6225514

pubmed:Citation

11

Methotrexate (MTX)-resistant sublines of malignant human cells were selected in vitro by stepwise increase in drug concentration in the medium. By this procedure a subline of Burkitt's lymphoma cells (RAJI) was made 290-fold resistant (RAJI/MTX-R), T-cell leukemia cells (CCRF-CEM) were obtained 210-fold resistant (CEM/MTX-R), and 3 MTX-resistant human osteosarcoma lines were selected: TE-85/MTX-R (19-fold resistant; relative to wild-type); MG-63/MTX-R (8-fold resistant); and SAOS-2/MTX-R (200-fold resistant). We also studied a B-cell lymphoblastoid line, WI-L2/m4, that was 13,000-fold resistant. Assay of cellular dihydrofolate reductase (DHFR) showed the following pattern of activity in resistant cell lines, relative to parental cell activity: RAJI/MTX-R, 550-fold increased; CEM/MTX-R, unchanged; TE-85/MTX-R, 4-fold increased; MG-63/MTX-R, 6-fold increased; SAOS-2/MTX-R, unchanged; and WI-L2/m4, 110-fold increased. Measurement of MTX membrane transport showed decreased uptake in CEM/MTX-R and SAOS-2/MTX-R, relative to parental cell lines. The other DHFR-overproducing cells all gave normal initial MTX uptake rates but increased total uptake. The DHFR-overproducing lines all had significant cross-resistance to both metoprine and trimetrexate; the two lines with defective MTX transport were not cross-resistant, and the CEM/MTX-R cells showed collateral sensitivity to these agents. Only minor cross-resistance to homofolic acid was found in all MTX-resistant lines. The highly MTX-resistant RAJI/MTX-R and WI-L2/m4 cells showed minor cross-resistance to the dual inhibitor of thymidylate synthetase and DHFR, CB3717 (5- and 15-fold, respectively). These studies demonstrated that, depending upon the mechanism of resistance, MTX-resistant human tumor cells may be effectively killed by antifolates with different routes of uptake into cells, or with a different enzyme target. Thus, there are at least three functionally distinct classes of folate antagonist with antitumor activity.

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MEDLINE

0008-5472

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5286-92

pubmed-meshheading:6225514-Antineoplastic Agents, pubmed-meshheading:6225514-Biological Transport, pubmed-meshheading:6225514-Burkitt Lymphoma, pubmed-meshheading:6225514-Cell Line, pubmed-meshheading:6225514-Drug Resistance, pubmed-meshheading:6225514-Folic Acid, pubmed-meshheading:6225514-Folic Acid Antagonists, pubmed-meshheading:6225514-Humans, pubmed-meshheading:6225514-Kinetics, pubmed-meshheading:6225514-Leukemia, Lymphoid, pubmed-meshheading:6225514-Lymphoma, pubmed-meshheading:6225514-Methotrexate, pubmed-meshheading:6225514-Osteosarcoma, pubmed-meshheading:6225514-Pyrimethamine, pubmed-meshheading:6225514-Quinazolines, pubmed-meshheading:6225514-Structure-Activity Relationship, pubmed-meshheading:6225514-T-Lymphocytes, pubmed-meshheading:6225514-Tetrahydrofolate Dehydrogenase, pubmed-meshheading:6225514-Trimetrexate

Patterns of cross-resistance to the antifolate drugs trimetrexate, metoprine, homofolate, and CB3717 in human lymphoma and osteosarcoma cells resistant to methotrexate.