<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">AER</journal-id><journal-title-group><journal-title>Advances in Enzyme Research</journal-title></journal-title-group><issn pub-type="epub">2328-4846</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/aer.2022.104006</article-id><article-id pub-id-type="publisher-id">AER-122263</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Biomedical&amp;Life Sciences</subject><subject> Engineering</subject><subject> Medicine&amp;Healthcare</subject></subj-group></article-categories><title-group><article-title>
 
 
  Molecular Docking Studies of Estrone-Coumarin Derivatives as Aromatase and 17&lt;i&gt;β&lt;/i&gt;-HSD1 Inhibitors Related to Hormone Receptor Positive (HR+) Breast Cancer
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Silvia</surname><given-names>Alejandra Meza-Ireta</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Blanca</surname><given-names>Colin-Lozano</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Penélope</surname><given-names>Merino-Montiel</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>José</surname><given-names>Luis Vega-Báez</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Sara</surname><given-names>Montiel-Smith</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref></contrib></contrib-group><aff id="aff1"><addr-line>Facultad de Ciencias Químicas, Ciudad Universitaria, Benemérita Universidad Autónoma de Puebla, Puebla, México</addr-line></aff><pub-date pub-type="epub"><day>09</day><month>12</month><year>2022</year></pub-date><volume>10</volume><issue>04</issue><fpage>83</fpage><lpage>100</lpage><history><date date-type="received"><day>11,</day>	<month>October</month>	<year>2022</year></date><date date-type="rev-recd"><day>27,</day>	<month>December</month>	<year>2022</year>	</date><date date-type="accepted"><day>30,</day>	<month>December</month>	<year>2022</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
  Hormone Receptor positive (HR+) breast cancer is the most common malignancy in women. New strategies in the treatments have targeted the estrogen biosynthesis pathways including the inhibition of the aromatase and 17
  <em>β</em>-HSD1 enzymes. The present work, describes the study of a new family of 9 hybrid compounds derived from estrone attached to a coumarin fragment, linked through different lengths of hydrocarbon chains. The activity of these compounds was evaluated by molecular docking with two relevant enzymes in breast cancer (HR+). It has been proposed nine compounds as 17
  <em>β</em>-HSD1 inhibitors and six as aromatase inhibitors. We found important interactions with key amino acids at the orthosteric site of each enzyme and their score values compared to the crystallographic ligand. The in silico analysis showed good score values in the proposed compounds, where the steroidal portion presented important interactions with Met374 and Tyr155 in aromatase and in 17
  <em>β</em>-HSD1 respectively. Highlighting Compounds 2, 5 and 8 with an aromatic ring at the C4 position of the coumarin moiety, which favored arene-H type interactions essential for protein-ligand recognition. In addition, the results related to the 17
  <em>β</em>-HSD1 enzyme demonstrated how the length of the linker influences the interaction; the best score was found for derivative 8 with a chain of 8 methylenes.
 
</p></abstract><kwd-group><kwd>Estrone</kwd><kwd> Coumarins</kwd><kwd> Aromatase Inhibitors</kwd><kwd> 17&lt;i&gt;β&lt;/i&gt;-HSD1 Inhibitors</kwd><kwd> Molecular Docking</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>1. Introduction</title><p>Hormone Receptor positive (HR+) breast cancer is the most aggressive and frequent malignant neoplasm in women, representing the main cause of oncological mortality [<xref ref-type="bibr" rid="scirp.122263-ref1">1</xref>]. In this regard, aromatase inhibitors are compounds that suppress estrogen biosynthesis through reversible blockade of this enzyme and are mainly used as aids in the treatment of this condition [<xref ref-type="bibr" rid="scirp.122263-ref2">2</xref>]. Aromatase belongs to the group of the cytochrome P450 family, and in breast tissue, it catalyzes the demethylation of carbon 19 of androstenedione, producing an 18-carbon phenolic estrogen, estrone E1 [<xref ref-type="bibr" rid="scirp.122263-ref3">3</xref>]. Furthermore, estrone sulfate is the most abundant circulating estrogen in postmenopausal women and it can be converted to estrone via sulfatase [<xref ref-type="bibr" rid="scirp.122263-ref4">4</xref>]. In the same way, the 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1) enzyme is involved in the catalytic reduction of estrone to estradiol in both pathways and it is overexpressed in breast cancer cells [<xref ref-type="bibr" rid="scirp.122263-ref5">5</xref>]. Moreover, the inhibition of this enzyme prevents the formation of estradiol (E2), a hormone that stimulates the growth of breast tumors and endometriosis through the activation of the Estrogen Receptor α (ERα) [<xref ref-type="bibr" rid="scirp.122263-ref6">6</xref>], therefore, it was proposed as an interesting pharmacological target.</p><p>It has been described steroidal and non-steroidal inhibitors for these molecular targets, steroid inhibitors usually bind reversibly to the catalytic site of the enzyme, mimicking either the substrate or the product. In this context, aromatase and 17β-HSD1 enzymes have in common that estrone bind to both [<xref ref-type="bibr" rid="scirp.122263-ref7">7</xref>].</p><p>However, these antiestrogen compounds have limitations: their mixed agonist, antagonist profile (ERα), and the development of tumor resistance, while the non-steroidal inhibitors showed low selectivity and inhibits other CYP450 isoforms. Based on the above, it is evident the necessity of new molecules with dual action, the selective inhibition of both targets and simultaneously to reduce the risk of adverse effects, drug interactions and resistance (<xref ref-type="fig" rid="fig1">Figure 1</xref>) [<xref ref-type="bibr" rid="scirp.122263-ref8">8</xref>] - [<xref ref-type="bibr" rid="scirp.122263-ref14">14</xref>].</p><p>Coumarins are molecules formed by the union of a benzene and an α-pyrone [<xref ref-type="bibr" rid="scirp.122263-ref15">15</xref>]. These molecules have shown a wide variety of pharmacological activities, mainly antiproliferative effects. In addition, it has been observed that coumarins show in vitro inhibitory activities of some enzymes involved in cancer, which could secondarily attenuate the clinical progress and the pathophysiological manifestations observed in this disease [<xref ref-type="bibr" rid="scirp.122263-ref16">16</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref17">17</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref18">18</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref19">19</xref>]. Moreover, estrone derivatives or other steroidal compounds have greater specificity than non-steroidal ones for binding to enzymes involved in estrogen biosynthesis [<xref ref-type="bibr" rid="scirp.122263-ref20">20</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref21">21</xref>]. Considering the described above, we chose a model of study derivatives of estrone bearing a coumarin fragment.</p><p>Leonetti et al. have reported that the chain length of carbon atoms that function as linkers, directly influences the potency of the molecules. The absence or the presence of very short or very large linkers results in the decrease of aromatase inhibition and selectivity (molecular promiscuity). Therefore, the length of the linker can affect the inhibitory potency by changing the position of the H-bond acceptors in the ligand binding site [<xref ref-type="bibr" rid="scirp.122263-ref22">22</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref23">23</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref24">24</xref>].</p><p>The drug development process requires a multidisciplinary effort comprising main stages: 1) target selection and validation; 2) compound screening and lead optimization; 3) preclinical studies; and 4) clinical trials [<xref ref-type="bibr" rid="scirp.122263-ref25">25</xref>]. Therefore, this whole process takes an average of 800 million dollars and 15 years to complete [<xref ref-type="bibr" rid="scirp.122263-ref26">26</xref>]; for this reason, tools such as Computer-Aided Drug Design (CADD) have gained popularity in recent years, playing an important role in drug development. Automated Molecular Docking is the most widely used instrument in CADD, its purpose is to propose a binding mode between two molecules, with overall minimum energy, considering the principle of complementarity of the structures and interaction forces involved in molecular recognition [<xref ref-type="bibr" rid="scirp.122263-ref27">27</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref28">28</xref>]. In this sense, there are different types of interactions that can be essential in the affinity of a ligand with a protein target and in the stability of a ligand-protein complex. The nature of the interactions is diverse, for example: hydrogen-bridging type interactions (caused by steric effects due to entropy and solvent-related forces), electrostatic forces (charges), van der Waals interactions (electrodynamics forces) and hydrophobic interactions. The type of interaction observed is dependent on the size, shape, and physicochemical properties of the amino acid residues of the binding pocket and the class and flexibility of the ligands [<xref ref-type="bibr" rid="scirp.122263-ref29">29</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref30">30</xref>].</p><p>Thus, Molecular Docking is very useful to predict the binding mode of a ligand to a protein and its possible affinity to it, optimizing the development and discovery of new bioactive molecules and/or drugs. It also improves the designation of the leading compounds through the structure-activity relationship, and facing the synthesis stage, it helps to filter and prioritize certain compounds from a large collection of molecules, saving time and costs.</p><p>Accordingly, it was decided to carry out molecular docking only of Compounds (1 - 6) with linkers of 4 and 6 carbon atoms on the aromatase enzyme.</p><p>The proposed molecules 1 - 6 (<xref ref-type="fig" rid="fig1">Figure 1</xref>) were designed based on the following pharmacophoric fragments: three coumarins as a polar group (non-steroidal fragment) attached through hydrocarbon chains of different lengths to estrone as an enzyme recognition group. In this work, we have designed and screened in silico a series of new estrone derivatives with different groups of coumarins against aromatase and 17β-HSD1 enzymes to find new chemical entities that could achieve benefits in the treatment of breast cancer (HR+).</p></sec><sec id="s2"><title>2. Materials and Methods</title><sec id="s2_1"><title>2.1. Molecular Docking</title><p>The crystal structures of the aromatase and 17β-HSD1 were obtained from the Protein Data Bank (https://www.rcsb.org/) with the codes PDB: 5 JKW and 1 FDT, respectively. The molecular docking was carried out with the Molecular Operating Environment software (https://www.chemcomp.com/MOE%20v2020.0901).</p><p>The unnecessary molecules were removed (H<sub>2</sub>O and SO<sub>4</sub>), the hydrogen atoms, charges and energy minimization were adjusted with the AMBER10: EHT force field and R-field solvation from the MOE suite. The ligands (1 - 6) were built with ChemDraw Professional 16.0 software. The minimization and ionization of the compounds were performed with AMBER10: EHT as the force field. As a placement function Triangle matcher was selected, the scores were calculated with the London ΔG function and the selection of the best poses was made using the GBVI/WSA ΔG (Generalized-Born Volume Integral/Weighted Surface area) scoring function. These parameters were established for docking validation. The binding site was defined using the crystallographic ligand (orthosteric site). For each ligand it was generated 100 repetitions and carried out 100 poses. The best binding poses were visually inspected, the pose that most overlapped with the crystallographic ligand was chosen and its scores (ΔG = kcal/mol) was reported. The graphical representations of ligand interactions were created in MOE.</p></sec><sec id="s2_2"><title>2.2. Docking Validation</title><p>The Docking protocols were validated, by a redocking into the aromatase and 17β-HSD1 ligand-binding sites with its co-crystal-ligands Testosterone (TST) and estradiol (E2) respectively. The Root Mean Square Deviation (RMSD) between the co-crystal ligand and the redocked molecule of aromatase was 0.2912 &#177; 0.018 &#197; and to the17β-HSD1 was 0.1381 &#177; 0.0086 &#197;. Validation was performed in triplicate.</p></sec></sec><sec id="s3"><title>3. Results and Discussion</title><sec id="s3_1"><title>3.1. Aromatase (CYP19A1)</title><p>To validate our model preparation, the Root Mean Square Deviation (RMSD) was included as a measure of re-docked success. In which a value of 0.2912 &#177; 0.018 &#197; was obtained. <xref ref-type="fig" rid="fig2">Figure 2</xref> shows the pose with the lowest RMSD and a score of −8.3711 kcal/mol. It can be observed that the hydrophobic side chains Trp224, Phe221, Phe134, Ile133, Val370 and Met374 are placed around the testosterone molecule (TST, crystallographic ligand), shaping the ligand binding pocket (<xref ref-type="fig" rid="fig2">Figure 2</xref>). In addition, TST bonds with its 17β-hydroxyl oxygen and receives a hydrogen bond from the amide backbone -NH of Met374 [<xref ref-type="bibr" rid="scirp.122263-ref31">31</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref32">32</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref33">33</xref>].</p><p>To explain the presumable binding mode with human aromatase, Compounds 1 - 6 were subjected to an in silico molecular docking. The results revealed that Compounds 1 - 6 fit into the binding pocket and the carbonyl group (C17) of the steroid moiety form a hydrogen bond interaction with Met374. This portion achieved good overlap with the TST at the binding site and exhibited hydrophobic interactions with the amino acids that make up this region (<xref ref-type="fig" rid="fig2">Figure 2</xref>). It is important to mention that Compounds 2 and 5 obtained the best scores of −12.0826 kcal/mol and −12.0233 kcal/mol, respectively (<xref ref-type="fig" rid="fig3">Figure 3</xref>). It is known that aromatic rings can act as hydrogen bond acceptors stablishing meaningful interactions with the amino acid residues [<xref ref-type="bibr" rid="scirp.122263-ref34">34</xref>], the benzene ring attached to the coumarin fragment in Compounds 2 and 5 forms a H-arene interaction type with the amino acids Val369 and Val370.</p><p>Unlike most cytochrome P450 enzymes, near the active site of the aromatase there is a cavity large enough to shelter a secondary interaction with the substrate or with an additional non-steroidal molecule, this interaction could influence the enzymatic activity of the aromatase [<xref ref-type="bibr" rid="scirp.122263-ref22">22</xref>]. In this context, the coumarin</p><p>moiety of the studied compounds showed interactions involving the aromatic rings, these interactions are critical for protein-ligand recognition [<xref ref-type="bibr" rid="scirp.122263-ref35">35</xref>]. Compounds (2 and 5) substituted with a benzene ring at C4 of the coumarin portion (<xref ref-type="fig" rid="fig4">Figure 4</xref>), showed arene-H type interactions, the electron-rich π cloud interacts with hydrogen atoms (Δ+) of the amino acids Val369 and Val370 in Compound 2 (-NH), and with Ala438 in Compound 5 (-CH<sub>3</sub>). These additional interactions could be related with the score values obtained by the different ligands (<xref ref-type="table" rid="table1">Table 1</xref>), and therefore, with their probably affinity to the aromatase.</p><table-wrap id="table1" ><label><xref ref-type="table" rid="table1">Table 1</xref></label><caption><title> Additional interactions with the aromatase enzyme</title></caption><table><tbody><thead><tr><th align="center" valign="middle" >Ligand</th><th align="center" valign="middle" >∆G Binding</th><th align="center" valign="middle" >Conventional Hidrogen Bond</th><th align="center" valign="middle" >Hydrophobic Interactions</th><th align="center" valign="middle" >Others</th></tr></thead><tr><td align="center" valign="middle" >*TST</td><td align="center" valign="middle" >−8.3711</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477</td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >1</td><td align="center" valign="middle" >−11.3929</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443 Phe430 Val369 Pro429 Met364 Ile132 Leu152 Met303 Ala438 Met446 Phe148 Ile442</td><td align="center" valign="middle" >Gly439</td></tr><tr><td align="center" valign="middle" >2</td><td align="center" valign="middle" >−12.0826</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443 Phe430 Val369 Pro429 Met364 Pro368</td><td align="center" valign="middle" >Val369 Val370</td></tr><tr><td align="center" valign="middle" >3</td><td align="center" valign="middle" >−11.3581</td><td align="center" valign="middle" >Met374 Ala438</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443 Ile132 Leu152 Met303 Ala438 Met446 Phe148 Ile442</td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >4</td><td align="center" valign="middle" >−11.7687</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443 Phe430 Pro429 Met364 Leu152 Met303 Ala438 Met446 Met447</td><td align="center" valign="middle" ></td></tr><tr><td align="center" valign="middle" >5</td><td align="center" valign="middle" >−12.0233</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443 Phe430 Val369 Pro429 Met364Ile132 Leu152 Met303 Ala438 Met446 Phe148 Met447 Phe203</td><td align="center" valign="middle" >Met303 Val370 Ala438</td></tr><tr><td align="center" valign="middle" >6</td><td align="center" valign="middle" >−11.7957</td><td align="center" valign="middle" >Met374</td><td align="center" valign="middle" >Trp224 Phe221 Phe134 Ile133 Val370 Met374 Ile305 Ala306 Val373 Leu372 Leu477 Ala307 Met311 Ala443Ile132 Leu152 Met303 Ala438 Met446 Phe148 Ile442</td><td align="center" valign="middle" >Met303 Cys437</td></tr></tbody></table></table-wrap><p>Moreover, Compounds 1, 3 and 6 displayed hydrogen bond interactions with Met374, a key residue for the ligand recognition and aromatase inhibition; furthermore, they showed additional interactions at the coumarin fragment. Compound 1 showed π-H type interactions with the Gly439 residue and the α-pyrone ring of the coumarin skeleton, Compound 3 formed a hydrogen bond with Ala438, residue which acts as a backbone donor, while for Compound 6, the residues Met303 and Cys437 (amino acids with a sulfur atom), behaved as side chain acceptors (<xref ref-type="fig" rid="fig5">Figure 5</xref>).</p><p>According to the structure/score relationship analysis (binding energy) it was predicted for Compounds 1 - 6 better scores than those of the crystallographic ligand TST. Moreover, no relevant difference was observed in the binding energy between the compounds with a chain of 4 and 6 carbon atoms (<xref ref-type="fig" rid="fig6">Figure 6</xref>). However, Compounds 2 and 5 with the benzene substituent at position 4 of the coumarin fragment obtained the best scores of −12.0826 and −12.0233 kcal/mol, respectively. This observation indicates that the aromatic type substituents improve and even reinforce the interaction with the aromatase binding site.</p></sec><sec id="s3_2"><title>3.2. 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1)</title><p>In the validation of the 17β-HSD1 enzyme, an RMSD value of 0.2067 &#177; 0.0228 &#197; was obtained. <xref ref-type="fig" rid="fig7">Figure 7</xref> shows the pose with the lowest RMSD and a score of</p><p>−7.2788 kcal/mol. In this image, estradiol (E2, crystallographic ligand) is located near the catalytic triad (Ser142, Tyr155 and Lys195), the 17β-hydroxyl oxygen accepts a hydrogen bond from the -OH group of Tyr155.</p><p>The lipophilic pocket of the 17β-HSD1 is formed by Gly92, Leu93, Gly94, Ala291, Phe192 and Val196, which is connected to a hydrophilic zone composed of Ser142, Tyr155, Glu194 and Lys195; this hydrophilic zone is crucial for the catalytic reaction of estradiol [<xref ref-type="bibr" rid="scirp.122263-ref36">36</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref37">37</xref>]. It has been observed that some inhibitors of 17β-HSD1, with a steroidal moiety attached to a polar fragment through different methylene chains, establish interactions between the polar group and the cofactor binding site. Among the compounds tested, those with the best results are the derivatives with linkers of 6 or 8 methylenes. [<xref ref-type="bibr" rid="scirp.122263-ref11">11</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref38">38</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref39">39</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref40">40</xref>].</p><p>To favor secondary interactions that might improve the scores observed for 17β-HSD1, it was added three compounds bearing eight carbon atoms as a linker. The nine Compounds 1 - 9 showed interactions of the arene-H type with Tyr155 (<xref ref-type="fig" rid="fig8">Figure 8</xref> and <xref ref-type="fig" rid="fig9">Figure 9</xref>) and some of them with the hydrophobic residues Pro187 and Phe259 at the binding site.</p><p>Notably, the presence of the coumarin attached through variable chain lengths to the A ring of the steroidal moiety has cause a reverse orientation of the molecule in the active site, with the A ring facing the catalytic site (Tyr155), and D ring pointing to the recognition edge of the binding site (<xref ref-type="fig" rid="fig8">Figure 8</xref> and <xref ref-type="fig" rid="fig9">Figure 9</xref>). This inverse orientation causes inhibition of the enzyme, forming a dead-end complex that cannot be catalyzed. This type of inhibition, also reported in other enzymes, has been related with high concentrations of substrate [<xref ref-type="bibr" rid="scirp.122263-ref41">41</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref42">42</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref43">43</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref44">44</xref>] [<xref ref-type="bibr" rid="scirp.122263-ref45">45</xref>].</p><p>In the conversion of E1 (estrone) to E2 catalyzed by 17β-HSD1, NADPH behave as a co-factor; at the cofactor binding site, NADPH is surrounded by the amino acids Gly9, Cys10, Ser11, Ser12, Ile14, Gly15, Arg37, Asn90, Gly92, and Lys195, forming important hydrogen-bonding interactions (<xref ref-type="fig" rid="fig1">Figure 1</xref>0) [<xref ref-type="bibr" rid="scirp.122263-ref32">32</xref>]. It can be observed that for the products 1 - 9, the aliphatic linkers together with the coumarin fragments are in the same NADPHs cofactor binding region. Furthermore, in Compounds 1, 4, 6, 8 and 9, the oxygens of the lactone portion act</p><p>as hydrogen bond acceptors of the residues Ser11, Ser12, Gly15, Asn90 and Lys195. Moreover, the electron-rich π cloud of the unsaturated lactone moiety of Compounds 3, 5 and 7 interacted with hydrogen atoms (Δ+) of the amino acids Ile14, Leu93 and Gly92 in an arene-H interaction type. Additionally, Compounds 2 and 8 bearing a Ph group at the C4 position of coumarin, show an arene-H type interaction with Gly92 and Arg37 respectively (<xref ref-type="fig" rid="fig1">Figure 1</xref>1).</p><p>Although all nine compounds obtained good scores compared to E2, as the methylene chain increased from 4 to 8 atoms, better scores were obtained, highlighting Compounds 7 and 8 with scores of −10.2370 kcal/mol and −11.3970 kcal/mol respectively (<xref ref-type="fig" rid="fig1">Figure 1</xref>1).</p></sec></sec><sec id="s4"><title>4. Conclusions</title><p>The in silico analysis showed good score values in the proposed compounds, the steroidal portion presented important interactions with Met374 and Tyr155 in the catalytic site of aromatase and 17β-HSD1 respectively. Notably, Compounds 2, 5 and 8 with an aromatic ring attached to C4 of the coumarin moiety, favored arene-H type interactions, essential for protein-ligand recognition. In addition, for the enzyme 17β-HSD1, it was observed how the length of the hydrocarbon chain influences in the number of binding points, being Compound 8 with a chain of eight methylenes, the one that presented the best score. This linker allows the steroidal portion to locate into the substrate binding site, while the coumarin portion interacts with the cofactor binding site with amino acids Arg37 and Ser11.</p><p>As a result of the analysis performed in this work, it can be concluded that the increment of the length of the linker up to 8 methylenes, optimizes the number of interactions at different sections of the enzyme. Moreover, it has been established an excellent starting point for the synthetic stage of these promising molecules as inhibitors of these two enzymes related to breast cancer (HR+). Molecular docking helped predict the binding mode of the designed Compounds 1 - 9 and their target proteins and predict the affinity and probable activity of the molecules. The synthesis and enzyme inhibition studies of these compounds will help to corroborate the most suitable structure against these molecular targets.</p></sec><sec id="s5"><title>Acknowledgements</title><p>Authors thank CONACYT-M&#233;xico (Grant 320334 “Paradigmas y Controversias 2022”). S. A. M.-I. thanks CONACYT-M&#233;xico for the predoctoral grant.</p></sec><sec id="s6"><title>Conflicts of Interest</title><p>The authors declare no conflicts of interest regarding the publication of this paper.</p></sec><sec id="s7"><title>Cite this paper</title><p>Meza-Ireta, S.A., Colin-Lozano, B., Merino-Montiel, P., Vega-B&#225;ez, J.L. and Montiel-Smith, S. (2022) Molecular Docking Studies of Estrone-Coumarin Derivatives as Aromatase and 17β-HSD1 Inhibitors Related to Hormone Receptor Positive (HR+) Breast Cancer. 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