LXRs mRNA and protein expression in tissues, gene-disease association, network and pathway enrichment analysis represents their important roles in regulating physiological function
We first examined both mRNA and protein expression across various tissues using publicly available RNA-seq databases and human protein atlas, respectively [36, 37]. LXR-α expression is primarily found in fat and is limited to the liver, kidney, intestine, fat tissue, lung, and spleen. While, almost every tissue and organ express LXR-β (Fig. 1a, b). LXR-α and LXR-β exhibit overlap in several tissues and their tissue distribution patterns differ significantly. The contrasting expression patterns imply distinct roles for LXR-α and LXR-β in controlling physiological processes. Gene disease association study suggested LXR-α has been linked to multiple metabolic diseases, such as atherosclerosis, coronary heart disease, metabolic syndrome, type 2 diabetes, and coronary hyperlipidemia, as determined by DISGENET [39]. LXR-β also linked to several metabolic disorders and carcinomas (Fig. 2a).
Network analysis predicted that LXRs are either directly interact or physically associate with enzymes (KDM1A and SUV39H1), transcription factors (RXRG, RXRA, RXRB, and NCOR1) transporters (PPARA), and other important proteins (EDF1, MDFI and CORO2A) (Fig. 2b). These enzymes, transcription factors, and transporters are well known for their role in the regulation of cholesterol and lipids. The major pathways involved for LXRs are also established by pathway enrichment analysis by WebGestalt. The pathways include cholesterol metabolism, nuclear receptors in lipid metabolism and toxicity, cholesterol and lipid homeostasis, oxysterols derived from cholesterol, PPAR Alpha Pathway, white fat cell differentiation, and PPAR signaling pathway (Fig. 2c). Together these data suggest that pharmacological LXR activation by small molecules could be a pharmacotherapeutic solution to intervene in atherosclerosis.
Molecular docking approach targeting LXR-α
The Protein Data Bank (PDB) ID 1UHL is used for the LXRα active site. The grid box size was set to 55X55X55 Å and its coordinates were set to X = 44.53, Y = -2.4883, Z = 21.7037. The docked structure overlapped with the co-crystallized structure to a large extent, and the docking method adequately simulated the ligand-protein interaction, as evidenced by the calculated root-mean-square deviation (RMSD) value of 1.931 Å, which fit within the accepted literature values (< 2 Å). The best conformation showed an affinity for T0901317, BMS-779788, BMS-852927, SR9243, GSK3987, AZ876, GW3965, 24(S)-hydroxycholesterol, LXR-623, 22(R)-hydroxycholesterol, and Oxycholesterol (Fig. 3 and Table 1). It has been shown that T0901317 has the highest binding affinity for LXRα of all the ligands studied, signifying that T0901317 has the highest potential for a strong interaction with LXR-α, which may lead to its inhibition and subsequent expression of its therapeutic effects. Figure 3a–c depicts the in-depth 2D and 3D interactions of T0901317 with different amino acids of LXR-α. Binding affinity for other molecules has been shown in Table 1. BMS-779788 interacts with PHE229, LEU260, VAL263, SER264, and ASP318, and Oxycholesterol, having the lowest docking score (-6.5 kcal/mol), interacts with PHE229, LEU260, VAL263, SER264, ASP318, and PHE326.
Table 1
Binding affinity of ligands within the binding pocket and interacting amino acid of LXR-α.
Ligand | 3D structure with protein | Binding Affinity (Kcal/mol) | rmsd/ub | rmsd/lb | Interacting amino acid |
T0901317 | | -10.2 | 2.153 | 1.402 | GLU308, VAL311, GLN313, SER383, ARG387, ILE389, LYS435 |
AZ876 | | -8.5 | 5.52 | 2.891 | ILE370, ARG373, ALA374, TRP376, LYS452, LEU504, PHE508 |
BMS-779788 | | -8.3 | 1.746 | 1.312 | GLU308, GLU312, HIS386, ARG387, ILE389, LEU396, LYS435 |
BMS-852927 | | -8.2 | 30.743 | 26.208 | ILE370, ARG373, ALA374, LYS452, ARG497, LEU501, LEU504, PHE503, ALA528 |
GSK3987 | | -7.4 | 8.99 | 3.51 | ILE370, ARG373, ALA374, GLU378, LEU501, LEU504, ALA528 |
LXR-623 | | -7.3 | 4.489 | 2.429 | ARG373, ALA374, ASN377, GLU378, LYS452, ARG497, LEU501, LEU504, MET525 |
SR9243 | | -7.2 | 10.006 | 3.63 | GLU312, HIS386, ARG387, ILE389, LEU396, LYS435, LEU438 |
GW3965 | | -7.0 | 4.685 | 2.761 | ARG373, ALA374, ASP450, ARG497, LEU504 |
24S-hydroxycholesterol | | -6.9 | 5.959 | 4.397 | ILE445, TYR468, LEU490, LEU493, PRO494 |
Oxycholesterol | | -6.5 | 2.06 | 1.466 | ARG387, ILE389, ARG443 |
*rmsd/lb (root mean square deviation/upper bound); *rmsd/lb(root mean square deviation/lower bound) |
GSK3987 has a binding affinity of − 7.4 kcal/mol and binds to the following amino acids: SER366, VAL386, GLU387, HIS390, PHE404, LEU408, LEU411, and ARG415. AZ876 has an affinity of − 8.5 kcal/mol towards LXR-α and interacts with the following amino acids: THR292, ARG369, PRO370, ASN371, ARG415, TRP443, and ASP444. GW3965 showed an affinity of − 7.0 kcal/mol and interacted with the following amino acids: ARG226, PHE229, VAL263, ARG305, and TYR306. While LXR-623 showed the affinity for LXR-α (− 7.3 kcal/mol), binds to the following amino acids: ARG373, ALA374, ASN377, GLU378, LYS452, ARG497, LEU501, LEU504, MET525. Further research is necessary to confirm the hypothesis that the increased number of interactions between the amino acids of LXR-α and the tested compounds is linked to higher binding affinities and greater potential for LXR-α activation.
Molecular docking approach targeting LXR-β
Similar to the protocol for LXR-α, the native PDB protein-ligand with ID 5JY3 was redocked, and the RMSD was calculated. In the case of LXR-β, the protein was co-crystallized with AZ876 (Fig. 4). The calculated RMSD value for docked versus co-crystallized AZ876 is 1.271 Å. The size of the grid box is unchanged (55X55X55 Å) and the coordinates are X = 31.0537, Y = 19.3507, and Z = 13.216. Figure 4a–c depicts the in-depth 2D and 3D interactions of AZ876 with different amino acids of LXR-β. Binding affinity for other molecules has been shown in Table 2.
Table 2
Binding affinity of ligands within the binding pocket and interacting amino acid of LXR-β.
Ligand | 3D structure with protein | Binding Affinity (Kcal/mol) | rmsd/ub | rmsd/lb | Interacting amino acid |
AZ876 | | -10.8 | 1.625 | 1.734 | PHE268, PHE271, LEU274, ALA275, MET312, PHE 329, LEU345, ILE353, HIS435 |
SR9243 | | -10.3 | 2.122 | 1.466 | PHE268, SER274, ALA275, ILE309, MET312, LEU313, PHE329, LEU330, LEU345, PHE349, ILE350, ILE353, HIS435 |
22R-hydroxycholesterol | | -9.8 | 1.731 | 1.857 | LEU274, ALA275, SER278, PHE 329, LEU345, HIS435 |
GW3965 | | -9.8 | 2.702 | 1.642 | PHE271, LEU274, ALA275, MET312, PHE329, PHE340, LEU345, HIS435 |
LXR-623 | | -9.8 | 1.387 | 1.766 | PHE268, LEU274, ALA275, LEU345, ILE353, HIS435 |
T0901317 | | -9.7 | 3.589 | 2.528 | PHE272, SER274, ALA275, GLU281, MET312, THR316, ARG319, PHE329, LEU330, LEU345, ILE353 |
GSK3987 | | -9.2 | 3.57 | 2.39 | ALA275, LEU345, HIS435 |
BMS-779788 | | -9.0 | 2.213 | 2.81 | PHE271, ALA275, ILE309, MET312, PHE329, PHE340, LEU345, HIS435 |
BMS-852927 | | -8.9 | 3.09 | 2.356 | PHE271, ALA275, LYS305, ILE309, MET312, PHE329, PHE340, LEU345, HIS435, SER436 |
Oxycholesterol | | -8.3 | 1.201 | 1.754 | PHE268, PHE271, MET312, ILE327, PHE329, PHE340, LEU345, ILE353 |
24S-hydroxycholesterol | | -8.1 | 2.714 | 2.472 | PHE268, LEU274, ALA275, MET312, PHE329, LEU345, ILE353, HIS435 |
rmsd/lb (root mean square deviation/upper bound); rmsd/lb(root mean square deviation/lower bound) |
Subsequently, other ligands, including AZ876, BMS-779788, BMS-852927, GSK3987, GW3965, LXR-623, SR9243, 24(S)-hydroxycholesterol, 22(R)-hydroxycholesterol and Oxycholesterol, all with demonstrated affinities for LXR-β, have been docked. Protein preparation was carried out according to the data presented in the materials and methods section. The binding affinities of the docked ligands are presented in Table 2. Of the examined ligands, AZ876 has the highest affinity for LXR-β, with − 10.8 kcal/mol, and interacts with the following amino acids: ILE25, ALA28, ALA29, GLN32, TRP62, ASN63, LEU66, ILE67, PHE70, LEU83, ALA84, ILE102, CYS189, HIS192, and PHE196 (Fig. 3). BMS-779788, which has a lower affinity than BMS-852927 and interacts with GLN32, TRP62, ASN63, LEU66, ILE67, PHE70, LEU83, ALA84 and ILE102, while BMS-852927 has an affinity of − 8.9 kcal/mol and interacts with ALA28, ALA29, GLN32, TRP62, ASN63, LEU66, ILE67, PHE70, LEU83, ALA84, and ILE102 (Table 2).
Virtual screening of the most promising compounds
In order to identify new compounds targeting LXR-α and LXR-β, a search for target compounds in the ZINC online database was performed using SwissSimilarity online platform. SwissSimilarity provides multiple compound databases for screening, including authorized pharmaceuticals, widely accessible commercial compounds, and acknowledged biomolecules [32]. Based on the structure of T0901317, the compound with the highest binding affinity to LXR-α, 8 structures (ZINC000001550221, ZINC000000985503, ZINC000058101934, ZINC000095464663, ZINC000003243391, ZINC000016130131, ZINC000001042265, ZINC000031669066) were found with similarity scores ranging from 0.985 to 0.526 (Fig. 5 and Table 3). The similarity score shows the similarity between T0901317 and the newly identified compounds (Fig. 5 and Table 3). The name assigned by the ZINC database, the chemical structure in 2D and 3D format, and the protein affinity resulting from the docking process for the three most relevant (highest binding affinities to LXR-α) compounds not used in medical practice are shown in Figs. 5 and 7.
Table 3
Binding affinity of newly ligands within the binding pocket and interacting amino acid of LXR-α.
Ligand | Similarity score | Binding Affinity (Kcal/mol) | rmsd/ub | rmsd/lb | Interacting amino acid |
ZINC000001550221 | 0.985 | -10.2 | 2.153 | 1.402 | ARG373, ALA374, ASN377, GLU378, LYS452, ARG497, LEU501, LEU504, MET525 |
ZINC000000985503 | 0.926 | -9.8 | 5.52 | 2.891 | GLU312, HIS386, ARG387, ILE389, LEU396, LYS435, LEU438 |
ZINC000058101934 | 0.837 | -10.13 | 1.746 | 1.312 | ARG373, ALA374, ASP450, ARG497, LEU504 |
ZINC000095464663 | 0.817 | -12.3 | 3.743 | 2.208 | ILE445, TYR468, LEU490, LEU493, PRO494 |
ZINC000003243391 | 0.709 | -9.6 | 8.99 | 3.51 | GLU378, ARG464, TYR468, PHE486, LEU490, LEU491, PRO494 |
ZINC000016130131 | 0.637 | -8.2 | 4.489 | 2.429 | ARG373, ALA374, ASN377, GLU378, LYS452, ARG497, LEU501, LEU504, MET525 |
ZINC000001042265 | 0.568 | -7.4 | 1.746 | 1.312 | ARG373, ALA374, ASP450, ARG497, LEU504 |
ZINC000031669066 | 0.526 | -7.3 | 3.743 | 2.208 | ILE445, TYR468, LEU490, LEU493, PRO494 |
rmsd/lb (root mean square deviation/upper bound); rmsd/lb(root mean square deviation/lower bound) |
The compound ZINC000095464663 presented the highest binding affinity for LXR-α in the present virtual screening study, suggesting that it may be a potential candidate for developing a drug to target LXR-α. The binding affinity quantifies the interaction intensity between a ligand and its target protein. It assesses the ligand–protein complex’s stability, and a more negative value suggests a greater affinity for binding. This range encompasses the binding affinity of ZINC000095464663, ZINC000058101934, ZINC000003243391, ZINC000016130131, ZINC000001042265, and ZINC000031669066 is shown in Table 3. Out of all the ligands tested, 2D analysis of compound ZINC000095464663 has revealed that it interacts with SER383, HIS386, ARG387, ILE389, ASP390, LYS435, LEU438 and GLU308, GLU312. The amino acids involved in the interactions were vander waals, alkyl, pi-alkyl, amide-pi stacked, conventional hydrogen bond, and carbon hydrogen bond. The most frequent type of interaction among these was a conventional hydrogen bond, followed by pi-sulfur, amide-pi stacked, alkyl, and pi-alkyl interactions with GLU312, ILE389, LYS435, and LEU438. Fluorine and benzene atoms, which are widely used to enhance the properties of chemical compounds, are responsible for the majority of the interactions between the molecule and the protein. The following amino acids interact with these functional groups: ARG387, ILE389, GLU308, SER383, HIS386 and GLU312. The N-{2‐[(1R)‐2,2,2‐trifluoro‐1‐hydroxyethyl]phenyl group interacts with GLU308 and SER383, benzene group interacts with GLU312, ARG387, ILE389, and sulfonamide group interacts with HIS386 and LYS435 (Fig. 6)
Like the protocol for LXR-α, molecular docking evaluation suggested that AZ876 had the highest affinity for the amino acids of the LXR-β protein. Based on the structure of AZ876, 400 ligands were identified with similarity scores ranging from 0.94 to 0.354 (Suppl. Table 1). The name assigned by the ZINC database, the 2D and 3D structure, the similarity score, and the affinity towards LXR-β resulting from the docking process for the ten most promising compounds not used in pharmacotherapies are shown in Fig. 7. The compound ZINC000021912925 presented the highest binding affinity for LXR-β in the present virtual screening study, suggesting that it may be a potential candidate for developing a drug to target LXR-β due to a possible effective interaction with the target (Fig. 7 and Table 4). The binding affinities of compounds targeting LXR-β have been reported in the literature from in silico studies to range from − 8.1 kcal/mol to − 10.8 kcal/mol. In the present analysis, the binding affinity of all the top ten molecules falls within the range commonly found in the scientific literature (Fig. 8 and Table 4). The compound ZINC000021912925 has the highest affinity for LXR-β and binds to PHE271, MET312, PHE329, LEU345, and HIS435 amino acids (Fig. 7). Although the N-(2,3‑dimethylphenyl) group interacts with the amino acids PHE271, LEU345, and HIS435; the 2,3‐dihydro‑1lambda6,2‐thiazol group in the molecule contributes only one interaction with the protein (Fig. 8).
Table 4
Binding affinity of newly identified top ten ligands within the binding pocket and interacting amino acid of LXR-β.
Ligand | Similarity score | Binding Affinity (Kcal/mol) | rmsd/ub | rmsd/lb | Interacting amino acid |
ZINC000021912925 | 0.816 | -11.7 | 2.122 | 1.466 | PHE272, SER274, ALA275, GLU281, MET312, THR316, ARG319, PHE329, LEU330, LEU345, ILE353 |
ZINC000021913093 | 0.795 | -10.8 | 1.625 | 1.734 | PHE268, LEU274, ALA275, LEU345, ILE353, HIS435 |
ZINC000021913098 | 0.787 | 10.03 | 1.325 | 1.724 | LEU274, ALA275, LEU345, ILE353, HIS435 |
ZINC000021913127 | 0.600 | -9.8 | 1.731 | 1.857 | ALA275, LEU345, HIS435 |
ZINC000095446598 | 0.496 | -9.8 | 2.702 | 1.642 | PHE271, ALA275, ILE309, MET312, PHE329, PHE340, LEU345, HIS435 |
ZINC000036398658 | 0.485 | -9.5 | 1.625 | 1.734 | PHE268, LEU274, ALA275, LEU345, ILE353, HIS435 |
ZINC000037207255 | 0.48 | -9.2 | 2.531 | 1.257 | PHE272, LEU274, ALA275, LEU345, ILE353, HIS435 |
ZINC000040555976 | 0.47 | -8.7 | 1.724 | 1.625 | PHE268, LEU274, ALA275, LEU345, ILE353, HIS435 |
ZINC000014043132 | 0.447 | -9.1 | 1.857 | 1.325 | GLU281, MET312, THR316, ARG319, PHE329, LEU330, LEU345, ILE353 |
ZINC000019867701 | 0.443 | -8.9 | 1.642 | 1.731 | SER274, ALA275, GLU281, MET312, THR316, ARG319, PHE329 |
*rmsd/lb (root mean square deviation/upper bound); *rmsd/lb(root mean square deviation/lower bound) |
In silico evaluation of the chemico-pharmacokinetic profile of the known and the newly identified compounds
To support potential candidate in drug discovery process, it is necessary to compute physicochemical descriptors and predict ADME parameters, pharmacokinetic properties, druglike nature, and medicinal chemistry of one or more small molecules. We assessed the chemico-pharmacokinetic profile of both known and newly identified compounds in silico, using the SwissADME. The results of chemico-pharmacokinetic parameters obtained after processing the data introduced into the platform is shown in Table 5 and Suppl. Tables 2, 3 and 4. Important features tested include physicochemical — Molecular Weight, Rotatable bonds, H-bond acceptors, H-bond donors, MR, TPSA; lipophilicity — iLOGP, XLOGP3, WLOGP, MLOGP, Silicos-IT Log P, Consensus Log P; water solubility — ESOL Log S, ESOL Solubility (mg/ml), ESOL Solubility (mol/l), ESOL Class, Ali Log S, Ali Solubility (mg/ml), Ali Solubility (mol/l), Ali Class, Silicos-IT LogSw, Silicos-IT Solubility (mg/ml), Silicos-IT Solubility (mol/l), Silicos-IT class; pharmacokinetics — GI absorption, BBB permeant, Pgp substrate, CYP1A2 inhibition, CYP2C19 inhibition, CYP2C9 inhibition, CYP2D6 inhibition, CYP3A4 inhibition, log Kp (cm/s); druglikeness — Lipinski violations, Ghose violations, Veber violations, Egan violations, Muegge violations, bioavailability score; medicinal chemistry — PAINS alerts, Brenk, alerts, Leadlikeness, violations, synthetic accessibility (Table 5 and Suppl. Tables 2, 3 and 4)
Table 5
Chemico-Pharmacokinetics features of T0901317, AZ876 and the newly identified molecule, determined in SwissADME
Features | T0901317 | ZINC000095464663 | AZ876 | ZINC000021912925 |
Physicochemical Properties |
MW | 481.33 | 399.31 | 439.57 | 414.43 |
#Heavy atoms | 31 | 26 | 31 | 29 |
#Aromatic heavy atoms | 12 | 12 | 12 | 12 |
Fraction Csp3 | 0.29 | 0.2 | 0.38 | 0.15 |
#Rotatable bonds | 8 | 6 | 5 | 7 |
#H-bond acceptors | 12 | 9 | 3 | 6 |
#H-bond donors | 1 | 2 | 1 | 1 |
MR | 89.46 | 79.68 | 132.74 | 109.93 |
TPSA | 65.99 | 74.78 | 78.1 | 118.23 |
Lipophilicity |
iLOGP | 2.84 | 1.92 | 3.7 | 2.83 |
XLOGP3 | 4.94 | 4.14 | 4.51 | 2.49 |
WLOGP | 9.51 | 7.08 | 4.56 | 2.52 |
MLOGP | 3.65 | 3.13 | 2.41 | 0.62 |
Silicos-IT Log P | 3.94 | 3.26 | 2.81 | 1.73 |
Consensus Log P | 4.98 | 3.91 | 3.6 | 2.04 |
Water Solubility |
ESOL Log S | -5.69 | -4.87 | -5.36 | -3.82 |
ESOL Solubility (mg/ml) | 9.72E-04 | 5.39E-03 | 1.91E-03 | 6.24E-02 |
ESOL Solubility (mol/l) | 2.02E-06 | 1.35E-05 | 4.33E-06 | 1.51E-04 |
ESOL Class | Moderately soluble | Moderately soluble | Moderately soluble | Soluble |
Ali Log S | -6.06 | -5.42 | -5.87 | -4.62 |
Ali Solubility (mg/ml) | 4.16E-04 | 1.53E-03 | 5.91E-04 | 9.99E-03 |
Ali Solubility (mol/l) | 8.65E-07 | 3.82E-06 | 1.34E-06 | 2.41E-05 |
Ali Class | Poorly soluble | Moderately soluble | Moderately soluble | Moderately soluble |
Silicos-IT LogSw | -6.56 | -6.06 | -6.74 | -5.64 |
Silicos-IT Solubility (mg/ml) | 1.34E-04 | 3.48E-04 | 8.05E-05 | 9.43E-04 |
Silicos-IT Solubility (mol/l) | 2.78E-07 | 8.71E-07 | 1.83E-07 | 2.28E-06 |
Silicos-IT class | Poorly soluble | Poorly soluble | Poorly soluble | Moderately soluble |
Pharmacokinetics |
GI absorption | Low | Low | High | High |
BBB permeant | No | No | No | No |
Pgp substrate | No | No | No | No |
CYP1A2 inhibitor | No | No | No | No |
CYP2C19 inhibitor | Yes | Yes | Yes | Yes |
CYP2C9 inhibitor | Yes | Yes | Yes | Yes |
CYP2D6 inhibitor | No | No | Yes | No |
CYP3A4 inhibitor | Yes | Yes | Yes | Yes |
log Kp (cm/s) | -5.73 | -5.8 | -5.78 | -7.06 |
Druglikeness |
Lipinski #violations | 0 | 0 | 0 | 0 |
Ghose #violations | 2 | 1 | 1 | 0 |
Veber #violations | 0 | 0 | 0 | 0 |
Egan #violations | 1 | 1 | 0 | 0 |
Muegge #violations | 1 | 0 | 0 | 0 |
Bioavailability Score | 0.55 | 0.55 | 0.55 | 0.55 |
Medicinal Chemistry |
PAINS #alerts | 0 | 0 | 1 | 0 |
Brenk #alerts | 0 | 0 | 0 | 0 |
Leadlikeness #violations | 3 | 2 | 2 | 1 |
Synthetic Accessibility | 2.66 | 3.07 | 4.25 | 3.63 |
Molecular weight indicates that all four compounds, T0901317 (481.33), ZINC000095464663 (399.31), AZ876 (439.57), and ZINC000021912925 (414.43) may exhibit rapid absorption and easy elimination (Table 5). These compounds meet all of Lipinski's criteria for estimating a small drug molecule's oral bioavailability: molecular weight less than 500 g/mol, maximum number of rotatable bonds less than 10, maximum number of H-bond donors and acceptors, and LogP (octanol–water partition coefficient) less than 5 (Table 5). According to the Lipinski principles, small, lipophilic, or hydrophobic molecules with a limited number of hydrogen bond donors and acceptors are more likely to achieve good oral bioavailability because they can easily pass through the intestines' cellular membrane and enter the bloodstream [33–35]. However, GI absorption of T0901317 ZINC000095464663 is low, while for AZ876 and ZINC000021912925, it is high. All other pharmacokinetics parameters are similar for all these four molecules, only log Kp (cm/s) is a little higher for ZINC000021912925 (Table 5). Important features were found that can help with the framework's design so that the two newly discovered compounds can be used in the future.