exploring inhibitory potential of curcumin against various cancer targets by in silico virtual...

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

DOI: 10.1007/s12539-014-0170-8

Exploring Inhibitory Potential of Curcumin against Various CancerTargets 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 therapeuticstrategies. Curcumin, a curcuminoid present in Curcuma longa, shown to exhibit antioxidant, anti-inflammatoryand anticarcinogenic properties. Present study, we aimed to analyze inhibitory properties of curcumin towardsvirulent proteins for various cancers by computer aided virtual screening. Based on literature studies, twentytwo receptors were selected which have critical virulent functions in various cancer. The binding efficiencies ofcurcumin towards selected targets were studied by molecular docking. Out of all, curcumin showed best resultstowards 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 proteinfor mesothelioma and glioma compared with their natural ligands. The calculated binding energies of their dockedconformations 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 conventionalantitumor agents, litreol and triterpene. Docking studies revealed that calculated binding energies of dockedcomplex of litreol and EGF, GST-PI and PDGFA were found to be −5.08 kcal/mol, −3.69 kcal/mol and −1.86kcal/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 studyconcluded that curcumin has better interacting properties towards these cancer targets than their normal ligandsand conventional antitumor agents. Our data pave insight for designing of curcumin as novel inhibitors againstvarious types of cancer.Key words: curcumin, anticarcinogenic, virtual screening, epidermal growth factor, glutathione-S-transferase Pigene, platelet-derived growth factor, litreol, triterpene, antitumor agents.

1 Introduction

Curcuma longa, a perennial plant native to South-east Asia is a member of the Zingiberacae (ginger)family of botanicals. Chief component of this plantis curcumin (diferuloylmethane) (Wilken et al., 2011;Chattopadhyay et al., 2004). It is identified as theactive principle of turmeric. Chemical structure ofcurcumin is bis-α, β-unsaturated β-diketone and ex-hibits keto-enol tautomerism. Curcumin exhibits an-tioxidant, anti-inflammatory (Jurenka, 2009), antimi-crobial and anticarcinogenic activities (Aggarwal et al.,2007). It also has hepatoprotective and nephroprotec-tive activities, suppresses thrombosis, protects against

∗Corresponding author.E-mail: [email protected]

myocardial infarction, and has hypoglycemic and an-tirheumatic properties. Curcumin has been tested onvarious animal models and human studies have been re-ported for its safety at very high doses (Ammon, 1991;Anand et al., 2008).

Cancer, characterized by the abnormal growth ofcells, has caused more deaths across the world. Re-cent reports revealed that there are 556400 nationalcancer deaths in India in 2010. Moreover, nearly 395400 (71%) cancer deaths occurred in people aged 30-69. At 30-69 years, the most common fatal cancerswere oral −22.9%, stomach −12.6%, lung −11.4%, cer-vical −17.1%, stomach −14.1% and breast −10.2%.Tobacco-related cancers represented 42.0% of male and18.3% of female cancer deaths and there were twice asmany deaths from oral cancers as lung cancers (Dik-

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

shitet al., 2012). This creates a greater need for pre-vention of cancer.

Cancer is governed by many numbers of proteins ofvaried function. These proteins can act as importantvirulent factors that can inhibit the pathway with theaid of ligands. These ligands functions to disrupt thecancer pathway and thus preventing its harmful effectsto the host cell. Curcumin has been one such ligandwhich has good pharmacological activity against differ-ent types of cancers (Aggarwal et al., 2004).

Curcumin has been studied in multiple human carci-nomas including melanoma, head and neck (Aggarwalet al., 2004; LoTempio et al., 2005), breast, colon, pan-creatic, prostate (Wang et al., 2008; Mukhopadhyay etal., 2001), oral (Elattar and Virji, 2000), and ovariancancers (Lin et al., 2007; Siwak et al., 2005). Epidemio-logical studies attribute the low incidence of colon can-cer in India to the chemo preventive and antioxidantproperties of diets rich in curcumin (Mohandas and De-sai, 1990). Anti-cancer effects of curcumin are charac-terized by comprehensive and diverse, targeting manylevels of regulation in the processes of cellular growthand apoptosis. In addition to the effects of curcumin onvarious transcription factors, oncogenes and signalingproteins, it also acts at various stages of carcinogenesiswhich occurs from the initial insights leading to DNAmutations through the process of tumorigenesis, growthand metastasis. Since, curcumin has been character-ized on its effects on multiple targets on the cell growthregulatory processes; it can be a potential chemother-apeutic agent for many human cancers (Wilken et al.,2011).

In our study we aim to screen the inhibitory proper-ties of curcumin against various cancer targets by com-puter aided virtual screening. We have analyzed theinteraction of curcumin with receptors of different typeof cancer which includes gastric cancer, prostate can-cer, malignant pleural mesothelioma, glioma, small celllung cancer, endometrial cancer, breast cancer etc. Wehave performed mutlireceptor docking with curcumin.To effectively screen the activity of curcumin, compar-ative study was carried out with herbal lead moleculessuch as litreol from Lithraea caustic and triterpene fromAnnona glabra.

2 Methodology

2.1 Selection of receptors

The receptors were selected based on their functionin the pathway of various types of cancers. Differenttypes of cancer pathways were analyzed from KyotoEncyclopedia of Genes and Genomes (Kanehisa andGoto, 2000) which includes cervical cancer, gastric can-cer, colorectal cancer, endometrial cancer, thyroid can-cer, hepatocellular carcinoma, oral cancer, esophagealcancer, bladder cancer, choriocarcinoma, glioma, laryn-

geal cancer, ovarian cancer, breast cancer, cholangio-carcinoma, alveolar rhabdomyosarcoma, prostate can-cer, malignant pleural mesothelioma, synovial sarcoma,hodgkin lymphoma, small cell lung cancer and vulvarcancer and receptors which play key role in the pathwaywere selected. The receptors selected for our studieshave shown in Table 1. The three dimensional struc-tures of these receptors were available in their nativeform in PDB (Berman et al., 2000) database. The threedimensional coordinates of the selected receptors wereretrieved from PDB database.

2.2 Selection of ligands

Structure of curcumin was obtained from NCBI Pub-chem database (Wang et al., 2012). To carry outthe comparative study, two ligands were also selected,litreol (Russoa et al., 2009) and triterpene (Struh etal., 2012). These are conventionally used anticancerousherbal substances for various types of cancers (Russoaet al., 2009). They are extracted from Lithraea caus-tic (flowering plants in the soapberry family) and An-nona glabra (Pond-apple) respectively. The pharma-cokinetics properties were screened using Pre-ADMETtool (Seal et al., 2009). Drug-likeliness, ADME profileand toxicity analysis were predicted for all the threeligands. The ADME includes rate of absorption, distri-bution, metabolism and excretion. Pre-ADMET usesCaco2-cell (human epithelial colorectal adenocarcinomacell lines) and MDCK (Madin-Darby Canine Kidney)cell models for oral drug absorption prediction and skinpermeability and human intestinal absorption model fororal and trans-dermal drug absorption prediction. Pre-ADMET predicts toxicity based on the Ames parame-ters and rodent carcinogenicity assays of rat and mouse(Seal et al., 2009).

2.3 Multi receptor docking

Molecular docking is performed to study thereceptor-ligand interaction which regarded as the ba-sis for structure based drug discovery. Docking stud-ies were performed by AutoDock 4.2 (Morris et al.,1996) by Lamarckian genetic algorithm. The catalyticand binding site of the target has been identified byAutoGrid. The structure and chemical properties ofthe active sites allow the recognition and binding ofthe ligand. Around 2,500,000 bioactive conformationswere generated by 10 iterations and the best confor-mations were screened in terms of lowest binding en-ergy generated in the clustering histogram. The inter-actions of curcumin with selected receptors were fur-ther compared with the interaction of those receptorswith their natural ligands. Further, the validations ofthe docking results were carried out using set of knownmolecules for each cancer receptors from available lit-erature. The calculated docking energy was comparedwith measured experimental binding energy associated

Interdiscip Sci Comput Life Sci (2014) 6: 13–24 15

Table 1 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 eachtype 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 1JDHGastric cancer, colorectal cancer, en-dometrial cancer, thyroid cancer, hep-atocellular carcinoma

1950 EGF Epidermal Growth Factor 1NQL Gastric cancer

1956 EGFR Epidermal Growth Factor Receptor kinase 3POZ

Oral cancer, esophageal cancer, gas-tric cancer, bladder cancer, choriocar-cinoma, cervical cancer, Glioma, La-ryngeal cancer

2064 ERBB2 Human Epidermal Growth Factor 2 3PP0

Gastric cancer, pancreatic cancer,bladder cancer, endometrial cancer,ovarian cancer, choriocarcinoma, cer-vical cancer, breast cancer, cholangio-carcinoma

208 AKT2 Protein kinase B 2X39 Ovarian cancer2263 FGFR2 Fibroblast Growth Factor Receptor 2 3B2T Gastric cancer2308 FOXO1 Forkhead box protein O1 3CO6 Alveolar rhabdomyosarcoma2950 GST-PI Glutathione S-transferase Pi gene 2A2R Prostate cancer3479 IGF1 Insulin-like growth factor 1 1TGR Malignant pleural mesothelioma

3480 IGF1R Insulin-like growth factor 1 receptor 1P4O Malignant pleural mesothelioma, syn-ovial sarcoma

367 AR Androgen receptor 2AX6 Prostate cancer

4193 MDM2 E3 ubiquitin-protein ligase 2AXIPenile cancer, choriocarcinoma, os-teosarcoma, alveolar rhabdomyosar-coma, glioma

4792 NFKBIANuclear factor of kappa light polypep-tide gene enhancer

1IKN Hodgkin lymphoma

5154 PDGFA Platelet-derived growth factor alpha chain 3MJK Malignant pleural mesothelioma, glioma5155 PDGFB Platelet-derived growth factor beta chain 3MJG Malignant pleural mesothelioma, glioma5290 PIK3CA Phosphatidylinositol-4, 5-bisphosphate 3-kinase 3HHM Ovarian cancer

5728 PTEN Phosphatase and tensin homolog 1D5R

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

5925 RB1 Retinoblastoma protein 2R7G

Chronic myeloid Leukemia, small celllung cancer, esophageal cancer, blad-der cancer, Breast cancer, osteosar-coma, glioma, hepatocellular carci-noma

595 CCNDI Cyclin D1-cyclin-dependent kinase 4 2W96Hairy cell leukemia, multiple myeloma,oral cancer, esophageal cancer, breastcancer, laryngeal cancer

596 BCL2 B-cell lymphoma 2 2W3L

Chronic myeloid Leukemia, small celllung cancer, gastric cancer, choriocar-cinoma, cervical cancer, kaposi’s sar-coma, nasopharyngeal cancer

7039 TGFA Transforming growth factor alpha 1MOX Gastric cancer

with known molecules for each receptor.

3 Results and discussion

3.1 Selection of receptors

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

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


variety of processes including carcinogenesis (Machinet al., 2002), control of cellular ageing and survival,regulation of circadian rhythm and lysosomal sortingof G protein-coupled receptors. Epidermal growthfactors (EGF) present in the extracellular domain ofmembrane-bound proteins and are involved in forma-tion of disulphide bonds (Stoscheck and King, 1986).Mutations can cause over expression and leads tocancer. Epidermal growth factor receptor (EGFR)(Mendelsohn and Baselga, 2006), transforming growthfactor, alpha (TGFA) (Greten et al., 2001), insulin-like growth factor 1 receptor (IGF1R) (Hewish et al.,2009) and erythroblastic leukemia viral oncogene ho-molog 2 (ERBB2) (Sauter et al., 1993) consists ofL domains and make up the bilobal ligand bindingsite. Akt murine thymoma viral oncogene homolog2 (AKT2) (Cicenas, 2008) and fibroblast growth fac-tor receptor 2 (FGFR2) (Byron, 2009) belong to ser-ine/threonine protein kinases. They form catalyticdomain and are involved in protein phosphorylation.Forkhead box O1 (FOXO1) (Maekawa et al., 2009)has HNF-3/fork head DNA-recognition motif resembleshistone H5. Function of glutathione S-transferase pi1(GST-PI) (Re et al., 2011) is conjugation of reducedglutathione to a variety of targets. Insulin-like growthfactor 1 (IGF1) (Heidegger et al., 2011) are secretedregulatory hormones. They are disulfide rich alphafold. Androgen receptor (AR) (Heinlein and Chang,2004) forms DNA binding domain of a nuclear hor-mone receptor. Mdm2, p53 E3 ubiquitin protein lig-ase homolog (MDM2) is an inhibitor of the p53 tumoursuppressor gene (Chene, 2003) binding the transactiva-tion domain and down regulates the ability of p53 toactivate transcription. Nuclear factor of kappa (NFK-BIA) (Curran et al., 2002) is a light polypeptide geneenhancer in B-cells inhibitor, alpha contains repeat-domain of membrane-binding mediates most bindingactivities of protein. Platelet-derived growth factor al-pha (PDGFA) polypeptide and platelet-derived growthfactor beta (PDGFB) (Liuet al., 2011) polypeptideare involved in signal transduction and is an endoge-nous inhibitor of protein phosphatase-1. PIK3CA -phosphatidylinositol-4, 5-bisphosphate 3-kinase, cat-alytic subunit alpha possess Ras-binding domains intheir N-termini. PTEN - phosphatase and tensin ho-molog play a key role in membrane binding. Retinoblas-toma 1 (RB1) (Chinnam and Goodrich, 2011) is re-quired for high-affinity binding to E2F-DP complexesand for maximal repression of E2F-responsive promot-ers, thereby acting as a growth suppressor by block-ing 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 varietyof cell systems including factor-dependent lymphohe-matopoietic and neural cells and regulates cell death

by controlling the mitochondrial membrane permeabil-ity.

3.2 Selection of ligands

Ligands were predicted for pharmacokinetic proper-ties using Pre-ADMET tool. Drug likeness, ADME andtoxicity predictions were performed. We have noticedthat Curcumin is well qualified in terms of pharma-cokinetic features such as human intestinal absorption,Caco2 (heterogeneous human epithelial colorectal ade-nocarcinoma) cell permeability, MDCK (Madin-Darbycanine kidney) cell permeability, skin permeability andblood brain barrier penetration. The toxicity studiesrevealed that curcumin found to be non carcinogen andnon mutagen predicted by Ames test and mouse car-cinogeniscity model respectively (Table 2). Hence, ourstudy showed that curcumin, qualifying most of therules can be a ideal drug candidate. Litreol is a deriva-tive of catechol carrying a pentadecenyl substituent atposition-3. Pharmacological predictions of this com-pound were comparatively low compared to curcumin.There was a violation in rule of 5; however, posses highblood brain barrier penetration. Triterpene is a ter-pene consisting of six isoprene units. Pharmacologicalpredictions were similar to litreol. The drug likelinessproperties and pharmacokinetic features are shown inTable 2.

3.3 Multi receptor docking of curcumin

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


Table 2 Pharmacokinetics prediction of the selected ligand using Pre-ADMET tool. Curcumin showedbetter drug like features and pharmacokinetic properties compared with Litreol and triterpene

Curcumin Litreol Triterpene

Drug likeness prediction

CMC like Rule Qualified Not 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

ADME prediction

Human Intestinal Absorption Well absorbed Well absorbed Well absorbed

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

Toxicity Prediction

Ames test

Ames TA100 (+S9) negative negative negative

Ames TA100 (-S9) negative negative negative


Ames TA1535 (-S9) negative negative negative


Ames TA98 (-S9) negative negative positive

Ames test Non-mutagen Non-mutagen Mutagen

Carcinogenicity

Carcinogenicity (Mouse) negative positive positive

Carcinogenicity (Rat) positive negative positive

120 (Fig. 1(b)). The binding energy of the best dockedconformation of various cancer drug targets with cur-cumin is shown in Table 3.

We have compared the interaction of curcumin andEGF, GST-PI and PDGFA with the natural ligandsof these receptors by docking studies (Table 5). Gefi-tinib (Li et al., 2004), Celecoxib (Howe et al., 2002)and Lapatinib (Medina & Goodin, 2008) are the nor-mal inhibitors for Epidermal Growth Factor (EGF).Our docking study revealed that the binding energy ofdocked complex of Gefitinib, Celecoxib and Lapatinibagainst EGF are identified to be 0.61 kcal/mol, 0.64kcal/mol and 6.33 kcal/mol respectively, higher thanthe binding energy of the docked complex of curcumin(−7.59 kcal/mol) and EGF. Moreover, the interactionsare not stabilized by hydrogen bonds. Similarly, theinteraction of buthionine sulfoximine (Yokomizo et al.,1995), common inhibitor of Glutathione S-transferasepi gene (GST-PI) and the receptor showed less bindingproperties (binding energy −5.90 kcal/mol) comparedto curcumin (−7.98 kcal/mol). Our study also showed

that Imatinib (Malavaki et al., 2013), common ligandfor Platelet-derived growth factor receptor (PDGFA),interacting with its receptor by binding energy of −2.66kcal/mol. Hence, our docking study clearly indicat-ing that curcumin has good binding efficiency and in-hibitory properties against these cancer receptors thannormal inhibitors.

The experimental binding energy associated with in-teraction of epidermal growth factor receptor (EGF)and standard ligand, Gefitinib were reported asΔΔGFR exptl = 0.90 kcal/mol (Balius and Rizz,2009). Our studies showed that calculated bindingenergy of the interaction between curcumin and EGF(−7.53 kcal/mol) was found better than the measuredexperimental binding energy between EGF and Gefi-tinib (+0.90 kcal/mol). The experimental binding en-ergy between platelet-derived growth factor receptor(PDGFA) and its common liagnd, Imatinib was re-ported as 0.2±0.6 kcal/mol (Aleksandrov and Simon-son, 2010). From our studies it is evident that the cal-culated binding energy of curcumin - PDGFA docked


(a) (b)

(c)

(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 residuespresent in the binding cavities were displayed in sticks diagram and curcumin is shown in molecular surface repre-sentation. The binding energies of docked complex were found to be −7.93 kcal/mol, −7.98 kcal/mol and −7.59kcal/mol respectively

complex (−7.93 kcal/ mol) is better than that of exper-imental binding of Imatinib - PDGFA (0.2 kcal/mol).Similarly, we noticed that calculated binding betweencurcumin and GST-PI is better than that of mesauredexperimental binding energy of buthionine sulfoximine,common ligand for GST-PI. From our comparativestudies, it is evident that curcumin has better bind-ing properties towards the selected cancer targets thantheir respective native ligands.

There are many reports revealed the validation ofinhibitory properties of curcumin screened by com-puter aided virtual screening. The anti-inflammatoryproperties 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 tumornecrosis factor-alpha converting enzyme (TACE) wererecently studied by molecular docking (Elumalai et al.,2012). The best conformations were selected based ondocking scores. The binding target GSK-3beta (−6.44kcal/mol) was found to be more selective for curcuminbinding 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 bondingwith various amino acids (Elumalai et al., 2012).We


Table 3 The receptor ligand interaction data ob-tained from the docking studies. The en-ergy of binding (kcal/mol) between cur-cumin and the best conformation of vari-ous cancerous drug targets is analyzed inkcal/mol

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

CDKN1A 1AXC −6.095

CTNNB1 1JDH −5.09

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 litreoland triterpene with selected cancer drugtargets. The binding energy (kcal/mol)indicated that the inhibitory properties ofthese ligands are poor compared with cur-cumin

Gene name PDB IDBinding 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

Table 5 Comparative analysis of the interaction ofcurcumin and natural ligands of selectedcancer receptors by docking studies. Thetable showed that curcumin has betterbinding efficiency than the normal ligandsof the selected receptors

Cancer

receptors

Normal

ligand

Docking energy

(kcal/mol)

Receptor and

normal ligand

Receptor

and curcumin

EGF Gefitinib −0.61

−7.59Celecoxib −0.64

Lapatinib +6.33

GST-PIButhionine

sulfoximine−5.90 −7.98

PDGFA Imatinib −2.66 −7.93

between curcumin and the selected drug targets. Sim-ilarly, various curcumin derivatives were screened aspotent androgen receptor antagonists by docking stud-ies were further confirmed by experimental validation(Xu et al., 2012). Recent studies revealed that cur-cumin analogues screened as novel EGFR inhibitors, akey cancer drug targets focused in our studies, showedantiproliferative properties against two human tumorcell lines (Hep G2 and B16-F10). Molecular dockingof these analogues into EGFR-TK active site revealedthat curcumin analogues have excellent inhibitory ac-tivity (Xu et al., 2013). Furthermore, studies suggestedthat human glyoxalase I (GLO-I) is a potential targetfor anti-tumor drug development and many curcuminderivatives were identified as novel lead molecules withhigh inhibitory properties against human GLO-I (Yuanet al., 2011). There are also report revealed that theinhibitory properties of curcumin towards drug tar-get glycogen synthase kinase. The inhibitory activ-ity of curcumin towards glycogen synthase kinase wasscreened by computer aided screening and validated byfurther studies (Bustanji et al., 2009). Hence, computeraided approaches are excellent platform to study the in-hibitory properties of various ligands and screen bettertherapeutic substances with profound pharmacokineticfeatures and druggish activities.

3.4 Docking with litreol and triterpene

Litreol and triterpene were subjected to dockingstudies with three receptors - EGF, GST-PI andPDGFA - with which curcumin showed better activ-ity. The docking studies showed that inhibitory activ-ities of litreol with these receptors are poor compared


(a) (b)

(c)

(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 bindingenergies 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 calcu-lated docking energy values of litreol with EGF, GST-PI and PDGFA were −5.08 kcal/mol, −3.69 kcal/moland −1.86 kcal/mol respectively. Interacting restudieswith EGF molecule were His 10, Asp 280, Asp 290, Pro308 and Aln 337 (Fig. 2(a)). Interacting residues withGST-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 bondsstabilized the interaction (Table 4). Hence, the bind-ing efficiency of litreol is less compared with curcumin,however, better than their native inhibitors. The bind-ing energy of the docked complex of triterpene againstEGF and PDGFA were found to be −4.02 kcal/moland −4.82 kcal/mol respectively and there were no hy-drogen 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)). Interact-ing residues with PDGFA were Ile 38, His 39, Val 95,Lys 97, Thr 98, Trp 120, Pro 121, Val 124, Arg 148, Val152 and Val 160 (Table 4). Furthermore, the inhibitoryactivity of triterpene against GST-PI was found to bepoor, it showed positive binding energies in all thetested conformation. Hence, our study revealed thatbinding efficiency of triterpene is also less comparedwith curcumin.

From our study, it is evident that curcumin has broadrange of inhibitory properties against various cancerdrug targets compared with many routinely used an-ticancer agents including their natural inhibitors. Bet-ter inhibitory properties and ideal pharmacokinetic fea-tures make curcumin as an ideal inhibitor and therapeu-tic substances against wide varieties of cancer. How-


(a)

(b)

(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 aidedvirtual screening, further experimental studies are re-quired to confirm the efficiency of these herbal leadagainst various cancer drug targets (Skariyachan et al.,2012). Our data would pave significant insights for suchkinds of studies.

4 Conclusion

Cancer accounts for 10-12% of total death worldwideand present therapies in oncology fail to evade most ofthe cancer effects. Hence, there is a pressing need toscreen novel leads that have wide range of anti-tumorproperties. Curcumin, chief component of turmeric, ex-

hibit antioxidant, anti-inflammatory, antimicrobial andanticarcinogenic activities. Present study revealed theinhibitory properties of curcumin against various cancerdrug targets by computer aided virtual screening. Com-puter aided predictions showed that curcumin was anideal drug candidate with better drug likeness and phar-macokinetic properties. This in silico study showedthat curcumin has better therapeutic significance thanroutinely used anticancer agents such as litreol, herballead isolated from Lithraea caustic and triterpene, aphyloligand isolated from Annona glabra. Further-more, our comparative study revealed that curcuminshowed better inhibitory activities against the virulentgene products of Epidermal Growth Factor (EGF), Glu-


tathione S-transferase pi gene (GST-PI) and Platelet-derived growth factor receptor (PDGFA) than their na-tive ligands. Our study concluded that the inhibitoryproperties of curcumin would pave novel therapeuticinsights against various types of cancers when presenttreatments in oncology fail to evade cancer. Presentdata pave crucial landmarks for further studies to vali-date curcumin as promising drug candidate against var-ious cancers.

Acknowledgements

The authors thankfully acknowledge Dr. G. S. Jagan-natha Rao, Senior Professor and Head, Department ofBiotechnology, Dayananda Sagar College of Engineer-ing and Dr. G. A. Ravishankar, Vice President (R & D)in Life Sciences, Dayananda Sagar Institutions and fortheir constant support and encouragement throughoutthe study.

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exploring inhibitory potential of curcumin against various cancer targets by in silico virtual...

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