Measuring cytotoxicity: A new perspective on LC₅₀

Background: Cytotoxicity in cell culture is typically expressed as LC ₅₀, the concentration of a given agent which is lethal to 50% of the cells. This number is dependent on the incubation time with the agent. Previously, a two-term exponential model has been proposed to describe cell growth after a cytotoxic event: y(t) = k₁ * exp(-d ₁*t) + k₂ * exp(d₂*t). A dose-response relationship was observed between the parameter k₂ in this formula and the concentration of the cytotoxic agent etoposide, in high-grade glioma cells was independent of incubation time. Materials and Methods: In order to test if the model can be applied more generally, DAOY medulloblastoma cells treated with MS275, a histone deacetylase inhibitor, were used. Results: The observed data fit the model well. Conclusion: The concentration at which k₂ is reduced by 50% is called KC ₅₀. It provides a far better description of the cytotoxicity of an agent in a specific cell line than the traditional LC₅₀.