppressed TS and PCNA protein expression in the distal colon tissue of CRC mice. These results suggest that quercetin has the potential to be used as an adjuvant with 5-FU for the treatment of CRC.

Formaldehyde regulates tetrahydrofolate stability and thymidylate synthase catalysis

Tetrahydrofolic acid and formaldehyde are key human metabolites but their physiologically relevant chemistry is undefined. Our NMR studies confirm formaldehyde as a product of tetrahydrofolic acid degradation but also reveal their reaction regulates the stability of tetrahydrofolic acid. These observations identify a novel non-enzymatic feedback mechanism regulating formaldehyde and folate metabolism that has important implications for folate-targeting chemotherapy in cancer and other diseases.

The deubiquitinating enzyme UCHL1 promotes resistance to pemetrexed in non-small cell lung cancer by upregulating thymidylate synthase

Rationale: Resistance to pemetrexed (PEM)-based chemotherapy is a major cause of progression in non-small cell lung cancer (NSCLC) patients. The deubiquitinating enzyme UCHL1 was recently found to play important roles in chemoresistance and tumor progression. However, the potential roles and mechanisms of UCHL1 in PEM resistance remain unclear.

Methods: Bioinformatics analyses and immunohistochemistry were used to evaluate UCHL1 expression in NSCLC specimens. Kaplan-Meier analysis with the log-rank test was used for survival analyses. We established PEM-resistant NSCLC cell lines by exposing them to step-wise increases in PEM concentrations, and in vitro and in vivo assays were used to explore the roles and mechanisms of UCHL1 in PEM resistance using the NSCLC cells.

Results: In chemoresistant tumors from NSCLC patients, UCHL1 was highly expressed and elevated UCHL1 expression was strongly associated with poor outcomes. Furthermore, UCHL1 expression was significantly upregulated in PEM-resistant NSCLC cells, while genetic silencing or inhibiting UCHL1 suppressed resistance to PEM and other drugs in NSCLC cells. Mechanistically, UCHL1 promoted PEM resistance in NSCLC by upregulating the expression of thymidylate synthase (TS), based on reduced TS expression after UCHL1 inhibition and re-emergence of PEM resistance upon TS restoration. Furthermore, UCHL1 upregulated TS expression, which mitigated PEM-induced DNA damage and cell cycle arrest in NSCLC cells, and also conferred resistance to PEM and other drugs.

Conclusions: It appears that UCHL1 promotes PEM resistance by upregulating TS in NSCLC cells, which mitigated DNA damage and cell cycle arrest. Thus, UCHL1 may be a therapeutic target for overcoming PEM resistance in NSCLC patients.

Identification of key genes and evaluation of clinical outcomes in lung squamous cell carcinoma using integrated bioinformatics analysis

Lung cancer is the leading cause of cancer-related mortality worldwide. Despite progress in the treatment of non-small-cell lung cancer, there are limited treatment options for lung squamous cell carcinoma (LUSC), compared with lung adenocarcinoma. The present study investigated the disease mechanism of LUSC in order to identify key candidate genes for diagnosis and therapy. A total of three gene expression profiles (GSE19188, GSE21933 and GSE74706) were analyzed using GEO2R to identify common differentially expressed genes (DEGs). The DEGs were then investigated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. A protein-protein interaction (PPI) network was constructed via the Search Tool for the Retrieval of Interacting Genes/Proteins, and visualized using Cytoscape software. The expression levels of the hub genes identified using CytoHubba were validated using the University of California, Santa Cruz (UCSC) database and the Human Protein Atlas. A Kaplan-Meier curve and Gene Expression Profiling Interactive Analysis were then employed to evaluate the associated prognosis and clinical pathological stage of the hub genes. Furthermore, non-coding RNA regulatory networks were constructed using the Gene-Cloud Biotechnology information website. A total of 359 common DEGs (155 upregulated and 204 downregulated) were identified, which were predominantly enriched in 'mitotic nuclear division', 'cell division', 'cell cycle' and 'p53 signaling pathway'. The PPI network consisted of 257 nodes and 2,772 edges, and the most significant module consisted of 66 upregulated genes. A total of 19 hub genes exhibited elevated RNA levels, and 10 hub genes had elevated protein levels compared with normal lung tissues. The upregulation of five hub genes (CCNB1, CEP55, FOXM1, MKI67 and TYMS; defined in Table I) were significantly associated with poor overall survival and unfavorable clinical pathological stages. Various ncRNAs, such as C1orf220, LINC01561 and MGC39584, may also play important roles in hub-gene regulation. In conclusion, the present study provides further understanding of the pathogenesis of LUSC, and reveals CCNB1, CEP55, FOXM1, MKI67 and TYMS as potential biomarkers or therapeutic targets.

Discovery of N-phenyl-(2,4-dihydroxypyrimidine-5-sulfonamido) phenylurea-based thymidylate synthase (TS) inhibitor as a novel multi-effects antitumor drugs with minimal toxicity

Thymidylate synthase (TS) is a hot target for tumor chemotherapy, and its inhibitors are an essential direction for anti-tumor drug research. To our knowledge, currently, there are no reported thymidylate synthase inhibitors that could inhibit cancer cell migration. Therefore, for optimal therapeutic purposes, combines our previous reports and findings, we hope to obtain a multi-effects inhibitor. This study according to the principle of flattening we designed and synthesized 18 of N-phenyl-(2,4-dihydroxypyrimidine-5-sulfonamido)phenyl urea derivatives as multi-effects inhibitors. The biological evaluation results showed that target compounds could significantly inhibit the hTS enzyme, BRaf kinase and EGFR kinase activity in vitro, and most of the compounds had excellent anti-cell viability for six cancer cell lines. Notably, the candidate compound L14e (IC₅₀ = 0.67 μM) had the superior anti-cell viability and safety to A549 and H460 cells compared with pemetrexed. Further studies had shown that L14e could cause G1/S phase arrest then induce intrinsic apoptosis. Transwell, western blot, and tube formation results proved that L14e could inhibit the activation of the EGFR signaling pathway, then ultimately achieve the purpose of inhibiting cancer cell migration and angiogenesis in cancer tissues. Furthermore, in vivo pharmacology evaluations of L14e showed significant antitumor activity in A549 cells xenografts with minimal toxicity. All of these results demonstrated that the L14e has the potential for drug discovery as a multi-effects inhibitor and provides a new reference for clinical treatment of non-small cell lung cancer.

Cross-Correlative Single-Cell Analysis Reveals Biological Mechanisms of Nanoparticle Radiosensitization

Nanoparticle radiosensitization has been demonstrated well to enhance the effects of radiotherapy, motivate the improvement of therapeutic ratios, and decrease morbidity in cancer treatment. A significant challenge exists in optimizing formulations and translation due to insufficient knowledge of the associated mechanisms, which have historically been limited to physical concepts. Here, we investigated a concept for the role of biological mechanisms. The mere presence of gold nanoparticles led to a down-regulation of thymidylate synthase, important for DNA damage repair in the radioresistant S-phase cells. By developing a cross-correlative methodology to reveal probabilistic gold nanoparticle uptake by cell sub-populations and the associated sensitization as a function of the uptake, a number of revealing observations have been achieved. Surprisingly, for low numbers of nanoparticles, a desensitization action was observed. Sensitization was discovered to preferentially impact S-phase cells, in which impairment of the DNA damage response by the homologous recombination pathway dominates. This small but radioresistant cell population correlates with much greater proliferative ability. Thus, a paradigm is presented whereby enhanced DNA damage is not necessarily due to an increase in the number of DNA double-strand breaks (DSBs) created but can be from a nanoparticle-induced impairment of the damage response by down-regulating repair proteins such as thymidylate synthase.

Quantitative structure-activity relationship of the thymidylate synthase inhibitors of Mus musculus in the series of quinazolin-4-one and quinazolin-4-imine derivatives

A quantitative structure-activity relationship analysis of the 2-methylquinazolin-4-one and quinazolin-4-imine derivatives, well-known antifolate thymidylate synthase (TYMS) inhibitors, has been performed in the range IC₅₀ = 0.4÷380000.0 nmoL/L using the GUSAR 2013 program. Based on the MNA and QNA descriptors using the self-consistent regression, 6 statistically significant consensus models for predicting the IC₅₀ numerical values have been constructed. These models demonstrate high and moderate prognostic accuracies for the training and external validation test sets, respectively. The molecular fragments of TYMS inhibitors regulating their antitumor activity are identified. The obtained data open opportunities for developing novel promising inhibitors of TYMS.

Astrocyte-elevated gene-1 confers resistance to pemetrexed in non-small cell lung cancer by upregulating thymidylate synthase expression

Previous studies have suggested that astrocyte-elevated gene-1 (AEG-1) contributes to the mechanisms of resistance to various chemotherapeutics. In this study, we investigated whether AEG-1 expression level correlated with that of thymidylate synthase (TS), as higher TS expression is known to be associated with the resistance to pemetrexed chemotherapy in patients with advanced lung adenocarcinoma. Using pemetrexed-resistant lung adenocarcinoma PC-9 cell line, we demonstrated that transfection of AEG-1 siRNA lowered TS expression and decreased pemetrexed IC₅₀ value. In contrast, overexpression of AEG-1 was associated with increased expression of TS and higher pemetrexed IC₅₀ value. Immunohistochemical staining of clinical biopsy samples showed that patients with lower AEG-1 expression had longer overall survival time. Moreover, analysis of repeated biopsy samples revealed that an increase in the TS level from baseline to disease progression was significantly associated with the elevation of AEG-1 expression. In conclusion, our data demonstrated that TS expression might be regulated by AEG-1 and that increased expression of these proteins contributes to lung cancer disease progression and may be associated with the development of resistance to pemetrexed.

Squamous non-small cell lung cancer as a distinct clinical entity

Traditionally, the treatment of lung cancer has been based on histologic type [non-small cell lung cancer (NSCLC) or small cell lung cancer], performance status, and stage of disease. However, more recently, treatment decisions are being made based on molecular and histologic characteristics of the tumor. Specifically, the subclassification of NSCLC as squamous or nonsquamous is important in the context of newer treatments because clinical data have demonstrated differences in the tolerability and activity of these agents. Although progress continues to be made in the treatment of nonsquamous NSCLC, a significant unmet need exists for patients with squamous NSCLC. For both targeted and chemotherapeutic agents, the majority of regulatory approvals and updates to clinical practice guidelines for advanced NSCLC have focused on nonsquamous disease. In addition, because of safety concerns, patients with squamous NSCLC have been excluded from a number of clinical trials of investigational agents, particularly those targeting angiogenesis. This review discusses the importance of histology for treatment selection in NSCLC and summarizes recently completed and ongoing trials of investigational agents in squamous NSCLC. In addition, exciting developments in next-generation sequencing of squamous NSCLC have highlighted differences between squamous and nonsquamous disease and revealed potential new therapeutic targets. Advances in the molecular genetics of squamous NSCLC and implications for therapy will also be reviewed. Although progress in squamous NSCLC has faced limitations, momentum is building toward the identification of more effective treatments for this patient population.

Predictive value of thymidylate synthase for the prognosis and survival of lung adenocarcinoma patients

Chemotherapy represents an important treatment modality for lung adenocarcinoma. Thymidylate synthase (TS) is an essential enzyme in DNA synthesis, and its overexpression has been associated with reduced sensitivity to antifolate agents. The aim of the current study was to investigate the expression of TS and the effect on prognosis in lung adenocarcinoma patients. Adenocarcinoma and adjacent carcinoma tissues were resected from 100 patients with lung adenocarcinoma and the TS levels were detected by immunohistochemical analysis. The values for overall survival (OS) and disease-free survival (DFS) were determined using the Kaplan-Meier analysis. The results indicated that the TS protein was expressed predominantly in adenocarcinoma tissues, which exhibited higher TS expression compared with the adjacent tissues (P<0.001). The statistical analysis indicated that TS expression was associated with the clinical stage and history of smoking (P<0.05). The Kaplan-Meier analysis results indicated that the DFS and OS in patients with high TS expression levels were significantly shorter compared with those with low expression levels (P<0.05). In conclusion, the results from this study suggested that TS may serve as an independent predictive factor for survival rate, which may indicate the prognosis of lung adenocarcinoma patients.

Downregulation of thymidylate synthase with arsenic trioxide in lung adenocarcinoma

Thymidylate synthase (TYMS) is an important chemotherapeutic target in non-small cell lung cancer (NSCLC). Arsenic trioxide (ATO) has been shown to suppress TYMS in a colonic cancer model. We examined the effects of TYMS suppression by ATO in lung adenocarcinoma. A panel of 4 lung adenocarcinoma cell lines was used to determine the effects of ATO treatment on cell viability, TYMS expression (protein and mRNA), E2F1 protein expression and TYMS activity. TYMS knockdown and overexpression were performed. Tumor growth inhibition in vivo was studied using a nude mouse xenograft model. ATO showed antiproliferative effects with clinically achievable concentrations (around 1.1-6.9 µM) in 4 lung adenocarcinoma cell lines. Downregulation of TYMS protein and mRNA expression, reduced TYMS activity, and suppressed E2F1 expression were demonstrated in lung adenocarcinoma with ATO. Cell viability was reduced by 15-50% with TYMS knockdown. Overexpression of TYMS led to a 2.7-fold increase in IC50 value with ATO treatment in H358 cells, but not in H23 cells. Using a xenograft model with H358 cell line, relative tumor volume was reduced to 44% that of the control following 8 days of treatment with 7.5 mg/kg ATO, and associated with significant downregulation of TYMS protein expression. In conclusion, ATO has potent in vitro and in vivo activity in lung adenocarcinoma, and is partially mediated by transcriptional downregulation of TYMS.

Unbiased transcriptome signature of in vivo cell proliferation reveals pro- and antiproliferative gene networks

Different types of mature B-cell lymphocytes are overall highly similar. Nevertheless, some B cells proliferate intensively, while others rarely do. Here, we demonstrate that a simple binary classification of gene expression in proliferating vs. resting B cells can identify, with remarkable selectivity, global in vivo regulators of the mammalian cell cycle, many of which are also post-translationally regulated by the APC/C E3 ligase. Consequently, we discover a novel regulatory network between the APC/C and the E2F transcription factors and discuss its potential impact on the G1-S transition of the cell cycle. In addition, by focusing on genes whose expression inversely correlates with proliferation, we demonstrate the inherent ability of our approach to also identify in vivo regulators of cell differentiation, cell survival, and other antiproliferative processes. Relying on data sets of wt, non-transgenic animals, our approach can be applied to other cell lineages and human data sets.

Serine, glycine and one-carbon units: cancer metabolism in full circle

One-carbon metabolism involving the folate and methionine cycles integrates nutritional status from amino acids, glucose and vitamins, and generates diverse outputs, such as the biosynthesis of lipids, nucleotides and proteins, the maintenance of redox status and the substrates for methylation reactions. Long considered a 'housekeeping' process, this pathway has recently been shown to have additional complexity. Genetic and functional evidence suggests that hyperactivation of this pathway is a driver of oncogenesis and establishes a link to cellular epigenetic status. Given the wealth of clinically available agents that target one-carbon metabolism, these new findings could present opportunities for translation into precision cancer medicine.

Current approaches for TYMS polymorphisms and their importance in molecular epidemiology and pharmacogenetics

TS is critical for providing the requisite nucleotide precursors in order to maintain DNA synthesis and repair. Furthermore, it is an important target for several drugs such as 5-fluorouracil and methotrexate. However, several mechanisms of resistance to TS inhibitors have been explained as linked to TYMS overexpression. Some authors have described the relationship between genetic polymorphisms on TYMS, in particular rs34743033, rs2853542 and rs34489327, with the development of several diseases and with the clinical response to drug therapy and/or survival. Nevertheless, the obtained results described in the literature are controversial, which has lead to a search strategy to understand the impact of these polymorphisms on molecular epidemiology and pharmacogenetics. With the progress of these scientific areas, early identification of individuals at risk of disease along with improvement in the prediction of patients’ outcome will offer a powerful tool for the translation of TYMS polymorphisms into clinical practice and individualization of treatments.

Does histology predict survival of advanced non-small cell lung cancer patients treated with platin-based chemotherapy? An analysis of the Eastern Cooperative Oncology Group Study E1594

INTRODUCTION

We conducted this analysis to determine whether survival of advanced NSCLC patients treated with platin-based chemotherapy doublets involving paclitaxel, docetaxel or gemcitabine was dependent on histological subtypes and treatment regimen.

METHODS

We retrospectively analyzed data from E1594, a front-line phase III study in which advanced NSCLC patients were randomized to receive one of four regimens: cisplatin-paclitaxel, cisplatin-gemcitabine, cisplatin-docetaxel, and carboplatin-paclitaxel. Patients were classified into four histology groups: squamous cell (SCC), adeno- (AC), large cell (LCC) and others including not otherwise specified (O/NOS) carcinoma. Logrank test was performed to compare overall survival (OS) and progression free survival (PFS) distributions according to histology as well as treatment.

RESULTS

Of 1139 patients including 716 men and 423 women, AC was the most common subtype (56.8%), followed by SCC (19.7%), O/NOS (17.0%) and LCC (6.5%). Men were more likely to have SCC and women were more likely to have AC (p = 0.002). Among the four histology groups, there was no imbalance in regard to race, performance status, weight loss, brain metastasis or treatment. In each histology group, we found no significant difference in OS and PFS between the four chemotherapy regimens. Conversely, in each treatment arm, the survival outcome was similar between the four histology subtypes.

CONCLUSIONS

Our analysis suggests that histology does not predict survival benefit in advanced NSCLC patients treated with first-line platin-based doublets involving paclitaxel, docetaxel or gemcitabine.

Pharmacodynamic assay of thymidylate synthase activity in peripheral blood mononuclear cells

A simple, selective, and sensitive method utilizing tritium ((3)H) release from (3)H-deoxyuridine 5'-monophosphate (dUMP) substrate for accurate and precise determination of the low basal thymidylate synthase activity (TSA) in normal healthy peripheral blood mononuclear cells (PBMCs) was developed and validated. The method is based on the removal of the remaining substrate after the TSA reaction by absorption onto activated carbon and measurement of the supernatant fluid by liquid scintillation counting. The method background was substantially decreased by using lyophilized substrate and optimized binding conditions of remaining substrate onto carbon after TSA reaction. The concentration of cofactor N (5),N (10) methylene-(6R,S)-tetrahydrofolate was increased to obtain maximal TSA. Method sensitivity was further increased by omission of ethylenediaminetetraacetic acid from the reaction mix and by using longer reaction times. The validation parameters included specificity, linearity, sensitivity, precision, and stability. The lower limit of quantification was 25 μg PBMC cytosolic lysate, which released 1.4 pmol (3)H/h. TSA was stable in PBMC pellets stored for 6 months at -80 °C. The applicability of the method was demonstrated by the successful determination of TSA in PBMC cytosolic lysates from ten healthy volunteers with and without the specific TSA inhibitor FdUMP.

Thymidylate synthase protein expression by IHC and gene copy number by SISH correlate and show great variability in non-small cell lung cancer

INTRODUCTION

Increased expression of thymidylate synthase (TS) is thought to be associated with resistance to TS-targeting drugs, e.g., pemetrexed.

METHODS

TS protein expression (PE) and gene copy number (GCN) were assayed using immunohistochemistry and silver in situ hybridization, respectively, on primary tumors of 189 resected non-small cell lung patients. Associations with pathological and clinical features and prognosis were explored.

RESULTS

Median immunohistochemistry H-score was 220 (range, 10-380) on a 0 to 400 scale; 17% of the patients had a TS expression of 300 or more. TS PE expression did not significantly differ by histology and did not significantly associate with disease-free survival (DFS) or overall survival (OS). However, there was a tendency for increased DFS (p = 0.12) and OS (p = 0.12) in PE positive (>median) squamous-cell carcinoma (SCC) patients. Median GCN was 2.5 genes/nucleus (range, 1.4-9.6); 29% of patients had GCN of 3 or more, 7% of 4 or more and 0.8% amplification. GCN differed by histology (p = 0.015); 50% of SCCs having GCN more than 2.5 versus 32% of adenocarcinomas. There was no significant relationship between TS GCN and DFS or OS; however, a trend toward better DFS (p = 0.18) and OS (p = 0.10) with increased GCN in SCCs was observed. TS GCN was significantly correlated with PE (r = 0.30, p = 0.0009).

CONCLUSIONS

TS PE and GCN vary widely in non-small cell lung and correlate significantly with each other. TS GCN is higher in SCCs, whereas TS PE does not associate with histological subtypes, clinical features, or survival. Variability of TS PE and GCN may indicate potential benefit from pemetrexed therapy in selected SCC patients.

Cell fate control gene therapy based on engineered variants of human deoxycytidine kinase

The safety of cell therapy applications can be enhanced by the introduction of Cell Fate Control (CFC) elements, which encode pharmacologically controlled cellular suicide switches. CFC Gene Therapy (CFCGT) offers the possibility of establishing control over gene-modified cells (GMCs) with regards to their proliferation, differentiation, or function. However, enzymes commonly employed in these approaches often possess poor kinetics and high immunogenicity. We describe a novel CFCGT system based on engineered variants of human deoxyCytidine Kinase (dCK) that overcomes limitations of current modalities. Mutants of dCK with rationally designed active sites that make them thymidine-activating were stably introduced into cells by recombinant lentiviral vectors (LVs). Transduced cells maintained growth kinetics and function. These dCK mutants efficiently activate bromovinyl-deoxyuridine (BVdU), L-deoxythymidine (LdT), and L-deoxyuridine (LdU), which are otherwise not toxic to wild-type cells. We show that mutant dCK-expressing Jurkat, Molt-4, and U87mg cells could be efficiently eliminated in vitro and in xenogeneic leukemia and tumor models in vivo. We also describe a fusion construct of the thymidine-activating dCK to the cytoplasmic tail-truncated LNGFR molecule and applications to in vivo eradication of primary human T cells. This novel CFCGT system offers unique plasticity with respect to the wide range of prodrugs it can potentiate, and can be used as a reliable safety switch in cell and gene therapy.

Expression and pharmacological inhibition of thymidylate synthase and Src kinase in nonsmall cell lung cancer

The combination of cytotoxic chemotherapy with signaling pathway inhibitors represents a potential strategy to improve the treatment of nonsmall cell lung cancer (NSCLC). Thymidylate synthase (TS) is an enzyme essential for DNA synthesis, and its overexpression has been associated with the reduced sensitivity to antifolate agents. Src is a tyrosine kinase that modulates the cytotoxicity of cancer cells after drug treatment, and in vitro data indicate that its inhibition could revert the resistance to TS-inhibiting drugs. Our study investigated the significance of TS and Src expression in NSCLC tissues, and the effects of their pharmacological inhibition in cell lines. In tumor and normal tissues from 94 resected NSCLC patients, TS and Src transcript levels were found positively correlated (R(S) = 0.66), associated with patients smoking history and overall survival. At multivariate analysis, TS gene expression was an independent prognostic factor (relative risk (RR) = 1.78, from 1.16 to 2.72; p < 0.01). Immunohistochemical detection in tumor specimens confirmed that Src kinase activation, evaluated by phospho-specific antibody, was associated to a higher TS expression. In cell lines, dasatinib, a Src-inhibiting agent, synergistically enhanced pemetrexed-cytotoxicity of A549 cells, as evaluated by MTT and apoptosis assays. The biological explanation for this interaction was based on the upregulation of TS messenger RNA and protein levels induced by pemetrexed, which was significantly prevented by dasatinib cotreatment. The data of our study suggest that TS and Src may belong to a common pathway that bears prognostic significance in NSCLC, and that Src represents a potential target to improve the efficacy of TS-inhibiting agents.

Molecular predictors of response to chemotherapy in non-small cell lung cancer

Lung cancer is the leading cause of cancer-related mortality in the United States with 222,520 new cases and 157,300 deaths anticipated in 2010. The primary objective of any cancer treatment is to improve patient outcomes including overall survival and quality of life while minimizing treatment toxicity. As our knowledge of the molecular mechanisms involved in the pathogenesis of lung cancer evolves, improved methods of therapeutic selection may help clinicians better realize these goals. Such selection may be accomplished by examining biomarkers within patients' tumors that may provide prognostic information such as risk of recurrence in early stage disease or predict benefit from specific therapies regardless of disease stage. Three such biomarkers have emerged--excision repair cross-complementation group 1, the regulatory subunit of the ribonucleotide reductase enzyme, and thymidylate synthase--and are actively being evaluated in patients with non-small cell lung cancer. This review will focus on the role of these biomarkers as predictive and/or prognostic markers in the selection of chemotherapy regimens in non-small cell lung cancer patients.

Death receptor 5 and cellular FLICE-inhibitory protein regulate pemetrexed-induced apoptosis in human lung cancer cells

Pemetrexed is a clinically available anti-folate therapeutic agent used in combination with cisplatin for the management of patients with malignant pleural mesothelioma and advanced non-small cell lung cancer. Pemetrexed inhibits three enzymes in purine and pyrimidine synthesis necessary for precursor DNA nucleotides which in turn disrupts growth and survival of normal and cancer cells. The mechanism by which pemetrexed induces apoptosis remains largely uncharacterised. In the current study, we examined the downstream effect of pemetrexed in inducing apoptosis in lung cancer cells. We showed that pemetrexed induced apoptosis via up-regulation of Death Receptor 5 (DR5), an important death receptor for tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL). In addition, we discovered a synergistic effect of combination pemetrexed and recombinant TRAIL in inducing apoptosis. Modulating DR5 induction by small interfering RNA abrogated the ability of pemetrexed to induce apoptosis. In addition, silencing of C/EBP homologous protein (CHOP) expression reduced DR5 expression, demonstrating that the transcriptional factor CHOP has a pivotal role on DR5 up-regulation following pemetrexed treatment. In addition, enforced expression of cellular FLICE-inhibitory protein (c-FLIP), a known inhibitor of caspase 8, protected neoplastic cells from apoptosis despite pemetrexed and/or TRAIL therapy. Thus, our findings demonstrate the efficacy and mechanistic underpinnings of pemetrexed-induced apoptosis, and they suggest pemetrexed may have clinical utility when used in combination with TRAIL for the management of patients with lung cancer.

Thymidylate synthase as a determinant of pemetrexed sensitivity in non-small cell lung cancer

Background:

Although a high level of thymidylate synthase (TS) expression in malignant tumours has been suggested to be related to a reduced sensitivity to the antifolate drug pemetrexed, no direct evidence for such an association has been demonstrated in non-small cell lung cancer (NSCLC). We have now investigated the effect of TS overexpression on pemetrexed sensitivity in NSCLC cells.

Methods:

We established NSCLC cell lines that stably overexpress TS and examined the effects of such overexpression on the cytotoxicity of pemetrexed both in vitro and in xenograft models. We further examined the relation between TS expression in tumour specimens from NSCLC patients and the tumour response to pemetrexed by immunohistochemical analysis.

Results:

The sensitivity of NSCLC cells overexpressing TS to the antiproliferative effect of pemetrexed was markedly reduced compared with that of control cells. The inhibition of DNA synthesis and induction of apoptosis by pemetrexed were also greatly attenuated by forced expression of TS. Furthermore, tumours formed by TS-overexpressing NSCLC cells in nude mice were resistant to the growth-inhibitory effect of pemetrexed observed with control tumours. Finally, the level of TS expression in tumours of non-responding patients was significantly higher than that in those of responders, suggestive of an inverse correlation between TS expression and tumour response to pemetrexed.

Conclusion:

A high level of TS expression confers a reduced sensitivity to pemetrexed. TS expression is thus a potential predictive marker for response to pemetrexed-based chemotherapy in NSCLC patients.

A human ribonuclease induces apoptosis associated with p21WAF1/CIP1 induction and JNK inactivation

Background

Ribonucleases are promising agents for use in anticancer therapy. Among the different ribonucleases described to be cytotoxic, a paradigmatic example is onconase which manifests cytotoxic and cytostatic effects, presents synergism with several kinds of anticancer drugs and is currently in phase II/III of its clinical trial as an anticancer drug against different types of cancer. The mechanism of cytotoxicity of PE5, a variant of human pancreatic ribonuclease carrying a nuclear localization signal, has been investigated and compared to that of onconase.

Methods

Cytotoxicity was measured by the MTT method and by the tripan blue exclusion assay. Apoptosis was assessed by flow cytometry, caspase enzymatic detection and confocal microscopy. Cell cycle phase analysis was performed by flow cytometry. The expression of different proteins was analyzed by western blot.

Results

We show that the cytotoxicity of PE5 is produced through apoptosis, that it does not require the proapoptotic activity of p53 and is not prevented by the multiple drug resistance phenotype. We also show that PE5 and onconase induce cell death at the same extent although the latter is also able to arrest the cell growth. We have compared the cytotoxic effects of both ribonucleases in the NCI/ADR-RES cell line by measuring their effects on the cell cycle, on the activation of different caspases and on the expression of different apoptosis- and cell cycle-related proteins. PE5 increases the number of cells in S and G₂/M cell cycle phases, which is accompanied by the increased expression of cyclin E and p21^WAF1/CIP1 together with the underphosphorylation of p46 forms of JNK. Citotoxicity of onconase in this cell line does not alter the cell cycle phase distribution and it is accompanied by a decreased expression of XIAP

Conclusions

We conclude that PE5 kills the cells through apoptosis associated with the p21^WAF1/CIP1 induction and the inactivation of JNK. This mechanism is significantly different from that found for onconase.