w ww . e l s e v i e r . c o m / l o c a t e / b j p
Original
Article
Cytotoxic
diterpenoids
from
the
roots
of
Salvia
lachnocalyx
Hossein
Hadavand
Mirzaei
a,
Omidreza
Firuzi
a,
Bernd
Schneider
b,
Ian
T.
Baldwin
c,
Amir
Reza
Jassbi
a,∗aMedicinalandNaturalProductsChemistryResearchCenter,ShirazUniversityofMedicalSciences,Shiraz,Iran bForschungsgruppeBiosynthese/NMR,Max-Planck-InstitutfürchemischeÖkologie,Jena,Germany
cAbteilungfürMolekulareÖkologie,Max-Planck-InstitutfürchemischeÖkologie,Jena,Germany
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received26July2016 Accepted11January2017 Availableonline28March2017
Keywords: Salvialachnocalyx
Diterpenoid NMR Cytotoxicity
a
b
s
t
r
a
c
t
SalvialachnocalyxHedge,Lamiaceae,isanendemicsagewhichgrowsnaturallyintheFarsProvinceofIran. ThephytochemicalanalysesoftherootsofS.lachnocalyxledtotheisolationoffiveknownditerpenoids: ferruginol(1),taxodione(2),sahandinone(3),4-dehydrosalvilimbinol(4)andlabda-7,14-dien-13-ol(5). Theirchemicalstructureswereelucidatedusingone(1Hand13C)andtwodimensional(COSY,HSQC
andHMBC)NMRspectroscopicdataaswellaselectronimpactmassspectra.Thecytotoxicityofthe purifiedcompoundswasevaluatedagainstthreehumancancercelllines;MOLT-4(acutelymphoblastic leukemia),HT-29(colorectaladenocarcinoma)andMCF7(breastadenocarcinoma)andalloftheisolated compoundsshowedconsiderablecytotoxicactivityagainstthesecelllines.Compounds2and3(IC50
range:0.41–3.87g/ml)withendocyclic␣,-unsaturatedcarbonylfunctionalgroup,exhibitedthe high-estcytotoxicactivitiescomparedtotheothercompounds(IC50range:6.85–17.23g/ml).Inconclusion,
compounds2and3arepresentedascompoundsthatdeservefurtherinvestigationoftheirbiological activities.
©2017SociedadeBrasileiradeFarmacognosia.PublishedbyElsevierEditoraLtda.Thisisanopen accessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
ThegenusSalvia,Laminaceae,consistsofmorethan900species thatarewidelydispersedthroughouttheworld.Thereare61Salvia
speciesnaturallygrowinginIran,seventeenofthemareendemic (Jamzad, 2012).Several species of Salvia are pharmacologically active and have beenwidely usedin folk medicine (Wu et al., 2013;Firuzietal.,2013;Jassbietal.,2017).Bioassay-guided purifi-cationof chemicalconstituentsofSalviaspecieshasresultedin theisolationofmanybioactivephytochemicalssuchasflavonoids, phenolics, terpenoids and steroids (Jassbi et al., 2017). Among them,morethan550diterpenoidshavebeenreportedfrom differ-entSalviaspecies(KaboucheandKabouche,2008),mostofwhich haveshownabroadspectrumofinterestingbiologicalactivities andecologicalroles,thatincludeantimicrobial,anticancer, antivi-ral,antioxidantandanti-inflammatoryactivities(González,2015; Jassbietal.,2017).Amongdifferentclassesofanticancerdrugs, naturalproductsremainamainsourceofpotentialdrugstotreat humantumors.Accordingtoarecentpublicationontheroleof nat-uralproductsinthefieldofanticancerdrugs,about75%ofsmall
∗ Correspondingauthor.
E-mail:jassbiar@sums.ac.ir(A.R.Jassbi).
moleculeswithanticancereffecthavebeendirectlyorindirectly derivedfromnaturalproducts(NewmanandCragg,2016).
SalvialachnocalyxHedgeisanendemicsagewhichgrows nat-urallyintheFarsProvinceofIran(Jamzad,2012).Recently,three sesterterpenelactones,twosesterterpenoids,threeflavonoids,two steroids,onenorditerpenoidandonetriterpenoidwerereported from an acetone extract of the aerial parts of S. lachnocalyx
(FarimaniandMazarei,2014).Furthermore,theessentialoilofS. lachnocalyxhasbeenanalyzedbyGC–MSandbicyclogermacrene, ␣-pinene, sabineneand -pinene have been detectedasmajor constituents(MirzaandBahernik,2007).Tothebestofour knowl-edge,thepresentreportisthefirstbioassay-guidedphytochemical analysesoftherootsofS.lachnocalyxforisolationandstructural elucidationofitscytotoxicactivenaturalproducts.
Materialandmethods
Reagentsandchemicals
Fetalbovineserum(FBS),phosphatebufferedsaline(PBS),RPMI 1640 and trypsin were purchased from Biosera (Ringmer, UK). Acetonitrile(ACN,HPLCgrade),dichloromethane(DCM),dimethyl sulfoxide (DMSO), methanol (MeOH), silica gel (70–230 mesh) foropencolumn chromatographyandpre-coated silicagelF254 TLC aluminum sheets were obtained from Merck (Darmstadt,
http://dx.doi.org/10.1016/j.bjp.2017.01.009
Germany). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)waspurchasedfromSigma–Aldrich(St.Louis,MO, USA),whilecisplatinand penicillin/streptomycinwereprovided fromEBEWEPharma(Unterach,Austria).
Instrumentation
ThepurifiedcompoundsweresubjectedtoNMRspectroscopy measurements on a Bruker Avance 400 spectrometer (BioSpin GmbH,Rheinstetten,Germany)atresonancefrequenciesof400.13 for1Hand100.6MHzfor13C.1Hand13CNMRweremeasuredin CDCl3withTMSasaninternalstandard.Massspectra(EI-MS)were recordedonanAgilent5975CinertGC/MSDinstrument.
Theoptimizationofseparationconditionsandtheevaluation ofpuritypercentageoftheisolatedcompoundswereassessedby analyticalHPLCusingdifferentgradientsofACNandH2OonaRP C18HPLCcolumn(Eurospher-100,250×4.6mm,Knauer,Berlin, Germany)usingaKnauersystem(Knauer),thatconsistedofa K-1800pumpandaK-2500UV–Visdetector.
SeparationsonpreparativeHPLC(prep.HPLC)weredeveloped ona Knauer system,that consistedofa K-1800pump,withan RPC18(EurospherII100-5C18,250×20mmIDwithpre-column 30×20mmID)column,elutedisocraticallywithACN/H2O(85:15) at20ml/min.TheK-2500UV–visdetectorwassetat210nm
OpticalrotationsweremeasuredonaKrüssP8000polarimeter.
Plantmaterial
TherootsofSalvialachnocalyxHedge,Lamiaceae,werecollected fromEghlidintheFarsProvince,Iran,inMay2015andidentifiedby MojtabaAsadollahi,planttaxonomistattheMedicinalandNatural ProductsChemistryResearchCenter(MNCRC).Avoucherspecimen (No.94-3-8-4)wasdepositedattheMNCRC,ShirazUniversityof MedicalSciences,Fars,Iran.
Extraction,fractionationandpurification
The air-dried, ground roots of S. lachnocalyx (400g) were extractedwithDCM(3×2l)atroomtemperaturefor twodays. The extracts were filtered and the solvent was evaporated underreduced pressureat 40◦C.The concentratedextract (6g;
yield=1.5%,w/w)wassubjectedtoopencolumnchromatography (100×5cm)oversilicagel(110g,70–230mesh).Theelutionofthe columnwasperformedusingann-hexanewithgradientofDCMup to100%,andthenfollowedbyincreasingthepolarityofthemobile phasetopureMeOH.Thischromatographicseparation afforded 49fractions.AftercheckingthepurityoffractionsbyTLC,similar fractions were pooled to afford overall 22 fractions (F1–F22). FractionF15,elutedwithhexane-DCM(80:20),wasevaporatedto dryness(420mg),reconstitutedinMeOH,centrifugedat5000×g for10minandfilteredthrougha0.45msyringefilterbeforeHPLC analyses.Theresidue(70mg)andtheupperlayer(350mg)were storedseparately.Apartofthemethanolsolublefraction(20l, 200g/ml) was repeatedly analyzed by analytical HPLC with varioussolventsystemstooptimizetheseparationconditions.The optimalconditionswereusedfortheprep.HPLCandthefractions werecollectedmanuallyaccordingtothechromatographic pro-files.Then,20lofeachofthefractionsobtainedbyprep.HPLC wereinjectedontotheanalyticalHPLCcolumntoevaluatetheir purity.ThepuritywasmeasuredbyHPLCpeak-areanormalized method.AccordingtotheanalyticalHPLCresults,thefractionswith identicalretentiontimeswerecombined andevaporated under reducedpressuretoaffordthepurenaturalproducts.Purification byprep.HPLCaffordedcompound1(13mg,HPLCpurity≥98%),
2 (43mg, HPLC purity≥97%), 3 (144mg, HPLC purity≥95%), 4
(17mg,HPLCpurity≥97%),and5(9mg,HPLCpurity≥97%).The
purephytochemicalswerestoredat−20◦Cuntilperformingthe
spectroscopicexperimentsandcytotoxicityassays.
Celllinesandculture
HT-29(humancolorectaladenocarcinoma,Cellbanknumber: IBRC C10097) cell line was purchased from Iranian Biological ResourcesCenter,Tehran,Iran,whileMCF7(humanbreast ade-nocarcinoma, Cell bank number: C135) and MOLT-4 (human lymphoblastic leukemia, Cell bank number: C149) cells were obtainedfromNationalCellBankofIran,PasteurInstitute,Tehran, Iran.Thecells wereculturedin sterileT25flasks inRPMI1640 mediumsupplementedwith10%v/vfetalbovineserum,penicillin (100units/ml)andstreptomycin(100g/ml).HT-29andMCF7cell linesweregrowninmonolayercultures,whileMOLT-4cellswere growninsuspensionculturesinhumidifiedaircontaining5%CO2 at37◦C.
Cytotoxicityassay
Theinhibitoryeffectofpurifiedcompoundsoncancercell pro-liferationwasassessed bytheMTT reduction assay(Mosmann, 1983).Thiscolorimetricassayisbasedontheconversionofthe yellowtetrazoliumbromide(MTT)tothepurpleformazanbythe action ofmitochondrial dehydrogenaseenzymesin viable cells. ThepurifiedcompoundsweredissolvedinDMSO,andthendiluted ingrowthmediumatleast400times.Cellswereseededin 96-wellplatesatthedensityof50,000cells/mlin100lofgrowth medium.After24hofincubationat37◦C,50lofthemediumwas
exchangedwith50loftestcompoundsdilutedinfreshgrowth medium(3–4differentconcentrations).After72hoffurther incu-bation,themediumofeachwellwasreplacedbyRPMIwithout phenolredcontainingMTT0.5mg/mlandincubatedat37◦Cfor
correctionat655nmusingamicroplatereaderandpercentages ofantiproliferativeactivitywascalculatedcomparedtountreated controlwells.IC50valuedefinedastheconcentrationthatcaused 50%ofmaximuminhibitionofcellviabilitywascalculatedby plot-tingpercentageofinhibitionagainstcompoundconcentrationwith CurveExpertsoftware,version1.3forWindows.
Spectroscopicdataoftheconstituents
Ferruginol(1):Yellow crystals;C20H30O;[˛]D27 −25◦ (c0.04,
CHCl3);1HNMR(CDCl3,400.13MHz):ı=6.83(1H,s,H-14),6.63 (1H,s,H-11),4.48(1H,brs, OH),3.12(1H,heptet,J=6.9Hz, H-15),2.84(1H,dt,J=14.4,7.5Hz,H-7a),2.77(1H,m,H-7b),2.17(1H, brd,J=12.7Hz,H-1␣),1.85(1H,dd,J=12.1,7.5Hz,H-6a),1.73(1H, m,H-2a),1.65(1H,dd,J=12.2,6.7Hz,H-6b),1.58(1H,m,H-2b), 1.47(1H,brd,J=13.5Hz,H-3a),1.40(1H,dd,J=12.7,3.1Hz,H-1b), 1.33(1H,dd,J=12.5,2.3Hz,H-5),1.30(1H,m,H-3b),1.25(3H,d,
J=6.9Hz,H-16),1.23(3H,d,J=6.9Hz,H-17),1.17(3H,s,H-20), 0.94(3H,s,H-18),0.92(3H,s,H-19);13CNMR(CDCl
3,100.6MHz): ı=150.7(C-12),148.7(C-9),131.6(C-13),127.3(C-8),126.1(C-14), 110.9(C-11),50.3(C-5),41.7(C-3),38.9(C-1),37.5(C-10),33.4 (C-18),33.2(C-4),29.7(C-7),26.8(C-15),24.8(C-20),22.7(C-16),22.5 (C-17),21.6(C-19),19.3(C-2),19.2(C-6);El-MS:m/z(rel.int.):286 [M]+(100).
Taxodione(2):Darkyellowcrystals;C20H26O3;[˛]D27+37◦ (c 0.2,CHCl3);1HNMR(CDCl3,400.13MHz):ı=7.56(1H,s, OH), 6.88(1H,s,H-14),6.20(1H,s,H-7),3.07(1H,heptet,J=6.9Hz, H-15),2.93(1H,m,H-1),2.59(1H,s,H-5),1.75(1H,m,H-1␣),1.69 (1H,m,H-2),1.60(1H,m,H-2␣),1.39(1H,m,H-3),1.26(6H,s, H-19,H-20),1.20(1H,m,H-3␣),1.15(3H,d,J=6.9Hz,H-16),1.16(3H, d,J=6.9Hz,H-17),1.11(3H,s,H-18);13CNMR(CDCl
3,100.6MHz): ı=201.0(C-6),181.7(C-12),145.3(C-13),145.0(C-11),139.9 (C-8),136.1(C-14),133.9(C-7),125.6(C-9),63.0(C-5),42.9(C-10), 42.6(C-3),37.0(C-1),33.2(C-18),32.9(C-4),27.1(C-15),22.0 (C-19),21.8(C-20),21.6(C-17),21.2(C-16),18.5(C-2);El-MS:m/z(rel int.):314[M]+(100).
Sahandinone (3): Red crystals; C20H24O2; 1H NMR (CDCl3, 400.13MHz):ı=7.35(1H, d, J=7.8Hz, H-6),7.07 (1H, s, H-12), 7.03(1H,d,J=7.8Hz,H-7),5.29(1H,t,J=7.1Hz,H-3),3.08(2H, m,H-1),3.01(1H,heptet,J=6.9Hz,H-15),2.39(3H,s,H-20),2.19 (2H,ddd,J=6.8,8.7,7.8Hz,H-2),1.70(3H,s,H-18),1.60(3H,s, H-19),1.17(3H,d,J=6.9Hz,H-16),1.19(3H,d,J=6.9Hz,H-17); 13CNMR(CDCl
3,100.6MHz):ı=182.5(C-11),181.5(C-14),148.1 (C-10),144.5(C-13),140.3(C-12),140.2(C-5),136.6(C-6),134.9 (C-9),132.8(C-4),128.5(C-8),128.0(C-7),123.8(C-3),30.2(C-1), 27.5(C-2),26.9(C-15),25.7(C-18),21.34(C-16),21.34(C-17),19.7 (C-20),17.4(C-19);El-MS:m/z(relint.):296[M]+(43),227(100). 4-Dehydrosalvilimbinol (4): Deep yellow crystals; C20H26O4; [˛]D27−47◦(c0.1,CHCl
3);1HNMR(CDCl3,400.13MHz):ı=7.10 (1H,d,J=7.6Hz,H-7),6.99(1H,d,J=7.6Hz,H-6),6.89(1H,s, H-14),4.91(2H,brs,H-19),2.97(1H,heptet,J=6.5Hz,H-15),2.94 (1H,m,H-2a),2.65(1H,m,H-2b),2.44(1H,dd,J=11,4.3Hz,H-10), 2.30(1H,m,H-1a),2.25(3H,s,H-20),2.03(3H,s,H-18),1.81(1H, ddd,J=15.2,10.7,5.4Hz,H-1b),1.14(3H,d,J=6.5Hz,H-16),1.12 (3H,d,J=6.5Hz,H-17);13CNMR(CDCl
3,100.6MHz):ı=201.7 (C-3),149.1(C-4),141.7(C-12),137.3(C-11),137.3(C-5),136.3(C-8), 130.1(C-7),135.3(C-14),128.2(C-13),126.4(C-6),111.7(C-19), 74.5(C-9),46.0(C-10),26.9(C-15),26.0(C-2),25.0(C-1),24.5 (C-18),21.5(C-17),21.4(C-16),19.8(C-20);El-MS:m/z(relint.):330 [M]+(6),225(100).
Labda-7,14-dien-13-ol(5):Viscouscolorlessoil;C20H34O;[˛]D27 +25◦(c0.1,CHCl
3);1HNMR(CDCl3,400.13MHz):ı=5.93(1H,dd, J=17.4,10.8Hz,H-14),5.37(1H,brs,H-7),5.21(1H,dd,J=17.4,
1.2Hz,H-15trans),5.06(1H,dd,J=10.8,1.2Hz,H-15cis),1.96(1H,m,
H-6a),1.87(1H,m,H-6b),1.84(1H,m,H-1a),1.80(1H,d,m,H-12a), 1.67(3H,s,H-17),1.57(1H,m,H-9),1.53(1H,m,H-2a),1.47(1H,
m,H-11a),1.45(1H,dd,J=5.6,2.4Hz,H-2b),1.42(1H,m,H-12b), 1.38(1H,m,H-3a),1.28(3H,s,H-16),1.21(1H,m,H-11b),1.16(1H, m,H-5),1.15(1H,m,H-3b),0.93(1H,m,H-1b),0.87(3H,s,H-18), 0.85(3H,s,H-19),0.75(3H,s,H-20);13CNMR(CDCl
3,100.6MHz): ı=145.1(C-14),135.3(C-8),122.2(C-7),111.7(C-15),73.6(C-13), 55.2(C-9),50.2(C-5),44.9(C-12),39.2(C-1),42.3(C-3),37.0(C-10), 33.16(C-18),32.9(C-4),27.5(C-16),23.8(C-6),22.2(C-17),21.8 (C-19),21.2(C-11),18.8(C-2),13.6(C-20);El-MS:m/z(relint.):290 [M]+(1),204(100).
Resultsanddiscussion
Ferruginol (1), taxodione (2), sahandinone (3), 4-dehydrosalvilimbinol (4) and labda-7,14-dien-13-ol (5) were purified using silica gel-open column chromatography and RP 18preparativeHPLCanalysesoftheDCMextractfromtheroots ofS.lachnocalyx.Thestructuresofthepurifiedcompoundswere elucidatedusingtheirEI-MS,1D(1Hand13C)and2D(COSY,HSQC andHMBC)NMRspectroscopicdataandbycomparingthemwith those reported in the literature for the authentic compounds (Carman et al., 1973; Topcu et al., 1996; Tezuka et al., 1998; Rodríguez,2003;Jassbietal.,2006).
The1Hand13CNMRspectroscopicdataofcompounds1and2 thatwereisolatedfromSalviachorassanicaandS.deserta(Tezuka etal.,1998;Tayarani-Najaranetal.,2013)fullymatchedwiththose reportedinthisstudy.TheEIMS,1Hand13CNMRspectroscopic datarecordedforcompound3witharearrangedabietane diter-penoidstructure,thatwerereportedfromtherootsextractsofS. sahendicaandS.rhytideawereinagreementwiththerespective spectroscopicdataforsahandinonereportedfromS.lachnocalyx
(Jassbietal.,2006;Jassbietal.,2016).Compound4,withthesame rearrangedcarbonskeletonofcompound3,wasisolatedfromthe rootsofS.limbataandshowedthesamespectroscopicdataasthose reportedhereforcompound4.ThestereochemistryatC-9and C-10,becauseoflackof1HNMRsignalforC-9(OH)couldnotbe determined,ineitherofthereports(Topcuetal.,1996).Although theconfigurationattheabovementionedstereocentershavenot beendeterminedwithNOESYorchiropticalmethods,molecular mechanicscalculationsofthemoststableconformerssuggested orientationofH-10andOH-9(Topcuetal.,1996).
The1Hand13CNMR spectroscopicdataofcompound5 sug-gested a labdane-type diterpenoid which was similar to those reportedintheliteratureforlabda-7,14-dien-13-olandthe con-figurationatC-13wasdeterminedtobeSbymeasuringtheoptical rotation(+25◦)whichwassimilartothatobservedintheliterature
(+20◦),whiletheoppositeepimershowedsmallermagnitude;[␣]
D
−1.8◦(Carmanetal.,1973;Jassbietal.,2016).
Assessmentofcytotoxicactivityofcompoundsisolatedfrom therootsofS.lachnocalyx(1–5)inourstudyshowedthat allof thesederivativespossessedreasonablecytotoxiceffectsagainstthe tested celllines(Fig.1).Amongtheisolatedcompounds, 2and
3showedthehighestactivitieswithIC50valuesintherangeof 0.41–3.87g/mlincomparisontocisplatinasthepositivecontrol andMOLT-4,HT-29andMCF7celllineswerethemostsesnstive linestothetestedphytochemicals,respectively(Table1).
Compound1hasbeenreportedintheresin oftheMiro tree (Podocarpusferrugineus)(BrandtandNeubauer,1939)aswellas severalotherspecies andhasexhibited variousbiological activ-ities, including antimicrobial, antiprotozoal, anti-inflammatory, antioxidant,cardioprotective,antihypertensiveandalsoreported asacytotoxicagent(Ulubelenetal.,2000;Ulubelenetal.,2002; Samoylenkoetal.,2008;Chenetal.,2011;Yaoetal.,2012;Ebrahimi etal.,2013;RungsimakanandRowan,2014).Bioassay-guided iso-lationofthechemicalconstituentsoftherootsofS.chorassanica
20
16
12
8
4
0
1 2 3 4 5 Cisplatin
Compounds
IC
50
(
µ
g/ml)
MOLT-4 HT-29 MCF-7
Fig.1. DiterpenoidsisolatedformtherootsofS.lachnocalyx.
Table1
Anti-proliferativeeffectsofditerpenoidsisolatedfromtherootsofSalvialachnocalyx
againsthumancancercelllines.
Compound IC50(g/ml)
MOLT-4 HT-29 MCF-7
1 11.5±0.81 9.73±1.23 11.82±0.58
2 0.54±0.05 2.76±0.37 3.87±0.62
3 0.41±0.04 1.78±0.33 3.20±0.60
4 6.85±0.80 13.43±1.31 17.02±1.48
5 12.3±0.49 9.58±2.01 17.23±1.89 Cisplatin 0.75±0.08 3.41±0.23 1.7±0.35
Valuesarepresentedasmean±S.E.M.of3–5experiments.Cisplatinwastestedas areferencecytotoxicagent.
twoleukemiacancercelllines,HL-60andK562cancercellswith IC50valuesof19.51,7.73M,respectively(Tayarani-Najaranetal., 2013).Compound1thatwasisolatedfromS.sahendicashowed activityagainstMIAPaCa-2(humanpancreaticcancercellline)with IC50=25.9M(Fronzaetal.,2011).
Compound2 hasbeenreportedfromtheleavesofTaxodium distichum(Kupchan etal., 1969)and therootsofseveral mem-bersofSalviaspecies(Tezukaetal.,1998;Tayarani-Najaranetal., 2013)andhasshowncytotoxicpotentialagainstvarioushuman cancercelllines(Topcuetal.,2003;Ku ´zmaetal.,2012;Burmistrova etal.,2013;Tayarani-Najaranetal.,2013).Forinstance,itinhibited thegrowth of BC1 (human breast cancer, IC50 1.2g/ml), LU1 (humanlungcancer,IC505.1g/ml),COL2(humancoloncancer, IC50 0.7g/ml),LNCaP(human prostatecancer, IC50 0.7g/ml), P388(mouselymphoblasticleukemia,IC500.3g/ml),andA2780 (humanovariancancer,IC509g/ml)celllines(Topcuetal.,2003). In anotherstudy,compound 2 showed highanticanceractivity againstMOLT-3(leukemia),MCF-7(breastadenocarcinoma), SK-MEL-1(melanoma), U937 (leukemia), HL-60 (leukemia)human cancercelllines,withIC50valuesof1.8,>30,9.6,3,4.8M, respec-tively(Burmistrovaetal.,2013).
Compound3waspreviouslyisolatedasoneofthemajor con-stituentsfromtherootsofS.sahendicaandS.rhytidea(Jassbietal., 2006;Jassbietal.,2016).Fronzaandco-workershavealsoreported cytotoxiceffectsofcompound3againsthumanpancreaticcancer cellline(MIAPaCa-2)withanIC50valueof10.2M(Fronzaetal., 2011).
Compound 4 was isolated from the roots of Salvia limbata
(Topcuetal.,1996).Tothebestofourknowledge,nobiological activity is reported for this compound in the literature. Com-pound5 was isolated from Asterspathulifolius, Asteraceae, and reported as a cytotoxic agent against four human cancer cell lines,SK-OV-3 (ovarian adenocarcinoma),SK-MEL-2 (malignant melanoma),XF498 (centralnervous systemtumor), and HCT15
(colonadenocarcinoma)cellswithEC50valuesof2.4,8.7,4.4,9.5 and9.1g/ml,respectively(Leeetal.,2005).
Comparisonofourresultswiththepreviouslyreportedfindings revealsthatthisisthefirststudyofcytotoxiceffectsofcompounds
3–5againstMOLT-4,HT-29andMCF7humancancercelllines. Fur-thermore,thecytotoxicactivityofcompound1againstHT-29and compound2againstMOLT-4andHT-29cellsalsorepresentnew findings.
Assessmentof structure-activityrelationshipsoftheisolated compoundsrevealedthatcompounds2and 3,whichcontained endocyclic ␣,-unsaturated carbonyl functional group showed higheractivities(IC50valuesof0.41–3.87g/ml)comparedtothe othercompoundswiththesameabietane(1),rearranged-abietane (4)andlabdane(5)skeletons,butno␣,-unsaturatedcarbonyls intheirrings(IC50valuesof6.85–17.23g/ml).Evencompound4 withanexocyclicunsaturatedketonewasnotasactiveas3with thesamecarbonskeleton.
Ourcurrentstudyandpreviousfindingsonseveralcompounds with␣,-unsaturatedcarbonylmoiety,suggestedthatthepresence ofan␣,-unsaturatedcarbonylgroupplaysaroleasakey phar-macophoreforexhibitingcytotoxicactivity(Nakayachietal.,2004; Wuetal.,2012;Daietal.,2015).Inthisregard,structure-activity studieshaveshownthat␣,-unsaturatedcarbonylfunctionofthe compoundsfacilitatesthealkylationofcellularthiolgroupsina Michaeltypeadditionreactionthatcausescelldamageand cyto-toxicity(Amslinger,2010;Nordetal.,2014).
Conclusion
Insummary,fiveknownditerpenoidswereisolatedfromthe DCM extract of theroots of S. lachnocalyx and theirstructures were elucidated by the spectroscopic data. The isolated diter-penoidsshowedinvitrocytotoxicactivityagainstMOLT-4,HT-29 andMCF7humancancercelllines.Amongthem, compounds2
and3withendocyclic␣,-unsaturatedcarbonylfunctionalgroup demonstrateda remarkablecytotoxiceffectincomparison with cisplatinasastandardchemotherapeuticagent.Theobtained evi-denceshowedtherootsofS.lachnocalyxmeritfurtherinvestigation asapotentialsourceofbiologicallyactivecompounds.
Ethicaldisclosures
Protectionofhumanandanimalsubjects. Theauthorsdeclare thatnoexperimentswereperformedonhumansoranimalsfor thisstudy.
Confidentialityofdata. Theauthorsdeclarethatnopatientdata appearinthisarticle.
Righttoprivacyandinformedconsent. Theauthorsdeclarethat nopatientdataappearinthisarticle.
Authors’contribution
ARJ:Supervisedthestudiesinanalyzingnaturalproductsand determiningthestructuresofnaturalproducts,helpedinwriting thepaper,HHM:PhDStudent;apartofhisdissertation,OF: Super-visedthestudiesinassessmentofbiologicalactivity,contributed tothepreparationandwritingthemanuscript;BS:PerformedNMR spectroscopyandscientificadvising;ITB:Scientificsupportingthe projectandhelpingineditingthemanuscript.
Conflictsofinterest
Acknowledgments
TheauthorswishtoacknowledgethefinancialsupportsofVice ChancellorforResearch,ShirazUniversityofMedicalsciences,Iran, and Alexandervon Humboldt Foundation (grantnumber:3.4 – IRN/1101775).WethankMr.MehdiZareforcollectingS. lachno-calyx.ThisstudywaspartofthePhDthesisofHosseinHadavand Mirzaei.
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