Insert Document Number
Insert Publication Date
External Review Draft
Strategic Plan for the Future of Toxicity
Testing at the U.S. Environmental
Protection Agency
NOTICE: THIS DOCUMENT IS A PRELIMINARY DRAFT. It has not been formally
released by the U.S. Environmental Protection Agency and should not at this stage be
construed to represent Agency policy. It is being circulated for comment.
Prepared for the U.S. Environmental Protection Agency by members of the Future of
Toxicity Testing Workgroup, a group of EPA's Science Policy Council
Office of the Science Advisor
Science Policy Council
U.S. Environmental Protection Agency
Washington, DC 20460
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DISCLAIMER
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use. Notwithstanding any use of mandatory language such as "must" and
"require" in this document with regard to or to reflect scientific practices, this document does not
and should not be construed to create any legal rights or requirements.
11
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Future of Toxicity Testing Workgroup
Workgroup Co-Chairs
Michael Firestone
Office of Children's Health and Environmental Education
Robert Kavlock
Office of Research and Development
Hal Zenick
Office of Research and Development
Science Policy Council Staff
Melissa Kramer
Office of the Science Advisor
Workgroup Representatives
Marcia Bailey, Region 10
Arden Calvert, Office of the Chief Financial Officer
Laurel Celeste, Office of General Counsel
Vicki Dellarco, Office of Pollution, Pesticides, and Toxic Substances
Scott Jenkins, Office of Air and Radiation
Gregory Miller, Office of Policy, Economics, and Innovation
Nicole Paquette, Office of Environmental Information
Santhini Ramasamy, Office of Water
William Sette, Office of Solid Waste and Emergency Response
Other Contributors
Katherine Anitole, OPPTS Thomas Knudsen, ORD
Hugh Barton, ORD Julian Preston, ORD
Norman Birchfield, OSA Kathleen Raffaele, OSA
Michael Brody, OCFO Ram Ramabhadran, ORD
Rory Conolly, ORD James Samet, ORD
David Dix, ORD Patricia Schmieder, ORD
Stephen Edwards, ORD Banalata Sen, OPPTS
Andrew Geller, ORD Imran Shah, ORD
Karen Hamernik, OPPTS Linda Sheldon, ORD
Jean Holmes, OPPTS John Vandenberg, ORD
Richard Judson, ORD Maurice Zeeman, OPPTS
in
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Table of Contents
LIST OF FIGURES V
LIST OF TABLES V
ACRONYMS VI
1. INTRODUCTION 1
2. REGULATORY APPLICATIONS AND IMPACTS 4
2.1 CHEMICAL SCREENING AND PRIORITIZATION 4
2.2 TOXICITY PATHWAY-BASED RISK ASSESSMENT 4
2.3 INSTITUTIONAL TRANSITION 5
3. TOXICITY PATHWAY IDENTIFICATION AND CHEMICAL SCREENING AND PRIORITIZATION 7
3.1 STRATEGIC GOAL 1: TOXICITY PATHWAY IDENTIFICATION AND ASSAY DEVELOPMENT 8
3.2 STRATEGIC GOAL 2: CHEMICAL PRIORITIZATION 9
4. TOXICITY PATHWAY-BASED RISK ASSESSMENT 10
4.1 STRATEGIC GOAL 3: TOXICITY PATHWAY KNOWLEDGEBASES 11
4.2 STRATEGIC GOAL4: VIRTUAL TISSUES, ORGANS, AND SYSTEMS: LINKING EXPOSURE, DOSIMETRY, AND
RESPONSE 12
4.3 STRATEGIC GOAL 5: HUMAN EVALUATION AND QUANTITATIVE RISK ASSESSMENT 14
5. INSTITUTIONAL TRANSITION 15
5.1 STRATEGIC GOAL 6: OPERATIONAL TRANSITION 15
5.2 STRATEGIC GOAL 7: ORGANIZATIONAL TRANSITION 17
5.3 STRATEGIC GOAL 8: OUTREACH 17
6. FUTURE STEPS 20
APPENDIX: OTHER RELATED ACTIVITIES 21
REFERENCES 24
IV
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LIST OF FIGURES
Figure 1. Toxicity Pathways 2
Figure 2. Toxicity Pathways Target Multiple Levels of Biological Organization 7
Figures. ToxCast™ 9
Figure 4. Toxicity Pathways to Dose-Response 10
Figure 5. Knowledgebase Development 12
Figure 6. Relative (%) emphasis of the three main components of this strategic plan over its
expected 20-year duration 20
LIST OF TABLES
Table 1. Strategic Plan: Applications and Impacts 10
v
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ACRONYMS
ACToR Aggregated Computational Toxicology Resource
FIFRA Federal Insecticide, Fungicide, and Rodenticide Act
FTTW Future of Toxicity Testing Workgroup
HTS High Through-put Screening
MO A Mode of Action
NRC National Research Council of the National Academies
QSAR Quantitative Structure-Activity Relationship
SAR Structure-Activity Relationships
VI
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1. INTRODUCTION
EPA bases its regulatory decisions on a wide range of tools and information that represent the best
available science. In some situations, where very limited or no animal toxicity data exist, EPA may
use tools such as structure-activity relationships (SAR) and quantitative structure-activity
relationship (QSAR) modeling, together with information on exposure to make decisions about
priority setting and the need for further evaluation (e.g., for new chemicals in the toxics program,
high production volume chemicals, and pesticide inerts). To establish regulatory standards, EPA
relies heavily on toxicity testing in experimental animal models. As such, toxicity testing and
related research is currently a multi-billion dollar activity that engages thousands of research
scientists, risk assessors, and risk managers throughout the world. To that end, the historical path
taken in toxicity testing of environmental agents has generally been either to make incremental
modifications to existing tests or to add additional tests to cover endpoints not previously
considered (e.g., developmental neurotoxicity). This approach has led over time to a continual
increase in the number of tests, cost of testing, use of laboratory animals, and time to develop and
review the resulting data. Moreover, the application of current toxicity testing and risk assessment
approaches to meet existing, and evolving, regulatory needs has encountered challenges in
accommodating increasingly complex issues (e.g., life-stage sensitivity, mixtures, varying
exposure scenarios, cumulative risk, understanding mechanisms of toxicity and their implications
in assessing dose-response, and characterization of uncertainty)1.
While the challenges of such information gaps are great, the explosion of new scientific tools in
computational, informational, and molecular sciences offers great promise to address these
challenges and greatly strengthen toxicity testing and risk assessment approaches. Proven benefits
have been demonstrated in allied fields such as medicine and pharmaceuticals. Although untapped,
the potential application to toxicity testing and risk assessment has also been recognized by EPA as
witnessed by the issuance of a series of papers that provided guidance on the use of genomic data.2
To better anticipate the potential contribution of new technologies and scientific advances to issues
associated with toxicity testing and risk assessment, EPA commissioned the National Research
Council (NRC) in 2004 to review existing strategies (NRC, 2006) and develop a long range vision
for toxicity testing and risk assessment (NRC, 2007). In the subsequent release of Toxicity Testing
in the 21st Century: a Vision and a Strategy a landmark transformation in toxicity testing and risk
assessment is envisioned that focuses on "toxicity pathways."3 This approach is based on the
rapidly evolving scientific understanding of how genes, proteins, and small molecules interact to
form molecular pathways that maintain cell function. The goal is to determine how exposure to
environmental agents can perturb these pathways causing a cascade of subsequent key events
leading to adverse health effects. This sequence of events is illustrated in Figure 1 wherein the
1 These limitations have been described more fully in .4 Review of the Reference Dose and Reference Concentration
Processes: http://www.epa.gov/ncea/iris/RFD_FINAL[l].pdf
2 Interim Policy on Genomics (2002): http://www.epa.gov/osa/spc/genomics.htm: Genomics White Paper (2004):
http://www.epa.gov/osa/pdfs/EPA-Genomics-White-Paper.pdf: Interim Guidance for Microarray-Based Assays
(2007): http://www.epa.gov/osa/spc/pdfs/epa interim guidance for microarrav-based assavs-external-
review draftpdf.
3 Toxicity pathways are cellular response pathways that, when sufficiently perturbed, are expected to result in
adverse health effects.
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introduction of an environmental stressor may trigger such a cascade. Successful application of
these new scientific tools and approaches will inform and produce more credible decision-making
with an increased efficiency in design and costs and a reduction in animal usage.
Other agencies have also recognized
the need for this transformative shift,
including the National Institute for
Environmental Health Sciences' in
their Roadmap for the Future and the
Food and Drug Administration in
their Critical Path Program. In
anticipating the emergence, and
potential, of this new scientific
paradigm, ORD and some of EPA's
regulatory programs have also begun
to redirect resources in intramural
and extramural research programs to
"jump start" the process of
transformation. For example, ORD
created the National Center for
Computational Toxicology4 in 2006
and reoriented research being
conducted under several of its
multiyear research plans.
Recognizing the need to partner to
Biologic
Inputs
Source
Fate/Transport
Exposure
Tissue Dose
*
Biologic Interaction
Perturbation
Toxicity Pathways: Cellular
response pathways that,
when su fficien tly
perturbed, are expected
to result in adverse health
effects.
Adaptive Stress
Responses
Morbidity
and
Mortality
Modfied from NRC, 2007
Figure 1. Toxicity Pathways. Toxicity pathways describe the
processes by which perturbations of normal biological processes due
to exposure to a stressor (e.g., chemical) produce changes sufficient
to lead to cell injury and subsequent events (modified from NRC,
2007).
achieve the vision and goals laid out by the NRC, EPA recently signed a Memorandum of
Understanding for research cooperation with the National Toxicology Program and the National
Institutes of Health Chemical Genomics Center as a substantive step forward in building
collaborations across sister Federal agencies.5 EPA is also working actively at the international
level with programs such as the Organization for Economic Cooperation and Development
(OECD) through the Molecular Screening Initiative, the Integrated Approaches for Testing and
Assessment Workgroup, Test Guideline Committees, and the QSAR Expert Group to ensure
global harmonization of any new approach that originates from the research program. A more
complete listing of these collaborations may be found in Appendix 1.
In response to the release of the NRC reports, EPA has established a cross-Agency workgroup,
the Future of Toxicity Testing Workgroup (FTTW), under the auspices of the Science Policy
Council. The FTTW has produced this current document, a Strategic Plan for the Future of
Toxicity Testing at EPA, which will serve as a blueprint for ensuring a leadership role for EPA in
pursuing the directions and recommendations presented in the NRC report. In this document, a
strategy is presented that is consistent with the NRC directions and recommendations and that
will advance the ability of the Agency to incorporate this new science paradigm into toxicity
4 Computational toxicology is the application of mathematical and computer models and molecular biological
approaches to improve the Agency's prioritization of data requirements and risk assessments (from A Framework
for a Computational Toxicology Research Program, EPA 600/R-03/065).
5 http://www.epa.gov/comptox/articles/comptox_mou.html
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testing and risk assessment practices. The topics to be covered include (1) the applications and
impacts/benefits for various types of regulatory activities (Section II), (2) the research to be
conducted to facilitate the screening and prioritization of environmental agents (Section III), (3)
the implementation of a toxicity pathway-based approach to risk assessment (Section IV), and
(4) the critical companion component, namely, the institutional transition that must occur before
the changes can be fully implemented (Section V).
As described in Section VI, the workgroup recognizes that the full implementation of the vision
set out in this strategy will require a significant investment of resources over a long period of
time. While the workgroup has identified a range of partners in this effort and some planning on
the relative role of these partners has been developed, the specific areas of work to be
conducted/funded by EPA versus these other partners needs to be further assessed. Decisions on
these relative roles will have a significant impact on EPA resources required to implement the
vision.
Since the NRC charge and report centered on advancing toxicity testing for assessing human
health effects of environmental agents, this strategic plan is presented primarily within that
context. However, under environmental legislative mandates (e.g., the Toxic Substances Control
Act; the Federal Insecticide, Fungicide, and Rodenticide Act; and the Clean Water Act), most
EPA programs must regulate compounds to ensure both environmental and human health risks
are properly managed. Since statutory language and/or resulting policy typically require single
regulatory decisions for a chemical(s) that encompass environmental and human health risks at
the same time, accelerated and cost effective approaches for both areas are critical to realize
programmatic benefits. As in the human health arena, development and application of
approaches described in this strategy apply to ecotoxicology and risk assessment as well. Notable
progress is being made within EPA laboratories on the development and use of toxicity pathway
models and the creation of prioritization schemes, toxicology knowledgebases, and systems
biology models in the field of environmental science. The bringing together of relevant
disciplines to share data and integrate models is critical to fully achieve increased efficiency in
toxicity testing and a reduction in animal usage for both human health and environmental risk
assessment. Consequently, the Agency will be implementing this strategy in a manner that
addresses both human health and ecological risk assessment. Future versions of the strategy will
summarize progress made in advancing integrated testing and assessment capability and revisit
remaining challenges.
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2. REGULATORY APPLICATIONS AND IMPACTS
The research arising from implementation of this strategy will change the nature of the methods,
models, and data that will inform the major components of the risk assessment process (i.e.,
hazard identification, dose response, exposure assessment, and risk characterization). Without
attempting to be all-inclusive, Table 1 presents some of the major cross-office applications and
impacts of these new scientific approaches, with more in-depth discussion of the planned work
described in Sections III-V. The three components of this strategic plan, namely, Chemical
Screening and Prioritization, Toxicity Pathway-Based Risk Assessment, and Institutional
Transition, are not independent elements but rather highly interactive and integrative efforts that
will maximize the value and application of the research generated.
2.1. Chemical Screening and Prioritization
An ongoing need of several regulatory offices is to have tools to assist in chemical screening and
prioritization, e.g., high production volume chemicals, air toxics, the drinking water Contaminant
Candidate Lists, and Superfund chemicals. These programs consider anticipated exposure and
hazard to select chemicals to evaluate in longer-term, whole-animal laboratory studies. An early
use for data developed under the new paradigm will be as an efficient and cost effective screen
for several types of chemical toxicity. Thus, risk assessors could use in silico (computer-based)
technologies and structure/molecular/bioactivity profiling from diagnostic high-throughput/m
vitro assays, along with predicted exposure/dose information, to predict chemicals most likely to
cause hazards of concern for humans. This approach will also enable risk assessors to determine
the specific effects, in vivo data, and exposures that would be most useful to assess, quantify, and
manage. As the technology develops, the Agency will be able to screen previously untested
chemicals using libraries of chemical, molecular, biological, and toxicological data and models
to produce a list of chemicals based on the types of adverse effects that they are most likely to
produce in standard animal bioassays.
2.2. Toxicity Pathway-Based Risk Assessment
The current approach to risk assessment includes uncertainties associated with (1) the human
relevance of laboratory animal studies (species extrapolation), (2) the use of high doses in
animals to estimate risk associated with lower environmental/ambient exposures (dose
extrapolation), and (3) predicting the risk to susceptible populations. In recent years, the
consideration of such issues has been better informed by the incorporation of information on
potential modes of action through which toxicity may be expressed. The approach outlined
earlier in Figure 1 focuses on perturbations in baseline biological processes that may lead down
toxicity pathways to adverse health outcome(s). Combining this information with distributional
data on population characteristics of exposure and dose (magnitude, frequency, and duration)
provides a scientifically based approach for reducing the uncertainties associated with current
risk assessments.
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Table 1. Strategic Plan: Applications and Impacts
Toxicity Pathway
Identification and
Chemical Screening &
Priori tization
Toxicity Pathway-Based Risk Assessment
Institutional Transition
01
=
Need to screen 10,000's
of chemicals for wide
range of endpoints in a
manner that considers
mechanistic knowledge
and the potential for
human exposure.
For many chemicals, the current approach
relies on expensive animal testing that takes
time to conduct and review. Limitations in the
design of in vivo studies often prevent
complete evaluation of all endpoints and
hazard/risk scenarios of concern.
Limited understanding of biological
mechanisms most often leads to uncertainty in
the interpretation of results when considering
cumulative risk or when extrapolating in vitro
to in vivo or across doses, life stages, species,
or genetic diversity.
Implementing the new approach will
require significant institutional investment
in operational and organizational transition
and in public outreach.
O>
Need to limit cost and
animal usage, improve
timeliness, and decrease
uncertainty in testing
decisions
New scientific understanding and tools in
molecular, computational, and information
sciences with a proven track record in allied
areas such as medicine and Pharmaceuticals
represent a path forward.
EPA lacks appropriate expertise and
sufficient funding to fully and most
efficiently utilize the new toxicity testing
technologies when making regulatory
decisions, especially with respect to
understanding life stage and genetic
susceptibility.
03
o.
I
Z
Identification of toxicity
pathways for key
toxicological endpoints.
Combine in silica and
bioprofiles from HTS6
along w/ QSAR
approaches linked to
animal study data.
Reliance on increased understanding of how
perturbations of biological processes at
environmentally relevant concentrations
trigger events (i.e., toxicity pathway(s)) that
may lead to adverse health outcomes.
Develop linked exposure/dose models to
inform dosing levels for toxicity testing and
inform risks.
Fully adopting the new paradigm should
be supported by mechanistically based
proof-of-concept and verification studies.
Further, such adoption will require training
of existing staff and hiring new staff
conversant in state-of-the-science
knowledge in fields such as toxicology,
biochemistry, bioinformatics, etc.
03
O.
Offices would be better
able to direct efforts and
resources to chemicals
with greatest potential
risk. Significant increase
in efficiency with marked
reduction in cost for
testing by EPA or others.
Less reliance on the types of extrapolations
and associated uncertainties incorporated
currently into EPA risk assessments. The
uncertainty associated with EPA's regulatory
decisions and/or impact analyses that rely on
these risk assessments will also be decreased.
A well informed public will have greater
confidence as EPA greatly expands the
number of chemicals assessed for possible
risks and improves existing strategies for
hazard and risk assessment!
2.3. Institutional Transition
Implementing major changes in toxicity testing of environmental contaminants and incorporating
new types of toxicity data into risk assessment will require significant institutional change:
6 High-Throughput Screening (HTS) refers to robotic technologies developed by the pharmaceutical industry for
drug development that enable the ability to evaluate the effects of hundreds to thousands of chemicals per day on
molecular, biochemical or cellular processes.
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• Operational transition - how EPA will transition to the use of new types of data and
models for toxicity testing and risk assessment;
• Organizational transition - how EPA will deploy resources necessary to implement the
new toxicity testing paradigm such as hiring of scientists with particular scientific
expertise and training of existing scientific staff;
• Outreach - efforts by EPA to share information with the public and improve risk
communication.
The process of moving from research to regulatory acceptance for implementing new science
related to toxicity testing will be an iterative and long-term effort (likely encompassing more
than a decade). Essential to this iterative process will be the demonstration that the predictive
nature of these new approaches is superior to that of our current practices for toxicity testing and
risk assessment. It will be critical to begin activities geared toward regulatory acceptance early in
the process of implementing this strategic plan.
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3. TOXICITY PATHWAY IDENTIFICATION AND CHEMICAL SCREENING
AND PRIORITIZATION
The advancements in biotechnology brought about by the sequencing of the human genome and
the investment in high throughput screening tools to mine large chemical libraries for potential
drugs have for the first time allowed a broad scale, unbiased examination of the molecular and
cellular targets of chemicals. At this time, the examination of the relationships between the
molecular and cellular targets of chemicals and the traditional endpoints of toxicity is at an early
stage of development. Even upon characterization of these types of relationships, significant
phenotypic data will be required to critically establish the role of toxicity pathways in evaluating
hazards and risks. The great potential is that identification of a toxicity pathway and
development of an in vitro bioassay for studying its chemical interactions will enable evaluation
of the effects of thousands of chemicals in that pathway. Broadening this approach to the many
toxicity pathways present in living systems allows a new avenue for identifying those chemicals
that pose the greatest potential hazard. Knowledge of the toxicity pathways triggered by any one
chemical will also allow targeting of specific in vivo tests to more fully characterize the potential
hazard and risk. The identification of toxicity pathways for key target tissues, organs, and
lifestages, and their linkage across levels of biological organization and exposure pathways and
intensities are core elements of this strategy.
As indicated in Figure 2, chemicals may interact with a single pathway (the blue chemical) or
multiple pathways (the yellow chemical). Also, multiple pathways can lead to the same
expression of toxicity in the target organ as signaling pathways converge on common elements.
It is important to note that multiple
modes of action (MOAs)7 for any
particular adverse response likely
exist, and that many environmental
pollutants are likely to have multiple
MO As. Two critical components of
the toxicity pathway concept are (1)
extending knowledge of molecular
perturbations and cell signaling
pathways to understand linkages
between levels of biological
organization and (2) extending
knowledge of in vitro markers to
understand in vivo markers and adverse outcomes (see Section V). Demonstration of plausible
connectivity along the MOA from initiating event to adverse outcome will serve as the rationale
for using data from subcellular or cell-based in vitro assays (e.g., receptor binding, enzyme
inhibition, etc.) in prioritizing chemicals for testing in more complex, time-consuming, and
costly assays as well as in predictive computer modeling. As toxicity pathways are identified,
relevant in vitro assays can be utilized and their results compared to in vivo studies as appropriate
given the need to predict effects in humans or other species. Mixtures or their components could
Receptors / Enzymes / etc.
Direct Molecular Interaction
Pathway Regulation /
Genomics
Cellular Processes
Tissue / Organ / Organism Tox Endpoint
Figure 2. Toxicity Pathways Target Multiple Levels of
Biological Organization.
Mode of Action (MOA) is defined as a sequence of key events and processes, starting with interaction of an agent
with a cell, proceeding through operational and anatomical changes, and resulting in an adverse health effect.
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be evaluated in this manner, and as knowledge grows, it will be possible to predict where
interaction with multiple toxicity pathways might be expected to lead to non-additive outcomes.
Therefore, the research described here focuses on two major strategic goals:
1) Identification of toxicity pathways and deployment of in vitro assays to characterize the
ability of chemicals to perturb those pathways in different biological contexts, and
2) Implementation of ToxCast , with an initial focus on providing input for chemical
prioritization, shifting over time to providing input for dose-response modeling.
Exposure science also plays a large role in this strategy. Simple and reliable screening models
are needed that predict exposures to chemicals so that information from the full source-to-
outcome continuum is brought into consideration in the evaluation of chemicals. Models should
evaluate exposure based on the life cycle of intended product use and the physical-chemical
properties of the chemicals. This research includes the expansion of computational chemistry
methods to predict exposures as well as methods to predict release into the environment during
product life cycle. Several screening-level models are currently under development in Canada
and Europe. Research in this area should be coordinated with these groups to facilitate an
international approach for chemical screening.
3.1. Strategic Goal 1: Toxicity Pathway Identification and Assay Development
The most systematic and extensive approach currently underway for screening and prioritization
is EPA's ToxCast™.8 Fully implementing the proposed strategy for more efficient toxicity testing
will utilize a combination of the more exploratory ToxCast chemical signature approach (see
Strategic Goal 2), and the more hypothesis-driven approaches to elucidating toxicity pathways.
Developing systems-based models will require comprehensive identification of the biological
processes that can result in toxicity when they are perturbed by chemical exposures. Therefore,
toxicity pathway identification and development of appropriate in vitro assays to characterize the
dose-response and time course of perturbations to those pathways will be needed. Measurement
of chemical form and concentration from in vitro assays will also be important in hypothesis-
driven research that seeks to establish linkages between perturbations of toxicity pathways and
adverse effects, as well as for establishing structure-activity relationships. These research goals
will utilize a range of methods (e.g., transcriptomic, proteomic, metabolomic, cellular, and
biochemical analyses) to identify toxicity pathways using in vivo and in vitro systems. The in
vitro assays and toxicity pathways already included in the ToxCast™ project will be a part of this
research, but additional assays providing greater coverage of relevant toxicity pathways will
need to be developed. For example, developmental neurotoxicity key responses are known to
include cell proliferation, apoptosis, differentiation (into different cell types and creating
different functionality/architecture of a cell), neurite outgrowth, synaptogenesis, and myelination
(Coeke et a/., 2007, Lien et a/., 2007), but the underlying molecular pathways are not yet
completely identified. Through the informed use of newer 'systems-based' approaches (Edwards
& Preston, 2008), the flow of molecular regulatory information underlying the control of these
cellular events can be characterized, classified, and modeled. To facilitate use in risk assessment,
these studies should be coupled with MOA-based studies, including animal and human
components as described in Strategic Goal 4.
1 http://www.epa.gov/comptox/toxcast/
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Current priorities for research include developing in vitro assays for the key targets of
environmental chemicals for which limited knowledge is available (e.g., developmental
neurotoxicity, immunotoxicity, reproductive toxicity) as well as for relatively well-characterized
toxicity pathways such as stress response signaling. Comparative approaches using samples from
a range of species, including rodents (or other species used in toxicity testing), humans, and
proposed alternative species (e.g., Danio rerio, zebrafish) could be valuable. In addition, studies
representative of the full range of human variability will be necessary to characterize processes
that may occur more readily in sensitive populations (e.g., asthmatics) or at certain life stages
(e.g., prenatal development). Additional emphasis needs to be placed on toxicities demonstrated
to occur in humans. For example, clinical trials or post-marketing surveillance for
Pharmaceuticals sometimes find effects that are not currently well assessed by in vivo animal
toxicity studies, and some of these pathways may be important for environmental chemicals with
respect to human variability or exposure to complex mixtures.
3.2. Strategic Goal 2: Chemical Prioritization
This strategy extends approaches that are currently under development for EPA's ToxCast
program to include greater coverage of toxicity pathways and chemicals. The goal of the
ToxCast™ program is to provide a comprehensive assessment of toxicity pathways for a
relatively low cost per chemical (current estimates are in range of $15-20,000). ToxCast (see
Figure 3) was designed to collect data from a wide range of in vitro assays, mostly mechanistic
in nature, to prioritize which
chemicals to test further and which '"wfrotesting '" s"'coanalysis
in vivo studies were likely most * •••••••
important. This screening and , ]
prioritization approach provides a = & !•••! ^^^
near-term benefit during an "J""
extended transition to the more HTS Bioinf
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4. TOXICITY PATHWAY-BASED RISK ASSESSMENT
The goals of the proposed new strategy for toxicity testing include collecting mechanistic data,
largely in vitro, for the purpose of predicting human risk from exposure to chemicals. Prediction
of in vivo effects in humans requires a combination of measurements and computer modeling to
link in vitro responses to tissue dosimetry to alterations in the structure and function of tissues
and organs. A substantial challenge will be to address the range of human variability arising from
differences in age, life stage, genetics, disease susceptibility, epigenetics, diet, disease status, and
other factors that potentially influence or interact with toxicity pathways.
The initial process for predicting human risk under this new approach could be summarized as
(1) characterizing or predicting potential human exposures, (2) estimating the resulting chemical
dosimetry (magnitude, frequency, and duration) for target pathways, tissues or organs, (3)
measuring toxicity pathway response at doses consistent with human exposures, (4) predicting
the in vivo human response resulting from pathway perturbations, (5) quantifying of the range of
human variability and susceptibility, and (6) validating predictions utilizing in vivo systems (e.g.,
laboratory animals, human data). The current state of the science of toxicity evaluation is
depicted in the top row of Figure 4. Following administration of the chemical to the test animal
Envi nan mental
Chemicals
Mo le cu la r
Sensing
Cellular
Signaling
Tissue
Responses
Knowledgebase
Toxicity
Path ways
Molecular
Networks
Cellular
Networks
Virtual
Tissues
Dose-Response
Figure 4. Toxicity Pathways to Dose-Response. The vertical arrows at each step in the process reflect the
iterative nature of experimentation and modeling needed to gain full understanding of both the toxicity pathway
determination and the relationship to normal biology.
(usually at high doses), genomic approaches are used to detect alterations in molecular pathways,
the data are mined to describe the ensuing cellular alterations (e.g., oxidative stress damage,
mitochondrial dysfunction), and tissue changes are confirmed at the level of morphology or
10
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function. It is important that increased emphasis be placed on examination of exposure
concentrations that are more reflective of real-world condition. This traditional approach to
toxicity testing will continue into the foreseeable future, but it will be augmented by
computational models (up to the level of virtual tissues) that integrate the information into
predictive models of response based upon the underlying biology (the bottom row in Figure 4).
The vertical arrows at each step in the process reflect the iterative nature of experimentation and
modeling needed to gain full understanding of both the toxicity pathway determination and the
relationship to unperturbed biology.
The key difference in future toxicity evaluations will be the transition to a focus on ways in
which molecular pathways (as detected by in vitro models) are perturbed by chemical exposure
throughout the range of exposures from environmental to the higher dose levels commonly used
in contemporary toxicity studies. Dosimetry measurements coupled with computational
modeling will be critical for predicting in vivo exposure levels of concern and for determining
relevant in vitro concentrations. Some responses of targeted toxicity pathways can be evaluated
in simpler cell culture models, whereas, in other cases, multiple in vitro assays may be necessary
for the integration of multiple pathways that produce in vivo responses. These situations would
require biologically based models for the responses as well as for chemical dosimetry in order to
predict the integrated in vivo response.
Implementing this new paradigm requires organization of existing scientific information;
computational methods for exposure, chemical dosimetry, and perturbations of biological
processes; and evaluation of the methods for risk assessment applications. The research program
to implement this element of the strategy is defined by three goals: development of toxicity
pathway and exposure knowledgebases; development of virtual tissues, organs, and systems; and
evaluation of human relevance.
4.1. Strategic Goal 3: Toxicity Pathway Knowledgebases
The 2007 NRC report postulates that there is a finite number of toxicity pathways (i.e., in the
hundreds) that could be queried using in vitro assays to obtain insights into the ability of
chemicals to perturb those pathways. It refers to several stress pathways (e.g., oxidative stress
response) and notes the general listing of signaling pathways in a previous NRC report (2006).
However, an inventory of toxicity pathways and their involvement in a variety of toxicological
responses needs to be created. Likewise, from exposure science there needs to be a
complementary effort focusing on those chemical properties and computational methods that
could be used to reliably predict behaviors in the environment and exposures. This effort would
include information on stability in the environment, likely routes for exposure, potential for
bioaccumulation, and extent of metabolism. Therefore, a strategic goal is the development of a
knowledgebase for toxicity pathways and exposure. Knowledgebases differ from traditional
databases in the extent of integration of information and the inclusion of tools that can draw
inferences from amongst the diverse elements.
The knowledgebase would serve a variety of functions throughout the research and development
effort associated with implementing this new approach to toxicity testing and will become a
standard tool in the risk assessments of the future. ACToR (Figure 5), the Aggregated
Computational Toxicology Resource under development in ORD, is an example of the needed
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ACToR API
Chemical ID.
Chemical structure
Tabular Dala.
Links to Web
Resources
Specialized Toxicology Databases
Biological
Reference
Data
Data Mining
Figure 5. Knowledgebase Development. ACToR brings together a diverse set of
currently unlinked resources available from internal and external sources into a
system with a user friendly interface to readily mine and analyze toxicity data.
approach of bringing
together diverse types of
information into a system
where interrelationships
of individual database
elements (e.g., traditional
toxicology, chemical
structure information,
high throughput screening
data, molecular pathway
analysis, chemical data
repositories, peer
reviewed published
literature, and internal
Agency databases) can be
explored and utilized. Key steps in development of these knowledgebases include: (1) creating
electronic repositories of existing toxicity information; (2) developing semantics for describing
toxicity pathways; (3) automating pathway inference tools to aid in discovering mechanistic links
between genomic information and molecular and cellular observations; (4) creating a toolbox
with a user-friendly interface to organize, access, and analyze toxicity pathway assay results.
4.2. Strategic Goal 4: Virtual Tissues, Organs, and Systems: Linking Exposure,
Dosimetry, and Response
Computational techniques relevant to this strategy fall into two general branches: knowledge-
discovery (data-collection, mining, and analysis) represented in Strategic Goal 3, and dynamic
computer simulation (mathematical modeling at various levels of detail) described in this
section. The central premise of the latter approach is that critical effects of environmental agents
on molecular-, cellular-, tissue-, and organ-level pathways can be captured by computational
models that focus on the flow of molecular regulatory information (Knudsen & Kavlock, 2008).
This information flow is influenced by genetic and environmental signals, with the net outcome
being the emergent properties associated with baseline or abnormal collective cell behavior.
Thus, computational systems modelling will be used to predict organ injury due to chemical
exposure by simulating: (1) the dynamics and characteristics of exposure and dose, (2) the
dynamics of perturbed molecular pathways, (3) their linkage with processes leading to alterations
of cell state, and (4) the integration of the molecular and cellular responses into a physiological
tissue model. By placing a strong emphasis on understanding the biology of the system and the
key regulatory components, these virtual tissue models represent a significant opportunity to
better understand the linkage between chemically induced alterations in toxicity pathways and
effects at the organ level. This research represents an ambitious effort, conceivable for the first
time due to the current technological advances. Virtual tissue and organ system models will
initially include liver, cardiopulmonary function, selected immune system tissues, multi-organ
endocrine axes, and developing embryonic tissues. Development of these virtual tissue and organ
systems will require newly generated data across phylogenetic systems to both fill data gaps
identified within the iterative process and test the predictive nature of these virtual systems.
Comparative studies should include pathways fundamentally reliant upon cell signaling (e.g., cell
proliferation, apoptosis, cell adhesion), intermediary metabolism (e.g., glycolysis, oxygen
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utilization, fatty acid biosynthesis), differentiation-specific functions (e.g., extracellular matrix
remodeling), and other categories as developed above (see Strategic Goal 1) to ensure that
predictions are broadly applicable. The wealth of existing data from NTP assays, published
reports, and previous EPA intramural studies will be leveraged wherever possible with additional
experiments designed to fill data gaps. Such efforts will also help answer how well in vitro
experimental systems represent the full range of diverse cells present in the human body, how
variability observed in the human population can modify quantitative predictions of in vivo dose-
response, how exposure conditions influence outcomes, and how well the virtual tissue models
represent the underlying processes.
Not all toxicity pathways are likely to be expressed in every tissue, and likewise not all tissues
are likely to manifest adverse outcomes following chemical perturbation. Some toxicities are
manifest only when multiple cell types and specific cell-cell interactions are present. Other
toxicities may be dependent upon tissue geometry and three-dimensional architecture. Examples
include signaling between hepatocytes and Kupffer cells, or the many forms of signaling
between epithelial and mesenchymal cells. As such, developers of virtual cells, tissues, organs,
and systems must always bear in mind the need to remain relevant to the processes critical to
expressions of toxicity in vivo. This translates to a continued role over the foreseeable future for
in vivo systems in the development of this research strategy and implementation.
A premise of the new toxicity testing strategy is that computational methods combined with an
understanding of biological and exposure processes can be used to develop a more efficient and
accurate approach for predicting risks from many chemicals. On the exposure side, models have
been developed and are available that predict fate and transport, environmental concentration,
exposures, and doses. These models work at multiple scales; for multiple sources, routes, and
pathways; and for multiple chemicals, although each model only addresses a single process or
compartment. Research is needed to combine these models across various scales to develop a
linked source-to-outcome modeling framework, to evaluate the framework using multiple
chemicals and exposure scenarios, and to improve the computational efficiency for the approach.
Ultimately, these exposure models will be linked to the virtual tissue models for utilizing in vitro
toxicity test results in quantitative risk assessments. Given the complexity of the challenges
present in addressing each of these components, this effort represents a long-term goal of the
strategy. However, efforts must begin now to put us on the path to achieving the ultimate vision
of Toxicity Testing in the 21st Century.
The derived computational models must accurately describe the processes and mechanisms that
determine exposure and effect. They must have reliable input parameters in order to quantify
these processes. On the exposure side, our current understanding of processes and factors for
many classes of chemicals and pathways (i.e., dermal and incidental ingestion) is limited. New
approaches will be evaluated that will allow us to address the most significant uncertainties.
Relational databases populated with data on exposures, exposure factors, activity patterns, and
biomarkers will be developed as described. Informatic approaches or applications of network
theory could potentially be used to provide a better understanding of important exposures, as
well as exposure/response relationships. In the 2007 NRC report, emphasis was placed on
biomarkers and their role in relating real world exposure to in vivo and in vitro biological
response. They were also proposed as primary indicators in surveillance programs for tracking
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predicted exposures and health outcomes. Because of this emphasis, novel approaches for using
biomarkers and integrating them into new risk assessment approaches will be investigated.
4.3. Strategic Goal 5: Human Evaluation and Quantitative Risk Assessment
The critical challenge of this new vision for toxicity testing using mechanistic in vitro assays,
targeted in vivo testing, and computational models is to demonstrate that it successfully and
adequately predicts human toxicological responses. Proof of concept efforts need to address this
challenge both retrospectively and prospectively. Existing human data from pharmaceutical and
environmental studies will be used to the extent possible. Human data could come from a range
of sources including case reports, epidemiological studies (e.g., from the National Children's
Study), and clinical trials. EPA has extensive experience obtaining human clinical data following
exposure to the criteria air pollutants (e.g., ozone, particulate matter) and other chemicals (e.g.,
MTBE). Engagement of the pharmaceutical industry and the Food and Drug Administration to
access toxicity findings from clinical trials of drugs that were successfully registered or that
failed to be registered would be a desirable component of this effort. Limited data may be
available for some nutrients or dietary supplements as well.
Such efforts will help address the question of the extent to which "key events" that are predictive
of ultimate endpoints (whether cancer or immunosuppression or kidney disease) must be
demonstrated or whether the perturbation of baseline biological processes sufficient to induce
substantial cellular level response (e.g., a stress response) should be considered an adequate
endpoint for risk assessment. Linking a specific pathway perturbation to a particular target organ
endpoint has the advantage of predicting outcomes that are already used in risk assessment,
while alternative approaches raise issues of which endpoints should and should not be considered
for risk assessment. This approach is relatively straightforward for some effects (e.g., hemolysis
of red blood cells by EGBE, where the effect and the mode of action leading to it are
qualitatively the same, even if quantitatively different). Linkage is more complicated for effects
observed in animals that may predict human effects that are related, but not identical to, the
outcomes in animals (e.g., developmental effects in an animal model may predict developmental
effects in humans, but the exact manifestation might be different). Cleary this aspect will need to
be addressed on a case-by-case basis as we gain experience.
To be useful in evaluation of risk to humans, the pathway-based efforts must be tied to a known
mode of action, preferably via the use of quantitative biologically based, dose-response models.
Understanding of the relevant mode of action will enable the identification of bioindicators for
key event parameters (linked to toxicity pathways) that can be monitored in human studies.
These bioindicators could be measured in observational human studies to provide in vivo data to
support the underlying pathway-based model. In addition, genetic susceptibility in humans
identified via whole genome association studies will provide support for pathway-based models
when genes critical for a key toxicity pathway are associated with susceptibility. Finally, the use
of quantitative models requires estimation of uncertainty and variability in the predictions from
in vitro assays and computational models. Formal methods for model evaluation are essential for
demonstrating the success of this new approach to toxicity testing and risk assessment.
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5. INSTITUTIONAL TRANSITION
Implementing major changes in toxicity testing of environmental contaminants and incorporating
new types of toxicity data into risk assessment will require significant institutional changes. This
section will touch upon three major thrusts of implementing institutional transition: operational
transition; organizational transition; and outreach.
5.1. Strategic Goal 6: Operational Transition
Operational transition covers the technical aspects associated with EPA's implementation of a
new toxicity testing paradigm and associated changes in risk assessment. It will consider such
disparate topics as the importance of grounding the science, working with outside partners and
issues associated with the use of new models and tools.
The NRC "envision[s] a future in which tests based on human cell systems can serve as better
models of human biologic responses than apical studies in different species." Achieving such a
future however will require substantial research to study and define various toxicity pathways. In
evaluating various possible options for the future of toxicity testing, the NRC eventually choose
an option (Option III) involving both in vitro and in vivo tests but based primarily upon human
biology and the attendant use of substantially fewer animal studies that would be focused on
mechanism and metabolism. Their vision for the next 10 to 20 years relies on understanding
perturbations of critical cellular responses and the use of computational approaches for assessing
hazard and risk.
Although it is infeasible to denote a specific timeline for how long it will take to substantially
complete the strategic goals associated with toxicity pathway identification, chemical screening
and prioritization, and toxicity pathway-based risk assessment, this plan takes the view that
advances are likely to be gradual over the next decade or two. The good news is that toxicity
testing research efforts have already begun moving EPA and others towards the use of in silico
technologies and high throughput testing systems. The speed at which we are able to complete
this transition will depend on the availability of increased research funding. It is important to
note that our understanding of toxicity pathways for some apical endpoints (e.g. hepatotoxicity)
may be developed at a faster pace than others (e.g., neurotoxicity) thus, allowing more rapid
introduction of newer high-throughput in vitro testing methods.
Grounding the Science - From a broad regulatory perspective, data used by EPA to support
regulatory decisions will be shaped by the statutory language covering the action, regulatory
policies, and the resulting time and resources allocated to the assessment. Use of data must also
be consistent with the EPA guidance articulated in a number of science policy and guidance
documents. These include toxicity test guidelines, risk assessment guidelines9, information
quality guidelines10, and peer review guidance.11
To implement this new paradigm, regulators, stakeholders, and the public will need to develop
confidence that the data generated can be used effectively and that public health will continue to
9 http://www.epa.gov/risk/guidance.htm
10 http://www.epa.gov/quality/informationguidelines/
11 http://www.epa.gov/peerreview/pdfs/Peer%20Review%20HandbookMay06.pdf
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be protected. A step-wise implementation is envisioned: first, experience will be gained from
proof of concept studies using data from chemicals (e.g., pesticides) with a large set of toxicity
data developed using the current paradigm. Availability of both new and traditional types of data
will allow extrapolation and comparison of results across methodologies guided by the existing
MO A framework with toxicity pathways linked to a key event-based description of the MOA.
Optimally, early success stories that meet programmatic needs in specific areas such as MOA
analyses or cumulative risk assessments will demonstrate the broader applicability of
computational toxicology within the Agency. Reliability of the testing paradigm will need to be
evaluated via a comprehensive development and review process, involving public comment,
harmonization with other agencies and international organizations, and peer review by experts in
the field. Bringing new methods into regulatory practice will require several phases starting from
the development of the science and technologies, to technology transfer and building the
regulatory infrastructure, to incorporation of the new tools into decision making.
Because this transformative paradigm will rely on new and complex science and will likely be
surrounded by some controversy, an important part of regulatory acceptance will be to conduct
research that will verify the approaches and models that will come to replace much of the way
toxicity testing and risk assessments are conducted in the Agency today. An important
component of the effort to develop new approaches to testing will be to translate the research
into regulatory applications.
Issues Associated With the Use of New Methods and Models - For this new paradigm to be
successful, new methods and models should be thoroughly evaluated prior to their application
and use in regulatory decision making. The computer-based models used by the Agency should
be publicly available. Testing methods should be accompanied by documentation that describes
(1) the method and its theoretical basis, (2) the techniques used to verify that the method is
accurate, and (3) the process used to evaluate whether the method and the results are sufficient to
provide an adequate basis for its use in regulatory decision making. Access to data to allow for
third party independent replication of results, to the extent practicable, is essential. Such review
is appropriate before the Agency relies on data from such a method.12
Working With Outside Partners -Appendix 1 provides details about the many outside parties
EPA will need to partner with in order to implement this strategic plan including:
• Other Federal bodies such as the National Toxicology Program (NTP) and the NIH
Chemical Genomics Center (NCGC), with whom EPA has a memorandum of
understanding to collaborate;
• The Interagency Coordinating Committee on the Validation of Alternative Methods
(ICCVAM), which is made up of representatives from 15 Federal agencies that generate
or use toxicological data;
• Foreign governmental parties and programs such as REACH, which is the new European
Union Regulation on Registration, Evaluation, Authorization, and Restriction of
Chemicals that went into effect June 1, 2007;
12 See http://epa.gov/crem/library/CREMguidancedraftl2_03.pdf
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• The OECD (Organization for Economic Co-Operation and Development), which
represents over 30 countries in the Americas, Europe and Asia;
• Academia;
• Chemical industry; and
• Non-governmental organizations.
Case Study Development - Significant challenges, such as interpretation and communication of
data obtained using new toxicity testing approaches, will emerge under a new paradigm for
toxicity testing. A key feature of a successful communication strategy will be to develop case
studies using new kinds of data that can serve as a basis to explore, evaluate, and most
importantly explain hazard, dose-response, and exposure information in a risk assessment
framework. Characterization of risk information, both qualitative and quantitative, in a manner
suitable for communication to risk managers will be a significant challenge for the research and
risk assessment community, but it will be crucial if the new toxicity testing paradigm is to reach
its potential.
5.2. Strategic Goal 7: Organizational Transition
Organizational transition is meant to cover changes in direction over time with regard to
deployment of resources necessary to implement the new toxicity testing paradigm such as hiring
of scientists with particular scientific expertise and training of existing scientific staff.
As noted in Section II, several intra-agency, interagency, and international activities are already
underway to begin the transformation that will change the nature of toxicity data generated and
how it is used to assess chemically induced risks to human health. Substantial funding will be
needed to provide the scientific basis for creating new testing tools; to develop and standardize
data-storage, data-access, and data-management systems; to evaluate predictive power for
humans; and to improve the understanding of the implications of test results and how they can be
applied in risk assessments used in environmental decision-making.
5.3. Strategic Goal 8: Outreach
Outreach consists of those efforts that will be used to help educate the public and stakeholders as
well as improve risk communication.
In reaching out to the public, it will be important to re-emphasize points made by then EPA
Administrator Carol Browner, in a 1995 memorandum to senior agency staff about the agency's
policy related to its new Risk Characterization Program. This memorandum described the
importance of adhering to the "core values of transparency, clarity, consistency, and
reasonableness (which) need to guide each of us in our day-to-day work; from the toxicologist
reviewing the individual (scientific) study, to the exposure and risk assessors, to the risk
manager, and through to the ultimate decision-maker." Further, "because transparency in
decision-making and clarity in communication will likely lead to more outside questioning of our
assumptions and science policies, we must be more vigilant about ensuring that our core
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assumptions and science policies are consistent and comparable across programs, well grounded
in science, and that they fall within a 'zone of reasonableness.'"
13
Stakeholder Involvement - Implementation of a paradigm shift in toxicity testing and related
changes to risk assessment methods and practices will require a sustained effort over many years
- remember that the NRC envisioned some ten to twenty years to reach their goal. This transition
to new methods and approaches will need to be transparent, including efforts to share
information with both the public and risk managers. It will be critical to effectively communicate
with stakeholders (scientists, Federal and state agencies, industry, the mass media,
nongovernmental organizations) about the new tools and the overall program regarding its
strengths, limitations, and uncertainties. One way to enhance stakeholder involvement and ensure
cooperation is to hold periodic workshops where all parties can gather to share information and
progress; another tool is for EPA to establish a web portal to detail advancements in the science
and relate these to improvements in risk assessment methods and practice.
Collaboration among different elements in the research community involved in relevant research
on new testing approaches will be needed to take advantage of the new knowledge, technologies,
and analytical tools as they are developed, and collaboration between research and regulatory
scientists will be vital to ensure that the methods developed can be reliably used in risk
assessments of various types (initially qualitative, but ultimately both qualitative and
quantitative). Mechanisms for ensuring sustained communication and collaboration, such as data
sharing, will also be needed. Independent review and evaluation of the new toxicity testing
paradigm should be conducted to provide advice for midcourse corrections, weigh progress,
evaluate new and emerging methods, and make any necessary refinements in light of new
scientific challenges/advances. This may be accomplished using existing EPA mechanisms for
peer review, e.g., through reviews by the Board of Scientific Counselors, the Science Advisory
Board, and the FIFRA Scientific Advisory Panel. For testing that the Agency may wish to
require, performance standards should be considered so that individual methods from any
qualified source may be used.
Risk Communication - Communicating with policy makers and the public is an important part
of any risk management exercise. The complexity of the emerging toxicity testing paradigm and
how new types of data and information will be used to assess risk will make communication of
results challenging; consequently, the Agency must work to build public trust in the adopted
technologies. As the science moves away from well-established animal models, a significant
effort must be made to share information with risk assessors/managers and the public by clearly
describing test results and methodologies in a transparent manner. A fundamental aspect of
gaining public trust is transparency. Therefore, education and effective communication with
stakeholders (scientists, regulatory authorities, industry, the mass media, and nongovernmental
organizations) on the strengths, limitations, and uncertainties of the new tools/paradigm will be
critical.
Given that these new methods will be less intuitive than looking for traditional effects in whole
animal studies, communication strategies will be very important. At this time, much of EPA's
effort in this area is presented on the Agency's National Center for Computational Toxicology
13 http://www.epa.gov/oswer/riskassessment/pdf/1995_0521_risk_characterization_program.pdf
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website.14 As the new toxicity testing paradigm continues to evolve, the Agency will need to be
vigilant in maintaining an interactive website to describe each individual assay or method in use
and where it fits into the exposure-response continuum.
When communicating about risk, it is important for the agency to address the source, cause,
variability, uncertainty, and the potential adversity of the risks, including the degree of
confidence in the risk assessment methodology, the rationale for the risk management decision,
and the options for reducing risk (U.S. EPA, 1995; U.S. EPA, 1998). EPA will continue to
interact with stakeholders in order to develop and maintain effective informational tools.
14 National Center for Computational Toxicology (NCCT)
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6. FUTURE STEPS
This strategic plan describes an ambitious and substantive change in the process by which
chemicals are evaluated for the toxicity. The NRC (2007) suggested that such a transformation
would require up to $100M per year in funding over a 10-20 period to have a reasonable chance
of reaching the goals. Even including the resources of sister Agencies, the overall Federal budget
for the collaborative efforts does not approach the NRC proposed level of funding. Decision on
the relative role of EPA vis-a-vis other partners will have a major impact on the resources that
EPA needs to dedicate to this effort. These decisions will have to be made as the strategy is
implemented. Explanation of these decisions, their rationale, and implications will be included in
a subsequent implementation plan.
Regardless of whatever level of funding is ultimately applied to the vision of a more efficient and
effective chemical safety evaluation effort, translation of this strategy into research and activities
related to operational and organizational change will require development of an implementation
plan as well as periodic peer review of directions and progress. Representatives from those EPA
organizations most involved and impacted by the new vision will play key roles in the
implementation program. The Science Advisory Board and/or the Board of Scientific Counselors
will play key roles in the scientific peer review of the program. As noted in Section IV, there will
be a progression in the
implementation efforts from an
early focus on hazard
identification to a growing
emphasis on the use of toxicity
pathway characterization in risk
assessment. Support for
institutional transitions is also
expected to increase over time as
the tools and technologies
emerge out of the research
programs and become available
for regulatory use. Figure 6
depicts one potential way that the
— Screening/Prioritization
— Toxicity Pathways in
Risk Assessment
Institutional Transition
2010
2015 2020
Year
2025
level of effort of the three main
activities involved in this strategy
could change over time.
Figure 6. Relative (%) emphasis of the three main components of
this strategic plan over its expected 20-year duration.
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APPENDIX: OTHER RELATED ACTIVITIES
Other US Government Activities
The National Toxicology Program (NTP) at the National Institute of Environmental Health
Sciences (NIEHS) coordinates toxicological testing programs within the Department of Health
and Human Services15. Similar to EPA, NTP is developing the use of computational models, in
vitro assays, and non-mammalian in vivo assays targeting key pathways, molecular events, or
processes linked to disease or injury for incorporation into a transformed chemical testing
paradigm.
The NIH Chemical Genomics Center (NCGC) of the National Human Genome Research
Institute conducts ultra high throughput screening assays as part of the NIH's Molecular
Libraries Initiative within the NIH Roadmap
A Memorandum of Understanding16 was recently signed by EPA, the NTP, and the NCGC to
collaborate on generating a comprehensive map of the biological pathways affected by
environmental chemical exposures and use this map to predict how potential chemical toxicants
will affect various types of cells, tissues, and individuals. The hope is to refine many of the
toxicity tests performed on animals and eventually supplant them with in vitro testing and
computational prediction (Collins etal., 2008).
In 2004 the Food and Drug Administration (FDA) produced a report17 addressing the need to
translate the rapid advances in basic biomedical sciences into new preventions, treatments and
cures. FDA holds large databases of human, animal, and in vitro data for screening drug
candidates for toxicity that may also be useful for screening environmental chemicals. The
FDA's National Center for Toxicological Research (NCTR) aims to develop methods for the
analysis and integration of genomic, transcriptomic, proteomic, and metabolomic data to
elucidate mechanisms of toxicity18. NCTR has coordinated the Microarray Quality Control
(MAQC) project, with numerous partners including EPA (Shi et al., 2006). In addition, NCTR
has provided its Array Track database to EPA for storage of genomics data for research and
possible regulatory use.
The Interagency Coordinating Committee on the Validation of Alternative Methods
(ICCVAM) was established by law in 2000 to promote development, validation, and regulatory
acceptance of alternative safety testing methods. ICCVAM is made up of representatives from 15
Federal agencies that generate or use toxicological data. Emphasis is on alternative methods that
will reduce, refine, and/or replace the use of animals in testing while maintaining and promoting
scientific quality and the protection of human health and the environment19. The NTP
Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM)
administers and provides scientific support for ICCVAM. ICCVAM/NICEATM evaluates test
method submissions and nominations, prepares technical review documents, and organizes
15 http://ntp.mehs.mh.gov/ntp/mainjages/NTPVision.pdf
16 http://www.epa.gov/ncct/articles/comptox mou.html:
17 http://69.20.19.211/oc/initiatives/criticalpath/whitepaper.html
18 http://www.fda.gov/nctr/overview/mission.htm
19 http://iccvam.niehs.nih.gov/about/ni QA.htm
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scientific workshops and peer review meetings. For example, ICCVAM/NICEATM recently
.20
released a report that describes two in vitro cytotoxicity tests that can be used for estimating
starting doses for acute oral toxicity tests, thereby reducing the number of animals used.
Related Activities by Foreign Governments
A new European Union regulation on Registration, Evaluation, Authorization, and
Restriction of CHemicals (REACH) went into effect June 1, 2007. The main goals of REACH
are (1) to improve the protection of human health and the environment from risks associated with
chemicals in commerce and (2) to promote alternative test methods. REACH requires
manufacturers and importers to demonstrate they have appropriately identified and managed the
risks of substances produced or imported in quantities of one ton or more per year per company.
The new European Chemicals Agency (ECHA)21 will manage the system databases, coordinate
evaluation of chemicals, and run a public database of hazard information22.
The European Centre for the Validation of Alternative Methods (ECVAM)23 coordinates
the validation of alternative test methods in the European Union. ECVAM develops, maintains,
and manages a database on alternative procedures and promotes the development, validation, and
international recognition of alternative test methods.
The Korean Center for the Validation of Alternative Methods (KoCVAM) is a branch of
NITR, the National Institute of Toxicological Research. NITR is collaborating with the Korean
Society for Alternatives to Animal Experiments (KSAAE) to refine methods in acute oral,
reproductive/development, genetic, and endocrine toxicity testing24.
The Organization for Economic Co-Operation and Development (OECD) represents 30
countries in the Americas (including the United States), Europe, and Asia. The OECD
"Guidelines for the Testing of Chemicals" provides a collection of internationally harmonized
testing methods for a number of toxicological endpoints using in vivo, in vitro, and even
alternative approaches.25 Test guidelines can be updated to reflect scientific advances and the
state of the science if member countries agree to do so. A few OECD workgroups and efforts
address issues relevant to this EPA strategy, e.g., the OECD QSAR Toolbox26 and the joint
OECD/IPCS (International Programme for Chemical Safety) Toxicogenomics Working Group,
which has developed a proposal for a Molecular Screening Project, modeled after EPA's
ToxCast program.
Academia
Numerous U.S. academic researchers and centers are funded by NIH or EPA's National Center
for Environmental Research to develop assays and analysis methods that might be helpful to the
20 http://iccvam.niehs.nih.gov/methods/acutetox/inv nrutmer.htm
21 http://echa.europa.eu/reach eahtml
22 http://ec.europa.eu/environment/chemicals/reach/reach intro.htm
23 http://ecvam.jrc.cec.eu.int/index.htm
24 http://wwwsoc.nii.ac.jp/isaae/PARK.pdf
25 http://titania.sourceoecd.org/vl=856000/cl=23/nw=l/rpsv/periodical/pl5 about.htm?jnlissn=1607310x
26 http://www.oecd.Org/document/23/0.3343.en 2649 37465 33957015 1 1 1 37465.00.html
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goals of this EPA research strategy. This includes two Bioinformatics Centers funded by EPA in
2006.
The European Commission funds several large academic, government, and industry consortia
that are conducting research that could lead to effective in vitro toxicity tests. The CASCADE
Network of Excellence27 studies human health effects of chemical residues and contaminants in
food and drinking water, designing assays to elucidate estrogen, testosterone, and thyroid
hormone pathways for the development of mechanism- and disease-based test methods. The aim
of the carcinoGENOMICS28 project is to develop in vitro methods for assessing the
carcinogenic potential of compounds. ReProTect29 is optimizing an integrated set of
reproductive/developmental tests for a detailed understanding of gametogenesis, steroidogenesis,
and embryogenesis that can support regulatory decisions.
Industry
The European Partnership for Alternative Approaches to Animal Testing (EPAA)30 is a
joint initiative from the European Commission and a number of companies and trade federations.
Its purpose is to promote the development of alternative approaches to safety testing. The EPAA
focuses on mapping existing research; developing new alternative approaches and strategies; and
promoting communication, education, validation, and acceptance of alternative approaches.
Non-Governmental Organizations (NGOs)
The Johns Hopkins Center for Alternatives to Animal Testing31 supports the creation,
development, validation, and use of alternatives to animals in research, product safety testing,
and education. Similarly, AltTox.org32 provides information on non-animal methods for toxicity
testing including a table33 that summarizes the alternative testing methods by endpoint that have
been approved or endorsed internationally by at least one regulatory agency.
27 http://www.cascadenet.org/
28 http://www.carcinogenomics.eu/
29 http://www.reprotect.eu/
30 http://ec.europa.eu/enterprise/epaa/index en.htm
31 http://altweb.jhsph.edu/index.htm
32 http://www.alttox.org/about/
33 http://www.alttox.org/ttrc/validation-ra/validated-ra-methods.html
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