Thymidine Phosphorylase Activity Research Articles

Comparison of in vitro metabolic conversion of capecitabine to 5-FU in rats, mice, monkeys and humans - toxicological implications

Capecitabine is an oral anticancer prodrug which is converted to 5-fluorouracil (5-FU) via 3 enzymatic steps, these being 5'-deoxy-5-fluorocytidine (5'-DFCR), 5'-deoxy-5-fluorouridine (5'-DFUR), and finally 5-FU by carboxylesterase (CES), cytidine deaminase (CDA), and thymidine phosphorylase (TP), respectively. Because rats, mice and monkeys are used for preclinical safety studies, we investigated the in vitro conversion from capecitabine to 5-FU by hepatic and intestinal mucosal microsomes and cytosols, to compare their metabolic activity to that of humans. Capecitabine was hydrolyzed to 5'-DFCR in hepatic and intestinal mucosal microsomes in these animal species. In humans and monkeys, CL(int) (V(max)/K(m)) for the hydrolysis of capecitabine in intestine (expressed as µl/min/g tissue) was much lower than that in hepatic microsomes but, in rats and mice, CL(int) was higher in intestine than in liver. In humans and monkeys, similar K(m) values and inhibition patterns by tetrahydrouridine (THU) a CDA inhibitor, were observed in CDA activity of hepatic and intestinal cytosols. However, rats showed very low CDA activity and mice showed non-Michaelis-Menten kinetics and a different inhibition pattern by THU. K(m) values for TP activity were almost similar in rats, mice, monkeys and humans. In conclusion, it was confirmed that monkeys are a suitable animal model for the safety assessment of capecitabine in terms of metabolic enzymes and it was suggested that higher toxic incidences in mouse small intestine were related to high hydrolytic activity of capecitabine in the small intestine.

Abstract P2-09-24: Relationship of Capecitabine Response to Thymidine Phosphorylase Expression and Overall Survival in Advanced Breast Cancer

Abstract Background: Capecitabine is an oral fluoropyrimidine carbamate that is metabolised to FU through three enzymatic steps. Thymidine phosphorylase (TP) is involved in the final step of the conversion from 5'-deoxy-5-fluorouridine (5'-DFUR) to 5-FU. TP is highly expressed in cancer cells compared to normal tissue. By exploiting this difference in TP activity, capecitabine is activated and preferentially converted into 5-FU within tumours. Besides this, TP is identical to platelet-derived endothelial cell growth factor (PD-ECGF), a known angiogenic factor. While TP expression is predictive of benefit from capecitabine in colorectal cancer (CRC), initial studies in advanced breast cancer (ABC) examining the predictive value of TP and related enzymes have produced mixed results. Furthermore, whether response to capecitabine is associated with any overall survival (OS) benefit has not been studied. Materials and Methods: This retrospective study analysed 92 ABC patients who received at least one cycle of capecitabine for locally advanced or metastatic disease with intention to treat. Best responses to capecitabine (assessed clinically or by imaging) whilst patients were on capecitabine were included for analysis. TP expression was analysed by immunohistochemistry in primary excised samples. Composite TP scoring (including cytoplasm and stroma) was used to define TP status. Chi-squared tests were carried out to find associations between TP and clinical factors. Kaplan Meier survival curves were produced for relapse free survival and OS. The logrank statistic was calculated to test independence of the survival curves by category. Results: On multivariate analysis, when the TP composite factor was added to a Cox regression model for OS using age, ER, grade, nodal status and size, it appeared to act as an independent prognostic factor for OS after first primary (hazard ratio: 0.45, p=0.01). Overall, responses included partial response (PR) in 38% and stable disease (SD) for 3 months or longer in 25% patients. There was no statistically significant correlation for capecitabine response and TP status. Also there was no significant difference in time to first relapse or from first relapse to start of capecitabine stratified by response, showing that response was not intrinsically related to better prognosis or slower growing cancers. However, there was a significantly prolonged OS equivalent for both SD and PR to capecitabine (logrank, p=0.02). Discussion: Most studies in ABC have not found high TP expression alone to predict better response to capecitabine. The results of our study, the largest to date, confirm these findings. A combined approach studying plasma levels of 5'-DFUR along with intra-tumoral TP should be investigated further. Interestingly, the finding of high TP as an independent prognostic factor could be due to deprivation of thymidine needed for proliferation, but this also needs further investigation. By analysing the long term course of breast cancer based on ultimate pattern of response, this study suggests a substantial benefit of capecitabine even though second or third line. It also suggests that if patients achieve SD therapy should continue. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-09-24.

56. Mitochondrial abnormalities in a new cell model of MNGIE syndrome

Background: MNGIE syndrome (mitochondrial neurogastrointestinal encephalopathy) is caused by mutations in the thymidine phosphorylase (TP) gene. It is characterized by progressive external ophthalmoparesis, neuropathy, leukoencephalopathy and gastrointestinal dysmotility leading to cachexia and early death. The reduction in TP activity results in reduced mtDNA synthesis, causing impaired mitochondrial function. Development of cell models would be helpful in the assessment of potential therapeutic options.

POG01 Anti-thymidine phosphorylase antibodies in the diagnosis of mitochondrial neurogastrointestinal encephalomyopathy

BackgroundMitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive condition, characterised by peripheral neuropathy, gastrointestinal dysmotility, asymptomatic cerebral white matter lesions and mitochondrial myopathy, and caused by mutations in the gene...

Upregulation of thymidine kinase activity compensates for loss of thymidylate synthase activity in Mycoplasma pneumoniae

Thymidylate, an essential building block of DNA, is synthesized either from deoxyuridylate by thymidylate synthase (TS) or thymidine (dT) by thymidine kinase (TK). Thymidylate kinase (TMPK) phosphorylates dTMP to dTTP. Thymidine phosphorylase (TP) catalyses reversible phosphorolysis of dT. Using transposon mutagenesis M. pneumoniae TS gene (thyA/MPN320) was interrupted and requirement of these enzymes was studied. We found that TK activity and transcript levels and TP activity, but not TMPK or TS activity, are growth-phase-regulated, with induction at the exponential growth phase and a decline after the stationary phase. Inactivation of thyA results in upregulation of TK transcript and a 10-fold increase in TK activity, reduced TMPK level and it had no effect on TP activity. The level of [3H]-dT uptake and incorporation into DNA in the thyA mutant correlates with increases in TK activity, suggesting that dT uptake and metabolism is TK-dependent and that upregulation of TK activity in the thyA mutant compensates for the lack of ThyA activity. [3H]-dU uptake was low compared with dT, and incorporation of radioactivity into DNA in the thyA mutant indicates the presence of an alternative TS. Our results suggest that TK and TMPK are potential targets for the development of Mycoplasma-specific antibiotics.

Mitochondrial neurogastrointestinal encephalomyopathy associated with progressive hearing loss

We report a rare case of mitochondrial neurogastrointestinal encephalomyopathy with hearing loss. A 46-year-old woman presented with a three-year history of progressive, bilateral hearing loss and tinnitus. She had been suffering from unexplained abdominal pain and diarrhoea for 20 years. When first seen, her otoscopic findings were normal, and pure tone audiometry showed mild and moderate hearing loss in her right and left ears, respectively. She also had: bilateral ophthalmoparesis, neck and limb muscle weakness, and hypoactive deep tendon reflexes on neurological examination; diffuse leukoencephalopathy on magnetic resonance imaging of the brain; and markedly reduced leukocyte thymidine phosphorylase activity. On the basis of these findings, the patient was diagnosed with mitochondrial neurogastrointestinal encephalomyopathy. Mitochondrial neurogastrointestinal encephalomyopathy is an autosomal recessive disease caused by mutation of the thymidine phosphorylase gene, and is characterised by ophthalmoparesis, peripheral neuropathy, leukoencephalopathy, gastrointestinal symptoms and abnormal mitochondria in muscle cells. Current advances in genetic research may reveal a higher prevalence of mitochondrial disorders than had previously been thought. Otolaryngologists should be aware of mitochondrial neurogastrointestinal encephalomyopathy and other rare genetic disorders when managing patients with progressive hearing loss.

Increased Migration by Stimulation of Thymidine Phosphorylase in Endothelial Cells of Different Origin

Thymidine phosphorylase (TP) catalyzes the phosphorylytic cleavage of thymidine to thymine and deoxyribose-1-phosphate. The latter may be involved in the angiogenic stimulation of TP. In the present study, we investigated whether thymidine and deoxyribose (dR) could stimulate angiogenesis in vitro of two types of endothelial cells (isolated from umbilical veins (HUVEC) and endothelial colony forming cells (ECFC)), and whether the stereoisomer L-deoxyribose (L-dR) and the thymidine phosphorylase inhibitor (TPI) could reduce this. Both cell types had a low TP activity. Thymidine increased the migration of both HUVECs and ECFCs, but dR only that of the ECFCs. The invasion was not changed by any of the agents tested. In conclusion, TP may play a role in the migration of HUVECs and ECFCs, but not the invasion.

Trifluorothymidine Resistance Is Associated with Decreased Thymidine Kinase and Equilibrative Nucleoside Transporter Expression or Increased Secretory Phospholipase A2

Trifluorothymidine (TFT) is part of the novel oral formulation TAS-102, which is currently evaluated in phase II studies. Drug resistance is an important limitation of cancer therapy. The aim of the present study was to induce resistance to TFT in H630 colon cancer cells using two different schedules and to analyze the resistance mechanism. Cells were exposed either continuously or intermittently to TFT, resulting in H630-cTFT and H630-4TFT, respectively. Cells were analyzed for cross-resistance, cell cycle, protein expression, and activity of thymidine phosphorylase (TP), thymidine kinase (TK), thymidylate synthase (TS), equilibrative nucleoside transporter (hENT), gene expression (microarray), and genomic alterations. Both cell lines were cross-resistant to 2'-deoxy-5-fluorouridine (>170-fold). Exposure to IC(75)-TFT increased the S/G(2)-M phase of H630 cells, whereas in the resistant variants, no change was observed. The two main target enzymes TS and TP remained unchanged in both TFT-resistant variants. In H630-4TFT cells, TK protein expression and activity were decreased, resulting in less activated TFT and was most likely the mechanism of TFT resistance. In H630-cTFT cells, hENT mRNA expression was decreased 2- to 3-fold, resulting in a 5- to 10-fold decreased TFT-nucleotide accumulation. Surprisingly, microarray-mRNA analysis revealed a strong increase of secretory phospholipase-A2 (sPLA2; 47-fold), which was also found by reverse transcription-PCR (RT-PCR; 211-fold). sPLA2 inhibition reversed TFT resistance partially. H630-cTFT had many chromosomal aberrations, but the exact role of sPLA2 in TFT resistance remains unclear. Altogether, resistance induction to TFT can lead to different mechanisms of resistance, including decreased TK protein expression and enzyme activity, decreased hENT expression, as well as (phospho)lipid metabolism. Mol Cancer Ther; 9(4); 1047-57. (c)2010 AACR.

Efficacy and safety of capecitabine in combination with docetaxel and mitomycin C in patients with pre-treated pancreatic, gallbladder, and bile duct carcinoma

Preclinical data indicate the improvement of the antitumor activity of capecitabine by mitomycin C and docetaxel through upregulation of thymidine phosphorylase activity. Therefore, we have established a combination regimen of these drugs (DocMitoCape), which demonstrated preliminary activity especially in bile duct and pancreatic carcinoma. Here we report the safety and efficacy of the DocMitoCape regimen in pre-treated patients with gallbladder, bile duct, or pancreatic carcinoma. Treatment consisted of capecitabine (2,000 mg/m(2) days 1-14) in combination with docetaxel (40 mg/m(2) day 1) and mitomycin C (4 mg/m(2) day 1). Cycles were repeated on day 22. Toxicity was graded according to NCI-CTC criteria, and the antitumor activity was assessed by RECIST criteria. Twenty-eight pre-treated patients with a median age of 59 suffering from pancreatic, gallbladder, intra- (IHCCC) or extrahepatic (EHCCC) bile duct carcinoma were included. Eleven patients had received ≥2 lines of prior chemotherapy. A total of 183 and a median of six cycles were administered (range 1-21). The mean dose intensity was as follows (cycles 1-2/3-4; %): capecitabine 97/92, docetaxel 100/100, mitomycin C 99/100. Main adverse events grades 2/3/4 were (n): leukocytopenia 3/2/2, anemia 13/4/0, thrombocytopenia 3/1/0, nausea/vomiting 2/1/0, diarrhea 5/1/0, hand-foot-skin reaction 7/0/0. Six patients achieved partial and seven patients minor remissions, while six patients had stable disease adding to a tumor control rate of 68%. Median progression-free and overall survival was 4.5 (range 1.0-44.9) and 6.8 months (range 1.5-44.9), respectively, calculated from the start of treatment. In all, the DocMitoCape regimen exhibited a favorable safety profile and a high rate of tumor stabilizations in patients with pre-treated gallbladder, bile duct and pancreatic carcinoma. It might be considered after failure of standard regimens in these types of cancer.

Biochemical abnormalities in a patient with thymidine phosphorylase deficiency with fatal outcome

Deficiency of the cytosolic enzyme thymidine phosphorylase (TP) causes a multisystem disorder called mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome. Clinical symptoms are gastrointestinal dysfunction, muscle involvement and neurological deterioration. TP deficiency is biochemically characterised by accumulation of thymidine and deoxyuridine in body fluids and compromised mitochondrial deoxyribose nucleic acid (mtDNA) integrity (depletion and multiple deletions). In this report we describe a patient with the clinical and biochemical features related to the end stage of the disease. Home parenteral nutrition had started to improve the clinical condition and preparations were initiated for stem cell transplantation (SCT) as a last resort treatment. Unfortunately, the patient died during the induction phase of SCT. This report shows that TP deficiency is a severe clinical condition with a broad spectrum of affected tissues. TP deficiency can be easily determined by the measurement of pyrimidine metabolites in body fluids and TP activity in peripheral blood leucocytes. Early detection and treatment may prevent the progress of the clinical symptoms and, therefore, should be considered for inclusion in newborn screening programmes.

ML17032 trial: capecitabine/cisplatin versus 5-fluorouracil/cisplatin as first-line therapy in advanced gastric cancer

The combination of infusional 5-fluorouracil (5-FU) and cisplatin is commonly used for the treatment of advanced gastric cancer. Capecitabine is an oral fluoropyrimidine designed to mimic a continuous infusion of 5-FU, and its use can prevent the need for cumbersome intravenous catheters and hospitalization of patients. Capecitabine has another pharmacologic advantage over intravenous 5-FU as it is preferentially activated by 5-FU in tumor tissue, which has higher activity of thymidine phosphorylase than normal tissue, resulting in selective accumulation of 5-FU within tumor tissue. The final analysis of a large, international, multicenter Phase III trial (ML17032) comparing capecitabine/cisplatin versus 5-FU/cisplatin as first-line therapy in patients with advanced gastric cancer was recently published in Annals of Oncology. The purpose of this review is to summarize the ML17032 study, and to discuss the impact and implications of the results.

Sustained Complete Metabolic Remission After Allogeneic Hematopoietic Stem Cell Transplantation in Patients with Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE).

Abstract 1181Poster Board I-203MNGIE is an autosomal recessive disorder of nucleotide metabolism due to TYMP gene mutations that cause loss of activity of thymidine phosphorylase (TP). As a result, thymidine (Thd) and deoxyuridine (dUrd) plasma and tissue levels increase and cause nucleotide pool imbalances. This leads to instability of mitochondrial DNA with loss of mitochondrial respiratory chain functions. Clinical consequences manifest as a multisystemic disease with severe gastrointestinal dysmotility, most severe cachexia (BMI 10-17 kg/m2 in our patients), ptosis and/or ophthalmoparesis, peripheral neuropathy and leukencephalopathy. While TP is not expressed in all tissues, cellular and plasma Thd and dUrd levels appear to be in equilibrium among all body compartments. Mononuclear white blood cells and platelets are rich in TP activity and can transiently restore TP activity upon transfusions. Therefore allogeneic HSCT was tested as a permanent replacement therapy by several teams. A coorperative group under the auspices of the WBMT collected the global experiences. So far, 10 patients underwent an attempt for HSCT between 2005-2009. One patient stopped conditioning due to toxicity and did not proceed to transplantation. Nine patients had 12 allogeneic HSCT. They were 6 males and 3 females with a median age of 28y (range 10-41y) at transplantation. All were symptomatic at time of HSCT (5 on parenteral nutrition). A variety of different conditioning regimens and GvHD prevention strategies were used. Fludarabine was included in all conditioning regimens, combined with busulfan or cyclosphoshamide, melphalan, thiotepa or TBI. T cell depletion (TCD) with ATG, alemtuzumab or in vitro TCD was performed in 10 HSCT. GvHD prevention with sirolimus or calcineurin inhibitors was used in combination with mycophenolate mofetil or methotrexate. Graft source for first transplants was peripheral blood stem cells (PBSC) in 4, bone marrow (BM) in 3 and cord blood in 2. PBSC and BM donors were HLA-identical siblings in 2, phenotypic identical parent in 1 and unrelated donors in 4 (3 with 10/10 HLA-match, 1 with 9/10-match). Engraftment was problematic. Three primary graft failures and two late graft failures were observed. A second HSCT was performed in three patients, all engrafted but two died due to TRM. The two patients without a second HSCT died from their disease. Four patients developed acute GvHD grade I-IV.To date, five patients are alive 8-48 months posttransplant, three after related PBSC-HSCT, one after unrelated BM-HSCT (10/10-HLA identical), one after two HSCTs with BM and PBSC respectively from the same unrelated 10/10-HLA identical donor. In all of these patients metabolism normalized as measured by normal Thd and dUrd levels. All surviving patients are off parenteral nutrition without further weight loss or increase in body weight. Gastrointestinal symptoms improved and in the two patients with the longest follow up a slight improvement of neurological symptoms can be observed now. Further time is needed to determine whether other disturbed organ functions will be reversible. Conclusion:Allogeneic HSCT can restore full metabolic function and halt and restore clinical signs and symptoms in this otherwise unrelenting progressive disease. Engraftment was identified as a key obstacle. Still, the optimal transplant regimen needs to be defined to improve patients' outcome. A common consensus transplant protocol and disease specific pre- and posttransplant evaluation protocol was developed with participation of all involved teams. Disclosures:Gratwohl:Amgen: Research Funding; Roche: Research Funding; Novartis: Research Funding; BMS: Research Funding; Pfizer: Research Funding. Hirano:Athena Diagnostics: Speakers Bureau; Pfizer: Research Funding.

Late-onset MNGIE without peripheral neuropathy due to incomplete loss of thymidine phosphorylase activity

Mitochondrial NeuroGastroIntestinal Encephalomyopathy (MNGIE) is an autosomal recessive disorder characterized by severe gastrointestinal dysmotility, cachexia, peripheral neuropathy, ptosis, ophthalmoplegia, and leukoencephalopathy with early onset and severe prognosis. Mutations in the TYMP/ ECGF1 gene cause a loss of thymidine phosphorylase catalytic activity, disrupting the homeostasis of intramitochondrial nucleotide pool. We report a woman with a very late onset of MNGIE, lacking peripheral neuropathy. Thymidine phosphorylase activity was markedly reduced in cultured fibroblasts, but only mildly reduced in buffy coat, where the defect is usually detected, and plasma thymidine was mildly increased compared to typical MNGIE patients. TYMP/ ECGF1 analysis detected two heterozygous mutations, including a novel missense mutation. These findings indicate that a partial loss of thymidine phosphorylase activity may induce a late-onset and incomplete MNGIE phenotype.

Antiangiogenic and Antitumor Activity of 6-(2-Aminoethyl)Amino-5-Chlorouracil, a Novel Small-Molecule Inhibitor of Thymidine Phosphorylase, in Combination with the Vascular Endothelial Growth Factor-Trap

Tumors produce multiple proangiogenic factors, making it unlikely that agents targeting a single angiogenic pathway will be sufficient to treat the spectrum of tumors that occur clinically. Platelet-derived endothelial cell growth factor has angiogenic activity in vitro and in vivo and is overexpressed in most human cancers, where its expression has been correlated with increased microvessel density, more aggressive tumors, and poorer patient prognosis. Platelet-derived endothelial cell growth factor is identical to the enzyme thymidine phosphorylase (TP), and unlike other angiogenic factors, the proangiogenic actions of TP are dependent on its enzyme activity. A potent and specific small-molecule inhibitor of the catalytic activity of TP, 6-(2-aminoethyl)amino-5-chlorouracil (AEAC), was tested for antiangiogenic and antitumor activity in human cancer xenografts in vivo. Oral administration of AEAC caused 40% to 50% reductions in the growth of A549 non-small cell lung cancer and PANC-1 pancreatic cancer xenografts, but it was not active against a second pancreatic tumor, BxPC-3. AEAC reduced the microvessel density in the tumors, providing evidence for an antiangiogenic action. Equal or better activity was seen when the mice were treated with the vascular endothelial growth factor (VEGF)-Trap, a soluble VEGF decoy receptor, and the combination of AEAC and VEGF-Trap produced additive antitumor activity that was significantly greater than the VEGF-Trap alone. In the A549 tumors, the combination produced tumor regressions. These studies show antitumor activity for a drug targeting TP and suggest that inhibitors of TP could be used to augment the clinical efficacy of drugs targeting the VEGF pathway.

Functional analysis of pyrimidine biosynthesis enzymes using the anticancer drug 5‐fluorouracil inCaenorhabditis elegans

Pyrimidine biosynthesis enzymes function in many cellular processes and are closely associated with pyrimidine antagonists used in cancer chemotherapy. These enzymes are well characterized from bacteria to mammals, but not in a simple metazoan. To study the pyrimidine biosynthesis pathway in Caenorhabditis elegans, we screened for mutants exhibiting resistance to the anticancer drug 5-fluorouracil (5-FU). In several strains, mutations were identified in ZK783.2, the worm homolog of human uridine phosphorylase (UP). UP is a member of the pyrimidine biosynthesis family of enzymes and is a key regulator of uridine homeostasis. C. elegans UP homologous protein (UPP-1) exhibited both uridine and thymidine phosphorylase activity in vitro. Knockdown of other pyrimidine biosynthesis enzyme homologs, such as uridine monophosphate kinase and uridine monophosphate synthetase, also resulted in 5-FU resistance. Uridine monophosphate kinase and uridine monophosphate synthetase proteins are redundant, and show different, tissue-specific expression patterns in C. elegans. Whereas pyrimidine biosynthesis pathways are highly conserved between worms and humans, no human thymidine phosphorylase homolog has been identified in C. elegans. UPP-1 functions as a key regulator of the pyrimidine salvage pathway in C. elegans, as mutation of upp-1 results in strong 5-FU resistance.

G.P.3.02 Late-onset MNGIE without peripheral neuropathy due to incomplete loss of thymidine phosphorylase activity

G.P.3.02 Late-onset MNGIE without peripheral neuropathy due to incomplete loss of thymidine phosphorylase activity

A novel TYMP mutation in a French Canadian patient with mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disorder characterized by gastrointestinal, extraocular muscle, peripheral nerve, and cerebral white matter involvement. Mutations in the nuclear gene TYMP encoding for thymidine phosphorylase (TP) cause loss of TP activity, systemic accumulation of its substrates in plasma and tissues, as well as alterations in mitochondrial DNA including deletions, depletion, and somatic point mutations. To date, more than 30 mutations have been reported in diverse ethnic populations. We present herein the clinical, neuroimaging, neuromuscular, and molecular findings of the first French Canadian patient with MNGIE caused by a novel homozygous invariant splicing site (IVS5 +1 G>A) mutation of the TYMP gene.

Chemotherapy-induced thymidine phosphorylase modulation in colorectal cancer

e15050 Background: Thymidine phosphorylase (TP) is an inducible enzyme responsible for nucleoside metabolism, antiapoptosis activity, and promotion of angiogenesis. In addition, conversion of the prodrug capecitabine (C) to its active form depends on TP activity. Preliminary evidence suggests that TP immunohistochemical expression may predict benefit from first-line treatment of metastatic colorectal cancer (CRC) with C plus irinotecan. Several chemotherapeutic agents have been shown to modulate TP expression. The aim of the present analysis was to verify if TP expression differs among primary and paired metastases in CRC patients, or may vary depending on patients’ exposure to chemotherapy. Methods: TP expression was evaluated by immunohistochemistry (clone p-P-GF.44C, Abcam, Cambridge, UK) in a series of 120 primary CRC and their matched distant metastases. Tsuda's scoring system was adopted, defining TP expression as negative (score 0–1) or positive (score 2–3). Results: Data on the first 57 patients are here presented. Sites of biopsied metastases were liver (n=41), lung (n=10), and peritoneum (n=6). Metastases were asynchronous in 42% of patients. Higher TP expression was observed in primary cancers than in metastases (36.8% vs. 15.8%, p=0.007). Among patients who received at least one cycle of chemotherapy before metastasis sampling (38.6%), a TP expression decrease was demonstrated in only 13% of metastatic samples. Oppositely, a significantly higher proportion of untreated patients lost TP expression in metastasis sites (36%, p=0.01). Conclusions: In advanced CRC patients, TP expression tend to decrease in metastases, particularly in those patients who did not receive chemotherapy before metastatic sampling. Although intratumoral heterogeneity and other causes of discrepancy cannot be excluded, true chemotherapy-induced modulation of TP may be hypothesized. No significant financial relationships to disclose.

Biomodulation of capecitabine by weekly paclitaxel and carboplatin in patients with advanced solid tumor malignancies: A dose-escalating phase I study

2569 Background: A principal determinant of the therapeutic index with capecitabine-based treatment is the grade of thymidine phosphorylase (TP) activity in malignant tissue. The beneficial interactions of paclitaxel and carboplatin in upregulation of TP promise to make capecitabine more tumor specific and to provide the expected synergy. On the basis of the time-dependency and transiency for this upregulation we performed a phase I study of capecitabine in combination with weekly paclitaxel and carboplatin (CTX). Methods: Patients with advanced solid tumors received carboplatin on day 1, paclitaxel on days 1, 8, 15 and capecitabine orally twice a day on days 8–21, every 4 weeks. There were 5 planned dose levels (DL 1–5). Paclitaxel was escalated from 60 mg/m2 to 80 mg/m2 (DL 4) then 100 mg/m2 (DL 5). Capecitabine from 500 mg/m2 bid to 750 mg/2 bid (DL 2) then 1000 mg/m2 bid (DL 3–5). Carboplatin dose was fixed at AUC 6. Paraffin-embedded tissue was evaluated for expression of TP, thymidylate synthase and dihydropyrimidine dehydrogenase by immunohistochemistry. Results: 32 patients from Ohio State University (OSU) were enrolled. 84% had prior therapy. The most common grade 3/4 toxicities were neutropenia (59%), leukopenia (56%), and fatigue (16%). DLTs included neutropenic fever (1), prolonged neutropenia or thrombocytopenia (2) and diarrhea (1). The MTD was at DL 2. There were 10 confirmed responses [4 CR (esophagus, stomach, unknown primary and ampullary); 6 PRs (Pancreas (3), unknown primary, anal and esophagus] and stabilization of disease > 3 months in 12 patients. In normal tissue, there was no difference in expression levels of both TS and TP. On the other hand, in cancer tissue, TP levels seem to correlate with response whereas TS did not. Conclusions: CTX demonstrates acceptable tolerability. The recommended doses for phase II studies are capecitabine 750 mg/m2 bid, paclitaxel 60 mg/m2/week and carboplatin AUC=6. The acceptable toxicity profile in this dose schedule, and the promising antitumor activity observed warrant further evaluation of this regimen. Two phase II trials are already underway at OSU using this regimen for patients with pancreatic cancer and adenocarcinomas of unknown primary, the latter already actively enrolling patients. Pretreatment tumoral TP levels may help predict patients that are more likely to respond to CTX. Correlation of IHC data with responses will be presented at the meeting. [Table: see text]

The dual role of thymidine phosphorylase in cancer development and chemotherapy

Thymidine phosphorylase (TP), also known as “platelet‐derived endothelial cell growth factor” (PD‐ECGF), is an enzyme, which is upregulated in a wide variety of solid tumors including breast and colorectal cancers. TP promotes tumor growth and metastasis by preventing apoptosis and inducing angiogenesis. Elevated levels of TP are associated with tumor aggressiveness and poor prognosis. Therefore, TP inhibitors are synthesized in an attempt to prevent tumor angiogenesis and metastasis. TP is also indispensable for the activation of the extensively used 5‐fluorouracil prodrug capecitabine, which is clinically used for the treatment of colon and breast cancer. Clinical trials that combine capecitabine with TP‐inducing therapies (such as taxanes or radiotherapy) suggest that increasing TP expression is an adequate strategy to enhance the antitumoral efficacy of capecitabine. Thus, TP plays a dual role in cancer development and therapy: on the one hand, TP inhibitors can abrogate the tumorigenic and metastatic properties of TP; on the other, TP activity is necessary for the activation of several chemotherapeutic drugs. This duality illustrates the complexity of the role of TP in tumor progression and in the clinical response to fluoropyrimidine‐based chemotherapy. © 2009 Wiley Periodicals, Inc. Med Res Rev, 29, No. 6, 903–953, 2009