| Abstract |
The human T-cell lymphoblast line CCRF-CEM was grown in progressively
higher concentrations of methotrexate (MTX) over a period of several
months. Multistep selection resulted in the establishment of CEM/R1 and
CEM/R3 sublines able to grow in 0.2 and 2.0 muM MTX, respectively. Both
resistant cell lines had a dihydrofolate reductase (MR) activity 10-20
fold elevated over that of the sensitive line. Resistance in CEM/R3 cells
was also associated with a marked decreasee in 3H-MTX transport. Southern
blot analysis of restriction enzyme digested DNAs from sensitive and
CEM/R1 cells, using 32P, nick-translated human DHFR cDNA probe,
demonstrated amplification of DHFR genes in the CEM/R1 line. Cytogenetic
analysis showed that CEM/R1 cells contained an elongated marker chromosome
having a homogeneous staining region not present in the sensitive cells.
The inhibitory effect of two new folate antagonists was evaluated in
these resistant sublines, as well as in CEM/R4, a HTX resistant subline
(obtained from H. Lazarus) characterized by impaired HTX transport but
normal levels of DHFR. The drugs studied were trimetrezate (JB-11, TMQ,
2,4-diamino-S-methyl-6[(3,4,5-trimethoxyanilino)methyl]quinazoline) and
triazinate (TZT, Baker's anti-fol), now in clinical trial.
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