EMEA基因毒性雜質(zhì)限度指南4

第頁20190628EMEA/CHMP/QWP/251344/2019基因毒性雜質(zhì)限度指南（中英文對照）London,28June2019CPMP/SWP/5199/02EMEA/CHMP/QWP/251344/2019TheEuropeanAgencyfortheEvaluationofMedicinalProducts歐洲共同體藥物評審委員會(EMEA)COMMITTEEFORMEDICINALPRODUCTSFORHUMANUSE人用藥品委員會(CHMP)GUIDLINEONTHELIMITSOFGENOTOXICIMPURITIES基因毒性雜質(zhì)限度指南DESCUSSIONINTHESAFETYWORKINGPARTY安全工作組之內(nèi)的討論June2019-October2019TRANSMISSIONTOCPMPCPMP傳遞December2019RELEASEFORCONSULTATION專家討論December2019DEADLINEFORCOMMENTS建議收集最后期限March2019DISCUSSIONINTHESAFETYWORKINGPARTYANDQUALITYWORKINGPARTY安全工作組和質(zhì)量工作組之間的討論June2019-February2019TRANSMISSIONTOCPMP轉(zhuǎn)移給CPMPMarch2019RE-RELEASEFORCONSULTATION再次放行給顧問團June2019DEADLINEFORCOMMENTS收集意見的最后期限D(zhuǎn)ecember2019DISCUSSIONINTHESAFETYWORKINGPARTYANDQUALITYWORKINGPARTY安全工作組和質(zhì)量工作組之間的討論February2019-May2019ADOPTIONBYCHMP被CHMP采用28June2019DATEFORCOMINGINTOEFFECT生效日期01January2019KEYWORDS關(guān)鍵詞Impurities;Genotoxicity;Thresholdoftoxicologicalconcern(TTC);Structureactivityrelationship(SAR)GUIDLINEONTHELIMITSOFGENOTOXICIMPURITIES基因毒性雜質(zhì)限度指南TABLEOFCONTENTS目錄EXECUTIVESUMMARY內(nèi)容摘要31.INTRODUCTION介紹32.SCOPE范圍33.LEGALBASIS法律依據(jù)34.TOXICOLOGICALBACKGROUND毒理學(xué)背景45.RECOMMENDATIONS建議45.1GenotoxicCompoundsWithSufficientEvidenceforaThreshold-RelatedMechanism具有充分證據(jù)證明其閾值相關(guān)機理的基因毒性化合物45.2GenotoxicCompoundsWithoutSufficientEvidenceforaThreshold-RelatedMechanism不具備充分證據(jù)支持其閾值相關(guān)機理的基因毒性化合物55.2.1PharmaceuticalAssessment藥學(xué)評價55.2.2ToxicologicalAssessment毒理學(xué)評價55.2.3ApplicationofaThresholdofToxicologicalConcern毒理學(xué)擔憂閾值應(yīng)用55.3DecisionTreeforAssessmentofAcceptabilityofGenotoxicImpurities基因毒性雜質(zhì)可接受性評價決策樹7REFERENCES.參考文獻8EXECUTIVESUMMARY內(nèi)容摘要ThetoxicologicalassessmentofgenotoxicimpuritiesandthedeterminationofacceptablelimitsforsuchimpuritiesinactivesubstancesisadifficultissueandnotaddressedinsufficientdetailintheexistingICHQ3Xguidances.Thedatasetusuallyavailableforgenotoxicimpuritiesisquitevariableandisthemainfactorthatdictatestheprocessusedfortheassessmentofacceptablelimits.Intheabsenceofdatausuallyneededfortheapplicationofoneoftheestablishedriskassessmentmethods,i.e.datafromcarcinogenicitylong-termstudiesordataprovidingevidenceforathresholdmechanismofgenotoxicity,implementationofagenerallyapplicableapproachasdefinedbytheThresholdofToxicologicalConcern(TTC)isproposed.ATTCvalueof1.5μg/dayintakeofagenotoxicimpurityisconsideredtobeassociatedwithanacceptablerisk(excesscancerriskof<1in100,000overalifetime)formostpharmaceuticals.Fromthisthresholdvalue,apermittedlevelintheactivesubstancecanbecalculatedbasedontheexpecteddailydose.Higherlimitsmaybejustifiedundercertainconditionssuchasshort-termexposureperiods.基因毒性雜質(zhì)的毒理學(xué)評估和這些雜質(zhì)在活性藥物中的可接受標準的測定是一件困難的事情，并且在現(xiàn)有的ICHQ3X指南中也沒有詳細的規(guī)定?，F(xiàn)有的關(guān)于基因毒性雜質(zhì)的相關(guān)數(shù)據(jù)是容易變化的，也是對雜質(zhì)可接受標準如何進行評價的主要影響因素。如果缺少風險評估方法所需要的數(shù)據(jù)，比如，致癌作用的長期研究數(shù)據(jù)，或為基因毒性的閥值提供證據(jù)的數(shù)據(jù)，一般建議使用一般通用的被定義為毒理學(xué)關(guān)注的閾值（TTC）的方法。一個“1.5μg/day”的TTC值，即相當于每天攝入1.5μg的基因毒性雜質(zhì)，被認為對于大多數(shù)藥品來說是可以接受的風險（一生中致癌的風險小于十萬分之1）。按照這個閥值，可以根據(jù)這個預(yù)期的每日攝入量計算出活性藥物中可接受的雜質(zhì)水平。較高的臨界值可以在特定的條件下，如短期暴露周期等，進行推算。1.INTRODUCTION介紹Ageneralconceptofqualificationofimpuritiesisdescribedintheguidelinesforactivesubstances(Q3A,ImpuritiesinNewActiveSubstances)ormedicinalproducts(Q3B,ImpuritiesinNewMedicinalProducts),wherebyqualificationisdefinedastheprocessofacquiringandevaluatingdatathatestablishesthebiologicalsafetyofanindividualimpurityoragivenimpurityprothelevel(s)specified.Inthecaseofimpuritieswithagenotoxicpotential,determinationofacceptabledoselevelsisgenerallyconsideredasaparticularlycriticalissue,whichisnotspecificallycoveredbytheexistingguidelines.在原料藥（Q3A）和藥物制劑（Q3B）的雜質(zhì)指導(dǎo)原則中，雜質(zhì)限度確定的依據(jù)包括各個雜質(zhì)的生物安全性數(shù)據(jù)或雜質(zhì)在某特定含量水平的研究概況。而對于遺傳毒性雜質(zhì)限度的確定，通常都認為是特別關(guān)鍵的問題，但目前尚無相關(guān)的指導(dǎo)原則。2.SCOPE范圍ThisGuidelinedescribesageneralframeworkandpracticalapproachesonhowtodealwithgenotoxicimpuritiesinnewactivesubstances.Italsorelatestonewapplicationsforexistingactivesubstances,whereassessmentoftherouteofsynthesis,processcontrolandimpuritypronotprovidereasonableassurancethatnoneworhigherlevelsofgenotoxicimpuritiesareintroducedascomparedtoproductscurrentlyauthorisedintheEUcontainingthesameactivesubstance.ThesamealsoappliestovariationstoexistingMarketingAuthorisationspertainingtothesynthesis.Theguidelinedoes,however,notneedtobeappliedretrospectivelytoauthorisedproductsunlessthereisaspecificcauseforconcern.本指導(dǎo)原則闡述了如何處理新原料藥中遺傳毒性雜質(zhì)的一般框架和實際方法。該指導(dǎo)原則也適用于已有原料藥的新申請，如果其合成路線、過程控制和雜質(zhì)研究尚無法確保不會產(chǎn)生新的或更高含量的遺傳毒性雜質(zhì)（及EU目前批準的相同原料藥相比）。該指導(dǎo)原則同樣適用于已上市原料藥有關(guān)合成方面的補充申請。除非有特殊原因，本指導(dǎo)原則不適用于已上市的產(chǎn)品。Inthecurrentcontexttheclassificationofacompound(impurity)asgenotoxicingeneralmeansthattherearepositivefindingsinestablishedinvitroorinvivogenotoxicitytestswiththemainfocusonDNAreactivesubstancesthathaveapotentialfordirectDNAdamage.Isolatedinvitrofindingsmaybeassessedforinvivorelevanceinadequatefollow-uptesting.Intheabsenceofsuchinformationinvitrogenotoxicantsareusuallyconsideredaspresumptiveinvivomutagensandcarcinogens.目前對于基因毒性雜質(zhì)的分類主要是指：在以DNA反應(yīng)物質(zhì)為主要研究對象的體內(nèi)體外試驗中，如果發(fā)現(xiàn)它們對DNA有潛在的破壞性，那可稱之為基因毒性。如果有足夠的后續(xù)試驗，可由單獨的體外試驗結(jié)果，對它的體內(nèi)關(guān)聯(lián)性進行評估。在缺乏這樣的信息時，體外基因毒性物質(zhì)經(jīng)常被考慮為假定的體內(nèi)誘變劑和致癌劑。3.LEGALBASIS法規(guī)依據(jù)ThisguidelinehastobereadinconjunctionwithDirective2019/83/EC(asamended)andallrelevantCHMPGuidancedocumentswithspecialemphasison:在閱讀該指南時有必要參考“Directive2019/83/EC”以及相關(guān)的CHMP指南文件，特別是以下幾個指南：ImpuritiesTestingGuideline:ImpuritiesinNewDrugSubstances(CPMP/ICH/2737/99,ICHQ3A(R))NoteforGuidanceonImpuritiesinNewDrugProducts(CPMP/ICH/2738/99,ICHQ3B(R))NoteforGuidanceonImpurities:ResidualSolvents(CPMP/ICH/283/95)NoteforGuidanceonGenotoxicity:GuidanceonSpecificAspectsofRegulatoryGenotoxicityTestsforPharmaceuticals(CPMP/ICH/141/95,ICHS2A)NoteforGuidanceonGenotoxicity:AStandardBatteryforGenotoxicityTestingofPharmaceuticals(CPMP/ICH/174/95,ICHS2B)4.TOXICOLOGICALBACKGROUND毒理學(xué)背景Accordingtocurrentregulatorypracticeitisassumedthat(invivo)genotoxiccompoundshavethepotentialtodamageDNAatanylevelofexposureandthatsuchdamagemaylead/contributetotumourdevelopment.Thusforgenotoxiccarcinogensitisprudenttoassumethatthereisnodiscerniblethresholdandthatanylevelofexposurecarriesarisk.根據(jù)目前的研究實踐，具有（體內(nèi)）遺傳毒性的化合物在任何暴露量下都有可能對DNA產(chǎn)生損傷，而這種損傷可能會引發(fā)腫瘤。因此，對于遺傳毒性致癌物質(zhì)，應(yīng)謹慎認為不存在明確的閾值，任何暴露量下都存在風險。However,theexistenceofmechanismsleadingtobiologicallymeaningfulthresholdeffectsisincreasinglyacknowledgedalsoforgenotoxicevents.Thisholdstrueinparticularforcompoundsinteractingwithnon-DNAtargetsandalsoforpotentialmutagens,whicharerapidlydetoxifiedbeforecomingintocontactwithcriticaltargets.Theregulatoryapproachtosuchchemicalscanbebasedontheidentificationofacriticalno-observed-effectlevel(NOEL)anduseofuncertaintyfactors.然而，對于一些遺傳毒性事件，其產(chǎn)生生物學(xué)意義的閾值效應(yīng)的機理正越來越為人所了解。對于非DNA靶點的化合物和潛在致突變劑更是如此，因為它們在及關(guān)鍵靶點接觸前就已經(jīng)去毒化了。對于這些化合物，研究的基礎(chǔ)可以是確定關(guān)鍵的未觀察到影響的劑量（NOEL）和采用不確定因子。EvenforcompoundswhichareabletoreactwiththeDNAmolecule,extrapolationinalinearmannerfromeffectsinhigh-dosestudiestoverylowlevel(human)exposuremaynotbejustifiedduetoseveralprotectivemechanismsoperatingeffectivelyatlowdoses.However,atpresentitisextremelydifficulttoexperimentallyprovetheexistenceofthresholdforthegenotoxicityofagivenmutagen.Thus,intheabsenceofappropriateevidencesupportingtheexistenceofathresholdforagenotoxiccompoundmakingitdifficulttodefineasafedoseitisnecessarytoadoptaconceptofalevelofexposurethatcarriesanacceptablerisk.即使對能及DNA分子發(fā)生反應(yīng)的化合物，由于低劑量時有多種有效的保護機制存在，而不能將高劑量下的影響以線性方式外推到很低的（人）暴露水平。不過，目前要用實驗方法證明某誘變劑的遺傳毒性閾值仍然非常困難。所以，在缺乏恰當?shù)淖C據(jù)支持遺傳毒性閾值存在的情況下，確定安全劑量很困難，因此非常有必要采用一個可接受風險的暴露水平概念。5.RECOMMENDATIONS建議AsstatedintheQ3Aguideline,actualandpotentialimpuritiesmostlikelytoariseduringsynthesis,purificationandstorageofthenewdrugsubstanceshouldbeidentified,basedonasoundscientificappraisalofthechemicalreactionsinvolvedinthesynthesis,impuritiesassociatedwithrawmaterialsthatcouldcontributetotheimpurityprothenewdrugsubstance,andpossibledegradationproducts.Thisdiscussioncanbelimitedtothoseimpuritiesthatmightreasonablybeexpectedbasedonknowledgeofthechemicalreactionsandconditionsinvolved.Guidedbyexistinggenotoxicitydataorthepresenceofstructuralalerts,potentialgenotoxicimpuritiesshouldbeidentified.Whenapotentialimpuritycontainsstructuralalerts,additionalgenotoxicitytestingoftheimpurity,typicallyinabacterialreversemutationassay,shouldbeconsidered(Doboetal.2019,Mülleretal.2019).WhileaccordingtotheQ3Aguidelinesuchstudiescanusuallybeconductedonthedrugsubstancecontainingtheimpuritytobecontrolled,studiesusingisolatedimpuritiesaremuchmoreappropriateforthispurposeandhighlyrecommended.正如Q3A指導(dǎo)原則所述，根據(jù)合理的化學(xué)反應(yīng)機理分析，在新的原料藥合成、純化和貯存過程中很有可能產(chǎn)生實際的和潛在的雜質(zhì)。依據(jù)現(xiàn)有的“可能引起遺傳毒性的結(jié)構(gòu)”數(shù)據(jù)庫，潛在的遺傳毒性雜質(zhì)應(yīng)能被確認。如果潛在的雜質(zhì)含有可引起遺傳毒性的結(jié)構(gòu)單元，該雜質(zhì)應(yīng)考慮進行遺傳毒性試驗（一般是細菌回復(fù)突變試驗）（Dobo等，2019）。雖然Q3A指導(dǎo)原則認為這些研究采用含有那些需控制雜質(zhì)的原料藥進行是可行的，但用分離出來的雜質(zhì)進行這些研究更恰當，也是高度推薦的方法。Fordeterminationofacceptablelevelsofexposuretogenotoxiccarcinogensconsiderationsofpossiblemechanismsofactionandofthedose-responserelationshipareimportantcomponents.Basedontheaboveconsiderationsgenotoxicimpuritiesmaybedistinguishedintothefollowingtwoclasses:根據(jù)以上論述，遺傳毒性雜質(zhì)可以歸納成以下兩類：-Genotoxiccompoundswithsufficient(experimental)evidenceforathreshold-relatedmechanism有充分閾值相關(guān)機理證據(jù)（實驗）的遺傳毒性化合物-Genotoxiccompoundswithoutsufficient(experimental)evidenceforathreshold-relatedmechanism無充分閾值相關(guān)機理證據(jù)（實驗）的遺傳毒性化合物5.1GenotoxicCompoundsWithSufficientEvidenceforaThreshold-RelatedMechanism具有充分證據(jù)證明其閾值相關(guān)機理的基因毒性化合物Examplesofmechanismsofgenotoxicitythatmaybedemonstratedtoleadtonon-linearorthresholdeddose-responserelationshipsincludeinteractionwiththespindleapparatusofcelldivisionleadingtoaneuploidy,topoisomeraseinhibition,inhibitionofDNAsynthesis,overloadingofdefencemechanisms,metabolicoverloadandphysiologicalperturbations(e.g.inductionoferythropoeisis,hyper-orhypothermia).非線性或閾值明確的劑量效應(yīng)關(guān)系的遺傳毒性機理包括：及細胞分化過程中紡錘體相互作用；拓撲異構(gòu)酶抑制；DNA合成抑制；過度的防御機制；代謝過度和生理性干擾（如誘導(dǎo)紅血球生成，高體溫和低體溫）。For(classesof)compoundswithclearevidenceforathresholdedgenotoxicity,exposurelevelswhicharewithoutappreciableriskofgenotoxicitycanbeestablishedaccordingtotheprocedureasoutlinedforclass2solventsintheQ3CNoteforGuidanceonImpurities:ResidualSolvents.Thisapproachcalculatesa“PermittedDailyExposure”(PDE),whichisderivedfromtheNOEL,orthelowestobservedeffectlevel(LOEL)inthemostrelevant(animal)studyusing“uncertaintyfactors”(UF).有明確遺傳毒性閾值的化合物，不產(chǎn)生遺傳毒性風險的暴露水平可以被確定，方法可參照Q3C“雜質(zhì)指導(dǎo)原則”中二類溶劑的限度確定方法。該方法可計算“每日最大允許暴露量”（PDE），數(shù)據(jù)來源于“不確定因數(shù)”動物研究中的NOEL（未觀察到效果的最低水平）或觀察到效果的最低水平（LOEL）。5.2GenotoxicCompoundsWithoutSufficientEvidenceforaThreshold-RelatedMechanism不具備充分證據(jù)支持其閾值相關(guān)機理的基因毒性化合物Theassessmentofacceptabilityofgenotoxicimpuritiesforwhichnothresholdmechanismsareidentifiedshouldincludebothpharmaceuticalandtoxicologicalevaluations.Ingeneral,pharmaceuticalmeasurementsshouldbeguidedbyapolicyofcontrollinglevelsto“aslowasreasonablypracticable”(ALARPprinciple),whereavoidingisnotpossible.LevelsconsideredbeingconsistentwiththeALARPprinciplefollowingpharmaceuticalassessmentshouldbeassessedforacceptabilityfromatoxicologicalpointofview(seedecisiontree&followingsections).對于此類遺傳毒性雜質(zhì)，研究應(yīng)包括藥學(xué)和毒理學(xué)評估?？傊?，如果雜質(zhì)無法避免，藥學(xué)方面的控制應(yīng)遵循“合理可行的最低限量”原則（ALARP原則）。符合ALARP原則的雜質(zhì)水平再經(jīng)毒理學(xué)方面的進一步評估，以驗證其合理性（見決策樹和以下章節(jié)）。5.2.1PharmaceuticalAssessment藥學(xué)評價Aspecificdiscussion–aspartoftheoveralldiscussiononimpurities(seeQ3A(R))–shouldbeprovidedintheapplicationwithregardtoimpuritieswithpotentialgenotoxicity.申請材料應(yīng)提供關(guān)于潛在遺傳毒性雜質(zhì)的特別討論資料（見Q3A（R））。Arationaleoftheproposedformulation/manufacturingstrategyshouldbeprovidedbasedonavailableformulationoptionsandtechnologies.Theapplicantshouldhighlight,withinthechemicalprocessandimpurityproactivesubstance,allchemicalsubstances,usedasreagentsorpresentasintermediates,orside-products,knownasgenotoxicand/orcarcinogenic(e.g.alkylatingagents).需要根據(jù)現(xiàn)在的配方選擇和技術(shù)，提供證明所選的配方/生產(chǎn)策略合理性的證據(jù)。申請人應(yīng)在合成工藝和雜質(zhì)研究部分重點指出所有的化學(xué)物質(zhì)，包括用到的試劑、中間體、副產(chǎn)物，哪些是已知遺傳毒性和/或致癌性物質(zhì)（如烷化劑）。Moregenerally,reactingsubstancesandsubstanceswhichshow“alertingstructure”intermsofgenotoxicitywhicharenotsharedwiththeactivesubstanceshouldbeconsidered(seee.g.Doboetal.2019).Potentialalternativeswhichdonotleadtogenotoxicresiduesinthefinalproduct,shouldbeusedifavailable.值得關(guān)注的是，雖然有些含有“可能引起遺傳毒性的結(jié)構(gòu)”（alertingstructure）的反應(yīng)試劑及最終活性物質(zhì)并沒有共同結(jié)構(gòu)，但也要考慮它們的遺傳毒性(seee.g.Doboetal.2019).。如果有可能，應(yīng)該對它們進行一些替代研究，以使最終產(chǎn)品中不會引入基因毒性殘留。Ajustificationneedstobeprovidedthatnoviablealternativeexists,includingalternativeroutesofsynthesisorformulations,differentstartingmaterials.Thismightforinstanceincludecaseswherethestructure,whichisresponsibleforthegenotoxicand/orcarcinogenicpotentialisequivalenttothatneededinchemicalsynthesis(e.g.alkylationreactions).需要提供充分的論證來說明沒有可行的替代方法存在，包括可替代的合成路線或配方，不同的起始物料等。比如，應(yīng)證明具有遺傳毒性和/或致癌性的結(jié)構(gòu)在化學(xué)合成中（如烷化反應(yīng)）是必需的。Ifagenotoxicimpurityisconsideredtobeunavoidableinadrugsubstance,technicalefforts(e.g.purificationsteps)shouldbeundertakentoreducethecontentofthegenotoxicresiduesinthefinalproductincompliancewithsafetyneedsortoalevelaslowasreasonablypracticable(seesafetyassessment).Dataonchemicalstabilityofreactiveintermediates,reactants,andothercomponentsshouldbeincludedinthisassessment.如果遺傳毒性雜質(zhì)在原料中不可避免，則應(yīng)該采取適當?shù)募夹g(shù)（如純化步驟）降低該雜質(zhì)的含量，以滿足安全性要求，或符合“合理可行的最低限量”原則（見安全評估）。藥學(xué)評估還應(yīng)包括反應(yīng)中間體、反應(yīng)物和其它組件等的化學(xué)穩(wěn)定性研究。Detectionand/orquantificationoftheseresiduesshouldbedonebystate-of-the-artanalyticaltechniques.應(yīng)該使用比較先進的分析檢測技術(shù)來檢測和量化這些殘留的雜質(zhì)。5.2.2ToxicologicalAssessment毒理學(xué)評價Theimpossibilityofdefiningasafeexposurelevel(zeroriskconcept)forgenotoxiccarcinogenswithoutathresholdandtherealizationthatcompleteeliminationofgenotoxicimpuritiesfromdrugsubstancesisoftenunachievable,requiresimplementationofaconceptofanacceptablerisklevel,i.e.anestimateofdailyhumanexposureatandbelowwhichthereisanegligiblerisktohumanhealth.鑒于在沒有明確閾值的前提下定義安全暴露水平（零風險）是不可能的，且從原料藥中完全除去遺傳毒性雜質(zhì)經(jīng)常是很難做到的，所以有必要提出一個“可接受風險水平”（acceptablerisklevel）的概念，比如估算一個“每日最大暴露量”值，低于該暴露量時就可以忽略其對人體健康的風險。ProceduresforthederivationofacceptablerisklevelsareconsideredintheAppendix3oftheQ3CNoteforGuidanceonImpurities:ResidualSolventsforClass1solvents.However,theseapproachesrequireavailabilityofadequatedatafromlong-termcarcinogenicitystudies.對于可接受風險水平的推導(dǎo)過程請參見Q3C（雜質(zhì)指南注釋:一類溶液殘留）中的附件三。然而，應(yīng)用這些方法必須有足夠多的長期致癌性研究數(shù)據(jù)。Inmostcasesoftoxicologicalassessmentofgenotoxicimpuritiesonlylimiteddatafrominvitrostudieswiththeimpurity(e.g.Amestest,chromosomalaberrationtest)areavailableandthusestablishedapproachestodetermineacceptableintakelevelscannotbeapplied.Calculationof“safetymultiples”frominvitrodata(e.g.Amestest)areconsideredinappropriateforjustificationofacceptablelimits.Moreover,negativecarcinogenicityandgenotoxicitydatawiththedrugsubstancecontainingtheimpurityatlowppmlevelsdonotprovidesufficientassuranceforsettingacceptablelimitsfortheimpurityduetothelackofsensitivityofthistestingapproach.Evenpotentmutagensandcarcinogensaremostlikelytoremainundetectedwhentestedaspartofthedrugsubstance,i.e.atverylowexposurelevels.Apragmaticapproachisthereforeneededwhichrecognisesthatthepresenceofverylowlevelsofgenotoxicimpuritiesisnotassociatedwithanunacceptablerisk.大多數(shù)情況下，遺傳毒性雜質(zhì)的毒理學(xué)評估只是局限于雜質(zhì)的體外研究（如Ames試驗，染色體畸變試驗），但這些方法并不適用于確定雜質(zhì)可接受的攝入水平。也就是說，根據(jù)體外數(shù)據(jù)（如Ames試驗）計算雜質(zhì)的“安全倍數(shù)（safetymultiples）”、進而確定可接受的限度，是不合適的。此外，用含有較低（ppm級）雜質(zhì)水平的原料藥研究其致癌性和遺傳毒性，即使得出陰性結(jié)果也不足以確保該雜質(zhì)限度的合理性，因為這種試驗方法缺少必要的靈敏度。有些具有很強致突變性和致癌性物質(zhì)及原料藥一起進行試驗時，因為在非常低的暴露水平情況下，很有可能因為低于檢測限而無法檢出。所以，如果認識到含量非常低的遺傳毒性雜質(zhì)不存在“不可接受的風險”（unacceptablerisk），那么可以采取實用的方法來控制該雜質(zhì)。5.2.3ApplicationofaThresholdofToxicologicalConcern毒理學(xué)相關(guān)的閾值應(yīng)用Athresholdoftoxicologicalconcern(TTC)hasbeendevelopedtodefineacommonexposurelevelforanyunstudiedchemicalthatwillnotposeariskofsignificantcarcinogenicityorothertoxiceffects(Munroetal.2019,KroesandKozianowski2019).ThisTTCvaluewasestimatedtobe1.5μg/person/day.TheTTC,originallydevelopedasa“thresholdofregulation”attheFDAforfoodcontactmaterials(Rulis1989,FDA1995)wasestablishedbasedontheanalysisof343carcinogensfromacarcinogenicpotencydatabase(Goldetal.1984)andwasrepeatedlyconfirmedbyevaluationsexpandingthedatabasetomorethan700carcinogens(Munro1990,Cheesemanetal.2019,Kroesetal.2019).Theprobabilitydistributionofcarcinogenicpotencieshasbeenusedtoderiveanestimateofadailyexposurelevel(μg/person)ofmostcarcinogenswhichwouldgiverisetolessthanaoneinamillion(1x10-6)upperboundlifetimeriskofcancer(“virtuallysafedose”).Furtheranalysisofsubsetsofhighpotencycarcinogensledtothesuggestionofa10-foldlowerTTC(0.15μg/day)forchemicalswithstructuralalertsthatraiseconcernforpotentialgenotoxicity(Kroesetal.2019).“毒理學(xué)關(guān)注的閾值”用于定義那些不會產(chǎn)生顯著致癌性或其他毒性作用、但又未明確研究的化合物的“常見暴露量”（commonexposurelevel）(Munroetal.2019,KroesandKozianowski2019)。該TTC估計值是1.5μg/人/日。TTC概念最早來源于FDA關(guān)于食品接觸材料的“規(guī)定閾值”（athresholdofregulation）（Rulis1989,FDA1995），該閾值根據(jù)對致癌能力數(shù)據(jù)庫(Goldetal.1984)中343種致癌物質(zhì)的分析結(jié)果得出。隨后該數(shù)據(jù)庫擴大到700多個致癌性物質(zhì)(Munro1990,Cheesemanetal.2019,Kroesetal.2019)，這種分析結(jié)果不斷得到重復(fù)驗證。通過對致癌能力的概率分布進行評價，可以得到一個對大多數(shù)致癌物質(zhì)適用的“日常攝入水平(μg/person)”，此水平造成的一生中患癌癥的風險小于正常風險水平的上限1x10-6（真實的安全劑量）。對于含有“可能引起遺傳毒性結(jié)構(gòu)”的化合物，其TTC應(yīng)嚴格10倍（0.15μg/日）（Kroesetal.2019）。However,forapplicationofaTTCintheassessmentofacceptablelimitsofgenotoxicimpuritiesindrugsubstancesavalueof1.5μg/day,correspondingtoa10-5lifetimeriskofcancercanbejustifiedasforpharmaceuticalsabenefitexists.ItshouldberecognizedinthiscontextthatthemethodsonwhichtheTTCvalueisbased,aregenerallyconsideredveryconservativesincetheyinvolvedasimplelinearextrapolationfromthedosegivinga50%tumourincidence(TD50)toa1in106incidence,usingTD50dataforthemostsensitivespeciesandmostsensitivesite(several“worstcase”assumptions)(Munroetal.2019).然而，用TTC評估原料藥中的遺傳毒性雜質(zhì)限度，1.5μg/日（相當于10萬分之一的患癌風險）是可以接受的。應(yīng)該承認，基于TTC值控制遺傳毒性雜質(zhì)是非常保守的，因為這只是根據(jù)從產(chǎn)生50%腫瘤發(fā)生率（TD50）到百萬分之一致癌率的劑量線性推導(dǎo)得到的，而且TD50數(shù)據(jù)是用最敏感的動物和最敏感的部位研究得到的（幾個“最壞條件”假設(shè)）（Munroetal.2019）。SomestructuralgroupswereidentifiedtobeofsuchhighpotencythatintakesevenbelowtheTTCwouldbeassociatedwithahighprobabilityofasignificantcarcinogenicrisk(Cheesemanetal.2019,Kroesetal.2019).Thisgroupofhighpotencygenotoxiccarcinogenscomprisesaflatoxin-like-,nitroso-,andazoxy-compoundsthathavetobeexcludedfromtheTTCapproach.Riskassessmentofmembersofsuchgroupsrequirescompound-specifictoxicitydata.有幾個結(jié)構(gòu)基團被認定為具有非常高的基因毒性，它們即使被攝入低于TTC值的量也會面臨非常高的基因毒性風險(Cheesemanetal.2019,Kroesetal.2019)。這些高致癌性物質(zhì)包括黃曲霉素類、N-亞硝基物和偶氮類化合物，不適用TTC方法。這類化合物的風險評估需采用專門的毒性數(shù)據(jù)。TheremaybereasonstodeviatefromtheTTCvaluebasedontheprogenotoxicityresults.根據(jù)基因雜質(zhì)概況，有些情況下會偏離TTC值。PositiveresultfrominvitrostudiesonlymayallowtoexemptanimpurityfromlimitationatTTCleveliflackofinvivorelevanceofthefindingsisconvincinglydemonstratedbasedonaweight-ofevidenceapproach(seeICHS2guidelines).Thisapproachwillusuallyneednegativeresultswiththeimpurityfromsomeadditionalinvitroand/orappropriateinvivotesting.假如按照證據(jù)權(quán)衡法能充分證明“結(jié)果缺乏體內(nèi)相關(guān)性”，體外試驗的陽性結(jié)果也僅能在TTC水平上排除一個雜質(zhì)(參見ICH指南S2)。這種方法經(jīng)常需要在額外的體外試驗和/或合理的體內(nèi)試驗，并且得到雜質(zhì)的陰性結(jié)果。ATTCvaluehigherthan1.5μg/daymaybeacceptableundercertainconditions,e.g.short-termexposure,fortreatmentofalife-threateningcondition,whenlifeexpectancyislessthan5years,orwheretheimpurityisaknownsubstanceandhumanexposurewillbemuchgreaterfromothersources(e.g.food).Genotoxicimpuritiesthatarealsosignificantmetabolitesmaybeassessedbasedontheacceptabilityofthemetabolites.某些情況下TTC值高于1.5μg/日也是可以接受的，如短期用藥；用于治療威脅生命疾病的藥物；或人的存活期少于5年；或該雜質(zhì)是已知物質(zhì)，人體從其他途經(jīng)（如食物）獲得的暴露量遠遠高于藥物途經(jīng)。如果遺傳毒性雜質(zhì)本身就是重要的代謝物，那么該雜質(zhì)可以根據(jù)代謝物的可接受限度進行控制。TheconcentrationlimitsinppmofgenotoxicimpurityindrugsubstancederivedfromtheTTCcanbecalculatedbasedontheexpecteddailydosetothepatientusingequation(1).采用下列公式，從TTC值和日服用劑量，可以計算出原料藥中的基因毒性雜質(zhì)的濃度限度。(1)Concentrationlimit(ppm)=TTC[μg/day]/dose(g/day]濃度限度（ppm）=TTC[μg/day]/劑量(g/day]TheTTCconceptshouldnotbeappliedtocarcinogenswhereadequatetoxicitydata(long-termstudies)areavailableandallowforacompound-specificriskassessment.對于有確切毒性數(shù)據(jù)（長期毒性研究）的致癌性物質(zhì)不宜使用TTC概念，應(yīng)進行特定化合物風險評估。IthastobeemphasizedthattheTTCisapragmaticriskmanagementtoolusingaprobabilisticmethodology,i.e.thereisahighprobabilitythata10-5lifetimecancerriskwillnotbeexceededifthedailyintakeofagenotoxicimpuritywithunknowncarcinogenicpotential/potencyisbelowtheTTCvalue.TheTTCconceptshouldnotbeinterpretedasprovidingabsolutecertaintyofnorisk.應(yīng)強調(diào)，TTC是一個實用性的風險管理方法，是按概率方法學(xué)估算的。比如按這一概念，如果某未知致癌性遺傳毒性雜質(zhì)的攝入量低于TTC值，那么就可以保證患癌風險控制在十萬分之一之內(nèi)。但TTC概念不能被理解為確保絕對無風險。5.3DecisionTreeforAssessmentofAcceptabilityofGenotoxicImpurities基因毒性可接受性評價決策樹(shadedboxes=pharmaceuticalassessment,whiteboxes=toxicologicalassessment)（陰影框=藥學(xué)評價，白框=毒理學(xué)評價）1)Impuritieswithstructuralrelationshiptohighpotencycarcinogens(seetext)aretobeexcludedfromtheTTCapproach1)結(jié)構(gòu)上及高致癌性物質(zhì)有關(guān)的雜質(zhì)（見正文）不能采用TTC法。2)Ifcarcinogenicitydataavailable:Doesintakeexceedcalculated10-5cancerlifetimerisk?2)如果有致癌性數(shù)據(jù)：攝入量超過10-5患癌風險嗎？3)Case-by-caseassessmentshouldin