Legislative trends, advances in testing predictive tools

Outline • Evolution of Chemicals Legislation – Addressing much larger numbers of substances in Canada, Europe, U.S. • Predictive Tools – Physiologically Based Pharmacokinetic (PBPK) Modelling – Hazard • Combined Exposure to Multiple Chemicals • The Need for More Efficient Testing Strategies • ReadingInformation Sources Evolving Legislative Mandates for Industrial Chemicals • Most chemicals already in use at the time of introduction of modern chemicals legislation in Europe and North America (late 1980’s) were “grandfathered” – No testing, assessment were required • New chemicals required assessment • Between the late 1980s and late 1990s, countries focussed assessments on approx. 100 out of the tens to hundreds of thousands of industrial chemicals in use (i.e., 0.1% to 1%)

Developments in Chemical Risk

Assessment

Legislative Trends, Advances in

Testing & Predictive Tools

M.E (Bette) MeekMcLaughlin CentreUniversity of Ottawabmeek@uottawa.ca

CRIBangkok

1

• Evolution of Chemicals Legislation

– Addressing much larger numbers of substances in

Canada, Europe, U.S

• Predictive Tools

– Physiologically Based Pharmacokinetic (PBPK) Modelling

– Hazard

• Combined Exposure to Multiple Chemicals

• The Need for More Efficient Testing Strategies

• Reading/Information Sources

2

Evolving Legislative Mandates for

Industrial Chemicals

• Most chemicals already in use at the time of introduction

of modern chemicals legislation in Europe and North

America (late 1980’s) were “grandfathered”

– No testing, assessment were required

• New chemicals required assessment

• Between the late 1980s and late 1990s, countries

focussed assessments on approx 100 out of the tens to hundreds of thousands of industrial chemicals in use

(i.e., 0.1% to 1%)

100 100,000

3

Evolving Legislative Mandates for

Industrial Chemicals (Cont’d)

• Chemicals which were considered:

– E.g , Benzene,

– formaldehyde,

– asbestos, etc

• Increasingly, legislation is requiring

– E.g., 23, 000 in Canada

– 130, 000 in Europe

4

Evolving Legislative Mandates for

Existing Chemicals (Cont’d)

• Canada

– “Categorization” (i.e., systematic priority setting) for

23, 000 chemicals by Sept., 2006 under the Canadian Environmental Protection Act (CEPA)

• Europe

– Registration, Evaluation and Authorization of

Chemicals (REACH) (2007)

• Volume trigger and hazard based

• Consistency between Existing (n = 130, 000) and New Chemicals

Comparing U.S., Canada and EU

Approaches

U.S.

ChAMP

Canada Chemical Management Plan 2

EU REACH Registration & Authorization Candidate List

Announce Challenge

Notice to Obtain More Info

DSL Categorization/

Prioritization

500 High Priority Chemicals

Substance Profiles

Risk Assessments

Risk Management

Chemicals with Identified Info Needs

Registration Dossier

Registration Dossier

≥ 1,000 t ≥ 100 t ≥ 1 t

Registered (2008-2018)

2008 and Ongoing

2011

Evaluation Restriction

Candidate List

Authorization

2015 2013 2011 2009

2018 2013 2010

Starts in 2009

2006

2006

REACH New Chemicals

≥ 1 t

Pre-REACH Existing Chemicals in Commerce

≥ 1 t

1 DSL = Canadian Environmental Protection Act Domestic Substances List

2 Other aspects of the CMP are not shown on this figure.

1,000 t = 2.2 M lbs.; 100 t = 220k lbs.; 1 t = 2.2k lbs.

Current TSCA Inventory

Resetting

the Inventory

IUR Chemicals

Organics

SPP

Inorganics HPV Challenge

The Canadian Environmental

Protection Act (CEPA)

• Under CEPA ’88, assessments for specified numbers of Priority Substances (5 yr timeframe)

– N= 44 on Priority Substances List (PSL) 1

– N= 25 on PSL 2

– Risk management now implemented for most

considered “toxic” under CEPA

• CEPA ’99 extended our mandate to all Existing

Substances in Canada (n=23,000)

– Categorization of the Domestic Substances List (DSL)

by September, 2006 (priority setting),

– screening,

– full (Priority Substances) assessment

7

CATEGORIZATION of the

Domestic Substances List

(DSL) (First Phase) (n=23,000)

Decisions of Other Jurisdictions

Public Nominations

No further action under this

Greatest Potential

for Human Exposure

Substances that are Persistent or

Bioaccumulative

“Inherently Toxic”

to Humans

“Inherently Toxic” to non-Human Organisms

SCREENING ASSESSMENT (Second Phase)

CEPA 1999 Existing Substances Program

Simple and Complex Priority Setting Tools

EXPOSURE

Simple Exposure Tool (SimET) - Relative ranking of all DSL substances based on submitters

(S),quantity (Q) and expert ranked use (ERU)

Complex Exposure Tool (ComET) - Quantitative plausible maximum age-specific estimates of environmental and consumer exposure for individuals based on use scenario (sentinel

products), phys/chem properties & bioavailability

HAZARD

Simple Hazard Tool (SimHaz) - Identification of high or low hazard compounds by various

agencies based on weight of evidence and expert opinion/consensus

Complex Hazard Tool (ComHaz) - Hierarchical approach for multiple endpoints & data sources (e.g., (Q)SAR) including preliminary weight of evidence framework

Potential for exposure influential in setting priorities Included simple use profiling for all 23, 000 chemicals, more complex use

profiling for priorities

Registration, Evaluation, Authorization of

Chemicals (REACH) within Europe

• Registration of manufactured/imported chemical

substances > 1 tonne/year (Industry)

• Increased information and communication throughout the supply chain

• Evaluation of some registration dossiers (Agency & Member States)

• Authorisation for use of substances of very high

concern (CMR, PBT, vPvB, similar properties)

• Restrictions: “Safety net” (Can be initiated by

Member States and the Commission)

-> European Chemicals Agency to manage the

system

REACH Registration

Aim

• Manufacturers and importers (of substances and

substances in preparations) obtain/generate information

on their substances and

• Use this knowledge to ensure responsible and

well-informed management of the risks of chemicals

throughout their life cycle

– Communication in Safety Data Sheet

No formal acceptance - industry retains responsibility

REACH Registration

Dead-lines

By 2010:

- all substances >1000 tonne/yr

- All substances>1 tonne/yr & classified as

carcinogenic, mutagenic, reproductive toxins,

- All substances > 100 tonne/year & very toxic to the aquatic environment

By 2013:

- substances > 100 tonne/a

By 2018:

- substances > 1 tonne/a

Implications of Regulatory Developments to

Consider All Chemicals

• Need for increased efficiency in risk assessment

– Processing much larger numbers of

14

Physiologically Based Pharmacokinetic (PBPK) Models in Risk Assessment

• Estimating internal dose measures for extrapolation across species, groups, routes, doses, time & age

– Physiology (weights of organs and tissues and blood flows)

– Physical – chemical and biochemical

constants of the compounds

• “Verified” against experimental data

Rate of change = Input - Output (Krishnan and Andersen 2007)

16

Value of PBPK Models

• Increasing accuracy of risk estimates and understanding of uncertainty and

variability

• Help to interpret biomonitoring data

– X ug/L of chemical X in blood = ???? risk

for the individual or population

• Reducing reliance on animal testing

– Biologically meaningful quantitative

framework in which in vitro data can be

more effectively utilized

Computational (Predictive) Hazard Tools

• Increasingly, computerized analysis is being

• What are they?

Analogues

Structure Activity Analysis, (SAR)

Quantitative Structure Activity Analysis

(QSAR)

Analogue Tools and (Q)SARS

structures (for which there may be more data)

• Structure Activity Relationship Models

(SARS) predict toxicity based on structural fragments of substances believed to be

associated with toxicity (structural alerts)

• Quantitative structure activity relationship

structural parameters and/or physical chemical characteristics & toxicity

– E.g., electronic states, log Kow, etc

Predictive Hazard Tools

• How do they work?

– Based on databases of toxicological information

– Compare structures and physical/chemical

characteristics for chemical with data on their toxicity

to predict toxicity for “like” chemicals

• What helps?

– Automated analysis (software tools)

20

21

« The genotoxicity of quinones is associated with their ability to undergo enzymatic and non-enzymatic redox cycling

with their corresponding semiquinone radical [Bolton et al] As a result they generate superoxide anion radicals that

can be converted to powerfully oxidising hydroxyl radicals that can cause oxidative damage to DNA In addition … »

R9 R10 R11

R12 R18

R17

R15

R16 R14 R13

O

O

R1 R2 R3 R4

O

O

R5 R6

R7, R8 and R13 = O, S, N-R19 R14 = S, N-R19

Which Descriptors are Important to Distinguish

between Safe and Toxic Chemicals?

Safe?

O O

The Need for Combining Output of

Predictive Models

• Because we don’t know exactly which

characteristics best predict toxicity, we use

a combination of models

– “weight of evidence”

• Comprehensive, integrated judgment of

all relevant information supporting conclusions regarding potential toxicological effects

–Consistency, specificity, biological plausibility

24

How do Predictive Hazard Tools

Contribute?

• For human health-related effects, they contribute most in the consideration of cancer/genotoxicity data

– Wider range of supporting data from in vitro

studies of genotoxicity

– Some mechanistic basis (i.e., interaction with DNA)

25

Organization for Economic Co-operation and Development (Q)SAR Application Toolbox

• Improve accessibility of (Q)SAR methods

Example Questions in the (Q)SAR

Toolbox

• Is the chemical included in regulatory inventories or

existing chemical categories?

• Has the chemical already been assessed by other

agencies/organizations?

• Would you like to search for available data on

assessment endpoints for each chemical?

• Explore a chemical list for possible analogues using predefined, mechanistic, empiric (structural similarity) and custom built categorization schemes?

• Identify chemicals with analogous metabolism or toxic mechanisms?

• Group chemicals based on common metabolite?

27

"The Threshold of Toxicological

Concern”(TTC)

• Exposure level considered to present “negligible risk” for chemicals for which toxicological data are not available

–based on chemical structure and toxicity data (dose-response) for structurally related

chemicals for a range of endpoints

• Structure-activity analysis

–Includes a structure based decision tree but

no software tool, currently

28

The “TTC” (Threshold of Toxicological

Concept – “TTC”

DOSE 00

O

O Compound X – Unknown Toxicity

Compounds of same class included

in the Database

30

Group the compound into a class based on chemical characteristics

Predicts Dose-Reponse based on:

History of the TTC

• Introduced and used principally in the food area (regulatory use – mid 90’s)

– food contact materials

• US Food and Drug Administration (FDA)

• European Food Safety Agency (EFSA)

– flavouring agents

• Joint FAO/WHO Expert Committee on Food Additives (JECFA),

• Being considered for other areas

– E.g., industrial chemicals, food additives,

cosmetics and pesticides

31

TTCs for Different Chemical

Chemical with Structural

32

Threshold of Toxicological

Concern (TTC)

90 µg/day (0.15 mg/kg/d )

540 µg/day (0.90 mg/kg/d )

1800 µg/day (3 mg/kg/d)

Structural alerts for genotoxicity

or no data?: TTC=0.15 µg/day

5 th

NOEL/100 (mg/kg/day)

Exclusions to the TTC

TTC Cannot be Used for:

• Local (site of contact) and lung (via inhalation) effects

• Dermal irritation or sensitization

• Proteins / allergenicity

• Metals and metal containing compounds

• Compounds with structural alerts for high potency

carcinogenicity (must be evaluated separately)

• Compounds expected to be bioaccumulative (e.g.,

dioxins)

• Others

34

Application of the TTC - Steps

• 1 Check to see if one of the excluded

substances

• 2 Are there structural alerts for

genotoxicity?

• 3 What is estimated exposure?

• 4 To what class does the compound

belong?

– Decision tree

35

Limitations of the TTC

• Limited coverage/applicability domain

– Excluded chemicals and effects

• Database not large for certain types of chemicals

• Cumbersome

• Limited automation

• Relies on limited chemical descriptor

• Limited transparency

– Difficult to access the underlying database

• Potentially limited application

– TTC values are low

– Applicable to non hazardous chemicals such as

flavouring agents

36

ANY LOCAL BIOACTIVATION

- not reflected by plasma

INTERACTION WITH INTRACELLULAR TARGET(s)

INTRACELLULAR CHANGES

Combined Exposures

M.E (Bette) MeekMcLaughlin CentreUniversity of Ottawabmeek@uottawa.ca

39

Assess Data Quality Only Qualitative Assessment

Relative Potency Factors

Hazard Index

Response Addition

inadequate adequate

Whole Mixture

Sufficiently Similar Mixture

Mixture

of Concern

Group of Similar Mixtures

Components

Toxicologically Similar

Toxicologically Independent Interactions

Comparative Potency

Environmental Transformation

Assessment for Combined Exposures

State of the Art

Rm

r1

r2 r3

Rm

Dose Addition Independent Joint Action Interaction (> or <

dose addition)

40

x

Yes, no further action required

No, continue with iterative refinement as needed (i.e more complex exposure

& hazard models

Is the margin

of exposure adequate?

Tiered Exposure Assessments

Tiered Hazard Assessments

semi-Tier 1

Generic exposure scenarios using conservative point estimates

Tier 2

Tier 3

Probabilistic exposure estimates

Refined exposure assessment, increased use

of actual measured data

Tier 0

Default dose addition for all components

Tier 1

Refined potency based

on individual POD, refinement of POD

42

Nature of exposure?

Is exposure likely?

Co-exposure within a relevant timeframe?

Rationale for considering compounds in an assessment group?

Evolution of Toxicity Testing

M.E (Bette) MeekMcLaughlin CentreUniversity of Ottawabmeek@uottawa.ca

CRIBangkok

43

• Examines how the entire genome is involved in biological responses to environmental toxicants and stressors

• Combines information from mRNA profiling, cell

or tissue protein profiling, as a basis to better understand:

– mode of action

– genetic susceptibility

Mode of action information from gene profiling

Characteristic gene expression profiles induced by non- genotoxic

carcinogens liver after 5 or 7 days of treatment

Mode of Action – Integrating Genomic

Data - Conazoles

• Fungicides

– Used in agriculture and medicine

• Critical effects

– Thyroid tumours in rats

– Liver tumours in mice

• Similar mode of action hypothesized to lead to both types of tumours

• Toxicogenomic data help to identify mode of

action

48

Proposed Key Events

• Nuclear receptor activation (transcriptional

profile)

• Inhibition of Cyp 51 (site of action of fungicide)

• Altered mitosis (suggested by inhibition of

• Oxidative stress (transcriptional profile)

Note: Not DNA reactive (standard in vitro and in vivo

The Committee’s Vision

Toxicity Testing in the 21st Century:

A Vision and A Strategy

Final Report Released June 12, 2007

Evolution of Toxicity Testing

• Shift away away from adverse endpoints to early changes of toxicity pathways

• More extensive use of computational toxicology and high throughput in vitro screening tests

• Broadest coverage of chemicals, end points, life stages

• Fewest animals; least suffering per animal

• Lowest cost; least time

• Detailed mechanistic and dose information for

human health risk assessment

Inputs

Normal Biologic Function

Morbidity and Mortality

Cell Injury

Adaptive Stress Responses

Early Cellular Changes

Exposure Tissue Dose Biologic Interaction

Perturbation

Low Dose Higher Dose Higher yet

Toxicity Pathway: A cellular response pathway that, when sufficiently

affected (perturbed), is expected to result in an adverse health effect.