Effect of ecteinascidin-743 on the interaction between DNA binding proteins and DNA

Ecteinascidin-743 (ET-743) is a tetrahydroisoquinoline alkaloid isolated from Ecteinascidia turbinata, a tunicate growing in mangrove roots in Caribbean. It has been shown to bind in the minor groove of DNA forming covalent adducts by reaction of the N2 of guanine with the carbinolamine moiety. We investigated ET-743 ability to inhibit the binding of different transcription factors to their consensus sequences by using gel shift assays. We have selected three types of factors: (i) oncogene products such as MYC, c-MYB and Maf; (ii) transcriptional activators regulated during the cell cycle as E2F and SRF; and (iii) general transcription factors such as TATA binding protein (TBP), Sp1 and NF-Y. We observed no inhibition of the binding of Sp1, Maf, MYB and MYC. Inhibition of DNA binding was observed for TBP, E2F, SRF at ET-743 concentrations ranging from 50 to 300 microM. The inhibition of binding of NF-Y occurs at even lower concentrations (i.e. 10-30 microM) when the recombinant subunits of NF-Y are preincubated with the drug, indicating that the inhibition of NF-Y binding does not require previous ET-743 DNA binding. Since NF-Y is a trimer containing two subunits with high resemblance to histones H2B and H2A, we have investigated the effect of ET-743 on nucleosome reconstitution. ET-743 caused a decrease of the nucleosomal band at 100 nM, with the complete disappearance of the band at 3-10 microM. These data suggest that the mode of action of this novel anticancer drug is related to its ability to modify the interaction between some DNA binding proteins and DNA.

The antitumour activity of alkylating agents is not correlated with the levels of glutathione, glutathione transferase and O6-alkylguanine-DNA-alkyltransferase of human tumour xenografts. EORTC SPG and PAMM Groups

Twenty-three human xenografts, including five colon, five gastric, nine lung (three small cell lung cancer) and four breast carcinomas, were investigated for their sensitivity to nitrosoureas, dacarbazine (DTIC), cyclophosphamide (CTX) and cisplatin (DDP). In 12 cases, at least one of the drugs produced complete or partial remission, in 2, a minor regression was observed and in the other 9, treatment was ineffective. The level of sensitivity to each drug, using a score from 1 to 5, was correlated to three biochemical parameters reported to be involved in resistance to alkylating agents: glutathione (GSH), glutathione transferase (GST) and O6-alkylguanine-DNA-alkyltransferase (AGT). A wide variability was found in these parameters in the xenografts investigated. No correlation was found between any of the three parameters and sensitivity to the drugs used or between sensitivity to one drug and to any of the other drugs tested. These results illustrate the complexity of the question of resistance to alkylating agents and indicate that, at least in xenografts, the biochemical parameters examined are not predictive of response to alkylating agents.

Prevalence and etiology of gastroduodenal ulcer in HIV-positive patients: a comparative study of 497 symptomatic subjects evaluated by endoscopy

OBJECTIVE

In 497 HIV-positive (+) patients with upper digestive tract symptoms, 23 (5%) had gastroduodenal ulcers (GDU) at upper endoscopy.

METHODS

To establish the causes of GDU in this setting, 16 of these patients who had had comprehensive histological evaluation (group I) were compared with 20 HIV+ subjects with upper gastrointestinal symptoms but without ulcer (group II), and with 16 seronegative patients with GDU (group III). Eighty-one percent of group I subjects and 90% of group II patients had C3 AIDS. The presence of gastritis and Helicobacter pylori, fungi, mycobacteria, viruses (especially cytomegalovirus [CMV] and herpes simplex [HSV]), and parasites was determined in all three groups by histopathological and microbiological studies.

RESULTS

The prevalence of chronic active gastritis was 13/16 (81%) in group I, 12/20 (60%) in group II, and 15/16 (94%) in group III. It was associated with H. pylori in group III, and with opportunistic pathogens in groups I and II and with none in group III. H. pylori was detected in 5/16 patients (31%) in group I, in 12/20 (60%) in group II, and 11/16 (69%) in group III. Cytomegalovirus was histologically diagnosed in 8/16 patients (50%) in group I and in 1/20 (5%) in group II. This virus was the only factor shown to be significantly associated with GDU in these cases (p = 0.0046). Cryptosporidium was found in 2/16 (12.5%) patients in group I, in 1/20 (5%) in group II, and in none in group III. Differences between groups I and II were not statistically significant. No other organisms were observed in the three groups.

CONCLUSIONS

Gastroduodenal ulcers were infrequent in HIV+ subjects with upper digestive tract symptoms and CMV was the only organism significantly associated with GDU in HIV+ patients. Among HIV+ patients, H. pylori was an uncommon cause of ulcer. Among HIV+ subjects with ulcer, chronic active gastritis was more common than H. pylori and it was associated with other pathogens. Finally, HIV+ patients with GDU should have endoscopic biopsies to detect opportunistic infections, especially CMV, because H. pylori infection is uncommon.

[Acute low digestive hemorrhage in testicular choriocarcinoma]

We report a case in which acute intestinal hemorrhage was the initial manifestation in the evolution of choriocarcinoma of the testis. The diagnosis of bleeding was difficult and required laparotomy. Metastatic lesion of the small bowel should be considered a possible cause of intestinal bleeding in patients with testicular choriocarcinoma.

Effect of G:C-->A:T transition, potentially arising from O6-guanine alkylation, in the transcription regulation of c-fos serum response element

O6-meGs, if not repaired before cell undergo DNA synthesis, can cause erroneous pairing of thymine resulting in a G:C-->A:T transition, after the next DNA replication. It is known that the presence of O6-meG in promoter sequences inhibits the specific binding of transcription factors. Little is known on the effect of G:C-->A:T transitions on this binding. c-fos SRE was used as a model to study the effect of different G:C-->A:T transitions (at the positions -305, -306, -316, -319 and -320) in terms of SRE specific DNA-binding and functional ability to activate transcription of a reporter gene. The electromobility shift assay and a transient transfection assay were used. The G:C-->A:T transition at -320 caused 92% inhibition, while mutations at the positions -305, -306, -316 and -319 caused respectively 55, 43, 19 and 44% inhibition. The findings indicate that some G:C-->A:T transitions, potentially arising from O6-guanine methylation, can impair the regulation of c-fos transcription.

p21WAF1-derived peptides linked to an internalization peptide inhibit human cancer cell growth

We tested the ability of synthetic peptides derived from p21(WAF1), fused to the internalization peptide sequence derived from Antennapedia, to inhibit the growth of cancer cells in two human ovarian cancer cell lines expressing wild-type p53 or not. Two fused peptides corresponding to p21(WAF1) regions 17-33 and 63-77 inhibited cell growth in both cell lines while the same peptides without the internalization sequence were inactive. The fused peptides prevented growth at concentrations which inhibited cyclin-dependent kinase 2 and cdc2 activity, thus demonstrating that the peptides act by mimicking the action of p21(WAF1) on kinases. This study illustrates the potential pharmacological use of small peptides fused with the Antennapedia internalization sequence in proliferative disorders. The approach may be extended to other diseases in which cell penetration of a peptide may be of therapeutic benefit. More stable drug-like molecules with better pharmacological properties could be designed based on the results obtained with peptides.

Characterization of a protein recognizing minor groove binders-damaged DNA

By using electromobility shift assay (EMSA), we have identified a protein able to recognize the DNA only if it was previously reacted with minor groove binders. This protein binds with very high affinity AT containing DNA treated with minor groove binders such as distamycin A, Hoechst 33258 and 33342, CC-1065 and ethidium bromide minor groove intercalator, but not with major groove binders such as quinacrine mustard, cisplatin or melphalan, or with topoisomerase I inhibitor camptothecin or topoisomerase II inhibitor doxorubicin. This protein was found to be present in different extracts of human, murine and hamster cells, with the human protein which appears to have a molecular weight slightly lower than that of the other species. This protein was found to be expressed both in cancer and normal tissues. By using molecular ultrafiltration techniques as well as southwestern analysis it was estimated that the apparent molecular weight is close to 100 kDa. We can exclude an identity between this protein and other proteins, with a similar molecular weight previously reported to be involved in DNA damage recognition/repair, such as topoisomerase I, mismatch repair activities such as the prokaryotic MutS protein and its human homologue hMSH2 or proteins of the nucleotide excision repair system such as ERCC1, -2, -3 and -4.

Simultaneous immunoaffinity purification of O6-methyl, O6-ethyl-, O6-propyl- and O6-butylguanine and their analysis by gas chromatography/mass spectrometry

A sensitive and specific method has been developed for the simultaneous analysis of different O6-alkylguanines. The cross-reactivity of two different antibodies raised against O6-methylguanosine and O6-butylguanosine for a series of O6-alkylguanines was exploited for the immunoaffinity purification of biological samples before quantitative analysis by gas chromatography/mass spectrometry. The method can be applied to the detection of O6-alkylguanines in DNA and appears to be useful for studying chemical carcinogen mechanisms in animals and possibly for the detection of human exposure to alkylating agents.

Detection of O6-butyl- and O6-(4-hydroxybutyl)guanine in urothelial and hepatic DNA of rats given the bladder carcinogen N-nitrosobutyl(4-hydroxybutyl)amine

N-Nitrosobutyl(4-hydroxybutyl)amine (BBN) is a selective bladder carcinogen in rats. Its organ specificity may depend on several factors, including metabolic activation, DNA alkylation and repair within the target organ. Metabolic activation of BBN, which is asymmetrical, may result in butylating and 4-hydroxybutylating species. To test this view, BBN was administered as a single oral dose of 20 or 120 mg/rat or six doses of 20 mg/rat over 2 weeks. The animals given the single 120 mg dose were killed 3, 6 and 24 h after treatment. Rats given 20 mg or 6 x 20 mg BBN were killed 24 h after the last dose. DNA from liver and urothelial cells was hydrolyzed and analyzed for O6-butylguanine (O6-BuG) and O6-(4-hydroxybutyl)guanine [O6-(4-OH-Bu)G] as their pentafluorobenzyl-trimethylsilyl derivatives by high-resolution gas chromatography--negative ion chemical ionization mass spectrometry with selective ion recording after immunoaffinity extraction. Polyclonal antibodies raised against O6-(4-hydroxybutyl)-guanosine [O6-(4-OH-Bu)GR] were coupled to CNBr-activated Sepharose 4B. This was mixed with a gel coupled to antibodies raised against O6-BuG, already available in the laboratory, and the mixed gel was used for the one-step sample clean-up, enrichment and extraction of O6-(4-OH-Bu)G and O6-BuG from hydrolyzed DNA. O6-BuG in urothelial DNA of rats given a single dose of 120 mg BBN increased from 0.44 +/- 0.12 mumol/mol guanine (mean +/- SE) 3 h after treatment, to 17.9 +/- 7.23 mumol/mol guanine at 24 h. O6-(4-OH-Bu)G in the same tissue was 7.7 +/- 3.19 mumol/mol guanine 3 h after treatment and 12.2 +/- 7.01 mumol/mol guanine at 24 h. O6-BuG and O6-(4-OH-Bu)G were always lower in the liver than in urothelial cells. Twenty-four hours after a single dose of 20 mg BBN, urothelial O6-BuG was 5.41 +/- 1.73 mumol/mol guanine and did not accumulate after six doses of 20 mg/rat BBN, since it was 2.59 +/- 1.23 mumol/mol guanine 24 h after the last dose. O6-BuG in liver DNA was detectable after the single dose of 20 mg, but not after 6 x 20 mg/rat BBN. O6-(4-OH-Bu)G was not detected in either the bladder or the liver after 20 mg or after the six doses of BBN.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of O6-methylguanine on DNA damage and cytotoxicity of temozolomide in L1210 mouse leukemia sensitive and resistant to chloroethylnitrosoureas

Temozolomide is a new anticancer agent which in the early clinical investigation has shown promising antitumor activity. It decomposes spontaneously to the active metabolite of DTIC (MTIC). Temozolomide is more cytotoxic against L1210 than against a subline L1210/BCNU, resistant to chloroethylnitrosoureas. Using [methyl-3H] temozolomide we found that after 1 h exposure the amount of O6-methylguanine (O6mGua) was twice as high in L1210 than in L1210/BCNU whereas the amount of N7 mGua was approximately the same in the two cell lines. O6-alkylguanine DNA alkyltransferase (AT) levels were higher in L1210/BCNU than in L1210, supporting the view that the resistance to methyltriazenes is probably related to the efficient repair of O6mGua in L1210/BCNU. Exposure of L1210/BCNU cells to 0.4 mM O6mGua for 24 h resulted in a depletion of AT and in a higher temozolomide-induced cytotoxicity. In the sensitive cell line L1210, temozolomide activity was not potentiated by O6mGua pretreatment. Moreover, in L1210/BCNU, O6mGua increased DNA single-strand breaks caused by temozolomide, suggesting that O6-guanine alkylation induces an excision repair mechanism in cells depleted in AT.

DNA damage induced by alachlor after in vitro activation by rat hepatocytes

We investigated the ability of alachlor to cause DNA damage by measuring single-strand breaks (SSB) in DNA, after metabolic activation by freshly isolated rat hepatocytes. Incubation of different concentrations of alachlor with rat hepatocytes led to numerous metabolites. The majority, isolated and identified by GC-MS analysis, were products arising from reactions catalyzed by the P-450 monooxygenase system, arylamidase and flavin mixed-function oxidase/cytochrome P-450 monooxygenase. The results, using freshly isolated rat hepatocytes, showed that in these conditions several potentially DNA damaging metabolites were produced; this experimental condition was used to assess DNA damage induced by the mixture of alachlor and its metabolites. The alkaline elution technique showed that at 200 microM and more clearly at 400 microM there were some small fragments that eluted in the first fraction. This fragmentation was probably due to alachlor cytotoxicity. In addition to the small DNA fragments eluting in the first fraction there were other larger DNA fragments. These DNA-SSB were most evident at the alachlor concentration of 400 microM, but also at 200 microM and 100 microM, whereas at 10 microM the DNA elution rate appeared comparable to that of controls. The results suggest that some unstable and DNA-reactive metabolites might interact with DNA causing SSB and such interaction might be important in relation to the mechanism of alachlor-induced DNA damage. However, it may not be possible to clarify whether SSB are the result of direct DNA interaction of the compound or of secondary cellular processes after chemical treatment.

O6-methylguanine inhibits the binding of transcription factors to DNA

To study the effect of methylation of O6-guanine on the binding of cellular factors to different DNA sequences, modified oligonucleotides were constructed, in which O6-Methylguanine (O6-MeG) replaced some guanines. The DNA sequences utilized were: the region of the c-fos promoter containing the binding site for serum response factor (SRF); the region of the HIV LTR containing two binding sites for the transcription factor NF kappa B; the region of the HIV LTR containing three binding sites for the cellular factor sp1. After incubation of labeled oligonucleotides, either unmodified or containing O6-MeG, with nuclear extracts obtained from different cell lines, gel retardation assays indicated that the presence of O6-MeG resulted in inhibition of binding of cellular factors to DNA sequences located in the promoter regions of genes. This inhibition was not the same for all modified oligonucleotides but dependent on the position in which O6-MeG was located. The results obtained indicate that alkylation of O6-guanine affects the binding of transcription factors and thereby possibly the regulation of genes expression.

Determination of O6-butylguanine in DNA by immunoaffinity extraction/gas chromatography-mass spectrometry

A sensitive, specific, and rapid method for quantitating the minor adduct O6-butylguanine (O6BuG) in hydrolyzed DNA has been developed by combining immunoaffinity chromatography and high resolution gas chromatography-negative ion chemical ionization-mass spectrometry. Polyclonal antibodies raised against O6BuG were coupled to CNBr-activated Sepharose 4B and used for sample clean-up and extraction of the specific O6-alkylguanine. After addition of O6BuG and its deuterium labeled analogue (O6BuG-D7), used as internal standard, hydrolyzed DNA was applied on the immunoaffinity column and washed with water, and the immunoadsorbed butylated guanines were eluted with acetone/water cetome/water (95/5) before gas chromatographic derivatization. O6BuG and O6BuG-D7 were analyzed and quantitated by high resolution gas chromatography-negative ion chemical ionization-mass spectrometry as their pentafluorobenzyl-trimethylsilyl derivatives. Immunoaffinity column capacity and O6BuG recovery from this column were 1.53 nmol O6BuG/column and 62 +/- 5%, respectively. The method was applied to evaluate O6BuG levels in DNA butylated in vitro with 10 mM N-nitroso-Nr-butylurea or isolated from rats given an i.p. dose of 185 mg/kg N-nitroso-N-butylurea or N-nitrosodibutylamine. In the first case the level of modifications present in calf thymus DNA was 104 mumol O6BuG/mol guanine, and in the second case O6BuG in liver DNA was about 6 times higher after N-nitroso-N-butylurea (2.11 mumol O6BuG/mol guanine) than after N-nitrosodibutylamine (0.34 mumol O6BuG/mol guanine) treatment. These results indicate that O6BuG formed in vivo can be isolated and quantitated by this method, which may also be useful for studying DNA damage and repair mechanisms.

Alpha-oxidative metabolism of the bladder carcinogens N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine within the rat isolated bladder

The most widely accepted metabolic pathway leading to the formation of reactive intermediates from nitrosamines involves enzymatic hydroxylation at the carbon atom alpha to the nitroso moiety. All subsequent steps are non-enzymatic reactions and the final result is the stoichiometric formation of a cationic product and molecular nitrogen. Thus the amount of molecular nitrogen evolved can be used as an indicator of alpha-hydroxylation. The use of doubly 15N-labelled nitrosamines and the detection of 15N2 by MS makes it simpler to measure the extent of alpha-hydroxylation. We have studied the alpha-oxidation of doubly 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine (BBN) and its metabolite N-nitrosobutyl(3-carboxypropyl)amine (BCPN), two potent urinary bladder carcinogens in animals, within the target organ. Various amounts of 15N-labelled BBN ranging from 0.1 to 5 mumol were incubated at 37 degrees C for 4 h in the isolated rat bladder and the formation of 15N2 was measured by GC-MS. 15N2 production was linear up to 1 mumol and represented approximately 0.1% of the substrate incubated. Time-course experiments showed that 15N2 production was linear over a 6 h incubation period, ranging from 2.16 +/- 0.05 to 4.55 +/- 0.33 nmol/mg urothelial cell protein. 15N-labelled BCPN (1-5 mumol) was also incubated within the rat isolated bladder. 15N2 production from BCPN was approximately 10 times less than that from BBN. The results indicate that, though to a lower extent, the target organ activates 15N-labelled BBN and BCPN through the alpha-hydroxylation pathway.

Pharmacokinetic profile and metabolism of N-nitrosobutyl-(4-hydroxybutyl)amine in rats

N-Nitrosodibutylamine and its omega-hydroxylated metabolite N-nitrosobutyl(4-hydroxybutyl)amine (NB4HBA) induce tumors in the urine bladder of different animal species through their common urinary metabolite N-nitrosobutyl(3-carboxypropyl)amine (NB3CPA), resulting from the oxidation of the alcoholic group of NB4HBA to a carboxylic group. NB4HBA disappearance from blood, the formation of its main metabolites, NB3CPA and NB4HBA-glucuronide (NB4HBA-G), and their urinary excretion, were investigated in rats after an i.v. dose of 1 mg/kg (5.7 mumol/kg). NB3CPA and NB4HBA-G formation was readily detectable 2 min after treatment and levels were still measurable at 120 and 30 min, respectively. The parent compound disappeared from blood 90 min after injection. The NB4HBA blood concentration-time profile was adequately described by a one-compartmental linear model. NB4HBA half-life was 8 min, total body clearance and renal clearance were 86.1 and 0.22 ml/min/kg, respectively. The 0-96-h urinary excretion of NB4HBA was 0.3% of the administered dose. NB3CPA half-life was 15 min; NB3CPA and NB4HBA-G urinary excretion were 36 and 11.7%, respectively, urinary excretion of known compounds accounting for less than 50%. After i.v. injection of NB3CPA equimolar to the NB4HBA dose, only 50% of unchanged compound was recovered in the urine and after NB4HBA-G, 41% of the administered dose was excreted unchanged, NB3CPA accounting for 10%. Thus NB3CPA and NB4HBA-G might undergo further biotransformation, suggesting that NB3CPA may not be the ultimate carcinogen responsible for urinary bladder tumor induction.

Development of an experimental model for studying bladder carcinogen metabolism using the isolated rat urinary bladder

The isolated rat urinary bladder was used to study this organ's capacity to metabolize chemical carcinogens. In our experimental conditions, the urinary bladder carcinogen N-nitrosobutyl(4-hydroxybutyl)amine was oxidized to N-nitrosobutyl(3-carboxypropyl)amine. A time-dependent increase was observed in the amount of N-nitrosobutyl(3-carboxypropyl)amine formed and simultaneous disappearance of N-nitrosobutyl(4-hydroxybutyl)amine added, indicating that the bladder can metabolize N-nitrosobutyl(4-hydroxybutyl)amine to the metabolite considered responsible for tumor induction in the urinary bladder of laboratory animals. At 15, 30, 60, and 120 min the percentages of N-nitrosobutyl(3-carboxypropyl)amine formed were 11, 22, 36, and 64%, respectively, and 62, 48, 37, and 26% of N-nitrosobutyl(4-hydroxybutyl)amine remained unchanged. When N-nitrosodibutylamine was introduced into the isolated urinary bladder and incubated for 120 min, its oxidized metabolites N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine were formed, amounting to, respectively, 0.13 and 0.06% of the substrate added. The glucuronide of N-nitrosobutyl(4-hydroxybutyl)amine was incubated in the isolated rat urinary bladder both as a buffer and as a urine solution in order to detect cellular and urinary beta-glucuronidase activity. In both systems N-nitrosobutyl(4-hydroxybutyl)amine released was about 1% at 4 h and this percentage did not increase at 6 h. N-Nitrosobutyl(3-carboxypropyl)amine was detectable at 2 h and reached 0.2% of the substrate incubated at 6 h. The results indicate that the urinary bladder may play a role in activating bladder carcinogens.

Effect of butylated hydroxyanisole on in vitro and in vivo nitrosation of dibutylamine

The effect of the food additive butylated hydroxyanisole on the nitrosation of dibutylamine was studied in vitro and in vivo, in rats. At the highest concentration tested, butylated hydroxyanisole significantly inhibited the in vitro formation of N-nitrosodi-n-butylamine from dibutylamine and nitrite by 35%. This effect was not observed in animals given dibutylamine, NaNO2 and butylated hydroxyanisole by gavage in the same ratio that produced an effect in vitro. The oral administration of butylated hydroxyanisole to rats given 0.5% nitrate in the drinking water and dibutylamine (0.38 mmol/kg 3 times/day p.o.) was also with no effect, although the experimental model used proved suitable for studying the modulating effect on endogenous nitrosation of different chemicals such as ascorbic acid or potassium thiocyanate. The discrepancy between in vitro and in vivo results is discussed.