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Ratre P, Mishra K, Dubey A, Vyas A, Jain A, Thareja S. Aromatase Inhibitors for the Treatment of Breast Cancer: A Journey from the Scratch. Anticancer Agents Med Chem 2020; 20:1994-2004. [DOI: 10.2174/1871520620666200627204105] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 02/25/2020] [Accepted: 03/15/2020] [Indexed: 01/08/2023]
Abstract
Background:
Estrogens are essential for the growth of breast cancer in the case of premenopausal as
well as in postmenopausal women. However, most of the breast cancer incidences are reported in postmenopausal
women and the concurrent risk surges with an increase in age. Since the enzyme aromatase catalyses
essential steps in estrogen biosynthesis, Aromatase Inhibitors (AIs) are effective targeted therapy in patients
with Estrogen Receptor positive (ER+) breast cancer. AIs are more effective than Selective Estrogen Receptor
Modulators (SERMs) because they block both the genomic and nongenomic activities of ER. Till date, first,
second and third-generation AIs have been approved by the FDA. The third-generation AIs, viz. Letrozole,
Anastrozole, Exemestane, are currently used in the standard treatment for postmenopausal breast cancer.
Methods:
Data were collected from Medline, PubMed, Google Scholar, Science Direct through searching of
keywords: ‘aromatase’, ‘aromatase inhibitors’, ‘breast cancer’, ‘steroidal aromatase inhibitors’, ‘non-steroidal
inhibitors’ and ‘generations of aromatase inhibitors’.
Results:
In the current scenario of breast cancer chemotherapy, AIs are the most widely used agents which reveal
optimum efficacy along with the least side effects. Keeping in view the prominence of AIs in breast cancer
therapy, this review covered the detailed description of aromatase including its role in the biosynthesis of estrogen,
biochemistry, gene expression, 3D-structure, and information of reported AIs along with their role in breast
cancer treatment.
Conclusion:
AIs are the mainstream solution of the ER+ breast cancer treatment regimen with the continuous
improvement of human understanding of the importance of a healthy life of women suffering from breast cancer.
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Affiliation(s)
- Pooja Ratre
- School of Pharmaceutical Sciences, Guru Ghasidas Central University, Bilaspur-495 009 (C.G.), India
| | - Keerti Mishra
- School of Pharmaceutical Sciences, Guru Ghasidas Central University, Bilaspur-495 009 (C.G.), India
| | - Amit Dubey
- Chhattisgarh Council of Science and Technology, Raipur-492 014 (C.G.), India
| | - Amber Vyas
- University Institute of Pharmacy, Pt. Ravishankar Shukla University, Raipur-492 010 (C.G.), India
| | - Akhlesh Jain
- School of Pharmaceutical Sciences, Guru Ghasidas Central University, Bilaspur-495 009 (C.G.), India
| | - Suresh Thareja
- School of Pharmaceutical Sciences, Guru Ghasidas Central University, Bilaspur-495 009 (C.G.), India
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2
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Jha T, Adhikari N, Halder AK, Saha A. Ligand- and Structure-Based Drug Design of Non-Steroidal Aromatase Inhibitors (NSAIs) in Breast Cancer. Oncology 2017. [DOI: 10.4018/978-1-5225-0549-5.ch004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Aromatase is a multienzyme complex overexpressed in breast cancer and responsible for estrogen production. It is the potential target for designing anti-breast cancer drugs. Ligand and Structure-Based Drug Designing approaches (LBDD and SBDD) are involved in development of active and more specific Nonsteroidal Aromatase Inhibitors (NSAIs). Different LBDD and SBDD approaches are presented here to understand their utility in designing novel NSAIs. It is observed that molecules should possess a five or six membered heterocyclic nitrogen containing ring to coordinate with heme portion of aromatase for inhibition. Moreover, one or two hydrogen bond acceptor features, hydrophobicity, and steric factors may play crucial roles for anti-aromatase activity. Electrostatic, van der Waals, and p-p interactions are other important factors that determine binding affinity of inhibitors. HQSAR, LDA-QSAR, GQSAR, CoMFA, and CoMSIA approaches, pharmacophore mapping followed by virtual screening, docking, and dynamic simulation may be effective approaches for designing new potent anti-aromatase molecules.
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3
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Baravalle R, Valetti F, Catucci G, Gambarotta G, Chiesa M, Maurelli S, Giamello E, Barone I, Catalano S, Andò S, Di Nardo G, Gilardi G. Effect of sildenafil on human aromatase activity: From in vitro structural analysis to catalysis and inhibition in cells. J Steroid Biochem Mol Biol 2017; 165:438-447. [PMID: 27616271 DOI: 10.1016/j.jsbmb.2016.09.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 09/05/2016] [Accepted: 09/06/2016] [Indexed: 11/15/2022]
Abstract
Aromatase catalyses the conversion of androgens into estrogens and is a well-known target for breast cancer therapy. As it has been suggested that its activity is affected by inhibitors of phosphodiesterase-5, this work investigates the potential interaction of sildenafil with aromatase. This is carried out both at molecular level through structural and kinetics assays applied to the purified enzyme, and at cellular level using neuronal and breast cancer cell lines. Sildenafil is found to bind to aromatase with a KD of 0.58±0.05μM acting as a partial and mixed inhibitor with a maximal inhibition of 35±2%. Hyperfine sublevel correlation spectroscopy and docking studies show that sildenafil binds to the heme iron via its 6th axial water ligand. These results also provide information on the starting molecular scaffold for the development of new generations of drugs designed to inhibit aromatase as well as phosphodiesterase-5, a new emerging target for breast cancer therapy.
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Affiliation(s)
- Roberta Baravalle
- Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy
| | - Francesca Valetti
- Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy
| | - Gianluca Catucci
- Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy
| | - Giovanna Gambarotta
- Department of Clinical and Biological Sciences, University of Torino, Regione Gonzole, 10-10043 Orbassano, Italy
| | - Mario Chiesa
- Department of Chemistry, University of Torino, via Pietro Giuria 7, 10125, Torino, Italy
| | - Sara Maurelli
- Department of Chemistry, University of Torino, via Pietro Giuria 7, 10125, Torino, Italy
| | - Elio Giamello
- Department of Chemistry, University of Torino, via Pietro Giuria 7, 10125, Torino, Italy
| | - Ines Barone
- Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Arcavacata di Rende, CS, Italy
| | - Stefania Catalano
- Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Arcavacata di Rende, CS, Italy
| | - Sebastiano Andò
- Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Arcavacata di Rende, CS, Italy
| | - Giovanna Di Nardo
- Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy; CrisDi, Interdepartmental Center for Crystallography, via Pietro Giuria 7, 10125, Torino, Italy.
| | - Gianfranco Gilardi
- Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy; CrisDi, Interdepartmental Center for Crystallography, via Pietro Giuria 7, 10125, Torino, Italy.
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4
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Jha T, Adhikari N, Halder AK, Saha A. Ligand- and Structure-Based Drug Design of Non-Steroidal Aromatase Inhibitors (NSAIs) in Breast Cancer. QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS IN DRUG DESIGN, PREDICTIVE TOXICOLOGY, AND RISK ASSESSMENT 2015. [DOI: 10.4018/978-1-4666-8136-1.ch011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Aromatase is a multienzyme complex overexpressed in breast cancer and responsible for estrogen production. It is the potential target for designing anti-breast cancer drugs. Ligand and Structure-Based Drug Designing approaches (LBDD and SBDD) are involved in development of active and more specific Nonsteroidal Aromatase Inhibitors (NSAIs). Different LBDD and SBDD approaches are presented here to understand their utility in designing novel NSAIs. It is observed that molecules should possess a five or six membered heterocyclic nitrogen containing ring to coordinate with heme portion of aromatase for inhibition. Moreover, one or two hydrogen bond acceptor features, hydrophobicity, and steric factors may play crucial roles for anti-aromatase activity. Electrostatic, van der Waals, and p-p interactions are other important factors that determine binding affinity of inhibitors. HQSAR, LDA-QSAR, GQSAR, CoMFA, and CoMSIA approaches, pharmacophore mapping followed by virtual screening, docking, and dynamic simulation may be effective approaches for designing new potent anti-aromatase molecules.
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5
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Khatri Y, Luthra A, Duggal R, Sligar SG. Kinetic solvent isotope effect in steady-state turnover by CYP19A1 suggests involvement of Compound 1 for both hydroxylation and aromatization steps. FEBS Lett 2014; 588:3117-22. [PMID: 24997347 DOI: 10.1016/j.febslet.2014.06.050] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Revised: 06/03/2014] [Accepted: 06/13/2014] [Indexed: 10/25/2022]
Abstract
CYP19A1, or human aromatase catalyzes the conversion of androgens to estrogens in a three-step reaction through the formation of 19-hydroxy and 19-aldehyde intermediates. While the first two steps of hydroxylation are thought to proceed through a high-valent iron-oxo species, controversy exists surrounding the identity of the reaction intermediate that catalyzes the lyase and aromatization reaction. We investigated the kinetic isotope effect on the steady-state turnover of Nanodisc-incorporated human CYP19A1 to explore the mechanisms of this reaction. Our experiments reveal a significant (∼ 2.5) kinetic solvent isotope effect for the C10-C19 lyase reaction, similar to that of the first two hydroxylation steps (2.7 and 1.2). These data implicate the involvement of Compound 1 as a reactive intermediate in the final aromatization step of CYP19A1.
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Affiliation(s)
- Yogan Khatri
- Department of Biochemistry, University of Illinois Urbana-Champaign, 505 S. Goodwin Avenue, Urbana, IL 61801, United States
| | - Abhinav Luthra
- Department of Biochemistry, University of Illinois Urbana-Champaign, 505 S. Goodwin Avenue, Urbana, IL 61801, United States
| | - Ruchia Duggal
- Department of Biochemistry, University of Illinois Urbana-Champaign, 505 S. Goodwin Avenue, Urbana, IL 61801, United States
| | - Stephen G Sligar
- Department of Biochemistry, University of Illinois Urbana-Champaign, 505 S. Goodwin Avenue, Urbana, IL 61801, United States.
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6
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Pedrini N, Ortiz-Urquiza A, Huarte-Bonnet C, Zhang S, Keyhani NO. Targeting of insect epicuticular lipids by the entomopathogenic fungus Beauveria bassiana: hydrocarbon oxidation within the context of a host-pathogen interaction. Front Microbiol 2013; 4:24. [PMID: 23422735 PMCID: PMC3573267 DOI: 10.3389/fmicb.2013.00024] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 01/30/2013] [Indexed: 01/15/2023] Open
Abstract
Broad host range entomopathogenic fungi such as Beauveria bassiana attack insect hosts via attachment to cuticular substrata and the production of enzymes for the degradation and penetration of insect cuticle. The outermost epicuticular layer consists of a complex mixture of non-polar lipids including hydrocarbons, fatty acids, and wax esters. Long chain hydrocarbons are major components of the outer waxy layer of diverse insect species, where they serve to protect against desiccation and microbial parasites, and as recognition molecules or as a platform for semiochemicals. Insect pathogenic fungi have evolved mechanisms for overcoming this barrier, likely with sets of lipid degrading enzymes with overlapping substrate specificities. Alkanes and fatty acids are substrates for a specific subset of fungal cytochrome P450 monooxygenases involved in insect hydrocarbon degradation. These enzymes activate alkanes by terminal oxidation to alcohols, which are further oxidized by alcohol and aldehyde dehydrogenases, whose products can enter β-oxidation pathways. B. bassiana contains at least 83 genes coding for cytochrome P450s (CYP), a subset of which are involved in hydrocarbon oxidation, and several of which represent new CYP subfamilies/families. Expression data indicated differential induction by alkanes and insect lipids and four CYP proteins have been partially characterized after heterologous expression in yeast. Gene knockouts revealed a phenotype for only one (cyp52X1) out of six genes examined to date. CYP52X1 oxidizes long chain fatty acids and participates in the degradation of specific epicuticular lipid components needed for breaching the insect waxy layer. Examining the hydrocarbon oxidizing CYP repertoire of pathogens involved in insect epicuticle degradation can lead to the characterization of enzymes with novel substrate specificities. Pathogen targeting may also represent an important co-evolutionary process regarding insect cuticular hydrocarbon synthesis.
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Affiliation(s)
- Nicolás Pedrini
- Facultad de Ciencias Médicas, Instituto de Investigaciones Bioquímicas de La Plata (CCT La Plata CONICET-UNLP)La Plata, Argentina
| | | | - Carla Huarte-Bonnet
- Facultad de Ciencias Médicas, Instituto de Investigaciones Bioquímicas de La Plata (CCT La Plata CONICET-UNLP)La Plata, Argentina
| | - Shizhu Zhang
- Department of Microbiology and Cell Science, University of FloridaGainesville, FL, USA
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal UniversityNanjing, China
| | - Nemat O. Keyhani
- Department of Microbiology and Cell Science, University of FloridaGainesville, FL, USA
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7
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Zhang S, Widemann E, Bernard G, Lesot A, Pinot F, Pedrini N, Keyhani NO. CYP52X1, representing new cytochrome P450 subfamily, displays fatty acid hydroxylase activity and contributes to virulence and growth on insect cuticular substrates in entomopathogenic fungus Beauveria bassiana. J Biol Chem 2012; 287:13477-86. [PMID: 22393051 DOI: 10.1074/jbc.m111.338947] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Infection of insects by the entomopathogenic fungus Beauveria bassiana proceeds via attachment and penetration of the host cuticle. The outermost epicuticular layer or waxy layer of the insect represents a structure rich in lipids including abundant amounts of hydrocarbons and fatty acids. A member of a novel cytochrome P450 subfamily, CYP52X1, implicated in fatty acid assimilation by B. bassiana was characterized. B. bassiana targeted gene knockouts lacking Bbcyp52x1 displayed reduced virulence when topically applied to Galleria mellonella, but no reduction in virulence was noted when the insect cuticle was bypassed using an intrahemoceol injection assay. No significant growth defects were noted in the mutant as compared with the wild-type parent on any lipids substrates tested including alkanes and fatty acids. Insect epicuticle germination assays, however, showed reduced germination of ΔBbcyp52x1 conidia on grasshopper wings as compared with the wild-type parent. Complementation of the gene-knock with the full-length gene restored virulence and insect epicuticle germination to wild-type levels. Heterologous expression of CYP52X1 in yeast was used to characterize the substrate specificity of the enzyme. CYP52X1 displayed the highest activity against midrange fatty acids (C12:0 and C14:0) and epoxy stearic acid, 4-8-fold lower activity against C16:0, C18:1, and C18:2, and little to no activity against C9:0 and C18:0. Analyses of the products of the C12:0 and C18:1 reactions confirmed NADPH-dependent regioselective addition of a terminal hydroxyl to the substrates (ω-hydroxylase). These data implicate CYP52X1 as contributing to the penetration of the host cuticle via facilitating the assimilation of insect epicuticle lipids.
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Affiliation(s)
- Shizhu Zhang
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611, USA
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8
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Sohl CD, Guengerich FP. Kinetic analysis of the three-step steroid aromatase reaction of human cytochrome P450 19A1. J Biol Chem 2010; 285:17734-43. [PMID: 20385561 DOI: 10.1074/jbc.m110.123711] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytochrome P450 19A1 (P450 19A1), the aromatase, catalyzes the conversion of androgens to estrogens through a sequential three-step reaction, generating 19-hydroxy and 19-aldehyde intermediates en route to the product estrogen. A procedure for the heterologous expression and purification of P450 19A1 in Escherichia coli was developed (k(cat) of 0.06 s(-1) for the conversion of androstenedione to estrone). Binding of the substrate and intermediates show low micromolar dissociation constants and are at least two-step processes. Rates of reduction of the iron were fast in the presence of substrate, either intermediate, or product. P450 19A1 is a distributive rather than a processive enzyme, with the sequential reaction allowing free dissociation of the intermediates as revealed by pulse-chase experiments. Conversion of androstenedione to estrone (under single turnover conditions) generated a progress curve showing changes in the concentrations of the substrate, intermediates, and product. A minimal kinetic model containing the individual rate constants for the steps in P450 19A1 catalysis was developed to globally fit the time course of the overall reaction, the dissociation constants, the two-step ligand binding, the distributive character, the iron-reduction rates, and the steady-state conversion of the 19-hydroxy androstenedione and 19-aldehyde androstenedione intermediates to estrone.
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Affiliation(s)
- Christal D Sohl
- Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA
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9
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Guengerich FP, Martin MV, Sohl CD, Cheng Q. Measurement of cytochrome P450 and NADPH-cytochrome P450 reductase. Nat Protoc 2009; 4:1245-51. [PMID: 19661994 DOI: 10.1038/nprot.2009.121] [Citation(s) in RCA: 266] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Cytochrome P450 (P450) enzymes are important in the metabolism of steroids, vitamins, carcinogens, drugs and other compounds. Two of the commonly used assays in this field are the measurements of total P450 and NADPH-P450 reductase in biological preparations. A detailed protocol is presented for the measurement of P450 by its spectral properties, along with a protocol for measuring NADPH-P450 reductase by its NADPH-cytochrome c reduction activity. Each assay can be completed in 5-10 min. Detailed explanations for the rationale of particular sequences in the protocols are provided, along with potential confounding problems.
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Affiliation(s)
- F Peter Guengerich
- Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
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10
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Abstract
Estrogens are biosynthesised from androgens by the CYP450 enzyme complex called aromatase. Aromatase is expressed in the ovary, placenta, brain, bone, adipose tissue and breast tissue. In breast cancer, intratumoural aromatase is the source for local estrogen production in the tissue. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in estrogen-dependent breast cancer. The potent and selective third-generation aromatase inhibitors anastrozole, letrozole and exemestane were introduced to the market as endocrine therapy in postmenopausal patients failing anti-estrogen therapy alone, or multiple hormonal therapies. Anastrozole and letrozole are both non-steroidal aromatase inhibitors that compete with the substrate for binding to the enzyme active site. Exemestane is a mechanism-based steroidal inhibitor that mimics the substrate, is converted by the enzyme to a reactive intermediate, and results in inactivation of aromatase. These third-generation aromatase inhibitors are currently approved as first-line therapy for the treatment of postmenopausal women with metastatic estrogen-dependent breast cancer. The use of an aromatase inhibitor as initial therapy, or after treatment with tamoxifen, is now recommended as adjuvant hormonal therapy for postmenopausal women with hormone-dependent breast cancer. Several clinical studies of aromatase inhibitors focus on the use of these agents in the adjuvant setting, for the treatment of early breast cancer. Recently published results show improved responses with these agents compared with tamoxifen.
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Affiliation(s)
- Robert W Brueggemeier
- Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, 500 West 12th Avenue, Columbus, OH 43210, USA.
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11
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Abstract
Estradiol, the most potent endogenous estrogen, is biosynthesized from androgens by the cytochrome P450 enzyme complex called aromatase. Aromatase is present in breast tissue, and intratumoral aromatase is the source of local estrogen production in breast cancer tissues. Inhibition of aromatase is an important approach for reducing growth-stimulatory effects of estrogens in estrogen-dependent breast cancer. Steroidal inhibitors that have been developed to date build upon the basic androstenedione nucleus and incorporate chemical substituents at varying positions on the steroid. Nonsteroidal aromatase inhibitors can be divided into three classes: aminoglutethimide-like molecules, imidazole/triazole derivatives, and flavonoid analogs. Mechanism-based aromatase inhibitors are steroidal inhibitors that mimic the substrate, are converted by the enzyme to a reactive intermediate, and result in the inactivation of aromatase. Both steroidal and nonsteroidal aromatase inhibitors have shown clinical efficacy in the treatment of breast cancer. The potent and selective third-generation aromatase inhibitors, anastrozole, letrozole, and exemestane, were introduced into the market as endocrine therapy in postmenopausal patients failing antiestrogen therapy alone or multiple hormonal therapies. These agents are currently approved as first-line therapy for the treatment of postmenopausal women with metastatic estrogen-dependent breast cancer. Several clinical studies of aromatase inhibitors are currently focusing on the use of these agents in the adjuvant setting for the treatment of early breast cancer. Use of an aromatase inhibitor as initial therapy or after treatment with tamoxifen is now recommended as adjuvant hormonal therapy for a postmenopausal woman with hormone-dependent breast cancer.
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Affiliation(s)
- Robert W Brueggemeier
- College of Pharmacy, The Ohio State University, 500 West 12th Avenue, Columbus, Ohio 43210-1291, USA.
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Balthazart J, Baillien M, Charlier TD, Ball GF. Calcium-dependent phosphorylation processes control brain aromatase in quail. Eur J Neurosci 2003; 17:1591-606. [PMID: 12752377 DOI: 10.1046/j.1460-9568.2003.02598.x] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Increased gene transcription activated by the binding of sex steroids to their cognate receptors is one important way in which oestrogen synthase (aromatase) activity is regulated in the brain. This control mechanism is relatively slow (hours to days) but recent data indicate that aromatase activity in quail preoptic-hypothalamic homogenates is also rapidly (within minutes) affected by exposure to conditions that enhance Ca2+-dependent protein phosphorylation. We demonstrate here that Ca2+-dependent phosphorylations controlled by the activity of multiple protein kinases including PKC, and possibly also PKA and CAMK, can rapidly down-regulate aromatase activity in brain homogenates. These phosphorylations directly affect the aromatase molecule itself. Western blotting experiments on aromatase purified by immunoprecipitation reveal the presence on the enzyme of phosphorylated serine, threonine and tyrosine residues in concentrations that are increased by phosphorylating conditions. Cloning and sequencing of the quail aromatase identified a 1541-bp open reading frame that encodes a predicted 490-amino-acid protein containing all the functional domains that have been previously described in the mammalian and avian aromatase. Fifteen predicted consensus phosphorylation sites were identified in this sequence, but only two of these (threonine 455 and 486) match the consensus sequences corresponding to the protein kinases that were shown to affect aromatase activity during the pharmacological experiments (i.e. PKC and PKA). This suggests that the phosphorylation of one or both of these residues represents the mechanism underlying, at least in part, the rapid changes in aromatase activity.
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Affiliation(s)
- J Balthazart
- Center for Cellular and Molecular Neurobiology, Research Group in Behavioural Neuroendocrinology, University of Liège, 17 place Delcour (Bat. L1), B-4020 Liège, Belgium.
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13
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Conley A, Mapes S, Corbin CJ, Greger D, Graham S. Structural determinants of aromatase cytochrome p450 inhibition in substrate recognition site-1. Mol Endocrinol 2002; 16:1456-68. [PMID: 12089342 DOI: 10.1210/mend.16.7.0876] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The porcine gonadal form of aromatase cytochrome P450 (P450arom) exhibits higher sensitivity to inhibition by the imidazole, etomidate, than the placental isozyme. The residue(s) responsible for this functional difference was mapped using chimeragenesis and point mutation analysis of the placental isozyme, and the kinetic analysis was conducted on native and mutant enzymes after overexpression in insect cells. The etomidate sensitivity of the placental isozyme was markedly increased by substitution of the predicted substrate recognition site-1 (SRS-1) and essentially reproduced that of the gonadal isozyme by substitution of SRS-1 and the predicted B helix. A single isoleucine (I) to methionine (M) substitution at position 133 of the placental isozyme (I(133)M) was proven to be the critical residue within SRS-1. Residue 133 is located in the B'-C loop and has been shown to be equally important in other steroid-metabolizing P450s. Single point mutations (including residues 110, 114, 120, 128, 137, and combinations thereof among others) and mutation of the entire B and C helixes were without marked effect on etomidate inhibitory sensitivity. The same mutation (I(133)M) introduced into human P450arom also markedly increased etomidate sensitivity. Mutation of Ile(133) to either alanine (I(133)A) or tyrosine (I(133)Y) decreased apparent enzyme activity, but the I(133)A mutant was sensitive to etomidate inhibition, suggesting that it is Ile(133) that decreases etomidate binding rather than Met(133) increasing enzyme sensitivity. Androstenedione turnover and affinity were similar for the I(133)M mutant and the native placental isozyme. These data suggest that Ile(133) is a contact residue in SRS-1 of P450arom, emphasize the functional conservation that exists in SRS-1 of a number of steroid-hydroxylating P450 enzymes, and suggest that substrate and inhibitor binding are dependent on different contact points to varying degrees.
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Affiliation(s)
- Alan Conley
- Department of Population Health and Reproduction, University of California School of Veterinary Medicine, Davis, California 95616, USA.
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14
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Abstract
Estrogens are involved in numerous physiological processes and have crucial roles in certain disease states, such as mammary carcinomas. Estradiol, the most potent endogenous estrogen, is biosynthesized from androgens by the cytochrome P450 enzyme complex called aromatase. Aromatase is found in breast tissue and the importance of intratumoral aromatase and local estrogen production is being unraveled. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in estrogen-dependent breast cancer. Steroidal and nonsteroidal aromatase inhibitors have shown clinical efficacy for the treatment of breast cancer. The initial nonselective nature of nonsteroidal inhibitors, such as aminoglutethimide, has been greatly reduced in the later generations of inhibitors, anastrozole and letrozole. Mechanism-based steroidal inhibitors, such as 4-hydroxyandrostenedione and exemestane produce potent aromatase inhibition in patients. The potent and selective third-generation aromatase inhibitors, anastrozole, letrozole and exemestane, are approved for clinical use as first-line endocrine therapy in postmenopausal women with metastatic hormone-dependent breast cancer and as second-line endocrine therapy in postmenopausal patients failing antiestrogen therapy alone or multiple hormonal therapies.
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15
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Current literature in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2001; 36:1324-1333. [PMID: 11754125 DOI: 10.1002/jms.99] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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