Differentiation of EC cells in vitro by the fluorescent dye Hoechst 33342

Breaking a Dogma: High-Throughput Live-Cell Imaging in Real-Time with Hoechst 33342

Automated high-throughput live cell imaging (LCI) enables investigation of substance effects on cells in vitro. Usually, cell number is analyzed by phase-contrast imaging, which is reliable only for a few cell types. Therefore, an accurate cell counting method, such as staining the nuclei with Hoechst 33342 before LCI, will be desirable. However, since the mid-1980s, the dogma exists that Hoechst can only be used for endpoint analyses because of its cytotoxic properties and the potentially phototoxic effects of the excitation light. Since microscopic camera sensitivity has significantly improved, this study investigates whether this dogma is still justified. Therefore, exposure parameters are optimized using a 4× objective, and the minimum required Hoechst concentration is evaluated, allowing LCI at 30-min intervals over 5 days. Remarkably, a Hoechst concentration of only 57 × 10-9 m significantly inhibits proliferation and thus impairs cell viability. However, Hoechst concentrations between 7 × 10-9  and 28 × 10-9 m can be determined, which are neither cytotoxic nor impacting cell viability, proliferation, or signaling pathways. The method can be adapted to regular inverted fluorescence microscopes and allows, for example, to determine the cytotoxicity of a substance or the transduction efficiency, with the advantage that the analysis can be repeated at any desired time point.

Thyroid tumor-initiating cells: increasing evidence and opportunities for anticancer therapy (review)

Accumulating evidence supports the notion that thyroid cancer is initiated by tumor-initiating cells (TICs) (commonly known as cancer stem cells), which are thought to play a crucial role in malignant progression, therapeutic resistance and recurrence. Thyroid TICs have been isolated and identified using specific biomarkers (such as CD133), the side population, sphere formation and aldehyde dehydrogenase activity assays. Although their characteristics remain largely unknown, TICs provide an attractive cellular mechanism to explain therapeutic refractoriness. Efforts are currently being directed toward the identification of therapeutic strategies that could target these cells. The present review discusses the cellular origins of TICs and the main approaches used to isolate and identify thyroid TICs, with a focus on the remaining challenges and opportunities for anticancer therapy.

Identification and characterization of side population cells from adult human dental pulp after ischemic culture

INTRODUCTION

Stem cells have been isolated by their ability to efflux Hoechst 33342 dye and are referred to as the side population (SP). Because the lack of specific surface markers has hindered the isolation and subsequent biochemical characterization of dental pulp stem cells, this study sought to determine the existence of SP cells and the expression of ABCG2 in human dental pulp and evaluate whether such SP cells had features associated with stem cells.

METHODS

First, we defined the localization of the SP in healthy and inflammatory human dental pulp. Then, SP cells were isolated from human dental pulp after ischemic culture with flow cytometry and the Hoechst 33342 dye efflux assay. Sorted cells were subjected to several tests to determine whether the isolated SP cells displayed features consistent with the stem cell phenotype, including the colony-forming capacity, the multilineage differentiation ability in vitro, and the expression of stem cell markers. We also evaluated the effect of long-term culture on the marker ABCG2.

RESULTS

SP cells in human dental pulp possess mesenchymal stem cell characteristics such as colony-forming efficiency, self-renewal, and multilineage differentiation capabilities and are able to differentiate into odontoblast/osteoblast-like cells, adipocytes, neural-like cells, and endothelial cells. However, under the present conditions, ABCG2 expression decreased along with cell passage.

CONCLUSIONS

SP cells in human dental pulp were enriched in stem cells compared with main population cells after ischemic culture, suggesting a potential use for these subfractions of human dental pulp stem/progenitor cells in tissue engineering, but the culture condition in vitro should be improved before tissue regeneration.

The utility and limitations of neurosphere assay, CD133 immunophenotyping and side population assay in glioma stem cell research

The newly proposed glioma stem cell (GSC) hypothesis may re-model the way we diagnose and treat the tumor, which highlights the need for a complete knowledge on the genetic and epigenetic "blueprints" of GSCs. To identify the true "stemness" signatures, pure GSC populations are primarily needed. Reliable in vitro methods enriching for GSCs and thereby identifying the key stem-like characteristics constitute the preliminary step forward. We discuss in this review the current widely used methods for enriching and isolating GSCs, namely neurosphere assay, CD133 Immunophenotyping and side population assay, and detail their limitations and potential pitfalls that could complicate interpretation of corresponding results.

Characterisation of normal and cancer stem cells: one experimental paradigm for two kinds of stem cells

The characterisation of normal stem cells and cancer stem cells uses the same paradigm. These cells are isolated by a fluorescence-activated cell sorting step and their stemness is assayed following implantation into animals. However, differences exist between these two kinds of stem cells. Therefore, the translation of the experimental procedures used for normal stem cell isolation into the research field of cancer stem cells is a potential source of artefacts. In addition, normal stem cell therapy has the objective of regenerating a tissue, while cancer stem cell-centred therapy seeks the destruction of the cancer tissue. Taking these differences into account is critical for anticipating problems that might arise in cancer stem cell-centred therapy and for upgrading the cancer stem cell paradigm accordingly.

Effects of Hoechst 33342 on C2C12 and PC12 cell differentiation

Accumulative evidence demonstrates that normal as well as cancer stem cells can be identified as a side population following Hoechst 33342 staining and flow cytometric analysis. This popular method is based on the ability of stem cells to efflux this fluorescent vital dye. We demonstrate that Hoechst 33342 can affect cell differentiation, suggesting potential complications in the interpretation of data.

Hoechst 33342 induces apoptosis in HL-60 cells and inhibits topoisomerase I in vivo

CONTEXT

Bisbenzimides (Hoechst 33342 and Hoechst 33258) are cell-permeable, adenine-thymine-specific dyes that bind to the minor groove of DNA and stain DNA. Hoechst 33342 induces apoptosis in BC3H-1 myocytes and hepatoma cells.

OBJECTIVE

To determine if Hoechst 33342 or Hoechst 33258 induces apoptosis in human promyelocytic leukemia cells (HL-60) and inhibits topoisomerase I activity.

DESIGN

A variety of methods were used to detect apoptosis: cell viability (trypan blue exclusion), nuclear fluorescence staining (Hoechst 33342 or Hoechst 33258 stained for 10 minutes), flow cytometric quantitation of annexin binding to phosphatidylserine, and DNA fragmentation (agarose gel electrophoresis). Topoisomerase I activity was determined by a plasmid unwinding assay.

SETTING

A large teaching hospital and research laboratories.

PATIENTS

None.

INTERVENTION

None.

MAIN OUTCOME MEASUREMENTS

Apoptosis is characterized by decreased cell viability, condensation of nuclear chromatin, increased phosphatidylserine translocation, and DNA fragmentation into oligonucleosomes composed of multiples of 180 to 200 base pairs. Inhibition of endogenous nuclear topoisomerase I is detected by the absence of plasmid unwinding from a tightly coiled to relaxed form.

RESULTS

Hoechst 33342, but not Hoechst 33258, induced apoptosis in the HL-60 cells in a time- and dose-dependent manner. Endogenous nuclear topoisomerase I activity in HL-60 cells was inhibited by treatment with Hoechst 33342 but not Hoechst 33258.

CONCLUSION

Hoechst 33342-induced HL-60 cell apoptosis may be related to the dye's inhibition of topoisomerase I activity.

Hoechst 33342 induces apoptosis and alters tata box binding protein/DNA complexes in nuclei from BC3H-1 myocytes

Hoechst 33342 and Hoechst 33258 bind to adenine-thymine rich regions of the minor groove of DNA. Hoechst 33342, but not Hoechst 33258, induces BC3H-1 myocyte cell death and DNA fragmentation into an internucleosomal pattern characteristics of apoptosis. Hoechst 33342 has been shown to inhibit endogenous nuclear topoisomerase I activity. Another enzymatic activity utilizing the minor groove of DNA, the initiation of RNA polymerase II activity by formation of a TATA box binding protein/TATA box promoter complex, is shown to be altered using a gel mobility shift assay. A [32P]-labeled 24-oligonucleotide containing a TATA box element formed one molecular weight complex in control and Hoechst 33258 treated cells. The presence of Hoechst 33342 (26.7 microM) decreased the amount of the control complex and increased the presence of lower molecular weight species suggesting degradation of nuclear TBP and/or release of other transcription factors from the complex creating a smaller sized molecular complex which retains TATA box binding capacity. These results suggest that the pathway utilized to induce apoptosis in BC3H-1 myocytes may also involve the alteration of normal TBP/DNA complex formation and reduction in the initiation of new transcription.

Transcriptional regulation of differentiation, selective toxicity and ATGCAAAT binding of bisbenzimidazole derivatives in human melanoma cells

To study the relationship between the structure of minor groove ligands and their affinity for specific DNA sequences that regulate gene transcription, three analogues of the A-T-specific DNA minor groove ligands Hoechst 33258 and Hoechst 33342 were synthesized with 5, 8 or 12 carbons in an aliphatic chain attached to the phenolic oxygen of the molecule. There was a striking bimodal relationship between toxicity to HeLa cells and the lipophilicity of the five analogues, toxicity being low for the compounds with a free hydroxyl (Hoechst 33258) or a 12-carbon substituent, yet high for the 5-carbon analogue. Selective killing of human melanoma cells compared with normal fibroblasts was observed for the Hoechst analogue with a 12-carbon chain attached. Hoechst 33258 itself was selectively toxic for the MM96E melanoma cell line compared with other cell lines, induced a highly dendritic morphology, increased tyrosinase activity and tyrosinase mRNA but decreased the level of gp75 (TRP-1) mRNA; message for a third pigment gene, Pmel-17, was unchanged. Tyrosinase activity was decreased in the resistant A2058 melanoma cell line and transcription was affected to a lesser extent than in MM96E. Expression of gp75 protein and two intermediate filament proteins was inhibited by Hoechst 33258 in MM96E cells. There was no major difference in the amount of 125I-Hoechst 33258 taken up by sensitive and resistant cells. Of the five derivatives studied, the parent drug Hoechst 33258 and the 2-carbon analogue (Hoechst 33342) were found to have the most inhibitory effect on affinity of octamer binding proteins for the ATGCAAAT consensus sequence found in the promoter region of certain genes associated with proliferation and differentiation. In contrast to Distamycin A (also an A-T-specific minor groove ligand), Hoechst 33258 displaced proteins already bound to the octamer motif. The G-C ligand chromomycin A3 exhibited a different spectrum of cell toxicity and tyrosinase stimulation compared with Hoechst 33258. Chromomycin A3 but not Hoechst 33258, strongly inhibited the zinc-dependent transcriptional activity of the sheep metallothionein-Ia promoter in reporter gene assays of transfected cells. Since the six metal-responsive elements of the promoter are GC-rich, this provides independent evidence for the sequence-specificity of transcriptional inactivation by one of these drugs in melanoma cells. Overall, the results suggest that Hoechst 33258 acts by inhibiting the transcription of specific genes, cell lines evidently differing in the accessibility to drugs of certain A-T-rich sequences.

Expression of histone and alkaline phosphatase genes in UMR 106-01 rat osteoblast-like cells exposed to the Hoechst dye H33342

The fluorescent Dye H33342 (H342) is a bis-benzimidazole used for intravital fluorescent staining. In this report, we found that H342 completely abolished histone 2a mRNA but had no effect on alkaline phosphatase gene expression and protein synthesis in UMR 106-01 rat osteoblast-like cells. The complete loss of histone 2a mRNA occurred after only 20 min of treatment with H342. This effect is unlikely to be a result of inhibition of DNA synthesis, which was only partly suppressed. The mechanism of the action of H342 on histone 2a mRNA is presently unknown.

The linking of anticancer drugs, cell cycle blocks, and differentiation: implications in the search for antineoplastic drugs

The quest for anticancer drugs has been primarily directed at agents that interfere with cell replication, yet the basis for drug-induced cytotoxicity remains unsolved. In our previous studies we noted a relationship between a mitotic block and commitment to terminal differentiation in the murine (Friend) erythroleukemia (FEL) cell. Since anticancer drugs are known to often block cell cycle transit typically in G2/mitosis, we tested a number of anticancer drugs with various modes of action and found that they all committed FEL cells to differentiate. Furthermore, other G2/mitosis-blocking drugs were also effective in inducing commitment. These results suggest (1) a causal relationship involving anticancer drugs, cell cycle block and differentiation, (2) that the search for new anticancer drugs utilize a differentiation assay and include G2/mitosis-blocking agents.

Effects of a DNA-specific fluorochrome, Hoechst 33258, on mouse sperm motility and fertilizing capacity

DNA specific fluorochrome (Hoechst 33342 and 33258) as non-toxic stains, have been widely used to measure cell density and proliferation, detect sperm-egg fusion, and observe the development of pre-implantation embryos. It has been reported that Hoechst 33342 at a concentration of 10 micrograms ml-1 had significant inhibition on embryo cleavage. In this study, we incubated B6D2F1 mouse sperm and eggs with different concentrations of Hoechst 33258, 0, 1.0, 10.0, 20.0, 100 micrograms ml-1. We found that: (1) 100 micrograms ml-1 of H-33258 significantly decreased the sperm motility at 90 min and 4 h. (P less than 0.05), (2) 20 micrograms ml-1 and 100 micrograms ml-1 of Hoechst 33258 significantly inhibited mouse fertilization in vitro (P less than 0.05), and (3) 1.0 micrograms ml-1 and 10.0 micrograms ml-1 Hoechst 33258 had no effect on fertilization rate. But when we pre-incubated sperm at 10 micrograms ml-1 Hoechst 33258 for 90 min, and inseminated oocytes in the medium with same concentration of Hoechst 33258, the embryo cleavage was significantly inhibited.