AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

2 CANCER ASSESSMENT DOCUMENT

EVALUATION OF THE CARCINOGENIC POTENTIAL OF



## Aminocyclopyrachlor

PC Code 288008

Final

November 9

, 2011



### C ANCER 

### A SSESSMENT 

### R EVIEW 

### C OMMITTEE

HEALTH EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMSAMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

4 TABLE OF CONTENTS

Executive Summary

................................ ................................ ................................ ......................... 5

I. Introduction

................................ ................................ ................................ ................................ . 7

II. Background Information

................................ ................................ ................................ ............ 7

III. Evaluation of Carcinogenic ity Studies

................................ ................................ ...................... 8

1. Combined Chronic Toxicity / Carcinogenicity Study in Rats

................................ ........... 8

2. Carcinogenicity Study in Mice

................................ ................................ ...................... 16

IV. Toxicology

................................ ................................ ................................ .............................. 16

1. Metabolism

................................ ................................ ................................ .................... 16

2. Mutagenicity

................................ ................................ ................................ .................. 17

3. Structure Activity Relationship

................................ ................................ ...................... 19

4. Subchronic and C hronic Toxicity

................................ ................................ .................. 19

5. Mod e of Action Studies.........................................................................19

V. Committee’s Assessment of the Weight

- of

- the Evidence

................................ ....................... 2 0

VI. Classification of Carcinogenic Potential

................................ ................................ ................ 2 1

VII. Quantific ati on of Carcinogenicity

................................ ................................ ......................... 2 1

VIII. Bibliography

................................ ................................ ................................ .......................... 2 1AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

5 EXECUTIVE SUMMARY

On August 1 7, 2011 , the Cancer Assessment Review Committee (CARC) of the Health Effects

Division of the Office of Pesticide Programs met to evaluate the carcinogenic potential of

aminocyclopyrachlor.

Jessica Ryman of Risk Assessment Branch IV presented the chronic toxicity/ carcinogenicity

study in rats ( MRID 48333607 ) and the carcinogenicity study in mice (MRID 48333606 )

. Aminocyclopyrachlor technical was administered to Crl:CD(SD) rats (70/sex/dose) at dietary

dose levels of 0, 600, 2000, 6000, or 18000 ppm (0/0, 27/29, 97/100, 279/309, 892/957 mg/kg

bw/day in males/females) for 2 years to assess carcinogenicity. A satellite group of animals

(10/sex/dose) was sacrificed at one year to assess chronic toxicity. Aminocyclopyrachlor was

administered to young adult m ale and female Crlj:CDl(ICR) mice (60/sex/group) in diets that

contained 0, 300, 1000, 3000, or 7000 ppm DPX

- MAT28 for approximately 18 months. This

corresponded to doses of approximately 0/0, 39/50, 133/171, 393/527, and 876/1190 mg/kg

bw/day in males/fe males. Mutagenicity data and structure activity relationship data were also

discussed.

The Committee considered the following for a weight

- of

- evidence determination of the

carcinogenic potential of aminocyclopyrachlor

.

Carcinogenicity

Rat

• Bra in Tumors: The CARC concluded that the brain tumors (glial cell tumors and granular

cell tumors) observed in male rats were spontaneous lesions and were not considered to be

treatment

- related. This was based on the following weight

- of

- evidence consideratio ns : 1) Although there were significant trends and pair

- wise comparisons at the high dose for

astrocytomas and glial cell tumors combined by the Peto analysis, the incidences were

within the historical control range. For granular cell tumors, there wa s a significant trend

only, but no significant pair

- wise comparison of any dose group with the controls. In

addition, the Fishers Exact test showed trends only and no pair

- wise comparisons of any

dose level with the controls for combined glial tumors and for granular cell tumors. 2 ) No

supporting treatment

- related pre

- neoplastic lesions were observed in the brain (or any other

tissue). (Chemicals known to cause brain tumors also are commonly tumor i genic in other

tissues, J. Plet cher, Consulting Pathologist

, Personal Communication); 3 ) The tumors

occurred at the limit dose; no other tumors were seen; 4) No treatment

- related brain

neoplastic lesio ns were observed in female rats

. 5 ) No evidence of genotoxicity was

observed in in vitro or in vivo genotoxicity s tudies. 6 ) Brain levels of radioactivity after

administration of aminocyclopyrachlor at times corresponding to peak plasma concentration

were very low (<0.01%) and were undetectable after 72 hours. ; 7) the Pathology Peer

Review also concluded that the brai n tumors were spontaneous tumors and not treatment

-AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

6 related (MRID 48333607).

• Adequacy of Dosing: Dosing was considered adequate, and not excessive, for assessing

carcinogenicity since the high dose approached the limit dose in both sexes (892/957 mg/kg

bw/day in males/females). The high dose also caused mild decreases on body weight

(decrease up to 12%) and body weight gain (decrease up to 11%) in both sexes during the

study , but had resolved by the conclusion of the study.

M ouse

• There were no tr eatment

- related increases in tumor incidence s in either sex.

• Adequacy of Dosing: Dosing was considered adequate since the high dose in this study

approached the limit dose (876/1190 mg/kg/day in males/females). No adverse effects

(including change s in body weight) were observed at this dose level.

Mutagenicity: There is no concern for mutagenicity.

Structure Activity Relationship: There is no sufficient basis for SAR concern.

Classification and Q uantification of C arcinogenic P otential

In ac cordance with the EPA's Final Guidelines for Carcinogen Risk Assessment (March, 2005)

, the CARC classified aminocyclopyrachlo r as “Not L ikely to be Carcinogenic to Humans.”

There were no treatment

- related tumors seen in male or female rats or mice at dose s that were

adequate to assess carcinogenicity. There is also no concern for mutagenicity.

Quantification of carcinogenicity is not required.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

7 I. INTRODUCTION

On August 17 , 20 11 , the Cancer Assessment Review Committee (CARC) of the Health Effects

Divis ion of the Office of Pesticide Programs met to evaluate the carcinogenic potential of

aminocyclopyrachlor.

II. BACKGROUND INFORMATION

Aminocyclopyrachlor is a pyrimidine carboxylic acid herbicide that was registered for non

- food

use in 2010. It is no w being registered for the first food use on rangeland, pastures, and

Conservation Reserve Program ( CRP ) acres. There are three forms of aminocyclopyrachlor:

the parent acid (PC Code 288008), the potassium salt (PC Code 288010 ), and the methyl ester

(am inocyclopyrachlor

- methyl, PC Code 288009). All three forms are components of both

manuf acturing and end

- use products . A minocyclopyrachlor is considered the active ingredient

due to rapid hydrolysis of aminocyclopyrachlor

- methyl to aminocyclopyrachlor by cellular

esterases. The pesticidal mode of action of aminocyclopyrachlor is dysregulation of gene

prod ucts involved in auxin receptor activity, which interferes with normal shoot and root

development to stop the growth of weeds.

The only tumors observ ed in chronic toxicity/carcinogenicity studies in two species were brain

tumors in m ale rats. The registrant contend s that these tumors are not treatment

- related, based on

a consensus opinion following peer review by six board

- certified pathologists.

NH Cl OH

NH Cl CH

NH Cl

Aminocyclopyrachlor

(a.i.) Aminocyclopyrachlor

- methyl

(methyl ester) Aminocyclopyrachlor, K salt

(Parent acid)AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

8 III. EVALUATION OF CARCINOGENICITY STUDIES

1. Co mbined Chronic Toxicity/Carcinogenicity Study in Rats

Moon, Kyoung. (2010). DPX

- MAT28 Technical: Carcinogenicity 2

- Year Feeding Study in Rats.

Korea Institute of Toxicology, Daejeon, Republic of Korea. Laboratory Study Number:

IG07280, November 24, 2010 , MRID 48333607. Unpublished.

A. Experimental Design

Aminocyclopyrachlor technical ( DPX

- MAT28, Lot/batch# J

- 868

- 001

- 3 , Purity 88.3

- 90.5% ) was

administered to Crl:CD(SD) rats (70/sex/dose) at dietary dose levels of 0, 600, 2000, 6000, or

18000 ppm (0/0, 2 7/29, 97/100, 279/309, 892/957 mg/kg bw/day in males/females) for 2 years to

assess carcinogenicity. A satellite group of animals (10/sex/dose) was sacrificed at one year to

assess chronic toxicity.

B. Statistical Analysis by HED

B rain tumors were ob served only in male rats . N o tumors were observed in female rats or in

mice of either sex

. Statistical analyses were run on male rat mortality and brain tumor data.

C . Discussion of Survival Data

There was no statistically significant trend in mortalit y with increasing doses of

a minocyclopyrachlor in male rats ; however, there was a statistically significant negative pair

wise comparison of the 600 ppm dose group with the controls at p < 0.05 (Table 1) (TXR No.

0055738)

.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

9 Table 1. Aminocyclopyrachlor

– Crl:CD(SD) Rat Study (MRID 48333607)

Male Mortality Rates + and Cox or Generalized K/W Test Results

Weeks

Dose (ppm) 1

- 26 27

- 52 52 i 53

- 78 79

- 105 f Total

0 1/80 1/79 10/78 12/68 29/56 43/70

(61)

600 0/80 0/80 10/80 14/70 17/56 31/70

(44) *n

2000 3/80 6/ 77 10/71 8/61 28/53 45/70

(64)

6000 0/80 4/80 10/76 10/66 33/56 47/70

(67)

18,000 0/80 3/80 10/77 6/67 25/61 34/70

(49)

+ Number of animals that died during interval/Number of animals alive at the beginning of the

interval.

i Interim sacrifice at week 52

. f Final sacrifice at weeks 104

- 105.

n =negative pair

- wise comparison with control

( )Percent.

Note: Time intervals were selected for display purposes only.

Significance of trend denoted at control

. Significance of pair

- wise comparison with cont rol denoted at dose level.

If * , then p < 0.05. If ** , then p < 0.01.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

10 D . Neoplastic lesions

Male rats had statistically significant trends at p < 0.01, and significant pair

- wise

comparisons of the 18,000 ppm dose group with the controls at p < 0.0 5, for (malignant) brain

astrocytomas and combined astrocy t oma, glioma and oligodendrogliomas. There were

statistically significant trends in (malignant) brain gliomas at p < 0.05 and in brain granular cell

tumors at p < 0.01. It should be noted that the first brain glioma was observed at week 50 and

that only week 52 interim sacrifice animals in the control and 18,000 ppm dose groups were

examined. All interim sacrifice animals are considered to be “at risk” since the interim sacrifice

occurred after we ek 50, therefore, all interim sacrifice animals should have received full

histopathological evaluations. Potentially more animals could have had tumors which would

have been diagnosed if these animals had been examined. The statistical analyses of the tu mors in the male rats were based upon Peto’s Prevalence Test (Tables 2 a and 2b ) (TXR No. 0055738)

.

Since the effect on survival was not dose

- related, t he statistical analyses of the brain

tumors in male rats were also run using the Fisher’s Exact T est and Exact Test for T rend . For

combined glial cell tumors and the granular cell tumors, there was a statistically significant trend

only, but no significant p air

- wise comparison at any dose ( Tables 3a and 3b )

.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

11 Table 2 a . Aminocyclopyrachlor

– Crl:CD(SD) Rat Study (MRID 48333607)

Male Brain Tumor Rates + and

Peto’s Prevalence Test Results

Dose (ppm)

0 600 2000 6000 18,000

Astrocytomas

(%)

p = 0/64

(0)

0.00130** 0/66

(0)

- 0/60

(0)

- 1/65

(2)

0.16290 3 a /65

(5)

0.03760*

Gliomas

(%)

p = 0/78

(0)

0.02 052* 0/70

(0)

- 0/62

(0)

- 0/66

(0)

- 1 b /78

(1)

0.12883

Oligodendrogliomas

(%)

p = 0/27

(0)

0.48486 0/39

(0)

- 0/25

(0)

- 1 c /22

(5)

0.13397 0/36

(0)

-

Combined

(%)

p = 0/78

(0)

0.00058** 0/70

(0)

- 0/62

(0)

- 2/66

(3)

0.07203 4/78

(5)

0.0 1696*

+Number of tumor bearing animals/Number of animals examined, excluding those that died before observation of

the first tumor.

a First astrocytoma observed at week 63, dose 18,000 ppm.

b First glioma observed at week 50, dose 18,000 ppm.

c First oligod endroglioma observed at week 105 in an interim sacrifice animal, dose 6000 ppm.

Note: Significance of trend denoted at control

. Significance of pair

- wise comparison with control denoted at dose level.

If * , then p < 0.05. If ** , then p < 0.01.

Hist orical control data from the performing lab (taken from p. 42 of the Study Report)

**•** Malignant As trocytoma: Incidence † : 26/2146 (1.2 1 %), Range (per study) : 0

- 4.9%

**•** Malignant Glioma a : Incidence †: 3/2146 (0.14%), Range (per study) 0

- 1.92%

**•** Malignant Oligode ndroma: Incidence †: 3/2146 (0.14%), Range 0

- 2.0%

†2146 male brains examined in 30 carcinogenicity studies

a including “undifferentiated glioma”AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

12 Table 2b . Aminocyclopyrachlor

– Crl:CD(SD) Rat Study (MRID 48333607)

Male Brain Tumor Rates + and

Peto’s Pr evalence Test Results

Dose (ppm)

0 600 2000 6000 18,000

Granular Cell Tumors

(%)

p = 0/35

(0)

0.00190** 0/42

(0)

- 0/35

(0)

- 0/34

(0)

- 2 a /40

(5)

0.05452

+Number of tumor bearing animals/Number of animals examined, excluding those that die d

before observation of the first tumor.

a First granular cell tumor observed at week 98, dose 18,000 ppm.

Note: Significance of trend denoted at control

. Significance of pair

- wise comparison with control denoted at dose level.

If * , then p < 0.05. If ** , then p < 0.01.

Historical control data

**•** Granular cell tumors: Incidence: 8/2146 (0.37%), Range: 0

- 2.0%AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

13 Table 3a. Aminocyclopyrachlor

– Crl:CD(SD) Rat Study (MRID 48333607)

Male Combined Brain Tumor Rates +

(Astrocytomas, Gliomas and Oligodendro gliomas) and

Fisher’s Exact Test and Exact Test for Trend Test Results

Dose (ppm)

0 600 2000 6000 18,000

Combined

(%)

p = 0/78

(0)

0.00349** 0/70

(0)

1.00000 0/62

(0)

1.00000 2/66

(3)

0.20833 4 a /78

(5)

0.06009

+Number of tumor bearing animals/Nu mber of animals examined, excluding those that died

before week 53.

a First tumor observed at week 50, dose 18,000 ppm.

Table 3b. Aminocyclopyrachlor

– Crl:CD(SD) Rat Study (MRID 48333607)

Male Brain Tumor Rates + and

Fisher’s Exact Test and Exact Test f or Trend Test Results

Dose (ppm)

0 600 2000 6000 18,000

Granular Cell Tumors

(%)

p = 0/68

(0)

0.03927* 0/70

(0)

1.00000 0/61

(0)

1.00000 0/66

(0)

1.00000 2 a /66

(3)

0.24071

+Number of tumor bearing animals/Number of animals examined, excludi ng those that died

before observation of the first tumor.

a First granular cell tumor observed at week 98, dose 18,000 ppm.

Note: Significance of trend denoted at control

. Significance of pair

- wise comparison with control denoted at dose level.

If *

, then p < 0.05. If ** , then p < 0.01.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

14 Pathology Peer Review

The registrant contends that the brain tumors observed in male rats were not treatment

- related.

This conclusion was reached after a Pathology Peer Review Group organized by Experimental

Pat hology Laboratories, Inc. (Sterling, VA USA ) was convened in order to review the brain

histopathology and interpret the findings. (Note: this group is referred to in the Study Repo rt as
a Pathology Working Group (PWG). Although this Group followed the Ag ency’s guidance for

conducting a PWG in 83

- 6 , the Group was convened before the Study Report was written and

not afterward. As such, the Group’s expert opinion is incorporated into the Study Report and is

not a separate document. To avoid confusion, this group is referred to herein as a Pathology Peer

Review Group ) . This Group was composed of 5 independent consulting pathologists with

expertise in rodent toxicity and carcinogenicity studies, and with specific expertise in

neuropathology. A sixth pathol ogist with similar background served as the chairperson and

author of the final report. All of the brain histopathology slides were independently reviewed by

one of the Group pathologists prior to the P athology Peer Review Group meeting to confirm the

fi ndings of the Study pathologist. During the Group’s meeting, the brain slides with neoplastic

findings were coded and reviewed by each panel member. Following this independent review,

the panel members reached consensus on the diagnosis for each slide and conducted a weight

- of

evidence evaluation to determine if any histopathological findings were spontaneous or

associated with test substance administration.

The P a thology Peer Review Group concluded that the astrocytomas in the high dose males were

not t reatment related. The basis for this conclusion was:

**•** No evidence of non

- neoplastic glial cell proliferation caused by the test substance in male

or female rats at any dose.

**•** No decrease in tumor latency in the high dose groups compared to other treatmen t groups

with tumors.

**•** The age of onset of astrocytomas (Days 393

- 728) were consistent with age

- related

neoplasms.

**•** No treatment

- related brain neoplasms were observed in female rats.

**•** No preferential accumulation of aminocyclopyrachlor in the brain as comp ared to other

tissues.

**•** No evidence of gen otoxicity was observed in genotoxicity assays.

The full Report of the Pathology Peer Review Group is available in MRID 48833607.

E

. Non

- neoplastic lesions

All non

- neoplastic lesions in the 1

- year interim sac rifice animals and in the 2 year main study

group animals were consistent with background lesions that are typical of rats of this age and

strain.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

15 F

. Adequacy of Dosing for Assessment of Carcinogenicity

Dosing was adequat e , and not excessive, for assess ing carcinogenicity since t he high dose

approached the limit dose in both sexes (892/957 mg/kg bw/day in males/females). The hi gh

dose also caused mild decreases on body weight ( decrease up to 12 %) and body weight gain

( decrease up to 11 %) in both sexes d uring the study that had resolved by the conclusion of the

study (see Table 4 below)

.

Table 4

– Body weights (BW)

g±SD 0 600 ppm 2000 ppm 6000 ppm 18,000 ppm

MALES initial BW 216.3 ± 12.82

(N=80) 216.2 ± 12.27

(N=80) 216.3 ± 11.34

(N=80) 210.4 ± 10.40

(N=80) 214.2 ± 10.70

(N=80)

Day 189 656.3 ± 63.25

(N=79) 664.0 ± 72.90

(N=80) 664.3 ± 75.47

(N=79) 647.8 ± 81.24

(N=80) 616.8 ± 56.79**

( ↓ 6%)

(N=80)

Day 385 813.2 ± 81.11

(N=67) 816.1 ± 86.22

(N=69) 819.7 ± 108.73

(N=61) 820.2 ± 113.91

(N=66) 751.5 ± 81.69**

(N=6 6)

( ↓ 8%)

Day 539 860.0 ± 115.31

(N=57) 877.0 ± 114.69

(N=59) 870.6 ± 116.75

(N=54) 884.5 ± 155.21

(N=59) 801.9 ± 124.85**

(N=63)

( ↓ 7%)

Final BW 877.3 ± 139.43

(N=27) 879.3 ± 152.83

(N=39) 856.2 ± 170.70

(N=27) 840.9 ± 165.12

(N=25) 788.5 ± 163.19

(N=36)

FEMALES Initial BW 158.7 ± 9.65

(N=80) 158.6 ± 8.74

(N=80) 157.1 ± 8.94

(N=80) 155.0 ± 8.39*

(N=80)

( ↓2%) 154.2 ± 9.90**

(N=80)

( ↓3%)

Day 189 345.8 ± 40.75

(N=80) 349.5 ± 34.08

(N=80) 349.6 ± 31.11

(N=79) 346.2 ± 32.50

(N=80) 324.2 ± 28.47**

(N=79)

( ↓6%)

Day 385 441.9 ± 80.88

(N=66) 438.3 ± 6 8.10

(N=69) 441.7 ± 68.40

(N=68) 445.6 ± 53.91

(N=69) 402.7 ± 54.09**

(N=66)

( ↓9%)

Day 539 505.1 ± 111.38

(N=59) 500.2 ± 98.55

(N=52) 503.6 ± 98.90

(N=54) 500.8 ± 73.09

(N=54) 442.5 ± 72.41**

(N=56)

( ↓12%)

Final BW 535.2 ± 153.47

(N=27) 538.7 ± 82.23

(N=27) 533.3 ± 121.84

(N =25) 518.8 ± 86.13

(N=26) 487.3 ± 85.64

(N=23)

*Significant differences from control at p<0.01

**Significant differences from control at p<0.01AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

16 2. Carcino genicity Study in Mice

Jung

- Im Huh, Ph.D. (2010). DPX

- MAT28 Technical: Carcinogenicity 18

- Month Feeding S tudy

in Mice. Korea Institute of Toxicology, Republic of Korea. Laboratory Study Number: IG07280,

October 15, 2010 MRID 48333606. Unpublished.

A. Experimental Design

Aminocyclopyrachlor (Batch /Lot# J

- 868

- 001

- 3 , Purity 88.3

- 90.5% ) was administered to yo ung adult male and female Crlj:CDl(ICR) mice (60/sex/group) in diets that contained 0, 300, 1000,

3000, or 7000 ppm DPX

- MAT28 for approximately 18 months. This corresponded to doses of

approximately 0/0, 39/50, 133/171, 393/527, and 876/1190 mg/kg bw/day in males/females.

B. Discussion of Survival and Tumor Data

The performing laboratory did not find any treatment

- related changes in survival in either sex.

There were also no treatment

- related increases in tumor incidence in either sex. Therefore, no

in

- house statistical analyses were performed.

C. Non

- neoplastic lesions

All non

- neoplastic lesions were consistent with background lesions that are typical of mice of

this age and strain.

D. Adequacy of Dosing for Assessment of Carcinogenicity

The high dose in this study approached the limit dose (876/1190 mkd in males/females). No

adverse effects (including changes in body weight) were observed at this dose level. Dosing was

considered adequate and not excessive

.

IV. TOXICOLOGY

1. Metabolism

Pharmacokinetic studies in rats show that both aminocyclopyrachlor and aminocyclopyrachlor

methyl are rapidly absorbed, with peak concentrations occurring in plasma and red blood cells

(RBCs) at 0.3

- 1.0 hours for aminocyclopyrachlor and at 0.3

- 0.6 hours after dosing for

aminocyclopyrachlor

- methyl. Aminocyclopyrachlor

- methyl was rapidly metabolized to

aminocyclopyrachlor (within 30 minutes). No other metabolites were identified for either

compound. The areas under the curve (AUCs) for both compounds sc aled with dose, indicating

that metabolic processes were not saturated. The (plasma) elimination half

- life of

aminocyclopyrachlor of 5.6

- 5.7 hours was shorter than that for aminocyclopyrachlor

- methyl atAMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

17 8.7

- 13.3 hours. The majority of the administered dose of both compounds was excreted within

24 h, although elimination differed slightly. For aminocyclopyrachlor, 35.8

- 53.71% was

eliminated in the urine and 31.4

- 48.0% was eliminated in the feces. For aminocyclopyrachlor

methyl, the majority was recove red in the urine 78.80

- 78.82%, with a smaller amount eliminated

in the feces (1.72

- 4.57%). Neither aminocyclopyrachlor n or aminocyclopyrachlor

- methyl was

eliminated as expired air. No sex differences in absorption, distribution, metabolism, or

excretion were observed for either aminocyclopyrachlor or aminocyclopyrachlor

- methyl.

Repeated

- dose metabolism studies with aminocyclopyrachlor and aminocyclopyrachlor

- methyl

showed that radioactivity was found primarily in the GI tract and GI contents, with brai n levels

of radioactivity at less than 0.01% at the peak time after administration. Brain levels of

radioactivity were undetectable after 72 hours.

2. Mutagenicity

Genotox icity studies were conducted using aminocyclopyrachlor or aminocyclopyrahclor

- met hyl

as the test material (Table 5) . For aminocyclopyrachlor, there was no evidence of induced

mutant colonies over background in the presence or absence of S9 activation in in vitro bacterial

or mammalian gene mutation assays. There was also no eviden ce of chromosomal aberrations

induced over background in the presence or absence of S9 activation in vitro

. In vivo, t here were

no increases in the frequency of micronucleated polychromatic erythrocytes in bone marrow.

For aminocyclopyrachlor

- methyl

, in vitro bacterial gene mutation studies showed no evidence

of mutant colonies over background in the presence or absence of S9 activation.

Together, these studies indicate that aminocyclopyrahclor

- methyl and aminocyclpyrahclor are not genotoxic.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

18 Table 5

- Genotoxicity Studies

Aminocyclopyrachlor

Gene Mutation

870.5100

In vitro Bacterial Gene Mutation 47560019 (2007)

Acceptable/guideline

0, 50, 150, 500, 1500, or 5000

μg/plate (+/

- S9) There was no evidence of induced

mutant colonies over backgr ound in

the presence or absence of S9

- activation.

Gene Mutation

870.5300

In vitro Mammalian Cells Gene

Mutation (Chinese Hamster Ovary

Cells) 47560020 (2007)

Acceptable/guideline

0, 750, 1000, 1500, 1750, or 2150

μg/mL (+/

- S9) There was no evidence of induced

mutant colonies over background in

the presence or absence of S9

- activation.

Cytogenetics

870.5375

In vitro Mammalian Cytogenetics

Chromosomal Aberration Assay

human peripheral blood

lymphocytes 47560021 (2007)

Acceptable/guideline

0, 267, 53 4, 1068, or 2136 μg/mL

(+/

- S9) There was no evidence of

chromosome aberrations induced

over background in the presence or

absence of S9

- activation.

Cytogenetics

- other

870.5395 In Vivo Mammalian

Cytogenetics

- Erythrocyte

Micronucleus

- mouse 47560022 (2007 )

0, 500, 1000, or 2000 mg/kg (limit

dose) No significant increase in the

frequency of micronucleated

polychromatic erythrocytes in bone

marrow after any treatment time.

Aminocyclopyrachlor

- methyl

Gene Mutation

870.5100

In vitro Bacterial Gene Mutatio n 47560033 (2005)

Acceptable/Non

- guideline

0, 100, 333, 1000, 3333, or 5000

μg/plate (+/

- S9) There was no evidence of induced

mutant colonies over background in

the presence or absence of S9

- activation.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

19 3. Structure

- Activity Relationship

Aminocyclopy rachlor has three structural alerts/features (monocyclic heterocyclic aromatic

amine, halogenated aromatic, nucleoside analog) of potential carcinogenic activity; however, the

predictive capability of these features tends to be limited or marginal. The con cern is further

mitigated by the presence of a carboxylic acid moiety (which can promote rapid excretion), the

ring position of chlorine (not ortho to ring nitrogen and therefore not a good leaving group), and

the bulky cyclopropane substituent. This is s upported by the submitted experimental data

showing rapid excretion of the chemical and lack of genotoxicity. Overall, there is no sufficient

basis for SAR concern.

4. Subchronic and Chronic Toxicity

Toxic effects of aminocyclopyrachlor and aminocyclop yrachlor

- methyl via the oral route of

exposure (in the diet) in subchronic (90

- Day) rodent studies were limited to decreases in body

weights ( ≤10%), body weight gains, food consumption, and food efficiency in both sexes when

these compounds were administer ed to rats at the limit dose (1000 mg/kg/day) with no adverse

effects observed in mice. Similar results were observed in chronic toxicity/carcinogenicity

studies in rats and mice conducted near the limit dose. Only mild effects were observed on body

wei ght in rats, which were limited to sporadic decreases in body weight of up to 12% that

recovered by the end of the study. No adverse effects were observed in mice.

5. Mode of Action Studie s

No mode of action studies were submitted.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

20 V. COMMITTEE’S A SSESSMENT OF THE WEI GHT

- OF

- THE EVIDENCE

The Committee considered the following for a weight

- of

- evidence determination of the

carcinogenic potential of aminocyclopyrachlor.

1. Carcinogenicity

Rat

• Brain Tumors: The CARC concluded that the brain tumors (glial cell tumors and granular

cell tumors) observed in male rats were spontaneous lesions and were not considered to be

treatment

- related. This was based on the following weight

- of

- evidence considerations : 1) Although there were significant trends and pair

- wise comparisons at the high dose for

astrocytomas and glial cell tumors combined by the Peto analysis, the incidences were

within the historical control range. For granular cell tumors, there was a significant trend

only, but no significant pair

- wise comparison of any dose group with the controls. In

addition, the Fishers Exact test showed trends on ly and no pair

- wise comparisons of any

dose level with the controls for combined glial tumors and for granular cell tumors. 2 ) No

supporting treatment

- rel ated pre

- neoplastic lesions were observed in the brain (or any other

tissue). (Chemicals known to cause brain tumors also are commonly tumor i genic in other

tissues, J. Plet cher, Consulting Pathologist, Personal Communication); 3 ) The tumors

occurred at the limit dose; no other tumors were seen; 4) No treatment

- related brain

neoplastic lesio ns were observed in female rats

. 5 ) No evidence of genotoxicity was

observed in in vitro or in vivo genotoxicity studies. 6 ) Brain levels of radioactivity after

administr ation of aminocyclopyrachlor at times corresponding to peak plasma concentration

were very low (<0.01%) and were undetectable after 72 hours. ; 7) the Pathology Peer

Review also concluded that the brain tumors were spontaneous tumors and not treatment

relat ed (MRID 48333607).

• Adequacy of Dosing: Dosing was considered adequate, and not excessive, for assessing

carcinogenicity since the high dose approached the limit dose in both sexes (892/957 mg/kg

bw/day in males/females). The high dose also caused mil d decreases on body weight

(decrease up to 12%) and body weight gain (decrease up to 11%) in both sexes during the

study, but had resolved by the conclusion of the study.

M ouse

• There were no treatment

- related increases in tumor incidence s in either s ex.

• Adequacy of Dosing: Dosing was considered adequate , and not excessive, since the

high dose in this study approached the limit dose (876/1190 mg/kg/day in

males/females). No adverse effects (including changes in body weight) were observed at

th is dose level.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

21 2. Mutagenicity: There is no concern for mutagenicity.

3. SAR : There is no sufficient basis for SAR concern

.

VI. CLASSIFICATION OF CARCINOGENIC POTE NTIAL

In accordance with the EPA's Final Guidelines for Carcinogen Risk Assessment (March, 2005)

, the CARC classified aminocyclopyrachlor as “Not L ikely to be Carcinogenic to H umans.”

There were no treatment

- related tumors seen in male or female rats or mice at doses that were

adequate to assess carcinogenicity and there was no concern for mutagenicity.

VII. QUANTIFICA T I ON OF CARCINOGENICIT Y

Quantification of carcinogenicity is not required

.

VII. BIBLOGRAPHY

47560019 Wagner, V.; VanDyke, M. (2008) DPX

- MAT28 Technical: Bacterial Reverse

Mutation As say. Project Number: AC02HJ/503/BTL, 17293, H/27937. Unpublished study

prepared by Bioreliance and Dupont Haskell Laboratory.

47560020 Clarke, J. (2007) DPX

- MAT28 Technical: In vitro Mammalian Cell Gene Mutation

Test (CHO/HGPRT Assay) . Project Number: AC02HJ/782/BTL, 17293, 515. Unpublished

study prepared by Bioreliance and Dupont Haskell Laboratory.

47560021 Gudi, R.; Rao, M. (2007) DPX

- MAT28 Technical: In vitro Mammalian

Chromosome Aberration Test in Human Peripheral Blood Ly mphocytes. Project Number:

AC02HJ/341/BTL, DUPONT/22709, 17293. Unpublished study prepared by Bioreliance.

47560022 Krsmanovic, L.; Huston, T. (2007) DPX

- MAT28 Technical: Mouse Bone Marrow

Erythrocyte Micronucleus Test: Final Report. Project Numbe r: AC02HJ/123/BTL, 17293, 572.

Unpublished study prepared by Dupont Haskell Laboratory and Bioreliance.

47560033 Ford, L. (2005) IN

- KJM44: Bacterial Reverse Mutation Test. Project Number:

DUPONT/17971, 15744, 502. Unpublished study prepared by E.I. du Pont de Nemours and

Company. 33 p.

48333606 Jung

- Im Huh, Ph.D. (2010). DPX

- MAT28 Tech nical: Carcinogenicity 18

- Month

Feeding Study in Mice. Korea Institute of Toxicology, Republic of Korea. Laboratory Study

Number: IG07280, October 15, 2010 Unp ublished

.AMINOCYCLOPYRACHLOR CANCER ASSESSMENT DOCUMENT FINAL

22 48333607 Moon, Kyoung. (2010). DPX

- MAT28 Technical: Carcinogenicity 2

- Year Feeding

Study in Rats. Korea Institute of Tox icology, Daejeon, Republic of Korea. Laboratory Study

Number: IG07280, November 24, 2010, MRID Unpublished

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Brunsman, L. 2011. Aminocyclopyrachlor Qualitative Risk Assessment Based On Crl:CD(SD)

Rat Dietary Study. August 3, 2011. TXR No. 0055738.