Mammalian cell transformation induced by chromium(vi) compounds in the presence of nitrilotriacetic acid

Abstract

We used a soft agar assay on cultured Syrian hamster fibroblasts to determine the ability of nitrilotriacetic acid (NTA) and Cr(VI) compounds to induce malignant cell transformation. Induction of extended anchorage-independent growth was detected in BHK 21/c13 cells by scoring colonies of transformed cells visible to the naked eye 20-25 d after plating in growth medium containing agar. Survival was determined by plating cells in liquid medium without agar and by counting the number of macroscopic colonies after 7-10 d. Mitomycin C and 4-nitroquinoline 1-oxide were used as reference direct transforming agents, with clearly positive results. In our hands no increase of the spontaneous transformation rate of BHK cells was induced by NTA concentrations ranging from 2 X 10(-3) to 10(-2) M, although the survival index was significantly reduced above 4 X 10(-3) M NTA. Two Cr(VI) compounds, K2Cr2O7, which is highly soluble in water, and CaCrO4, which is partially soluble, were tested in the soft agar assay either in the absence or in the presence of NTA. When used alone, both compounds behaved as positive transforming agents. NTA increased 4 or 10 times the cytotoxicity and the transforming activity of CaCrO4 and K2Cr2O7, respectively. As the amounts of soluble Cr(VI) detectable in the K2Cr2O7 and CaCrO4 solutions were not increased in the presence of NTA, a synergistic interaction between NTA and soluble Cr(VI) is inferred.