Biomedical subjects

Y J Abul-Hajj

Publications and source records attributed to Y J Abul-Hajj.

At least 19 recordsLinked to original sources

PubMed1999

Estrogen-nucleic acid adducts: dissection of the reaction of 3, 4-estrone quinone and its radical anion and radical cation with deoxynucleosides and DNA.

Previous studies from our laboratory have shown that 3,4-estrone quinone (3,4-EQ) can redox-cycle and is capable of inducing single-strand DNA breaks in MCF-7 breast cancer cells, as well as reacting with various deoxynucleosides to give several estrogen-nucleic acid adducts. While reactions of 3,4-EQ with all the deoxynucleosides under acidic conditions gave only the N7-Gua adduct, which could proceed by Michael addition, reactions of 3,4-EQ under reductive conditions gave several adducts, including the N7-Gua, C8-Ade, C8-Gua, N3-Thy, and N4-Cyt adducts, suggesting the involvement of a 3,4-EQ radical species. The question as to which of the reactive species, the estrogen quinone or the estrogen semiquinone, that is responsible for estrogen's genotoxic activity has been the subject of recent investigations in several laboratories. To explore this in more detail, we carried out studies on the reactivity of 3,4-EQ, the 3,4-EQ radical anion, and the 3, 4-EQ radical cation with both deoxynucleosides and calf thymus DNA under different pH conditions. Both stable and unstable adducts with guanine and thymine were observed from reactions with DNA. Although adduct levels were somewhat different, the adduct profiles obtained from reactions of 3,4-EQ and its radical anion with both DNA and deoxynucleosides were quite similar and were found to be significantly different from product profiles obtained from reactions with the 3,4-EQ radical cation. Studies conducted with the human breast tumor cell line MCF-7 demonstrated the formation of the N7- and C8-Gua adducts in which the profiles were similar to those obtained from reactions of 3,4-EQ with DNA. These results suggest that the reactive species that is responsible for adduct formation under physiological conditions is most likely to be the 3,4-EQ radical anion.

Anions↗

PubMed1997

6 beta-Propynyl-substituted steroids: mechanism-based enzyme-activated irreversible inhibitors of aromatase.

The synthesis and aromatase inhibitory profile of 6 alpha and 6 beta-propargyl androstenedione and estrenedione are described. The targeted compounds 1 and 2 were prepared by addition of the propargyl Gringard to the 5 alpha,6 alpha-epoxy bisketal 6 or the 5 alpha,6 alpha-epoxy diacetate 7 followed by dehydration of the 6 beta-propargyl 5 alpha-hydroxy diones 10 and 11 using thionyl chloride. Treatment of the 6 beta-propargyl analogs 1 and 2 with hydrochloric acid gave the corresponding 6 alpha-propargyl isomers 3 and 4. Inhibitory activity of the synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1 beta-3H]-4-androstenedione as substrate. Under initial velocity assay condition of low product formation, the inhibitors demonstrated potent inhibition of aromatase, with apparent KiS ranging from 10 to 66 nM, with the Km for androstenedione being 55 nM. 6 alpha-Propargylandrost-4-ene-3,17-dione and 6 alpha-propargylestr-4-ene-3,17-dione were found to be potent competitive inhibitors of aromatase (Ki 37 and 66 nM, respectively). On the other hand the 6 beta-propargylandrost-4-ene-3,17-dione (6 beta-PAD) and 6 beta-propargylestr-4-ene-3,17-dione (6 beta-PED) were found to bind to aromatase with an apparent Ki of 10 and 48 nM, respectively, as well as cause rapid time-dependent, first-order inactivation of aromatase in the presence of NADPH, whereas no inactivation was observed in the absence of NADPH. Substrate protects the enzyme from inactivation, but beta-mercaptoethanol does not, suggesting that the 6 beta-propargyl analogs 6 beta-PAD and 6 beta-PED are mechanism-based inactivators of aromatase. Energy-minimization calculations and molecular modeling studies indicate three global minima for each of the 6 beta-propargyl analogs in which one of the conformers is proposed to be responsible for the inactivation of aromatase.

Aromatase Inhibitors↗

PubMed1997

Potent growth inhibitory activity of zidovudine on cultured human breast cancer cells and rat mammary tumors.

Originally designed as an antitumor agent, zidovudine (AZT) has exhibited only marginal tumor growth inhibitory activity. Recently, three abstracts have described positive clinical outcomes for a small number of patients with advanced breast cancer treated with weekly infusions of either methotrexate or cisplatin and AZT. Consequently, we conducted a preclinical study of the anti-breast cancer and anti-mammary tumor activity of AZT. Here we have demonstrated that AZT, alone, has a preferential in vitro and in vivo effect on breast and mammary cancer cells. It is 1000 times as potent as an inhibitor of the in vitro growth of the human breast cancer cell line MCF-7 (IC50 = 10 +/- 5 nM) than of the growth of the T-cell leukemia cell line CEM (IC50 = 14 +/- 2 microM). A novel mechanism for this preferential effect on growth is indicated by the 3-4-fold increase in production of phosphorylated AZT (mono-, di-, and triphosphate) in MCF-7 relative to CEM. We extended these in vitro observations to in vivo studies in rats and found that AZT is a potent in vivo inhibitor of the growth of methylnitrosourea-induced rat mammary tumors without any apparent toxic effects on internal organs. These preclinical results demonstrate, for the first time, that AZT has significant anti-breast cancer activity and strongly suggest that the clinical usefulness of this drug is worthy of investigation.

Animals↗

PubMed1997

Estrogen-nucleic acid adducts: reaction of 3,4-estrone o-quinone with nucleic acid bases.

Metabolic activation of estradiol leading to the formation of catechol estrogens is believed to be a prerequisite for its genotoxic effects. Previous studies have shown that 3,4-estrone quinone (3,4-EQ) can redox-cycle and is capable of inducing exclusively single-strand DNA breaks in MCF-7 breast cancer cells [Nutter et al. (1991) J. Biol. Chem. 226, 16380-16386]. These studies, however, could not provide conclusive evidence about the mechanism of estrogen carcinogenesis. In order to explore this in more detail, we have shown previously that 3,4-EQ can react with adenine under electrochemical reductive conditions to yield an estrogen-nucleic acid adduct [Abul-Hajj et al. (1995) J. Am. Chem. Soc. 117, 6144-6145]. In this paper, we report the synthesis and identification of seven estrogen-nucleic acid adducts obtained from reaction of 3,4-EQ with adenine, thymine, and cytosine. Initial purification of reaction mixtures using TLC followed by HPLC gave sufficient quantities of reaction products for identification using 1H-NMR and mass spectral determinations. Reaction of 3,4-EQ with adenine, thymine, and cytosine gave the following estrogen-nucleic acid adducts: 8-(4-hydoxyestrone-1-yl)adenine, 3-adenylimino-1,5(10)-estradiene-4,17-dione,4-adenylimino-1, 5(10)-estradiene-3,17-dione, N1- [4-hydroxyestrone-1(alpha,beta)-yl]thymine, N4-(4-hydroxyestrone-1- yl)cytosine, and N4-(4-hydroxy- estrone-2-yl)cytosine. No reaction products were obtained with guanine presumably due to poor solubility in DMF.

Deoxyribonucleosides↗

PubMed1997

Estrogen-nucleic acid adducts: reaction of 3,4-estrone-o-quinone radical anion with deoxyribonucleosides.

Metabolic activation of estradiol leading to the formation of catechol estrogens is believed to be a prerequisite for its genotoxic effects. Previous studies have shown that 3,4-estronequinone (3,4-EQ) can redox-cycle and is capable of inducing exclusively single-strand DNA breaks in MCF-7 breast cancer cells [Nutter et al. (1991) J. Biol. Chem. 226, 16380-16386]. These studies, however, could not provide conclusive evidence about the mechanism of estrogen carcinogenesis. In order to explore this in more detail, we have shown previously that 3,4-EQ can react with adenine under electrochemical reductive conditions to yield an estrogen-nucleic acid adduct [Abul-Hajj et al. (1995) J. Am. Chem. Soc. 117, 6144-6145]. In this paper, we report the synthesis and identification of nine estrogen-nucleic acid adducts obtained from reaction of 3,4-EQ with deoxycytidine, deoxythymidine, deoxyadenosine, and deoxyguanosine. Purification of reaction mixtures using HPLC gave sufficient quantities of reaction products for identification using 1H-NMR and mass spectral determinations. Reaction of 3,4-EQ with dCyd, dThd, dAdo, and dGuo gave the following estrogen-nucleic acid adducts: N4-(4-hydroxyestron-1-yl)deoxycytidine, N4-(4-hydroxyestron-2-yl)deoxycytidine, N3-(4-hydroxyestron-1-yl)thymine, N3-(4-hydroxyestron-1-yl)deoxythymidine, N6-(4-hydroxyestron-1-yl)deoxyadenosine, 8-(4-hydroxyestron-1-yl)adenine, N2-(4-hydroxyestron-1-yl)deoxyguanosine, 8-(4-hydroxyestron-1-yl)guanine, and 8-(4-hydroxyestron-2-yl)guanine. Adduction through the NH2 group of dAdo, dGuo, and dCyd results in formation of chemically stable adducts. On the other hand, adduction at C-8 led to the formation of several depurination adducts identified as 4-OHE1-1-C8-Gua, 4-OHE1-2-C8-Gua, and 4-OHE1-1-C8-Ade.

Anions↗

PubMed1997

Estrogen-nucleic acid adducts: guanine is major site for interaction between 3,4-estrone quinone and COIII gene.

The carcinogenicity of estrogens in rodents and man has been attributed to either alkylation of cellular macromolecules and/or redox-cycling, generation of active radicals and DNA damage. Metabolic activation of estradiol leading to the formation of catechol estrogens is believed to be a prerequisite for its genotoxic effects. 4-Hydroxyestradiol is a potent inducer of tumors in hamsters. Previous studies have shown that 3,4-estrone quinone (3,4-EQ) can redox-cycle and is capable of inducing exclusively single strand DNA breaks in MCF-7 breast cancer cells, as well as react with various nucleophiles including amino acids and nucleic acids to give Michael addition products. In this paper we examined the nature of the interaction of 3,4-EQ with COIII gene and analysed the estrogen-DNA adducts by 32P-post-labeling. The reaction of 3,4-EQ with the COIII gene followed by polymerase arrest assay showed several stop sites in which guanine was preferentially attacked by 3,4-EQ and, to a lesser extent, with Ade, Cyt and Thy. 32P-Post-labeling analysis of the reaction of 3,4-EQ with COIII gene gave one major adduct which was found to be identical to that obtained from reaction of dGMP with 3,4-EQ. The observation that obstruction of in vitro replication of COIII template bound to 3,4-EQ suggests that estrogen quinone adducted lesions can arrest DNA polymerase. These results indicate that 3,4-EQ may be genotoxic and may provide one possible explanation for the carcinogenic effects of estrogens.

Binding Sites↗

PubMed1996

Reactions of 3,4-estrone quinone with mimics of amino acid side chains.

Reaction of 3,4-estrone o-quinone (3,4-EQ) with several amino acid side chain mimics, including 4-ethylphenol, 4-methylimidazole, acetic acid, and propanethiol, gave a mixture of several products including the catechol, Michael addition products, and dimeric products of the catechol. On the other hand, several other amino acid side chain mimics, including ethanol, acetamide, 1-ethylguanidine, and 3-methylindole, did not result in any addition products or catechol formation. Michael addition to 3,4-EQ with 4-methylimidazole, acetate, and 4-ethyl phenoxide resulted in 1,4-addition, leading to C-1 adducts while reaction with propanethiol gave the C-2 addition product.

Amino Acids↗

PubMed1995

Probing the hydrophobic pocket of the active site of aromatase with 4-phenoxy-7 alpha-(phenylthio)-4-androstene-3,17-dione.

In order to examine the nature of the hydrophobic pocket at the active site of aromatase, we carried out the synthesis, biochemical evaluation, and molecular modeling studies on 4-phenoxy-7 alpha-(phenylthio)-4-androstenedione 2. Aromatase inhibitory activity of 2 was found to be significantly weaker than that of the 4- and 7 alpha-mono(phenylthio)-substituted derivatives of androstenedione. These results along with those obtained from the modeling studies suggest the existence of a single hydrophobic pocket corresponding to the alpha-face in the C4, C6, C7 region of androstenedione.

Androstenedione↗

PubMed1995

Aromatase inhibitors: effect of ring A and ring B unsaturation on aromatase inhibition by 4-thiosubstituted derivatives of 4-androstene-3,17-dione.

The synthesis and biological evaluation of 4-thiosubstituted derivatives of 1,4-androstadienedione, 4,6-androstadienedione, and 1,4,6-androstatrienedione as inhibitors of aromatase are described. Inhibitory activity of synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1 beta-3H]androstenedione as substrate. Under initial velocity assay conditions of low product formation, the inhibitors demonstrated potent inhibition of aromatase, with apparent Kis ranging from 9.8 to 137 nM and with Km for androstenedione being 38 nM. However, unlike other 1,4-androstadienediones and 1,4,6-androstatrienediones in which time-dependent inactivation was observed, the 4-thiosubstituted analogs were found to be competitive inhibitors and did not produce any time-dependent inactivation of aromatase.

Androstanols↗

PubMed1995

Synthesis and evaluation of 4-substituted-4-androstene-3,17-dione derivatives as aromatase inhibitors.

The synthesis and biological evaluation of 4-amino-, 4-alkoxy-, 4-aryloxy-, 4-alkyl- and 4-aryl-4-androstenedione derivatives as inhibitors of estrogen synthetase (aromatase) are described. Inhibitory activity of synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1 beta-3H] androstenedione as substrate. Synthesized compounds exhibiting aromatase inhibitory activity were evaluated further under initial velocity conditions to determine apparent Ki values. Several compounds were effective competitive inhibitors and have apparent Ki values ranging from 38 to 1290 nM, with the apparent Km for androstenedione being 47 nM. Alkylation or arylation of 4-N, S, or O-substituted steroids results in compounds that are effective competitive inhibitors that are devoid of time-dependent inactivation and that the free pair of electrons on N, S, or O is not an essential requirement for 4-substituted androstenedione derivatives to be effective aromatase inhibitors. The results obtained from this investigation are consistent with our previous studies which show that aromatase has a hydrophobic pocket in the active site around the C-4 alpha region of androstenedione.

Androstenedione↗

PubMed1991

Characterization of DNA damage induced by 3,4-estrone-o-quinone in human cells.

The DNA damage induced in a human breast cancer cell line treated with 1,5 (10)-estradiene-3,4,17-trione (3,4-estrone-o-quinone; 3,4-EQ) has been measured qualitatively and quantitatively. Single-strand (ss) but not double-strand (ds) DNA breaks were formed in MCF-7 cells treated with 3,4-EQ. The ss DNA breaks formed in MCF-7 cells were partially repaired after incubation of cells in 3,4-EQ-free media for 2 and 4 h (i.e. 33 and 23% repair, respectively, as compared to the ss DNA breaks in cells after a 1-h exposure to 3,4-EQ without a recovery period). The formation of interstrand DNA cross-links was demonstrated in MCF-7 cells exposed to the bifunctional alkylating agent, mitomycin C, but not in those exposed to 3,4-EQ. Protein-linked DNA breaks were detected in MCF-7 cells after exposure to camptothecin and etoposide but not 3,4-EQ, suggesting that the ss DNA breaks induced by 3,4-EQ are unlikely to be mediated via topoisomerases. The induction of ss DNA breaks was detected in the estrogen receptor-negative cell line, BT-20, after exposure to 3,4-EQ. Furthermore, excess estradiol in culture media did not prevent 3,4-EQ-induced ss DNA breaks, suggesting that the DNA damage was not mediated via the estrogen receptor. Evaluation of the newly synthesized quinone analogue, 5,6,7,8-tetrahydro-1-2-naphthoquinone, in the ss DNA breakage assay revealed that the A and B ring moiety of 3,4-EQ is sufficient to produce ss DNA breaks in MCF-7 cells.

Breast Neoplasms↗

PubMed1991

Importance of oxygen functions in the biological hydroxylation of flavonoids by Absidia blackesleeana.

1. The synthesis and microbiological transformation of 2-phenyl-1-tetralone (compound 3, 1-deoxyisoflavanone), 3-phenyl-1-tetralone (compound 4, 1-deoxyflavanone), 2-phenylchroman (compound 7, 4-deoxyflavanone), 3-phenylchroman (compound 8, 4-deoxyisoflavanone) and 1,2-dihydro-3-phenylnaphthalene (compound 10, 1,4-dideoxy-dehydroflavanone) by Absidia blackesleeana are described. 2. Compounds 3, 4, 7 and 8 were hydroxylated at the 4'-position while compound 10 was not utilized as a substrate. The two phenylchroman analogues 7 and 8 gave approximately the same yield (22% and 26%, respectively) of the 4'-hydroxylation products, while the phenyltetralone analogues 3 and 4 showed significant differences in 4'-hydroxylation (2% and 47%, respectively).

Flavonoids↗

PubMed1990

Aromatase inhibition by 4-thiosubstituted-4-androstene-3,17-dione derivatives.

The synthesis and evaluation of 4-thiosubstituted-4-androstenedione analogs as inhibitors of estrogen synthetase (aromatase) is described. All compounds were prepared by the addition of various thiol reagents to 4 beta,5 beta-epoxyandrostanedione. Inhibitory activity of synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1 beta-3H]4-androstene-3,17-dione as substrate. Synthesized compounds exhibiting high inhibitory activity were further evaluated under initial velocity conditions to determine apparent Ki values. Several compounds were effective competitive inhibitors, and have apparent Ki values ranging from 34 to 52 nM, with the apparent Km for androstenedione being 54 nM. The results of these studies demonstrate a tightly fitted enzyme pocket that can accommodate bulky substituents at the C-4 position of androstenedione not to exceed 4.3 A in width and 5.5 A in length.

Androstenedione↗

PubMed1990

Synthesis and biological activity of 4-methylestradiol.

The synthesis of 4-methylestradiol (4-ME2) was carried out by reductive aromatization of 4-methyl-1,4-androstadiene-3-one-17 beta-ol. The relative binding affinity of 4-ME2 was found to be 10 and 25% of estradiol at 0 and 25 degrees C, respectively. 4-ME2 had considerably weaker uterotrophic activity relative to estrone and was found to have no antiuterotrophic activity.

Animals↗

PubMed1990

Synthesis and biologic activities of 11 beta-substituted estradiol as potential antiestrogens.

The effect of attachment of a dimethylaminoethoxy or a dimethylaminopropoxy group at the 11 beta-position of estradiol (E2) on its relative binding affinity (RBA) to estrogen receptor (ER) and intrinsic biologic activity is described. The binding of 11 beta-[2-(N,N-dimethylamino) ethoxy]estra-1,3,5(10)-triene-3,17 beta-diol (4) and 11 beta-[3-(N,N- dimethylamino)propoxy]estra-1,3,5(10)-triene-3,17 beta-diol (5) to the ER from immature rat uterine tissue was measured relative to that of [3H]E2 by a competitive binding assay. It was found that the 11 beta-substituted E2 analogs have considerably lower RBA to ER than the corresponding parent compound. The intrinsic activity of compounds 4 and 5 were studied in terms of uterotrophic and antiuterotrophic activity. It was found that the uterotrophic activity of these compounds was drastically reduced compared with E2. However, no antiuterotrophic activity was observed in these compounds at dosages ranging from 1 to 100 micrograms/rat/d.

Animals↗

PubMed1990

Reaction of thiol nucleophiles with 1,2-epoxy- and 4,5-epoxy-estrene-3-one-17 beta-ols.

Four ring A steroidal epoxyenones as probable intermediate in the formation of catechol estrogens were synthesized. The isomeric 1 alpha,2 alpha-epoxy-17 beta-hydroxyestr-4-en-3-one (9) and 1 beta,2 beta-epoxy-17 beta-hydroxyestr-4-en-3-one (8) were synthesized from 17 beta-hydroxy-5 alpha-estra-3-one. The isomeric 4 alpha,5 alpha-epoxy-17 beta-hydroxyestr-1-en-3-one (11) and 4 beta,5 beta-epoxy-17 beta-hydroxyestr-1-en-3-one (10) were prepared from 19-nortestosterone. The reaction of 9 and 10 with sodium/ethanethiol resulted in the formation of three types of reactions leading to multiple products: 1,4-addition, opening of epoxide, and epoxide opening followed by dehydration. Reaction of 8 with ethanethiol gave only one compound identified as 2-ethanethio-1,4-estradien-17 beta-ol-3-one, while reaction of 9 with ethanethiol gave an unusual product identified as 4-estren-1 alpha,17 beta-diol-3-one. Unlike reaction of ethanethiol with 9 and 10, reaction with N-acetylecysteine or glutathione results in epoxide opening followed by dehydration leading to the formation of estradiol-4-thioethers.

Epoxy Compounds↗

PubMed1990

Aromatase inhibition by flavonoids.

Several synthetic flavones were found to inhibit the aromatization of androstenedione to estrone catalyzed by human placental microsomes. Twenty-one compounds were tested and the IC50 of the most active were: flavone, 10 microM; 7-hydroxyflavone, 0.5 microM; 7,4'-dihydroxyflavone, 2.0 microM; flavanone, 8.0 microM; and 4'-hydroxyflavanone, 10 microM. Most of the others had IC50 values ranging from 80 to greater than 200 microM. These findings show that 4'-hydroxylation results in either no change or very little change in IC50 for flavanone, isoflavone and isoflavanone as well as other ring A hydroxylated flavones. Derivatives of flavone with a hydroxyl substituent at position 5, 6 and 7 were also screened. 7-Hydroxyflavone (11) was the most effective competitive inhibitor (IC50 = 0.5 microM) with an apparent Ki value of 0.25 microM. Compound 11 also induced a change in the absorption spectrum of the aromatase cytochrome P-450 which is indicative of substrate displacement. The relative binding affinities of the flavonoid analogs were determined and only ring A adn ring B dihydroxylated analogs were found to bind to the estrogen receptor.

Animals↗

PubMed1990

Microbiological transformation of flavone and isoflavone.

1. Flavone and isoflavone were subjected to microbial transformation studies. Screening with 80 fungal species showed that flavone was transformed by a large number of microorganisms and in higher yields than isoflavone. 2. Large-scale fermentations of flavone followed by isolation and characterization of metabolites using spectroscopic analysis showed the formation of 4'-hydroxyflavone, 3',4'-dihydroxyflavone and two cleavage products identified as o-hydroxyphenyl-hydroxymethyl ketone and 1-(o-hydroxyphenyl)-1,2-ethanediol. However, fermentation of isoflavone gave only 4'-hydroxyisoflavone and 3',4'-dihydroxyisoflavone.

Biotransformation↗