Human Herpes Simplex Virus-1 depletes APOBEC3A from nuclei

APOBEC3 family of DNA-cytosine deaminases inactivate and mutate several human viruses. We constructed a human cell line that is inducible for EGFP-tagged APOBEC3A and found A3A predominantly in the nuclei. When these cells were infected with Herpes Simplex Virus-1, virus titer was unaffected by A3A expression despite nuclear virus replication. When A3A expression and virus infection were monitored, A3A was found predominantly to be nuclear in infected cells up to 3 h post-infection, but was predominantly cytoplasmic by 12 h. This effect did not require the whole virus, and could be reproduced using the UL39 gene of the virus which codes for a subunit of the viral ribonucleotide reductase. These results are similar to the reported exclusion of APOBEC3B by Epstein Barr virus ortholog of UL39, BORF2, but HSV1 UL39 gene product appears better at excluding A3A than A3B from nuclei.

Expression of Stathmin1 in gastric adenocarcinoma

BACKGROUND

Over expression of Stathmin1 (STMN1), activation-induced cytidine deaminase (AID) and protein kinase C iota (PKCi) proteins participate in the regulation of carcinogenesis. In the present study, we investigated the expression of STMN1 in patients with gastric adenocarcinoma and also determined the correlation of STMN1 with AID and PKCi proteins.

MATERIALS AND METHODS

This study was conducted in the Tokushima University Hospital between September 2009 and September 2010 on a total of 59 patients with gastric adenocarcinoma. Stathmin1, AID and PKCi protein expressions were evaluated by immuno-histochemistry in gastric adenocarcinoma.

RESULTS

A strong expression of STMN1 was significantly associated with gender- and poorly differentiated gastric adenocarcinoma (p<0.05). A high mRNA level of STMN1 was found in the tumor tissue of gastric adenocarcinoma compared to non-tumor tissue (p<0.05). In addition, STMN1 expression was significantly correlated with AID and PKCi protein expressions in gastric adenocarcinoma (p<0.05).

CONCLUSION

High mRNA level of the Stathmin1 gene was significantly expressed in gastric tumor tissue than non-tumor and strong expression of STMN1 protein is correlated with poorly-differentiated gastric adenocarcinoma.

The mechanisms regulating the subcellular localization of AID

Activation induced deaminase (AID) is a unique enzyme that directly introduces mutations in the immunoglobulin genes to generate antibody diversity during the humoral immune response. Since this mutator enzyme poses a measurable risk of off-target mutation, which can be deleterious or transforming for a cell, several regulatory mechanisms exist to control its activity. At least three of these mechanisms affect AID subcellular localization. It was recently found that AID is actively imported into the nucleus, most likely through importin-α/β recognizing a structural nuclear localization signal. However, AID is largely excluded from the nucleus in steady state thanks to two mechanisms. In addition to nuclear export through the exportin CRM1, a mechanism retaining AID in the cytoplasm exists. Cytoplasmic retention hinders the passive diffusion of AID into the nucleus playing an important role in the nuclear exclusion of AID. Subcellular localization of AID also determines its stability. The regulation of the nuclear fraction of AID by these many mechanisms has functional implications for antibody diversification.

Cholangiocarcinomas associated with long-term inflammation express the activation-induced cytidine deaminase and germinal center-associated nuclear protein involved in immunoglobulin V-region diversification

Cholangiocarcinoma (CCA) represents a model of tumor development after long-term inflammation which causes DNA damage or impairs DNA repair mechanism. AID and GANP, both appearing in antigen-driven B cells, are involved in affinity maturation of the immunoglobulin V-region with increased somatic mutation. A normal cholangiocyte line showed the induction of AID transcripts after stimulation with TNF-alpha, whereas ganp transcripts appeared constitutively in this cell line. Next, we examined the expression of AID and GANP in clinical CCA specimens to obtain information whether their expression levels are associated with the malignant grade of CCA. AID expression was similarly detected in the clinical cases of both well-differentiated and poorly-differentiated CCAs. On the contrary, GANP expression was detected in CCA cells at a higher level in the nucleus of poorly-differentiated CCAs with shorter survivals than in that of well-differentiated CCAs. The high and low cases of nuclear GANP expression showed no change in the frequency of the TP53 mutations, however, further investigation by in vitro experiment demonstrated that the high GANP expression caused the increased number of gammaH2AX foci after DNA damage by ionizing-irradiation. These results suggest that GANP is involved in regulation of DNA repair mechanism and the abnormal over-expression of GANP together with AID might be associated with rigorous DNA damage, potentially causing the malignant development of CCAs during long-term inflammation.

Frequent occurrence of B-cell lymphomas in angioimmunoblastic T-cell lymphoma and proliferation of Epstein-Barr virus-infected cells in early cases

Secondary lymphomas occurring in the setting of angioimmunoblastic T-cell lymphoma (AILT) are considered to be rare. Their occurrence has been attributed to Epstein-Barr virus (EBV)-associated lymphoproliferations. A previous study detected a dysregulated hypermutation process in B-cells of AILT. The present study aimed at estimating the frequency of B-cell lymphomas in AILT. By studying the expression of EBV and activation-induced cytidine deaminase (AID) as an indicator of hypermutating cells, we assessed whether B-cell lymphoproliferations in AILT were strictly associated with EBV and whether hypermutation might contribute to lymphomagenesis. Among 161 cases of AILT, diagnosed between 1996 and 2005 at the lymph node registry, Frankfurt, Germany, 19 cases were detected that also had B-cell non-Hodgkin lymphoma (NHL) and two cases had classical Hodgkin lymphoma (HL). EBV was detected in tumour cells of 7/18 NHL and both HL, suggesting that factors other than EBV contribute to lymphomagenesis. AID was expressed in AILT in large cells disseminated in the tissue, implying that the process of somatic hypermutation is ongoing in AILT, although the GC architecture is disrupted. This might be relevant in the development of secondary lymphomas.

Arsenic trioxide induces p53-dependent apoptotic signals in myeloma cells with SiRNA-silenced p53: MAP kinase pathway is preferentially activated in cells expressing inactivated p53

Mutations in p53 are the most common genetic abnormality in cancers. Arsenic trioxide (ATO) is an effective chemotherapeutic agent for the treatment of acute promyelocytic leukemia (APL) and is being tested in phase II studies in various types of cancers. We have shown that ATO is a potent inducer of apoptosis in multiple myeloma cells, engaging primarily the intrinsic apoptotic pathway in cells expressing w.t. p53 and the extrinsic apoptotic pathway in cells expressing mutant p53. To further establish the differential apoptotic signals of ATO in relation to p53 functional status we studied the activation of the intrinsic and the extrinsic apoptotic pathways in IM9 myeloma cells expressing w.t. p53 following silencing of p53 and p21 with the corresponding SiRNAs-GFP constructs. In untransfected cells or in cells transfected with GFP-empty vector construct we observed weak apoptosis concomitant with mild depolarization of mitochondrial membrane, depletion of reduced glutathione and release of cytochrome c. Following silencing of p53 or p21 we observed extensive apoptosis concomitant with extensive depolarization of mitochondrial membrane and depletion of reduced glutathione. We also observed in these cells activation of the extrinsic apoptotic pathway through upregulation of APO2/TRAIL and APO2/TRAIL-R2, activation of caspase 8, degradation of FLIP-L and release of apoptosis inducing factors from mitochondria, instead of cytochrome c. In addition, we observed marked activation of the MAP kinase pathway and dephosphorylation of Akt in p53 or p21 silenced cells. Hence, silencing of p53 or p21 in IM9 myeloma cells results in diversion of apoptosis to the extrinsic pathway and sensitization of myeloma cells to ATO.

Monocyte fructose 1,6-bisphosphatase and cytidine deaminase enzyme activities: potential pharmacodynamic measures of calcitriol effects in cancer patients

PURPOSE

To determine, in peripheral blood monocytes (PBM), whether the enzymatic activities of fructose 1,6-bisphosphatase (FBPase), cytidine deaminase (CDDase) and 24-hydroxylase (CYP24), enzymes regulated by calcitriol are useful pharmacodynamic (PD) measures of calcitriol effects in cancer patients.

METHODS

Cancer patients enrolled in a phase I clinical trial of calcitriol and carboplatin were studied. Baseline and calcitriol-induced changes in FBPase, CDDase and CYP24 activities were measured in PBM collected before, 6, 24, and 48 h after administration of calcitriol, prior to carboplatin, in doses ranging from 4 to 11 mug daily for 3 consecutive days (QDx3). Normal FBPase, CYP24 and CDDase activities were measured in PBM from untreated healthy volunteers.

RESULTS

Baseline activities in PBM from cancer patients and healthy volunteers were (median and range): 1.0 (0.0-43.5) and 4.4 (3.1- 8.2) nmol/min/mg protein for FBPase (P = 0.002); 2.5 (0.9-9.3) and 0.8 (0.4-2.0) fmol/h/10(6) cells for CYP24 (P = 0.016), and 5.6 (2.5-22.3) and 6.6 (1.1-47.4) nmol/min/mg protein for CDDase (P > 0.05), respectively. All calcitriol doses achieved peak serum calcitriol levels > x3 the physiological levels, increased cancer patient PBM FBPase activity to normal levels and decreased CDDase activity to undetectable levels within 48 h, with no significant change in CYP24 activity. These enzyme activity changes were not associated with hypercalcemia.

CONCLUSIONS

Calcitriol treatment-induced increase in FBPase and decrease in CDDase activities in cancer patient PBM are potential early and sensitive non-hypercalcemia PD measures of calcitriol effects.

Validation of real-time reverse-transcription-polymerase chain reaction for quantification of capecitabine-metabolizing enzymes

Capecitabine is an oral fluoropyrimidine carbamate activated sequentially in both liver and tumor tissues by carboxylesterases, cytidine deaminase, and thymidine phosphorylase. 5-Fluorouracil is inactivated by dihydropyrimidine dehydrogenase and targets thymidylate synthase. Here we report the validation of the real-time polymerase chain reaction assay for the quantification of the transcripts of the different enzymes involved in capecitabine activation. The method is specific, sensitive, and linear over 2-3 logs of RNA input. It is reproducible with less than 5% intraday variability and less than 10% interday variability. Five reference genes were tested for normalization. POLR2A was selected since it reduced variability between samples, demonstrated levels of expression similar to those of the genes of interest, and its expression was not modified by capecitabine treatment in samples from preclinical studies. The method was robust as the gene expression profiles from six colon cancer cell lines obtained by this method were similar to microarray data. Finally, the method was able to detect changes in gene expression in xenograft tumors treated with capecitabine. It could therefore constitute the method of choice for future correlative studies in patients receiving capecitabine.

Activation-induced cytidine deaminase (AID) is expressed in normal spermatogenesis but only infrequently in testicular germ cell tumours

Activation-induced cytidine deaminase (AID) is essential for somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin genes in antigen-dependent B-cell maturation. SHM is not restricted to immunoglobulin gene loci, raising the possibility of a function for AID in other cell types. In this study, it is shown that AID is expressed in spermatocytes in the human testis. AID was mostly cytoplasmic but nuclear AID was also observed in a proportion of cells, in keeping with the DNA deamination model of AID function. Intratubular germ cell neoplasia unclassified (IGCNU), the precursor lesion of testicular cancers, was AID-negative. Seminomas also lacked AID expression. Nuclear and cytoplasmic AID expression was observed in three of 32 mixed non-seminomatous germ cell tumours. The results provide evidence for a physiological role for AID outside the immune system. AID expression in spermatocytes points to a role in meiosis. It remains uncertain whether AID may also contribute to the genetic aberrations characteristically found in testicular germ cell tumours. The consistent absence of detectable AID expression in atypical spermatogonia of IGCNU and its rare expression in germ cell tumours suggest that continued expression of AID is not involved in the pathogenesis of germ cell tumours.

Expression of activation-induced cytidine deaminase is regulated by cell division, providing a mechanistic basis for division-linked class switch recombination

Class switch recombination (CSR) is the process by which B cells alter the effector function properties of their Ig molecules. The decision to switch to a particular Ig isotype is determined primarily by the mode of B cell activation and cytokine exposure. More recent work indicates that the likelihood or probability of switching increases with successive cell divisions and is largely independent of time. We have analyzed different molecular features of CSR using cell division as a reference point in an attempt to gain insight into the mechanism of division-linked switching. Our results indicated that the accessibility of Ig heavy chain constant regions targeted for CSR was established after the cells had undergone a single cell division and did not vary significantly with subsequent cell divisions. In contrast, expression of activation-induced cytidine deaminase (AID) mRNA was found to increase with successive divisions, exhibiting a striking correlation with the frequency of CSR. Levels of AID in a given division remained constant at different time points, strongly suggesting that the regulation of AID expression was division-linked and independent of time. In addition, constitutive AID expression from a transgene accelerated division-linked CSR. Thus, we propose that the division-linked increase in AID expression provides an underlying molecular explanation for division-linked CSR.

In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia

Factors that reduce the intracellular concentration of triphosphorylated cytarabine (ara-CTP), the active form of cytarabine (ara-C), may induce chemoresistance in acute myeloid leukaemia (AML) patients. These factors include reduced influx of ara-C by the hENT1 transporter, reduced phosphorylation by deoxycytidine kinase (dCK), and increased degradation by high Km cytoplasmic 5'-nucleotidase (5NT) and/or cytidine deaminase (CDD). Increased levels of DNA polymerase alpha (DNA POL) and reduced levels of topoisomerase I (TOPO I) and topoisomerase II (TOPO II) have also been detected in ara-C-resistant cell lines. To determine whether these factors are implicated in clinical ara-C resistance, we analysed the expression of these parameters at diagnosis, using reverse transcription polymerase chain reaction, in the blast cells of 123 AML patients treated with ara-C. At diagnosis, hENT1, dCK, CDD, 5NT, TOPO I, TOPO II, DNA POL and MDR1 were expressed in 83%, 22%, 7%, 37%, 59%, 37%, 39% and 16% of patients respectively. In univariate analysis, patients with expression of 5NT or DNA POL at diagnosis had significantly shorter disease-free survival (DFS). In multivariate analysis, DNA POL positivity and hENT1 deficiency were related to a shorter DFS. In univariate analysis, patients with 5NT-positive blasts had significantly shorter overall survival (OS). In multivariate analysis, shorter OS was related to DNA POL positivity. These results suggest that expression of DNA POL, 5NT and hENT1 at diagnosis may be resistance mechanisms to ara-C in AML patients.

Identification of the yeast cytidine deaminase CDD1 as an orphan C-->U RNA editase

Yeast co-expressing rat APOBEC-1 and a fragment of human apolipoprotein B (apoB) mRNA assembled functional editosomes and deaminated C6666 to U in a mooring sequence-dependent fashion. The occurrence of APOBEC-1-complementing proteins suggested a naturally occurring mRNA editing mechanism in yeast. Previously, a hidden Markov model identified seven yeast genes encoding proteins possessing putative zinc-dependent deaminase motifs. Here, only CDD1, a cytidine deaminase, is shown to have the capacity to carry out C-->U editing on a reporter mRNA. This is only the second report of a cytidine deaminase that can use mRNA as a substrate. CDD1-dependent editing was growth phase regulated and demonstrated mooring sequence-dependent editing activity. Candidate yeast mRNA substrates were identified based on their homology with the mooring sequence-containing tripartite motif at the editing site of apoB mRNA and their ability to be edited by ectopically expressed APOBEC-1. Naturally occurring yeast mRNAs edited to a significant extent by CDD1 were, however, not detected. We propose that CDD1 be designated an orphan C-->U editase until its native RNA substrate, if any, can be identified and that it be added to the CDAR (cytidine deaminase acting on RNA) family of editing enzymes.

The pharmacodynamic basis for the increased antileukaemic efficacy of cytosine arabinoside-based treatment regimens in acute myeloid leukaemia with a high proliferative activity

The current study was initiated to explore the mechanisms underlying the previously demonstrated association between the proliferative activity of leukaemic blasts and the response to cytosine arabinoside (AraC)-based therapy in de novo acute myeloid leukaemia (AML). The activity of key enzymes of AraC metabolism-deoxycytidine kinase (DCK), cytidine deaminase (DCD) and polymerase alpha (PolyA) were determined in blast cells from 33 patients. In addition, formation and retention of intracellular levels of AraC triphosphate (AraCTP) and DNA incorporation of AraC were measured, as was the proliferative activity of leukaemic blasts by [3H]-TdR incorporation before and after stimulation with granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte CSF (G-CSF) for 48 h. AraC incorporation into the DNA (median 0.60 pmol/105 cells) was significantly related to the proliferative activity of AML blasts (r = 0.74, P < 0.001). Similarly, priming with GM-CSF or G-CSF increased both the proliferative activity of AML blasts by a median of 1.84- and 1.64-fold, respectively, and the incorporation of AraC into the DNA (1.29- and 1.40-fold respectively). In contrast, no relationship was found between the endogenous proliferative activity (EPA) and enzyme activities regulating AraC activation (DCK; median 4.70 pmol/min/mg protein), inactivation (DCD; median 2.92 pmol/min/mg protein) or inhibitory effects (PolyA; median 1.50 pmol/min/mg protein), nor the formation or retention of AraCTP (median 306.1 ng/107 cell and 1.6 h respectively). When samples were grouped according to EPA (more than or less than the median), slowly proliferating specimens had a higher response to cytokine priming for proliferative activity and incorporation of AraC into DNA. Clinical data of 15 patients were available. Although all eight patients with a high endogenous proliferative activity reached complete remission, only four out of seven patients with a low proliferative activity responded, whereas the other three patients were non-responders (P = 0.077).

Re-evaluation of the colorimetric assay for cytidine deaminase activity

This study re-evaluated the colorimetric assay for cytidine deaminase (CTD), and showed that the optimum conditions were pH 7.5, 37 degrees C, and up to 24 h. In addition, this method was found to require protein precipitation. Following these modifications, intra-assay and inter-assay coefficients of variation were below 5 per cent, indicating that the assay was highly reliable. CTD activity was determined in 282 serum samples from 206 normal pregnant women by the incubation of 100 microliters of serum and 400 microliters of 1.4 mmol/l cytidine substrate for 16 h at 37 degrees C. Following protein precipitation, the ammonia liberated during conversion was measured by a colorimetric procedure. The mean (+/- SD) CTD activity was 7.31 +/- 2.50 U at 3-12 weeks of gestation, 8.70 +/- 2.12 U at 13-24 weeks, 7.59 +/- 2.25 U at 25-36 weeks, and 7.29 +/- 2.16 U at 37-42 weeks. High levels of CTD activity were found in patients with abruptio placentae and amnionitis associated with intrauterine fetal death (IUFD). The increase in CTD activity was noted from 3 days to 1 week before the confirmation of IUFD. The placenta contains extremely high levels of CTD, but cord serum does not. Thus, the excessive elevation of CTD activity was probably derived from progressive placental damage. This modified CTD assay was concluded to be simple and reliable, and may perhaps be useful in detecting pregnancy disorders.

Cloning of a functional cDNA for human cytidine deaminase (CDD) and its use as a marker of monocyte/macrophage differentiation

We have identified a cDNA clone for human cytidine deaminase (EC 3.5.4.5) during an investigation which aimed at cloning novel gene expression products related to monocyte/macrophage differentiation. The derived amino acid sequence of the clone comprises 145 residues yielding a molecular mass for the polypeptide of 16.1 kDa and exhibits a nearly 50% homology to cytidine deaminase from Bacillus subtilis. Cytidine deaminase activity of the cloned sequence could be demonstrated in a prokaryotic expression system. The mRNA is highly expressed in granulocytes while expression is very low in fibroblasts, chondrocytes, monocytes, and T- as well as B-cell lines. The mRNA can be induced in monocytes, the monocytoid cell line U937 and the myeloblastic line HL 60 by the differentiation inducer calcitriol.

Cytidine deaminase and lactoferrin in inflammatory synovial fluids. Indicators of local polymorphonuclear cell function?

Cytidine deaminase (CD) is a cytoplasmatic enzyme present predominantly in polymorphonuclear cells (PMNC) in inflamed joints. Lactoferrin is situated in the secondary granules of PMNC and is released by secretory/phagocytic stimuli, whereas CD is released mainly upon cell lysis. To study the release of these molecules in arthritic conditions we measured CD and lactoferrin levels in synovial fluid (SF) drawn from patients with rheumatoid arthritis (RA), crystal pyrophosphate disease (CPPD), psoriatic arthropathy, reactive arthritis, spondylarthropathy, and osteoarthrosis. CD activity was highest in SF from RA and CPPD followed by psoriatic arthropathy, reactive arthritis and spondylarthropathy. Lactoferrin concentrations were highest in CPPD followed by RA, reactive arthritis, psoriatic arthropathy, and spondylarthropathy. Both CD and lactoferrin levels were low in osteoarthrosis SF. Although SF CD activity and lactoferrin levels correlated well in all diagnostic groups, the ratio between CD and lactoferrin was higher for RA, psoriatic arthropathy, and spondylarthropathy compared to reactive arthritis and CPPD. This suggests predominant release by PMNC lysis in the more chronic arthritis groups and more degranulation in the more episodic CPPD and reactive arthritis groups. CD activity and lactoferrin levels correlated significantly with SF cell counts in the RA and psoriatic arthropathy groups.

The measurement of nucleoside deaminases by high performance liquid chromatography and their use in clinical chemistry

The measurement of the nucleoside deaminases--cytidine deaminase, guanosine deaminase and adenosine deaminase--by reversed phase high performance liquid chromatography is reviewed. The clinical value of assaying the enzyme activity is discussed for each of these enzymes. Both cytidine deaminase and adenosine deaminase measurements have proven clinical value, although the use of the assay of cytidine deaminase in the diagnosis of pre-eclampsia is probably not helpful.

Determination of cytidine deaminase activity in synovial fluid by HPLC

A reversed-phase high-performance liquid chromatographic method for the determination of cytidine deaminase activity in synovial fluid is described. Diluted synovial fluid was incubated for 10 min at 56 degrees C with 0.4 mM cytidine. The protein in 5 vol of incubate was then precipitated using 1 vol of trichloroacetic acid (20% m/v) and the substrate, cytidine, and the product, uridine, were determined in the resultant supernatant. These substances were separated by reversed-phase HPLC using 0.05 M potassium dihydrogen orthophosphate (pH 6.5) containing methanol (3% v/v) and were detected at 280 nm. The enzyme activity was determined by measuring uridine formation. The effects of substrate concentration, pH and reaction temperature on uridine formation are described.

Protective, tumor-selective dual pathway activation of 5-fluoro-2'-deoxycytidine provided by tetrahydrouridine in mice bearing mammary adenocarcinoma-755

Treatment of C57BL X DBA/2 F (hereafter called BD2F) mice bearing ascitic mammary adenocarcinoma-755 (ADC-755) with [3H]-5-fluoro-2'-deoxycytidine ([3H]FdCyd) plus tetrahydrouridine (H4Urd) resulted in antimetabolite pool sizes indicative of a tumor-selective, dual pathway metabolism of FdCyd via both cytidine deaminase and deoxycytidine kinase. In contrast to the high levels of all RNA- and DNA-level antimetabolites (as assayed by high performance liquid chromatography) derived from FdCyd found in tumor tissue, normal tissues (bone marrow, intestine, liver, and spleen) and serum metabolized FdCyd to only a small extent following FdCyd plus H4Urd treatment. RNA-level antimetabolite pools and 5-fluoro-2'-deoxyuridine (FdUrd) were generally 100-fold lower in normal than in tumor tissue, and 5-fluoro-2'-deoxyuridylate was 10- to 15-fold lower in normal than in tumor tissue. The use of [3H]FdUrd, on the other hand, resulted in the formation of higher levels (10- to 40-fold) of DNA- and RNA-level antimetabolites in normal tissue and lower levels (1/8) of 5-fluoro-2'-deoxyuridylate in tumor tissue. Both [3H]FdCyd plus H4Urd and [3H]FdUrd were utilized at their optimal drug doses. FdUrd- and FdCyd-derived metabolic products incorporated into the RNA and DNA of normal and tumor tissue of BD2F mice bearing ADC-755 were also examined. The drug combination [3H]FdCyd plus H4Urd resulted in the selective incorporation of antimetabolites into tumor RNA and DNA; only a very small extent of antimetabolites incorporated into normal tissue RNA and DNA. FdCyd was incorporated 5- to 10-fold greater in tumor than intestine, liver, or spleen following FdCyd plus H4Urd administration. FdCyd incorporation was 190-fold greater in tumor than in bone marrow. Mice bearing ADC-755 treated with [3H]-FdUrd resulted in only marginal selectivity in terms of antimetabolite incorporation in tumor tissue. Deoxycytidylate and cytidine deaminase enzyme assays have confirmed that H4Urd administration effectively inhibited normal cytidine deaminase activities, while only weakly inhibiting the elevated levels found in tumor tissue. Thymidine kinase, deoxycytidine kinase, deoxycytidylate deaminase, and cytidine deaminase have been shown previously to be significantly elevated in the mouse tumor model used; these enzymatic elevations are also characteristic of many human tumors. Treatment with FdCyd plus H4Urd resulted in 17 of 30 cures against ADC-755 compared to 4 of 20 and 0 of 20 for 5-fluorouracil and 5-fluoro-2'-deoxyuridine treatments, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of 5-trifluoromethyldeoxycytidine and tetrahydrouridine to circumvent catabolism and exploit high levels of cytidine deaminase in tumors to achieve DNA- and target-directed therapies

5-Trifluoromethyl-2'-deoxycytidine (F3methyl-dCyd), when coadministered with tetrahydrouridine (H4Urd), surpasses the efficacy of 5-trifluorothymidine and 5-trifluoromethyl-2'-deoxycytidine when administered alone as demonstrated with adenocarcinoma 755 and Lewis lung carcinoma as solid tumors implanted in C57BL X DBA/2 F1 mice. It appears that the reason for the heightened efficacy of F3methyl-dCyd, when coadministered with low concentrations of H4Urd, is decreased systemic deamination and subsequent systemic catabolism by pyrimidine nucleoside phosphorylases, which do not act on deoxycytidine and its analogues. Furthermore, the elevated levels of cytidine deaminase in these mouse tumors may result in selective conversion of F3methyl-dCyd to 5-trifluorothymidine at the tumor site. This suggests an approach to the treatment of human tumors possessing elevated levels of cytidine deaminase such as certain leukemias, bronchogenic carcinoma of the lung, adenocarcinomas of the colon and rectum, astrocytomas, and certain tumors which are refractory to chemotherapy with 1-beta-D-arabinofuranosylcytosine. In contrast to fluorinated pyrimidines in current use, F3methyl-dCyd + H4Urd potentially allows an exclusive DNA-, rather than both a DNA- and RNA-, directed approach. The major mechanism of the antitumor activity of F3methyl-dCyd appears to be via inhibition by 5-trifluorothymidine-5'-monophosphate of thymidylate synthetase, the target enzyme of fluoropyrimidine analogues in current use. However, the established and potential differences in the mode of action, anabolism, nature of incorporation into DNA, repair and cofactor requirements of F3methyl-dCyd and its anabolites, compared to that of the commonly utilized fluorinated pyrimidines, indicate that F3methyl-dCyd + H4Urd is a novel combination of agents. In comparative studies with Lewis lung carcinoma, F3methyl-dCyd (+ H4Urd) was shown to surpass the efficacies of 5-fluorouracil and 5-fluorodeoxyuridine and to be essentially equal in efficacy to 5-fluorodeoxycytidine (+ H4Urd). The optimum established protocol against Lewis lung carcinoma is F3methyl-dCyd, 175 mg/kg, + H4Urd, 25 mg/kg, once per day for 7 days. Studies utilizing high concentrations of H4Urd coadministered with F3methyl-dCyd indicate that the major pathway of tumor inhibition is via conversion of F3methyl-dCyd to 5-trifluorothymidine in view of the fact that tumor inhibition diminishes at doses of H4Urd which result in extensive (93%) inhibition of tumor cytidine deaminase.(ABSTRACT TRUNCATED AT 400 WORDS)

Establishment of human KB cells resistant to 1-beta-D-arabinofuranosylcytosine, and mechanisms of cellular resistance in isolated clones

A subline of human KB cells that was resistant to 1-beta-D-arabinofuranosylcytosine (ara-C) was established by continuous exposure of the cells to increasing concentrations of ara-C. Thirteen resistant clones were isolated from the resistant subline (KB/ara-C). KB/ara-C showed 1,300-fold higher resistance than the parent KB cells to ara-C; the most resistant clones, clones 7 and 10, showed 1,330-fold higher resistance. In the absence of ara-C, the resistance of the parent KB/ara-C cells was stable for at least 14 weeks, whereas that of clone 7 was stable for 10 weeks, but was slightly less after 14 weeks. The ara-C kinase and ara-C deaminase activities of the 13 clones and the cellular uptake of ara-C by several clones were measured. In general the clones showed decreased deoxycytidine kinase activity and decreased cellular uptake of ara-C. Most clones had higher cytidine deaminase activity than KB cells, but some had activity similar to that of the KB cells. A clear inverse relationship was found between the ara-C sensitivity of the clones and their kinase activity, but not their deaminase activity or their ara-C uptake. These results clearly demonstrate that a major mechanism of ara-C resistance of these human KB cells was a decrease in the activity of the ara-C activating enzyme deoxycytidine kinase. The parent KB/ara-C cells showed no clear cross-resistance to various antitumor agents other than an ara-C derivative, including metabolic inhibitors, alkylating agents, DNA binders and mitotic spindle poisons.

Influence of tetrahydrouridine on the pharmacokinetics of intrathecally administered 1-beta-D-arabinofuranosylcytosine

Tetrahydrouridine (THU), a potent inhibitor of cytidine deaminase, has been shown to increase the antitumor activity of 1-beta-D-arabinofuranosylcytosine (ara-C) both in vitro and in vivo. In initial studies, which examined the cerebrospinal fluid (CSF) pharmacokinetics of intrathecally (i.t.) administered THU, the drug was found to be slowly cleared from the CSF with alpha and beta half-lives of 1 and 8 hr, respectively. In subsequent experiments, both i.v. pretreatment with THU and concomitant i.t. injection of THU were found to retard the disappearance of i.t. ara-C from the CSF, although the effect of i.t. THU was more profound. ara-C given alone was cleared from CSF with alpha and beta half-lives of 27.5 +/- 6.7 and 115.6 +/- 0.4 (S.D.) min, respectively. Pretreatment with i.v. THU resulted in alpha and beta half-lives of 10.4 +/- 1.5 and 85.7 +/- 11.1, respectively, whereas concomitant administration of i.t. THU resulted in a single half-life of 96 +/- 0.7. The mean calculated clearance rates for ara-C alone, ara-C plus i.v. THU, and ara-C plus i.t. THU were 7.5, 6.2, and 4.2 ml/hr, respectively. This effect appeared to be primarily due to THU inhibition of ara-C deamination, since a decrease in formation of 1-beta-D-arabinofuranosyluracil in the CSF was observed when ara-C was given in the presence of THU (either i.t. or i.v.). No acute neurotoxicity was noted after administration of either i.t. THU alone or i.t. THU with ara-C. The ability of THU to alter CSF ara-C pharmacokinetics may have potential therapeutic value.

Detection after electrophoresis of enzymes involved in ammonia metabolism using L-glutamate dehydrogenase as a linking enzyme

The use of L-glutamate dehydrogenase (GLUD) as a reagent in staining mixtures to detect the isozymes of enzymes which catalyze the production of ammonia has been investigated. Methods have been devised for the electrophoresis and detection, using GLUD, of seven enzymes: cytidine deaminase, adenosine deaminase, adenosine monophosphate deaminase, arginase, argininosuccinase, D-amino acid oxidase, and D-aspartate oxidase. GLUD-linked staining methods appear to be sensitive, specific, and of general application.

Cytidine deaminase: a new genetic polymorphism demonstrated in human granulocytes

Cytidine deaminase in human white blood cells has three electrophoretic phenotypes representing the homozygous and heterozygous expression of two common alleles, CDA1 and CDA2, at an autosomal locus. To explain the multibanded pattern of the heterozygote, the enzyme is assumed to have a tetrameric structure.