Enzymes of the de novo and salvage pathways for pyrimidine biosynthesis in normal colon, colon carcinoma, and xenografts

Non-metabolic role of UCK2 links EGFR-AKT pathway activation to metastasis enhancement in hepatocellular carcinoma

Up-regulation of Uridine-cytidine kinase 2 (UCK2), a rate-limiting enzyme of the pyrimidine salvage pathway, has been suggested in HCC, but the detailed molecular mechanisms and therapic role of UCK2 remain elusive. Bioinformatic analyses revealed that UCK2 might be a key up-regulated metabolic gene in HCCs. The expressional pattern and prognostic value of UCK2 were further examined in a large number of clinical samples. Functional assays based on site-directed mutagenesis showed that UCK2 promoted cell proliferation in a metabolic manner, but non-catalytically facilitates HCC metastasis. Mechanistically, in response to EGF, UCK2 interacted with EGFR to block EGF-induced EGFR ubiquitination and degradation, which resulted in elevated EGFR-AKT pathway activation and metastasis enhancement in HCCs. Concurrent pharmacological targeting on UCK2 and EGFR showed synergistic effects on HCC treatment. This study disclosed the non-metabolic role of UCK2 and suggested the therapeutic potential of concurrent blocking the metabolic and non-metabolic roles of UCK2 in HCC treatment.

Bcl-2 family proteins, beyond the veil

Apoptosis is an important part of both health and disease and is often regulated by the BCL-2 family of proteins. These proteins are either pro- or anti-apoptotic, existing in a delicate balance during homeostasis. They are best known for their role in regulating the activation of caspases and the execution of a cell in response to a variety of stimuli. However, it is often forgotten that these BCL-2 family proteins also have important roles to play in cell maintenance that are not associated with apoptosis. These include roles in regulating processes such as cell cycle progression, mitochondrial function, autophagy, intracellular calcium concentration, glucose and lipid metabolism, and the unfolded protein response. In addition to these established alternate functions, further discoveries are being made that have potential therapeutic benefits in diseases such as cancer. BOK, a BCL-2 family protein thought comparable to multidomain pro-apoptotic proteins BAX and BAK, has recently been identified as a key player in metabolism of and resistance to the commonly used chemotherapeutic 5-FU. As a result of such findings, which could see the potential use of BOK as a biomarker for 5-FU sensitivity or mimetic molecules as a resensitization strategy, new targets and mechanisms of pathology may arise from further investigation into the realm of alternate functions of BCL-2 family proteins.

Impact of the Uridine⁻Cytidine Kinase Like-1 Protein and IL28B rs12979860 and rs8099917 SNPs on the Development of Hepatocellular Carcinoma in Cirrhotic Chronic Hepatitis C Patients-A Pilot Study

Background and objectives: The hepatitis C virus (HCV) is the major causative agent of hepatocellular carcinoma (HCC) in the western world. The efficacy of surveillance programs for early detection of HCC is not satisfactory: many tumors are diagnosed at the late, incurable stages. Therefore, there is a need in reliable prognostic markers for the proper follow-up of HCV-positive patients. The aim of the present study was to assess the prognostic value of the uridine⁻cytidine kinase-like protein 1 (UCKL-1), a putative oncoprotein, together with genetically determined polymorphisms in the interleukin 28B (IL28B) gene (rs12979860, rs8099917) in the development of HCC in HCV-positive cirrhotic patients. Materials and Methods: We included 32 HCV cirrhotic patients, 21 (65.6%) of whom had HCC. The expression of UCKL-1 was assessed in liver tissue sections, using immunohistochemistry. For IL28B rs12979860 and rs8099917 genotype analysis, the corresponding genomic regions were amplified by polymerase chain reaction (PCR) with appropriate primers. Results: We have found that UCKL-1 expression was significantly increased in HCC (p = 0.003). The presence of rs8099917 TT single-nucleotide polymorphism (SNP) elevated the chances of HCC manifestation more than sevenfold (OR = 7.3, p = 0.0273). The presence of rs12979860 CC SNP also heightened HCC chances more than sevenfold (OR = 7.5, p = 0.0765). Moreover, in the HCC group, a combination of IL28B rs12979860 non-TT and rs8099917 TT genotypes was observed more often, compared with the non-HCC group. Other combinations of IL28B rs12979860 and rs8099917 SNIPs were associated with a reduced risk of HCC development, approximately at the same extent. Conclusions: The presence of IL28B rs8099917 TT and rs12979860 CC SNPs, but not the intensity of UCKL-1 expression, is strongly associated with increased chances of HCC development in HCV-positive cirrhotic patients.

Selective Cytotoxicity of Dihydroorotate Dehydrogenase Inhibitors to Human Cancer Cells Under Hypoxia and Nutrient-Deprived Conditions

Human dihydroorotate dehydrogenase (HsDHODH) is a key enzyme of pyrimidine de novo biosynthesis pathway. It is located on the mitochondrial inner membrane and contributes to the respiratory chain by shuttling electrons to the ubiquinone pool. We have discovered ascofuranone (1), a natural compound produced by Acremonium sclerotigenum, and its derivatives are a potent class of HsDHODH inhibitors. We conducted a structure–activity relationship study and have identified functional groups of 1 that are essential for the inhibition of HsDHODH enzymatic activity. Furthermore, the binding mode of 1 and its derivatives to HsDHODH was demonstrated by co-crystallographic analysis and we show that these inhibitors bind at the ubiquinone binding site. In addition, the cytotoxicities of 1 and its potent derivatives 7, 8, and 9 were studied using human cultured cancer cells. Interestingly, they showed selective and strong cytotoxicity to cancer cells cultured under microenvironment (hypoxia and nutrient-deprived) conditions. The selectivity ratio of 8 under this microenvironment show the most potent inhibition which was over 1000-fold higher compared to that under normal culture condition. Our studies suggest that under microenvironment conditions, cancer cells heavily depend on the pyrimidine de novo biosynthesis pathway. We also provide the first evidence that 1 and its derivatives are potential lead candidates for drug development which target the HsDHODH of cancer cells living under a tumor microenvironment.

Introduction of a fluorine atom at C3 of 3-deazauridine shifts its antimetabolic activity from inhibition of CTP synthetase to inhibition of orotidylate decarboxylase, an early event in the de novo pyrimidine nucleotide biosynthesis pathway

The antimetabolite prodrug 3-deazauridine (3DUrd) inhibits CTP synthetase upon intracellular conversion to its triphosphate, which selectively depletes the intracellular CTP pools. Introduction of a fluorine atom at C3 of 3DUrd shifts its antimetabolic action to inhibition of the orotidylate decarboxylase (ODC) activity of the UMP synthase enzyme complex that catalyzes an early event in pyrimidine nucleotide biosynthesis. This results in concomitant depletion of the intracellular UTP and CTP pools. The new prodrug (designated 3F-3DUrd) exerts its inhibitory activity because its monophosphate is not further converted intracellularly to its triphosphate derivative to a detectable extent. Combinations with hypoxanthine and adenine markedly potentiate the cytostatic activity of 3F-3DUrd. This is likely because of depletion of 5-phosphoribosyl-1-pyrophosphate (consumed in the hypoxanthine phosphoribosyl transferase/adenine phosphoribosyl transferase reaction) and subsequent slowing of the 5-phosphoribosyl-1-pyrophosphate-dependent orotate phosphoribosyl transferase reaction, which depletes orotidylate, the substrate for ODC. Further efficient anabolism by nucleotide kinases is compromised apparently because of the decrease in pK(a) brought about by the fluorine atom, which affects the ionization state of the new prodrug. The 3F-3DUrd monophosphate exhibits new inhibitory properties against a different enzyme of the pyrimidine nucleotide metabolism, namely the ODC activity of UMP synthase.

Metabolic activation of zebularine, a novel DNA methylation inhibitor, in human bladder carcinoma cells

Zebularine (2(1H)-pyrimidinone riboside, Zeb), a synthetic analogue of cytidine that is a potent inhibitor of cytidine deaminase, has been recently identified as a general inhibitor of DNA methylation. This inhibition of DNA methyltransferase (DNMT) is hypothesized to be mechanism-based and result from formation of a covalent complex between the enzyme and zebularine-substituted DNA. Metabolic activation of Zeb thus requires that it be phosphorylated and incorporated into DNA. We have quantitatively assessed the phosphorylation and DNA incorporation of Zeb in T24 cells using 2-[(14)C]-Zeb in conjunction with gradient anion-exchange HPLC and selected enzymatic and spectroscopic analyses. The corresponding 5'-mono-, di- and triphosphates of Zeb were readily formed in a dose- and time-dependent manner. Two additional Zeb-containing metabolites were tentatively identified as diphosphocholine (Zeb-DP-Chol) and diphosphoethanolamine adducts. Intracellular concentrations of Zeb-TP and Zeb-DP-Chol were similar and greatly exceeded those of other metabolites. DNA incorporation occurred but was surpassed by that of RNA by at least seven-fold. Equivalent levels and similar intracellular metabolic patterns were also observed in the Molt-4 (human T-lymphoblasts) and MC38 (murine colon carcinoma) cell lines. For male BALB/c nu/nu mice implanted s.c. with the EJ6 variant of T24 bladder carcinoma and treated i.p. with 500mg/kg 2-[(14)C]-Zeb, the in vivo phosphorylation pattern of Zeb in tumor tissue examined 24h after drug administration was similar to that observed in vitro. The complex metabolism of Zeb and its limited DNA incorporation suggest that these are the reasons why it is less potent than either 5-azacytidine or 5-aza-2'-deoxycytidine and requires higher doses for equivalent inhibition of DNMT.

Epstein-Barr virus encoded nuclear protein EBNA-3 binds a novel human uridine kinase/uracil phosphoribosyltransferase

BACKGROUND

Epstein-Barr virus (EBV) infects resting B-lymphocytes and transforms them into immortal proliferating lymphoblastoid cell lines (LCLs) in vitro. The transformed immunoblasts may grow up as immunoblastic lymphomas in immuno-suppressed hosts.

RESULTS

In order to identify cellular protein targets that may be involved in Epstein-Barr virus mediated B-cell transformation, human LCL cDNA library was screened with one of the transformation associated nuclear antigens, EBNA-3 (also called EBNA-3A), using the yeast two-hybrid system. A clone encoding a fragment of a novel human protein was isolated (clone 538). The interaction was confirmed using in vitro binding assays. A full-length cDNA clone (F538) was isolated. Sequence alignment with known proteins and 3D structure predictions suggest that F538 is a novel human uridine kinase/uracil phosphoribosyltransferase. The GFP-F538 fluorescent fusion protein showed a preferentially cytoplasmic distribution but translocated to the nucleus upon co-expression of EBNA-3. A naturally occurring splice variant of F538, that lacks the C-terminal uracil phosphoribosyltransferase part but maintain uridine kinase domain, did not translocate to the nucleus in the presence of EBNA3. Antibody that was raised against the bacterially produced GST-538 protein showed cytoplasmic staining in EBV negative Burkitt lymphomas but gave a predominantly nuclear staining in EBV positive LCL-s and stable transfected cells expressing EBNA-3.

CONCLUSION

We suggest that EBNA-3 by direct protein-protein interaction induces the nuclear accumulation of a novel enzyme, that is part of the ribonucleotide salvage pathway. Increased intranuclear levels of UK/UPRT may contribute to the metabolic build-up that is needed for blast transformation and rapid proliferation.

Sensitivity of human cancer cells to the new anticancer ribo-nucleoside TAS-106 is correlated with expression of uridine-cytidine kinase 2

TAS-106 [1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine] is a new anticancer ribo-nucleoside with promising antitumor activity. We have previously presented evidence suggesting that the TAS-106 sensitivity of cells is correlated with intracellular accumulation of the triphosphate of TAS-106, which may be affected both by cellular membrane transport mechanisms and uridine-cytidine kinase (UCK) activity. Since the presence of a UCK family consisting of two members, UCK1 and UCK2, has recently been reported in human cells, we investigated the relation between expression of UCK1 and UCK2 at both the mRNA and protein levels and UCK activity (TAS-106 phosphorylation activity) in a panel of 10 human cancer cell lines. Measurement of UCK activity in these cell lines revealed that it was well correlated with the cells' sensitivity to TAS-106. In addition, the mRNA or protein expression level of UCK2 was closely correlated with UCK activity in these cell lines, but neither the level of expression of UCK1 mRNA nor that of protein was correlated with enzyme activity. We therefore compared the protein expression level of UCK2 in several human tumor tissues and the corresponding normal tissues. Expression of UCK2 protein was barely detectable in 4 of the 5 human tumor tissues, but tended to be high in the pancreatic tumor tissue. It could not be detected at all in any of the normal tissues. Thus, expression of UCK2 appeared to be correlated with cellular sensitivity to TAS-106, and it may contribute to the tumor-selective cytotoxicity of TAS-106.

Expression of uridine and thymidine phosphorylase genes in human breast carcinoma

Uridine phosphorylase (UPase) and an angiogenic enzyme, thymidine phosphorylase (dThdPase) are involved in degradation of the pyrimidine nucleosides through phosphorolysis. The expression levels of UPase and dThdPase are higher in human solid tumors including breast carcinomas than in normal tissues. To clarify the correlation between the expression levels of UPase and dThdPase genes and the clinicopathological factors, mRNA levels of these enzymes were examined by RT-PCR in 43 breast carcinomas. UPase gene expression was not correlated with dThdPase gene expression (regression coefficient R = 0.032). Although the expression level of the dThdPase gene was correlated with angiogenesis, detected by immunostaining endothelial cells (R = 0.66), that of UPase gene was not (R = 0.044). These results suggest that UPase does not have a strong angiogenic activity. The UPase gene expression levels in tumors of patients who relapsed were significantly higher than in those from patients who did not (p = 0.039). Although the expression levels of neither UPase or dThdPase were associated with age, pT, pN, pM, estrogen or progesterone receptor positivity, the patients with the higher levels of UPase gene expression had worse survival (p = 0.0038) than those with lower levels. In contrast, the expression of dThdPase gene was not related to relapse or survival of these patients with breast carcinoma. Our findings suggest that the expression level of UPase gene may be an independent prognostic marker in human breast carcinoma.

Phosphorylation of uridine and cytidine nucleoside analogs by two human uridine-cytidine kinases

Uridine-cytidine kinases (UCK) have important roles for the phosphorylation of nucleoside analogs that are being investigated for possible use in chemotherapy of cancer. We have cloned the cDNA of two human UCKs. The approximately 30-kDa proteins, named UCK1 and UCK2, were expressed in Escherichia coli and shown to catalyze the phosphorylation of Urd and Cyd. The enzymes did not phosphorylate deoxyribonucleosides or purine ribonucleosides. UCK1 mRNA was detected as two isoforms of approximately 1.8 and approximately 2.7 kb. The 2.7-kb band was ubiquitously expressed in the investigated tissues. The band of approximately 1.8 kb was present in skeletal muscle, heart, liver, and kidney. The two isoforms of UCK2 mRNA of 1.2 and 2.0 kb were only detected in placenta among the investigated tissues. The genes encoding UCK1 and UCK2 were mapped to chromosome 9q34.2-9q34.3 and 1q22-1q23.2, respectively. We tested 28 cytidine and uridine nucleoside analogs as possible substrates of the enzymes. The enzymes phosphorylated several of the analogs, such as 6-azauridine, 5-fluorouridine, 4-thiouridine, 5-bromouridine, N(4)-acetylcytidine, N(4)-benzoylcytidine, 5-fluorocytidine, 2-thiocytidine, 5-methylcytidine, and N(4)-anisoylcytidine. The cloning and recombinant expression of the two human UCKs will be important for development of novel pyrimidine ribonucleoside analogs and the characterization of their pharmacological activation.

Antitumor activity and pharmacokinetics of TAS-106, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine

We examined the effects of dosage schedule on antitumor activity in vitro and in vivo to determine the optimal administration schedule for a new nucleoside antimetabolite 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106). The cytotoxicity of TAS-106 in vitro against human tumors was evaluated at three drug exposure periods. TAS-106 exhibited fairly potent cytotoxicity even with 4 h exposure, and nearly equivalent and sufficiently potent cytotoxicity with 24 and 72 h exposures. These results suggest that long-term exposure to TAS-106 will not be required to achieve maximal cytotoxicity. The antitumor activity of TAS-106 in vivo was compared in nude rat models bearing human tumors on three administration schedules, once weekly, 3 times weekly, and 5 times weekly for 2 or 4 consecutive weeks. TAS-106 showed strong antitumor activity without serious toxicity on all three schedules, but the antitumor activity showed no obvious schedule-dependency in these models. When tumor-bearing nude rats were given a single i.v. dose of [(3)H]TAS-106, tumor tissue radioactivity tended to remain high for longer periods of time as compared to the radioactivity in various normal tissues. Furthermore, when the metabolism of TAS-106 in the tumor was examined, it was found that TAS-106 nucleotides (including the active metabolite, the triphosphate of TAS-106) were retained at high concentrations for prolonged periods. These pharmacodynamic features of TAS-106 may explain the strong antitumor activity without serious toxicity, observed on intermittent administration schedules, in nude rat models with human tumors. We therefore consider TAS-106 to be a promising compound which merits further investigation in patients with solid tumors.

Activities of adenosine deaminase and 5'-nucleotidase in cancerous and noncancerous human colorectal tissues

In order to characterize human colorectal cancer, much attention has been paid to enzyme studies. However, little is known about the correlation between the levels of key enzymes of purine nucleotide pathway and some clinical and biological indicators of tumor invasiveness and aggressiveness. Adenosine deaminase (ADA) and 5'-nucleotidase (5'-NT) were measured in cancerous and cancer-free adjacent large bowel tissues from 38 patients with colorectal carcinoma. We have analyzed the relationship between the enzyme levels and some clinical and pathological parameters. The enzymes' activities were markedly higher in primary tumors than in corresponding normal mucosae. The ADA level in tumor tissue was significantly correlated with lymph node metastasis, histologic type, tumor location, and patient's age, whereas the 5'-NT level showed a significant correlation with tumor grade and tumor location. ADA activity in tumor tissues was significantly higher in patients whose clinical course remained stable than in those with recurrent diseases. The purine metabolism and salvage pathway activity of purine nucleotides are accelerated in the cancerous human colorectal tissue. Although our findings suggest that these enzymes' activities are most likely related to the same histomorphological architecture of the tumor, the authors believe that long-term follow-up studies are needed to evaluate the prognostic value of purine enzymes for colorectal cancer.

Phase II study of 5-fluoruracil leucovorin and azidothymidine in patients with metastatic colorectal cancer

The primary objective of this study was to determine the response rate of patients with metastatic colorectal cancer to combined therapy with 5-fluorouracil (5-FU), leucovorin, and intravenous azidothymidine (AZT), a thymidine nucleoside analog. By itself, AZT has limited antineoplastic efficacy. However, experimental studies indicate that 5-FU enhances the antitumor activity of AZT by inhibiting synthesis of normal thymidine nucleotides with which AZT competes for incorporation into nucleic acids. A phase I study defined the maximum tolerated dose of AZT as 7 g/m2 with hypotension during the infusion being the dose-limiting toxicity. A phase II study was performed with oral leucovorin (100 mg p.o. hourly for 4 h prior to 5-FU and 4 h and 8 h after 5-FU), bolus 5-FU (400 mg/m2) followed 1 h later by a 2-h infusion of AZT (7 g/m2). Treatment was given weekly for 4 weeks followed by a 1-week break, which constituted a cycle of therapy. Responses were evaluated after every two cycles. Patients continued on therapy as long as they tolerated treatment and did not have progressive disease. Of 15 evaluable patients who had received no chemotherapy there was 1 complete response and 4 partial responses (a 33% response rate), whereas only 1 of 6 patients who had received prior adjuvant chemotherapy had a partial response (17%). An additional 10 patients had stable disease lasting 2-14 months. Therapy was well tolerated with the only one instance each of grade 3 nausea and vomiting, diarrhea, anemia, and hypotension. Approximately 50% of treatments were accompanied by mild hypotension, which was easily corrected by increasing the rate of normal saline infusion. There was no difficulty administering this regimen in the outpatient setting. While the overall response rate (29%) is comparable to that seen with combinations of 5-FU and leucovorin alone, in most reported series a considerably higher dose of 5-FU was utilized than in this study. Since patients in the present study experienced relatively little 5-FU toxicity, increasing the dose of 5-FU in this regimen would appear to be feasible and might result in a higher response rate.

Pyrimidine nucleotide metabolism in human colon carcinomas: comparison of normal tissues, primary tumors and xenografts

The activities of 5 enzymes involved in the pyrimidine metabolism were measured in xenografts of 8 human colon adenocarcinomas and in the corresponding primary tumors and normal tissues. The enzymes studied were thymidine kinase, thymidine phosphorylase, uridine kinase, uridine phosphorylase and thymidylate synthase. With the exception of the phosphorylases in one tumor, all enzyme activities were higher in primary tumors than in the corresponding normal tissues. The average activities of thymidine kinase and thymidylate synthase were of the same order of magnitude in xenografts and in primary tumors. The uridine metabolizing enzymes tend to have a higher activity in xenografts than in primary tumors. The most consistent and significant change was a sharp decrease in thymidine phosphorylase activity in xenografts as compared to primary tumors. Whether or not the difference in thymidine phosphorylase activity between xenografts and primary tumors is related to the contribution of non-cancerous cells in primary tumors remains to be determined. However, these results raise questions concerning the representativeness of xenografts with reference to primary tumors and suggest that care should be taken in the application of this model.

A comparison of 5-fluorouracil metabolism in human colorectal cancer and colon mucosa

The metabolism of 5-fluorouracil (5-FU) was studied in biopsy specimens of primary colorectal cancer and healthy colonic mucosa obtained from previously untreated patients immediately after surgical removal. The conversion of 5-FU to anabolites was measured under saturating substrate (5-FU) and cosubstrate concentrations. For all enzymes, the activity was about threefold higher in tumor tissue compared with healthy mucosa of the same patient. The activity of pyrimidine nucleoside phosphorylase with deoxyribose-1-phosphate (dRib-1-P) was about tenfold higher (about 130 and 1200 nmol/hr/mg protein in tumors) than with ribose-1-phosphate (Rib-1-P), both in tumor and mucosa. Synthesis of the active nucleotides (5-fluoro-uridine-5'-monophosphate [FUMP] and 5-fluoro-2'-deoxyuridine-5'-monophosphate [FdUMP]) was studied by adding physiologic concentrations of adenosine triphosphate (ATP) to the reaction mixture; the rate of FdUMP synthesis was 50% of that of FUMP (about 4 and 7 nmol/hr/mg protein in tumors). Direct synthesis of FUMP from 5-FU in the presence of 5-phosphoribosyl-1-pyrophosphate (PRPP) was about 2 nmol/hr/mg protein. With the natural substrate for this reaction, orotic acid, the activity was about 14-fold higher. To obtain insight into the recruitment of precursors for these cosubstrates, the authors also tested the enzyme activity of pyrimidine nucleoside phosphorylase with inosine and ribose-5-phosphate (Rib-5-P, as precursors for Rib-1-P) and deoxyinosine (as a precursor for dRib-1-P); enzyme activities were approximately 7%, 7%, and 3%, respectively, of that with the normal substrates, both in tumors and mucosa. However, when ATP and Rib-5-P were combined, the synthesis of FUMP was about 70% of that with PRPP, but only in tumors. In normal tissues no activity was detectable. These data suggest a preference of colon tumor over colon mucosa for the conversion of 5-FU to active nucleotides by a direct pathway; a selective antitumor effect of 5-FU may be related to this difference.

Enhancement of fluorouracil therapy by the manipulation of tissue uridine pools

Evidence for transport systems that actively concentrate uridine in normal tissues provides a previously unexploited opportunity for manipulation to therapeutic advantage. The ability to expand these pools in a tissue-specific manner by administration of exogenous uridine, inhibition of uridine phosphorylase with BAU or blockade of the facilitated transport of nucleosides with dipyridamole is established. If the apparent defect in the active transport mechanism for uridine in neoplastic cells in culture as well as several model tumors reflect the properties of human neoplasms, a new exploitable therapeutic difference may exist. These approaches may, in the near future, increase the therapeutic effectiveness not only of fluorouracil and the other fluoropyrimidines but also of other agents which disrupt uridine metabolism such as PALA and pyrazofurin.

Chromosomal and enzymatic patterns provide evidence for two types of human colon cancers with abnormal nucleotide metabolism

Correlated chromosomal and enzymatic studies are reported in a series of 13 human colon cancers. Two distinct chromosomal patterns are found: one with many losses, called monosomic type and another with many gains, called trisomic type. Chromosome 18, which carries the gene for thymidylate synthase (TS) is always missing in the monosomic type, in which TS activity is low. On the contrary, TS activity is high in the trisomic type on the average. The long arm of chromosome 17, which carries the gene for thymidine kinase (TK), is frequently duplicated in both monosomic and trisomic types, in which TK activities are high. It is found that most other deletions affect chromosomes carrying genes for enzymes of the de novo pathways whereas most other gains affect chromosomes carrying genes for enzymes of salvage pathways for synthesis of nucleotides. The importance of this finding is discussed.

Pyrimidine nucleosides enhance the efficacy of inhibitors of pyrimidine biosynthesis in cultured hepatocellular carcinoma cells

Inhibition of colony formation in cultured hepatocellular carcinoma cells of the rat was used to test the efficacy of inhibitors of de novo pyrimidine biosynthesis as potential anticancer drugs. N-(phosphonacetyl)-L-aspartic acid (PALA) (10 and 100 micrograms/ml) and 5-aza-5,6-dihydroorotic acid (DHOX) (100 micrograms/ml) inhibited the formation of colonies and these inhibitions were completely reversed by inclusion of 0.1 mM uridine, the end product of de novo pyrimidine biosynthesis, in the culture medium. With some lots of fetal bovine serum where PALA and DHOX had little effect on inhibiting colony formation, addition of 0.1 mM cytidine restored the inhibitory characteristics of PALA and, to some extent, DHOX. The results demonstrate that cytidine levels modulate the inhibitions of hepatoma colony formation by both PALA and DHOX and that co-administration of these drugs together with cytidine provides a simple expedient to increase drug efficacy.

Enzyme activities in biopsy specimens from large-bowel mucosa in colorectal adenomas and carcinomas

Biopsy specimens from 29 adenomas, 17 adenocarcinomas, and 6 synchronous adenomas in cancer patients and from uninvolved mucosa of all main segments of the large bowel were examined histologically and assayed for a series of organelle marker enzymes. Six enzymes--lactase, sucrase, alkaline phosphatase, 5'-nucleotidase, acid phosphatase, and N-acetyl-beta-D-glucosaminidase--showed less activity in adenomas than in adjacent uninvolved mucosa and in specimens from controls. Cancer tissue had higher gamma-glutamyltransferase and lower lactase, alkaline and acid phosphatases, and N-acetyl-beta-D-glucosaminidase activities than specimens from uninvolved mucosa in cancer patients and control patients. Enhanced alkaline phosphatase and N-acetyl-beta-D-glucosaminidase activities were seen in uninvolved mucosa of cancer patients as compared with those of adenoma and control patients. Evidence has been found for multienzyme analysis to identify adenomas with signs of malignant transformation and carcinomas with poor prognosis.

Enzyme activities in biopsy specimens from large-bowel mucosa in ulcerative colitis

Biopsy specimens from all main segments of the large bowel, obtained from 16 patients with ulcerative colitis, were examined histologically and assayed for a series of organelle marker enzymes. Compared with a control group of 20 subjects, significant dependence on diagnosis was demonstrated for N-acetyl-beta-D-glucosaminidase (p less than 0.01) and monoamine oxidase (p less than 0.05), when dependence on segment was taken into account. Significant correlation with degree of inflammatory cell infiltration was seen in the gamma-glutamyltransferase (p less than 0.0001), 5'-nucleotidase (p less than 0.05), and monoamine oxidase (p less than 0.0001) activities. Patients with dysplasia had lower activity of N-acetyl-beta-D-glucosaminidase (p less than 0.05) than those without dysplasia when evaluated by two-way analysis of variance modified for repeated measurements. Multienzyme analysis could distinguish between specimens with dysplasia and aneuploidy and those without when discriminant analyses were used.

Relationship between 5-fluoro-2'-deoxyuridylate, 2'-deoxyuridylate, and thymidylate synthase activity subsequent to 5-fluorouracil administration, in xenografts of human colon adenocarcinomas

5-Fluorouracil (FUra) has been administered to mice bearing xenografts of human colon adenocarcinomas. In two tumor lines, HxGC3 and HxVRC5, intrinsically resistant to FUra, 2'-deoxyuridylate (dUMP) accumulated 13.4- and 23.9-fold above basal levels. In HxELC2 xenografts, which demonstrated some sensitivity to FUra, there was a decrease in dUMP concentration after drug administration. Maximal intratumor levels of 5-fluoro-2'-deoxyuridylate (FdUMP) were found at 1 hr, but decreased in all tumor lines by 4 hr after administration of FUra. Data derived in tumor cytosols suggested that FdUMP levels in situ were not rate-limiting for formation of covalent ternary complex, but that accumulation of dUMP would retard the rate of complex formation. Subsequent to administration of FUra, thymidylate synthase activity was reduced greater than 75% in all tumors, but it recovered rapidly in tumors resistant to FUra. In addition, the pretreatment level of activity of thymidylate synthase was 12.7-fold greater in HxVRC5 tumors than in HxELC2 tumors. This elevated activity in HxVRC5 tumors appears not to be a consequence of gene amplification. Formation of FdUMP or the accumulation of dUMP did not correlate with the activity of phosphatases measured at pH 5.8 or pH 9.2 in each tumor line. Further, inhibition of phosphatase activity did not alter, significantly, the net rate of dissociation of the FdUMP-thymidylate synthase-[6R]-CH2-H4PteGlu complex.