Quantitative aspects of transplacental tumor induction with ethylnitrosourea in rats.

Abstract

JamesA.Swenberg,AdalbertKoestner,WolfgangWechsler,2andRobertH.DenlmgerDepartmentofVeterinarvPathobiology.TheOhioStateUniversity,Columbus,Ohio43210SUMMARYDose-response relationships oftransplacental tumorinductionwiththeresorptivecarcinogen,ethylnitrosourea,wereinvestigated inSprague-DawleyandFischerrats.Neuroectodermaltumorswereproducedinoffspringofallratsexposedtoasingledoseofethylnitrosourea, 1,5,20,or50-mg/kg,neartheendofgestation.Theincidenceofexperimentallyinducedneoplasmswasdirectlyproportionaltothedoseofcarcinogen,whilemeansurvivaltimeswereinverselyrelatedtoexposure.Thelocationoftumorsvariedwiththedoseofcarcinogenandstrainofrat.Braintumorswerethecauseofdeathfor69%oftheFischerratsexposedtoethylnitrosourea, 50mg/kg,whereasonly27%ofsimilarlyexposedSprague-Dawleyratsdiedofbraintumors.Asignificantlylongersurvivaltimewasdemonstratedforratsthatdiedofgliomascomparedwiththosethatdiedofneurinomasorependymomas.Thisinvestigationdemonstratesthattheageatwhichananimaldevelopsneoplasiafollowingtransplacentalexposuretoacarcinogendependsonthelevelofexposureandthetumortype.Thissuggeststhattumorsofadults,aswellasofchildren,maybeduetotransplacentalexposuretocarcinogenicagents.INTRODUCTIONMuchoftherecentlyexpandedinterestinenvironmentalpathologystemsfromthedemonstrationthatmanychemicalsarecapableofinducingtumorsatsitesdistanttotheirapplication,i.e.,resorptivecarcinogens.AmongthemostinterestingexamplesaretheresorptiveTV-nitrosocompounds.TheinitialrecognitionofthecarcinogenicpropertiesofthisgroupofcompoundsiscreditedtoMageeandBarnes(22),whodemonstratedthathepaticcarcinomascouldbeinducedinratsfollowingthefeedingofdimethylnitrosamine. Morerecently,Druckreyetal.(10)publishedacompendiumof65W-nitrosocarcinogens,mostofwhichareorganspecific.Oneofthemostintriguingofthesecompounds istheacylalkylnitrosamide,ENU.3ENUhasbeenshowntoproducetumorsofmanyorganswhenadministeredasasingledosetoadultrats.Itsabilitytoinduceneuroectodermaltumorsin100%oftheoffspringfollowingasingletransplacental1SupportedinpartbyNIHGrantsCA11224andGM1052.zVisitingprofessorfromtheMax-Planck-InstitutefA¼rHirnforschung,5KA¶ln-Merheim.Ostmerheimerstrasse200,Germany.3Theabbreviationusedis:ENU.jV-ethyWV-nitrosourea.ReceivedJuly10,1972;acceptedAugust29,1972.exposure has stimulated its useinexperimentalneurooncology.TheexquisitesensitivityoftheratfetalnervoussystemtoENUwasfirstdemonstratedinpapersbyDruckreyetal.(8),IvankovicandDruckrey(16),andIvankovicetal.(17)andhassubsequentlybeenconfirmedbyothers(12,14,19,20,34).Thesestudieshavedemonstratedthataslittleas2%oftheadult50%lethaldoseresultedina63%incidenceofneuroectodermal tumors.Inadditiontoitscarcinogenicproperties,ENUhasbeenshowntobeapotentteratogen(11,16,33).Thismayallowfuturestudiesintotheperplexingproblemofneoplasticpredispositionofhamartomasandteratologicalsyndromes.ThepurposeofthiscommunicationistoevaluatetheeffectsofvariousdosesofENUontheincidence,location,andtypeofneuroectodermaltumorsinducedtransplacentallyinrats.Exposurestothecarcinogenrangedfromlessthan0.5%oftheadult50%lethaldosetotwicethatnecessarytoinduceneoplasmsin100%oftheoffspring.InmostpreviousinvestigationsENUwasadministeredtopregnantratsonthe15thdayofgestation.Sinceithadbeendemonstratedthatthesusceptibilityofthefetustothiscarcinogenwasgreatestattheendofgestation(16),wechosetostudythedose-responserelationshipstoENUfollowingtransplacentalexposureofthefetusonthe20thdayofgestation.Sprague-DawleyandFischerratswereusedtoevaluatepotentialstraindifferencesintheexpressionofneoplastictransformationinducedbyENU.MATERIALSANDMETHODSTwotofourpregnantSprague-Dawley(CD)rats(CharlesRiver,Wilmington,Mass.)wereinoculatedwithENU,1,5,20,or50mg/kg,viathelateraltailveinonthe20thdayofgestation.ThreeadditionalFischer(CDF)ratswereinoculatedwithENU,50mg/kg,onthe20thdayofgestation.TheENU(fromProfessorH.Druckrey,Freiburg,Germany)wasfreshlypreparedbydissolving10mg/mlinsterile0.9%NaClsolutionandadjustingthepHto4.5withcrystallineascorbicacid.Approximatelyequalnumbersofmaleandfemaleoffspringwerewhelpedbytheinoculatedmothers.Theoffspringwereweanedat28daysofageandhousedinindividualcagesinisolatedrooms.AllanimalswerefedautoclavedPurinaLabChow5010Candwateradlibitum.Ratswereexamineddailyandweighedweeklythroughouttheexperimentalperiod.Progressiveneurologicalsignsandweightlosswereusedtoselectanimalsforcloserobservation.Allexperimentalratsweresubjectedtoacompletenecropsy2656 CANCERRESEARCHVOL.32