Synchronization and Desynchronization of Cells by Interventions on the Spindle Assembly Checkpoint

Development of Automated Microscopy-Assisted High-Content Multiparametric Assays for Cell Cycle Staging and Foci Quantitation

The investigation of cell cycle stage-dependent processes in a population of cells is often performed using flow cytometry. While this approach is high-throughput, it is relatively low in resolution and unable to measure phenotypic changes or processes occurring in subcellular compartments. We integrated automated microscopy with newly developed informatics workflow that enabled the quantitation of multiple fluorescent markers from specific subnuclear regions throughout a population of cells. Telomeres protect chromosome termini and prevent cellular aging. Cancer cells lengthen telomeres by synthesizing new TTAGGG repeats by the enzyme telomerase, while others activate recombination-dependent alternative lengthening of telomeres (ALT). A key feature of the ALT pathway is the specific clustering of promyelocytic leukemia (PML) nuclear bodies at telomeres. These ALT-associated PML bodies (APBs) common in tumors of mesenchymal origin have gained in diagnostic use in the past decade. Here we applied recent improvements in automated microscopy and developed novel informatics workflows for quantitation of multiple fluorescent markers from specific subnuclear regions at the single cell level. Key to this workflow are customized machine learning algorithms within HCS Studio™ Cell Analysis which automatically identify and segment cells into defined regions of interest based on fluorescent markers, measure marker intensities and compute marker colocalizations in specific segmented regions. These multiparametric cellular assays assess cell cycle dynamics as well as the interactome of APBs, are amenable to adherent cells and histological sections, and are adaptable for use with additional markers. In the future we anticipate exploiting these algorithms for a wide range of research questions related to telomere biology with potential to facilitate clinical development of ALT detection assays to benefit patients with these often-poor prognosis tumors. © 2020 International Society for Advancement of Cytometry.

Elucidating the mechanism of action of domatinostat (4SC-202) in cutaneous T cell lymphoma cells

Background

Targeting epigenetic modifiers is effective in cutaneous T cell lymphoma (CTCL). However, there is a need for further improvement of this therapeutic approach. Here, we compared the mode of action of romidepsin (FK228), an established class I histone deacetylase inhibitor, and domatinostat (4SC-202), a novel inhibitor of class I HDACs, which has been reported to also target the lysine-specific histone demethylase 1A (LSD1).

Methods

We performed MTS assays and flow cytometric analyses of propidium iodide or annexin V-stained cells to assess drug impact on cellular proliferation, cell cycle distribution, and survival. Histone acetylation and methylation as well as caspase activation was analyzed by immunoblot. Gene expression analysis was performed using NanosString technology. Knockdown and knockout of LSD1 was achieved with shRNA and CRISPR/Cas9, respectively, while the CRISPR/Cas9 synergistic activation mediator system was used to induce expression of endogenous HDACs and LSD1. Furthermore, time-lapse fluorescence microscopy and an in vitro tubulin polymerization assay were applied.

Results

While FK228 as well as 4SC-202 potently induced cell death in six different CTCL cell lines, only in the case of 4SC-202 death was preceded by an accumulation of cells in the G2/M phase of the cell cycle. Surprisingly, apoptosis and accumulation of cells with double DNA content occurred already at 4SC-202 concentrations hardly affecting histone acetylation and methylation, and provoking significantly less changes in gene expression compared to biologically equivalent doses of FK228. Indeed, we provide evidence that the 4SC-202-induced G2/M arrest in CTCL cells is independent of de novo transcription. Furthermore, neither enforced expression of HDAC1 nor knockdown or knockout of LSD1 affected the 4SC-202-induced effects. Since time-lapse microscopy revealed that 4SC-202 could affect mitotic spindle formation, we performed an in vitro tubulin polymerization assay revealing that 4SC-202 can directly inhibit microtubule formation.

Conclusions

We demonstrate that 4SC-202, a drug currently tested in clinical trials, effectively inhibits growth of CTCL cells. The anti-cancer cell activity of 4SC-202 is however not limited to LSD1-inhibition, modulation of histone modifications, and consecutive alteration of gene expression. Indeed, the compound is also a potent microtubule-destabilizing agent.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0719-4) contains supplementary material, which is available to authorized users.