Gibberellic acid

CASRN 77-06-5

Tox21 Chemical QC: Pass, purity and mw confirmed

ER QSAR Prediction: Inactive (EAS=8.13)

Gibberellic Acids are naturally occurring plant hormones. Gibberellic Acids are used in 

agriculture as plant regulators to stimulate both cell division and cell elongation that 

affect leaves as well as stems (eventually affecting fruit development and fruit set). 

Applications of Gibberellic Acids can also hasten plant maturation and seed germination. 

Because they are naturally occurring compounds and have a nontoxic mode of action in 

target plants, Gibberellic Acid and related isomers have been classified as biochemical 

pesticides (http://www.epa.gov/oppsrrd1/REDs/factsheets/4110fact.pdf).

Two developmental toxicity studies for Gibberellic Acids were reviewed by the EPA. In 

the first study, rats were dosed at 0, 100, or 1,000 mg/kg/day for 8 weeks without 

significant chemical, hematological or pathologic evidence of toxicity. The maternal 

toxicity NOEL was greater than 1,000 mg/kg/day (HTD). In the second study, rabbits 

were dosed at 0, 300, or 1,000 mg/kg/day; the highest concentration caused increased 

mortality, abortion rates, clinical signs of toxicity, and gross pathological observations. 

The maternal and developmental NOELs were established at 300 mg/kg/day. 

(http://www.epa.gov/oppsrrd1/REDs/factsheets/4110fact.pdf).

One published reference was considered guideline-like (PMID 7442448). This study 

used the Ovx mouse model with sc dosing beginning at either postnatal day 70 or 110; 

the results are summarized in the table below. Gibberellic acid demonstrated a agonistic 

effect after five consecutive days of treatment at a dose of .0001 mg/day.
PMID Result Model Species Route Duration LEL

(mg/day)

7442448 POS Ovx_PND70 Mouse sc 5 d .0001

7442448 POS Ovx_PND110 Mouse sc 5 d .0001

Giberellic acid was inactive in the ToxCast ER assays and the ER Pathway model.

Octamethylcyclotetrasiloxane (D4)

CASRN 556-67-2

Tox21 Chemical QC: Inconclusive, Analysis in progress

ER QSAR Prediction: Inactive (EAS=3.73e-7)
Octamethylcyclotetrasiloxane (D4) is used in the formulation of various hair care, skin 

care, and deodorant products, as well as topical pharmaceuticals and as a component in

breast implants. Depending on the product type, the concentration of D4 in formulations 

varies between 0.1-and 54%. Certain food products are processed using silicone antifoam 

containing octamethyltetracyclosiloxane. Inhalation studies in Sprague Dawley rats and 

New Zealand White rabbits revealed no evidence of developmental toxicity or 

teratogenicity up to the highest dose levels tested, i.e. 700 ppm for rats and 500 ppm for 

rabbits. However, effects on female rat fertility were identified at 700 ppm characterized 

by reduced numbers of eggs ovulated and a decrease in implantation sites and litter size.

(http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_035.pdf)

Octamethylcyclotetrasiloxane (D4) showed positive uterotrophic results in two published 

references that were considered guideline-like (PMID 11509742 and 14575643). One 

study used immature rats and started oral dosing at two different time points, PND 18 and 

PND21, and the other used ovariectomized mice and oral dosing; the results are 

summarized in the table below. Both studies observed a positive response at extremely 

high doses, which may result in plasma level concentrations that are above the 

concentration range tested in the HTS assays.

PMID Result Model Species Route Duration LEL

(mg/kg/day)

11509742 POS Immature_PND21 Rat p.o. 4 d 3162

11509742 POS Immature_PND18 Rat p.o. 4 d 3162

14575643 POS Ovx_PND42-49 Mouse p.o. 3 d 250

Interestingly, this compound was active in the two transactivation assays from the 

Attagene platform run in HepG2 cells, as shown in the left panel of the plot below, 

and was therefore predicted by the model to act via technology-specific assay 

interference. The top tested concentration in these assays was 200 uM, twice that of 

any other assay, supporting the idea that this compound may need to be tested at 

higher concentrations to observe the potential estrogenic activity. These assays also 

have limited metabolic capacity, which may be necessary for the endocrine activity 

of D4 in vivo.
Triclosan 

CASRN 3380-34-5

Tox21 Chemical QC: Pass, purity and mw confirmed

ER QSAR Prediction: Borderline (EAS=14.6)

Triclosan is a diphenyl ether derivative used in cosmetics and toilet soaps as an 

antiseptic, and has both bacteriostatic and fungistatic action. In rats, the 

Reproductive/Developmental LOAEL is 150 mg/kg/day, based on reduced viability of 

pups and reduced body weights, and in mice the developmental LOAEL is 75 mg/kg/day 

based on irregular ossification of the skull. In a rabbit developmental toxicity study, no 

treatment related effects were observed up to 150 mg/kg/day.

(http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5564&loc=ec_rcs)

One published reference on Triclosan was considered guideline-like (PMID 22062131). 

This study used the immature rat model with oral dosing starting at PND 19; the results 

are summarized in the table below
PMID Result Model Species Route Duration LEL

(mg/kg/day)

22062131 POS Immature_PND19 Rat p.o. 3 d 7.5

This compound was active in one of the transactivation assays from the Attagene 

platform run in HepG2 cells, as shown in the left panel of the plot below, and the 

Tox21 ERa beta-lactamase antagonist assay (orange line), but at concentrations 

concurrent with overt cytotoxicity (gray box). The top tested concentration in these 

assays was 200 uM, twice that of any other assay, supporting the idea that this 

compound may need to be tested at higher concentrations to observe the potential 

estrogenic activity. The ATG assay also has limited metabolic capacity, which may be 

necessary for the endocrine activity of triclosan in vivo.

Methyl Paraben 

CASRN 99-76-3

Tox21 Chemical QC: Pass, purity and mw confirmed

ER QSAR Prediction: Positive (EAS=18.5)
Methyl paraben is a stable, non-volatile compound used as an inhibitor of yeasts and 

molds, an anti-microbial preservative in foods, beverages, cosmetics, parenteral solutions, 

topical antibiotics, corticosteroid preparations, and galencials, and as a vehicle for 

ophthalmic solution. This widespread production and use may result in its release to the 

environment through various waste streams. There is a tolerance of zero established for 

residues of methylparaben in milk from dairy animals. Residues of methyl phydroxybenzoate are exempted from the requirement of a tolerance when used as a 

preservative (Limit: meets specifications of Food Chemical Codex; not to exceed 0.1% in 

formulations). It is hydrolyzed to p-hydroxybenzoic acid, conjugated, and rapidly 

excreted in the urine; there is no evidence of accumulation. Acute and chronic toxicity 

studies in animals indicate that methyl paraben is non-toxic by various dosing routes. 

Methyl paraben is not carcinogenic or mutagenic, nor is it teratogenic or embryotoxic. 

(http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=7456&loc=ec_rcs#x332)

Methyl paraben showed conflicting uterotrophic results in two published references that 

were considered guideline-like (PMID 9875295 and 15697177). One study used 

immature rats and with either oral or s.c. dosing and saw negative results in both 

protocols, and the other also used immature rats and s.c. dosing but saw a positive result 

at 55 mg/kg/day; the results are summarized in the table below.

PMID Result Model Species Route Duration LEL or HDT

(mg/kg/day)

9875295 NEG Immature_PND21 Rat p.o. 3 d 800

9875295 NEG Immature_PND21 Rat s.c. 3 d 80

15697177 POS Immature_PND21 Rat s.c. 3 d 55

Methyl paraben was active at high concentrations in the two transactivation assays 

from the Attagene platform run in HepG2 cells (pink lines) and the ERa-ERb protein 
complementation assay (green line), as shown in the left panel of the plot below, 

and was predicted by the model to act via technology-specific assay interference, 

with a very small AUC score for ER agonism as well (R1=0.0077). This compound 

may also need to be tested at higher concentrations or be metabolized to observe 

the potential estrogenic activity. 

4-Hydroxybenzoic acid

CASRN 99-96-7

Tox21 Chemical QC: Pass, purity and mw confirmed

ER QSAR Prediction: Positive (EAS=22.5)

4-Hydroxybenzoic acid is used as a chemical intermediate, in synthetic drugs, and as a 

food preservative up to 0.1% (limits set by FDA). This may result in its release to the 

environment through various waste streams.

(http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=135&loc=ec_rcs)
4-Hydroxybenzoic acid showed conflicting uterotrophic results in three published 

references that were considered guideline-like (PMID 9417843, 15697177 and 

17904329). All studies used s.c. dosing, the positive result was seen in ovariectomized 

mice, and both studies with immature rats yielded negative outcomes; the results are 

summarized in the table below.

PMID Result Model Species Route Duration LEL or HDT

(mg/kg/day)

9417843 POS OVX_PND49 Mouse s.c. 3 d 5

15697177 NEG Immature_PND21 Rat s.c. 3 d 150 

17904329 NEG Immature_PND20 Rat s.c. 3 d 1000 

4-Hydroxybenzoic acid was inactive in the ToxCast ER assays and the ER Pathway 

model, as shown in the plot below.

Permethrin 

CASRN 52645-53-1

Tox21 Chemical QC: Inconclusive, Analysis in progress

ER QSAR Prediction: Inactive (EAS=12.7)
Permethrin is a pyrethroid insecticide commonly used as a topical treatment for scabies 

and lice infestations. It mediates the voltage-dependent sodium ion permeability of 

excitable membranes, and is known to interact with CYP2B6 and CYP3A4.

(http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=40326&loc=ec_rcs)

Permethrin showed conflicting uterotrophic results in two published references that were 

considered guideline-like (PMID 9875295 and 15697177). One study used 

ovariectomized rats and oral dosing and saw a negative result at doses up to150 

mg/kg/day, and the other study used immature rats and s.c. dosing and saw a positive 

result at 800 mg/kg/day; the results are summarized in the table below. The positive 

response was observed at an extremely high dose, which may result in plasma level 

concentrations that are well above the concentration range tested in the HTS assays

PMID Result Model Species Route Duration LEL or HDT

(mg/kg/day)

12052007 NEG OVX_PND42 Rat p.o. 3 d 150

15599112 POS Immature_PND19 Rat s.c. 3 d 800
Permethrin was active at high concentrations in the two transactivation assays from 

the Attagene platform run in HepG2 cells, as shown in the left panel of the plot 

below, and was predicted by the model to act via technology-specific assay 

interference. All of the aforementioned activity occurred in the same concentration 

range where cytotoxicity was also observed. This compound may also need to be 

tested at higher concentrations or be metabolized to observe the potential 

estrogenic activity.

Reserpine

CASRN 50-55-5

Tox21 Chemical QC: Pass, purity and mw confirmed

ER QSAR Prediction: Inactive (EAS=3.34)

Reserpine is an antipsychotic and antihypertensive drug that irreversibly blocks the 

uptake (and storage) of norepinephrine and dopamine into synaptic vesicles by inhibiting 
the Vesicular Monoamine Transporters (VMAT). Dosing is typically up to 0.5 mg orally 

once a day. Reserpine has been discontinued in some countries due to its many

interactions and side effects.

(http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5770&loc=ec_rcs)

Reserpine had conflicting result in the uterotrophic literature. One published reference 

was considered guideline-like (PMID 23027998). This study used the Ovx mouse model 

with either po and sc dosing; the results are summarized in the table below. Reserpine

demonstrated a weak agonistic effect after seven consecutive days of treatment at the 

highest dose and only by the sc route of exposure. 

PMID Result Model Species Route Duration LEL or Max tested 

(mg/kg/day)

23037998 NEG Ovx Mouse p.o. 7 d 1000

23037998 POS Ovx Mouse s.c. 7 d 3

Reserpine was active in the Tox21 ERa beta-lactamase antagonist assay at concentrations 

approaching cytotoxic activity, as shown in the left-hand plot, but had ER Pathway model 

scores of 0 for both agonism and antagonism.