Cytotoxicity and Cell Viability

The effect of a cytotoxic treatment can depend on both concentration and exposure time. Continuous impedance measurements make it possible to observe the response across a concentration range and generate dose-response curves at multiple timepoints from the same experiment.

In this study, SKOV3 cancer cells were plated at 5,000 cells per well in a CytoView-Z 96-well plate. After 24 hours, the cells were treated with nine concentrations of doxorubicin in half-log increments ranging from 0.01 to 100 µM.

Increasing concentrations of doxorubicin produced progressively lower resistance measurements, indicating greater loss of cell attachment and viability. Cytolysis was calculated by comparing the treatment response with the no-treatment control.

The Hill equation was fitted to cytolysis measurements collected 72 hours after treatment. The calculated EC50 for doxorubicin was 0.43 µM.

SKOV3 cancer cells were plated at 5,000 cells per well in a CytoView-Z 96-well plate. After 24 hours, cells were treated with nine concentrations of doxorubicin ranging from 0.01 to 100 µM. Increasing doxorubicin concentrations produced lower resistance measurements and greater cytolysis. Dose-response analysis at 72 hours post-dose produced a calculated EC50 of 0.43 µM.

Why the complete time course matters

A dose-response relationship can change during an experiment. An endpoint selected too early may underestimate a delayed cytotoxic response, while a later endpoint may obscure differences in response kinetics.

Real-time measurements allow dose-response curves and EC50 values to be evaluated at multiple stages of the same experiment. Researchers can select an analysis timepoint based on the observed biology rather than choosing one before the treatment response is known.

The final extent of cell death is only one component of a cytotoxic response. The time required for a treatment to produce that effect can provide additional information about treatment activity and mechanism.

The Maestro Z platform continuously records changes in impedance after treatment. Using an untreated cell-growth control and a full-lysis control, the response can be normalized to calculate percent cytolysis throughout the experiment.

The resulting time-course data can also be used to calculate kill time 50, the amount of time required for a treatment to produce 50% cytolysis under the selected experimental conditions.

In the example shown, A549 cells were treated with doxorubicin 24 hours after plating and monitored for an additional 36 hours. The continuous measurements captured the progression of treatment-induced cytolysis and enabled kill time 50 to be calculated from the same experiment.
 

A549 cells were treated with doxorubicin 24 hours after plating and monitored for an additional 36 hours. Measurements from no-treatment and full-lysis controls were used to calculate percent cytolysis continuously and determine the time required to reach 50% cytolysis.

The figures above highlight the dynamic cytotoxic response over time. The percentage of cytolysis, or cell death, can be tracked in real time, and the time to 50% cell death (kill time₅₀) provides insight into the kinetics and efficacy of a treatment's cytotoxicity. 

All products and application data are for research use only and not intended for human diagnostic or therapeutic uses.

Distinguishing rapid and delayed cytotoxicity 

Two treatments may produce similar levels of cell death at the final endpoint but reach that result at different rates.

Continuous cytolysis measurements help distinguish rapid, gradual, and delayed responses that could appear equivalent in a conventional endpoint assay. These kinetic differences may be useful when comparing compounds, concentrations, treatment combinations, or cell models.

Impedance increases as adherent cells attach, spread, and cover the electrode area. This relationship allows impedance to serve as a label-free indicator of relative cell number, growth, and viability.

In the example shown, Calu-3 cells were plated at densities ranging from 6,400 to 51,200 cells per well. Impedance measurements collected four hours after plating increased linearly with cell number and closely correlated with MTT measurements across the same range of cell densities.

Unlike an MTT assay, however, impedance measurements are not limited to a single endpoint. The same wells can be monitored before treatment, during the response, and through the end of the experiment without adding assay dyes or destroying the cell culture.

Calu-3 cells were plated at densities ranging from 6,400 to 51,200 cells per well. Impedance measured four hours after plating increased linearly with cell number and correlated with measurements from an optical MTT assay. Unlike the endpoint measurement, impedance can be recorded continuously from the same wells.

Information gained beyond the endpoint

Correlation with an established endpoint assay supports the use of impedance as an indicator of relative cell number and viability.

Continuous impedance measurements also provide information that a single MTT measurement cannot capture, including:

• the condition of the cells before treatment;
• the onset of the treatment response;
• changes in response rate;
• temporary stabilization or recovery;
• the relationship between treatment duration and viability.
   

Real-time impedance assays can be scaled to evaluate multiple treatments, concentrations, and experimental conditions while preserving the complete response time course.

In this study, SKOV3 cells were plated in four CytoView-Z 96-well plates. Twenty-four hours after cell seeding, the cells were treated with two test compounds using six-point concentration ranges with full-log intervals.

Cytolysis was calculated relative to no-treatment and full-lysis controls. Dose-response analysis was performed separately for each compound and plate.

The calculated EC50 values were similar across the replicate plates, with low overall percent coefficient of variation. The results demonstrate reproducible dose-response measurements across multiple plates.

The Maestro TrayZ platform enables simultaneous impedance measurements from four plates, allowing researchers to evaluate more compounds, cell models, concentrations, or experimental conditions in parallel.
 

SKOV3 cells were plated in four CytoView-Z 96-well plates and treated with two compounds using six-point concentration ranges. Dose-response analysis produced similar EC50 values across the replicate plates, with low overall plate-to-plate variability.

Scaling cytotoxicity studies without losing kinetic data

High-throughput cytotoxicity studies require both experimental scale and consistency.

Multi-plate real-time measurements allow researchers to increase throughput while evaluating:

• plate-to-plate variability;
• concentration-dependent effects;
• differences in treatment kinetics;
• EC50 reproducibility;
• the performance of controls across multiple plates.