Measurements of alkali-labile DNA damage and protein-DNA crosslinks after 2450 MHz microwave and low-dose gamma irradiation in vitro

In vitro experiments were performed to determine whether 2450 MHz microwave radiation induces alkali-labile DNA damage and/or DNA-protein or DNA-DNA crosslinks in C3H 10T(1/2) cells. After a 2-h exposure to either 2450 MHz continuous-wave (CW) microwaves at an SAR of 1.9 W/kg or 1 mM cisplatinum (CDDP, a positive control for DNA crosslinks), C3H 10T(1/2) cells were irradiated with 4 Gy of gamma rays ((137)Cs). Immediately after gamma irradiation, the single-cell gel electrophoresis assay was performed to detect DNA damage. For each exposure condition, one set of samples was treated with proteinase K (1 mg/ml) to remove any possible DNA-protein crosslinks. To measure DNA-protein crosslinks independent of DNA-DNA crosslinks, we quantified the proteins that were recovered with DNA after microwave exposure, using CDDP and gamma irradiation, positive controls for DNA-protein crosslinks. Ionizing radiation (4 Gy) induced significant DNA damage. However, no DNA damage could be detected after exposure to 2450 MHz CW microwaves alone. The crosslinking agent CDDP significantly reduced both the comet length and the normalized comet moment in C3H 10T(1/2) cells irradiated with 4 Gy gamma rays. In contrast, 2450 MHz microwaves did not impede the DNA migration induced by gamma rays. When control cells were treated with proteinase K, both parameters increased in the absence of any DNA damage. However, no additional effect of proteinase K was seen in samples exposed to 2450 MHz microwaves or in samples treated with the combination of microwaves and radiation. On the other hand, proteinase K treatment was ineffective in restoring any migration of the DNA in cells pretreated with CDDP and irradiated with gamma rays. When DNA-protein crosslinks were specifically measured, we found no evidence for the induction of DNA-protein crosslinks or changes in amount of the protein associated with DNA by 2450 MHz CW microwave exposure. Thus 2-h exposures to 1.9 W/ kg of 2450 MHz CW microwaves did not induce measurable alkali-labile DNA damage or DNA-DNA or DNA-protein crosslinks.     

Characterization of adriamycin-resistant human breast cancer cells which display overexpression of a novel resistance-related membrane protein

Development of multidrug resistance due to overexpression of P-glycoprotein (Pgp), a cell membrane drug efflux pump, occurs commonly during in vitro selections with adriamycin (Adr). Pgp-mediated drug resistance can be overcome by the calcium channel blocker verapamil (Vp), which acts as a competitive inhibitor of drug binding and efflux. In order to identify other mechanisms of Adr resistance, we isolated an Adr-resistant subline by selecting the human breast cancer cell line MCF-7 with incremental increases of Adr in the presence of 10 microgram/ml verapamil. The resultant MCF-7/AdrVp subline is 900-fold resistant to Adr, does not overexpress Pgp, and does not exhibit a decrease in Adr accumulation. It exhibits a unique cross-resistance pattern: high cross-resistance to the potent Adr analogue 3'-deamino-3'-(3-cyano-4-morpholinyl)doxorubicin, lower cross-resistance to the alkylating agent melphalan, and a sensitivity similar to the parental cell line to vinblastine. The levels of glutathione and glutathione S-transferase are similar in the parental line and the Adr-resistant subline. Topoisomerase II-DNA complexes measured by the potassium-sodium dodecyl sulfate precipitation method shows a 2-3 fold decrease in the resistant subline. The MCF-7/AdrVp cells overexpress a novel membrane protein with an apparent molecular mass of 95 kDa. Polyclonal antibodies raised against the P-95 protein demonstrate a correaltion between the level of expression and Adr resistance. Removal of Adr but not verapamil from the selection media results in a decline in P-95 protein levels that parallels a restoration of sensitivity to Adr. Immunohistochemistry demonstrates localization of the P-95 protein on the cell surface. The demonstration of high levels of the protein in clinical samples obtained from patients refractory to Adr suggests that this protein may play a role in clinical drug resistance.     

Formation of DNA adducts by formaldehyde-activated mitoxantrone.

Recent studies with the anthracycline Adriamycin have demonstrated its activation by formaldehyde and subsequent binding to DNA in vitro. Since formaldehyde levels are known to be higher in cells of myeloid origin and the structurally related drug mitoxantrone is most effective against cancers of myeloid origin, this indicates a possible role of formaldehyde in the activation of mitoxantrone. In vitro studies revealed that the activation of mitoxantrone by formaldehyde leads to the formation of drug-DNA adducts. These adducts stabilised DNA such that they functioned as virtual interstrand crosslinks. The interstrand crosslinks were formed in the presence of mitoxantrone and formaldehyde in a time- and concentration-dependent manner. In the absence of formaldehyde no crosslinks were formed, indicating a key role in drug activation and DNA binding. The adducts (virtual crosslinks) were relatively unstable with 50% crosslinks remaining after 10 min at 60 degrees C in 45% formamide. Like Adriamycin, the mitoxantrone-formaldehyde-DNA crosslinks are heat labile and do not display the stability associated with covalent interstrand crosslinks.     

Synthesis and monoamine transporter binding properties of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes

A series of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes were prepared and evaluated for affinities at dopamine, serotonin, and norepinephrine transporters using competitive radioligand binding assays. The 2beta-[3'-(substituted benzyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (3a-h) showed high binding affinities for the dopamine transporter (DAT). The IC(50) values ranged from 5.9 to 22nM. On the other hand, the 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (4a-h), with IC(50) values ranging from 65 to 173nM, were approximately 3- to 25-fold less potent than the corresponding 2beta-[3'-(substituted benzyl)isoxazol]tropanes. All tested compounds were selective for the DAT relative to the norepinephrine transporter (NET) and serotonin transporter (5-HTT). 3Beta-(4-Methylphenyl)-2beta-[3'-(4-fluorobenzyl)isoxazol-5-yl]tropane (3b) with IC(50) of 5.9nM at the DAT and K(i)s of 454 and 113nM at the NET and 5-HTT, respectively, was the most potent and DAT-selective analog. Molecular modeling studies suggested that the rigid conformation of the isoxazole side chain in 4a-h might play an important role on their low DAT binding affinities.     

60 Hz magnetic field exposure induces DNA crosslinks in rat brain cells

In previous research, we found an increase in DNA strand breaks in brain cells of rats acutely exposed to a 60 Hz magnetic field (for 2 h at an intensity of 0.5 mT). DNA strand breaks were measured with a microgel electrophoresis assay using the length of DNA migration as an index. In the present experiment, we found that most of the magnetic field-induced increase in DNA migration was observed only after proteinase-K treatment, suggesting that the field caused DNA-protein crosslinks. In addition, when brain cells from control rats were exposed to X-rays, an increase in DNA migration was observed, the extent of which was independent of proteinase-K treatment. However, the X-ray-induced increase in DNA migration was retarded in cells from animals exposed to magnetic fields even after proteinase-K treatment, suggesting that DNA-DNA crosslinks were also induced by the magnetic field. The effects of magnetic fields were also compared with those of a known DNA crosslink-inducing agent mitomycin C. The pattern of effects is similar between the two agents. These data suggest that both DNA-protein and DNA-DNA crosslinks are formed in brain cells of rats after acute exposure to a 60 Hz magnetic field.     

Comparison of the reactions of chemically reactive analogs of U-G-A and of A-U-G with ribosomes of Escherichia coli.

The chemically reactive analog of U-G-A, 5'-(4-(Bromo-[2-14C] acetamido) phenylphospho) - uridylyl-(3'-5') - guanylyl-(3'-5') adenosine has a 20 fold lower affinity to 70S ribosomes than the corresponding analog of A-U-G though the U-G-A analog also preferentially reacts with protein S18 of 70S ribosomes. This reaction programs ribosomes for EF-T dependent Trp-tRNATrp-suIII binding. Therefore, it is concluded that this protein is part of the A'-site of the ribosomal codon binding site. Reaction of the U-G-A analog with 30S subunits lead to a predominant crosslinking of U-G-A to proteins S4 and S18. In contrast, a comparable reaction of the A-U-G analog with 30S subunits lead to a predominant crosslinking of A-U-G to proteins S4 and S12 (Pongs, O., Stoffler, G.A., Lanka, E., (1975) J. Mol. Biol. 99, 301). Since protein S12 is located at the 'P' site of the ribosomal codon binding site, it is proposed that the U-G-A analog does not bind at this site.     

DNA damage induced by carcinogenic lead chromate particles in cultured mammalian cells.

Particulate lead chromate is a highly water-insoluble cytotoxic and carcinogenic agent, but its mechanism of action remains obscure. We investigated its effects on DNA damage in CHO cells after a 24-h exposure using alkaline or neutral filter elution and cytogenetic studies. Concentrations (0.08, 0.4 and 0.8 micrograms/cm2), which reduced the colony-forming efficiency of CHO cells to 94, 50 and 10%, respectively, produced dose-dependent DNA single-strand breaks and DNA-protein crosslinks, but no DNA double-strand breaks or DNA-DNA crosslinks were observed. The single-strand breaks were absent from cells given a 24-h recovery period after removal of the treatment medium, even though most of the particles remained adhered to cells and to the culture dish. In contrast, both the DNA-protein crosslinks and chromosomal aberrations persisted even after the 24-h recovery period. These results suggest that the mechanism of the particle-induced early DNA single-strand breaks may be different from DNA-protein crosslinks and the lesions leading to chromosomal aberrations, or alternatively, that the repair of single-strand breaks is more efficient than the repair of DNA-protein crosslinks in the unavoidable continuing presence of carcinogen. These results also suggest that the chromosome damage may be related to the persistent DNA-protein crosslinks, and further confirm the genotoxic activity of carcinogenic lead chromate particles.     

Two-dimensional nuclear magnetic resonance studies of an intercalation complex between the novel semisynthetic anthracycline 3'-deamino-3'-(2-methoxy-4-morpholinyl)-doxorubicin and the hexanucleotide duplex d(CGTACG).

The complex of the hexanucleotide duplex d(CGTACG) and the antitumor drug 3'-(2-methoxy-4-morpholinyl)-doxorubicin was investigated by two-dimensional 1H nuclear magnetic resonance spectroscopy. After complete assignment of the non-exchanging DNA protons and nearly all drug protons, eight nuclear Overhauser enhancement interactions between drug and DNA were measured at short mixing times. A model was built which shows that the overall structure is very similar to the related daunomycin complex, with the new morpholinyl-substituent extending further into the minor groove of the DNA double helix. The structural information is used for the discussion of the possible formation of DNA-adducts by the new anticancer drug.     

Adriamycin disrupts phosphatidylserine import into the mitochondria of permeabilized CHO-K1 cells

The action of adriamycin (an inhibitor of precursor protein import into mitochondria) upon phosphatidylserine (PtdSer) import into mitochondria was examined in permeabilized CHO-K1 cells. The decarboxylation of nascent PtdSer to phosphatidylethanolamine was used as an indicator reaction for the lipid translocation process. Adriamycin was without effect upon new PtdSer synthesis but blocked the time- and translocation-dependent decarboxylation of this lipid at the mitochondrial inner membrane of permeabilized cells. The effect of adriamycin was concentration-dependent with an IC50 of 150 microM and was not due to direct inhibition of PtdSer decarboxylase. To determine at which level of PtdSer transport adriamycin was working, the adriamycin-treated permeabilized cells were incubated with 1-acyl-2-[N-(6-[(7-nitrobenz-2-oxa-1,3-diazo-4-yl)] aminocaproyl)]phosphatidyl[1'-14C] serine (NBD-Ptd[1'-14C]Ser), and its decarboxylation was determined. Since the NBD-Ptd[1'-14C]Ser freely partitions into all cell membranes, it can partition into the outer mitochondrial membrane in an ATP-independent fashion. The NBD-Ptd[1'-14C]Ser was readily decarboxylated in an ATP-independent manner in permeabilized cells. Adriamycin inhibited the decarboxylation of NBD-Ptd[1'-14C]Ser, thereby indicating that it can act upon lipid transport processes between the outer and inner mitochondrial membrane.     

CB 1954 (2,4-dinitro-5-aziridinyl benzamide) becomes a DNA interstrand crosslinking agent in Walker tumour cells

Walker tumour cells were shown to be uniquely sensitive to CB 1954 when compared with other cells in vitro. CB 1954 forms DNA-DNA interstrand crosslinks in a time-dependent manner in Walker tumour but not Chinese hamster cells. The absence of interstrand crosslinks in hamster cells was not due to a lack of uptake of drug but rather to a failure to convert (probably by bioreduction) CB 1954 to the required reactive difunctional intermediate.     

A continuous fluorometric assay for cytochrome P-450-dependent mixed function oxidases using 3-cyano-7-ethoxycoumarin

A direct fluorometric procedure for the continuous determination of cytochrome P-450-dependent mixed function oxidases, using 3-cyano-7-ethoxycoumarin substrate, is described. The reaction product, 3-cyano-7-hydroxycoumarin, is fluorescent at neutral pH values (excitation and emission wavelength maxima: 408 and 450 nm, respectively). Using hepatic microsomal preparations from control rats, the enzyme(s) had an apparent Km of 16 microM. Vmax values (0.5 nmol/min/mg protein) were induced 6- and 21-fold by pretreatment of rats with phenobarbitone and about 50- to 100-fold more sensitive than the ethoxyresorufin deethylase assay. Reaction rates using 3-cyano-7-pentoxycoumarin as substrate were generally much lower than with the ethoxy analog. 3-Cyano-7-ethoxycoumarin can also be used as a substrate to measure mixed function oxidases in isolated hepatocytes. However, 3-cyano-7-hydroxycoumarin shows a time- and concentration-dependent loss of fluorescence when incubated with such cells. This causes an approximately 5% underestimate of the true reaction rates.     

Structurally diverse 5-substituted pyrimidine nucleosides as inhibitors of Leishmania donovani promastigotes in vitro

The following structurally diverse 5-substituted-2'-deoxyuridine nucleosides displayed potent in vitro antileishmanial activity: 5-formyl, 5-(2,2,-dicyanovinyl)-, 5-(2-cyano-2-ethoxycarbonylvinyl), 5-(2-cyano-2-methoxycarbonylvinyl)-, 5-(2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-chromen-4-yl)- and related congeners, and the 5-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-4H-pyrazol-4-ylidene) group.     

Analysis of chromate-induced DNA-protein crosslinks with the comet assay

Modifications of the comet assay have been introduced to measure crosslinks by determining the reduction of induced DNA migration. Our previous results indicated that the modified protocol of the alkaline comet assay is a sensitive tool for the detection of formaldehyde-induced DNA-protein crosslinks. But results for mitomycin C and cisplatin suggested that the modified protocol is not well suited for the evaluation of DNA-DNA crosslinkers. We now used the comet assay to investigate in V79 cells the effect of potassium chromate (K(2)CrO(4)), another DNA-protein crosslinker, to see whether the results obtained for formaldehyde can be generalized. However, chromate did not reduce spontaneous or radiation-induced DNA migration in the alkaline (pH 13) comet assay but led to a small but significant induction of DNA migration. A crosslinking effect of chromate could also not be detected with the alkaline comet assay after postincubation of cells in normal medium after chromate treatment to enable repair of other (migration-inducing) lesions that might mask the crosslinking effect. Exposure of slides to proteinase K further increased DNA migration of chromate-treated cells, thus indicating the presence of DNA-protein crosslinks. In contrast to the alkaline comet assay, a "neutral" version at pH 9 was suited to demonstrate reduced induction of DNA migration after gamma-irradiation of chromate-treated cells. The crosslinking effect was seen immediately at the end of the chromate treatment as well as after a 3h postincubation period. Using the "neutral" protocol in combination with proteinase K, we were able to demonstrate the presence of DNA-protein crosslinks as the probable cause for the migration-reducing effect. Further investigations will have to show whether this protocol can be recommended as a universal approach for the detection of DNA-protein crosslinks and also of DNA-DNA crosslinks with the comet assay.     

The stereochemical course of thiophosphoryl group transfer catalyzed by T4 polynucleotide kinase

The stereochemical course of the phosphoryl transfer reaction catalyzed by T4 polynucleotide kinase has been determined using the chiral ATP analog, (Sp)-adenosine-5'-(3-thio-3-[18O]triphosphate). T4 polynucleotide kinase catalyzes the transfer of the gamma-thiophosphoryl group of (Sp)-adenosine-5'-(3-thio-3-[18O]triphosphate) to the 5'-hydroxyl group of ApA to give the thiophosphorylated dinucleotide adenyl-5'-[18O]phosphorothioate-(3'-5')adenosine. A sample of adenyl-5'-[18O]phosphorothioate-(3'-5')adenosine was subjected to venom phosphodiesterase digestion. The resulting adenosine-5'-[18O]phosphorothioate was shown to have the Rp configuration, thus indicating that the thiophosphoryl transfer reaction occurs with overall inversion of configuration of phosphorus.     

Effect of JH III and substituted oxime ethers on the in vitro protein and RNA synthesis in male accessory reproductive gland (MARG) of Spodoptera litura (F.)

The physiological action of two substituted oxime ethers namely: 4'-(2,6,6-trimethyl-2-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-propylether (compound No. 3) and 4'-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-pentylether (compound No. 34,) were compared with that of JH III in an in vitro assay to monitor the synthesis of RNA and protein in male accessory reproductive gland (MARG) of Spodoptera litura by using 3H-leucine and 3H-uridine, respectively. Both the compounds have stimulated protein synthesis compare to control. Compound No 34 is slightly more effective than JH III in increasing the protein synthesis at physiological concentration of 10(-6) and 10(-5) M. Compound No 3 and JH III have doubled the RNA synthesis and increased the protein synthesis by 1.5 times over the control at 10(-4) to 10(-6) M concentrations. While JH III at 10(-5) M significantly enhanced RNA synthesis, similar effect is produced only at 10(-3) M by compound No 3 and 34.     

Dithiocarbamic acid esters as anticancer agent. Part 1: 4-substituted-piperazine-1-carbodithioic acid 3-cyano-3,3-diphenyl-propyl esters

A variety of 4-N atom substituted derivatives were synthesized and evaluated for their in vitro anticancer activities using 4-methylpiperazine-1-carbodithioic acid 3-cyano-3,3-diphenyl-propyl ester 4 as lead compound. Among them, compound 6a without any substituent on 4-N atom (R(1) = H) was found to be the most active anticancer agent with IC(50) = 5.3 microM against HL-60 and IC(50) = 11.5 microM against Bel-7402, respectively. Increase in the polarity and/or introduction of suitable acyl groups at the 4-N atom of the lead compound 4 are favorable for the improvement of activity.     

3'-(N-hydroxyimino)-2',3-dideoxynucleosides and their derivatives: synthesis, broad spectrum antiviral properties and synthetical application for the preparation of other nucleoside analogues.

A series of 3'-(N-hydroxyimino)-2',3'-dideoxynucleosides bearing different nucleic bases has been prepared. In vitro antiviral activity studies showed that among these compounds the thymine derivative possesses significant activity against HIV, HSV, EBV and HBV. Conveniently 5'-protected 3'-(N-hydroxyimino)-2',3'-dideoxythymidine was further used as a synthon for the preparation of other nucleoside analogues.     

2,2-Bis(ethoxycarbonyl)- and 2-(alkylaminocarbonyl)-2-cyano-substituted 3-(pivaloyloxy)propyl groups as biodegradable phosphate protections of oligonucleotides

Oligonucleotides bearing biodegradable phosphate protecting groups have been synthesized on a solid support. For this purpose, two dimeric building blocks, viz. 5'-O-(4,4'-dimethoxytrityl)-(R(P),S(P))-O(P)-[2,2-bis(ethoxycarbonyl)-3-(pivaloyloxy)propyl]-P-thiothymidylyl-(3',5')-thymidine 3'-[O-(2-cyanoethyl)-N,N-diisopropylphosphoramidite] (1) and 5'-O-(4,4'-dimethoxytrityl)-(R(P),S(P))-O(P)-[2-cyano-2-(2-phenylethylaminocarbonyl)-3-(pivaloyloxy)propyl]thymidylyl-(3',5')-thymidine 3'-(H-phosphonate) (2), were prepared. Phosphoramidite 1 was incorporated into an phosphorothioate oligothymidylate sequence on a base-labile hydroquinone-O,O'-diacetic acid linker (Q-linker) and on a photolabile 4-alkoxy-5-methoxy-2-nitrobenzyl carbonate linker (11). H-Phosphonate 2 was, in turn, incorporated into an oligothymidylate sequence only on the photolabile linker. Kinetics of the removal of the protecting groups by porcine liver esterase and subsequent retro aldol condensation/phosphate elimination were then studied. While the pro-oligonucleotide that contained only one phosphate protection gave the deprotected phosphorothioate oligonucleotide in a quantitative yield, the enzymatic step was markedly decelerated upon increasing the number of protection groups, and hence chain cleavage started to compete.     

Synthesis of novel analogues of marine indole alkaloids: mono(indolyl)-4-trifluoromethylpyridines and bis(indolyl)-4-trifluoromethylpyridines as potential anticancer agents.

Mono(indolyl)-4-trifluoromethylpyridines and bis(indolyl)-4-trifluoromethylpyridines were synthesized using Suzuki cross-coupling reaction between 2-chloro-4-trifluoromethylpyridine 9, 2,6-dichloro-4-trifluoromethylpyridine 6 or 2,6-dichloro-3-cyano-4-trifluoromethylpyridine 23 and N-tosyl-3-indolylboronic acid 10. They were evaluated for cytotoxic activity against P388 and A-549 cells with IC(50) values. 4-Trifluoromethyl-2,6-bis[3'-(N-tosyl-6'-methoxylindolyl)]pyridine 18 was identified as the most potent in this series.     

Evaluation of substituted oxime ethers for growth regulatory activity against Spodoptera litura (F.)

Insect growth regulatory activity (IGR) of fifty-two substituted oxime ethers were evaluated against an important polyphagous lepidopteran crop pest, Spodoptera litura (F.). A number of compounds produced symptoms comparable to exogenously applied juvenile hormone. Maximum IGR activity was exhibited by 4'-(2,6,6-trimethyl-2-cyclohexen- -yl)-3'-buten-2'(E)-ketoxime-N-O-alkyl ether with an ED50 (morphological) of 40 microg g(-1) body weight, compared to 20 microg g(-1) of JH III. Two more compounds namely 4'-(2,6,6-trimethyl-2-cyclohexen-1-yl)-3'-buten-2'(Z)-ketoxime-N-O-methyl propyl ether (ED50 192 microg g(-1)) and 4'-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-pentyl ether (ED50 380 microg g(-1)) showed considerable IGR activity, whereas 4'-(2,6,6-trimethyl-2-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-pentyl ether was found to be toxic to the larvae (ED50 268 microg g(-1)). Three compounds used in this study were also synergised by piperonyl butoxide (PBO). The synergistic ratios were found in the range of 1.33 to 4.605. The ovicidal activity of the oxime ethers is not significant.