BioinformaticsInfrastructureFacility,Nagaland University, Lumami-798627, Nagaland, India.
Citation:BhomickPC,SinghSP,DebCR, et al.MolecularInteractionStudiesofChitosanCross-linkedCompoundsasDrugDeliverySubstrateforAnticancerAgents. JBiomedicalSci.2016,5:3.
Molecular Interaction Studies of Chitosan Cross-linked Compounds as Drug Delivery
Substrate for Anticancer Agents
AbstractChitosanisknownforitsabsorptionandadhesionpropertyanditisanon-toxicbiodegradableheteropolymer.Ithasastrongaffinityforwaterandhighdegreeofsolubilityinacidicmedium.Inaddition,chitosanhydrogelsshowedlowmechanicalstrengthandminimumabilitytocontrolthedeliveryofencapsulatedcompounds.Andhence,inthisinvestigationasetofcompoundscrosslinkedwithChitosanwasscreenedforanticanceragentusingcomputationaltechnique(moleculardocking)againstNOSenzyme (PDB ID: 4NOS). The resultwas interesting asmajority ofthe compounds screened turned up with favorable molecular interaction andbindingaffinityasevidencedfromthedockingscore.Furthermorethemolecularinteraction analysis represents the cross linked compounds possessed heavymolecular interaction at the active site residue of the enzyme. Thus, Chitosancrosslinkedcompoundstargetthespecificactivesiteresidueandhencecanbeused in future for drug delivery.
IntroductionHydrogelsarecross-linkedpolymericnetworksthattrapwaterinthepolymermatricesmainlybysurfacetensionandareusuallythreedimensionalwhilemostofitspropertiescanbealteredbystructuralmodification[1,2].Akindofhydrogelcalledchitosanis findingwideapplication inmanyareas suchas fuel cells, oilencapsulation, wound dressing and especially in drug deliveryin recent years [3-6]. Chitosan [β-(1,4)-2-amino-2-deoxy-d-glucopyranose] is a non-toxic biodegradable hetero polymer,hasagoodabsorptionandadhesionproperty.Itisaweakbaseobtainedbydeacetylationofchitin[3].Becauseoftheiraffinityforwaterandhighdegreeofsolubilityinacidicmedium,chitosanhydrogels comparatively shows low mechanical strengthand minimum ability to control the delivery of encapsulatedcompounds[7],therebyfacilitatingchemicalmodificationbyitsaminoandhydroxylgroups.Forahydrogeltobeintroducedinabiologicalsystems,itscompatibilityshouldbetakenintoaccountwhile it is seen that the pharmacy world will benefit fromhydrogels likechitosanbecauseof itshydrophilicity,flexibility,versatility,highwaterabsorptivity,andgreatercompatibilitywiththebiologicalsystem.It isalsoachoiceforthepharmaceuticalworldbecauseof its long lifespan incirculationandpossibilityof being actively or passively targeted to the known biophase
like cancer cells [8]. Chitosan can be blended with differentcrosslinkingagenttoproduceachemicallyactivehydrogelsforbioapplications. Like the amino group of chitosan can lead toionicinteractionbetweenandanionicgroups.Theseinteractionscanproducehydrogelswithdifferentmaterialpropertieswhichdependuponthesizeoftheanionicagentsandchargedensity,alsoondegreeofdeacetylationandamountofchitosanpolymer.
2016Vol. 5 No. 3:18
Journal of Biomedical SciencesISSN 2254-609X
This Article is Available in: www.jbiomeds.com2
Chitosancrosslinkedwithpolyelectrolyteshavebeenproducedbywater-solublenegativelychargedmoleculeslikeDNA,alginate,hyaluronicacid,proteinslikegelatinpolyacrylicacidandmostlythe stability of these compounds depends on solvent, chargedensity,temperature,ionicstrength,andpH[9-12].
TheNOSenzymesconsistofoxygenasedomainthatbindsarginine,tetrahydrobiopterinandhemeandreductasedomainwithFADand FMN prosthetic groups. They are complex, homodimerichemeenzymewhichproducesfreeradicalnitricoxidethatleadstovarietyofage-relateddiseases[13-15].Nitricoxidesynthase(NOS)incellsareofthreeisoforms.Neuronal/brainNOS(nNOS),endothelial NOS (eNOS) and inducible NOS (iNOS). nNOS andeNOSbelongstoconstitutiveNOS(cNOS)andNOproducedfromthistypehelpsinmaintainingnormalvasoactivitythroughaCa2+ -dependent pathway and also as a neurotransmitter for signaltransmission.WhileNOproducedfromiNOScantriggerseveraldisadvantage cellular responses and can cause some diseasesincludingsepsis,strokeandinflammation,[13-19].
Inthepresentinvestigationchitosancrosslinkedcompoundswere screened as inhibitors of iNOS revealing chitosan as agoodcarrierfordeliveringandunloadingthedrugatspecifictarget.
Materials and MethodChemical dataset The 2D structure of Diethylsquarate, Glutaraldehyde,Formaldehyde, Ethyleneglycol diglycildylether, BlockedDiisocyanate,PhloreticandActivatedQuinonecross-linkedwithChitosan was generatedwith Chemoffice 2010. The energy ofthesecross-linkedcompoundswerefurtheroptimizedusingMM2forcefieldmethodandsaveas sybylmol2 (threedimensional)fileformatusingChemOffice2010.
Protein preparation The 3D structure of human inducible nitric oxide synthase(PDB ID:4NOS)wasdownloaded from theProteinDatabankBank(http://www.rcsb.org/).Thecoordinatesofthisenzymeis complexedwithwatermolecules and ironprotoporphyrinIX (heme) along with the Cofactors such as BH4, Zn+2 atom. Moreoverthe3Dstructurehasaresolutionof2.25Å.makingit anexcellent choice formoleculardocking studies. All thewater molecules were removed for the molecular dockingsimulation purpose since they are not taken into accountduringthescoringfunction[20].
Further, the potential ligand binding site of the enzyme waspredictedusingMVD.Thebindingsitehaveavolumeof470.02A3and1158.84A2.Thebindingsitewassetinsidearestrictionsphereofradius15A°(X0.65,Y99.58,Z11.19)usingMVD.
ThentheChitosancrosslinkedcompoundswerethenimportedinMVD.TheBondflexibilityofthecrossliknedcompoundswassetaswellasthesidechainflexibilityofresiduesnearthepotentialligandbindingsitewassetwithatoleranceof1.10andstrengthof0.90fordockingsimulations.TheRMSDthresholdwassetat2.00Åformultipleclusterposes.Thedockingalgorithmwassetat 1,500maximum iterationwith simplex evolution size of 50andaminimumof20runswereperformedforeachofthecrosslinkedcompound.Thebestposewasconsideredforsubsequentprotein-ligandinteractionanalysis.
MoleculardockingwascarriedoutusingMVDwhichisbasedonadifferentialevolutionalgorithm.ThealgorithmofMVDconsidersthe sumof the intermolecular interactionenergybetween theligandandtheproteinandtheintramolecularinteractionenergyof the ligand. Thedockingenergy scoring function isbasedonthemodifiedpiecewiselinearpotential(PLP)withnewhydrogenbondingandelectrostatictermsincluded.Fulldescriptionofthealgorithm anditsreliabilitycomparedtoothercommondockingalgorithmisdescribedbyThomsenetal.[20].
Results and DiscussionThe molecular docking simulation revealed the cross linkedcompoundsbindattheactivesiteoftheNOS.Fromthedockingscore, it is revealed that the MolDock score holds favorableinteractionfortheChitosanCrosslinkedcompoundsviz.DiethylSquarate (-181.13 kJmol-1), Formaldehyde (-179.522 kJmol-1), Glutaraldehyde (-145.48 kJmol-1), Blocked Diisocynate (-105.27kJmol-1),ActivatedQuinone(-104.72kJmol-1)intermsofnegativeenergy (Table 1).WhileEthyleneglycoldiglycildylether,PhloreticacidandGenepindonotpossessedafavourableinteraction.
TheMolDockscoringfunction(MolDockScore)whichdeterminedthebindingaffinityinthepresentinvestigationisderivedfromthePiecewiseLeastPotential (PLP)scoring functions.TheMolDockscoring function further improves the PLP scoring functionswithnewhydrogenbondingtermandnewchargeschemes.Thedockingscoringfunction,EScore,isdefinedbythefollowingenergyterms:
EScore=Einter+Eintra
Where,
Einteristheligand-proteininteractionenergy
Eintra is the internal energy of the ligand
Further, the ligand-protein interaction calculation using ligandenergy inspector for the Chitosan cross linked compounds isshowninTable 2whichindicatestheligand-proteininteractionenergy and its molecular interaction distances along with the
interactingatoms.Itisobservedthatthecompoundsalsoexhibitmolecular interaction with the Cofactor HEM molecule. Thus,indicating a strong binding affinity towards the active site ofNOS. The snap shots illustrating the protein-ligand interactionof Chitosan cross linkedwith Diethyl Squarate, Formaldehyde,Glutaraldehyde,BlockedDiisocyanateandActivatedQuinoneisshown inFigures 1-5 respectively.Hence, from thefigures theplausibilityofChitosancrosslinkedcompoundsdeliveringligandsatagivenspecifictargetisviable.
AcknowledgementThe authors would like to acknowledge the Department ofBiotechnology,MinistryofScienceandTechnology,GovernmentofIndia,NewDelhiforthenecessarysupport.PCBacknowledgedtheDepartmentofScienceandTechnology (DST),GovernmentofIndiaforDST-INSPIREfellowship(IF150297).
2016Vol. 5 No. 3:18
Journal of Biomedical SciencesISSN 2254-609X
This Article is Available in: www.jbiomeds.com8
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