Thymidylate synthase as an oncogene: a novel role for an essential DNA synthesis enzyme

Preclinical Applications of 3'-Deoxy-3'-[18F]Fluorothymidine in Oncology - A Systematic Review

The positron emission tomography (PET) tracer 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) has been proposed to measure cell proliferation non-invasively in vivo. Hence, it should provide valuable information for response assessment to tumor therapies. To date, [18F]FLT uptake has found limited use as a response biomarker in clinical trials in part because a better understanding is needed of the determinants of [18F]FLT uptake and therapy-induced changes of its retention in the tumor. In this systematic review of preclinical [18F]FLT studies, comprising 174 reports, we identify the factors governing [18F]FLT uptake in tumors, among which thymidine kinase 1 plays a primary role. The majority of publications (83 %) report that decreased [18F]FLT uptake reflects the effects of anticancer therapies. 144 times [18F]FLT uptake was related to changes in proliferation as determined by ex vivo analyses. Of these approaches, 77 % describe a positive relation, implying a good concordance of tracer accumulation and tumor biology. These preclinical data indicate that [18F]FLT uptake holds promise as an imaging biomarker for response assessment in clinical studies. Understanding of the parameters which influence cellular [18F]FLT uptake and retention as well as the mechanism of changes induced by therapy is essential for successful implementation of this PET tracer. Hence, our systematic review provides the background for the use of [18F]FLT in future clinical studies.

Erk5 contributes to maintaining the balance of cellular nucleotide levels and erythropoiesis

An adequate supply of nucleotides is essential for accurate DNA replication, and inappropriate deoxyribonucleotide triphosphate (dNTP) concentrations can lead to replication stress, a common source of DNA damage, genomic instability and tumourigenesis. Here, we provide evidence that Erk5 is necessary for correct nucleotide supply during erythroid development. Mice with Erk5 knockout in the haematopoietic lineage showed impaired erythroid development in bone marrow, accompanied by altered dNTP levels and increased DNA mutagenesis in erythroid progenitors as detected by exome sequencing. Moreover, Erk5-depleted leukemic Jurkat cells presented a marked sensitivity to thymidine-induced S phase stalling, as evidenced by increased H2AX phosphorylation and apoptosis. The increase in thymidine sensitivity correlated with a higher dTTP/dCTP ratio. These results indicate that Erk5 is necessary to maintain the balance of nucleotide levels, thus preventing dNTP misincorporation and DNA damage in proliferative erythroid progenitors and leukemic Jurkat T cells.

One-Carbon Metabolism in Prostate Cancer: The Role of Androgen Signaling

Cancer cell metabolism differs significantly from the metabolism of non-transformed cells. This altered metabolic reprogramming mediates changes in the uptake and use of nutrients that permit high rates of proliferation, growth, and survival. The androgen receptor (AR) plays an essential role in the establishment and progression of prostate cancer (PCa), and in the metabolic adaptation that takes place during this progression. In its role as a transcription factor, the AR directly affects the expression of several effectors and regulators of essential catabolic and biosynthetic pathways. Indirectly, as a modulator of the one-carbon metabolism, the AR can affect epigenetic processes, DNA metabolism, and redox balance, all of which are important factors in tumorigenesis. In this review, we focus on the role of AR-signaling on one-carbon metabolism in tumorigenesis. Clinical implications of one-carbon metabolism and AR-targeted therapies for PCa are discussed in this context.

Overexpression of thymidylate synthase (TYMS) is associated with aggressive tumor features and early PSA recurrence in prostate cancer

Thymidylate synthase (TYMS) plays a role in DNA synthesis and is a target for 5-fluorouracil. In this study TYMS was analyzed by immunohistochemistry on a tissue microarray containing 11,152 prostate cancers. TYMS expression was higher in neoplastic than in normal prostate epithelium and was detectable in 72.9% of 10,223 interpretable cancers. It was considered strong in 21.9%, moderate in 33.4% and weak in 17.6% of tumors. TYMS overexpression was associated with deletions at 5q21 (p < 0.0001), 6q15 (p < 0.0001) and 3p13 (p = 0.0083) and gradually increased with the total number of these deletions present in the respective cancer sample (p < 0.0001). TYMS expression was unrelated to PTEN deletions (p = 0.9535) but tightly linked to high Gleason grade, advanced pathological tumor stage and early PSA recurrence (p < 0.0001). The prognostic value of TYMS was independent from the ERG status and deletions at 3p13, 5q21, and 6q15. In multivariate analyses the prognostic role of TYMS expression was independent of Gleason grade, pT stage, preoperative PSA, pN stage, or resection margins. TYMS expression analysis might result in clinically useful information in prostate cancer. The striking link to some but not all chromosomal aberrations might suggest a mechanistical link with specific types of DNA damage.

Evaluation of Thymidylate Synthase Expression in Prostate Cancer

Thymidylate synthase (TS), a key enzyme in DNA synthesis, is over-expressed in a variety of cancer cells. 5-Fluorouracil, an anticancer agent clinically used against various cancers, including prostate cancer, inhibits DNA synthesis by binding TS. In this study, we investigated expression of TS in prostate cancer and its prognostic significance. Seventy-five prostatic tissue specimens were obtained from patients who had undergone prostate biopsy for diagnosis of prostate cancer. We analyzed the cancerous tissue specimens for TS expression using immunohistochemistry. TS expression was significantly increased in patients with bone metastasis. No relationship was found between expression of TS and the other clinicopathological findings. Because TS expression could be used as a prognostic parameter in patients with prostate cancer, an accurate prediction of prognosis might help to select patients for more intensive surgical, hormonal, or chemotherapeutic approaches, including 5-fluorouracil. Additional prospective studies are warranted to define the role of TS in selecting patients for adjuvant therapy for prostate cancer.

TAS-102: a novel antimetabolite for the 21st century

TAS-102, a novel antimetabolite combination chemotherapy agent, consists of a rediscovered antimetabolite agent, trifluorothymidine (trifluridine) combined with the metabolic inhibitor of thymidine phosphorylase, tipiracil, in a 1:0.5 molar ratio. Mechanism of action studies suggest that this agent works by incorporation into DNA. Both preclinical and clinical studies demonstrate that this agent is noncross-resistant with 5-fluorouracil. Tipiracil may also have antiangiogenic effects through inhibition of thymidine phosphorylase. Recent randomized Phase II and III trials demonstrate clinical activity (improved progression-free survival, time to decrease in performance status, prolonged overall survival) in metastatic colorectal cancer refractory to all standard agents. Monotherapy with TAS-102 has now been approved for this indication in Japan and in the USA.

TAS-102, a novel antitumor agent: a review of the mechanism of action

Inhibition of nucleoside metabolism is an important principle in cancer therapy as evidenced by the role of fluoropyrimidines, such as 5-fluorouracil (5-FU), and antifolates in the treatment of many cancers. TAS-102 is an oral combination therapy consisting of trifluridine (FTD), a thymidine-based nucleoside analog, plus tipiracil hydrochloride (TPI), a novel thymidine phosphorylase inhibitor that improves the bioavailability of FTD. TAS-102 has demonstrated efficacy in 5-FU-refractory patients based on a different mechanism of action and has been approved for the treatment of metastatic colorectal cancer in Japan. This review describes the mechanism of action of TAS-102, highlighting key differences between TAS-102 and 5-FU-based therapies. While both FTD and 5-FU inhibit thymidylate synthase (TS), a central enzyme in DNA synthesis, sufficient TS inhibition by FTD requires continuous infusion; therefore, it is not considered a clinically relevant mechanism with oral dosing. Instead, the primary cytotoxic mechanism with twice-daily oral dosing, the schedule used in TAS-102 clinical development, is DNA incorporation. FTD incorporation into DNA induces DNA dysfunction, including DNA strand breaks. Uracil-based analogs such as 5-FU may also be incorporated into DNA; however, they are immediately cleaved off by uracil-DNA glycosylases, reducing their ability to damage DNA. Moreover, the TPI component may enhance the durability of response to FTD. With its distinct mechanism of action and metabolism, TAS-102 is a promising treatment option for patients resistant to or intolerant of 5-FU-based fluoropyrimidines.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Properties of phosphorylated thymidylate synthase

Thymidylate synthase (TS) may undergo phosphorylation endogenously in mammalian cells, and as a recombinant protein expressed in bacterial cells, as indicated by the reaction of purified enzyme protein with Pro-Q® Diamond Phosphoprotein Gel Stain (PGS). With recombinant human, mouse, rat, Trichinella spiralis and Caenorhabditis elegans TSs, expressed in Escherichia coli, the phosphorylated, compared to non-phosphorylated recombinant enzyme forms, showed a decrease in Vmax(app), bound their cognate mRNA (only rat enzyme studied), and repressed translation of their own and several heterologous mRNAs (human, rat and mouse enzymes studied). However, attempts to determine the modification site(s), whether endogenously expressed in mammalian cells, or recombinant proteins, did not lead to unequivocal results. Comparative ESI-MS/analysis of IEF fractions of TS preparations from parental and FdUrd-resistant mouse leukemia L1210 cells, differing in sensitivity to inactivation by FdUMP, demonstrated phosphorylation of Ser(10) and Ser(16) in the resistant enzyme only, although PGS staining pointed to the modification of both L1210 TS proteins. The TS proteins phosphorylated in bacterial cells were shown by (31)P NMR to be modified only on histidine residues, like potassium phosphoramidate (KPA)-phosphorylated TS proteins. NanoLC-MS/MS, enabling the use of CID and ETD peptide fragmentation methods, identified several phosphohistidine residues, but certain phosphoserine and phosphothreonine residues were also implicated. Molecular dynamics studies, based on the mouse TS crystal structure, allowed one to assess potential of several phosphorylated histidine residues to affect catalytic activity, the effect being phosphorylation site dependent.

Hedgehog signaling sensitizes glioma stem cells to endogenous nano-irradiation

The existence of therapy resistant glioma stem cells is responsible for the high recurrence rate and incurability of glioblastomas. The Hedgehog pathway activity plays an essential role for self-renewal capacity and survival of glioma stem cells. We examined the potential of the Sonic hedgehog ligand for sensitizing of glioma stem cells to endogenous nano-irradiation. We demonstrate that the Sonic hedgehog ligand preferentially and efficiently activats glioma stem cells to enter the radiation sensitive G2/M phase. Concomitant inhibition of de novo thymidine synthesis with fluorodeoxyuridine and treatment with the Auger electron emitting thymidine analogue 5-[I-125]-Iodo-4′-thio-2′-deoxyuridine ([I-125]ITdU) leads to a fatal nano-irradiation in sensitized glioma stem cells. Targeting of proliferating glioma stem cells with DNA-incorporated [I-125]ITdU efficiently invokes the intrinsic apoptotic pathway despite active DNA repair mechanisms. Further, [I-125]ITdU completely inhibits survival of glioma stem cells in vitro. Analysis of non-stem glioblastoma cells and normal human astrocytes reveals that glioma stem cells differentially respond to Sonic hedgehog ligand. These data demonstrate a highly efficient and controllable single-cell kill therapeutic model for targeting glioma stem cells.

The acetyl-CoA carboxylase enzyme: a target for cancer therapy?

As a rate-limiting enzyme, the acetyl-CoA carboxylase (ACC) is essential for fatty acid synthesis. Traditionally, the ACC has been a target of metabolic syndrome and obesity. Recent research has demonstrated that malignant tumors have a high energy flow, thus having a great ability to synthesize fatty acids. ACCs are occasionally found to be overexpressed in cancer cells, and using chemical or RNA interference to inhibit ACC can lead to cancer cell cycle arrest and apoptosis. This suggests that ACC and relative fatty acids may be critical for the survival of cancer cells. In this review, we summarize the role of ACC in tumor development. We also discuss the signaling pathways possibly affected by ACC, which may give insight into future research for cancer therapy.

Replication stress and cancer

Genome instability is a hallmark of cancer, and DNA replication is the most vulnerable cellular process that can lead to it. Any condition leading to high levels of DNA damage will result in replication stress, which is a source of genome instability and a feature of pre-cancerous and cancerous cells. Therefore, understanding the molecular basis of replication stress is crucial to the understanding of tumorigenesis. Although a negative aspect of replication stress is its prominent role in tumorigenesis, a positive aspect is that it provides a potential target for cancer therapy. In this Review, we discuss the link between persistent replication stress and tumorigenesis, with the goal of shedding light on the mechanisms underlying the initiation of an oncogenic process, which should open up new possibilities for cancer diagnostics and treatment.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma

Malignant pleural mesothelioma is a global health issue. Arsenic trioxide (ATO) has been shown to suppress thymidylate synthase (TYMS) in lung adenocarcinoma and colorectal cancer, and induce apoptosis in acute promyelocytic leukemia. With TYMS as a putative therapeutic target, the effect of ATO in mesothelioma was therefore studied. A panel of 5 mesothelioma cell lines was used to study the effect of ATO on cell viability, protein expression, mRNA expression and TYMS activity by MTT assay, western blot, qPCR and tritium-release assay, respectively. The knockdown of TYMS and E2F1 was performed with a specific siRNA. Phosphatidylserine externalization and mitochondrial membrane depolarization were measured by Annexin V and JC-1 staining respectively. The in vivo effect of ATO was studied using a nude mouse xenograft model. Application of ATO demonstrated anticancer effects in the cell line model with clinically achievable concentrations. Downregulation of TYMS protein (except H226 cells and 1.25 µM ATO in H2052 cells) and mRNA expression (H28 cells), pRB1 (H28 cells) and E2F1 and TYMS activity (except H226 cells) were also evident. E2F1 knockdown decreased cell viability more significantly than TYMS knockdown. In general, thymidine kinase 1, ribonucleotide reductase M1, c-myc and skp2 were downregulated by ATO. p-c-Jun was downregulated in H28 cells while upregulated in 211H cells. Phosphatidylserine externalization, mitochondrial membrane depolarization, downregulation of Bcl-2 and Bcl-xL, and upregulation of Bak and cleaved caspase-3 were observed. In the H226 xenograft model, the relative tumor growth was aborted, and E2F1 was downregulated while cleaved caspase-3 was elevated and localized to the nucleus in the ATO treatment group. ATO has potent antiproliferative and cytotoxic effects in mesothelioma in vitro and in vivo, partially mediated through E2F1 targeting (less effect through TYMS targeting). There is sound scientific evidence to support the clinical application of ATO in treatment of mesothelioma.

Standing the test of time: targeting thymidylate biosynthesis in cancer therapy

Over the past 60 years, chemotherapeutic agents that target thymidylate biosynthesis and the enzyme thymidylate synthase (TS) have remained among the most-successful drugs used in the treatment of cancer. Fluoropyrimidines, such as 5-fluorouracil and capecitabine, and antifolates, such as methotrexate and pemetrexed, induce a state of thymidylate deficiency and imbalances in the nucleotide pool that impair DNA replication and repair. TS-targeted agents are used to treat numerous solid and haematological malignancies, either alone or as foundational therapeutics in combination treatment regimens. We overview the pivotal discoveries that led to the rational development of thymidylate biosynthesis as a chemotherapeutic target, and highlight the crucial contribution of these advances to driving and accelerating drug development in the earliest era of cancer chemotherapy. The function of TS as well as the mechanisms and consequences of inhibition of this enzyme by structurally diverse classes of drugs with distinct mechanisms of action are also discussed. In addition, breakthroughs relating to TS-targeted therapies that transformed the clinical landscape in some of the most-difficult-to-treat cancers, such as pancreatic, colorectal and non-small-cell lung cancer, are highlighted. Finally, new therapeutic agents and novel mechanism-based strategies that promise to further exploit the vulnerabilities and target resistance mechanisms within the thymidylate biosynthesis pathway are reviewed.

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.

Nucleotide metabolism, oncogene-induced senescence and cancer

Senescence is defined as a stable cell growth arrest. Oncogene-induced senescence (OIS) occurs when an activated oncogene is expressed in a normal cell. OIS acts as a bona fide tumor suppressor mechanism by driving stable growth arrest of cancer progenitor cells harboring the initial oncogenic hit. OIS is often characterized by aberrant DNA replication and the associated DNA damage response. Nucleotides, in particular deoxyribonucleotide triphosphates (dNTPs), are necessary for both DNA replication and repair. Imbalanced dNTP pools play a role in a number of human diseases, including during the early stages of cancer development. This review will highlight what is currently known about the role of decreased nucleotide metabolism in OIS, how nucleotide metabolism leads to transformation and tumor progression, and how this pathway can be targeted as a cancer therapeutic by inducing senescence of cancer cells.

Analysis of 320 gastroenteropancreatic neuroendocrine tumors identifies TS expression as independent biomarker for survival

Thymidylate synthase (TS), a critical enzyme for DNA synthesis and repair, is both a potential tumor prognostic biomarker as well as a tumorigenic oncogene in animal models. We have now studied the clinical implications of TS expression in gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) and compared these results to other cell cycle biomarker genes. Protein tissue arrays were used to study TS, Ki-67, Rb, pRb, E2F1, p18, p21, p27 and menin expression in 320 human GEP-NETs samples. Immunohistochemical expression was correlated with univariate and multivariate predictors of survival utilizing Kaplan Meier and Cox proportional hazards models. Real time RT-PCR was used to validate these findings. We found that 78 of 320 GEP-NETs (24.4%) expressed TS. NETs arising in the colon, stomach and pancreas showed the highest expression of TS (47.4%, 42.6% and 37.3%, respectively), whereas NETs of the appendix, rectum and duodenum displayed low TS expression (3.3%, 12.9% and 15.4%, respectively). TS expression in GEP-NETs was associated with poorly differentiated endocrine carcinoma, angiolymphatic invasion, lymph node metastasis and distant metastasis (p < 0.05). Patients with TS-positive NETs had markedly worse outcomes than TS-negative NETs as shown by univariate (p < 0.001) and multivariate (p = 0.01) survival analyses. Expression of p18 predicted survival in TS-positive patients that received chemotherapy (p = 0.015). In conclusion, TS protein expression was an independent prognostic biomarker for GEP-NETs. The strong association of increased TS expression with aggressive disease and early death supports the role of TS as a cancer promoting agent in these tumors.

Thymidylate synthase expression and p21(WAF1)/p53 phenotype of colon cancers identify patients who may benefit from 5-fluorouracil based therapy

Background

Studies on the expression of thymidylate synthase (TS) in colorectal cancers (CRCs) have failed to provide unequivocal prognostic or predictive information. Here, we assessed the prognostic significance of TS expression in Astler-Coller stage B2 and C CRCs defined by a p21^WAF1/p53 immunophenotype in patients subjected to 5-fluorouracil (5FU)-based adjuvant therapy.

Methods

A cohort of 189 CRCs was asssessed for TS, p21^WAF1 and p53 expression on tissue microarrays using immunohistochemistry, and associations with disease-free survival (DFS) and overall survival (OS) of the patients were assessed using univariate and multivariate analyses.

Results

TS expression led to the stratification of patients with colon cancer, but not rectal cancer, with immunophenotypes other than p21^WAF1+/p53- (referred to as P&P) into subgroups characterized by a worse (P&P TS+) and a better (P&P TS-) DFS and OS, in univariate (P = 0.006 and P = 0.005, respectively) and multivariate (P = 0.0004 and P = 0.002, respectively) analyses. The p21^WAF1+/p53- immunophenotype was associated with a favorable prognosis, irrespective of TS expression.

Conclusions

The strong association observed between the P&P TS+ immunophenotype and a worse DFS and OS suggests a predictive significance of TS expression for 5FU-based adjuvant therapy in patients with colon cancers exhibiting the P&P immunophenotype. In addition, our findings suggest that the appropriate target for assessment of TS expression as a prognostic/predictive marker is a subgroup of colon cancers with an immunophenotype other than p21^WAF1+/p53-, and that only in this subgroup high TS expression is associated with an unfavorable DFS and OS. Therefore, we suggest that assessing TS expression in conjunction with p21^WAF1/p53 immunophenotyping of colon cancers may improve the selection of patients suitable for 5FU-based adjuvant chemotherapy.

Crystal structure of phosphoramide-phosphorylated thymidylate synthase reveals pSer127, reflecting probably pHis to pSer phosphotransfer

Crystal structure is presented of the binary complex between potassium phosphoramidate-phosphorylated recombinant C. elegans thymidylate synthase and dUMP. On each monomer a single phosphoserine residue (Ser127) was identified, instead of expected phosphohistidine. As (31)P NMR studies of both the phosphorylated protein and of potassium phosphoramidate potential to phosphorylate different amino acids point to histidine as the only possible site of the modification, thermodynamically favored intermolecular phosphotransfer from histidine to serine is suggested.

Defining the communication between agonist and coactivator binding in the retinoid X receptor α ligand binding domain

Retinoid X receptors (RXRs) are obligate partners for several other nuclear receptors, and they play a key role in several signaling processes. Despite being a promiscuous heterodimer partner, this nuclear receptor is a target of therapeutic intervention through activation using selective RXR agonists (rexinoids). Agonist binding to RXR initiates a large conformational change in the receptor that allows for coactivator recruitment to its surface and enhanced transcription. Here we reveal the structural and dynamical changes produced when a coactivator peptide binds to the human RXRα ligand binding domain containing two clinically relevant rexinoids, Targretin and 9-cis-UAB30. Our results show that the structural changes are very similar for each rexinoid and similar to those for the pan-agonist 9-cis-retinoic acid. The four structural changes involve key residues on helix 3, helix 4, and helix 11 that move from a solvent-exposed environment to one that interacts extensively with helix 12. Hydrogen-deuterium exchange mass spectrometry reveals that the dynamics of helices 3, 11, and 12 are significantly decreased when the two rexinoids are bound to the receptor. When the pan-agonist 9-cis-retinoic acid is bound to the receptor, only the dynamics of helices 3 and 11 are reduced. The four structural changes are conserved in all x-ray structures of the RXR ligand-binding domain in the presence of agonist and coactivator peptide. They serve as hallmarks for how RXR changes conformation and dynamics in the presence of agonist and coactivator to initiate signaling.

Breaking the invulnerability of cancer stem cells: two-step strategy to kill the stem-like cell subpopulation of multiple myeloma

In multiple myeloma, the presence of highly resistant cancer stem cells (CSC) that are responsible for tumor metastasis and relapse has been proven. Evidently, for achieving complete response, new therapeutic paradigms that effectively eradicate both, CSCs and bulk cancer populations, need to be developed. For achieving that goal, an innovative two-step treatment combining targeting of thymidine de novo synthesis pathway and a nanoirradiation by the Auger electron emitting thymidine analogue (123/125)I-5-iodo-4'-thio-2'-deoxyuridine ((123/125)I-ITdU) could be a promising approach. The pretreatment with thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FdUrd, 1 μmol/L for 1 hour) efficiently induced proliferation and terminal differentiation of isolated myeloma stem-like cells. Moreover, FdUrd stimulation led to a decreased activity of a functional CSC marker, aldehyde dehydrogenase (ALDH). The metabolic conditioning by FdUrd emerged to be essential for enhanced incorporation of (125)I-ITdU (incubation with 50 kBq/2 × 10(4) cells for 4 days) and, consequently, for the induction of irreparable DNA damage. (125)I-ITdU showed a pronounced antimyeloma effect on isolated tumor stem-like cells. More than 85% of the treated cells were apoptotic, despite activation of DNA repair mechanisms. Most important, exposure of metabolically conditioned cells to (125)I-ITdU resulted in a complete inhibition of clonogenic recovery. This is the first report showing that pretreatment with FdUrd sensitizes the stem-like cell compartment in multiple myeloma to apoptosis induced by (125)I-ITdU-mediated nanoirradiation of DNA.

Targeting thymidylate synthase in colorectal cancer: critical re-evaluation and emerging therapeutic role of raltitrexed

INTRODUCTION

5-fluorouracil continues to be the cornerstone of treatment for colorectal cancer. Although fluoropyrimidines are generally considered as well-tolerated drugs, severe toxicities can be a major clinical problem, and the recommended prolonged infusion of 5-fluorouracil provokes discomfort in patients. Raltitrexed (Tomudex), a quinazoline analogue of folinic acid, is a selective and direct thymidylate synthase (TS) inhibitor with a convenient 3-weekly schedule of administration.

AREAS COVERED

In this review, through critical insight into the mechanism of action and main clinical experiences, the authors suggest the necessity to reconsider raltitrexed as a valuable anticancer drug and as a suitable option for colorectal cancer. The authors highlight its emerging therapeutic role in clinical practice for patients with fluoropyrimidine-induced cardiotoxicity or a significant history of cardiac disease.

EXPERT OPINION

This review discusses if TS could still be a relevant target for colorectal cancer in the era of molecular therapy and if raltitrexed should still be considered a drug with a life-threatening toxicity. Furthermore, this review discusses the principal combination clinical experiences of raltitrexed and its emerging therapeutic role in clinical practice as a suitable option for colorectal cancer patients with fluoropyrimidine-induced cardiotoxicity or a significant history of cardiac disease.

53BP1 sensitizes breast cancer cells to 5-fluorouracil

Chemoresistance of breast cancer is a worldwide problem for breast cancer and the resistance to chemotherapeutic agents frequently led to the subsequent recurrence and metastasis. In our previous study, we have found that 53BP1 showed a gradual decrease during the progression of breast cancer and loss of 53BP1 was associated with metastasis and poor prognosis in breast cancer. Here we aimed to reveal whether 53BP1 could sensitize breast cancer to 5-Fu. We found that ectopic expression of 53BP1 can significantly sensitize breast cancer cells to 5-Fu while knockdown of 53BP1 conferred the resistance. The in vivo experiments confirmed that overexpression of 53BP1 in combination with 5-Fu markedly inhibited growth of xenotransplanted tumors in nude mice when compared to either agent alone. Furthermore, we demonstrated that 53BP1 regulated the sensitivity to 5-Fu through thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPYD). The present studies provide a new clue that combination of 5-Fu and 53BP1 could be a potential novel targeted strategy for overcoming breast cancer chemoresistance.

Thymidylate synthase gene polymorphism and survival of colorectal cancer patients receiving adjuvant 5-fluorouracil

Limited studies indicate a possible association of 5'-UTR thymidylate synthase enhancer region polymorphism and treatment outcome in patients medicated with 5-fluorouracil (5-FU). The study was designed to verify the relationship in patients with colorectal cancer (CRC), a Polish population that received 5-FU-based adjuvant chemotherapy. The study analyzed 145 Astler-Coller B2 and C CRC patients. Genotyping for a variable number of tandem repeats and G to C single-nucleotide polymorphism in the 5'-UTR of the thymidylate synthase (TS) gene was carried out. TS genotypes were classified into high expression (high TS) and low expression types (low TS). High TS was found in 22.8% of patients. The right-side tumors were more frequently associated with high TS than the left-side tumors (p=0.024). High TS was only found in 9.3% of rectal tumors, but in 29.7% of colon cancers (p=0.0042). Disease-free survival after 20 months (DFS 20) was longer in subjects with low TS than in high TS (p=0.043). Patients who underwent chemotherapy had longer DFS 20 in the low TS than in the high TS subgroup (p=0.051). The low TS was found to be an independent good prognostic factor for DFS 20 in the whole group as well as in the subgroup treated with chemotherapy (p=0.024 and p=0.034, respectively). Patients with low TS did not show any differences in DFS 20 whether they were treated with adjuvant chemotherapy or not. Proximal CRC tumors are characterized by higher TS expression genotypes than distal tumors, and are at significantly greater risk of early recurrence during the first 20 months after surgery.

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.

TYMS serves as a prognostic indicator to predict the lymph node metastasis in Chinese patients with colorectal cancer

OBJECTIVE

The current study is to evaluate the effect of thymidylate synthase (TYMS) on lymph node metastasis (LNM) in Chinese colorectal cancer (CRC) patients, and develop potential LNM-associated biomarkers for CRC.

DESIGN AND METHODS

Differences in TYMS gene expression between primary CRC with LNM (LNM CRC) and without LNM (non-LNM CRC) were assessed using quantitative real-time PCR analysis in 100 Chinese colorectal cancer patients. The relationship between clinicopathological parameters and prognosis of candidate biomarkers was also examined in the experiment.

RESULTS

TYMS was significantly upregulated in LNM CRC compared with non-LNM CRC, which was confirmed by real-time quantitative polymerase chain reaction. Overexpression of TYMS was significantly associated with LNM (P<0.001), advanced TNM stage (P<0.001), increased 5-year recurrence rate (P<0.001) and decreased 5-year overall survival rate (P<0.001). Univariate and multivariate analyses indicated that TYMS expression was an independent prognostic factor for recurrence and survival of CRC patients (P<0.05).

CONCLUSIONS

TYMS effect on lymph node metastasis in CRC might serve as a potential biomarker for LNM and a prognostic factor in CRC. Over-expression of TYMS is a predicting factor to the poor outcome in clinical colorectal cancer patients.

Combined 5-FU and ChoKα inhibitors as a new alternative therapy of colorectal cancer: evidence in human tumor-derived cell lines and mouse xenografts

Background

Colorectal cancer (CRC) is the third major cause of cancer related deaths in the world. 5-fluorouracil (5-FU) is widely used for the treatment of colorectal cancer but as a single-agent renders low response rates. Choline kinase alpha (ChoKα), an enzyme that plays a role in cell proliferation and transformation, has been reported overexpressed in many different tumors, including colorectal tumors. ChoKα inhibitors have recently entered clinical trials as a novel antitumor strategy.

Methodology/Principal Findings

ChoKα specific inhibitors, MN58b and TCD-717, have demonstrated a potent antitumoral activity both in vitro and in vivo against several tumor-derived cell line xenografts including CRC-derived cell lines. The effect of ChoKα inhibitors in combination with 5-FU as a new alternative for the treatment of colon tumors has been investigated both in vitro in CRC-tumour derived cell lines, and in vivo in mouse xenografts models. The effects on thymidilate synthase (TS) and thymidine kinase (TK1) levels, two enzymes known to play an essential role in the mechanism of action of 5-FU, were analyzed by western blotting and quantitative PCR analysis. The combination of 5-FU with ChoKα inhibitors resulted in a synergistic effect in vitro in three different human colon cancer cell lines, and in vivo against human colon xenografts in nude mice. ChoKα inhibitors modulate the expression levels of TS and TK1 through inhibition of E2F production, providing a rational for its mechanism of action.

Conclusion/Significance

Our data suggest that both drugs in combination display a synergistic antitumoral effect due to ChoKα inhibitors-driven modulation of the metabolization of 5-FU. The clinical relevance of these findings is strongly supported since TCD-717 has recently entered Phase I clinical trials against solid tumors.

Overexpression of thymidylate synthetase confers an independent prognostic indicator in nasopharyngeal carcinoma

Data mining on public domain identified that thymidylate synthetase (TYMS) and dihydrofolate reductase (DHFR) transcripts were significantly higher expressed in nasopharyngeal carcinoma (NPC). In the folate pathway, TYMS catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5,10-methylenetetrahydrofolate [5,10-CH2=THF, derived from tetrahydrofolate (THF)], as a cofactor. This function maintains the thymidine-5-prime monophosphate pool critical for DNA replication and repair and, THF is generated from dihydrofolate (DHF) through the activity of DHFR. Immunoexpression of TYMS and DHFR were retrospectively assessed in biopsies of 124 consecutive NPC patients without initial distant metastasis and treated with consistent guidelines. The outcome was correlated with clinicopathological features and patient survivals. Results indicated that high TYMS (50%) expressions were correlated with primary tumor (p=0.008) and AJCC stage (p=0.006), and high DHFR (50%) expression were correlated with nodal status (p=0.039) and AJCC stage (p=0.029) (7th American Joint Committee on Cancer), respectively. In multivariate analyses, high TYMS expression emerged as an independent prognosticator for worse disease-specific survival (p<0.001), distal metastasis-free survival (p=0.002) and local recurrence-free survival (p<0.001), along with AJCC stage. Therefore, TYMS expression is common and associated with adverse prognosticators and might confer tumor aggressiveness through dysregulation of the nucleotide biosynthetic process.

Mechanistic evaluation of the signaling events regulating curcumin-mediated chemosensitization of breast cancer cells to 5-fluorouracil

5-Fluorouracil (5-FU) is the first rationally designed antimetabolite, which achieves its therapeutic efficacy through inhibition of the enzyme thymidylate synthase (TS), which is essential for the synthesis and repair of DNA. However, prolonged exposure to 5-FU induces TS overexpression, which leads to 5-FU resistance in cancer cells. Several studies have identified curcumin as a potent chemosensitizer against chemoresistance induced by various chemotherapeutic drugs. In this study, we report for the first time, with mechanism-based evidences, that curcumin can effectively chemosensitize breast cancer cells to 5-FU, thereby reducing the toxicity and drug resistance. We found that 10 μM 5-FU and 10 μM curcumin induces a synergistic cytotoxic effect in different breast cancer cells, independent of their receptor status, through the enhancement of apoptosis. Curcumin was found to sensitize the breast cancer cells to 5-FU through TS-dependent downregulation of nuclear factor-κB (NF-κB), and this observation was confirmed by silencing TS and inactivating NF-κB, both of which reduced the chemosensitizing efficacy of curcumin. Silencing of TS suppressed 5-FU-induced NF-κB activation, whereas inactivation of NF-κB did not affect 5-FU-induced TS upregulation, confirming that TS is upstream of NF-κB and regulates the activation of NF-κB in 5-FU-induced signaling pathway. Although Akt/PI3kinase and mitogen-activated protein kinase pathways are activated by 5-FU and downregulated by curcumin, they do not have any role in regulating the synergism. As curcumin is a pharmacologically safe and cost-effective compound, its use in combination with 5-FU may improve the therapeutic index of 5-FU, if corroborated by in vivo studies and clinical trials.

Overexpression of the mitochondrial folate and glycine-serine pathway: a new determinant of methotrexate selectivity in tumors

Previous studies have documented the roles of transport via the reduced folate carrier, retention via polyglutamylation, and increased levels of the target enzyme, dihydrofolate reductase in sensitivity to methotrexate. Recent studies have shown that the mitochondrial enzymes in the cellular metabolism of serine, folate, and glycine are overexpressed in a subset of human cancers and that their expression is required for tumor maintenance. In this Perspective article, we propose that the expression of mitochondrial enzymes in the metabolism of serine and glycine, in addition to those involved in folate metabolism, are determinants of the response to methotrexate. Furthermore, we show that myc activation in tumors is associated with upregulation of these enzymes. We propose that patients whose tumors show this phenotype will be sensitive to folate antagonists targeting thymidylate or purine biosynthesis.

Polymorphic thymidylate synthase gene impacts on overall survival of patients with epithelial ovarian cancer after platinum-based chemotherapy

Aim: High levels of TS have been associated with a worse clinical outcome in several cancers including epithelial ovarian cancer (EOC). The TS gene (TYMS) is highly polymorphic and has an effect on mRNA/protein expression. Materials & methods: Six TYMS polymorphisms were investigated for overall survival (OS) in 216 EOC patients: TYMS 1494ins/del, TSER (variable number of tandem repeats of 28 bp), TSER G>C, TYMS 1053C>T, TYMS IVS6-68C>T and TYMS 1122A>G. Results: In a multivariate analysis, TYMS 1494 del/del genotype was associated with a significant increased OS compared with the ins/ins genotype (hazard ratio: 0.36; 95% CI: 0.16–0.82, p = 0.01). Similar results were obtained for the mutant genotypes TYMS 1053TT and TYMS IVS6-68TT. The event-free survival was significantly higher in TYMS 1053TT patients compared with wild-type patients (p = 0.05). Conclusion: TYMS 1494ins/del, 1053C>T and IVS6-68C>T polymorphisms can be prognostic markers for OS in patients with EOC, independently from stage at diagnosis, median age and tumor histotype.

Original submitted 11 May 2012; Revision submitted 10 August 2012

FASN and CD36 predict survival in rituximab-treated diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma is the most common lymphoid malignancy, as it accounts for approximately one third of all patient cases of non-Hodgkin's lymphoma. Patients with diffuse large B-cell lymphoma have markedly different treatment outcomes, suggesting a need for reliable prognostic factors and novel therapeutic approaches. De novo fatty acid synthesis is an important metabolic driver of tumor in multiple malignancies. In this retrospective study, we analyzed expression of fatty acid synthase (a key enzyme in de novo fatty acid synthesis), Spot 14 (thyroid hormone responsive Spot 14, a nuclear protein that promotes expression of genes involved in fatty acid synthesis), and CD36 (the cell surface channel for exogenous fatty acid uptake) in patients with diffuse large B-cell lymphoma and their clinical significance. We observed that overexpression of fatty acid synthase is negatively associated with overall survival (p=0.001) and progression-free period (p=0.004) in patients with diffuse large B-cell lymphoma. Multivariate analysis showed that fatty acid synthase overexpression is an independent prognostic marker of aggressive clinical course. For the first time, we report CD36 as an independent protective factor in patients treated with rituximab. Thus, fatty acid synthase and CD36 expression may serve as prognostic markers to predict response to treatment and survival in diffuse large B-cell lymphoma patients. Fatty acid synthase may also be a potential therapeutic target in lymphoid malignancies.

Correlation between thymidylate synthase gene polymorphisms and efficacy of pemetrexed in advanced non-small cell lung cancer

One of the target genes of pemetrexed (PEM), thymidylate synthase (TS), has been shown to have a close association with its efficacy. TS gene polymorphisms have been shown to be associated with the efficacy of antifolate treatment in enteron tumors. The purpose of this study was to investigate the clinical significance of TS gene polymorphisms in patients with advanced NSCLC receiving PEM-based treatment. The variable nucleoid tandem repeat in the 5′-UTR region was amplified and detected using fluorescently labeled multiplex short tandem repeat polymerase chain reaction. The polymorphism in the 3′-UTR region of the TS gene was detected using the Taqman probe. Efficacy of PEM was assessed according to the Response Evaluation Criteria in Solid Tumors, version 1.1. None of the genotypes were associated with gender, smoking status and age. Disease control rate (DCR), objective response rate (ORR) and progression-free survival (PFS) were similar between patients harboring 2R and 3R alleles (PFS, p=0.518; DCR, p=0.631; ORR, p=0.541), as well as those with a 6-bp insertion and 6-bp deletion (PFS, p=0.776; DCR, p=0.626; ORR, p=0.330). To study the combined effect of TS polymorphisms, the study population was divided into three groups: 2R&6 del, 2R&6 ins and 3R&6 del. No significant differences were observed among the different groups according to DCR (p=0.517), ORR (p=0.611) and PFS (p=0.938). In conclusion, polymorphisms of the TS gene do not appear to be a prognostic marker for advanced NSCLC patients receiving PEM-based treatment.

Remodeling of central metabolism in invasive breast cancer compared to normal breast tissue - a GC-TOFMS based metabolomics study

Background

Changes in energy metabolism of the cells are common to many kinds of tumors and are considered a hallmark of cancer. Gas chromatography followed by time-of-flight mass spectrometry (GC-TOFMS) is a well-suited technique to investigate the small molecules in the central metabolic pathways. However, the metabolic changes between invasive carcinoma and normal breast tissues were not investigated in a large cohort of breast cancer samples so far.

Results

A cohort of 271 breast cancer and 98 normal tissue samples was investigated using GC-TOFMS-based metabolomics. A total number of 468 metabolite peaks could be detected; out of these 368 (79%) were significantly changed between cancer and normal tissues (p<0.05 in training and validation set). Furthermore, 13 tumor and 7 normal tissue markers were identified that separated cancer from normal tissues with a sensitivity and a specificity of >80%. Two-metabolite classifiers, constructed as ratios of the tumor and normal tissues markers, separated cancer from normal tissues with high sensitivity and specificity. Specifically, the cytidine-5-monophosphate / pentadecanoic acid metabolic ratio was the most significant discriminator between cancer and normal tissues and allowed detection of cancer with a sensitivity of 94.8% and a specificity of 93.9%.

Conclusions

For the first time, a comprehensive metabolic map of breast cancer was constructed by GC-TOF analysis of a large cohort of breast cancer and normal tissues. Furthermore, our results demonstrate that spectrometry-based approaches have the potential to contribute to the analysis of biopsies or clinical tissue samples complementary to histopathology.

Epigenetics and chemoresistance in colorectal cancer: an opportunity for treatment tailoring and novel therapeutic strategies

Colorectal cancer is the second leading cause of cancer-related deaths in the world. Despite many therapeutic opportunities, prognosis remains dismal for patients with metastatic disease, and a significant portion of early-stage patients develop recurrence after chemotherapy. Epigenetic gene regulation is a major mechanism of cancer initiation and progression, through the inactivation of several tumor suppressor genes. Emerging evidence indicates that epigenetics may also play a key role in the development of chemoresistance. In the present review, we summarize epigenetic mechanisms triggering resistance to three commonly used agents in colorectal cancer: 5-fluorouracil, irinotecan and oxaliplatin. Those epigenetic biomarkers may help stratify colorectal cancer patients and develop a tailored therapeutic approach. In addition, epigenetic modifications are reversible through specific drugs: histone-deacetylase and DNA-methyl-transferase inhibitors. Preclinical studies suggest that these drugs may reverse chemoresistance in colorectal tumors. In conclusion, an epigenetic approach to colorectal cancer chemoresistance may pave the way to personalized treatment and to innovative therapeutic strategies.

Thymidylate synthase inhibitors for non-small cell lung cancer

INTRODUCTION

The folate-dependent enzyme thymidylate synthase (TS) plays a pivotal role in DNA replication/repair and cancer cell proliferation, and represents a valid target for the treatment of several tumor types, including NSCLC. NSCLC is the leading cause of cancer-related mortality, and several TS inhibitors have gone into preclinical and clinical testing, with pemetrexed emerging for its approval and widespread use as first-/second-line and maintenance therapy for this disease.

AREAS COVERED

This review summarizes the therapeutic options in NSCLC, as well as the background and rationale for targeting TS. The authors also review recent pharmacogenetic studies and data from clinical trials evaluating novel TS inhibitors, hoping that the reader will gain a comprehensive overview of the field of TS inhibition, specifically relating to drugs used or being developed for lung cancer patients.

EXPERT OPINION

TS is a validated target in NSCLC. However, benefits from conventional chemotherapy in NSCLC have plateaued, and more cost-effective results should be obtained with individualized treatment. Accordingly, the clinical success for TS inhibitors may depend on our ability to correctly administer these agents following biomarker-driven patient selection, including TS genotype and expression, and using the right combination 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.

Treatment recommendations for metastatic colorectal cancer

Metastatic colorectal cancer (CRC) represents an important health problem in which several biological predictive and prognostic factors have been identified, including clinical features and molecular markers that might influence the response to treatment. Actually, certain prognostic factors are considered key elements, along with disease extent, for deciding the therapeutic approach. However, a distinction between resectable/potentially resectable and unresectable patients must be made in order to establish an adequate therapeutic strategy. Different drugs and chemotherapy regimens are currently available, and their administration depends on patient characteristics, disease-related factors and the treatment objective. Moreover, special situations such as peritoneal carcinomatosis and local treatment of CRC in the setting of metastatic disease should be considered when deciding the most appropriate treatment strategy. This article reviews all the previously mentioned issues involved in the management of metastatic CRC and suggests some general recommendations for its treatment.

Expression of p21WAF1 in Astler-Coller stage B2 colorectal cancer is associated with survival benefit from 5FU-based adjuvant chemotherapy

In several, but not all, previous studies, positive p21^WAF1 expression has been suggested as an indicator of a good prognosis in patients with stage III/IV colorectal cancer. However, it is not known whether the same is true for stage B2 patients. The purpose of this study is to assess the influence of p21^WAF1 expression in tumor cells on disease-free survival (DFS) and overall survival (OS) of Astler–Coller stage B2 and C patients with colorectal cancer who underwent 5-fluorouracil-based adjuvant chemotherapy. Nuclear p21^WAF1 was detected by immunohistochemistry in tissue microarrays from 275 colorectal cancers. The expression of p21^WAF1 was associated with DFS (p = 0.025) and OS (p = 0.008) in the subgroup of stage B2 patients that was treated with adjuvant chemotherapy. In multivariate analysis, it remained the only independent prognostic parameter in relation to DFS and OS (p = 0.035 and p = 0.02, respectively). In the subgroup of 72 stage B2 patients with positive p21^WAF1 expression but not in the subgroup of 61 stage B2 patients with negative p21^WAF1 expression, adjuvant chemotherapy was associated with better DFS (85% 5-year survival versus 65% without chemotherapy, p = 0.03) and OS (96% versus 82%, p = 0.014). In the combined stage B2 and C group of patients treated with adjuvant chemotherapy, positive p21^WAF1 expression was also associated with better DFS and OS (p = 0.03, p = 0.002, respectively). Expression of p21^WAF1 in colorectal tumor cells identifies a subgroup of Astler–Coller stage B2 patients who could benefit significantly from 5FU-based chemotherapy and may improve the selection of patients for adjuvant chemotherapy.

Enhanced growth inhibition by combined DNA methylation/HDAC inhibitors in lung tumor cells with silenced CDKN2A

Aberrant hypermethylation at CpG sites within the CDKN2A gene is associated with silencing and has been proposed as a target for reactivation using both DNA methylation and histone deacetylation inhibitors. This study investigates the role of selecting tumor samples with a silenced as compared to deleted CDKN2A locus when assessing the efficacy of DNA methyltransferase inhibitor, zebularine, combined with the HDAC inhibitor, depsipeptide. Non-small cell lung cancer cell lines with defined CDKN2A status were analyzed by MTS assay to determine the effect of zebularine or zebularine combined with depsipeptide on tumor cell growth. We observed that zebularine treatment resulted in inhibition of cell growth in 11 out of 12 lung cancer cell lines with silenced CDKN2A, but no cell growth inhibition was detected in the 7 lung cancer cell lines tested with deleted CDKN2A (p>0.001). In addition, we found that the combination of 30 microM zebularine and 6 or 7 nM depsipeptide resulted in a synergistic inhibition of cell growth in tumor cells with silenced CDKN2A (p<0.001, CI=0.70 and 0.57, respectively) but not in tumor cells with deleted CDKN2A. In conclusion, tumor cells with methylated CDKN2A are more sensitive to zebularine than cell lines with deleted CDKN2A and the combination of zebularine/depsipeptide results in a synergistic effect on cell growth inhibition that is also linked with the presence of silenced CDKN2A. Thus, combination of DNA methyltransferase and HDAC inhibitors may be a potential treatment for lung cancer patients, but careful selection of patients will be needed to optimize the benefit of this regimen.

TS expression predicts postoperative recurrence in adenocarcinoma of the lung

BACKGROUND

Not all patients with lung cancer require postoperative adjuvant chemotherapy after a complete resection. However, no useful markers for either selecting appropriate candidates or for predicting clinical recurrence exist.

METHODS

Tumor specimens were collected from 183 consecutive patients who underwent a complete resection for lung adenocarcinoma from 2003 to 2007 in our department. We analyzed the thymidylate synthase (TS) and dihydrofolate reductase (DHFR) expressions in the primary lung adenocarcinoma by immunohistochemisty.

RESULTS

The strong expression of TS and DHFR was identified in 39 (21.3%) and 120 (65.6%) patients, respectively. The strong TS expression was identified in 11 (39.3%) of 28 patients and 28 (18.1%) of 155 patients in patients with and without recurrence, respectively (p=0.012). The strong DHFR expression was also identified in 23 (82.1%) and 97 (62.6%) of the patients with and without recurrence, respectively (p=0.045). Logistic regression models indicated the strong TS expression to be an independent factor for tumor recurrence. The strong TS and DHFR expression was associated with a poorer disease-free survival (DFS) according to the survival analysis. A multivariate analysis demonstrated the strong TS expression to be independently associated with an increased risk for poor DFS.

CONCLUSIONS

The strong TS expression may be a useful marker for predicting postoperative recurrence in patients with lung adenocarcinoma following surgery.

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

Background:

Thymidylate synthase (TS), a key enzyme in the de novo synthesis of thymidine, is an important chemotherapeutic target for malignant tumours including lung cancer. Although inhibition of TS has an antiproliferative effect in cancer cells, the precise mechanism of this effect has remained unclear.

Methods:

We examined the effects of TS inhibition with an RNA interference-based approach. The effect of TS depletion on the growth of lung cancer cells was examined using colorimetric assay and flow cytometry.

Results:

Measurement of the enzymatic activity of TS in 30 human lung cancer cell lines revealed that such activity differs among tumour histotypes. Almost complete elimination of TS activity by RNA interference resulted in inhibition of cell proliferation in all tested cell lines, suggestive of a pivotal role for TS in cell proliferation independent of the original level of enzyme activity. The antiproliferative effect of TS depletion was accompanied by arrest of cells in S phase of the cell cycle and the induction of caspase-dependent apoptosis as well as by changes in the expression levels of cyclin E and c-Myc. Moreover, TS depletion induced downregulation of the antiapoptotic protein X-linked inhibitor of apoptosis (XIAP), and it seemed to activate the mitochondrial pathway of apoptosis.

Conclusion:

Our data provide insight into the biological relevance of TS as well as a basis for clinical development of TS-targeted therapy for lung cancer.