Docking Analysis
Due to the roles growth factor receptors play in the development and progression of cancer, it is necessary to develop suitable drug candidates that can effectively inhibit growth factors at the sites of receptors with little or no effects. Binding affinity between ligands and receptors is determined by the binding energy, the lower the energy the higher the binding affinity [9]. For this purpose, 50 bioactive compounds were screened against ERRB2/HER2, ERRB3/HER3, VEGFR-2, VEGFR-3 and FGFR-2. Commonly used anticancer drugs (Dovitinib and Gefitinib) that have activities against the target receptors were docked against the proteins and their binding energies used as comparison with the binding energies of the selected. After docking, the binding energy(kcal/mol), number of hydrogen bond, inhibitory constant (μM/nM) and amino acids involved in hydrogen bonding were noted.
Out of the 50 phytochemicals, 14 have binding energy comparable to the standard drug for HER2 (Table 1, Fig. 1). Dovitinib and Gefitinib have binding energy of-6.03Kcal/mol and -6.59Kcal/mol respectively, with amino acid involved in hydrogen bond as LYS1326 and GLN1329 for Dovitinib and LEU1291 for Geftinib
Table1. Interaction of phytochemicals with target protein HER-2
Phytochemicals
|
Binding Energy (Kcal/mol)
|
Inhibition constant(µM)
|
Number of Hydrogen bond
|
Amino Acids involved in hydrogen bonding
|
Andrographolide
|
-7.19
|
5.32
|
3
|
GLU 1290, LEU 1291, LEU 1354, SER 1294, LYS 1355, ILE 1295
|
Colchicine
|
-8.07
|
1.21
|
3
|
ILE 1295, PHE 1293, LYS 1287
|
Corydine
|
-6.63
|
13.83
|
4
|
GLN 1319, SER 1294, PHE 1293, ILE 1295
|
Crocetin
|
-7.39
|
3.86
|
2
|
ASN 1359, ILE 1295
|
Curdione
|
-7.14
|
5.81
|
2
|
LEU 1291, GLY 1292
|
Nimbolide
|
-7.55
|
2.91
|
2
|
LYS 1355, PHE 1293
|
Oleanolic acid
|
-7.87
|
1.71
|
1
|
PHE 1293
|
Panaxadiol
|
-7.08
|
6.45
|
2
|
ILE 1293, LEU 1291
|
Panaxatriol
|
-6.94
|
8.23
|
1
|
PHE 1293
|
Salvicine
|
-6.61
|
14.18
|
4
|
LEU 1291, PHE 1357, LYS 1287, PRO 1289
|
Tetrandrine
|
-7.06
|
6.67
|
1
|
SER 1294
|
Ursolic acid
|
-7.32
|
4.34
|
2
|
ILE 1295, LEU 1291
|
Withaferin A
|
-8.29
|
833.27nM
|
2
|
THR 1316, SER 1294
|
Hecogenin
|
-9.00
|
252.95nM
|
2
|
ILE 1295, PRO 1289
|
Dovitinib (Standard drug)
|
-6.03
|
37.91
|
2
|
LYS 1326, GLN 1329
|
Gefitinib (Standard drug)
|
-6.59
|
14.83
|
1
|
LEU 1291
|
19 phytochemicals for HER3 as shown in Table 2 and Fig. 2, having Dovitinib and Gefitinib with binding energy of-8.77Kcal/mol and -6.89Kcal/mol, with amino acid involved in hydrogen bond as LEU771 for Dovitinib and CYS721 and LEU771 for Geftinib.
Table 2. Interaction of phytochemicals with target protein HER-3
Phytochemicals
|
Binding Energy (Kcal/mol)
|
Inhibition constant (µM)
|
Number of Hydrogen bond
|
Amino Acids involved in hydrogen bonding
|
Andrographolide
|
8.07
|
1.21
|
4
|
LYS 723, LEU 771, GLY 774, ASP 833
|
Bassic acid
|
-8.14
|
1.08
|
2
|
PRO 772, ASN 820
|
Crocetin
|
-7.81
|
1.90
|
2
|
GLN 769, LYS 853
|
Curdione
|
-7.26
|
4.76
|
0
|
-
|
Etoposide
|
-7.51
|
3.12
|
4
|
LEU 771, LYS 723, PHE 701, ASN 815
|
Genkwanin
|
-7.00
|
7.37
|
3
|
LEU 771, LYS 723, ASP 833
|
Licochalcone A
|
-7.04
|
6.90
|
2
|
LYS 723, VAL 753
|
Nectandrin B
|
-7.23
|
4.98
|
2
|
ASN 820, PHE 834
|
Nimbolide
|
-7.83
|
1.81
|
3
|
PHE 701, LYS 723, LYS 853
|
Oleanolic acid
|
-9.86
|
59.54nM
|
3
|
THR 768, LYS 723, ARG 819
|
Panaxadiol
|
-10.04
|
43.39nM
|
0
|
----
|
Panaxatriol
|
-8.91
|
296.37nM
|
1
|
ASP 833
|
Salvicine
|
-8.83
|
337.56nM
|
2
|
ASP 833, GLN 769
|
Tetrandine
|
-7.34
|
4.18
|
1
|
ARG 781
|
Theaflavin
|
-7.90
|
1.62
|
5
|
LEU 771, GLN 769, CYS 721, THR 768, ASP 833
|
Tylophorine
|
-7.55
|
2.94
|
2
|
CYS 721, LYS 723
|
Ursolic acid
|
-9.72
|
75.31nM
|
1
|
ARG 819
|
Withaferin A
|
-11.69
|
2.69nM
|
3
|
VAL 753, ASP 833, LEU 771
|
Hecogenin
|
-10.50
|
20.16nM
|
3
|
CYS 721, ASP 833, ASP 778
|
Dovitinib (Standard drug
|
8.77
|
373.68nM
|
1
|
LEU 771
|
Gefitinib (Standard drug)
|
-6.89
|
8.83
|
2
|
CYS 721, LEU 771
|
6 phytochemicals for VEGFR-2 shown in Table 3 and Fig. 3 with-8.84Kcal/mol and -8.70Kcal/mol binding energies for Dovitinib and Gefitinib respectively and amino acids GLU917 for Dovitinib and ASP1046 and CYS919 for Geftinib.
Table 3 Interaction of phytochemicals with target protein VEGFR-2
Phytochemicals
|
Binding Energy (Kcal/mol)
|
Inhibition constant (nM)
|
Number of Hydrogen bond
|
Amino Acids involved in hydrogen bonding
|
Oleanolic acid
|
-9.05
|
231.22
|
2
|
ARG 1027, 1LE 1044
|
Panaxadiol
|
-9.51
|
106.28
|
3
|
ARG 1027, HIS 1026, ILE 1044
|
Panaxatriol
|
-9.13
|
202.47
|
3
|
ARG 1027, HIS 1026, 1LE 1044
|
Ursolic acid
|
-9.11
|
210.11
|
3
|
ASP 814, ARG 1027, ILE 1044
|
Withaferin A
|
-9.53
|
103.00
|
2
|
GLU 885, ILE 1025
|
Hecogenin
|
-9.82
|
314.06
|
2
|
ARG 1027, GLU 818
|
Dovitinib (Standard drug)
|
-8.84
|
331.58
|
1
|
GLU 917
|
Gefitinib (Standard drug)
|
-8.70
|
422.57
|
2
|
ASP 1046, CYS 919
|
10 phytochemicals for VEGFR-3 as seen in Table 4 and Fig. 4 with binding energy of -6.07Kcal/mol and -5.94Kcal/mol for dovitinib and Geftinib respectively, having amino acid SER455, GLN457, LEU454 for Dovitinib and ASN515, TYR448 GLU391 for Geftinib.
Table 4 Binding Parameters between ligands and target protein VEGFR-3
Phytochemicals
|
Binding Energy (Kcal/mol)
|
Inhibition constant (µM)
|
Number of Hydrogen bond
|
Amino Acids involved in hydrogen bonding
|
Bassic acid
|
-6.14
|
31.80
|
2
|
GLU 344, ASN 515
|
Nectandrin B
|
-6.08
|
34.69
|
3
|
GLY 513, ASN 515, THR 394
|
Nimbolide
|
-6.58
|
15.08
|
1
|
LEU 454
|
Oleanolic acid
|
-7.59
|
2.75
|
3
|
SER 537, SER 455, LEU 454
|
Panaxadiol
|
-7.11
|
6.10
|
1
|
LEU 454
|
Panaxatriol
|
-6.79
|
10.49
|
1
|
ASN 515
|
Tetrandine
|
-6.44
|
19.13
|
|
|
Ursolic acid
|
-7.42
|
3.65
|
2
|
LEU 452, GLY 513
|
Withaferin A
|
-7.27
|
4.72
|
3
|
LEU 452, VAL 418, THR 394
|
Hecogenin
|
-7.45
|
3.44
|
1
|
LEU 452
|
Dovitinib (Standard drug)
|
-6.07
|
35.59
|
3
|
SER 455, GLN 457, LEU 454
|
Gefitinib (Standard drug)
|
-5.94
|
44.14
|
3
|
ASN 515, TYR 448, GLU 391
|
Lastly, 19 phytochemicals have binding energy comparable to standard drug for FGFR-2 (Table 5, Fig. 5),dovitinib has an energy of -6.72Kcal/mol with amino acid involved in hydrogen bond as ASN571, whilegeftinib has binding energy as and -7.84Kcal/mol and amino acid ALA567. From these results, we selected 13 phytochemicals with lowest binding energy comparable to standard drugs found in at least three of the target proteins, these where used for furtherinsilico studies.
Table 5. Interaction of phytochemicals with target protein FGFR-2
Phytochemicals
|
Binding Energy (Kcal/mol)
|
Inhibition constant (µM)
|
Number of Hydrogen bond
|
Amino Acids involved in hydrogen bonding
|
Andrographolide
|
-7.42
|
3.62
|
1
|
ALA 567
|
Bassic acid
|
-7.64
|
2.51
|
4
|
GLU 574, GLU 489, ASP 644, LYS 517
|
Chrysin
|
-6.82
|
10.06
|
2
|
ALA 567, LEU 487
|
Curdione
|
-7.27
|
4.69
|
1
|
LYS 517
|
Emodin
|
-7.37
|
3.94
|
3
|
GLU 565, ALA 567, LEU 487
|
Eriodyctiol
|
-6.72
|
11.96
|
3
|
GLU 565, ALA 567, GLU 574
|
Isorhamnetin
|
-6.87
|
9.26
|
5
|
LEU 487, ALA 567, GLU 565, ASP 644, GLU 534
|
Nectandrin B
|
-7.50
|
3.20
|
3
|
ASN 571, GLU 574, LYS 517
|
Nimbolide
|
-8.17
|
1.03
|
3
|
ALA 567, ASN 631, GLU 565
|
Oleanolic acid
|
-8.77
|
372.58nM
|
1
|
GLU 489
|
Panaxadiol
|
-9.02
|
244.6nM
|
1
|
GLU 574
|
Panaxatriol
|
-8.61
|
486.38nM
|
1
|
GLU 574
|
Salvicine
|
-7.86
|
1.73
|
2
|
GLU 574, ASN 571
|
Tetrandine
|
-7.69
|
2.32
|
2
|
GLU 604, TYR 606
|
Theaflavin
|
-6.90
|
8.71
|
5
|
ASP 644, GLU 534, ALA 567, ASN 571, GLU 489
|
Tylophorine
|
-7.61
|
2.66
|
1
|
LYS 517
|
Ursolic acid
|
-8.61
|
490.22nM
|
3
|
ASP 644, LYS 517, GLU 574
|
Withaferin A
|
-8.63
|
469.67nM
|
3
|
GLU 565, ALA 567, LYS 517
|
Hecogenin
|
-8.87
|
314.06nM
|
1
|
ALA 567
|
Dovitinib (Standard drug)
|
-6.72
|
11.80
|
1
|
ASN 571
|
Gefitinib (Standard drug)
|
-7.84
|
1.80
|
1
|
ALA 567
|
Pharmacokinetic and Drug-likeness Screening of Phytochemicals
Drug properties of the 13 selected phytochemicals were screened by Lipinski rule of five and ADME, which was followed by determining the bioavailability radar and bioactive score of the ligands. The Lipinski’s rule of five checked parameters like molecular weight, hydrogen donor, hydrogen acceptor, lipophilicity, and molar refractivity [17, 18].Andrograholide, Bassic acid, Curdione, Nectandrin B, Nimbolide, salvicine, Withaferin A and Hecogenin satisfied all the five criteria of Lipinski, Tetrandine did not pass the criteria while the others have deviation in at most one of the criteria which is still acceptable (Table 6).
Table 6 Analysis of phytocompounds by Lipinski’s Rule of 5
Phytochemicals
|
Mass
|
Hydrogen bond donor
|
Hydrogen bond acceptor
|
LOGP
|
Molar Refractivity
|
Andrographolide
|
350
|
3
|
5
|
1.96
|
93.5
|
Bassic acid
|
486
|
4
|
5
|
4.305
|
135.46
|
Curdione
|
236
|
0
|
2
|
3.55
|
69.73
|
Nectandrin B
|
344
|
2
|
5
|
4.19
|
94.21
|
Nimbolide
|
466
|
0
|
7
|
3.74
|
119.39
|
Oleanolic acid
|
456
|
2
|
3
|
7.233
|
132.68
|
Panaxadiol
|
460
|
2
|
3
|
6.74
|
133.81
|
Panaxatriol
|
476
|
3
|
4
|
5.71
|
135.20
|
Salvicine
|
330
|
2
|
4
|
2.86
|
93.96
|
Tetrandine
|
622
|
0
|
8
|
7.16
|
177.68
|
Ursolic acid
|
456
|
2
|
3
|
7.09
|
132.61
|
Withaferin A
|
470
|
2
|
6
|
3.35
|
124.46
|
Hecogenin
|
430
|
1
|
4
|
4.92
|
118.11
|
Dovitinib (Standard drug)
|
392
|
4
|
6
|
2.23
|
111.83
|
Gefitinib (Standard drug)
|
446.5
|
1
|
7
|
4.28
|
118.15
|
The phytochemicals were screen for ADME properties calculated from Swiss ADME a free web tool which predicts and evaluates pharmacokinetics and drug-likeness of molecules and built on several models [19]. In silico pharmacokinetics of the ligands as showed in Table 7 reveals that the drug-likeness and pharmacokinetics of some of the phytochemicals are comparable to the standard drugs. The Estimated solubility (ESOL) showed the phytochemicals curdione, andrographolide and salvicine to be more soluble than the standard drugs Dovitinib and Gefitinib with lipophilicity comparable to Dovitinib but less than Gefitinib. Lipophilicity is expressed as iLogP affects the absorption of drug, the lower the iLOGP value the higher the absorption and vice versa. Gastroinstinal absorption (GIA) and blood brain barrier (BBB) permeation are predicted by BOILED model which utilizes the polarity and lipophility of compounds [20]. GIA was high for all the ligands except oleanolic acid and ursolicacid.In line with this, the bioavailabilty score of all the ligands falls in the normal range except that of ursolic and oleanolic acids. Major therapeutic agents are substrates to p-glycoprotein, which in most cases have the potential to reduce absorption, permeability, oral bioavailability and retention time of drugs [21, 22].P-glycoproteins are overly expressed in cancer cells, a major barrier in cancer treatment that causes drug efflux and making chemotherapy quite ineffective [22, 23].Hence ligands that are non-substrate of p-gp are most preferable for cancer treatment.
Table 7. In silico Pharmacokinetics of ligands using Swiss ADME
Phytochemicals
|
ESOL (Log S)
|
GIA
|
BBB Permeant
|
P-gp Substrate
|
CYP3A4 Inhibitor
|
CYP1A2 Inhibitor
|
(iLOGP)
|
Bioavailabilty Score
|
Andrographolide
|
-3.18 (S)
|
High
|
No
|
Yes
|
No
|
No
|
2.45
|
0.55
|
Bassic acid
|
-5.91 (MS)
|
High
|
No
|
Yes
|
No
|
No
|
3.32
|
0.56
|
Curdione
|
-2.91 (S)
|
High
|
Yes
|
No
|
No
|
No
|
2.80
|
0.55
|
Nectandrin B
|
-4.42 (MS)
|
High
|
Yes
|
Yes
|
Yes
|
No
|
2.75
|
0.55
|
Nimbolide
|
-3.94 (S)
|
High
|
No
|
Yes
|
No
|
No
|
3.51
|
0.55
|
Oleanolic acid
|
-7.32 (PS)
|
Low
|
No
|
No
|
No
|
No
|
3.92
|
0.85
|
Panaxadiol
|
-6.96 (PS)
|
High
|
No
|
No
|
No
|
No
|
4.61
|
0.55
|
Panaxatriol
|
-6.22 (PS)
|
High
|
No
|
Yes
|
No
|
No
|
4.24
|
0.55
|
Salvicine
|
-3.58 (S)
|
High
|
Yes
|
No
|
No
|
No
|
2.93
|
0.55
|
Ursolic acid
|
-7.23 (PS)
|
Low
|
No
|
No
|
No
|
No
|
4.01
|
0.85
|
Withaferin A
|
-4.97 (MS)
|
High
|
No
|
Yes
|
No
|
No
|
3.39
|
0.55
|
Hecogenin
|
-5.55 (MS)
|
High
|
Yes
|
Yes
|
No
|
No
|
4.02
|
0.55
|
Dovitinib (Standard drug)
|
-3.66 (S)
|
High
|
No
|
Yes
|
No
|
Yes
|
2.26
|
0.55
|
Gefitinib (Standard drug)
|
-5.05 (MS)
|
High
|
Yes
|
No
|
Yes
|
No
|
4.04
|
0.55
|
As shown in Table 7, Most of the phytochemicals are non-inhibitors of CYP3A4 and CYP1A2, members of drug metabolizing enzymes cytochrome P450, an enzyme that possesses important role in drug metabolism. The interaction of cytochrome 450 isoenzymes with drug could either result in either rapid metabolism when the drug is a substrate of any CYP causing induction or accumulation of the drug when the drug is an inhibitor that causes inhibition, which in both cases are undesirable [24]. Therefore in silico analysis in predicting the interaction of compounds or drugs with CYP isoenzymes is important in drug development process.
Bioavailability Radar
Bioavailability radar provides a rapid assessment at the drug likeness of a compound. As seen in Figure 6, the pink area shows the optimal range of each parameter, when considering the parameters of a phytocompound the radar plot of the compound has to fall in the pink area in order to be considered drug-like, hence, the ligandsare either predicted to be orally bioavailable or not orally bioavailable via the radar plot. Flexibility (FLEX) and polarity (polar) are two essential properties that determine the bioavailabilty of compounds. Flexibility is determined by rotatable bonds, compounds with rotatable bonds >10 are predicted to have low oral bioavailability while polarity as determined bytopological polar surface implies that compound with TPSA >20 Å2<130Å2 have high oral bioavailability [24]. Seven of the phytochemicals (Andrographolide, curdione, Nectandrin B, Nimbolide, Salvicine, Withaferin A and Hecogenic) under study are noted to satisfy the radar plot criteria, hence can be suggested to be orally bioavailable.
Bioactivity score
Bioactivity score is used to calculate the drugability properties of ligands such as GPCR, ICM, KI, NRL, PI and EI. Molinspiration online server was used to predict the scores of the ligands. Scores greater than 0.00 denote high activity, scores ranging from -0.5 to - 0.00 shows moderate activity while scores lower than −0.5 implies inactivity [25]. The phytochemicals under study showed a good score of high to moderate activity except for Hecogenic that showed inactivity in KI with a score of -0.57 as shown in Table 8. For GPCR and NRL, Andrographolide showed the highest score of 0.32 and 0.94 respectively, salivicine showed the highest score of 0.50 for ICM, Withaferin A had the highest score of 0.94for EI, while Andrographolide and Salivicine both showed high score of 0.26 for PI. Comparing this to the standard drugs Dovitinib has good scores for all the properties while Gefitinib showed inactivity in some of the properties as seen in Table 8. Good bioactivity scores revealed the potentials of these bioactives as potent therapeutic agents, the higher the scores the better the activity.
Table 8. Bioactivity Score of Compounds using Molinspiration
Compound
|
GPCR
|
ICM
|
KI
|
NRL
|
PI
|
EI
|
Andrographolide
|
0.32
|
0.17
|
-0.01
|
0.94
|
0.26
|
0.81
|
Bassic acid
|
0.23
|
-0.28
|
-0.35
|
0.79
|
0.16
|
0.66
|
Curdione
|
-0.26
|
-0.01
|
-1.04
|
-0.05
|
-0.040
|
-0.33
|
Nectandrin B
|
0.08
|
-0.16
|
-0.16
|
0.20
|
-0.14
|
0.10
|
Nimbolide
|
0.22
|
0.22
|
-0.36
|
0.32
|
0.04
|
0.36
|
Oleanolic acid
|
0.26
|
-0.06
|
-0.40
|
0.77
|
0.15
|
0.65
|
Panaxadiol
|
0.16
|
0.15
|
-0.26
|
0.54
|
0.19
|
0.66
|
Panaxatriol
|
0.19
|
0.16
|
-0.27
|
0.55
|
0.19
|
0.73
|
Salvicine
|
0.10
|
0.50
|
-0.06
|
0.30
|
0.26
|
0.61
|
Ursolic acid
|
0.28
|
-0.03
|
-0.50
|
0.89
|
0.23
|
0.69
|
Withaferin A
|
0.07
|
0.14
|
-0.49
|
0.76
|
0.15
|
0.94
|
Hecogenin
|
0.05
|
0.04
|
-0.57
|
0.47
|
0.08
|
0.61
|
Dovitinib (Standard drug)
|
0.23
|
0.10
|
0.84
|
-0.01
|
-0.06
|
0.27
|
Gefitinib (Standard drug)
|
-0.18
|
-0.54
|
-0.07
|
-0.62
|
-0.67
|
-0.26
|