TK6 Cells Research Articles

Mutagenicity and genotoxicity evaluation of 15 nitrosamine drug substance-related impurities in human TK6 cells

Nitrosamine drug substance-related impurities (NDSRIs) are a sub-category of N-nitrosamine drug impurities that share structural similarity to the corresponding active pharmaceutical ingredient. The mutagenicity of NDSRIs is poorly understood. We previously tested a series of NDSRIs using the Enhanced Ames Test (EAT). In this follow-up study, we further examined the genotoxicity and mutagenicity of 15 of these NDSRIs in human TK6 cells. Seven EAT-positive NDSRIs, including N-nitroso-nortriptyline, N-nitroso-fluoxetine, N-nitroso-desmethyl-diphenhydramine, N-nitroso-duloxetine, N-nitroso-lorcaserin, N-nitroso-varenicline, and N-nitroso-sertraline, induced concentration-dependent increases in micronuclei after bioactivation with hamster liver S9. These NDSRIs were also mutagenic in the TK and HPRT gene mutation assays, consistent with their positive EAT results. In the presence of hamster liver S9, the eight EAT-negative NDSRIs were negative in the micronucleus assay and negative for mutation induction. Using TK6 cells endogenously expressing a single human cytochrome P450 (CYP), we found that CYP2C19, CYP2B6, CYP2A6, and CYP3A4 are key enzymes activating the genotoxicity and mutagenicity of these NDSRIs. Overall, the hamster S9-mediated TK6 cell mutagenicity results agreed with those observed in the EAT, indicating consistency in the mutagenic responses produced by NDSRIs across different testing systems. These data support the use of EAT for hazard identification and safety assessment of NDSRIs.

Transcription factor Nrf2 regulating the interaction of p16 facilitates hydroquinone-induced malignant transformation of TK6 cells by accelerating cell proliferation

The nuclear factor erythroid 2-related factor 2 (Nrf2) is overexpressed in multiple tumor cells. Nevertheless, the role of Nrf2 in malignant transformation induced by hydroquinone (HQ) is unknown. Here, we hypothesized that Nrf2 might participate in HQ-induced malignant transformation of TK6 cells, a line of normal human lymphoblastoid cells, by accelerating cell proliferation and regulating cell cycle progression. The data indicated that TK6 cells chronically exposed to HQ continuously activated Nrf2-Keap1 signaling pathway. Furthermore, we found that defects in Nrf2 inhibited cell proliferation and prevented cells from entering S phase from G1 phase. Mechanistically, Nrf2 is involved in cell cycle abnormalities induced by prolonged exposure to HQ by binding to p16, thereby activating the p16/Rb signaling pathway. Taken together, Nrf2 might be a potential driver of carcinogenesis that promotes malignant cell proliferation and affects cell cycle distribution.

Assessment of the In Vitro Phosphatidylinositol Glycan Class A (PIG-A) Gene Mutation Assay Using Human TK6 and Mouse Hepa1c1c7 Cell Lines.

Gene mutations linked to diseases like cancer may be caused by exposure to environmental chemicals. The X-linked phosphatidylinositol glycan class A (PIG-A) gene, required for glycosylphosphatidylinositol (GPI) anchor biosynthesis, is a key target locus for in vitro genetic toxicity assays. Various organisms and cell lines may respond differently to genotoxic agents. Here, we compared the mutagenic potential of directly genotoxic ethyl methane sulfonate (EMS) to metabolically activated pro-mutagenic polycyclic aromatic hydrocarbons (PAHs). The two classes of mutagens were compared in an in vitro PIG-A gene mutation test using the metabolically active murine hepatoma Hepa1c1c7 cell line and the human TK6 cell line, which has limited metabolic capability. Determination of cell viability is required for quantifying mutagenicity. Two common cell viability tests, the MTT assay and propidium iodide (PI) staining measured by flow cytometry, were evaluated. The MTT assay overestimated cell viability in adherent cells at high benzo[a]pyrene (B[a]P) exposure concentrations, so PI-based cytotoxicity was used in calculations. The spontaneous mutation rates for TK6 and Hepa1c1c7 cells were 1.87 and 1.57 per million cells per cell cycle, respectively. TK6 cells exposed to 600 µM and 800 µM EMS showed significantly higher mutation frequencies (36 and 47 per million cells per cell cycle, respectively). Exposure to the pro-mutagen benzo[a]pyrene (B[a]P, 10 µM) did not increase mutation frequency in TK6 cells. In Hepa1c1c7 cells, mutation frequencies varied across exposure groups (50, 50, 29, and 81 per million cells per cell cycle when exposed to 10 µM B[a]P, 5-methylcholanthrene (5-MC), chrysene, or 16,000 µM EMS, respectively). We demonstrate that the choice of cytotoxicity assay and cell line can determine the outcome of the Pig-A mutagenesis assay when assessing a specific mutagen.

Genotoxicity of selected cannabinoids in human lymphoblastoid TK6 cells

Natural non-psychoactive cannabinoids such as cannabigerol (CBG), cannabidiol (CBD), cannabichromene (CBC), cannabidivarin (CBDV), and cannabinol (CBN) are increasingly consumed as constituents of dietary products because of the health benefits claims. Cannabinoids may reduce certain types of pain, nausea, and anxiety. Anti-inflammatory and even anti-carcinogenic properties have been discussed. However, there are insufficient data available regarding their potential (geno-)toxic effects. Therefore, we tested CBG, CBD, CBC, CBDV, and CBN for their genotoxic potential and effects on mitosis and cell cycle in human lymphoblastoid TK6 cells. The selected cannabinoids (except CBDV) induced increased micronuclei formation, which was reduced with the addition of a metabolic activation system (S9 mix). CBDV induced micronuclei only after metabolic activation. Mitotic disturbances were observed with all tested cannabinoids, while G1 phase accumulation of cells was observed for CBG, CBD and CBDV. The genotoxic effects occurred at about 1000-fold higher concentrations than are reported as blood levels from human consumption. However, the results clearly indicate a need for further research into the genotoxic effects of cannabinoids. The mechanism of the mitotic disturbance, the shape of the dose–response curves and the possible effects of mixtures of cannabinoids are aspects which need clarification.

Mutagenic and genotoxic in silico QSAR prediction of dimer impurity of gliflozins; canagliflozin, dapaglifozin, and emphagliflozin and in vitro evaluation by Ames and micronucleus test

Canagliflozin, Dapagliflozin, and Empagliflozin, glucagon-like peptide-1 receptor agonists, are indicated for managing type II diabetes. Although the genotoxicity profiles of these drugs are well-explored, limited information exists regarding the genotoxic potential of their impurities. In this investigation, the dimer impurities of Canagliflozin, Dapagliflozin, and Empagliflozin underwent both in silico and in vitro assessments for mutagenic potential. Tester strains of Salmonella typhimurium and Escherichia coli were subjected to the Ames test, utilizing concentrations of up to 1 µg per plate, with and without the presence of metabolic activation. Evaluation of micronucleus induction in TK6 cells was conducted through a micronucleus test, exploring concentrations up to 500 µg/mL, with or without the presence of exogenous metabolic activation. Under the specific test conditions, the dimer impurities of Canagliflozin, Dapagliflozin, and Empagliflozin showed no evidence of mutagenicity or clastrogenicity, establishing their in vitro classification as nonmutagenic. These findings align with negative in silico predictions from quantitative structure–activity relationship (QSAR) analyses for mutagenicity and genotoxicity of the dimer impurities. Collectively, these studies contribute clinically relevant safety information by confirming that the dimer impurities of Canagliflozin, Dapagliflozin, and Empagliflozin are nonmutagenic and nongenotoxic, emphasizing the consistency between in silico and in vitro data.

Levothyroxine synthesis impurities are neither mutagenic nor genotoxic: Insilico, Ames test and micronucleus test studies

In vitro and in silico tests were used to assess the possible genotoxicity and mutagenicity of five impurities that may be present in levothyroxine, a drug used for thyroid hormone replacement therapy. Neither ToxTree nor VEGA (Virtual Models for evaluating the properties of chemicals within a global architecture) identified cause for concern for any of the impurities. Ames test results (doses up to 1 mg per plate), with or without metabolic activation, were negative. The micronucleus test with TK6 (human lymphoblastoid) cells, at doses up to 500 µg/mL, with or without metabolic activation, also gave negative results.

A multi-biomarker micronucleus assay using imaging flow cytometry

Genetic toxicity testing assesses the potential of compounds to cause DNA damage. There are many genetic toxicology screening assays designed to assess the DNA damaging potential of chemicals in early drug development aiding the identification of promising drugs that have low-risk potential for causing genetic damage contributing to cancer risk in humans. Despite this, in vitro tests generate a high number of misleading positives, the consequences of which can lead to unnecessary animal testing and/or the abandonment of promising drug candidates. Understanding chemical Mode of Action (MoA) is vital to identifying the true genotoxic potential of substances and, therefore, the risk translation into the clinic. Here we demonstrate a simple, robust protocol for staining fixed, human-lymphoblast p53 proficient TK6 cells with antibodies against ɣH2AX, p53 and pH3S28 along with DRAQ5™ DNA staining that enables analysis of un-lysed cells via microscopy approaches such as imaging flow cytometry. Here, we used the Cytek® Amnis® ImageStream®X Mk II which provides a high-throughput acquisition platform with the sensitivity of flow cytometry and spatial morphological information associated with microscopy. Using the ImageStream manufacturer’s software (IDEAS® 6.2), a masking strategy was developed to automatically detect and quantify micronucleus events (MN) and characterise biomarker populations. The gating strategy developed enables the generation of a template capable of automatically batch processing data files quantifying cell-cycle, MN, ɣH2AX, p53 and pH3 populations simultaneously. In this way, we demonstrate how a multiplex system enables DNA damage assessment alongside MN identification using un-lysed cells on the imaging flow cytometry platform. As a proof-of-concept, we use the tool chemicals carbendazim and methyl methanesulphonate (MMS) to demonstrate the assay’s ability to correctly identify clastogenic or aneugenic MoAs using the biomarker profiles established.

IL-6 knockdown in a model of the human bone marrow, abrogates DNA damage induction in bystander cells post-chemotherapy induced cytokine release syndrome

Following infection or exposure to therapeutic agents, an aggressive immune response may result, termed cytokine storm (CS) or cytokine release syndrome. Here the innate immune system becomes uncontrolled, leading to serious consequences including possible death. Patients surviving CS are at greater risk for de novo tumorigenesis, but it is unclear if any specific cytokines are directly responsible for this outcome. De novo tumorigenesis has been observed in donated cells exposed to CS following haematopoietic stem cell transplant (HSCT).Modelling HSCT, we firstly demonstrated the release of CS levels from the HS-5 human bone marrow stromal cell line, post-exposure to chemotherapy. We then exposed the TK6 lymphoblast cell line to healthy and storm doses of IL-6 and measured increased genotoxicity via the micronucleus assay. During HSCT, haematopoietic cells are exposed to a complex mix of cytokines, so to determine if IL-6 was integral in a chemotherapy-induced bystander effect, we attempted to inhibit IL-6 from HS-5 cells using resatorvid or siRNA, treated with chlorambucil or mitoxantrone, and then co-cultured with bystander TK6 cells. Whilst resatorvid did not reduce IL-6 and did not reduce micronuclei in the bystander TK6 cells, siRNA inhibition reduced IL-6 to healthy in vivo levels, and micronuclei aligned with untreated controls.Our data suggests that exposure to high IL-6 (in the absence of inflammatory cells) has potential to induce genetic damage and may contribute to de novo tumorigenesis post-CS. We suggest that for individuals with a pro-inflammatory profile, anti-IL-6 therapy may be an appropriate intervention to prevent complications post-CS.

Role of the PARP1/NF-κB Pathway in DNA Damage and Apoptosis of TK6 Cells Induced by Hydroquinone.

Hydroquinone(HQ) is a widely used industrial raw material and is a topical lightening product found in over-the-counter products. However, inappropriate exposure to HQ can pose certain health hazards. This study aims to explore the mechanisms of DNA damage and cell apoptosis caused by HQ, with a focus on whether HQ activates the nuclear factor-κB (NF-κB) pathway to participate in this process and to investigate the correlation between the NF-κB pathway activation and poly(ADP-ribose) polymerase 1(PARP1). Through various experimental techniques, such as DNA damage detection, cell apoptosis assessment, cell survival rate analysis, immunofluorescence, and nuclear-cytoplasmic separation, the cytotoxic effects of HQ were verified, and the activation of the NF-κB pathway was observed. Simultaneously, the relationship between the NF-κB pathway and PARP1 was verified by shRNA interference experiments. The results showed that HQ could significantly activate the NF-κB pathway, leading to a decreased cell survival rate, increased DNA damage, and cell apoptosis. Inhibiting the NF-κB pathway could significantly reduce HQ-induced DNA damage and cell apoptosis and restore cell proliferation and survival rate. shRNA interference experiments further indicated that the activation of the NF-κB pathway was regulated by PARP1. This study confirmed the important role of the NF-κB pathway in HQ-induced DNA damage and cell apoptosis and revealed that the activation of the NF-κB pathway was mediated by PARP1. This research provides important clues for a deeper understanding of the toxic mechanism of HQ.

Visualization strategies to aid interpretation of high-dimensional genotoxicity data.

This article describes a range of high-dimensional data visualization strategies that we have explored for their ability to complement machine learning algorithm predictions derived from MultiFlow® assay results. For this exercise, we focused on seven biomarker responses resulting from the exposure of TK6 cells to each of 126 diverse chemicals over a range of concentrations. Obviously, challenges associated with visualizing seven biomarker responses were further complicated whenever there was a desire to represent the entire 126 chemical data set as opposed to results from a single chemical. Scatter plots, spider plots, parallel coordinate plots, hierarchical clustering, principal component analysis, toxicological prioritization index, multidimensional scaling, t-distributed stochastic neighbor embedding, and uniform manifold approximation and projection are each considered in turn. Our report provides a comparative analysis of these techniques. In an era where multiplexed assays and machine learning algorithms are becoming the norm, stakeholders should find some of these visualization strategies useful for efficiently and effectively interpreting their high-dimensional data.

Human plasma can modulate micronucleus frequency in TK6 and OE33 cells in vitro

In this paper, we studied the potential genotoxic effects of human plasma from healthy volunteers, as well as patients with gastro-oesophageal reflux disease, Barrett’s oesophagus (BO) and oesophageal adenocarcinoma (OAC) using the oesophageal adenocarcinoma cell line (OE33) and the lymphoblastoid cell line (TK6). Both TK6 and OE33 cells were treated with plasma (10 % volume, replacing foetal bovine serum (FBS) or horse serum (HS)) at different time points of 4 h (for the micronucleus (Mn) assay and the invasion assay) and 24 h (for the cell cycle studies). Plasma-induced effects on DNA damage levels, cell viability and the cell cycle were studied by the micronucleus assay, cytokinesis block proliferation index (CBPI) and flow cytometry respectively. The expression of IL-8 in supernatants of TK6 cells and IFN-β in OE33 cells was also analysed by enzyme-linked immunosorbent assay (ELISA). Finally, we carried out an assessment of cellular invasion of OE33 cells following plasma treatment.The results of the micronucleus assay confirmed the genotoxicity of direct plasma treatment from some participants through the increase in DNA damage in TK6 cells. Conversely, some individual patient plasma samples reduced background levels of TK6 cell Mn frequency, in an anti-genotoxic fashion. In TK6 cells, (on average) plasma samples from patients with Barrett’s oesophagus induced higher micronucleus levels than healthy volunteers (p= 0.0019). There was little difference in Mn induction when using plasma versus serum to treat the cells in vitro. Cell cycle results showed that direct plasma treatment had a marked impact on OE33 cells at 24 h (p=0.0182 for BO and p=0.0320 for OAC) by decreasing the proportion of cells in the S phase, while plasma exposure was less impactful on the cell cycle of TK6 cells. Invasion of OE33 cells was also seen to be non-significantly affected by plasma treatment of OE33 cells.The addition of N-acetyl cysteine NAC in a dose-dependent matter did not alter the formation of Mn in TK6 cells, suggesting that reactive oxygen species (ROS) are not the root cause of plasma’s genotoxicity. The concentration of IL-8 in TK6 cells and IFN-β in OE33 cells was significantly higher in cells treated with OAC-derived plasma than in the untreated negative control. Collectively, our results demonstrate that plasma-specific effects are detectable which helps us better understand some important aspects of the biology of blood-based biomarkers under development.

Liver-on-chip model and application in predictive genotoxicity and mutagenicity of drugs

Currently, there is no test system, whether in vitro or in vivo, capable of examining all endpoints required for genotoxicity evaluation used in pre-clinical drug safety assessment. The objective of this study was to develop a model which could assess all the required endpoints and possesses robust human metabolic activity, that could be used in a streamlined, animal-free manner. Liver-on-chip (LOC) models have intrinsic human metabolic activity that mimics the in vivo environment, making it a preferred test system. For our assay, the LOC was assembled using primary human hepatocytes or HepaRG cells, in a MPS-T12 plate, maintained under microfluidic flow conditions using the PhysioMimix® Microphysiological System (MPS), and co-cultured with human lymphoblastoid (TK6) cells in transwells. This system allows for interaction between two compartments and for the analysis of three different genotoxic endpoints, i.e. DNA strand breaks (comet assay) in hepatocytes, chromosome loss or damage (micronucleus assay) and mutation (Duplex Sequencing) in TK6 cells. Both compartments were treated at 0, 24 and 45 h with two direct genotoxicants: methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS), and two genotoxicants requiring metabolic activation: benzo[a]pyrene (B[a]P) and cyclophosphamide (CP). Assessment of cytochrome activity, RNA expression, albumin, urea and lactate dehydrogenase production, demonstrated functional metabolic capacities. Genotoxicity responses were observed for all endpoints with MMS and EMS. Increases in the micronucleus and mutations (MF) frequencies were also observed with CP, and %Tail DNA with B[a]P, indicating the metabolic competency of the test system. CP did not exhibit an increase in the %Tail DNA, which is in line with in vivo data. However, B[a]P did not exhibit an increase in the % micronucleus and MF, which might require an optimization of the test system. In conclusion, this proof-of-principle experiment suggests that LOC-MPS technology is a promising tool for in vitro hazard identification genotoxicants.

Linc01588 deletion inhibits the malignant biological characteristics of hydroquinone-induced leukemic cells via miR-9-5p/SIRT1

Leukemia caused by environmental chemical pollutants has attracted great attention, the malignant leukemic transformation model of TK6 cells induced by hydroquinone (HQ) has been previously found in our team. However, the type of leukemia corresponding to this malignant transformed cell line model needs further study and interpretation. Furthermore, the molecular mechanism of malignant proliferation of leukemic cells induced by HQ remains unclear. This study is the first to reveal the expression of aberrant genes in leukemic cells of HQ-induced malignant transformation, which may correspond to chronic lymphocytic leukemia (CLL). The expression of Linc01588, a long non-coding RNA (lncRNA), was significantly up-regulated in CLL patients and leukemic cell line model which previously described. After gain-of-function assays and loss-of-function assays, feeble cell viability, severe apoptotic phenotype and the increased secretion of TNF-α were easily observed in malignant leukemic TK6 cells with Linc01588 deletion after HQ intervention. The tumors derived from malignant TK6 cells with Linc01588 deletion inoculated subcutaneously in nude mice were smaller than controls. In CLL and its cell line model, the expression of Linc01588 and miR-9–5p, miR-9–5p and SIRT1 were negative correlation respectively in CLL and cell line model, while the expression of Linc01588 and SIRT1 were positive correlation. The dual-luciferase reporter assay showed that Linc01588 & miR-9–5p, miR-9–5p & SIRT1 could bind directly, respectively. Furthermore, knockdown of miR-9–5p successfully rescued the severe apoptotic phenotype and the increased secretion of TNF-α caused by the Linc01588 deletion, the deletion of Linc01588 in human CLL cell line MEC-2 could also inhibit malignant biological characteristics, and the phenotype caused by the deletion of Linc01588 could also be rescued after overexpression of SIRT1. Moreover, the regulation of SIRT1 expression in HQ19 cells by Linc01588 and miR-9–5 P may be related to the Akt/NF-κB pathway. In brief, Linc01588 deletion inhibits the malignant biological characteristics of HQ-induced leukemic cells via miR-9–5p/SIRT1, and it is a novel and hopeful clue for the clinical targeted therapy of CLL.

Collaborative Study of Thresholds for Mutagens: Adaptive Responses in the Micronucleus Test and Gene Induction by Mutagenic Treatments.

We have been conducting a collaborative study on the thresholds of mutagens. In our previous examinations of cell activity and cell proliferation as endpoints, both displayed hormesis. This time, we conducted experiments to determine thresholds using the micronucleus test as an endpoint. The micronucleus test was conducted using Chinese hamster CHL/IU cells and mouse lymphoid L5178Y cells. Additionally, we conducted preliminary investigations into the gene expression using human TK6 cells. When adhesive CHL/IU cells were treated with mitomycin C (MMC), and the hormetic response was examined, hormesis was not observed clearly. When L5178Y cells were treated with methyl methanesulfonate (EMS), AF-2, MMC, and colchicine, all of them exhibited an adaptive response. Additionally, cross-adaptive responses using AF-2 and MMC or EMS and MMC were conducted, both combinations showed a cross-adaptive response. When the gene expression patterns of six genes were investigated by RT-PCR after treatment with MMC, EMS, and H2O2 using TK6 cells, two genes, GADD45A and P21, were induced in a dose- and time-dependent manner. Adaptive responses arise from preconditioning. As hormesis is inherently linked to preconditioning, adaptive responses observed in this study strongly suggest that hormesis was induced, hence existence of thresholds.

Adapting the in vitro micronucleus assay (OECD Test Guideline No. 487) for testing of manufactured nanomaterials: recommendations for best practices.

The current Organisation for Economic Co-Operation and Development test guideline number 487 (OECD TG No. 487) provides instruction on how to conduct the in vitro micronucleus assay. This assay is one of the gold standard approaches for measuring the mutagenicity of test items; however, it is directed at testing low molecular weight molecules and may not be appropriate for particulate materials (e.g. engineered nanoparticles [ENPs]). This study aimed to adapt the in vitro micronucleus assay for ENP testing and underpins the development of an OECD guidance document. A harmonized, nano-specific protocol was generated and evaluated by two independent laboratories. Cell lines utilized were human lymphoblastoid (TK6) cells, human liver hepatocytes (HepG2) cells, Chinese hamster lung fibroblast (V79) cells, whole blood, and buffy coat cells from healthy human volunteers. These cells were exposed to reference ENPs from the Joint Research Council (JRC): SiO2 (RLS-0102), Au5nm and Au30nm (RLS-03, RLS-010), CeO2 (NM212), and BaSO4 (NM220). Tungsten carbide-cobalt (WC/Co) was used as a trial particulate positive control. The chemical controls were positive in all cell cultures, but WC/Co was only positive in TK6 and buffy coat cells. In TK6 cells, mutagenicity was observed for SiO2- and both Au types. In HepG2 cells, Au5nm and SiO2 showed sub-two-fold increases in micronuclei. In V79 cells, whole blood, and buffy coat cells, no genotoxicity was detected with the test materials. The data confirmed that ENPs could be tested with the harmonized protocol, additionally, concordant data were observed across the two laboratories with V79 cells. WC/Co may be a suitable particulate positive control in the in vitro micronucleus assay when using TK6 and buffy coat cells. Detailed recommendations are therefore provided to adapt OECD TG No. 487 for testing ENP.

Use of Lentivirus-Based Method for Establishing TK6 Human Cell Lines Expressing Cytochrome P450 and its Applications in Genotoxicity Testing.

The human lymphoblastoid cell line TK6 stands out as the most widely employed human cell line in genotoxicity testing, as recommended by various testing guidelines for in vitro assessments. Nevertheless, like many testing cell lines, TK6 lacks functional phase I drug-metabolizing enzymes crucial for chemical genotoxicity evaluations. This protocol introduces a lentivirus-based methodology for establishing a panel of TK6-derived cell lines, each expressing one of 14 cytochrome P450s (CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5, and CYP3A7). The utilization of a lentiviral expression system ensures stable transduction, offering notable advantages such as sustained transgene expression, high transduction efficiency, positive selection feasibility, and user-friendly application. Additionally, we present a detailed procedure for validating the enhanced expression of each CYP in the established cell lines through real-time PCR, western blotting, and mass spectrometry analysis. Lastly, we exemplify the application of these CYP-expressing TK6 cell lines in genotoxicity testing, employing a flow-cytometry-based in vitro micronucleus test. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Lentivirus production and transduction for TK6 cells Support Protocol: Selecting a single clone of CYP-expressing TK6 cells Basic Protocol 2: Validation of CYP expression in TK6 cell lines Basic Protocol 3: Application of transduced cell lines in flow-cytometry-based micronucleus assay.

CDK4/6 inhibitor-induced bone marrow micronuclei might be caused by cell cycle arrest during erythropoiesis

BackgroundA micronucleus test is generally used to evaluate the genotoxic potential of chemicals. Exaggerated erythropoiesis, as occurs following bleeding, may induce an unexpected increase in micronucleus frequency. This false positive result would be typical in a genotoxicity study due to the enhanced progression of the cell cycle that restores decreased blood cells. The cyclin-dependent kinase (CDK) family is known to play an essential role in preventing genomic instability. Conversely, a selective CDK4/6 inhibitor PD0332991, clinically named Palbociclib, is reported to have genotoxic potential, shown by positive results in both in vitro and in vivo micronucleus studies. To clarify the mechanism by which cell cycle arrest induced by a CDK4/6 inhibitor increases micronucleus frequency, we investigated the positive results of the bone marrow micronucleus test conducted with PD0332991.ResultsRats treated with PD0332991 exhibited increased micronucleus frequency in an in vivo bone marrow micronucleus test whereas it was not increased by treatment in human lymphoblastoid TK6 cells. In addition, all other genotoxicity tests including the Ames test and the comet assay showed negative results with PD0332991. Interestingly, PD0332991 treatment led to an increase in erythrocyte size in rats and affected the size distribution of erythrocytes, including the micronucleus. The mean corpuscular volume of reticulocytes (MCVr) in the PD0332991 treatment group was significantly increased compared to that of the vehicle control (83.8 fL in the PD0332991, and 71.6 fL in the vehicle control.). Further, the average micronucleated erythrocytes (MNE) size of the PD0332991 group and vehicle control was 8.2 and 7.3 µm, respectively. In the histogram, the vehicle control showed a monomodal distribution with a peak near 7.3 µm. In contrast, the PD0332991 group showed a bimodal distribution with peaks around 7.5 and 8.5 µm. Micronucleated erythrocytes in the PD0332991 group were significantly larger than those in the vehicle control.These results suggest that the increase in micronucleus frequency induced by the CDK4/6 inhibitor is not due to genotoxicity, but is attributable to disturbance of the cell cycle, differentiation, and enucleation of erythroblasts.ConclusionsIt was suggested that the positive outcome of the in vivo bone marrow micronucleus test resulting from treatment with PD0332991 could not be attributed to its genotoxicity. Further studies to clarify the mechanism of action can contribute to the development of drug candidate compounds lacking intrinsic genotoxic effects.

Comparative analysis of micronucleus induction and DNA damage biomarkers in TK6 and A375 cells using flow cytometry.

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.

Microfluidic measurement of intracellular mRNA with a molecular beacon probe towards point-of-care radiation triage.

In large-scale radiation exposure events, the ability to triage potential victims by the received radiation dosage is crucial. This can be evaluated by radiation-induced biological changes. Radiation-responsive mRNA is a class of biomarkers that has been explored for dose-dependency with methods such as RT-qPCR. However, these methods are challenging to implement for point-of-care devices. We have designed and used molecular beacons as probes for the measurement of radiation-induced changes of intracellular mRNA in a microfluidic device towards determining radiation dosage. Our experiments, in which fixed TK6 cells labeled with a molecular beacon specific to BAX mRNA exhibited dose-dependent fluorescence in a manner consistent with RT-qPCR analysis, demonstrate that such intracellular molecular probes can potentially be used in point-of-care radiation biodosimetry. This proof of concept could readily be extended to any RNA-based test to provide direct measurements at the bedside.

DNMT1 regulates hypermethylation and silences hsa_circ_401351 in hydroquinone-induced malignant TK6 cells.

Benzene and its metabolite hydroquinone (HQ) are widely used in daily life, and long-term exposure to benzene or HQ can induce acute myeloid leukemia (AML). Circular RNAs (circRNAs) are mostly produced by reverse splicing of gene exon mRNA precursors. The modulation of circRNA expression is connected to leukemia progression; however, the molecular mechanism is still unknown. In this study, the cells were divided into four groups: PBS control group (PBS-TK6), TK6 malignantly transformed cells induced by 10.0 μmol/L HQ (HQ-TK6), and HQ-TK6 cells treated with 5 μmol/L 5-AzaC (DNA methyltransferase inhibitor) for 24 h (HQ + 5-AzaC). HQ-TK6 cells were treated with 200 nmol/L TSA (histone deacetylation inhibitor) for 24 h (HQ + TSA). qRT-PCR was used to identify the differential hsa_circ_401351 expression between the four groups. We further determined the hsa_circ_401351 promoter methylation level with methylation-specific PCR. DNMT1 and DNMT3b were knocked down by CRISPR/Cas9 to elucidate the specific molecular mechanism of hsa_circ_401351 in HQ-TK6 cells. CCK-8 and flow cytometry detected cell proliferation and apoptosis, respectively, after hsa_circ_401351 was overexpressed in HQ-TK6 cells. Compared with the PBS-TK6 group, the expression of hsa_circ_401351 was found to be lower in the HQ-TK6 group. Nevertheless, treatment with 5-AzaC or TSA increased hsa_circ_401351 expression, with the upregulation being more pronounced in the TSA group. The expression of hsa_circ_401351 in the DNMT1 knockdown group was dramatically increased by 50% compared to that in the control group, and the DNA methylation level of the hsa_circ_401351 promoter region was decreased. When hsa_circ_401351 was overexpressed, HQ-TK6 cell proliferation was significantly slowed after 48 h compared with the control group. Flow cytometry showed that cells were mainly arrested in G1 phase, and apoptosis was significantly enhanced. Similarly, qRT-PCR and Western blot data showed significant reductions in Caspase-3 mRNA and protein production, and Bcl-2 mRNA levels were also elevated. Overall, our research showed that elevated DNMT1 expression in HQ-TK6 cells increased methylation levels and decreased expression of the hsa_circ_401351 promoter region, limiting its ability to suppress HQ-TK6 cell growth and enhance apoptosis.