Interdiscip Sci Comput Life Sci (2014) 6: 13–24 DOI: 10.1007/s12539-014-0170-8

Exploring Inhibitory Potential of Curcumin against Various Cancer Targets by in silico Virtual Screening Arpitha Badarinath MAHAJANAKATTI1 , Geetha MURTHY2 , Narasimha SHARMA1,3 , Sinosh SKARIYACHAN1∗ 1

(R & D Center, Department of Biotechnology, Dayananda Sagar College of Engineering, Bangalore 560078, Karnataka, India) 2 (Department of Bioinformatics, PES Institute of Technology, Bangalore 560085, Karnataka, India) 3 (Infosys, Bangalore 560100, Karnataka, India)

Received 4 May 2013 / Revised 4 June 2013 / Accepted 17 June 2013

Abstract: Various types of cancer accounts for 10% of total death worldwide which necessitates better therapeutic strategies. Curcumin, a curcuminoid present in Curcuma longa, shown to exhibit antioxidant, anti-inflammatory and anticarcinogenic properties. Present study, we aimed to analyze inhibitory properties of curcumin towards virulent proteins for various cancers by computer aided virtual screening. Based on literature studies, twenty two receptors were selected which have critical virulent functions in various cancer. The binding efficiencies of curcumin towards selected targets were studied by molecular docking. Out of all, curcumin showed best results towards epidermal growth factor (EGF), virulent protein of gastric cancer; glutathione-S-transferase Pi gene (GST-PI), virulent protein for prostate cancer; platelet-derived growth factor alpha (PDGFA), virulent protein for mesothelioma and glioma compared with their natural ligands. The calculated binding energies of their docked conformations with curcumin found to be −7.59 kcal/mol, −7.98 kcal/mol and −7.93 kcal/mol respectively. Further, a comparative study was performed to screen binding efficiency of curcumin with two conventional antitumor agents, litreol and triterpene. Docking studies revealed that calculated binding energies of docked complex of litreol and EGF, GST-PI and PDGFA were found to be −5.08 kcal/mol, −3.69 kcal/mol and −1.86 kcal/mol respectively. The calculated binding energies of triterpene with EGF and PDGFA were found to be −4.02 kcal/mol and −3.11 kcal/mol respectively, whereas GST-PI showed +6.07 kcal/mol, indicate poor binding. The predicted pharmacological features of curcumin found to be better than litreol and triterpene. Our study concluded that curcumin has better interacting properties towards these cancer targets than their normal ligands and conventional antitumor agents. Our data pave insight for designing of curcumin as novel inhibitors against various types of cancer. Key words: curcumin, anticarcinogenic, virtual screening, epidermal growth factor, glutathione-S-transferase Pi gene, platelet-derived growth factor, litreol, triterpene, antitumor agents.

1 Introduction Curcuma longa, a perennial plant native to Southeast Asia is a member of the Zingiberacae (ginger) family of botanicals. Chief component of this plant is curcumin (diferuloylmethane) (Wilken et al., 2011; Chattopadhyay et al., 2004). It is identified as the active principle of turmeric. Chemical structure of curcumin is bis-α, β-unsaturated β-diketone and exhibits keto-enol tautomerism. Curcumin exhibits antioxidant, anti-inflammatory (Jurenka, 2009), antimicrobial and anticarcinogenic activities (Aggarwal et al., 2007). It also has hepatoprotective and nephroprotective activities, suppresses thrombosis, protects against ∗

Corresponding author. E-mail: [email protected]

myocardial infarction, and has hypoglycemic and antirheumatic properties. Curcumin has been tested on various animal models and human studies have been reported for its safety at very high doses (Ammon, 1991; Anand et al., 2008). Cancer, characterized by the abnormal growth of cells, has caused more deaths across the world. Recent reports revealed that there are 556400 national cancer deaths in India in 2010. Moreover, nearly 395 400 (71%) cancer deaths occurred in people aged 3069. At 30-69 years, the most common fatal cancers were oral −22.9%, stomach −12.6%, lung −11.4%, cervical −17.1%, stomach −14.1% and breast −10.2%. Tobacco-related cancers represented 42.0% of male and 18.3% of female cancer deaths and there were twice as many deaths from oral cancers as lung cancers (Dik-

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Interdiscip Sci Comput Life Sci (2014) 6: 13–24

shitet al., 2012). This creates a greater need for prevention of cancer. Cancer is governed by many numbers of proteins of varied function. These proteins can act as important virulent factors that can inhibit the pathway with the aid of ligands. These ligands functions to disrupt the cancer pathway and thus preventing its harmful effects to the host cell. Curcumin has been one such ligand which has good pharmacological activity against different types of cancers (Aggarwal et al., 2004). Curcumin has been studied in multiple human carcinomas including melanoma, head and neck (Aggarwal et al., 2004; LoTempio et al., 2005), breast, colon, pancreatic, prostate (Wang et al., 2008; Mukhopadhyay et al., 2001), oral (Elattar and Virji, 2000), and ovarian cancers (Lin et al., 2007; Siwak et al., 2005). Epidemiological studies attribute the low incidence of colon cancer in India to the chemo preventive and antioxidant properties of diets rich in curcumin (Mohandas and Desai, 1990). Anti-cancer effects of curcumin are characterized by comprehensive and diverse, targeting many levels of regulation in the processes of cellular growth and apoptosis. In addition to the effects of curcumin on various transcription factors, oncogenes and signaling proteins, it also acts at various stages of carcinogenesis which occurs from the initial insights leading to DNA mutations through the process of tumorigenesis, growth and metastasis. Since, curcumin has been characterized on its effects on multiple targets on the cell growth regulatory processes; it can be a potential chemotherapeutic agent for many human cancers (Wilken et al., 2011). In our study we aim to screen the inhibitory properties of curcumin against various cancer targets by computer aided virtual screening. We have analyzed the interaction of curcumin with receptors of different type of cancer which includes gastric cancer, prostate cancer, malignant pleural mesothelioma, glioma, small cell lung cancer, endometrial cancer, breast cancer etc. We have performed mutlireceptor docking with curcumin. To effectively screen the activity of curcumin, comparative study was carried out with herbal lead molecules such as litreol from Lithraea caustic and triterpene from Annona glabra.

2 Methodology 2.1

Selection of receptors

The receptors were selected based on their function in the pathway of various types of cancers. Different types of cancer pathways were analyzed from Kyoto Encyclopedia of Genes and Genomes (Kanehisa and Goto, 2000) which includes cervical cancer, gastric cancer, colorectal cancer, endometrial cancer, thyroid cancer, hepatocellular carcinoma, oral cancer, esophageal cancer, bladder cancer, choriocarcinoma, glioma, laryn-

geal cancer, ovarian cancer, breast cancer, cholangiocarcinoma, alveolar rhabdomyosarcoma, prostate cancer, malignant pleural mesothelioma, synovial sarcoma, hodgkin lymphoma, small cell lung cancer and vulvar cancer and receptors which play key role in the pathway were selected. The receptors selected for our studies have shown in Table 1. The three dimensional structures of these receptors were available in their native form in PDB (Berman et al., 2000) database. The three dimensional coordinates of the selected receptors were retrieved from PDB database. 2.2

Selection of ligands

Structure of curcumin was obtained from NCBI Pubchem database (Wang et al., 2012). To carry out the comparative study, two ligands were also selected, litreol (Russoa et al., 2009) and triterpene (Str¨ uh et al., 2012). These are conventionally used anticancerous herbal substances for various types of cancers (Russoa et al., 2009). They are extracted from Lithraea caustic (flowering plants in the soapberry family) and Annona glabra (Pond-apple) respectively. The pharmacokinetics properties were screened using Pre-ADMET tool (Seal et al., 2009). Drug-likeliness, ADME profile and toxicity analysis were predicted for all the three ligands. The ADME includes rate of absorption, distribution, metabolism and excretion. Pre-ADMET uses Caco2-cell (human epithelial colorectal adenocarcinoma cell lines) and MDCK (Madin-Darby Canine Kidney) cell models for oral drug absorption prediction and skin permeability and human intestinal absorption model for oral and trans-dermal drug absorption prediction. PreADMET predicts toxicity based on the Ames parameters and rodent carcinogenicity assays of rat and mouse (Seal et al., 2009). 2.3

Multi receptor docking

Molecular docking is performed to study the receptor-ligand interaction which regarded as the basis for structure based drug discovery. Docking studies were performed by AutoDock 4.2 (Morris et al., 1996) by Lamarckian genetic algorithm. The catalytic and binding site of the target has been identified by AutoGrid. The structure and chemical properties of the active sites allow the recognition and binding of the ligand. Around 2,500,000 bioactive conformations were generated by 10 iterations and the best conformations were screened in terms of lowest binding energy generated in the clustering histogram. The interactions of curcumin with selected receptors were further compared with the interaction of those receptors with their natural ligands. Further, the validations of the docking results were carried out using set of known molecules for each cancer receptors from available literature. The calculated docking energy was compared with measured experimental binding energy associated

Interdiscip Sci Comput Life Sci (2014) 6: 13–24 Table 1

15

Selection of probable drug targets from various types of cancers for structure based drug screening. The drug targets were screened based on the virulent function in the metabolic pathways of each type of cancer. The structural coordinates of these drug targets were retrieved from PDB

Gene No.

Gene name

Drug target (gene products)

PDB ID

Type of cancer

1026

CDKN1A

Proliferating Cell Nuclear Antigen

1AXC

Cervical cancer

1499

CTNNB1

beta-catenin

1JDH

1950

EGF

Epidermal Growth Factor

1NQL

1956

EGFR

Epidermal Growth Factor Receptor kinase

3POZ

Gastric cancer, colorectal cancer, endometrial cancer, thyroid cancer, hepatocellular carcinoma Gastric cancer Oral cancer, esophageal cancer, gastric cancer, bladder cancer, choriocarcinoma, cervical cancer, Glioma, Laryngeal cancer Gastric cancer, pancreatic cancer, bladder cancer, endometrial cancer, ovarian cancer, choriocarcinoma, cervical cancer, breast cancer, cholangiocarcinoma Ovarian cancer Gastric cancer Alveolar rhabdomyosarcoma Prostate cancer Malignant pleural mesothelioma

2064

ERBB2

Human Epidermal Growth Factor 2

3PP0

208 2263 2308 2950 3479

AKT2 FGFR2 FOXO1 GST-PI IGF1

Protein kinase B Fibroblast Growth Factor Receptor 2 Forkhead box protein O1 Glutathione S-transferase Pi gene Insulin-like growth factor 1

2X39 3B2T 3CO6 2A2R 1TGR

3480

IGF1R

Insulin-like growth factor 1 receptor

1P4O

367

AR

Androgen receptor

2AX6

Prostate cancer

Malignant pleural mesothelioma, synovial sarcoma

4193

MDM2

E3 ubiquitin-protein ligase

2AXI

Penile cancer, choriocarcinoma, osteosarcoma, alveolar rhabdomyosarcoma, glioma

4792

NFKBIA

Nuclear factor of kappa light polypeptide gene enhancer

1IKN

Hodgkin lymphoma

5154 5155 5290

PDGFA PDGFB PIK3CA

Platelet-derived growth factor alpha chain Platelet-derived growth factor beta chain Phosphatidylinositol-4, 5-bisphosphate 3-kinase

3MJK 3MJG 3HHM

Malignant pleural mesothelioma, glioma Malignant pleural mesothelioma, glioma Ovarian cancer

5728

PTEN

Phosphatase and tensin homolog

1D5R

Small cell lung cancer, prostate cancer, endometrial cancer, vulvar cancer, breast cancer, malignant melanoma, glioma, hepatocellular carcinoma

5925

RB1

Retinoblastoma protein

2R7G

Chronic myeloid Leukemia, small cell lung cancer, esophageal cancer, bladder cancer, Breast cancer, osteosarcoma, glioma, hepatocellular carcinoma

595

CCNDI

Cyclin D1-cyclin-dependent kinase 4

2W96

Hairy cell leukemia, multiple myeloma, oral cancer, esophageal cancer, breast cancer, laryngeal cancer

596

BCL2

B-cell lymphoma 2

2W3L

7039

TGFA

Transforming growth factor alpha

1MOX

with known molecules for each receptor.

3 Results and discussion 3.1

Selection of receptors

The receptors were selected based on their functionality in various cancer pathways. Twenty two re-

Chronic myeloid Leukemia, small cell lung cancer, gastric cancer, choriocarcinoma, cervical cancer, kaposi’s sarcoma, nasopharyngeal cancer Gastric cancer

ceptors were selected based on the functional role in the pathway. Cyclin-dependent kinase inhibitor 1A (CDKN1A) play a key role in negative control of cell cycle progression (Jalili et al., 2012). They are also involved in cell cycle arrest at the G1 phase. Catenin (cadherin-associated protein), beta 1(CTNNB1) interact with other proteins and are important in a wide

16

variety of processes including carcinogenesis (Machin et al., 2002), control of cellular ageing and survival, regulation of circadian rhythm and lysosomal sorting of G protein-coupled receptors. Epidermal growth factors (EGF) present in the extracellular domain of membrane-bound proteins and are involved in formation of disulphide bonds (Stoscheck and King, 1986). Mutations can cause over expression and leads to cancer. Epidermal growth factor receptor (EGFR) (Mendelsohn and Baselga, 2006), transforming growth factor, alpha (TGFA) (Greten et al., 2001), insulinlike growth factor 1 receptor (IGF1R) (Hewish et al., 2009) and erythroblastic leukemia viral oncogene homolog 2 (ERBB2) (Sauter et al., 1993) consists of L domains and make up the bilobal ligand binding site. Akt murine thymoma viral oncogene homolog 2 (AKT2) (Cicenas, 2008) and fibroblast growth factor receptor 2 (FGFR2) (Byron, 2009) belong to serine/threonine protein kinases. They form catalytic domain and are involved in protein phosphorylation. Forkhead box O1 (FOXO1) (Maekawa et al., 2009) has HNF-3/fork head DNA-recognition motif resembles histone H5. Function of glutathione S-transferase pi 1(GST-PI) (Re et al., 2011) is conjugation of reduced glutathione to a variety of targets. Insulin-like growth factor 1 (IGF1) (Heidegger et al., 2011) are secreted regulatory hormones. They are disulfide rich alpha fold. Androgen receptor (AR) (Heinlein and Chang, 2004) forms DNA binding domain of a nuclear hormone receptor. Mdm2, p53 E3 ubiquitin protein ligase homolog (MDM2) is an inhibitor of the p53 tumour suppressor gene (Ch`ene, 2003) binding the transactivation domain and down regulates the ability of p53 to activate transcription. Nuclear factor of kappa (NFKBIA) (Curran et al., 2002) is a light polypeptide gene enhancer in B-cells inhibitor, alpha contains repeatdomain of membrane-binding mediates most binding activities of protein. Platelet-derived growth factor alpha (PDGFA) polypeptide and platelet-derived growth factor beta (PDGFB) (Liuet al., 2011) polypeptide are involved in signal transduction and is an endogenous inhibitor of protein phosphatase-1. PIK3CA phosphatidylinositol-4, 5-bisphosphate 3-kinase, catalytic subunit alpha possess Ras-binding domains in their N-termini. PTEN - phosphatase and tensin homolog play a key role in membrane binding. Retinoblastoma 1 (RB1) (Chinnam and Goodrich, 2011) is required for high-affinity binding to E2F-DP complexes and for maximal repression of E2F-responsive promoters, thereby acting as a growth suppressor by blocking the G1-S transition of the cell cycle. Cyclin D1 (CCNDI) regulates cyclin dependent kinases (CDKs) (Takano et al., 1999). B-cell CLL/lymphoma 2 (BCL2) (Hockenbery, 1994) suppresses apoptosis in a variety of cell systems including factor-dependent lymphohematopoietic and neural cells and regulates cell death

Interdiscip Sci Comput Life Sci (2014) 6: 13–24

by controlling the mitochondrial membrane permeability. 3.2

Selection of ligands

Ligands were predicted for pharmacokinetic properties using Pre-ADMET tool. Drug likeness, ADME and toxicity predictions were performed. We have noticed that Curcumin is well qualified in terms of pharmacokinetic features such as human intestinal absorption, Caco2 (heterogeneous human epithelial colorectal adenocarcinoma) cell permeability, MDCK (Madin-Darby canine kidney) cell permeability, skin permeability and blood brain barrier penetration. The toxicity studies revealed that curcumin found to be non carcinogen and non mutagen predicted by Ames test and mouse carcinogeniscity model respectively (Table 2). Hence, our study showed that curcumin, qualifying most of the rules can be a ideal drug candidate. Litreol is a derivative of catechol carrying a pentadecenyl substituent at position-3. Pharmacological predictions of this compound were comparatively low compared to curcumin. There was a violation in rule of 5; however, posses high blood brain barrier penetration. Triterpene is a terpene consisting of six isoprene units. Pharmacological predictions were similar to litreol. The drug likeliness properties and pharmacokinetic features are shown in Table 2. 3.3

Multi receptor docking of curcumin

Multi receptor docking was performed to analyze the inhibitory action of curcumin with the various cancer receptors which can be considered as probable drug targets. The best docked conformations were selected based on the lowest docking energy (binding energy) of docked complex, number of interacting residues and number of hydrogen bonds. Our study revealed that, curcumin showed best binding properties towards all receptors we have screened. Curcumin showed its better inhibitory activity against three main receptors, EGF, GST-PI and PDGFA. The Epidermal Growth Factor (EGF) acts as potential drug targets for gastric cancer (Liu et al., 2011), glutathione S-transferase Pi gene (GST-PI) plays a crucial role in the development of prostate cancer (Re et al., 2011) and platelet-derived growth factor alpha chain (PDGF) has virulent function in malignant pleural mesothelioma and glioma (Liuet al., 2011). The binding energy from the docking studies was found to be −7.59 kcal/mol, −7.98 kcal/mol and 7.93 kcal/mol respectively. Interaction of curcumin with GST-PI and PDGFA was enhanced by formation of hydrogen bonds. The main residues interacting with curcumin in PDGFA are Glu 43, Ile 83, Glu 125 and Cys 179 (Fig. 1(a)). Interacting residues present the best pose of EGF were His 10, Met 87, Ala 89, Gly 288, Asp 290, Glu 306 and Lys 384 (Fig. 1(c)). Interacting residues of GST-PI and Curcumin was found to be Lys

Interdiscip Sci Comput Life Sci (2014) 6: 13–24 Table 2

17

Pharmacokinetics prediction of the selected ligand using Pre-ADMET tool. Curcumin showed better drug like features and pharmacokinetic properties compared with Litreol and triterpene Curcumin

Litreol

Triterpene

Not Qualified

Drug likeness prediction CMC like Rule

Qualified

Not Qualified

CMC like Rule Violations

0

1

3

MDDR like Rule

Mid-structure

Mid-structure

Mid-structure

Rule of Five

Suitable

Suitable

Suitable

Lead like Rule

Suitable

Violated

Violated

Lead like Rule Violations

0

1

2

Well absorbed

Well absorbed

Well absorbed

ADME prediction Human Intestinal Absorption Caco2 Cell Permeability

Middle permeability

High permeability

Middle permeability

MDCK Cell Permeability

Middle permeability

Middle permeability

Middle permeability

Blood Brain Barrier Penetration

Low absorption to CNS

High absorption to CNS

High absorption to CNS

Ames TA100 (+S9)

negative

negative

negative

Ames TA100 (-S9)

negative

negative

negative

Ames TA1535 (+S9)

negative

negative

negative

Ames TA1535 (-S9)

negative

negative

negative

Ames TA98 (+S9)

negative

negative

negative

Ames TA98 (-S9)

negative

negative

positive

Ames test

Non-mutagen

Non-mutagen

Mutagen

Carcinogenicity (Mouse)

negative

positive

positive

Carcinogenicity (Rat)

positive

negative

positive

Toxicity Prediction Ames test

Carcinogenicity

120 (Fig. 1(b)). The binding energy of the best docked conformation of various cancer drug targets with curcumin is shown in Table 3. We have compared the interaction of curcumin and EGF, GST-PI and PDGFA with the natural ligands of these receptors by docking studies (Table 5). Gefitinib (Li et al., 2004), Celecoxib (Howe et al., 2002) and Lapatinib (Medina & Goodin, 2008) are the normal inhibitors for Epidermal Growth Factor (EGF). Our docking study revealed that the binding energy of docked complex of Gefitinib, Celecoxib and Lapatinib against EGF are identified to be 0.61 kcal/mol, 0.64 kcal/mol and 6.33 kcal/mol respectively, higher than the binding energy of the docked complex of curcumin (−7.59 kcal/mol) and EGF. Moreover, the interactions are not stabilized by hydrogen bonds. Similarly, the interaction of buthionine sulfoximine (Yokomizo et al., 1995), common inhibitor of Glutathione S-transferase pi gene (GST-PI) and the receptor showed less binding properties (binding energy −5.90 kcal/mol) compared to curcumin (−7.98 kcal/mol). Our study also showed

that Imatinib (Malavaki et al., 2013), common ligand for Platelet-derived growth factor receptor (PDGFA), interacting with its receptor by binding energy of −2.66 kcal/mol. Hence, our docking study clearly indicating that curcumin has good binding efficiency and inhibitory properties against these cancer receptors than normal inhibitors. The experimental binding energy associated with interaction of epidermal growth factor receptor (EGF) and standard ligand, Gefitinib were reported as ΔΔGFR exptl = 0.90 kcal/mol (Balius and Rizz, 2009). Our studies showed that calculated binding energy of the interaction between curcumin and EGF (−7.53 kcal/mol) was found better than the measured experimental binding energy between EGF and Gefitinib (+0.90 kcal/mol). The experimental binding energy between platelet-derived growth factor receptor (PDGFA) and its common liagnd, Imatinib was reported as 0.2±0.6 kcal/mol (Aleksandrov and Simonson, 2010). From our studies it is evident that the calculated binding energy of curcumin - PDGFA docked

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Interdiscip Sci Comput Life Sci (2014) 6: 13–24

(a)

(b)

(c) Fig. 1

Molecular docking studies of curcumin and cancer drug targets, (a) Platelet-derived growth factor alpha (PDGFA), (b) Glutathione-S-transferase Pi gene (GST-PI) and (c) epidermal growth factor (EGF). The interacting residues present in the binding cavities were displayed in sticks diagram and curcumin is shown in molecular surface representation. The binding energies of docked complex were found to be −7.93 kcal/mol, −7.98 kcal/mol and −7.59 kcal/mol respectively

complex (−7.93 kcal/ mol) is better than that of experimental binding of Imatinib - PDGFA (0.2 kcal/mol). Similarly, we noticed that calculated binding between curcumin and GST-PI is better than that of mesaured experimental binding energy of buthionine sulfoximine, common ligand for GST-PI. From our comparative studies, it is evident that curcumin has better binding properties towards the selected cancer targets than their respective native ligands. There are many reports revealed the validation of inhibitory properties of curcumin screened by computer aided virtual screening. The anti-inflammatory properties of curcumin with potent cancer drug tar-

gets such as glycogen synthase kinase (GSK-3beta), p38 mitogen activated protein kinase (MAPK), COX, interleukin-1beta converting enzyme (ICE) and tumor necrosis factor-alpha converting enzyme (TACE) were recently studied by molecular docking (Elumalai et al., 2012). The best conformations were selected based on docking scores. The binding target GSK-3beta (−6.44 kcal/mol) was found to be more selective for curcumin binding when compared with MAPK (−4.08 kcal/mol), COX (−7.35 kcal/mol), ICE (−4.02 kcal/mol), TACE (−6.38 kcal/mol) and their respective native ligands. The interactions were stabilized by hydrogen bonding with various amino acids (Elumalai et al., 2012).We

Interdiscip Sci Comput Life Sci (2014) 6: 13–24 Table 3

The receptor ligand interaction data obtained from the docking studies. The energy of binding (kcal/mol) between curcumin and the best conformation of various cancerous drug targets is analyzed in kcal/mol

19 Table 5

Comparative analysis of the interaction of curcumin and natural ligands of selected cancer receptors by docking studies. The table showed that curcumin has better binding efficiency than the normal ligands of the selected receptors Docking energy

Gene name

PDB ID of the gene

Binding energy (kcal/mol)

AKT2

2X39

−7.38

AR

2AX6

−5.62

BCL2

2W3L

−6.60

CCNDI

2W96

−6.06

Gefitinib

−0.61

CDKN1A

1AXC

−6.095

Celecoxib

−0.64

CTNNB1

1JDH

−5.09

Lapatinib

+6.33

EGF

1NQL

−7.59

EGFR

3POZ

−5.45

ERBB2

3PP0

−6.51

FGFR2

3B2T

−6.25

FOXO1

3CO6

−6.83

GST-PI

2A2R

−7.98

IGF1

1TGR

−5.05

IGF1R

1P4O

−6.8

MDM2

2AXI

−5.52

NFKBIA

1IKN

−6.64

PDGFA

3MJK

−7.93

PDGFB

3MJG

−6.14

PIK3CA

3HHM

−4.55

PTEN

1D5R

−5.79

RB1

2R7G

−6.36

TGFA

1MOX

−6.87

Table 4

The docking interactions between litreol and triterpene with selected cancer drug targets. The binding energy (kcal/mol) indicated that the inhibitory properties of these ligands are poor compared with curcumin

Gene name PDB ID

Binding energy of interaction (kcal/mol) Litreol

Triterpene

EGF

1NQL

−5.08

−4.02

GST-PI

2A2R

−3.69

+6.07

PDGFA

3MJK

−1.86

−3.11

have also noticed the similar kinds of stabilizing forces

Cancer

Normal

receptors

ligand

EGF

GST-PI

Buthionine

(kcal/mol) Receptor and

Receptor

normal ligand

and curcumin

−7.59

−5.90

−7.98

−2.66

−7.93

sulfoximine PDGFA

Imatinib

between curcumin and the selected drug targets. Similarly, various curcumin derivatives were screened as potent androgen receptor antagonists by docking studies were further confirmed by experimental validation (Xu et al., 2012). Recent studies revealed that curcumin analogues screened as novel EGFR inhibitors, a key cancer drug targets focused in our studies, showed antiproliferative properties against two human tumor cell lines (Hep G2 and B16-F10). Molecular docking of these analogues into EGFR-TK active site revealed that curcumin analogues have excellent inhibitory activity (Xu et al., 2013). Furthermore, studies suggested that human glyoxalase I (GLO-I) is a potential target for anti-tumor drug development and many curcumin derivatives were identified as novel lead molecules with high inhibitory properties against human GLO-I (Yuan et al., 2011). There are also report revealed that the inhibitory properties of curcumin towards drug target glycogen synthase kinase. The inhibitory activity of curcumin towards glycogen synthase kinase was screened by computer aided screening and validated by further studies (Bustanji et al., 2009). Hence, computer aided approaches are excellent platform to study the inhibitory properties of various ligands and screen better therapeutic substances with profound pharmacokinetic features and druggish activities. 3.4

Docking with litreol and triterpene

Litreol and triterpene were subjected to docking studies with three receptors - EGF, GST-PI and PDGFA - with which curcumin showed better activity. The docking studies showed that inhibitory activities of litreol with these receptors are poor compared

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Interdiscip Sci Comput Life Sci (2014) 6: 13–24

(a)

(b)

(c) Fig. 2

Molecular docking studies of Litreol and selected cancerous drug targets, (a) Epidermal growth factor (EGF), (b) Platelet-derived growth factor alpha (PDGFA) and (c) Glutathione-S-transferase Pi gene (GST-PI). The binding energies of the docked complexes were identified as −5.08 kcal/mol, −1.86 kcal/mol and −3.69 kcal/mol respectively

with the inhibitory properties of curcumin. The calculated docking energy values of litreol with EGF, GSTPI and PDGFA were −5.08 kcal/mol, −3.69 kcal/mol and −1.86 kcal/mol respectively. Interacting restudies with EGF molecule were His 10, Asp 280, Asp 290, Pro 308 and Aln 337 (Fig. 2(a)). Interacting residues with GST-PI were Lys 120, Ala 121 and Gln 125 (Fig. 2(c)) and the interacting residues with PDGFA were Cys 96, Lys 97, Ser 143, His 146, Arg 148, Glu 176 and Cys 177 (Fig. 2(b)). Moreover, there were no hydrogen bonds stabilized the interaction (Table 4). Hence, the binding efficiency of litreol is less compared with curcumin, however, better than their native inhibitors. The binding energy of the docked complex of triterpene against EGF and PDGFA were found to be −4.02 kcal/mol and −4.82 kcal/mol respectively and there were no hydrogen bonds stabilized the interactions. Interacting

residues with EGF were Glu 40, Asp 290, Ala 289, Gly 288, Glu 306 and Pro 308 (Fig. 3(a)). Interacting residues with PDGFA were Ile 38, His 39, Val 95, Lys 97, Thr 98, Trp 120, Pro 121, Val 124, Arg 148, Val 152 and Val 160 (Table 4). Furthermore, the inhibitory activity of triterpene against GST-PI was found to be poor, it showed positive binding energies in all the tested conformation. Hence, our study revealed that binding efficiency of triterpene is also less compared with curcumin. From our study, it is evident that curcumin has broad range of inhibitory properties against various cancer drug targets compared with many routinely used anticancer agents including their natural inhibitors. Better inhibitory properties and ideal pharmacokinetic features make curcumin as an ideal inhibitor and therapeutic substances against wide varieties of cancer. How-

Interdiscip Sci Comput Life Sci (2014) 6: 13–24

21

(a)

(b) Fig. 3

Molecular docking studies of Tritepene and selected drug targets, (a) Epidermal growth factor (EGF) and (b) Platelet-derived growth factor alpha (PDGFA). The binding energies were found to be −4.02 kcal/mol and −3.11 kcal/mol respectively. The ligand does not have stable interactions with glutathione-S-transferase Pi gene (GST-PI)

ever, present data is mainly based on computer aided virtual screening, further experimental studies are required to confirm the efficiency of these herbal lead against various cancer drug targets (Skariyachan et al., 2012). Our data would pave significant insights for such kinds of studies.

4 Conclusion Cancer accounts for 10-12% of total death worldwide and present therapies in oncology fail to evade most of the cancer effects. Hence, there is a pressing need to screen novel leads that have wide range of anti-tumor properties. Curcumin, chief component of turmeric, ex-

hibit antioxidant, anti-inflammatory, antimicrobial and anticarcinogenic activities. Present study revealed the inhibitory properties of curcumin against various cancer drug targets by computer aided virtual screening. Computer aided predictions showed that curcumin was an ideal drug candidate with better drug likeness and pharmacokinetic properties. This in silico study showed that curcumin has better therapeutic significance than routinely used anticancer agents such as litreol, herbal lead isolated from Lithraea caustic and triterpene, a phyloligand isolated from Annona glabra. Furthermore, our comparative study revealed that curcumin showed better inhibitory activities against the virulent gene products of Epidermal Growth Factor (EGF), Glu-

22

tathione S-transferase pi gene (GST-PI) and Plateletderived growth factor receptor (PDGFA) than their native ligands. Our study concluded that the inhibitory properties of curcumin would pave novel therapeutic insights against various types of cancers when present treatments in oncology fail to evade cancer. Present data pave crucial landmarks for further studies to validate curcumin as promising drug candidate against various cancers.

Acknowledgements The authors thankfully acknowledge Dr. G. S. Jagannatha Rao, Senior Professor and Head, Department of Biotechnology, Dayananda Sagar College of Engineering and Dr. G. A. Ravishankar, Vice President (R & D) in Life Sciences, Dayananda Sagar Institutions and for their constant support and encouragement throughout the study.

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