Efficient protection of cells from the genotoxicity of nitrosoureas by the retrovirus-mediated transfer of human O6-methylguanine-DNA methyltransferase using bicistronic vectors with human multidrug resistance gene 1

Mutat Res. 1998 Jun 5;401(1-2):133-41. doi: 10.1016/s0027-5107(98)00002-5.


Retrovirus-mediated transfer of O6-methylguanine-DNA methyltransferase (MGMT; E.C. and a human multidrug-resistance gene (MDR1) confers resistance to nitrosoureas and natural product antitumor agents, respectively. In a previous study, we constructed two bicistronic retroviral vectors, Ha-MDR-IRES-MGMT and Ha-MGMT-IRES-MDR, that allow co-expression of the MGMT gene and the MDR1 gene to protect cells from the toxicity of combination chemotherapy. Each cell transduced with Ha-MDR-IRES-MGMT or Ha-MGMT-IRES-MDR showed high-level resistance to vincristine and 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosou rea (ACNU), indicating that the two drug-resistance genes can be functionally co-expressed from these vectors. In the present study, we examined whether the expression of MGMT from these MDR1-MGMT bicistronic retroviral vectors could protect cells from the genotoxicity of nitrosoureas. Three independent Ha-MDR-IRES-MGMT-transduced clones and three independent Ha-MGMT-IRES-MDR-transduced clones of HeLa MR cells showed 12-23-fold and 27-30-fold higher MGMT activity than the parental cells. These clones are more resistant to ACNU mutagenicity measured by the frequency of the emergence of 6-thioguanine-resistant colonies after ACNU treatment over the frequency seen in the parental cells. The ACNU-induced sister chromatid exchange (SCE) was markedly suppressed in these clones. Murine bone marrow cells were transduced with either Ha-MDR-IRES-MGMT or Ha-MGMT-IRES-MDR. Non-selected populations of the transduced cells showed only marginal increases in drug resistance and MGMT activity. Remarkable increase in drug resistance and MGMT activity were observed after a short exposure of the transduced cells to vincristine. The Ha-MDR-IRES-MGMT-transduced, vincristine-selected bone marrow cells showed 27-fold resistance to vincristine, 7-fold resistance to ACNU, and 10-fold higher MGMT activity than the non-transduced, non-selected cells. The Ha-MGMT-IRES-MDR-transduced, vincristine-selected cells showed 8-fold resistance to vincristine, 16-fold resistance to ACNU and 19-fold higher MGMT activity than the non-transduced, non-selected cells. The rates of ACNU-induced SCE in the vincristine-selected cells were as follows: non-transduced cells (non-selected) and HaMDR-transduced cells>Ha-MDR-IRES-MGMT-transduced cells>Ha-MGMT-IRES-MDR-transduced cells. Again, the only marginal levels of increases in the rates of ACNU-induced SCE were observed in non-selected population of the transduced cells. These results indicate that the MDR1-MGMT bicistronic retrovirus vectors would be useful to protect normal hematopoietic cells from nitrosourea-induced mutagenesis, and drug-selectable bicistronic constructs would have great advantage over non-selectable vectors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Marrow Cells / cytology
  • Bone Marrow Cells / drug effects*
  • Drug Resistance, Multiple / genetics*
  • Genes*
  • Genetic Vectors
  • Humans
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mutagenicity Tests
  • Nimustine / toxicity*
  • O(6)-Methylguanine-DNA Methyltransferase / biosynthesis
  • O(6)-Methylguanine-DNA Methyltransferase / genetics
  • O(6)-Methylguanine-DNA Methyltransferase / metabolism*
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / metabolism
  • Retroviridae
  • Sister Chromatid Exchange / drug effects*
  • Transfection
  • Vincristine / toxicity


  • Recombinant Proteins
  • Nimustine
  • Vincristine
  • O(6)-Methylguanine-DNA Methyltransferase