• 5-Fluorouracil
• Pancreatic ductal adenocarcinoma
• TMPRSS4
• siRNA

• Humans
• Carcinoma, Pancreatic Ductal/mortality
• Carcinoma, Pancreatic Ductal/genetics
• Carcinoma, Pancreatic Ductal/drug therapy
• Carcinoma, Pancreatic Ductal/pathology
• Carcinoma, Pancreatic Ductal/surgery
• Pancreatic Neoplasms/genetics
• Pancreatic Neoplasms/drug therapy
• Pancreatic Neoplasms/mortality
• Pancreatic Neoplasms/pathology
• Pancreatic Neoplasms/surgery
• Serine Endopeptidases/genetics
• Serine Endopeptidases/metabolism
• Chemotherapy, Adjuvant
• Male
• Female
• Fluorouracil/administration & dosage
• Aged
• Membrane Proteins/genetics
• Membrane Proteins/metabolism
• Middle Aged
• Survival Rate
• Gene Expression
• Cell Movement
• Adult
• Aged, 80 and over
• Prognosis
• Biomarkers, Tumor/metabolism
• Biomarkers, Tumor/genetics

• Cancer
• DNA repair
• Deoxynucleoside triphosphate (dNTP) metabolism
• Genome stability

• Humans
• Genomic Instability
• Neoplasms/genetics
• Neoplasms/metabolism
• Neoplasms/pathology
• Deoxyribonucleotides/metabolism
• Animals

• 2018-02114 Vetenskapsrådet
• 19-0056-JIA Cancerfonden
• PR2019-0014 Barncancerfonden
• 2022-00304 Dr Åke Olssons Stiftelse för Haematologisk Forskning
• 2021-01143 Stiftelsen Felix Mindus Bidrag till Leukemiforskningen
• 2022-01253 Loo och Hans Ostermans Stiftelse för Medicinsk Forskning
• 2022-01910 Karolinska Institutet

• Hepatocellular carcinoma
• Nomogram
• Radiomics
• Thymidylate synthase

• Humans
• Carcinoma, Hepatocellular/diagnostic imaging
• Carcinoma, Hepatocellular/pathology
• Gadolinium DTPA
• Liver Neoplasms/diagnostic imaging
• Liver Neoplasms/pathology
• Nomograms
• Retrospective Studies
• Thymidylate Synthase
• Magnetic Resonance Imaging

• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou
• 2020-WS-106 Science and Technology Planning Project of Fuzhou

• Colorectal cancer
• DTYMK
• H-score
• Prognosis

Targeted drugs have greatly improved the therapeutic outcome of non‐small cell lung cancer (NSCLC) patients compared with conventional chemotherapy, whereas about one‐third of patients are so far not suitable for targeted therapy due to lack of known driver oncogenes such as a mutated receptor tyrosine kinase (RTK) genes. In this study, we aimed to identify therapeutic targets for this subgroup of NSCLC patients.

We performed genome‐wide CRISPR/Cas9 screens in two NSCLC cell lines carrying wild‐type TP53 and receptor tyrosine kinase (wtTP53‐RTK) genes using a GeCKO v2.0 lentiviral library (containing 123411 sgRNAs and targeting 19050 genes). MAGeCKFlute was used to analyse and identify candidate genes. Genetic perturbation and pharmacological inhibition were used to validate the result in vitro and in vivo.

The Genome‐wide CRISPR/Cas9 screening identified MDM2 as a potential therapeutic target for wtTP53‐RTK NSCLC. Genetic and pharmacological inhibition of MDM2 reduced cell proliferation and impaired tumour growth in the xenograft model, thus confirming the finding of the CRISPR/Cas9 screening. Moreover, treatment by a selective MDM2 inhibitor RG7388 triggered both cell cycle arrest and apoptosis in several NSCLC cell lines. Additionally, RG7388 and pemetrexed synergistically blocked the cell proliferation and growth of wtTP53‐RTK tumours but had limited effects for other genotypes.

We identified MDM2 as an essential gene and a potential therapeutic target in wtTP53‐RTK NSCLC via a genome‐wide CRISPR/Cas9 screening. For this subgroup, treatment by RG7388 alone or by its combination with pemetrexed resulted in significant tumour inhibition.

• CRISPR/Cas9 screen
• MDM2
• NSCLC
• RG7388

• CRISPR-Cas Systems/genetics
• Carcinoma, Non-Small-Cell Lung/drug therapy
• Carcinoma, Non-Small-Cell Lung/genetics
• Carcinoma, Non-Small-Cell Lung/pathology
• Humans
• Lung Neoplasms/drug therapy
• Lung Neoplasms/genetics
• Lung Neoplasms/pathology
• Pemetrexed/therapeutic use
• Receptor Protein-Tyrosine Kinases/genetics
• Receptor Protein-Tyrosine Kinases/therapeutic use
• Tumor Suppressor Protein p53/genetics
• Tumor Suppressor Protein p53/therapeutic use

• National Natural Science Foundation of China

• Carcinoma, Pancreatic Ductal/genetics
• DNA/chemistry
• DNA-(Apurinic or Apyrimidinic Site) Lyase/metabolism
• Endonucleases/metabolism
• G-Quadruplexes
• Humans
• Pancreatic Neoplasms/metabolism
• Proto-Oncogene Proteins p21(ras)/genetics
• Proto-Oncogene Proteins p21(ras)/metabolism
• Pancreatic Neoplasms

• R01 CA216853 NCI NIH HHS
• P20 GM103427 NIGMS NIH HHS
• P30 GM106397 NIGMS NIH HHS
• P30 CA036727 NCI NIH HHS
• R01 CA163649 NCI NIH HHS
• R03 CA235214 NCI NIH HHS
• National Institutes of Health
• Nebraska Department of Health and Human Services
• National Science Foundation

Fluoropyrimidines represent the backbone of many combination chemotherapy regimens for the treatment of solid cancers but are still associated with toxicity and mechanisms of resistance. In this review, we focused on the epigenetic modifiers histone deacetylase inhibitors (HDACis) and on their ability to regulate specific genes and proteins involved in the fluoropyrimidine metabolism and resistance mechanisms. We presented emerging preclinical and clinical studies, highlighting the mechanisms by which HDACis can prevent/overcome the resistance and/or enhance the therapeutic efficacy of fluoropyrimidines, potentially reducing their toxicity, and ultimately improving the overall survival of cancer patients.

Although fluoropyrimidines were introduced as anticancer agents over 60 years ago, they are still the backbone of many combination chemotherapy regimens for the treatment of solid cancers. Like other chemotherapeutic agents, the therapeutic efficacy of fluoropyrimidines can be affected by drug resistance and severe toxicities; thus, novel therapeutic approaches are required to potentiate their efficacy and overcome drug resistance. In the last 20 years, the deregulation of epigenetic mechanisms has been shown to contribute to cancer hallmarks. Histone modifications play an important role in directing the transcriptional machinery and therefore represent interesting druggable targets. In this review, we focused on histone deacetylase inhibitors (HDACis) that can increase antitumor efficacy and overcome resistance to fluoropyrimidines by targeting specific genes or proteins. Our preclinical data showed a strong synergistic interaction between HDACi and fluoropyrimidines in different cancer models, but the clinical studies did not seem to confirm these observations. Most likely, the introduction of increasingly complex preclinical models, both in vitro and in vivo, cannot recapitulate human complexity; however, our analysis of clinical studies revealed that most of them were designed without a mechanistic approach and, importantly, without careful patient selection.

Most patients with hepatocellular carcinoma (HCC) are in the middle or advanced stage at the time of diagnosis, and the therapeutic effect is limited. Therefore, this study aimed to verify whether deoxythymidylate kinase (DTYMK) increased in HCC and was an effective therapeutic target in HCC. The findings revealed that the DTYMK level significantly increased and correlated with poor prognosis in HCC. However, nothing else is known, except that DTYMK could catalyze the phosphorylation of deoxythymidine monophosphate (dTMP) to form deoxythymidine diphosphate (dTDP). A number of experiments were performed to study the function of DTYMK in vitro and in vivo to resolve this knowledge gap. The knockdown of DTYMK was found to significantly inhibit the growth of HCC and increase the sensitivity to oxaliplatin, which is commonly used in HCC treatment. Moreover, DTYMK was found to competitively combine with miR-378a-3p to maintain the expression of MAPK activated protein kinase 2 (MAPKAPK2) and thus activate the phospho-heat shock protein 27 (phospho-HSP27)/nuclear factor NF-kappaB (NF-κB) axis, which mediated the drug resistance, proliferation of tumor cells, and infiltration of tumor-associated macrophages by inducing the expression of C-C motif chemokine ligand 5 (CCL5). Thus, this study demonstrated a new mechanism and provided a new insight into the role of mRNA in not only encoding proteins to regulate the process of life but also regulating the expression of other genes and tumor microenvironment through the competing endogenous RNA (ceRNA) mechanism.

De novo thymidylate synthesis is a crucial pathway for normal and cancer cells. Deoxythymidine monophosphate (dTMP) is synthesized by the combined action of three enzymes: serine hydroxymethyltransferase (SHMT1), dihydrofolate reductase (DHFR) and thymidylate synthase (TYMS), with the latter two being targets of widely used chemotherapeutics such as antifolates and 5‐fluorouracil. These proteins translocate to the nucleus after SUMOylation and are suggested to assemble in this compartment into the thymidylate synthesis complex. We report the intracellular dynamics of the complex in cancer cells by an in situ proximity ligation assay, showing that it is also detected in the cytoplasm. This result indicates that the role of the thymidylate synthesis complex assembly may go beyond dTMP synthesis. We have successfully assembled the dTMP synthesis complex in vitro, employing tetrameric SHMT1 and a bifunctional chimeric enzyme comprising human thymidylate synthase and dihydrofolate reductase. We show that the SHMT1 tetrameric state is required for efficient complex assembly, indicating that this aggregation state is evolutionarily selected in eukaryotes to optimize protein–protein interactions. Lastly, our results regarding the activity of the complete thymidylate cycle in vitro may provide a useful tool with respect to developing drugs targeting the entire complex instead of the individual components.

• cancer metabolism
• protein-protein complex
• purine synthesis
• thymidylate synthesis
• transient interactions

• 5-FU resistance
• JTE-013
• S1PR2 internalization
• colorectal cancer
• endoplasmic reticulum calcium ([Ca2+]ER)
• sphingosine-1-phosphate (S1P)
• uracil generation

• Activating Transcription Factor 4/metabolism
• Animals
• Antineoplastic Agents/therapeutic use
• Colorectal Neoplasms/drug therapy
• Colorectal Neoplasms/metabolism
• Drug Resistance, Neoplasm/drug effects
• Drug Resistance, Neoplasm/physiology
• Endoplasmic Reticulum/metabolism
• Female
• Fluorouracil/therapeutic use
• HCT116 Cells
• Humans
• Lysophospholipids/metabolism
• Male
• Mice, Inbred C57BL
• Middle Aged
• Ribonucleases/metabolism
• Signal Transduction/physiology
• Sphingosine/analogs & derivatives
• Sphingosine/metabolism
• Sphingosine-1-Phosphate Receptors/metabolism
• Tumor Suppressor Proteins/metabolism
• Uracil/metabolism
• Mice

• U-DNA-Seq
• anti-cancer drug treatment
• chromosomes
• gene expression
• genome-wide mapping
• human
• super-resolution microscopy
• uracil-DNA

• Antineoplastic Agents/pharmacology
• DNA/analysis
• DNA/biosynthesis
• DNA/chemistry
• DNA/genetics
• Genome/drug effects
• Genome/genetics
• Genomics
• HCT116 Cells
• Humans
• Microscopy
• Sequence Analysis, DNA
• Uracil/analysis
• Uracil/biosynthesis
• Uracil/chemistry

• R01 CA076584 NCI NIH HHS
• R35 GM134947 NIGMS NIH HHS
• R35 GM136250 NIGMS NIH HHS
• R01 GM108119 NIGMS NIH HHS
• C37/A18784 Cancer Research UK
• National Research, Development and Innovation Office of Hungary
• Ministry of Human Capacities
• National Institutes of Health

• Chemotherapy
• Gastric cancer
• TAS-102
• Third line

• Antineoplastic Combined Chemotherapy Protocols/therapeutic use
• Biochemical Phenomena
• Drug Combinations
• Humans
• Pyrrolidines/therapeutic use
• Stomach Neoplasms/drug therapy
• Thymine
• Trifluridine/therapeutic use
• Uracil/analogs & derivatives
• Uracil/therapeutic use

• pharmacodynamics
• bacterial physiology
• microbiome
• symbiosis

• Animals
• Caenorhabditis elegans/drug effects
• Caenorhabditis elegans/microbiology
• Caenorhabditis elegans/physiology
• Dietary Supplements
• Escherichia coli/drug effects
• Escherichia coli/metabolism
• Floxuridine/pharmacokinetics
• Floxuridine/toxicity
• Folic Acid/metabolism
• Food-Drug Interactions
• Gastrointestinal Microbiome/drug effects
• Gastrointestinal Microbiome/physiology
• Serine/pharmacology
• Thymidine/analogs & derivatives
• Thymidine/metabolism
• Thymidine/pharmacokinetics
• Thymidine/pharmacology
• Uracil Nucleotides/metabolism
• Uracil Nucleotides/pharmacokinetics

• T32 GM136577 NIGMS NIH HHS
• P40 OD010440 NIH HHS
• R24 OD024624 NIH HHS
• L30 TR000589 NCATS NIH HHS
• R35 ES028365 NIEHS NIH HHS
• S10 RR025616 NCRR NIH HHS
• P30 DK056341 NIDDK NIH HHS

DNA glycosylases are enzymes that initiate the base excision repair pathway, a major biochemical process that protects the genomes of all living organisms from intrinsically and environmentally inflicted damage. Recently, base excision repair inhibition proved to be a viable strategy for the therapy of tumors that have lost alternative repair pathways, such as BRCA-deficient cancers sensitive to poly(ADP-ribose)polymerase inhibition. However, drugs targeting DNA glycosylases are still in development and so far have not advanced to clinical trials. In this review, we cover the attempts to validate DNA glycosylases as suitable targets for inhibition in the pharmacological treatment of cancer, neurodegenerative diseases, chronic inflammation, bacterial and viral infections. We discuss the glycosylase inhibitors described so far and survey the advances in the assays for DNA glycosylase reactions that may be used to screen pharmacological libraries for new active compounds.

• DNA glycosylases
• DNA repair
• drug targets

• Bacterial Infections/drug therapy
• Bacterial Infections/enzymology
• DNA Glycosylases/antagonists & inhibitors
• DNA Repair
• Drug Discovery
• Enzyme Inhibitors/pharmacology
• Enzyme Inhibitors/therapeutic use
• Humans
• Inflammation/drug therapy
• Inflammation/enzymology
• Neoplasms/drug therapy
• Neoplasms/enzymology
• Neurodegenerative Diseases/drug therapy
• Neurodegenerative Diseases/enzymology
• Small Molecule Libraries/pharmacology
• Small Molecule Libraries/therapeutic use
• Virus Diseases/drug therapy
• Virus Diseases/enzymology

• antimetabolite inhibitors
• base excision repair
• oxidative damage
• replication stress
• translesion synthesis

• Lung cancer
• chemotherapy
• non-small cell lung cancer (NSCLC)
• pemetrexed
• resistance

In patients with colorectal liver metastases (CRLM), predictive markers for response to preoperative chemotherapy are lacking. The aim of the present study was to evaluate the expression of thymidylate synthase (TS) and excision repair cross-complementation group 1 (ERCC1) as predictive markers in CRLM. A total of 24 patients with CRLM were included in this study. Tumor response was evaluated using the tumor regression grade (TRG) and Response Evaluation Criteria in Solid Tumors (RECIST) methods. TS and ERCC1 expression in paired CRLM and primary lesions were assessed by immunohistochemistry. We analyzed correlations between i) the response to preoperative chemotherapy evaluated by TRG and RECIST, ii) TS and ERCC1 expression and the response evaluated by TRG and RESICT, and iii) TS and ERCC1 expression in matched pairs of primary tumor and CRLM. The preoperative chemotherapy response evaluated by TRG and RECIST was significantly associated (P=0.0005). The response based on RECIST criteria and TRG was significantly associated with TS expression in the primary tumor (P=0.0272, and P=0.0137, respectively). No correlations were detected between marker expression in the primary tumor and in CRLM for either TS or ERCC1 (P=0.371 and P=1.00, respectively). Our data suggested that TS expression in the primary tumor is a predictive marker of preoperative chemotherapy response in CRLM based on both TRG and RECIST methods.

• chemosensitivity
• colorectal cancer
• colorectal liver metastases
• excision repair cross-complementation group 1
• preoperative chemotherapy
• thymidylate synthase

• Cell Line, Tumor
• Cell Proliferation/drug effects
• Cell Survival/drug effects
• Deoxyuridine/analogs & derivatives
• Deoxyuridine/pharmacology
• Drug Resistance, Neoplasm/drug effects
• Drug Synergism
• Gene Knockdown Techniques/methods
• Gene Knockout Techniques
• HCT116 Cells
• Humans
• Mutation
• Neoplasms/drug therapy
• Neoplasms/genetics
• Pemetrexed/pharmacology
• RNA, Small Interfering/pharmacology
• Tumor Suppressor Protein p53/antagonists & inhibitors
• Tumor Suppressor Protein p53/genetics
• Uracil-DNA Glycosidase/deficiency

• P30 CA043703 NCI NIH HHS

Nucleotide metabolism in cancer cells can influence malignant behavior and intrinsic resistance to therapy. Here we describe p53-dependent control of the rate-limiting enzyme in the pyrimidine catabolic pathway, dihydropyrimidine dehydrogenase (DPYD) and its effect on pharmacokinetics of and response to 5-fluorouracil (5-FU). Using in silico/chromatin-immunoprecipitation (ChIP) analysis we identify a conserved p53 DNA-binding site (p53BS) downstream of the DPYD gene with increased p53 occupancy following 5-FU treatment of cells. Consequently, decrease in Histone H3K9AC and increase in H3K27me3 marks at the DPYD promoter are observed concomitantly with reduced expression of DPYD mRNA and protein in a p53-dependent manner. Mechanistic studies reveal inhibition of DPYD expression by p53 is augmented following thymidylate synthase (TS) inhibition and DPYD repression by p53 is dependent on DNA-dependent protein kinase (DNA-PK) and Ataxia telangiectasia mutated (ATM) signaling. In-vivo, liver specific Tp53 loss increases the conversion of 5-FU to 5-FUH₂ in plasma and elicits a diminished 5-FU therapeutic response in a syngeneic colorectal tumor model consistent with increased DPYD-activity. Our data suggest that p53 plays an important role in controlling pyrimidine catabolism through repression of DPYD expression, following metabolic stress imposed by nucleotide imbalance. These findings have implications for the toxicity and efficacy of the cancer therapeutic 5-FU.

• Amino Acid Sequence
• Antimetabolites, Antineoplastic/chemistry
• Binding Sites
• Crystallography, X-Ray
• Herpesvirus 8, Human/enzymology
• Ligands
• Models, Molecular
• Molecular Structure
• Nucleoside-Phosphate Kinase/chemistry
• Quinazolines/chemistry
• Sequence Homology, Amino Acid
• Thiophenes/chemistry

• National Research Foundation of Korea
• - Ministry for Food, Agriculture, Forestry and Fisheries, Korea

Oesophageal squamous cell carcinoma (ESCC) is the sixth most common cause of cancer-associated death in the world and novel therapeutic alternatives are urgently warranted. In this study, we investigated the anti-tumour activity and underlying mechanisms of melatonin, an indoleamine compound secreted by the pineal gland as well as naturally occurring plant products, in ESCC cells and revealed that melatonin inhibited proliferation, migration, invasion and induced mitochondria-dependent apoptosis of ESCC cells in vitro and suppressed tumour growth in the subcutaneous mice model in vivo. Furthermore, after treatment with melatonin, the expressions of pMEK, pErk, pGSK3β and pAkt were significantly suppressed. In contrast, treatment of the conventional chemotherapeutic drug fluorouracil (5-Fu) resulted in activation of Erk and Akt, which could be reversed by co-treatment with melatonin. Importantly, melatonin effectively enhanced cytotoxicity of 5-Fu to ESCC in vitro and in vivo. Together, these results suggested that inhibition of Erk and Akt pathway by melatonin have an important role in sensitization of ESCC cells to 5-Fu. Combined 5-Fu and melatonin treatment may be appreciated as a useful approach for ESCC therapy that warrants further investigation.

While the focus of attempts to classify cell death programs has finally shifted in 2010s from microscopy-based morphological characteristics to biochemical assays, more recent discoveries have put the underlying assumptions of many such assays under severe stress, mostly because of the limited specificity of the assays. On the other hand, proteomics can quantitatively measure the abundances of thousands of proteins in a single experiment. Thus proteomics could develop a modern alternative to both semiquantitative morphology assessment as well as single-molecule biochemical assays. Here we tested this hypothesis by analyzing the proteomes of cells dying after been treated with various chemical agents. The most striking finding is that, for a multivariate model based on the proteome changes in three cells lines, the regulation patterns of the 200–500 most abundant proteins typically attributed to household type more accurately reflect that of the proteins directly interacting with the drug than any other protein subset grouped by common function or biological process, including cell death. This is in broad agreement with the 'rigid cell death mechanics' model where drug action mechanism and morphological changes caused by it are bijectively linked. This finding, if confirmed, will open way for a broad use of proteomics in death modality assessment.

• Antifolate resistance
• Antifolates
• Cancer
• Chemotherapy
• FPGS
• Folate homeostasis
• Folates
• Intracellular retention
• Polyglutamylation

• 5-Fluorouracil
• Antimicrobial activity
• Biopolymer
• Chitosan–PVA/Na+MMT
• Drug release
• Montmorillonite

• DNA methyltransferase inhibitors
• Drug synergy
• Epigenetic therapy
• Histone deacetylation and methylation inhibitors
• Solid tumors

• 5-Fluorouracil
• Müller glia
• Ouabain
• Photoreceptor
• Regeneration

• EIF5A2
• chemoresistance
• esophageal squamous cell carcinoma (ESCC)
• stemness

• Adult
• Aged
• Antineoplastic Agents/pharmacology
• Apoptosis/drug effects
• Apoptosis/genetics
• Blotting, Western
• Carcinoma, Squamous Cell/drug therapy
• Carcinoma, Squamous Cell/genetics
• Carcinoma, Squamous Cell/surgery
• Cell Line, Tumor
• Docetaxel
• Drug Resistance, Neoplasm/drug effects
• Drug Resistance, Neoplasm/genetics
• Esophageal Neoplasms/drug therapy
• Esophageal Neoplasms/genetics
• Esophageal Neoplasms/surgery
• Female
• Fluorouracil/pharmacology
• Gene Expression Regulation, Neoplastic
• Humans
• Immunohistochemistry
• Kaplan-Meier Estimate
• Male
• Middle Aged
• Neoplastic Stem Cells/drug effects
• Neoplastic Stem Cells/metabolism
• Paclitaxel/pharmacology
• Peptide Initiation Factors/genetics
• Peptide Initiation Factors/metabolism
• RNA-Binding Proteins/genetics
• RNA-Binding Proteins/metabolism
• Retrospective Studies
• Reverse Transcriptase Polymerase Chain Reaction
• Taxoids/pharmacology
• Eukaryotic Translation Initiation Factor 5A

• S-1
• gallbladder cancer
• gene expression

• aptamers
• chemotherapeutics
• drug delivery
• nucleoside analogues
• targeted therapy

Antifolates have a crucial role in the treatment of various cancers by inhibiting key enzymes in purine and thymidylate biosynthesis. However, the frequent emergence of inherent and acquired antifolate resistance in solid tumors calls for the development of novel therapeutic strategies to overcome this chemoresistance. The core of solid tumors is highly hypoxic due to poor blood circulation, and this hypoxia is considered to be a major contributor to drug resistance. However, the cytotoxic activity of antifolates under hypoxia is poorly characterized. Here we show that under severe hypoxia, gene expression of ubiquitously expressed key enzymes and transporters in folate metabolism and nucleoside homeostasis is downregulated. We further demonstrate that carcinoma cells become completely refractory, even at sub-millimolar concentrations, to all hydrophilic and lipophilic antifolates tested. Moreover, tumor cells retained sensitivity to the proteasome inhibitor bortezomib and the topoisomerase II inhibitor doxorubicin, which are independent of cell cycle. We provide evidence that this antifolate resistance, associated with repression of folate metabolism, is a result of the inability of antifolates to induce DNA damage under hypoxia, and is attributable to a hypoxia-induced cell cycle arrest, rather than a general anti-apoptotic mechanism. Our findings suggest that solid tumors harboring a hypoxic core of cell cycle-arrested cells may display antifolate resistance while retaining sensitivity to the chemotherapeutics bortezomib and doxorubicin. This study bears important implications for the molecular basis underlying antifolate resistance under hypoxia and its rational overcoming in solid tumors.

• Hsp90 inhibitor
• MSH2
• Non-small-cell lung cancer
• Pemetrexed
• p38 MAPK

To determine whether 5-fluorouracil (5-FU) sensitivity is associated with the mRNA expressions of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and thymidine phosphorylase (TP) in patients with hepatocellular carcinoma (HCC) treated with 5-FU-based transarterial chemoembolization (TACE).

Formalin-fixed, paraffin-embedded tumor specimens from 40 patients treated with 5-FU-based TACE were selected for the examination of TS, DPD, and TP expression level by a quantitative real-time reverse transcription- polymerase chain reaction (PCR) technique. Patients were categorized into high and low expression groups according to the median expression level of each enzyme. Associations between the mRNA expression levels of TS, DPD, and TP and clinical parameters including treatment efficacies, clinicopathological factors, and prognosis were assessed.

High DPD expression was associated with worse treatment outcome, including intrahepatic disease progression rate (hazard ratio [HR] for high DPD versus low DPD, 2.212; 95% confidence interval [CI], 1.030–4.753; P = 0.042), extrahepatic disease progression rate (HR for high versus low DPD, 3.171; 95% CI, 1.003–10.023; P = 0.049), and progression-free survival (HR for high versus low DPD, 2.308; 95% CI, 1.102–4.836; P = 0.027). No correlation was found between the mRNA expression of TS/TP and treatment outcome.

DPD mRNA expression level was negatively correlated with the clinical outcomes of HCC patients treated with 5-FU-based TACE. These results provide indirect evidence that high DPD mRNA expression is a predictive marker of treatment resistance for 5-FU.

• 5-fluorouracil
• dihydropyrimidine dehydrogenase
• hepatocellular carcinoma
• thymidine phosphorylase
• thymidylate synthase
• transarterial chemoembolization

Although treatment options for cancer patients are increasing every year, the drug resistance problem remains very present. It is very difficult to find a drug that acts equally on tumours of the same histology as the individual's genetic characteristics often determine the response to treatment. Furthermore, tumours that initially respond to anti-tumour therapy are able to adapt and develop resistance to the drug, while others do not. In addition, this usually implies resistance development to agents to which the cells have not been exposed, a phenomenon called cross-resistance or multidrug resistance. Given this situation, it has been suggested that the most appropriate treatment would be able to act in parallel on multiple pathways constitutively altered in tumour cells. Pemetrexed is a multitargeted antifolate that exerts its activity against folate-dependent enzymes involved in de novo pyrimidine and purine synthesis. It is currently in use in combination with cisplatin against malignant pleural mesothelioma and non-squamous non-small cell lung cancer with favourable results. By real-time RT-PCR gene expression assays and restoration viability assays we demonstrated that Pemetrexed targets folate-dependent enzymes involved in de novo biosynthesis of purines differently depending on the intrinsic genetic characteristics of the tumour. These differences did not, however, interfere either with the initial response to the drug or with the activation of apoptotic pathways. In addition, these genetic fingerprints can differentiate two groups of tumours: those capable of developing resistance to antifolate, and not capable. These results may be useful to employ targets gene expression as resistance markers, a valuable tool for identifying patients likely to receive combination therapy to prevent the development of resistance.