Monitoring the Activation of the DNA Damage Response Pathway in a 3D Spheroid Model

In vitro assays for investigating the FLASH effect

FLASH radiotherapy is a novel technique that has been shown in numerous preclinical in vivo studies to have the potential to be the next important improvement in cancer treatment. However, the biological mechanisms responsible for the selective FLASH sparing effect of normal tissues are not yet known. An optimal translation of FLASH radiotherapy into the clinic would require a good understanding of the specific beam parameters that induces a FLASH effect, environmental conditions affecting the response, and the radiobiological mechanisms involved. Even though the FLASH effect has generally been considered as an in vivo effect, studies finding these answers would be difficult and ethically challenging to carry out solely in animals. Hence, suitable in vitro studies aimed towards finding these answers are needed. In this review, we describe and summarise several in vitro assays that have been used or could be used to finally elucidate the mechanisms behind the FLASH effect.

Genome Damage Sensing Leads to Tissue Homeostasis in Drosophila

DNA repair is a critical cellular process required for the maintenance of genomic integrity. It is now well appreciated that cells employ several DNA repair pathways to take care of distinct types of DNA damage. It is also well known that a cascade of signals namely DNA damage response or DDR is activated in response to DNA damage which comprise cellular responses, such as cell cycle arrest, DNA repair and cell death, if the damage is irreparable. There is also emerging literature suggesting a cross-talk between DNA damage signaling and several signaling networks within a cell. Moreover, cell death players themselves are also well known to engage in processes outside their canonical function of apoptosis. This chapter attempts to build a link between DNA damage, DDR and signaling from the studies mainly conducted in mammals and Drosophila model systems, with a special emphasis on their relevance in overall tissue homeostasis and development.

A high-throughput imaging and nuclear segmentation analysis protocol for cleared 3D culture models

Imaging and subsequent segmentation analysis in three-dimensional (3D) culture models are complicated by the light scattering that occurs when collecting fluorescent signal through multiple cell and extracellular matrix layers. For 3D cell culture models to be usable for drug discovery, effective and efficient imaging and analysis protocols need to be developed that enable high-throughput data acquisition and quantitative analysis of fluorescent signal. Here we report the first high-throughput protocol for optical clearing of spheroids, fluorescent high-content confocal imaging, 3D nuclear segmentation, and post-segmentation analysis. We demonstrate nuclear segmentation in multiple cell types, with accurate identification of fluorescently-labeled subpopulations, and develop a metric to assess the ability of clearing to improve nuclear segmentation deep within the tissue. Ultimately this analysis pipeline allows for previously unattainable segmentation throughput of 3D culture models due to increased sample clarity and optimized batch-processing analysis.

Effects of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells

PURPOSE

To investigate the effects of ionizing radiation on telomere length and telomerase activity in human lens epithelial cells. There are studies suggesting evidence of telomere length in association with opacity of the lens; however, these studies have been conducted on Canine Lens cells. Our study was designed to understand further the effects of different doses of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells from three Donors.

MATERIALS AND METHODS

For this study, embryonic human lens epithelial (HLE) cells from three donors, obtained commercially were cultured. Telomere length and telomerase activity were measured after each passage until cells stopped growing in culture. This was repeated on irradiated (0.001 Gy, 0.01 Gy, 0.02 Gy, 0.1 Gy, 1 Gy and 2 Gy) cells. DNA damage response using the H2AX and telomere dysfunction foci assays were also examined at 30 mins, 24 hours, 48 hours and 72 hours postirradiation.

RESULTS AND CONCLUSION

We have demonstrated genetic changes in telomere length and oxidative stress, which may be relevant to cataractogenesis. Our study shows that in control cells telomere length increases as passage increases. We have also demonstrated that telomere length increases at higher doses of 1.0 Gy and 2.0 Gy. However, telomerase activity decreases dose dependently and as passages increase. These results are not conclusive and further studies ex vivo measuring lens opacity and telomere length in the model would be beneficial in a bigger cohort, hence confirming a link between telomere length, cataractogenesis and genetic factors.

Modeling tumor cell adaptations to hypoxia in multicellular tumor spheroids

Under hypoxic conditions, tumor cells undergo a series of adaptations that promote evolution of a more aggressive tumor phenotype including the activation of DNA damage repair proteins, altered metabolism, and decreased proliferation. Together these changes mitigate the negative impact of oxygen deprivation and allow preservation of genomic integrity and proliferative capacity, thus contributing to tumor growth and metastasis. As a result the presence of a hypoxic microenvironment is considered a negative clinical feature of many solid tumors. Hypoxic niches in tumors also represent a therapeutically privileged environment in which chemo- and radiation therapy is less effective. Although the negative impact of tumor hypoxia has been well established, the precise effect of oxygen deprivation on tumor cell behavior, and the molecular signals that allow a tumor cell to survive in vivo are poorly understood. Multicellular tumor spheroids (MCTS) have been used as an in vitro model for the avascular tumor niche, capable of more accurately recreating tumor genomic profiles and predicting therapeutic response. However, relatively few studies have used MCTS to study the molecular mechanisms driving tumor cell adaptations within the hypoxic tumor environment. Here we will review what is known about cell proliferation, DNA damage repair, and metabolic pathways as modeled in MCTS in comparison to observations made in solid tumors. A more precise definition of the cell populations present within 3D tumor models in vitro could better inform our understanding of the heterogeneity within tumors as well as provide a more representative platform for the testing of therapeutic strategies.