A Bioassay for the Cytotoxicity of Gemcitabine Using the Marine Ciliate Euplotes vannus

Abstract

This study investigated the cytotoxicity of gemcitabine using the marine ciliate Euplotes vannus as the test organism. The median lethal concentrations (LC₅₀ values) were determined using acute toxicity tests within an exposure time of 30 min with 0, 6, 12, 24, and 48 mg mL⁻¹ gemcitabine. The median inhibition effect (IC₅₀ value) on the growth of the ciliate cells was examined using chronic toxicity tests within 5 days (120 h) after exposure for 30 min with 0, 0.7, 3.5, 7, and 14 mg mL⁻¹ gemcitabine. The 30-min LC₅₀ value was 10.66mg mL⁻¹. The LC₅₀ values decreased with increasing exposure times and well fitted to the toxicity curve equation LC₅₀ = 10.93 + 28.4e^−0.19t (R² =0.93; P < 0.05, t=exposure time). The IC₅₀ value for growth rates was 7.05 mg mL⁻¹, and the inhibition effect on growth rates well fitted to the model equation r_%= 0.8681e^−0.0782Cgem (r_% means growth rate with inhibition by gemcitabine, C_gem means concentrations of gemcitabine, R² =0.99 and P< 0.05). The LC₅₀ values of a wide range of gemcitabine concentrations could therefore be predicted for any given exposure time. These results suggest that the clinical dose of gemcitabine (20mg mL⁻¹) was higher than the 30-min LC₅₀ value, which was almost the same as the 6-min LC₅₀ value (19.88 mg mL⁻¹) for E. vannus cells. The results also demonstrate that E. vannus can be used as a robust test organism for bioassays of chemotherapeutic drugs during short exposure periods.