The University of North Carolina
at Chapel Hill
Toxicology 207: Advanced Toxicology
Regulatory Aspects of
Developmental and Reproductive Toxicology
Rochelle W. Tyl, Ph.D., DABT
Senior Fellow
Developmental and Reproductive Toxicology
(DART)
Senior Director, DART Studies
RTI International
Research Triangle Park, NC
(e-mail: rwt@rti.org)
Monday, December 4, 2006
9:00 - 9:50 a.m.
2304 McGavran-Greenberg
1
Regulated Materials
1.
U.S. FDA (Food and Drug Administration)
a.
Food additives (preservatives, dyes, etc.)
b.
Vitamins (not "natural products")
c.
Food substitutes
i.
Fat substitutes
ii.
Artificial sweeteners
d.
Pharmaceuticals
e.
Veterinary pharmaceuticals
f.
Food use pesticides
g.
Food use chemicals (chemical wrapping, artificial sausage skins, etc.)
h.
Medical devices
NOTE: Attention to mechanism, disease state, clinical trials (IND, NDA)
2.
U.S. EPA (Environmental Protection Agency)
a.
U.S. FIFRA (Federal Insecticide, Fungicide and Rodenticide Act)
i.
Pesticides
ii.
Food use pesticides
iii.
Biological pesticides (e.g., "BT" - Bacillus thuringensis)
iv.
Biochemical pesticides
v.
Engineered plants (transgenic plants make pesticides)
NOTE: Attention to nontarget species, environmental migration (contamination) (registration,
re-registration)
b.
U.S. TSCA (Toxic Substances Control Act)
i.
Commodity chemicals
--
ii.
paints, paint thinners, inks, plasticizers, plastics, medical supplies,
PVC piping, solvents, carpets, car parts, etc.
Options
--
test rules
--
negotiated test agreement
--
voluntary submissions/programs
(e.g., HPV [High Production Volume] initiative)
NOTE: Minimal information required for PMN, SNUR; EPA has 90 days to respond
2
Drug Discovery and Development
(NIDA TR&D Preclinical Workshop, 6/20/00)
Typical Toxicity Studies and Costs Per Compound
A.
Basic Acute Studies for Initial Review
1.
Acute iv range-find in rats
$12,000
2.
Acute oral (po) range-find in rats
12,000
3.
Definitive oral (po) study
35,000
4.
14-day, range-find in rats
75,000
5.
16-day MTD and 14-day fixed dose study in dogs
80,000
6.
Ames assay (mutagenicity/carcinogenicity)
3,000
TOTAL
B.
$217,000
Additional Studies for IND
1.
28-day study in rats with two-week recovery
$80,000
2.
28-day study in dogs with two-week recovery
200,000
3.
Battery of three mutagenicity studies
100,000
4.
Cardiovascular study with cpd alone in dog
45,000
5.
GI motility and renal tests in rats
25,000
6.
Acute drug interactions between cpd and (e.g., cocaine, ethanol, morphine)
in rodents
110,000
Cardiovascular interaction between cpd and (e.g., cocaine) in unrestrained dogs
350,000
7.
TOTAL
C.
$945,000
Studies to Go to Phase IIa
1.
Segment II in rats
$90,000
2.
Segment II in rabbits
110,300
TOTAL
D.
$200,000
Studies to Initiate NDA
1.
90-day study in rats
$218,000
2.
90-day study in dogs
400,000
TOTAL
E.
$618,000
Studies to Complete NDA
1.
Segment I and III reproduction in rats
$348,000
2.
One-year study in dogs
639,000
3.
Two-year carcinogenicity study in rats
980,000
4.
Two-year carcinogenicity study in mice
980,000
TOTAL
$2,947,000
GRAND TOTAL
$5,545,000
3
New Millenium Drug Discovery and Development
(NIDA Div. Treatment, Research, and Development: Preclinical Workshop, 6/20/00)
Off Patent
Patent
Target
Hit
Lead
SAC
Proj.
Structure Activity
Correlations
HTS
In Silico
Combinational
Safety and PK Testing
Libraries
"Computational Toxicology"
Chem/Phys/PK Properties
In Vitro
SAC
Tox and PK
Carcinogenicity Predictions
Testing
"e - R&D"
IND
NDA
Investigational
New Drug
Application
New Drug
To
Market
$$
Phase IV
Preclinical
Safety/PK
Postmarketing
Surveillance
In Vivo
Efficacy/Toxicity
Pharmacoeconomics
Safety
Phase
In Vitro
I
In Vivo
Healthy
Volunteers
Pharmacology
Earlier Failures
and
Improved SACs
Microarrays
Pharmacogenomics
Proteomics
Time:
8-13 years
Cost:
$350-600 M
OTC
II
III
Pilot
Clinical
Patients
Trials
$$
4
5
Developmental Toxicity Testing
Soon after the thalidomide disaster in the late 1950s and early 1960s, the U.S.
FDA assumed regulatory responsibilities for requiring specific testing paradigms "for the
appraisal of safety of new drugs for use during pregnancy and in women of childbearing
potential.”1. A letter was sent from the Chief of the Drug Review Branch, U.S. FDA, to
all corporate medical directors,1 establishing what became known as the Guidelines for
Reproductive Studies for Safety Evaluation of Drugs for Human Use. These guidelines
(Figure 1) encompassed three test intervals: Phase I (Segment I), with prebreeding and
mating exposures, to provide information on possible effects on breeding, fertility,
implantation, pre- and postimplantation development (Figure 1A); Phase II (Segment II),
with exposures during major organogenesis, to provide information on possible effects
on in utero survival and morphological growth and development, including teratogenesis
(Figure 1B); and Phase III (Segment III), with exposures from the onset of the fetal
period through weaning of the offspring, to provide information on parturition, lactation,
late intrauterine (fetal) and postnatal growth and development, puberty, and
reproductive function of F1 offspring (Figure 1C).
The procedures for Segment II
studies have essentially been followed by the U.S. EPA, 2,3,4 Japan,5 Canada,6 Great
Britain,7 and the OECD.8
6
Figure 1. FDA Segment I, II, and III Studies
A. SEGMENT I: FERTILITY STUDY
G
PBE - 28-70 days
Q
M - 14 days
F0 Males
gd 0
gd 7
gd 13-15
N
F0 Females and
F1 Litters
PBE - 14 days
Q
F0 Females
EC
N
F0 Males
Information on: breeding, fertility, nidation, and pre- and postimplantation development
B. SEGMENT II: DEVELOPMENTAL TOXICITY STUDY
G
gd 0
gd 6
gd 15
N gd 17-18 (mice) or 20-21 (rats)
Q M
rodent females
gd 6-15
G
gd 0
gd 6-7
gd 18-19
N gd 29-30
Q M
rabbit females
Information on: maternal toxicity, embryotoxicity, fetotoxicity, teratogenicity
C. SEGMENT III: PERINATAL AND POSTNATAL STUDY
G
Q
L
W
M
F0 females
G
gd
0
gd or
6
gd
15
parturition
(pnd 0)
PWHP (F1)
pnd 21
DL
VP
PPS
L
M
EC
F1 females
gd 0
pnd 0
N
F2 pups
pnd 4
N F1 males
and females
N
F0 females
Information on: maternal toxicity, in utero growth and development, parturition, lactation, postnatal growth and
development, puberty, reproductive functions of offspring
Direct exposure to adults
No exposure
Q = Quarantine
M = Mating
G = Gestation
gd = gestational day
L = Lactation
W = Wean
N = Necropsy
pnd = postnatal day
PBE = Prebreed exposure period
DL = Developmental landmarks
VP = Acquisition of vaginal patency
PPS = Acquisition of preputial separation
EC = Estrous cyclicity (for F0 females in Segment I and F1 females in Segment III)
PWHP = Postwean holding period (minimum 49 days; F1 offspring at least 70 days old at end of period)
7
Recently, attempts have been made to make testing guidelines for reproductive
and developmental toxicity studies consistent among major nations. The International
Conference on Harmonization (ICH), representing the U.S. (FDA), the European
Community (EC), and Japan, has promulgated testing guidelines for registering
pharmaceuticals within the three regions.9 They are similar to the original FDA guidelines
and assess exposure during prebreeding, mating, and gestation, until implantation on
gestational day 6 (Study 4.1.1), exposures from implantation to weaning (Study 4.1.2),
exposures only during organogenesis (Study 4.1.3), and combined single and two-study
designs. ICH Study 4.1.3 is, in fact, identical to the U.S. FDA Segment II study, and ICH
Study 4.1.2 is similar to the U.S. FDA Segment III study, except that exposures start at
the beginning of organogenesis instead of at the end.
Draft guidelines 10 and final
guidelines17 from the U.S. EPA, OPPTS (Office of Prevention, Pesticides and Toxic
Substances) for developmental toxicity studies have also recently been promulgated, and
the U.S. EPA TSCA Final Guidelines15. The U.S. FDA19 and OECD21 have also recently
revised their guidelines.
The Segment II study had traditionally been termed a “teratology study,” since the
initial focus was on structural malformations (terata). It is currently more appropriately
termed a “developmental toxicity study,” as it evaluates (and the term "developmental
toxicity" encompasses) a spectrum of possible in utero outcomes for the conceptus,
including death, malformations, deficits (usually functional), and developmental delays. It
is important to note that a Segment II Study evaluates only structural growth and
development of offspring and only during in utero development. The parameters assayed
are fetal body weights and the appearance of external, visceral, and skeletal structures.
For example, if the organs are the right size, shape, and color, and in the correct location,
they are judged to be normal.
There is no assessment for microscopic integrity or
function and no way to assess functional effects that might have occurred (or become
evident) during postnatal life if the fetuses had been born (these concerns are addressed
by different testing paradigms).
A comparison of the old and new testing guidelines for developmental toxicity
assessment is as follows.
8
Differences Between Old and New Developmental Toxicity Test Guidelines
MATERNAL ENDPOINTS
Event/Parameter
Previous Requirementsa
Current Requirementsb
Maternal Evaluations
Assignment to dose group
Not specified
Assignment by a body weight
dependent random procedure
Definition of high dose level
Should induce some overt
maternal toxicity, but not more
than 10% maternal deaths
Should induce developmental and/or
maternal toxicity, but not more than
10% maternal deaths
Test substance
administration: period of
dosing
During the major period of
organogenesis: days 6-15 in
rodents and 6-18 (or 7-19 FIFRA)
in rabbits
Dose from implantation through
termination (days 6-20 or 21 in rats,
6-17 or 18 in mice, and 6-29 or 30 in
rabbits): option to begin on GD 0;
ICH retains original dosing period21
Test substance
administration: dose
adjustment
Dosage based upon the body
weight at the start of test
substance administration or
adjusted periodically by body
weight
Dosage adjusted periodically
throughout the period of
administration by body weight
Number of pregnant
animals at termination
(presumed pregnant
animals assigned to study)
Rodents: 20 per group
Rabbits: 12 per group
Rodents and rabbits: 20 litters per
group (females with implantation
sites at termination)
Maternal postmortem data:
ovarian corpora lutea
counts
Data required for all species
except mice (TSCA only)
Data required for all species
(including mice)
Rodents: Assignment of
fetuses for evaluation
One-third to one-half of each litter
assigned for skeletal evaluation,
the remainder for visceral
evaluation
One-half of each litter assigned for
skeletal evaluation, the remainder for
visceral evaluation
Rabbits: Coronal sectioning
Not required
Required (50% serial sections,
50% coronal sections)
Ossified and cartilaginous
skeletal evaluation
Only ossified specified (alizarin red
S stain)
Both ossified and cartilaginous
skeletal examination required
(unspecified method of staining;
usually alizarin red S for ossified
bone and alcian blue for
cartilaginous bone and other
structures), all species
Fetal Evaluations
a Requirement under FIFRA, TSCA, and FDA
b OPPTS (EPA TSCA and FIFRA) Draft Guidelines, Public Draft, February 1996, and Final Guidelines
“Prenatal Developmental Toxicity Study OPPTS 870.3700”, TSCA Final Guidelines 799.9370 (August
15, 1997), FDA Guidelines
9
All previous governmental testing guidelines specified exposure beginning after
implantation is complete and continuing until the completion of major organogenesis. This
corresponds to gd 6 through 15 for rodents and gd 6 through 18 (FDA and TSCA) or gd 7
through 19 (FIFRA) for rabbits, if the day of impregnation is designated gd 0. In a departure
from the previous guidelines, recently released draft10 and final17,19 developmental toxicity
testing guidelines specify exposure during the entire gestational period, from gd 0 through
scheduled sacrifice at term or from gd 6 to term.
The rationale for starting exposures after implantation is complete is based on two
possible confounding scenarios:
1.
If the initial (parent) test material is teratogenic and the metabolite(s) is not, and if
metabolism is induced by exposure to the parent compound, then exposure beginning
earlier than implantation (with concomitant induction of enzymes and enhanced
metabolism) will result in the conceptuses being exposed to less of the teratogenic moiety,
and the study may be falsely negative.
2.
If the test chemical and/or metabolites interferes with implantation, then exposure prior to
implantation will result in few or no conceptuses available for examination11.
However, there are situations when initiation of exposure should begin prior to completion
of implantation. These include:
1.
For exposure regimens that are anticipated to result in slow systemic absorption; e.g.,
cutaneous application, subcutaneous insertion, or dosing via feed or water, steady-state,
maximal blood levels may not be attained until the very end (or beyond) of organogenesis
if exposures begin on gd 6 or 7.
2.
For materials which are known to have accumulative toxicity (due to build-up of chemical
and/or insult) after repeated exposures, exposure should begin on gd 0 (or earlier) so that
the conceptuses are developing in a fully affected dam.
3.
For materials, which are known to deplete essential components, such as vitamins,
minerals, cofactors, etc., exposures should begin early enough so that the dam is in a
depleted state by the start of organogenesis (or by gd 0).
4.
For materials, which are innocuous as the parent chemical but which are metabolized to
teratogenic forms, exposures should begin early enough so that postimplantation
conceptuses are exposed to maximal levels of the teratogenic metabolites.
5.
For materials which are known not to interfere with pre-implantation growth and
development or with implantation11.
10
The termination of exposures was specified as the end of major organogenesis. It is
signaled by the closure of the secondary palate and the change in designation of the conceptus
from embryo to fetus. The cessation of exposure allows for a postexposure recovery period for
both the dam and the fetuses, and an assessment can be made regarding whether the observed
maternal effects (body weights, clinical observations) are transient or permanent. However, fetal
evaluations generally take place at term, and there is no commonly employed way to detect early
adverse effects on the conceptus that resolve (are repaired or compensated for) earlier in
gestation. What is observed at term is the net result of the original insult and any repair or
compensation that occurred subsequently in the conceptus, and a detailed evaluation of the dam
after a post-exposure period (i.e., no detailed information of the dam during the exposure period).
In addition, exposure until term includes the period of male fetal reproductive system
differentiation in utero which begins on gd 13-14 in rodents so possible endocrine disrupters may
be detected. These considerations may be the basis for the requirement in the new U.S. EPA
OPPTS draft10 and final,17 and the U.S. FDA19 and OECD21 final developmental toxicity testing
guidelines (Figure 2) for exposure continuing until terminal sacrifice. 11 Interestingly, the recent
ICH testing guidelines9 have retained the maternal exposures only during major organogenesis.
11
Figure 2. New U.S. EPA, OECD, and FDA Prenatal Developmental Toxicity
(“Segment II”) Study Exposure Durations
OPPTS 1996 Draft Guidelines; Final Guidelines, 1998 (870.3700); and TSCA Final Test
Guidelines, 1997 (799.9370); U.S. FDA Guidelines (2000); OECD Guidelines
G
GD 0
Q
GD 6
M
N
GD 17-18 (mice)
GD 20-21 (rats)
GD 29-30 (rabbits)
N fetuses
at term
OR
G
GD 0
Q
GD 6
M
N
GD 17-18 (mice)
GD 20-21 (rats)
GD 29-30 (rabbits)
N fetuses
at term
Key:
Q = Quarantine
M = Mating
G = Gestation
N = Necropsy
GD = gestational day
Direct exposure of dams/does
Possible indirect exposure of conceptuses via
transplacental transfer of parent compound and/
or metabolites
No exposure
12
Figure 3. ICH Study Designs
A.
Study of Fertility and Early Embryonic Development (4.1.1), Rodent (see Phase I)
F0 males
PBE
Q
4 weeks
F0 females
G
Q
M
GD 0 GD 6
GD 15
GD 20
3 weeks
N
F0 males
OR
N
N
F0 females
F0 females
Assess: Maturation of gametes, mating behavior, fertility, preimplantation, implantation
B.
Study for Effects on Prenatal and Postnatal Development, Including Maternal Function
(4.1.2), Rodent (see Phase III)
G
Q M
GD
0
L
W
selected F1 pups
M G
pnd
4
N
L
F1 females
and F2 litters
pnd 21
GD
6
parturition
pnd 0
Assess:
N
F0 females
N
F1 males
Toxicity relative to nonpregnant females, prenatal and postnatal
development of offspring, growth and development of offspring, functional deficits (behavior,
maturation, reproduction)
C.
Study for Effects on Embryo-Fetal Development (4.1.3), Rodent and
Nonrodent (see Phase II)
G
GD 0
Q M
N F0 females and F1 litters on GD 20
GD
6
GD
15
Assess: Toxicity relative to nonpregnant females, embryo/fetal death, altered growth of
offspring, and structural changes of offspring in utero
13
FIGURE 3 (continued)
D.
Single Study Design (4.2), Rodents (combine 4.1.1 and 4.1.2)
F0 males
Q
PBE
M
F0 females
Q
GD 0
G
3 weeks
pnd 21
GD 20
N
F0 males
L
W pnd 21
selected F1 pups M G
N
1/2 F0 females
and F1 litters
N
F1 females
and F2 litters
N
F1 males
N
1/2 F0 females
and F1 litters
E.
Two-Study Design (4.3), Rodents
4.1.1 with 4.1.2: 1/2 F0 females and F1 litters necropsied on GD 20
1/2 F0 females and F1 litters necropsied on pnd 21
(retained selected F1 pups followed through mating and gestation of F2 litters)
Q=
PBE =
M=
G=
L=
W=
N=
GD =
pnd =
Quarantine
Prebreed Exposure Period
Mating
Gestation
Lactation
Wean
Necropsy
Gestational Day
Postnatal Day
Direct exposure of adults
14
Reproductive Toxicity Testing
The U.S. FDA Segment I and III studies have been essentially combined in the
U.S. EPA-mandated reproductive toxicity testing guidelines for both TSCA12 and
FIFRA13 since 1985 (graphically presented in Figure 4).
The proposed U.S. EPA
OPPTS draft17 and final18 guidelines (and the TSCA final testing guidelines16) (Figure 5),
the U.S. FDA final guidelines (Figure 6), and the OECD 41622 final guidelines have the
same overall design, but have included additions to improve the sensitivity of the study
design, to assess reproductive endpoints (structural and functional) in a robust animal
model (the rat), with special attention to detection of possible endocrine disrupters. All
current study designs include a long prebreed exposure period for the initial animals
(designed the F0 generation), beginning after weaning to encompass at least one
complete spermatogenic cycle, mating, gestation, and lactation with exposures
continuing, culling litters (designated F1) on pnd 4 to a fixed size, necropsy of parental
animals, retention of selected F1 pups for a long prebreed with mating, gestation, and
lactation of F2 litters as in the first generation, with termination of the study at the
weaning of the F2 litters. The F1 generation is the one generation, which has the
potential for exposure beginning as gametes (in the F0 parents) through their
reproductive performance. (In contrast, F0 animals begin exposures at 5-9 weeks of
age, and F2 animals are potentially exposed from gametes through lactation, all indirect
through their parents, the F1 generation.)
A comparison of the old and new testing guidelines for reproductive toxicity
assessments is as follows.
15
Figure 4. Previous Two-Generation Study Design (EPA)
Q
PBE
M
G
L
F0
M
G
L
W
PBE
M
G
L
M
G
L W
F1
F2
KEY:
Q = Quarantine
PBE =Prebreed exposure
M = Mating
G = Gestation
L = Lactation
W = Weaning
Direct exposure
Possible indirect exposure via placental and/or lactational transfer
Direct and possibly indirect exposure if test material is in the diet or
drinking water as pups begin to self-feed and self-drink by third week of
lactation
16
Figure 5. New Two-Generation Study Design (EPA, FDA, and OECD and FDA)a
PBE
Q
M
G
L
F0
N F0 females
ECE
N F0 males
M
G
L
W
PBE
M
G
L
F1
N F1 females
NW
S
VP
PPS
N F1 males
ECE
M
G
LW
F2
NW
AGD
S
a
EPA18 and FDA20 provide for a possible second litter per generation (i.e., F1a and F1b; F2a and
F2b).
KEY:
Q = Quarantine
PBE =Prebreed exposure
M = Mating
G = Gestation
L = Lactation
W = Weaning
N = Necropsy
ECE = Estrous cyclicity evaluations
S = Standardize litters on pnd 4 to 8-10
VP = Acquisition of vaginal patency
PPS = Acquisition of preputial separation
AGD = Measurement of anogenital distance in F2 pups on pnd 0
if "triggered"
NW = Necropsy F1 and F2 weanlings, up to three/sex/litter
Direct dietary exposure
Possible indirect exposure from transplacental and/or translactational exposure
Both direct and possible indirect exposure if test material is in feed or drinking water (nursing pups begin
self-feeding and self-drinking in last week of lactation)
17
Figure 6
FDA Two-Generation Reproduction and Teratology Study
(FDA Redbook 2000, IV.C.9.a)
Timeline
(weeks)
0
F0
2
4
6
8
10
10-week PBE
Q
12
14
16
18
P
L
M
20
22
24
26
28
30
32
34
36
38
40
H
M
42
44
N F0 females
N F0 males
G
P L W
10-week PBE
M
G
P L
G
F1a
gd 20
VP
PPS
S
G
Developmental Landmarks
Optional:
P L W
F2a
N
S
AGD
-- Type I immunotoxicity in F0 dams and F1 male and female offspring
-- Functional Type II immunotoxicity testing in retained F0 parents, or satellite F1 and/or F2 postweanlings
-- Neurotoxicity screening in offspring (F1 and/or F2a)
Q=
N=
necropsy
PBE = prebreed exposure
quarantine (1 wk)
W=
weaning (on pnd 21)
M=
mating (2 wks)
S=
standardize litters to ten pups (with equal sex ratio) on pnd 4
G=
gestation (3 wks)
H=
holding period between breedings
L=
lactation (3 wks)
P=
parturition (delivery)
gd =
gestational day
PPS = acquisition of preputial separation in F1a males
AGD = measurement of anogenital distance on pnd 0
VP =
acquisition of vaginal patency in F1a females
N
F1 males
G
F2b
N F1a dams
and F2b fetuses
on gd 20
Use for optional
teratology study
18
BUT, there are criticisms:
1.
Current guidelines only follow one offspring/sex/litter to adulthood. Will we miss
subtle lesions or effects at low incidence? Should more pups per litter be retained
postwean? This will not improve statistical power since that is based on live
numbers of litters/group, but it will improve the characterization of parameters for
each litter.
2.
Current guidelines trigger anogenital distance in F2 offspring if effects on
reproductive development are detected in F1 offspring (e.g., delays in acquisition of
puberty, alterations in estrous cyclicity, etc.). Since F2 offspring are terminated at
weaning, effects on AGD in F2 newborn pups cannot be related to any postwean
effects such as puberty, estrous cycling, adult reproductive system structures, or
functions.
Easy fix: Measure AGD in F1 animals, which are thoroughly evaluated through
sexual maturity and reproduction. AGD is considered the most sensitive indicator
of anti-androgenic activity and can be a good (but not perfect) predictor of effects in
older animals and/or at higher doses.
3.
Current test guidelines do not specify examination of preweanling males for
retained nipples and/or areolae (indicator of anti-androgen activity) or preweanling
females for decreased nipples or areolae (from androgenic activity).
Easy fix: Examine F1 and F2 preweanlings (pnd 11-13) for number of nipples
and/or areolae.
4.
Current testing guidelines do not require use of a positive control group (or
“reference chemical”). Use of positive control (successfully) indicates the animal
model is sensitive to perturbation in endpoints of concern, and that the performing
laboratory is competent to detect effects if they occurred. There is no prohibition of
its use…
5.
Current testing guidelines do not require assessment of hormone levels in the
blood. Most mammalian hormones are released into circulation in a pulsatile
pattern with additional diurnal and seasonal rhythms. A single blood sample taken
at necropsy may not be informative. Multiple samples over time under basal and
challenge conditions will be much more useful, but this would require cannulated
animals or multiple tail sticks, etc., which could confound the assessment of
treatment-related reproductive effects. In addition, hormonal changes are the basis
for regulation of homeostatis. They are supposed to change in response to
changes in the external or internal environment and are not adverse, per se. The
consequences, if any, from altered hormone levels are the endpoints of concern. A
separate study or a satellite group or groups is highly recommended for these
assessments.
19
NEW RISK ASSESSMENT/RISK MANAGEMENT PARADIGM
Science-Based
Risk Assessment
Scientific Research
Laboratory and Field
Observations/Measurements
Risk Management
Development of
Regulatory Options
Toxicity
Assessment
Extrapolation Methods
Linked Databases
RA Identifies
Research Needs
Risk
Characterization
Cell Signaling
Pathway Research
Gene-Environment
Research
Genomics/Proteomics
Population
Characterization
Public Health,
Social, Ethical,
Economic, Political
Implications
New Research
Informs RA
Exposure
Assessment
Modified from: NRC, 2000; Scientific Frontiers in Developmental Toxicity and Risk Assessment
Regulatory
Decision(s)
Implementation
20
COMPARISON OF
HAZARD ASSESSMENT
1. Hazard: “Intrinsic capacity of the test chemical to do harm”
2. Basic research
VERSUS
RISK ASSESSMENT
1. Risk: The probability that exposure to the test chemical
--
by relevant routes of administration
--
small numbers/group
--
at doses down to environmentally relevant levels
--
typically high doses
--
during susceptible periods of development (in utero,
--
strange and wonderful routes
3. Identify (and validate) new endpoints
perinatal, peripubertal, adult, senescent)
will result in adverse outcome(s)
--
cell signaling pathways
2. Science-based risk assessment
--
gene-environment interactions
--
robust study designs
--
“-omics” (e.g., genomics, proteomics, metabolomics)
--
large numbers/group
4. New research informs risk assessment
--
range of doses
5. These studies are not used for risk assessment
--
relevant routes, timing
--
use of validated endpoints
3. Involves both toxicity and exposure assessments
--
if hazard is high but no exposure, then no risk
--
if hazard is low but ubiquitous in environment,
then likely high risk
4. Risk assessment identifies new research needs
5. Risk characterization  regulatory decisions (risk mgmt.)
20
REFERENCES
1
Goldenthal, E. I. (Chief, Drug Review Branch, Division of Toxicological Evaluation, Bureau of Scientific
Standards and Evaluation), Guidelines for Reproduction Studies for Safety Evaluation of Drugs for
Human Use, March 1, 1966.
2
U.S. Environmental Protection Agency (EPA), Toxic substances control act (TSCA) test guidelines:
Final rule, Federal Register, 50, 39412, 1987.
3
U.S. Environmental Protection Agency (EPA), Pesticides assessment guidelines (FIFRA), subdivision
F. Hazard Evaluation: Human and Domestic Animals, Section 83-3 (Final Rule). Available from
NTIS (PB86-108958), Springfield, VA, 1984.
4
U.S. Environmental Protection Agency (EPA), Pesticide assessment guidelines, subdivision F hazard
evaluation: humans and domestic animals, series 83-3, rat or rabbit developmental toxicity study,
June, 1986 (NTIS PB86-248184), as amended in Federal Register 53(86), Section 158.340, May 4,
1988.
5
Japanese Guidelines of Toxicity Studies, Notification No. 118 of the Pharmaceutical Affairs Bureau,
Ministry of Health and Welfare. 2. Studies of the Effects of Drugs on Reproduction, Yakagyo Jiho Co.,
Ltd., Tokyo, Japan, 1984.
6
Canada Ministry of Health and Welfare, Health Protection Branch, The testing of chemicals for
carcinogenicity, mutagenicity and teratogenicity. The Ministry of Ottawa, 1973.
7
United Kingdom, Committee on Safety of Medicines: Notes for guidance on reproduction studies,
Department of Health and Social Security, Great Britain, 1974.
8
Organization for Economic Cooperation and Development (OECD), Guideline for Testing of
Chemicals: Teratogenicity, Director of Information, Paris, France, 1981.
9
Food and Drug Administration (FDA) (1994). International Conference on Harmonisation (ICH);
Guideline for Detection of Toxicity to Reproduction for Medicinal Products; Availability; Notice.
Section 4.1.3, Study for Effects on Embryo-Fetal Development. Federal Register 59(183), 48749,
September 22, 1994.
10
U.S. EPA (1996). OPPTS (Office of Prevention, Pesticides and Toxic Substances) Health Effects
Test Guidelines, OPPTS 870.3700, Prenatal Developmental Toxicity Study (Public Draft, February,
1996).
11
_
Tyl, R. W. and Marr, M. C. (1996). Chapter 7. Developmental Toxicity Testing Methodology, In:
Handbook of Developmental Toxicology (R. D. Hood, Editor), CRC Press, Inc. (September, 1996).
12
U.S. EPA (1985). Toxic Substances Control Act, EPA (TSCA) Section 798.4700, Reproduction and
Fertility Effects. Federal Register 50 (188), 39432-39433 (September 23, 1985).
13
U.S. EPA (1989). Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) EPA Guidelines for
Pesticide Registration (Subdivision F, Hazard Evaluation: Human and Domestic Animals, Section 845), August 17, 1989.
14
U. S. EPA (1996). Office of Prevention, Pesticides and Toxic Substances (OPPTS), Health Effects
Test Guidelines, OPPTS 870.3800, Reproduction and fertility effects (Public Draft February, 1996).
21
15
U.S. EPA (1997). Toxic Substances Control Act Test Guidelines; Final Rule 40 CFR Part 799.9370
“TSCA prenatal developmental toxicity.” Federal Register 62(158), 43832-43834 (August 15, 1997).
16
U.S. EPA (1997). Toxic Substances Control Act Test Guidelines, Final Rule 40 CFR Part 799.9380
“TSCA reproduction and fertility effects.” Federal Register 62(158), 43834-43838 (August 15, 1997).
17
U.S. EPA (1998). Office of Prevention, Pesticides and Toxic Substances (OPPTS). Health Effects
Test Guidelines OPPTS 870.3700, Prenatal Developmental Toxicity Study; Final Guideline, August
1998.
18
U.S. EPA (1998). Office of Prevention, Pesticides and Toxic Substances (OPPTS). Health Effects
Test Guidelines OPPTS 870.3800, Reproduction and Fertility Effects; Final Guideline, August 1998.
19
U.S. FDA (2000). Center for Food Safety and Applied Nutrition Redbook 2000. IV.C.9.b. Guidelines
for Developmental Toxicity Studies. July 20, 2000.
20
U.S. FDA (2000). Center for Food Safety and Applied Nutrition Redbook 2000. IV.C.9.c. Guidelines
for Reproductive Studies. July 20, 2000.
21
OECD (2001). OECD Guideline for the Testing of Chemicals; Proposal for Updating Guideline 414:
“Prenatal Developmental Toxicity Study,” pp. 1-11, adopted January 22, 2001.
22
OECD (2001). OECD Guideline for the Testing of Chemicals; Proposal for Updating Guideline 416:
“Two-Generation Reproduction Toxicity Study,” pp. 1-13, adopted January 22, 2001.