group 6 follow-up of in vivo positive results
DESCRIPTION
5 TH INTERNATIONAL WORKSHOP ON GENOTOXICITY TESTING Basel, August 17-19, 2009. Group 6 Follow-up of in vivo positive results Follow-up of 2005 IWGT and subsequent work done by HESI IVGT on “follow-up of in vitro positive results”. - PowerPoint PPT PresentationTRANSCRIPT
Group 6
Follow-up of in vivo positive results
• Follow-up of 2005 IWGT and subsequent work done by HESI IVGT on “follow-up of in vitro positive results”.
• Takes into consideration the new data and information available on dose-response curves and mode of action.
5TH INTERNATIONAL WORKSHOP ON GENOTOXICITY TESTING
Basel, August 17-19, 2009
Name Region e-mail
1 Jan Van Bentem Europe, Netherlands Regulatory [email protected]
2 Ricardo Crebelli Europe, Italy Regulatory [email protected]
3 Kerry Dearfield USA Regulatory [email protected]
4 George Douglas Canada Regulatory [email protected]
5 Peter Farmer Europe, UK Academic [email protected]
6 Elmar Gocke Europe, Switzerland Industry [email protected]
7 Baskhar Gollapudi USA Industry [email protected]
8 Makoto Hayashi Japan Regulatory [email protected]
9 David Lovell Europe, UK Academic [email protected]
10 Werner Lutz Europe, Germany Academic [email protected]
11 Takehiko Nohmi Japan Academic [email protected]
12 Jim MacGregor, Rapporteur
USA Consultant [email protected]
13 Daniel Marzin Europe, France Regulatory [email protected]
14 Martha Moore USA Regulatory [email protected]
15 David Phillips Europe, UK Academic [email protected]
16 Lutz Műller, Co-Chair
Europe, Switzerland Industry [email protected]
17 Véronique Thybaud, Chair
Europe, France Industry [email protected]
Tripartite group: three main regions, Scientists from academic laboratories, regulatory authorities and industry
Participants of “In vivo follow-up” workgroup
Not able to attend
Topics:Topic 1: Use of in vitro results in the designand interpretation of in vivo assays
Topic 2: Quantitative aspects of the doseresponse curve
Topic 3: Evaluation and impact of Mode of Action
Topic 4: Update on in vivo models
C*: agreement both on principle and wording
No C*: agreement on principle, wording to be refined (lack oftime).
5TH IWGT in Basel, 2009Group 6: Follow-up of positives results
Topic 1
Use of in vitro results in the design and interpretation of in vivo assays
• 2005 IWGT and IVGT flow chartsKerry Dearfield
5TH IWGT in Basel, 2009Group 6: Follow-up of positives results
Shown to be due to confounding factors? e.g. culture conditions & interactions, cell-specific metabolism, impurities.
In vitro “clear” positive results
− Conduct in vivotests (selection depending on available data).
− Interpret in vivoresults in relation to all available information.
Analyze the existing genotoxicity data.
No Yes
Available information confirms the
concern.
Can the in vivo data help improve WOE and assessment of the potential risk for human associated to
the usage?
No further testing. Consider as potentially genotoxic.
No
Yes
No Yes
Evaluate the in vitropositive results with the in vivodata.
Available information confirms the
concern.
No
Conclude as genotoxic.No follow-up necessary.
Yes
Conclude (by WOE and/or MOA
evaluation) of low concern.
No follow-up necessary.
Conclude (by WOE and/or MOA) of low concern for human
risk associated to the usage.
No follow-up necessary.
Review all available datafor WOE and MOA:- SAR, physico-chemistry, ADME, PB/PK, etc.
3
Conduct additional testingif data not yet available, consider:
− in vitro genotoxicity tests to confirm the results, and assess the types of genetic damage,
− assays to evaluate possible interaction with DNA (DNA reactive),
− assays to evaluate a non DNA-reactive mechanism.
3
1
4
6
5
2
5
6
Shown to be due to confounding factors? e.g. culture conditions & interactions, cell-specific metabolism, impurities.
In vitro “clear” positive resultsIn vitro “clear” positive results
− Conduct in vivotests (selection depending on available data).
− Interpret in vivoresults in relation to all available information.
− Conduct in vivotests (selection depending on available data).
− Interpret in vivoresults in relation to all available information.
Analyze the existing genotoxicity data.Analyze the existing genotoxicity data.
No Yes
Available information confirms the
concern.
Available information confirms the
concern.
Can the in vivo data help improve WOE and assessment of the potential risk for human associated to
the usage?
Can the in vivo data help improve WOE and assessment of the potential risk for human associated to
the usage?
No further testing. Consider as potentially genotoxic.
No further testing. Consider as potentially genotoxic.
No
Yes
No Yes
Evaluate the in vitropositive results with the in vivodata.
Evaluate the in vitropositive results with the in vivodata.
Available information confirms the
concern.
Available information confirms the
concern.
No
Conclude as genotoxic.No follow-up necessary.
Conclude as genotoxic.No follow-up necessary.
Yes
Conclude (by WOE and/or MOA
evaluation) of low concern.
No follow-up necessary.
Conclude (by WOE and/or MOA
evaluation) of low concern.
No follow-up necessary.
Conclude (by WOE and/or MOA) of low concern for human
risk associated to the usage.
No follow-up necessary.
Conclude (by WOE and/or MOA) of low concern for human
risk associated to the usage.
No follow-up necessary.
Review all available datafor WOE and MOA:- SAR, physico-chemistry, ADME, PB/PK, etc.
Review all available datafor WOE and MOA:- SAR, physico-chemistry, ADME, PB/PK, etc.
33
Conduct additional testingif data not yet available, consider:
− in vitro genotoxicity tests to confirm the results, and assess the types of genetic damage,
− assays to evaluate possible interaction with DNA (DNA reactive),
− assays to evaluate a non DNA-reactive mechanism.
Conduct additional testingif data not yet available, consider:
− in vitro genotoxicity tests to confirm the results, and assess the types of genetic damage,
− assays to evaluate possible interaction with DNA (DNA reactive),
− assays to evaluate a non DNA-reactive mechanism.
Conduct additional testingif data not yet available, consider:
− in vitro genotoxicity tests to confirm the results, and assess the types of genetic damage,
− assays to evaluate possible interaction with DNA (DNA reactive),
− assays to evaluate a non DNA-reactive mechanism.
33
11
44
66
55
22
55
66
IVGT Review group: Flow chart for follow-up actions
Topic 1: Statements• The endpoint studied in vivo needs to be appropriate, e.g.,
the same as that found increased in vitro or a surrogate shown to be appropriate for predicting that same endpoint. It is recognized that some systems are not specific to a single endpoint, and this must be taken into account. C*
• The selection of tissue(s) should consider tissue exposure, ADME information compound metabolism, and other toxicological considerations. C*
• If in vitro test(s) are positive, and in vivo tests are conducted, the risk can be considered to be negligible if follow-up test(s) in appropriate tissues and endpoints in vivo at appropriate doses show that the in vitro results are probably not of concern in vivo. C*
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 2: Quantitative aspects of the doseresponse curve
• Viracept case study:Genotoxicity data in animals, dose-response curves and statistical assessment, and risk assessment for the human exposure. Elmar Gocke and Lutz Müller
• Quantitative aspects of in vivo risk and the potential role of new flow cytometric genetic toxicity assays
Jim MacGregor
• Analysis of dose-response curves (threshold, NOEL, etc) Werner Lutz
• Potential modifiers of dose-response curves. Could additional effects (e.g. induction of cell proliferation) lower the apparent threshold?
Véronique Thybaud
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 2: StatementsFor risk assessment – in vivo follow up of positives (afterreview of Viracept data):
• Transgenic animals are acceptable surrogates to internal genes for risk assessment. C*
• For risk assessment, internal dose is a key element, and may include:
– Cmax/AUC
– Surrogate endpoints, DNA/protein adducts.
• Nonlinear response curves can be shown in vivo, even with DNA-reactive agents, but must be demonstrated with appropriate data.
– Statistical scrutiny must be applied.
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 2: Statements• Hazard-screening is sufficient for public health protection if current
screening tests (in vitro mutation and chromosomal aberration plus in vivo chromosomal damage) are negative, but when in vivo genotoxicity is identified then additional in vivo data are necessary to define risk in relation to exposure.
• Dose and exposure metrics must be justified in each situation.
• Cross-species extrapolation should consider the same factors used for other toxicity endpoints: e.g., relative metabolism, PK differences, surface area scaling, plus DNA repair differences and relative apoptosis efficiency. C*
• Secondary factors (i.e., potential modifiers of dose-response curves) such as cell proliferation may modify mutagenic responses, therefore risk assessment must take this into account. C*– The impact of the secondary mechanisms) may be tissue specific. C*
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 2: Statements• Agents documented to induce genetic damage via
interaction with non-DNA targets are expected to exhibit a “threshold” below which damage does not occur.– For such “threshold” mechanisms, the NOGEL is appropriate
metric to which additional safety margins may be applied. • For “DNA-reactive” genotoxicants:
– DNA primary damage can be used for exposure, while stable mutations should be used for risk assessment.
– Some agents may exhibit a [“practical threshold”]: i.e., a dose below which exposure does not add significantly to background rates of DNA damage.
– Additional data are necessary to determine if generalizations can be made to define “practical thresholds” of concern for genotoxic/mutagenic damage.
– Consensus is needed about appropriate analytical (statistical) methods of defining thresholds and risk levels (e.g., margin of exposure).
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 3: Evaluation and impact of Mode of Action • Genotoxic versus non-genotoxic mechanisms: feed-back
from Genotoxic and Carcinogenic Thresholds in Tokyo. Takehiko Nohmi
• Use of in vivo mutation data to inform MOA for cancer. Martha Moore
• Examples of species, tissue and high dose specific effect, and mechanistic studies.
Daniel Marzin• Evaluation (and regulation) of in vivo positives with
adequate negative carcinogenicity data: example a substance recently evaluated in an European regulatory body.
Riccardo crebelli
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 3: Statements • The better the information and data (e.g., MOA)
the more certainty you will have in interpreting the dose-response curve. This leads to less uncertainty when determining an acceptable exposure level. C*
• In case of MOA analysis and extrapolation to human:– All data should be used, not only genotoxicity data.– In vitro studies may be designed to address
mechanistic questions, and aid extrapolation to human.
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 3: Statements • Mode of action of individual compounds is decisive
for risk assessment.• Mechanisms underlying the shape of the dose-
response curve should be investigated more thoroughly in vitro and in vivo.
• Genotoxicity should be examined in target organs of chemical carcinogens, using the same species and strains, when possible.
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 3: Statements (may need more work)• In vivo mutagenicity can be associated with adverse
effects other than cancer, and this endpoint warrants consideration in risk assessment.
– Negative carcinogenicity data may not give by default reassurance on the lack of genotoxicity in vivo for in vitro genotoxins.
– For in vitro genotoxins the possibility of somatic (and eventually germ cell) effects in vivo is to be considered, even in presence of negative carcinogenicity data.
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 4: Update on in vivo Models
• Current status of F344 gpt delta rats for in vivo mutagenesis.
Takehiko Nohmi
• Comparison between transgenes and endogenous genes. George Douglas
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Topic 4: Statements • TGR assays provide data of comparable quality and
predictivity for carcinogenicity compared to other standard mutagenicity tests.
• They can be used effectively to follow up results of other in vivo tests, (as well as in vitro tests).
• TGR assays fill a need in current regulatory practices (e.g. in vivo follow-up).
• Need to continue development of in vivo assays, esp. multi-endpoint, multi-species assays (including Human).
• Promising assays include:– Pig-a, flow cytometric micronucleus assays– gptΔ rats and mice.
5TH IWGT in Basel, 2009Follow-up of in vivo positives results
Thank you!
5TH INTERNATIONAL WORKSHOP ON GENOTOXICITY TESTING
Basel, August 17-19, 2009