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G Ciarrocchi

Publications and source records attributed to G Ciarrocchi.

At least 37 records · Page 2Linked to original sources
PubMed1992

DNA binding properties of FCE24517, an electrophilic distamycin analogue.

The distamycin derivative FCE24517 binds both reversibly and irreversibly to DNA. At 37 degrees C, the drug originates reversible complexes that are strong enough to survive to the electrophoretic separation of the substrate. These complexes slowly evolve to covalent adducts (10(-4) adducts/bp/h) that eventually degenerate to single-strand breaks (1.5 x 10(-5) nicks/bp/h). The site of attack by the drug can be any base in the vicinity of AT-rich regions of the double helix. Rapidly reassociating duplex DNA molecules, indicative of the presence of cross-links, are observed only upon boiling of DNA with FCE24517. While the low rates of formation of covalent adducts and DNA breaks could be relevant for the long-term biological effects of FCE24517, the specific formation of strong but still reversible complexes with DNA could be matched to the drastic and sudden reduction of thymidine incorporation induced by this electrophilic distamycin.

Antineoplastic Agents↗
PubMed1991

Correlation between anthracycline structure and human DNA ligase inhibition.

A total of 19 anthracycline derivatives were tested for their ability to interfere in vitro with the action of the human replicative DNA ligase. Only those with the sugar devoid of unmodified amino groups or with large configurational modifications were found to be inactive. Maximal inhibition of DNA-joining activity was found to require a 4'-deoxy-3'-amino sugar. Self-adenylation of DNA ligase was largely insensitive to these drugs. An important general finding is that slight modifications of the anthracycline structure have pronounced effects on DNA-ligase-inhibitory activity and might be related to the specificity of anthracycline anti-tumour activity.

Adenosine Monophosphate↗
PubMed1991

Specific inhibition of human DNA ligase adenylation by a distamycin derivative possessing antitumor activity.

The antiviral distamycin A and its phenyl mustard derivative FCE24517 possessing antitumor activity were tested for their ability to inhibit macromolecular synthesis in three human and one murine cell line. While distamycin A was poorly active in these systems, FCE24517 inhibited DNA synthesis efficiently, RNA synthesis to a lower extent and had little effect on protein synthesis. These findings suggest that the in vivo activity of FCE24517 derives from the specific inhibition of DNA synthesis. When the two drugs were tested on several enzymes involved in human DNA metabolism a strikingly similar pattern of inhibition appeared, with distamycin A being the more potent. Both drugs showed: A), no inhibitory activity against thymidine kinase and DNA primase; B), low activity against DNA topoisomerases I and II and the 3'-5' exonuclease associated with the DNA polymerase epsilon; C), high activity against DNA polymerases alpha and epsilon, uracil-DNA glycosylase and the joining activity of the replicative DNA ligase; D), the highest inhibitory activity against the AMP-dependent DNA relaxing activity of DNA ligase. The strong in vitro inhibition of several DNA enzymatic activities, including DNA ligase, do not match with the in vivo activities of the two drugs. However a unique difference was observed: only FCE24517 inhibited the DNA-independent reaction of adenylation of human DNA ligase while the adenylation reaction of T4 and E. coli DNA ligase was unaffected by either drug. It is still unclear whether these properties are relevant for modulating the killing activity of FCE24517 against proliferating cells both in culture and in vivo. Nevertheless FCE24517 is the first known molecule capable of interacting directly and specifically with human DNA ligase.

Adenosine Monophosphate↗
PubMed1990

Use of ATP, dATP and their alpha-thio derivatives to study DNA ligase adenylation.

Bacteriophage-T4 and human type I DNA ligases were found capable of self-adenylating upon exposure to both ribo- and deoxyribo-[alpha-35S]thio-ATP. However, the joining reaction does not take place in the presence of the deoxyribotriphosphates. Enzyme adenylation is reversed in all cases by an excess of PPi, but the rate of reversion is lower with thio derivatives. Therefore thio derivatives can be used to study the adenylation of DNA ligases and to search for specific inhibitors of the first step of the ligation reaction. In addition we show that thio derivatives can be used to detect DNA ligase adenylation activity covalently bound to a solid matrix.

Adenosine Triphosphate↗
PubMed1990

The effect of the minor groove binding agent DAPI (4,6-diamidino-2-phenyl-indole) on DNA-directed enzymes: an attempt to explain inhibition of plasmid expression in Escherichia coli [corrected].

The activity of DAPI, on a number of DNA-directed enzymes involved in DNA topology, transcription, replication and repair, is reported in this paper. DAPI was always more inhibitory than ethidium bromide, in particular against RNA polymerase and DNA ligase, which seemed to be specifically affected. While the effect on RNA polymerase is likely due to a preferential occupancy of the promoter region, that on DNA ligase could rely upon a mechanism of steric hindrance in the minor groove. These phenomena, independently from an alteration of the tertiary structure of DNA by the ligand, can account for the previously reported inhibition of plasmid expression in Escherichia coli.

DNA Ligases↗
PubMed1990

Effects of DNA-binding drugs on T4 DNA ligase.

A number of DNA intercalating and externally binding drugs have been found to inhibit nick sealing, cohesive and blunt end ligation, AMP-dependent DNA topoisomerization and EDTA-induced DNA nicking mediated by bacteriophage T4 DNA ligase. The inhibition seems to arise from drug-substrate interaction so that formation of active DNA-Mg2(+)-AMP-enzyme complex is impaired while assembled and active complexes are not disturbed by drug binding to the substrate.

Adenosine Monophosphate↗
PubMed1990

Structure-activity relationships of N2-substituted guanines as inhibitors of HSV1 and HSV2 thymidine kinases.

A series of N2-phenylguanines was synthesized and tested for inhibition of the thymidine kinases encoded by Herpes simplex viruses type 1 and type 2. Compounds with hydrophobic, electron-attracting groups in the meta position of the phenyl ring such as m-trifluoromethyl (m-CF3PG, IC50 = 0.1 microM) were the most potent inhibitors of both enzymes. Many derivatives were significantly more potent against the type 2 thymidine kinase, and can effectively discriminate between the two enzymes. Among other N2-substituted guanines, alkyl and benzyl derivatives were moderately potent inhibitors, and the type 2 enzyme was again more sensitive than the type 1 enzyme. None of the compounds inhibited the thymidine kinase isolated from the host HeLa cell line, suggesting that members of this class of compounds may be useful nonsubstrate, antiviral compounds for latent herpesvirus infections.

Chemical Phenomena↗
PubMed1989

A double-loop model for the replication of eukaryotic DNA.

Coordinated DNA synthesis of both strands at the replication fork by a fixed 'replisome' may cause dynamic and topological problems. Based upon known properties of DNA helicase, DNA primase and DNA topoisomerases, and on novel properties of DNA polymerases and DNA ligase, we propose a 'double-loop' model for the replication of eukaryotic DNA that could minimize such problems.

Animals↗
PubMed1989

Autoantibodies to DNA topoisomerase II in cryptogenic fibrosing alveolitis and connective tissue disease.

Sera from patients with autoimmune lung and connective tissue diseases were investigated for antibodies to topoisomerase II. Anti-topoisomerase II antibodies were detected by ELISA in 37% of sera from patients with cryptogenic fibrosing alveolitis (CFA), in one (8%) case of sarcoidosis and in 31% of sera from systemic lupus erythematosus (SLE) patients. Sera from rheumatoid arthritis, juvenile rheumatoid arthritis, progressive systemic sclerosis, Sjögren's syndrome and undifferentiated connective tissue disease were negative. CFA and sarcoidosis sera strongly reacted in immunoblotting with a 170 kD protein, also recognized by rabbit antiserum to recombinant topoisomerase II, while SLE sera presented a weak reaction. Pre-adsorption with dsDNA dramatically decreased the topoisomerase II binding in ELISA by the most positive SLE serum, but did not affect the binding by the most positive CFA serum, thus indicating that anti-topoisomerase II reactivity of SLE sera is probably due either to cross-reacting antibodies or, in part, to minor DNA contamination of our enzyme preparation. The determination of DNA topoisomerase II relaxation activity, performed after incubation with antibody-positive sera, showed that only CFA sera precipitate enzymatic activity. The finding that CFA presents antibodies to an enzyme essential to cell survival stresses the role of autoimmunity in the pathogenesis of idiopathic pulmonary fibrosis. This may offer further insight into the cause of autoimmune disease and prove a valuable tool in the study of enzyme molecular biology.

Adolescent↗
PubMed1989

Nucleoside analogs as non-substrate inhibitors of herpes simplex viruses thymidine kinase.

We have examined the capacity of a series of 6-substituted pyrimidine and 2-substituted purine derivatives to inhibit mammalian thymidine kinase and the thymidine kinases encoded by type 1 and type 2 herpes simplex viruses. Several N2-substituted guanine and deoxy guanosine derivatives displayed selective inhibitory activity against the HSV-1 and HSV-2 thymidine kinases by competing with the phosphorylation of thymidine, suggesting a possible novel pharmacological approach to herpes viruses infections.

Cells, Cultured↗
PubMed1988

Multiple roles of DNA ligase at the replication fork.

The loss of superhelical turns from a covalently closed duplex DNA exposed to bacteriophage T4 DNA ligase in the presence of AMP and Mg2+ has recently been found to be gradual and not sudden (Montecucco, A. and Ciarrocchi, G. (1988) Nucleic Acids Res. 16, 7369-7381). In this paper, we show that the AMP-dependent DNA relaxation catalyzed by human and E. coli DNA ligases also takes place according to a step-wise mechanism. DNA relaxation is inhibited by pyrophosphate, by ATP (or NAD in the case of the E. coli enzyme) and by high ionic strength and is essentially distributive with the human or T4 DNA ligases, and processive with the bacterial one. The AMP-dependent ability of DNA ligases to relax DNA might allow these enzymes to relieve possible topological complications of the nascent double helix generated by the replication of the lagging strand.

Adenosine Monophosphate↗
PubMed1988

AMP-dependent DNA relaxation catalyzed by DNA ligase occurs by a nicking-closing mechanism.

In the presence of AMP and Mg2+, a covalently closed duplex DNA containing negative superhelical turns was treated with DNA ligase isolated from bacteriophage T4-infected E. coli. This resulted in the gradual and not sudden loss of superhelical turns as for example in the case of type I DNA topoisomerase. All DNA products remain covalently closed. Since T4 enzyme-mediated DNA relaxation is inhibited by both pyrophosphate and by ATP this suggests that DNA relaxing and DNA joining activities probably coincide. EDTA addition in the presence of a large excess of enzyme, induces the formation of nicked DNA products while protein denaturing treatments are not very effective. Our observations might suggest an involvement of the relaxing activity of DNA ligase during the ligation process.

Adenosine Monophosphate↗
PubMed1988

DNA unwinding and inhibition of T4 DNA ligase by anthracyclines.

The ability to alter DNA tertiary structure of ten anthracycline derivatives whose antitumor potency is known was studied by an assay that makes use of nicked circular DNA and bacteriophage T4 DNA ligase. This assay allows the detection of tertiary structure alterations caused by DNA binding of both intercalating and non-intercalating drugs. The determination of these events can be obtained at different temperatures in the range of activity of DNA ligase. The results indicate that anthracyclines alter the DNA tertiary structure but this property does not correlate with their cytotoxic or antitumor activities. An additional interesting finding was that several anthracyclines inhibit T4 DNA ligase. The inhibition can be complete and is a cubic function of drug concentration. The inhibition of DNA ligase does not correlate with the ability of anthracyclines to alter the tertiary structure of DNA but is dependent from the presence of an amino group on the sugar ring.

Antibiotics, Antineoplastic↗