QSAR in CANCER ASSESSMENT

PURPOSE and AGENDA

Gilman VeithDuluth MN

May 19-21, 2010

McKim Workshop Goals

Summarize regulatory contexts for hazard identification and risk estimation of carcinogenesis

Review progress on alternative methods for estimating endpoints needed in cancer assessment

Discuss the need for a mechanistic framework for improving the transparency of alternative models

Identify examples of chemical categories for which alternatives reliably predict outcomes of rodent assays

REGULATORY CONTEXTS

Precautionary Perspective

“What additional other test results would I want to see before I am willing to conclude a chemical is safe?”

Holistic Risk Perspective

“How can I identify greatest carcinogenic risks among all chemicals regardless of their testing status?”

HAZARD CLASSIFICATION CARCINOGENICITY

IARC

GHS

EPA

ACGIH

Description/Status of Available Data

1 1A 1 A1 Human carcinogen, definite, human studies

2A 1B 2 A2 Probably human, animal data multiple species, no epi data

2B 2 3 A3 Possibly human, suspected, some animal data

3 4 A4 Not classifiable, inadequate data to assess

4 5 A5 Probably not human, not suspected, no tumors in at least two species

HAZARD CLASSIFICATION CARCINOGENICITY

Carcinogenic to Humans (epi data required)

Likely to be Carcinogenic to Humans (tumors in two species)

Suggestive Evidence of Carcinogenic Potential

Inadequate Information to Assess Carcinogenic Potential

Not Likely to be Carcinogenic to Humans (no tumors in two species)

DATA DRIVEN HAZARD ASSESSMENT

CARCINOGENIC POTENTIAL

DATA DRIVEN HAZARD ASSESSMENT

CARCINOGENIC POTENTIAL

New Product

Development

Testing/AssessmentRequirements

NumberOfChemicals

Safety Assessment Process

INITIAL HAZARD ASSESSMENTS

Screening Information Datasets – SIDS

Globally Harmonised System of C&L – GHS

REACH –Dossier Testing Plan Reviews

TSCA –PMNs (predictive hazard identification)

QSAR in chemical engineering has always been used to focus attention/resources on specific activities

QSAR orders chemicals according to intrinsic attributes and generates initial hypotheses for more strategic use of testing and assessment resources

Structural alerts are a convenient and transparent approach to identifying hazard-specific priorities

STREAMLINING DATA REQUIREMENTS

MolecularInitiating

Events

Chemical Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

Conceptual Framework

Schultz et al. 2006. SAR QSAR in Environ.Res. 17(4) 1-16.

MolecularInitiating

Events

Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

Conceptual Framework

QSARQSAR ResponseResponsePathways Pathways

Chemistry/Chemistry/BiochemistryBiochemistry

MolecularInitiating

Events

Chemical Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

Conceptual Framework

Mortality-systemic toxicity

-disease-cancer

Impaired Development

-terata-prenatal deficits

Reproductive Fitness-fertility

-viable offspring

Chemical Inventories andCategories(~200,000)

InteractionMechanisms

-Nonspecific Targets

-Atom Center Targets

-Receptor Targets

MolecularInitiating

Events

Chemical Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

At the Molecular Initiating Event

The QSAR Question is:

“How many other chemicalscan interact at this target?”

While the Assessment Question is:

“What are the known biologicaleffects from this altered target….organelles, cells , organs, species ”

LibraryOf

MolecularInitiating

Events

Chemical Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

From the Library of Initiating Events

Chemical Chemical ProfilersProfilers

Available in Available in A Variety of A Variety of

Commercial & Commercial & Public Software Public Software

TargetsInteractions

Structural Requirements

Conformations

Metabolic SimulatorsInventories

LibraryOf

MolecularInitiating

Events

Chemical Speciation

and

Metabolism

MeasurableBiological

Effects

Adverse Outcomes

ParentChemical

From the Library of Initiating Events

DNABinding

Altered Genes/Proteins

Genetic Instability/

Cell Immortality

Acquisition ofTumorigenicity

PrematureDeath

GROUPING BY CANCER PATHWAYS

Genotoxic Carcinogenesis Direct DNA damage through abiotic chemical “binding” Most electrophiles bind to many DNA/protein sites Metabolic differences impact cell, organ, species

sensitivity

Epigenetic Carcinogenesis Cytoxicity-induced cell proliferation Receptor-mediated pathways Disturbance of homeostatic control Loss of immune surveillance Oxidative Stress- Indirect DNA damage Loss of intercellular communication

SCREENING LEVEL HAZARD ID

Direct DNA

Binding

Nongenotoxic

Mechanisms

ActivatedMetabolites

Indirect DNA

Damage

ParentChemica

l Individual

Initiating Events/Structur

al Alerts

Grouping Data for Interacti

onCategori

es

StructuralEvidence

of Cancer

Potential

Category with

Data for Cancer Potential

No EvidenceOf Cancer Potential

Simulated 2-Acetylaminofluorene

Metabolism

NH

O

NH

O

OH

NH

O

O

NH2

O

HO

O

NHOH

O

N+HO

NH

OHO

NH

O

O

NH

O

O

NH

OHO

NH

OHO

OHNH

OHO

OH

NH

OHO

O

NH

OHO

O

N+H

HO

ON+H

OH

O

. . . . . .

NHX

OO

X = H, OH,

O

Activated metabolites

Models for the Metabolism Gap

PATHWAYS IN REACTIVE CHEMICALS

MichaelAddition

Schiff baseFormation

SN2

Acylation

MichaelAddition

Schiff baseFormation

SN2

Acylation

AtomCentered

Irreversible(Covalent)Binding

AtomCentered

Irreversible(Covalent)Binding

InteractionMechanisms

MolecularInitiatingEvents

In vivoEndpoints

Pr-S AdductsGSH OxidationGSH DepletionNH2 AdductsRN AdductsDNA Adducts

Pr-S AdductsGSH OxidationGSH DepletionNH2 AdductsRN AdductsDNA Adducts

In vitroEndpoints

Death

ImpairedGrowth

Impaired Development

Impaired Reproduction

Cancer

Membrane Alteration

___

Oxidative Stress

___

Genotoxicity

OXIDATIVE STRESS from GSH DEPLETION

Pr-S Adducts

GSH Oxidation

GSH Depletion

NH2 Adducts

RN Adducts

DNA Adducts

Oxidative

Stress

Cell toxicit

y

Other Effects

DirectGSH

Reactions

AlteredSynthes

is

Oxidation

How Many Ways to Deplete GSH? How Many Downstream Effects?

Mode of Action

Receptor-mediated pathways

Disturbance of homeostaticcontrol

Loss of immune surveillance

Oxidative Stress- Indirect DNA damage

Loss of intercellular communication

Cytotoxicity-induced cell proliferation

GENOTOXICITY

Direct DNA Damage

Indirect DNA Damage

NON-GENOTOXICITY

Receptor-mediated pathways

Disturbance of homeostaticcontrol

Loss of immune surveillance

Oxidative Stress- Indirect DNA damage

Loss of intercellular communication

Cytotoxicity-induced cell proliferation

GENOTOXICITY

Direct DNA Damage

Indirect DNA Damage

NON-GENOTOXICITY

DNA Mechanism #1DNA Mechanism #2DNA Mechanism #3

DNA Mechanism #n……………………………

Prot Mechanism #1Prot Mechanism #2Prot Mechanism #3……………………………Prot Mechanism #n

AR BindingER BindingAromatase Inh.Thyroid Disturbance

Mechanism/AlertMode of action

Receptor-mediated pathways

Disturbance of homeostaticcontrol

Loss of immune surveillance

Oxidative Stress- Indirect DNA damage

Loss of intercellular communication

Cytotoxicity-induced cell proliferation

GENOTOXICITY

Direct DNA Damage

Indirect DNA Damage

NON-GENOTOXICITY

Mechanism/Alert

DNA #1DNA #2DNA #3

DNA #n………….

Prot #1Prot #2Prot #3…………..Prot #n

AR BindingER BindingAromatase Inh.Thyroid Disturbance

Mechanism/Metabolites

DNA Mechanism #1-Met 1…mDNA Mechanism #2-Met 1…mDNA Mechanism #3-Met 1…m

……………………………DNA Mechanism #3-Met 1…m

Prot Mechanism #1 - Met 1..mProt Mechanism #2 - Met 1..mProt Mechanism #3 - Met 1..m

……………………………Prot Mechanism #n - Met 1..m

Receptor-mediated pathways -Met 1…m

Disturbance of homeostatic control -Met 1…m

Loss of immune surveillance-Met 1…m

Oxidative Stress- Indirect DNA damage -Met 1…m

Loss of intercellular comm.-Met 1…m

Cytotoxicity-induced cell proliferation-Met 1…m

Mode of action

Receptor-mediated pathways

Disturbance of homeostaticcontrol

Loss of immune surveillance

Oxidative Stress- Indirect DNA damage

Loss of intercellular communication

Cytotoxicity-induced cell proliferation

GENOTOXICITY

Direct DNA Damage

Indirect DNA Damage

NON-GENOTOXICITY

Mechanism/Alert

DNA #1DNA #2DNA #3

DNA #n………….

Prot #1Prot #2Prot #3…………..Prot #n

AR BindingER BindingAromatase Inh.Thyroid Disturbance

Mechanism/Metabolites

Receptor-mediated pathways -Met 1…m

Disturbance of homeostatic control -Met 1…m

Loss of immune surveillance-Met 1…m

Oxidative Stress- Indirect DNA damage -Met 1…m

Loss of intercellular comm.-Met 1…m

Cytotoxicity-induced cell proliferation-Met 1…m

DNA #1-Met 1…mDNA #2-Met 1…m

……………………………DNA #3-Met 1…m

Prot #1 - Met 1..mProt #2 - Met 1..mProt #3 - Met 1..m……………………………Prot #n - Met 1..m

DNA #3-Met 1…m

In vitro data

Ames Ames+S9 CA CA+S9 MLA MLA+S9 CTA

Mode of action

Receptor-mediated pathways

Disturbance of homeostaticcontrol

Loss of immune surveillance

Oxidative Stress- Indirect DNA damage

Loss of intercellular communication

Cytotoxicity-induced cell proliferation

GENOTOXICITY

Direct DNA Damage

Indirect DNA Damage

NON-GENOTOXICITY

Mechanism/Alert

DNA #1DNA #2DNA #3

DNA #n………….

Prot #1Prot #2Prot #3…………..Prot #n

AR BindingER BindingAromatase Inh.Thyroid Disturbance

Mechanism/Metabolites

Receptor-mediated pathways -Met 1…m

Disturbance of homeostatic control -Met 1…m

Loss of immune surveillance-Met 1…m

Oxidative Stress- Indirect DNA damage -Met 1…m

Loss of intercellular comm.-Met 1…m

Cytotoxicity-induced cell proliferation-Met 1…m

DNA #1-Met 1…mDNA #2-Met 1…m

……………………………DNA #3-Met 1…m

Prot #1 - Met 1..mProt #2 - Met 1..mProt #3 - Met 1..m……………………………Prot #n - Met 1..m

DNA #3-Met 1…m

In vitro data

Ames

Ames+S9

CA

CA+S9

MLA

MLA+S9

CTA

In vivo data

COMET UDS CA MN(BN) CTA RCA

Mode of action