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Sun X, Spellman RA, Engel M, Rubitski E, Schuler M. Comparative analysis of micronucleus induction and DNA damage biomarkers in TK6 and A375 cells using flow cytometry. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2024; 65:25-46. [PMID: 38333939 DOI: 10.1002/em.22585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 01/19/2024] [Accepted: 01/20/2024] [Indexed: 02/10/2024]
Abstract
Previously, we introduced an alternative adherent A375 cell line for clastogenicity and aneugenicity testing using a high content imaging platform. To further characterize the performance of A375 cells, we investigated the sensitivity and specificity of A375 and TK6 cells by directly comparing micronucleus (MN) induction, cytotoxicity (relative cell counts, viability, and apoptosis), clastogenicity (γH2AX), and aneuploidy markers (pH 3, MPM-2, and polyploidy) using flow cytometric methods. We evaluated 14 compounds across different mechanisms (non-genotoxic apoptosis inducers, clastogens, and aneugens with either tubulin binding or aurora kinase inhibiting phenotypes) at 4-h and 24-h post treatment. Both aneugens and clastogens tested positive for micronucleus induction in both cell lines. Apoptosis continued to be a confounding factor for flow cytometry-based micronuclei assessment in TK6 cells as evidenced by positive responses by the three cytotoxicants. Conversely, A375 cells were not affected by apoptosis-related false positive signals and did not produce a positive response in the in vitro micronucleus assay. Benchmark dose response (BMD) analysis showed that the induction of micronuclei and biomarkers occurred at similar concentrations in both cell lines for clastogens and aneugens. By showing that A375 cells have similar sensitivity to TK6 cells but a greater specificity, these results provide additional support for A375 cells to be used as an alternative adherent cell line for in vitro genetic toxicology assessment.
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Affiliation(s)
- Xiaowen Sun
- Pfizer Research and Development, Groton, Connecticut, USA
| | | | - Maria Engel
- Pfizer Research and Development, Groton, Connecticut, USA
| | | | - Maik Schuler
- Pfizer Research and Development, Groton, Connecticut, USA
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Sanders J, Thienpont A, Anthonissen R, Vanhaecke T, Mertens B. Impact of experimental design factors on the potency of genotoxicants in in vitro tests. Mutagenesis 2022; 37:248-258. [PMID: 36448879 DOI: 10.1093/mutage/geac025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 11/14/2022] [Indexed: 12/02/2022] Open
Abstract
Previous studies have shown that differences in experimental design factors may alter the potency of genotoxic compounds in in vitro genotoxicity tests. Most of these studies used traditional statistical methods based on the lowest observed genotoxic effect levels, whereas more appropriate methods, such as the benchmark dose (BMD) approach, are now available to compare genotoxic potencies under different test conditions. We therefore investigated the influence of two parameters, i.e. cell type and exposure duration, on the potencies of two known genotoxicants [aflatoxin B1 and ethyl methanesulfonate (EMS)] in the in vitro micronucleus (MN) assay and comet assay (CA). Both compounds were tested in the two assays using two cell types (i.e. CHO-K1 and TK6 cells). To evaluate the effect of exposure duration, the genotoxicity of EMS was assessed after 3 and 24 h of exposure. Results were analyzed using the BMD covariate approach, also referred to as BMD potency ranking, and the outcome was compared with that of more traditional statistical methods based on lowest observed genotoxic effect levels. When comparing the in vitro MN results obtained in both cell lines with the BMD covariate approach, a difference in potency was detected only when EMS exposures were conducted for 24 h, with TK6 cells being more sensitive. No difference was observed in the potency of both EMS and aflatoxin B1 in the in vitro CA using both cell lines. In contrast, EMS was more potent after 24 h exposure compared with a 3 h exposure under all tested conditions, i.e. in the in vitro MN assay and CA in both cell lines. Importantly, for several of the investigated factors, the BMD covariate method could not be used to confirm the differences in potencies detected with the traditional statistical methods, thus highlighting the need to evaluate the impact of experimental design factors with adequate approaches.
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Affiliation(s)
- Julie Sanders
- Department of Chemical and Physical Health Risks, Sciensano, Brussels, Belgium.,Department of In Vitro Toxicology and Dermato-Cosmetology, Vrije Universiteit Brussel, Brussels, Belgium
| | - Anouck Thienpont
- Department of Chemical and Physical Health Risks, Sciensano, Brussels, Belgium.,Department of In Vitro Toxicology and Dermato-Cosmetology, Vrije Universiteit Brussel, Brussels, Belgium
| | - Roel Anthonissen
- Department of Chemical and Physical Health Risks, Sciensano, Brussels, Belgium
| | - Tamara Vanhaecke
- Department of In Vitro Toxicology and Dermato-Cosmetology, Vrije Universiteit Brussel, Brussels, Belgium
| | - Birgit Mertens
- Department of Chemical and Physical Health Risks, Sciensano, Brussels, Belgium
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Sun X, Rubitski E, Spellman RA, Engel M, Schuler M. A new imaging platform (iScreen) allows for the concurrent assessment of micronucleus induction and genotoxic mode of action in human A375 cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2022; 63:230-245. [PMID: 35703118 DOI: 10.1002/em.22496] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 05/21/2022] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Genotoxicity testing guidelines require the assessment of the clastogenic and aneugenic potential of compounds. While in vitro micronucleus assays detect both types of endpoints, it requires labor-intensive microscopic scoring and does not discriminate between the two modes of actions. Here, we present a novel high-content imaging platform in A375 human cells that addresses the need for rapid scoring while providing additional mechanistic information. We evaluated the new platform with 12 compounds, three compounds from each mechanistic class (clastogen, aneugen tubulin binder, aneugen aurora inhibitor, and nongenotoxicant) following 4- and 24-h compound treatments. The approach we developed is first discriminating between genotoxicant and nongenotoxicant using an image analysis algorithm to quantify micronucleus induction below a 60% cytotoxicity cutoff. Then it uses centromere protein A (CENPA) staining for the genotoxic compounds to discriminate between aneugens and clastogens. Lastly, we use phosphorylated histone H2AX Ser139 (γH2AX) staining to confirm clastogenicity and changes in phosphorylated histone 3 Ser10 (pH 3) and increases in polyploidy in mitotic cells to discriminate between aneugens that bind tubulin from those that affect aurora kinases. All compounds were correctly classified, and we showed by using benchmark dose-response analysis that the imaging platform in A375 cells is at least as sensitive as the MicroFlow® assay in TK6 cells for genotoxicant but appears to be more specific for the nongenotoxicants. A detailed comparison of the cell lines and a more comprehensive validation with a much larger compound set, predictive and dose-response modeling will be presented in the future.
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Affiliation(s)
- Xiaowen Sun
- Pfizer Research, Development, and Medical, Groton, Connecticut, USA
| | | | | | - Maria Engel
- Pfizer Research, Development, and Medical, Groton, Connecticut, USA
| | - Maik Schuler
- Pfizer Research, Development, and Medical, Groton, Connecticut, USA
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Hollingshead BD, Khan N, Schuler M, Radi Z. Development challenges for carcinogenicity risk assessments of topical drugs. J Toxicol Sci 2022; 47:1-11. [PMID: 34987136 DOI: 10.2131/jts.47.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The nonclinical safety package to support development and approval of drugs intended to be administered by topical application generally follows International Council for Harmonisation multidisciplinary 3 (ICH M3) and topic specific safety (ICH S) guidances. However, some aspects of topical drug development may require case-by-case determination of nonclinical safety strategies. The necessity to conduct a dermal rodent carcinogenicity study is one such example that is not considered an obligate component of a nonclinical safety data package for drug approval. While absence of systemic exposure, as stated in ICH M3, is a primary reason to forego a dermal carcinogenicity assessment, there may also be other factors for consideration in determining the need for a life-time carcinogencity study by dermal route to aid in the overall human cancer risk assessment. We therefore reviewed nonclinical carcinogencity data packages from drugs approved by the FDA or PMDA over a ~25 year time period to evaluate outcomes of oral versus topical carcinogencity studies and to understand their utility for informing the overall human risk assessment. We also discuss various other properties of topical small molecules that could impact the decisions to conduct a dermal life-time rodent carcinogenicity study. Collectively, the need to conduct 2-year dermal carcinogenicity studies in rodents should be determined case-by-case and consider scientific factors such existing systemic toxicity and carcinogenicity study data, anticipated drug exposures in skin, skin evaluation from the chronic minipig toxicity study, and genetic toxicity profile.
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Affiliation(s)
- Brett D Hollingshead
- Pfizer Drug Safety Research and Development, 1 Portland Street Cambridge, MA, USA
| | - Nasir Khan
- Pfizer Drug Safety Research and Development, 445 Eastern Point Road, Groton, CT, USA
| | - Maik Schuler
- Pfizer Drug Safety Research and Development, 445 Eastern Point Road, Groton, CT, USA
| | - Zaher Radi
- Pfizer Drug Safety Research and Development, 1 Portland Street Cambridge, MA, USA
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Yamamoto H, Shibuya K, Fukushima T, Hashizume T. Effects of antioxidant capacity on micronucleus induction by cigarette smoke in mammalian cells. MUTATION RESEARCH. GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2022; 873:503427. [PMID: 35094812 DOI: 10.1016/j.mrgentox.2021.503427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/10/2021] [Accepted: 11/11/2021] [Indexed: 06/14/2023]
Abstract
We have compared micronucleus (MN) induction by cigarette smoke in the L5178Y, TK6, and CHL/IU cell lines. The test sample was total particulate matter of 3R4F reference cigarette smoke, suspended in DMSO. After 3-h treatment, with or without a rat liver S9 metabolic activation system, followed by 24-h recovery, dose-dependent MN increases were seen in all cell lines. However, CHL/IU and TK6 cells were more resistant than L5178Y cells (comparison by Benchmark Doses with PROAST software). 3R4F smoke generates reactive oxygen species (ROS). Therefore, we explored the relationship between the sensitivities to 3R4F smoke and the antioxidant capacities of the cell lines. While the total antioxidant capacities were not significantly different among the cell lines, cellular glutathione (GSH) was higher in CHL/IU cells than in L5178Y cells. Pretreatment of CHL/IU cells with a GSH precursor, N-acetylcysteine (NAC), reduced the genotoxicity/cytotoxicity of 3R4F, whereas an inhibitor of GSH biosynthesis, buthionine sulfoximine (BSO), enhanced it. The effects of NAC and BSO were also seen after treatment with allyl isothiocyanate, a ROS-generating chemical, but not with mitomycin C, a ROS-independent genotoxicant. Pretreatment with NAC increased cellular thiol levels. From the present results, the genotoxicity and cytotoxicity of cigarette smoke differs among these cell lines in a manner that may be related to their antioxidant thiol levels.
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Affiliation(s)
- Haruna Yamamoto
- Scientific Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba-ku, Yokohama, Kanagawa, 227-8512, Japan.
| | - Kaori Shibuya
- Scientific Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba-ku, Yokohama, Kanagawa, 227-8512, Japan.
| | - Toshiro Fukushima
- Scientific Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba-ku, Yokohama, Kanagawa, 227-8512, Japan.
| | - Tsuneo Hashizume
- Scientific Product Assessment Center, R&D Group, Japan Tobacco Inc., 6-2 Umegaoka, Aoba-ku, Yokohama, Kanagawa, 227-8512, Japan.
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