Thymidylate synthase mRNA level in adenocarcinoma of the stomach: a predictor for primary tumor response and overall survival

Prediction of response to preoperative chemotherapy in adenocarcinomas of the esophagogastric junction by metabolic imaging

PURPOSE

Preoperative chemotherapy in patients with gastroesophageal cancer is hampered by the lack of reliable predictors of tumor response. This study evaluates whether positron emission tomography (PET) using fluorine-18 fluorodeoxyglucose (FDG) may predict response early in the course of therapy.

PATIENTS AND METHODS

Forty consecutive patients with locally advanced adenocarcinomas of the esophagogastric junction were studied by FDG-PET at baseline and 14 days after initiation of cisplatin-based polychemotherapy. Clinical response (reduction of tumor length and wall thickness by > 50%) was evaluated after 3 months of therapy using endoscopy and standard imaging techniques. Patients with potentially resectable tumors underwent surgery, and tumor regression was assessed histopathologically.

RESULTS

The reduction of tumor FDG uptake (mean +/- 1 SD) after 14 days of therapy was significantly different between responding (-54% +/- 17%) and nonresponding tumors (-15% +/- 21%). Optimal differentiation was achieved by a cutoff value of 35% reduction of initial FDG uptake. Applying this cutoff value as a criterion for a metabolic response predicted clinical response with a sensitivity and specificity of 93% (14 of 15 patients) and 95% (21 of 22), respectively. Histopathologically complete or subtotal tumor regression was achieved in 53% (eight of 15) of the patients with a metabolic response but only in 5% (one of 22) of the patients without a metabolic response. Patients without a metabolic response were also characterized by significantly shorter time to progression/recurrence (P =.01) and shorter overall survival (P =.04).

CONCLUSION

PET imaging may differentiate responding and nonresponding tumors early in the course of therapy. By avoiding ineffective and potentially harmful treatment, this may markedly facilitate the use of preoperative therapy, especially in patients with potentially resectable tumors.

Molecular markers predictive of response to chemotherapy in gastrointestinal tumors

Gastrointestinal cancers account for a large amount of human tumors. Surgery is the standard treatment for localized gastrointestinal cancer, but in a large number of patients, tumors are unresectable at time of diagnosis and even when resectable, survival is often poor. Current attempts to improve these results include the use of chemotherapy in the adjuvant setting, in the advanced disease, or as neoadjuvant treatment. However, less than half the patients respond to chemotherapeutic treatments, mostly reporting important side-effects. The identification of molecular markers, such as p53, thymidylate synthase, K-ras, and others, may provide an important tool for medical oncologists in defining subsets of patients with gastrointestinal cancers more suitable to benefit from chemotherapy or from experimental therapies. The relationship between the clinical outcome to anticancer drugs and molecular markers in gastrointestinal tumors has been reviewed. Available data are promising, but most of them arise from retrospective and small studies. Well designed, prospective trials are warranted to change the target approach from a general to an individual treatment strategy.

Determinants of prognosis and response to therapy in colorectal cancer

Identification of the molecular determinants of 5-fluorouracil (5-FU) and irinotecan (CPT-11) efficacy and toxicity is critically important for the development of more efficient and less toxic treatment strategies for patients with colon cancer. We have identified molecular predictors of response to chemotherapy with 5-FU and survival in patients with advanced colorectal cancer. Low gene expression levels of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and thymidine phosphorylase (TP) are associated with response and survival. Preliminary data suggest that gene expression levels of topoisomerase I, p21, bcl-2, and ICE may be predictive of response to therapy with CPT-11. Increased toxicity seen in patients treated with CPT-11 may be explained by polymorphism in the UGT1A1 gene, which is responsible for glucuronidation of the active metabolite of CPT-11.

Predictive molecular markers in non-small cell lung cancer

Recent biotechnologic knowledge has enabled the discovery of a cornucopia of genetic abnormalities commonly involved not only in cancer but also in other diseases ranging from the plague to arteriosclerosis. The wealth of possibilities uncovered by this knowledge inspires the hope that today's dream of a unified concept of common treatment for multiple diseases could become a future reality. This review arbitrarily categorizes recent findings into five major areas. First, cisplatin resistance associated with the nucleotide excision repair pathway can help clinical oncologists to choose between cisplatin and noncisplatin combinations. Second, the relevant role of nuclear factor-kappa B as a predictor of chemosensitivity can lead to the development of new drugs abrogating nuclear factor-kappa B expression. Third, the presence of tubulin mutations, which are directly involved in resistance to microtubule-interactive drugs, can guide chemotherapy based on taxane or nontaxane combinations. In addition, certain chromosomal deletions affect genes involved in deoxyribonucleotide synthesis, like ribonucleotide reductase, that intervene in gemcitabine metabolism; this raises interest in investigating deletion at chromosome 11p15.5 as a potential mechanism of gemcitabine resistance. Finally, an overwhelming number of publications have analyzed genes involved in cell cycle regulation and development as predictive markers of survival; however, where these pieces fit into the puzzle of cancer management is still unclear.

Expression of thymidylate synthase in gastric cancer patients treated with 5-fluorouracil and doxorubicin-based adjuvant chemotherapy after curative resection

We evaluated the expression of thymidylate synthase (TS) in locally advanced gastric cancer patients treated with adjuvant chemotherapy after curative resection and investigated the association between TS expression and clinicopathologic characteristics including prognosis of the patients. TS expression was evaluated by immunohistochemical staining using TS106 monoclonal antibody in 103 locally advanced gastric cancer patients (stage IB-IV) who underwent 5-fluorouracil (5-FU) and doxorubicin-based adjuvant chemotherapy after curative resection. 65 patients (63%) had primary tumours with high TS expression (> or = 25% of tumour cells positive), and 38 patients (37%) demonstrated low TS expression (< 25% of tumour cells positive or no staining). High TS expression was associated with male gender (P = 0.002), poorly differentiated histology (P = 0.015), and mixed type in Lauren's classification (P = 0.027). There were no statistically significant differences in 4-year disease-free survival (60.0% vs. 57.2%, P = 0.548) and overall survival (59.6% vs. 59.3%, P = 0.792) between high-TS group and low-TS group. In conclusion, although high TS expression was associated with poorly differentiated histology and mixed type in Lauren's classification, it did not predict poor disease-free and overall survival in gastric cancer patients treated with 5-FU and doxorubicin-based adjuvant chemotherapy after curative resection. Further prospective studies including the evaluation of other biological markers associated with the resistance to 5-FU and doxorubicin are necessary.

Adjuvant therapy for gastric cancer: a reality at last

Gastric cancer remains a significant healthcare problem throughout the world and is usually diagnosed at a fairly advanced stage in the West. Despite complete resection of the primary tumor, most patients eventually experience a relapse and die of recurrent disease. Extended surgery has not been shown to improve survival in Western studies. There have been a large number of adjuvant chemotherapy trials over the past several decades, most with negative results. More recently, there is hope for improving these dismal results with a meta-analysis showing a benefit for adjuvant chemotherapy and a large randomized trial, INT-0116, which has just reported a significant survival advantage with combined chemoradiation. These results make adjuvant therapy for completely resected gastric carcinoma the new standard of care, except in the uncommon setting of early intramucosal cancers.

Prolonged and enhanced suppression of thymidylate synthase by weekly 24-h infusion of high-dose 5-fluorouracil

We have recently demonstrated that HDFL (high-dose 5-FU 2600 mg m-2 week-1 and leucovorin 500 mg m-2 week-1, weekly 24-h infusion) is highly active in the treatment of gastric cancer. To further clarify the possible mechanism underlying the improved activity of HDFL compared with conventional 5-FU regimens, we conducted in vitro studies examining the effect of these regimens on the differential regulation of thymidylate synthase (TS) in NCI-N87, a human gastric cancer cell line. The expected serum concentrations of 5-FU are 100-200 mM (lasting for less than 30 min) and 5-10 mM (lasting for 24 h) for the conventional 5-FU regimens (bolus injection or short intravenous infusion of 5-FU 370-500 mg m-2) and the HDFL regimens, respectively. Western blot analysis revealed that 24-h exposure of NCI-N87 to 2.5-10.0 mM of 5-FU resulted in a dose-dependent depletion of free TS, lasting for more than 24 h. In contrast, 30-min exposure of NCI-N87 to 200 mM of 5-FU resulted in a less than 12-h depletion of free TS. Moreover, 24-h exposure to 5-FU resulted in a higher S-phase blockade and enhanced cytotoxicity. In both modes of 5-FU treatment, the initial rapid depletion of free TS was accompanied by a rapid increment of a higher-molecular-weight TS molecule, suggesting that rapid formation of the ternary complex was the key mechanism of 5-FU action during this period. Northern blot analysis showed that the steady-state mRNA of TS was not affected by either of the schedules. We conclude that 24-h exposure of gastric cancer cells to low concentration of 5-FU resulted in better suppression of free TS, a higher degree of S-phase blockade, and enhanced cytotoxicity compared to 30-min exposure to high concentration of 5-FU. These in vitro results may help explain the improved clinical efficacy of HDFL regimens compared to conventional 5-FU regimens.

5-Fluorouracil: forty-plus and still ticking. A review of its preclinical and clinical development

5-Fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) are pyrimidine analogs that have been part of the therapeutic armamentarium for a variety of solid tumors for over forty years. 5-FU has customarily required intravenous administration due to poor and erratic oral bioavailability, while FdUrd has generally been employed for regional administration to the liver or the peritoneal cavity. A great deal of knowledge has been gained concerning the cellular pharmacology and mechanism of action of 5-FU since it was first synthesized in the late 1950's. A more thorough understanding of the factors influencing the metabolic activation of 5-FU and its cellular effects has generated considerable interest in combining it with both modulatory agents such as leucovorin and methotrexate that enhance its metabolism or cytotoxic effects. In addition, 5-FU has also been employed to enhance the therapeutic activity of other antineoplastic agents or modalities such as cisplatin and ionizing radiation with which it can synergize. Appreciation of the clinical pharmacology of 5-FU and FdUrd have led to a variety of schedules that are clinically useful. The preclinical and clinical pharmacology of 5-FU is reviewed to provide a basis for exploring the novel approaches to permit oral administration of 5-FU or its prodrugs that will be described in other articles in this issue.

Gastric cancer

Gastric adenocarcinoma is the most common malignancy of the upper gastrointestinal tract. During the past two decades it has migrated toward the gastroesophageal junction. Gastroesophageal reflux and obesity may play a role. Recent research suggests that a number of biologic and molecular differences exist in patients with gastric cancer. Further investigation in these areas may help in predicting outcome and directing therapy. Gastric cancer is not a curable condition when metastases are present. However, postoperative chemotherapy plus chemoradiotherapy, in the Intergroup trial 0116, prolonged the overall and disease-free survival rates of patients after a curative (R0) resection. It should be considered the new standard of care in patients with gastric cancer who have undergone curative resection with stage Ib-IV disease. Preoperative therapy strategies may increase the likelihood of R0 resection and remain an area of active investigation. Finally, development of more active agents is needed for the treatment of metastatic tumors.

Establishment and characterization of 5-fluorouracil-resistant gastric cancer cells

Two 5-fluorouracil (5-FU)-resistant cell lines from a Korean gastric cancer cell line were established by incubation of the cells with increasing concentration of 5-FU, and the resultant cell lines showed an over 800-fold increased resistance to 5-FU. To identify the mechanism of 5-FU resistance, the expressions of genes involved in 5-FU metabolism were examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Expressions of orotate phosphoribosyltransferase (OPRT), thymidine phosphorylase (TP), and uridine phosphorylase (UP) were significantly downregulated in these cell lines, resulting in low incorporation of 5-FU into nucleic acids. In contrast, an increased expression of thymidine kinase (TK) was observed in 5-FU-resistant cells. These results strongly indicate that blocking of 5-FU incorporation into nucleic acids and TK overexpression may play a major role in 5-FU resistance in these cells. Interestingly, these cell lines showed cross-resistance to paclitaxel, cisplatin, and doxorubicin, suggesting that other factors such as HSP27 and Mn-SOD could be also involved in the mechanism of multidrug resistance in these cell lines.

Deoxyuridine triphosphatase (dUTPase) expression and sensitivity to the thymidylate synthase (TS) inhibitor ZD9331

Uracil DNA misincorporation and misrepair of DNA have been recognized as important events accompanying thymidylate synthase (TS) inhibition. dUTPase catalyses the hydrolysis of dUTP to dUMP, thereby maintaining low intracellular dUTP. We have addressed the relationship between dUTPase expression and cellular sensitivity to TS inhibition in four human lung tumour cell lines. Sensitivity (5-day MTT assay) to the growth inhibitory effects of the non-polyglutamatable, specific quinazoline TS inhibitor ZD9331, varied up to 20-fold (IC(50)3-70 nM). TS protein expression correlated with TS activity (r(2)= 0.88, P = 0.05). Intracellular concentrations of drug following exposure to ZD9331 (1 microM, 24 h) varied by approximately 2-fold and dTTP pools decreased by > 80% in all cell lines. No clear associations across the cell lines between intracellular drug concentrations, TS activity/expression, or TTP depletion could be made. dUTPase activity varied 17-fold and correlated with dUTPase protein expression (r(2)= 0.94, P = 0.03). There was a striking variation in the amount of dUTP formed following exposure to ZD9331 (between 1.3 and 57 pmole 10(-6)cells) and was in general inversely associated with dUTPase activity. A large expansion in the dUTP pool was associated with increased sensitivity to a 24-h exposure to ZD9331 in A549 cells that have low dUTPase activity/expression. dUTPase expression and activity were elevated (approximately 3-fold) in two variants of a human lymphoblastoid cell line with acquired resistance to TS inhibitors, further suggesting an important role for this enzyme in TS inhibited cells.

Thymidylate synthase quantitation and in vitro chemosensitivity testing predicts responses and survival of patients with isolated nonresectable liver tumors receiving hepatic arterial infusion chemotherapy

BACKGROUND

Patients with isolated, nonresectable liver tumors may receive regional hepatic arterial infusion (HAI) chemotherapy with response rates of about 50%. The objective of this study was to investigate the value of thymidylate synthase (TS) determination in combination with in vitro chemosensitivity testing to predict the responses and survival of patients receiving HAI.

METHODS

TS mRNA expression was quantitated using a reverse transcription-polymerase chain reaction technique with beta-actin as the internal standard. In vitro chemosensitivity testing was performed with tumor cell suspensions using the human tumor colony-forming assay (HTCA).

RESULTS

An analysis of the test combination in 24 consecutive patients revealed that 77% (10 of 13) of the sensitive and 9% (1 of 11) of the resistant patients had complete or partial clinical responses. Sensitive patients were 8.5-fold more likely to respond (P = 0.0036) and displayed with 32 months (range, 5-75 months) a longer median survival than resistant patients with 17 months (range, 3-28 months, P = 0.003). Analysis of the Kaplan-Meier curves revealed that sensitive patients had a higher overall survival probability, as determined by the log rank test (P = 0.044).

CONCLUSIONS

These results suggest that the clinical outcomes of patients receiving HAI therapy may be predictable with TS quantitation and HTCA. It is possible, therefore, that this combination may be used in the future to select patients with liver tumors who will benefit from HAI before the start of regional chemotherapy.

Thymidylate synthase expression in patients with colorectal carcinoma using a polyclonal thymidylate synthase antibody in comparison to the TS 106 monoclonal antibody

Colorectal cancer is one of the most common human cancers, for which 5-fluorouracil (5FU) is usually part of the treatment. Thymidylate synthase (TS), the target enzyme for 5FU, can be predictive for the outcome of 5FU-based therapy. TS levels in tumor samples can be determined with radiochemical enzyme assays, RT-PCR, and immunohistochemical staining. We validated TS immunohistochemistry with a polyclonal rabbit anti-human TS antibody using the avidin-biotin method. This antibody can be used on paraffin-embedded, formalin-fixed material using an antigen retrieval method with citrate buffer and microwave treatment. The antibody shows a granular cytosolic staining pattern. The reproducibility in cross-sections from colorectal tumors from 50 patients was 90% and the interobserver variability was acceptable with a kappa of 0.45. On Western blotting it detects purified TS at 36 kD, while in 5FU-treated cells the ternary complex between FdUMP, TS, and 5, 10-methylene-tetrahydrofolate is clearly visible at 38 kD, with no other interfering bands. In a separate set of tumors, immunostaining was compared with enzyme levels; Western blots correlated with enzyme levels. Because both this polyclonal antibody and the monoclonal antibody TS-106 are being used for large-scale studies, we also determined whether they could be used interchangeably. No differences were observed. This polyclonal antibody is specific and gives reproducible results. A study on a larger scale is ongoing to determine the role of TS as a predictive parameter in patients with colorectal cancer treated either with postoperative adjuvant 5FU/levamisole or with surgery only.

A dose-finding study of raltitrexed (tomudex) with cisplatin and epirubicin in advanced gastro-oesophageal adenocarcinoma

The standard treatment for advanced gastro-oesophageal cancer in the UK is epirubicin, cisplatin and continuous infusion 5-fluoruracil by an indwelling central venous catheter (ECF), which has significant morbidity. Raltitrexed (tomudex), a specific inhibitor of thymidylate synthase with a long plasma terminal half-life (50-100 h) has activity in gastro-intestinal tract malignancy. To reduce the Hickman line-associated morbidity of ECF; we have conducted a dose-finding study of tomudex combined with epirubicin and cisplatin. Twenty-four patients (22 males, two female), median age 63 years (range 21-75), ECOG performance status < or =2 with histologically proven, unresectable or metastatic gastric (14 patients), gastro-oesophageal junction (nine patients) or oesophageal (one patient) adenocarcinoma received treatment with 3-weekly cisplatin 60 mg m(-2), epirubicin 50 mg m(-2) and tomudex at doses of 2 mg m(-2), 2.5 mg m(-2) or 3 mg m(-2) in successive cohorts. Six patients were treated per dose level with no intra-patient dose escalation. Dose escalation occurred after six patients had completed at least one cycle of chemotherapy at the previous dose level. After defining the maximum tolerated dose a further six patients were treated at the preceding dose level to assess toxicity at the proposed phase II dose. A total of 102 cycles (50% completed 6 cycles) were administered. The dose-limiting toxicities are neutropenia and diarrhoea occurring in 2/6 patients at the 3 mg m(-2) dose level. Of those patients evaluable for response, there were eight partial and one complete response (overall response rate 38%). The median survival was 9.9 months. ECT is an active regimen in oesophagogastric adenocarcinoma. The recommended dose of tomudex for further study in combination with epirubicin and cisplatin is 2.5 mg m(-2).

Colorectal cancer staging and adjuvant chemotherapy

Colorectal cancer is a significant cause of morbidity and mortality in Western populations. The standard of care for staging patients with colorectal cancer to determine prognosis and identify patients who will receive adjuvant therapy continues to be histopathology of regional lymph nodes. However, the significant variability in survival within each staging category likely reflects the heterogeneity of detecting micrometastatic disease employing this technique. Novel molecular markers of micrometastases currently in development will permit more accurate staging of patients with colorectal cancer. These advances in staging will distinguish patients who will maximally benefit from adjuvant therapy from those who have an especially good prognosis in whom chemotherapy can be avoided. In addition, new adjuvant chemotherapeutic agents, novel combinations of those agents and creative dosing schedules currently being investigated will offer considerable advantages with respect to ease of administration, safety and tolerability, quality of life and efficacy. Ultimately, it is anticipated that advances in molecular diagnostics will define unique biochemical characteristics of patients' tumours, permitting individualization of chemotherapeutic regimens employing novel agents that specifically exploit those characteristics.

19F-MRS studies of fluorinated drugs in humans

The use of 19F-NMR as a noninvasive probe to measure directly the pharmacokinetics of drugs at their target (effector) site(s) is illustrated in this article by human studies with 5-fluorouracil (5-FU). This drug, and several of its metabolites, have been measured in vivo in animals and in patients using standard clinical MRI systems. Using a pharmacokinetic imaging approach the parameter that can be measured most readily is the tumoral t(1/2) of 5-FU. Patients whose tumoral t(1/2) of 5-FU is equal to/greater than 20 min are designated as "trappers", and those whose tumoral t(1/2) of 5-FU is less are nontrappers. Trapping of 5-FU in tumors is a necessary, albeit not a sufficient condition, for response. Problems associated with the technical aspects of these measurements have been discussed, as well as how modulators and other agents will affect the tumoral t(1/2) of 5-FU. The rationale for the biological processes underlying the fate of 5-FU in humans has been illustrated with the use of a 12 compartment model, where several of the steps have been discussed and the consequences of their inhibition/stimulation related to the noninvasive studies that can be performed with modulators of the action of 5-FU. These 19F-NMR studies have now been extended to other fluoropyrimidines, some of which are prodrugs of 5-FU, and others where the fluorine atoms are on the ribose ring. These studies also reveal information that has both scientific and clinical significance. The studies presented here illustrate some of the potential and some of the usefulness of 19F-MRS in patient management and in drug development. It is a technique that has proven itself.

Expression of thymidylate synthase in human non-small cell lung cancer

5-Fluorouracil (5-FU) has been used worldwide, and the correlation between its effects and thymidylate synthase (TS) expression has been reported in gastrointestinal malignancy. But the significance of TS expression for 5-FU-based chemotherapy has rarely been reported in non-small cell lung cancer (NSCLC). We investigated surgically resected specimens of 23 consecutive patients with previously untreated NSCLC. We used immunohistochemistry and western blot analysis with anti-TS polyclonal antibody to evaluate the existence of TS, and fluorodeoxyuridine-5'-monophosphate (FdUMP) binding assay to evaluate the enzymic activity of TS. We found that 14 samples (60.9%) were positive immunohistochemically, and that the results of immunohistochemistry closely reflected the enzymic activity measured by FdUMP binding assay (ranging from 1.8 to 56.9 pmol/g protein). These results seem to support our experience that 5-FU and its derivatives are clinically significantly effective as a postoperative adjuvant chemotherapy against NSCLC.

The expression of thymidine phosphorylase correlates with angiogenesis and the efficacy of chemotherapy using fluorouracil derivatives in advanced gastric carcinoma

The expression of thymidine phosphorylase (TP) and the density of microvessel in advanced gastric carcinoma were examined by immunohistochemistry to evaluate the significance of TP. The expression of TP was negative in 72 cases, positive in 54. The microvessel density correlated with the expression of TP. In total cases, patients with TP-positive tumours survived longer than those with TP-negative tumours. In patients treated with fluorouracil derivatives (FUs), the expression of TP significantly correlated with favourable prognosis and with unfavourable prognosis in those not treated with FUs. The patients with TP-positive tumours, the prognosis of patients treated with FUs was significantly better than that of those not treated with FUs. In patients with TP-positive tumours, treatment with FUs and lymph node metastasis were independent prognostic factors according to the Cox proportional hazards model. Depth of invasion and lymph node metastasis were independent prognostic factors in patients with TP-negative tumours. The determination of the expression of TP might be useful for predicting the efficacy of post-operative chemotherapy using FUs to prevent recurrence in advanced gastric carcinoma patients who undergo curative gastrectomy.

Response to neoadjuvant chemotherapy best predicts survival after curative resection of gastric cancer

OBJECTIVE

In Western populations, long-term survival rates after curative resection of gastric cancer remain extremely poor. The lack of effective adjuvant therapy has prompted the evaluation of neoadjuvant approaches. Since 1988, we have conducted three separate phase II trials using neoadjuvant chemotherapy to treat patients with potentially resectable gastric cancer. The present study was conducted to evaluate whether response to neoadjuvant chemotherapy is predictive of survival in patients with resectable gastric cancer.

METHODS

Eighty-three patients with pathologically confirmed gastric adenocarcinoma were treated with neoadjuvant chemotherapy before planned surgical resection. Response was assessed by upper gastrointestinal series, endoscopy, computed tomography scan, and pathologic examination.

RESULTS

For the three phase II trials, clinical response rates ranged from 24% to 38%. Three patients (4%) had a complete pathologic response. Sixty-one patients (73%) underwent a curative resection. Median follow-up was 26 months. Univariate analysis revealed T stage, number of positive nodes, and response to chemotherapy to be significant predictors of overall survival. However, on multivariate analysis, response to chemotherapy was found to be the only independent prognostic factor.

CONCLUSIONS

Response to neoadjuvant chemotherapy is the single most important predictor of overall survival after neoadjuvant chemotherapy for gastric cancer. These findings support further evaluation of neoadjuvant approaches in the treatment of this disease.

Circumvention of 5-fluorouracil resistance in human stomach cancer cells by uracil phosphoribosyltransferase gene transduction

A human stomach cancer cell line with acquired resistance to 5-fluorouracil (5-FU), NUGC-3/5FU/ L, has been found to possess reduced ability to convert 5-FU into active metabolites. We attempted in vitro gene therapy for this 5-FU-resistant cell line. NUGC-3 and NUGC-3/5FU/L cells were infected with recombinant adenovirus (Ad) containing Escherichia coli uracil phosphoribosyltransferase (UPRT) gene driven by CAG promoter (CA), AdCA-UPRT, and changes in their 5-FU metabolism and sensitivity were investigated. Activities of orotate phosphoribosyltransferase increased from 10.2 and 1.56 (nmol/mg protein/30 min) in the uninfected cells of NUGC-3 and NUGC-3/5FU/L to 216 and 237, respectively, after the transfection of UPRT gene. The 5-FU nucleotide level in the acid-insoluble fraction increased from 7.32 to 15.9 (pmol/mg protein) in NUGC-3 cells on infection with AdCA-UPRT, and in NUGC-3/5FU/L cells it increased from 1.91 to 21.4. The 50% growth-inhibition concentration (IC50) was 12.7 micromol/liter for NUGC-3 and much higher than 100 micromol/liter for NUGC-3/5FU/L, indicating over 8-fold resistance. NUGC-3/ SFU/L transfected with the UPRT gene showed very high sensitivity to 5-FU with an IC50 of 3.2 micromol/liter. The high resistance in this metabolic activation-deficient cell line was thus completely reversed by transduction of an exogenous gene coding for a 5-FU-anabolizing enzyme.

Relationship between protein levels and gene expression of dihydropyrimidine dehydrogenase in human tumor cells during growth in culture and in nude mice

Protein levels and gene expression of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme for degradation of 5-fluorouracil, were studied in two human tumor cell lines (fibrosarcoma HT-1080 and pancreatic carcinoma MIAPaCa-2) in various growth phases of the cultured cells and of tumor xenografts implanted into nude mice. DPD catalytic activity and DPD protein content in cytosolic preparations were determined by means of radioenzymatic assay and western blot analysis, respectively. Relative DPD mRNA expression was determined by using a semi-quantitative reverse transcription-polymerase chain reaction in which glyceraldehyde-3-phosphate dehydrogenase mRNA was used as an internal standard. DPD activity and protein content in cultures of both cell lines increased in proportion to cell density (DPD activities ranged from undetectable to 84 pmol/min/mg protein in the HT-1080 cells and from undetectable to 335 pmol/min/mg protein in the MIAPaCa-2 cells). DPD mRNA levels, on the other hand, tended to decrease slightly during cell growth. DPD activity and protein content in HT-1080 tumor xenografts increased during growth in proportion to tumor weight (DPD activities ranged from 7 to 131 pmol/min/mg protein), but DPD mRNA levels did not correlate with tumor weight. DPD activity and protein content in MIAPaCa-2 tumor xenografts did not change much, and seemed to have already plateaued, since the tumors were small (weighing about 30 mg). These findings suggest that DPD protein expression during tumor growth is controlled at the post-transcriptional level.

Immunohistochemical evaluation of thymidylate synthase in gastric carcinoma using a new polyclonal antibody: the clinical role of thymidylate synthase as a prognostic indicator and its therapeutic usefulness

BACKGROUND

Before this study was conducted, the clinical and therapeutic significance of immunohistochemical evaluation of thymidylate synthase (TS) in patients with gastric carcinoma had not yet been clarified.

METHODS

TS was immunohistochemically evaluated in 134 gastric carcinomas using anti-TS antibody. TS expression, 11 clinicopathologic variables, and survival were studied, and the correlations among them were investigated.

RESULTS

The groups with high and low TS levels consisted of 56 and 78 patients, respectively. Granular cytoplasmic staining patterns of tumor cells were produced by immunohistochemical staining of the gastric carcinoma tissues. The grade of TS staining was significantly correlated with three clinicopathologic variables: depth of invasion, peritoneal metastasis, and stage of the carcinoma (P < 0.05). A univariate analysis revealed that the 5-year survival was significantly better for the low TS group than for the high TS group (P < 0.05): 65.2% for the low TS group and 43.2% for the high TS group. The group with high grade TS staining who received chemotherapy because of the advanced stage of their disease had worse prognoses even if they received adjuvant chemotherapy. A multivariate analysis revealed that four variables (peritoneal metastasis, lymphatic invasion, liver metastasis, and TS staining grade) independently contributed to survival (P < 0.05). The hazard ratio for the group with low grade TS staining was 0.464 compared with the group with high grade staining.

CONCLUSIONS

The immunohistochemical evaluation of TS using this anti-TS antibody may be clinically and therapeutically useful in determining the prognosis of gastric carcinoma patients.

New antimetabolites in cancer chemotherapy and their clinical impact

It is almost 50 years since antimetabolites were first found to have clinical antitumour activity, with Farber's discovery that aminopterin could cause remission in acute leukaemia. In the following 10 years, methotrexate, 6-mercaptopurine and 5-fluorouracil (5-FU) found their way into clinical practice. Subsequently, cytosine arabinoside was found to have activity in acute leukaemia, but, until recently, other significant developments have involved optimizing the efficacy of existing antimetabolites, including the use of leucovorin with methotrexate or 5-FU. Recently, new antimetabolites have become a fertile area for anti-cancer drug research. Gemcitabine (GEMZAR) has emerged as an important new agent in several tumour types, including pancreatic, non-small-cell lung, bladder, breast and ovarian cancers. Capecitabine is an intriguing new prodrug, offering tumour selectivity and prolonged tumour exposure to 5-FU. More potent thymidylate synthase inhibitors have also emerged; raltitrexed is now commercially available for the treatment of colorectal cancer. Others under development include LY231514, which has other sites of action, hence the acronym MTA (multi-targeted antifolate). A novel target is glycinamide ribonucleotide formyltransferase (GARFT) and LY309887 and AG2034 are undergoing clinical investigation as GARFT inhibitors. A critical element with LY309887 appears to be co-administration of folate. It seems entirely possible that several novel antimetabolites will establish themselves in clinical practice in future for the treatment of solid tumours.

High expression of thymidylate synthase is associated with the drug resistance of gastric carcinoma to high dose 5-fluorouracil-based systemic chemotherapy

BACKGROUND

In the past 4 years, the weekly 24-hour infusion of high dose 5-fluorouracil (5-FU) and leucovorin in the treatment of patients with advanced gastric carcinoma has been prospectively studied at the authors' institution. This has enabled them to explore the possibility that the level of expression of thymidylate synthase (TS), the target enzyme of 5-FU, is related to the drug sensitivity of gastric carcinoma to 5-FU-based chemotherapy.

METHODS

To be eligible for this study, patients were required to have received high dose 5-FU and leucovorin chemotherapy (weekly 24-hour infusions of 5-FU, 2,600 mg/m2, and leucovorin, 300 mg/m2) and to have had adequate prechemotherapy gastric carcinoma tissues for immunohistochemical study. TS106 monoclonal antibody was used to detect the expression of TS. A visual scoring system, which ranged from 0 to 3+, was adopted by 2 independent pathologists to semiquantitate the intensity of TS expression.

RESULTS

Between 1993 and 1996, a total of 30 patients, 18 men and 12 women, with a median age of 61.5 years, were enrolled. Of these patients, 16 (53.3%) and 14 (46.7%) had high and low expression of TS, respectively. Two of the 16 patients (12.5%) with high expression of TS and 13 of the 14 patients (92.9%) with low expression of TS responded to chemotherapy (P < 0.001, chi-square test). The median overall survival was 10 months for patients with low TS expression and 4 months for patients with high TS expression (P < 0.01, log rank test).

CONCLUSIONS

The data from this study suggest that the expression of TS, as determined by immunohistochemistry, is a relatively reliable indicator of whether 5-FU should be used in the treatment of patients with gastric carcinoma.

Thymidylate synthase inhibition: a structure-based rationale for drug design

Thymidylate synthase (TS) is a very interesting target in antiproliferative diseases. Its inhibition causes thimineless death of the cells and compounds inhibiting TS are widely used in anticancer therapy. The classical antifolate TS inhibitors are structural analogs of the folate cofactor; they often share the same metabolic pathways and this causes the development of resistance inside the cells. A detailed analysis of the available x-ray crystal structures of the complexes of the enzyme with different substrates and inhibitors support the finding of a structural basis of their biological activity. TS inhibitors nonstructural analog of folate, non-analog antifolate inhibitors (NAAI), are welcome as a new interesting research topic. Among the most recent and interesting ones, compounds from Agouron related to the indole structure, are independent on the folate metabolism, highly active and specific for human TS. Other compounds, phthalein derivatives, can inhibit TS enzymes from various sources and show an interesting biological activity profile: they inhibit better bacterial and fungal TS than human TS. The x-ray crystal structures of some of these inhibitors with TS show that they bind in a different binding site from that of the classical folate TS inhibitors. This indicates a potential allosteric binding site useful for future drug discovery studies.

A clinically applicable assay for tumoral thymidylate synthase combining reverse transcriptase-PCR and high-performance liquid chromatography

The main clinically relevant cellular target of 5-fluorouracil (5-FU) is the enzyme thymidylate synthase (TS). Both preclinical data and clinical data in digestive tract cancer indicate that an increased amount of TS in tumours can predict for 5-FU resistance. We developed an automated method combining the principle of RT-PCR coupled with HPLC separation and quantification. The RT-PCR HPLC method was applied to TS determination in tumoral biopsies from patients with colorectal cancer. The PCR samples were separated and quantified using a polystyrene divinylbenzene C 18 column. Within 22 min, it was possible to elute 18 peaks representing DNA sizes ranging from 34 to 622 bp. Both separation and quantification of beta 2 microglobulin (beta 2m, internal standard) and TS PCR products were achieved in approximately 10 min per sample. Validation of the RT-PCR HPLC method was established by comparing RT-PCR quantification of TS after electrophoresis and HPLC and by comparing the RT-PCR quantification of TS after HPLC with the classical biochemical method. The proposed HPLC method offers a 10-50 fold sensitivity advantage over electrophoresis. In addition, this RT-PCR HPLC procedure allows not only the quantification of TS expression but also the direct collection of unaltered amplified DNA sequence which could be useful for sequencing analysis, since TS mutations have been described. The present RT-PCR HPLC method for determining TS expression in tumoral biopsies is a valuable analytical approach as it is specific, sensitive and clinically applicable.

Thymidylate synthase is a predictor for response and resistance in hepatic artery infusion chemotherapy

The value of intratumoral thymidylate synthase (TS) quantitation as a predictive parameter for hepatic artery infusion (HAI) chemotherapy in patients with colorectal liver metastases was investigated. Relative TS mRNA levels were determined in 29 tumor samples using a quantitative RT-PCR amplification method. The median level of expression was 3.0 x 10(-3) (no units) and varied considerably among the tumors over a range of 135-fold. Patients with low TS levels were 4.1-fold more likely to respond (P < 0.03) compared to patients with high TS levels. Our results indicate that TS quantitation is a valuable predictive marker for tumor response to HAI therapy.

Relevance of tumoral folylpolyglutamate synthetase and reduced folates for optimal 5-fluorouracil efficacy: experimental data

The purpose of this study was to investigate folate-related predictors of 5-fluorouracil (5-FU) cytotoxicity in the presence or absence of l-folinic acid (l-FA). Intracellular concentrations of the reduced folates (tetrahydrofolate + 5,10-methylenetetrahydrofolate) and folylpolyglutamate synthetase (FPGS) activity were determined in 14 human cancer cell lines expressing a spontaneous sensitivity to 5-FU. On these 14 cell lines grown without l-FA supplementation, a significant positive correlation was demonstrated between basal intracellular folate concentration and FPGS activity. 5-FU sensitivity (IC50 range 0.6-25.4 microM) was not related to the basal intracellular folate concentration, whereas, significantly, it was linked to FPGS activity (range 2.5-11.1 pmol/min/mg protein): the higher the FPGS activity, the greater the 5-FU sensitivity. Under l-FA supplementation (0.01-300 microM), intracellular reduced folates increased continuously without evidence of saturation in all cell lines; the pattern of accumulation was independent of the FPGS activity. l-FA enhanced 5-FU cytotoxicity by a factor of 1.9-6.4 in 12 of the 14 cell lines. In the 12 FA-sensitive cell lines, the l-FA concentrations allowing 90% of maximum 5-FU potentiation [l-FA]90 ranged between 0.7 and 107.9 micro M (median 1.9); in contrast, the intracellular concentrations of reduced folates allowing 90% of maximum 5-FU potentiation were much less variable (range 7.6-38.3, median 24.8 pmol/mg protein). In the presence of [l-FA]90, 5-FU sensitivity remained significantly correlated to the basal FPGS activity. In addition, reduced folates were measured in 96 tumoral samples (50 head and neck, 16 colon, 30 liver metastases from colorectal cancer) taken before treatment. Almost all investigated tumours had folate concentrations below the median concentration required for optimal 5-FU potentiation in vitro: median levels (range, pmol/mg protein) were 3.8 (0-17.7) for head and neck, 5.8 (2.3-12.0) for colon and 12.1 (1.7-118.5) for liver metastases. Above all, these data establish the relevance of FPGS activity for predicting the efficacy of 5-FU modulated by FA or not and point to the potential clinical interest of FPGS determination in human tumours.

Critical factors for optimizing the 5-fluorouracil-folinic acid association in cancer chemotherapy

BACKGROUND

The 5-fluorouracil (FU)-folinic acid (FA) association has demonstrated clinical efficacy in colorectal cancer, both in adjuvant and metastatic situations. However, there is no clear consensus about the optimal FU-FA schedule and dose. In addition, it would be of interest to identify FU-FA-responsive tumors.

DESIGN

Our purpose was to review preclinical and clinical data dealing with prediction of FU-FA sensitivity and optimization of FU-FA schedules.

RESULTS

Preclinical studies have highlighted the importance of thymidylate synthase (TS), the cellular target of the FU-FA mechanism of action, for predicting FU sensitivity. It appears that the more sensitive cell lines express the lowest TS activity. Interestingly, the cell lines sensitive to FA supplementation are those more sensitive to FU. The role of TS in FU-FA responsiveness has been clearly demonstrated in patients with colorectal and gastric cancers. Preliminary in vitro and clinical data have shown that the folylpolyglutamate synthetase (FPGS), the enzyme responsible for folate polyglutamylation, is another promising tool for identifying FU-FA-responsive tumors. So far, results of clinical trials do not form a clear consensus regarding the need to administer high FA doses for improving FU-FA treatment. Experimental studies on human cancer cell lines have demonstrated the wide variability among cell lines, ranging from 0.05 to 200 microns, of 1 FA concentrations required for maximal FU potentiation. In addition, pharmacokinetic studies have reported a significant variability of active folates in plasma after administration of standard-dose FA. Altogether, these observations favour high-dose FA administration to achieve high folate concentrations in plasma and thus to counteract the variability of the 1 FA concentrations required. With respect to the choice of FU-FA schedule, it appears from experimental data that increasing the duration of exposure to FA enhances FU-FA cytotoxicity, probably through an increased formation of reduced folate polyglutamate forms. Considering the S-phase specificity of FU cytotoxicity as well as its rapid elimination from plasma, a schedule of prolonged exposure to both FU and FA should be considered preferable.

CONCLUSIONS

Results of the new FU-FA administration schedules such as the one consisting of a 2-hour FA administration followed by a combination of FU bolus and FU infusion, or the chronomodulated FU-FA infusion, open up promising approaches for improving the therapeutic index of FU-FA chemotherapy. Finally, future clinical studies should investigate tumoral parameters pharmacologically linked to FU-FA sensitivity such as pre-treatment TS and FPGS activities. Such tumoral investigations along with FU and FA pharmacokinetic investigations should provide a better understanding of inter-patient variability in response to FU-FA therapy and an optimal management of this chemotherapy regimen.