Fundamental Toxicological Sciences Vol. 4(2017) No. 4

In addition to low molecular weight drugs, many antibody drugs have been developed in recent years. The safety of these drugs is mainly evaluated in animal toxicity experiments and it is difficult to detect all the toxicities that may occur in humans. Although trastuzumab (Herceptin^®), an antibody drug that is used for the treatment of breast cancer, as well as E-8010, a low molecular inhibitor of phosphodiesterase-5, did not cause cardiotoxicity (e.g. dysfunction, QT prolongation, and arrhythmias) in monkeys, they caused cardiotoxicity in humans. The present study examined, whether or not the human cardiotoxicity of these drugs could be predicted using cardiomyocytes derived from human-induced pluripotent stem cells (hiPS-CMs) using an MED64-multielectrode array and assessed the usefulness of hiPS-CMs in antibody drug testing. At 1 and 3 mg/mL, trastuzumab prolonged the field potential duration (QT interval on electrocardiography) by ≥ 10% and induced arrest, respectively. At 0.1 and 1 µmol/L, E-8010 prolonged the field potential duration by ≥ 10% and induced early after-depolarization (proarrhythmia), respectively. The human cardiotoxicity induced by trastuzumab and E-8010 could be predicted using hiPS-CMs. It was thought that a multielectrode array using hiPS-CMs would be a useful tool for predicting the clinical cardiotoxicity of antibody drug candidates in addition to small molecular drug candidates in the preclinical setting.

4,4’-Methylenediphenyl diisocyanate (MDI) is a cross-linking agent. Chemical reactivity of MDI with endogenous substances such as albumin and glutathione (GSH) is assumed to be responsible for MDI toxicity. We examined the cytotoxic effect of MDI on rat thymocytes, under the condition that endogenous biological substances except for cells were nominally absent, in order to study chemico-biological interactions between MDI and cells. The treatment of 10-50 µM MDI for 3 hr significantly increased the side scatter signal intensity of cytograms, without affecting forward scatter intensity. The increase in side scatter signal intensity by MDI was associated with an increase in cell lethality. The treatment of cells with 50 µM MDI for 3 hr increased cell lethality without increasing the population of preapoptotic annexin V-positive living cells. In contrast, H₂O₂ at 100 µM significantly increased the population of annexin V positive living cells prior to cell death. MDI at 30-50 µM did not affect the increase in cell lethality induced by H₂O₂ or A23187. Simultaneous application of 50 µM GSH did not affect the cytotoxicity of 50 µM MDI. It was therefore concluded that the process of cell death induced by MDI could not be attributed to oxidative stress and intracellular Ca²⁺ overload, and that MDI possesses cytotoxic actions that are not significantly related to its chemical reactivity with GSH.

The disposition of perfluorododecanoic acid (PFDoA), a perfluorocarboxylic acid with 12 carbon atoms, was studied in male rats. Rats received an oral administration of PFDoA at a dose of 50 mg/kg. The body weights of PFDoA-treated rats were slightly less than those of vehicle-treated control rats. PFDoA administration resulted in an increase in liver weight; it was highest at 5 days after the treatment and gradually decreased thereafter. Higher liver weight was observed until 70 days after the treatment. Concentrations of PFDoA in plasma and various tissues were estimated up to 70 days after dosing. A large amount of PFDoA was found in the liver. The PFDoA concentration was 263.94 ± 32.94 μg/g in the liver; the value was 7.93 times higher than that of serum 5 days after treatment. The hepatic PFDoA amount was found to be 29.63% of the dose. A certain amount of PFDoA was found in the brain and adipose tissues where perfluorocarboxylic acids with less than 11 carbon atoms were sparsely distributed. The half-life of PFDoA was 55.3, 49.3, 52.4, 57.1, and 49.8 days for serum, liver, kidneys, brain, and adipose tissue, respectively. PFDoA increased hepatic levels of mRNA for Cyp4A10, Acot1, and Acox1, target genes of PPARα, suggesting that PFDoA can activate PPARα, as was observed with other PFCAs. Elevated levels of these 3 genes were observed 70 days after treatment, and the levels were less than those at 7 days. The differences between PFDoA and PFCAs with less than 11 carbon atoms were discussed.

Cadmium alters the temporal dynamics of various cellular proteins, including heat shock proteins and protooncogenes. To reveal the molecular dynamics during cadmium cytotoxicity, we investigated the conventional nucleocytoplasmic transport pathways. Western blot analyses revealed that exposure of porcine kidney LLC-PK₁ cells to cadmium (10 µM) temporally induced HSP 70 and Ran in the cytoplasm and Ran and RCC1 in the nucleus. RCC1 could be detected in the nucleus as early as 1 hr after exposure of the cells to the metal. Thus, HSP70-Ran-RCC1 transport system appears to be involved in early phase cadmium cytotoxicity.

There are many subclones of human breast cancer MCF-7 cells that respond to different degrees of estrogen and that have been used for testing the estrogenic activity of environmental chemicals such as bisphenol A. Here, we examined the estrogenicity of bisphenol A in an MCF-7 subclone. It was not able to detect the increment of BrdU incorporation by neither 10^-7 M bisphenol A alone nor 10 ng/mL epidermal growth factor (EGF) alone in the cells (1 x 10⁴ cells) up to 50 hr. However, in the presence of 10 ng/mL EGF, bisphenol A dramatically increased cell proliferation (ED₅₀ = 10 pM). The synergistic responses were the chemical concentration-dependent manner. Thus, in this study, we demonstrate the new insight into the action of bisphenol A in the MCF-7 subclonal cell.