Microcolony Size Distribution Assay Enables High-Throughput Cell Survival Quantitation

Antitumor effects of new glycoconjugated PtII agents dual-targeting GLUT1 and Pgp proteins

A novel and highly efficient dual-targeting Pt^II system was designed to improve the drug delivery capacity and selectivity in cancer treatment. The dual-targeting monofunctional Pt^II complexes (1-8) having glycosylated pendants as tridentated ligand were achieved by introducing glycosylation modification in the thioaminocarbazone compounds with potential lysosomal targeting ability. The structures and stability of 1-8 were further established by various techniques. Molecular docking studies showed that 2 was efficiently docked into glucose transporters protein 1 (GLUT1) and P-glycoprotein (Pgp) proteins with the optimal CDocker-interaction-energy of -64.84 and -48.85 kcal mol^-1. Complex 2 with higher protein binding capacity demonstrated significant and broad-spectrum antitumor efficacy in vitro, even exhibiting a half maximal inhibitory concentration (IC₅₀) value (∼10 μM) than cisplatin (∼17 μM) against human lung adenocarcinoma cells (A549). The inhibitor experiment revealed GLUT-mediated uptake of 2, and the subcellular localization experiment in A549 also proved that 2 could be localized in the lysosome, thereby causing cell apoptosis. Moreover, cellular thermal shift assay (CETSA) confirmed the binding of 2 with the target proteins of GLUT1 and Pgp. The above results indicated that 2 represents a potential anticancer candidate with dual-targeting functions.

Fluorescence Sheds Light on DNA Damage, DNA Repair, and Mutations

DNA damage can lead to carcinogenic mutations and toxicity that promotes diseases. Therefore, having rapid assays to quantify DNA damage, DNA repair, mutations, and cytotoxicity is broadly relevant to health. For example, DNA damage assays can be used to screen chemicals for genotoxicity, and knowledge about DNA repair capacity has applications in precision prevention and in personalized medicine. Furthermore, knowledge of mutation frequency has predictive power for downstream cancer, and assays for cytotoxicity can predict deleterious health effects. Tests for all of these purposes have been rendered faster and more effective via adoption of fluorescent readouts. Here, we provide an overview of established and emerging cell-based assays that exploit fluorescence for studies of DNA damage and its consequences.

Applications of CometChip for Environmental Health Studies

Environmental exposures have long been known to impact public health and safety. For example, exposures to airborne particulates, heavy metals in water, or certain industrial chemicals can contribute to aging and to risk of developing cancer and other diseases. Environmental factors can impact health in a variety of ways, but a key concern is DNA damage, which can lead to mutations that cause cancer. Cancer can take years to develop following chemical exposure; however, one way to predict carcinogenicity in a more practical time frame is by studying the chemical's ability to induce DNA damage. The comet assay (or single-cell gel electrophoresis assay) has been used successfully for genotoxicity testing. The comet assay allows for the detection of DNA strand breaks via analysis of DNA migration during electrophoresis. Previously, the Engelward laboratory, in collaboration with the Bhatia laboratory, developed the CometChip for measurements of DNA damage and repair. The CometChip is a high-throughput comet assay that improves user reproducibility and significantly shortens total assay time. Here, we describe how the high-throughput CometChip platform can be used to measure DNA damage in established cell lines, animal models, and human samples. We also discuss technical challenges associated with these studies and provide recommendations on how to achieve optimal results for researchers interested in adopting this assay.

A cautionary tale about the use of colony-forming efficiency as a proxy for the survival of mesenchymal stem cells

Colony-forming efficiency is a time-honored metric of the proliferation potential of mesenchymal stem cells (MSCs). This commentary raises a concern about the practice of using colony-forming efficiency as a proxy for cell survival. A recently published study from my laboratory investigated this issue. A marker of cellular aging, CD264, was employed to separate human bone marrow MSCs into populations of CD264⁻ cells and culture-matched, aging CD264⁺ cells with high and low colony-forming efficiency, respectively. In vitro cell survival was evaluated with a single-cell assay; in vivo survival by bioluminescence imaging of MSCs attached to scaffolds that were implanted ectopically in immunodeficient mice. In our study, in vitro and in vivo survival of the MSC populations was independent of colony-forming efficiency. This finding indicates that caution should be exercised before using colony-forming efficiency as an indirect metric of cell survival. Direct measurement of survival may be required. Awareness of this issue should foster a robust experimental design and, thereby, facilitate the translation of MSC research into clinical practice.

Optical Single Cell Resolution Cytotoxicity Biosensor Based on Single Cell Adhesion Dot Arrays

Low cost, easy to use cell viability tests are needed in the pharmaceutical, biomaterial, and environmental industries to measure adverse cellular effects. We present a new methodology to track cell death with high resolution. Adherent cells commonly detach from the surface when they die, but some toxic compounds promote cell adhesion. A methodology that enables both dynamic detachment monitoring but also rapid detection of toxic effects of compounds that promote cell adhesion would constitute a step forward toward high-throughput cytotoxicity measurements. We achieved dynamic digital quantification of cell viability by simple optical imaging using "single cell adhesion dot arrays" (SCADA), fibronectin (FN) dot arrays designed to accommodate a single cell on each fibronectin dot. For cytotoxicity measurements, cell-filled SCADA substrates were exposed to K₂CrO₄, HgSO₄ salts, and dimethyl sulfoxide (DMSO). The toxic effect of DMSO and K₂CrO₄ was dynamically monitored by measuring the cell detachment rate during more than 30 h by quantifying the number of occupied dots in the SCADA array. HgSO₄ inhibited cellular detachment from the surface, and cytotoxicity was monitored using the trypan blue life/death assay directly on the surface. In all cases, the cytotoxicity effects were easily monitored with single cell resolution, and the results were comparable to previous reports. SCADA enabled dynamic measurements at the highest resolution due to the digital measuring in this method. The integration of SCADA substrates into microfluidic platforms will provide a practical tool that will extend to fundamental research and commercial applications.

HTS-Compatible CometChip Enables Genetic Screening for Modulators of Apoptosis and DNA Double-Strand Break Repair

Dysfunction of apoptosis and DNA damage response pathways often drive cancer, and so a better understanding of these pathways can contribute to new cancer therapeutic strategies. Diverse discovery approaches have identified many apoptosis regulators, DNA damage response, and DNA damage repair proteins; however, many of these approaches rely on indirect detection of DNA damage. Here, we describe a novel discovery platform based on the comet assay that leverages previous technical advances in assay precision by incorporating high-throughput robotics. The high-throughput screening (HTS) CometChip is the first high-throughput-compatible assay that can directly detect physical damage in DNA. We focused on DNA double-strand breaks (DSBs) and utilized our HTS CometChip technology to perform a first-of-its-kind screen using an shRNA library targeting 2564 cancer-relevant genes. Conditions of the assay enable detection of DNA fragmentation from both exogenous (ionizing radiation) and endogenous (apoptosis) sources. Using this approach, we identified LATS2 as a novel DNA repair factor as well as a modulator of apoptosis. We conclude that the HTS CometChip is an effective assay for HTS to identify modulators of physical DNA damage and repair.

Survival of aging CD264+ and CD264- populations of human bone marrow mesenchymal stem cells is independent of colony-forming efficiency

In vivo mesenchymal stem cell (MSC) survival is relevant to therapeutic applications requiring engraftment and potentially to nonengraftment applications as well. MSCs are a mixture of progenitors at different stages of cellular aging, but the contribution of this heterogeneity to the survival of MSC implants is unknown. Here, we employ a biomarker of cellular aging, the decoy TRAIL receptor CD264, to compare the survival kinetics of two cell populations in human bone marrow MSC (hBM-MSC) cultures. Sorted CD264⁺ hBM-MSCs from two age-matched donors have elevated β-galactosidase activity, decreased differentiation potential and form in vitro colonies inefficiently relative to CD264^- hBM-MSCs. Counterintuitive to their aging phenotype, CD264⁺ hBM-MSCs exhibited comparable survival to matched CD264^- hBM-MSCs from the same culture during in vitro colony formation and in vivo when implanted ectopically in immunodeficient NIH III mice. In vitro and in vivo survival of these two cell populations were independent of colony-forming efficiency. These findings have ramifications for the preparation of hBM-MSC therapies given the prevalence of aging CD264⁺ cells in hBM-MSC cultures and the popularity of colony-forming efficiency as a quality control metric in preclinical and clinical studies with MSCs.