Thyroid hormone system disruption (THSD) is a growing concern in chemical hazard assessment due to its impact on human and environmental health and the scarce methods available for assessing the THSD potential of chemicals. In particular, the general lack of validated in silico and in vitro methods for assessing THS activity is of high concern. This manuscript provides an inventory of test methods relevant to THSD. Building on the Organisation for Economic Co-operation and Development (OECD) Guidance Document 150 and recent international developments, we highlight progress in in silico and in vitro methods, as well as in vivo assays. The provided inventory categorizes available methods according to the levels of the OECD Conceptual Framework, with an assessment of the validation status of each method. At Level 1, 12 in silico models that have been statistically validated and are directly related to THSD have been identified. At Level 2, 67 in vitro methods have been listed including those assessed in key initiatives such as the European Union Network of Laboratories for the Validation of Alternative Methods (EU-NETVAL) validation study to identify potential thyroid disruptors. At Levels 3-5, THSD-sensitive endpoints are being included in existing fish-based OECD Test Guidelines to complement amphibian assays. In total, the inventory counts 108 entries comprising established methods (e.g., OECD Test Guidelines) as well as citable methods that are under further development and in some cases are ready for validation or in the initial stages of validation. This work aims to support the ongoing development of strategies for regulatory hazard assessment, such as integrated approaches to testing and assessment (IATAs), for endocrine disruptors, addressing critical gaps in the current testing landscape for THSD in both human and environmental health contexts.

Endocrine disruption - the potential of chemicals, such as industrial chemicals or pesticides, to disrupt hormonal systems and cause adverse health effects - is of growing concern due to its impact on human and environmental health and the scarce methods available for assessing such hazards. In particular, the limited methods available for assessing disruption of the thyroid hormone system, is of high concern. This manuscript provides an inventory of test methods relevant for the assessment of thyroid hormone system disruption. We highlight progress in different types of methods such as computer simulations, cell-based methods, non-mammalian embryo-based methods and animal methods and include an assessment of the readiness of each method for implementation in chemical evaluations. In total, the inventory counts 108 entries comprising already established methods as well as recent developments. This work aims to support the ongoing development of strategies for evaluating endocrine disruption, addressing critical gaps in the current testing landscape for thyroid hormone system disruption in both human and environmental health contexts.

• Keywords
• One Health, Thyroid hormone system disruption, endocrine disruption, new approach methods,
• Publication type
• Journal Article MeSH
• Review MeSH

Several commercially available triorganotin compounds were previously found to function as agonist ligands for nuclear retinoid X receptor (RXR) molecules. Triphenyltin isoselenocyanate (TPT-NCSe), a novel selenium atom containing a derivative of triorganotin origin, was found to represent a new cognate bioactive ligand for RXRs. TPT-NCSe displayed a concentration- and time-dependent decrease in the cell viability in both human breast carcinoma MCF-7 (estrogen receptor positive) and MDA‑MB‑231 (triple negative) cell lines. Reactive oxygen species levels generated in response to TPT-NCSe were significantly higher in both carcinoma cell lines treated with TPT-NCSe when compared to mock-treated samples. Treatment with 500 nM TPT-NCSe caused a decrease in SOD1 and increased SOD2 mRNA in MCF-7 cells. The levels of SOD2 mRNA were more increased following the treatment with TPT-NCSe along with 1 μM all-trans retinoic acid (AtRA) in MCF-7 cells. An increased superoxide dismutase SOD1 and SOD2 mRNA levels were also detected in combination treatment of 500 nM TPT-NCSe and 1 μM AtRA in TPT-NCSe-treated MDA-MB-231 cells. The data have also shown that TPT-NCSe induces apoptosis via a caspase cascade triggered by the mitochondrial apoptotic pathway. TPT-NCSe modulates the expression levels of apoptosis‑related proteins, Annexin A5, Bcl‑2 and BAX family proteins, and finally, it enhances the expression levels of its cognate nuclear receptor subtypes RXRalpha and RXRbeta.

• Keywords
• Apoptosis, Breast cancer, Retinoid X receptor, Triorganotin isoselenocyanates,
• MeSH
• Apoptosis drug effects   MeSH
• Humans MeSH
• Ligands MeSH
• MCF-7 Cells MeSH
• Cell Line, Tumor MeSH
• Breast Neoplasms * drug therapy   metabolism   pathology   MeSH
• Organotin Compounds * pharmacology   MeSH
• Organoselenium Compounds pharmacology   chemistry   MeSH
• Cell Proliferation drug effects   MeSH
• Reactive Oxygen Species metabolism   MeSH
• Retinoid X Receptors metabolism   MeSH
• Superoxide Dismutase-1 metabolism   genetics   MeSH
• Superoxide Dismutase metabolism   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Ligands MeSH
• Organotin Compounds * MeSH
• Organoselenium Compounds MeSH
• Reactive Oxygen Species MeSH
• Retinoid X Receptors MeSH
• SOD1 protein, human MeSH Browser
• Superoxide Dismutase-1 MeSH
• Superoxide Dismutase MeSH
• superoxide dismutase 2 MeSH Browser
• triphenyltin MeSH Browser

The human PXR (pregnane X receptor), a master regulator of drug metabolism, has essential roles in intestinal homeostasis and abrogating inflammation. Existing PXR ligands have substantial off-target toxicity. Based on prior work that established microbial (indole) metabolites as PXR ligands, we proposed microbial metabolite mimicry as a novel strategy for drug discovery that allows exploiting previously unexplored parts of chemical space. Here, we report functionalized indole derivatives as first-in-class non-cytotoxic PXR agonists as a proof of concept for microbial metabolite mimicry. The lead compound, FKK6 (Felix Kopp Kortagere 6), binds directly to PXR protein in solution, induces PXR-specific target gene expression in cells, human organoids, and mice. FKK6 significantly represses pro-inflammatory cytokine production cells and abrogates inflammation in mice expressing the human PXR gene. The development of FKK6 demonstrates for the first time that microbial metabolite mimicry is a viable strategy for drug discovery and opens the door to underexploited regions of chemical space.

• Keywords
• drugs, microbial metabolite, mimics, pregnane X receptor, therapy,
• MeSH
• Cytokines MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Ligands MeSH
• Molecular Mimicry * MeSH
• Mice MeSH
• Organoids MeSH
• Pregnane X Receptor chemistry   MeSH
• Intestines MeSH
• Inflammation MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• Cytokines MeSH
• Ligands MeSH
• Pregnane X Receptor MeSH

The mechanisms contributing to toxic effects of airborne lower-chlorinated PCB congeners (LC-PCBs) remain poorly characterized. We evaluated in vitro toxicities of environmental LC-PCBs found in both indoor and outdoor air (PCB 4, 8, 11, 18, 28 and 31), and selected hydroxylated metabolites of PCB 8, 11 and 18, using reporter gene assays, as well as other functional cellular bioassays. We focused on processes linked with endocrine disruption, tumor promotion and/or regulation of transcription factors controlling metabolism of both endogenous compounds and xenobiotics. The tested LC-PCBs were found to be mostly efficient anti-androgenic (within nanomolar - micromolar range) and estrogenic (at micromolar concentrations) compounds, as well as inhibitors of gap junctional intercellular communication (GJIC) at micromolar concentrations. PCB 8, 28 and 31 were found to partially inhibit the aryl hydrocarbon receptor (AhR)-mediated activity. The tested LC-PCBs were also partial constitutive androstane receptor (CAR) and pregnane X receptor (PXR) agonists, with PCB 4, 8 and 18 being the most active compounds. They were inactive towards other nuclear receptors, such as vitamin D receptor, thyroid receptor α, glucocorticoid receptor or peroxisome proliferator-activated receptor γ. We found that only PCB 8 contributed to generation of oxidative stress, while all tested LC-PCBs induced arachidonic acid release (albeit without further modulations of arachidonic acid metabolism) in human lung epithelial cells. Importantly, estrogenic effects of hydroxylated (OH-PCB) metabolites of LC-PCBs (4-OH-PCB 8, 4-OH-PCB 11 and 4'-OH-PCB 18) were higher than those of the parent PCBs, while their other toxic effects were only slightly altered or suppressed. This suggested that metabolism may alter toxicity profiles of LC-PCBs in a receptor-specific manner. In summary, anti-androgenic and estrogenic activities, acute inhibition of GJIC and suppression of the AhR-mediated activity were found to be the most relevant modes of action of airborne LC-PCBs, although they partially affected also additional cellular targets.

• Keywords
• Airborne polychlorinated biphenyls, Endocrine disruption, HydroxyLated PCBs, Metabolism of xenobiotics, Tumor promotion,
• MeSH
• Cell Line MeSH
• Endocrine Disruptors metabolism   toxicity   MeSH
• Epithelial Cells drug effects   MeSH
• Hydroxylation MeSH
• Constitutive Androstane Receptor MeSH
• Air Pollutants toxicity   MeSH
• Humans MeSH
• Neoplasms metabolism   MeSH
• Polychlorinated Biphenyls metabolism   toxicity   MeSH
• Pregnane X Receptor MeSH
• Receptors, Cytoplasmic and Nuclear metabolism   MeSH
• Signal Transduction drug effects   MeSH
• Receptors, Steroid metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Endocrine Disruptors MeSH
• Constitutive Androstane Receptor MeSH
• Air Pollutants MeSH
• Polychlorinated Biphenyls MeSH
• Pregnane X Receptor MeSH
• Receptors, Cytoplasmic and Nuclear MeSH
• Receptors, Steroid MeSH

The acceleration of drug efflux activity realized by plasma membrane transporters in neoplastic cells, particularly by P-glycoprotein (P-gp, ABCB1 member of the ABC transporter family), represents a frequently observed molecular cause of multidrug resistance (MDR). This multiple resistance represents a real obstacle in the effective chemotherapy of neoplastic diseases. Therefore, identifying cytotoxic substances that are also effective in P-gp overexpressing cells may be useful for the rational design of substances for the treatment of malignancies with developed MDR. Here, we showed that triorganotin derivatives—tributyltin-chloride (TBT-Cl), tributyltin-bromide (TBT-Br), tributyltin-iodide (TBT-I) and tributyltin-isothiocyanate (TBT-NCS) or triphenyltin-chloride (TPT-Cl) and triphenyltin-isothiocyanate (TPT-NCS)—could induce the death of L1210 mice leukemia cells at a submicromolar concentration independently of P-gp overexpression. The median lethal concentration obtained for triorganotin derivatives did not exceed 0.5 µM in the induction of cell death of either P-gp negative or P-gp positive L1210 cells. Apoptosis related to regulatory pathway of Bcl-2 family proteins seems to be the predominant mode of cell death in either P-gp negative or P-gp positive L1210 cells. TBT-Cl and TBT-Br were more efficient with L1210 cells overexpressing P-gp than with their counterpart P-gp negative cells. In contrast, TBT-I and TPT-NCS induced a more pronounced cell death effect on P-gp negative cells than on P-gp positive cells. Triorganotin derivatives did not affect P-gp efflux in native cells measured by calcein retention within the cells. Taken together, we assumed that triorganotin derivatives represent substances suitable for suppressing the viability of P-gp positive malignant cells.

• Keywords
• L1210 cells, P-glycoprotein, apoptosis, calcein cell retention, multidrug resistance, triorganotin derivatives,
• MeSH
• Cytotoxins * chemical synthesis   chemistry   pharmacokinetics   pharmacology   MeSH
• Leukemia drug therapy   genetics   metabolism   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Neoplasm Proteins biosynthesis   genetics   MeSH
• ATP Binding Cassette Transporter, Subfamily B biosynthesis   genetics   MeSH
• Gene Expression Regulation, Leukemic drug effects   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• ABCB1 protein, human MeSH Browser
• Cytotoxins * MeSH
• Neoplasm Proteins MeSH
• ATP Binding Cassette Transporter, Subfamily B MeSH