Table 1.

Cytotoxicity of incubating V79 cells with 20 µM 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO)

carboxy-PTIO (20 µM)	–	+
Colony-forming efficiency	0.92 (±0.070)	0.91 (±0.050)
Mutation frequency	2.6 × 10−5 (±7.8 × 10−6)	2.6 × 10−5 (±6.0 × 10−6)