Biomedical subjects

B B Hasinoff

Publications and source records attributed to B B Hasinoff.

At least 19 recordsLinked to original sources

PubMed2002

Regulation of B16F1 melanoma cell metastasis by inducible functions of the hepatic microvasculature.

We have previously shown that circulating intravascular cells generally arrest by mechanical restriction in the hepatic sinusoids, causing rapid release of nitric oxide (NO) which is cytotoxic to these cells and inhibits their growth into metastatic tumours. Here, we present evidence that these NO-dependent cytotoxic mechanisms are susceptible to upregulation by lipopolysaccharide (LPS). Five x 10(5) fluorescently labelled melanoma cells were injected into the mesenteric vein of C57BL/6 mice to effect their localisation in the hepatic microvasculature. Test mice were then given 1 mg/kg LPS intraperitoneally (i.p.) to activate the microvascular cells. By electron paramagnetic resonance (EPR) spectroscopy, the expression of NO in the liver was significantly increased by 8 h in the LPS-treated mice. The non-selective NO synthase inhibitor L-NAME inhibited the induction of NO by LPS, while its inactive enantiomer D-NAME had no significant effect. Using immunohistochemistry (IHC), iNOS-positive microvascular cells were detected in the terminal portal venule (TPV) region of the liver 8 h after LPS stimulation. LPS treatment also increased the retention of melanoma cells in the liver between 8 and 24 h, especially in the TPV region. Eight hours after cell injection, local expression of VCAM-1 and ICAM-1 was detected by double-label immunohistochemistry at the sites of tumour cell arrest. Expression of these adhesion molecules was enhanced in mice treated with LPS. Using flow cytometry, 98% of the B16F1 melanoma cells expressed VLA-4, the counter receptor of VCAM-1, and approximately 1.5% expressed LFA-1, the counter receptor of ICAM-1. LPS did not significantly alter the expression of either counter receptor on melanoma cells in vitro or in vivo. By DNA end-labelling, the rates of melanoma cell apoptosis were significantly increased from 8 to 24 h in the TPV region (but not in the sinusoids) of LPS-treated mice. Fourteen days after tumour cell injection, the LPS-treated mice had a significantly smaller hepatic metastatic tumour burden than the control mice. These data suggest that LPS can inhibit the metastasis of melanoma cells in the liver by inducing the expression of NO and adhesion molecules by the hepatic endothelium. The induction of iNOS and the inducible cytotoxic effect of LPS appear to be primarily located within the TPV region of the liver acinus.

Animals↗

PubMed2001

High-throughput fluorescence flow-injection topoisomerase II inhibition assay.

A high-throughput fluorescence flow-injection assay is described, suitable for determining the catalytic inhibition of DNA topoisomerase II. The method, which separates high molecular mass trypanosome kinetoplast DNA from its decatenated product by centrifugation, should be useful for the rapid and accurate screening of potential anticancer topoisomerase II inhibitors and the determination of their inhibition constants. Advantages of the flow-injection method over agarose gel electrophoresis and radioactive centrifugation assays are that it is faster, more sensitive, highly linear in its response to product formation, and does not require the production of radioactive trypanosome kinetoplast DNA substrate.

Animals↗

PubMed2001

The use of serum levels of cardiac troponin T to compare the protective activity of dexrazoxane against doxorubicin- and mitoxantrone-induced cardiotoxicity.

PURPOSE: To compare the protective effect of dexrazoxane (DRZ) against cardiotoxicity induced by doxorubicin (DXR) and mitoxantrone (MTX). METHODS: Adult male spontaneously hypertensive rats (SHR) were treated with 1 mg/kg DXR (i.v.) or 0.5 mg/kg MTX (i.v.), either alone or 30 min after 25 mg/kg DRZ (i.p.) weekly for up to 12 weeks. Animals treated with DXR alone either died (n = 2) or were killed (n = 3) at a cumulative dose of 10 mg/kg. The severity of cardiac lesions (cytoplasmic vacuolization and myofibrillar loss) were graded semiquantitatively by light microscopy on a scale of 0 to 3. RESULTS: Cardiac lesions were observed in all SHR given DXR or MTX alone, and were attenuated in those given DRZ prior to either DXR (mean lesion scores 2.7 vs 1.5; P < 0.05) or MTX (mean lesion scores 2.0 vs 1.25; P < 0.05). Cardioprotection was also demonstrated by monitoring serum levels of cardiac troponin T (cTnT), which were elevated in all animals receiving DXR or MTX alone. These elevations were attenuated in SHR given the combination of DXR and DRZ (mean values 0.79 ng/ml vs 0.24 ng/ml; P < 0.05) and MTX and DRZ (mean values 0.19 ng/ml vs 0.04 ng/ ml; P < 0.05). Biochemical studies have shown that both DXR and MTX form potentially cardiotoxic complexes with iron. ADR-925 (the hydrolysis product of DRZ) and other chelators (EDTA, diethylenetriaminepentaacetic acid and desferrioxamine) removed Fe(III) from its complex with MTX or DXR. CONCLUSIONS: The present study showed that DRZ significantly attenuates the cardiotoxicity induced by DXR and MTX, and that this protective activity can be assessed by morphological evaluation of cardiac tissues and by monitoring the concentrations of cTnT in serum.

Animals↗

PubMed2001

Synthesis and biological activity of a photoaffinity etoposide probe.

The epipodophyllotoxin etoposide is a potent and widely used anticancer drug that targets DNA topoisomerase II. The synthesis, photochemical, and biological testing of a photoactivatable aromatic azido analogue of etoposide also containing an iodo group is described. This azido analogue should prove useful for identifying the etoposide interaction site on topoisomerase II. Irradiation of the azido analogue and an aldehyde-containing azido precursor with UV light produced changes in their UV--visible spectra that were consistent with photoactivation. The azido analogue strongly inhibited topoisomerase II and inhibited the growth of Chinese Hamster Ovary cells. Azido analogue-induced topoisomerase II--DNA covalent complexes were significantly increased subsequent to UV irradiation of drug-treated human leukemia K562 cells as compared to etoposide-treated cells. These results suggest that the photoactivated form of etoposide is a more effective topoisomerase II poison either by interacting directly with the enzyme or with DNA subsequent to topoisomerase II-mediated strand cleavage.

Animals↗

PubMed2001

The catalytic DNA topoisomerase II inhibitor dexrazoxane (ICRF-187) induces differentiation and apoptosis in human leukemia K562 cells.

The bisdioxopiperazines ICRF-187 (dexrazoxane), ICRF-193, and ICRF-154 are catalytic noncleavable complex-forming inhibitors of DNA topoisomerase II that do not produce protein-linked DNA strand breaks. In this study, we showed that bisdioxopiperazines induced erythroid differentiation, inhibited human leukemia K562 cell growth, and caused a slow induction of apoptosis. Dexrazoxane treatment caused DNA endoreduplication resulting in large highly polyploid cells. This result suggested the lack of a DNA topoisomerase II activity-based cell cycle checkpoint. The percentage of K562 cells that became apoptotic was much larger than the percentage of cells that stained for hemoglobin, suggesting that prior differentiation was not required for induction of apoptosis. Use of the Bcr-Abl tyrosine kinase inhibitor STI-571 resulted in a reduction in Bcl-xL levels and potentiation of dexrazoxane-induced apoptosis related to an earlier onset and more extensive cleavage of caspase-3. These results indicated that dexrazoxane-induced apoptosis is associated with a caspase-3 activation/cleavage pathway. In addition, these results were consistent with the antiapoptotic signaling function of Bcr-Abl to regulate expression of Bcl-xL. The ability of dexrazoxane to induce differentiation and apoptosis suggests that bisdioxopiperazines may be useful in treating some types of leukemia.

Antineoplastic Agents↗

PubMed2000

B16 melanoma cell arrest in the mouse liver induces nitric oxide release and sinusoidal cytotoxicity: a natural hepatic defense against metastasis.

The formation of liver metastases involves interactions between intravascular cancer cells and the hepatic microvasculature. Here we provide evidence that the arrest of intravascular B16F1 melanoma cells in the liver induces a rapid local release of nitric oxide (NO) that causes apoptosis of the melanoma cells and inhibits their subsequent development into hepatic metastases. B16F1 melanoma cells (5 x 10(5)) labeled with fluorescent microspheres were injected into the portal circulation of C57BL/6 mice. The production of NO in vivo was detected by electron paramagnetic resonance spectroscopy ex vivo using an exogenous NO-trapping agent. A burst of NO was observed in liver samples examined immediately after tumor cell injection. The relative electron paramagnetic resonance signal intensity was 667 +/- 143 units in mice injected with tumor cells versus 28 +/- 5 units after saline injection (P < 0.001). Two-thirds of cells arrested in the sinusoids compared with the terminal portal venules (TPVs). By double labeling of B16F1 cells with fluorescent microspheres and a TdT-mediated UTP end labeling assay, we determined that the melanoma cells underwent apoptosis from 4-24 h after arrest. The mean rate of apoptosis was 2-fold greater in the sinusoids than in the TPVs at 4, 8, and 24 h after injection (P < 0.05-0.01). Apoptotic cells accounted for 15.9 +/- 0.8% of tumor cells located in the sinusoids and 7.1 +/- 0.9% of tumor cells in the TPVs. The NO synthase inhibitor N(G)-nitro-L-arginine methyl ester completely blocked the NO burst (P < 0.001) and inhibited the apoptosis of B16F1 cells in the sinusoids by 77%. However, the rate of tumor cell apoptosis in the TPVs was not changed. There were 5-fold more metastatic nodules in the livers of N(G)-nitro-L-arginine methyl ester-treated mice (P < 0.05). The inactive enantiomer N(G)-nitro-D-arginine methyl ester had no effect on the initial NO burst or on apoptosis of tumor cells in vivo. Both annexin V phosphatidylserine plasma membrane labeling and DNA end labeling of apoptotic cells were demonstrated after a 5-min exposure (a time equivalent to the initial transient NO induction in vivo) of B16F1 cells to a NO donor in vitro. These results identify the existence of a natural defense mechanism against cancer metastasis whereby the arrest of tumor cells in the liver induces endogenous NO release, leading to sinusoidal tumor cell killing and reduced hepatic metastasis formation.

Animals↗

PubMed2000

The catalytic DNA topoisomerase II inhibitor dexrazoxane (ICRF-187) induces endopolyploidy in Chinese hamster ovary cells.

The bisdioxopiperazines, including dexrazoxane (ICRF-187), are catalytic or noncleavable complex-forming inhibitors of DNA topoisomerase II that do not produce DNA strand breaks. In this study we show that dexrazoxane inhibits the division of Chinese hamster ovary (CHO) cells resulting in marked increases in cell size (up to 80 microm in diameter), volume (up to 150-fold greater), and ploidy (as high as 32N). This last result indicates that the dexrazoxane-induced DNA reduplication was restricted to once per cell cycle. Kinetic analysis of the flow cytometry data indicated that the conversion between successively higher ploidy levels was progressively slowed at longer times of exposure to dexrazoxane. Both the protein and DNA content of dexrazoxane-treated CHO cells increased linearly over time in the same proportion. Light and electron microscopic studies of dexrazoxane-treated cells showed ring-like multilobulated nuclei. Immunohistochemical staining of dexrazoxane-treated cells showed that F-actin and acetylated alpha-tubulin were present in large, highly organized networks. Immunohistochemical staining of the dexrazoxane-treated CHO cells also showed that the topoisomerase II alpha colocalized with the DNA of the multilobulated nuclei. Staining of gamma-tubulin revealed that the dexrazoxane-treated cells contained multiple centrosomes, indicating that dexrazoxane prevents cytokinesis but not centrosome reduplication. It is concluded that dexrazoxane inhibits CHO cytokinesis in cells by virtue of its ability to inhibit topoisomerase II.

Animals↗

PubMed1999

Stereoselective metabolism of dexrazoxane (ICRF-187) and levrazoxane (ICRF-186).

A chiral HPLC method has been developed to separate razoxane (ICRF-159) in blood plasma into its enantiomers dexrazoxane (ICRF-187) and levrazoxane (ICRF-186). Dexrazoxane is clinically used as a doxorubicin cardioprotective agent and little is known of its in vivo metabolism. After intravenous administration of 20 mg/kg of razoxane to rats, the razoxane was eliminated from the plasma with a half-time of approximately 20 min. The levrazoxane:dexrazoxane ratio continuously increased with time to a value of 1.5 at 150 min, indicating that dexrazoxane is metabolized faster than levrazoxane. These results, confirmed with studies on liver supernatants, are consistent with the hypothesis that dihydropyrimidine amidohydrolase in the liver and kidney is responsible for the preferential metabolism of dexrazoxane in the rat compared to levrazoxane. It is possible that on a dose-per-dose basis marginally higher therapeutic levels of levrazoxane might be achieved in the heart tissue for a longer time compared to dexrazoxane due to dihydropyrimidine amidohydrolase-based metabolism in the liver and kidney. However, given the relatively small difference in elimination of the two enantiomers, it would be difficult to predict from this study whether or not dexrazoxane or levrazoxane might be more efficacious in reducing cardiotoxicity.

Animals↗

PubMed1999

The cardioprotective and DNA topoisomerase II inhibitory agent dexrazoxane (ICRF-187) antagonizes camptothecin-mediated growth inhibition of Chinese hamster ovary cells by inhibition of DNA synthesis.

Dexrazoxane (ICRF-187), which is clinically used to reduce doxorubicin-induced cardiotoxicity, has cell growth inhibitory properties through its ability to inhibit the catalytic activity of DNA topoisomerase II. A study was undertaken to investigate whether preincubating Chinese hamster ovary cells (CHO) with dexrazoxane prior to camptothecin treatment resulted in potentiation. Camptothecin is a DNA topoisomerase I poison. It was found that pretreating CHO cells with concentrations of dexrazoxane sufficient to strongly inhibit topoisomerase II for periods from 18 to 96 h resulted in significant antagonism of camptothecin-mediated growth inhibition. Lower concentrations that were sufficient to cause partial inhibition of topoisomerase II and partial dexrazoxane-mediated cell growth inhibition had little effect on camptothecin-mediated growth inhibition. Neither topoisomerase I protein levels nor camptothecin-induced topoisomerase I-DNA covalent complexes were affected by dexrazoxane concentrations that were sufficient to cause antagonism of camptothecin-induced growth inhibition. However, under these experimental conditions, dexrazoxane caused a decrease in DNA synthesis. Therefore, results presented here confirm the importance of the DNA synthesis-dependent replication fork interaction with topoisomerase I-DNA covalent complexes for the expression of camptothecin activity. It is concluded that dexrazoxane and camptothecin analogs should be used with caution in combination chemotherapy.

Animals↗

PubMed1999

Mechanisms of beneficial effects of probucol in adriamycin cardiomyopathy.

Probucol, a lipid-lowering drug, has been shown to offer protection against adriamycin-induced cardiomyopathy. In order to define the mechanism of this protection, we examined changes in antioxidants and lipid peroxidation in hearts as well as lipids in hearts and plasma from rats treated with either adriamycin or adriamycin and probucol with appropriate controls. Any potential free radical quenching as well as growth inhibitory effects of probucol were also examined using Chinese hamster ovary (CHO) cells in culture. In animal model, adriamycin caused a significant depression in glutathione peroxidase and increased plasma and cardiac lipids as well as lipid peroxidation. Probucol treatment modulated adriamycin-induced cardiomyopathic changes and increased glutathione peroxidase and superoxide dismutase activities. In the presence of adriamycin under hypoxic conditions, formation of adriamycin semiquinone radical was detected by ESR. The cell growth in these cultures was also inhibited by adriamycin in a dose-dependent manner. Probucol had no effect on adriamycin-induced growth inhibition as well as formation of semiquinone radicals. It is proposed that probucol protection against adriamycin cardiomyopathy is mediated by increased antioxidants and lipid-lowering without any effect on free radical production.

Animals↗

PubMed1999

Relative plasma levels of the cardioprotective drug dexrazoxane and its two active ring-opened metabolites in the rat.

A postcolumn derivatization reversed-phase high-pressure liquid chromatography method has been developed to detect and separate the one-ring open intermediates of dexrazoxane (ICRF-187) in blood plasma. Dexrazoxane is clinically used as a doxorubicin cardioprotective agent and may act by preventing iron-based oxygen-free radical damage through the iron-chelating ability of its one-ring open intermediates and its fully rings opened hydrolysis product ADR-925. Little is known of the in vivo metabolism of dexrazoxane to its one-ring open intermediates, which may be two of the active forms of dexrazoxane. The one-ring open intermediates were detected within 5 min of i.v. administration of dexrazoxane to rats, suggesting that dexrazoxane is rapidly metabolized in vivo. The plasma concentrations of the one-ring open intermediates varied from 4 to 9% and 6 to 24% of the dexrazoxane concentrations at 5 and 120 min, respectively. The relatively small changes in the levels of the one-ring open intermediates with time suggest that a dynamic steady state is occurring. The ratio of the concentrations of the two one-ring open intermediates was similar to that previously seen for the in vitro dihydropyrimidine amidohydrolase-catalyzed hydrolysis of dexrazoxane. These results are consistent with the hypothesis that dihydropyrimidine amidohydrolase in the liver and kidney is responsible for the metabolism of dexrazoxane in the rat.

Animals↗

PubMed1998

Comparison of the chronic toxicity of piroxantrone, losoxantrone and doxorubicin in spontaneously hypertensive rats.

Comparisons were made of the toxic effects produced in the heart, kidney and small intestine of spontaneously hypertensive rats (SHR) by the administration of 12 consecutive weekly doses of doxorubicin (1 mg/kg), and high, intermediate and low doses of piroxantrone (3, 1.5 and 0.75 mg/kg) and losoxantrone (1, 0.5 and 0.25 mg/kg). Animals receiving saline were used as controls. The toxicities of the three drugs were evaluated by clinical chemistry and hematological determinations, light microscopy and transmission electron microscopy. The severity of the histologic alterations in heart, kidney and small intestine was assessed semiquantitatively. Biochemical and molecular modeling studies were made to evaluate the formation of complexes of Fe(III) with piroxantrone and losoxantrone. The cardiac (myofibrillar loss and dilatation of the sarcoplasmic reticulum) and renal (glomerular vacuolization, tubular damage and laboratory evidence of a nephrotic syndrome) lesions induced by all three agents had similar features. However, the cardiac lesions induced by losoxantrone and doxorubicin were significantly more severe (Billingham scores) than those produced by piroxantrone. The renal lesions induced by piroxantrone and losoxantrone were less severe than those produced by doxorubicin. Similarly losoxantrone and piroxantrone-induced intestinal alterations (denudation of epithelial layer and inflammatory cellular infiltration) were less severe than those occurring after treatment with doxorubicin. Both losoxantrone and piroxantrone were shown to form Fe(III): drug complexes that may cause oxidative damage to various tissues.

Animals↗

PubMed1998

Ferrous sulphate interacts with captopril.

AIMS: To determine if iron binds strongly to captopril and reduces captopril absorption. METHODS: A variety of in vitro experiments was conducted to examine iron binding to captopril and a randomized, double-blind, placebo controlled, cross-over study design was used to assess the in vivo interaction. Captopril (25 mg) was coingested with either ferrous sulphate (300 mg) or placebo by seven healthy adult volunteers. Subjects were phlebotomized and had blood pressure measured at 0, 0.25, 0.5, 1, 2, 4, 6, 8, and 12 h post ingestion. A 1 week washout period was used. RESULTS: The coingestion of ferrous sulphate and captopril was associated with a 37% (134 ng ml(-1) h, 95% CI 41-228 ng ml(-1) h, P = 0.03) decrease in area under the curve (AUC) for unconjugated plasma captopril. There were no substantial changes in Cmax (mean difference; -32; 95% CI -124-62 ng ml(-1) (P = 0.57)) or in tmax (mean difference; 0; 95% CI -18-18 min (P = 0.65)) for unconjugated captopril when captopril was ingested with iron. There was a statistically insignificant increase in AUC for total plasma captopril of 43% (1312 ng ml(-1) h, 95% CI -827-3451 ng ml(-1) h P = 0.27) when captopril was ingested with iron. The addition of ferric chloride to captopril resulted in the initial rapid formation of a soluble blue complex which rapidly disappeared to be replaced by a white precipitant. The white precipitate was identified as captopril disulphide dimer. There were no significant differences in systolic and diastolic blood pressures between the treatment and placebo groups. CONCLUSIONS: Co-administration of ferrous sulphate and iron results in decreased unconjugated captopril levels likely due to a chemical interaction between ferric ion and captopril in the gastrointestinal tract. Care is required when coprescribing captopril and iron salts.

Adult↗

PubMed1998

The one-ring open hydrolysis intermediates of the cardioprotective agent dexrazoxane (ICRF-187) do not inhibit the growth of Chinese hamster ovary cells or the catalytic activity of DNA topoisomerase II.

Dexrazoxane (ICRF-187), which is clinically used to reduce doxorubicin-induced cardiotoxicity, has growth inhibitory properties through its ability to inhibit the catalytic activity of DNA topoisomerase II. Because the bisdioxopiperazine dexrazoxane undergoes significant ring-opening hydrolysis under physiological conditions to form two one-ring open hydrolysis intermediates, a study was undertaken to determine if these two intermediates had either any growth inhibitory or topoisomerase II inhibitory effects. Neither of the one-ring open intermediates exhibited growth inhibitory effects towards Chinese hamster ovary cells nor were they able to inhibit topoisomerase II. Thus, it was concluded that only intact dexrazoxane is able to inhibit the catalytic activity of topoisomerase II.

Animals↗

PubMed1998

Chemical, biological and clinical aspects of dexrazoxane and other bisdioxopiperazines.

The bisdioxopiperazine dexrazoxane (ICRF-187) has proven to be clinically very effective in reducing the cardiotoxicity of doxorubicin and other anthracyclines. Doxorubicin is thought to exert its toxicity through iron-based oxygen free radical-induced oxidative stress on the relatively unprotected cardiac muscle. Upon hydrolysis, dexrazoxane forms a compound similar to ethylenediaminetetraacetic acid (EDTA) which, like EDTA, is a strong chelator of iron. Dexrazoxane presumably exerts its cardioprotective effects by either binding free or loosely bound iron, or iron complexed to doxorubicin, thus preventing or reducing site-specific oxygen radical production that damages cellular components. The chemistry, biochemistry, and cell biology of dexrazoxane and other bisdioxopiperazines are discussed. The pre-clinical studies demonstrating the protective effects of dexrazoxane against toxicities caused by doxorubicin, other anthracyclines, bleomycin, alloxan, acetaminophen, and oxygen are also discussed. In vitro and in vivo studies of the cardioprotective and other effects of other bisdioxopiperazines are also covered. Also discussed are the anti-metastatic and radiosensitization effects of razoxane and dexrazoxane. The current clinical status of dexrazoxane in preventing anthracycline-induced toxicities in both adult and pediatric patients is reviewed.

Animals↗

PubMed1998

Chemistry of dexrazoxane and analogues.

The bisdioxopiperazine dexrazoxane (DEX; ICRF-187) has proven to be clinically effective in reducing the cardiotoxicity of doxorubicin and the toxicity of other anthracyclines. Doxorubicin and the other anthracyclines are thought to exert their toxicity through iron-based oxygen free radical-induced oxidative stress on the relatively unprotected cardiac muscle. On hydrolysis, DEX forms a compound (ADR-925) similar in structure to EDTA, which, like EDTA, is a strong chelator of iron and other metal ions. Dexrazoxane presumably exerts its cardioprotective effects by either binding free or loosely bound iron, or iron complexed to doxorubicin, thus preventing or reducing site-specific oxygen radical production that damages cellular components. The hydrolysis-activation of DEX to ADR-925 can occur through either enzymatic or nonenzymatic routes. Iron(III)-anthracycline complexes are directly able to promote ring-opening hydrolysis of DEX. Both ferrous and ferric ions (as well as several other divalent metal ions) can promote the hydrolysis of the one-ring open intermediates of DEX to ADR-925, which suggests that these intermediates may be pharmacologically active. Paradoxically, the ferric complex of ADR-925 has been shown to be capable of being reductively activated to mediate hydroxyl radical formation. This observation suggests that DEX may be acting through its ability to prevent site-specific oxygen radical damage by iron-anthracycline complexes.

Anthracyclines↗

PubMed1997

Antioxidants and dipyridamole inhibit HIV-1 gp120-induced free radical-based oxidative damage to human monocytoid cells.

Reactive oxygen species (ROS) may play an important role in HIV-1 pathogenesis and HIV-1 gp120-induced neurotoxicity. Our studies determined the extent to which gp120 increased ROS production in human monocytic U937 cells and the effectiveness of various agents, including dipyridamole (DPR), in blocking these responses. The thiobarbituric acid-reactive substances (TBARS) assay was used as a measure of recombinant gp120 (HIV-1[3B])-induced oxidative damage to U937 cells. As a control, TBARS production was measured using a hypoxanthine/xanthine superoxide generating system. There was gp120-induced oxidative damage in U937 cells with a concentration that produces 50% of maximal effect (apparent EC50 value) of 11 pM. Polyclonal antiserum to gp120 significantly (p < 0.05) inhibited gp120-induced oxidative damage. gp120-induced oxidative damage was significantly inhibited 81% (p < 0.01) by catalase/superoxide dismutase, 53% (p < 0.05) by (+/-)-alpha-tocopherol, 78% (p < 0.01) by desferrioxamine, and 82% (p < 0.01) by ethylene diamine tetraacetic acid (EDTA). These results indicate that gp120 is capable of promoting iron-based oxygen free radical damage to U937 cells. DPR potently (p < 0.05) inhibited both hypoxanthine/xanthine- and gp120-induced oxidative damage with concentrations that produce 50% inhibition (apparent IC50 values) of 1.3 microM for hypoxanthine/xanthine and 1.0 microM for gp120. Therapeutic intervention against ROS production may prevent HIV-1 neurotoxicity.

Anti-HIV Agents↗

PubMed1997

Characterization of a Chinese hamster ovary cell line with acquired resistance to the bisdioxopiperazine dexrazoxane (ICRF-187) catalytic inhibitor of topoisomerase II.

A Chinese hamster ovary (CHO) cell line highly resistant to the non-cleavable complex-forming topoisomerase II inhibitor dexrazoxane (ICRF-187, Zinecard) was selected. The resistant cell line (DZR) was 1500-fold resistant (IC50 = 2800 vs 1.8 microM) to continuous dexrazoxane exposure. DZR cells were also cross-resistant (8- to 500-fold) to other bisdioxopiperazines (ICRF-193, ICRF-154, and ICRF-186), and somewhat cross-resistant (4- to 14-fold) to anthracyclines (daunorubicin, doxorubicin, epirubicin, and idarubicin) and etoposide (8.5-fold), but not to the other non-cleavable complex-forming topoisomerase II inhibitors suramin and merbarone. The cytotoxicity of dexrazoxane to both cell lines was unchanged in the presence of the membrane-active agent verapamil. DZR cells were 9-fold resistant to dexrazoxane-mediated inhibition of topoisomerase II DNA decatenation activity compared with CHO cells (IC50 = 400 vs 45 microM), but were only 1.4-fold (IC50 = 110 vs 83 microM) resistant to etoposide. DZR cells contained one-half the level of topoisomerase II protein compared with parental CHO cells. However, the specific activity for decatenation using nuclear extract topoisomerase II was unchanged. Etoposide (100 microM)-induced topoisomerase II-DNA complexes in DZR cells and isolated nuclei were similarly one-half the level found in CHO cells and in isolated nuclei. However, the ability of 500 microM dexrazoxane to inhibit etoposide (100 microM)-induced topoisomerase II-DNA covalent complexes was reduced 4- to 6-fold in both DZR cells and nuclei compared with CHO cells and nuclei. In contrast, there was no differential ability of aclarubicin or merbarone to inhibit etoposide-induced topoisomerase II-DNA complexes in CHO compared with DZR cells and isolated nuclei. It was concluded that the DZR cell line acquired its resistance to dexrazoxane mainly through an alteration in the topoisomerase II target.

Aclarubicin↗