High-Throughput Screening to Advance In Vitro Toxicology: Accomplishments, Challenges, and Future Directions

Traditionally, chemical toxicity is determined by in vivo animal studies, which are low throughput, expensive, and sometimes fail to predict compound toxicity in humans. Due to the increasing number of chemicals in use and the high rate of drug candidate failure due to toxicity, it is imperative to develop in vitro, high-throughput screening methods to determine toxicity. The Tox21 program, a unique research consortium of federal public health agencies, was established to address and identify toxicity concerns in a high-throughput, concentration-responsive manner using a battery of in vitro assays. In this article, we review the advancements in high-throughput robotic screening methodology and informatics processes to enable the generation of toxicological data, and their impact on the field; further, we discuss the future of assessing environmental toxicity utilizing efficient and scalable methods that better represent the corresponding biological and toxicodynamic processes in humans.

Liver three-dimensional cellular models for high-throughput chemical testing

Drug-induced hepatotoxicity is a leading cause of drug withdrawal from the market. High-throughput screening utilizing in vitro liver models is critical for early-stage liver toxicity testing. Traditionally, monolayer human hepatocytes or immortalized liver cell lines (e.g., HepG2, HepaRG) have been used to test compound liver toxicity. However, monolayer-cultured liver cells sometimes lack the metabolic competence to mimic the in vivo condition and are therefore largely appropriate for short-term toxicological testing. They may not, however, be adequate for identifying chronic and recurring liver damage caused by drugs. Recently, several three-dimensional (3D) liver models have been developed. These 3D liver models better recapitulate normal liver function and metabolic capacity. This review describes the current development of 3D liver models that can be used to test drugs/chemicals for their pharmacologic and toxicologic effects, as well as the advantages and limitations of using these 3D liver models for high-throughput screening.

The SARS-CoV-2 spike protein binds and modulates estrogen receptors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein binds angiotensin-converting enzyme 2 as its primary infection mechanism. Interactions between S and endogenous proteins occur after infection but are not well understood. We profiled binding of S against >9000 human proteins and found an interaction between S and human estrogen receptor α (ERα). Using bioinformatics, supercomputing, and experimental assays, we identified a highly conserved and functional nuclear receptor coregulator (NRC) LXD-like motif on the S2 subunit. In cultured cells, S DNA transfection increased ERα cytoplasmic accumulation, and S treatment induced ER-dependent biological effects. Non-invasive imaging in SARS-CoV-2-infected hamsters localized lung pathology with increased ERα lung levels. Postmortem lung experiments from infected hamsters and humans confirmed an increase in cytoplasmic ERα and its colocalization with S in alveolar macrophages. These findings describe the discovery of a S-ERα interaction, imply a role for S as an NRC, and advance knowledge of SARS-CoV-2 biology and coronavirus disease 2019 pathology.

The SARS-CoV-2 spike protein binds and modulates estrogen receptors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein binds angiotensin-converting enzyme 2 (ACE2) at the cell surface, which constitutes the primary mechanism driving SARS-CoV-2 infection. Molecular interactions between the transduced S and endogenous proteins likely occur post-infection, but such interactions are not well understood. We used an unbiased primary screen to profile the binding of full-length S against >9,000 human proteins and found significant S-host protein interactions, including one between S and human estrogen receptor alpha (ERα). After confirming this interaction in a secondary assay, we used bioinformatics, supercomputing, and experimental assays to identify a highly conserved and functional nuclear receptor coregulator (NRC) LXD-like motif on the S2 subunit and an S-ERα binding mode. In cultured cells, S DNA transfection increased ERα cytoplasmic accumulation, and S treatment induced ER-dependent biological effects and ACE2 expression. Noninvasive multimodal PET/CT imaging in SARS-CoV-2-infected hamsters using [ 18 F]fluoroestradiol (FES) localized lung pathology with increased ERα lung levels. Postmortem experiments in lung tissues from SARS-CoV-2-infected hamsters and humans confirmed an increase in cytoplasmic ERα expression and its colocalization with S protein in alveolar macrophages. These findings describe the discovery and characterization of a novel S-ERα interaction, imply a role for S as an NRC, and are poised to advance knowledge of SARS-CoV-2 biology, COVID-19 pathology, and mechanisms of sex differences in the pathology of infectious disease.

Identification of environmental chemicals that activate p53 signaling after in vitro metabolic activation

Currently, approximately 80,000 chemicals are used in commerce. Most have little-to-no toxicity information. The U.S. Toxicology in the 21st Century (Tox21) program has conducted a battery of in vitro assays using a quantitative high-throughput screening (qHTS) platform to gain toxicity information on environmental chemicals. Due to technical challenges, standard methods for providing xenobiotic metabolism could not be applied to qHTS assays. To address this limitation, we screened the Tox21 10,000-compound (10K) library, with concentrations ranging from 2.8 nM to 92 µM, using a p53 beta-lactamase reporter gene assay (p53-bla) alone or with rat liver microsomes (RLM) or human liver microsomes (HLM) supplemented with NADPH, to identify compounds that induce p53 signaling after biotransformation. Two hundred and seventy-eight compounds were identified as active under any of these three conditions. Of these 278 compounds, 73 gave more potent responses in the p53-bla assay with RLM, and 2 were more potent in the p53-bla assay with HLM compared with the responses they generated in the p53-bla assay without microsomes. To confirm the role of metabolism in the differential responses, we re-tested these 75 compounds in the absence of NADPH or with heat-attenuated microsomes. Forty-four compounds treated with RLM, but none with HLM, became less potent under these conditions, confirming the role of RLM in metabolic activation. Further evidence of biotransformation was obtained by measuring the half-life of the parent compounds in the presence of microsomes. Together, the data support the use of RLM in qHTS for identifying chemicals requiring biotransformation to induce biological responses.

XRCC1 counteracts PARP poisons, Olaparib and Talazoparib, and a clinical alkylating agent, Temozolomide, by promoting the removal of trapped PARP1 from broken DNA

Base excision repair (BER) removes damaged bases by generating single‐strand breaks (SSBs), gap‐filling by DNA polymerase β (POLβ), and resealing SSBs. A base‐damaging agent, methyl methanesulfonate (MMS) is widely used to study BER. BER increases cellular tolerance to MMS, anti‐cancer base‐damaging drugs, temozolomide, carmustine, and lomustine, and to clinical poly(ADP ribose)polymerase (PARP) poisons, olaparib and talazoparib. The poisons stabilize PARP1/SSB complexes, inhibiting access of BER factors to SSBs. PARP1 and XRCC1 collaboratively promote SSB resealing by recruiting POLβ to SSBs, but XRCC1^−/− cells are much more sensitive to MMS than PARP1^−/− cells. We recently report that the PARP1 loss in XRCC1^−/− cells restores their MMS tolerance and conclude that XPCC1 facilitates the release of PARP1 from SSBs by maintaining its autoPARylation. We here show that the PARP1 loss in XRCC1^−/− cells also restores their tolerance to the three anti‐cancer base‐damaging drugs, although they and MMS induce different sets of base damage. We reveal the synthetic lethality of the XRCC1^−/− mutation, but not POLβ^−/−, with olaparib and talazoparib, indicating that XRCC1 is a unique BER factor in suppressing toxic PARP1/SSB complex and can suppress even when PARP1 catalysis is inhibited. In conclusion, XRCC1 suppresses the PARP1/SSB complex via PARP1 catalysis‐dependent and independent mechanisms.

Profiling the Tox21 Chemical Collection for Acetylcholinesterase Inhibition

BACKGROUND

Inhibition of acetylcholinesterase (AChE), a biomarker of organophosphorous and carbamate exposure in environmental and occupational human health, has been commonly used to identify potential safety liabilities. So far, many environmental chemicals, including drug candidates, food additives, and industrial chemicals, have not been thoroughly evaluated for their inhibitory effects on AChE activity. AChE inhibitors can have therapeutic applications (e.g., tacrine and donepezil) or neurotoxic consequences (e.g., insecticides and nerve agents).

OBJECTIVES

The objective of the current study was to identify environmental chemicals that inhibit AChE activity using in vitro and in silico models.

METHODS

To identify AChE inhibitors rapidly and efficiently, we have screened the Toxicology in the 21st Century (Tox21) 10K compound library in a quantitative high-throughput screening (qHTS) platform by using the homogenous cell-based AChE inhibition assay and enzyme-based AChE inhibition assays (with or without microsomes). AChE inhibitors identified from the primary screening were further tested in monolayer or spheroid formed by SH-SY5Y and neural stem cell models. The inhibition and binding modes of these identified compounds were studied with time-dependent enzyme-based AChE inhibition assay and molecular docking, respectively.

RESULTS

A group of known AChE inhibitors, such as donepezil, ambenonium dichloride, and tacrine hydrochloride, as well as many previously unreported AChE inhibitors, such as chelerythrine chloride and cilostazol, were identified in this study. Many of these compounds, such as pyrazophos, phosalone, and triazophos, needed metabolic activation. This study identified both reversible (e.g., donepezil and tacrine) and irreversible inhibitors (e.g., chlorpyrifos and bromophos-ethyl). Molecular docking analyses were performed to explain the relative inhibitory potency of selected compounds.

CONCLUSIONS

Our tiered qHTS approach allowed us to generate a robust and reliable data set to evaluate large sets of environmental compounds for their AChE inhibitory activity. https://doi.org/10.1289/EHP6993.

Pold4, the fourth subunit of replicative polymerase δ, suppresses gene conversion in the immunoglobulin-variable gene in avian DT40 cells

The replicative polymerase δ (Polδ), consisting of four subunits, plays a pivotal role in chromosomal replication. Pold4, the smallest subunit of Polδ, is believed to contribute to the regulation of replication by facilitating repair in response to DNA damage. However, that contribution has not been fully elucidated. We here show that Pold4 contributes to the suppression of gene conversion in immunoglobulin-variable (IgV) gene diversification in the chicken DT40 lymphocyte cell line, where gene conversion diversifies the IgV gene through intragenic homologous recombination (HR) between diverged pseudo-V segments. IgV gene conversion is initiated by activation-induced cytidine deaminase-mediated uracil formation in the IgV gene, which in turn converts into an abasic site, leading to replication arrest. POLD4^-/- cells exhibited an increased rate of IgV gene conversion. Moreover, the gene-conversion tract was lengthened and the usage of pseudo-V segments was altered, showing a preference, to use the diverged sequence as a donor in POLD4^-/- cells. These data suggest that Pold4 is involved in the regulation of HR-mediated gene conversion in IgV diversification. By contrast, the rate in HR-mediated, sister-chromatid exchange and gene-targeting induced by an I-SceI endonclease-mediated DNA double-strand break exhibited by POLD4^-/- cells was indistinguishable from that by wild-type cells. These findings indicate that the functionality of general HR is preserved in POLD4^-/- cells. In conclusion, Pold4 is involved in the suppression of IgV-gene conversion without affecting the general functionality of HR.

Application of In Vitro Metabolism Activation in High-Throughput Screening

In vitro methods which incorporate metabolic capability into the assays allow us to assess the activity of metabolites from their parent compounds. These methods can be applied into high-throughput screening (HTS) platforms, thereby increasing the speed to identify compounds that become active via the metabolism process. HTS was originally used in the pharmaceutical industry and now is also used in academic settings to evaluate biological activity and/or toxicity of chemicals. Although most chemicals are metabolized in our body, many HTS assays lack the capability to determine compound activity via metabolism. To overcome this problem, several in vitro metabolic methods have been applied to an HTS format. In this review, we describe in vitro metabolism methods and their application in HTS assays, as well as discuss the future perspectives of HTS with metabolic activity. Each in vitro metabolism method has advantages and disadvantages. For instance, the S9 mix has a full set of liver metabolic enzymes, but it displays high cytotoxicity in cell-based assays. In vitro metabolism requires liver fractions or the use of other metabolically capable systems, including primary hepatocytes or recombinant enzymes. Several newly developed in vitro metabolic methods, including HepaRG cells, three-dimensional (3D) cell models, and organ-on-a-chip technology, will also be discussed. These newly developed in vitro metabolism approaches offer significant progress in dissecting biological processes, developing drugs, and making toxicology studies quicker and more efficient.

Two-Dimensional Cellular and Three-Dimensional Bio-Printed Skin Models to Screen Topical-Use Compounds for Irritation Potential

Assessing skin irritation potential is critical for the safety evaluation of topical drugs and other consumer products such as cosmetics. The use of advanced cellular models, as an alternative to replace animal testing in the safety evaluation for both consumer products and ingredients, is already mandated by law in the European Union (EU) and other countries. However, there has not yet been a large-scale comparison of the effects of topical-use compounds in different cellular skin models. This study assesses the irritation potential of topical-use compounds in different cellular models of the skin that are compatible with high throughput screening (HTS) platforms. A set of 451 topical-use compounds were first tested for cytotoxic effects using two-dimensional (2D) monolayer models of primary neonatal keratinocytes and immortalized human keratinocytes. Forty-six toxic compounds identified from the initial screen with the monolayer culture systems were further tested for skin irritation potential on reconstructed human epidermis (RhE) and full thickness skin (FTS) three-dimensional (3D) tissue model constructs. Skin irritation potential of the compounds was assessed by measuring tissue viability, trans-epithelial electrical resistance (TEER), and secretion of cytokines interleukin 1 alpha (IL-1α) and interleukin 18 (IL-18). Among known irritants, high concentrations of methyl violet and methylrosaniline decreased viability, lowered TEER, and increased IL-1α secretion in both RhE and FTS models, consistent with irritant properties. However, at low concentrations, these two compounds increased IL-18 secretion without affecting levels of secreted IL-1α, and did not reduce tissue viability and TEER, in either RhE or FTS models. This result suggests that at low concentrations, methyl violet and methylrosaniline have an allergic potential without causing irritation. Using both HTS-compatible 2D cellular and 3D tissue skin models, together with irritation relevant activity endpoints, we obtained data to help assess the irritation effects of topical-use compounds and identify potential dermal hazards.

PDIP38/PolDIP2 controls the DNA damage tolerance pathways by increasing the relative usage of translesion DNA synthesis over template switching

Replicative DNA polymerases are frequently stalled at damaged template strands. Stalled replication forks are restored by the DNA damage tolerance (DDT) pathways, error-prone translesion DNA synthesis (TLS) to cope with excessive DNA damage, and error-free template switching (TS) by homologous DNA recombination. PDIP38 (Pol-delta interacting protein of 38 kDa), also called Pol δ-interacting protein 2 (PolDIP2), physically associates with TLS DNA polymerases, polymerase η (Polη), Polλ, and PrimPol, and activates them in vitro. It remains unclear whether PDIP38 promotes TLS in vivo, since no method allows for measuring individual TLS events in mammalian cells. We disrupted the PDIP38 gene, generating PDIP38^-/- cells from the chicken DT40 and human TK6 B cell lines. These PDIP38^-/- cells did not show a significant sensitivity to either UV or H₂O₂, a phenotype not seen in any TLS-polymerase-deficient DT40 or TK6 mutants. DT40 provides a unique opportunity of examining individual TLS and TS events by the nucleotide sequence analysis of the immunoglobulin variable (Ig V) gene as the cells continuously diversify Ig V by TLS (non-templated Ig V hypermutation) and TS (Ig gene conversion) during in vitro culture. PDIP38^-/- cells showed a shift in Ig V diversification from TLS to TS. We measured the relative usage of TLS and TS in TK6 cells at a chemically synthesized UV damage (CPD) integrated into genomic DNA. The loss of PDIP38 also caused an increase in the relative usage of TS. The number of UV-induced sister chromatid exchanges, TS events associated with crossover, was increased a few times in PDIP38^-/- human and chicken cells. Collectively, the loss of PDIP38 consistently causes a shift in DDT from TLS to TS without enhancing cellular sensitivity to DNA damage. We propose that PDIP38 controls the relative usage of TLS and TS increasing usage of TLS without changing the overall capability of DDT.

SPARTAN promotes genetic diversification of the immunoglobulin-variable gene locus in avian DT40 cells

Prolonged replication arrest on damaged templates is a cause of fork collapse, potentially resulting in genome instability. Arrested replication is rescued by translesion DNA synthesis (TLS) and homologous recombination (HR)-mediated template switching. SPARTAN, a ubiquitin-PCNA-interacting regulator, regulates TLS via mechanisms incompletely understood. Here we show that SPARTAN promotes diversification of the chicken DT40 immunoglobulin-variable λ gene by facilitating TLS-mediated hypermutation and template switch-mediated gene-conversion, both induced by replication blocks at abasic sites. SPARTAN^-/- and SPARTAN^-/-/Polη^-/-/Polζ^-/- cells showed defective and similar decrease in hypermutation rates, as well as alterations in the mutation spectra, with decreased dG-to-dC transversions and increased dG-to-dA transitions. Strikingly, SPARTAN^-/- cells also showed reduced template switch-mediated gene-conversion at the immunoglobulin locus, while being proficient in HR-mediated double strand break repair, and sister chromatid recombination. Notably, SPARTAN's ubiquitin-binding zinc-finger 4 domain, but not the PCNA interacting peptide domain or its DNA-binding domain, was specifically required for the promotion of immunoglobulin gene-conversion, while all these three domains were shown to contribute similarly to TLS. In all, our results suggest that SPARTAN mediates TLS in concert with the Polη-Polζ pathway and that it facilitates HR-mediated template switching at a subset of stalled replication forks, potentially by interacting with unknown ubiquitinated proteins.

The dominant role of proofreading exonuclease activity of replicative polymerase ε in cellular tolerance to cytarabine (Ara-C)

Chemotherapeutic nucleoside analogs, such as Ara-C, 5-Fluorouracil (5-FU) and Trifluridine (FTD), are frequently incorporated into DNA by the replicative DNA polymerases. However, it remains unclear how this incorporation kills cycling cells. There are two possibilities: Nucleoside analog triphosphates inhibit the replicative DNA polymerases, and/or nucleotide analogs mis-incorporated into genomic DNA interfere with the next round of DNA synthesis as replicative DNA polymerases recognize them as template DNA lesions, arresting synthesis. To address the first possibility, we selectively disrupted the proofreading exonuclease activity of DNA polymerase ε (Polε), the leading-strand replicative polymerase in avian DT40 and human TK6 cell lines. To address the second, we disrupted RAD18, a gene involved in translesion DNA synthesis, a mechanism that relieves stalled replication. Strikingly, POLE1^exo−/− cells, but not RAD18^−/− cells, were hypersensitive to Ara-C, while RAD18^−/− cells were hypersensitive to FTD. gH2AX focus formation following a pulse of Ara-C was immediate and did not progress into the next round of replication, while gH2AX focus formation following a pulse of 5-FU and FTD was delayed to the next round of replication. Biochemical studies indicate that human proofreading-deficient Polε-exo⁻ holoenzyme incorporates Ara-CTP, but subsequently extend from this base several times less efficiently than from intact nucleotides. Together our results suggest that Ara-C acts by blocking extension of the nascent DNA strand and is counteracted by the proofreading activity of Polε, while 5-FU and FTD are efficiently incorporated but act as replication fork blocks in the subsequent S phase, which is counteracted by translesion synthesis.

Chromatin remodeler ALC1 prevents replication-fork collapse by slowing fork progression

ALC1 (amplified in liver cancer 1), an SNF2 superfamily chromatin-remodeling factor also known as CHD1L (chromodomain helicase/ATPase DNA binding protein 1-like), is implicated in base-excision repair, where PARP (Poly(ADP-ribose) polymerase) mediated Poly(ADP-ribose) signaling facilitates the recruitment of this protein to damage sites. We here demonstrate the critical role played by ALC1 in the regulation of replication-fork progression in cleaved template strands. To analyze the role played by ALC1 as well as its functional relationship with PARP1, we generated ALC1^-/-, PARP1^-/-, and ALC1^-/-/PARP1^-/- cells from chicken DT40 cells. We then exposed these cells to camptothecin (CPT), a topoisomerase I poison that generates single-strand breaks and causes the collapse of replication forks. The ALC1^-/- and PARP1^-/- cells exhibited both higher sensitivity to CPT and an increased number of chromosome aberrations, compared with wild-type cells. Moreover, phenotypes were very similar across all three mutants, indicating that the role played by ALC1 in CPT tolerance is dependent upon the PARP pathway. Remarkably, inactivation of ALC1 resulted in a failure to slow replication-fork progression after CPT exposure, indicating that ALC1 regulates replication-fork progression at DNA-damage sites. We disrupted ATPase activity by inserting the E165Q mutation into the ALC1 gene, and found that the resulting ALC1^-/E165Q cells displayed a CPT sensitivity indistinguishable from that of the null-mutant cells. This observation suggests that ALC1 contributes to cellular tolerance to CPT, possibly as a chromatin remodeler. This idea is supported by the fact that CPT exposure induced chromatin relaxation in the vicinity of newly synthesized DNA in wild-type but not in ALC1^-/- cells. This implies a previously unappreciated role for ALC1 in DNA replication, in which ALC1 may regulate replication-fork slowing at CPT-induced DNA-damage sites.

ALC1/CHD1L, a chromatin-remodeling enzyme, is required for efficient base excision repair

ALC1/CHD1L is a member of the SNF2 superfamily of ATPases carrying a macrodomain that binds poly(ADP-ribose). Poly(ADP-ribose) polymerase (PARP) 1 and 2 synthesize poly(ADP-ribose) at DNA-strand cleavage sites, promoting base excision repair (BER). Although depletion of ALC1 causes increased sensitivity to various DNA-damaging agents (H₂O₂, UV, and phleomycin), the role played by ALC1 in BER has not yet been established. To explore this role, as well as the role of ALC1’s ATPase activity in BER, we disrupted the ALC1 gene and inserted the ATPase-dead (E165Q) mutation into the ALC1 gene in chicken DT40 cells, which do not express PARP2. The resulting ALC1^-/- and ALC1^-/E165Q cells displayed an indistinguishable hypersensitivity to methylmethane sulfonate (MMS), an alkylating agent, and to H₂O₂, indicating that ATPase plays an essential role in the DNA-damage response. PARP1^-/- and ALC1^-/-/PARP1^-/- cells exhibited a very similar sensitivity to MMS, suggesting that ALC1 and PARP1 collaborate in BER. Following pulse-exposure to H₂O₂, PARP1^-/- and ALC1^-/-/PARP1^-/- cells showed similarly delayed kinetics in the repair of single-strand breaks, which arise as BER intermediates. To ascertain ALC1’s role in BER in mammalian cells, we disrupted the ALC1 gene in human TK6 cells. Following exposure to MMS and to H₂O₂, the ALC1^-/- TK6 cell line showed a delay in single-strand-break repair. We therefore conclude that ALC1 plays a role in BER. Following exposure to H₂O_2,ALC1^-/- cells showed compromised chromatin relaxation. We thus propose that ALC1 is a unique BER factor that functions in a chromatin context, most likely as a chromatin-remodeling enzyme.

Determination of genotoxic potential by comparison of structurally related azo dyes using DNA repair-deficient DT40 mutant panels

Azo dyes, including Sudan I, Orange II and Orange G, are industrial dyes that are assumed to have genotoxic potential. However, neither the type of DNA damage induced nor the structural features responsible for toxicity have been determined. We used a panel of DNA-repair-pathway-deficient mutants generated from chicken DT40 cells to evaluate the ability of these azo dyes to induce DNA damage and to identify the type of DNA damage induced. We compared the structurally related azo dyes Sudan I, Orange II and Orange G to identify the structural features responsible for genotoxicity. Compared with wild type cells, the double-strand break repair defective RAD54^-/-/KU70^-/- cells were significantly more sensitive to Sudan I, but not to Orange II or Orange G. The quantum-chemical calculations revealed that Sudan I, but not Orange II or Orange G, has a complete planar aromatic ring structure. These suggest that the planar feature of Sudan I is critical to the inducing of double-strand breaks. In summary, we used a DNA-repair mutant panel in combination with quantum-chemical calculations to provide a clue to the chemical structure responsible for genotoxicity.

Cytotoxic and genotoxic profiles of benzo[a]pyrene and N-nitrosodimethylamine demonstrated using DNA repair deficient DT40 cells with metabolic activation

Benzo[a]pyrene and N-nitrosodimethylamine are major genotoxic compounds present in cigarette smoke, food and oil. To examine the type(s) of DNA damage induced by these compounds, we used a panel of DNA-repair-pathway-deficient mutants generated from chicken DT40 cells and achieved metabolic activation of the test compounds by including rat liver S9 mix. Consistent with expections, benzo[a]pyrene and N-nitrosodimethylamine require metabolicactivation to become genotoxic. The REV3(-/-) mutant cell line exhibited the highest sensitivity, in terms of increased cytotoxicity, to the both compounds after metabolic activation consistent with the known ability of these two compounds to induce DNA adducts. Strikingly, we found that the RAD54(-/-)/KU70(-/-) cell line, a mutant defective in the repair of double-strand breaks, is sensitive to benzo[a]pyrene, suggesting that this compound also induces strand breaks in these cells. In this study we combined a previously employed method, metabolic activation by S9 mix, with the use of a DNA-repair mutant panel, thereby broadening the range of compounds that can be screened for potential genotoxicity.

Development of a targeted flip-in system in avian DT40 cells

Gene-targeting to create null mutants or designed-point mutants is a powerful tool for the molecular dissection of complex phenotypes involving DNA repair, signal transduction, and metabolism. Because gene-targeting is critically impaired in mutants exhibiting attenuated homologous recombination (HR), it is believed that gene-targeting is mediated via homologous recombination, though the precise mechanism remains unknown. We explored gene-targeting in yeast and avian DT40 cells. In animal cells, gene-targeting is activated by DNA double strand breaks introduced into the genomic region where gene-targeting occurs. This is evidenced by the fact that introducing double strand breaks at targeted genome sequences via artificial endonucleases such as TALEN and CRISPR facilitates gene-targeting. We found that in fission yeast, Schizosaccharomyces pombe, gene-targeting was initiated from double strand breaks on both edges of the homologous arms in the targeting construct. Strikingly, we also found efficient gene-targeting initiated on the edges of homologous arms in avian DT40 cells, a unique animal cell line in which efficient gene-targeting has been demonstrated. It may be that yeast and DT40 cells share some mechanism in which unknown factors detect and recombine broken DNA ends at homologous arms accompanied by crossover. We found efficient targeted integration of gapped plasmids accompanied by crossover in the DT40 cells. To take advantage of this finding, we developed a targeted flip-in system for avian DT40 cells. This flip-in system enables the rapid generation of cells expressing tag-fused proteins and the stable expression of transgenes from OVA loci.

Fabry Disease Presenting with Multiple Hemorrhagic Cerebral Infarction

We describe a 57-year-old woman, a heterozygote for Fabry disease who had multiple hemorrhagic cerebral infarctions. Her clinical course and radiological findings suggested cardiogenic cerebral embolus, but distinction from multiple cerebral infarction associated with Fabry disease seemed necessary. Our present case is reported with reference to the literature to introduce various types of stroke, which can develop in patients with Fabry disease.

Quantitative analysis of estrogen receptor-alpha and -beta messenger RNA expression in human pancreatic cancers by real-time polymerase chain reaction

Recent studies have disclosed the presence of a second estrogen receptor (ER; ER-beta) in addition to a classical ER-alpha. ER-beta mRNA expression has yet to be studied in pancreatic cancers. Thus, we studied the expression of ER-alpha and ER-beta mRNA in pancreatic cancers (n=29) by real-time quantitative reverse transcriptase-polymerase chain reaction, and compared the expression levels in pancreatic cancers with those in breast cancers (n=116) which are typical estrogen-dependent tumors. Breast cancers were divided into two groups, ER-positive and ER-negative, according to the ER status determined by enzyme immunoassay. ER-alpha mRNA levels were significantly (P<0.01) higher in ER-positive (679.4+/-74.7 fmol/microg RNA) than ER-negative (159.7+/-33.4) breast cancers, and pancreatic cancers showed significantly (P<0.01) lower ER-alpha mRNA levels (17.5+/-10.0) than ER-negative breast cancers. On the other hand, ER-beta mRNA levels were significantly (P<0.01) higher in ER-negative (14.1+/-1.6) than ER-positive breast cancers (7.9+/-1.0), and pancreatic cancers showed significantly (P<0.01) higher ER-beta mRNA levels (28.1+/-5.1) than ER-negative breast cancers. Accordingly, ER-alpha/ER-beta mRNA ratios were significantly (P<0.01) lower in pancreatic cancers (0.94+/-053) than in ER-positive (203.9+/-34.5) and ER-negative (21.9+/-5.2) breast cancers. ER-beta2 mRNA variant expression was significantly (P<0.05) higher in pancreatic cancers than in ER-positive and ER-negative breast cancers, and, on the contrary, ER-beta1 mRNA variant expression was significantly (P<0.01) lower in pancreatic cancers than in ER-positive and ER-negative breast cancers. These results suggest a possibility that ER-beta (ER-beta2) plays a more important role than ER-alpha in pancreatic cancers.

Bone marrow micrometastases detected by RT-PCR for mammaglobin can be an alternative prognostic factor of breast cancer

PURPOSE

To evaluate a new prognostic factor of breast cancer, bone marrow micrometastases which was detected by RT-PCR for mammaglobin, a sensitive molecular marker of breast cancer, was examined.

MATERIALS AND METHODS

One hundred and eleven samples from stage I-III breast cancer patients were examined. Bone marrow micrometastases and clinicopathological parameters, which were age, tumor size, lymph node metastasis and status of the estrogen receptor, were evaluated for the prognostic factor by statistical analysis.

RESULTS

Median follow-up time was 21.1 months. Thirty-three (29.7%) out of 111 samples were RT-PCR positive. Eight cases (24.2%) in this group showed recurrent lesions in the distant organs. Whereas six (7.7%) out of 78 RT-PCR negative patients had distant recurrences. In the premenoposal patients, and in the patients with axillary lymph node metastases, RT-PCR positive cases showed significantly higher distant recurrent rate. Bone marrow micrometastases, axillary nodal status, and estrogen receptor were independent prognostic factors for breast cancer by both univariate and multivariate analysis.

CONCLUSIONS

Bone marrow micrometastases detected by RT-PCR for mammaglobin can be a useful predictive marker for early distant recurrence of breast cancer.

Clinical significance of micrometastases in axillary lymph nodes assessed by reverse transcription-polymerase chain reaction in breast cancer patients

We evaluated the clinical significance of micrometastases in axillary lymph nodes (AxLNs) of breast cancer patients for prediction of prognosis. Archived formalin-fixed paraffin-embedded AxLN specimens from 129 node-negative breast cancer patients diagnosed by routine H&E staining between 1986 and 1990 were subjected to carcinoembryonic antigen-specific reverse transcription-PCR analysis. Micrometastases were detected in 40 of 129 (31.0%) node-negative breast cancer patients. After a median follow-up period of 105.6 months, log-rank test analysis indicated that 10-year disease-free and overall survival rates by Kaplan-Meier methods were significantly better in patients without micrometastases than in patients with micrometastases [disease-free survival, 87.6% versus 66.1% (P = 0.0008); overall survival, 93.7% versus 67.8% (P = 0.0024)]. The presence of micrometastases in AxLNs was revealed by multivariate analyses to be an independent and significant predictor of clinical outcome. The hazard ratio was 3.992 (95% confidence interval, 1.293-12.323; P = 0.0161) for relapse and 4.293 (95% confidence interval, 1.043-17.675; P = 0.0436) for cancer-related death. The molecular staging of AxLNs using reverse transcription-PCR is useful for prediction of clinical outcome in early-stage breast cancer patients and can provide a powerful and sensitive complement to routine histopathological analysis.

Prevention of cross-contamination during sampling procedure in molecular detection for cancer micrometastasis

Reverse transcriptase-polymerase chain reaction (RT-PCR) techniques have been widely employed as an ultra-sensitive method for detection of micrometastases in patients with various types of malignancies. Messenger RNA of a specific marker gene is a target for RT-PCR amplification to examine the presence of micrometastases in body fluids or tissues obtained from human. We developed the RT-PCR assay specific for rat beta-actin mRNA, which cannot detect human counterpart and assessed how much contamination of rat tissues can influence the result of RT-PCR assay and how to avoid the influence of the contamination in RT-PCR assay.

Selection of mRNA markers for detection of lymph node micrometastases in breast cancer patients

The aim of this study was to search for specific and sensitive mRNA markers or a combination of markers for RT-PCR detection of micrometastases in axillary lymph nodes (LNs) from patients with breast cancer. LNs (n=177) from 17 patients were examined with Cytokeratin20 (CK20), melanoma-associated genes (MAGE1, MAGE3), carcinoembryonic antigen (CEA), prostate-specific antigen (PSA), mammaglobin (MGB1) and mammaglobin B (MGB2) as molecular markers. CK20, MAGE1 and MAGE3 were slightly positive in primary tumors and CEA, PSA, MGB1 and MGB2 were highly positive. MGB1 and MGB2 were 100% positive in HE-positive LNs while CEA and PSA were only 35.7% and 57.1% positive. MGB1 and MGB2 were also 30.1% and 17.8% positive in HE-negative nodes. Thus, MGB1 and MGB2 are specific and a combination of the two should be useful for detection of micrometastases in axillary LNs of breast cancer patients.

Identification of a 7-cM region of frequent allelic loss on chromosome band 16p13.3 that is specifically associated with anaplastic thyroid carcinoma

A total of 17 primary thyroid cancer specimens including seven anaplastic cancers, two papillary cancers adjacent to the anaplastic cancers, and eight papillary cancers were analyzed for loss of heterozygosity (LOH) on chromosome arm 16p. All tumors of anaplastic cancer showed LOHs at one or more loci, and a 7-cM region of the smallest deleted region was found on 16p13.3 between D16S423 and D16S406. This LOH was specifically found in the anaplastic cancer and not in the papillary thyroid cancer. Our present results suggest localization of the putative tumor suppressor gene on 16p13.3, which is likely to play an important role in the anaplastic transformation of thyroid cancer.

Detection of microsatellite alterations in nipple discharge accompanied by breast cancer

Nipple discharge in breast cancer cases was examined loss of heterozygosity (LOH). DNA samples were extracted from both supernatant and cell pellet components of the discharge, and examined for LOH at microsatellite markers, D11S1818, D11S2000, D16S402, D16S504, D16S518, D17S520, and D17S786. At least one LOH was found in either the supernatant or cell pellet in seven out of 10 patients (70%). Five of seven samples, which were cytologically negative, were LOH positive, and only one case, which was cytologically positive, showed no LOH on the markers examined. All three samples, which were judged 'negative' by CEA measurement (<400 ng/ml), were LOH positive. This method could be a useful novel diagnostic modality for nonpalpable breast cancer with nipple discharge.

Mammaglobin B as a novel marker for detection of breast cancer micrometastases in axillary lymph nodes by reverse transcription-polymerase chain reaction

A novel reverse transcription-polymerase chain reaction (RT-PCR) assay using mammaglobin B gene was developed for detection of breast cancer micrometastases in axillary lymph nodes. Fourteen primary breast cancers and 56 axillary lymph nodes from six patients with primary breast cancer and 15 control lymph nodes from non-cancer bearing patients were subjected to this assay. The transcript of mammaglobin B gene was detected in none of the control lymph nodes, but in all of the 14 primary breast cancers. Eleven out of the 56 lymph nodes from the patients, which were shown to be positive by histological examination, were also proven positive by this assay. On the other hand, fourteen of the 45 (31%) histologically negative lymph nodes were also shown to express mammaglobin B mRNA, which suggested the presence of micrometastases in these lymph nodes. RT-PCR using mammaglobin B gene could therefore be a useful tool for detection of micrometastases of breast cancer.

[A case report: effective trans-arterial neoadjuvant chemotherapy with docetaxel for a local advanced breast cancer patient]

Recently, there have been some reports about the effectiveness of docetaxel for breast cancer patients who had polychemotherapy previously in vein. We report here a case of a 47-year-old woman, who had been diagnosed as local advanced breast cancer. She was given trans-arterial chemotherapy with docetaxel after four series of CEF (cyclophosphamide, epirubicin, fluorouracil) therapy resulted in PD (progressive disease). Local disease was successfully controlled, and she could undergo standard radical mastectomy.

Comparative genomic hybridization defines frequent loss on 16p in human anaplastic thyroid carcinoma

Anaplastic thyroid cancer (ATC) is one of the malignant tumors with the poor prognosis that is thought to arise from well-differentiated thyroid cancer (DTC). To investigate the molecular mechanism of ATC, we studied genomic alterations of eight ATC cell lines and three DTC cell lines by means of the comparative genomic hybridization (CGH) method. Loss of 16p was observed in five of eight ATC cell lines (62. 5%), but none of the three DTC cell lines showed loss of this chromosome arm. It is notable that loss of 18q [7/8 of ATC (87.5%), 2/3 of DTC (67%)] and gain of 20q [5/8 of ATC (62.5%), 3/3 of DTC (100%)] were frequently seen in both histologic types. Our results suggest that there is a gene in 16p that is closely associated with transformation from well-differentiated thyroid cancer to anaplastic cancer.

Evaluation of three types of support surfaces for preventing pressure ulcers in patients in a surgical intensive care unit

Because critical care nurses recognize that many of their patients are at risk for pressure ulcer development, they provide them with support surfaces that can reduce this risk. Few reported studies, however, are available to help these nurses choose these surfaces wisely. This project was a new-product evaluation that compared the clinical effectiveness of three types of support surfaces: two dynamic mattress replacement surfaces and a static foam mattress replacement. Members of a convenience sample of 110 patients admitted to a surgical intensive care unit each used one of the three support surfaces. When each patient was placed on one of the three surfaces, the evaluators rated likelihood of pressure ulcer development (Braden Scale score) and assessed the skin for pressure ulcers. The evaluators repeated the Braden Scale score weekly and the skin assessment three times each week. Nine patients (8%), three patients on each support surface, acquired pressure ulcers. The log-rank test did not find a statistically significant difference between the three types of support surfaces with respect to the risk of pressure ulcer development. Stepwise Cox proportional hazards regression revealed a statistically significant relationship between the risk of developing a pressure ulcer, the averaged total Braden Scale score, and the averaged score for the sensory perception subscale of the Braden Scale. Although these three surfaces were comparable in effectiveness, they were not comparable in cost. Both dynamic mattress replacement surfaces cost approximately $2000 each, whereas the cost of the static foam mattress replacement was only $240 each. The results of this product evaluation should encourage other nurses to evaluate patient care products carefully before making recommendations.