Evolution of GLP‐1 Receptor Agonists for Diabetes Treatment

EvolutionofGLP

1ReceptorAgonistsfor DiabetesTreatment

Diabetesisamajorpublichealthproblemthatisapproachingepidemicproportions globallySincetheuseofanimalinsulinforthetreatmentofdiabetesin1922,aboutnine majorclassesofdrugsforthetreatmentofdiabeteshavebeendiscoveredanddeveloped worldwide,includingsulfonylureas,biguanides,α-glucosidaseinhibitors,insulins, thiazolidinediones(TZDs),meglitinides,GLP1RAs,DPP4inhibitors,andSGLT2 inhibitors

Amongthesenineclassesofdrugs,GLP1RAlowersglycatedhemoglobinlevels extremelyimpressiveamongnoninsulinproducts,anditslongerhalflifeallowsittobe administeredonceaweek,orlonger.Fromthecurrenttrendofclinicalapplication, GLP-1RAdrugshavebecomethemostpromisingglucose-loweringdrugsinthemarket

DiscoveryofGLP-1

Inthemidtolate20thcentury,intestinalextractswerefoundtohavebloodglucose loweringeffectInaddition,injectingglucoseintotheintestinewasabletostimulatethe productionofmoreinsulinthaninjectingitintothevein.Thesefindingsinitiatedthestudy oftheincretinhormoneInthe1970s,thefirstincretinhormone,glucose-dependent insulinotropicpolypeptide(GIP),wasdiscovered,andglucagonlikepeptide1(GLP1), wassubsequentlydiscovered

Bythe1980s,theaminoacidandgenesequencesofproglucagon(Figure1)were unraveledItcanbeobservedthatproglucagonisnotexpressedbyasinglegene,butis embeddedinalargergene,andwhenthislargegeneexpressesalargepeptidechain (calledpreprohormones),itisthencleavedbyspecificenzymesandpost-translationally modifiedtofinallyobtainfragmentswithdifferentbiologicalactivities.Proglucagonis mainlyexpressedintheintestine,pancreasandhindbrainIntestinalandbraincells containprohormoneconvertase1(PC1),whichisabletocleaveproglucagoninto Glicentin,Oxyntomodulin,GLP1,GLP2andIP2,whilepancreaticisletcellscontain prohormoneconvertase2(PC2),whichcapableofcleavingproglucagonintoGlucagon andMPGF(Figure1)Therefore,GLP1inhumanbloodismainlysecretedthroughthe intestine

GLP-1RAMechanismofAction

GLP-1(glucagon-likepeptide-1)isahormonesecretedbytheintestinaltractduring feeding,whichenhancesinsulinsecretionandinhibitsglucagonsecretioninaglucose concentrationdependentmanner,anddelaysgastricemptyingtoreducetheamountof foodeatenthroughcentralappetitesuppressionGLP1RAexertsitsglucoselowering effectbystimulatingGLP1receptors,whichnotonlyhassignificantglucoselowering efficacy,butalsohastheadvantageoflowincidenceofhypoglycemia

Inaddition,becausethetissuesinwhichtheGLP1receptorisexpressedarenotlimited tothegastrointestinalandpancreaticglands,GLP1RAcanreducecardiovascularriskin additiontoloweringglucoseandreducingbodyweightThesearebenefitsthatinsulinand thevastmajorityoforalhypoglycemicagentsdonothave

EvolutionofGLP1GLP-1RAs

Currently,therearenineGLP1RAsapprovedformarketingworldwide(Table1),mainly forthetreatmentofdiabetesandobesity,ofwhichtirzepatideisanoveldual GLP1RA/GIPRagonist.

Table1.ApprovedGLPRAs

In2005,Exendin4(Exenatide/BYETTA),theworld'sfirstGLP1RA,wasapprovedbythe FDAfortheadjuvanttreatmentoftype2diabeteswithtwoinjectionsperday(BID).

In2009,NovoNordisk'sLiraglutide(Victoza)wasapprovedbytheEMAandinJanuary 2010bytheFDAforthetreatmentoftype2diabetes.Liraglutidehasdemonstratedboth cardiovascularbenefitsinadditiontoitsexcellentglucose-loweringeffectsAlso, Liraglutidewastheworld'sfirstoncedailyGLP1RAdrug.

ToaddresstheproblemofonceadayinjectionsofLiraglutide,LillylaunchedDulaglutide, whichisadministeredonceaweekandwasapprovedbytheFDAin2014forthe treatmentoftype2diabetesDulaglutidesalessurgedstartingin2019andbecamethe topsellerinGLP1RAin2020.

In2017,NovoNordisklauncheditsblockbusterproduct,Semaglutide(Ozempic),withan extendedhalflifeof7days,enablingonceaweekdosing.In2019,theFDAapproves semaglutide(Rybelsus),thefirstoralGLP-1analogtreatmentforadultswithtype2 diabetes

BiopharmaPEG https://wwwbiochempegcom In2022,EliLillylaunchedTirzepatide,anoveldualGLP1RA/GIPRagonistadministered onceweeklybysubcutaneousinjectionthatactivatesbothGLP-1andGIPreceptorsGIP (glucosedependentinsulinotropicpolypeptide)isahormonethatmaycomplementthe effectsofGLP-1receptoragonistsPreclinicalstudieshaveshownthatGIPmayreduce bodyweightbyreducingfoodintakeandincreasingenergyconsumption,andin combinationwithGLP1receptoragonists,mayhaveagreatereffectonpatients'blood glucoseandbodyweight

GLP-1RAs:ChallengesandSolutions

TheshortactionprofileofnativeGLP-1imposesamajorchallengetowardsitssuccessful clinicalutilizationToovercomethislimitation,variousstrategieshavebeenappliedto extendthehalflifeofGLP1andtoaccelerateitsinvivoactionandpotency

Figure3MethodstoenhanceGLP1Raction,source:reference[1]

(1)PreventionfromDPP4degradation.Thisisthemostcommonlyusedapproach, anditsstrategyistomodifythesecondNterminalaminoacidposition(Ala8)toprotect fromdegradationbyDPP4Thisstructuralmodificationhasbeenappliedtoexenatide, lixisenatide,semaglutide,dulaglutideandalbiglutide

(2)Bindingtoalbumin.Albiglutide(GlaxoSmithKline)isafusionoftwoGLP1molecules withhumanalbumin,whichincreasestheproteolyticstabilityofGLP1andslowsrenal clearance,extendingthehalflifeto120hAlbuminbindstotheneonatalFcreceptor (FcRn)inapHdependentmanner,thusavoidingdegradation.Uponendocytosisbythe endothelialcells,albuminbindstotheFcreceptor(FcRn)duringendosomalacidification, whichsortstheintracellulartraffickingofthealbuminawayfromdegradativelysosomes andbacktotheplasmamembranewhereitcanonceagainreenterthegeneral circulation.

Figure4FcRnstructure&FcRnsalvagepathwayforIgGSource:Reference[4]

(3)Acylationwithfattyacids.ByfusingGLP1withfattyacidsforacylation,the molecularselfassociationispromoted,thusprolongingthediffusiontimeofthedrugfrom theinjectionsite.Inaddition,thefattyacidfractioncanbereversiblyandnoncovalently boundtohumanserumalbumin(HSA),slowingdowntherenalclearanceThisstrategy hasbeenappliedtoliraglutideandsemaglutidewithhalflivesof12hand160h, respectively

(4)PEGylation.Polyethyleneglycol(PEG)isawatersolubleinertpolymerthatreduces therenalclearanceofthedrugandprolongsthehalf-life,inadditiontoenhancingwater solubilityandpreventingproteolysisThelinkagebetweenPEGandthedrugmolecule canbeeitherstableordegradable,thelatterbeingcommonlyusedforprodrugsMost importantly,itdoesnotaffectthefoldingstabilityoftheconjugatedproteinThisstrategyis usedforPEGLoxenatidefromHaosenPharmaceutical

BiopharmaPEG,aleadingPEGlinkersupplier,offersPEGylationasacosteffective modificationofpeptideswhichhasthepotentialtoimprovebioavailabilitycomparedtothe nmodifiedmolecule

(5)FcfusionAsalreadymentioned,GLP1fusedtoalbuminisabletoescapelysosomal degradationInasimilarway,fusionofGLP1withIgGcanachievethesameeffect (Figure4)Thisstrategyhasbeenappliedtodulaglutide,wheretwoGLP1moleculesare fusedtotheFcfragmentofIgG4,increasingthehalflifewhilereducingtherenal eliminationduetotheincreasedmolecularweight

(6)Sustainedreleaseformulations.Bydureon®(AstraZeneca)isanextendedrelease (ER)formulationofExenatidethatrequiresonlyonceaweekdosingSustainedreleaseis

BiopharmaPEG https://wwwbiochempegcom achievedbyincorporatingexendin4into0.06mmdiameterbiodegradablemicrospheres containing50:50poly(D,L-lactide-co-glycolide)(PLG)polymerandsucroseInthehuman body,thePLGpolymersslowlydegradethroughthenoncatalyzedhydrolysisoftheester linkagesintolacticacidandglycolicacid,whicharefinallyeliminatedascarbondioxide andwater

(7)Oralformulation

Weallknowthatpeptidedrugsgenerallycannotbetaken orallybecausestomachaciddegradesthemdirectly,butSemaglutidehasachieveda breakthroughInRybelsus®(NovoNordisk),Semaglutideformsanoncovalentlinkage withN[8(2hydroxybenzoyl)aminocaprylate](SNAC),whichprotectsthepeptidefrom degradationbyenzymesandacidsandacceleratesitstargetedreleaseandabsorptionin thestomach

Figure5Theoryoforalsemaglutideabsorption,source:reference[5]

Summary

HalfacenturyhaspassedsincethediscoveryofGLP1,whichhasprovidedanewway forhumanstofightdiabetesToday,thereisstillalargenumberofGLP1Ragonists enteringclinicaltrials,whichwillleadtoabigexplosioninthefuture,solet'swaitandsee together

BiopharmaPEGsuppliespolyethyleneglycol(PEG)derivatives,monodispersePEGs, customPEGderivativesynthesisandPEGylationservicesworldwide,fromR&Dthrough GMPcommercialquantities,forpreclinical,clinicaltrials,andcommercialproductsfor pharma,biotech,medicaldevices,anddiagnosticsAnd,BiopharmaPEGnow providessemaglutidesidechainwiththebestpriceandhighquality.

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References:

[1]Tan,Q,Akindehin,SE,Orsso,CE,Waldner,RC,DiMarchi,RD,Müller,TD,& Haqq,A.M.(2022).RecentAdvancesinIncretinBasedPharmacotherapiesforthe TreatmentofObesityandDiabetesFrontiersinendocrinology,13,838410 https://doiorg/103389/fendo2022838410

[2]Drucker,DJ,Habener,JF,&Holst,JJ(2017)Discovery,characterization,and clinicaldevelopmentoftheglucagonlikepeptidesTheJournalofclinicalinvestigation, 127(12),42174227https://doiorg/101172/JCI97233

[3]Reed,J,Bain,S,&Kanamarlapudi,V(2020)Recentadvancesinunderstandingthe roleofglucagonlikepeptide1F1000Research,9,F1000FacultyRev239 https://doiorg/1012688/f1000research206021

[4]Baldwin,W.M.,3rd,Valujskikh,A.,&Fairchild,R.L.(2019).TheneonatalFcreceptor: KeytohomeostasiccontrolofIgGandIgGrelatedbiopharmaceuticalsAmericanjournal oftransplantation:officialjournaloftheAmericanSocietyofTransplantationandthe AmericanSocietyofTransplantSurgeons,19(7),18811887 https://doi.org/10.1111/ajt.15366

[5]Twarog,C,Fattah,S,Heade,J,Maher,S,Fattal,E,&Brayden,DJ(2019) IntestinalPermeationEnhancersforOralDeliveryofMacromolecules:AComparison betweenSalcaprozateSodium(SNAC)andSodiumCaprate(C10)Pharmaceutics,11(2), 78https://doiorg/103390/pharmaceutics11020078

[6]https://newsvanderbiltedu/2013/08/01/golden-goose/

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