Nuclear thymidylate synthase expression, p53 expression and 5FU response in colorectal carcinoma

The novel anti-cancer fluoropyrimidine NUC-3373 is a potent inhibitor of thymidylate synthase and an effective DNA-damaging agent

INTRODUCTION

Fluoropyrimidines, principally 5-fluorouracil (5-FU), remain a key component of chemotherapy regimens for multiple cancer types, in particular colorectal and other gastrointestinal malignancies. To overcome key limitations and pharmacologic challenges that hinder the clinical utility of 5-FU, NUC-3373, a phosphoramidate transformation of 5-fluorodeoxyuridine, was designed to improve the efficacy and safety profile as well as the administration challenges associated with 5-FU.

METHODS

Human colorectal cancer cell lines HCT116 and SW480 were treated with sub-IC₅₀ doses of NUC-3373 or 5-FU. Intracellular activation was measured by LC-MS. Western blot was performed to determine binding of the active anti-cancer metabolite FdUMP to thymidylate synthase (TS) and DNA damage.

RESULTS

We demonstrated that NUC-3373 generates more FdUMP than 5-FU, resulting in a more potent inhibition of TS, DNA misincorporation and subsequent cell cycle arrest and DNA damage in vitro. Unlike 5-FU, the thymineless death induced by NUC-3373 was rescued by the concurrent addition of exogenous thymidine. 5-FU cytotoxicity, however, was only reversed by supplementation with uridine, a treatment used to reduce 5-FU-induced toxicities in the clinic. This is in line with our findings that 5-FU generates FUTP which is incorporated into RNA, a mechanism known to underlie the myelosuppression and gastrointestinal inflammation associated with 5-FU.

CONCLUSION

Taken together, these results highlight key differences between NUC-3373 and 5-FU that are driven by the anti-cancer metabolites generated. NUC-3373 is a potent inhibitor of TS that also causes DNA-directed damage. These data support the preliminary clinical evidence that suggest NUC-3373 has a favorable safety profile in patients.

Rabdosianone I, a Bitter Diterpene from an Oriental Herb, Suppresses Thymidylate Synthase Expression by Directly Binding to ANT2 and PHB2

Simple Summary

In the present study, we found the novel pleiotropic regulation of the oncogene product thymidylate synthase (TS) by a chemical biology approach to identify rabdosianone I-binding proteins. Rabdosianone I, which is extracted from a traditional Asian herb Isodon japonicus Hara for longevity, suppressed TS expression at mRNA and protein levels. We immobilized rabdosianone I onto nano-magnetic beads and identified two mitochondrial proteins, adenine nucleotide translocase 2 (ANT2) and prohibitin 2 (PHB2), as the direct targets of rabdosianone I in cancer cells. Mechanistically, the knockdown of ANT2 or PHB2 promoted proteasomal degradation of the TS protein. In addition, PHB2 reduced TS mRNA levels. Thus, we provide previously unknown mechanisms of TS regulation by ANT2 and PHB2 and propose the possibility of rabdosianone I as a promising lead compound for the discovery of a novel TS suppressor.

Abstract

Natural products have numerous bioactivities and are expected to be a resource for potent drugs. However, their direct targets in cells often remain unclear. We found that rabdosianone I, which is a bitter diterpene from an oriental herb for longevity, Isodon japonicus Hara, markedly inhibited the growth of human colorectal cancer cells by downregulating the expression of thymidylate synthase (TS). Next, using rabdosianone I-immobilized nano-magnetic beads, we identified two mitochondrial inner membrane proteins, adenine nucleotide translocase 2 (ANT2) and prohibitin 2 (PHB2), as direct targets of rabdosianone I. Consistent with the action of rabdosianone I, the depletion of ANT2 or PHB2 reduced TS expression in a different manner. The knockdown of ANT2 or PHB2 promoted proteasomal degradation of TS protein, whereas that of not ANT2 but PHB2 reduced TS mRNA levels. Thus, our study reveals the ANT2- and PHB2-mediated pleiotropic regulation of TS expression and demonstrates the possibility of rabdosianone I as a lead compound of TS suppressor.

Cellular Mechanisms Accounting for the Refractoriness of Colorectal Carcinoma to Pharmacological Treatment

Simple Summary

Colorectal cancer (CRC) causes a high number (more than 800,000) of deaths worldwide each year. Better methods for early diagnosis and the development of strategies to enhance the efficacy of the therapeutic approaches used to complement or substitute surgical removal of the tumor are urgently needed. Currently available pharmacological armamentarium provides very moderate benefits to patients due to the high resistance of tumor cells to respond to anticancer drugs. The present review summarizes and classifies into seven groups the cellular and molecular mechanisms of chemoresistance (MOC) accounting for the failure of CRC response to the pharmacological treatment.

Abstract

The unsatisfactory response of colorectal cancer (CRC) to pharmacological treatment contributes to the substantial global health burden caused by this disease. Over the last few decades, CRC has become the cause of more than 800,000 deaths per year. The reason is a combination of two factors: (i) the late cancer detection, which is being partially solved by the implementation of mass screening of adults over age 50, permitting earlier diagnosis and treatment; (ii) the inadequate response of advanced unresectable tumors (i.e., stages III and IV) to pharmacological therapy. The latter is due to the existence of complex mechanisms of chemoresistance (MOCs) that interact and synergize with each other, rendering CRC cells strongly refractory to the available pharmacological regimens based on conventional chemotherapy, such as pyrimidine analogs (5-fluorouracil, capecitabine, trifluridine, and tipiracil), oxaliplatin, and irinotecan, as well as drugs targeted toward tyrosine kinase receptors (regorafenib, aflibercept, bevacizumab, cetuximab, panitumumab, and ramucirumab), and, more recently, immune checkpoint inhibitors (nivolumab, ipilimumab, and pembrolizumab). In the present review, we have inventoried the genes involved in the lack of CRC response to pharmacological treatment, classifying them into seven groups (from MOC-1 to MOC-7) according to functional criteria to identify cancer cell weaknesses. This classification will be useful to pave the way for developing sensitizing tools consisting of (i) new agents to be co-administered with the active drug; (ii) pharmacological approaches, such as drug encapsulation (e.g., into labeled liposomes or exosomes); (iii) gene therapy interventions aimed at restoring the impaired function of some proteins (e.g., uptake transporters and tumor suppressors) or abolishing that of others (such as export pumps and oncogenes).

Therapeutic Targeting of Mitochondrial One-Carbon Metabolism in Cancer

One-carbon (1C) metabolism encompasses folate-mediated 1C transfer reactions and related processes, including nucleotide and amino acid biosynthesis, antioxidant regeneration, and epigenetic regulation. 1C pathways are compartmentalized in the cytosol, mitochondria, and nucleus. 1C metabolism in the cytosol has been an important therapeutic target for cancer since the inception of modern chemotherapy, and "antifolates" targeting cytosolic 1C pathways continue to be a mainstay of the chemotherapy armamentarium for cancer. Recent insights into the complexities of 1C metabolism in cancer cells, including the critical role of the mitochondrial 1C pathway as a source of 1C units, glycine, reducing equivalents, and ATP, have spurred the discovery of novel compounds that target these reactions, with particular focus on 5,10-methylene tetrahydrofolate dehydrogenase 2 and serine hydroxymethyltransferase 2. In this review, we discuss key aspects of 1C metabolism, with emphasis on the importance of mitochondrial 1C metabolism to metabolic homeostasis, its relationship with the oncogenic phenotype, and its therapeutic potential for cancer.

A novel intraperitoneal therapy for gastric cancer with DFP-10825, a unique RNAi therapeutic targeting thymidylate synthase, in a peritoneally disseminated xenograft model

Purpose

In advanced gastric cancer, peritoneal dissemination is a life‐threatening mode of metastasis. Since the treatment options with conventional chemotherapy remain limited, any novel therapeutic strategy that could control such metastasis would improve the outcome of treatment. We recently developed a unique RNA interference therapeutic regimen (DFP‐10825) consisting of short hairpin RNA against thymidylate synthase (TS shRNA) and cationic liposomes. The treatment with DFP‐10825 has shown remarkable antitumor activity in peritoneally disseminated human ovarian cancer–bearing mice via intraperitoneal administration. In this study, we expanded DFP‐10825 to the treatment of peritoneally disseminated gastric cancer.

Methods

DFP‐10825 was administered intraperitoneally into mice with intraperitoneally implanted human gastric cancer cells (MKN45 or NCI‐N87). Antitumor activity and host survival benefits were monitored. Intraperitoneal distribution of fluorescence‐labeled DFP‐10825 was monitored in this MKN45 peritoneally disseminated mouse model.

Results

Intraperitoneal injection of DFP‐10825 suppressed tumor growth in two peritoneally disseminated cancer models (MKN45 and NCI‐N87) and increased the survival time of the MKN45 model without severe side effects. Throughout the treatment regimen, no significant body weight loss was associated with the administration of DFP‐10825. Interestingly, after intraperitoneal injection, fluorescence‐labeled DFP‐10825 retained for more than 72 hours in the peritoneal cavity and selectively accumulated in disseminated tumors.

Conclusions

Intraperitoneal injection of DFP‐10825 demonstrated effective antitumor activity without systemic severe adverse effects via the selective delivery of RNAi molecules into disseminated tumors in the peritoneal cavity. Our current study indicates that DFP‐10825 could become an alternative option to improve the outcomes of patients with peritoneally disseminated gastric cancer.

Nuclear Folate Metabolism

Despite unequivocal evidence that folate deficiency increases risk for human pathologies, and that folic acid intake among women of childbearing age markedly decreases risk for birth defects, definitive evidence for a causal biochemical pathway linking folate to disease and birth defect etiology remains elusive. The de novo and salvage pathways for thymidylate synthesis translocate to the nucleus of mammalian cells during S- and G2/M-phases of the cell cycle and associate with the DNA replication and repair machinery, which limits uracil misincorporation into DNA and genome instability. There is increasing evidence that impairments in nuclear de novo thymidylate synthesis occur in many pathologies resulting from impairments in one-carbon metabolism. Understanding the roles and regulation of nuclear de novo thymidylate synthesis and its relationship to genome stability will increase our understanding of the fundamental mechanisms underlying folate- and vitamin B₁₂-associated pathologies.

Deoxyuracil in DNA and disease: Genomic signal or managed situation?

Genomic instability is implicated in the etiology of several deleterious health outcomes including megaloblastic anemia, neural tube defects, and neurodegeneration. Uracil misincorporation and its repair are known to cause genomic instability by inducing DNA strand breaks leading to apoptosis, but there is emerging evidence that uracil incorporation may also result in broader modifications of gene expression, including: changes in transcriptional stalling, strand break-mediated transcriptional upregulation, and direct promoter inhibition. The factors that influence uracil levels in DNA are cytosine deamination, de novo thymidylate (dTMP) biosynthesis, salvage dTMP biosynthesis, dUTPase, and DNA repair. There is evidence that the nuclear localization of the enzymes in these pathways in mammalian cells may modify and/or control the levels of uracil accumulation into nuclear DNA. Uracil sequencing technologies demonstrate that uracil in DNA is not distributed stochastically across the genome, but instead shows patterns of enrichment. Nuclear localization of the enzymes that modify uracil in DNA may serve to change these patterns of enrichment in a tissue-specific manner, and thereby signal the genome in response to metabolic and/or nutritional state of the cell.

Deciphering the potential value of 5-fluorouracil metabolic enzymes in predicting prognosis and treatment response of colorectal cancer patients

Introduction:

5-flourouracil (5-FU) is one of the standard chemotherapeutic drugs used today in the treatment of colorectal cancer patients. Disruption of 5-FU metabolic pathway may contribute to altered effectiveness towards 5-FU-based therapy. Hence, the study of 5-FU metabolizing enzymes might have the potential efficacy to predict survival and response to treatment in colorectal cancer patients.

Materials and methods:

Immunohistochemical localization of 5-FU metabolic enzymes (TS, MTHFR, DPYD, and TP) was evaluated in 143 untreated patients with colorectal cancer; their prognostic and predictive values were also evaluated.

Results:

Immuno-positivity for TS, MTHFR, DPYD, and TP was observed in 77%, 75%, 88%, and 96% of colorectal cancer patients, respectively. Univariate survival analysis in total patients showed that low DPYD expression significantly predicted adverse overall survival ( P=0.042). Moreover, subgroup of colon cancer patients with low TS expression was associated with unfavorable prognosis. TP expression also emerged as a prognosticator in the subgroup of early and advanced stage patients. Additionally, when effect of co-expression of 5-FU metabolic enzymes was evaluated in total patients, low coexpression of all four proteins was predictive of poor overall survival than for individuals expressing high coexpression of these proteins ( P=0.045). In contrast, none of the 5-FU metabolic enzymes—either singly or on coexpression—emerged as a useful biomarker of potential therapeutic value when evaluated in the subgroup of patients treated with 5-FU alone or 5-FU plus oxaliplatin.

Conclusion:

The above findings suggest that coexpression of 5-FU metabolic enzymes possess significant prognostic value and could be useful biomarkers in colorectal cancer patients.

Dietary Uridine Decreases Tumorigenesis in the ApcMin/+ Model of Intestinal Cancer

BACKGROUND

Dietary deoxyuridine and uridine have been shown to have opposing effects on neural tube defect (NTD) incidence in the serine hydroxymethyltransferase 1 (Shmt1+/- ) mouse model of folate-responsive NTDs, which are mediated by changes in de novo thymidylate biosynthesis. Alterations in folate-mediated one-carbon metabolism that protect against NTDs increased cancer risk in some studies.

OBJECTIVE

This study examined the effects of the dietary pyrimidine nucleosides uridine, thymidine, or deoxyuridine on intestinal tumorigenesis in the ApcMin/+ mouse model [a mouse model lacking one copy of the adenomatosis polypsis coli (APC) gene] of spontaneous intestinal tumor formation. This study also evaluated the effects of uridine and deoxyuridine in culture medium on antifolate efficacy in Caco-2 and HeLa cell lines.

METHODS

ApcMin/+ male mice (n = 10-14/group) were fed folate-deficient diets containing uridine, thymidine, or deoxyuridine from weaning until 17 wk of age. Total intestinal tumors were analyzed and biomarkers of folate status and metabolism were measured, including plasma folate concentrations, colon uracil content, and SHMT1 concentrations.

RESULTS

ApcMin/+ mice fed dietary uridine showed a 50% reduction in total intestinal tumors, but neither dietary deoxyuridine nor thymidine affected tumorigenesis. Dietary nucleoside supplementation also increased plasma folate concentrations in ApcMin/+ mice, as has been observed in the Shmt1+/- mouse model. Neither uridine nor deoxyuridine in culture media affected antifolate efficacy in either HeLa or Caco-2 cell lines.

CONCLUSIONS

Dietary uridine, which is teratogenic in mice, decreases intestinal tumor formation in the ApcMin/+ mouse model. Dietary uridine mimics the effect of the common methylene tetrahydrofolate reductase (MTHFR) C677T variant in protecting against colorectal cancer, while contributing to the risk of NTDs.

Targeting nuclear thymidylate biosynthesis

Thymidylate (dTMP) biosynthesis plays an essential and exclusive function in DNA synthesis and proper cell division, and therefore has been an attractive therapeutic target. Folate analogs, known as antifolates, and nucleotide analogs that inhibit the enzymatic action of the de novo thymidylate biosynthesis pathway and are commonly used in cancer treatment. In this review, we examine the mechanisms by which the antifolate 5-fluorouracil, as well as other dTMP synthesis inhibitors, function in cancer treatment in light of emerging evidence that dTMP synthesis occurs in the nucleus. Nuclear localization of the de novo dTMP synthesis pathway requires modification of the pathway enzymes by the small ubiquitin-like modifier (SUMO) protein. SUMOylation is required for nuclear localization of the de novo dTMP biosynthesis pathway, and disruption in the SUMO pathway inhibits cell proliferation in several cancer models. We summarize evidence that the nuclear localization of the dTMP biosynthesis pathway is a critical factor in the efficacy of antifolate-based therapies that target dTMP synthesis.

Distinct gene expression profiles of proximal and distal colorectal cancer: implications for cytotoxic and targeted therapy

Colorectal cancer (CRC) is a heterogeneous disease with genetic profiles and clinical outcomes dependent on the anatomic location of the primary tumor. How location impacts the molecular makeup of a tumor and how prognostic and predictive biomarkers differ between proximal versus distal colon cancers is not well established. We investigated the associations between tumor location, KRAS and BRAF mutation status, and the mRNA expression of proteins involved in major signaling pathways, including tumor growth (EGFR), angiogenesis (VEGFR2), DNA repair (ERCC1) and fluoropyrimidine metabolism (TS). FFPE tumor specimens from 431 advanced CRC patients were analyzed. The presence of 7 different KRAS base substitutions and the BRAF V600E mutation was determined. ERCC1, TS, EGFR and VEGFR2 mRNA expression levels were detected by RT-PCR. BRAF mutations were significantly more common in the proximal colon (p<0.001), whereas KRAS mutations occurred at similar frequencies throughout the colorectum. Rectal cancers had significantly higher ERCC1 and VEGFR2 mRNA levels compared to distal and proximal colon tumors (p=0.001), and increased TS levels compared to distal colon cancers (p=0.02). Mutant KRAS status was associated with lower ERCC1, TS, EGFR, and VEGFR2 gene expression in multivariate analysis. In a subgroup analysis, this association remained significant for all genes in the proximal colon and for VEGFR2 expression in rectal cancers. The mRNA expression patterns of predictive and prognostic biomarkers as well as associations with KRAS and BRAF mutation status depend on primary tumor location. Prospective studies are warranted to confirm these findings and determine the underlying mechanisms.

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.

Novel MEK inhibitor trametinib and other retinoblastoma gene (RB)-reactivating agents enhance efficacy of 5-fluorouracil on human colon cancer cells

Chemotherapy for colorectal cancer has become more complicated and diversified with the appearance of molecular-targeting agents. 5-Fluorouracil (5-FU) has been a mainstay of chemotherapy for colorectal cancer, but it is still unknown whether the combining of 5-FU with novel molecular-targeting agents is effective. Thymidylate synthase (TS) is a direct target of 5-FU, and the low TS level has been generally supposed to sensitize 5-FU's efficacy. We therefore hypothesized that RB-reactivating agents could enhance the efficacy of 5-FU, because the RB-reactivating agents could suppress the function of transcription factor E2F of TS gene promoter. We used three RB-reactivating agents, trametinib/GSK1120212 (MEK inhibitor), fenofibrate (PPARα agonist), and LY294002 (PI3K inhibitor), with 5-FU against human colon cancer HT-29 and HCT15 cells. Trametinib induced p15 and p27 expression and reduced cyclin D1 levels in HT-29 cells. Fenofibrate also dephosphorlated ERK1/2 and reduced cyclin D1 levels in HT-29 cells. LY294002 induced p27 expression in HCT15 cells. All three agents caused dephosphorylation of RB protein and G1-phase arrest with a reduction of TS expression. As a consequence, the combination of 5-FU with each of the agents resulted in a significant decrease of colony numbers in HT-29 or HCT15 cells. These results suggest "RB-reactivation therapy" using molecular-targeting agents to be a new strategy for 5-FU-based chemotherapy. In particular, we strongly expect trametinib, which was discovered in Japan and was recently submitted to FDA for approval, to be used together with established regimens for colorectal cancer.

Cancer of the colon and rectum: potential effects of sex-age interactions on incidence and outcome

Background

Sex differences in epidemiological, clinical and pathological characteristics of colorectal cancer have been under intensive investigation for the last three decades. Given that most of the sex-related differences reported were also age-related, this study sought to determine the potential effect of a sex-age interaction on colorectal cancer development and progression.

Material/Methods

Statistical data on sex- and age-specific colon or rectal cancer incidence, disease stage and survival for white persons were derived from the United States Surveillance, Epidemiology and End Results (SEER) Program. Age-specific incidence rates in 2002–2006 were analyzed by 5-year age groups (45–49, 50–54, 55–59, 60–64, 65–69, 70–74, 75–79, 80–84 years) in men and women. Sex differences were measured by calculating rate differences (RD) and rate ratios (RR). Equivalent analyses for a similar time period were performed for stage distribution and 5-year relative survival.

Results

Age-specific incidence rates were higher for men, for all life-time periods. However, the magnitude of the male predominance was age-dependent. The RR and RD did not remain constant over time: they increased gradually with age, peaked at 70–74 years, and declined thereafter. The distribution of stage at diagnosis was similar between men and women, but women seemed to have better survival, until the age of 64 years for colon cancer and 74 years for rectal cancer.

Conclusions

There seem to be significant age-related sex differences in the incidence of colorectal cancer, and maybe also in its prognosis.

Relationship between thymidylate synthase and p53 and response to FEC versus taxane adjuvant chemotherapy for breast carcinoma

Many drugs can be used for adjuvant therapy of breast cancer, including anthracyclines, cyclophosphamide, 5-fluorouracil (5-fU) and, recently, taxanes (TXT) have shown promising results. 5-FU blocks thymidylate synthase (TS) which cross-links p53 mRNA, inhibiting its synthesis. TS overexpression is one of the main mechanisms involved in 5-FU drug resistance. Enough p53 mutations can confer resistance to chemotherapy using anthracyclines and 5-FU, while are associated with improved responses to TXT. The aim of this study was to examine the TS and p53 levels in tumor samples and to compare the efficacy of FEC (5-FU, epirubicin, cyclophosphamide) and TXT chemotherapy in a group of patients with differing TS and p53 status. We examined 84 breast tumor samples using immunohistochemistry. TS and p53 levels were inversely related, and TS and p53 positivity was significantly associated with the failure of FEC treatment and with a good response to TXT therapy (p <0.001). This confirms the predictive role of these two markers, which should be considered when choosing the appropriate adjuvant therapy for breast cancer.

Trafficking of intracellular folates

The role of metabolic compartmentation in spatially organizing metabolic enzymes into pathways, regulating flux through metabolic pathways, and controlling the partitioning of metabolic intermediates among pathways is appreciated, but our understanding of the mechanisms that establish metabolic architecture and mediate communication and regulation among interconnected metabolic pathways and networks is still incomplete. This review discusses recent advancements in our understanding of metabolic compartmentation within the pathways that constitute the folate-mediated one-carbon metabolic network and emerging evidence for a need to regulate the trafficking of folates among compartmentalized metabolic pathways.

Contribution of thymidylate synthase to gemcitabine therapy for advanced pancreatic cancer

OBJECTIVES

Thymidylate synthase (TS) inhibitors activate human equilibrative nucleoside transporter 1. We evaluated the contribution of TS expression to determine a treatment method providing an effect from gemcitabine (GEM).

METHODS

The expression of 5-fluorouracil (5-FU) and GEM metabolic factors (5-FU: TS, dihydropyrimidine dehydrogenase, orotate phosphoribosyltransferase; GEM: human equilibrative nucleoside transporter 1, deoxycytidine kinase, cytidine deaminase, 5'-nucleotidase) were studied in 7 pancreatic cancer cell lines by Western blotting, and drug resistance was evaluated by 3-[4,5-dimethylthiazol]-2,5-dephenyl tetrazolium bromide assay. The expression of 5-FU factors was observed immunohistochemically in resected pancreatic cancer specimens.

RESULTS

Gemcitabine concentrations that inhibited colony formation by 50% correlated with TS protein expression (P = 0.0169). With a 5-FU non-growth-inhibiting dose, GEM concentrations that inhibited colony formation by 50% were significantly reduced by one fourth to one tenth. Knockout of TS expression by small interfering RNA decreased resistance to GEM in the cell lines (P = 0.0019). Immunohistochemically, TS expression related to disease-free survival time of patients treated with GEM (P = 0.0224). A high expression of 5-FU factors was detected: orotate phosphoribosyltransferase: differentiated cases (P = 0.0137), lower T factor (P = 0.0411); dihydropyrimidine dehydrogenase: nerve invasion (P = 0.0188), lymph node recurrence (P = 0.0253); TS, positive N factor (P = 0.0061).

CONCLUSIONS

The expression of TS provides an alternative source of substrate for DNA synthesis and positively correlates with GEM resistance and shortened patient survival.

Relationship of polymorphism of the tandem repeat sequence in the thymidylate synthase gene and the survival of stage III colorectal cancer patients receiving adjuvant 5-flurouracil-based chemotherapy

BACKGROUND

The aim of this study was to determine whether the different polymorphisms in the thymidylate synthase (TS) gene, novel G>C single nucleotide polymorphism (SNP) and variable number of tandem repeat (VNTR), may be related with disease-free survival (DFS) in patients with stage III colorectal cancer receiving adjuvant chemotherapy.

METHODS

The study included 201 patients with pathologic TNM stage III colon cancer who received adjuvant 5-fluorouracil (5-FU)-based chemotherapy after surgery. DNA was extracted from fresh tumor tissue and sequenced. Patients with TS genotypes of 2R3G, 3C3G, or 3G3G were assigned to a high expression group, and those with 2R2R, 2R3C, or 3C3C, to a low expression group.

RESULTS

Frequencies of the TS tandem repeat polymorphisms among the tumor genotypes were 6.0% in 2R2R, 25.4% in 2R3R, and 68.7% in 3R3R. The low expression group included 52 patients (25.9%), and the high expression group included 149 patients (74.1%). Groups classified according to possession of VNTR, SNP, and low- or high-expression genotypes did not differ significantly in DFS. In multivariate analysis, only tumor stage showed significant prognostic value (hazard ratio (HR) 2.05, 95% CI = 1.24-3.37, P = 0.005).

CONCLUSIONS

TS polymorphisms do not predict clinical outcome of colorectal cancer patients treated with adjuvant 5-FU-based chemotherapy.

Nuclear thymidylate synthase expression in sporadic colorectal cancer depends on the site of the tumor

Colorectal carcinoma (CRC) is a heterogeneous disease with specific epidemiological, pathological, molecular, and clinical characteristics that depend on the location of the tumor relative to the splenic flexure. Thymidylate synthase (TS) is a major target of 5-fluorouracil-based chemotherapy for CRC and high expression of this enzyme in tumor cells can influence the effect of therapy. We examined differences in TS protein expression in nuclei of tumor cells between CRCs located proximal and distal to the splenic flexure. Nuclear TS was detected by immunohistochemistry with a TS 106 monoclonal antibody on tissue microarrays constructed from 269 CRCs. The median histological score of nuclear TS expression of all proximal tumors was two times higher (p = 0.0003) and in men three times higher (p = 0.00023) than that found in distal tumors. In multivariate analysis which included age, sex, Astler-Coller stage, histological grade, and site, only proximal location of the tumor was identified as an independent factor associated with higher TS expression (odds ratio 2.46, 95% confidence interval = 1.29-4.70, p = 0.0062). These results demonstrate significant differences in nuclear TS expression between proximal and distal cancers and suggest the potential importance of the site of the tumor for proper stratification of patients for chemotherapy.

Correlation Between Thymidylate Synthase Protein Expression and Gene Polymorphism with Clinicopathological Parameters in Colorectal Carcinoma

5-Fluorouracil (5-FU) represents the basis of chemotherapy for colorectal carcinoma, inhibiting thymidylate synthase (TS), an essential enzyme for DNA replication. Previous studies have associated high TS protein expression by tumor cells with poor outcome of patients with colorectal carcinoma, but others have refuted these findings. In view of the potential role of TS as predictive parameter and the lack of consensus in the literature, the present study compared 2 methods: protein expression and gene polymorphism, correlating them with clinicopathological findings. Immunohistochemical detection of TS in tumor cells and detection of gene polymorphism in the blood were performed in 32 patients with colorectal carcinoma treated with 5-FU. No correlation was found between TS protein expression and gene polymorphism. Neither method correlated with survival, tumor staging, and tumor histological grading. This result possibly reflects a complex tumor response to 5-FU therapy, where TS is just one of the involved proteins.

AQUA analysis of thymidylate synthase reveals localization to be a key prognostic biomarker in 2 large cohorts of colorectal carcinoma

CONTEXT

Increased thymidylate synthase expression is a marker for decreased survival in colorectal cancer.

OBJECTIVE

Thymidylate synthase localizes to both the nucleus and cytoplasm, but how the relationship of these expression levels affects colon cancer outcome has yet to be determined.

DESIGN

Using AQUA, we assessed prognosis of thymidylate synthase expression as a function of subcellular localization in 2 retrospective cohorts of colorectal carcinoma. We used the first cohort (n = 599) as a training set, subsequently validating optimal expression cut points in the second cohort (n = 447).

RESULTS

A significant association between decreased 5-year disease-specific survival and increased nuclear expression (16% decreased survival [72% to 56%] for the top 60% of nuclear-expressing tumors [P < .001]) and cytoplasmic expression (12% decreased survival [70% to 58%] for the top 54% of cytoplasmic-expressing tumors [P = .02]) was observed for the training set. A higher nuclear to cytoplasmic ratio also correlated significantly with decreased survival (15% decreased survival [66% to 51%] for the top 25% of tumors [P < .001]). Applying these findings to the validation set, as a function of time to recurrence, only the ratio (P = .03 [expression ratio]; P = .18 [nuclear]; P = .71 [cytoplasmic]) showed a significant association with decreased time to recurrence. Additionally, the expression ratio significantly added to the prognostic value given by the primary tumor pathologic classification and nodal status.

CONCLUSIONS

These data suggest the relationship of nuclear to cytoplasmic thymidylate synthase expression, given as a ratio of continuous AQUA scores, to be a strong predictor of colon cancer survival.

Predictive value of Ki67 and p53 in locally advanced rectal cancer: Correlation with thymidylate synthase and histopathological tumor regression after neoadjuvant 5-FU-based chemoradiotherapy

AIM: To investigate the predictive value of Ki67 and p53 and their correlation with thymidylate synthase (TS) gene expression in a rectal cancer patient cohort treated according to a standardized recommended neoadjuvant treatment regimen.

METHODS: Formalin fixed, paraffin embedded pre-therapeutical tumor biopsies (n = 22) and post-therapeutical resection specimens (n = 40) from patients with rectal adenocarcinoma (clinical UICC stage II/III) receiving standardized neoadjuvant 5-fluorouracil (5-FU) based chemoradiotherapy were studied for Ki67 and p53 expression by immunohistochemistry and correlated with TS mRNA expression by quantitative TaqMan real-time PCR after laser microdissection. The results were compared with histopathological tumor regression according to a standardized semiquantitative score grading system.

RESULTS: Responders (patients with high tumor regression) showed a significantly lower Ki67 expression than non-responders in the pre-therapeutical tumor biopsies (81.2% vs 16.7%; P < 0.05) as well as in the post-therapeutical resection specimens (75.8% vs 14.3%; P < 0.01). High TS mRNA expression was significantly correlated with a high Ki67 index and low TS mRNA expression was significantly correlated with a low Ki67 index in the pre-therapeutical tumor biopsies (corr. coef. = 0.46; P < 0.01) as well as in the post-therapeutical resection specimens (corr. coef. = 0.40; P < 0.05). No significant association was found between p53 and TS mRNA expression or tumor regression.

CONCLUSION: Ki67 has, like TS, predictive value in rectal cancer patients after neoadjuvant 5-FU based chemoradiotherapy. The close correlation between Ki67 and TS indicates that TS is involved in active cell cycle processes.

Folate-mediated one-carbon metabolism

Tetrahydrofolate (THF) polyglutamates are a family of cofactors that carry and chemically activate one-carbon units for biosynthesis. THF-mediated one-carbon metabolism is a metabolic network of interdependent biosynthetic pathways that is compartmentalized in the cytoplasm, mitochondria, and nucleus. One-carbon metabolism in the cytoplasm is required for the synthesis of purines and thymidylate and the remethylation of homocysteine to methionine. One-carbon metabolism in the mitochondria is required for the synthesis of formylated methionyl-tRNA; the catabolism of choline, purines, and histidine; and the interconversion of serine and glycine. Mitochondria are also the primary source of one-carbon units for cytoplasmic metabolism. Increasing evidence indicates that folate-dependent de novo thymidylate biosynthesis occurs in the nucleus of certain cell types. Disruption of folate-mediated one-carbon metabolism is associated with many pathologies and developmental anomalies, yet the biochemical mechanisms and causal metabolic pathways responsible for the initiation and/or progression of folate-associated pathologies have yet to be established. This chapter focuses on our current understanding of mammalian folate-mediated one-carbon metabolism, its cellular compartmentation, and knowledge gaps that limit our understanding of one-carbon metabolism and its regulation.

The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer

INTRODUCTION

High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to microsatellite stable (MSS) cancers.

OBJECTIVE

This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC).

RESULTS AND DISCUSSION

5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed.

CONCLUSION

Available evidence suggests that MSI-H CRC have different behaviour patterns and response to chemotherapy compared with MSS CRC.

The prognostic significance of thymidylate synthase and dihydropyrimidine dehydrogenase in colorectal cancer of 303 patients adjuvantly treated with 5-fluorouracil

Cytotoxic effect of 5-fluorouracil 5-FU is mediated through inhibition of thymidylate synthase (TS), and 5-FU is catabolised by dihydropyrimidine dehydrogenase (DPD). Efficacy of 5-FU may therefore depend on the TS and DPD activity of colorectal cancer. Archival tumour specimens from 303 consecutive patients were analysed for the expression of TS and DPD using immunohistochemistry. All patients were completely resected for colorectal cancer stages II-III and have subsequently received adjuvant treatment with 5-FU. In a multivariate analysis adjusting for the impact of bowel obstruction and vascular tumour invasion, diffuse TS pattern was significantly associated with increased risk of recurrence (hazard ratio (HR) = 1.9; 95% confidence interval (CI): 1.1-3.2; p = 0.02), but without significant association to death (HR = 1.6; 95% CI: 0.9-2.8; p = 0.08). High TS intensity was not significantly associated with lower risk of recurrence (HR = 0.6; 95% CI: 0.3-1.1; p = 0.07) or death (HR = 0.6; 95% CI: 0.3-1.2; p = 0.2). High DPD intensity was significantly associated with increased risk of recurrence (HR = 1.5; 95% CI: 1.1-2.3; p = 0.03) and death (HR = 1.6; 95% CI: 1.1-2.5; p = 0.02). Patients with a combination of low TS and high DPD intensity were at significantly increased risk of both recurrence (HR = 2.1; 95% CI: 1.0-4.2; p = 0.04) and death (HR = 2.0; 95% CI: 1.0-4.0; p = 0.05). No relationship between tolerability and toxicity of 5-FU and TS and DPD expression was found. It is concluded that characterizing colorectal carcinomas by TS and DPD expression may disclose subsets of patients with significantly greater risk of disease recurrence and early death. This may be utilized in the selection of patients for treatment approaches and for decision on follow-up programs.

Schedule-dependent activity of 5-fluorouracil and irinotecan combination in the treatment of human colorectal cancer: in vitro evidence and a phase I dose-escalating clinical trial

Several schedules of 5-fluorouracil (FU) and irinotecan (IRI) have been shown to improve overall survival in advanced colorectal cancer (CRC). Preclinical evidence suggests that the sequential administration of IRI and FU produces synergistic activity, although their clinical use has not been fully optimised. We investigated the interaction between short-term exposure to SN-38, the active metabolite of IRI, and prolonged exposure to FU in human CRC HT-29 cells and observed that the synergism of action between the two agents can be increased by extending the time of cell exposure to FU and reducing the interval between administration of the two agents. Based on these findings, we performed a phase I trial in 25 advanced CRC patients using a modified IRI/FU regimen as first-line therapy and evaluated three dose levels of IRI (150-300 mg/m(2)) and two of continuous infusion of FU (800-1000 mg/m(2)) in a 3-weekly schedule. The most severe grade III-IV toxicities were neutropoenia in four cycles and diarrhoea in three. One patient achieved complete response (4%), 12 a partial response (48%), the overall response rate was 52% (+/-20, 95% CI); seven of 25 patients had stable disease (28%), the overall disease control was 80% (+/-16, 95% CI). This modified IRI/FU schedule is feasible and exhibits potentially interesting clinical activity.

ERbeta isoform expression in colorectal carcinoma: an in vivo and in vitro study of clinicopathological and molecular correlates

Colorectal carcinoma shows several sex-related differences with regard to incidence, response to chemotherapy and microsatellite instability. These differences may relate to differential expression of ERbeta1 (wild-type) as well as the truncated ERbeta2 and ERbeta5 splice variant isoforms, which have recently been detected in normal and malignant colorectal epithelium. This hypothesis was tested through the study of ERbeta isoform protein and/or mRNA expression amongst 91 primary colorectal carcinoma cases and 20 colorectal carcinoma cell lines. Study of the latter showed an absolute correlation between mRNA and protein expressions for ERbeta1 and ERbeta2. ERbeta1 and ERbeta2 protein expression was lost in 22% and 49%, respectively, of the primary colorectal carcinomas. By contrast, ERbeta5 expression was found in all primary colorectal carcinomas and all colorectal carcinoma cell lines studied. Lower ERbeta1 protein expression was associated with poorer differentiation, higher pT stage and absence of microsatellite instability. Higher ERbeta2 protein expression was associated with right-sided location and presence of lymph node metastases. Protein expression of ERbeta1 correlated positively with expression of the oestrogen-responsive protein trefoil factor 1 (TFF1). There was no correlation between ERbeta protein isoform expression and response to 5-fluorouracil therapy, tumour proliferation, or thymidylate synthase expression. These data suggest that ERbeta1 and/or ERbeta2 isoform expression may have prognostic value and may explain sex-related differences in microsatellite instability and colorectal carcinoma. The opposing associations shown by ERbeta1 and/or ERbeta2 in relation to colorectal carcinoma are in keeping with differential activities shown by the two isoforms.

Genetic factors influencing pyrimidine-antagonist chemotherapy

Pyrimidine antagonists, for example, 5-fluorouracil (5-FU), cytarabine (ara-C) and gemcitabine (dFdC), are widely used in chemotherapy regimes for colorectal, breast, head and neck, non-small-cell lung cancer, pancreatic cancer and leukaemias. Extensive metabolism is a prerequisite for conversion of these pyrimidine prodrugs into active compounds. Interindividual variation in the activity of metabolising enzymes can affect the extent of prodrug activation and, as a result, act on the efficacy of chemotherapy treatment. Genetic factors at least partly explain interindividual variation in antitumour efficacy and toxicity of pyrimidine antagonists. In this review, proteins relevant for the efficacy and toxicity of pyrimidine antagonists will be summarised. In addition, the role of germline polymorphisms, tumour-specific somatic mutations and protein expression levels in the metabolic pathways and clinical pharmacology of these drugs are described. Germline polymorphisms of uridine monophosphate kinase (UMPK), orotate phosphoribosyl transferase (OPRT), thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and methylene tetrahydrofolate reductase (MTHFR) and gene expression levels of OPRT, UMPK, TS, DPD, uridine phosphorylase, uridine kinase, thymidine phosphorylase, thymidine kinase, deoxyuridine triphosphate nucleotide hydrolase are discussed in relation to 5-FU efficacy. Cytidine deaminase (CDD) and 5'-nucleotidase (5NT) gene polymorphisms and CDD, 5NT, deoxycytidine kinase and MRP5 gene expression levels and their potential relation to dFdC and ara-C cytotoxicity are reviewed.

Maintenance Therapy to Suppress Micrometastasis: The New Challenge for Adjuvant Cancer Treatment

The palliative efficacy of cytotoxic drugs is routinely assessed using tumor shrinkage (response) rates shown in clinical trials. Although adjuvant drug therapy has a goal distinct from that of palliative therapy (i.e., to prolong survival by inhibiting progression of micrometastatic disease), it is widely assumed that the adjuvant efficacy of a drug will parallel its response rate ("activity") in advanced stages of the disease. Reconsideration of this assumption seems timely in view of recent developments: the realization that many predictors of short-term tumor response correlate inversely with long-term survival outcomes; the characterization of tumor progression as a discontinuous process that may include dormant phases; the understanding that micrometastasis is therapeutically suppressible by a variety of mechanisms including direct tumor cell kill, cytotoxic disruption of paracrine growth signals from normal tissues, and targeted inhibition of prometastatic pathways; the recognition that tumor dormancy not only blocks the antimetastatic efficacy of cytotoxic drugs but also represents a therapeutic end point for metastasis-suppressive noncytotoxic drugs such as hormone inhibitors; and the insight that optimal adjuvant drug therapy is likely to include both induction and maintenance components. The traditional view of cytoreductive response as a prerequisite for adjuvant drug efficacy thus merits reappraisal, with a view to accelerating incorporation of novel noncytotoxic maintenance therapies into controlled studies.

Nuclear expression of thymidylate synthase in colorectal cancer cell lines and clinical samples

Thymidylate synthase (TS) [TYMS; OMIM reference number (188,350)] is normally considered to be a cytoplasmic enzyme. However, a few reports have suggested it may also be present in the nucleus. To explore this in more detail, we used a highly specific polyclonal antibody to TS and a combination of techniques, including immunocytochemistry, confocal microscopy, cell fractionation, and Western blotting. We developed cell line HeLa-55, a HeLa derivative that grossly overexpresses TS. Although the vast majority of TS was in the cytoplasm, some TS also was seen in the nucleus. TS in parental HeLa cells and in normal human fibroblasts was seen exclusively in the cytoplasm. HeLa-55 cells exposed to 5-fluorodeoxyuridine were fractionated and examined by Western blotting. Interestingly, both free TS and the ternary complex of TS were seen in the cytoplasmic fraction but only free TS was detected in the nuclear fraction. Amongst different cell lines examined, HCT-15 and normal fibroblasts showed no nuclear TS, HCC-2998 and SW-620 showed a small amount of nuclear TS, and HT-29, RKO, and HCT-116 showed a strong nuclear TS signal. Nuclear staining was clearly evident in some clinical colorectal specimens, both normal and malignant. This staining was definitively shown to be TS by competition with recombinant TS protein. A putative leucine-rich nuclear export sequence was identified but its function could not be confirmed. We conclude that small amounts of TS protein is present in the nucleus of some cell types but further work is needed to determine the significance of this observation.

Single nucleotide polymorphism in the 5' tandem repeat sequences of thymidylate synthase gene predicts for response to fluorouracil-based chemotherapy in advanced colorectal cancer patients

Thymidylate synthase (TS) is the primary target of 5-fluorouracil (5-FU). A VNTR polymorphism in the TS promoter region is associated with the efficacy of 5-FU-based chemotherapy in colorectal cancer. A common G>C SNP at the 12th nucleotide of the second repeat in the TS*3 alleles has been recently described. The combination of SNP and VNTR allows the definition of 3 TS alleles: *2, *3G and *3C. The aim of our study was to evaluate the predictive value of clinical response and survival of these new defined TS alleles. TS genotypes of 89 patients diagnosed with metastatic colorectal cancer and undergoing 5-FU-based chemotherapy were carried out. The clinical outcome was evaluated according to the genotype (high expression genotype: *2R/*3G; *3C/*3G; *3G/*3G; and low expression genotype: *2R/*2R; *2R/*3C; *3C/*3C. A higher overall response was observed in the group of patients with a low expression genotype (p = 0.035). The probability of achieving a clinical response of patients with a low expression-related genotype was 2.9 higher than that of the other group (95% CI = 1.03-5.6, p = 0.04). The median time to progression was 12 months and 9 months in the low and high expression groups, respectively (p = 0.07, log rank test). Overall survival was significantly longer in the low expression group. In this group the median OS was not achieved at 50 months of follow-up in contrast to the 20 months observed in the high expression group (p = 0.03). TS genotype was an independent predictor of progression-free and overall survival in the Cox regression models after adjustment to the other clinical variables. The selection of patients who are likely to respond to 5-FU therapy may be considerably improved if the TS genotype were to include both the VNTR and the SNP located within the promoter region of the gene.

Expression of thymidylate synthase is correlated with proliferative activity in non-small cell lung cancer (NSCLC)

Many experimental studies have revealed that enhanced thymidylate synthase (TS) expression is significantly correlated with higher proliferative activity of tumor cells, which may account for a poor prognosis of high-TS patients. However, only a few clinical studies have focused on the correlation between TS status and cell proliferation. Therefore, we assessed the correlation between TS expression and proliferative index (PI) as a marker of cell proliferation or p53 status in a total of 109 patients with completely resected pathologic stage I, non-small cell lung cancer (NSCLC). PI was defined as the percentage of tumor cells with positive staining against proliferative cell nuclear antigen (PCNA). The mean PIs of TS-high and TS-low tumors were 48.2% and 34.4% respectively, showing a significantly higher proliferative activity of TS-high tumor (P=0.020); when stratified according to histological type, the difference was significant in adenocarcinoma (P=0.038), but not in squamous cell carcinoma. There was no significant correlation between TS expression and p53 status. In conclusion, tumor cells with higher TS expression have higher proliferative activity in NSCLC, especially in adenocarcinoma.

Correlation of thymidylate synthase, thymidine phosphorylase and dihydropyrimidine dehydrogenase with sensitivity of gastrointestinal cancer cells to 5-fluorouracil and 5-fluoro-2’-deoxyuridine

AIM: To determine the expression levels of three metabolic enzymes of fluoropyrimidines: thymidylate synthase (TS), thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) in seven human gastrointestinal cancer cell lines, and to compare the enzyme levels with the sensitivity to 5-fluorouracil (5-FU) and 5-fluoro-2’-deoxyuridine (FdUrd).

METHODS: TS, TP and DPD mRNA levels were assessed by semi-quantitative RT-PCR, TP and DPD protein contents were measured by ELISA. Fifty percent inhibitory concentrations of growth (IC50), representing the sensitivity to drugs, were determined by MTT assay.

RESULTS: IC50 values ranged from 1.28 to 12.26 uM for 5-FU, and from 5.02 to 24.21 uM for FdUrd, respectively. Cell lines with lower DPD mRNA and protein levels tended to be more sensitive to 5-FU (P < 0.05), but neither TS nor TP correlated with 5-FU IC50 (P > 0.05). Only TS mRNA level was sharply related with FdUrd sensitivity (P < 0.05), but TP and DPD were not (P > 0.05). A correlation was found between mRNA and protein levels of DPD (P < 0.05), but not TP (P < 0.05).

CONCLUSION: DPD and TS enzyme levels may be useful indicators in predicting the antitumor activity of 5-FU or FdUrd, respectively.

Evaluation of thymidylate synthase protein expression by Western blotting and immunohistochemistry on human colon carcinoma xenografts in nude mice

In this study we investigated the relationship between thymidylate synthase (TS) protein expression, evaluated by Western blotting analysis and by immunohistochemistry (IHC), and growth rate in human colon xenograft tumors in nude mice. Human colon cancer cell lines were used to induce xenograft tumors and the tumor mass growth rate was calculated by measuring tumor size variations over time. TS 106 monoclonal antibody was used for both Western blotting and IHC TS detection. Tumor cell growth fraction was measured by Ki67/MIB1 immunolabeling and tumor cell growth rate by evaluating the mean nucleolar size in silver-stained sections. TS Western blotting values were related to tumor mass growth rate (p<0.001) and cell growth rate (p=0.002) but not to cell growth fraction (p=0.676). The degree of the IHC staining showed only a trend to be associated with TS protein expression measured on Western blotting, and was not related either to tumor mass growth or cell proliferation rate. Tumor xenografts were also characterized for TS promoter tandem repeat and p53 status. No relationship was observed between these variables and TS expression evaluated by both Western blotting and IHC analysis. Our results demonstrate that TS expression evaluated by Western blotting analysis is directly related to the tumor mass growth rate and question the use of the IHC approach to obtain precise quantitative information on TS expression in tumor samples.

Role of biological markers in the clinical outcome of colon cancer

We investigated a number of biological markers, evaluated under strict intralaboratory quality control conditions, in terms of their role in predicting clinical outcome of patients with colon cancer treated with 5-FU-containing regimens. Colon cancer tissue from 263 patients enrolled onto two randomised clinical trials were studied for their cytofluorimetrically determined DNA content and their immunohistochemically evaluated microvessel density, vascular endothelial growth factor expression, thymidylate synthase expression and tumour lymphocyte infiltration. Disease-free survival and overall survival of patients were analysed as a function of the different variables. At a median follow up of 57 months, age, gender and Dukes' stage showed an impact on disease-free survival, whereas no biological marker emerged as an indicator of better or worse disease-free survival. Only histological grade and Dukes' stage were found to influence overall survival. The different biological variables, studied with particular attention for determination reliability, proved to have no impact on the clinical outcome of patients with colon cancer. Therefore, other markers must be identified to complement clinico-pathological variables in the management of this disease.