Derivation and Study of Human Epithelial Cell Lines Resistant to Killing by Chromium Trioxide

Abstract

CrO₃ is cytotoxic for human epithelial 293 kidney cells over a narrow concentration range of ∼2–8 μM (D₅₀ ∼3.0 μM); significantly greater toxicity is observed in clonogenic assays (D₅₀ ∼0.1–1.0 μM). Survival of a small fraction of cells (≤0.1%) at CrO₃ concentrations between 10⁻⁵ to 10⁻³ M, and first-order kinetics of cytotoxicity, rationalized the derivation of a new panel of transformed human epithelial cell lines resistant to cytotoxic concentrations of CrO₃ over the range of 5–100 μM. Wild-type and Cr-resistant 293 cell lines display similar morphology under phase microscopy, but wild-type cells grow faster and reach stationary phase sooner than Cr-resistant cells. The Cr-resistant phenotype is stable, and it is specific, since Cr-resistant cells are killed by NiSO₄ or by CdCl₂ at concentrations equivalent to those that kill wild-type cells. Toxicity analysis curves subjected to target theory suggest that the Crresistant cell lines have fewer Cr-sensitive “targets” and have undergone a “loss of function” compared to wild-type cells. This loss of function may be related to significantly lower rates of uptake of Na₂ ⁵¹CrO₄, which correlate inversely with CrO₃ concentrations used for the selection and maintenance of the Cr-resistant lines, and to reduced levels of an ∼96-kDa protein in comparison to wild-type cells. This new panel of Cr-resistant transformed human epithelial kidney cell lines will be useful in comparative studies of genetic resistance and sensitivity to human Cr(VI) toxicity, sulfate transport, and growth control differences between wild-type and Crresistant cells.

This work was supported by the UCSD Superfund and National Institute of Environmental Health Sciences (ES10337). We thank Rizlan Bencheikh, Anna Obratzsova, and Brad Tebo for helpful discussion, and Leasing Yang for technical assistance.