Vol. 1, 2017 — Featured publications for the IncuCyte® Live-Cell Analysis System

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IMMUNOLOGY

ESCRT-III acts downstream of MLKL to regulate necroptotic cell death and its consequences

Regulation of immunogenic cell death

Necroptosis is defined as an “immunogenic” cell death and is a form of regulated necrosis governed by the RIPK3-mediated activation of MLKL pseudokinase which induces disruption of the plasma membrane. The components and signals that regulate necroptosis activity are currently under investigation. In this study, Gong et al. examined the mechanism by which ESCRT-III antagonizes necroptosis. They found the following:

• MLKL activation leads to Ca⁺⁺ influx and phosphatidylserine (PS) exposure on the cell surface prior to plasma membrane (PM) disruption during necroptosis.
• Live-cell imaging studies using the IncuCyte revealed PS exposure in necroptotic cells results from shedding of damaged PM ‘bubbles’ and showed they resulted from ESCRT-III antagonizing MLKL-dependent PM permeabilization and cell death.
• ESCRT-III functions downstream of MLKL to delay necroptosis and sustain survival of cells in order to enable them sufficient time to release inflammatory signals to surrounding cells and induce T cell activation.
• ESCRT-III can ‘resuscitate’ and preserve survival of cells with active MLKL.

Read the full paper in Cell, April 2017

IMMUNOLOGY

MLKL activation triggers NLRP3-mediated processing and release of IL-1β independently of gasdermin-D

Mechanisms of activation and regulation of the lytic cell death program

Unlike apoptosis, necroptosis and pyroptosis represent ‘alternative forms’ of lytic programmed cell death. Pyroptosis is triggered by inflammasome-mediated activation of the inflammatory caspases that promotes inflammation through caspase-mediated processing of cytokines IL-1β and IL-18.

In studies of the inherent mechanistic link between the execution of the necroptotic program inflammasome activation and caspase-mediated processing of cytokines, a team lead by Andrew Oberst at the Center for Innate Immunity and Immune Disease, University of Washington, Seattle, demonstrated:

• Cell death assays utilizing the IncuCyte® bioimager established a link between direct activation of MLKL and cell death and its independence of caspase-1 and RIPK3.
• MLKL is an endogenous activator of the NLRP3 inflammasome, and MLKL activation causes cell membrane disruption and is sufficient to induce the concurrent processing and release of IL-1B independent of pyroptotic effector gasdermin-D.
• MLKL activation triggers potassium efflux and assembly of the NLRP3 inflammasome, which is essential for both the processing and activity of IL-1B during necroptosis.

Read the full paper in The Journal of Immunology, March 2017

ONCOLOGY

Vemurafenib and trametinib reduce expression of CTGF and IL-8 in ^V600EBRAF melanoma cells

Complexity of ^V600EBRAF melanoma targeted drug therapies

Targeted therapies to the BRAF/MEK/ERK pathway have had a significant impact on prognosis and survival of patients with advanced melanoma. However, off-target effects and acquired resistance are often observed in these patients, warranting further studies to gain a better understanding of melanoma response to inhibitors of the BRAF/MEK/ERK pathway in order to develop more effective treatments for melanoma.

In the current study, researchers from Poland utilized six melanoma cell populations harboring an activating mutation in BRAF (V600E) to characterize their response to vemurafenib (PLX) and trametinib (TRA), two FDA approved drugs for the treatment of advanced melanoma, at both the cellular and molecular level.  The authors found that:

• While all harbor the ^V600EBRAF activating mutation, the six melanoma cell lines exhibit phenotypic diversity at both cellular and molecular levels, along with variant subpopulations with distinctive phenotypes that defined the behavior of the entire population.
• Cytostatic activity and specificity of these drugs for the BRAF/MEK/ERK pathway was confirmed using the IncuCyte live-cell analysis system and reagents. However, these drugs produced both positive and negative effects on the melanoma cell populations.
• Positive: Consistent with cytostatic effects, both drugs reduce CTGF and IL-8 expression. Drug-induced inhibition of IL-8 expression was accompanied by diminished NF-κB activity and ERK1/2-dependent reduction of CTGF expression. This occurred despite phenotypic diversity between cell lines.
• Negative: Increased expression of CD271, a melanoma stem-like marker, was also observed, an undesired effect that warrants considering development of combination treatments that also address melanoma stem-like cells.

Read the full paper in Laboratory Investigation, February 2016

IMMUNO-ONCOLOGY

Exploring drug dosing regimens in vitro using real-time 3D spheroid tumor growth assays

Real-time 3D spheroid models for cancer drug discovery

In vitro spheroid tumor models are being developed that better mimic the in vivo physiological context of tumors, leading to more efficient discovery of drugs and drug targets, and predictive pharmacological responses.

Here, scientists from the laboratory of Dr. Marc Ferrer at the NIH describe the development of a real-time tumor spheroid formation, HTS-compatible screening assay platform in order to provide a physiologically relevant cell model system to bridge the gap between monolayer model systems and costly clinical studies. 11 different chemotherapeutic compounds were tested in a dose respondent manner, and GFP expression was continuously measured in Hey-A8-GFP cells. The researchers reported the following:

• The tumor spheroid assay enables real-time measurements of tumor growth and long-term drug dosing regimens using an IncuCyte Live-Cell Analysis System.
• Hey-A8-GFP tumor spheroids were established in 384-well round-bottom ULA plates. Spheroid size, cell viability and cell death were monitored and showed that full size was reached after 5 days. Cell death at the core was observed 6 days later, likely due to hypoxia and lack of nutrients, highlighting the importance spheroid size for these assays.
• Dosing performed at 48h and 120h showed significant differences in response in the 3D tumor spheroids. Drug studies in more simplistic, monolayer-based models confirmed these were not the result of shifts in proliferation rates resulting from the spheroid microenvironment. These studies illustrate the importance of the sphere size and the time of dosing in the observed drug potency and efficacy when designing physiologically relevant tumor spheroid assays for drug discovery.

Read the full paper in SLAS Discovery, March 2017

CELL MIGRATION

Hypoxia enhances the wound-healing potential of adipose-derived stem cells in a novel human primary keratinocyte-based scratch assay

Optimized wound healing assay better mimics in vivo re-epithelialization

The wound healing properties of adipose-derived stem cells (ASCs) have been demonstrated in pre-clinical studies, as ASCs secrete soluble factors which promote angiogenesis, keratinocyte re-epithelization, and protect against apoptosis. However, to harness their potential for use in regenerative therapies, more effective in vitro models are needed to study the various aspects of ASC wound healing properties. The laboratory group of Dr. Trine Fink at Aalborg University in Denmark demonstrate that ASC-keratinocyte scratch assays can be modified to better mimic in vivo re-epithelization and model wound healing properties of ASCs. Their findings show that:

• Primary keratinocytes, despite them differing from transformed keratinocytes, can provide a valid in vitro cell line model for ASCs through optimization, in particular of calcium levels in the conditioned culture media.
• Real-time kinetic scratch wound assays (IncuCyte®), which quantify the rate of growth and migration, provide an integrated solution for measuring different media effects on morphology and wound healing of keratinocytes.
• Conditioned media from normoxic ASCs increases the rate of wound closure by primary keratinocytes, which is further increased with media from hypoxia-exposed ASCs.

Read the full paper in International Journal of Molecular Medicine. February 2017