rethinking carcinogenicity assessment for agrochemicals ...class/read across. guidance document with...
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2020 Society of Toxicology Carcinogenesis Webinar Series
Rethinking Carcinogenicity Assessment For Agrochemicals
Retrospective Analysis
Sabitha Papineni, DVM, Ph.D
CortevaTM Agriscience
19 February 2020
✓This speaker is employed by CortevaTM Agriscience
✓This speaker has no other conflict of interests to declare
✓ Any opinions expressed in this presentation are those of the speaker and do not necessarily reflect the opinions of CortevaTM
Agriscience
Disclosure
Regulatory Testing of Agrochemicals
• An agrochemical product undergoes >100 rigorous studies to support the health, safety and environmental
assessments required for registrations.
• From a mammalian toxicology perspective, agrochemicals have the most comprehensive data requirements
of any chemical sector, including pharmaceuticals.
Mammalian Toxicology Testing Requirements
• ADME Studies
• Acute Toxicity Testing• oral, dermal, inhalation, skin & eye irritation, sensitization
• Subchronic Toxicity Testing (Rat, Mouse & Dog)
• Chronic Toxicity Testing (Rat)
• Carcinogenicity Testing (Rat & mouse)
• Reproductive Testing (Rat)
• Developmental/Teratogenicity (Rat & Rabbit)
• Mutagenicity/Genotoxicity Testing (In vitro & In vivo)
• Neurotoxicity (Acute & Subchronic)
• Repeated Dermal (Rat or Rabbit)
18 or 24 mon
Mouse 2 year Rat At least
560 rats
At least
400 Mice
Rodent Cancer Bioassay Agrochemicals
Default Data Requirement
EPA’s Commitment to End Animal Testing by 2035
• The EPA will reduce its requests for, and our funding of, mammal studies by 30 percent by 2025 and eliminate
all mammal study requests and funding by 2035.
• Any mammal studies requested or funded by the EPA after 2035 will require Administrator approval on a case-by-case
basis.
https://www.epa.gov/newsreleases/administrator-wheeler-signs-memo-reduce-animal-testing-awards-425-million-advance
Cancer Bioassay Weight of Evidence Criteria
Cancer
Bioassay
WoE
Criteria
Rodent Cancer Bioassay
Earlier recognition of pesticides that pose or do not
pose carcinogenic risk
“ReCAAP”
Rethinking
Carcinogenicity
Assessment
for
Agrochemicals
Project
Check-box
approach
Studies Required
Acute Oral Toxicity
Acute Dermal Toxicity
Acute Inhalation Toxicity
Acute Eye Irritation
Acute Dermal Irritation
Skin Sensitization
90-Day Oral Toxicity in Rodents
90-Day Oral Toxicity in Non-rodents
21/28-Day Dermal Toxicity
90-Day Dermal Toxicity
90-Day Inhalation Toxicity
Developmental Toxicity in Rodents
Developmental Toxicity in Non-rodents
Reproduction and Fertility Effects
Chronic Toxicity in Rodents
Chronic Toxicity in Non-rodents
Carcinogenicity in Rats
Carcinogenicity in Mice
Weight of Evidence
approach
Rodent Cancer
BioassayMetabolism
Sub-chronic
Genotoxicity
Exposure
Hormone
Disruption
Immune
Suppression
Read-across
Based on scientific understanding of
potential triggers and indicators of
carcinogenesis
Cancer
Bioassay
WoE
Criteria
Immune SuppressionSubchronic
Data
Genotoxicity
Pesticidal
MoA
Mechanistic Data
Exposure
Hormonal Perturbation
ADME
Chemical Class/Read
across
Guidance
Document
with
WoE
Framework
Case
Studies
ReCAAP Project Overview
Regulatory
Review
Identify Gaps
Retrospective
Review
Rodent Cancer
Bioassay
Phase I Phase II Phase III
Metabolism
Sub-chronic
Genotoxicity
Exposure
Hormone
Disruption
Immune
Suppression
Read-across
Cancer Bioassay WoE Criteria
Cancer
Bioassay
WoERodent Cancer Bioassay
Uncertainty/
Data gapsFocused
data generation
No Bioassay needed
➢ Completion of retrospective analysis
➢ Determine if the WoE predicts the cancer risk by comparing it to the bioassay results
➢ Identify any gaps and revise the criteria accordingly
➢ Develop a guidance document with WoE framework for carcinogenicity assessment
Cancer Classification
Not Likely to be Carcinogenic to Humans at doses that do not induce cellular
proliferation in the liver or thyroid glands (1)
Not Likely to be Carcinogenic to Humans at doses that do not cause
urothelium cytotoxicity (1)
Not Likely to be Carcinogenic to Humans at doses that do not induce a
proliferative response in the liver (1)
Likely to be Carcinogenic to Humans (2)
Suggestive Evidence of Carcinogenic Potential (4)
Not Likely to be Carcinogenic to Humans (6)
Case Studies Chemical Distribution (n = 15)
Halauxifen-methyl
Case Study
What is Halauxifen-methyl?
• Herbicide also known as ArylexTM
• Rapidly hydrolyzed in the liver to Halauxifen acid
Halauxifen acid
(Primary metabolite)Halauxifen-methyl
ester
(Parent molecule)
Systemic Exposure is to Halauxifen acid
Rapid
Current Chromatogram(s)
min10 20 30 40
mAU
0
200
400
600
800
1000
1200
1400
Area: 12
32.39
11.3
34
Area: 34
8.177
16.0
65
Area: 48
006.8
30.7
33
Area: 25
44.21
37.8
67
Area: 13
8.361
40.0
48
Print of window 38: Current Chromatogram(s)
Instrument 1 6/24/2010 10:40:45 AM Page 1 of 1
Halauxifen acid: 0-12 hr urine
(male- 10 mg/kg)
(7.7 mg/kg acid recovery )
Halauxifen-methyl and Halauxifen acid
Bioequivalence
Halauxifen
Halauxifen
Acyl
glucuronide
O-demethylated
Halauxifen
and conjugates
Current Chromatogram(s)
min0 10 20 30 40
mAU
0
100
200
300
400
500
600
700
800
900
Area: 27
2.756
9.35
9
Area: 20
92.18
11.9
59
Area: 20
0.322
16.6
45
Area: 37
217.5
32.4
74
Area: 41
7.627
37.5
09
Area: 26
23.75
38.0
76
Area: 14
7.648
40.2
08
Print of window 38: Current Chromatogram(s)
Instrument 1 6/24/2010 10:42:32 AM Page 1 of 1
Halauxifen
Halauxifen
Acyl
glucuronideO-demethylated
Halauxifen
and conjugates
Halauxifen Methyl: 0-12 hr urine
(male- 10 mg/kg)
(8.1 mg/kg acid recovery)
Bridging Package on
Halauxifen-methyl
Bridging Data Strategy• Core data package was developed on Halauxifen acid
• Halauxifen acid was shown to have no carcinogenic potential in the 2-year rat and 18-mon mouse assays.
• ADME
• Acute six pack
• Genotoxicity
• 28- and 90-day rat
• Developmental rat and rabbit
• 28-day Dermal
Bridging Data Strategy
28-Day Halauxifen-methyl vs. Acid Comparison
Doses Conclusions
Halauxifen
Acid
Rat 28-day
10, 50, 250, and
750 mg/kg/day
NOAEL: 250 mkd (♂, ♀)
Target organ: Kidney
Halauxifen-Methyl
Rat 28-day
10, 52, 261, and
782 mg/kg/day
NOAEL: 10 mkd (♂),
52 mkd (♀)
Main target organ: Liver
7-day Rat Mode of Action Study:Liver Effects
Halauxifen-methyl Halauxifen acid
At 782 mg/kg/day:
Increased liver weight
with hepatocyte
hypertrophy
At 750 mg/kg/day:
No liver effects
Halauxifen acid
Core Toxicology Package
2 Year Cancer Bioassay
Halauxifen-methyl is AhR activator
• Associated with rodent liver effects
• Prototypical AhR ligands include Dioxin
• Human Relevant MoA
Prototypical AhR Ligand
• Dioxin
• Metabolically stable– Long t1/2
– Bioaccumulates
• Sustained AhR activation– ↑Cyp1a1 levels
• Hepatic Effects – Hepatic proliferation not until
> 14 weeks of sustained exposure
• Relevant to Humans
Halauxifen-methyl- is it a prototypical AhR ligand?
How do we evaluate a rodent liver MoA that could be relevant to humans?
Determine exposure of Halauxifen-methyl in liver
- Understand metabolism differences in different matrices
Mode-of-Action (MoA)
-AhR activation (dose response)
-In vitro species differences- rat, mouse and humans
Hepatocellular Proliferation (dose response)
Key
Event 1
Key
Event 2
Key
Event 3
Characterize Liver MoA
Enters Liver via Portal Vein
“Saturation of Hydrolysis”
Occurs
AhR-mediated Liver Toxicity
Human Relevance:Hydrolysis of Halauxifen-methyl to
Halauxifen acid
Halauxifen
methyl ester
Enters GI
Tract
Absorption
Enters Systemic
Circulation as
Halauxifen acid
Liver Hydrolysis Rate
Humans > Rodents
8 min vs. 30 min
GI Hydrolysis
Rate
Humans >
Rodents
Prototypical AhR Ligand
• Dioxin
• Metabolically stable– Long t1/2
– Bioaccumulates
• Sustained AhR activation– ↑Cyp1a1 levels
• Hepatic Effects – Hepatic proliferation not until
> 14 weeks of sustained exposure
• Relevant to Humans
Non Prototypical-AhR Ligand• Omeprazole (Prilosec),
Halauxifen-methyl
• Rapid metabolism and clearance from the liver
• Transient AhR Activation
• Cyp1a1 levels at baseline after 4 days of recovery
• Hepatic Effects– Proliferation at 4 weeks
– Reversible
• Relevant to Humans?
Halauxifen methyl- not a prototypical AhR ligand
Human Relevance:Halauxifen-methyl mediated AhR activation in Rat
and Human Primary Hepatocytes
Rat Human
Cyp1a1
Induction
Primary
Hepatocytes
147-fold2.9 to 34-fold
Average:
11-fold
AhR activation in rat >>>> humans
•Halauxifen-methyl ester• is NOT a prototypical AhR activator
• rapidly metabolized
• rapidly eliminated
• has a threshold for liver effects in rats • NOAEL of 10 mg/kg/day
• Systemic exposure is to Halauxifen acid - NOT an AhR activator
• Human Relevance: • Liver Toxicokinetics: rat slower metabolism than human
• Toxicodynamics: AhR activation in rat >>> human
•Conservative human dietary exposure estimate• is 0.0001 mg/kg bw/day
• margin of exposure relative to the rat NOAEL >100,000 fold
• data are protective of human health
Halauxifen-methyl MoA
Cancer Classification
“not likely to be carcinogenic to humans” Halauxifen-acid
“not likely to be carcinogenic to humans at doses that do not induce Cyp1a1 expression (a biomarker for
AhR activation)”
Halauxifen- methyl
No cancer bioassay conducted
Mechanistic Studies
All Apical Effects Result From Prior Changes At The Molecular Level
Apical Effect
Transcriptome Profiling and Toxicity
Big Data
Genome-Wide Gene
Expression (15,000
Endpoints)
Toxicological Insight
Ali & Qadir, Big Data for Human Development, 2016
HESI eSTAR Committee Predictive Chronic/Cancer Projects
1. Carcinogenomics Project
• Being led by scientists from Merck and the US EPA but multisector involvement
• Aim is to develop short-term study transcriptional biomarkers predicting tumor outcome in rats
2. Molecular Point of Departure Project
• Led by scientists from Corteva and NIEHS but multisector involvement
• Aim is to develop a framework to derive an in vivo transcriptome POD for use in chemical risk assessment
that will produce a human health-protective POD without needing to link the transcriptomic change with a
specific adverse effect, mechanism, or mode of action.
POSTERS
Rethinking Carcinogenicity Assessment for Agrochemicals
(ReCAAP)
Abstract/Poster Board Number: 2200/P558
Date: Tuesday, 17 March
Time: 9–10:45 am
Location: CC Exhibit Hall
Abstract/Poster Board Number: 2231/P612
Date: Tuesday, 17 March
Time: 2:15–4:30 pm
Location: CC Exhibit Hall
WORKSHOP
Human-Relevant Carcinogenicity Testing: Tools for Cancer Assessment in 2020 and Beyond
Date: Tuesday, 17 March
Time: 8–10:45 am
Location: Room 304A
Chair: Nicole Kleinstreuer, NTP NICEATM, US
Co-chair: Gina Hilton, PETA International Science Consortium Ltd.
Upcoming Presentations at SOT 2020
Colleagues@
• CortevaTM Agriscience
• Dow Toxicology Lab, Midland, MI
• Haskell R&D Center, CortevaTM, Wilmington, DE
ReCAAP team
Thank you for your attention !
Contact Information
Dr. Warren Casey, PhD, DABTNational Toxicology Program
Acting Chief of Biomolecular Screening Branch
Email: [email protected]
Dr. Sabitha Papineni, DVM, PhDCortevaTM Agriscience
Global Senior Regulatory Toxicologist
Email: [email protected]