Molecular mechanism of mutagenesis induced by olaquindox using a shuttle vector pSP189/mammalian cell system

Olaquindox, a quinoxaline 1,4-dioxide derivative from quindoxin, is widely used as an animal growth promoter in China. We tested olaquindox as a mutagen in a SV40-based shuttle vector pSP189 and African green kidney cell (Vero E6 cell line) system to define the safety of olaquindox as a food-additive for animals. When applied at 6.6 microg/ml, olaquindox caused 12 times higher mutation frequency in comparison to untreated controls. More than 70% of base substitutions happened at G:C base pairs featuring G:C to T:A or G:C to A:T conversions. Frequency of point mutations for in vitro modified plasmids was also dramatically increased from the spontaneous background level. Olaquindox-induced mutations did not occur randomly along the supF shuttle vector, but instead, had a hot spot at base pair #155 which accounts for 37% of total mutations. Olaquindox-induced mutations also showed sequence-specificity in which most point mutations occurred at site N in a 5'-NNTTNN-3' sequence while most tandem bases deletion and rearrangement were seen at the 5'-ANGGCCNAAA-3' sequence. We conclude that olaquindox induces DNA mutation, therefore, should not be used as an additive to promote animal growth.