Prevalidation Study Plan for Sliced Testes Assay Gary Timm Presented to EDMVS August 20, 2003

Prevalidation Study Plan for Sliced Testes Assay

Gary Timm

Presented to EDMVS

August 20, 2003

Sliced Testes Assay Prevalidation/Validation Study Plan

• June EDMVS Meeting Discussed: – Objectives of validation study– Data interpretation procedure– Basic sliced testes protocol– Prevalidation study design– Reference chemicals– Laboratory selection– Validation study design– Measurements of reliability– Data analysis and reporting

June Proposal for Prevalidation Studies

• Conduct prevalidation studies in two laboratories– Baseline study– Pilot study – Multichemical study

June Proposal for Prevalidation Studies (2)

• Baseline study– Run optimized protocol – 3 runs without hCG– 3 runs with hCG challenge– Measure testosterone formation and LDH– No test chemical– Three replicate studies


• Pilot studies of positive controls– Aminoglutethimide (positive control)– Ethane dimethanesulfonate (Leydig cell

toxicant)– Two labs– Three replicates


• Multichemical studies– 9 chemicals– 2 laboratories– 2 replicate studies

• Validation in 6 laboratories would begin after the successful conclusion of these studies

EDMVS Responses to Questions

1. Does the EDMVS agree with the stated objectives and data interpretation in the proposed Validation Study Plan? Yes, but:

• Concerns expressed about the assay– Accuracy and sensitivity of sliced testes assay– Potentially better assays on the horizon; don’t invest

too heavily in sliced testes assay– Need a reliable means to detect Leydig cell toxicity


2. Does the EDMVS agree with the structure of the prevalidation and validation Program?

• Yes, agreed that two laboratories was a reasonable choice for prevalidation.

• Concern that program should be more efficient– Do we need to look at data from multiple

time points or is end of assay OK?– Use data from prevalidation to pick number

of labs for validation, do not rely on literature values


• Concerns about positive control chemicals– Aminoglutethimide may not be a good positive

control chemical– EDS may not be a good cytotoxicant reference

chemical• Concerns about reference chemicals

– Should not attempt to cover every known mode of action, use phamacologic agents of known mode of action

– Ideally should choose only chemicals with a single mode of action, however selectivity seems to be dose dependent.

– Should include several cytotoxicants during prevalidation


3. Have we selected appropriate measures of reliability?

– Yes, but the endpoints being used for the power calculations need to be clearly stated

– Need to verify linearity in baseline Testosterone production curve

– Should estimate potency of test chemicals by calculating an EC10 or EC50.


4. Are the number of replicates taken over both prevalidation and validation sufficient to generate robust statistics?

– Yes, three replicates seems sufficient in prevalidation. If the variability is small, consider reducing to 2 in validation

– Need to add more negative chemicals– Negatives should include evaluation of

influence of pH and osmolality


5. Should dosing solutions be prepared centrally or on site?

– The stock solution should be prepared centrally

– Dilutions should be made on site with instructions provided by the lead lab or chemical repository


6. Do doses need to be confirmed by analytical chemistry?

– The identity and purity of the neat test substance should be checked by the chemical repository

– The suitability and solubility of the test substance should be checked and the concentration of stock solution should be confirmed by the repository

– Labs should save aliquots of dosing solutions should for analysis; analysis should be performed only “for cause”


6. Naïve labs/trained labs issue– No naïve labs! Training is necessary to

minimize interlaboratory difference in techniques

– Competency of labs should be demonstrated by conducting a positive control prior to full validation effort

– Incompetent laboratories should be excluded

Issue: Leydig cell toxicity

• Concerns:– Don’t want false positive by artificially high in

vitro dosing that kills cells– Don’t want general cytotoxicants to trigger

positive, 2 gen is wrong follow-up for general cytotoxicants

– May be “red herring.” If cytotoxic to Leydig cells at biologically relevant concentration levels, isn’t this a legitimate positive?

Leydig cell toxicity (cont)

• EPA Options: 1. Use LDH assay for cell viability

2. Use 3β-HSD staining specific for Leydig cell viability instead of the more general LDH assay

Issue: Choice of reference chemicals

• EPA confirmed by search of literature that selectivity is not unique but is dose dependent.

• EPA will select reference chemicals that work at key stages of steroidogenesis

• EPA will run 4 known cytotoxicants to select the best positive control for cytotoxicity

EPA Listened and Redesigned Prevalidation Program• Focus only on prevalidation; validation will be a

separate work assignment.• Redesigned the prevalidation program: lead lab

and 3 participating labs• Lead lab:

– Baseline, testes variability study– Test of positive control– Cytotoxicity studies– Multichemical studies– Training of participating laboratories’ personnel

Redesigned Prevalidation Program

• Participating Laboratories (3) and lead lab– Baseline studies in triplicate

• measure testosterone with and without hCG• no test chemical

– Positive control studies• Positive control (aminoglutethimide)• Reference cytotoxicant

Baseline and Testes Variability Study(Lead Lab)

• Purpose: – To demonstrate competence of lead lab using

optimized assay– To obtain testosterone production data as a function

of time in the absence of inhibitors– To estimate Leydig cell density after 4 hr incubation– To evaluate the variability in contralateral testes

fragments to decide on future experimental design:• Randomized fragments• Block design using single testes

Baseline and Testes Variability Study(Lead Lab)

• Study Design:– 5 animals– 24 runs (a run corresponds to an incubation vial

containing 1 testes fragment)– Incubate for 4 hours with and without hCG– 3 replicate studies with measurements (samples) at 5

time points for runs 1-6. (A replicate study is an independent study.)

– 2 replicate studies with measurements at 2 and 4 hrs (incubation times) for fragments 7-24

Baseline and Testes Variability Study

Sample time

hCG Animal Testis Fragment number

Run

0-5 N 1-3 A 1 1-3

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

2,4 Y 1 B 1,2 7,8

2,4 Y 2 A 3,4 9,10

2,4 Y 2 B 1,2 11,12

2,4 Y 3 A 3,4 13,14

2,4 Y 3 B 1,2 15,16

2,4 Y 4 A 1,2 17,18

2,4 Y 4 B 1,2 19,20

2,4 Y 5 A 1,2 21,22

2,4 Y 5 B 1,2 23,24

Baseline Study Design

Sample Type

hCG Number runs

Testes fragment

Media N 3 1-3

Media Y 3 4-6

Sample type hCG Number runs Testes fragment

Media-vehicle

controlN 3 1-3

Media-vehicle

controlY 3 4-6

Media +AG (low)

Y 3 7-9

Media +AG (med)

Y 3 10-12

Media +AG (high)

Y 3 13-15

Positive Control Study Design

Cytotoxicity Study Design


Media control N 3 1-3Media control Y 3 4-6Positive control Y 3 7-9Toxicant A- low Y 3 10-12Toxicant A- med Y 3 13-15Toxicant A- high Y 3 16-18Toxicant B- low Y 3 19-21Toxicant B- med Y 3 22-24Toxicant B- high Y 3 25-27

Multichemical Study Design


Media control N 3 1-3

Media control Y 3 4-6

Positive control Y 3 7-9

Cytotox control Y 3 10-12

Chemical A-low Y 3 13-15

Chem A- med Y 3 16-18

Chem A- high Y 3 19-21

Chem A- high N 3 22-24

Chemical B- low Y 3 25-27

Chem B- med Y 3 28-30

Chem B- high Y 3 31-33

Chem B- high N 3 34-36

Reference Chemicals by Mode of Action

Mode of Action Chemical Mode 2

P450SCC Aminoglutethimide Aromatase

P450SCC Ketoconazole P450c17, arom

cAMP inhibitor Bisphenol A ER binder

cAMP inhibitor Lindane

StAR Dimethoate



3β-HSD Genestein ER binder

3β-HSD Epostane

P450c17 Flutamide AR antagonist

P450c17 Econazole Aromatase



Aromatase Prochloraz

5α-reductase Finasteride

Leydig cell toxicant Ethane dimethanesulfonate

Negative chemical Vinclozolin AR binder

Summary

• Lead lab:– Baseline, testes variability study– Test of positive control– Cytotoxicity studies– Multichemical studies– Training of participating laboratories’ personnel

• Participating Laboratories (3) and lead lab– Baseline studies in triplicate – Positive control studies in triplicate

• Estimated completion 4-30-2004

Documents

Prevalidation Study Plan for Sliced Testes Assay Gary Timm Presented to EDMVS August 20, 2003