1

QSAR-based Prediction of Inhalation Toxicity

Kendall B. Wallace, Eli Petkova, Gilman D. Veith

University of Minnesota – Duluth Medical School &

International QSAR Foundation

Incorporating elements of dosimetry and reactivity to predict biological response

Human Airway

Chemical disposition

(free vapor)-

• VP

• SolH2O• Chemical Reactivity

Biological Response -

• Protein adduct -

immune surveillance

� Asthma, T-cell mediated hypersensitivity

� Irritation/inflammation/tissue necrosis

2

Factors affecting pulmonary response

noneLowLowCarbon

monoxide

Lower

terminal

airways

HighLowPhosgene

Isocyanates

Large and

intermediate

airways

HighModerateChlorine

Upper airwaysHighHighAmmonia

Upper airwaysModerateHighAcetaldehyde

Pulmonary

Toxicity

Chemical

Reactivity

Water

Solubility

Chem Name

�Although inhalation toxicity data have been compiled in selected open access databases, the entries are limited and have seldom been subjected to rigorous peer review.

�Thus, although these databases may suffice for general reference purposes, the data is frequently ambiguous and of questionable quality.

�As a result, models of inhalation toxicity derived from these databases have largely been unsuccessful and doubts have been cast regarding the validity of QSAR approaches to inhalation toxicology.

The QSAR Inhalation Toxicity Database

3

�The inhalation toxicity database (ITDB) is an effort to compile high quality inhalation data published in the open literature and government reports as well as publicly available unpublished toxicity reports using strict Q/A standards.

�ITDB has a goal of eventually becoming an international and widely distributed resource for high quality inhalation toxicity data that can be used to better characterize inhalation toxicity with minimal animal testing.

The Inhalation Toxicity Database

� We have embarked on compiling an exhaustive mammalian inhalation toxicity database using strict standards of peer review to insure only high-quality studies are included.

� Currently focus on acute (4 hr) inhalation by rats

� About 200 unique chemicals, 86 – tested for acute toxicity in rat/4h

� Limited short-term mouse data

� Expanding to include other species as well as repeat exposure and chronic inhalation data

� Preliminary analyses of the database.……….

Current Status of the ITDB

4

Modeling Assumptions

• Obstructive disorders– Low vapor pressure

– High water solubility

– High chemical reactivity

• Restrictive disorders– Low vapor pressure

– Low water solubility

– High chemical reactivity

• MoA - specific disease

• Non-specific, narcotic-like effects – Low vapor pressure

– Low water solubility

– Low chemical reactivity

LC50/rat/4h vs Vapor Pressure

Data was compiled from the literature.

•From mid 50s to present *

•All chemicals tested as vapors **

•Consistent exposure conditions ***

•Different rat strains

* Guidelines somewhat vary with time

**Specified (aimed ) in the experiment but sometimes might not be truth

***Exposure time constant, number of animals and observation periods vary-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor Pressure, mmHg

LC50

,mm

ol/m

3LC50, mmol/m3

Vapor Pressure, mmHg

5

LC50 /rat/4h vs Vapor Pressure for chemicals previously classified as

NONNONNONNON----REACTIVEREACTIVEREACTIVEREACTIVE

y = 0.705x + 1.4719

R2 = 0.9277

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC50, m

mol /

m3

LC50, mmol/m3

Vapor Pressure, mmHg

HYDROCARBONSHYDROCARBONSHYDROCARBONSHYDROCARBONSHYDROCARBONSHYDROCARBONSHYDROCARBONSHYDROCARBONS are a good examples for narcosis

Nonane, hexane, isoprene, butadiene, isobutylene, butane, 2-metylpentene-1, 2-metylpentene-2, styrene

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC50, m

mol /

m3

LC50, mmol/m3

Vapor Pressure, mmHg

6

No similar relationship of

LC50/VP for NITRITESNITRITESNITRITESNITRITES

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC50

, mm

ol/ m

3LC50, mmol/m3

Vapor Pressure, mmHg

LC50/VP relationship

for AMINES

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC50, m

mol /

m3

LC50, mmol/m3

Vapor Pressure, mmHg

Allylamine, CAS 107-11-9

7

ACRYLATES & METHACRYLATES

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC

50, m

mol /

m3

LC50, mmol/m3

Vapor Pressure, mmHg

For ACRYLATES & METHACRYLATES there is no relationship with Vapor Pressure but significant correlation with GSH reactivity

LC50 vs GSH reactivity

for acrylates and methacrylates

LogLC50 = 0.28logEC50 + 2.01

R2 = 0.91

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

Log EC50,mM

LogL

C50

, mm

ol/m

3

-2

-1

0

1

2

3

4

5

-2 -1 0 1 2 3 4

Vapor pressure, mmHg

LC

50, m

mol

/ m

3LC50, mmol/m3

Vapor Pressure, mmHg

LC50, mmol/m3

EC50, mM

8

Solubility in air andLethal Concentrationvs Vapor Pressurefor narcotics (rat/4h)

-6

-5

-4

-3

-2

-1

0

-1 0 1 2 3 4

Solubility in Air / LC50

Vapor Pressure, mmHg

Solubility in air andLethal Concentrationvs Vapor Pressurefor ethers (mouse//15 min)

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0 0.5 1 1.5 2 2.5 3 3.5 4

Vapor Pressure, mmHG

Sol A

ir &

LC

50,

mol/l

Solubility in Air / LC50

Vapor Pressure, mmHg

9

� Fish and mammal inhalation baseline toxicity are not directly comparable because the external media are different

�However, blood thermodynamic activity for LC50(nar) is the same in fish and mammal

�At steady-state, the activity in air/water equals the activity in blood by definition :

α = С x γ

α – activity; C- concentration; γ-activity coefficient

Baseline Toxicity

� The thermodynamic activity at any concentration can be estimated by dividing by the solubility in the

medium

� activity for narcosis in fish = LC50(fish)/water solubility

activity for narcosis in rat = LC50 (rat)/air solubility

� if activity for narcosis in fish and rat were equal, the plot of LC50 versus solubility in exposure medium should be the same

Baseline Toxicity

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Solubility in Water or Air vs LC50 in Fish or Rat

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0 1

Solubility, mol/l

LC

50,

mo

l/l

LC50 fish vs WaterSolubility

LC50 rat vs AirSolubility

Solubility in Water or Air vs LC50 in Fish or Rat (combined)

LC50rat vs LC50fish*Kh

-8

-7

-6

-5

-4

-3

-2

-1

0

-5 -4 -3 -2 -1 0

log LC50 rat

Lo

g (

LC

50 f

ish

*Kh

)

LC50rat vs LC50fish*Kh

11

LogLC50 for fish or rat vs Solubility in water or air

y = 0.7847x - 1.6059

R2 = 0.889

-6

-5

-4

-3

-2

-1

0

-6 -5 -4 -3 -2 -1 0 1 2

Solubility, mol/l

LC50, mol/l

LC50fish vs LogWsol

LC50rat vs LogAirsol

LogLC50 for fish or rat vs Solubility in water or air

2.5 Endocrine active industrial chemicals:

Release and occurrence in the environment

Concentration response curves for all

mixture components

12

-11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1

-10

0

10

20

30

40

50

60

70

80

90

100

110

E2 rbtER (cyto)

SDP rbtER (cyto)

E2 hERαααα (recomb-LBD)

SDP hERαααα (recomb-LBD)

solubility limit

Binding Assays4,4'-sulfonyldiphenol

RBA %

0.0020

0.0055

Log Concentration (M)

Bin

din

g (

%)

-11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1

-10

0

10

20

30

40

50

60

70

80

90

100

110

E2 rbtER (cyto)

SDP rbtER (cyto)

E2 hERαααα (recomb-LBD)

SDP hERαααα (recomb-LBD)

solubility limit

Binding Assays4,4'-sulfonyldiphenol

RBA %

0.0020

0.0055

Log Concentration (M)

Bin

din

g (

%)

CR

TL

0

10

20

30

40

50

60

70

80

90

100

Log Concentration (M)

-10 -9 -8 -7 -6 -5 -4 -3 -2

solubility limitRBA %

0.0008

ND

Binding Assays ethylparaben

E2 rbtER (cyto)

EP rbtER (cyto)

E2 hERαααα(recomb-LBD)

EP hERαααα (recomb-LBD)

Bin

din

g (

%)

CR

TL

0

10

20

30

40

50

60

70

80

90

100

Log Concentration (M)

-10 -9 -8 -7 -6 -5 -4 -3 -2

solubility limitRBA %

0.0008

ND

Binding Assays ethylparaben

E2 rbtER (cyto)

EP rbtER (cyto)

E2 hERαααα(recomb-LBD)

EP hERαααα (recomb-LBD)

Bin

din

g (

%)

13

CR

TL

0

10

20

30

40

50

60

70

80

90

100

Log Concentration (M)

-10 -9 -8 -7 -6 -5 -4 -3 -2125

150

175

200

225

250

275

300

325

350

RBA %

0.00057

0.0098

Binding Assays resorcinol sulfide

E2 hERαααα (recomb-full)FP

RES hERαααα (recomb-full)FP

E2 rbtER (cyto)

RES rbtER (cyto)

Bin

din

g (

%)

Po

lariza

tion

(mp

)

CR

TL

0

10

20

30

40

50

60

70

80

90

100

Log Concentration (M)

-10 -9 -8 -7 -6 -5 -4 -3 -2125

150

175

200

225

250

275

300

325

350

RBA %

0.00057

0.0098

Binding Assays resorcinol sulfide

E2 hERαααα (recomb-full)FP

RES hERαααα (recomb-full)FP

E2 rbtER (cyto)

RES rbtER (cyto)

Bin

din

g (

%)

Po

lariza

tion

(mp

)

4-n-Amylaniline

CTRL

0

10

20

30

40

50

60

70

80

90

100

110

AAN rbt Vtg

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1

Control rbt Vtg

1.0×105

1.0×106

1.0×107

1.0×108

AAN rbtER (cyto)

Log Concentration (M)

[3H

]-E

2 B

ind

ing

(%

)/F

ecu

nd

ity

(%

dec

rea

se)

VT

G m

RN

A c

op

ies/4

00 n

g to

tal R

NA

14

4-n-Amylaniline

CTRL

0

10

20

30

40

50

60

70

80

90

100

110

AAN rbt Vtg

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1

Control rbt Vtg

1.0×105

1.0×106

1.0×107

1.0×108

AAN rbtER (cyto)

Log Concentration (M)

[3H

]-E

2 B

ind

ing

(%

)/F

ecu

nd

ity

(%

dec

rea

se)

VT

G m

RN

A c

op

ies/4

00 n

g to

tal R

NA

4-n-Amylaniline

CTRL

0

10

20

30

40

50

60

70

80

90

100

110

AAN rbt Vtg

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1

Control rbt Vtg

1.0×105

1.0×106

1.0×107

1.0×108

AAN rbtER (cyto)Medaka Fecundity

In vivo Water Exposure

Log Concentration (M)

[3H

]-E

2 B

ind

ing

(%

)/F

ecu

nd

ity

(%

dec

rea

se)

VT

G m

RN

A c

op

ies/4

00 n

g to

tal R

NA

15

4-n-Amylaniline

CTRL

0

10

20

30

40

50

60

70

80

90

100

110

AAN rbt Vtg

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1

Control rbt Vtg

1.0×105

1.0×106

1.0×107

1.0×108

AAN rbtER (cyto)Medaka Fecundity

In vivo Water Exposure

Medaka Fecundity

Predicted in vivo LiverSteady State Concentration

Log Concentration (M)

[3H

]-E

2 B

ind

ing

(%

)/F

ecu

nd

ity

(%

dec

rea

se)

VT

G m

RN

A c

op

ies/4

00 n

g to

tal R

NA