Table 1.

Hydrophobicity ($\text{Log\hspace{0.17em}}{K}_{ow}$), half maximal inhibitory concentration (${\text{IC}}_{50}$), 20% maximal inhibitory concentration (${\text{IC}}_{20}$), and relative binding potency (RBP) values obtained from transthyretin (TTR) and thyroid hormone receptor ligand-binding domain (TR-LBD) binding assays; cell proliferation and relative activity (RA) values obtained from the GH3 cell proliferation assay for tetrabromobisphenol A (TBBPA), TBBPA mono-ether structural analogs [TBBPA-mono(glycidyl ether) (TBBPA-MGE), TBBPA-mono(allyl ether) (TBBPA-MAE), and TBBPA-mono(2,3-dibromopropyl ether) (TBBPA-MDBPE)], TBBPA bis-ether derivatives [TBBPA-bis(glycidyl ether) (TBBPA-BGE), TBBPA-bis(allyl ether) (TBBPA-BAE), and TBBPA-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE)], thyroxine (${\mathrm{T}}_4$) and triiodothyronine (${\mathrm{T}}_3$).

		TTR		$\text{TR}\mathrm{\alpha }\text{-LBD}$		$\text{TR}\mathrm{\beta }\text{-LBD}$		GH3
Compound	$\text{Log\hspace{0.17em}}{K}_{ow}$	${\text{IC}}_{50}$ ($\mathrm{\mu }\mathrm{M}$)	RBPa	${\text{IC}}_{20}$ ($\mathrm{\mu }\mathrm{M}$)	RBP	${\text{IC}}_{20}$ ($\mathrm{\mu }\mathrm{M}$)	RBP	Effectb	RAc
TBBPA	7.46	0.2	1.00	1.5	1.00	5.0	1.00	1.1	1.00
TBBPA-MGE	7.31	0.5	0.40	8.0	0.18	6.0	0.83	1.2	1.09
TBBPA-MAE	8.42	0.1	2.00	6.0	0.25	4.0	1.25	1.6	1.45
TBBPA-MDBPE	9.36	1.0	0.20	50.0	0.03	20.0	0.25	4.6	4.18
TBBPA-BGE	7.15	NAd	ND	NA	NA	25.0	0.20	ND	ND
TBBPA-BAE	9.37	NA	ND	NA	NA	25.0	0.20	ND	ND
TBBPA-BDBPE	11.26	NA	ND	NA	NA	NA	NA	ND	ND
${\mathrm{T}}_4$e	—	0.2	1.00	—	—	—	—	—	—
${\mathrm{T}}_3$e	—	—	—	0.1	15.00	0.05	100.00	—	—

Note: The $\text{Log\hspace{0.17em}}{K}_{ow}$ values of the chemicals were obtained from ChemBioDraw. Twenty percent maximal inhibitory concentration (${\text{IC}}_{20}$) or half maximal inhibitory concentration (${\text{IC}}_{50}$) values were obtained from linear interpolation between two concentrations located at approximately the 20% or 50% inhibition level. —, not applicable; DMSO, dimethyl sulfoxide; NA, not available; ND, not detected; RA, relative activity; RBP, relative binding potency.

^aRBP compared with TBBPA (set as 1.00).

^bEffect: GH3 cell proliferation effect compared with the control group (0.1% DMSO), obtained by calculating the absorbance at $450\text{\hspace{0.17em}nm}$ for the compound of interest divided by the absorbance at $450\text{\hspace{0.17em}nm}$ for the control group (0.1% DMSO).

^cRA compared with TBBPA (set as 1.00).

^dThe addition of the compound led to displacement of the fluorescence probe from TR-LBDs or TTR and did not provide an ${\text{IC}}_{20}$ or ${\text{IC}}_{50}$ value).

^eThe ${\mathrm{T}}_4$ and ${\mathrm{T}}_3$ results were obtained from our previous study (Qin et al. 2019).