Table 1.

Copy number of DHFR in parental and MTX-resistant HT29 cells receiving a second round of MTX treatment

DHFR copy number at the initiation of the second treatmentDHFR copy number after the second treatment*Resistant foci
Clone 223.9219.16Full
Clone E0.62Not resistant0
Clone M0.8710.167
Clone N1.18Not resistant0
Clone P1.536.898
  • NOTE: Relative values respect peripheral blood DNA (1 corresponds to a diploid DHFR copy number). No correction for the ploidy of the cell has been applied.

    Abbreviation: ND, not determined.

  • * Increasing concentrations of MTX up to 10−7 mol/L as described in Materials and Methods.

  • Number of colonies in a T25 flask seeded with 105 cells after the treatment with 10−7 mol/L MTX.

  • MTX-resistant clone maintained in MTX.