Table 1

Spontaneous and MNNGa-induced mutation frequencies of pS189 shuttle vector in the control and hTERT-transfected oral fibroblasts

NHOF were transfected with pS189 plasmids, exposed to MNNG for 2 h, and incubated in fresh medium for 24 h. The pS189 plasmids were recovered and introduced into E. coli MBM7070. Mutagenesis assay was performed as described previously (26) . Cells at PD 65 were used for the assay.

CellsMNNG (μg/ml)Plasmid recoveredMutagenesis frequency (%)
no. of mutants/no. of total colonies
NHOF00/127050
1.51350/143059.4
Fneo01/154260.006
1.51931/1799310.7
FT-100/121890
1.5759/176134.3b
FT-301/108600.009
1.5746/117896.3b
  • a MNNG, N-methyl-N′-nitro-N-nitrosoguanidine; hTERT, human telomerase reverse transcriptase; NHOF, normal human oral keratinocytes; PD, population doubling.

  • b Significantly lower than the mutation frequency in NHOF and Fneo exposed to MNNG (1.5 μg/ml; χ2 test).