Data Selection for Calculating the Acceptable Intake of ......5 Ethylene Oxide is Genotoxic •...
Transcript of Data Selection for Calculating the Acceptable Intake of ......5 Ethylene Oxide is Genotoxic •...
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Data Selection for Calculating
the Acceptable Intake of
Ethylene Oxide (CAS# 75-21-8)
Zhanna Sobol
May 2, 2018
Genetic Toxicology Association Annual Meeting – PDE Workshop
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Acknowledgments
• Pamela Heard
• Michelle Kenyon
• Krista Dobo
• Will Drewe
• Georgia Clarke
• Liz Lepley
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Outline
• Background on Ethylene Oxide
• Review study selection guidance in ICH M7 Addendum
• Describe Available carcinogenicity studies for Ethylene Oxide
• Discussion Question 1 – What study would you choose?
• Describe Pfizer’s selection of best study for AI calculation
• Additional considerations for AI
• Discussion Question 2 – Should additional considerations be
factored into AI calculation?
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Ethylene Oxide is a Flammable Gas
• Potential for Human Exposure
– major industrial chemical used for synthesis of numerous
products such as ethylene glycol (antifreeze and polyester)
– Used as cold sterilizing agent for food and medical equipment
– Fumigant and fungicide
– Humans may be exposed through environmental contamination
of air/water or in the workplace where ethylene oxide is utilized
– Amounts in food are low as ethylene oxide evaporates or breaks
down shortly after fumigation
• Regulatory and/or Published Limits
– OSHA PEL (permissible exposure limit) = 1 ppm (averaged over
an 8-hour workshift) = 1.8 mg/m3 = 18 mg/day
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Ethylene Oxide is Genotoxic
• Mechanism of Genotoxicity – direct-acting alkylating agent (epoxide)
• In vitro
– positive for induction of reverse mutations in strains TA98, TA100, TA102, TA1535, TA1537 and in E. coli with and without metabolic activation
– sister chromatid exchanges in human lymphocytes
– unscheduled DNA synthesis in mouse germ cells
– forward mutations (HPRT assay) in Chinese Hamster Ovary cells
• In vivo
– translocations in mice
– micronuclei in mouse bone marrow cells (NTP, 1987)
– chromosomal aberrations in bone marrow of rats (NTP, 1987)
– In workers caused chromosomal aberrations and sister chromatid exchange in peripheral lymphocytes and micronuclei in bone-marrow cells (ATSDR, 1990)
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Ethylene Oxide is Carcinogenic
• Linear extrapolation from a
carcinogenicity study is the
appropriate approach for
calculating a compound-
specific limit
• Which study to choose?
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ICH M7 Addendum Guidance for Study Selection
• Carcinogenicity studies are not considered robust when:
– < 50 animals per dose per sex
– < 3 dose levels
– Lack of concurrent controls
– Intermittent dosing (< 5 days per week)
– Dosing for less than lifetime
• Exception
–
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Additional Considerations
• Selection of Tumor and Site
– Lowest TD50 for organ site, animal species and sex from the most robust study
– Do not use data compiled from “all Tumor Bearing Animals” (TBA)
– mixed tumor types (e.g.,adenomas and carcinomas) in one tissue (e.g., liver) can be used
– lowest TD50 is considered a more conservative estimate than harmonic mean
• Route of administration
– If tumor sites did not appear to be route-specific, the TD50 from the route with the lowest TD50 value should be used
– If tumors are site-specific without distal tumors and TD50 is lower than for other routes, warrants separate AI
• Human relevance of rodent carcinogenicity study findings
– Forestomach tumors, tumors at site of contact only without distal tumors
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Which TD50 Should I choose?
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Carcinogenicity Studies with Ethylene Oxide in CPDB
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7
Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
7.43
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Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
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Workshop Question 1: Which Value would you choose?
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7A.
B.
C.
D.
E.
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Our Approach
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Carcinogenicity Studies with Ethylene Oxide in CPDB
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7
Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
7.43
Not relevant
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Carcinogenicity Studies with Ethylene Oxide in CPDB
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7
Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
7.43
Too high
Too high
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Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
7.43
Carcinogenicity Studies with Ethylene Oxide in CPDB
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7
Included in ICH M7
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Study Animals/
dose group
Duration/
Exposure
Controls Doses
(adjusted doses)+Most sensitive tumor
site/sex
TD50(mg/kg/d)++
NTP 1987
(TR326)
50/sex/group
B6C3F1 mice
6h/day, 5
days/wk,
102 weeks,
inhalation
50 50 and 100 ppm
(24.7 and 49.4
mg/kg/day)
Lung multiple tumor
type/female
61.8
Lynch et al.,
1984
80/male/
Fischer 344
rats, pooled
controls*
7h/day, 5
days/wk,
104 weeks,
inhalation
80 50 and 100 ppm
(12.8 and 25.6
mg/kg/day)
Peritoneum
Mesothelioma/male
30.8
Snellings et
al., 1984
120/male
and female/
Fischer 344
rats**
6h/day, 5
days/wk,
104 weeks,
inhalation
120 10, 33, 100 ppm
(2.2, 7.2, 21.9
mg/kg/day)
Brain multiple tumor
type/male
70.7
Dunkelberg
1982
50/female/Sp
rague-
Dawley rats
2 days/wk,
150 weeks,
gavage
50 7.5 and 30 mg/kg
(2.14 and 8.57
mg/kg/day)
primarily
forestomach tumors
without distal site
tumors
7.43
Carcinogenicity Studies with Ethylene Oxide in CPDB
++Taken from the CPDB. The TD50 values represent the TD50 from the most sensitive tumor site, species, and sex for each study.
TD50 (mg/kg/day)
Rat Mouse
21.3 63.7
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AI Calculated based 30.8
• Lifetime AI = TD50/50,000 x 50kg
• Lifetime AI = 30.8 mg/kg ÷ 50,000 × 50 kg× 1000 µg
• Lifetime AI = 30.8 µg/day
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Additional Consideration
“Higher acceptable intakes may be justified when human exposure to the impurity will be much greater from other sources e.g., food, or endogenous metabolism (e.g., formaldehyde).”
• Ethylene Oxide is generated endogenously from ethylene (Bolt 2000)
– lipid peroxidation
– oxidation of free methionine
– oxidation of hemin in hemoglobin
– and metabolism of intestinal bacteria
• Endogenous levels and risk assessment calculated based on DNA lesions and epidemiological data (Kirman 2004)
• An exposure to ~0.1 ppm ethylene oxide for working lifetime would lead to a theoretical cancer risk of 1 x 10-5 (Valdez-Flores 2011)
– 0.1 ppm = 0.183 mg/m3 = 1.8 mg/day (10 m3 of air breathed in an 8-hour work day)
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References
• Lynch, D. W., Lewis, T. R., Moorman, W. J., Burg, J. R., Groth, D. H., Khan, A., Ackerman, L. J., and Cockrell, B. Y. Carcinogenic and toxicologic effects of inhaled ethylene oxide and propylene oxide in F344 rats. Toxicol. Appl. Pharmacol. 76: 69-84(1984).
• Snellings, W. M., Weil, C. S., and Maronpot, R. R. A two-year inhalation study of the carcinogenic potential of ethylene oxide in Fischer 344 rats. Toxicol.Appl.Pharmacol. 75: 105-117(1984).
• Dunkelberg, H. Carcinogenicity of ethylene oxide and 1,2-propylene oxide upon intragastric administration to rats. Br. J. Cancer 46: 924-933(1982).
• ICH M7(R2). Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk
• Bolt, H.M. (2000) Carcinogenicity and Genotoxicity of Ethylene Oxide: New Aspects and Recent Advances, Critical Reviews in Toxicology, 30:5, 595-608
• Kirman CR, Sweeney LM, Teta MJ, Sielken RL, Valdez-Flores C, Albertini RJ, Gargas ML (2004) Addressing nonlinearity in the exposure-response relationship for a genotoxic carcinogen: Cancer potency estimates for ethylene oxide. Risk Analysis 24: 1165-1183
• Valdez-Flores C, Sielken RL Jr, Teta MJ (2011). Quantitative cancer risk assessment for ethylene oxide inhalation in occupational settings. Arch Toxicol 85:1189-1193