tirs 2015 day 4 risk assessment harpur - american college of … 2015_day 4_risk... ·...

Toxicology for Industrial and Regulatory Scientistsgy g y

Risk Assessment

Ernie Harpur PhD ATS FBTSErnie Harpur PhD ATS FBTSInstitute of Cellular Medicine

Newcastle UniversityNewcastle UniversityUK

Email: [email protected]

April 30th, 2015

Lecture Outline and Key MessagesLecture Outline and Key Messages

What is meant by Hazard, Risk, Risk (Safety) Evaluation and Risk Management in context of Drug Development?

(Acceptable) Risk versus Benefit? (Acceptable) Risk versus Benefit? Methodologies – what are the steps? It’s never too early to start and the process is continuous Plan ahead ground your safety plan in science monitor revise in the light Plan ahead, ground your safety plan in science, monitor, revise in the light

of new information,

It’s a team effort – each member (discipline) brings a different perspective – good communication is essential

Un-interpreted data are virtually worthless (except to raise alarm)

Mechanistic understanding can be extremely valuableg y All of the above underpins good decision making

Think ahead – The value of a study is only as good as its design

Slide 2ACT—Toxicology for Industrial Regulatory Scientists

Above all THINK

RA should be driven by science and logic and clearl and logic and clearly

communicated

Slide 3ACT—Toxicology for Industrial Regulatory Scientists 3

Key Message

Thinking ahead helps to avoid the unexpected


Key MessagesKey Messages

If you don’t know where you are going, any path will take you there

Even if you do know your destination

h kyou have make good choices as to the route of getting hthere


The best route is not necessarily theThe best route is not necessarily theThe best route is not necessarily the The best route is not necessarily the most obvious or directmost obvious or direct

A Few Definitions and Principles (1)

Hazard is the /id titsource/identity

of potential pharm



Risk is contextualcontextual



Risk is the probability (likelihood) that an adverse

outcome will occur in a person or group that is

exposed to a particular hazard. Mathematically,

the probability of harm lies between 0 and 1 but, inthe probability of harm lies between 0 and 1 but, in

reality, estimation of risk is at best semi-

quantitative limited by unknowns andquantitative, limited by unknowns and

uncertainties



Risk assessment is the process used to estimate the likelihood that health will be affected adversely under alikelihood that health will be affected adversely under a specific set of conditionsRisk assessments are:Part science and part value judgmentp j gNever free of uncertainties and rely on Weight of EvidenceInherently conservativeUseful for decision-makingIterative as new data become informationIterative – as new data become information

Safety is the probability that harm will not occur under specified conditions; the state of being reasonably free from harm

1Safety α

Risk

conditions; the state of being reasonably free from harm


Risk Management with objective of Risk MitigationRisk Mitigation

Process of identifying evaluating selectingProcess of identifying, evaluating, selecting, and implementing actions to reduce risk to human health and ecosystemsFocus on information derived from risk

assessment but, inevitably other factors -cultural, ethical, political, social, economic and technological - can play a role in the decision process

REMS = Risk Evaluation and Mitigation Strategy


g gy

Nothing is totally safe There is always some risk* (concept of acceptable

risk – which is contextual)

Individuals have variable perception of risk and some are willing to engage in high risk activities (e.g. extreme sports, smoking)

However, where evaluation of the risk is in the hands of others, society has become intolerant of risk-taking, i.e. is risk averse

Risk assessment is not an exact science – industry and regulators often come to different conclusions based on evaluation of the same data

The regulators are the ultimate arbiters of what is acceptable risk

* Zero risk or 100% safety is not attainable


Zero risk or 100% safety is not attainable

Degree of acceptable risk depends on a lot of things including potential benefitg p

Nature of the toxicological finding (genetic, carcinogenic reproductive etc) and extent to which it carcinogenic, reproductive etc) and extent to which it can be monitored

Nature of the disease being treated S lf li iti h i lif th t i Self-limiting vs chronic severe or life threatening

(e.g. cancer) Prevalence of disease and/or requiring unsupervised q g p

medication (e.g. asthma) Vulnerable populations (e.g. children) Presence of factors likely to enhance individual Presence of factors likely to enhance individual

variability (e.g. polymorphic metabolism) Unmet medical need vs availability of effective

t t t


i.e. benefit/risk evaluationtreatments

Risk assessment (RA) ( )

Can be applied to almost any activity in lifeactivity in life.

Toxicologists are concerned mostly with chemical risks.


Chemical risks of concern to T i l i t (1)Toxicologists (1)

(Where human exposure is unintended)(Where human exposure is unintended)

• Natural substances (e.g. fungal toxins) Industrial (e g solvents)Industrial (e g solvents) Industrial (e.g. solvents)Industrial (e.g. solvents)• Agro (e.g. pesticides - designed to kill selectively)• Food residues (e.g. growth promoters)• Food contaminants (e.g. from packaging materials)Environmental (e.g. ecological effects of manEnvironmental (e.g. ecological effects of man--made made

chemicals, including medicines)chemicals, including medicines)

Relevant in context of Drug DevelopmentRelevant in context of Drug Development


gg

Chemical risks of concern to T i l i t (2)Toxicologists (2)

(Where human exposure is intentional)( p )

• Food additives (e.g. preservatives, colourants)• Chemical warfare agents• Chemical warfare agentsRecreational drugs (alternative use of alternative use of

therapeutic drugstherapeutic drugs or ‘designer’ drugs)MedicinesMedicinesMedicinesMedicines

Relevant in context of Drug DevelopmentRelevant in context of Drug Development

‘chemical’ = ‘compound’ = ‘molecule’ = ‘drug candidate’

drug/medicine


g/

Small Molecules versus Biologicals

As you have heard there are many striking y y gdifferences in the approach to safety evaluation of potential Biotherapeutics (versus conventional small molecules) e gsmall molecules), e.g.Nature (and methods of evaluation) of the potential

hazardsEstimation of a safe starting dose in PhIThis talk focuses on Risk Assessment of small

molecules although some of the principles aremolecules, although some of the principles are also relevant to the special case of Biotherapeutics


p

RA in Drug Development

RA in Drug Development has several facets, including:

• RA of occupational exposure during manufacture

• RA of alternative use (Drug Abuse LiabilityAssessment or DALA)

• RA f i t l i t• RA of environmental impact

This lecture is focused on: A t f th i k f d ff t i h t ki Assessment of the risk of adverse effects in humans taking new

medicines in clinical trials and for treatment of disease after marketing Includes risks associated with excipients, impurities, degradants as


gwell as API (active pharmaceutical ingredient)

Is the key purpose of Pharmaceutical Toxicology

Key Components of RA

Hazard identification (inherent toxic t ti l)potential)

Hazard characterization (relationship to dose, exposure, metabolism, species differences, mechanism, reversibility etc)Evaluation of relevance for humans and

safety marginssa ety a g sMonitorability – biomarkers?


Safety Evaluation of Medicines is aMulti Component ProcessMulti-Component Process

11 T t l tiT t l ti1.1. Target evaluationTarget evaluation

2.2. Hazard Identification andHazard Identification andCharacteri ationCharacteri ation

Predictive Predictive CharacterizationCharacterization

3.3. Evaluation of relevance for humansEvaluation of relevance for humansprocessprocess

4. Evaluation of risk versus benefit4. Evaluation of risk versus benefit-- concept of concept of acceptableacceptable riskriskpp pp

5. Clinical Safety Plan; Risk Mitigation Strategy5. Clinical Safety Plan; Risk Mitigation Strategy

6 Confirmation of safety through monitored6 Confirmation of safety through monitored


6. Confirmation of safety through monitored 6. Confirmation of safety through monitored clinical useclinical use

RA is a continuum throughout Discovery g y

and Development


Example of an Nonclinical Safety Program

Phase I/IIaLead Candidate

6 ‐10years

Preclinical Phase IIb Phase III Regul.

ProgramDISCOVERY DEVELOPMENT

Phase I/IIaIdentification Identification

Preclinical Phase IIb Phase IIIReview

GLP•Genetox Screening • Carcinogenicity• Pre‐ and Post‐Natal Tox•Non‐Standard Studies **

• Exploratory Safety Pharm• In vitro EmbryoTox Test

Internal decision Making

•Genetox Package• Safety Pharm Package

• Fertility Tox• Embryofetal Tox• Chronic Tox

GLPGLP•RF Tox

• Screening Repro Tox (if any)

* RF = Range‐Finding, • Safety Pharm Package• Short‐term Repeated‐dose Tox•RF Pregnant Rat / Rabbit *•Non‐Standard Studies **

•RF Carcinogenicity•Non‐Standard Studies **

g g,** Unplanned studies (e.g. safety

assessment of impurities, mechanistic studies)


Internal and Regulatory decision Making

RA is a continuum throughout Discovery and Development (1)Development (1)

Prior to first administration to humans we can speak of Preclinical Risk AssessmentHowever, the context , “translation to humans”,

drives the processpBegins in Discovery with assessment of risks

inherent in the pharmacological targetContinues with selection of the candidate withContinues with selection of the candidate with

lowest risk (already a trade off with other properties associated with efficacy)Pre-clinical RA should incorporate all availablePre clinical RA should incorporate all available

information, including prior knowledge (any information on the pharmacological or chemical class available from the literature: this may include


class available from the literature: this may include clinical information)

RA is a continuum throughout Discovery and Development (2)Development (2)

Risk assessment continuesRisk assessment continues throughout clinical development,

dd d f ll t j t itiaddressed formally at major transition points (key input to good decisions)It is the first step in the process of

developing a safety managementdeveloping a safety management programme with the objective of Risk Minimisation


Minimisation

RA in Discovery and Development

Important always to think aheadImportant always to think aheadRemember the primary goal – to

mitigate riskmitigate risk Can influence timing Choice of model Study design – choice of endpoints (biomarkers) E er st d sho ld be seen as an Every study should be seen as an opportunity to generate information useful to decision making


useful to decision making

Example of RA strategy in Discovery

Leadd ifi i

Candidated ifi i

Preclinical

DISCOVERY

Leadi i i

Target Identification IdentificationOptimizationSelection

•On‐target/Off‐target liability

•In silico analyses (other end points) •Genotoxicity Tier I (In silico +/‐ Ames II)•Cytotoxicity Tier I assaysC di l (i ili hERG)

•Genotoxicity Tier II (In silico, Ames II +/‐MNT vitro and follow‐up)

•Cytotoxicity Tier I assays (hepatocytes)

•Cardiovascular (in silico + hERG)

•Cytotoxicity Tier I assays (hepatocytes)•In vitro Embryotoxicity (or Zebra fish)•Cardiovascular (hERG, other ion channels if warranted)

•Toxicity Tier II functional assays (if warranted)


•7 – 14 day exploratory rat study•Cardiovascular (in vitro + in vivo)•Repro tox screening (case‐by‐case)

Decision making can be aidedDecision making can be aided by a decision treey


Genetox Evaluation and Decision Tree during Discovery: An Example

Discovery Phase Preclinical PhaseDevelopmentDecision

No structural alert:

y p

Standard battery of assays:•AMES• in vitro CA or MLA• in vivo MNT

AMES II

( + )

( ‐ )

GO( + )

( ‐ )

GOin vitro MNT

No structural alert: Do an Ames II for Development

Decision

Standard battery :• AMES( )

If no other compoundsIf other compounds

In silicofor prioritization

NO GOEvaluate other compounds ‐Chemical

• AMES• in vitro CA (notMLA)

in vivo MNT Additional studies:

• In vivo CA

Cautious Go with modified

( ‐ )

( + )

Exploratory In vivoMNT/CA

Structural alert: Do an Ames II

MNT = Micronucleus TestCA = Chromosome Aberration TestMLA = Mouse Lymphoma Test

NO GOOptimization • In vivo UDS

• Mechanistic studies: DNA interaction

Risk Assessment

FIHpackage

asap


MLA = Mouse Lymphoma TestUDS = unscheduled DNA Synthesis FIH = First in Human

Embryofetal Tox Evaluation and Decision Tree during Discovery:An Example

Standard battery of studies:

Discovery Phase

( ‐ )In Vitro EmbryoTox1

Preclinical/clinical PhaseDevelopmentDecision

•EFT Rat / Rabbit ( + )

GOEmbryoTox

Is EFT a NoGo for the project?

If no other compoundsIf other compounds

yes NO

NO GOEvaluate other compounds If

Cautious Go with

( ‐ )

( + )

Exploratory EFT study in rodent Consider early EFT package

NO GO

compounds . If all positive,

perform in vivostudy with lead

Go with modified

FIHpackage

( + )

EFT: Embryofetal toxicityFIH = First In Human


1 Oncologics and biologics should be evaluated on a case‐by‐case basis

The conduct of animal The conduct of animal studies is linked to the

phase of clinical studies is linked to the

phase of clinical pdevelopment

pdevelopment

Timely delivery of interpreted data from Timely delivery of interpreted data from animal studies is essential to enable rapid

clinical development


pDependent on a reliable clinical plan

RESEARCH/DISCOVERYPRINCIPAL NON‐CLINICAL SAFETY STUDY

Selection ofdevelopment candidate

SAFETY STUDY REQUIREMENTS • Repeat dose tox: 14 days

• Genetic toxicity testing• Safety pharmacology candidate

(PRECLINICAL PHASE)

• Safety pharmacology

• Reproductive tox: fertility and embryo foetal development

First administration to humansPhase I

y p• Chronic tox; equivalent duration

• Reproductive tox: pre- and

DECISION POINTS IN CLINICALPhase IIa and IIb

postnatal development• Carcinogenicity studies

DECISION POINTS IN CLINICAL DEVELOPMENT (REGULATORY

HURDLES)

Phase IIa and IIb

Ph III


Phase IIIMAMarketing Authorization

Relative importance of animal studies to Safety Evaluation

PRE‐

CLINICAL

CLINICAL

DEVELOPMENT

MARKETED

PRODUCT

PHASE IVPHASE I‐III PHASE IV

Human Use

( )

Relative Importance of Findings in Animal gStudies

( )


First Administration to Humans

Approval to market

Risk Assessment is a Multidisciplinary Effort

RA used to be conducted prior to submission of an application for marketing authorisation Still a requirement (provision of REMS – Risk Evaluation and Mitigation Strategy)

Now recognised that this should begin much earlier -before FIH: evaluation of risk should drive the development and implementation of a Clinical Safetydevelopment and implementation of a Clinical Safety Plan Begins with determination of a safe starting dose and dose escalation strategy in

Ph I C i i h h i f f i i d i ll h f li i l Continues with choice of safety monitoring during all phases of clinical

development

Good communication is important as is mutual respect for individual roles and contributionsfor individual roles and contributionsToxicologists should be proactive in presenting

information (implies interpretation of the data) as early as possible but avoiding premature communication


as possible but avoiding premature communication causing unnecessary alarm (a fine line)

Core of a Safety Evaluation ProgrammeConduct of a well defined

and standardised series of studies*

Rodent and Range of dose levels, Extensive range ofnon-rodent speciesappropriate routes of

administrationmeasurements

Definition of toxicity and estimation of safety ratios

Evaluation of risk for humans

* Does not preclude integration of additional science‐driven endpoints, for example to provide mechanistic insight or evaluate a biomarker


for example to provide mechanistic insight or evaluate a biomarker

Study Design is KEY

Core Study Designs: Facilitate preparation of individual study protocols Help to ensure uniform standards Diminish the risk of non compliance with worldwide Diminish the risk of non-compliance with worldwide

regulatory requirements

B tBut

Should be modified to satisfy scientific needs


Concept of Safety Ratio (based on Exposure)Concept of Safety Ratio (based on Exposure)Concept of Safety Ratio (based on Exposure) Concept of Safety Ratio (based on Exposure) is still at the core of a is still at the core of a

Quantitative Risk AssessmentQuantitative Risk AssessmentQua a e s ssess eQua a e s ssess e

S f R iExposure at NOAEL in most sensitive animal species

Safety Ratio =p p

Exposure in human at therapeutic dose


Interpretation of Relevance of Findings

Extrapolation Across Species - Uncertainty FactorsFactors

HUMAN VARIABILITYSPECIES DIFFERENCES

Default UF =10 Default UF =10


Helps determine what magnitude of Safety Ratio is acceptable

How can we improve the assessment ofHow can we improve the assessment ofHow can we improve the assessment of How can we improve the assessment of the risk of an adverse effect being the risk of an adverse effect being

manifest in humans?manifest in humans?manifest in humans?manifest in humans?


We need to fully understand the nature of the toxic effect:-effect:-

characterise in detail characterise in detail

study the relationship to metabolism and plasma concentrationsplasma concentrations

are there species differences?

is the effect reversible?

h t th h i ? what are the mechanisms?


Evolution of the ScientificEvolution of the ScientificEvolution of the ScientificEvolution of the Scientificand Regulatory and Regulatory Climate Climate ––

A t f M h iA t f M h i b db dAcceptance of MechanismAcceptance of Mechanism--based based decision Makingdecision Makingdecision Makingdecision Making


In the Beginning In the Beginning -- Default Default Options in Options in RARAg gg g pp

Defined as the option chosen on the basis of Defined as the option chosen on the basis of l i tifi k l d d i k tl i tifi k l d d i k tgeneral scientific knowledge and risk assessment general scientific knowledge and risk assessment

policy that appears to be the best choice in the policy that appears to be the best choice in the absence of data to the contrary.absence of data to the contrary.absence of data to the contrary.absence of data to the contrary.

Example:Example: the assumption that humans are at least the assumption that humans are at least iti t t i ff t th t itiiti t t i ff t th t itias sensitive to toxic effects as the most sensitive as sensitive to toxic effects as the most sensitive

responding animal species.responding animal species.

Since default options are intentionally selected to be Since default options are intentionally selected to be conservative, they are more likely to overestimate conservative, they are more likely to overestimate


than to underestimate risk to human health.than to underestimate risk to human health.

Science and Judgement in Risk AssessmentScience and Judgement in Risk Assessment

““As scientific knowledge increases, the science policy As scientific knowledge increases, the science policy choices made by the agency and Congress should choices made by the agency and Congress should have less impact on regulatory decisionhave less impact on regulatory decision--making.making.

Better data andBetter data and increased understanding of biological increased understanding of biological mechanismsmechanisms should enable risk assessments that are should enable risk assessments that are less dependent on conservative default assumptionsless dependent on conservative default assumptionsless dependent on conservative default assumptions less dependent on conservative default assumptions and more accurate as predictions of human risk.”and more accurate as predictions of human risk.”

1994 R t* f itt f th N ti l A d f1994 R t* f itt f th N ti l A d f1994 Report* of a committee of the National Academy of 1994 Report* of a committee of the National Academy of Sciences/National Research Council (Requested by US EPA)Sciences/National Research Council (Requested by US EPA)

*Risk Assessment of Hazardous Air Pollutants*Risk Assessment of Hazardous Air Pollutants


The Essential Value of Understanding The Essential Value of Understanding Mechanisms is not aMechanisms is not a recentrecent conceptconceptMechanisms is not a Mechanisms is not a recent recent conceptconcept

“Only if mechanisms are understood is it possible to “Only if mechanisms are understood is it possible to extrapolate toxicity measurements across species extrapolate toxicity measurements across species and from the large doses used in experimental and from the large doses used in experimental animals to the exposures experienced by man.”animals to the exposures experienced by man.”

* From the conclusions of Study Group Report: Long* From the conclusions of Study Group Report: Long--term term Toxic Effects. The Royal SocietyToxic Effects. The Royal Society (1978)(1978)


Benefit of Mechanistic Information inDrug DevelopmentDrug Development

Retrospective Review of 17 Compounds Withdrawn from DevelopmentRetrospective Review of 17 Compounds Withdrawn from Development

Factors confirming the decision to terminate development in 13 casesFactors confirming the decision to terminate development in 13 casesFactors confirming the decision to terminate development in 13 casesFactors confirming the decision to terminate development in 13 cases

1.1. No, or very low, safety margin (Tox Dose/Ther Dose)No, or very low, safety margin (Tox Dose/Ther Dose)

2.2. Lack of understanding of the mechanism of toxicity or its relevance for Lack of understanding of the mechanism of toxicity or its relevance for manman

3.3. Clear indication the lesion has relevance for manClear indication the lesion has relevance for man

Decision to terminate development questioned in 4 casesDecision to terminate development questioned in 4 casesDecision to terminate development questioned in 4 casesDecision to terminate development questioned in 4 cases

Knowledge, current at the time of retrospective review, (i.e. a better Knowledge, current at the time of retrospective review, (i.e. a better understanding of the lesion) might have led to a decision to continue understanding of the lesion) might have led to a decision to continue development if available at the time.development if available at the time.

R. Brimblecombe (1990) The Importance of Retrospective Comparisons. In: AnimalR. Brimblecombe (1990) The Importance of Retrospective Comparisons. In: AnimalToxicity Studies: Their Relevance for Man Proceedings of a CMR SymposiumToxicity Studies: Their Relevance for Man Proceedings of a CMR Symposium


Toxicity Studies: Their Relevance for Man. Proceedings of a CMR Symposium.Toxicity Studies: Their Relevance for Man. Proceedings of a CMR Symposium.

MechanismMechanism--based risk Assessment of Chemicalsbased risk Assessment of Chemicals

Rapid development and application of the science Rapid development and application of the science of using mechanistic data in chemical risk of using mechanistic data in chemical risk assessment in recent yearsassessment in recent years

Growing consensus in the scientific/regulatory Growing consensus in the scientific/regulatory community of the value of incorporating community of the value of incorporating mechanistic data into risk assessmentsmechanistic data into risk assessmentsmechanistic data into risk assessmentsmechanistic data into risk assessments

Regulatory acceptance has been demonstratedRegulatory acceptance has been demonstrated(e g(e g globulin)globulin)(e.g. (e.g. 2u2u--globulin)globulin)

Emphasis has been on assessment of Emphasis has been on assessment of i i i ki i i k


carcinogenic riskcarcinogenic risk

What is Meant by the Study of Mechanisms?

In In the context of drug developmentthe context of drug development

Understanding enough of theUnderstanding enough of the mechanism (or mode)mechanism (or mode) ofof Understanding enough of the Understanding enough of the mechanism (or mode) mechanism (or mode) of of toxic action to explain or predict species differences toxic action to explain or predict species differences and confidently assess the risk for humans.and confidently assess the risk for humans.

Our understanding is never complete.Our understanding is never complete.

Reliance on “weight of evidence”Reliance on “weight of evidence”


Risk Assessment – The pieces of the Jigsaw Puzzle

NOAEL andNOAEL and

ConcentrationConcentrationresponseresponsel ti hil ti hi

Adverse effectAdverse effectin animals and/orin animals and/or

safety marginsafety margin relationshipsrelationshipsin animals and/orin animals and/orhumanshumans

AnatomicalAnatomicaland clinicaland clinical

Past experiencePast experiencewith relatedwith related and clinicaland clinical

pathologypathologywith relatedwith relatedcompoundscompounds

SeriousnessSeriousnessand/orand/or

reversibility ofreversibility ofeffecteffect Availability ofAvailability ofSpeciesSpecies


effecteffect Availability ofAvailability ofbiomarkerbiomarker

SpeciesSpeciesdifferences in effectdifferences in effect

Mechanistic data can, on occasion, help complete the puzzle

d

Concentrationresponse

Adverse effectin animals

NOAEL andsafety margin

responserelationships

a a sand/or humans

MECHANISMSPast experiencewith relatedcompounds

Anatomicaland clinicalpathology

SpeciesSeriousness

and/or Availability of

compounds p gy

Speciesdifferences

and/orreversibility of

effect

Availability ofbiomarker


Mechanisms

Timecourse of Species difference inTimecourse ofpathogenesis

Reversibility

Species difference inanatomy, physiology

and biochemistry

Exposure and

M l l

Biochemicaleffects

ppharmacokinetics

Induction/inhibitionof cyt P450’s


MolecularTarget

Metabolism/Chemical reactivity

The Incorporation of Mechanistic Information in the RiskThe Incorporation of Mechanistic Information in the RiskAssessment Process in Drug DevelopmentAssessment Process in Drug Developmentg pg p

Adverse effect detected inanimal or clinical study

Characterize lesion asfully as possible Significance is

adequatelyd t d

Significance isuncertain

Relate to Metabolismand/or Exposure

understood

Propose mechanistichypothesis

Draw on existing

knowledge(lit t )

Understand mechanism anddefine species differences

ASSESS RISKFOR HUMANS

(literature)

Conduct studies totest hypothesis define species differences FOR HUMANStest hypothesis

Results

Revisehypothesis

Stop Development Risk Acceptable?YES

NO


ResultsInconsistent

with hypothesis

Identify newlead candidate orredesign molecule

ContinueDevelopment

YES

Mechanistic Understanding and Human RiskMechanistic Understanding and Human RiskAssessmentAssessmentAssessmentAssessment

What constitutes adequate evidence to support a What constitutes adequate evidence to support a mechanistic hypothesis must be decided on a case-by-case basis and changes with time.

Thus, existing knowledge and experience with other compounds can be valuable in formulating a p gmechanistic hypothesis and in human risk assessment.

Ultimately good clinical studies (guided by mechanistic Ultimately good clinical studies (guided by mechanistic understanding) are required to demonstrate that relevant toxic changes do not occur in patients.


Example of the use of Example of the use of M h i ti D t t tM h i ti D t t tMechanistic Data to support Mechanistic Data to support

Risk Evaluation in Clinical Risk Evaluation in Clinical DevelopmentDevelopment


Example : Compound XExample : Compound X

Animal findings pointed to a serious pathologyAnimal findings pointed to a serious pathology with potential relevance for humansClinical studies on holdNeeded information to provide confidence that

the risk for humans was lowCharacterization of the mechanism provided

reassuring data that humans would be much less vulnerable than animals AND a relevantless vulnerable than animals AND a relevant (mechanism-based) biomarker


Toxicology FindingsToxicology Findings

Time- and dose-dependent pathology in the rat and, to a much lesser extent, the monkey:visceral lesions comprising multi-organ infiltration of

macrophages ith characteristicall distended c toplasmmacrophages with characteristically distended cytoplasm

brain lesions - degenerative and reactive changes including PAS positive inclusions in neurons, gliosis, infiltration with microglial cells and (rat only) perivascular PAS positive enlarged macrophages

P th l i t k d bl tPathologist remarked resemblance to pathology of Gaucher’s disease.


Gaucher’s diseaseGaucher’s disease

Lipid storage disease - sphingolipidosis - caused by deficiency of the enzyme glucosylceramidase

Deficiency leads to accumulation of substrate - Deficiency leads to accumulation of substrate glucosylceramide - in macrophages of the RE system, primarily liver, spleen and bone marrow

CNS involvement in some cases (Gaucher types II & III); lesions in the brain attributed to accumulation of glucosylsphingosine, a cytotoxic substrate


Hypothetical Biochemical Mechanism of Hypothetical Biochemical Mechanism of ToxicityToxicity

Glycosphingolipid Ceramide Sphingosine

ToxicityToxicity

Glycosphingolipid Ceramide Sphingosinecatabolism

Glucosylceramide Glucosylsphingosine

GlucosylceramidaseCpd X Cpd XCeramide Sphingosine

Cpd Cpd X


Glucosylceramidase (GCase) InhibitionGlucosylceramidase (GCase) Inhibition

Confirmed that administration of Cpd X caused inhibition of GCase in rat and monkey Evident after a single dose up to 80 90% depending on Evident after a single dose - up to 80-90% depending on

dose, tissue and species Maintained during chronic administration Reversible within 1 month Reversible within ~1 month Seen in all animal species tested (rat, mouse, hamster,

dog, monkey); some differences in magnitude and dose responsedose-response


GCase Inhibition and Lesions in Rat BrainGCase Inhibition and Lesions in Rat Brain

100%250

150

200tiv

ityo

tein

/hr)

33%100

150

Sp

ecifi

c A

co

se/m

g p

ro

23% 22% 19% 19%50

Mea

n S

nm

ol g

luco

00 0.3 1 3 10 30

(

Brain lesions - - - - + ++Cpd x (mg/kg/day)


Brain lesions + ++

Modified Hypothesis for Mechanism of ToxicityModified Hypothesis for Mechanism of Toxicity

Glucosylceramidase inhibition Substrate accumulation Lesions

glucosylceramidase inhibition - does not cause toxicity per se but is the essential first step

hi h t i itwhich triggers it.

substrate accumulation - gradual process, d di id l GC ti itdepending on residual GCase activity, synthesis rates etc.

l i d l h “ iti l l l” f lesions - develop when “critical level” of substrate is reached - glucosylceramide in viscera, glucosylsphingosine in brain.


Brain Lesions and Brain GS in RatBrain Lesions and Brain GS in Rat

600

400

500

phin

gosin

e ul

atio

nnt

rols)

200

300

Gluc

osyls

pac

cum

u(%

Con

0

100

0 0.3 1 3 10 30

Brain lesions - - - - + ++Cpd x (mg/kg/day)


Implications for HumansImplications for Humans

Are humans likely to be a susceptible species?role of metabolism in inhibition

andandinter-species differences in

metabolismmetabolism…..


Metabolism and GCase InhibitionMetabolism and GCase Inhibition

Cpd X undergoes extensive metabolism

Inhibition of GCase requires metabolism demonstrated usingdemonstrated usingliver microsomes +/- NADPHcultured hepatocytes +/- inhibitor of Cpd X metabolism

Which metabolite is responsible for inhibition? Are there species differences i it f ti ?in its formation?


Identification of Cpd X Metabolite Involved in Identification of Cpd X Metabolite Involved in Glucosylceramidase InhibitionGlucosylceramidase InhibitionGlucosylceramidase InhibitionGlucosylceramidase Inhibition

NCF3

SR57746 OH

OH

OH

OH

O

RCpd X

NCF3

Conduritol B-Epoxide

Potent and specific inhibitor of glucosylceramidase

OH

RIntermediary

Epoxide

N

O

R

NCF3

OH

NCF3 OH

OH

OHTetrol Derivative(s)

NCF3

OH

OR R R

Dihydrodiol Derivative Intermediaryepoxide


OHOH OH

OHOHOH

epoxide

Glucosylceramidase Inhibition by Cpd X and Glucosylceramidase Inhibition by Cpd X and Pro imal Metabolite in Hepatic MicrosomesPro imal Metabolite in Hepatic MicrosomesProximal Metabolite in Hepatic MicrosomesProximal Metabolite in Hepatic Microsomes

d 1 Dihydrodiol2IC50 (µM)

Cpd X1 DihydrodiolMetabolite

S-D Rat > 30 3.8

Monkey > 30 19.7

Human > 30 92.3

1 Highest conc. Tested = 30M

2 Hi h t T t d 100M


2 Highest conc. Tested = 100M

Inter-species variability in metabolic pathways

Cpd XDihydrodiolmetabolite Dihydrodiol

epoxideepoxide

SpragueSprague--Dawley Dawley RatRat

Glucuronide

MonkeyMonkeyGlucuronide

Inactive metabolite

HumanHumanGlucuronide

Inactive metabolite


Glucuronide

Inhibition of GCase by Cpd X in Cultured Inhibition of GCase by Cpd X in Cultured HepatocytesHepatocytes

Human

HepatocytesHepatocytes

80

100

ITY

ntro

l)

Monkey

60

AC

TIV

Ive

to C

on

20

40

GC

ase

(Rel

ativ

Sprague-Dawley Rat

0

20

0.001 0.01 0.1 1 10 100


Cpd X(µM)

Conclusion on Mechanism

Proposed Gaucher mechanism of toxicity strongly p y g ysupported by substrate accumulation studies in brain (and liver)

Inhibition of GCase is the essential first step for lesion developmentGCase activity is a mechanistically relevant biomarker

Measure in clinical trials to assess human susceptibility

Lymphocytes present an accessible and relevant tissueLymphocytes present an accessible and relevant tissue

No inhibition of GCase in patients in clinical trials


Human Lymphocyte Human Lymphocyte

10

GlucosylceramidaseGlucosylceramidase

789

10

ctiv

ity

Placebo (n=11)

1 mg SR57746A (n=8)Cpd X

3456

mid

ase

Ac

/mg/

hr) 2mg SR57746A (n=11)Cpd X

-1012

cosy

lcer

am(n

mol

/

-3-2

Glu

c

Change from Baseline (6 months)


Benefits of the Application Benefits of the Application of Mechanistic of Mechanistic Toxicology inToxicology in Drug DevelopmentDrug DevelopmentToxicology in Toxicology in Drug DevelopmentDrug Development

Continued development of molecules Reassurance of safety through increased understanding of i ifi f l i b i f i diff isignificance of lesions, basis of species differences in response

etc……………or

Earlier, informed decision to terminate development of

Improved choice of drug candidates Mechanism based models (in vitro/in vivo) of target organ toxicity

molecules which exhibit significant toxicity of relevanceto humans

Mechanism based models (in vitro/in vivo) of target organ toxicityfor rapid screening

Enhanced design of molecules Improved basis for SAR and molecular design

Enhanced design of clinical protocols (e.g. availability of relevant biomarkers)


of relevant biomarkers) Improved quality of regulatory submissions

IMPROVING RISK ASSESSMENT FOR HUMANSIMPROVING RISK ASSESSMENT FOR HUMANS

Looking to the future


Scientific Approach to Risk Assessment –Back to the FutureBack to the Future

SAFETYSEVALUATION

• Rational process

• Apply good science

• Scientific logic is paramount

• Challenge the conventional

Extend knowledge

• Challenge the conventional

IMPROVING RISKASSESSMENT FOR

MAN

of mechanisms

Exploit innovativetechniques


MANTrain and develop toxicologists

The future is here – to the extent that iwe want to use it

Incorporate innovative approaches that capitalize upon novel technologies and approaches

T i t i t i t b l i Transcriptomics, proteomics, metabolomics High content screening Pathway analysisy y Predictive computational models Novel cell types and Transgenic animals Non in asi e imaging Non-invasive imaging Novel biomarkers


Additional Reading

Reviews

Pritchard, JF et al (2003) Making better Drugs: Decision gates in Non-Clinical Drug Development. Nat Rev Drug Disc, 2, 542-553

Guth, BD (2007) Preclinical Cardiovascular Risk Assessment in modern Drug Development. Tox Sci, 97, 4-20

Kramer, JA et al (2007) The Application of Discovery Toxicology and Pathology towards the Design of safer Pharmaceutical Lead Candidates Nat Rev Drugtowards the Design of safer Pharmaceutical Lead Candidates. Nat Rev Drug Disc, 6, 636-649

Stevens, JL and Baker, TK (2009) The Future of Drug Safety Testing: Expanding the View and Narrowing the Focus. Drug Discovery Today, 14, 162-167.

Merlot, C (2010) Computational Toxicology – a Tool for early Safety Evaluation. Drug Discovery Today, 15, 16-22.


Additional Reading

Application of genomics in drug safety assessment

MacGregor, JT (2003) The Future of Regulatory Toxicology: Impact of the g ( ) g y gy pBiotechnology Revolution. Tox Sci, 75,236-248

Cohen, S (2004) Risk Assessment in the Genomic Era. Tox Path, 32(Suppl. 1), 3-8

Mayne, JT et al (2006) Informed Toxicity Assessment in Drug Discovery: Systems-based Toxicology. Curr Opin Drug Disc Dev, 9, 75-83

Ryan, TP et al (2008) Strategic Applications of Toxicogenomics in early Drug Discovery. Curr Opin Pharmacol, 8, 654-660


Additional Reading

The use of mechanistic information

Stevens, JL (2006) Future of Toxicology – Mechanisms of Toxicity and Drug Safety: Where do we go from here? Chem Res Tox, 19, 1393-1401

Guengerich FP (2011) Mechanisms of Drug Toxicity and Relevance toGuengerich, FP (2011) Mechanisms of Drug Toxicity and Relevance to Pharmaceutical development. Drug Metab Pharmacokinet, 26, 3-14

Toxicity Testing in the 21st CenturyToxicity Testing in the 21 Century

MacDonald, JS and Robertson, RT (2009) Toxicity Testing in the 21st Century: A View from the Pharmaceutical Industry. Tox Sci, 110, 40-46

Throckmorton, DC (2009) Regulatory Perspective on the Integration of Preclinical and Clinical Safety Data. Presentation at HESI meeting. http://www.hesiglobal.org/files/public/Of%20Interest/ILSIHESI2009Throckmorton.pdf


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