Cardiovascular disease risk factors associated with low level of physical activity in postmenopausal Polish women

OBJECTIVES

To determine whether physical activity level could have an effect on cardiovascular disease (CVD) risk factors in Polish postmenopausal women.

METHODS

We studied the associations of physical activity (PA) level with obesity indices, unfavorable lipid profile parameters and the insulin resistance index HOMA in 343 postmenopausal Polish women selected from an urban population, aged 50-60.

RESULTS

In the tested sample, a low level of PA significantly increased odds ratios for CVD risk factors such as BMI ≥ 30 kg/m(2), total body fat (TBF) > 75 th percentile, gynoid fat deposit (GFD) > 75 th percentile, total cholesterol (TC) ≥ 5 mM, low-density lipoprotein cholesterol (LDL-C) > 3 mM and HOMA ≥ 1.95.

CONCLUSIONS

Obesity and some metabolic CVD risk factors in postmenopausal women are directly associated with low PA level. Postmenopausal urban women should be persuaded to be physically active, as even moderate activity level seems to be sufficient to reduce the CVD risk in this group of individuals.

ADRB3 and PPARγ2 gene polymorphisms and their association with cardiovascular disease risk in postmenopausal women

OBJECTIVES

The contribution of heritability to the development of cardiovascular disease (CVD) is of interest as the identification of genes enhancing the susceptibility of individuals to CVD may help the design of clinical interventions optimized for the individual's genome.

METHODS

We studied the associations of polymorphism of ADRB3 and PPARγ2 genes with obesity indices, unfavorable lipid profile parameters and insulin resistance index HOMA in 343 postmenopausal women.

RESULTS

No association was found between tested polymorphisms and CVD risk factors such as total cholesterol ≥ 5.0 mmol/l, high density lipoprotein cholesterol < 1.2 mmol/l, low density lipoprotein cholesterol > 3.0 mmol/l and triacylglycerols > 1.7 mmol/l. The presence of arterial hypertension and HOMA value ≥ 1.95 were also not related to these polymorphisms. A significant association between PPARγ2 gene polymorphism and total body fat mass (odds ratio = 1.90 at p = 0.037) as well as android fat deposit mass (odds ratio = 1.82 at p = 0.048) was found.

CONCLUSIONS

CVD risk factors in postmenopausal women are not directly associated with the polymorphisms of PPARγ2 and ADRB3 genes. We suggest that some indirect link between PPARγ2 gene polymorphism and susceptibility of postmenopausal women to CVD may exist. This suggestion is based on our finding that high total body fat mass and high android fat deposits are associated with the presence of the Pro12Ala allele of the PPARγ2 gene.

Cytotoxicity, cellular uptake and DNA damage by daunorubicin and its new analogues with modified daunosamine moiety

Daunorubicin (DRB) and its two analogues containing a trisubstituted amidino group at the C-3' position of the daunosamine moiety have been compared regarding their cytotoxic activity, cellular uptake, subcellular localization and DNA damaging properties. An analogue containing in the amidino group a morpholine moiety (DRBM) as well as an analogue with a hexamethyleneimine moiety (DRBH), tested against cultured L1210 cells, exhibited lower cytotoxicity then DRB. The decrease of cytotoxic activity was not related to cellular uptake and subcellular localization of drugs. Although all tested drugs were active in the induction of DNA breaks and DNA-protein crosslinks, they differed in the mechanism of induction of DNA lesions. DRB produced DNA breaks mediated solely by topoisomerase II, whereas DRBM and DRBH induced two types of DNA breaks by two separate processes. The first is related to the inhibition of topoisomerase II and the second presumably reflects a covalent binding of drug metabolites to DNA. It is hypothesized that the replacement of the primary amino group (-NH(2)) at the C-3' position of the daunosamine moiety by a trisubstituted amidino group (-N=CH-NRR) may be a route to the synthesis of anthracycline derivatives with enhanced ability to form covalent adducts to DNA.

Inhibition of RNA synthesis in vitro and cell growth by anthracycline antibiotics

New derivatives of doxorubicin and daunorubicin with amidine group bonded to daunosamine at C-3' atom and bearing the morpholine ring attached to the amidine group have been recently synthesized. Their cytotoxic activities and effects on RNA synthesis in vitro were assayed. The drug concentrations inhibiting mouse leukaemia L1210 cell growth to 50% were about two- and three fold higher for the derivatives compared to doxorubicin and daunorubicin respectively. Inhibition of phage T7 RNA polymerase by the non-covalently interacting derivatives was also slightly lower than that by the parent compounds. As doxorubicin and daunorubicin, their amidine derivatives in the presence of dithiothreitol and Fe(III) ions are activated and covalently bind to DNA. The adducts formed affect RNA polymerase activity. Several bands corresponding to prematurely terminated RNA chains are observed by means of polyacrylamide gel electrophoresis. The patterns of bands are virtually identical for all the anthracyclines studied here and are similar to the terminations induced by actinomycin D. This observation is consistent with a notion that the adducts are formed at guanine in GpC sequences which are also binding sites of actinomycin D. A substantial difference between daunorubicin and its amidine derivative is shown by means of high performance liquid chromatography. The derivative undergoes rapid rearrangements in the presence of dithiothreitol and Fe(III) ions, while daunorubicin is stable for several hours under these conditions. The results presented here indicate that the amidine derivatives despite bulky morpholine substitution exhibit biological activity in the systems used here.

Uptake of acridinecarboxamide derivatives by L1210 cells

The uptake of six 9-aminoacridinecarboxamide derivatives by L1210 cells in relation to their lipophilicity and cytotoxic activity was studied. The amount of acridines taken up by cells was estimated by fluorimetric measurements. It was found that the uptake efficiency of this class of compounds by cells depends on the size of carboxamide residue as well as on position of the substituent. The increase of size of carboxamide chain resulted in the loss of capability of acridines to penetrate cell membrane. Cytotoxic effects of acridines were well correlated with the level of drugs accumulated by cells, whereas no clear correlation between uptake and lipophilicity was observed. It is concluded that uptake of 9-aminoacridinecarboxamides is the most important factor determining their antiproliferative activity.

Uptake of acridinecarboxamide derivatives by L1210 cells

The uptake of six 9-aminoacridinecarboxamide derivatives by L1210 cells in relation to their lipophilicity and cytotoxic activity was studied. The amount of acridines taken up by cells was estimated by fluorimetric measurements. It was found that the uptake efficiency of this class of compounds by cells depends on the size of carboxamide residue as well as on position of the substituent. The increase of size of carboxamide chain resulted in the loss of capability of acridines to penetrate cell membrane. Cytotoxic effects of acridines were well correlated with the level of drugs accumulated by cells, whereas no clear correlation between uptake and lipophilicity was observed. It is concluded that uptake of 9-aminoacridinecarboxamides is the most important factor determining their antiproliferative activity.

Cytotoxic and DNA-damaging properties of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and its analogues

An antitumor drug N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and its three close structural analogs N-[2-(hydroxyethylamino)ethyl]acridine-4-carboxamide (DACAH), N-[2-(dimethylamino)ethyl]-9-aminoacridine-4-carboxamide (amino-DACA), and N-[2-(hydroxyethylamino)ethyl]-9-aminoacridine-4-carboxamide (amino-DACAH) were studied for their ability to inhibit RNA synthesis in vitro and to form topoisomerase II-mediated DNA lesions in relation to cell-killing activity. All tested compounds induced chromatin lesions characteristic of topoisomerase II-blocking drugs (DNA breaks and DNA-protein cross-links) in treated cells, but were much less active than reference antileukemic acridine m-AMSA (4'-(9-acridinylamino)-methanesulfon-m-anisidide). The ability to form these lesions was dependent on the structure of the 4-carboxamide side-chain, which seems to be an important factor affecting the drug transport rate through cell membrane. A 4-carboxamide chain with an N-2-(dimethylamino)ethyl moiety resulted in more efficient transport through cell membranes, higher cytotoxicity, and DNA-damaging activity. The mode of action of acridine-4-carboxamides was further elucidated by their incubation with cells in the presence of antitopoisomerase II agents of a known mechanism of inhibition. These were: bisdioxopiperazine (ICRF-187), a catalytic inhibitor of topoisomerase II, and etoposide (VP-16), an inducer of a cleavable complex of the enzyme with DNA. The cytotoxicity of DACA and its analogs was not antagonized by preincubating cells with ICRF-187. All tested acridines protected cells against DNA breakage induced by VP-16, but the extent of protection varied significantly. Amino-DACA, which easily penetrates cell membrane, fully inhibited DNA break formation, whereas other analogs exhibited a low degree of protection when used at high concentration. Our results suggest that the acridine-4-carboxamides discussed here are poor topoisomerase II poisons and that this enzyme is not their main target.

Inhibition of mammalian topoisomerase I by 1-nitro-9-aminoacridines. Dependence on thiol activation

The cytotoxic activity, susceptibility to thiol activation and ability of eight 1-nitroacridine derivatives to stabilize the topoisomerase I-DNA cleavable complex, were compared. Among the acridines tested three compounds exhibited high ability to stabilize the cleavable complex. This ability was correlated with susceptibility to thiol activation as well as with cytotoxic activity. Our results suggest that 1-nitroacridine-DNA adducts interfering with topoisomerase I action may contribute to the lethal effects of some 1-nitroacridine derivatives.

Inhibition of mammalian topoisomerase I by 1-nitro-9-aminoacridines. Dependence on thiol activation

The cytotoxic activity, susceptibility to thiol activation and ability of eight 1-nitroacridine derivatives to stabilize the topoisomerase I-DNA cleavable complex, were compared. Among the acridines tested three compounds exhibited high ability to stabilize the cleavable complex. This ability was correlated with susceptibility to thiol activation as well as with cytotoxic activity. Our results suggest that 1-nitroacridine-DNA adducts interfering with topoisomerase I action may contribute to the lethal effects of some 1-nitroacridine derivatives.

Nitracrine and its congeners--an overview

1. An anticancer drug, nitracrine 1-nitro-9(3'3'-dimethylaminopropylamino)acridine (Ledakrin, C-283) exhibits potent cytostatic effects which can be ascribed to interactions of the drug with DNA. 2. The reduction of the nitro group of nitracrine is one of the activation steps leading to the drug covalent binding to DNA and proteins both in subcellular systems and in the cell. 3. DNA-drug non-covalent interactions and covalent complexes are examined in several model systems and compared with the properties of a number of derivatives with programmed structural changes. 4. DNA-protein crosslinks and interstrand crosslinks are detected in the cells following exposition to the drug. 5. The drug exhibits selective toxicity and radiosensitization effects to hypoxic mammalian cells.

Are lethal effects of nitracrine on L5178Y cell sublines associated with DNA-protein crosslinks?

Nitracrine (Ledakrin, 1-nitro-9-(3,3-N,N-dimethylaminopropylamino)-acridine) is of interest as a DNA intercalator and alkylator with very high cytotoxic potency, especially against hypoxic cells. DNA-DNA crosslinks [Konopa et al., Chem Biol Interact 43: 175-197, 1983; Pawlak et al., Cancer Res 44: 4289-4296, 1984] or DNA-protein crosslinks (DPCs) [Woynarowski et al., Biochem Pharmacol 38: 4095-4101, 1989; Szmigiero and Studzian, Biochim Biophys Acta 1008: 339-345, 1989] are related to the toxicity of the drug. The cytotoxic effect of and DNA damage induced by nitracrine were measured in two sublines of mouse lymphoma L5178Y, LY-R (resistant to ionizing radiation) and LY-S (sensitive to ionizing radiation). LY-R cells were more sensitive to nitracrine (D10 = 0.11 microM) than LY-S (D10 = 0.35 microM) when treated for 1 hr at 37 degrees. To a DNA-DNA crosslinking agent, mitomycin C, the comparative sensitivity was opposite. LY-R cells were more resistant to this drug than LY-S cells (D10 = 7.1 vs 2.3 microM). DNA damage induced by nitracrine was measured by the alkaline elution method and by nitrocellulose filter binding assay. Nitracrine treatment with biologically relevant concentrations (0.1-3.0 microM, 1 hr, 37 degrees) induced only DPCs. Interstrand crosslinks and DNA breaks were not detected. Nitracrine produced about two times more DPCs in LY-R cells than in LY-S cells. Both sublines removed 50% of initial lesions during 2 hr post-treatment incubation. The greater sensitivity of LY-R cells to nitracrine is thus not related to the efficiency of DNA repair, but may be a consequence of enhanced initial damage in the form of DPCs. This finding is consistent with the latter lesion being responsible for the cytotoxicity of nitracrine.

Effects of alkylating metabolites of ifosfamide and its bromo analogues on DNA of HeLa cells

The in vitro cytotoxicity and mechanism of action of three alkylating compounds: an active metabolite of ifosfamide (1, isophosphoramide mustard, N,N'-bis(2-chloroethyl)phosphorodiamidic acid) and its bromo substituted analogues, 2 (one chlorine atom replaced by bromine atom) and 3 (two chlorine atoms replaced by bromine atoms), were studied in cultured HeLa cells. Alkaline elution analysis of cellular DNA demonstrated the presence of concentration- and time-dependent interstrand crosslinks, DNA-protein crosslinks and alkali-labile sites (ALSs) in HeLa cells following a 1 hr exposure to the compounds. The bromo analogues were more cytotoxic than 1 and exhibited higher crosslinking potency. The time-course of crosslink formation and removal for the three compounds was similar. ALSs in DNA were produced by all tested drugs but 3 exhibited exceptionally high activity and was able to induce two kinds of alkali-labile lesion (fast- and slow-appearing) whereas 1 and 2 generated only slow-appearing ones. The results suggest that 1 and 2 are more specific in their reaction with DNA in that they produced a lesser variety of lesions than 3. A potential advantage of 2 over 1 seems to be its higher DNA interstrand crosslinking activity.

Induction of DNA-protein crosslinks by antitumor 1-nitro-9-aminoacridines in L1210 leukemia cells

Ledakrin [1-nitro-9-(3'-dimethylamino-N-propylamino)acridine], an antitumor drug of the 1-nitro-9-aminoacridine family, was able to induce DNA-protein crosslinks in intact L1210 leukemia cells, as demonstrated by the potassium-dodecyl sulfate precipitation technique. Ledakrin-induced DNA-protein crosslinks were not readily reversible nor were they accompanied by DNA double-strand breaks. Also, ledakrin produced virtually no crosslinks in isolated nuclei. Ledakrin-induced DNA-protein crosslinks seemed not to be mediated by topoisomerase II, unlike well-established effects of a chemically related antitumor drug, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). Four ledakrin analogs of divergent cytotoxic potencies also induced DNA-protein crosslinks but not DNA double-strand breaks in intact L1210 cells. A significant positive correlation existed between the ability of ledakrin and its 1-nitro analogs to induced DNA-protein crosslinks and the antiproliferative effects of these drugs. The results are consistent with the previously shown ability of 1-nitro-9-aminoacridines to covalently bind to macromolecules after metabolic activation in the cell. In addition to previously demonstrated DNA interstrand crosslinks and monofunctional adducts, DNA-protein crosslinks constitute another type of DNA lesion induced by 1-nitro-9-aminoacridines.

DNA damage and cytotoxicity of nitracrine in cultured HeLa cells

The effects of nitracrine (1-nitro-9-(3,3-N,N-dimethylaminopropylamino)acridine on DNA of cultured HeLa cells were studied. DNA strand breakage and interstrand cross-linking as well as DNA-protein cross-linking were measured by means of an alkaline elution technique and were compared with the cytotoxic effect of the drug. Interstrand cross-links were not detectable in the concentration range that inhibited cell growth up to 99%. DNA single-strand breaks were found when cells were treated with highly cytotoxic doses of the drug. DNA breakage was not reparable and exhibited a tendency to increase during incubation after drug removal. The only chromatin lesion induced by sublethal doses of nitracrine were DNA-protein cross-links which persisted for 24 h after drug treatment. It is concluded that DNA breaks represent degraded DNA from dying cells, whereas DNA-protein cross-links are specific cellular lesions, which may be responsible for the cell-killing effect of nitracrine.

In vitro binding of nitracrine to DNA in chromatin

In the presence of sulfhydryl compounds nitracrine, an anticancer drug, binds covalently to DNA. The accessibility of DNA in chromatin both to nitracrine and to 8-methoxypsoralen, which was used as a reference compound in this study, when assayed in NaCl concentrations from 0 to 2 M show similar characteristics. The initial decrease reaches a minimum at 0.15 M NaCl above which dissociation of non-histone proteins and histones at higher ionic strengths is demonstrated by an increase in accessible sites. The relative accessibility of DNA in chromatin to nitracrine is, however, lower than that found for 8-methoxypsoralen. Partial dissociation of chromatin with 0.7 M NaCl increases the accessibility of DNA in chromatin when assayed in the absence of NaCl but has no apparent influence when estimated at ionic strength close to physiological conditions.

DNA binding, cytotoxicity and inhibitory effect on RNA synthesis of two new 1-nitro-9-aminoacridine dimers

Two 1-nitro-9-aminoacridine dimers were prepared: one bearing a spermine flexible linking chain, compound 4, the other a rigid dipiperidine-type linker, compound 7. Both dimers elicited a higher affinity constant for DNA than the parent monomeric drug nitracrine 2. This affinity was several orders lower than what was found for other dimeric compounds having the same linkers and no nitro group on the acridine ring (3, 5, 6 and 8). Bisintercalation was evidenced for compound 4 by viscosimetric measurements. In the absence of dithiothreitol, an inhibitory effect of RNA synthesis in vitro was observed for all the tested compounds except 2 and 7. In the presence of dithiothreitol, 4 and 7 formed irreversible complexes with DNA of decreased template properties. The level of the dimers binding was lower than that of the parent compound 2. Cross-links were detected by means of hydroxylapatite chromatography in a complex of the dimer bearing a flexible linking chain, compound 4 with DNA, while the compound 7-DNA complex eluted in the single-stranded DNA region. The extent of cytotoxicity of the two 1-nitro-9-aminoacridine dimers against L1210 cultured cells was different.

Inhibition of DNA-dependent RNA synthesis by 8-methoxypsoralen

The effect of the photobinding of 8-methoxypsoralen to phage T7 DNA on different steps of RNA synthesis in vitro was assayed. Total RNA synthesis is reduced to a few percent and the transcript size is decreased, as shown by means of gel filtration on a Sepharose 4B column when DNA of the adduct content of six drug molecules per 10(3) nucleotides is used. The initiation of RNA chains seems to be less affected, as inferred from an abortive initiation assay. Synthesis of pppApU on DNA of the same adduct content is inhibited to 34% of the corresponding controls, while the overall RNA synthesis is inhibited to 6%. The amount of the enzyme needed for maximal retention of DNA, the kinetics of its binding and the decay of the polymerase-DNA complex at high ionic strength (or on decrease of the temperature) are similar with DNA either irradiated in the absence of the drug or DNA bearing six 8-methoxypsoralen molecules per 10(3) nucleotides. It is concluded from this study that 8-methoxypsoralen partially inhibits initiation and blocks movement of RNA polymerase along the template, inducing premature termination. It does not appear to influence the binding of the enzyme to DNA.

H2O2 as a DNA fragmenting agent in the alkaline elution interstrand crosslinking and DNA-protein crosslinking assays

A method for DNA fragmentation by H2O2 in the DNA alkaline elution procedure is described. Treatment of cell suspensions for 1 h with 100 microM H2O2 or 5 mM H2O2 at 0-1 degree C resulted in DNA breakage equivalent to doses of 300 and 3000 rad of gamma-rays, respectively. The elution profiles were reproducible and H2O2 was used for measurements of interstrand crosslinks and DNA-protein crosslinks induced in HeLa cells by mitomycin C, cis-diamminedichloroplatinum(II), and trans-diamminedichloroplatinum(II). The comparison of data obtained with the use of H2O2 and gamma-rays has shown that both methods have similar sensitivity and reproducibility.

Thyroliberin and other neurohormones have no detectable direct effect on RNA synthesis in isolated nuclei

Effect of thyroliberin, somatostatin, vasopressin and luliberin on RNA synthesis in isolated calf pituitary, brain cortex, rat liver and rat brain nuclei was assayed. None of the examined neuropeptides affected RNA synthesis.

A filter incubation method for the determination of potentially crosslinkable sites in DNA in mammalian cells

A method for the determination of DNA monoadducts capable of forming interstrand crosslinks in mammalian cells is described. Such monoadducts were produced by brief treatment of cells with cis-diamminedichloro-Pt(II) (cis-DDP), 1-(2-chloroethyl)-1-nitrosourea (ClEtNU), L-phenylalanine mustard (L-PAM), or diaziridinylbenzoquinone (AZQ). The method is an alkaline elution procedure in which the DNA from lysed cells is incubated on polycarbonate filters at pH 10 and 37 degrees C. During this incubation, the progressive formation of interstrand crosslinking was observed in drug-treated cells. In the case of ClEtNU and AZQ, DNA strand breaks also formed, due to the presence of labile lesions in the DNA. This made quantitation of interstrand crosslinks difficult for these drugs. For cis-DDP and L-PAM, however, there was no significant production of strand breaks and the assay for interstrand crosslinks was quantifiable.

DNA strand scission and cross-linking by diaziridinylbenzoquinone (diaziquone) in human cells and relation to cell killing

The effects of 3,6-diaziridinyl-2,5-bis(carboethoxyamino)-1,4-benzoquinone (diaziquone; AZQ) on various cell types were studied in relation to two chemical reactivities that this drug would be expected to have intracellularly. AZQ can undergo a reduction-oxidation cycle of the quinone function; this could generate free radicals which could produce DNA damage, especially DNA strand scission. The second reactivity, based on the two aziridine groups, could produce alkylation reactions that could produce DNA cross-links. DNA strand breakage and cross-linking were measured by alkaline elution and were compared with cell killing assayed by colony survival. Among the cell strains studied (human IMR-90, VA-13, and HT-29 and mouse L1210), marked differences were found in the magnitudes of DNA strand breakage and interstrand cross-linking produced by AZQ. Most striking, IMR-90 cells exhibited substantial strand breakage and little or no interstrand cross-linking, whereas the reverse was true for HT-29 cells. Cell killing correlated well with interstrand cross-linking but did not correlate with strand scission in these cell lines. It is concluded that AZQ produces DNA strand breaks and interstrand cross-links by different mechanisms which vary independently among different cell lines.

Mechanisms of DNA strand breakage and interstrand cross-linking by diaziridinylbenzoquinone (diaziquone) in isolated nuclei from human cells

AZQ had been found to produce DNA strand breaks and interstrand cross-links in intact cells; evidence had indicated that these two DNA lesions arise by different chemical mechanisms and vary independently in degree in different cell types. In the present work, the mechanisms of the production of DNA strand breaks and interstrand cross-links by AZQ were studied in isolated cell nuclei. This system avoided the problem of poor penetration of test substances into cells. The DNA lesions were measured by means of the alkaline elution technique. It was found that the production of DNA strand breaks by AZQ in isolated nuclei required the addition of a reducing agent such as NADPH and was almost completely prevented by superoxide dismutase. This indicates that the mechanism of DNA strand breakage involves transfer of an electron from a reduced form of AZQ to molecular oxygen. Unexpectedly, interstrand cross-linking also was enhanced greatly by previous reduction of AZQ by NADPH or NaBH4. However, this reaction was not inhibited by superoxide dismutase. General alkylating activity of AZQ also was stimulated by reduction; the pH-dependence of this reaction was determined. The mechanism of DNA interstrand cross-linking by AZQ was surmised to stem from alkylation reactions of the two aziridine groups. The findings suggest the possibility that AZQ or related compounds may function as bioreductive alkylating agents which might be selectively toxic to hypoxic tissues.

Effect of intercalating and groove-binding ligands on formation of covalent complexes between nitracrine (Ledakrin, C-283) or 8-methoxypsoralen and DNA

The effect of ethidium bromide, actinomycin D, distamycin A and netropsin on covalent binding of nitracrine (1-nitro-9-(3,3-N,N-dimethylaminopropylamino)acridine, Ledakrin, C-283) and 8-methoxypsoralen to DNA was examined. The competition was assayed either directly with [3H]- and [14C]nitracrine or indirectly by estimation of transcriptional template activity of nitracrine-DNA and 8-methoxypsoralen-DNA complexes formed in the presence of the ligands. A higher protective effect of ethidium bromide and distamycin on the photo-binding of 8-methoxypsoralen than on the dithiothreitol-dependent attachement of nitracrine to DNA assayed at 0.15 M KCl or NaCl was observed. The non-intercalating antibiotics showed lower competitive effect on 8-methoxypsoralen binding than ethidium bromide. Actinomycin D showed relatively low competition for both drugs with DNA. In contrast to the reaction of 8-methoxypsoralen, the decrease of nitracrine binding in the presence of competing ligands considerably depends on ionic strength. Particularly high inhibition of the adduct formation in the presence of ethidium at 1 M KCl was shown, while the amount of nitracrine bound in the presence of distamycin increases at elevated ionic strength. The results may indicate steric demands of the reaction between nitracrine and DNA.

Thiol-dependent inhibition of RNA synthesis in vitro by acridines: structure-inhibition relationships

In the presence of sulfhydryl compounds an anticancer drug, 1-nitro-9-aminoalkylacridine derivative, forms with DNA irreversible, probably covalent, complexes of decreased template properties. Five 9-substituted 1-nitro-9-aminoacridine derivatives of cytostatic activity show irreversible thiol-dependent inhibitory effects on the RNA synthesis in vitro system while equal inhibition is observed both in the presence and in the absence of dithiothreitol with biologically inactive analogues of nitrocrine. In the absence of sulfhydryl compounds the inhibition depends on the planarity of the acridine ring. Hence, both 1-nitro-9-aminoalkylacridine and tetrahydroacridine derivatives show low inhibitory effect.

Some properties of the irreversible complexes of nitracrine (ledakrin, C-283) with polynucleotides

In the presence of sulfhydryl compounds an anticancer drug nitracrine (NA), 1-nitro-9-aminoalkylacridine derivative forms strong, probably covalent complexes with DNA. It has been found that it binds with similar efficiency to RNA and DNA exhibiting a certain preference for single-stranded structure. At NA/polynucleotide ratio of 0.15 and nucleic acids concentration 100 microgram/ml the numbers of drug molecules bound per 10(3) nucleotides were about 10--13 for native calf thymus DNA, 19--28 for denatured DNA and 23--36 for RNA. Some base specificity to guanine is observed both in polydeoxyribo- and polyribonucleotides. The complexes of NA with DNA and double-stranded synthetic polynucleotides exhibit decreased transcriptional template activity in bacterial RNA synthesis in vitro system except poly(A) synthesis on poly(dA) x poly(dT) which is insensitive to the drug. The drug binding in vitro leads to cross-link formation in DNA as shown by means of ultraviolet spectrophotometry and hydroxylapatite chromatography of heat-denatured NA-DNA complexes. The amount of the double bonds introduced by the drug is however relatively low as compared with cross-linking of irradiated 8-methoxy-psoralen-DNA (MOP-DNA) complexes.